ABSTRACT. Introduction: Pedicle screw fixation commonly uses a manual probe technique for preparation and insertion of the screw. However, the accuracy of obtaining a centrally located path using the probe is often dependent on the experience of the surgeon and may lead to increased complications. Fluoroscopy and navigation assistance improves accuracy but may expose the patient and surgeon to excessive radiation. DSG measures electrical conductivity at the tip and provides the surgeon with real-time audio and visual feedback based on differences in tissue density between cortical and cancellous bone and soft tissue. The authors investigated the effectiveness of DSG for training residents on safe placement of pedicle screws.

Methods: 15 male cadaveric thoracolumbar spine specimens were fresh-frozen at the time of expiration. Residents were assigned 3 specimens each and randomized by pedicle side and order of technique for pedicle screw placement (free-hand versus DSG). Fluoroscopy and other navigation assistance were not used for pedicle preparation. All specimens were imaged using CT following insertion of all pedicle screws. The accuracy was assessed by a senior radiologist and graded as within (≤ 2mm breach) or outside (> 2mm breach) the pedicle.

Results: 15 specimens were dissected in standard fashion to expose the thoracolumbar spine (T7-L5). 5 residents were randomized and assigned 3 specimens each to prepare bilateral pedicles from T8 to L5 (60 pedicles per resident) using either PediGuard or free-hand technique. A total of 249 pedicle screws were placed. Post-procedure CT scans demonstrated 214 (85.9%) screws within the pedicle. Breach rate for the DSG group was 8.2% and 19.7% for the non-DSG group, with an overall reduction of 58% (p=0.025)

Conclusion: The use of Dynamic Surgical Guidance decreased the pedicle screw placement learning curve in residents, while improving breach rate by 58%. This study demonstrates that DSG has the potential for resident education and refinement in operative technique.

ABSTRACT. Objective: To compare between the CAMISS-TLIF group and the OP-TLIF group in the clinical efficacy and radiographic manifest. Methods: This study was a registration study, selected 27 patients with lumbar spondylolisthesis from May 2011 to March 2014 in our hospital. Patients in one group are treated with computer assisted navigation minimally invasive TLIF (CAMISS -TLIF) while the others are treated with the OP-TLIF (OPEN-TLIF). The former group has 13 cases while the latter group has 14 cases. We collected information and present statistical analysis on the following aspects in order to compare the two different surgical methods of treatment. They are the operation duration, blood loss, days of hospitalization, the preoperative and follow-up JOA and JOA improvement rate, the preoperative and follow-up ODI scores, the preoperative and follow-up VAS and Odom's criteria. By analyzing the follow-up CT results, we compare the pedicle screw accuracy rate between the two groups in order to make a comprehensive assessment of these two surgical methods. Results: There is a significant difference in blood loss, follow-up JOA improvement rate and follow-up ODI scores between the CAMISS-TLIF group and OP-TLIF group (P <0.05), while in other fields there is no statistically significant differences. Conclusion: CAMISS-TLIF surgical approach has an advantage of less blood loss, less muscle stripping, smaller surgical trauma and more quickly recovery after surgery.

