ABSTRACT. Although physical and ultrasound (US)-based screening for congenital deformities of the hip (developmental dysplasia of the hip, or DDH) is routinely performed in most countries, one of the most commonly performed maneuvers done under ultrasound observation - dynamic assessment - has been shown to be relatively unreliable and is associated with significant misdiagnosis rates, on the order of 29%. Our overall research objective is to develop a quantitative method of assessing hip instability, which we hope will standardize diagnosis across different raters and health-centers, and may perhaps improve reliability of diagnosis. To quantify dynamic assessment, we propose to use the variability in femoral head coverage (FHC) measurements within multiple US scans collected during a dynamic assessment. In every US scan, we use our recently-developed automatic FHC measuring tool which leverages phase symmetry features to approximate vertical cortex of ilium and a random forest classifier to identify approximate location of the femoral head. Having estimated FHC in each scan, we estimate the change in FHC across all the US scans during a dynamic assessment and compare this change with variability of FHC found in previous studies. Our findings - in a dynamic assessment on an infant done by an orthopaedic surgeon, the femoral centre moved by up to 19% of its diameter during distraction, from 55% FHC to 74% FHC. This variability is similar to the variability of FHC in static US scans reported in previous studies, so the variability in FHC readings we found are not indicative of any subluxation or dislocation of the infant’s femoral head. Our clinician’s qualitative assessment concluded the hip to be normal and not indicative of instability. This suggests that our technique likely has sufficient resolution and repeatability to quantify differences in laxity between stable and unstable hips, although this presumption will have to be confirmed in a subsequent study with additional subjects. The long-term significance of this approach to evaluating dynamic assessments may lie in increasing early diagnostic sensitivity in order to prevent dysplasia remaining undetected prior to manifesting itself in early adulthood joint disease.

ABSTRACT. Additive manufacturing has enabled a radical change in how surgeons reconstruct massive acetabular defects in revision hip surgery. We report on the early clinical and radiological results from our methods for surgical planning, design, and implantation of 3D printed trabecular titanium implants in a cohort of patients with large unclassifiable pelvic defects. We set up a prospective investigation involving 7 consecutive patients. Inclusion criteria was the following: 1) A history of previous total hip replacement; and 2) Current imaging showing at least a Paprosky 3B defect. Planned acetabular inclination and version was 40 and 20 respectively. Post operatively all patients had a CT scan which was analysed with software to determine component position and compared to planned. Outpatient review was done at 2 weeks (For wound), 6 weeks (for weight bearing and fixation) and 52 weeks (for fixation and infection) post-operative. The median age at surgery was: 65 years (40-78). The median bone defect volume was 140cm3. Median surgery length was 5.2 hours (3-6.25). Median blood loss was 1300mL (450-2000). Radiologically, components were stable and no screw breakages were identified. Achieved inclination was 41.0 (29.0-55.6) and achieved version was 15.8 (3.8-43.6). Median Oxford Hip score improved from 9 (2-44) to 25 (18-32). We have demonstrated a new series of pre, intra and post-operative methods for reconstruction of unclassifiable acetabular bony defects. Initial clinical and radiological results are excellent considering the severity of the bony defects. We recommend the use of our or similar methods when trying to reconstruct these defects.

ABSTRACT. Over the past decades, computer-aided navigation system has experienced tremendous development for minimizing the risks and improving the precision of the surgery. Nowadays, some commercially-available and self-developed surgical navigation systems have already been tested and proved successfully for clinical applications. However, all of these systems use computer screen to render the navigation information such as the real-time position and orientation of the surgical instrument, virtual path of preoperative surgical planning, so that the surgeons have to switch between the actual operation site and computer screen which is inconvenient and impact the continuity of surgery. In recent years, Augmented Reality (AR)-based surgical navigation is a promising technology for clinical applications. In the AR system, virtual and actual reality are mixed, offering real-time, high-quality visualization of an extensive variety of information to the users. Therefore, in this study, a pilot study of a surgical navigation system for orthopedics based on optical see-through augmented reality (AR-SNS) is presented, which encompasses the preoperative surgical planning, calibration, registration, and intra-operative tracking. With the aid of AR-SNS, the surgeon wearing the optical see-through head-mounted display can obtain a fused image that the 3D virtual critical anatomical structures are aligned with the actual structures of patient in intra-operative real-world scenario, so that some disadvantages of the traditional surgical navigation are overcome (For example, surgeon is no longer obliged to switch between the real operation scenario and computer screen), and the safety, accuracy, and reliability of the surgery may be improved.

