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08:00-09:15 Session 1: Special Poster Teasers
Location: Europa
Effect of Computer-Assisted, Minimally Invasive Surgical Technique on Reducing Total Cost in Primary Hip Arthroplasty

ABSTRACT. Introduction. Evolving payment models create new opportunities for assessment of patient care based on total cost over a defined period of time. The purpose of this study was to assess cost of care for total hip arthroplasty performed with and without navigation. Methods. The total reimbursement for services performed following primary THA for patients insured by Medicare was analyzed for a group of patients at a single institution (FY 2013 and 2014). The population included data on 356 nonrandomized patients who had surgery performed using the same pre-operative education, OR, PACU, PT, nursing, and case management. A total of 38 patients underwent THA by an anterior exposure, 219 had surgery performed by a posterior exposure, and 99 had surgery performed by the superior exposure utilizing patient-specific mechanical surgical navigation. Patients were unselected with the exception of the anterior hips which represented 38% of the surgeons THA practice. Reimbursement for all in-patient and outpatient services performed over the initial 90-day period from surgical admission was compared across surgical techniques. Reimbursement includes the sum of all payments including the hospital, physicians, skilled nursing facilities, home care, out-patient care, and readmission. Results. Total average 90 day cost was $24,848 for THA performed using posterior exposure, $21,446 for the selected anterior exposure, and $20,268 for the superior exposure with navigation. The cost of care for treatment by the superior exposure with navigation was statistically significantly less than the posterior exposure (p<0.001) but not significantly less than the selected anterior exposure patients (p=0.287). Medicare in-patient reimbursements for patients treated by the superior exposure with mechanical surgical navigation was significantly less than the selected anterior exposure group (p<0.002) and the posterior exposure group (p<0.001). Overall, 84% of patients with the superior exposure were discharged directly to home versus 69% in the selected anterior group and 60% in the posterior group.

Concepts for Developing Interoperable Software Frameworks Implementing the New IEEE 11073 SDC Standard Family

ABSTRACT. The long overdue IEEE 11073 Service-oriented Device Connectivity (SDC) standard proposals for networked and surgical devices provides vendor-independent interoperability and therefore room for improved workflow and new functionality in the operating room. Research and development in this domain remains also highly topical in orthopaedic surgery. Due to the novelty and complexity of the SDC standard family, there is currently a lack of open source public implementations. Such implementations have to overcome several non-trivial challenges, mainly because the complexity of the standards has to be reflected in the software design and implementation. The SDC standard family comes in three different parts and all three standard proposals must be considered when designing and implementing standard conform device communication. In this work, we address these challenges and discuss and compare two design approaches for different programming languages (C++ and Java). Suitable software engineering principles are used to ensure a clean design approach. Practical guidelines are given on how to integrate existing third party components and tools in the framework and the development process, respectively. General feasibility is demonstrated by outlining interoperability between two software frameworks developed using different design concepts.

Robotic Assisted Fixation of Sacral Fractures – Initial Experience
SPEAKER: Yoram Weil

ABSTRACT. Robotic assisted fixation of sacral fractures – initial experience

Unstable sacral fractures are challenging for orthopaedic trauma surgeons. In most cases percutaneous fixation techniques are utilized after reduction. However, these techniuqes are not risk free mainly due to anatomical considerations. Screw misplacement is quite common and concerning. As spine surgery evolved, a miniature robotic guidance system was successfully utilized in pedicular screw insertion. The aim of the study was to demonstrate th use of the miniature robot in the fixation of unstable sacral fracutres. Patients and Methods: 9 patients with unstable sacral fracutres without significant displacement were eligible for percutaneous fixation. These included 7 traumatic fractures and 2 pathological fractures. All fixation constructs were planned using a preoperative CT scans. The patients were placed prone and the robot was mounted on a Dynamic Reference Bridge (DRB) and a 2 verification fluoroscopic images were taken. The robot was mounted on the DRB and was sent by the computer to point to the desired screw(s) trajectory. The guide wires were inserted through stab wounds and screws were placed subsequently. CT scans were made postoperatively and fluoroscopic and operative time were recorded intraoperatively. Results: Mean patient age was 29 (17-63) number of screws ranged 1-6 (average 2). Mean operative time was 50 min (range 15-90), and average fluoroscopic time was 18 sec (7-42). None was the screw was misplaced. Conclusion: Robotic assisted fixation of sacral fracture is promising. At this time it is limited to nondisplaced fractures.

Assessment of an Intraoperative X-Ray Imaging Analysis System for Measurement of Acetabular Cup Position in Total Hip Arthroplasty

ABSTRACT. INTRODUCTION The purpose of this study is to assess the validity of an intraoperative system for the measurement of cup orientation based on plain AP in comparison with those of CT using the same definition and reference plane.

MATERIALS AND METHODS Fifteen patients were assessed in this study. All surgeries were performed in the lateral decubitus position. Measurement of cup orientations on plain radiographs were calculated according to the recommended protocol of the intraoperative radiographic measurement system including the ‘draw ellipse function’. Measurement of cup orientations on CTs were calculated by first, determining the Anterior pelvic plane coordinate system on a 3D surface model and its relationship to the functional supine CT coordinate system and second, the vector orthogonal to the open plane of the acetabulum is determined by creating a best-fit plane of cup rim points entered on multiplanar views. Radiographic inclination and anteversion are then calculated relative to the functional CT coordinate system and to the anterior pelvic plane.

Results There were statistically significant differences between the measurements of anteversion on the intraoperative plain radiographic system compared to the CT measurements (p < .05). The distribution of difference between two measurements showed < 5° in 4 hips, 5° to < 10° in 7 hips, and 10° or more was in 4 hips in anteversion.

DISCUSSION In this study, All AP radiographs were intraoperatively taken in the lateral decubitus position. Even with the requirement of optimally appearing intraoperative AP radiographs according to the protocol and attempted correction of pelvic tilt using anatomical ratios, accurate measurement of acetabular anteversion using the plain radiographic system demonstrated difficulties. In conclusion, the use of an intraoperative measurement system based on plain AP radiographs is relatively reliable in estimating the inclination of acetabular component, but > 10° difference from CT measurement was seen in 4/15 (27%) hips. Therefore, anteversion of acetabular component is poorly assessed by the system. As patient’s pelvic orientation directly alters the cup orientation on the surgical table, knowledge of the accuracy of intraoperative assessment systems will assist surgeons with intraoperative decision-making that can improve patient care.

The Interleaved Partial Active Shape Model Search (IPASM) Algorithm – a Novel Approach Towards 3D Ultrasound-Based Bone Surface Reconstruction

ABSTRACT. In applications such as biomechanical simulations or implant planning, bone surfaces of the knee are most often reconstructed from computed tomography or magnetic resonance imaging data. Here, ultrasound (US) might serve as an alternative imaging modality. However, established methods cannot directly be transferred to US due to differences in imaging quality and underlying physics.

In this paper, we present a generalisation of the well-known active shape model search algorithm (ASM) that allows for segmenting various structures in US volume images that are too large to be captured with a single recording. The multi-view segmentation approach uses a-priori knowledge in the form of a statistical shape model (SSM) as is the case with the classical ASM. This allows to extrapolate missing information and to generate shapes that comply with the underlying distribution of some training data. The main differences are, however, that the SSM is not only adapted to a single image but to multiple images and that the adaption process is interleaved. As a result, within each iteration the surface information of all sub-volumes is propagated and used in all subsequent steps.

In-silico tests were conducted to investigate how this algorithm would perform in real tracked US data. US volume images were split in slightly overlapping sub-volumes, noise was added, and the alignment was distorted. We could show that the algorithm is capable of reconstructing shapes in the lower millimetre range and for some cases even with submillimetric accuracy. The algorithm is hardly affected by orientation errors below 5 degrees and displacement errors below 5 mm; above these limits, the average absolute SDE as well as its associated variance increases.

Automation of a Flexscope for Laser Osteotomy
SPEAKER: Gabor Kosa

ABSTRACT. Flexible endoscopes are commonly employed in various minimally invasive surgeries. Typically, Flexoscopes are used in interventions that require minimal number of ports and maneuverability in the target area such as natural orifice transluminal endoscopic surgery. In orthopedic surgeries, these endoscopes are not used because interventions like drilling and osteotomy necessitate large forces that can be only exerted by rigid tools. In contrast to traditional orthopedic tools, laser osteotomy does not require mechanical contact with the bone. Consequently, flexible tools can be used for the cutting process. Furthermore, the use of lasers is advantageous from the aspects of accuracy and faster healing of the bone. Importantly, high accuracy and satisfactory cutting performance of the laser osteotomy can only be reached through stable, dexterous, and precise guidance by a robotic platform. In this paper, we first present a custom-designed robotic platform that allows precise control of the flexoscope’s pose. The robot is anthropomorphically inspired from a human arm in the aspects of link length, joint arrangement and operation method. A special holder was designed to transform the flexible endoscope into a semi rigid endoscope to provide a stable insertion platform for the laser tool enabling only the tip to bend at the end of the holder. The robot will be able to move and orient the laser accurately, while following an uneven bone surface in the target area of the osteotomy.

Computer-Assisted TKA : Long-Term Outcomes at a Minimum Follow-up of 10 Years of 129 E-Motion FP Mobile Bearing Prostheses

ABSTRACT. The aim of this study was to assess long-term outcomes of the e-Motion FP ultra congruent TKA with mobile-bearing platform, setup with computer assisted surgery. Our null hypothesis was that long-term outcomes were satisfactory or superior to the other implants design reported outcomes. A retrospective monocentric study was conducted between January 2002 and December 2005, on 243 knees in 225 patients of a mean age of 71 +/- 5 years (65-85) who underwent a TKA of first intention. The series consists of 222 knee osteoarthritis, 7 rheumatoid arthritis and 14 osteonecrosis of the femoral condyles. All prostheses were navigated with the Orthopilot™ system. 129 knees in 117 patients were reviewed at a mean follow-up of 135 ± 12.8 months (120-165). 108 patients were lost to follow-up (76 dead). Only one aseptic loosening was found at 10 years of follow-up. No complication concerning wear or tibial plateau insert dislocation was noted. The mean prosthesis survival rate at 11.3 years was 99.2% with aseptic loosening, wear or failure of the prosthesis as an endpoint. The mean IKS score at the last follow-up was 189.5 ± 13.6 points (137-200). The mean HKA angle was 180 ± 2° (174-186°) with 92.3% of the prostheses aligned at 180° +/- 3° which was the preoperative objective. This study confirms our initial hypothesis, that the outcomes of the TKA e-Motion FP with ultra-congruent mobile-bearing were satisfactory at more than 10 years of follow-up. Navigation, whose accuracy is well established, probably contributed to the quality of the results.

Robust 3D Kinematic Analysis of Total Knee Arthroplasty Using Statistical Motion Model

ABSTRACT. 3D kinematic analysis methods of total knee arthroplasty (TKA) in the 2D/3D registration using X-ray fluoroscopic images and knee implants model have needed time-consuming and labor-intensive manual operations in some process, particularly for the pose estimation of tibial component. In this study, we present robust and automatic 3D kinematic analysis method of tibial component using statistical motion model. The used 2D/3D registration technique is based on a robust feature-based (contour-based) algorithm. In our present method, a statistical motion model which represents average and variability of joint motion is incorporated into the robust feature-based algorithm. In this study, a statistical motion model for relative knee motion of the tibial component with respect to the femoral component was created from previous a lot of analyzed 3D kinematic data of TKA and utilized. In order to validate the feasibility and effectiveness of 3D pose estimation for the tibial component using the present method, experiments using X-ray fluoroscopic images of 20 TKA patients under the squatting knee motion were conducted. For assessment of the automation performance of the tibial component model, the automation rate was calculated. As results of the experiments, 3D pose of the tibial component model for all X-ray images except for the first frame was full-automatically stably-estimated, and the automation rate was 80.1 %. Consequently, the present method did not need labor-intensive manual operations for 3D pose estimation of the tibial component, and is thought to be very helpful for practical clinical application.

Significant Effect of Hip Labrum on Computational Kinematic Simulation During Hip Motion

ABSTRACT. Computational kinematic simulation has been applied to the hip for understanding of femoroacetabular impingement (FAI). However, since previous studies tried only bone to bone contact simulation in the hip joint, investigation of Femur-labrum contact might be more important than bone-to-bone contact.

The purpose of this study was to investigate the effect of the acetabular labrum on ROM simulation of the hip joint. For this purpose, we compared maximum internal rotation under simulations of anterior impingement test.

Thirteen asymptomatic subjects were analyzed by 3D femur, acetabulum, and labrum models from computed tomography arthrograms. For this ROM simulation, angles of maximal internal rotation was studied in 10˚ increments between 70 and 110˚ flexion and in 10 ˚ increments between 0 ˚ to 20 ˚ adduction to simulate the anterior impingement test.

The ROM in the femur-labrum contact model was significantly smaller than that of the femur-acetabulum contact model (p < 0.001). The difference between at each point both two simulations was approximate 20 degrees.

Bone-to-bone contact simulations may still be informative in the evaluation of relative change in ROM on the basis of a surgical intervention (e.g. before and after femoral osteochondroplasty). However, some of the absolute values (e.g. maximum flexion angle) from these simulations might not be served as a useful reference. From this standpoint, the effect of the labrum on intra-articular impingement evaluated in current study can contribute to the errors in estimation of impingement and ROM using kinematic simulations of the hip joint.

Feasibility of Using Optical Sensing to Measure Bore Depth in Surgical Bone Drilling
SPEAKER: Daniel Demsey

ABSTRACT. Daniel Demsey BASc MD1, Juan Pablo Gomez Arrunategui BASc1, Nicholas J Carr MD1, Antony J Hodgson PhD1 1University of British Columbia, Vancouver, V6T 1Z4, Canada,

The depth gauge is used in many osteosynthesis surgeries to measure drilled bore depth for screw selection, and has significant limitations. Its use has been shown to contribute to placement of incorrectly sized screws, which can lead to adverse outcomes in patients. We have developed an automatic depth gauge prototype which mounts on an existing surgical drill and makes use of an optical sensor. This builds off previous work in our lab which showed that drilled bore depth could be computed from continuous measurement of drill displacement relative to the bone. We tested our device in animal models and compared it with digital calipers as a gold standard. In a simple porcine model the prototype showed potentially superior performance (mean error 2.05mm, SD 0.67mm) compared with the conventional depth gauge (mean error 0.83 mm, SD 1.55 mm). However, this could not be reproduced in a more realistic porcine model. An automated depth gauge mounted on a conventional surgical drill shows potential as a replacement for the existing depth gauge, but the design needs to be refined for use in an operating room setting.

Development of a Haptic System to Assess Wrist Control in Healthy and Injured Test Subjects

ABSTRACT. Wrist injuries are commonly presented in hand clinics. However, current clinical assessments of wrist control (Active (AROM) and Passive Range of Motion (PROM) and resisted testing) and proprioceptive deficit are highly subjective and qualitative which highlights the necessity for improved methods with the aid of modern technology. This study evaluated the feasibility of using a Sigma.7 (Force Dimension Inc.) haptic device to assess wrist function and control objectively, repeatedly, and quantitatively. Specifically, we sought to accomplish three aims: first, conduct workspace and loading capacity analysis to show that the haptic system can replicate clinical tasks; second, to establish a control system and safety functions to safely integrate the clinical assessments with high quality data; third, to demonstrate the types of data and novel testing that can be achieved. In the present study, the workspace’s 3D model was built in Matlab to conduct mathematical and experimental verification of workspace capacity. The haptic device was found to permit the four most fundamental wrist motions that constitute most clinical wrist assessments: Extension, Flexion, Ulnar Deviation (UD) and Radial Deviation (RD). Loading capacity was verified to be capable of performing AROM, PROM and resisted tests. Additionally, a preliminary proprioceptive evaluation was developed for this haptic device to provide a quantitative approach to assess a participant’s ability to sense and react to external force. Clinical proprioceptive assessment trials of performing Dart Throwers’ motion under three different loading case (zero, constant, variable) applied by the device further consolidate the evaluation of its efficacy. The feasibility assessment and proof of concept results demonstrate that a haptic application for wrist assessment which uses a Sigma.7 device has the potential to transform qualitative wrist assessments into highly quantitative and reliable tests within a clinical and/or research environment.