ABSTRACT. Introduction: The education of residents in the proper placement of pedicle screws is key to the safety of the surgery. The more experienced the surgeon, the more accurately the pedicle screws tend to be placed. A physical bone model, with properties and tactile feel similar to human bone, was developed with the intention of using the bone model to train residents in pedicle screw placement. The purpose of this study was to test whether the model improves the performance of orthopaedic residents when cannulating spinal pedicles, as judged by the number of breaches, and to gain feedback from the residents on their experiences. Materials and Methods: Six orthopaedic residents were recruited, with ethics approval. Prior to testing, the residents were given an instructional video describing the correct cannulation of a lumbar vertebra. The residents were each provided with 12 bones mounted in holders: 3 for initial skills assessment, 6 for free practice, and 3 for final skills assessment. In the pre- and post-practice sets, the 3 bone models had different properties: weak, normal and strong. The residents were asked to complete both pre and post-testing questionnaires. The number of breaches was counted in initial and final bone testing. The forces for each bone model were compared using an ANOVA; these were followed by post-hoc t-tests if significant (p<0.05). Results: All but one of the residents improved the number of breaches with practice, and the one that did not improve did not make the same breaches twice. The total number of breaches in the final testing (14) was lower than in the initial testing (31). The entry points chosen by the residents were all deemed appropriate as per the video instruction. The resident with the most experience had the least number of breaches; the resident with the least amount of experience had the most breaches. Discussion: The reduction of the number of breaches between the initial and final testing indicates that the residents did learn. Overall the response from the residents was positive; they all indicated they would like to have the simulator as part of their training; most even indicated an interest to use them outside of training hours. Almost all indicated that the bones felt more realistic than those currently available (if they were aware of them). Positively, the more surgical experience the resident had, the more their survey responses indicated a positive impression of the bones.

ABSTRACT. Introduction: We report a single-center, prospective, randomized study for pedicle screw insertion, by using a Computer Assisted Surgery (CAS) technique with three dimension (3D) intra-operative images intensifier versus conventional surgical procedure. Methods: 143 patients (68 women and 75 men) were included in this study. 72 patients underwent conventional surgery (C = conventional). 71 patients were operated on with the help of a 3D intra-operative imaging system (N = navigated). We performed 34 percutaneous surgeries in group N and 37 in group C; 25 open surgeries in group N and 35 in group C. 382 screws were implanted in group C and 174 in group N. We mesured the pedicle screw running-time, and surgeon’s radiation exposure. All pedicle runs were assessed according to Heary’s classification by two independent radiologists on a post-operative CT. Results: 3D Fluoronavigation appeared less accurate with percutaneous procedures (24% of misplaced pedicle screws versus 5% in Group C) (p=0,007), but more accurate in opened surgeries (5% of misplaced pedicle screws versus 17% in Group C) (p=0,025). In this study, 3D-fluoroscopy navigation increases the instrumentation time, with a strongly higher radiation rate. Conclusion: Therefore, our work hypotheses are partially confirmed according to the type of analyzed criteria.

ABSTRACT. Minimally invasive (MIS) screw fixation for Hangman’s fracture can decrease iatrogenic soft-tissue injury compared with conventional open approach, but increase the risk of instrumentation-related complications due to lack of anatomical landmarks. With the advantages, the intraoperative three-dimensional fluoroscopy-based navigation (ITFN) system seems to be an inherent partner for MIS techniques. The purpose of this study was to evaluate the accuracy and feasibility of MIS techniques incorporating with ITFN for treating Hangman’s fracture. 20 patients with Hangman’s fracture underwent C2-C3 pedicle screw fixation using ITFN. 6 patients used MIS technique, with the other 14 patients using conventional open technique. Preoperative visual analogue score (VAS) was 5.7±1.4 in CAOS-MIS group and 5.5±0.9 in CAOS-open group. Operative time, blood loss and postoperative neurovascular complications were recorded. The accuracy of screw positions was studied by postoperative CT scan. All patients were followed up for at least 6 months and the fusion status was ascertained by dynamic radiographs. The average operative time was 134.2±8.0 min in CAOS-MIS group and 139.3±25.8 min in CAOS-open group, and there was no significant difference between the two (p>0.01). The blood loss was 66.7±25.8 ml in CAOS-MIS group and 250.0±141.4 ml in CAOS-open group. Statistical difference existed with CAOS-MIS group significant less than CAOS-open group (p<0.01). A total of 80 screws were inserted. No screw-related neurovascular injury was observed. Postoperative CT scan revealed 83.3% (20/24) screws of grade 1 and 16.7% screws of grade 2 (4/24) in CAOS-MIS group, meanwhile 89.3% screws of grade 1 (50/56) and 10.7% screws of grade 2 (6/56) in CAOS-open group. There was no grade 3 screw detected. Fisher’s exact test showed there was no statistical difference between these two groups (p>0.01). There was no statistical difference in preoperative VAS between these two groups (p>0.01). Compared with the CAOS-open group (1.7±0.6), neck pain VAS at 6-month follow-up in CAOS-MIS group (0.3±0.5) was significantly lower (p<0.01). Solid fusion was demonstrated in all the cases by dynamic radiographs. So it is feasible and safe for percutaneous minimally invasive C2-C3 pedicle screw fixation for Hangman’s fracture using intraoperative three-dimensional fluoroscopy-based navigation, which can also decreases the incidence of postoperative neck pain.

