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08:15-10:00 Session 13: Hip
Antony J. Hodgson (The University of British Columbia, Canada)
Kamal Deep (Golden Jubilee National Hospital, Glasgow UK, UK)
Hidetoshi Hamada (Osaka university graduate school of medicine, Japan)
Keisuke Uemura (Osaka university graduate school of medicine, Japan)
Masaki Takao (Osaka university graduate school of medicine, Japan)
Nobuhiko Sugano (Osaka university graduate school of medicine, Japan)
Changes in Pelvic Sagittal Tilt in Supine, Standing, and Sitting Positions During 20 Years of Follow-up After Total Hip Arthroplasty
PRESENTER: Hidetoshi Hamada

ABSTRACT. Aims: To analyze (1) chronological changes in pelvic sagittal tilt (PST) in the supine, standing, and sitting positions; (2) PST shifts with positional changes among these 3 positions during 20 years of postoperative follow-up; (3) differences between preoperative supine PST and postoperative standing PST (Δ standing); and (4) predictors for Δ standing at 20 years Methods: In 41 subjects underwent THA in our institution, anterior pelvic plane in supine, standing, and sitting positions was measured as PST using pelvic radiographs preoperatively, at 1, 10, and 20 years postoperatively. We focused on Δ standing to assess additive change of chronological PST change and PST shift with positional change from preoperative supine PST. Predictors for Δ standing at 20 years were analyzed. Posterior changes and shifts were given a negative value. Results: Supine and standing PSTs changed by −5° and −10°, respectively, whereas sitting PST showed no change over 20 years. The PST shift from standing to sitting positions changed from −34° preoperatively to −23° after 20 years. Δ standing showed posterior change during the follow-up (–12° at 20 years). Δ standing at 20 years was negatively correlated with the occurrence of vertebral fractures but positively correlated with preoperative PST shift from supine to standing positions. 【Discussion】This first report on PST for 20 years following THA demonstrated over 20 years supine and standing PST changed posteriorly with the change in supine PST being half that of standing PST, the posterior PST shift from standing to sitting positions decreased.

Keisuke Uemura (Osaka University graduate school of medicine, Japan)
Masaki Takao (Osaka University graduate school of medicine, Japan)
Akitomo Inoue (Osaka University graduate school of medicine, Japan)
Hidetoshi Hamada (Osaka University graduate school of medicine, Japan)
Wataru Ando (Osaka University graduate school of medicine, Japan)
Nobuhiko Sugano (Osaka University graduate school of medicine, Japan)
Femoral Head Reduction Osteotomy for Legg–Calvé–Perthes Disease Using CAOS Technology
PRESENTER: Keisuke Uemura

ABSTRACT. In advanced cases of Legg–Calvé–Perthes disease (LCPD) with severe deformity and subluxation of the femoral head, femoral head reduction osteotomy (FHRO) may be performed to achieve containment of the femoral head. However, FHRO is technically demanding and prone to complications if performed improperly. In this study, we report the first case of FHRO that was performed for a 13-year-old girl with LCPD of the right hip using CT-based navigation. The lateral pillar classification was type C, and severe adduction and extension contracture (-15° and -10°, respectively) were observed due to head deformity. CT-based navigation (Orthomap, Stryker) was applied after trochanteric osteotomy and surgical dislocation to mark the osteotomy line under navigation guidance. Two osteotomies were made with care to the branches of the medial circumflex femoral artery, and a trapezoidal segment of bone was removed. The remaining two parts of the femoral head were fixed with two screws, and osteophytes were removed to improve the femoral head sphericity. At two months after FHRO, bone formation at the osteotomy site and suitable containment of the femoral head were confirmed on x-rays. The patient could flex 90° and abduct 30° without pain. In summary, CT-based navigation allowed accurate execution of the optimally planned FHRO for LCPD with a severe femoral head deformity. Long-term follow-up is mandatory for evaluating the clinical outcomes, including radiographic evaluation of the remodeling of the femoral head.

Joshua Twiggs (360 Med Care, Australia)
Christopher Jones (WA Orthopaedics, Australia)
Piers Yates (WA Orthopaedics, Australia)
Max Hardwick-Morris (360 Med Care, Australia)
Brad Miles (360 Med Care, Australia)
Leg Length Discrepancy Assessment in Total Hip Arthroplasty: Time to Get It Right
PRESENTER: Joshua Twiggs

ABSTRACT. INTRODUCTION: Leg Length Discrepancy (LLD) is a common pre- and postoperative issue in total hip arthroplasty (THA) patients. The ‘Gold Standard’ for measuring LLD has historically been on a weightbearing AP pelvic radiograph. However, this does not capture many potential sources of LLD. The aim of this study was to determine if Long Leg (EOS) radiology can provide a more reproducible & holistic measurement of LLD.

METHODS: 93 patients who underwent a THA received a standardized preoperative EOS scan, AP Radiograph, and clinical LLD assessment. 16 measurements were taken along both anatomic and functional axes and measured twice by an Orthopaedic Fellow and Surgical Planning Engineer to calculate intra-operator reproducibility and correlations between measurements.

RESULTS SECTION: Strong correlations were observed for all EOS measurements (r > 0.9). The strongest correlation with AP x-ray (inter-teardrop line) was observed for functional-ASIS-to-floor (functional) (r = 0.57), much weaker than the correlations between EOS measurements. ASIS-to-ankle measurements exhibited a high correlation to other linear measurements and the highest ICC (r = 0.97). Using ASIS-to-ankle, 33% of patients had an absolute LLD of greater than 10mm, which was statistically different from the inter-teardrop LLD measurement (p < 0.005).

DISCUSSION: We found that the ‘Gold Standard’ measurement of LLD does not correlate well with long leg measurements and may not provide a holistic understanding of LLD. ASIS-to-ankle demonstrated greater detection of potential LLD than other EOS and X-ray measurements. Full length, functional imaging modalities may become the new ‘Gold Standard’ to measure LLD.

Erel Ben-Ari (Division of Orthopedic Surgery, Tel-Hashomer "Sheba" Medical Center, Sackler School of Medicine, Ramat Gan, Israel)
Christian Oakley (Department of Orthopedic Surgery, NYU Langone Health, New York, New York, United States)
Nina Fisher (Department of Orthopedic Surgery, NYU Langone Health, New York, New York, United States)
Morteza Meftah (Department of Orthopedic Surgery, NYU Langone Health, New York, New York, United States)
Matthew Hepinstall (Department of Orthopedic Surgery, NYU Langone Health, New York, New York, United States)
Ran Schwarzkopf (Department of Orthopedic Surgery, NYU Langone Health, New York, New York, United States)
Is There a Difference in Post-Operative Pain and Narcotic Prescriptions Between Navigation, Robotic, and Conventional Unassisted Total Hip Arthroplasty?

ABSTRACT. Introduction: The impact of technology use on patient-reported outcomes and post-operative pain medication use remains uncertain. The purpose of this study was to investigate how the use of intraoperative technology in primary THA affects patient-reported pain scores and opioid prescriptions after surgery.

Methods: This was a retrospective analysis of patients who underwent primary THA at a single academic institution between January 2017 and December 2020. Patients were separated into 3 groups: computer-assisted navigation, robot-assisted, or conventional THA. Operative time, LOS, 90-day opioid prescription amounts (quantified by morphine milligram equivalents [MME]), and postoperative VAS pain scores were compared. For clinical outcomes, multivariate regression and ANCOVA were used to control for all significant demographic differences.

Results: Of the 5,877 cases identified, 2,213 (37.7%) used navigation, 399 (6.8%) used robotics, and 3,265 (55.5%) used no technology. After controlling for demographic factors, operative time was longer for robotics cases compared to navigation and conventional cases (119.6±34.1 vs. 107.2±28.2 vs. 100.8±39.1 minutes, respectively, p<0.001). Additionally, robotics and conventional cases had longer hospital LOS than navigation cases (p<0.001). VAS pain scores were higher in the robotics and navigation cohorts compared to conventional THA (4.10±2.31 vs. 4.06±2.24 vs. 3.73±2.33, respectively, p<0.001). Conventional and robotics cases had higher 90-day opioid prescription amounts (168.4±142.4 vs. 190.2±178.5 vs. 135.2±147.4 MME, p<0.001). 90-day readmission and revision rates were similar between groups.

Conclusion: Patients undergoing THA with technology had significantly different postoperative opioid prescription than conventional group, although may not be clinically significant. Navigation group had the lowest LOS and 90-day MME.

