Development of a Computational Model to Predict the In Vivo Contact Mechanics of Modern Total Knee Arthroplasty

This dissertation focuses on the development of a computationally efficient and fast method that incorporates the kinematics obtained from fluoroscopy and extends it to the prediction of the in-vivo contact mechanics at the femoro-tibial articulation in modern knee implants for the deep knee bend activity. In this endeavor, this dissertation deals with the use of an inverse dynamic rigid body model characterizing the slip and roll behavior observed in the femoro-polyethylene articulation and a coupled deformation model where the polyethylene in knee implants are modeled as hexahedral discrete element networks. The performance of this method is tested by comparing force predictions from a telemetric knee and finite element analysis. Finally, the method is applied to study the in vivo contact mechanics and mechanics of the quadriceps mechanism in six popular knee designs. During the deep knee bend activity, the contact force generally increased with flexion. However, the medial lateral forces were not equally distributed and the medial lateral force distribution generally varied from 60%- 40% at full extension to as high as 75%-25% at full flexion in some patients. Also, the magnitude of axial force in the superior-inferior direction was the highest and was found to contribute around 98%-99% of the total load acting at the femorotibial joint. The forces in the medio-lateral and antero-posterior directions were low and the maximum magnitude observed was around 0.5BW. The contact areas and contact pressures were much more sensitive to the geometries involved and the in vivo kinematics. Though no definite pattern was observed for the variation of the contact areas throughout flexion, the contact pressures increased in both condyles with increasing flexion. Also, the contact pressures on the medial condyle were higher than the contact pressures observed in the lateral condyle. The patellofemoral and the quadriceps force ratio increased with the increase in flexion while the patellar ligament and the quadriceps force ratio decreased with increasing flexion. In some patients at high flexion, the quadriceps force and as a result the patellofemoral, patellar ligament and the knee contact forces were found to decrease due to the wrapping of the quadriceps coupled with posterior movement of the femoral condyles leading to the increase in the quadriceps moment arm

Model-based shape matching of orthopaedic implants in RSA and fluoroscopy

Model-based shape matching is commonly used, for example to measure the migration of an implant with Roentgen stereophotogrammetric analysis (RSA) or to measure implant kinematics with fluoroscopy. The aim of this thesis was to investigate the general usability of shape matching and to improve the reliability of shape matching for RSA and fluoroscopy. Several improvements were made to the usability and reliability of model-based shape matching for RSA and fluoroscopy. An automatic contour detection approach was proposed, integrating directly into the estimation of position and orientation of the implant. The accuracy of such estimation was also improved by taking the relation between implant parts into account. The robustness of model-based shape matching was assessed when it is applied fully automatically, demonstrating that manual supervision remains necessary. The standardization of validating new fluoroscopic methods could be a welcome addition to the biomechanical field, making it a lot easier to compare results between methods and experiments. As the technology of fluoroscopy advances, the amount of high quality data is getting larger, and may soon grow beyond the capabilities of manual, supervised pose estimation methods. It is therefore imperative that fully automatic unsupervised methods are developed.UBL - phd migration 201

Patient Specific Alignment, Anatomy, Recovery and Outcome in Total Knee Arthroplasty

Total knee arthroplasty (TKA), despite being an otherwise highly successful medical operation, has a recurrent problem of dissatisfaction and recurrent pain rates in the 15-20% range. A variety of factors contribute to this incidence of dissatisfaction which can broadly be considered to fall into one of three groups: factors driven by the surgical outcome, pre-existing factors relating to the patients psychology, appropriateness for surgery or expectation level, and factors driven by the patient’s recovery and their management during that recovery process. With consideration to the extensive variation between patients, it is reasonable to posit that addressing patient specific factors in selection for surgery, alignment of components during surgery and post-operative management may reduce the instance of post-operative dissatisfaction. The first goal of this thesis was to understand the variation of patient anatomy as it relates to standard practice in TKA. Following the finding of extensive variation, a bio-mechanical rigid body dynamics simulation of the knee joint was developed to determine the degree to which this variation was reflected in the kinematic behaviour of the implanted knees. Later studies showed extensive kinematic variation that was responsive to variation in the alignment of the components as well as well as significantly related to patient reported outcome. Later studies further investigated how outcome related to patient selection for surgery and recovery of the patient as measured with simple activity monitoring. From this work, a pre-operative simulation assessment tool has been developed, the Dynamic Knee Score (DKS), and paired with selection and recovery management tools forms the basis of 360 Knee Systems surgical planning and patient management, which has been used in over 3,000 primary TKA’s to date