ABSTRACT. Purpose. To validate a small, easy to use and cost-effective augmented marker-based hybrid navigation system for peri-acetabular osteotomy surgery. Methods. A cadaver study including 3 pelvises (6 hip joints) undergoing navigated PAO was performed. Inclination and anteversion of two navigation systems for PAO were compared during acetabular reorientation. The hybrid system consists of a tracking unit which is placed on the patient’s pelvis and an augmented marker which is attached to the patient’s acetabular fragment. The tracking unit sends a video stream of the augmented marker to the host computer. Simultaneously, the augmented marker sends orientation output from an integrated inertial measurement unit (IMU) to the host computer. The host computer then computes the pose of the augmented marker and uses it (if visible) to compute acetabular orientation. If the marker is not visible, the output from the IMU is used to update the orientation. The second system served as ground truth and is a previously developed and validated optical tracking-based navigation system. Results. Mean absolute difference for inclination and anteversion (N = 360) was 1.34 degrees and 1.21 degrees, respectively. The measurements from our system show a very strong correlation to the ground-truth optical tracking-based navigation system for both inclination and anteversion (0.9809 / 0.9711). Conclusion. In this work we successfully demonstrated the feasibility of our system to measure inclination and anteversion during acetabular reorientation.

ABSTRACT. The hip center (HC) in Computer Assisted Orthopedic Surgery (CAOS) can be determined either with anatomical (AA) or functional approaches (FA). AA is considered as the reference while FA compute the hip center of rotation (CoR). Four main FA can be used in CAOS: the Gammage, Halvorsen, pivot, and least-moving point (LMP) methods. The goal of this paper is to evaluate and compare with an in-vitro experiment (a) the four main FA for the HC determination, and (b) the impact on the HKA.

The experiment has been performed on six cadavers. A CAOS software application has been developed for the acquisitions of (a) the hip rotation motion, (b) the anatomical HC, and (c) the HKA angle. Two studies have been defined allowing (a) the evaluation of the precision and the accuracy of the four FA with respect to the AA, and (b) the impact on the HKA angle.

For the pivot, LMP, Gammage and Halvorsen methods respectively: (1) the maximum precision reach 14.2, 22.8, 111.4 and 132.5 mm; (2) the maximum accuracy reach 23.6, 40.7, 176.6 and 130.3 mm; (3) the maximum error of the frontal HKA is 2.5°, 3.7°, 12.7° and 13.3°; and (4) the maximum error of the sagittal HKA is 2.3°, 4.3°, 5.9°, 6.1°.

The pivot method is the most precise and accurate approach for the HC localization and the HKA computation.

ABSTRACT. Functional approaches for the localization of the hip center (HC) are widely used in Computer Assisted Orthopedic Surgery (CAOS). These methods aim to compute the HC defined as the center of rotation (CoR) of the femur with respect to the pelvis. The Least-Moving-Point (LMP) method is one approach which consists in detecting the point that moves the least during the circumduction motion. The goal of this paper is to highlight the limits of the native LMP (nLMP) and to propose a modified version (mLMP).

A software application has been developed allowing the simulation of a circumduction motion of a hip in order to generate the required data for the computation of the HC. Two tests have been defined in order to assess and compare both LMP methods with respect to (1) the camera noise (CN) and (2) the acetabular noise (AN).