Max Hardwick-Morris (360 Med Care, Australia)
Joshua Twiggs (360 Med Care, Australia)
Kunaal Kacker (Alfred Health, Australia)
Jitendra Balakumar (Melbourne Orthopaedic Group, Australia)
Brad Miles (360 Med Care, Australia)
Functional Femoral Anteversion: Axial Rotation of the Femur and Its Implications for Stem Version Targets in Total Hip Arthroplasty

ABSTRACT. INTRODUCTION: It is well known that the pelvis undergoes rotation between positions. Less well known is that the femur undergoes functional femoral rotation (FFR) between positions too. Prior studies have investigated anatomic femoral anteversion (AFA)4–7 but have failed to consider the impact of rotation in functional positions. This study aimed to profile the variability of a new measurement, Functional Femoral Anteversion (FFA) in a population of patients undergoing total hip arthroplasty (THA).

METHODS: 1008 consecutive patients undergoing THA were measured for supine and standing FFR as well as AFA. Adding standing or supine FFR to the AFA resulted in FFA for that position, with positive FFR associated with external rotation of the femur.

RESULTS SECTION: 460 (46%) patients had standing FFR (internal or external) of greater than 10°. 335 (33%) patients exhibited an absolute change in FFR (internal or external rotation) of greater than 10°. A moderate, negative linear relationship was observed between AFA and standing external femoral rotation (p << 0.001, R = -0.46).

DISCUSSION: Functional alignment of the femur is under-studied. It is now understood that both the pelvis and femur can rotate substantially between functional positions, altering the orientation of both components. Given this, measuring femoral anteversion only in relation to anatomic landmarks, as AFA does, could be seen as analogous to only considering the cup orientation in a supine anteroposterior radiograph, as it does not provide an understanding of the functional position of the femoral component.

Satoshi Kamihata (Osaka University, Japan)
Wataru Ando (Osaka University, Japan)
Keisuke Uemura (Osaka University, Japan)
Hidetoshi Hamada (Osaka University, Japan)
Masaki Takao (Osaka University, Japan)
Nobuhiko Sugano (Osaka University, Japan)
Effect of Hip Flexion Contracture on Pelvic Sagittal Tilt in the Supine Position
PRESENTER: Satoshi Kamihata

ABSTRACT. The functional pelvic plane (FPP) which adopts the natural pelvic sagittal tilt in the supine position is a good reference of the pelvis zero-position to aim the cup angle or to measure ROM of the hip. In the case of hip flexion contracture, the pelvic sagittal tilt may change after total hip arthroplasty (THA) due to the release of contracture. However, the effects of hip contracture have not studied in detail. The purpose of this study is to clarify whether the hip flexion contracture changes the pelvic sagittal tilt in the supine position before and after THA. 300 patients who underwent primary THA in our hospital were the subject of this study. We measured the hip extension angle manually and divided the participants into two groups, depending on whether the pre-operative hip extension angle was less than 0° (hip flexion contracture group) or not (non-contracture group). The pelvic sagittal tilt and the femoral flexion angle were investigated using computed tomography (CT) images taken preoperatively and within 3 months postoperatively. The flexion contracture was remained in the hip flexion contracture group postoperatively, but it decreased significantly (p<0.001). The pelvic sagittal tilt in the two groups showed no significant differences between preoperative and postoperative THA. Our study found that the hip flexion contracture did not influence the preoperative pelvic tilt when CT images were taken in the comfortable supine position. Moreover, even after the flexion contracture was improved by THA, the pelvic sagittal tilt did not change.

Aziliz Guezou-Philippe (Laboratory of Medical Image Processing (LaTIM), France)
Wistan Marchadour (Laboratory of Medical Image Processing (LaTIM), France)
Jean-Philippe Pluchon (University Hospital of Brest, France)
Hoel Letissier (University Hospital of Brest, France)
Christian Lefevre (University Hospital of Brest, France)
Eric Stindel (University Hospital of Brest, France)
Guillaume Dardenne (University Hospital of Brest, France)
Functional Safe Zone for Cup Orientation in THA

ABSTRACT. The usual safe zone for cup orientation in THA is not suitable for all patients, as the pelvic tilt varies with the movements of daily activities. A new Functional Safe Zone (FSZ) is proposed that considers the pelvic tilt in different positions. The aims of this study were to validate the proposed FSZ and to evaluate how the pelvic mobility impact it.

We measured the pelvic tilts of 30 patients when standing, sitting and supine, using our ultrasound-based device and computed their FSZs. The FSZs accuracy was assessed using a Computer-Aided-Design (CAD) software. The pelvic mobility influence onto the FSZ was assessed by jointly analysing the patients’ FSZs and their pelvic tilt difference between positions.

The true FSZ provided by the CAD software and the estimated FSZ were similar by 92% and differed by less than 0.5° at borders and at the mean orientation. Patients with stiff pelvic mobility obtained small FSZs, and conversely, patients with large pelvic tilt variations between positions obtained large FSZs.

The proposed method allows the computation of a patient-specific FSZ without requiring additional X-ray or CT images. Patients having a low pelvic mobility with a higher risk of postoperative instability could be better managed using this FSZ.

Kamal Deep (NHS, UK)
Anjan Prabhakara (NHS, UK)
Gurpreet Singh (Indian Armed Forces Medical Services, India)
Vivek Mahajan (NHS, UK)
Mohammed Sameer (NHS, UK)
The Transverse Acetabular Ligament and 40 Degree Inclination as a Guide to Cup Orientation in Total Hip Arthroplasty
PRESENTER: Anjan Prabhakara

ABSTRACT. Background: The ideal intra-operative reference to position the acetabular component is a matter of debate. We aimed to record the native acetabular orientation and compare it with the cup that is positioned parallel to the TAL with an inclination of 40°. We hypothesized that majority of the recordings with this technique would be withing the historical safe zones.

Methods: 70 consecutive patients undergoing imageless navigated THA were studied. After excision of osteophytes, a trial component matching the size of un-reamed acetabular cavity was aligned with native acetabulum to record the orientation with respect to anterior pelvic plane. Subsequently the orientation was recorded by positioning the trial component parallel to the TAL with inclination of 40°.

Results: Mean inclination and anteversion of the native acetabulum was 53.79° (40 to 72) and 11.98° (-11 to 38). Mean anteversion when the cup was positioned along the TAL with 40° inclination was 18.21° (-4 to 42). 21.4% and 22.86% of native acetabular recordings were within the safe zones proposed by Lewinnek et al., and Harrison et al., (Strathclyde) respectively. The corresponding safe zone inliers when the cup was positioned parallel to the TAL in 40° inclination were 60% and 70% respectively. The difference between the recordings from either referencing techniques was statistically significant (p value = 0.007 and 0.008). Native acetabular anteversion was significantly higher in females (p value 0.002).

Conclusion: Positioning the cup in 40 degrees of inclination while being parallel to TAL substantially increases the chances (by 40-50%) of orienting the cup within the safe zone as compared to native acetabular rim, although this does not happen in 100% of cases. The study shows the quantitative measurements and that anteversion increases as the inclination decreases. Even being parallel to TAL and in desirable inclination, this may not be ideal orientation for everyone or to fall in safe zone for everyone. The anteversion differs significantly with gender and between different persons. A knowledge about this will assist the surgeon in component placement during THA.

10:00-10:30Coffee Break
10:30-11:18 Session 14: Biomechanics & Modelling
Valérie Burdin (IMT Atlantique, Brest, France, France)
Joshua W Giles (Orthopaedic Technologies and Biomechanics Lab, University of Victoria, Canada)
Sonja Grothues (Chair of Medical Engineering, Helmholtz Institute for Biomedical Engineering, RWTH Aachen University, Germany)
Luisa Berger (Chair of Medical Engineering, Helmholtz Institute for Biomedical Engineering, RWTH Aachen University, Germany)
Klaus Radermacher (Chair of Medical Engineering, Helmholtz Institute for Biomedical Engineering, RWTH Aachen University, Germany)
Automated Analysis of Morpho-Functional Interbone Parameters of the Knee Based on Three Dimensional (3D) Surface Data
PRESENTER: Sonja Grothues

ABSTRACT. Interbone parameters of the knee are of relevance in clinical practice, e.g. for the assessment of the functional anatomy of the individual patient. However, respective landmark identification and parameter derivation is mostly done manually. An automated analysis could enable the processing of large datasets, which could again enable the derivation of reference ranges or safe zones for various populations. Hence, the aim of this study was to automate the derivation of interbone parameters from 3D surface data of the knee and to evaluate the method’s robustness against a large dataset. A dataset of 414 knees from patients scheduled for total knee arthroplasty (TKA) was available for the analysis. For each case, knee surface models derived from CT as well as coordinates of the hip and ankle joint centers were available. Eight interbone parameters of the knee were identified in a literature research and an existing framework for morphological analysis of the knee was extended, in order to automatically calculate those parameters. The interbone analysis succeeded for 405 (97.8%) cases. After the exclusion of implausible cases, 373 (90.1%) parameter sets remained for statistical analysis. Differences in methodology, populations, imaging technique etc. complicate the comparison with values from literature. However, for similar studies a good agreement in parameter values was found. The workflow presented proved robust against a large dataset of knee surface models. In the future, information about the bones relative position in the active, weight-bearing situation should be incorporated, in order to assess the impact on knee interbone parameters.