ABSTRACT. Simulation is an effective adjunct to the traditional surgical curriculum, though access to these technologies is often limited and costly. The objectives of this work were to develop a freely accessible virtual pedicle screw simulator and to improve the clinical authenticity of the simulator through integration of low-cost motion tracking. The open-source medical imaging and visualization software, 3D Slicer, was used as the development platform for the virtual simulation. 3D Slicer contains many features for quickly rendering and transforming 3D models of the bony spine anatomy from patient-specific CT scans. A step-wise pedicle screw insertion workflow module was developed which emulated typical pre-operative planning steps. This included taking anatomic measurements, identifying insertion landmarks, and choosing appropriate screw sizes. Monitoring of the surgeon’s simulated tool was assessed with a low-cost motion tracking sensor in real-time. This allowed for the surgeon’s physical motions to be tracked as they defined the virtual screw’s insertion point and trajectory on the rendered anatomy. Screw insertion was evaluated based on bone density contact and cortical breaches. Initial surgeon feedback of the virtual simulator with integrated motion tracking was positive, with no noticeable lag and high accuracy between the real-world and virtual environments. The software yields high fidelity 3D visualization of the complex geometry and the tracking enabled coordination of motion to small changes in both translational and angular positioning. Future work will evaluate the benefit of this simulation platform with use over the course of resident spine rotations to improve planning and surgical competency.

ABSTRACT. One of the more difficult tasks in surgery is to apply the optimal instrument forces and torques necessary to conduct an operation without damaging the tissue of the patient. This is especially problematic in surgical robotics, where force-feedback is totally eliminated. Thus, force sensing instruments emerge as a critical need for improving safety and surgical outcome. We propose a new measurement system that can be used in real fracture surgeries to generate quantitative knowledge of forces/torques applied by surgeon on tissues. We instrumented a periosteal elevator with a 6-DOF load-cell in order to measure forces/torques applied by the surgeons on live tissues during fracture surgeries. Acquisition software was developed in LabView to acquire force/torque data together with synchronised visual information (USB camera) of the tip interacting with the tissue, and surgeon voice recording (microphone) describing the actual procedure. Measurement system and surgical protocol were designed according to patient safety and sterilisation standards. The developed technology was tested in a pilot study during real orthopaedic surgery (consisting of removing a metal plate from the femur shaft of a patient) resulting reliable and usable. As demonstrated by subsequent data analysis, coupling force/torque data with video and audio information produced quantitative knowledge of forces/torques applied by the surgeon during the surgery. The outlined approach will be used to perform intensive force measurements during orthopaedic surgeries. The generated quantitative knowledge will be used to design a force controller and optimised actuators for a robot-assisted fracture surgery system under development at the Bristol Robotics Laboratory.