The mLMP and nLMP error is respectively: (1) 0.5±0.2 mm and 9.3±1.4 mm for a low CN, 21.7±3.6 mm and 184.7±13.1 mm for a high CN, and (2) 2.2±1.2 mm and 0.5±0.3 mm for a low AN, 35.2±18.5 mm and 13.0±8.2 mm for a high AN.

In conclusion, mLMP is more robust and accurate than the nLMP algorithm.

ABSTRACT. Introduction Hip dysplasia is a complex three-dimensional deformities of the hip joint and can cause hip pain in young and active patients in the child-bearing age. CT-based 3D Imaging can enhance diagnosis and allows planning of periacetabular osteotomy (PAO). CT scan is the Gold standard for 3D Imaging but requires radiation doses up to 20mSv for the pelvis. We aimed to reconstruct 3D models based on radiation-free routine MRI of the hip joint. Therefore we compared 3D models of the proximal femur and acetabulum reconstructed from CT and MRI data. Aims: (1) What is the mean surface distance between 3D models from CT and MRI data? (2) Do diagnostic parameters for PAO Planning correlate for reconstructed 3D models from CT and MRI data?

Methods Comparative, prospective study involving 17 symptomatic patients (20 hips) with hip pain due to FAI or hip dysplasia. Patients with previous operations involving screw fixation were excluded. CT scan and MRI of the entire pelvis and distal femoral condyles were obtained routinely for diagnostic preoperative evaluation. Standardized threshold-based manual segmentation was performed using commercial software (AMIRA). CT scans were obtained with 1mm and 2mm slice thickness, MRIs were obtained with 1mm slices for the hip joint and for the pelvis separately for manual segmentation. Both 3D models of the MRI and CT were used in PAO planning software. (1)Mean and standard deviation of the surface distance between 3D models reconstructed from CT and MRI data were calculated. CT-based and MR-based Surfaces of the 3D models of the proximal femur and of the acetabulum were compared. (2) Specific software for PAO planning was used to calculate Anteversion, Inclination, LCE angle, anterior, posterior and total coverage. Results (1) Mean surface distance was 0.76 mm +/- 0.13 for the proximal femur and 0.95 mm (SD +/-0.26) for the acetabulum. Median surface distance was 0.41mm (Maximum 0.59 mm) for the proximal femur and 0.47mm (Max. 1.08 mm) for the acetabulum. (2) Correlation for 6 diagnostic parameters was excellent (r=0.97). Conclusion MR-based 3D models of the hip joint are as accurate as CT-based 3D models. MR-based 3D models allow radiation-free preoperative PAO planning. Routine clinical application and reconstruction of MR-based 3D models can reduce CT scans in young and active patients.

ABSTRACT. Please refer to file uploaded in regular paper submission as this site does not allow more than 2500 characters.

ABSTRACT. Steimer David, MD; Eduardo M. Suero, MD; Ullrich Luecke, MD; Timo Stuebig, MD; Christian Krettek, MD; Emmanouil Liodakis, MD Trauma Department, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany

INTRODUCTION To test whether there are differences in postoperative mechanical and component alignment, and in functional results, between conventional, navigated and patient-specific total knee arthroplasties in a low-volume center?

MATERIAL METHODS Retrospective cohort study of 391 patients who received conventional, navigated or patient-specific primary cemented TKA in a low-volume hospital.

RESULTS The risk of mechanical alignment outliers was 89% lower in the navigated group compared to the conventional TKA group. There was a 63% lower risk of femoral component malalignment and a 66% lower risk of tibial component malalignment in the navigated group. No significant reduction in the risk of malalignment was seen in the patient-specific group. Total WOMAC and Oxford scores were no different between the three techniques. The patient-specific group reported better WOMAC pain scores. PSI TKA was 33% more expensive than conventional TKA and 28% more expensive than Navigated TKA.

DISSCUSSION Navigated TKA improved alignment, but neither navigated nor patient-specific TKA improved functional outcomes. Patient-specific TKA was more expensive, with little additional benefit. Clinical relevance: The routine use of patient-specific instrumentation in low-volume centers is not supported by the currently available data.

