ABSTRACT. Introduction: Total knee arthroplasty (TKA) for damaged cartilage has been steadily improving. Artificial knee joints for TKA are designed by implant manufacturers, and doctors choose the most appropriate. However, each patient has their own unique skeleton and bone shape, and so it is better to design a precise implant for each patient. Some researchers have proposed custom-made implants which will improve the operation, enable minimally invasive surgery, earlier rehabilitation, and earlier recovery. The major problem of custom-made implants is that they are costly and time consuming to design, evaluate and manufacture.

Methods: We propose a novel method, in which custom implants are designed by homologous deformation. The dynamic feature of homologously deformed implants is the same as the original, so they can be used if the size is fitted to the patient’s bone and there is sufficient durability. Therefore, we have developed a semi-customizing system with which the implant position and homologous size are easily determined based on computer tomography (CT) data (Figure 1), and the finite element method can be performed to calculate the stress on the designed implant in that position. This software can be used in a usual computer, at the time of surgery planning can be planned using the mobile device to be able to determine the semi-customizing parameters intuitively.

Results: In the experiment, a custom-made implant was designed and produced using actual patient data by an orthopedist in our system, and the stress characteristics between the custom implant and the original were compared. In this case, the ratio of the scale change by homologous deformation was 0.96 times. Although the original implants front flange size protrudes without adaptation to the patient bone is almost gone protruding portion in the semi-custom implants. The results of stress analysis by the finite element method, the custom-made implant was higher principal stress value compared to the original implant.

Discussion: Our approach is a method of making an implant adapted for the bone shape of the patient deforms the scale to achieve a time and monetary cost of the verification with respect to shapes. Although the principal stress of semi-custom implant is greater than the original implants, the principal stress of the semi-custom implant can be estimated because of the change in the principal stress is maintaining a substantially constant ratio irrespective of the orientation.

ABSTRACT. BACKGROUND: Patients have been shown to be poor at self-reporting stiffness following Total Knee Arthroplasty (TKA)1.  Early manipulation is known to improve range of motion in patients with post operative stiffness2.  Impairments in Range of Motion can be signs of stiffness, infection or poor rehabilitation.  Detecting stiffness only at routine six-week follow-up can mean early treatment opportunities are missed.   Although tele-rehabilitation with video-conferencing has been used to assess patients in the home environment, this is labour intensive and expensive3.  Remote assessment would allow geographically isolated patients access to improved follow up and potentially reduce need for long distance travel for clinical assessment. We report use of a novel device (accelerometer tracker + tablet) to remotely assess patients’ Range of Motion (RoM) at home.   The device was originally designed to aid rehabilitation of young athletes guided by physiotherapist.  A pilot was therefore undertaken to assess translation of this technology to an older and less firm patient cohort. The aim of this pilot device-test study was to assess feasibility of remote recording of range of motion data post TKA in an elderly patient group from both technical and educational perspectives.

METHOD: 49 TKA patients (mean age 62±7) were provided with a Kit containing RoM tracker and tablet.  The tracker device was connected to the tablet via Bluetooth and contained an accelerometer and gyroscope to measure the (reference) horizontal plane and movement.  The device reference parameters state accurate measurement of rotational change in 360 degrees relative to the earth’s magnetic field with accuracy to one degree.  Three dimensional movement in x,y and z planes with both rotation and linear movement was accurate to 0-10 degrees. The tracker was attached with a velco strap to the lateral lower leg, immediately proximal to the lateral malleolus as a consistent landmark.  Flexion and extension of the knee was performed with patient in supine position and guided by the tablet to assess the arc of knee movement.  The short exercise test was performed once daily during the patients’ normal post-operative exercise regime.  The tablet device required connection to home broadband via Wifi to upload data to a master unit at the base hospital. Education was undertaken on the ward following surgery with a demonstration and explanatory leaflet.  Ability to use the device over a 6 week period was then assessed by tracking the data loaded to the master unit and via patient feedback forms.  Educators feedback was assessed at completion.  Due to large geographic population area, all education was performed prior to discharge, and telephone advice was available following discharge.

RESULTS:  44/49 (90%) patients registered a remote RoM reading, with 55% managing 5 or more remote readings.  Patient reported issues included difficulty with broadband connection, problems with the tracker connection to tablet and charging difficulties.  Small icons and popup windows caused problems for some patients. Educators reported patient selection change through the time period to recruit (usually younger) patients more familiar with tablet devices and access to home broadband. Education time reduced during the test period, but was still reported as a cause of difficulty.

DISCUSSION:  Portable accelerometers have become widely available in phone and tablet devices, but only recently used in arthroplasty research4,5.  This study showed that remote assessment of RoM is possible using a portable device with gyroscope/accelerometer and tablet.  High early use of the device was achieved with respect to remote readings, however there was a high drop out rate within the first few days after surgery.  Unfamiliarity with computer technology in an elderly patient cohort and difficulties with wifi, Bluetooth and broadband all contributed to early patient difficulties. Patient selection and education is crucial to achieve compliance.  Education time is a potential barrier to wide adoption. Further developments include the software interface to enlarge icons and reduce number of steps.  Printed pictorial guides and video may also aid education, particularly with elderly patients and have been developed for future studies.  3G tablet devices have been developed to resolve the connection issues with broadband. Range of motion data demonstrated that remote collection was feasible, however the angular data was not assessed during this device test as the accelerometer is currently being validated to ensure clinical accuracy.

ABSTRACT. Introduction: The introduction of robotic technology into orthopaedic surgery presents a novel approach to removing bone tissue with a burr head drill. The use of a burr head drill can remove bone tissue and can be used with all implant designs but leaves different surface roughness compared to manual bone cutting saws. We investigate mechanical properties based solely on the effect of surface roughness associated with the use of the burr head and manual saw to determine if the surface roughness affects tensile and shear pull-off strengths, and whether the cement has a preference of surface roughness for adhesion.

Methods: Artificial bone material was used to create tensile and shear test samples in which two parallel surfaces were created normal to (tensile) and parallel to (shear) the loading direction. Surfaces were prepared either using a 6mm burr (rough) or a standard band saw (smooth). Either medium or high viscosity bone cement was used to adhere the surfaces together. Specimens were loaded, under tension (n=146) or shear (n=86) conditions, until failure. For the mixed group, it was noted which side the cement was originally applied to, and which surface failed. Specimens of pure cement were also created and tested in tension.

Results & Discussion: The results showed that viscosity did not affect the mechanical behaviour of the pure cement specimens, when adhered to two surfaces significant differences were apparent (P < 0.05). Surface roughness under tensile conditions does affect the mechanical properties with smooth surface outperforming the rough (P < 0.05) whereas surface roughness has no effect on mechanical properties under shear conditions. Nevertheless the cement adhered to the rough surface preferentially, with the smooth interface failing first.

ABSTRACT. Introduction: This project aimed to design a methodology for knee laxity assessment to enable a novice to replicate the technique of experienced clinicians.

Methods: Twenty volunteers (9 female, 11 male) were recruited, mean age 26 (22-55), mean BMI 25.4 (17.9-31.8). The novice used a non-invasive navigation system with optical trackers mounted via elasticated strapping and a custom made structure to maintain knee flexion. Assessments were carried out 5˚, 15˚, 30˚ and 45˚ flexion. Coronal laxity was assessed by applying a moment of 18 Nm. An AP drawer test used standardised force application below the patella. Five volunteers also underwent clinical assessment by an experienced orthopaedic surgeon as the ‘gold-standard’ measurement. Coefficients of Repeatability (CR) were calculated; CR<3° for laxity and CR<3mm for AP drawer were considered clinically acceptable.

Results: Fifteen volunteers were successfully assessed. Four participants had the clinical assessment. The novice showed acceptable varus laxity assessment at 15° (CR=2.8), and valgus laxity assessments at 5° (CR=2.2) and 15° (CR=2.7). The experienced surgeon demonstrated acceptable varus laxity assessment at 5° (CR=1.5) and valgus laxity assessments at 5° (CR=1.6), 15° (CR=2.8) and 30° (CR=2.2). The AP drawer test demonstrated a poor level of repeatability but CRs were very similar for novice and experienced surgeon for all assessments (all within 1mm).

Discussion: This study demonstrated that with a standardised protocol a complete novice can obtain similar levels of repeatability for laxity assessment as an experienced clinician particularly with small degrees of flexion. This could point to application of the non-invasive IR system both as a potential training tool and a method to bypass the training curve exhibited early on in orthopaedic careers.

ABSTRACT. Total hip arthroplasty (THA) is an effective operation for patients with hip osteoarthritis; however, patients with hip dysplasia present a particular challenge. Our novel study examined the effect of robotic-assisted THA in patients with hip dysplasia.. Nineteen patients at two centers presented with hip dysplasia.We found that components were placed according to the preoperative plan, there was a significant improvement in the modified Harris Hip Score from 31 to 84 (p<0.001), an improvement in hip range of motion (flexion improvement from 66 º to 91º, p<0.0001), a significant correction of leg length discrepancy (17.5 vs. 4 mm, p<.0002), and no short-term complications.. Robotic-assisted THA can be a useful method to ensure adequate component positioning and excellent outcomes in patients with hip dysplasia.

ABSTRACT. Unicompartmental Knee Replacement (UKR) is an orthopaedic surgical procedure in which the damaged portion of the knee is surgically replaced by an implant. This reduces pain and improves function in the knee. Previous work has shown the high accuracy of a hand-held robotic system for UKR. In this work, we compare the rotational implant alignment obtained by using the robotic system versus that obtained while using a conventional system for UKR. Our results show that compared to the conventional approach, the robotic system enables superior accuracy in rotational alignment of the implants for UKR procedures.

ABSTRACT. Introduction: Adolescent Idiopathic Scoliosis (AIS) is the most prevalent type of scoliosis, affecting 1-3% of children aged 10-16. AIS is diagnosed and monitored using two dimensional (2D) X-ray imaging. Studies have shown that frequent exposure to radiation increases the risk of breast cancer, leukemia and prostate cancer later in life. Furthermore, trying to identify a three dimensional deformity from 2D plane images additionally causes problems during monitoring and measurement of the deformity.

Methods: For this work, we propose a new framework for the enhancement of bone surfaces, from extended field of view US volumes obtained using electromagnetic tracking, using a combination of a new gradient based smoothing and saliency based feature extraction method.

Results & Discussion: The results show that the proposed method is effective for sharpening major bone edges by increasing the steepness of transition while eliminating a manageable degree of imaging artifacts. The run time for the proposed method was 0.5 seconds per slice. Collection of a 616×660×1300 extended field of view volume was achieved under 1min.

ABSTRACT. High tibial osteotomy (HTO) is a well-established procedure to treat varus malaligned knees. However, accurate pre- and intra- operative measurements are necessary to success treatment. Preoperative planning of HTO procedure is generally performed on the X-ray images. The result of this planning procedure include deviations which are interobserver difference, patient position, and image parameters. Furthermore, developed intraoperative measurement tool is also inconvenient and complex. To make the HTO procedure more accurate and simple, we suggest preoperative virtual HTO procedure and 3D printed spacer. The accuracy of the 3D printed spacer HTO was evaluated by porcine experiment.

ABSTRACT. Introduction: In total hip arthroplasty (THA), the orientation of the acetabular cup is an important factor in preventing postoperative complications such as dislocation, accelerated wear and loosening. Computed tomography (CT)-based navigation is a well-documented assist tool for optimal implant placement, and several reports have described clinical outcomes in terms of the precision of the cup angle. The objective of this study is to investigate the accuracy of cup placement in THA using CT-based navigation system.

Methods: From January 2012 to February 2013, a total of 168 hips in 154 patients underwent THA at our institution, using a CT-based navigation system. Among them, in 150 hips (89%) the navigation procedure was carried out successfully without loosening of trackers, and 150 hips were analysised so far (24 men, 126 women). The mean age of the patients was 63 years and mean body mass index (BMI) was 24. Using two personal computers, we adjusted the differences in pelvic orientation and inclination between preoperative and postoperative CT images. Cup alignments (inclination and anteversion) were measured from the postoperative CT images. Then clinical accuracy (difference between preoperative planning and postoperative CT measurement) and measurement error (difference between intraoperative record and postoperative CT measurement) were computed and verified. Furthermore, approach (anterior and posterolateral approach groups) and surgeons (expert and beginner groups) compared, respectively.

Results: The clinical accuracy of cup inclination and anteversion was 1.4°±1.4° (range; -6° to 8° ) and 2.3° ± 2.3° (range; -9° to 10° ), respectively. The measurement error of cup inclination and anteversion was 1.1±1.0° (range; -5° to 4°) and 1.2±1.0° (range; -5° to 4°), respectively. No significant differences in accuracy were identified between anterior and posterolateral approaches or between expert and beginner surgeon groups.

Discussion: In this study, clinical accuracy and measurement error were the best compared with the past report of our institution. We found that there were no differences between anterior and posterolateral approach or between experienced surgeons and beginners in terms of cup placement accuracy. These findings suggest that, if properly used, surgeon can achieve accurate placement of acetabular cup with this navigation system irrespective of surgical approach or surgeons’ experience. In conclusion, clinical accuracy and measurement error of cup alignment using CT-based navigation system for 150 cases of THA was excellent.