Evaluating the Biomechanical, Functional, and Clinical Outcomes of Bicruciate Stabilized Total Knee Arthroplasty

Total knee arthroplasty (TKA) is the only solution for treating arthritis of the knee joint. Although it is successful at reducing pain and returning function to affected joints, one in five patients still report dissatisfaction following their operation. Bicruciate stabilized (BCS) TKA was developed to improve outcomes by replicating normal knee structure and function. The biomechanical, functional, and clinical outcomes for the BCS design were investigated in this thesis through radiographic imaging techniques, wearable sensor systems, and questionnaires in a cohort of TKA patients. A stereo x-ray technique, called radiostereometric analysis (RSA), assesses implant fixation by tracking micromotion of TKA devices relative to the bone. Risk of implant loosening can be predicted based on the magnitude of these micromotions. This thesis found micromotion of the BCS TKA was within safe thresholds for both the gap balancing and measured resection techniques, indicating sufficient fixation to the bone occurs and the BCS TKA is not expected to have elevated revision risks due to implant loosening. The exact cause of patient dissatisfaction after TKA is unknown. This thesis sought to find any differences in objective data between satisfied and dissatisfied patients with a BCS TKA. RSA was used to measure implant micromotion and tibiofemoral contact kinematics. A sensor system tracked measures of patient function during a timed-up-and-go functional test, and patient-reported outcomes were collected. We found no difference in implant micromotions or patient function between satisfied and dissatisfied patients. However, dissatisfied patients had more anterior contact on the lateral condyle of the knee in early flexion, and more pain and unmet expectations. Finally, correlations were found between implant micromotion and tibiofemoral contact kinematics. Contact patterns indicating reduced posterior femoral rollback in the lateral compartment correlated with greater implant micromotion. Since BCS TKA aims to replicate normal knee kinematics and guide posterior rollback, it was concluded that undesired kinematics resulted in greater micromotions, and a greater risk of implant loosening. Overall, the restoration of kinematics—particularly in the lateral compartment—in BCS TKA appears to be important for reducing implant migrations, improving pain and feeling in the knee, and ultimately, enhancing patient satisfaction

Applied AI/ML for automatic customisation of medical implants

Most knee replacement surgeries are performed using ‘off-the-shelf’ implants, supplied with a set number of standardised sizes. X-rays are taken during pre-operative assessment and used by clinicians to estimate the best options for patients. Manual templating and implant size selection have, however, been shown to be inaccurate, and frequently the generically shaped products do not adequately fit patients’ unique anatomies. Furthermore, off-the-shelf implants are typically made from solid metal and do not exhibit mechanical properties like the native bone. Consequently, the combination of these factors often leads to poor outcomes for patients. Various solutions have been outlined in the literature for customising the size, shape, and stiffness of implants for the specific needs of individuals. Such designs can be fabricated via additive manufacturing which enables bespoke and intricate geometries to be produced in biocompatible materials. Despite this, all customisation solutions identified required some level of manual input to segment image files, identify anatomical features, and/or drive design software. These tasks are time consuming, expensive, and require trained resource. Almost all currently available solutions also require CT imaging, which adds further expense, incurs high levels of potentially harmful radiation, and is not as commonly accessible as X-ray imaging. This thesis explores how various levels of knee replacement customisation can be completed automatically by applying artificial intelligence, machine learning and statistical methods. The principal output is a software application, believed to be the first true ‘mass-customisation’ solution. The software is compatible with both 2D X-ray and 3D CT data and enables fully automatic and accurate implant size prediction, shape customisation and stiffness matching. It is therefore seen to address the key limitations associated with current implant customisation solutions and will hopefully enable the benefits of customisation to be more widely accessible.Open Acces

The Effect of Loading, Plantar Ligament Disruption and Surgical Repair on Canine Tarsal Bone Kinematics