ABSTRACT. Background: There are limited previous findings detailed biomechanical properties following implantation with mechanical and kinematic alignment method in robotic total knee arthroplasty (TKA) during walking. The purpose of this study was to compare clinical and radiological outcomes between two groups and gait analysis of kinematic, and kinetic parameters during walking to identify difference between two alignment method in robotic total knee arthroplasty.

Methods: Sixty patients were randomly assigned to undergo robotic-assisted TKA using either the mechanical (30 patients) or the kinematic (30 patients) alignment method. Clinical outcomes including varus and valgus laxities, ROM, HSS, KSS and WOMAC scores and radiological outcomes were evaluated. And ten age and gender matched patients of each group underwent gait analysis (Optic gait analysis system composed with 12 camera system and four force plate integrated) at minimum 5 years post-surgery. We evaluated parameters including knee varus moment and knee varus force, and find out the difference between two groups.

Results: The mean follow up duration of both group was 8.1 years (mechanical method) and 8.0 years (kinematic method). Clinical outcome between two groups showed no significant difference in ROM, HSS, WOMAC, KSS pain score at last follow up. Varus and valgus laxity assessments showed no significant inter-group difference. We could not find any significant difference in mechanical alignment of the lower limb and perioperative complicatoin. In gait analysis, no significant spatiotemporal, kinematic or kinetic parameter differences including knee varus moment (mechanical=0.33, kinematic=0.16 P>0.5) and knee varus force (mechanical=0.34, kinematic=0.37 P>0.5) were observed between mechanical and kinematic groups.

Conclusions: The results of this study show that mechanical and kinematic alignment method provide comparable clinical and radiological outcomes after robotic total knee arthroplasty in average 8 years follow-up. And no functional difference were found between two knee alignment methods durning walking.

ABSTRACT. INTRODUCTION The patient-specific templates (PST) for total knee arthroplasty (TKA) have been developed to improve accuracy of implantation, decrease operating time and decrease costs. There remains controversy about the accuracy of PST in comparison with either navigated or conventional instruments. Furthermore, the learning curve after introducing PST has not been well defined. The goal of the present study was to perform quality control with a commercially available navigation system and the CUCUM test when introducing PST technique at our academic department. MATERIAL AND METHODS The first 50 TKAs implanted with the use of PST at an academic department were scheduled to enter in a prospective, observational study. PSTs were designed to obtain a neutral coronal alignment. All TKAs were implanted by an experienced, high volume senior consultant with high experience in knee navigation. PSTs were carefully positioned over the bone and articular surfaces to the best fit position, without any navigated information. Then the 3D femoral and tibia PSTs positioning were recorded by the navigation system. The difference between expected and achieved position was calculated, and an accuracy score was calculated and plotted according to the rank of observation into a CUSUM test. RESULTS There was no significant difference between the numerical values of femur plan and femur PST positioning for all four items. There was a significant difference between the numerical values of tibia plan and tibia PST positioning for all four items except the sagittal orientation. The knee score was still out of control after the 20th case. Both femur and tibia scores were still out of control after the 20th case as well. The decision was taken to interrupt the study after the 20th case as the learning curve appeared unacceptably long in comparison to the routine navigated technique. DISCUSSION Introduction of PST in an academic center may involve a significant learning curve: the process remained out of control even after 20 procedures. The present results contradict the common belief that introduction of PSTs is easy and does not require special instruction. These results indicate that surgeons should have only a progressive confidence with the self-sitting of PSTs when introducing this technology. The decision was taken to discontinue using PSTs for TKA.