ABSTRACT. 【Background】We developed a CT based navigation system for total hip arthroplasty. The purpose of this study was to evaluate the accuracy of the newly developed navigation system in comparison with commercially available CT-based navigation systems for acetabular sockets.【Method】30 consecutive uncemented THAs were performed. The newly developed navigation system was a CT based, surface matching type navigation system (N-navi). We performed registration using the BrainLAB navigation system (BLN) then we performed registration using N-navi on the same situation. We measured the cup angle about inclination and anteversion. We measured the actual angle by CT. We evaluated the accuracy between the intra-operative results and the post-operative results. In addition, we measured the registration period. 【Results】The absolute value of the difference between the intra-operative and the post-operative date, the mean difference of inclination using BLN was 6.8±6.2°, using N-navi was 3.3±2.6°, and the difference was significant (p<0.05). The mean difference of anteversion using BLN was 5.5±5.4°, and using N-navi was 3.1±2.5°, the difference was significant(p<0.05). The registration period using BLN was 173±48 seconds, and using N-navi was 745±301 seconds, thus the difference was significant (p<0.01). 【Discussion】The accuracy of N-navi was superior on both inclination and anteversion. It proved the N-navi system had enough accuracy for THA. However, it took more registration time. We need to search for more effective points to make the registration more accurate and less invasive.

ABSTRACT. Introduction: Fracture surgery of long bone has several problems related to radiation exposure, mal-alignment after surgery, and hardness of lower limb traction. We have developed a musculoskeletal repairing robotic system for repairing damaged musculoskeletal region in limbs with improved accuracy and safety. In this study, we analysed about surgical procedure of the robotic fracture surgery using a femur fracture model with the developed robotic system.

Methods: Two orthopedic surgeons evaluated the robotic system from mock fracture surgeries with femur fracture models and the required time of each procedure is analysed.

Results & Discussion: Reduction results with the robotic system which shows five millimeters and three degrees level are clinically acceptable. And the proposed scenario was good enough to conduct robot assisted fracture surgery. However, we find out that more convenient and fast surgical preparation and a user friendly registration method are required from the time analysis.

ABSTRACT. Introduction: Patient-specific instrumentation (PSI) was developed to improve the accuracy of component positioning through custom cutting blocks constructed based on pre-operative three dimensional imaging in total knee arthroplasty (TKA). The purpose of this study was to compare the clinical and radiological outcomes between the patients who underwent PSI assisted TKA or conventional TKA.

Methods: Sixty four patients (64 knees) underwent TKA by a single surgeon: 32 patients (32knees) underwent TKA with PSI, 32 patients (32 knees) underwent TKA with conventional instrumentation. The mean age of the patients was 67.6 years, and the mean follow-up duration is 26.2 months. Patients were evaluated preoperatively and after surgery. We evaluated clinical outcomes including knee range of motion, Hospital for Special Surgery (HSS), Western Ontario and McMaster Universities Arthritis Index (WOMAC), Knee Society (KS) function and pain scores. We also compared radiological outcomes including mechanical axis, coronal and sagittal alignment.

Results: We found no significant differences in any clinical outcomes between the PSI assisted TKA group and the conventional TKA group. In terms of radiological outcomes, the PSI assisted TKA group had fewer alignment outliers.

Discussion: We found that PSI assisted TKA restores limb alignment better than conventional TKA, but PSI does not confer a substantial advantage in early functional outcomes after TKA. Further follow-up is needed to ascertain the long-term impact of these findings.

ABSTRACT. A CLOUD BASED SYSTEM FOR AUTONOMOUS ORTHOPAEDIC SURGERY PLANNING F. Liu, J.W. Giles, J. Li, F.M. Rodriguez y Baena Mechatronics In Medicine Lab, Imperial College London, London, SW7 2AZ, UK, fangde.liu@imperial.ac.uk Computer-based pre-operative planning is an increasingly significant and burdensome aspect of orthopaedic surgical practice. In addition, surgeons are often faced with complex degenerative conditions that pose significant challenges with respect to their ability to produce a surgical plan which can accurately reconstruct a joint's healthy anatomy. However, big data and high performance computing technology make it possible for computers to perform many tedious pre-planning tasks autonomously. This will significantly reduce the surgeon's pre-operative planning burden. When deployed in the cloud, hospitals can access this planning capability without the need to install high performance computer hardware. In this paper we describe a cloud computing based proof-of-concept system that plans surgical procedures autonomously. Deep learning enables computers to identify anatomical structures from medical images, while a high performance design optimization system can find the best surgical plan from millions of options. The automatic planning system is composed of three components: (1) an Intuitive Mixed Reality Web-based User Interface, (2) a Big Data based Image Processing System, and (3) a High Performance Design Optimization System. The user interacts with the first of these components using any web browser, while the second two components are deployed in the cloud, shifting the computational load away from the user's local device. This system was applied to two clinical case studies that pose particular challenges to pre-operative planning: multi-planar tibial osteotomy and total shoulder arthroplasty with severe glenoid erosion. In each case, the system was able to segment the anatomy with reasonable accuracy and optimize planning based on pre-defined cost functions. However, the limited training datasets available for each case and the lack of fully quantifiable objective functions meant that planning results still require further refinement. Despite these shortcomings, this work illustrates that a cloud based solution has the potential to leverage massive computing power and big data to automatically optimize some very challenging tasks in orthopaedic surgery, while shifting the computational burden to a low cost cloud computing service.

ABSTRACT. Introduction: The goal of this study was to validate the measurement of anterior knee laxity of gross specimens by the GNRB system by comparison with a navigation system taken as the reference tool.

Methods: 5 pairs of fresh frozen gross specimens were analyzed. The knee was positioned at 20° of flexion on a special splint. An increasing calibrated postero-anterior force was applied; the tibia anterior translation was measured simultaneously by the GNRB ® system and a navigation system for each applied force and compared with appropriate statistical tests. Three settings were used: intact ACL and ALL, section of ACL or ALL (randomly assigned to each knee of a pair), section of ACL and ALL.

Results: The mean paired difference between GNRB and navigated measurements irrespective from the applied force and the ligamentous status was 0.12 ± 1.8 mm (ns). Only 28 paired differences (23 %) were greater than ± 2 mm. There was a strong correlation between both measurements (R²=0.91) (figure 1). There was a good coherence between both measurements (R²=0.029).

Discussion: The hypothesis was rejected. The GRNB and navigated measurements of anterior knee laxity were not different for all situations tested. Neither statistically significant nor clinically relevant difference was identified between GNRB and navigation measurements of the anterior knee laxity, whatever ligamentous status concerning ACL and ALL. The use of this device for routine evaluation of ACL deficient knees or after ACL reconstruction may be recommended. However, the accuracy of the procedure should be assessed.

ABSTRACT. Introduction: The objective of this study is to compare kinematics between NRG and Triathlon during stair motion, and to evaluate the influence of the articular design in AP single-radius TKA.

Methods: We examined 21 knees in 18 patients (NRG group: 10 knees in 7 patients, Triathlon group: 11 knees in 11 patients) with a clinically successful posterior stabilized total knee arthroplasty (TKA). Under fluoroscopic surveillance, each patient performed stair ascending and descending motions. Femorotibial motion was analyzed using 2D/3D registration technique, which uses computer-assisted design (CAD) models to reproduce the spatial position of the femoral, tibial components from single-view fluoroscopic images. We determined the images of the ground touch of the TKA leg on the first step and selected the following four phases: 1) at foot strike (FS) (non-weight-bearing), 2) during stance phase before crossleg motion (full weight-bearing), 3) during stance phase after crossleg motion (still weight-bearing), and 4) at foot off (FO) (non-weight-bearing). We evaluated the knee flexion angle, rotation angle, varus-valgus angle, anteroposterior translation of the femorotibial contact point for both the medial and lateral sides of the knee and post-cam engagement. Measurement results were analyzed statistically using Mann-Whitney U-test. Values of P < 0.05 were considered statistically significant.

Results: During stair descending, the mean flexion angle at FS was 4.1 ± 3.1° in NRG groups and 8.0 ± 3.7° in Triathlon groups. Knees were gradually flexed from FS to FO. During stair ascending, Knees were gradually extended from FS to FO. There is no significant difference between two groups in rotation angle. In NRG group, varus position was observed at FO during stair descending and from stance phase after crossleg motion to FO during stair ascending. In AP translation, there is no significant difference between two groups during stair descending. On the other hand, the medial contact point in Triathlon group was -4.7 ± 1.9 mm at FS and then it moved 1.9 ± 1.9 mm anterior while shifting weight to the leg during stair ascending. During stair descending, post-cam engagement was observed 2 knees from stance phase after crossleg motion in NRG group. On the other hand, 7 knees in Triathlon group were engaged. The mean flexion angle of the engagement was 62.1 ± 2.4° in NRG group and 37.9 ± 10.0° in Triathlon group. During stair ascending, post-cam engagement was observed in all knees from FS. The mean flexion angle of the engagement was 58.7 ± 10.3° in NRG group and 34.2 ± 16.9° in Triathlon group.

Discussion: Even though same AP single-radius TKA, the kinematics might be different with the difference of ML radius and insert design during stair motion.

ABSTRACT. Introduction: During the evaluation of CAOS systems, the error generated by the guidance system has been generally overlooked. One critical aspect of this accuracy relates to the acquisition of the hip center, basis of all measurements concerning the femoral component positioning relative to the mechanical axis. The purpose of this study was to assess the reproducibility of this acquisition, its robustness to external conditions, and its ease of use, in a next generation guidance system, with a compact localization system.

Methods: Hip center of two fresh frozen cadaveric knees from 2 different specimens were acquired using a custom software application in an image-free CAOS system. One knee was healthy, while the other one was osteoarthritic.Three different operators successively performed the hip center acquisition under 6 different conditions. Each acquisition was repeated three times, making a total of 54 different acquisitions per knee. The guidance system was setup as usual, fixing an active optical tracker on the femur. Additionally, another active optical tracker was fixed to the pelvis to track the pelvis motion and create an absolute reference. The hip center was computed using the ExactechGPS software, based on the least moving point method (LMP), without using the pelvis tracker, with standard filters and checks. Those results were then compared to the average on all acquisitions of the pivot point algorithm using the pelvis tracker as a reference, which is reported by previous studies as extremely robust, it was considered as our gold standard in our study. Statistical analysis (ANOVA) of inter-operators, inter-knees, and perturbations compared to normal conditions was performed with statistical significance defined as p<0.05. Residuals distances were expressed in term of Varus/Valgus and Flexion of the femoral component.

Results: Range of residuals is [-1.2°;2.4°] for Varus/Valgus and [-1.4°;1.4°] for Flexion. Inter-specimen results show a significant difference in spread distance, between the healthy knee and the OA knee. There is a statistically significant difference for one perturbation of the acquisition but representing only 0.2° of HKA angle average (1.2° max) (p=0.03). No statistical differences were found regarding a dependency to the operator, or to other pertubations of the acquisition. This study shows that the method used in the ExactechGPS software to detect the hip center is accurate and reliable.

Discussion: Presented results showed a thicker dispersion than previous studies [3]. However, some conditions of acquisitions still may lead to error superior to 1.5°, even if acceptable compared to the range of error commonly defined at ± 3°. To avoid such situations, secondary filters have been added.

ABSTRACT. Introduction: Understanding global variations of how computer-assisted orthopaedic surgery (CAOS) total knee arthroplasty TKA is performed may greatly benefit the interpretation of the outcomes from different clinical sites, as well as development of CAOS systems to better address geographic-specific operative needs. This study investigated geographic variations in the application of a contemporary CAOS system in TKA.

Methods: A retrospective review was performed 4000+ TKAs from October 2012 to January 2016 using a CAOS system. A total of 682 personalized surgical profiles were extract and divided into 4 geographic groups: United States (US), Europe (EU), Asia (AS), and Australia (AU). Analysis of each geographic group was carried out on the surgical profiles and compared between groups for cruciate-retaining (CR) and posterior-stabilized (PS) TKAs. Clinically relevant statistical differences (CRSD, significant differences in means ≥1°/mm) were identified (significance defined as p<0.05).

Results: Despite the general agreement across regions, differences were observed in the percentage of preference in the surgical parameters. CRSDs were found between geographic regions in the resection parameters (posterior tibial slope, tibial resection depth, and femoral flexion) for both CR and PS TKA profiles. Differences in percentage of preference were found both in anatomical references (tibial varus/valgus, tibial resection depth, femoral varus/valgus, femoral axial rotation, and ankle center) and surgical steps (application of gap balancing technique and resection workflow).

Discussion: This study demonstrated that geographic differences exist in the surgeons’ preference of surgical parameters, anatomical references, and surgical workflow steps during TKA. The variation sometimes can be clinically significant. To date, this is the first study that offered a detailed look of how TKAs are carried out during the application history of a specific CAOS system. As such, variation due to the operational differences of multiple systems was avoided. The findings may benefit further improvement of design and development of instrument systems that suit global needs, both for conventional and CAOS TKAs.