Medical Optical Localizer Based on Apple iPhone Smartphone

ABSTRACT. Medical navigation providing intraoperative localization of medical instruments plays a crucial role in computer assisted surgery (CAS). Several different multiple-camera standalone optical localizers are available on the market nowadays. Our aim was to develop, easy-to-use, low-cost and portable medical localizer based on iPhone 6S camera. We decided to develop a specialized smartphone app which is able to detect two rigid bodies (RB) on the camera screen and estimate their position both in devices and global coordinate system using sensor fusion with smartphones accelerometer and gyroscope. In the procedure one RB serve as reference and the other is attached to the tool. The prototype was preliminary calibrated using 2D and 3D VDI/VDE 2634 standard. Validation procedure involved measurements of the position and distance of two RBs placed 500 mm from each other in a distance of 1 meter to the smartphones camera. The measurements were taken from three different angles: -30°, 0°, 30° regarding RBs plane. The standard deviation of the measured distance was 0.62 mm with average measured distance of 498.0 mm. The other tests were made in a test-setup where the virtual offset of ultrasound probe was added to one of the RBs so the distance between probe and reference was 195 mm. The tests showed that the position of ultrasound probe is estimated with standard deviation of 0.70 mm and the average measured distance is 195.18 mm. Due to the promising results of those evaluations, we plan to perform more specific tests in clinical setup in near future.

Towards a Surgical Phase Detection Using Markov Logic Networks

ABSTRACT. The use of assistance functions for diagnosis and surgical interventions has become an evolving area for mastering challenges of contemporary medicine. Inter alia, these assistance functions can help to prevent malpractices and preserve a high level of satisfaction for patients as well as employees. To enable such functions in context of a computer-assisted orthopaedic surgery (CAOS), we elaborate the use of Markov Logic Networks (MLNs) for modelling surgical phases. In contrast to commonly researched systems for surgical process modelling, MLNs combine rule-based as well as probabilistic approaches. This allows us to integrate soft and hard constraints into our network – which greatly expands the scenery of currently researched models for phase detection in surgical interventions. In our contribution, we present the necessary fundamentals of MLNs and show the application to a comprehensible test case. The results are promising concerning the use of MLNs for surgical phase detection. In particular, MLNs have shown two advantages: Firstly, due to their template characteristics, few logic rules allow to model numerous interdependencies between the different surgical phases. Secondly, the combination of probabilistic and logic approaches allows to handle sensor inaccuracies and misclassifications of features directly. E.g., the inaccuracy of a sensor can be expressed by reducing the weight of corresponding formulas, allowing for a softening of constraints.

Individual Cooling and Compression System for Accelerated Swelling Reduction on Fractures

ABSTRACT. After a fracture injury a swelling of the skin soft tissue results which prevents an early operation. In order to shorten the waiting time until the decrease of the swelling, the metabolism-reducing effect of mild local hypothermia and the swelling-reducing effect of compression therapy should be used in a device anatomically adjusted to the patient. For the best possible treatment, a regulation of the cooling and compression parameters should be carried out by means of sensor technology in order to allow an adaptation to the individual patient. Based on medical studies, parameter areas relevant to patients could be determined. These were implemented in first functional models for a cooling system and a compression system. Anatomically adapted cooling and pressure chambers allow a good physical coupling of the system to humans. The first test results, considering the heat emission and the skin elasticity properties of the human body, show that both rapid cooling can be achieved in a range of between 17 and 20°C of skin temperature within 4 min, and that under a pressure effect of between 10 and 20 kPa in the pressure chambers a pressure on the human tissue can be produced up to 15 kPa. The cooling system based on Peltier elements is capable of transporting a heat flow up to 10 W. The quiet, maintenance-free Peltier elements also increase the patient's acceptance. In the pressure chambers, a temporally overlapping generation of pressure pulses can imitate the process of natural walking by the effect of muscle pumps and contribute to a technical lymphatic drainage. By detecting the inflammation area with the aid of netlike-arranged temperature sensors and measuring the internal pressure of the pressure chambers in the case of a swelling tissue, cooling can be carried out at a determined point and the occurrence of, for example, a compartment syndrome can be prevented by regulating the pressure. At present still ongoing, promising developments of models for the consideration of the temperature distribution and pressure differences in the cardiovascular system should enable a determination of optimized cooling and pressure curves adapted to the individual human. In this way, the best possible control circuits should be identified using medical expert knowledge.

Precise Single Column Resection and Reconstruction with Femoral Head plus THR for Malignant Pelvic Tumors
SPEAKER: Xiaohui Niu

ABSTRACT. Introduction Precise resection with safe surgical margin could cure the patients while saving healthier host bone for relative simple reconstruction. Some malignant pelvic tumor may affect the anterior or posterior column at the acetabula area. The purpose of this study is to evaluate the precise single column resection and reconstruction with femoral head plus THR for malignant pelvic tumors. Materials and Methods This is a clinical cases study. From Dec. 2007 to February 2015, 19 patients with primary malignant tumors of the pelvis were enrolled in the study. The diagnosis included 16 cases of chondrosarcoma, 1 case of undifferentiated polymorphic sarcoma, 1 case of Ewing's sarcoma and 1 case of solitary plasmacytoma. All tumors were resected with safe surgical margins, which were proved by the postoperative specimen evaluation. Anterior column was involved in 17 cases and posterior column in 2 cases. Ten of 19 tumors were resected assisted by computer navigation. Femoral heads were used to reconstruct anterior or posterior column defects and fixed by screws; THR was used for the joint reconstruction. Oncologic outcome and function were evaluated by regular follow-up. Results The follow up time was more than 12 months in 14 cases with the average of 54.6 months (median 56, range 13-118) months. Surgical margins contained wide resection in 12 cases and marginal resection in 7 cases. The bony wide resection rate was 90% (9/10) in the navigation group and 77.8% (7/9) in free hand group respectively. One patient with Ewing's sarcoma died 14 months postoperative due to lung metastasis. There was only one case with chondrosarcoma was found recurrence in 61 months postoperatively, who was in the navigation group and having marginal margin resection. There was one prosthesis removed due to prosthesis infection (14 months postoperatively). There were another two Discussion The current treatment method is oncological safe and functional with less complications. The hardware is relatively cost effective and right on the shelf. However, this procedure is highly skill needed.

Navigation Assisted Geographic Resection and Allograft Reconstruction for Extremity Bone Tumors
SPEAKER: Xiaohui Niu

ABSTRACT. Introduction The geographic resection for cortex surface tumor of the bone has many challenges.The aim of this study is to evaluate the precision of navigation assisted surgical geographic resection and allograft reconstructions for bone tumors. To verify navigation technique facilitate resection and improve the allograft matching rate and reduce the gap. Materials and Methods We analyzed 23 consecutive extremities primary bone tumors, including distal femur 16, proximal tibia 5 and 2 distal tibia. Mostly were parosteal osteosarcoma, periosteal osteosarcoma, and periosteal chondrosarcoma. We import the patient’s data into the Stryker navigation system for preoperative bone cutting design, CT & MRI fusion for more clearly and safe tumor margin, simulate geographic resection line according to the tumor morphology. With the intraoperative image data and preoperative image fusion, the geographic resection line could be real-time guided by navigation system and we could execute accurately and more conveniently in tumor margin, allograft geographic taking out and transplant matching. Results The mean operation time is 267 (135-450) mins. With a mean and median follow-up of 32.9 and 32 months respectively (range, 3-74), 1 patients developed LR (1/23, 4.3%), 2 metastasis and dead (2/23,8.7%). All patients received satisfactory margin resection and accurate allograft matching. With femoral condyle involved in 2 GCT and 1 chondroblastoma cases, single condyle resection and unicompartmental arthroplasty of allograft used in these three patients. All transplanted allograft mean longitudinal diameter was 81.1 mm (42.9-127.1), the mean diameter was 40.8 mm (20.8-76.3), compare to the preoperative design for the tumor resection longitudinal diameter 80.4mm (40-125), it has no significant difference (P>0.05). The mean biggest gap space between the host bone and allograft was 3.5 mm (0.5-9). The mean and median allograft healing time was 17.6 and 18 months (8-21). The mean of functional scoring with Musculoskeletal Tumor Society (MSTS) for this group were 95.6±8.0%. Discussion (1) Computer navigation assisted accurate tumor resection and safe margin. (2) With high accuracy for geographic resection, there has good matching and small gap for allograft and host bone. (3) No difference between preoperative design and intraoperative execution with navigation guided precise operation. (4) Navigation technique reduces the maximum compensate for the error of imaging.

Application Specific Adaption of a Numerical Based Surgical Process

ABSTRACT. The reason for postoperative functional limitations after an Anterior Cruciate Ligament (ACL) reconstruction is usually inaccurate placement of the femoral and tibial tunnel. Patient-specific 3D simulations allow more accurate, economical and efficient interventions in such orthopedic surgeries. Patient-specific Finite Element Method FEM based on medical images has great potential to aid in clinical decision making, designing implants, planning surgeries and monitoring outcomes. We develop a technology workflow including a software pipeline for patient-specific preoperative planning and analysis of the knee joint.

A high resolution MRI dataset (0.3x0.3x0.3 mm) from a human cadaver knee was used to build a reference FE model comprised of bones, cartilage, menisci and ligaments (Ansys v16, Canonsburg, PA, USA). Material properties were chosen from the literature and boundary conditions were defined to simulate several clinical tests, e.g. Lachman test to investigate the stability of the ACL. A coronal and axial MRI dataset (0.3x0.3x3.6 mm) with clinical protocols was acquired, fused and registered to the reference MRI image using landmark-based rigid initialization followed by intensity-based multi-resolution b-spline deformable registration. Resulting 3D deformation fields were used to deform the geometry of the reference model to obtain a patient-specific FE model.

It is possible to obtain a patient-specific FE model from a clinical MRI dataset including all boundary conditions in less than 19 minutes on two cores with 3.5 GHz. Depending on the clinical simulation, solving the mechanical system is more time consuming. The biomechanically correct alignment of components for an ACL surgery is possible within a virtual environment. This workflow allows preoperative planning, analysis of acting forces and simulating the stability of the knee joint for an improved ACL surgery.

The results indicate a stable workflow for functional simulations of a patient-specific knee joint. Preoperative analysis of acting forces, stresses and strains is possible. The biomechanically correct alignment and implantation of components can be determined and patient-specific information regarding the resulting range of motion is obtained. This method supports the accurate placement of the femoral and tibial tunnel for an ACL surgery which reduces the risk of graft failure or unsatisfactory results and might reduce long-term degeneration observed after reconstruction.

Intra-Operative Registration of 3D Data Capture with Pre-Operative Plan for TKA
SPEAKER: Brad Miles

ABSTRACT. INTRODUCTION Total knee arthroplasty (TKA) is widely performed for improving pain and restoring function for patients with osteoarthritis (OA) and over 50000 primary procedures were performed in Australia in 2015 (Annual report 2016). Computer assisted pre-operative planning (CAPP) was introduced to enhance accuracy of rotational and translational alignment of components (Schep 2003). It can be done with 3D bone surface modelling from CT or MRI scans and take kinematics and surgeon work flow into account. Computer assisted intra-operative navigation is also accessed by some surgeons and consists of three elements: software platform, point positions from reference arrays captured and reference device attached to the patient’s bone (Bae 2011). By incorporating CAPP with navigation, a correlation between the patient’s anatomy from pre-operative images can be established by gathering intra-operative anatomical landmarks and/or surface points and is known as registration (Chan 2016). However, identifying landmarks and acquiring images intra-operatively and the registration quality can be time-consuming and/or prone to risk. Custom-designed registration software that could reduce the time and error and be incorporated into the surgical workflow is needed (Chan 2016). The aim of this study was to develop custom registration software using pre-operative planning and intra-operative 3D data capture and validate precision and repeatability using a preliminary Sawbones study.

Robot-Assisted Upper Cervical Spinal Surgery
SPEAKER: Mingxing Fan

ABSTRACT. The fundamental for upper cervical spinal surgery is screws fixation progress, however, anatomical variations of atlantoaxial vertebrae are wide, and the region is adjacent to important organ such as spine cords, oblongata and vertebral artery, all of which make the fixation harder. Robot-assisted navigation can make up for the above shortcomings, and has the potential to more improve the screw placement accuracy. We recently designed a robot system called TiRobot, which is based on intraoperative three-dimensional images. TiRobot has three components: the planning and navigation system, optical tracking system and robotic arm system. By combining navigation and robot techniques, TiRobot can guide the screw trajectories for orthopedic surgeries. TiRobot has been used in upper cervical surgeries with the approval from the Ethics Committee. There were 7 screws inserted during the surgeries, 1 screw for posterior C1-2 transarticular fixation, 1 screw for anterior odontoid fixation and 5 for C1 or C2 pedicel fixation. All surgeries were smoothly performed using TiRobot. According to the post-operation CT image data, all the screw placements were sufficient because there was no perforation of the spinal canal or any unexpected malposition. According to the Gertzbein-Robbins classification, all screws fell into group A. Furthermore, there was a discrepancy between the planned and the actual placements at the entry points and the end points. The average deviation in entry point and end point were 1.21 +/- 0.45mm and 1.19 +/- 0.36mm. These safe and accurate results make TiRobot the first medical robot could be used in upper cervical spinal surgery.

Non-Invasive Navigated Assessment of the Lower Limb Axis Prior to Total Knee Arthroplasty. Comparison with Conventional Navigated Assessment.

ABSTRACT. INTRODUCTION Assessment of the lower limb axis on long leg X-rays is recommended prior to total knee arthroplasty (TKA), but involves several biases. Navigated techniques are accurate and precise, but involve invasive fixation of arrays. A non-invasive navigated (NIN) technique has been developed to assess the lower limb axis prior to TKA. The purpose of the current study was to assess the accuracy and precision of this technique by comparison to the conventional, invasive navigated (IN) measurement technique.. MATERIAL AND METHODS All patients scheduled for a TKA from May 2015 to June 2015 were eligible for the study. NIN and IN measures were performed sequentially on a supine patient after general anesthesia. Following data were recorded: coronal mechanical femoro-tibial angle at maximal extension angle without stress and coronal mechanical femoro-tibial angle at 30° of knee flexion without stress. NIN and IN measures were compared with the appropriate statistical tests. Repeatability was assessed by calculation of the intra-class correlation coefficient (ICC) and its 95% confidence interval (CI). P < 0.05 was considered significant. RESULTS There was a significant difference between NIN and IN measures at maximal extension (p = 0.01) and at 30° of flexion (p = 0.02). There was a good correlation between NIN and IN measures at maximal extension (rho = 0.80, p < 0.05) and a weak correlation between NIN and IN measures at 30° of flexion (rho = 0.43, p < 0.05). There was a good agreement between NIN and IN measures at maximal extension (rho = 0.13, p = 0.43) with a systematic bias of +1.6 degrees. There was a good agreement between NIN and IN measures at 30° of flexion (rho = 0. 10, p = 0.56) with a systematic bias of +3.1 degrees. There was an excellent intra-observer repeatability at maximal extension (ICC = 0.70), and a poor intra-observer repeatability at 30° of flexion (ICC = 0.49). Inter-observer repeatability was excellent at maximal extension (ICC = 0.84), and poor at 30° of flexion (ICC = 0.55). DISCUSSION NIN measures differed significantly from IN measures for all three items analyzed; but were well correlated. These differences may occur because of skin motion artifact. Another confounding factor may be the difference between the two algorithms for NIN or IN calculation. Despite these limitations, the NIN system may help the surgeon to better plan a TKA.

