Automatic segmentation of high-and low-field knee MRIs using knee image quantification with data from the osteoarthritis initiative

Clinical studies including thousands of magnetic resonance imaging (MRI) scans offer potential for pathogenesis research in osteoarthritis. However, comprehensive quantification of all bone, cartilage, and meniscus compartments is challenging. We propose a segmentation framework for fully automatic segmentation of knee MRI. The framework combines multiatlas rigid registration with voxel classification and was trained on manual segmentations with varying configurations of bones, cartilages, and menisci. The validation included high- and low-field knee MRI cohorts from the Center for Clinical and Basic Research, the osteoarthritis initiative (QAI), and the segmentation of knee images10 (SKI10) challenge. In total, 1907 knee MRIs were segmented during the evaluation. No segmentations were excluded. Our resulting OAI cartilage volume scores are available upon request. The precision and accuracy performances matched manual reader re-segmentation well. The cartilage volume scan-rescan precision was 4.9% (RMS CV). The Dice volume overlaps in the medial/lateral tibial/femoral cartilage compartments were 0.80 to 0.87. The correlations with volumes from independent methods were between 0.90 and 0.96 on the OAI scans. Thus, the framework demonstrated precision and accuracy comparable to manual segmentations. Finally, our method placed second for cartilage segmentation in the SKI10 challenge. The comprehensive validation suggested that automatic segmentation is appropriate for cohorts with thousands of scans

Development of a finite element model of the knee using patient specific magnetic resonance imaging data and biomechanical testing of soft tissues

This thesis presents the findings of investigations carried out relating to the creation of full joint contact patient specific finite element models for correlation with biological studies in the study of Osteoarthritis (OA) development. To understand the relationship between altered loading and biological changes in articular cartilage (AC), a method for predicting stresses and strains experienced inside the tissues is required. An in-vitro study was conducted to explore the possibility of correlating finite element (FE) and gene expression study results. FE models were used to predict the stresses and strains inside the AC for explants subjected to different loading conditions. The study demonstrated that the accurate representation of AC surface geometry is crucial and current flat surface axisymmetric cylinder representations used in AC explant modelling introduces significant error in the prediction of tissue mechanical behaviour. Cutting of the AC explant to achieve a flat surface can affect the biological, mechanical and tribology behaviour of the tissue. Thus, a method for creating explant specific finite element models with the use of digital image correlation (DIC) was developed and is presented, allowing for surface layer preservation in AC explants for correlated gene expression and inverse FE. Reconstruction of tissue geometries from magnetic resonance (MR) imaging scan data of the knee was explored. It was possible to segment both hard and soft tissues from the same set of MR imaging scan data. Meshing of the geometries using a fundamentally voxel based algorithm proved to cause significant error in the segmented volume. An alternative contour based algorithm needs to be explored. Uncertainties concerning the presence and modelling of meniscotibial ligaments (MTLs) in full joint contact FE models found in literature were addressed. An anatomy study revealed that the MTLs are found in both the medial and lateral side of the joint around the periphery of the anterior, middle and posterior portion of the menisci. With the use of cross polarised light microscopy, it was established Page | VII that MTLs consist of Type I collagen orientated in the circumferential direction around the menisci. As a result, the MTLs were modelled as an anisotropic membrane. Using the full joint contact finite element model, the influence of MTLs on knee joint kinematics was investigated. It was found that the MTLs reinforce the function of the meniscal horns and circumferential fibres in the meniscus and help constrain the meniscus. Therefore, it was concluded that the MTLs are mechanically significant in the stabilisation of knee joints and should be included in knee models for accurate prediction of knee joint behaviour

Quantitative stereophotogrammetric & MRI evaluation of ankle articular cartilage and ankle joint contact characteristics