ABSTRACT. Introduction: As healthy knees demonstrate constitutional varus, some have proposed that restoration of a slight varus alignment in varus knees during total knee arthroplasty (TKA) may offer benefits to better postoperative natural kinematics. However in reality, it is a paramount technical challenge to determine and achieve a natural alignment using conventional TKA instruments with sufficient efficiency and accuracy. This study sought to demonstrate and evaluate a computer-assisted surgical technique aiming to restore individual natural alignment in the varus knees.

Methods: Thirty-four varus knees without significant soft-tissue deficiency were studied. The knees were selected from the primary posterior stabilized TKAs performed by the surgeon author using a computer-assisted orthopaedic surgery (CAOS) system via assessment of the varus/valgus deformity (preoperative deformity) at full extension in supine position after the arthrotomy. Before any bony resection, the surgeon applied a valgus stress at full extension to measure the maximum alignment correction allowed as guided by the soft-tissue, and set a natural alignment target in the CAOS system to guide the proximal tibia resection (some residual varus allowed). The TKA was then completed using a gap balancing technique guided by the CAOS system. The final achieved alignment was checked using the CAOS system (achieved alignment). The preoperative varus deformity, the natural alignment target, and the achieved alignment were compared and analyzed, with statistical significance defined as p<0.05.

Results: Significant corrections were applied to the varus knees investigated (achieved alignment vs. preoperative varus deformity, p<0.01). The natural alignment target in the male knees was on average 1.6° more varus than that in the female knees (p=0.03). No differences were found between natural alignment target and achieved alignment (p>0.2). Both the natural alignment target and the achieved alignment were close (<1°) to the reported constitutional varus angle for both genders. The mean error between the natural alignment target and the achieved alignment was less than 0.5° for both genders and pooled data.

Discussion: This study demonstrated that the use of the CAOS system greatly facilitated the surgical technique by offering the ability to quantify the alignment target, provide guidance to bony resection, and assess the accuracy of the achieved alignment. The CAOS system can be of great value in achieving the patient-specific surgical goal defined intraoperatively by the surgeons.

ABSTRACT. Introduction: Surgical parameters, such as the reconstructed posterior tibial slope (PTS), may impact the anteroposterior (AP) kinematics of cruciate-retaining total knee arthroplasty (CR TKA) designs. This study investigated the AP kinematics of a CR design in combination with variations in PTS.

Methods: Navigated CR TKAs were performed on 7 healthy cadaveric knees (PCL presumably intact) using special soft-tissue preserving tibial baseplates designed to easily modify the PTS. After implantation at each of the 4 PTSs (10°, 7°, 4°, and 1°), knee kinematics were measured by the navigation system through passive range of motion (ROM) tests. The AP displacement of the medial and lateral contact locations between the femoral and the tibial components were tracked. Additionally, the tibiofemoral AP translation (difference in AP displacement between the starting and ending contact locations) was calculated for each test for the flexion ranges of 30-60°, 60-90°, and 30-90°. The impacts of PTS on AP displacement and AP translation were studied with significance defined as p<0.05.

Results: Both the medial and lateral AP contact locations did not exhibit paradoxical sliding and gradually moved posteriorly with knee flexion. The lateral contact location was observed to be generally positioned posterior to the medial contact location. Increasing PTS from 1° to 4° resulted in significantly more posterior AP contact location for both medial and lateral compartments at 60° and 90° of flexion. For medial and lateral AP translation of the contact location, the only significant difference in flexion ranges was found between the PTSs of 1° and 4° for the flexion range of 60-90° (p = 0.04).

Discussion: This study demonstrated that PTS has significant impact on the AP kinematics of the CR TKA knees during early to 90° of flexion. The method developed for this study may be expended to various surgical parameters to investigate their impact on the TKA kinematics.

ABSTRACT. Introduction: Accurate restoration of the native soft-tissue envelope is fundamental for the clinical success of cruciate-retaining (CR) total knee arthroplasty (TKA). During this procedure, surgeons usually perform soft-tissue balancing via subjective assessment of knee kinematics through a range of flexion. Limited quantitative information is available on real-time intraoperative knee laxity. This study utilized a computer-assisted orthopedic surgery (CAOS) system to quantitatively assess parameters that may impact intraoperative assessment of the total varus-valgus laxity over the range of flexion in a CR TKA: arthrotomy and reconstructed posterior tibial slope (PTS).

Methods: CR TKAs were performed on 6 cadaveric knees (non-arthritic, PCL presumably intact) using a CAOS system. The implanted tibial baseplate was specifically designed to precisely and easily modify the PTS without damaging the soft-tissue envelope. Total varus-valgus laxity of the knees was measured as the varus to valgus rotation with a 10 N•m moment applied on medial and lateral side of the knee, respectively. Each measurement was repeated 3 times on the native knees, knees with open (patella reduced) and closed medial parapatellar arthrotomy, and after implantation at each of the 4 PTSs (10°, 7°, 4°, and 1°). The impacts of arthrotomy and PTS on the total varus-valgus laxity were assessed for flexion angle ranged from 20° to 90°, with statistical significance defined as p < 0.05. Clinically significant impact was identified with >3° of deviation.

Results: The intact knee generally exhibited increased total varus-valgus laxity with higher flexion, with on average 3.7° at 20° of flexion and 5.3° at 90° of flexion. A similar trend was observed in both arthrotomy and all 4 PTS groups. Both open and closed arthrotomy did not significantly change the total varus-valgus laxity. PTS of the reconstructed proximal tibia had no significant impact on the total varus-valgus laxity.

Discussion: The results from this study suggested that two of the surgical steps during a CR TKA, namely arthrotomy (patellar reduced) and choice of the PTS, did not significantly affect the intraoperative assessment of the total varus-valgus laxity. Most previous studies measured laxity postoperatively by clinical tests or radiographic analysis, which may be limited by inter-user variability or imaging resolution. The use of CAOS system can be an effective and accurate tool for assessing intraoperative knee functions for a better understanding of CR TKA.

ABSTRACT. Introduction: One of the effectiveness to improve clinical outcomes of Unicompartmental Knee Replacement (UKR) is an accurate component alignment. Although many surgical techniques of UKR can make the acceptable alignment, a new technology by using Robotic-arm Assisted can be made the alignment more perfectly. This study aimed to evaluate the accuracy of component placement and mechanical alignment between intra-operative planning by Robotic-arm Assisted Unicompartment Knee Replacement and post-operative result.

Methods: A Prospective cohort study of 20 patients with Medial Unicompartmental Osteoarthritis knee, aged 50 – 75 years, who underwent Robotic-arm Assisted Unicompartmental Knee Replacement between January to February 2015. First, we planned the component alignment and recorded implant alignment in computer. Second, we started bone cut as tibial cut, followed to femoral cut, then placed trial component. Last, we recorded all alignments in computer. One month later, post-operative, we examined the clinical outcomes as physical examination, full leg radiography was sent and measured mechanical axis and component alignments.

Results: 17 patients, average age 71.4 years, BMI 25.79 kg/m2 and hospital stay 4.06 days, were completed in the study. There were no significant difference of mechanical axis measurement between intra-operative plan and post-operative, the average error was 0.82 + 0.68 degree (p = 0.534). For the component alignment, there was no significant difference of posterior slope of tibial component between intra-operative plan and post-operative, the average error was 0.58 + 0.31 degree (P = 0.103), there were significantly difference in Varus/Valgus angulation of tibial component, the average error was 1.30 + 0.88 degree (P = 0.015), in Varus/Valgus angulation of femoral component, the average error was 0.63 + 0.58 degree (P = 0.018).

Discussion: Mechanical axis and posterior slope of tibial component alignment in UKR by using Robotic arm-Assisted for intra-operative plan is more accurate and less variable. Mismatch between intra-operative alignment and post-operative alignment, frequently causes by poor cementing technique of the prosthesis than incorrect bony cut. References : 1.Jess H Lonner, “Robotic Arm-assisted UKA Improves Tibial Component Alignment”, Clin Orthop Relat Res, Vol468, p141–146,2010. 2.PHILIPPE HERNIGOU, “Posterior Slope of the Tibial Implant and the Outcome of Unicompartmental Knee Arthroplasty”,J Bone Joint Surg,Vol 86-A,No3,p506-11,2004. 3.T M Coon,“Accuracy Of Robotically Assisted UKA”,J Bone Joint Surg,vol.93-B, 2011. 4.A. Mofidi,“Assessment OF Accuracy OF Robotically Assited Unicompartmental Arthroplasty (MAKOplasty)”,J Bone Joint Surg,Vol.94-B,2012.

ABSTRACT. Introduction: Malrotation of the femoral component in total knee arthroplasty (TKA) is cause of patellofemoral complications, ligament balancing of the knee or instability and polyethylene wear.Some studies have demonstrated improvement in accuracy of computer assisted surgery in the anteroposterior (AP) alignment in TKA.There is still unknown on determination of rotational alignment particularly on femoral component in computer assisted surgery helps in finding the accurate rotation or even improving rotation. The aim of this study was to evaluate the reliability of the femoral component rotation from intraoperative data record in computer-assisted navigation system(CAN-FRA) with postoperative femoral component rotation on computed tomography (CT-FRA).

Methods: In 51 underwent computer-assisted surgery TKAs for primary osteoarthritis of the knee with mean age of 69.51 years . All procedures were performed by a single surgeon. We used Intraclass correlation coefficient (ICC) to analyze the data between Intraoperative registration record of the femoral component rotation (CAN-FRA) and the postoperative femoral rotation on computed tomography (CT Scan).We measured the angle between the anatomical epicondylar axis and the posterior condylar axis of the implants(CT-FRA) at two separate time by three observers who were blinded for the intraoperative femoral rotation registration.

Results: Statistical analysis consisted of the mean intraoperative data record of femoral rotation(CAN-FRA) was 0.1º (range -4.5º – 5.5º). The postoperative femoral component rotation on CT showed a mean CT- FRA of -1.3º ( -4.6º– 4.4º) ( - Internal rotation/ + External rotation). The correlation coefficient of three observers was 0.92 ,0.94 and 0.93 and intraobservers was 0.91 , 0.85 and 0.90 respectively. The Intraclass correlation coefficient of the intraoperative data record in computer-assisted navigation system(CAN-FRA) versus the postoperative femoral component rotation (CT-FRA) was 0.71.

Discussion: This study shows that the rotational alignment of the femoral component using a computer-assisted navigation system is reliable and can help to achieve the optimal position of the femoral component and rotation alignment correction the position of a TKA.

ABSTRACT. Introduction: Patients with hallux valgus exhibit hypermobility of the first TMT joint and numerous studies have evaluated only two-dimensionally. However, hallux valgus deformity consists of 3-dimentional components including inversion and eversion. Therefore, we compare the 3D mobility of each joint of the first ray not only TMT joint but also the other joints that composed first ray between hallux valgus patients and healthy volunteers using non-weightbearing and weightbearing CTs with an original loading device.

Methods: The feet of 10 subjects were selected in hallux valgus patients and healthy volunteers. Subjects in both groups first underwent a non-weightbearing foot CT scan and a weightbearing foot CT scan by loading the subject’s body weight. Displacement of the distal bone relative to the proximal bone was quantified 3-dimentionally under non-weightbearing and weightbearing conditions.

Results: In hallux valgus patients, there were statistically significant differences in dorsiflexion, inversion, and adduction in the first TMT joint, and in eversion and abduction in the first MTP joint (p < 0.05). There were statistically significant differences in dorsiflexion and eversion in the talonavicular joint, and in eversion and abduction in the cuneonavicular joint (p < 0.05).

Discussion: Hypermobility extends across the entire first ray in hallux valgus patients in 3-dimentions. Our detailed 3-D analysis of the foot will enable a more accurate assessment of the deformity to assist surgeons in choosing the most appropriate method of treatment.

ABSTRACT. Introduction: Instabilities of the posterior pelvic ring can be stabilized with sacroiliacal screws. The authors favor implant removal after consolidation. Navigation is known to reduce radiation and soft tissue damage, but the required bone-reference (Schanz pin) can lead to complications. In 2012 a new method for pinless 2D-navigation was first described eliminating these drawbacks (Hofbauer et al., CAOS 2012, Seoul). We hypothesize that this new method can reduce soft tissue damage and radiation.

Methods: A human replica was developed to simulate realistic surgical conditions. A layer of modeling clay and foam was applied to block direct sight. An image intensifier with navigation was used [BrainLab/Siemens, Germany]. 50 surgeries were performed on the human model by one experienced surgeon (25 conventional and 25 navigated). In the conventional group the screw position was identified by taking several x-rays. In the navigated group the VectorVision trauma software was used. The reference base was fixed on a pelvic mold which was secured to the upper legs. A referenced pointer was advanced through the tissue while watching the virtual path on the navigation screen until it was placed inside the cannulated screw. The following parameters were recorded: total time [s], radiation time [s], dose-area product [cGy*cm²], numbers of x-rays taken and soft-tissue damage. After every surgery the layers of the human replica were completely restored. Level of significance was set to p<0.05.