Ten Year Survival of Navigation-Assisted Total Knee Arthroplasty.

ABSTRACT. INTRODUCTION Revisions may still occur after total knee arthroplasty (TKA), and some may be related to the implantation technique. Computer assistance may improve the accuracy of a TKA. Few long term results have been documented. The present study was designed to evaluate the long-term (more than 10 years) results of a TKA which was routinely implanted with help of a non-image based navigation system. The hypothesis of this study will be that the 10 year survival rate of this TKA will be improved in comparison to historical papers when analyzing survival rates and knee function as evaluated by the Knee Society Score (KSS). MATERIAL AND METHODS All patients operated on between 2001 and 2004 for implantation of a navigated TKA were included. Usual demographic and peri-operative items have been record. All patients were prospectively followed with clinical and radiological examination. All patients were contacted after the 10 year follow-up for repeat clinical and radiological examination (KSS, Oxford knee questionnaire and knee plain X-rays). Patients who did not return were interviewed by phone call. For patients lost of follow-up, family or general practitioner was contacted to obtain relevant information about prosthesis survival. Survival curve was plotted according to Kaplan-Meier. RESULTS 247 TKAs were implanted during the study time-frame. 225 cases had an optimal lower limb axis (HKA angle between 177° and 183°) after TKA (91%). Final follow-up (including death or revision) was obtained for 200 cases (81%). Clinical status after 10 years was obtained for 146 cases (59%). 4 prosthetic revisions were performed for mechanical reasons during the follow-up time (1%). The 10 year survival rate was 98%. No component was considered loose at the final radiographic evaluation. No polyethylene wear was detected at the final radiographic evaluation. DISCUSSION This study confirms our initial hypothesis, namely quite satisfactory results of navigated implanted TKA after more than 10 years. Navigation, whose precision is no longer to be demonstrated, probably contributed to the quality of the results. A more consistent anatomical reconstruction and ligamentous balance of the knee should lead to more consistent survival of the TKA. However, superiority of navigated TKA in comparison to conventional implanted TKA is difficult to prove because of the subtle differences expected in mostly underpowered studies. Longer term follow-up may be required.

10:30-12:00 Session 3: Knee Replacement (Clinical Studies) I
Location: Europa
Knee Periprosthetic Infections: CAOS Use in One Stage Procedures

ABSTRACT. INTRODUCTION The results of TKA revisions are less good than a primary TKA (1). The TKA revision frequency increases and we must prepare the next standard of these surgeries (4).The aim of this study was to evaluate the CAOS / one stage strategy to treat the knee PJIs (2, 3). MATERIALS In this prospective study, between September 2011 and december 2014, 41 patients treated for chronic knee PJI in a one stage revision. An imageless CAOS system (ExactechGPS, Blue-Ortho, Gieres) was used with a personnalized profile. All surgeries were performed with the same protocole and by using the same Optetrak CC knee components (Exactech, Gainesville, FL). All operations were performed by a single senior surgeon. Indications for the revision TKA were (1) revision of a primary TKA or unicondylar knee arthroplasty (n=27) or (2) revision of revisionTKA (n=15). The measurement of the HKA angle, the Oxford score and the ROM were evaluated pre and post-operatively.

RESULTS 27 males and 14 females with an average age of 71 years old (55-87) were treated for a PIJ (1 unicompartimental prosthesis, 26 TKA and 15 RTKA). The mean follow-up was 41 months (30 months - 6 years). The average time of surgery was 135 mn (120-195) for an average hospitalisation duration of 10 days (7-16). No postoperative outliers were reported (mean preop.: -1,6°+/_-5,1° - Post-op. -0,3°+/_ -1,4°). The average ROM were 115° (90-130°) (Fig. 1). The rate of success for the infection was 92,7%. We report no specific CAS complications and all the navigations were finalized. In this series of complex cases, the rate of infection healing is 92,7%.

DISCUSSION Using CAOS is a safe option with no specific complication. Combined with one stage procedures, it should be a optimal medicoeconomical strategy for Knee revisions.

This first series initiated the « GPS RTKA » project to create a dedicated software evaluated since January 2016 with immediate very good functional results and no complications. 2002;(404): 7-13

The Surgeon Plays an Important Role in Size Planning with Patient Specific Instrumentation for Total Knee Arthroplasty
SPEAKER: Paolo Ferrua

ABSTRACT. Patient specific instrumentation (PSI) for total knee arthroplasty (TKA) may improve component position and sizing. However, little has been reported about the accuracy of the default plan created by the manufacturer. The purpose of the study was to evaluate the reliability of the manufacturer plan and the impact of surgeon’s changes on the final accuracy of the cutting guide sizes. The planned sizes of 45 TKAs were prospectively recorded from the in the initial manufacturer’s proposal and from the final plan modified after surgeon’s evaluation and compared to the actually implanted sizes. The manufacturer’s initial proposal differed from the final implant in 20% of the femoral and 51.11% of the tibial components, while the surgeon’s plan in 13.33% of the femoral and 26.67% of the tibial components. Surgeon’s modifications in the pre-operative were carried out for 11.11% of the femoral components and 51.11% of the tibial ones (p = 0.0299). Appropriate modification occurred in of 88% and 76% of femoral and tibial changes respectively. The surgeon’s accuracy to predict the final component size was significantly different from that of the manufacturer and changes on the manufacturer’s plan were necessary to get an accurate preoperative plan of the implant sizes. Careful evaluation by an experienced knee surgeon is mandatory when planning TKA with PSI. Collaboration between surgeons and manufacturers may help obtain improved accuracy in PSI size planning.

Comparison of Rotational Alignment Between Anatomical Method and Classical Method in CAS TKA

ABSTRACT. The “correct” rotational alignment and “normal” rotational alignment may not be the same position. Because of natural tibial plateau has average 3° varus but classical TKA method make tibial cut perpendicularly to tibial mechanical axis. Consequently femoral rotational compensation to 3° becomes necessary. While anatomical TKA method performed tibial cut in 3° varus. Then posterior femoral cut will be parallel to posterior condylar axis and component rotation theoretically should be aligned in natural anatomy. This study compares the rotational alignment between two methods. Study conducted on 80 navigated TKAs with modified gap technique. Intraoperative femoral rotation retrieved from navigation. Rotational alignment was calculated using the Berger protocol with postoperative computerized tomography scanning. The alignment parameters measured were tibial and femoral component rotations and the combined component rotations. 57 knees with PS design can be classified into 35 knees as anatomical group and 22 knees as classical group. 23 knees with CR design had 12 knees as anatomical group and 11 knees as classical group. The intraoperative femoral rotation in anatomical group had less external rotation than classical group significantly in PS design (0.77°±1.03° vs 2.86°±1.49°, p = 0.00) and also had the same results in CR design (1.33°±1.37°vs 2.64°±0.81°, p = 0.012). However, the postoperative excessive femoral and tibial component rotation compared with native value and combined rotation had no significant differences between classical and anatomical method in both implant design. Using CAS TKA with gap technique showed no difference in postoperative rotational alignment between classical and anatomical method.

Extension and Flexion Coronal Alignment Measured with Computer Navigation in Osteoarthritic Knees Undergoing Primary Total Knee Arthroplasty
SPEAKER: Jef Neirynck

ABSTRACT. Background: Differences of dynamic (extension vs. flexion) coronal alignment in osteoarthritic (OA) knees undergoing primary total knee arthroplasty (TKA) remain poorly studied. Methods: Prospectively collected measurements of dynamic coronal alignment using an imageless computer-navigation system (Stryker©) during primary TKA were analyzed. Coronal alignment was represented by the hip-knee-ankle angle and determined at maximal extension and 90° flexion before making any bony cuts or ligamentous releases. Measurements were subgrouped according to coronal alignment in extension as varus (≤-3°), neutral (>-3°, <+3°) or valgus (≥+3°). Results: Of 545 knees (347 females), coronal alignment in extension was 261 (48%) varus, 197 (36%) neutral and 87 (16%) valgus. Varus extension alignment was more common in male vs. female OA knees (64% vs. 39%; p< .0001). Valgus extension alignment was more common in female vs male OA knees (19.5% vs 9.5%; p= .002). In flexion, 174 (66%) of varus OA knees remained varus and 6 (3.3%) evolved to valgus. Extension varus exceeding 10° in 29/261 (11%) varus knees remained flexion varus in 28 (96.5%). Mean (±SD) difference between extension and flexion in varus knees was 1.98° (±4.0°) valgus. Of 87 valgus knees, 44 (50.5%) remained valgus and 4 (4.5%) evolved into varus during flexion. Mean (±SD) difference between extension and flexion in valgus knees was 2.3° (±4.2°) varus. Dynamic coronal alignment was unchanged in 27/545 (4.9%) and alternated between varus and valgus in 10/348 (2.9%) varus or valgus AO knees. Conclusion: Different coronal alignment was observed in >95% of OA knees of which almost 3% alternated between varus and valgus. This insight of a dynamic coronal deformity might contribute to improving ligamentous release during TKA. Further studies including prognostic value and functional outcome are warranted.

Long-Term Follow up of Navigation TKA Using Multi Directional Mobile Bearing Design
SPEAKER: Je-Hyoung Yeo

ABSTRACT. Total knee arthroplasty using navigation system is known to be more effective than conventional methods in achieving more accurate bone resection and neutral alignment.1 Mobile bearing is also known to reduce wear and automatically correct rotational malalignment of the tibia but the long-term follow-up results of more than 10 years are extremely rare.2, 3 The purpose of this study is to investigate the results of clinical and radiologic long-term follow-up and complications of total knee arthroplasty using navigation and multi-directional mobile bearing. From 2003 to 2006, a total of 111 navigation TKAs using multi-directional mobile bearing design were carried out and reviewed retrospectively. TKAs were performed by two experienced surgeons at one institute. Of the 111 patients, 102 were women and 9 were men. The mean duration of follow-up was 11.4 ± 1.0 years (range, 10.1 to 14.08 years). Clinical outcomes were evaluated in terms of Knee Society Score, Hospital for Special Surgery score, Western Ontario and McMaster University (WOMAC) score, range of motion and complications. Long-term radiological outcomes and survival rates were evaluated at least 10 years. Average preoperative HSS score was 66.5 ± 9.8 and KSS pain and function score were 25.0 ± 11.8 and 44.5 ± 12.3, respectively. Scores improved to 94.1 ± 8.2, 46.6 ± 11.6 and 88.2 ± 14.6 at the last follow up, respectively. Mean preoperative WOMAC scores of 75.8 ± 16.5 improved to 13.8 ± 16.0 at last follow-up. Five knees required re-operation, two for liner breakage, one for liner wear, one for distal femoral fracture and one for infection. The estimated 10-year prosthesis survival rates for any reason and for prosthesis-related problems were 95.5% and 97.4% , respectively. TKAs using each techniques resulted in similar good clinical outcomes and postoperative leg alignments. Robotic and navigation TKA appeared to reduce the number of postoperative leg alignment outliers and revision rate compared to conventional TKA.

Long Term Study with Tissue Sparing Surgery and Computer Assistance in Knee Replacement: Bi-Uni Vs Total at 12 Years Minimum Follow-Study

ABSTRACT. Introduction: At a minimum 12 years follow-up the Authors performed a matched paired study between 2 groups: Bi-Unicompartimental (femoro-tibial) versus Total Knee Replacements, both navigated, they hypothesized that Bi-UKR guarantees a clinical score and patient satisfaction at least similar to TKR without differences in survivorship.

Materials and Methods: 19 BI-UKR (1999-2003) were included in the study (group A). Every single patients in group A was matched to a computer-assisted TKR implanted in the same period (group B). The clinical outcome was evaluated using the Knee Society Score, the GIUM Score and the WOMAC Arthritis Index. Radiographically the HKA angle and the Frontal Tibial Component angle (FTC) were. Statistical analysis of the results was performed and Kaplan-Meir survival rate was assessed in both the groups.

Results: No statistically significant difference was seen for the Knee Society, Functional and GIUM scores between the 2 groups. Statistically significant better WOMAC Function and Stiffness indexes were registered for the Bi-UKR group. All the TKR implants still remained positioned within 4 degrees of an ideal HKA angle of 180° and ideal FTC angle of 90° with a statistically significant better alignment compared to the Bi-UKR group. The Kaplan-Meier survival did not show any statistical significant differences in survivorship

Discussion: At 12 years minimum follow-up there are no significant differences in survivorship and clinical score despite a worse implant alignment WOMAC function and stiffness scores are still statistically better in the Bi-UKR group

Does Learning Curve Affect the Accuracy in Resection Alignment During Navigated Total Knee Arthroplasty?


Yifei Dai, Cyril Hamad, Amaury Jung, Laurent Angibaud Exactech Inc, Gainesville, FL, 32653, USA,

Computer-assisted orthopaedic surgery (CAOS) has been demonstrated to increase accuracy to component alignment of total knee arthroplasty compared to conventional techniques. The purpose of this study was to assess if learning affects resection alignment using a specific CAOS system. Nine surgeons, each with >80 TKA experience using a contemporary CAOS system, were selected. Prior to the study, six surgeons had already experienced with CAOS TKA (experienced), while the rest three were new to the technology (novice). The following surgical parameters were investigated: 1) planned resection, resection parameters defined by the surgeon prior to the bone cuts; 2) checked resection, digitalization of the realized resection surfaces. Deviations in the alignment between planned and checked resections were compared between the first 20 cases (in learning curve) and the last 20 cases (well past learning curve) within each surgeon. Any significance detected (p < 0.05) with >1° difference in means indicated clinically meaningful impact on alignment by the learning phase. Both pooled and surgeon-specific analysis exhibited no clinically meaningful significant difference between the first 20 and the last 20 cases from both experienced and novice surgeon groups. The resections in both the first 20 and the last 20 cases demonstrated acceptable rates of over 95% in alignment (<3° deviation) for both experienced and novice surgeons. This study demonstrated that independent of the surgeon’s prior CAOS experiences, the CAOS system investigated can provide an accurate and precise solution to assist in achieving surgical resection goals with no clinically meaningful compromise in alignment accuracy and outliers during the learning phase.