ABSTRACT. The knee joint displays a wide spectrum of laxity, from inherently tight to excessively lax even within the normal, uninjured population. The assessment of AP knee laxity in the clinical setting is performed by manual passive tests such as the Lachman test. Non-invasive assessment based on image free navigation has been clinically validated and used to quantify mechanical alignment and coronal knee laxity in early flexion. When used on cadavers the system demonstrated good AP laxity results with flexion up to 40°. This study aimed to validate the repeatability of the assessment of anteroposterior (AP) knee joint laxity using a non-invasive image free navigation system in normal, healthy subjects. Twenty-five healthy volunteers were recruited and examined in a single centre. AP translation was measured using a non-invasive navigation system (PhysioPilot) consisting of an infrared camera, externally mounted optical trackers and computer software. Each of the volunteers had both legs examined by a single examiner twice (two registrations). The Lachman test was performed through flexion in increments of 15º. Coefficients of Repeatability (CR) and Interclass Correlation Coefficients (ICC) were used to validate AP translation. The acceptable limits of agreement for this project were set at 3mm for anteroposterior tibial translation. The most reliable and repeatable AP translation assessments were at 30º and 45º, demonstrating good reliability (ICC 0.82, 0.82) and good repeatability (CR 2.5, 2.9). The AP translation assessment at 0º, 15º, 75º and 90º demonstrated moderate reliability (ICC ≤ 0.75), and poor repeatability (CR ≥3.0mm). The non-invasive system was able to reliably and consistently measure AP knee translation between 30° and 45° flexion, the clinically relevant range for this assessment. This system could therefore be used to quantify abnormal knee laxity and improve the assessment of knee instability and ligamentous injuries in a clinic setting.

ABSTRACT. Introduction: Scaphoid fractures are commonly treated with a single headless screw. There are different recommendations regarding the optimal location of this screw. The purpose of this study was to compare the location of screws placed for the treatment of acute scaphoid fractures with theoretical and virtual screw locations. Materials and Methods: 10 patients with acute scaphoid fractures treated surgically and with available pre- and postoperative CT scans were included. The scans were analysed using a 3D software model (Amira Dev 5.3, Mercury Computer Systems, Chelmsford, MA). On the preoperative CTs the displaced fractures were virtually reduced. Possible screw locations for fracture fixation were examined including one along the central third of the proximal fragment (central base screw), the scaphoid longitudinal axis calculated mathematically (PCA screw) and a screw placed perpendicular to the fracture plane (90 degree screw). The angle between the axes and fracture plains were measured. The angle and distance between the actual screw on the postoperative CT and the different virtual screw locations were measured as well. Results: The angles between the actual and virtual screws to the fracture plane were between a mean of 67 to 69 degrees. The angle between the axes was greatest between the 90 degree screws to the PCA and actual screws (mean 23 degrees both; p=0.034) and smallest between the central base screws and PCA to the actual screws (mean of 12.1 and 12.5 degrees, respectively; p=0.034). The difference between the entrance and exit points between the axes was between 3.1 to 4.8 mm other than the 90 degree screws which were 5.3 to 7.1 mm to the other axes (p=0.002). The PCA (mean 28.3 mm) were found to be longer than the actual screws (mean 25.4) or the 90 degree screws (mean 23.5) (p=0.034 and p=0.008 respectively). The 90 degree screws were shorter than the PCA or central base screws (p=0.008, p=0.034 respectively), but not the actual screws. Discussion: There were no significant differences in the angles between actual and virtual optimal screws other than the 90 degree screws. The PCA was found to be the longest screw and at a similar angle to the fractures as the other virtual screw options, other than the shorter 90 degree screw. Virtual reduction and preplanning of the screw location, using standard software, may enable the surgeon to place the longest screw along the PCA longitudinal axis. If placing a 90 degree screw is considered, this may be technically difficult or may necessitate a trans-trapezial approach.