ABSTRACT. Patient-specific instrumentation (PSI) has been greatly marketed in knee endoprosthetics for the past few years. By utilizing PSI, the prosthesis´ accuracy of fit should be improved. Besides, both surgical time and hospital costs should be reduced. Whether these proposed advantages are achieved in medial UKA remains unclear yet. The aim of this study was to evaluate the preoperative planning accuracy, time saving, and cost effectiveness utilizing PSI in UKA. Data from 22 patients (24 knees) with isolated medial unicompartmental knee osteoarthritis were analyzed retrospectively. The sample comprised sixteen men and six women (mean age 61 ± 8 years) who were electively provided with a UKA utilizing PSI between June 2012 and October 2014. For evaluation of preoperative planning accuracy (1) planned vs. implanted femoral component size, (2) planned vs. implanted tibial component size, and (3) planned vs. implanted polyethylene insert size were analyzed. Since UKA is a less common, technically demanding surgery, depending in large part on the surgeon´s experience, preoperative planning reliability was also evaluated with regard to surgeon experience. Moreover, actual surgical time and cost effectiveness utilizing PSI was evaluated. Preoperative planning had to be modified intraoperatively to a wide extend for gaining an optimal outcome. The femoral component had to be adjusted in 41.7% of all cases, the tibial component in 58.3%, and the insert in 87.5%. Less experienced surgeons had to change preoperative planning more often than experienced surgeons. Utilizing PSI increased surgical time regardless of experience. Linear regression revealed PSI-planning and surgeon inexperience as main predictors for increased surgical time. Additionally, PSI increased surgical costs due to e.g. enlarged surgical time, license fees and extraordinary expenditure for MRI scans. The preoperative planning accuracy depends on many different factors. The advertised advantages of PSI could not be fully supported in case of UKA on the basis of the here presented data – especially not for the inexperienced surgeon.

ABSTRACT. INTRODUCTION Soft tissue balancing in knee arthroplasty remains an art. To make it a science reliable quantification and reference values for soft tissue tension and contact loads are necessary [1,2,3]. This study intends to prove the concept of a compartmental load safe target zone as a clinical tool for balancing total knee arthroplasties by studying the relationship between post-balancing compartmental load distribution and patient satisfaction at 6 months. MATERIALS AND METHODS In this prospective non-randomized clinical series of 102 patients (110 knees), medial and lateral loads were recorded intra-operatively using a tibial liner load sensor system. All knees were balanced using specific algorithm sequences with a goal of equal distribution between compartments [5]. A safe target zone area was defined on a scatterplot graph displaying lateral versus medial loads. Individual points on the graft were coded with their satisfaction score at 6 months. RESULTS Eighty-two (82) cases satisfied the study criteria and were analysed. The boundaries of the safe zone were defined by combining absolute and relative load values. Fifty-seven (57) knees fitted in the defined zone and 25 lied outside. Excellent satisfaction scores were 4.2 times more likely to be in the safe zone. Poor scores were twice more likely to lie outside the zone. In the zone the median satisfaction score was 36/40, whereas outside the zone it fell to 31/40. DISCUSSION Load balancing of knee arthroplasty is a useful clinical tool. Early studies by a developing group showed increased satisfaction rates [4]. One problem remains the subjectivity of testing at the time of surgery [5]. Other studies have also pointed to the difficulty in defining a target zone for balancing [6-8]. Using specific ligamentous balance algorithms it is now possible to predictably achieve a balanced load differential within 15 lbs between compartments [9]. In this paper, we have demonstrated in a prospective series that a target zone can be defined as an area rather than a single ideal value. Within this zone satisfaction scores reach 90-95%. Of all excellent results there are 4.2 more within the zone than outside. Balancing a knee arthroplasty to medial and lateral compartment load values defined by a safe target zone can therefore be predictive of patient satisfaction.