Total Knee Arthroplasty Using a Contemporary Computer-Assisted Surgical System: a Review of Resection Alignment on 7000 Clinical Cases


As previous meta-analyses on the alignment outcomes of Computer-assisted orthopaedic surgery (CAOS) did not differentiate between CAOS systems, limited information is available on the accuracy of a specific CAOS system based on clinical cases. This study assessed the accuracy and precision of achieving surgical goals in approximately 7000 cases using a specific contemporary CAOS system. Alignment parameters were extracted from the technical logs of 6888 TKA surgeries performed between October 2012 and January 2017 using a contemporary CAOS system. The following surgical parameters were investigated: 1) planned resection defined by the surgeon prior to the bone cuts; 2) Checked resection defined as digitalization of the bony cuts. Deviations in alignment between planned and checked resections were evaluated, with acceptable resections defined as no more than 3° of resection deviations. For the tibial resection, deviations in tibial varus/valgus angle and posterior tibial slope were 0.06 ± 0.94° and -0.09 ± 1.73°, respectively. For the femoral resection, deviations in femoral varus/valgus angle amd femoral flexion were 0.00 ± 0.97° and -0.17 ± 1.44°, respectively. High percentages of the resections were found to be acceptable (>94% of the cases). The CAOS system investigated was shown to provide accurate and precise intra-operative assistance to the surgeon in achieving targeted resections. The study summarized a large number of cases spanning the application history of the specific CAOS system, including both experienced users and new adopters of the technology. The data provided a complete clinical relevant evaluation demonstrating its high accuracy and precision in resection alignment.

Ten Year Survival of Navigation-Assisted Unicompartmental Knee Arthroplasty.

ABSTRACT. INTRODUCTION Unicompartmental knee arthroplasty (UKA) is considered a highly successful procedure. However, complications and revisions may still occur, and some may be related to the operative technique. Computer assistance has been suggested to improve the accuracy of implantation of a UKA. The present study was designed to evaluate the long-term (more than 10 years) results of an UKA which was routinely implanted with help of a non-image based navigation system. MATERIAL AND METHODS All patients operated on between 2004 and 2005 for implantation of a navigated UKA were included. Usual demographic and peri-operative items have been record. All patients were prospectively followed with clinical and radiological examination. All patients were contacted after the 10 year follow-up for repeat clinical and radiological examination (KSS, Oxford knee questionnaire and knee plain X-rays). Patients who did not return were interviewed by phone call. For patients lost of follow-up, family or general practitioner was contacted to obtain relevant information about prosthesis survival. Survival curve was plotted according to Kaplan-Meier. RESULTS 57 UKAs were implanted during the study time-frame. Final follow-up (including death or revision) was obtained for 50 cases (88%). Clinical status after 10 years was obtained for 45 cases (80%). 4 prosthetic revisions were performed for mechanical reasons during the follow-up time (7%). The 10 year survival rate was 94%. No component was considered loose at the final radiographic evaluation. No polyethylene wear was detected at the final radiographic evaluation. DISCUSSION This study confirms our initial hypothesis, namely quite satisfactory results of a navigated implanted UKA after more than 10 years. Navigation, whose precision is no longer to be demonstrated, probably contributed to the quality of the results. A more consistent anatomical reconstruction and ligamentous balance of the knee should lead to more consistent survival of the UKA. However, superiority of navigated UKA in comparison to conventional implanted UKA is difficult to prove because of the subtle differences expected in mostly underpowered studies. Longer term follow-up may be required.

12:00-13:00 Session : Luncheon Seminar (Sponsored by Ziehm Imaging GmbH)

Christoph Josten 

"Improvement of quality and safety in orthopedic operations  by optimal intraoperative 3D imaging and navigation"

Further information at:

Location: Europa
13:00-14:00 Session 4: Afternoon Keynote - Dr Reinhart Poprawe, PhD (Fraunhofer Institute for Laser Technology)

Further information at:


Location: Europa
14:00-15:15 Session 5: Hip Replacement (Clinical Studies)
Location: Europa
Clinical Accuracy of a Smart Mechanical Navigation System for Cup Alignment as Measured by Post-Operative CT

ABSTRACT. Introduction: Navigation of acetabular component orientation is still not commonly performed despite repeated studies that show that more than ½ of acetabular components placed during hip arthroplasty are significantly malpositioned1 and that intraoperative radiographic assessment is unreliable. The current study uses postoperative CT to assess the accuracy of a smart mechanical navigation instrument system for cup alignment. Patients and Methods: Thirty seven hip replacements performed using a smart mechanical navigation device (the HipXpert System) had post-operative CT studies available for analysis. These post-operative CT studies were performed for preoperative planning of the contralateral side, one to three years following the prior surgery. An application specific software module was developed to measure cup orientation using CT (HipXpert Research Application, Surgical Planning Associates Inc., Boston, Massachusetts). The method involves creation of a 3D surface model from the CT data and then determination of an Anterior Pelvic Plane coordinate system. A multiplaner image viewer module is then used to create an image through the CT dataset that is coincident with the opening plane of the acetabular component. Points in this plane are input and then the orientation of the cup is calculated relative to the AP Plane coordinate space according to Murray’s definitions of operative anteversion and operative inclination. The actual cup orientation was then compared to the goal of cup orientation recorded when the surgery was performed using the system for acetabular component alignment. Results: For the thirty seven hips replacements, mean operative anteversion error was 1.1 degrees (SD 3.6, range -5.5 to 8.2). Mean operative inclination error was - 1.7 degrees (SD 3.0, range -8.0 to 5.6). There were no outliers in either anteversion or inclination. Conclusion: The current study demonstrates that the mechanical navigation system produces accurate cup alignment results as measured by post-operative CT and confirms the prior accuracy study performed using 2D/3D matching. This improved accuracy compared to robotic systems4 may be due to the wide-based nature of the docking mechanism and the elimination of the cumulative errors of registration and tracking inherent to more complex systems.

An Instrument Mounted Mini-Display for Intraoperative Guidance in Hip Surgery

ABSTRACT. Total hip replacement in Germany has been performed in 227293 cases in 2015 and tendency is increasing. Although it is a standard intervention, freehand positioning of cup protheses has frequently poor accuracy. Image-based and image-free navigation systems improve the accuracy but most of them provide target positions as alphanumeric values on large-size screens beneath the patient site. In this case the surgeon always has to move his head frequently to change his eye-focus between incision and display to capture the target values. Already published studies using e.g. IPod-based displays or LED ring displays show the chance for improvement by alternative approaches. Therefore, we propose a novel solution for an instrument-mounted small display in order to visualize intuitive instructions for instrument guidance directly in the viewing area of the surgeon. For this purpose a solution consisting of a MicroView OLED display with integrated Arduino microcontroller, equipped with a Bluetooth interface as well as a battery has been developed. We have used an optical tracking system and our custom-designed navigation software to track surgical instruments equipped with reference bodies to acquire the input for the mini-display. The first implementation of the display is adapted to total hip replacement and focuses on assistance while reaming the acetabulum. In this case the reamer has to be centered to the middle point of the acetabular rim circle and its rotation axis must be aligned to the acetabular center axis by Hakki. By means of these references the actual deviations between instrument and target pose are calculated and indicated. The display contains a cross-hair indicator for current position, two bubble level bars for angular deviation and a square in square indicator for depth control. All display parts are furnished with an adaptive variable scale. Highest possible resolution is 0.5 degrees angular, 1 millimeter for position and depth resolution is set to 2 mm. Compared to existing approaches for instrument-mounted displays the small display of our solution offers high flexibility to adjust the mounting position such that it is best visible for the surgeon while not constraining instrument handling. Despite of the small size, the proposed visualization symbols provide all information for instrument positioning in an intuitive way.

Accuracy of Cup Orientation in Total Hip Arthroplasty Using an Accelerometer-Based Navigation System (HipAlign)
SPEAKER: Yuki Maeda

ABSTRACT. The purpose of this preliminary study was to evaluate the feasibility and accuracy of HipAlign (OrthAlign, Inc., USA) system for cup orientation in total hip arthroplasty (THA). The subjects of this study were 5 hips that underwent primary cementless THA via a posterior approach in the lateral decubitus position. Evaluation 1; after reaming acetabular bone, a trial cup was placed in the reamed acetabulum in an aimed alignment using HipAlign. Then, the trial cup alignment was measured using HipAlign and CT-based navigation system in the radiographic definition. Evaluation 2; a cementless cup was placed in the reamed acetabular in an aimed alignment using CT-based navigation and cup alignment was measured using both methods. After operation, we measured the cup alignment using postoperative CT in each patient. In the results, the average cup inclination measured with HipAlign were around 5 degrees of true cup inclination angles. The average cup anteversion with HipAlign tended to be larger than that with CT-based navigation or postoperative CT in both evaluations. That is because there is a difference in the pelvic sagittal tilt between the lateral position and supine position. In conclusion, this study suggests that guiding cup alignment with the use of HipAlign is feasible through a posterior approach and the mean cup inclination measured with HipAlign showed an acceptable level of accuracy, but the mean cup anteversion is not reliable. We need a further modification for pelvic registration to improve the accuracy of cup anteversion.

EOS Revealed Correlation of the Anterior Pelvic Plane Angle with the Pelvic Alignment Parameters of Pre- and Post-Operative Patients in Supine and Standing Positions

ABSTRACT. The anterior pelvic plane (APP) angle is often used as a reference to decide pelvic alignment for hip surgeons. However, Rousseau criticized the validness of the APP angles because the APP angles in standing position measured on conventional standing X-ray films never showed correlation with the other pelvic alignment parameters, such as sacral slope (SS). We measured the APP angles, SS and pelvic tilt (PT) on the non-distorted anteroposterior (AP) and lateral digitally reconstructed radiography (DRR) images in supine position (with CT scans) and AP and lateral X-ray images in standing position (with EOS X-ray machine [EOS imaging, Paris, France]) by using of the same EOS software. Our data showed that the pre- and post-operative APP angles correlated with SS and PT in both supine and standing positions. Our non-distorted high quality images and the EOS software revealed these correlations. Therefore, we can still use the APP angles to decide pelvic alignment for patients who undergo total hip arthroplasty (THA). Recent papers demonstrated positional or chronological dramatic changes of the APP angles between pre- and post-operative states in patients who underwent THA. The EOS system will be a powerful tool to investigate these changes of the pelvic alignments.

Validation of Patient-Specific Surgical Guides for Femoral Neck Cutting in Total Hip Arthroplasty Through the Anterolateral Approach
SPEAKER: Takashi Sakai

ABSTRACT. The purpose of this experimental study was to elucidate the accuracy of neck-cut PSG setting, and femoral component implantation using neck-cut PSG in the THA through the anterolateral-approach relative to the preoperative planning goals, and to determine the usefulness of PSG compared with the procedure without PSG. A total of 32 hips from 16 fresh Caucasian cadaveric samples were used and classified into 4 groups: cementless anatomical stem implantation with wide-base-contact PSG (AWP: 8 hips, Fig.2); (2) cementless anatomical stem implantation with narrow-base-contact PSG (ANP: 8 hips, Fig.2); (3) cementless anatomical stem implantation without PSG (Control: 8 hips); and (4) cementless taper-wedge stem implantation with wide-base-contact PSG (TWP: 8 hips). The absolute error of PSG setting in the sagittal plane of the AWP group was significantly less than that of the ANP (p=0.003).THA with wide-base-contact PSG resulted in better alignment of the femoral component than THA without PSG or with narrow-base-contact PSG. Although the neck-cut PSG did not control the sagittal alignment of taper-wedge stem, the neck-cut PSG was effective to realize the preoperative coronal alignment and medial height for THA via the anterolateral approach regardless of the femoral component type.

Robotic-Assisted Total Hip Arthroplasty – Clinical Outcomes and Complication Rate
SPEAKER: Itay Perets

ABSTRACT. Background: Robotic assistance is being increasingly utilized in the surgical field in an effort to minimize human error. In this study, we report minimum two-year outcomes and complications for robotic-assisted total hip arthroplasty.

Methods: Data were prospectively collected and retrospectively reviewed between June 2011 and April 2014. Inclusion criteria were primary robotic-assisted THAs treating idiopathic osteoarthritis with ≥ 2-year follow-up. Demographics, operating time, complications, 2-year outcome scores and satisfaction, and subsequent surgeries were recorded.

Results: There were 181 cases eligible for inclusion, of which 162 (89.5%) had minimum 2-year follow-up. Eighty-nine females and 73 males were included. Forty-seven cases used an anterior approach and 115 used posterior approach. Mean age was 61.2 and mean BMI was 29.8. At latest follow-up, mean Visual Analog Scale for pain was 0.7, patient satisfaction was 9.3, Harris Hip Score was 91.1, and Forgotten Joint Score was 83.1. The mean time of surgery was 76.7 min. There were three (1.9%) greater trochanteric fractures and three (1.9%) calcar fractures. Postoperative complications included deep vein thrombosis (2 cases, 1.2%), femoral stem loosening (one case, 0.6%, treated with stem revision), infection (1 case, 0.6%, treated with single stage incision and drainage), aseptic hematoma (1 case, 0.6%, treated with single stage incision and drainage), and dropfoot (1 case, 0.6%). No leg length discrepancies (LLD) or dislocations were reported.

Conclusion: Robotic-assisted THA is a safe procedure with favorable short-term outcomes. In particular, the excellent Forgotten Joint Score results suggest that this procedure effectively replicates the feeling of the native hip.

Changing Anatomic Version Causes Loss of Peri-Prosthetic Bone Density After THA

ABSTRACT. The short tapered-wedge stem is popular worldwide because its stem alignment during stem insertion is easier to changing. However, stem version changing may affect physiological stress distribution. Therefore, we analyzed in this study the correlations between periprosthetic bone mineral density (BMD) changes and anteversion in patients who underwent total hip arthroplasty (THA) using a short tapered-wedge stem. The study included 44 patients (44 joints) who underwent THA with a TriLock stem. At baseline and at 6 and 24 months postoperatively, the BMDs in the seven Gruen zones were evaluated using dual-energy X-ray absorptiometry. BMD changes and stem alignment, that is, anteversion and anteversion error to the anatomical canal version, were analyzed. Significant negative correlations were found between BMD changes and absolute anteversion error in Gruen zones 1 and 7 at 6 and 24 months postoperatively (zone 1, 6M; rr= -0.36, p=0.016) (zone 7, 6M; rr=-0.36, p=0.019) (zone 1, 24M; rr= -0.45, p= 0.003) (zone 7, 24M; rr=-0.45, p= 0.004). Further, significant differences of BMD changes were found between over 5 degrees of anteversion error and under 5 degrees (zone 1, 6M; p=0.033) (zone 7, 6M; p=0.023) (zone 1, 24M; p=0.029) (zone 7, 24M; p=0.025) Excessive changing of anatomical anteversion affects periprosthetic BMD loss after THA. We recommend the insertion of the tapered-wedge stem along the anatomical canal anteversion.

15:45-16:30 Session 6: Poster Session
Location: Foyer OG
Percutaneous Screw Fixation for Pelvic Fractures by Fluoroscopic Navigation with Overlay of Real-Time Robotic C-Arm Cone Beam CT
SPEAKER: unknown

ABSTRACT. PURPOSE The purpose of this study was to evaluate the feasibility, accuracy, and complications of real-time 3D fluoroscopy navigation system in combination with guide-wire trajectory planning for pelvic percutaneous screw placement.

MATERIALS AND METHODS A total of 12 patients, 5 female and 7 male, mean aged 67 years, were included in this study. All patients were suffered from a high energy trauma like traffic accident (7 cases) and fall form height (5 cases). 3D cone beam CT (CBCT) images of the patients were acquired with a robotic C-arm in the hybrid OR. Then, the guide-wire trajectory was planned on the workstation. In the orthogonal multiplane images, the entry and end point manually selected. A virtual guide-wire trajectory was generated with its angulations and length calculated and displayed. The virtual trajectory was then projected and superimposed onto the real-time fluoroscopic images and displayed on a dedicated live monitor. The guide-wire was advanced under fluoroscopy by rotated the C-arm back and forth to monitor the guide-wire progression. In order to investigate the accuracy of screw placement using fluoroscopic navigation, we compared the absolute differences with preoperative and postoperative values form CT data as the screw trajectory angle along axial, coronal and sagittal plane against anterior pelvic plane using 3D analysis software.