ABSTRACT. Beside spine and pelvis surgery, computer-assisted guidance systems are not used frequently for musculoskeletal injuries. Main reason is the dependence on a fixed reference array that must be firmly attached to all moving parts. We investigated a novel fluoroscopy-based image guidance system in orthopaedic trauma surgery that uses a different technique. This was a prospective, not randomised single centre case series at a level I trauma centre. 45 patients with 46 injuries (foot 12, shoulder 10, long bones 7, hand and wrist 7, ankle 7, spine and pelvis 4) were included. Different surgical procedures were examined following the basic principles of the AO/ASIF. Main outcome measurements were the number of trials for implant placement, total surgery time, usability via user questionnaire and system failure rate. Furthermore we wanted to test the ability of the new system to be integrated in existing surgical workflows. In all cases, the trajectory function was used, inserting a total of 56 guided implants. The trajectory was the most popular feature used by surgeons (n=43, 93.5%), followed by the length measurement tool (n=29, 63%) and the bending function (n=17, 37%). The functions could be freely activated by the performing surgeon. The system failed when used in pelvic and spinal injuries, resulting in a total failure rate of 6.5% (n=3) of all included cases. The overall usability was rated as good, scoring 84.3%. This study examined the clinical application of a fluoroscopy-based image guidance system for different musculoskeletal injuries. Its major advantage is the high integrability in the accustomed surgical workflow and its connectivity with existing technical equipment. It can hardly be compared to known navigation solutions, since instruments are not tracked and fixed reference arrays are not required. Expected advantages should be explored in randomised studies.

ABSTRACT. Osteophytes are bony spurs on normal bone that develop as an adaptive reparative process due to excessive stress at/near a joint. As osteophytes develop from normal bone, they are not always well depicted in common imaging techniques (e.g. CT, MRI). This creates a challenge for preoperative planning and image-guided surgical methods that are commonly incorporated in the clinical routine of orthopaedic surgery. The study examined the accuracy of osteophyte detection in clinical CT and MRI scans of varying types of joints. The investigation was performed on fresh-frozen ex-vivo human resected joints identified as having a high potential for presentation of osteophytes. The specimens underwent varying imaging protocols for CT scanning and clinical protocols for MRI. After dissection of the joint, the specimens were subjected to structured 3D light scanning to establish a reference model of the anatomy. Scans from the imaging protocols were segmented and their 3D models were co-registered to the light scanner models. The quality of the osteophyte images were evaluated by determining the Root Mean Square (RMS) error between the segmented osteophyte models and the light scan model. The mean RMS errors for CT and MRI scanning were 1.169mm and 1.419mm, respectively. Comparing the different CT parameters, significance was achieved with scanning at 120kVp and 1.25mm slice thickness to depict osteophytes; significance was also apparent at a lower voltage (100kVp). Preliminary results demonstrate that osteophyte detection may be dependent on the degree of calcification of the osteophyte. They also illustrate that while some imaging parameters were more favourable than others, a more accurate osteophyte depiction may result from the combination of both MRI and CT scanning.

ABSTRACT. Implantation of intramedullary nail is a common treatment for long bone fracture. The conventional way to go through distal locking of intramedullary nail usually needs to take tens C-arm images. Exporsure of high X-ray dosage is harmful to medical persons and the patient. This paper proposes a novel path planning for distal locking of intramedullary nail. Based on the dimension parameters of C-arm X-ray projection model available from the specification of C-arm machine and determined by C-arm image guided navigation system, only one C-arm image is needed to determine the axial direction and position of the locking holes. A computer simulation to verify positioning accuracy has been done. The mean position error is 0.63 mm, and the mean axial direction error is 0.73 degree.

ABSTRACT. Introduction: The knee joint morphology varies from one ethnic group to another. Other factors contribute to this variation such as gender and the morphotype of the patients. To the authors’ knowledge, there are no studies in the literature regarding anthropometric parameters of the Arabian knee as it relates to knee implants. Purpose: The objective of this study was to measure the dimensions of the osteoarthritic knees of Arabian patients and to compare these measurements with the dimensions of six knee implants. Subjects and Methods: CT scans were used to collect morphologic data from the distal part of the femur and the proximal part of the tibia from 124 osteoarthritic knees. Anteriorposterior and mediolateral measurements were obtained from three dimensional resected bony surface. These measurements were compared with similar dimension for six different types of knee implants. Results: We found that Arabian knee were generally smaller than Caucasian knee, Arabian females were found to have smaller measurement values when compared with male. Most of proximal tibial plateau and femur condyles were asymmetrical Conclusion: Our data suggests mismatch between osteoarthritic Arabian knee and implant designs. This result suggest that to consider ethnic difference when designing Total knee implants.