Osteoarthritis and degenerative cartilage diseases affect millions of people. Therefore, there is huge interest in developing new therapies to repair, replace and/or regenerate cartilage. This necessitates advances in techniques which make earlier non-invasive diagnosis and objective quantitative evaluations of new therapies possible. Most previous research has focused on the knee and neglected the ankle joint. Hence, the aims of this thesis are to describe and quantify the geometric properties of ankle cartilage, to evaluate joint contact characteristics and develop techniques which allow quantitative measurements to be made in vivo. Chapters 3 and 6 describe the application of a high resolution stereophotography system for making highly accurate 3-D geometric models from which quantitative measurements of cartilage parameters and joint area contact can be made. Chapters 4 and 5 report the testing of image analysis algorithms designed to segment cartilage sensitive MR images. Work focused on initially on a semi-automated 2-D segmentation approach and subsequently on a pilot study of 3-D automated segmentation algorithm. The stereophotographic studies were highly accurately and demonstrated that ankle cartilage thickness is greater than previously reported with the thickest cartilage occurring where cartilage injuries are most commonly seen. Furthermore, joint contact area is larger than previously believed and corresponds to the regions of the thickest cartilage over the talar shoulders. The image analysis studies show that it is possible to accurately and reproducibly segment the thin cartilage layers of the ankle joint using a semi-automated approach. The feasibility of a fully automated 3D method for future clinical use is also shown. In conclusion this thesis presents novel methods for examining ankle articular cartilage in vitro and in vivo, showing that the thickest cartilage occurs in highly curved regions over the shoulders of the talus which correspond to regions of greatest contact. Importantly, the image analysis techniques may be used for future clinical monitoring of patients sustaining cartilage injuries or undergoing cartilage repair therapies

Dynamics, Electromyography and Vibroarthrography as Non-Invasive Diagnostic Tools: Investigation of the Patellofemoral Joint

The knee joint plays an essential role in the human musculoskeletal system. It has evolved to withstand extreme loading conditions, while providing almost frictionless joint movement. However, its performance may be disrupted by disease, anatomical deformities, soft tissue imbalance or injury. Knee disorders are often puzzling, and accurate diagnosis may be challenging. Current evaluation approach is usually limited to a detailed interview with the patient, careful physical examination and radiographic imaging. The X-ray screening may reveal bone degeneration, but does not carry sufficient information of the soft tissue conditions. More advanced imaging tools such as MRI or CT are available, but expensive, time consuming and can be used only under static conditions. Moreover, due to limited resolution the radiographic techniques cannot reveal early stage arthritis. The arthroscopy is often the only reliable option, however due to its semi-invasive nature, it cannot be considered as a practical diagnostic tool. Therefore, the motivation for this work was to combine three scientific methods to provide a comprehensive, non-invasive evaluation tool bringing insight into the in vivo, dynamic conditions of the knee joint and articular cartilage degeneration. Electromyography and inverse dynamics were employed to independently determine the forces present in several muscles spanning the knee joint. Though both methods have certain limitations, the current work demonstrates how the use of these two methods concurrently enhances the biomechanical analysis of the knee joint conditions, especially the performance of the extensor mechanism. The kinetic analysis was performed for 12 TKA, 4 healthy individuals in advanced age and 4 young subjects. Several differences in the knee biomechanics were found between the three groups, identifying age-related and post-operative decrease in the extensor mechanism efficiency, explaining the increased effort of performing everyday activities experienced by the elderly and TKA subjects. The concept of using accelerometers to assess the cartilage degeneration has been proven based on a group of 23 subjects with non-symptomatic knees and 52 patients suffering from knee arthritis. Very high success (96.2%) of pattern classification obtained in this work clearly demonstrates that vibroarthrography is a promising, non-invasive and low-cost technique offering screening capabilities

Quantitative stereophotogrammetric & MRI evaluation of ankle articular cartilage and ankle joint contact characteristics