RESULTS The average surgical time was 148 minutes (60 to 277 minutes) and blood loss was 12.1g (5 to 30g). Total 28 cannulated screws including 14 iliosacral screws, 5 iliac screws, 5 acetabular screws and 5 pubic screws were inserted. There were no complications including vascular injury, neural foramen perforations and postoperative infection. All patients could transfer wheelchair within a week and start rehabilitation. The absolutely differences for screw trajectory angle was significant difference in 4.8°(SD 3.9) for coronal plane and 11.3°(SD 11.9) for sagittal plane (p<0.05).

DISCUSSION Our results showed that this integrated 3D CBCT and fluoroscopic navigation enabled percutaneous screw fixation of pelvic fractures. Accuracy of screw insertion angles against sagittal plane was poor because of a power instrument interfere to see lateral view during screw insertion. Percutaneous screw fixation for pelvic fracture can be safely performed by navigation with 3D real-time fluoroscopy CBCT. However, accurate screw placement under real-time fluoroscopic navigation in lateral views were poor.


ABSTRACT. Consideration of the pre- and post-operative magnitude of the hip joint force R and its orientation Ɵ is of major importance for satisfactory long-term results in total hip arthroplasty. R and Ɵ can be computed by using biomechanical models with adapted geometrical/anthropometrical parameters taken from clinical X-ray images. The objective of this study was to evaluate the models of Pauwels and Debrunner based on digital reconstructed-radiographs (central projection) from 10 CT-datasets of patients treated with telemetric hip-implants by a comparison to corresponding in-vivo measurements. R and Ɵ were computed for 10 patients with patient-specific geometric/anthropometric parameters. The model adaption was based on 28 anatomical landmarks. The root-mean-square-error of R is smaller for Debrunner (0.59/vs./0.66), and for Ɵ it is smaller for Pauwels’ (4.47/vs./7.78). Mathematical models provide potentially valuable information regarding hip joint mechanics. Regarding R, in all of the 10 patients the predictions of Pauwels’ model are consistently higher than the in-vivo measurements. Debrunner computed R in 8 cases higher and in 2 cases lower than the corresponding in-vivo forces. Pauwels’ and Debrunner showed similar tendencies: in 8 cases an overestimation of R and in 2 cases contrary results. Regarding Ɵ we found that in 5 cases the predictions of Pauwels’ are consistently higher than the in-vivo measurements and also contrary to Debrunner. As previous studies showed, an unambiguous identification of most landmarks in a 2D X-ray image is difficult. The impact of the pelvic tilt on the computational result was not considered in our study. Further investigation of this aspect is part of our ongoing work.

Three-Dimentional Evaluation of Transacetabular Screw Position and Influence for Intraoperative Cup Movement in Total Hip Arthroplasty

ABSTRACT. The purpose of this study was to investigate transacetabular screw position and influence of transacetabular screw for intraoperative cup movement. 309 primary THAs were performed using cementless acetabular cup. Of these, 50 hips with transacetabular screws were included. A cementless acetabular cup was implanted using the CT-based hip navigation system according to the preoperative planning. Cup anteversion was based on modified combined anteversion theory while maintaining the radiographic inclination of the cup aimed at 40°. Intraoperatively, cup inclination and anteversion were recorded using navigation system before inserting transacetabular screw. Using postoperative CT date and navigation system software, screw insertion area was evaluated by 12 sectors modified quadrant system, and screw length, penetration to out of pelvis (≥ 3 mm) and alignment (medial inclination, posterior tilt) were measured. In addition, we compared intraoperative record of cup alignment and postoperative cup alignment in order to investigate the influence of transacetabular screw for intraoperative cup movement. A total of 92 screws were analyzed. There were wide variations in screw alignment and length. All screws except one were placed in posterosuperior and posteroinferior quadrants. The mean absolute error of the cup alignment was 0.6±0.8° for inclination and 0.6±0.7° for anteversion. These informations could be useful for transacetabular screw fixation intraoperatively.

Heat Resistant Electronic Modules for Intelligent Medical Sterile Containers
SPEAKER: Lukas Böhler

ABSTRACT. The digitalisation gets more and more important in our daily life. Also in medical technology instruments and devices need to become intelligent and be able to both collect and provide additional data. This research is about the development of an electronic sensor system for sterilisable medical containers. Hereby just a few concepts exist to equip the containers with sensor modules but the high temperature of 135 °C during the sterilisation is still a big challenge. The objective for this research is to find a heat resistant insulation for an electronic system with a power supply, sensors for both sterilisation and transport and a low power communication module. Furthermore, the thermal energy of the sterilisation shall be used for powering up the system. In a first step an epoxy resin was used to insulate the electronics and a high temperature battery. By using the temperature sensor of a Bluetooth module the module temperature could be measured during multiple steam sterilisations. Following, a partly insulated thermoelectric generator shall be used to get energy by the achieved temperature difference. First results show that the used epoxy resin limits the temperature to 81 °C. However, the resin was damaged after 21 sterilisation cycles due to its high mass and entrapped air. Therefore, the insulation needs to be minimized and the electronic components need to be able withstanding higher temperatures. Additionally, insulations with not yet considered materials will be tested. Also the possibility of insulating just heat-sensitive parts like the power elements will be investigated.

Patient-Specific Templates for Pedicle Screw Insertion in Spinal Fixation Surgery
SPEAKER: Mahmoud Hafez

ABSTRACT. Patient-specific templates for spine surgery would become an accurate alternative for conventional placement technique of pedicle screw and scoliosis. This technique relies on preoperative planning on computer software based on CT scans and requires secure fixation between the template and the lamina in a fit-and-lock fashion. This technique aims at reducing the operative time, operative steps, radiation exposure and the risk of misplacement, especially in patients with abnormal spine morphology.

PSI for Dog Knee Replacement
SPEAKER: Mahmoud Hafez

ABSTRACT. Total knee replacement is the standard treatment for advanced knee osteoarthritis. An improved method of treating an osteochondral defect for knee osteoarthritis of dogs is provided, which is a composite tissue for treating or preventing a disease, disorder, or condition associated with an osteochondral defect with new technique. The new technique of custom made instruments and implants for dog and small animals is applied for different breeds of dogs regardless of their sizes and weights. The tool is a custom made instruments, which is based on capture of image based (CT or computed X-ray) to be transferred to electronic 3D model and apply 3D preoperative planning to design the tools are used to perform the knee surgery.

Intraoperative 3D- Control of Instrumentations of the Upper Cervical Spine- Optimization and Improvement of Safety?

ABSTRACT. Introduction Depending on the type of fracture or pathology there are several operative treatment options such as the anterior lag screw osteosynthesis, the anterior transarticular C1 / 2- stabilisation or posterior techniques according Goel / Harms. All methods have in common that for the screw placement intraoperative imaging is used, since the development of 3D- C-Arms intraoperative controls in Ct quality are possible. This allows an increased accuracy at lower radiation exposure for the patient, as a postoperative CT can be avoided. Secondly, the instrumentation in critical anatomical regions can be controlled intraoperatively. The aim of this prospective study was to investigate the applicability and advantages of intraoperative imaging using a new 3D C-arm in the treatment of odontoid pathologies.

Patients and Methods Since 07/2015 at 33 patients (19f, 14m, age Ø72,6 years, r.:28- 95) with pathologies of the dens (24 fractures Type II Anderson/ D'Alonzo, 1 pseudarthrosis, 4 pathologic fractures, 2 Pseudarthrosis, 2 Rheumatoid Arthritis) 19 were stabilized from anterior (13x transarticular C1/2, 3x2 odontoid lag screws, 3x1odontoid lag screw) and 15 via posterior (Goel/ Harms) stabilisation.

Intraoperative K-wires were placed, then an intraoperative 3D scan (3D RFD, Ziehm GmbH) was performed and the image quality and the K-wire position was controlled. In case of a correct placement of the wires the screws were placed, in case of an incorrect placement the implants were changed immediately.

Results Out of a total 76 intraoperatively controlled implants 26 (88.15%) showed a regular position. In 9 (11.84%) cases an incorrect position was seen which was corrected intraoperatively. The image quality was evaluated in all cases as very good, the implementation of 3D scans was easy and fast to perform.

Conclusion Intraoperative 3D imaging is simple and fast to perform and increases the safety of screw placement in the upper cervical spine. Dislocations can be intraoperatively detected and corrected. Thus neurovascular complications with subsequent revision surgeries and postoperative CTs with increased radiation exposure for the patient can be avoided.

Change in Pelvic Sagittal Tilt After Corrective Long Fusion of Spine

ABSTRACT. The individual pelvic sagittal inclination (PSI) is an issue for cup alignment in total hip arthroplasty (THA). The pelvic position in supine or functional pelvic plane in supine have been recommended by many reports while some consider a standing pelvic position as the reference to aim an optimal cup alignment. PSI changes in various postures and even in the same posture, aging change it due to spinal degeneration and muscle weakness. The chronological PSI change is larger in standing than that in supine. It is expected that PSI in standing position may improve when spinal long fusion was performed. Therefore, the purpose of this study was to evaluate the change of PSI between pre- and post- corrective long fusion for adult spinal deformity (ASD). Total eight patients underwent corrective surgery for ASD between May 2014 and October 2016 were the subjects of this study. All are females with the average age of 70 years. There were two cases that underwent bilateral THA before spine surgery. The anterior pelvic plane (APP) through the most anterior aspect of the pubic tubercle and bilateral anterior superior iliac spines (ASISs) was used to measure PSI, which was defined as the angle between the APP and the vertical axis on the sagittal plane DRR. In addition, we measured the cup anteversion in two THA cases by using viewer software. The mean change in the preoperative PSI from supine to standing was 17° posteriorly. The mean change in the supine PSI from pre- to post-operation was 6.9° anteriorly, and that in the standing PSI was 17° anteriorly. The mean change in the postoperative PSI from supine to standing was 6.7° posteriorly. When we measured PSI on standard AP radiographs of the pelvis in two patients who underwent THA, the mean change in postoperative PSI from supine to standing was less than 3°.The mean change in cup anteversion on supine AP radiographs were 2.7°. As we expected, the change in PSI from supine to standing position was reduced by performing corrective surgery. In this study, the mean change of radiographic cup anteversion in supine after corrective long fusion was 2.7°and PSI in standing changed into the direction which reduce posterior impingement and anterior dislocation. Although the change in PSI after corrective spine surgery heavily depends on the spine surgeon’s philosophy of correction, corrective spine surgery should have a positive effect on cup alignment in standing and little influence on cup alignment in supine.

Handheld Robot for Bone Drilling Assistance
SPEAKER: unknown

ABSTRACT. Introduction of computer navigation systems has provided useful visual guidance for the surgeon to deliberately locate the tools to the anatomy. However, the tool positioning process is still manually performed. Sometimes the tool positioning may cause fatigue, stress and might be of risk to patient too. In this paper we designed a special purpose handheld robot for bone drilling. Meanwhile the coordinated controller assists the surgeon to precisely and safely drill the bone safely. Two force sensors are embedded at the handle and the cutter to measure the human exerted force and bone drilling force, respectively. The velocity command was then computed by the admittance controller for the robot controller. The motion of the control handle is positioned by the surgeon, while the surgical tool driven by the robot end-effector. The coordination between the human operator and the robot was designed so that the bone drilling can be performed more effectively than only image-navigation scenario. The drill was able to be maintained on the target trajectory with reasonable accuracy within 2 mm although the human operator has deviated the surgical tool up to 5 cm. The compensation function to guide the drill back to the planned path was very useful to prevent the drill’s breakage when penetrating through the holes on the bone plate in bone drilling procedure.

Fluoroscopy-Based Laser Projection System for Surgical Guidance and Its Calibration Methods

ABSTRACT. Introduction: We have developed a laser projection system, which can project laser on corresponding position to surgical planning drawn at a fluoroscopic image without an optical tracking system. In this paper, we introduce a spatial calibration method between a laser module and a fluoroscope for the laser projection and evaluate its accuracy with a mimic experimental system. Materials and Methods: The experimental system consists of a laser module, a distance measurement unit and a CCD camera. The laser modules can project arbitrary line on surface by reflecting a point source laser with two galvanometers. A calibration phantom is designed by combining a collimator for accurate laser pattern positioning and stainless steel ball arrays for calculation of an extrinsic parameter of a C-arm fluoroscopy. We set a projection plane having ruler in 400mm distance from the CCD camera, and set 54 points on the screen. The laser module projects points with respect to the set points, and a distance error between set points and projected points and angular error are calculated. Results: The distance errors is 1.5±1.9 mm (average ± standard deviation). Maximum error was 7.5 mm. Angular error was smaller than 2 degrees. Discussion: The laser projection system and its calibration method shows clinically acceptable accuracy and the clinical application is the next step.

Effect of Tibial Posterior Slope on Flexion and Extension Gaps Measured by Computer-Assisted Navigation

ABSTRACT. Background: Post-operative CT Tibial posterior slope was significantly improved in the CAN group, Tibial post slope effected in flexion gap & post-operative knee flexion, But no study in the effect of difference degree of Tibial posterior slope affects flexion gap. Objectives: To demonstrate the difference of Tibial posterior slope effected in intraoperative Flexion Gap, Extension Gap in using accuracy of CAN to control Tibial posterior slope, and demonstrate benefit of Tibial Posterior Slope that balancing the flexion and extension gap. Methods: An experimental cohort study of 60 patients in OA-knee, aged between 50 – 85 years, who undergoing TKA between September 2013 to June 2014; total 10 months. In Tibial cut step first, set Tibial posterior slope to 3, 5, 7 degree then measure flexion gap, extension gap in every degree of Tibial posterior slope by CAN. Results: 60 patients were enrolled. There were 5% male gender and 95% female gender. Average age were 69.3 + 7.37 years. BMI were 26.03 + 5.01 kg/m2. Equally in side of operation. The flexion gap measurement in tibial posterior slope 3, 5 and 7 degree were 15.43, 16.04 and 16.54 mm. The distance of flexion gap significantly increased (p-value < 0.01) when we increased tibial posterior slope from 3 to 5 and from 5 to 7 degree, the average increasing of flexion gap were 0.28 mm/degree. The extension gap of 3, 5 and 7 degree were 16.19, 16.80, 17.37 mm. The distance of extension gap significantly increased (p-value < 0.01) when we increased tibial posterior slope from 3 to 5 and from 5 to 7 degree, the average increasing of extension gap were 0.30 mm/degree. Conclusion: The increasing of Tibial Posterior Slope effected in both of flexion gap and extension gap, by increasing in 0.28 mm/degree in flexion gap and 0.30 mm/degree in extension gap.

Comparative Assessment of Upper Limb Performance to Evaluate a System Based on Inertial Measurement Units and Fuzzy Logic

ABSTRACT. Braulio Roberto Duarte Benitez, Catherine Disselhorst-Klug. Department of Rehabilitation & Prevention Engineering, Institute of Applied Medical Engineering, RWTH Aachen University, Aachen,52074, Germany

Introduction Currently, there are several methods to evaluate upper limb movements; they are mostly based on observation by physicians and physiotherapists, whose judgement is influenced by experience and subjective impressions. It is necessary to have support from new technology which can offer objective out-comes in order to focus on the assessment of patient’s movement performance.