ABSTRACT. Scoliosis is a disease that spine is curved sideways when viewed from the front. Most of cause is idiopathic in adolescence. Scoliosis effect progresses thoracic deformity, affect the respiratory and cardiovascular. Early detection of scoliosis is important for patients. Ready- made diagnosis scoliosis research has exposure from X-ray or ambiguous evaluation. It is known to clinically that relationship of thoracic deformity and scoliosis are dynamically changed constantly by the respiratory motion. The detection system of the respiratory motion was developed but it detects only still image. Therefore it is difficult to obtain the change of the shape continually and could not perform an accurate evaluation. We developed the system which obtain a trunk shape continually using a depth sensor. In this paper, I present a new method to evaluate the shape change of the human trunk by the breathing of the patient of scoliosis using this system.

ABSTRACT. Scoliosis is a disease that spine is curved sideways when viewed from the front. Most of cause is idiopathic in adolescence. Scoliosis effect progresses thoracic deformity, affect the respiratory and cardiovascular. Early detection of scoliosis is important for patients. Ready-made diagnosis scoliosis research has exposure from X-ray or ambiguous evaluation. It is known to clinically that relationship of thoracic deformity and scoliosis are dynamically changed constantly by the respiratory motion. The detection system of the respiratory motion was developed but it detects only still image. Therefore it is difficult to obtain the relationship of the breathing and could not perform an accurate evaluation. Therefore we applied a finite element method for the 3D models of a backbone and costal of scoliosis patient. In this paper, we described a relationship between the breathing movement and the scoliosis from the result.

ABSTRACT. INTRODUCTION Previous studies have reported that the satisfactory accuracy of cup alignment using mechanical navigation guide in collaboration with three-dimensional (3D) preoperative planning software for THA. However, its use has not been widely adopted in Japan because of paid license for use. We developed a modular mechanical navigation guide by attaching some components to conventional mechanical navigation guide for free license. The purpose of this study was to compare the accuracy of cup alignment between using free-license modular mechanical navigation guide and conventional mechanical guide.

PATIENTS AND METHODS A modular mechanical navigation guide was consist of the body, three modular adjustable arms and alignment indicator, which can attach the measure on the body for imput the distance of the line passing the point of bilateral anterior superior iliac spine (ASIS) by 3D planning software (Fig 2). On the other hand, conventional mechanical navigation guide were elaborate and simple instrument (Fig. 3). The both instruments is adjusted for each patient based on patient-specific anatomical pelvic plane (APP) from the 3D-CT imaging. There are three differences between the mechanical navigation guide and conventional navigation guide, length measurement method by manually or automatically, cup alignment guide were indicated by anatomical definition or radiographic definition and use for free licence or paid licence.To determine the accuracy of cup inclination or anteversion angles, the preoperative planning were compared with postoperative measured values using a validated 3D/ 3D matching method.

RESULTS In the study group, the mean cup inclination and anteversion angles were 38.9°± 2.9 (SD) and 17.7°± 4.0(SD), respectively. In the control group, the mean cup inclination and anteversion angles were 40.7°± 3.0 (SD) and 17.2°± (SD), respectively. There were no significant differences in the absolute error for inclination angle between the study and control group (1.7°±2.1 versus 2.4°±2.1, P＝0.14). Nor were there any significant differences in the error for anteversion angle (3.9°±3.0 versus 2.9°±2.0, P=0.09).