Elaheh Elyasi (TWINSIGHT, France)
Marek Bucki (TWINSIGHT, France)
Boubaker Asaadi (TWINSIGHT, France)
Antoine Perrier (TWINSIGHT, France)
Towards Automatic Generation of Patient-Specific Knee Models
PRESENTER: Elaheh Elyasi

ABSTRACT. Over the past three decades, finite element (FE) analysis has been used as a non-invasive approach in biomechanics to study the risk factors impacting the knee joint tissues. FE analysis normally involves three steps of pre-processing, processing and post-processing. For a FE analysis on the knee, the pre-processing step is particularly time-consuming and acts as an obstacle to clinical implementation. Therefore, we have designed a pipeline to reduce the pre-processing time required to build subject-specific FE models of the knee. The pipeline involves development and validation of an atlas model of the knee joint and features of the TwInsight software suit that use novel methodologies such as: 1) deep learning for automatic segmentation of the bones from computed tomography scans, 2) automatic generation of finite element meshes with hexahedral elements, and 3) anatomical inference algorithm to adapt the atlas model to the morphology of a subject and result in the subject’s personalized biomechanical model. The presented pipeline successfully enabled us to significantly reduce the pre-processing time required to generate a detailed subject-specific model of the knee joint. The predictions of the atlas model were validated against a human cadaveric study before using the model in the subject-specific pipeline and showed good accordance. The automatic segmentation algorithm reduced the segmentation time for lower limb bones from 3 hours (mean segmentation time by an expert) to one and a half minutes with a Dice score of 0.96 after training with a test dataset that included 23 scans of the lower extremity.

Jean-Rassaire Fouefack (INSERM, Followknee and LaTIM, Brest, France)
Guillaume Dardenne (INSERM, Followknee , LaTIM, CHU, Brest, France)
Bhushan Borotikar (Symbiosis Centre for Medical Image Analysis, Symbiosis International University, India)
Tinashe Mutsvangwa (Division of Biomedical Engineering, University of Cape Town, South Africa)
Valerie Burdin (INSERM, Followknee , LaTIM, CHU, IMT-Atlantique, Brest, France)
3D Reconstruction of Joints from Partial Data Using Multi-Object-Based Model: Towards a Patient-Specific Knee Implant Design

ABSTRACT. In clinical routine, the capture of three-dimensional (3D) bone geometry is crucial for surgical planning, implant placement and postoperative evaluation. Nevertheless, accurate 3D reconstruction of the knee joint for the estimation of patient-specific features remains a challenge, although it has been widely studied. In this context, statistical shape models (SSM) have been used to reconstruct a global shape from partial observations, based on their ability to capture the anatomical variation from different patients. However, these studies incorporate single object SSMs which limit their application for analyzing local bone morphology and thus they lack the capacity to analyze the human anatomy at the joint level. In this paper, we present a multi-object based framework for the 3D reconstruction of the knee joint using a dynamic multi-object Gaussian process model (DMO-GPM) and an adapted Markov Chain Monte Carlo (MCMC) based model fitting algorithm.

The results show that the knee is accurately reconstructed, especially around the joint contact surfaces. This is crucial because most of the patient-specific features required for the implant design, use landmarks in this area. The results suggest that the approach is robust and accurate to design personalized knee implants.

Max Hardwick-Morris (360 Med Care, Australia)
Joshua Twiggs (360 Med Care, Australia)
Mark Taylor (Flinders University, Australia)
Rami Al-Dirini (Flinders University, Australia)
Brad Miles (360 Med Care, Australia)
Jitendra Balakumar (Melbourne Orthopaedic Group, Australia)
Bill Walter (University of Sydney, Australia)
Validation of a Novel Computational Iliopsoas Impingement Detection Model for Surgical Planning

ABSTRACT. INTRODUCTION: Iliopsoas impingement occurs in 4-30% of patients after undergoing hip arthroplasty. Despite a relatively high incidence, there are few attempts at modelling the impingement between the iliopsoas and acetabular cup, and no attempts at modelling this in a representative cohort of subjects. The purpose of this study was to develop a novel computational model for quantifying the impingement between the iliopsoas and acetabular cup and validate its utility in a case-controlled investigation.

METHODS: This was a retrospective cohort study that included 25 symptomatic patients diagnosed with iliopsoas tendonitis and 25 patients not diagnosed with iliopsoas tendonitis. 3D models of each patient’s pelvis, operative femur, femoral stem, and acetabular cup were generated, and landmarked. These 3D models were simulated in a novel iliopsoas impingement detection model in both supine and standing pelvic positions. Impingement was quantified as ‘stretch’ of the iliopsoas by the acetabular cup, measured in millimeters. Logistic regression models were implemented to determine if the probability of pain could be predicted.

RESULTS SECTION: Statistically significant differences between the cohorts were observed for cup prominence and iliopsoas impingement in both supine and standing pelvic orientations. Logistic regression models determined that the impingement values significantly predicted the probability of groin pain.

DISCUSSION: We developed a computational model that can quantify iliopsoas impingement and verified its accuracy in a case-controlled investigation. This tool has the potential to be used preoperatively, to guide decisions about optimal cup placement, and postoperatively, to assist in the diagnosis of iliopsoas tendonitis.

11:18-12:00 Session 15: Spine
Leo Joskowicz (The Hebrew University of Jerusalem, Israel)
Antony J. Hodgson (The University of British Columbia, Canada)
Nicolas Lonjon (Montpellier University Hospital, France)
Benjamin Benac (eCential Robotics, France)
John Sledge (The Lafayette Bone and Joint Clinic, United States)
Mehdi Boudissa (Grenoble University Hospital, France)
Evaluation of a New Unified Robotic Platform: a Cadaver Study
PRESENTER: Benjamin Benac

ABSTRACT. Background The Spine Cobot System (eCential Robotics, France) is a new platform which unifies 2D/3D imaging, navigation and a robotic arm. The intent is to increase patient and surgeon safety without adding time or complexity to the surgical workflow. The primary endpoint of this cadaveric trial is to assess the precision and safety of pedicular screw positioning. The secondary endpoint is to confirm the system’s usability by the operative team.

Methods The Spine Cobot System is composed of a C-arm, a station which includes the software, an infrared camera and a collaborative robotic arm (cobot). Screw placement and neural safety were assessed. Precision of screw placement was determined by comparing the final 3D acquisition to the surgeon’s planned trajectory. Safety was quantified by 3 blinded surgeons using the Gertzbein-Robbins classification. Additionally, the usability of the integrated system for spine surgery was assessed. A system evaluation was performed in compliance with international standards (IEC, FDA).

Results Three experienced surgeons placed 90 pedicular screws in 3 prone cadavers. 100% (90/90) of the screws were accurately placed according to the Gertzbein-Robbins classification. 97% (87/90) were classified as Grade 0 and 3% (3/90) as Grade 1. The average pilot hole middle point distance deviation is 1.3mm +/- 0.88 mm. The average pilot hole angular deviation is 0.6° +/- 0.6°. Only 2 usability errors were observed during the workflow assessment, and none was critical for patient safety.

Conclusions This preliminary study shows the efficiency of the system for pedicular screw placement, with precision and safety results. This confirms the functionality of a unified system for usability and effectiveness.