Results: Median total time for conventional surgery was 100.6 s.In comparison it took 197.3s total time for the navigated group. Navigation was sign. slower [p=0.000]. Median radiation time for the conventional group was 7 s and 2 s for the navigated group which was sign. lower [p=0.000]. Median radiation dose-area product was 5.14 cGy*cm² for the conventional and 1.23 cGy*cm² for the navigated group which was sign. lower [p=0.000]. Median number of x-rays taken in the conventional group was 12 and in the navigated group 4 which was sign. lower [p=0.000]. Comparison of soft tissue damage revealed a median damage of 5 holes in the conventional and 1 hole in the navigated group which was significantly lower [p=0.000].

Discussion: This study shows that with 2D pinless navigation, radiation and soft tissue damage can be significantly reduced without the known risks of pin fixation. In the navigated group a median of only one direct path from skin incision to the entry point of the screw was needed. When applying this method on a patient less trauma could lead to faster recovery from surgery. In relation to all these advantages OR-time is longer when performing a navigated surgery.

ABSTRACT. Introduction: One of the limitations in imageless navigation is the variability in bony landmark registration among surgeons. The objective of this study was to determine intra and inter-observer reliability of the bony landmark registration in three surgeons with varying experience in imageless navigation THA.

Methods: The authors reviewed 60 cases receiving cementless THA with imageless navigation from June 2014 to April 2015. All cases were registered for anterior pelvic plane by three surgeons. The first surgeon (S1) is senior staff with experience, the second surgeon (S2) is junior staff with one year of experience (>50 cases) and the third surgeon (S3) is the 4th year orthopedic resident with no experience in imageless navigation. Using the final cup position of the experienced surgeon as the gold standard to determine the reliability of registration.

Results: There were no significant differences in cup abduction angle between (S1) and (S2) (p=0.27) and (S1) and (S3) (p=0.79). There was no significant difference in cup anteversion angle between (S1) and (S2) (p=0.1) but there was significant difference between (S1) and (S3) (p<0.001). For the intra-observer reliability, the ICCs of abduction angle was 0.95 for (S2) and 0.86 for (S3) and the ICCs of anteversion angle was 0.91 for (S2) and 0.86 for (S3). For the inter-observer reliability, the ICCs of abduction angle between (S1) and (S2) was 0.89 and between (S1) and (S3) was 0.87, the ICCs of anteversion angle between (S1) and (S2) was 0.8 and between (S1) and (S3) was 0.72.

Discussion: The reliability of registration was acceptable in abduction angle among surgeons. The reliability of registration was not acceptable only in anteversion angle between experienced (S1) and non-experienced surgeons (S3). For the surgeon with one year of experience in imageless navigation, the result of registration process was comparable to and reproducible with the experienced surgeon in both abduction and anteversion angles. References: 1.Hohmann E. A comparison between imageless navigated and manual freehand technique acetabular cup placement in THA. J Arthroplasty 2011;26:1078-82. 2.Najarian BC. Evaluation of component positioning in primary total hip arthroplasty using an imageless navigation device compared with traditional methods. J Arthroplasty 2009;24:15-21. 3.Suksathien Y. Acetabular cup placement in navigated and non-navigated THA. J Med Assoc Thai 2014;97(6):629-34. 4.Parratte S. The use of ultrasound in acquisition of the anterior pelvic plane in computer-assisted THA. J Bone Joint Surg 2008;90-B:258-63. 5.Osahi H. Intra- and intersurgeon variability in image-free navigation system for THA. Clin Orthop Relat Res 2009;467:2305-9.

ABSTRACT. Introduction: In general, the distal locking holes of intramedullary nails are difficult to be located intraoperatively because they are visible only under X-ray exposures and the nail deforms during the implantation process. Conventional approaches for distal locking of intramedullary nails are based on C-arm fluoroscopic images (Viant 1995, Zhu 2002, Neatpisarnvanit, et al. 2006), mechanical instruments (Windolf 2012), conventional down-the-beam method with tracked instrument (Diotte 2014), sensors (Hoffmann 2012), nail pose estimation (Yaniv 2005), or optimization method with single C-arm image (Zheng 2007). Most of them need to take more than two C-arm images or bundle with guidance devices for positioning distal locking holes.

Methods: Our research team had developed a new method for determining the positions and orientations of distal locking holes of intramedullary nails by using single C-arm image (Hsu 2015). This study extends the previous work by assessing the positioning accuracy of distal locking holes of a real intramedullary nail.

Results: Twenty-nine test cases with different imaging angles have been done and the positioning accuracy of all cases can enable a drill of 5mm in diameter to drill through the locking holes successfully.

ABSTRACT. Introduction: Total hip arthroplasty (THA) in the lateral position involves particularly large variance in the sagittal tilt of pelvis fixation, which affects the unprecision of the cup anteversion leading to poor outcomes. We have developed a new device in the lateral position, theoretically enabling fixation on the anatomical pelvic plane (APP) serving as the reference plane. The present study aimed to evaluate the usefulness of this device in comparison to the currently used device.

Methods: We studied 141 patients who underwent THA at our hospital. Two frontal plain X-rays of the pelvis were obtained preoperatively for each patient after pelvis fixation; one with the currently used lateral fixation device and the other with an APP lateral fixation device. The sagittal tilt of the pelvis in each position was measured with 3D template software, and variance in the sagittal tilt was compared between two devices.

Results: The mean bias in sagittal tilt relative to the functional pelvic plane (FPP) in the currently used device was -5.0 ± 4.8 degrees (minus means backward tilt) and was within 5 degrees relative to the FPP in 43%. The mean bias in sagittal tilt relative to the APP in the currently used device was -1.4 ± 7.3 degrees (backward tilt) and was within 5 degrees relative to the FPP in 47%. On the other hand, the mean bias in the sagittal tilt relative to the APP in the APP lateral position device was 1.7 ± 3.1 degrees (forward tilt) and was within 5 degrees relative to the APP in 89%. The APP lateral device significantly reduced the variance in the sagittal tilt.

Discussion: This device holds promise as a means of reducing the sagittal tilt in a simple, minimally invasive and highly cost-effective manner.

ABSTRACT. Introduction: We investigated the early dislocation rate of computer navigation (NAV)-assisted primary total hip arthroplasty (THA) through a posterior approach in order to clarify the short-term benefit of using a NAV.

Methods: We retrospectively reviewed the early dislocation rate of 475 consecutive primary THAs with femoral head sizes ≦32mm performed via posterior approach. All THAs were planned using a 3D-templating system based on the combined-anteversion theory, performed by single surgeon through a posterior approach with assistance of CT-based NAV for cup implantation. We classified all 475 joints into four groups: normal or mildly deformed hips (Group A; 308 joints), moderately deformed hips (Group B; 97 joints), severely deformed hips (Group C; 53 joints), and neuromuscular and cognitive disorders (Group D; 17 joints), and examined the dislocation rate for each group.

Results: We had eleven early dislocations (2.3%). All 11 cups were implanted within 5 degree of error from the preoperative planning. The dislocation rates according to group were 0.6% for group A (2/308), 0% for B (0/97), 9.4% for C (5/53), and 23.5% for D (4/17).

Discussion: In this series, most dislocations occurred in the highly risky or rare condition cases in groups C or D. In such cases, precise and appropriate cup implantation assisted by NAV could not completely prevent dislocation because of the patients’ specific special backgrounds. On the other hand, NAV was effective for prevent early dislocation in the normal or mild to moderately deformed joints such as those in groups A or B.

ABSTRACT. Introduction: Patient-specific templates (custom-made cutting guides) for TKA potentially have several advantages over conventional and other computer assisted techniques such as robotics and navigation. However, the process of all commercially available PST is cumbersome. Each of these PST is based on only one implant produced by the implant company. Most of these companies outsource some steps of PST such as imaging, preoperative planning, manufacturing of PST, packing/sterilization and then deliver PST to hospitals for the planned surgery. This process takes about 6 weeks and it is not controlled by surgeons or hospitals Methods: All five steps of PST (imaging, planning, PST production, packing/sterilization and surgery) were done in one location (inside the hospital). The planning was controlled by the surgeon. The PST was produced onsite by desktop 3D printers. Packing and sterilization was done onsite and then the surgery was done in the same hospital by the same surgeon who did the planning. Results: The process was feasible and the work cycle was easier and cheaper. The outcome of the process of 200 cases showed that CT-based imaging was easy and affordable. Planning was controlled by the surgeon. Polyamide nylon was the best available material and it was autoclavable. Desktop 3D printers were able to produce PST made of nylon but with some difficulties. The whole process could be done in as short duration as 3 days. Conclusion: The logistics for TKA using PST were made easy by the introduction of desktop 3D printers. It appears that PST could be used as a hospital-based technique

ABSTRACT. Introduction: We wanted to determine whether the course of the femoral artery differed according to the extent of developmental dysplasia of the hip by measuring the distance between the artery and pelvis.

Methods: 106 THA patients were grouped according to the Crowe Classification, with 22 patients in Crowe Group I, 24 patients in Group II, 21 patients in Group III and 24 patients in Group IV. In addition, 15 patients showed degenerative coxarthrosis following Chiari’s osteotomy. A computer tomography-based hip navigation system was used to measure the distance between the artery of the femur and the anterior wall of the pelvis at 6 axial planes located 10, 20, 30, 40, 50 and 60 mm from the pelvic tear drop. The measured distances of the Crowe Group I patients were compared against those of the other 4 groups.

Results: Significant differences were found between Group I and Groups III / Group I and IV at 10 and 40 mm from the pelvic tear drop. Significant differences were also seen at 20, 30 and 40 mm between Crowe Group I and the post-osteotomy group.

Discussion: These findings clearly showed that the artery tended to pass closer to the acetabulum in Crowe III and IV patients than in individuals with Crowe I patients. The femoral artery also passed close to the anterior pelvic wall in many patients with degenerative coxarthosis following Chiari's osteotomy. Caution is therefore required in Crowe III and IV patients or post-osteotomy THA patients.

ABSTRACT. Introduction: Though recently questioned, Neutral Mechanical Alignment (NMA) is generally targeted in Total Knee Arthroplasty (TKA). The alternative kinematic alignment (KA) has been proposed for better soft-tissue balance and supported via Patient-Specific Instrumentation (PSI). The aim of this study is to report clinical and kinematic results of patient operated using NMA and KA, the latter via modern PSI.

Methods: 20 patients were implanted with a cruciate-retaining fixed-bearing TKA prosthesis with patella resurfacing. 11 patients were operated targeting NMA (group A) via convention instrumentation and 9 patients targeting KA (group B) via PSI. All patients were assessed clinically using IKSS and KOOS scoring system pre- and post-operatively. At 6-month follow-up, these were also assessed biomechanically during motor task execution via video-fluoroscopy synchronized with EMG analysis. Knee motion was reconstructed to calculate knee rotations and anterior-posterior contact-point translations on tibial base-plate.

Results: At 12-month follow-up, knee and function IKSS were 78±20 and 80±23, worse than in group B, respectively 91±12 and 90±15. The same was found for KOOS. Knee rotations patterns were much more consistent over patients in group B. Generally, limited axial rotation and posterior compact-point translations were found. EMG analysis revealed muscle co-contraction in group A; this behaviour was not observed in group B, this perhaps proving more stability after TKA according KA.

Discussion: These results reveal that better performances occurs using KA than NMA. The less prolonged activation of the knee extensor muscles in TKA patients using KA suggest that a more natural soft tissue balance can occur in these TKAs.

ABSTRACT. Introduction: The restoration of a physiological range of motion (ROM) is still a major issue in total knee arthroplasty (TKA). In current practice the manually identified transepicondylar axis (TEA) is one geometric axis that is used as a surrogate of the flexion axis (FA) of the knee to guide the femoral component rotation at implantation. The hypothesis of this study was that the approximation of the FA using an automatically calculated axis based on the functional articulation surface of the femur (PFEA) is more accurate than using the manually identified TEA during flexion.

Methods: For ten subjects the angels between the FA and TEA as well as FA and PFEA were compared for increasing flexion. The FA was derived from five upright-MRI scans in increasing static flexion positions.

Results & Discussion: With a 50/50 distribution for the smallest angle between TEA/PFEA and the FA of the maximum flexion postion the results do not permit a conclusion regarding the hypothesis, whether one of the geometric axes is more suitable for the approximation of the FA during flexion. But the findings of this study highlight inter-individual differences in knee kinematics also regarding the validity of TEA as common geometric axis for the approximation of the FA over the entire ROM. Moreover, the potential of PFEA regarding robustness for the approximation of the FA in flexion has been demonstrated also considering the significant inter- and intraobserver error due to the manual identification of the TEA.

ABSTRACT. Introduction: High tibial oeteotomy (HTO) is realignment operation of the lower limb. HTO influences the gait posture and the loading pattern of the foot and ankle. It is difficult to anticipate the gait change after HTO in dynamic status. The purpose of this study was to develop the gait analysis system for simulation of the gait change in realignment operation of the knee.