Osteoarthritis and degenerative cartilage diseases affect millions of people. Therefore, there is huge interest in developing new therapies to repair, replace and/or regenerate cartilage. This necessitates advances in techniques which make earlier non-invasive diagnosis and objective quantitative evaluations of new therapies possible. Most previous research has focused on the knee and neglected the ankle joint. Hence, the aims of this thesis are to describe and quantify the geometric properties of ankle cartilage, to evaluate joint contact characteristics and develop techniques which allow quantitative measurements to be made in vivo. Chapters 3 and 6 describe the application of a high resolution stereophotography system for making highly accurate 3-D geometric models from which quantitative measurements of cartilage parameters and joint area contact can be made. Chapters 4 and 5 report the testing of image analysis algorithms designed to segment cartilage sensitive MR images. Work focused on initially on a semi-automated 2-D segmentation approach and subsequently on a pilot study of 3-D automated segmentation algorithm. The stereophotographic studies were highly accurately and demonstrated that ankle cartilage thickness is greater than previously reported with the thickest cartilage occurring where cartilage injuries are most commonly seen. Furthermore, joint contact area is larger than previously believed and corresponds to the regions of the thickest cartilage over the talar shoulders. The image analysis studies show that it is possible to accurately and reproducibly segment the thin cartilage layers of the ankle joint using a semi-automated approach. The feasibility of a fully automated 3D method for future clinical use is also shown. In conclusion this thesis presents novel methods for examining ankle articular cartilage in vitro and in vivo, showing that the thickest cartilage occurs in highly curved regions over the shoulders of the talus which correspond to regions of greatest contact. Importantly, the image analysis techniques may be used for future clinical monitoring of patients sustaining cartilage injuries or undergoing cartilage repair therapies

Spatial Sensors for Quantitative Assessment of Retrieved Arthroplasty Bearings

Evaluation of retrieved joint arthroplasty bearings provides unique evidence related to the physiological environment in which bearing materials are expected to perform. This dissertation describes the development of novel spatial sensors and measurement strategies for standardized, quantitative assessments of arthroplasty bearings, including total knee replacements, unicompartmental knee replacements, and total hip replacements. The approach is to assess bearings that endured a finite duration of function in patients, with particular emphasis on expanding our understanding of the biomechanical conditions specific to bearing function and wear in the physiological environment. Several quantifiable parameters are identified that prove comparable to pre-clinical in vitro tibological evaluations, including knee wear simulation and analytical modeling. These comparisons provide clinical relevance to the existing methodologies, helping to verify that the biomechanical simulations accurately represent the in vivo conditions they are meant to simulate. The broad objective of this dissertation is to improve the longevity and function of arthroplasty bearing materials and designs. Assessments from the retrieved prostheses are discussed within the context of developing comprehensive approaches for the prospective evaluation of new materials and designs in joint replacements

Tribological Investigation of Articular Cartilage Substitution in the Medial Compartmental Knee

In the development of any cartilage substitution device, an understanding of the tribological response of the natural joint, as well as the treated joint is of upmost importance. Many previous studies have investigated the tribology of potential cartilage substitution therapies, using small scale pin on plate experiments. The aim of the current study was to develop an anatomical and physiological simulation of the medial compartmental bovine knee joint and to use this simulation to investigate a number of cartilage substitution therapies for damaged or diseased knee joints. A pendulum friction simulator was used to apply physiological loading and motion to medial compartmental knees. The wear of the cartilage was characterised following the experiments using three different techniques: surface topography analysis, volumetric wear quantification using µMRI scans and histological assessment. Three main interventions were investigated using this novel anatomical simulation - the tribological response of meniscectomy, the effect of conformity of tibial hemiarthroplasty designs, and finally, a number of potential cartilage substitution materials were investigated as osteochondral repair devices in the femoral condyle. In the first two studies, the removal of the meniscus and a decrease of tibial hemiarthroplasty conformity, resulted in an elevation of the coefficient of friction, contact stress, friction shear stress and subsequently the wear and degradation of cartilage. In the defect repair study, biphasic defect repair materials (hydrogels) had a superior tribological performance to non-compliant single phase materials (stainless steel). Across the three studies, the use of non-biphasic materials and/or the loss of joint congruity resulted in a more rapid decrease of cartilage interstitial fluid pressurisation and biphasic fluid load support, resulting in increased cartilage solid-solid contact and increased wear. This tribological simulation can be used to investigate many potential knee joint intervention, from uni- or hemi-arthroplasty, cartilage defect repair, meniscus substitutes or tissue engineered substitutes. This simulation can be used to further our understanding of the tribological characteristics of more satisfactory and conservative therapies for damaged and diseased synovial joints