DISCUSSION The accuracy of cup alignment for the modular mechanical navigation guide was no difference compared with conventional mechanical navigation guide. The modular mechanical navigation guide for free license was a useful patients specific instruments, although it was a little complicated due to measure the parameters manually and be skilled with method for three dimensional preoperative planning.

ABSTRACT. Image registration is an important aspect in Computer Assisted Orthopaedic Surgery (CAOS). It is a process of developing a spatial relationship between pre-operative data, such as CT or MRI scans and the physical patient in operation theatre. Current image registration techniques for CAOS are invasive, time consuming and often take 15-20 minutes and are therefore costly. The rationale for this study was to develop a new operation theatre compliant, quick, cost effective, contactless, automated technique for image registration during CAOS using an accurate rigid body model of the ends of the exposed knee joint, produced by 3D laser scanner. Bespoke automated 3D laser scanning techniques based on the DAVID Laserscanner method were developed and were used to scan surface geometry of the articulating surfaces of tibio-femoral joints in cadaveric legs. The laser scanned cartilage models were registered with the pre-operative (MRI) models and the deviations were evaluated. Furthermore, trends in the deviations with respect to two variables (type of exposure: UKA and TKA, type of setup: Bespoke extrusion based and MAKO RIO based) were studied. Results indicated that the type of setup had no significant effect on the deviations, whereas TKA exposure provided larger deviations than UKA exposures, P>0.05. The laser scanner could repeatedly produce accurate 3D models of the human tibio-femoral joint in operation theatre. This study has provided proof of concept for a new automated shape acquisition and registration technique for CAOS with potential for providing quantitative assessment of the articular cartilage integrity during lower limb arthroplasty.

ABSTRACT. Highly porous bone fixation materials have become a key element in successful orthopedic device designs. Historically, various surfaces to allow biological fixation or on-growth have been applied as a coating to a pre-formed solid metal substrate. Representative coating surfaces include sintered beads, diffusion-bonded fiber metal, plasma sprayed titanium and tantalum porous metal. New manufacturing processes, however, provide for a design versatility and manufacturing repeatability not achievable with conventional porous materials. The ability to manufacture both a solid and a porous portion of an implant offers an advantage over secondary porous attachment processes such as diffusion bonding. For the first time, a broad range of properties can be engineered into a titanium porous/solid monoblock material.

Direct metal laser sintering (DMLS) of Ti-6Al-4V alloy was used to create a random porous structure technology (PST) which mimics trabecular bone. Three dimensional computer modeling and the DMLS manufacturing method allows for unique designs of porous materials. Using these concepts, compression plugs measuring 10.4 mm in diameter and 11.7 mm in height were produced using an EOS 280 laser sintering machine. The porous construct of these test samples can be seen in Figure 1. The strut size was 185.7 ± 8.4 µm. The pore size was 408.6 ± 89.5 µm and the overall porosity is 65.2 ± 3.1 %. Compressive testing was performed with an MTS machine. Modulus of elasticity was determined by measuring the slope of the stress strain line.

The Yield Strength was determined to be 176.13 ± 1.00 Mpa. The average Modulus of Elasticity was 3.48 ± 0.26 GPa, the failure mode of these specimens is a highly ductile collapse of the specimen upon itself. No debris was shed by the specimens as they were tested.

The compressive strength of PST is between that of trabecular and cortical bone and superior to other forms of advanced porous materials. The compressive modulus of PST is very similar to advanced porous materials. These results indicate that a component such as an acetabular cup made from PST would share loading with bone in a physiological manner and yet would be strong enough to take impact loading during implantation and survive in-vivo loads. For the first time, monoblock porous/solid materials can be tailored to better match the strength and/or stiffness of cortical and/or cancellous bone. With the DMLS process of manufacturing, it is even possible to produce an orthopedic implant with non-uniform porous properties if required by the application. The DMLS process also assures that a PST material once designed will be identically produced on every part. Future implant designs may be able to benefit from this new material / process.