Methods: We developed 4-dimensional gait analysis system for assessment of gait and posture included knee function. This system was combined CT images of the lower limb and motion capture data by the spherical skin marker matching technique. Force plate data was acquired for assessment of knee adduction moment. The simulation program for the planning of HTO was combined in this system. The simulation program was developed to predict the gait after re-alignment operation of the knee. The corrected 3-dimensional bone models of the lower limb walked on the basis of the pre-operative walking data. This program was validated by the patient after bilateral HTO for medial compartment ostoarthritis of the varus knee. Pre and post-operative natural walking data were taken for gait analysis. Pre-operative gait data was simulated to realignment operation of the knee. The knee adduction moment and the gait posture were compared the pre-operative gait data simulated HTO and the post-operative gait data.

Results & Discussion: The gait posture of 3D bone models showed almost the same movement between surgical simulation and real operation. The knee adduction moment during gait was similar between the surgical simulation data and post-operative data.

ABSTRACT. Introduction: Revision of pedicle screws is troublesome or challenging because of the fusion mass. Pedicular screws were inserted more accurately with computer assistance were reported by several authors. There is few study focusing on another screw placement in the same pedicle. Material Method: 89 patients who had a previous posterior instrumentation underwent revision spinal surgery with posterior spinal instrumentation due to another spinal disorder between 2001-2012. We used the computer-assisted to gain the screw access in the same pedicle which had another screw was inserted in 38 patients. All screws were analyzed using radiology, postoperative CT in the computer-assisted two screw placement cases. Perioperative data and improvement in clinical outcome scores from baseline are evaluated to determine the clinically significantly benefits of the procedure. Results: Two groups of 87 patients were similar at baseline with respect to age, gender. The conventional cohort was composed 51 patients. The computer-assisted Cohort was composed of 38 patients. There are no vascular or visceral major complications are related to the pedicle screw placement in two groups. In the final follow-up, 78% of the patients were satisfied with pain relief and increased walking ability. There were six patients with radioculopathy in the conventional cohort. The operative time, blood loss and plain radiography exposure are more significantly in the conventional group (p<0.05). Discussion & Conclusion: Revision of previous pedicle screws is troublesome or challangring because of the fusion mass. There are several methods of pedicle screw insertion to enhance safety, such as intraoperative radiography, free-hand method, and guide pins into the pedicles. However, pedicles screws malplacement rates of between 21.1 and 39.8% have been reported in clinical studies with conventional insertion techniques. It is reliable and safe to insert another screw in the same pedicle with image-guided computer navigation assistance. The removable of previous posterior instrumentation can be avoided in patients who need extend fusion due to junctional spinal disorders.

ABSTRACT. Introduction: The goal of the study was to measure the changes in the rotational knee laxity according to the status of the antero-lateral ligament (ALL) and of the anterior cruciate ligament (ACL).

Methods: 5 pairs of fresh frozen gross specimens were analyzed. The knee was positioned at 20° of flexion. An increasing calibrated internal/external torque was applied; the rotational knee motion was measured by a navigation system for each applied torque. Three settings were used: intact ACL and ALL, section of ACL or ALL (randomly assigned to each knee of a pair), section of ACL and ALL.

Results: The mean rotational laxity for intact knees was 27.1 ± 3.7 degrees. The mean paired increase was 0.8 degrees after ALL section, 1.2 degrees after ACL section, and 0.8 degrees after combined ALL and ACL section. There was no significant increase after ALL or ACL section. There was no significant difference after additional ALL section by ACL deficient knees. The mean knee stiffness in rotation for intact knees was 3.18 ± 0.7 Nm/degree. The mean paired increase was 0.16 Nm/degree after ALL section, 0.16 Nm/degree after ACL section, and 0.24 Nm/degree after ALL and ACL section. There was no significant increase after ALL or ACL section. There was no significant difference after additional ALL section by ACL deficient knees.

Discussion: Section of the ALL did not impact rotational knee laxity and rotational stiffness of the knee in comparison to normal knee, neither isolated or by ACL deficient knee.

ABSTRACT. Introduction: The goal of the study was to measure the changes in the anterior knee laxity according to the status of the antero-lateral ligament (ALL) and of the anterior cruciate ligament (ACL).

Methods: 5 pairs of fresh frozen gross specimens were analyzed. The knee was positioned at 20° of flexion. An increasing calibrated postero-anterior force was applied; the anterior tibia translation was measured by a navigation system for each applied force. Three settings were used: intact ACL and ALL, section of ACL or ALL (randomly assigned to each knee of a pair), section of ACL and ALL.

Results: The mean anterior tibia translation at 250 N was 5.3 ± 2.8 mm for intact knees. The mean paired increase was 1.2 mm after ALL section, 9.0 mm after ACL section, and 6.1 mm after combined ALL and ACL section. There was no significant increase after isolated ALL section. There was a significant increase after isolated ACL section. There was no significant increase after additional ALL section by ACL deficient knees. The mean knee stiffness in anterior translation for intact knees was 0.015 ± 0.02 N/mm. The mean paired increase was 0.01 N/mm after ALL section, 0.038 N/mm after ACL section, and 0.021 N/mm after combined ALL and ACL section. There was no significant increase after isolated ALL section. There was a significant increase after isolated ACL section. There was no significant difference after additional ALL section by ACL deficient knees.

Discussion: The expected role of ALL in controlling anterior knee laxity could not be confirmed.

ABSTRACT. Introduction: In modern orthopaedic surgery intraoperative imaging and visualization is of uttermost importance. Minimally invasive procedures are on the rise and with minimum surgical access the need to optimize instrument and implant visualization grows. 3D images may be one way to increase the need for intraoperative control. Aim of our study was to determine the effective dose and organ doses of a roboted flat panel C-arm in comparison to the gold standard in spine imaging, the computed tomography (CT).

Methods: A Rando-Alderson Phantom was used to measure radiation. Three standard protocols of a roboted 3D-C-arm were examined (standard full dose, no collimation; standard full dose, collimation; low dose, collimation) in comparison to two protocols of a CT (full dose spine protocol; low dose protocol). Two anatomical regions were examined, the thoracolumbar junction (focus L1) and the upper thoracic spine (focus Th6). Effetive dose and organ doses were determined for all protocols at the two regions.

Results: At the lumbar spine, the most exposed organ was the stomach (lowest: 3D low dose, 4.08 mSv; highest: 3D full dose without collimation: 15.78 mSv), followed by the bone marrow. At the thoracic spine, the most exposed organ was the oesophagus (lowest: 3D low dose, 1.15 mSv; highest: CT full dose, 11.11 mSv), followed by the bone surfaces and the lung. At the lumbar spine, the effective dose was lowest for the 3D C-arm low dose protocol (1.0 mSv). The CT low dose protocol caused a reduced effective dose in comparison to the full dose version (2.9 mSv vs. 5.0 mSv). The full dose 3D-C-Arm protocols showed no relevant difference regarding the collimation (4.4 mSv (no collimation) vs. 4.3 mSv (with collimation)).At the thoracic spine, similar effects were examined, while the dose in general was much lower in comparison to the lumbar spine.

Discussion: There is no safe threshold below which ionising radiation is considered harmless. Knowing this it is surprising that there is hardly any knowledge on the actual exposure that modern intraoperative imaging devices are causing. To safely facilitate modern C-arms intraoperatively, basic research is required to increase our understanding in the emission of radiation of the new technology. We were able to demonstrate, that low dose protocols allow to reduce the emission for both technologies. Especially the intraoperative 3D low dose protocols were radiation saving and, in comparison to a CT, can be obtained right on the OR table and therefore serve as immediate postoperative control with the situs still open, leaving the possibility for immediate revision if need be.

ABSTRACT. Introduction: Abnormal kinematics after cruciate-retaining total knee arthroplasty (CR TKA), such as paradoxical anterior femoral sliding on the tibia, may be caused by the improper reconstruction of the tibial posterior slope (PTS). Limitations of the previous investigations of the impact of PTS on CR TKA kinematics included sample size requirement, surgical variability, soft-tissue protection, and accuracy of the measurements. This developed and verified an improved, navigation based, soft-tissue preserving method for the study on this topic.

Methods: Seven navigated cemented CR TKAs were performed on fresh frozen healthy knees using special tibial baseplates that allowed easy and soft-tissue preserving modification of the PTS. After the CR TKA, passive range of motion (ROM) tests were performed at varying PTSs following the order of 10°, 7°, 4°, 1°, and back at 10°. The variability of the repeated measurements (Root mean square error: RMSE) and inter-surgeon variability was assessed. The test method was further verified by comparing the kinematics between the initial and the final ROM tests at 10° PTS. Statistical significance was defined as p < 0.05.

Results: The mean RMSEs of the repeated measurements were 0.19 ± 0.06 mm, 0.98 ± 0.37°, and 0.11 ± 0.03° for anteroposterior (AP) displacement, internal/external (IE) rotation, and hip-knee-ankle angle (HKA), respectively. Slight variations of RMSEs were observed across the flexion angles. No significant difference was found between the two surgeons for each sampled flexion angle in all kinematic parameters. Both the initial and final 10° PTS measurements exhibited similar kinematics with deeper flexion, including physiological femoral rollback (starting from ~ 50° flexion), external rotation of the femur relative to the tibia, and a more varus HKA. No significant differences were found between the two sets of measurements at 10° PTS.

Discussion: This study verified a set of methodology for the testing of the impact of PTS on CR TKA kinematics. The test method was shown to have good accuracy and insensitive to inter-surgeon variability. To our knowledge, this is the first study to verify the accuracy and repeatability of an investigation method for the impact of PTS on CR TKA kinematics. Based on the results, the authors recommend the proposed test method for future investigations on the effect of PTS on the postoperative knee kinematics.

ABSTRACT. Introduction: It is speculated that certain lower limb geometries could be predisposing factors for the occurrence of atypical femoral fractures. This is due to the fact that atypical femoral fractures start from anterolateral femoral cortex, where most of major tensile stress is applied, due to anterior and lateral bending of the femur. The purpose of our study was to investigate the radiographic characteristics of atypical femoral shaft fractures (AFSF) in Asian female patients.

Materials & Methods: We retrospectively analyzed 32 AFSFs in 22 patients, aged 50 years or over. Diagnosis of AFSF was made according to the ASBMR task force 2013 revised case definition. Age, gender, bisphosphonate use, femoral curvatures, and cortical thicknesses were evaluated. The femoral curvatures and cortical thicknesses of these patients were compared with those of ordinary femoral shaft fractures.

Results: All AFSF patients were female with a mean age of 73 years. All had a history of bisphosphonate use with a mean duration of 7.6 years. Femoral curvatures of the AFSF group were significantly higher than those of the control group on both anteroposterior (AP) and lateral radiographs after age correction. Mean femur curvatures on an AP radiograph were 13.33°±5.64° in the ASFS group, and 3.38°±3.74° in the control group (P<0.0001). Mean femur curvatures on the lateral radiograph were 17.38°±5.24° in the AFSF group, and 12.48°±4.15° in the control group (P=0.006). The adjusted lateral cortical thickness was 10.2±1.4mm in the AFSF group and 7.6±1.0mm in the control group (P< 0.0001, after age correction P<0.0001). Correlation analysis found a significant positive correlation between the lateral femoral bowing and the lateral cortical thickness index of the AFSF group (R=0.418, P=0.003) (Fig. 1).

Discussion: In conclusion, AFSFs in a sample of Asian female bisphosphonate users were associated with an increased anterolateral femoral curvature, and a thicker lateral femoral cortex. Although our study was not designed to evaluate the mechanisms of the effect of bisphosphonate on the AFSF group, the effect of bisphosphonate may increase the risk of AFSFs in the patients with anterolateral femoral bowing, and increased lateral femoral cortical thickness, by suppression of bone turn over, impairment of the bone quality and fracture healing process. Therefore, anterolateral bowing and lateral cortical thickening of femur in Asian females following long-term bisphosphonate use, can be considered as a high risk group of developing AFSFs.

ABSTRACT. Introduction: Accuracy and reliability in measurement of wrist range of motion (ROM) is necessary in clinical examination and evaluation. The Leap Motion Controller may be an easy and effective device for evaluating wrist ROM. The objective of this study was to determine the effectiveness and reliability of Leap Motion Controller in the measurement of wrist ROM, as compared with universal goniometer.

Methods: A comparison of wrist joint motion range measurement was performed in 33 healthy volunteers using a randomized method. Wrist ROM measurement was compared between Leap Motion Controller and universal goniometer. Volunteers had no previous history of wrist injury and/or surgery.

Results: Significant interobserver and intraobserver reliability was found in the measurement of wrist angle using the Leap Motion Controller. Average intraclass correlation coefficient comparing Leap Motion Controller and goniometer was: flexion 0.86, extension 0.92, radial deviation 0.53, and ulnar deviation 0.76 for examiner 1, and flexion 0.83, extension 0.92, radial deviation 0.69, and ulnar deviation 0.80 for examiner 2. For examiner 1, limits of agreement were -3.76 ± 10.56 for flexion, -0.21 ± 10.11 for extension, -3.88 ± 9.58 for radial deviation, and -2.45 ± 9.00 for ulnar deviation. For examiner 2, limits of agreement were -3.21 ± 12.15 for flexion, 0.45 ± 10.05 for extension, -0.15 ± 9.78 for radial deviation, and -0.15 ± 9.02 for ulnar deviation.