Materials and Methods This study was done on 16 stroke patients, using a system which is based on four Inertial Measurement Units (IMUs) which are composed of accelerometers, gyroscopes, and magnetometers. Each sensor was placed on each segment of the patient´s arm, i.e. scapula, arm, forearm, and hand. Every patient was told to perform a daily-life movements with the arm, such as “move the hand to the mouth” and “hand to the head” starting from a resting position while they were standing, or sitting when requiring a wheelchair. Repeated movements were performed continuously between 15 and 20 times, while the data from the IMUs were recorded. Afterwards, the data were processed to obtain the orientation of every segment of the arm, given as Euler angles in relation to a laboratory coordinate system. The Euler angles were run through a Fuzzy Logic algorithm. The resulting values from a specific repetition were compared with other repetitions of the same exercise, assigning a score to each repetition based on a final scaled value between 0 and 10. Physiotherapists were asked to evaluate the patients´ movements.

Results Physiotherapists were able to highlight certain physical characteristics from the movements on a specific period of the exercise; In contrast to physiotherapists, Fuzzy algorithm considers and processes what the patient performed during the entire exercise. The outcome from the Fuzzy algorithm offered an objective, stable and consistent movement evaluation which was independent of the performed task and the analysed patient.

Does Dorr Classification Reflect Bone Quality of Pelvis and Acetabulum?
SPEAKER: Ryota Nakaya

ABSTRACT. The purpose of the current study was to address how Dorr Classification correlated with bone mineral density (BMD) around acetabulum and pelvic ring using quantitative computed tomography (qCT). The subjects were 113 patients (90 females and 23 males) who underwent primary THA. They all had preoperative three-dimensional CT scan with a bone density phantom. Fifty cases were Dorr Type A, 47 cases were Type B and 16 cases were Type C. BMD of the following 10 locations of the pelvic ring and the acetabulum were measured on qCT; acetabular roof, anterior column, posterior column, sacroiliac facet, body of pubis, body of ischium, iliopubic eminence and ramus of ischium. Posterior column was divided into three parts, or upper, middle and lower parts. There were significant differences in BMD among three Dorr types only in the lower part of posterior column among the groups. Dorr Type C had significantly lower BMD in the upper part of the posterior column than Type A or B. Dorr Type A had significantly higher BMD in the middle part of the posterior column than Type B or C. There were no significant differences in the acetabular roof and the anterior column among the groups. Dorr Type A had significantly higher BMD in any locations of the pelvic ring than Type B or Type C, but there were no significant differences in any locations of the pelvic ring between Type B and C. In conclusion, Dorr classification is the most sensitive to BMD at the inferior part of posterior column but did not reflect BMD at the acetabular roof possibly due to osteoarthritic osteoblastic changes.

Deviation of Cup Alignment from Target Angle During Press-Fit Insertion

ABSTRACT. Introduction: Several factors leading to cup malalignment including preoperative pelvic tilt, inaccurate pelvic position on the operative table, pelvic movement during the operation and alignment change after screws fixation of the cup. Nowadays there are few studies about deviation of cup alignment from target angle during press-fit insertion as it may be the other cause of cup malalignment.

Objective: To evaluate the deviation of cup alignment from target angle during press-fit insertion by using imageless navigation and to define any influential factors including gender, age and side of operation.

Materials and methods: Between February and December 2016, the patients undergoing THA with imageless navigation were included in the present single-center study. Cup inclination angle was aimed at 40 degrees in all cases but the anteversion angle was varied depend on the stem anteversion in each case using combined anteversion technique. The final cup was aligned as target angle in both inclination and anteversion, the tracker was detached from the insertion handle and the surgeon inserted the cup until it was seated completely. The tracker was attached again to display both inclination and anteversion angles and these angles were recorded. Deviated Inclination Angles (DIA) and Deviated Anteversion Angles (DAA) in each case were calculated.

Results: There were 124 cases in the present study. The mean age of the patients was 60.2 years (25-93). There were equal in right-side operation and left-side operation, 62 cases each. There were 114 cases (91.9%) with DIA. The mean DIA was 2.65 (0-8, SD 1.66). The DIA decreased in 107 cases (86.3%) with 12 cases decreased 5 degrees or more. The DIA increased in 7 cases (5.6%) with 2 cases increased 5 degrees or more. There were 103 cases (83.1%) with DAA. The mean DAA was 2.3 (0-14, SD 2.3). The DAA increased in 78 cases (62.9%) with 11 cases increased 5 degrees or more. The DAA decreased in 25 cases (20.2%) with 4 cases increased 5 degrees or more. The DIA was higher in men than in women significantly (p=0.012). There was significant correlation between DAA and patient’s age (p=0.037). There were no significant difference between DIA or DAA and side of the operation.

Conclusion: There were significant changes in cup orientation during press-fit insertion detected by imageless navigation, which were considered as one of the possible cause of cup malalignment.

CAS Guided RFA Can Be a Safe and Effective Treatment in OFD like Adamantinoma in a Child.
SPEAKER: Paul Jutte

ABSTRACT. Background Osteo Fibrous Dysplasia (OFD) like adamantinoma is considered a benign condition that is usually located in the tibia. The condition is mainly found in children and has an association with classical adamantinoma, a malignancy of bone. The preferred treatment is surgical. The lesion often requires a segment resection to eradicate the tumor as the margins of healthy bone are often too small to save continuity of bone and the lesion is located in the cortical area. Segmental resection in a young child is associated with a high complication rate. To avoid these complications it would be ideal to spare the continuity of tibial bone by treating the tumor in situ. Radiofrequency Ablation (RFA) may be a safe and reliable option for treatment of OFD like adamantinoma, without vital tumor spill. To ensure accurate ablation, the guidance and monitoring of antenna placement, planning and execution are performed with computer assisted surgery (CAS).

Results Two young patients with OFD like adamantinoma of the tibia were treated with CAS guided open intra-operative RFA in our institution. Because of the heat generation and the proximity of the skin we performed the procedures half open. In both patients successful local tumor ablation was achieved without complications. At baseline MRI there was no sign of residual tumor activity in either patient.

Discussion Follow-up is short and number of treated patients too low to draw definitive conclusions yet. What we can say is that there is considerable less damage done to the patient if compared to classical open surgery like segmental resection or hemicortical resection. Another great advantage is that it allows accurate local tumor ablation without tumor spill and it does not prohibit a local resection as a plan b if there still is viable local tumor tissue visible on MRI. It allows classical treatment in case of insufficient ablation.

Conclusion Local tumor ablation with RFA has the potential to become a safe and effective treatment alternative in OFD like adamantinoma in a child.

Intra-Operative RFA Is a Safe and Effective Treatment for Primary Bone Tumors and Metastasis.
SPEAKER: Paul Jutte

ABSTRACT. Introduction Treatment of many bone tumors is mainly surgical. The lesions often require a resection or in low grade lesions, a curettage to eradicate the tumor, and it’s biological tumor activity. Surgical treatment is associated with a high complication rate, e.g. fracture, infection and blood loss next to functional loss. From an oncologic perspective there can be drawbacks with regard to contaminated margins, local recurrence and tumor spill. To avoid functional and moreover these oncological complications it would be ideal to spare the continuity of the affected bone by treating the tumor in situ. Radiofrequency Ablation (RFA) seems to fulfill in this purpose. This innovative technique has been proofed to be a safe, and reliable option for the treatment of small low grade chondrosarcoma / chondroid bone tumors. The purpose and effect of RFA on chondroid tumors could very well be equally effective in larger lesions, and more important, tumors of different etiology (consistency).

Results 26 patients with bone tumors were treated with intraoperative RFA. CAS guided in 8 cases and fluoroscopy guided in 12. In 6 cases image guidance was considered not necessary. The indications were as follows: 11 cartilage tumors (10 ACT, 1 grade 2 chondrosarcoma), 9 bone metastasis, 3 adamantinoma (2 OFD like), 1 Ewing, 1 giant cell tumor, 1 sarcoma NOS, 1 fibrous dysplasia. In 1 case there was a technical failure, therefore treatment was converted to a conventional surgery. Of 18 post op performed MRI scans, one bonescintigraphy and one SPECT CT 16 patients successfully underwent local tumor ablation without complications. Follow up revealed no local recurrences.

Discussion Local tumor ablation with intra-operative RFA can be a safe and effective treatment alternative in bone tumor and metastasis treatment. To guide and monitor exact antenna placement, planning and execution are performed with CAS or fluoroscopy. Unfortunately intra-operative local ablation temperature cannot be monitored, and is controlled post-operative by MRI. Longer follow up is needed to confirm the initially positive experience.

Conclusion Intraoperative RFA may be a valuable adjunct in the treatment of larger bone tumors as well. It cannot be recommended until further proof of its safety and efficacy is provided.

Wire Placement in the Lisfranc Joint Using a 2D Projection-Based Software Application for Mobile C-Arms: an Experimental Study in 20 Cadaver Specimens

ABSTRACT. In the surgical treatment of Lisfranc injuries, percutaneous wire transfixation of the tarsometatarsal complex can be challenging due to it’s small corridors and complex anatomy. A novel 2D projection-based software application detects Kirschner wires (K-wires) and automatically indicates their intended direction as a colored trajectory. The aim was to investigate whether the software facilitates K-wire placement in the Lisfranc joint for the inexperienced and the experienced surgeon. In 20 cadaver foot specimens, 5 K-wires were retrogradely placed into the tarsometatarsal complex from D1-D5 by an experienced and an inexperienced surgeon, with and without using the application. The specimens were presented in pairs; surgeons and software use were equally randomized. Number of placement attempts, duration of procedure, fluoroscopy time, and number of individual fluoroscopy images were recorded. Use of the software by the inexperienced surgeon significantly reduced the number of placement attempts from 14.2 to 8.8 (p=0.008). The application also reduced the number of fluoroscopy images from 44.8 to 40.8 (p=0.230). Duration of procedure and fluoroscopy time were not affected significantly. The experienced surgeon needed more placement attempts using the software (8.2 vs. 9.2; p=0.351). Duration of procedure, fluoroscopy time and number of fluoroscopy images increased while using the software, yet not significantly. During percutaneous K-wire transfixation of the Lisfranc joint, the novel software is a useful tool for the inexperienced surgeon. In our chosen study setting, the experienced surgeon did not benefit from the software. Due to its independency on fixed reference markers or registration processes, the software contributes to the procedures in orthopedic surgery.

Gesture Capture System of Surgical Hand Motion by Using MEMS Sensors for Rehabilitation Applications

ABSTRACT. In recent years, data glove has become one of the popular researching topics, although data glove products are not common now. Data gloves can provide easier control by direct hand actions. Many researchers use it in their research areas which include media, industrial design, and medical area. In the medical area, most of data gloves are used just as control interface of rehabilitation systems. It is rarely applied as a diagnosis supporting device in a rehabilitation process. We want to develop a data glove as a diagnosis device for rehabilitation. The new data glove can detect hand attitude. Doctor and therapist can use the data glove to diagnose hands ability of patients. This is helpful for patients after stroke and hand surgery. In the thesis, we get the hand motion by the attitude detecting data glove. Numbers of motion sensors are set on the back of the glove. The motion sensor includes an accelerometer, a gyroscope, and a magnetometer. Those are MEMS (Micro Electro Mechanical Systems) sensors. Data of the inertial sensor and the magnetic sensor are fused to get the attitude by AHRS algorithm. The attitude detection refers the magnetic field of the earth. The attitudes of sensors are gathered and the socket is sent to the computer by Wi-Fi. The hand attitude simulation and the joint angles are computed on the computer. Finally, the hand attitude is presented on screen with the limitation for impossible hand action. The bend angles of joints can be fetched by the vector computing. The result can be a reference for diagnosis.

Innovative Orthopedic Surgical Reduction Using Sensors Tracking System

ABSTRACT. This study is to construct a set of chip and electromagnetic combination of the surgical approach path tracking system, and the simulation operation of the reset method, records the path and displayed in the 3D graphical interface. The position and displacement of the distal end of the fracture and the relative displacement angle of the distal end of the fracture were analyzed by using the wire-line electromagnetic sensor and the wireless gyro sensor in the information fusion technique. The trajectory simulation was performed in the orthopedic technique. This system analyzes the position, displacement and physiologic angle of distal fracture of the fractures in the manipulation of traditional Chinese medicine. The research shows that the realization of trajectory simulation can provide digitized, fast and accurate information for users, and provide a practical and record-able platform for the digitization of Chinese orthopedics and orthodontic manipulation.

Mechanical Cup Navigator Based on the Anatomical-Pelvic-Plane Pelvic Lateral Positioner in Total Hip Arthroplasty

ABSTRACT. Background: The acetabular component orientation in total hip arthroplasty is of critical important to the good clinical results. However, traditional widely used cup alignment guides are reported to be relatively unreliable. The present study aims to compare a novel cup alignment guide, which can be attached to our anatomical pelvic plane (APP) pelvic lateral positioner for reducing discrepancies in sagittal pelvic tilt and indicate a targeted cup angle based on the APP, with a conventional cup alignment guide. Materials and Methods: The subjects were 110 hips of 110 patients who underwent unilateral THA using the APP positioner. The procedure was performed with the conventional cup alignment guide (conventional group; 60 hips) and with the novel cup navigator (mechanical navigator group; 50 hips). Postoperative cup angles and discrepancies of postoperative cup angles (inclination and anteversion angles) from the targeted angles were compared between two groups to evaluate the usefulness of these navigators. Results: The mean cup angles in the conventional group were 39.0°±5.3° for the inclination angle and 21.7°±6.4° for the anteversion angle, while those in the mechanical navigator group were 40.9°±3.4° and 19.3°±4.9°, respectively (p=0.014, p=0.003). The discrepancies from the targeted angles were 3.5°±3.1° for the inclination angle and 4.6°±3.4° for the anteversion angle in the conventional group and 2.5°±2.5° and 3.4°±3.0°, respectively, in the mechanical navigator group (p=0.079, p=0.046). Conclusion: The mechanical cup navigator easily attachable to the APP positioner is a tool that can improve the accuracy of cup placement in a simple, economical, and noninvasive manner in THA via the lateral position.

Rehabilitation of Patients with Congenital Pseudarthrosis of the Tibia

ABSTRACT. Congenital pseudarthrosis of the tibia (CPT) is a severe pediatric pathology that remains extremely challenging for management. Material and study results We analyzed the outcomes of 61 patients that were treated with the technologies of transosseous osteosynthesis in the period between 2000 and 2015. All the patients had pathological fractures. CPT was classified according to Crawford. Patients were divided into 4 groups in regard to the technologies of transosseous osteosynthesis used. Monofocal osteosynthesis was used in 27 cases, bifocal osteosynthesis in 25, and two patients were treated with polyfocal compression distraction osteosynthesis. The combination of the Masquelet induced membrane technique and Ilizarov bone transport was used in seven cases. The CPT area was bridged with an end of one of the fragments in five cases. Overlapping of bone fragments was used in nine patients. The split ends of both fragments were plunged into each other in 14 cases. Embedment of one fragment end into the other was used in 23 patients. Bridging of the defect area with a marginal bone fragment was done in three cases. Results Bone union was achieved in 60 patients after the first operation. Recurrences in the long-term happened in 35 cases (57.4%). One recurrence occurred in 16 cases; ten patients had two recurrences and three had three refractures each. Additional means of fixation should be used after removal of the Ilizarov apparatus in order to reduce recurrences. However, wearing an orthosis is uncomfortable and does not provide sufficient stability. In our opinion, a more logical solution is to use intramedullary rods or wires. Combination of the Ilizarov apparatus and intramedullary wires coated with hydroxyapatite were used in five patients. These patients did not have any recurrence at follow-ups from one year up to 6 years. Conclusion The advantages of transosseous osteosynthesis are its low invasiveness, high rates of short-term good and satisfactory outcomes, early weight-bearing, and the possibility to gradually correct multiplanar deformities and lengthen bone fragments in limb length discrepancy. A relative shortcoming is the necessity to wear the external fixator that worsens patient’s quality of life. However, the recurrence rate is rather high after the removal of the Ilizarov apparatus.