Level of evidence: Level V

Manuel Vossel (Chair of Medical Engineering, Helmholtz Institute for Biomedical Engineering, RWTH Aachen University, Germany)
Lukas Theisgen (Chair of Medical Engineering, Helmholtz Institute for Biomedical Engineering, RWTH Aachen University, Germany)
Klaus Radermacher (Chair of Medical Engineering, Helmholtz Institute for Biomedical Engineering, RWTH Aachen University, Germany)
Matías de la Fuente (Chair of Medical Engineering, Helmholtz Institute for Biomedical Engineering, RWTH Aachen University, Germany)
Accuracy Evaluation of Image-Based Virtual Fixtures in Robotic Laminectomy
PRESENTER: Manuel Vossel

ABSTRACT. The accuracy of image-based computer assisted orthopedic surgery highly depends on the accuracy of the registration step as well as image acquisition, planning and tool calibration. In this paper the accuracy of those steps is evaluated exemplarily for a robotic laminectomy. A high-resolution test bench was designed to compare the actual location of an object and the position to which the robotic system guides the surgical tool according to the image-based plan. Depending on the distance between the patient reference array and the tool array, average accuracies from 0.14 mm ± 0.17 mm to 0.42 mm ± 0.15 mm with a maximum error of 0.59 mm were measured. This very high accuracy is in the range of the thickness of the spinal dura mater.

Debarghya China (Johns Hopkins University, Baltimore MD, USA, United States)
Luke MacLean (Johns Hopkins University, Baltimore MD, USA, United States)
Kai Ding (Johns Hopkins University, Baltimore MD, USA, United States)
Jeffrey Siewerdsen (Johns Hopkins University, Baltimore MD, USA, United States)
Norbert Johnson (Globus Medical, Inc., Audubon PA, USA, United States)
Neil Crawford (Globus Medical, Inc., Audubon PA, USA, United States)
Ali Uneri (Johns Hopkins University, Baltimore MD, USA, United States)
Intraoperative Ultrasound Imaging for Vertebral Tracking in Spine Surgery

ABSTRACT. Surgical navigation and robot-assisted approaches have been shown to improve precision of spine surgery, which can facilitate minimally invasive surgical approaches, limit postoperative complications, and reduce revision rates. Current methods, however, provide limited or no support in tracking anatomical change that may occur due to patient repositioning, soft tissue deformation, and the intervention itself. This work reports a new approach using intraoperative ultrasound (US) imaging combined with a convolutional neural network to detect and track individual vertebrae during surgery. A tracked US approach streamline building a large, labeled image dataset, which was used in training a modified TernausNet to segment the posterior vertebral cortex. The approach was evaluated on two phantoms and two cadavers, demonstrating ~0.54 mm and ~0.77 mm mean surface distance errors, respectively. The inference runtime of 14±3 ms supports real-time tracking at 70 fps. The solution provides real-time imaging of the posterior vertebral cortex without use of ionizing radiation (cf. current standard of care). Future work will extend evaluation to alternative anatomical landmarks (e.g., cortex surfaces and point features), new scan trajectories (e.g., sagittal images to capture transverse processes), and support processing consecutive frames to reconstruct 3D landmarks.

12:00-13:00Lunch Break

Exhibition Hall

13:00-13:30 Session 16: After Lunch Symposium (Stryker)

My Experience with Mako Total Hip 4.0 presented by Pr Kouyoumdjian

13:30-15:00 Session 17: Knee II
Arnaud Clavé (Clinique Saint George, Nice, France, France)
Christopher Plaskos (OMNI, United States)
Stefano Di Paolo (Department for Life Quality Studies, University of Bologna, Italy)
Stefano Fratini (Rizzoli Orthopaedic Institute, Bologna, Italy, Italy)
Amit Meena (Rizzoli Orthopaedic Institute, Bologna, Italy, India)
Simone Bignozzi (Orthokey Italia srl, Italy)
Giulio Maria Marcheggiani Muccioli (Rizzoli Orthopaedic Institute, Bologna, Italy, Italy)
Stefano Zaffagnini (Rizzoli Orthopaedic Institute, Bologna, Italy, Italy)
Over Constraint Varus Valgus Laxity Leads to Worse Clinical Outcomes at Long Term Follow up in Total Knee Arthroplasty: Intraoperative Assessment Through Surgical Navigation System
PRESENTER: Simone Bignozzi

ABSTRACT. The purpose of the present study was to associate the intraoperative kinematics acquired with a computer navigation system with long-term clinical outcomes and survivorship in patients undergoing TKA to investigate the role of constraint in patients’ satisfaction. A surgical navigation system was used to verify bone resections, gaps, and implant positioning during TKA. Kinematic examination, i.e. varus-valgus at full-extended knee (VV0), varus-valgus at 30° of flexion (VV30), anterior/posterior displacement at 90° of flexion (AP90), passive range of motion (ROM) were performed. Long-term clinical assessment interviews were performed. The Knee Injury and Osteoarthritis Outcome Score (KOOS) was used to investigate patients’ clinical and functional status. Out of 165 patients, 120 met the inclusion criteria. The average follow-up time was 7.7±2.8 years. 7 patients had undergone revision surgery and were considered as a surgical failure with an overall survival rate of 94.2%, while the survival rate at 6, 8, 10 years was 98.8%, 97.4%, 93.6%, respectively. Clinical failure (KOOS score <70) was detected in 11 (9.2%), 10 (8.3%), 21 (17.5%), 39 (32.5%), 113 (94.2%) patients for the Symptoms, Pain, ADL, QoL, and Sport sub-scores, respectively. A statistically significant difference was found in KOOS-QoL between patients with and without clinical failure for the VV0 test (ES=0.58, p=0.022), with lower laxity for patients with score<70. Over-constraint kinematics during TKA surgery leads to worse clinical outcomes at long-term follow-up. Surgeons should be aware of the intraoperative ligament balancing and avoid over-constraint, especially in PS TKA designs.

Alexander Orsi (Corin, Australia)
Edgar Wakelin (Corin, United States)
Christopher Plaskos (OMNI, United States)
Simon Coffey (Nepean Hospital, Australia)
Stephen McMahon (The Avenue Hospital, Australia)
Inverse Kinematic TKA Achieves Similar Balance Profiles and More Closely Restores Native Joint Line Obliquity Compared to Simulated Gap Balancing
PRESENTER: Alexander Orsi

ABSTRACT. Inverse kinematic alignment (iKA) aims to restore the native tibial joint line while targeting soft tissue balance throughout flexion by adjusting femoral component position. We investigated the impact of an oblique tibial resection on mediolateral balance throughout flexion by comparing iKA with a simulated gap balancing (GB) workflow which used a neutral tibial resection.

Two surgeons performed 76 robotic assisted iKA TKA’s using the same cruciate retaining implant with predictive balancing. The native tibial joint line was restored accounting for cartilage wear. Predictive gap planning was used to adjust femoral component positioning to optimize balance. Final laxity was measured using a robotic joint tensioner. GB was simulated for each case using a neutral tibial resection, adjusting the femoral position to optimize balance, and default resections set to the implant thicknesses. ML balance, laxity, component alignment, and resection depths were compared between planned iKA (piKA) and planned GB (pGB).

piKA and pGB had similar ML balance and laxity throughout flexion, however piKA resected 1 mm less bone in extension and 1.9 mm less bone in flexion (p<0.001). Mean deviations from tibial and femoral native joint lines were significantly reduced in piKA compared to pGB (p<0.001).

iKA achieves balanced gap profiles similar to GB while recreating a more anatomic joint line and resecting less bone.

Laurent Angibaud (Exactech, United States)
Wen Fan (Exactech, United States)
Florian Kerveillant (Blue-Ortho, France)
Philippe Dubard (Blue-Ortho, France)
Marine Torrollion (Blue-Ortho, France)
Matthew Rueff (Exactech, United States)
Alexander Sah (Washington Hospital, United States)
James Huddleston (Stanford University Medical Center, United States)
Improved Mediolateral Gap Balance Achievement with Instrumented Navigated Total Knee Arthroplasty Compared to Conventional Instrumentation
PRESENTER: Laurent Angibaud

ABSTRACT. Total knee replacement (TKA) represents a well-established reconstructive procedure for end-stage knee joint disorders with the balancing of soft-tissue envelope throughout the full arc of motion as a newly emerging possibility. This cadaveric study evaluated the ability to achieve targeted mediolateral (ML) gap balance throughout the arc of motion using conventional mechanical instrumentation versus a computer-assisted orthopaedic surgery (CAOS) system featuring an intraarticular distractor while considering surgeon experience level. For the CAOS system, an intraarticular distractor applied a quasi-constant distraction force to the joint (instrumented) while the conventional system involved conventional spacers. Regardless of experience level, the instrumented TKAs were associated with a significantly lower ML gap differential than the conventional TKAs. In contrast, regardless of the type of instrumentation, there were no significant differences between the junior and senior surgeon mean gaps. Historically, soft tissue balancing during TKA has been reported as an art rather than a science. In this regard, the addition of dedicated technology to characterize the soft-tissue envelope during TKA has the potential to provide an augmented perspective to the surgeon and can be particularly beneficial for junior surgeons. The present study established that the usage of instrumented CAOS led to significantly lower ML gap differences than conventional instrumentation.