ABSTRACT. Gap balancing techniques aim to achieve equal and symmetric gaps in full extension and in flexion; however, little is known about the relationship between the laxity of the native and the replaced knee. In this study, a novel robotic-assisted ligament tensioning tool was used to measure the pre- and post- operative gaps to better understand their relationship when aiming for balance gaps in flexion and extension. The accuracy of a prediction algorithm for the post-operative gaps based on the native gap and implant alignment was evaluated in this study. Medial and lateral laxity in the native knee was smallest at full extension. The native gaps increase with flexion until 30 degrees where they plateaued for the remaining flexion range. The native lateral gap was larger than the medial gap throughout the flexion range. Planning for equal gaps at extension and flexion resulted with tightest gaps at these angles; however, the gaps in mid-flexion were 3-4 mm larger. Good agreement was observed between the post-operative results and the predicted gap from the software algorithm. The results showed that the native gaps are neither symmetric nor equal. In addition, aiming for equal gaps reduces the variation at zero and 90 degrees of flexion but could result in mid-flexion laxity. Advanced robotics-assisted instrumentation can aid in evaluation of soft-tissue tension and help in surgical planning of TKA. This allows the surgeon to achieve the targeted balance as well as record the final implant tension to correlate with clinical outcomes.

ABSTRACT. Introduction High tibial osteotomy (HTO) is a commonly used surgical technique for treating moderate medial knee-osteoarthritis (OA). While the procedure is generally effective at relieving symptoms, an accurate estimation of change in intraarticular contact pressures and contact surface area has not been developed. In the current study, we hypothesized that it would be possible to predict the change in intraarticular pressures based on extraarticular data acquisition. Material & Methods Seven cadavers underwent an HTO procedure with sequential 5º valgus realignment of the leg up to 15º of correction. A stainless-steel device with integrated load cell was used to axially load the leg. Pressure-sensitive sensors were used to measure intraarticular contact pressures. Intraoperative changes in alignment were monitored in real time using computer navigation. An axial loading force was applied to the leg in the caudal-craneal direction and gradually ramped up from 0 to 550 N. Generalized linear models were constructed to estimate the change in contact pressure based on extraarticular force and alignment data. Results Axial load results in axial angle changes and load distribution changes inside the knee joint. Preliminary analysis has shown that it is possible to predict lateral and medial compartment pressures using externally acquired data. For lateral compartment pressure estimation, the following equation had an R2 of 0.86: Lateral compartment pressure = -1.26*axial_force + 37.08*horizontal_force - 2.40*vertical_force - 271.66*axial_torque - 32.64*horizontal_torque + 18.98*vertical_torque - 24.97*varusvalgus_angle_change + 86.68*anterecurvature_angle_change - 17.33*axial_angle_change - 26.14. For medial compartment pressure estimation, the following equation had an R2 of 0.86: Medial compartment pressure = -2.95*axial_force - 22.93*horizontal_force - 9.48*vertical_force - 34.53*axial_torque + 6.18*horizontal_torque - 127.00*vertical_torque - 110.10*varusvalgus_angle_change - 15.10*anterecurvature_angle_change + 55.00*axial_angle_change + 193.91. Discussion In summary, we have established a framework for estimating the change in intraarticular contact pressures based on extraarticular computer-navigated measurements. Quantifying the resulting changes in load distribution, alignment changes, torque generation and deflection will be essential for generating appropriate algorithms able to estimate joint alignment changes based on applied loads.

ABSTRACT. Provision of prehabilitation prior to total knee arthroplasty (TKA) through a digital mobile application is a novel concept. Our research evaluates a resource effective and cost effective method of delivering prehabilitation. The primary aim of our research is to determine whether provision of prehabilitation through a mobile digital application impacts inpatient LOS after TKA. The secondary objective is to understand the effect of digital prehabilitation on hospital costs. An observational, retrospective analysis was performed on a consecutive case series of 64 patients who underwent TKA by a single surgeon over a 21 month period. Exercise provision varied from 3 months to 2 weeks prior to TKA. The outcomes of rehabilitation length of stay, total length of stay and total hospital costs were statistically significantly at p= 0.05. The rehabilitation length of stay was 3.79 days in the experimental and 7.33 days in the control group (p = 0.045), the total length of stay was 12.00 days in the control and 8.04 days in the experimental group (p=0.03) and the total cost of the hospital stay was $6357.35AUD for the control and $4343.22AUD for the experimental group (p=0.029). Our research shows a cost saving with this intervention, as measured by a reduction in rehabilitation length of stay. To our knowledge, this is the first piece of research that analyses the impact of the use of a mobile application providing pre-habilitation prior to TKA.