ABSTRACT. Introduction: Recent advances in 3D printing enable the use of custom patient-specific instruments to place drill guides and cutting slots for knee replacement surgery. However, such techniques limit the ability to intra-operatively adjust an implant plan based on soft-tissue tension and/or joint pathology observed in the operating room, e.g. cruciate/lateral ligament integrity. It is hypothesized that given the opportunity, a skilled surgeon will make intra-operative adjustments based on intra-operative information not captured by the hard tissue anatomy reconstructed from a pre-operative CT scan or standing x-ray. This study investigates the frequency and magnitude of intra-operative adjustments from a single orthopedic surgeon during 38 unicondylar knee arthroplasty (UKA) cases.

Methods: For each patient, a pre-operative plan was created based on the 3D bony anatomy, analogous to a plan created with patient-specific cutting blocks or customized implants. With robotic technology that utilizes pre-operative imaging, intra-operative navigation and robotic execution, this “anatomic” plan can be fine-tuned and adjusted based on the soft tissue envelope measured intra-operatively. The planned position, orientation and size of the components can be adjusted to achieve an optimal dynamic ligament balance prior to any bony cuts. This is the plan that is then executed under robotic guidance. Intra-operative adjustments are defined as any size, position or orientation changes occurring intra-operatively to the pre-operative anatomic plan.

Results: The surgeon adjusted the pre-operative implant plan in 86.8% of cases, leading to combined RMS changes of 2.0 mm and 2.1 degrees to the femoral implant, and 0.9 mm and 1.4 degrees to the tibial implant. The RMS femoral implant translations and rotations were 1.0, 1.5, 0.9 mm and 1.0, 1.0, 1.7 degrees in the medial, anterior, and superior directions, respectively. The RMS tibial implant translations and rotations were 0.2, 0.4, 0.8 mm and 1.3, 0.4, 0.6 degrees in the medial, anterior, and superior directions, respectively. Implant sizes were adjusted in 36.8% of cases, with all changes occurring to the femoral implant, and 13 out of those 14 cases showing a reduction in the femoral implant size.

Conclusions: These data support the hypothesis that surgical planning of UKA components based on accurate 3D dimensional reconstructions of anatomy alone is not adequate to create optimal implant gap spacing throughout flexion. Measurement and knowledge of the patient’s soft tissue envelope allows for significant changes to the implant plan prior to any bony cuts.

ABSTRACT. Accurate measurement of the lower limb anatomy is clinically important not only for applications such as implants selection and fracture management, but also for planning the corrective osteotomy operations in case of having excessive deformities. The purpose of the present study was to present a 3D analysing technique for the anatomical features of femur, which is simple, reliable and robust. We assessed 30 femur specimens of 15 subjects sampled by a random process across patients who introduced to Imam Khomeini hospital. The 3D models of the patients’ bones were generated from their computed tomography (CT) data. The models were then examined using an independent local coordinate system, defined based on three anatomical landmarks considered at the centre of the femoral head, and those of the posterior femoral condyles. The curvature of the femoral shaft was investigated using the centroid of the shaft on cross sections perpendicular to the curve. The distribution of torsion along the femoral shaft was assessed considering the Linea aspea longitudinal ridge as the reference. The femoral neck anteversion was found using the axis of femoral neck, defined from the midpoint of the neck to its head centre. The means of the curvatures of the femoral shaft in the local sagittal and coronal planes were 0.0196, 0.0211 and 0.0249 /mm, and 0.0040, 0.0045 and 0.0066 /mm, respectively, in the distal, middle and proximal parts of the shafts. The mean of the torsion angles in the middle third of the shafts was 0.5 degrees and that of the anteversion of the necks 13.3 degrees. The results indicated a wide range of inter-specimen variation, particularly for the torsional angle and curvature in the coronal plane, emphasizing the need for a much larger number of specimens.

ABSTRACT. Motion knee MRI