Laurent Angibaud (Exactech, United States)
Florian Kerveillant (Blue-Ortho, France)
Philippe Dubard (Blue-Ortho, France)
Marine Torrollion (Blue-Ortho, France)
Matthew Rueff (Exactech, United States)
Wen Fan (Exactech, United States)
James Huddleston (Stanford University Medical Center, United States)
Reliability of Laxity Acquisitions Under Controlled Load Environment During Navigated Total Knee Arthroplasty
PRESENTER: Laurent Angibaud

ABSTRACT. Proper soft tissue balancing during total knee arthroplasty (TKA) is critical to ensure successful clinical outcomes. As an attempt to offer an intra-operative characterization of the soft-tissue envelope, a novel method enables the possibility of acquiring the joint laxities under a quasi-constant distraction force throughout the entire range of motion. TKAs were performed using a computer-assisted orthopaedic surgery (CAOS) system on a fresh-frozen human cadaveric specimen. A total of 60 laxity acquisitions were performed by 5 surgeons using the CAOS system. There was an excellent interobserver reliability of the laxity acquisitions (ICC=0.913-0.992). Similarly, the intraobserver reliability was also excellent (ICC=0.846-0.984). These findings demonstrated that the acquisition of the knee joint laxities under the proposed controlled load environment is highly reliable.

Jean-Yves Jenny (University Hospital Strasbourg, France)
Florent Baldairon (University Hospital Strasbourg, France)
What Is the Deviation from the Native Knee Anatomy After Total Knee Arthroplasty According to the Technique Used. a Navigation-Based Analysis.
PRESENTER: Jean-Yves Jenny

ABSTRACT. Purpose The aim of this study was to analyze the deviation of the native coronal alignment of a population of patients undergoing TKA when implanting a TKA according to different alignment goals.

Methods Five hundred twenty navigated TKAs were analyzed. The following angles were measured with a computer image free navigation system: medial femorotibial mechanical angle without stress and with maximum manual stress to reduce deformation, and medial distal femoral mechanical angle. The native medial distal femoral and medial proximal tibial angles were calculated. The data were compared to the post-TKA anatomy according to five different alignment techniques.

Results Mechanical alignment: 187 cases (37.1%) had less than 3° difference between both native femoral and tibial alignment and prosthetic femoral and tibial alignment. Anatomic alignment: 292 cases (57.9%) had less than 3° difference between both native femoral and tibial alignment and prosthetic femoral and tibial alignment. Restricted mechanical alignment: 292 cases (57.9%) had less than 3° difference between both native femoral and tibial alignment and prosthetic femoral and tibial alignment. Kinematic alignment: by definition, all cases had no variation between native alignment and prosthetic alignment. Restricted kinematic alignment: 349 cases (67.1%) had less than 3° difference between both native femoral and tibial alignment and prosthetic femoral and tibial alignment.

Conclusion Different techniques of alignment during TKA lead to significantly different alteration of the native bone anatomy. The clinical relevance of this alteration remain to be defined.

Joshua Twiggs (360 Knee Systems, Australia)
David Parker (Sydney Orthopaedic Research Institute, Australia)
Brett Fritsch (Sydney Orthopaedic Research Institute, Australia)
Justin Roe (North Sydney Orthopaedic Research Group, Australia)
David Liu (John Flynn Hospital, Australia)
Brad Miles (360 Knee Systems, Australia)
Improvement of TKA Outcomes with Preoperative Simulation: Validation of a Patient Specific Planning Tool
PRESENTER: Joshua Twiggs

ABSTRACT. INTRODUCTION: Joint dynamics following TKA will influence the patient reported outcome, capturing tibio-femoral balance, motion and patello-femoral dynamics. Computational simulations allow joint dynamics outcomes to be studied across various alignment philosophies. This study aims to validate a previously developed algorithm (the Dynamic Knee Score, DKS) generated from simulated post-operative TKA joint dynamics and Patient Reported Outcomes.

METHODS: Landmarking and 3D registration of implants was performed on 1074 segmented pre- and post-operative CT scans of TKAs with Knee Injury and Osteoarthritis Outcomes (KOOS) Scores. The DKS was ran on the achieved implanted position and potential variant surgical plans which might have been followed in a counter factual study design.

RESULTS: Patient reported impairment with the knee catching and squatting was shown to be 30% lower (p=0.008) and 22% lower (p=0.038) in patients where the best possible DKS result was the one surgically achieved, as opposed to an alternate femoral rotation. Similar findings were found relating attainment of the best tibial slope and posterior femoral resection DKS plans to difficulty straightening the knee (p=0.005) and descending stairs (p=0.011).

DISCUSSION: An algorithmic outcome score assessing the outputs of a computational model of a deep knee bend (the DKS) has been shown to relate to a specific set of patient reported impairments post-TKA across a sample of over 1000 patients. The resultant algorithm can be applied in a pre-operative planning setting. Outcome optimization in the future may come from patient specific selection of an alignment strategy and simulations may be a technological enabler of this trend.

William Xiang (Weill Cornell Medical College, United States)
Eric Windsor (State University of New York Downstate Medical Center, United States)
Sheila Wang (Intellijoint Surgical, United States)
Allan Inglis (Hospital for Special Surgery, United States)
Peter Sculco (Hospital for Special Surgery, United States)
Validation of an Imageless Optical Computer-Assisted Navigation System for Total Knee Arthroplasty
PRESENTER: William Xiang

ABSTRACT. Introduction

Suboptimal implant placement during total knee arthroplasty (TKA) is associated with higher failure rates and decreased patient satisfaction. Thus, efforts to improve intraoperative surgical accuracy are of strong clinical interest. This study evaluated the accuracy and safety of a novel, imageless, computer-assisted navigation system (CAS) for TKA.


112 consecutive patients who underwent primary TKA between January-December 2020 with 2 board-certified, high-volume orthopedic surgeons using the same imageless CAS were retrospectively reviewed. Patient age, BMI, sex, postoperative complications, and reoperations were collected. Two trained reviewers independently assessed tibial and femoral component mechanical alignment measurements in a standardized manner on postoperative full-leg AP and lateral radiographs. The primary outcome was mean absolute degrees of difference for each measurement compared to intraoperative CAS measurements. Outcomes were reported as means ± standard deviation.


38%(N=43/112) of patients were male. Mean age was 69±8 years and mean BMI was 31.1±5.9.

The mean absolute difference was 1.5°±1.2° for femoral coronal alignment, 1.0°±0.8° for tibial coronal alignment, 2.2°±1.5° for femoral flexion, and 1.8°±1.6° for tibial slope.

Two patients(1.8%) underwent reoperation; specifically, 1 patient received a 1-stage revision for periprosthetic joint infection 5 months postoperatively and the other underwent lysis of adhesions 9 months postoperatively for arthrofibrosis.


This novel imageless CAS provides accurate readings within 2° for tibial and femoral coronal and sagittal alignment, and patients have low complication rates at early follow-up.


15:00-16:00 Session 18: Keynote II - La révolution de l'ADN

Pierre Crozet (Associate professor, Sorbonne Université) was trained as a plant biochemist and molecular biologist. After a PhD at Université Paris-Sud on Plant responses to stress, he continued this line of research during a post-doctorate at the Gulbenkian institute for Science in Lisbon, Portugal. Since 2016, he develops Synthetic Biology in microalgae, both in research and teaching. He is now the coordinator of the Synthetic Biology research axis. He coordinated the generation (design, build and test) of a Modular Cloning toolkit for C. reinhardtii in collaboration with 8 European laboratories30. He is PI of the iGEM team of Sorbonne Université since 2017 and member of the Scientific Advisory Board of the start-up Neoplants, SAS since 2019. He is also co-coordinating, with S. Lemaire, the DNA data storage research axis, recently developed in the team, that generated one patent (EP 193062478). This project led to the creation of a startup, Biomemory, which aims at developing sustainable DNA data storage solutions.