Discussion: Leap Motion Controller was found to be a reliable and precise tool for measurement of wrist motion as compared with universal goniometer, the current standard bedside technique.

ABSTRACT. Introduction: Recent literature suggests biomechanics, in addition to radiographic angles such as the center edge and acetabular index, may play an important role in planning and assessing periacetabular osteotomy. A Biomechanical Guidance System (BGS) has been developed to assist surgeons performing PAO. The BGS intraoperatively tracks the acetabular fragment location, measures radiological angles, and computes biomechanics using Discrete Element Analysis.

Methods: We performed ten consecutive PAO operations on patients (4 male, 6 female, average age 37 years) between November 2005 and January 2006. During PAO, the BGS recorded the intraoperative fragment position. Post-hoc analysis estimated the optimal fragment location by minimizing the peak pressure associated with either gait or a combination of gait, standing, and sitting. Comparisons between intraoperative and preoperative fragment locations were conducted.

Results: The intraoperative and optimal locations always exhibited lower contact pressure than described by the preoperative conditions. Results suggest that the gait only optimization differs from the combined-force optimization through rotations about the medio-lateral axis of 12.4 degrees, on average. Rotations about the inferior-superior axis demonstrated a sign difference, with gait-only optimization averaging 1.9 degrees of anteversion compared to 3.8 +/- 6.4 degrees of retroversion for the combined-force optimization. Comparing the radiographic angles suggests that the gait-only optimization aligns with surgical practice.

Discussion: Biomechanical planning may be a useful tool when performing PAO. Moreover, real-time assessment of the biomechanics may be beneficial. However, certain biomechanical measures may be of greater importance than others, such as gait compared to sitting.

ABSTRACT. Introduction: Minimally invasive orthopedic interventions often require accurate information for spatial relations of the medical instruments with respect to medical data and the patient’s anatomy. Surgical navigation systems are used to guide during such procedures, which are often costly and complex to setup with line-of-sight requirements. Moreover, the tracking is performed with respect to outdated pre-operative medical images. Alternatively, minimally invasive procedures are performed by acquiring several X-ray images using a C-arm. However, this requires frequent C-arm repositioning, resulting in a high task load and frustration for the surgical team, high X-ray exposure, and long surgical duration.

Methods: This work proposes an Augmented Reality visualization by fusing Digitally Reconstructed Radiographs (DRRs) rendered from CBCT with 3D surface information obtained from a 3D optical (RGBD) camera, which is attached to the detector plane of a mobile C-arm. To perform the calibration, a CBCT and RGBD scan are simultaneously acquired of an arbitrary phantom which has been introduced into the common views of the C-arm and the RGBD camera. Fast Point Feature Histogram is used to register these data sets, followed by the use of an Iterative Closest Point (ICP) algorithm to further refine the calibration. The proposed calibration algorithm is offline and the system remains self-contained.

Results & Discussion: A reasonable calibration accuracy of 2.58 mm is achieved using this technique. Results show lower surgical task load and reduced duration for simulated K-wire placements using the intuitive Augmented Reality visualization.

ABSTRACT. Introduction: Ultrasound (US) imaging is frequently used in early detection of Developmental Dysplasia of the Hip (DDH) to guide early non-invasive treatments aimed at reducing the need for surgery. In US-based diagnosis, the primary metric that characterizes the acetabular morphology of the infant hip is the alpha angle, which is the angle between the acetabular roof and the vertical cortex of the ilium. However, measuring α often suffers from high variability (standard deviations typically ranging from 3 to 7 degrees) that can lead to significant discrepancies between treatment recommendations made based on the results of the US examination and later clinical assessments . We recently proposed a novel method to reduce the subjective variability associated with determining the alpha angle by automating the angle extraction process. In this paper, we extend our previous work by automatically estimating the process parameters directly from the US images and by significantly expanding our clinical data set, which allowed us to compare the automatic and conventional manual approaches to measuring the alpha angle.

Methods: We investigated the performance of our automatic method on 693 B-mode US images (obtained as part of routine clinical care under appropriate institutional review board approval) from 35 patients.

Results: The automatic method significantly reduced the variability in measuring the alpha angle compared with the manual technique (p<0.05 using Wilcoxon signed rank test, ~9% reduction in variability), and the bias was slight - ~1.8deg lower with the automatic method. '

Discussion: While we have shown a minor reduction in variability with our automatic method, recent studies have shown that the alpha angle measured on a given 2D US slice can vary significantly with transducer orientation. In future work, we therefore plan to develop an intrinsically 3D dysplasia metric based on 3D US scans.

ABSTRACT. Introduction: In total knee arthroplasty the individual bone morphology is changed by the artificial implant geometry and placement, which might induce incompatibilities in the sensitive joint mechanisms, causing patient dissatisfaction and premature implant failure. Therefore, a comprehensive understanding of the governing parameters and a study of their effects on biomechanics of the individual patient are essential. The goal of our study was to develop and validate a simplified biomechanical simulation model considering articular surfaces where the patient-specific adaption process was aimed to be valid for data, which are commonly available in the clinical workflow.

Methods: The experimental data used in this study were part of the “Grand Challenge Competition to Predict In Vivo Knee Loads” (GCC). For the model adaption and validation the data from GCC3, GCC5 and GCC6 were used, since these were complete and the most reliable. The patient-specific model was developed from scratch in the software AnyBody. The lower extremity is represented by 3 segments (femur, tibia, patella) and the tibiofemoral joint contains 6 and the patellofemoral joint 5 degrees of freedom. The basic flexor and extensor muscles activated during two-leg squat, which has broad consensus to several everyday activities, were included. In order to stabilize the knee joint 6 ligamentous structures were included representing the posterior cruciate, collateral and patellofemoral ligaments. A generic pelvis served as body dummy to apply an external force to the lower extremity. The antagonistic ground reaction force was directly estimated based on the Newton–Euler equations of motion. The medial and lateral knee contact forces were recorded during two-leg squat simulation and compared to the corresponding in vivo measurements.

Results: The lateral contact forces compared well with the in vivo forces of all 3 patients (RMSE < 21 %BW) and the medial forces for GCC3 and GCC5 (RMSE < 26 %BW). However, for GCC6 the medial force was overpredicted which resulted in an overall high total force. Nevertheless, the differences of the total forces for GCC3 and GCC5 were small (RMSE < 26 %BW).

Discussion: The presented validated biomechanical model offers the opportunity to predict and study mechanics and kinematics which has the potential for integration into clinical workflow and to improve implant design and surgical outcome after TKA.

ABSTRACT. Introduction: In the case of total knee arthroplasties (TKA) a better outcome may be achieved by using patient-customized implants. The implant design is based on the actual bone surface obtained from medical imaging. Due to the degeneration of bone and cartilage, osteophytes (also known as bone spurs) may develop which show up in the acquired images and thus in the segmented surface data. The removal of osteophytes is conventionally performed during surgery and its removal in 3D surface data is necessary during implant planning as well as for biomechanical simulations. Since the osteophyte removal is cumbersome and time consuming, various methods for automatic osteophyte removal were developed in this study.

Methods: Bone surfaces (N = 413) of the distal femur were extracted from CT scans. The surfaces afflicted with osteophytes were manually processed by experts to obtain osteophyte free data. By subtracting diseased and non-diseased surfaces a map with sites of osteophytes was computed. Also, from this data a statistical shape model (SSM) was built up. The SSM was adapted to unknown data sets incorporating weights derived from the osteophyte map. Since statistical shape models are global in their nature, the SSM-based approach was compared with a morphing based approach (N-ICP-A) incorporating the same weighting mask. The advantage of the latter approach is that it can perfectly adapt to non-affected sites without any restrictions. The tests were carried out as leave-one-out cross validations.

Results & Discussion: The deviation between surfaces with manual osteophyte removal and surfaces with SSM-based osteophyte removal is in average (median) less than 0.8 mm if no weights were incorporated and less than 2 mm if weights were incorporated. Sites of osteophytes tended to be thickened. As to the morphing-based approach in average a deviation with less than 1.3 mm was observed. Here, sites of osteophytes tended to be shrunk. For all approaches, important areas such as the condyles remained unaffected.

ABSTRACT. Introduction: Open reduction and fixation of pelvis fracture often require an extensive surgical exposure. The risks of surgical wound problems, especially infection, are unavoidable. We proposed a two-step fracture reduction strategy. In the first step, the coarse reduction with computer assisted planning and robotic fracture reduction execution are carried out. In second step, the fine reduction with master-slave robotic manipulation reduces the residual displacement of fracture. In this paper, we focus only on the first step, the computer assisted PMR robot fracture reduction.

Methods: PMR Robot is used for Sacroiliac Joint Fracture Reduction. A set of images was used in computer assisted surgical planning for pelvis fracture reduction. Two pelvis sawbones models were artificially broken at the sacroiliac joint and at the symphysis pubis joint. The traditional classifications of pelvis fracture patterns were simulated as the initial fracture condition. PMR robot was controlled by data generated by pelvis fracture reduction planning procedure. Simplified 3D pelvis model and PMR robot were created and connected preoperatively. Artificial fractures were made on pelvis model and fittings were made between fractured pelvis model and background images of fractured pelvis in the same projected planes. Simulated fracture reduction of pelvis model would lead to generate the data for PMR robotic fracture reduction.

Results: Average errors of two fracture locations were measured: A, symphysis pubis and B, sacroiliac joint. The errors for AP Compression type were 4.0 mm in location A and 5.0 mm in location B. The errors for Lateral Compression type were 5.5 mm in location A and 6.0 mm in location B. Reduction on vertical shear type was not satisfactorily achieved, due to only partial use of range of motion in the PMR robot’s limited working space.

Discussion: Preliminary experiments showed that the system can perform well for the type I and II classes of the pelvis fracture. When it conducted reduction for type III pelvis fracture with rotation in sagittal plane, the robot system did not achieve the expected result. Consideration will be made to maximize PMR’s range of motion in its accessible working space.

ABSTRACT. Introduction: Cruciate-retaining (CR) total knee arthroplasty (TKA) is supposed that the posterior cruciate ligament (PCL) play an important role in roll back and stability of the knee after TKA. Dysfunction of PCL in CR TKA might cause paradoxical anterior movement in knee flexion. In this study, tibial cutting in Cruciate-retaining total knee arthroplasty (CR TKA) was simulated using a 3 dimensional (3D) model of the tibia to evaluate the residual attachment area of posterior cruciate ligament (PCL), both the anterolateral bundle (ALB) and the posteromedial bundle (PMB).

Methods: Forty knee with medial osteoarthritis (OA) scheduled TKA were included in this study. Three dimensional model of the only tibia was reconstructed from CT. Three dimensional models of the tibia and PCL was reconstructed from MRI. We determined the area of PCL tibia attachment using a markerless surface registration technique. Decision of the ALB and PMB was used each aspect of the fossa. Lateral articular cartilage thickness was assumed to 2mm. Three-dimensional tibial models bone cut was performed with 8mm depth of lateral tibial plateau with 0°,3°,5°,7°and 10° posterior slope. The percentage of ALB and PMB attachment after tibia resection was measured. Steel-Dwass tests were used for comparison each posterior tilt. Values of p<.05 were considered statistically significant.

Results: The percentage of ALB tibia attachment after tibia cutting 8mm with 0°,3°,5°,7°and 10° posterior tibial slope was 15.8±19.4%, 8.8±13.9%, 5.5±10.3% , 3.1±7.3% and 1.2±3.8% respectively. The percentage of PMB tibia attachment after tibia cutting 8mm with 0°,3°,5°,7°and 10° posterior tibial slope was 86.3±17.7%, 77.5±21.5%, 70.5±23.7% , 62.5±25.4% and 49.7±26.2% respectively. There was a significant difference in residual ALB attachment areas between 0 degree and more than 7 degrees (Fig.1) (p<0.001). There were significant differences among the residual PMB attachment area for a tibial cut of 8 mm with posterior tibial slope angles of 0° and 5°, 0° and 7°, 0° and 10° , 3° and 10°, 5° and 10°(p<0.005) (Fig. 2).

Discussion: The results in this study demonstrated that it is difficult to preserve enough ALB attachment after tibial bone cut in all cases scheduled TKA. The attachment of ALB was the same level as tibial plateau, as a results, most of ALB attachment was resected, if PCL attachment was preserved with bone island. The retained PCL in CR TKA might be insufficient PCL, in other words, majority of retained PCL might be composed from only PMB. Not normal PCL but partial (PMB) PCL retained CR TKA might affect the function of reconstructed knees. In the near future, we will investigate the relation between retained PCL and in vivo kinematics.