ABSTRACT. Evaluation of the post-operative implant position is not straightforward given the significant scatter during magnetic resonance imaging (MRI) and computed tomography (CT). In the contrary, bi-planar post operative x-rays are standard of care. Using these bi-planar x-rays, the 3D implant can now be determined when combining these images with 3D implant files and pre-operative CT data. Using data from 20 patients, this paper compares the obtained implant positions to the positions obtained from post-operative CT scans. On average, the differences between both measurement techniques are below 1mm and 1degree for the translational and rotational degrees of freedom respectively. It is therefore concluded that using post-operative x-rays is an effective method to assess the implant position and alignment.

ABSTRACT. While total knee arthroplasty has demonstrated clinical success, final bone cut and final component alignment can be critical for achieving a desired overall limb alignment. This cadaver study investigated whether robotic-arm assisted total knee arthroplasty (RATKA) allows for accurate bone cuts and component position to plan, compared to manual technique. Six cadaveric specimens (12 knees) were prepared by an experienced user of manual total knee arthroplasty (MTKA), who was inexperienced in RATKA. For each cadaveric pair, a RATKA was prepared on the right leg and a MTKA was prepared on the left leg. Final bone cuts and final component position to plan were measured relative to fiducials, and mean and standard deviations were compared. Measurements of final bone cut error for each cut show that RATKA had greater accuracy and precision to plan for femoral anterior internal/external (0.8±0.5° vs. 2.7±1.9°) and flexion/extension* (0.5±0.4° vs. 4.3±2.3°), anterior chamfer varus/valgus* (0.5±0.1° vs. 4.1±2.2°) and flexion/extension (0.3±0.2° vs. 1.9±1.0°), distal varus/valgus (0.5±0.3° vs. 2.5±1.6°) and flexion/extension (0.8±0.5° vs. 1.1±1.1°), posterior chamfer varus/valgus* (1.3±0.4° vs. 2.8±2.0°) and flexion/extension (0.8±0.5° vs. 1.4±1.6°), posterior internal/external* (1.1±0.6° vs. 2.8±1.6°) and flexion/extension (0.7±0.6° vs. 3.7±4.0°), and tibial varus/valgus* (0.6±0.3° vs. 1.3±0.7°) rotations, compared to MTKA, respectively (where * indicates a significant difference between the two operative methods based on 2-Variances testing, with α at 0.05). Measurements of final component position error show that RATKA had greater accuracy and precision to plan for femoral varus/valgus* (0.6±0.3° vs. 3.0±1.4°), flexion/extension* (0.6±0.5° vs. 3.0±2.1°), internal/external (0.8±0.5° vs. 2.6±1.6°), and tibial varus/valgus (0.7±0.4° vs. 1.1±0.8°) than the MTKA control, respectively. In general, RATKA demonstrated greater accuracy and precision of bone cuts and component placement to plan, compared to MTKA in this cadaveric study. For further confirmation, RATKA accuracy of component placement should be investigated in a clinical setting.