Eric Stindel (University Hospital of Brest, France)
16:00-16:30Coffee Break

Exhibition Hall

16:30-17:10 Session 19: Special Poster Teasers
Ferdinando Rodriguez Y Baena (Imperial College, UK)
Julien Lebleu (moveUP, Belgium)
Charles-Eric Winandy (moveUP, Belgium)
Ciaran McCourt (moveUP, Belgium)
Andries Pauwels (moveUP, Belgium)
Geza Kordas (The Cherwell Hospital, UK)
Wouter van Lysebettens (AZ Maria middelares, Belgium)
Philippe Van Overschelde (AZ Maria middelares, Belgium)
Poster 15: Does Your Approach Matter ?
PRESENTER: Ciaran McCourt

ABSTRACT. Background: There is controversy regarding the effect of different approaches on recovery after THR. Collecting detailed relevant data with satisfactory compliance is difficult.

Objectives: Our retrospective observational multi-center study aimed to find out if the data collected via a remote coaching app can be used to monitor the speed of recovery after THR using the anterolateral (ALA), posterior (PA) and the direct anterior approach (DAA).

Methods: 771 patients undergoing THR from 13 centers using the moveUP platform were identified. 239 had ALA, 345 DAA and 42 PA. There was no significant difference between the groups in the sex of patients or in preoperative HOOS Scores. There was however a significantly lower age in the DAA (64,1y) compared to ALA (66,9y), and a significantly lower Oxford Hip Score in the DAA (23,9) compared to PA(27,7). Step count measured by an activity tracker, pain killer and NSAID use was monitored via the app. We recorded when patients started driving following surgery, stopped using crutches, and their HOOS and Oxford hip scores at 6 weeks.

Results: Overall compliance with data request was 80%. Patients achieved their preoperative activity level after 25.8, 17,7 and 23.3 days, started driving a car after 33.6, 30.3 and 31.7 days, stopped painkillers after 27.5, 20.2 and 22.5 days, NSAID after 30.3 , 25.7, and 24.7 days for ALA, DAA and PA respectively. Painkillers were stopped and preoperative activity levels were achieved significantly earlier favoring DAA over ALA. Similarly, crutches were abandoned significantly earlier (39.9, 29.7 and 24.4 days for ALA, DAA and PA respectively) favoring DAA and PA over ALA. HOOS scores and Oxford Hip scores improved significantly in all 3 groups at 6 weeks, without any statistically significant difference between groups in either Oxford Hip or HOOS subscores.

Conclusion: No final conclusion can be drawn as to the superiority of either approach in this study but the remote coaching platform allowed the collection of detailed data which can be used to advise patients individually, manage expectations, improve outcomes and identify areas for further research.

David Wallace (Golden Jubilee National Hospital, UK)
Fahd Mahmood (Golden Jubilee National Hospital, UK)
Angela Deakin (Surgiconcept Ltd, UK)
Philip Riches (University of Strathclyde, UK)
Kamal Deep (Golden Jubilee National Hospital, UK)
Joseph Baines (Golden Jubilee National Hospital, UK)
Frederic Picard (Golden Jubilee National Hospital, UK)
Poster 16: Computer and Robotic Assisted Orthopaedic Knee Arthroplasty Surgery Did CAS Technologies Have Had an Impact on the Mainstream Principles and Concepts in the Orthopaedic Knee Forum? a Case Study on Alignment and Balancing for TKA.
PRESENTER: David Wallace

ABSTRACT. Computer technology is ubiquitous and relied upon in virtually all professional activities. Confounding this is orthopaedic surgery where less than 5% of surgeons are using computer-assisted technologies routinely. However, the impact of Computer Assisted Orthopaedic Surgery (CAOS) may go beyond adoption in theatre. We searched pubmed for all knee arthroplasty papers concerning knee alignment and balancing between 1976 and 2016, dividing the results into those related to CAOS and those not. Results were grouped by technology. Between 2001 and 2008, the number of publications regarding knee navigation multiplied by 20 mainly focused on this topic of alignment and balancing, with alignment papers paralleled between navigation and non-navigation until 2010. After 2010, when navigation publications decline the number of articles related to the knee alignment and balancing without navigation increased granting the value of assessing accurately intraoperative kinematic data to improve Total Knee Arthroplasty (TKA) outcomes. From 2008, patient specific instrumentation (PSI) publications greatly increase, but navigation decreases, while robotic publications rise from 2014. CAOS surgery publications on the search topic of alignment and balancing increased greatly between 2001 and 2018 which may suggest the impact of CAOS technology on this important knee orthopaedic forum segment.

Aouam Djamel (CDTA, Algeria)
Ronan Querrec (ENIB/CERV, France)
Thierry Duval (IMT Atlantique, France)
Nadia Zenati (Centre de développement des Technologies Avancées, Algeria)
Chafiaa Hamitouche (IMT Atlantique - Bretagne-Pays de la Loire, France)
Poster 17: Mixed Reality for Minimally Invasive Bone Tumor Ablation
PRESENTER: Aouam Djamel

ABSTRACT. Minimally invasive intervention requires accuracy and practice as it can be vital in complex and narrow places. In this paper we propose a solution based on augmented reality (AR) for the ablation of bone tumors. Our proposal deals with the preoperative and intraoperative phases of the procedure. The first part consists of the segmentation and 3D reconstruction of the structures of interest. The second part consists of the visualization in AR. This solution is intended to facilitate the tasks of surgeons and radiologists when planning RF needle insertion and trajectory in order to avoid excessive exposure to X-rays, which is a phase that requires more precision and knowledge of the morphology of the mass tumor. The second part offers AR assistance based on the planning of the preoperative phase. The solution we proposed is based on the use of HoloLens 2 headsets to provide better AR visualization and assistance.

Laurent Angibaud (Exactech, United States)
Wen Fan (Exactech, United States)
Philippe Dubard (Blue-Ortho, France)
Matthew Rueff (Exactech, United States)
Herman Prieto (University of Florida - Department of Orthopaedic Surgery, United States)
Hari Parvataneni (University of Florida - Department of Orthopaedic Surgery, United States)
Poster 18: Reliability of Laxity Acquisitions During Navigated Total Knee Arthroplasty – Comparison of Two Techniques
PRESENTER: Laurent Angibaud

ABSTRACT. Recent developments have focused on the intra-operative management of soft-tissue balancing in total knee arthroplasty (TKA) using a computer-assisted orthopaedic surgery (CAOS) system. The aim of this study was to determine and compare the reliability of acquiring the knee joint laxities during navigated TKA with a conventional method versus a newly developed instrumented technique that uses an intra-articular quasi-constant force distractor integrated with a CAOS system. A total of 96 laxity acquisitions throughout the arc of motion were performed for the conventional and instrumented procedures. For the instrumented technique, the inter- and intraobserver reliabilities were significantly higher than the conventional manual varus/valgus stress test technique, regardless of surgeon variability and experience. Soft-tissue balance, while being a key determinant in improving outcomes in TKA, is difficult to objectively assess at the time of the surgery. This study established that the acquisition of the knee joint laxities using an instrumented technique was consistently associated with a significantly higher reliability than the conventional technique.

David Wallace (Golden Jubilee National Hospital, UK)
Fahd Mahmood (Golden Jubilee National Hospital, UK)
Angela Deakin (Surgiconcept Ltd, UK)
Philip Riches (University of Strathclyde, UK)
Kamal Deep (Golden Jubilee National Hospital, UK)
Joseph Baines (Golden Jubilee National Hospital, UK)
Frederic Picard (Golden Jubilee National Hospital, UK)
Poster 20: Computer and Robotic Assisted Orthopaedic Knee Arthroplasty Surgery Who Drives Innovations?
PRESENTER: David Wallace

ABSTRACT. Computer assisted and Robotic technology in orthopaedic surgery is still not commonplace compared to un-assisted, conventional orthopaedic surgery. We analysed the relationship between patents and publications trend and question whether we could recognise a pattern which would confirm industry-driven innovation in orthopaedic surgery. Following the same methodology used by Dalton et al. in 2016, we searched pubmed for publications between 1980 and 2018 concerning unicompartmental, patient specific instrumentation, navigation and robotic knee arthroplasty, and patents registered under the “knee arthroplasty” or “knee replacement” label over the same period. Data was plotted using 4 point moving averages. Between 2004 and 2008, the number of publications regarding navigation multiplied by 20 following the number of patents registered during the same period. From 2008 onwards, the number of navigation publications declined while Patient Specific Instrumentation (PSI) publications increased also following patent investments from orthopaedic companies. Finally, robotic publications grew significantly pulled by massive patent registrations after 2012. It seems that the industry has finally found a lucrative economical model after many years of trial and errors and sustained driving innovations.