ABSTRACT. Introduction: Compared with the cruciate-retaining (CR) insert for total knee arthroplasty (TKA), the cruciate-substituting (CS) insert has an increased anterior lip, providing greater anterior constraint, and thus, can be used in cases of posterior cruciate ligament (PCL) sacrifice. However, studies have shown that the PCL acts as a stabilizer and has mechanoreceptors; therefore, the argument for PCL excision in CS TKA remains controversial. The purpose of this study was to analyze CS TKA kinematics and identify the role of the PCL.

Methods: Seven fresh-frozen lower-extremity cadaver specimens were analyzed using Orthomap® Precision Knee Navigation (Stryker Orthopaedics, Mahwah, NJ, USA). They were surgically implanted with Triathlon® components (Stryker Orthopaedics). Six patterns were analyzed: (1) natural knee; (2) only anterior cruciate ligament excision; (3) CS TKA, PCL retention, and bony island preservation; (4) CS TKA, PCL retention, and bony island resection; (5) CS TKA and PCL excision; and (6) CR TKA and PCL excision. The magnitudes of the condylar translation were evaluated.

Results: PCL excision patterns showed that the magnitude of anterior-posterior (AP) translation was higher in mid-flexion and lower in deep flexion than in other patterns. No statistically significant difference was found between two PCL excision patterns. Comparing two PCL retention patterns, the both posterior translation magnitudes in deep flexion were comparable to that of the natural knee. The AP translation magnitude was not dependents on the bony island.

Discussion: In conclusion, we had better retain the PCL in raised anterior lip type CS TKA to ensure physiological knee kinematics.

ABSTRACT. The use of bone cement on the long-term clinical outcomes and aseptic loosening has been well studied. However, to our knowledge, there is no previous work on the impact of cementing on the implant positioning during knee replacements. In this work, we examine the effect of cementing on the alignment of tibial and femoral implants in unicondylar knee replacement (UKR). Our results show that the position and orientation errors obtained in the cementing and the trialling positions are very similar. We also noted that the tibial implant moves into a more anterior position after cementing.

ABSTRACT. Introduction: UniKnee arthroplasty (UKA) is a resurfacing of one compartment of knee joint. Therefore, restoration of native mechanical alignment and joint line are considered as a successful UKA. Hungerford1 introduced anatomical tibial cut by tibial resection in 3°varus. However, there is no study documenting whether UKA with anatomical tibial cut has different clinical results from UKA with classical tibial cut or not.

Methods: 29 patients with medial compartment osteoarthritis knees scheduled to receive CAS mobile bearing UKA (OrthoPilot UKA v.3.0, B.Braun, Aesculap, Tuttlingen, Germany) from June 2015 to December 2015. Patients were classified into 2 groups. First group had 15 patients, tibia was cut with classical method. Second group had 14 patients, tibia was cut with anatomical method. WOMAC scores, Oxford knee scores and range of motion (ROM) were collected before surgery and 6 months later. Clinical data were reviewed and compared between group 1 and 2.

Results: Paired two tail t-test between groups 1 and 2 show no significant difference in WOMAC scores (P = 0.512), Oxford knee scores (P = 0.305) and range of motion (P = 0.667).

Discussion: Bellemans2 revealed a mechanical alignment of 3° varus and more in asymptomatic knee, so-called “constitutional varus” knee. Vector3 observed parallel joint line to the ground could be found in both neutral and constitutional varus knee. From this concepts, we performed CAS UKA to recreate a nearly native joint line orientation by selected angle of tibial bone cut according to native mechanical tibial alignment. Clinical outcomes, range of motion were found insignificant clinical difference between group 1 and 2, similarly to study by Ji-Hyun Yim4 in Robotic TKA. However, this concept needs to further study by increase number of patients and longer follow up time.

ABSTRACT. Introduction: The goal of the study was to compare a new method of non-invasive knee navigation with a standard, invasive navigation system requiring bony fixation of the arrays.

Methods: 20 patients scheduled for total or partial knee arthroplasty were included. Following measurements were recorded simultaneously by the two systems: coronal femoro-tibial mechanical angle (CMFA) in maximal extension without stress, CMFA in maximal extension with stress manual stress in varus and valgus (a positive value denotes varus angle). The same set of measurements was repeated at 30° of knee flexion. Comparisons between non-invasive and invasive measurements were performed with appropriate statistical tests.

Results:There was no significant difference for all measurements in full extension. There was a significant difference for varus stress measurement at 30° of flexion. There was a good correlation between non-invasive and invasive measurements of the CMFA in full extension, but not at 30° of flexion. The same results were observed for stress measurements. There was a good concordance between all measurements.

Discussion: The non-invasive navigation system seems a good alternative or a good supplement to conventional, invasive navigation. Non-invasive navigation is a reliable technique of measurement of the mechanical axis of the lower limb and of the varus/valgus knee laxity in extension, but the measurements in flexion are less reliable. The non-invasive navigation may be more accurate than radiographic measurements without radiation exposure. This system may be used for pre-operative and post-operative evaluation of the knee anatomy and function before and after knee arthroplasty.

ABSTRACT. Introduction: This study presents a consecutive series of patients younger than 55 years old who underwent to combined partial knee replacement (UKA+PFR, bi-UKR, bi-UHR +PFR) following prior articular knee fracture. The purpose of this paper was to determine the effectiveness of this surgical approach despite the worldwide tendency of using total knee artrhoplasty (TKA) in these challenging cases.

Methods: The study group (Group A) included a series of 27 patients who had developed a partial post-traumatic knee arthritis following either a distal femoral fracture or a proximal tibial fracture or both. All the patient were younger than 55 years old with stable knee, no flexion deformity and a range of motion of at least 100°. This group included 17 UKR+PFR implants, 7 bi-UKR and 3 Bi-UKR+ PFR. Patients in the study group were matched with patients who had undergone to a PS TKA for primary arthritis (Group B). Patients were matched for age, gender, pre-operative range of motion, severity of arthritis pre-operatively, type and grade of deformity and implant features. And both groups were computer assisted.

Results: There were no statistically significant differences in duration of hospital stay or intra-operative and post-operative complications between the two study groups. Surgical was statistically longer in combined partial knee replacement group. At a minimum follow-up of 36 months there were no statistically significant difference was seen for the Knee Society Score. WOMAC function and stiffness scores were statistically better in Group A. Implant alignment and radiological parameters were similar in both groups.

Discussion: To our knowledge this is the only series in literature dealing with combined partial knee replacement in post traumatic arthritis. This study demonstrated that in young patients affected by compartimental post-traumatic knee arthritis can be safely managed using a combined partial knee replacement approach without no higher rate of complications but with better functional results. Authors consider navigation as a mandatory tool in this high demanding surgery.

ABSTRACT. Introduction: Consistent soft tissue balancing has been aided by novel technologies that can quantify loads across the joint at the time of surgery [1-3]. In theory, compressive load equilibrium should be correlated with ligamentous equilibrium between the medial and lateral collateral ligaments. The authors propose to use the Coronal Angular Deviation Ratio (CADR) as a functional tool to quantify and track surgical changes in laxity of the collateral ligaments over time.

Methods: The study is a prospective IRB approved clinical study with three cohorts: (1) a surgical prospective study group (n=112 knees in101 patients) with balanced compartmental loads (2) a matched control group of non-operated high function patients (n=50); (3) a matched control group of high function knee arthroplasty recipients (n=50). Standard statistical analysis method is applied. The testing is performed using a validated angular deviation measuring device. The output variables for this report consist of the maximum numerical angular change of the knee in the coronal plane at 10 degrees of flexion produced by a controlled torque application of 10 Nm in the varus and valgus (VV) directions. This is reported as a ratio (CADR=Varus deviation / Total deviation).

Results: Pre-operative scatter graphs demonstrate a wide distribution of absolute VV values, reflecting the spectrum of pathological states. The relative distribution of angular deviation after surgery demonstrates clustering. The range is from 0 -5 degrees. The median CADR creeps from 0.50 pre-operatively to 0.58 at 6 months. Scatter graphs of angular deviation (valgus:varus) (Fig. 1) and frequency distribution histograms (Fig. 2) demonstrate post-operative clustering similar to that reported by the authors for kinetic loads after soft tissue balancing. The clustering effect appears to gradually dissipate over the ensuing 5 months, demonstrating a wider distribution width but with a median value distinctly favoring a tighter medial soft tissue envelope.

Discussion: The angular deviation changes form testing under standardized torque are similar to previously reported linear displacement values [4,5]. The observed shift toward a tighter medial side in this series, with a median CADR in extension of 0.58 at 6 months is similar to previous laxity studies [6]. This report specifically focuses on the apparent preferential stiffening of the medial side of the knee over time. A second and equally interesting finding is the departure from a tight cluster in the early post-operative period to a broader distribution, possibly reflecting individual ligamentous properties and activity levels.

ABSTRACT. Introduction: Soft-tissue balancing is an important part of total knee arthroplasty (TKA) surgery used to ensure joint stability throughout a full flexion range. Patient outcomes are dependent on the amount of laxity on the lateral and medial sides of the knee.

Methods: In this study coronal knee laxity was measured as varus-valgus (VV) angular displacement with a newly developed instrumented fixture. The goal was to provide a comparison of coronal laxity of subjects whose knees are normal and of subjects who had a successful TKA based on assessment score.

Results: Results showed that the coronal laxity of a normal intact knee differs significantly (p<0.05) from the laxity of a well-functioning TKA in the valgus range of motion. While, in the normal group, a larger range of laxity in the varus direction rather than in the valgus, is thought to reflect the anatomical properties of the medial collateral ligament (MCL), lateral collateral ligament (LCL), and of the lower limb anatomical alignment; in the TKA group, the different behavior of the coronal laxity in the valgus direction compared to the normal, could correspond with MCL releases performed at the time of surgery. In fact, depending on the quantity and the point of the release the stiffness of the ligament can be significantly compromise.

Discussion: This is the first study adopted to measure varus-valgus joint stability in a clinical setting using a portable instrumented fixture. By comparing TKA laxity with normal, we have determined that that medial collateral release at surgery may cause reduction of ligament stiffness. By using this fixture to determine varus-valgus laxity data we can compare clinical differences and how close functional outcomes get to achieving an ideal knee.

ABSTRACT. Introduction: The constraint of the soft tissue envelop determines the laxity and creates pretension of the knee in absence of muscle loading. Instrumented tibial inserts can therefore be used per-operatively. These inserts provide direct feedback on the load transferred through the medial and lateral condyle [1-3]. The question however remains as to what load levels should be targeted to restore the original ligament tension [4]. To clarify this issue, the load transferred through both condyles is evaluated in the native knee.

Methods: A series of eight non-arthritic fresh frozen knees has been tested using a dedicated test setup. Using this test setup, full lower limb specimens can be tested, mimicking surgical conditions. The pressure transferred through the medial and lateral compartment of the knee is evaluated by creating a slot below the tibial plateau, perpendicular to the mechanical axis. In this slot, 3D printed shims holding a Tekscan sensor type 4011 are inserted. The transferred load is thereby measured simultaneous to the knee kinematics.

Results: The load transferred through the knee is not constant through the range of motion. In full extension and early flexion, relative high loads are observed. The load through the medial compartment is thereby higher compared to the lateral compartment. Upon flexion, the total load rapidly decreases as the knee unlocks the screw home mechanism. From 15 degrees of flexion onwards, the majority of the load is transferred through the medial compartment. The load transferred through the lateral compartment almost vanishes, as shown by the compartmental load ratio in Fig 1.

Discussion: Under surgical conditions, the load transferred through the medial and lateral compartment of the knee is neither constant nor equal. The load is merely contributed to the tension in the medial and latter collaterals. In the contrary, the medial collateral ligament displays an isometric behavior [6]. If the tension in the native knee can serve as baseline for TKA surgery, these observations suggest that load balancing during TKA surgery should not necessarily target equal and constant load levels in the medial and lateral compartment. From a load point of view, optimal restoration of the native anatomy for neutrally aligned or slight varus knees is obtained by targeting a load of approximately 50 N in the medial compartment and allowing a marginally low load in the lateral compartment.

ABSTRACT. Introduction: We introduce a novel active tensioning system that can be used for dynamic gap-based implant planning as well as for assessment of final soft tissue balance after bone resections have been performed. We report on preliminary findings observed during early feasibility testing in cadavers with a prototype system.

Methods & Results: The system was evaluated on seven cadaver specimens, by seven orthopaedic surgeons. Dynamic gap acquisition repeatability throughout flexion ranged from 0.4 – 0.7mm standard deviation (SD) to 0.5 –1.4mm SD, depending on the specimen. During a blinded varus/valgus stress test, peak forces were significantly higher medially than laterally and exhibited a wide range across surgeons (70N – 310N). In the clinical assessment of ideal tension, all surgeons rated 50N as being “slightly loose” and 80N as “ideal” in extension. After cutting the femur and inserting the femoral trail, the forces acting on the tibial insert were measured and were observed to increase dramatically when the knee was brought from flexion into full extension and into hyper-extension. Forces in extension ranged from approximately 80N to 250N, depending on the specimen and the extension angle.