Combined Transosseous and Locked Intramedullary Osteosynthesis in Management of Pseudoarthrosis of the Femoral Diaphysis

ABSTRACT. 28patients with pseudarthrosis of the femoral diaphysis were treated with use of combined techniques of transosseous osteosynthesis (TO) and locked intramedullary nailing. Their outcomes were compared with 36 patients that also had pseudarthrosis of the femoral diaphysis that was managed with classical Ilizarov TO techniques. Patients of both groups had posttraumatic pseudoarthrosis. Combined techniques were used in 3 variants: 1)sequential use of distraction osteosynthesis with the Ilizarov apparatus and locked intramedullary nailing in 11 patients with pseudarthrosis and stiff deformities of the femur; 2) simultaneous use of distraction osteosynthesis with the Ilizarov apparatus and intramedullary nailing in 14 patients with pseudarthrosis associated with limb length discrepancy and in 1 patient with diaphyseal defect of the femur; 3) simultaneous use of compression and intramedullary osteosynthesis in 3 patients with pseudoarthrosis of of the femoral diaphysis when it was impossible to use reosteosynthesis with intramedullary implants. In the 1 group, the angulation was 38.5±3.6° and required gradual correction with the Ilizarov apparatus. In the 2 group, limb discrepancy was 5.3±0.4 that required segment lengthening. In the 3 group, dynamization of the nail and Ilizarov TO were performed. Compression of the pseudoarthrosis area was used in the postoperative period. Results In the 1 group, correction of angulation with the apparatus averaged 14.0±1.7 days. Consolidation was achieved from 3 to 5 months after the removal of the apparatus. In the 2 group, mean lengthening of the femur was 3.9±0.2 cm and restored a mean of 85.4±4.0% of bone loss. Distraction period was 34.7±1.8 on average and the index of TO was 12.8±0.9 days/cm. Distraction regenerates were formed in all the cases. Pseudarthrosis union was achieved in 12 patients (80%) in the period from 4 to 9 months. In the 3 group, fixation in the apparatus continued 90.0±15.6 days. Pseudarthrosis union was achieved in all the cases. Complications were classified according to D. Paley (1990). Rate of true complications made up 37.9 %. Deep infection happened in three patients (10.3%) in the period of the observation that was more than 6 months. Conclusion Classical technologies of TO require the use of external fixation during the entire period of treatment. Combined osteosynthesis enables to obtain good and satisfactory treatment outcomes at a long-term.

The Direct Repair of Unilateral Spondylolysis with the Guidance Aid of a Personalised Rapid Prototyping Template
SPEAKER: Janez Mohar

ABSTRACT. The prevalence of spondylolysis among athletes is higher than in general population. The repeated tension stresses caused by lumbar hyperextension and trunk twisting movements, together with anatomical predispositions can result in complete symptomatic fracture. Although less common and more benign, unilateral isthmic stress fractures tend to be resistant to conservative management if not properly addressed initially, therefore warranting operative treatment. An 18-year-old professional soccer goalie was diagnosed with a unilateral isthmic defect that prevented him from sports involvement. After a period of unsuccessful conservative treatment, a direct Buck’s repair of the defect was performed with the drill bit guidance of a personalised rapid prototyping 3D template. The patient’s clinical postoperative course was uneventful, follow-up imaging showed signs of bone healing and he managed to return to the previous physical activity level one year after surgery. At two year follow-up his Oswestry Disability Index score was 0 points and he was painless. The comparison of planned and actual lag screw position showed that the entry point offset on oblique coronal plane was 0.2 mm and 1.3 mm on X and Y axis, respectively. The difference in trajectory angle was 0.2 ° and 0.5 ° on oblique sagittal and oblique transverse plane, respectively. A personalised 3D template, used as a guidance aid in Buck’s repair, allows a higher degree of screw placement accuracy and simplifies the procedure compared to conventional technique. To the author’s knowledge, this is the first reported case of a direct spondylolysis repair with the use of patient specific rapid prototyping technology.

Dynamic Ligament Balancingr – an Innovative Approach in Balancing TKA

ABSTRACT. Introduction Ligament balancing in performing TKA is an upcoming topic to improve the results in TKA. A well balanced knee is working more proper together with the muscular stabilizing structures. Dynamic ligament balancing (DLB)R should give us the opportunity to check the balance of the ligaments at the beginning and the end of the surgery before implanting the definitive prosthesis. It is a platform independent, single-use device, which can be combined with all common types of knee prosthesis.

Materials and Methods DLBR consists of a set of 10 different sizes of baseplates including a feather of 50 to 60N (A). Together with a transducerbox and a tablet all datas can be stored for patient security. During the surgery after calibrating at the beginning the tibial cut is performed, where it should be 90° to the longitudinal axis respecting the right slope. Measurement before femoral cuts are performed and gives an information about the joint angle according to the anatomical and load axis. Mounting a pin positioning tool the femoral cut can be performed with the original cutting block of every set in extension and flexion. After positioning the femoral trial, testing is repeated and should show a balanced situation over all the ROM. The overall period datas were stored and compared to the subjective feeling of the patients.

Results Performing the first 20 patients shows a better balanced situation in all knees respecting the including factors. Especially young and active patients demonstrate a hugh benefit in coming earlier back to work and sport, elder patients reach independence earlier. No extension of the surgical time was seen, respecting the learning curve is a valueable benefit in higher accuracy and precision in TKA. All PROMs shows good and excellent results. The forgotten knee score shows a normal leading according to the short term.

The Effect of Postoperative Mechanical Axis Alignment on the Revision Rate of Primary Total Knee Arthroplasty After a Follow up of 10 Years
SPEAKER: Je-Hyoung Yeo

ABSTRACT. The purpose of this study is to evaluate the effect of postoperative mechanical alignment on clinical outcomes and revision rate by comparing acceptable mechanical axis group from neutral and an outlier mechanical axis. Between 2000 and 2006, clinical and radiographic data of 334 primary TKAs were retrospectively reviewed. Post-operative mechanical axis was investigated within 1 month after TKA. The first group was an acceptable group of 286 knees (85.6%, with mechanical axis of 0°±3°). The second group was an outlier group of 48 knees (14.4%, with mechanical axis of beyond 0°±3°). Clinical outcomes before surgery and at the final follow up were analyzed using scoring method such as Hospital for Special Surgery, Knee Society Score, and Western Ontario & McMaster Universities Osteoarthritis Index (WOMAC) score. Radiologic outcomes including changes of mechanical axis between immediate postop and last follow-up were evaluated. Postoperative complications and revision rates were also evaluated. The mean degrees in change of mechanical axis between immediate postop and last follow-up were greater in the outlier group (1.6°±2.7) than acceptable group (0.8°±2.4). No significance difference in clinical outcome was found between the two groups. The incidence of aseptic loosening, instability, polyethylene wear, polyethylene breakage, and periprosthetic fracture was 2/4/2/2/2 each in the acceptable group and 1/1/2/0/0 each in the outlier group. Six (2.1%) of 286 in the acceptable group and 4 (8.3%) of 48 in the outlier group were revised (p=0.04). The Kaplan-Meier survival analysis showed a tendency towards improved survival with restoration of neutral mechanical axis. However, such improvement was not statistically significant (p=0.25). Restoration of neutral limb alignment is a factor of total knee arthroplasty that can result in less revision rate and higher longevity. However, there are no significant differences in clinical outcomes between the two groups.

16:30-17:30 Session 7: Workflow, Integration, Internet of Things
Location: Europa
Sensor Integrated Instruments for Surgical Quality Assurance and Process Monitoring

ABSTRACT. Demographic changes will increase the number of surgical procedures in the next years. Therefore, quality assurance of clinical processes, such as the reprocessing of surgical instruments as well as intraoperative workflows will be of increasing importance to ensure patient safety. Surgical procedures are often complex and may involve risks for the patient. For fixation of screws, e.g. in case of pedicle screws, osteosynthesis plates or revision joint replacement surgery implants, the application of defined torques may be crucial in order to achieve optimal therapeutic results and minimal complication rates. In many cases a subjective rating of the surgeon is necessary as no adequate instrumentation is available. With the same subjective feeling, hammering or screwing in are performed to implant e.g. the acetabular component in THA.

Our actual work is dedicated to the implementation of a functional prototypes of sensor-integrated instruments for specific types of intervention (especially in traumatology) and the evaluation of the sensor integrated surgical instruments in combination with RFID technology for smart process optimization in the operating room as well as for reprocessing of surgical instruments and surgical management in combination with a knowledge-based planning, control and documentation system. Complementary (preferably wireless) sensors such for instrument identification, tracking or more complex measurements such as forces, torques, temperature or impacts during surgery as well as during reprocessing of reusable instruments could enable computer network based quality assurance in a much broader and comprehensive manner.

Within the framework of the OR.NET initiative we follow the approach to integrate wireless sensors for measurement of temperature, force-torque as well as inertial sensors for orientation and impact control, depending on the specific type of application for monitoring of workflows during surgery as well as during reprocessing of reusable instruments and devices. The integration of smart surgical instruments into an open networked operating room based on the open communication standard IEEE 11073 knowledge-based workflow system, can help to improve the process and quality management.

Intraoperative Workflow Optimization by Using a Universal Foot Switch for Open Integrated or Systems in Orthopaedic Surgery
SPEAKER: Armin Janss

ABSTRACT. Nowadays, foot switches are used in almost every operating theatre to support the interaction with medical devices. Foot switches are especially used to release risk-sensitive functions of e.g. the drilling device, the high-frequency device or the X-ray C-arm. In general, the use of foot switches facilitates the work, since they enable the surgeon to use both hands exclusively for the manipulation within the operation procedures. Due to the increasing number of (complex) devices controlled by foot switches, the surgeons face a variety of challenges regarding usability and safety of these human-machine-interfaces. In the future, the approach of integrated medical devices in the OR on the basis of the open communication standard IEEE 11073 gives the opportunity to provide a central surgical cockpit with a universal foot switch for the surgeon, enabling the interaction with various devices different manufacturers. In the framework of the ongoing OR.NET initiative founded on the basis of the OR.NET research project (2012-2016) a novel concept for a universal foot switch (within the framework of a surgical workstation) has been developed in order to optimize the intraoperative workflow for the OR-personnel. Here, we developed three wireless functional models of a universal foot switch together with a standardised modular interface for visual feedback via a central surgical cockpit display. Within the development of our latest foot switch, the requirements have been inter alia to provide adequate functionalities to cover the needs for the interventions in the medical disciplines orthopaedic surgery, neurosurgery and ENT. The evaluation has been conducted within an interaction-centered usability analysis with surgeons from orthopaedics, neurosurgery and ENT. By using the Thinking Aloud technique in a Wizard-of-Oz experiment the usability criteria effectiveness, learnability and user satisfaction have been analysed. Regarding learnability 83.25% of the subjects stated that the usage of the universal foot switch is easy to learn. An average of 77,2% of users rated the usability of the universal foot switch between good and excellent on the SUS scale. The intuitiveness of the graphical user interface has been approved with 91.75% and the controllability with 83.25%. Finally, 86% of the subjects stated a high user satisfaction.

Evaluation of the Use of Artificial X-Rays for Educational and Intraoperative Guidance During C-Arm Positioning

ABSTRACT. Fluoroscopic C-arms are operated by medical radiography technologists (RTs) in Canadian operating rooms (ORs).  While they do receive formal, accredited training, most of it is theoretical, rather than hands-on. During their first encounters in the OR, new RTs can experience difficulty achieving the radiographic views required by surgeons, often needing several scout X-rays during C-arm positioning.  Furthermore, ambiguous language by surgeons often inadequately conveys their request.  The result is often frustration, unnecessary radiation exposure, and added OR time. The purpose of this study was to evaluate the value of artificial X-rays in improving C-arm positioning performance, with inexperienced C-arm users.

            We developed an Artificial X-ray Imaging System (AXIS) that generates Digitally Reconstructed Radiographs (DRRs), or artificial X-ray images, based on the relative position of a C-arm and manikin.  30 participants were enrolled in the user study and performed four activities: an introduction session, an AXIS-guided evaluation, a non-AXIS-guided evaluation, and a questionnaire. The main goal of the study was to assess C-arm positioning performance with and without AXIS guidance. For each evaluation, the participants had to replicate a set of target X-ray images by taking real radiographs of the manikin with the C-arm. During the AXIS evaluation, artificial X-rays were generated at 2 Hz for guidance, while in the non-AXIS evaluation, the participants had to acquire real scout X-rays to guide them toward the correct view.

            For each imaging task the number of real X-rays and time required per task was recorded, and the C-arm’s pose was tracked and compared to the target pose to determine positioning accuracy; these were averaged for each participant and condition. Hypothesis testing on the means and paired t-tests were carried out using a significance level of α=0.05.

            On average, users took significantly fewer real scout X-ray images (53% fewer (2.8 vs 6.0), p<0.001) when guided by AXIS.  Lateral distance accuracy was improved by 10% for final C-arm positions and by 26% for the most accurate intermediate C-arm positions when guided by AXIS (p<0.05). There was no significant difference in average task time or angular accuracies between the AXIS and non-AXIS evaluations. Overall, we are encouraged by these findings and plan to further develop this system with the goal of deploying it both for training and intraoperative uses.

A Machine Learning Approach to Discriminate Between Soft and Hard Bone Tissues Using Drilling Sounds
SPEAKER: Vahid Zakeri

ABSTRACT. Bone drilling is conducted in many surgical disciplines such as orthopedics, maxillofacial, and spine surgery. Most of these procedures involve drilling of different bone materials including hard (cortical) and soft (cancellous) tissues. Identifying these tissues is essential for surgeons to minimize damage to underlying nerves and vessels. The sound signal generated during drilling is a valuable source of information that could potentially be employed. Such sounds can be captured readily and easily through non-contact sensors. Therefore, our goal in this preliminary study is to investigate whether drilling sounds can enable us to distinguish between cortical and cancellous tissues. A bovine tibial bone was drilled, and the cortical and cancellous drilling sounds were captured. Each sound record was divided into small windows with a length of 50 ms and a 50% overlap. The window length was selected small, because our intended longer-term application is to provide the surgeon with near-real-time feedback. Short time Fourier Transform (STFT) coefficients were extracted from each window and were averaged accordingly to obtain p features. A support vector machine (SVM) algorithm was used for classification, and its accuracy was evaluated for different number of features (p). Two training/testing scenarios were considered, atlas (ATL) and leave-one-out (LOO). The total accuracies for ATL and LOO were 100% and 93.8% respectively obtained for p=128. Our study on a single specimen demonstrated that it is possible to discriminate between cortical and cancellous bones based on relatively short 50 ms windows of drilling sounds.