Hisham Iqbal (Imperial College London, UK)
Ferdinando Rodriguez Y Baena (Imperial College, UK)
Poster 21: Augmenting Commercially Available CAOS Systems with Mixed-Reality
PRESENTER: Hisham Iqbal

ABSTRACT. Display technologies such as augmented reality (AR) have provided a pathway for creating immersive user interfaces for handling 3D medical data during surgery. To date, computer-assisted orthopaedic surgery (CAOS) systems rely on touchscreen displays to deliver a 2D user interface. In contrast, the use of AR-headsets allows for the 3D projection of medical data directly onto patient anatomy, removing the need for any 2D-3D mental re-mapping and enabling a surgeon to maintain focus on the operating site. In this study, a novel AR-assisted workflow was integrated with a commercially available CAOS system, enabling a HoloLens 2 headset to receive medical data during key stages of the procedure – patient registration and cutting. The AR workflow was co-registered with the CAOS system’s optical tracker, facilitating the rendering of patient-specific holograms in-situ, directly onto patient anatomy, during the patient-registration and cutting phases of simulated patellofemoral arthroplasty (PFA). A pre-clinical study recruited six non-clinical subjects to investigate the impact of using holographic guidance on mental workload when compared to standard CAOS display methods. When investigating the system’s usability, an investigation of mental workload was conducted, with a Task Load Index (TLX) survey finding no significant increases to mental workload associated with the use of AR in this study. Overall, this study reports successful initial deployment of AR in a pre-clinical setting for CAOS in a non-expert group, with no significant impairments to mental workload, presenting the potential to continue exploring more intuitive visual guidance options for future surgical applications.

Luke MacLean (The University of British Columbia, Canada)
Antony Hodgson (University of British Columbia, Canada)
Poster 22: Design of an Ultrasound-Emitting Drill Guide for Freehand Pedicle Screw Navigation
PRESENTER: Antony Hodgson

ABSTRACT. Spinal navigation improves pedicle screw placement accuracy compared with freehand or fluoroscopy-guided procedures, but suffers from a reliance on radiation, lack of access to expensive equipment, and difficulties accommodating intervertebral movement. We propose replacing optical tracking with self-localizing tools that have integrated ultrasound emitters. Poly-CMUT developments make manufacturing these tools more practical, but specific designs have not been proposed. Our goal was to determine the optimal design and to characterize its localization performance.

We ran 300 000 simulations to evaluate the localization accuracy of different designs. We varied five geometric parameters (drill guide diameter, drill guide length, number of ultrasound strips, number of elements per strip, and transducer configuration) and two algorithmic parameters (state estimation method and number of parallel starts). The tested algorithms included constrained and unconstrained optimization, an Unscented Kalman Filter, single and multi-start, and interior-point and global search optimization.

This study demonstrated that localization of an ultrasound-augmented drill guide seems feasible but only certain designs allow for clinically sufficient accuracy. The best localization algorithm used a multi-start interior-point optimization. A mixture of forward and lateral measurements performed best. The optimized design is a cylindrical cannula (diameter: 20mm, length 150mm), with a curved nose (radius: 5mm) and ten circumferentially arranged ultrasound strips (length: 32mm, 32 elements per strip). The final design was validated at 1000 positions within 50mm around the pedicle entry point.

The simulated accuracy suggests that physical prototyping will be successful, and supports continued development. Future work will focus on prototyping and validating the proposed design.

Matthew Hickey (The University of British Columbia, Canada)
Bassam Masri (The University of British Columbia, Canada)
Antony Hodgson (The University of British Columbia, Canada)
Poster 23: A Risk-Prioritized, Practice-Specific Framework for Evaluating the Cost-Effectiveness of Technology Assistance in Total Knee Arthroplasty
PRESENTER: Matthew Hickey

ABSTRACT. Previous work aiming to evaluate cost effectiveness of technology-assisted total knee arthroplasty (TA-TKA) has often overlooked key factors influencing revision risk (age at index surgery, BMI, and gender) and has usually only considered a limited number of intervention types and costs, all of which can impact cost-effectiveness estimations. In this study, we present a risk-prioritized, practice-specific framework for evaluating the cost effectiveness of TA-TKA, considering local TKA patient population demographics and TA-TKA system type when estimating the likely reduction in revision rates, improvements in quality-of-life years (QALYs), and the corresponding cost effectiveness of intervention. We simulated two contrasting clinical populations, applied the selective-use policy, and calculated the incremental cost effectiveness ratio and marginal cost effectiveness ratio for each TA-TKA technique at each risk cut-off level for each of the two clinical populations.

For PSI-TKA, cost effectiveness was predicted when treating up to ~20% of patients in the low-risk population and up to ~85% in the high-risk population. For NAV-TKA, no practice size was able to achieve cost savings or cost effectiveness in the lower-risk population. However, in the elevated-risk setting, cost effectiveness could be achieved in practice sizes as small as 300 TKA patients per year given a utilization rate of ~60%. In addition. RA-TKA only approaches being cost effective in elevated-risk populations with practice sizes of at least 900 patients per year and a utilization rate of ~70%. RA-TKA is predicted to be far from cost effective in practices of any size in a relatively lower-risk population.

Based on these simulations, it appears that a selective-use policy for TA-TKA that prioritizes use of technology assistance for patients at higher risk of revision is likely cost-effective under specific circumstances, depending on the precision and costs of the technology under consideration, annual surgical volume, and demographic characteristics of a particular practice. Overall, given the fixed and variable costs assumed here, patient-specific instrumentation is predicted to prove cost-effective in the widest range of circumstances, surgical navigation may prove cost-effective or cost neutral in a moderate range of circumstances, and robotic surgery is only likely to prove cost-effective in the largest practices having patient populations at an elevated risk of revision.

Marc-Olivier Gauci (IULS, CHU de Nice, UR2CA, UCA, France)
Manuel Olmos (IULS, CHU de Nice, UR2CA, UCA, France)
Caroline Cointant (IULS, CHU de Nice, UR2CA, UCA, France)
Pierre-Emmanuel Chammas (CHU de Montpellier, Hôpital Lapeyronie, France)
Nicolas Bronsard (IULS, CHU de Nice, UR2CA, UCA, France)
Manuel Urvoy (Imascap, France)
Albert Murienne (b<>com, Institut de Recherche Technologique, Cesson-Sévigné, Bretagne, France)
Jean-François Gonzalez (IULS, CHU de Nice, UR2CA, UCA, France)
Poster 24: Validation of the ShoulderROM Software for Measurement of Shoulder Ranges of Motion in Consultation: Coupling an RGB-D Video Camera to Artificial Intelligence
PRESENTER: Albert Murienne

ABSTRACT. Background: Clinical evaluation of the shoulder range of motion may vary significantly depending on the surgeon. We aim to validate an automatic shoulder range of motion (RoM) measurement system associating image acquisition by an RGB-D (Red Green Blue – Depth) video camera to an artificial intelligence (AI) algorithm.

Methods: Thirty healthy volunteers were involved in this experimental study. A 3D RGB-D sensor that simultaneously generated a color image and a depth map was used. Then, an open-access convolutional neural network algorithm that was programmed for shoulder recognition provided a 3D motion measure. Each volunteer adopted a randomized position successively. For each position, two observers made a visual and goniometric measurement, blind to the automated software which was implemented by an orthopedic surgeon.

Results: We found that the deviation between GonioREF and ShoulderROM was similar to that between VisualREF and ShoulderROM (95% LoA < 25°) and less than between VisualREF and GonioREF (95% LoA <12°). ShoulderROM showed “excellent” correlation with GonioREF for all positions except ER1, with a “very good” ICC. There was “very good” to “excellent” correlation between VisualREF and ShoulderROM.

Conclusion: RGB-D/AI combination is reliable in measuring shoulder RoM in consultation, compared to classic goniometry and visual observation.