Discussion: Our preliminary results indicate that gaps can be acquired dynamically under actively controlled tension with good repeatability, either freely by hand or with the leg in a leg holder. Our initial results also suggest that performing a blinded varus/valgus assessment (without force readings) may lead to the application of imbalanced loads mediolaterally and thus a biased assessment. Overall the prototype system successfully met the functional requirements in all operating modes evaluated and feedback on the usability and feasibility of the device for use in TKA was positive.

ABSTRACT. Introduction: One major challenge in bicortical screw fixation of small bone fractures is the correct selection of screw length to secure the plate to the bone. Surgeons select a screw by finding the hole depth using a depth gauge which is designed to hook onto the far cortex. This method of bone thickness measurement can be inaccurate in fixation of smaller bones requiring holes of 1-3 mm diameter because the diameter of the holes requires the depth gauge hook to be very narrow and thin, making it difficult to accurately locate and position against the far cortical bone surface. A more accurate method of measuring hole depth would decrease the risk of incorrect screw selection, improving surgical outcomes.

Methods: An on-depth drill gauge was built which identifies the depth of the far cortex of the bone by detecting the drill depth at the moment the drill plunges into the surrounding soft tissue. It uses a linear encoder to determine drill position; acceleration is derived using the position data. To test the method, 72 holes were drilled in lamb (n=18) and chicken (n=54) specimens and the depths measured using a standard depth gauge and the on-drill depth gauge.

Results: The on-drill depth gauge measurements showed a statistically significant decrease in mean error relative to the standard depth gauge (Wilcoxon Signed Ranks, 1 mm, p<0.01). Measurement error variance was smaller in the on-drill gauge, but the difference was not statistically significant (Brown-Forsythe, 0.1 mm, p=0.14).

Discussion: Implementation of this method is simpler than other on-drill depth measurement methods, and could remove a step in the fracture fixation process.

ABSTRACT. Introduction: Closed intramedullary nailing has been one of the most commonly used surgical procedure for treating long bone fracture in orthopaedic surgery. Distal locking has long been recognized as one of the most challenging steps. We present a novel system using ‘handle-integrated line-laser markers and drill-integrated inertial sensors’. With this system, we can localize the exact incision point which is vertical to the center of the distal locking hole and track the direction for drilling in real time.

Methods: A. Handle-integrated line-laser markers The module includes two line lasers projecting two individual lines on skin surface. By employing line lasers rather than dot-pointing lasers, the module can locate the exact incision point which is vertical to the center of the distal locking hole, regardless of the distance between the hole and the skin surface. Accurate 3D models of the nail and handle structures are constructed so that the laser mounting structure can be designed to prevent the angular distortion between the incision point and the distal locking hole which is caused by the axial mismatch. B. Drill-integrated inertial sensors To provide directional guidance for precise drilling, a current drilling direction should be accurately measured and visually fed back to the surgeon together with the information of target directional path toward the distal locking hole. Drill-integrated module consists of a 9-axis inertial sensor chip, a Bluetooth communication module, and a microprocessor unit. It allows a surgeon to check the current position and tilt angle of the progressing drill bit in real time so that the actual drilling path can be aligned with the target path given.

Results: The proposed system successfully localizes the incision point and displays the current drilling direction as well as the target drilling path. Experiment using femur sawbones was conducted to evaluate the accuracy of distal locking procedure performed with the proposed system. 45 trials were carried out in total and there was no case of failure. The distance error from the center of the distal locking hole was within 1.3 mm and the directional error was within 3 degrees.

Discussion: In this study, we developed a surgical navigation system using handle-integrated line-laser markers and drill-integrated inertial sensors. Incision spot for distal locking could be precisely shown on the skin that was perpendicular to the center of distal locking hole with laser guidance technique. We could also track the progressing direction of the drill bit and the angle toward the distal locking hole in real time with drill-integrated inertial sensors.

ABSTRACT. Introduction: Well balanced knees with good alignment are essential for a well-functioning TKA with long survival of its implants. This prospective randomized study comparing navigation assisted TKA and conventional TKA reported the clinical and radiological outcomes at a follow-up of 9 years. The purpose of this study was to compare the clinical and radiological outcomes for patients that underwent navigation assisted TKA or conventional TKA after long term follow-up.

Methods: A total of 80 patients (88 knees) were available for physical and radiological examination 9 years after TKA. Clinical outcomes were evaluated using Hospital for Special Surgery (HSS), Western Ontario and McMaster Universities Arthritis Index (WOMAC), Knee Society (KS) function and pain scores. And radiological outcomes of the component loosening and its survivorship during 9-year follow up were also evaluated.

Results: There were no significant differences in the field of clinical outcomes between the two groups. In terms of radiological outcomes, the navigation group had fewer alignment outliers (7.3% vs20%, p=0.006). Although the clinical outcomes showed no differences between the two groups, the survival rate was slightly better in the navigation group than in the conventional group without statistical significance (best case scenario; 100 % vs 95.3%, n.s., worst case scenario; 95.6 % vs 88.4%, n.s.).

Discussion: Navigation-assisted TKA produced better alignment outcomes and better survival rates than conventional instruments although some of the differences were not statistically significant.

ABSTRACT. Introduction: The most prominent femoral condyle is traditionally referenced for the distal femoral resection during total knee arthroplasty (TKA). This landmark may result in improper bone resection. Using intercondylar notch as the reference for distal femoral resection may provide potential advantages, such as robustness to degenerative cartilage wear and varus/valgus knee deformity. The aim of this study is to analyze if the intercondylar notch can be used to gauge distal femoral resection depth.

Methods: A retrospective review of 406 computer-navigated TKA (using two navigation systems) was performed. The planned and registered resection depths of the medial and lateral femoral condyles and the intercondylar region of the distal femur were extracted, as well as other surgical parameters. Knee range of motion was recorded intra- and post-operatively. Oxford Knee Score (OKS) and Knee Satisfaction Scores at minimum 12 months post-operatively were collected. The data was statistically analyzed with variability between the distal resection bony landmarks measured by Coefficient of Variance (CV). Regression analyses were performed to identify variables that impact the resection depth (significance defined as p<0.05).

Results: Twelve month clinical follow up demonstrated satisfactory outcomes. The use of navigation systems assisted accurate execution of the distal resection (difference in means between planned and registered depths < 0.37mm for all 3 landmarks). Bone depth of resection at the intercondylar notch had the lowest CV. Resection referencing intercondylar notch was affected by the type of implant, the type of pre-operative varus/valgus deformity as well as the amount of deformity. In contrast, it was not affected by gender, leg side, preoperative extension, and preoperative flexion, whereas the resections depths of the medial and lateral condyles were.

Discussion: Improper distal femoral resection results in residual fixed flexion deformity or an unstable joint gap. Our results demonstrated that femoral intercondylar notch is the most consistent and reproducible landmark for the depth of distal femoral resection during TKA. The use of navigation during TKA may further assist in achieving accurate resection depth.

ABSTRACT. Introduction: Navigation assisted total knee replacement (TKR) has been in clinical use since early 2000s. The radiographic alignment in navigation assisted TKR was shown to be superior to TKR using conventional technique. This study aimed to report the long term clinical and radiographic outcomes of navigation assisted TKR.

Methods: From November 2002 to December 2005, 49 TKRs were performed with imageless infrared navigation system (CAS TKR group). The results were compared with 144 TKRs performed with conventional technique in the same period (conventional group). There was no significant difference in the age, sex distribution, pre-operative range of motion, pre-operative deformity, Knee Society knee score and function score, and follow up duration between the two groups.

Results: There was significantly better femoral sagittal alignment (p < 0.001) and tibial coronal alignment (p = 0.037) in the CAS TKR group. There were no significant difference in the femoral coronal, tibial sagittal and overall coronal alignment between the two groups. There was no significant difference in the pre-operative and post-operative Knee Society knee score and function score between the two groups. Using revision surgery for all causes as endpoint, the survival rate was 92.2% in the CAS TKR group and 96.4% in the conventional group at 13.3 years (p = 0.468). Using aseptic loosening as endpoint, the survival rate was 94.2% in the CAS TKR group and 98.5% in the conventional group at 13.3 years (p = 0.293). The long term survivorship did not differ.

ABSTRACT. Introduction: Computer-assisted orthopaedic surgery (CAOS) can offer increased accuracy to total knee arthroplasty (TKA) compared to the conventional techniques. Previous meta-analyses on the alignment outcomes did not differentiate between CAOS systems, while system-dependency has been reported to influence alignment parameters. Limited information is available to benchmark the efficiency of a specific CAOS system based a large number of clinical cases. This study assessed the accuracy and precision of achieving surgical goals in more than 4000 cases using a specific contemporary CAOS system.

Methods: Surgical parameters were extracted from the technical logs of 4292 TKA surgeries performed between October 2012 and January 2016 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 and resection depths between planned and checked resections were evaluated. In the cases that contained a gap balancing step. The mediolateral and flexion-extension asymmetry of the joint gap was assessed based (a ratio of 1 indicates symmetric gap).

Results: For the tibial resection, deviations in tibial varus/valgus angle, posterior tibial slope, and resection depth were -0.05 ± 0.88°, 0.02 ± 1.58°, and 0.14 ± 1.54 mm, respectively. For the femoral resection, the deviation in femoral varus/valgus angle, femoral flexion, and resection depth were 0.00 ± 0.93°, 0.32 ± 1.39°, and 0.05 ± 1.33 mm, respectively. Mediolateral gap asymmetry was 0.99 ± 0.16 and 1.01 ± 0.19 for extension and flexion, respectively. Flexion-extension gap asymmetry was 1.15 ± 0.38 and 1.11 ± 0.44 for medial compartment and lateral compartment, respectively.

Discussion: This study demonstrated that the specific CAOS system used can provide accurate and precise intra-operative assistance to the surgeon in achieving bony resection targets and symmetric gaps. This study reviewed a large number of cases spanning the application history of the specific CAOS system, providing a complete clinically relevant evaluation of its accuracy and precision in terms of bony resection.

ABSTRACT. Introduction: Total knee Arthroplasty (TKA) inevitably perturbs the femoral medullary canal, which increases blood loss or morbidities associated with marrow embolization postoperative. Computer navigation TKA reportedly minimizes medullary disturbance to alleviate perioperative blood loss. We performed a prospective comparative study, enrolling 87 patients with osteoarthritic knees from March 2011 to December 2011 in our hospital. The patients were separated into two groups, according to the surgeon they visited.

Methods: Fifty-four patients underwent computer navigation TKAs and 33 had conventional TKAs. Levels of cell adhesion molecules (CAMs), including intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and platelet endothelial cellular adhesion molecule-1 (PECAM-1) in sera and hemovac drainage were measured by ELISA before and 24 hours after the surgery.

Results: We showed that patients receiving computer navigation TKAs had less blood loss and lower CAMs in serum and hemovac drainage after the operation. Less postoperative elevation of serum ICAM-1 (p=0.022) and PECAM-1 (p=0.003) from the preoperative baseline after the surgery was also noted.

Discussion: This study provides molecular evidence for the differential extent in vascular injury between conventional and navigation TKAs and sheds light on the possible benefits of computer navigation TKAs.

ABSTRACT. Introduction: During cemented total knee arthroplasty (TKA), the surgeon targets proper alignment of the leg and balanced flexion/extension gaps. Studies have been focused on the quality of cement fixation. However, limited information is available on the effect of the cement layer on the final component placement. The goal of the study was to assess the impact of cement layer on the tibial mechanical alignment and joint height during cemented TKA.

Methods: Navigated cemented cruciate-retaining (CR) TKAs were performed by two surgeons on 5 non-arthritic cadaveric legs. After the bony resection, the proximal tibial resection plane was acquired from the resected tibial surface by the navigation system (resection plane). Once the prosthesis was implanted through standard cementing techniques, the top surface of the tibial component was also probed and recorded by the navigation system. The bottom plane of the component was then calculated by offset the best fit plane from the probed points with the component thickness (component plane). The deviation of component alignment caused by the cement layer was calculated as the coronal and sagittal projection of the 3D angle between the resection plane and the component plane. The deviation of the component height (change in the joint height) was assessed as the distance between the two planes calculated at the lowest points on the medial and lateral tibial compartments. Statistical significance was defined as p<0.05.

Results: The deviation from the bony resection was 1.2±0.9° for varus/valgus alignment and 1.7±0.7° for posterior slope, with a tendency towards valgus (-0.2±1.6°) and reduced posterior slope (0.6±1.9°). The lateral compartment (2.4±0.9mm) had a generally higher increase in the height of the component compared to the medial compartment (1.0±0.9mm), the difference was close to being statistically significant (p=0.055).

Discussion: The finding of this study demonstrated that standard cement fixation during TKA may potentially influence the alignment and position of the tibial component. The formed cement layer generally results in elevated height, slightly more varus tibial alignment (overall limb valgus alignment) and less posterior slope in the implanted component. More than 2°/2mm of deviation was found in the sagittal alignment (2/5 knees), as well as medial (1/5 knees) and lateral (3/5 knees) component height, which may clinically impact the joint gap.