ABSTRACT. Joint assessment through manual physical examination is a fundamental skill that must be acquired by orthopaedic surgeons. These joint assessments allow surgeons to identify soft tissue injuries (e.g. ligament tears) which is critical in identifying appropriate treatment options. The difficulty in communicating the feeling of different joint conditions and the limited opportunities for practice can make these skills challenging to learn, resulting in reduced treatment effectiveness and increased costs. This research seeks to improve the training of joint assessment with the creation of a haptic joint simulator that can train surgeons with increased effectiveness. A first of its kind haptic simulator is presented, which incorporates: a newly defined kinetic knee simulation, a haptic device for user interaction, and a haptic control algorithm. The knee model has been specifically created for this application and allows six degree-of-freedom manipulation of the tibia while considering the effects of ten knee ligament bundles. The model has been mathematically formulated to allow for the high update rates necessary for smooth and stable haptic simulation. Two quantitative assessments were made of the model to confirm its clinical validity. The first was against the widely used OpenSim biomechanical simulation software. Simulations of the model’s performance for both anterior-posterior draw tests and varus-valgus rotation tests showed less than 0.7%RMSE for force and 5.5%RMSE for moments. Crucially, the proposed model could generate updated forces in less than 1ms, compared to 188ms for OpenSim. The second validation of the model was against a cadaveric knee that was tested using a validated robotic testing platform. This comparison showed that the model could generate similar force-motion pathways to the cadaveric knee after the model’s parameters were scaled to match. Having demonstrated that it is possible to create a computational knee model that has good conformance to gold-standard knee simulations and cadaveric recordings, while updating at less than 1ms, this research has overcome a major hurdle. The next stage of this research will be to incorporate the knee model into a full haptic simulator and perform skill acquisition trials. Given the effectiveness of past haptic training systems in aiding clinical skills acquisition, this research offers a promising way to improve surgeon training, and therefore also patient diagnosis and treatment.

ABSTRACT. Good clinical outcomes of Total Knee Arthroplasty (TKA) demand the ability to plan a surgery precisely and measure the outcome accurately. In comparison with plain radiograph, CT-based 3D planning offers several advantages. More specifically, CT has the benefits of avoiding errors resulting from magnification and inaccurate patient positioning. Additional benefits include the assessment in the axial plane and the replacement of 2D projections with 3D data. The concern on 3D CT-based planning, however, lies in the increase of radiation dosage to the patients. An alternative is to reconstruct a patient-specific 3D model of the complete lower extremity from 2D X-ray radiographs. This study presents a clinical validation of a novel technology called “3XPlan” which allows for 3D prosthesis planning using 2D X-ray radiographs. After a local institution review board (IRB) approval, 3XPlan was evaluated on 24 patients TKA. Pre-operatively, all the patients underwent a CT scan according to a standard protocol. Image acquisition consisted of three separate short spiral axial scans: 1) ipsilateral hip, 2) affected knee and 3) ipsilateral ankle. All the CT images were segmented to extract 3D surface models of both femur and tibia, which were regarded as the ground truth. Additionally, 2 X-ray images were acquired for each affected leg and were used in 3XPlan to derive patient-specific models of the leg. For 3D models derived from both modalities (CT vs. X-ray), five most relevant anatomical parameters for planning TKA were measured and compared with each other. Except for tibial torsion, the average differences for all other anatomical parameters are smaller than or close to 3 degrees.

ABSTRACT. Joint laxity assessments have been a valuable resource in order to understand the biomechanics and pathologies of the knee. Clinical laxity tests like the Lachman test, Pivot-shift test and Drawer test are, however, subjective of nature and will often only provide basic information of the joint. Stress radiography is another option for assessing knee laxity; however, this method is also limited in terms of quantifiability and one-dimensionality. This study proposes a novel non-invasive low-dose radiation method to accurately measure knee joint laxity in 3D. A method that combines a force controlled parallel manipulator device, a medical image and a biplanar x-ray system. As proof-of-concept, a cadaveric knee was CT scanned and subsequently mounted at 30 degrees of flexion in the device and placed inside a biplanar x-ray scanner. Biplanar x-rays were obtained for eleven static load cases. The preliminary results from this study displays that the device is capable of measuring primary knee laxity kinematics similar to what have been reported in previous studies. Additionally, the results also displays that the method is capable of capturing coupled motions like internal/external rotation when anteroposterior loads are applied. We have displayed that the presented method is capable of obtaining knee joint laxity in 3D. The method is combining concepts from robotic arthrometry and stress radiography into one unified solution that potentially enables unprecedented 3D joint laxity measurements non-invasively. The method potentially eliminates limitations present in previous methods and significantly reduces the radiation exposure of the patient compared to conventional stress radiography.