Masayuki Ito (Traumatology and reconstructive surgery center, Fukushima medical university, Japan)
Takashi Sato (Niigata medical center, Japan)
Syunsuke Sato (aiTRSC, Aizu chuo hospital / Dept. of traumatology and reconstructive surgery, Fukushima medical university, Japan)
Ryosuke Mashiko (Minami Aizu hospital, Japan)
Yumetaka Shinden (Dept. of Orthopedic surgery, Fukushima medical university, Japan)
Yosuke Mizuno (Dept. of emergency and disaster medicine, Gifu university, Japan)
Toshiyuki Suzuki (Dept. of anesthesiology, Hidaka hospital, Japan)
Satoshi Hatashita (Traumatology and reconstructive surgery center, Fukushima medical university, Japan)
Poster 25: Quantitative Fracture Evaluation with Three-Dimensional CT: Are CT Findings of Dislocation Immediately After a Fracture Correlated with Severity?
PRESENTER: Masayuki Ito

ABSTRACT. We attempted to measure and quantify the dislocation of the intertrochanteric femoral fracture from the preoperative three-dimensional computed tomographic (3D-CT) measurement using computer software. We hypothesized that the clinical outcome of a displaced fracture would be worse than that of a minimally displaced one. We investigated the correlation between the amount of fracture displacement and fracture classifications. The 80 patients who were able to provide adequate CT images participated in this study. The mean age was 87 years; 17 patients were male and 63 were female. We reconstructed 3D-CT images and measured the distance of fracture displacement, using a healthy side as a template, with 3D-CT software. We used the Jensen classification and Nakano 3D-CT classification to categorize the fractures, and we used the Kruskal–Wallis test to calculate the correlation between the amount of fracture displacement and the classification. The mean 3D transposition of the femoral head was 33.6 mm. The results showed that displacements tend to be larger in severe fracture types. For the correlation between the amount of fracture displacement and the Jensen classification, Nakano classification; p = 0.003, p = 0.008. This study was the first attempt to measure the amount of displacement of femoral trochanteric fractures on 3D-CT. To solve the problems still inherent in this procedure, mass data about femoral structure and artificial intelligence could be used. The results suggest that the amount of displacement may be correlated with the classification of fracture severity without skeletal traction. It is therefore necessary to investigate this correlation and fit for younger patients.

Estelle Liu (360 Med Care, Australia)
Max Hardwick-Morris (360 Med Care, Australia)
Joshua Twiggs (360 Med Care, Australia)
Kunaal Kacker (Alfred Health, Australia)
Jitendra Balakumar (Melbourne Orthopaedic Group, Australia)
Brad Miles (360 Med Care, Australia)
Poster 26: Internal Femoral Rotation & Anterior Pelvic Tilt in the Flexed Seated Position: Co-Incidence and Functional Consequences
PRESENTER: Estelle Liu

ABSTRACT. INTRODUCTION: The pelvis rotates through the sagittal plane during Activities of Daily Living (ADLs). Similarly, the femur rotates about its axial axis throughout these ADLs. Anterior pelvic tilt combined with Internal rotation (IR) after total hip arthroplasty (THA) can lead to anterior impingement and potential posterior dislocation. Our study sought to quantify the number of individuals in a THA population that exhibit at-risk coupled rotations of their femur and pelvis in the flexed seated position.

METHODS: Preoperatively, 101 patients who were undergoing THA were analysed for native anteversion, flexed seated pelvic tilt, flexed seated femoral rotation and supine pelvic tilt and femoral rotations as a baseline. Positive values were interpreted as anterior pelvic tilt and external femoral rotation.

RESULTS SECTION: 20% of patients exhibited both anterior rotation from supine-to-flexed seated and internal femoral rotation. 23% of patients exhibited at-risk changes in femoral rotation from supine-to-flexed seated (>10° of internal rotation). 19% of patient exhibited at-risk changes in pelvic from supine-to-flexed seated (>10° of anterior rotation).

DISCUSSION: Previous studies have investigated functional femoral rotation in standing and supine, but none have investigated functional femoral rotation in seated. Our study highlights the compounding factor of internal femoral rotation and anterior pelvic changes in driving an anterior impingement, with 20% of patients having both motions between supine and flexed seated. Surgeons should be aware of the coupled rotations of femoral rotation along and pelvic tilt in driving anterior impingement during chair rise and other dislocation-prone movements.

Justin Roe (North Sydney Orthopaedic Research Group, Australia)
David Parker (Sydney Orthopaedic Research Institute, Australia)
David Liu (Gold Coast Centre for Bone and Joint Surgery, Australia)
Brett Fritsch (Sydney Orthopaedic Research Institute, Australia)
Ishaan Jagota (360 Med Care, Australia)
Matthew Baker (360 Med Care, Australia)
Joshua Twiggs (360 Med Care, Australia)
Brad Miles (360 Med Care, Australia)
Poster 27: Validation of a Patient Outcome Prediction Tool Relative to Surgeon Predictions of Patient Outcome in Total Knee Arthroplasty
PRESENTER: Matthew Baker

ABSTRACT. INTRODUCTION There is a lack of consensus amongst surgeons about the eligibility criteria for a TKA, which has the potential to result in inappropriate recipients receiving a TKA. No existing patient outcome prediction tools have been validated directly against the predictions of surgeon. This study aims to investigate ability of the Patient Expectation Management (PEM) tool, an artificially intelligent predictive tool, relative to surgeon predictions of patient outcome.

METHODS A prospective study was performed involving 100 operated knees recruited from 4 experienced TKA surgeons. Pre- and post-operative KOOS were obtained for all patients. All patients were surveyed using the PEM tool and by Surgeons, each of which assessed the patient’s current pain state and provided a prediction for the patient’s post-operative pain outcome on a 100-point scale.

RESULTS The reported change in patient pain outcome for patients predicted to experience a significant improvement (change in KOOS Pain score ≥ 40) according to the PEM tool was 40.9 ± 13.0, compared to 21.9 ± 22.7 for patients predicted to experience an insignificant improvement (p < 0.001). These figures for the surgeon cohort predictions were 51.2 ± 23.2 and 50.0 ± 15.6, respectively.

DISCUSSION The PEM tool was able to predict significant improvements in patient pain outcomes more accurately than surgeons. Due to the this in addition to findings in its prior validation, the PEM tool can be implemented as an assistive tool for patient selection and has potential to assist in patient expectation management, both of which can positively impact post-operative patient reported outcomes.

Yves Vanderschelden (clinique cote d'emeraude st malo, France)
Alberto Grassi (Istituto Ortopedico Rizzoli, Italy)
Simone Bignozzi (Orthokey Italia srl, Italy)
Irene Asmonti (Orthokey Italia srl, Italy)
Stefano Zaffagnini (Istituto Ortopedico Rizzoli, Italy)
Poster 12: Kinematics and Early Clinical Outcomes of Navigated Total Knee Arthroplasty Through a Lateral Subvastus Approach
PRESENTER: Simone Bignozzi

ABSTRACT. INTRODUCTION: A computer assisted procedure with subvastus lateral approach has been utilized routinely by single surgeon. The use of navigation was used to plan resection based on ligament balancing and to guide implant positioning due to the reduced exposure on medial compartment. Purpose of this study is to evaluate pain, function, and implant kinematics at early follow up of this surgical technique. METHODS: 60 consecutive patients underwent CR TKA, through a lateral approach. Surgery was performed with navigation. Particular attention has been given to tibial and femoral implant planning based on ligament balance joint spaces and intra-operative kinematic throughout the range of motion. After implant fixation kinematics was registered. In order to verify the efficacy of surgical technique in reducing pain and function we focused at early follow up. The Knee Society Score (KSS) and pain score were obtained pre-operatively, at 1, 3, and 12 months. Differences between controls were analyzed with ANOVA for KSS score and Chi-square for Pain score. RESULTS: No intraoperative complications were registered, patellar tendon lesion or avulsion was noted. Preoperative average leg alignment was 4±6° varus (range 16 varus, 14 valgus), corrected to 0° (range 2 varus, 1 valgus) after surgery. After TKA medial pivot behavior was observed in all patients. Kinematic analysis showed rollback on lateral compartment for all patients, while on medial compartment rollback was lower or negligible. Less than 5% had a “Fair” or “Poor” KSS score after 3 months. Preoperatively 41% of patients reported severe pain; 50% moderate; 8% mild and 0% none. After 1 month pain was distributed as: 2% severe; 18% moderate; 55% mild and 25% none. After 3 months 50% of patients had mild and 50% had no pain. No patients reported moderate or severe pain. This data was maintained after 1 year, with 31% of patients with mild and 69% of patients no pain. No patients had moderate or severe pain (p<0.05). DISCUSSION AND CONCLUSION: TKA with lateral approach produced promising early outcomes in terms of pain, ROM and knee function, with only less than 5% of patients presenting sub-optimal clinical results after 3-month follow-up. Despite the symmetrical implant design, medial pivot behavior was observed in all patients. Respecting the medial ligamental envelop and intense use of computer assisted ligament balancing allow to optimize the medial stability and minimize the post-operative pain.

19:00-23:00 Gala Dinner – Oceanopolis (separate registration)

Bus departures: 18:30 : Arena, 18:45 : Oceania hotel