Our desire to describe the complex kinematic patterns found in nature often exceeds our ability to record, quantify and characterise them. Constantly faced with technological limitations, investigators may attempt to develop new techniques or reduce the complex motions to more simplified models. Perhaps due to technical limitations, the canine pes is commonly considered as a rigid structure, when in reality, this limb segment is comprised of multiple bones and ligaments and motion can readily be demonstrated during palpation. Despite the potentially important role that tarsal bone kinematics may play in energy conservation mechanisms and pathogenesis of injury or disease, there are no descriptions of normal canine tarsal kinematics during locomotion. A radiolucent cadaveric limb loading device was developed and used in conjunction with a computed tomography based kinematic measurement technique to produce the first description of canine tarsal bone kinematics in three dimensions. Tarsal bones were shown to undergo a complex, yet coordinated patterns of motion that facilitate dorsiflexion of the pes in the normal animal. The same technique was applied to specimens following sequential transection of the plantar ligament and revealed the roles of the various components of this ligament. Complete luxation of the proximal intertarsal joint occurred only after transection of the entire ligament, resulting in an inability to transmit force through this limb segment. The final chapter of this thesis, evaluated the ability of a laterally applied bone plate to re-establish force transmission through this limb segment, providing important information that may help to resolve the open question of what the most appropriate surgical repair technique is in these clinical cases

Articulated Statistical Shape Modelling of the Shoulder Joint

The shoulder joint is the most mobile and unstable joint in the human body. This makes it vulnerable to soft tissue pathologies and dislocation. Insight into the kinematics of the joint may enable improved diagnosis and treatment of different shoulder pathologies. Shoulder joint kinematics can be influenced by the articular geometry of the joint. The aim of this project was to develop an analysis framework for shoulder joint kinematics via the use of articulated statistical shape models (ASSMs). Articulated statistical shape models extend conventional statistical shape models by combining the shape variability of anatomical objects collected from different subjects (statistical shape models), with the physical variation of pose between the same objects (articulation). The developed pipeline involved manual annotation of anatomical landmarks selected on 3D surface meshes of scapulae and humeri and establishing dense surface correspondence across these data through a registration process. The registration was performed using a Gaussian process morphable model fitting approach. In order to register two objects separately, while keeping their shape and kinematics relationship intact, one of the objects (scapula) was fixed leaving the other (humerus) to be mobile. All the pairs of registered humeri and scapulae were brought back to their native imaged position using the inverse of the associated registration transformation. The glenohumeral rotational center and local anatomic coordinate system of the humeri and scapulae were determined using the definitions suggested by the International Society of Biomechanics. Three motions (flexion, abduction, and internal rotation) were generated using Euler angle sequences. The ASSM of the model was built using principal component analysis and validated. The validation results show that the model adequately estimated the shape and pose encoded in the training data. Developing ASSM of the shoulder joint helps to define the statistical shape and pose parameters of the gleno humeral articulating surfaces. An ASSM of the shoulder joint has potential applications in the analysis and investigation of population-wide joint posture variation and kinematics. Such analyses may include determining and quantifying abnormal articulation of the joint based on the range of motion; understanding of detailed glenohumeral joint function and internal joint measurement; and diagnosis of shoulder pathologies. Future work will involve developing a protocol for encoding the shoulder ASSM with real, rather than handcrafted, pose variation

Objective clinical performance outcome of total knee prostheses. A study of mobile bearing knees using fluoroscopy, electromyography and roentgenstereophotogrammetry

The aim of the thesis was to to assess with accurate and objective methods the function and fixation of total knee prostheses with special emphasis on mobile bearing total knee designs. The mobile bearing of a rotating platform design showed limited motion or no motion during a step-up task thereby nullifying the theoretical advantages of a mobile bearing prosthesis. Apatite coated implants show excellent mid-term Roentgen Stereophotogrammetric Analysis (RSA) results and offer some clinical advantages above cemented total knee arthroplasty. A prospective RSA study also revealed that the studied mobile bearing design is more predictable and forgiving with respect to micromotion of the tibial component than a posterior stabilised prosthesis. However, mobile bearing prostheses showed to be more demanding for the soft tissue structures surrounding the knee joint. The techniques used in gait analysis and fluoroscopy are sensitive for measurement errors. This restricts the applicability and interpretation of the results acquired when using these methods. In general one needs to be aware of the limitations of measurement tools since one needs accurate and objective methods to assess evidence about the clinical performance of (new) total knee prostheses.Biomet Nederland B.V., DePuy Nederland B.V., Mathys Orthopaedics B.V., Medis medical imaging systems B.V., Medis specials B.V., Smith & Nephew B.V, Stryker Nederland B.V., Wright Medical Nederland B.V., Zimmer Nederland B.V.UBL - phd migration 201