Software and Instrument Improvements Led to a Significant Time Reduction in Computer Assisted Tka: a Cadaveric Study.
SPEAKER: Frank Lampe

ABSTRACT. Computer navigation in total knee arthroplasty (TKA) has proven to significantly reduce the number of outliers in prosthesis positioning and to improve mechanical leg alignment. Despite these advantages the acceptance of navigation technologies is still low among orthopaedic surgeons. The time required for navigation might be a reason for the low acceptance. The aim of the study was to test whether software and instrument improvements made in an established navigation system could lead to a significant navigation acquisition time reduction. An improved and the current version of the TKA navigation software were used to perform surgery trials on a human cadaveric specimen by two experienced orthopedic surgeons. A significant effect of the “procedure” (navigation software version) on the navigation time (p< 0.001) was found, whereas the difference between surgeons was not significant (p= 0.2). There was no significant interaction between surgeon and navigation software version (p= 0.5). The improved version led to a significant navigation acquisition time reduction of 28%. Software and instrument improvements led to a statistically significant navigation acquisition time reduction. The achieved navigation acquisition time decrease was independent from surgeon. Specific instrument and software improvements in established navigation systems may significantly decrease the surgery time segments where navigation takes place. However, the total navigation acquisition time is low in comparison to the total surgery time.

17:30-18:30 Session 8A: New Technical Approaches
Location: Europa
A Smart Registration Assistant for Joint Replacement: Concept Demonstration

ABSTRACT. In robot-assisted orthopaedic surgery, registration is a key step, which defines the position of the patient in the robot frame so that the preoperative plan can be performed. Current registration methods have their limitations, such as the requirement of immobilising the limb or maintaining the line of sight (LOS). These issues cause inconvenience for the surgeons and interrupt the surgical workflow in the operating room. Targeting these issues, we propose a smart camera-robot registration system for joint replacement. The bone geometry, which is measured directly by a depth camera, is aligned to a preoperatively obtained bone model to calculate the pose of the target. Simultaneously, in order to avoid registration failure caused by LOS disruptions, the depth camera tracks objects that may occlude the target bone, and a robot manipulator is used to move the camera away from the nearest obstacle. An appropriate camera motion to “escape” the obstacle is calculated based on the position and velocity of the obstacle, with the aim of avoiding the occlusion efficiently without changing the general target position in the camera frame. The inverse kinematics of the robot is used to project the Cartesian velocity of the end-effector into the joint space, with kinematic singularities considered for stable robotic control. An admittance controller is designed as the human-robot interface so that the surgeon can directly set the robot configuration by hand according to a given intraoperative scenario. Simulations and experiments with a redundant manipulator were conducted to test the performance of a proof-of-concept implementation. The results show that the proposed obstacle avoidance method can effectively increase the distance between the obstacle and the LOS, which lowers the risk of registration failure due to obstacle occlusion. This pilot study is promising in reducing distractions to the surgeon and could help achieve a fluent and surgeon-centred workflow.

Implantation Accuracy of a Minimally Invasive Total Shoulder Arthroplasty Technique Using Novel Patient Specific Guides and Instruments: a Cadaveric Assessment

ABSTRACT. Patient Specific Instruments (PSIs) are becoming increasingly common in arthroplasty but have only been used with highly invasive surgical approaches that can result in significant complications. We have previously described a novel PSI for minimally invasive total shoulder arthroplasty and shown that it can accurately guide the creation of guide holes in the humerus and scapula. However, conducting shoulder replacement in a minimally invasive environment precludes the use of traditional instruments. In this work, we describe and evaluate the efficacy of a set of novel instruments that, in conjunction with our PSIs, enable accurate minimally invasive total shoulder arthroplasty to be achieved for the first time. The key components of this surgical procedure are: 1) a new minimally invasive posterior surgical approach that avoids the need for muscle transection; 2) a novel PSI that enables accurate guide tunnels to be simultaneously created in the humerus and scapula using a c-shaped drill guide that mates to the PSI; 3) a custom humeral head resection guide that uses the humeral guide tunnel; 4) a novel reamer and 3D metal printed gear mechanism for radial displaced drilling both powered by a central driver placed through the humeral head; and 5) custom impactors for glenoid and humeral implantation – the latter is achieved using a modular slap hammer that is guided by the central humeral drill hole. Accuracy of this system was assessed at each surgical step using an optical tracking camera and an iterative closest point registration method to map measurements to the pre-operative plan. The accuracy results for the physical PSI registration and guide hole drilling were found to be in line with our previously reported results: the intra-articular guide hole locations were 2.2mm and 3.9mm for the humerus and glenoid with angular errors of 2.8° and 8°, respectively. After humeral resection, the humeral cut plane had an angular error of 10.1°. The final humeral implant location had an error of 12.1° and 1.9mm. For the glenoid implant, the positional error was 3.8mm with angular errors of 3.3° ante-retroversion and 8.6° supero-inferior inclination. We believe that these initial results demonstrate that this minimally invasive PSI and instrumentation system can accurately guide total shoulder replacement while avoiding the complications of open surgery. A full cadaveric testing series is currently being completed.

Design of Flexible Implants for Preservation of Physiological Mobility Exploiting Additive Manufacturing
SPEAKER: Martin Kimm

ABSTRACT. Due to tumors or bone fractures caused by high mechanical impact, the affected tissue has to be removed. Preserving the physiological mobility after the treatment could prevent stress shielding or overload of the surrounding muscles and ligaments. In case of a critical vertebral body defect, the body and its attached disks have to be removed. Thereafter the adjacent vertebral bodies are braced together resulting in limited physiological spine movability. A flexible implant adapted to and preserving the patient-specific physiological spine mobility would be a desirable solution. Since Ti6Al4V is a common material for medical implants as well as in AM, it is used in this scientific study. Using design methodology tools, a systematic generation of possible solutions is achieved. Furthermore, already existing solid state hinges made of plastics with AM are taken as archetype and their design is adapted to the metal laser powder bed fusion (L-PBF) process. Therefore, an initial geometry design, based on a solid state hinge demonstrator made by TNO was created with Inventor 2016. By abstracting the vertebrae body segment, two contact surfaces, two joints with rotational degree of freedom (DOF) and axial suspension as well as one solid connection could be identified. As a first implant design, the abstracted joints are replaced by the designed hinges. By the application of simulation software tools the flexion behavior of the solid state hinge can be analyzed. Initial results show that the simulation of the flexion behavior corresponds with the AM specimen. The applied force necessary for bending the specimen depends on the thickness of the struts.

17:30-18:30 Session 8B: Total Hip Arthroplasty Safe Zones
Location: K3
The Safe Zone for Acetabular Component Orientation

ABSTRACT. Introduction: Cup malpositioning remains a common cause of dislocation, wear, osteolysis, and revision. The current study uses CT studies to assess the concept of a safe zone1 for acetabular orientation by comparing the orientation of acetabular components revised due to recurrent instability and to a series of stable hip replacements.

Methods: Cup orientation in 50 hips revised for recurrent instability was measured using CT. These hips were compared to a group of 184 stable hips measured using the same methods. The cup orientation was determined by first identifying Anterior Pelvic Plane Coordinate system landmarks on a 3D surface model. A multiplanar reconstruction module then allowed for the creation of a plane parallel with the opening plane of the acetabulum. The orientation of the cup opening plane in the AP Plane coordinate space was calculated according to Murray’s definitions of operative anteversion and operative inclination2. Both absolute cup position relative to the APP and tilt-adjusted cup position3 were calculated.

Results: Supine tilt-adjusted Operative anteversion for the anteriorly unstable hips was significantly higher than in the stable hips (p< .0001). Supine tilt-adjusted Operative anteversion for the posteriorly unstable hips was significantly lower than in the stable hips (p<.01). Alt in the supine position, all unstable hips had operative anteversion of less than 22.9 or more than 38.6 degrees or operative inclination of less than 30.6 or more than 55.9 degrees or both. The center of the “safe zone” is 30.7 +/- 7.8 degrees of tilt-adjusted operative anteversion and 42.4 +/- 13.5 degrees of operative inclination.

Conclusions. The current study demonstrates that most conventionally placed acetabular components are malpositioned but not all malpositioned acetabular components are associated with dislocation. Using acetabular revision for recurrent instability as the end point, a safe zone for acetabular component orientation does exist. The range is narrower for anteversion than for inclination. Improved methods of defining component positioning goals on a patient-specific basis and accurately placing the acetabular component may reduce the incidence of cup malposition and its associated complications.

1. Lewinnek GE et al. J Bone Joint Surg Am. 1978;60:217-20. 2. Murray DW. J Bone Joint Surg Br. 1993;75:228-32. 3. Babisch JW et al. J Bone Joint Surg AM. 2008;90:357-65.

The Combined Safe-Zone as a Guideline for Component Positioning in Navigated Total Hip Arthroplasty

ABSTRACT. Introduction: Computer navigation is a highly sophisticated tool in orthopedic surgery for component placement in total hip arthroplasty (THA). In order to apply it adequately it is of upmost importance that the targets the surgeon is trying to hit are well-defined. This concept considers all four component orientations: cup inclination (cIncl) and anteversion (cAV), stem antetorsion and neck-to-shaft angle. The optimizing goal in this concept is maximizing the size of the cSafe-Zone. Methods: A computerized 3D-model of a total hip prosthesis was used to systematically analyze all combinations of component orientations in automatized batch runs. Component orientations were varied for cup inclination, cup anteversion, neck antetorsion and neck inclination. Results: The combined Safe-Zone outlines spaces in a 3D-diagram that show the relationship between cup inclination, cup anteversion and neck anteversion, while the neck inclination is used as a curves parameter. These spaces include all component orientation that allow the predefined iROM without prosthetic impingement. In order to compare these results to Lewinnek’s recommendation cross-sections were taken at distinct neck antetorsions in 5° intervals. Conclusion: The new combined Safe-Zone (cSafe-Zone) includes all orientation parameters of both total hip components and such gives well-defined recommendations for combined positioning of both components. Ideally it can be introduced into a smart computer navigation system in order to compute in real-time the best combined orientation of both components.

Multi-Dimensional Range-of-Motion-Based Safe Zone for Patient-Specific Total Hip Arthroplasty
SPEAKER: Juliana Hsu

ABSTRACT. Proper component alignment is crucial for a successful total hip arthroplasty (THA). Some studies found safe cup orientations and corresponding stem antetorsions based on a defined desired range of motion (ROM) suitable for activities of daily living. These studies either used complex and time consuming 3D simulations or more simple mathematical formulas which cannot be extended to combined motions. With the method introduced in this work, any arbitrary motion can be applied. The ROM specified as the ROM of the femur relative to the pelvis is transformed into the ROM of the prosthesis neck relative to the cup for each cup orientation. For this transformation, the orientation and design of the stem are considered. The comparison of the neck and cup orientations is done using a 2D mapping of a 3D spherical surface which reduces the complexity of the calculation. We found that the femoral antetorsion as well as the neutral stem flexion and adduction have an influence on the resulting safe zone. The result is not just a combined anteversion but a combined orientation. For validating the plausibility of the algorithm, the resulting safe zones are compared to literature. Same results can be achieved using the same input data. Using this technique, a patient-specific safe zone based on the ROM can be derived and adjusted to the stem orientation.

Influence of Femoral Bowing on Range of Motion After Total Hip Arthroplasty

ABSTRACT. Background Influence of physiologic femoral bowing on range of motion (ROM) after total hip arthroplasty (THA) remains unknown. Methods The ROM was calculated from 100 hips in 90 patients who underwent THA using computed tomography data with a 3D dynamic analysis software. Lateral and anterior bowing angles of the femur were measured. A modular implant (Modulus system, Lima Corporate, Villanova di San Daniele del Friuli, Italy) was used for simulation. In all subjects, cup inclination, anteversion, and stem anteversion were set to 40°, 15°, and 30°, respectively. Results Lateral bowing of the femur was significantly correlated with flexion (125° neck, r = 0.506, p < 0.001; 135° neck, r = 0.480, p < 0.001), extension (125° neck, r = -0.577, p < 0.001; 135° neck, r = -0.576, p < 0.001), abduction (125° neck, r = -0.517, p < 0.001; 135° neck, r = -0.438, p < 0.001), and adduction (125° neck, r = 0.528, p < 0.001; 135° neck, r = 0.497, p < 0.001). Anterior bowing was significantly correlated with internal rotation with 90° flexion (125° neck, r = -0.520, p < 0.001; 135° neck; r = -0.354, p < 0.001) and internal rotation with 45° flexion and 15° adduction (125° neck, r = 0.392, p < 0.001; 135° neck; r = 0.488, p < 0.001). Conclusion This study demonstrated that there were significant differences in ROM after THA , which were dependent on the physiological bowing of the femur.

Relationship Between Pelvic Morphology and Functional Parameters in Standing Position for Patient-Specific Cup Planning in THA

ABSTRACT. The sagittal orientation of the pelvis commonly called pelvic tilt has an effect on the orientation of the cup in total hip arthroplasty (THA). Pelvic tilt is different between individuals and changes during activities of daily living. In particular the pelvic tilt in standing position should be considered during the planning of THA to adapt the target angles of the cup patient-specifically to minimize wear and the risk of dislocation. Methods to measure pelvic tilt require an additional step in the planning process, may be time consuming and require additional devices or x-ray imaging. In this study the relationship between three functional parameters describing the sagittal pelvic orientation in standing position and seven morphological parameters of the pelvis was investigated. Correlations might be used to estimate the pelvic tilt in standing position by the morphology of the pelvis in order to avoid additional measuring techniques of pelvic tilt in the planning process of THA. For 18 subjects a semi-automatic process was established to match a 3D-reconstruction of the pelvis from CT scans to orthogonal EOS imaging in standing position and to calculate the morphological and functional parameters of the pelvis subsequently. The two strongest correlations of the linear correlation analysis were observed between morphological pelvic incidence and functional sacral slope (r = 0.78; p = 0.0001) and between morphological pubic symphysis-posterior superior iliac spines-ratio and functional tilt of anterior pelvic plane (r = -0.59; p = 0.0098). The results of this study suggest that patient-specific adjustments to the orientation of the cup in planning of THA without additional measurement of the sagittal pelvic orientation in standing position should be based on the correlation between morphological pelvic incidence and functional sacral slope.

Measuring Pelvic Tilt with the Use of a Navigated Smart-Devices Based Ultrasound System
SPEAKER: Tobias Martin

ABSTRACT. The key for a successful total hip replacement (THR) and the longevity of the implant is the correct alignment of the acetabular cup which is to be considered as the most critical component. The alignment of the cup is defined with respect to anterior pelvic plane (APP). The APP defines the reference for the anteversion and inclination angles which sets the basis for the correct alignment of the implant. The angle of the plane is created by three distinct anatomical landmarks which are represented by two anterior superior iliac spines (ASIS) and the symphysis pubis. The angle of the APP in respect to the coronal plane defines the pelvic tilt (PT) which can be anterior or posterior. The rotation of the pelvis highly depends on the individual anatomy of the subject. This means that a neutral pelvic tilt (PT) in supine position is rarely observed and also may be dissimilar in standing position. In this paper we present a non-invasiveness and cost-effective prototype for measuring the patient-specific PT under the use of a navigated smart-device based ultrasound system for supporting surgery planning. In view of the non-invasiveness method the system can be used to measure pre- and postoperative pelvic orientation. With the use of an artificial hip reference model different cases were measured. The computed results look very promising with a standard deviation of ±1°.

19:00-23:00 Session : Young Investigators Chill Out

Meeting point at check-in (further information on printed proceedings).