213 research outputs found
Three-dimensional assessment of impingement risk in geometrically parameterised hips compared with clinical measures
Abnormal bony morphology is a factor implicated in hip joint soft tissue damage and an increased lifetime risk of osteoarthritis. Standard two-dimensional radiographic measurements for diagnosis of hip deformities, such as cam deformities on the femoral neck, do not capture the full joint geometry and are not indicative of symptomatic damage. In this study, a three-dimensional geometric parameterisation system was developed to capture key variations in the femur and acetabulum of subjects with clinically diagnosed cam deformity. The parameterisation was performed for Computed Tomography scans of 20 patients (10 female, 10 male). Novel quantitative measures of cam deformity were taken and used to assess differences in morphological deformities between males and females. The parametric surfaces matched the more detailed, segmented hip bone geometry with low fitting error. The quantitative severity measures captured both the size and position of cams, and distinguished between cam and control femurs. The precision of the measures was sufficient to identify differences between subjects that could not be seen with the sole use of two-dimensional imaging. In particular, cams were found to be more superiorly located in males than in females. As well as providing a means to distinguish between subjects more clearly, the new geometric hip parameterisation facilitates the flexible and rapid generation of a range of realistic hip geometries including cams. When combined with material property models, these stratified cam shapes can be used for further assessment of the effect of the geometric variation under impingement conditions
Doctor of Philosophy
dissertationGeometric abnormalities of the human hip joint, as found in femoroacetabular impingement (FAI) and acetabular dysplasia, alter hip biomechanics and may be the primary causes of osteoarthritis in young adults. However, empirical evidence of direct correlations between abnormal geometry, altered biomechanics, and osteoarthritis is scarce. Also, clinical measures used to diagnose FAI and dysplasia still have substantial limitations, including questions about their reliability, assumptions about hip joint geometry and their ability to definitively distinguish pathologic from normal hips. The goals of this dissertation are twofold. First, a set of tools are presented and applied to quantify three-dimensional (3D) anatomical differences between hips with FAI and control subjects. The 3D tools were developed, validated and applied to patients with a subtype of FAI, called cam FAI, to improve basic understanding of the spectrum of FAI deformities, and to provide meaningful new metrics of morphology that are relatable to current diagnostic methods and translate easily for clinical use. The second goal of this dissertation is to improve our understanding of intra-articular hip contact mechanics as well as hip joint kinematics and muscle forces. To do so, a finite element study of intraarticular cartilage contact mechanics was completed with a cohort of live human subjects, using a validated modeling protocol. Finally, musculoskeletal modeling was used with gait data from healthy subjects and acetabular dysplasia patients to provide preliminary estimates of hip joint kinematics, kinetics, and muscle forces and compare differences between the groups. The translational methods of this dissertation utilized techniques from orthopaedics, computer science, physical therapy, mechanics, and medical imaging. Results from this dissertation offer new insight into the complex pathomechanics and pathomorphology of FAI and acetabular dysplasia. Application and extension of the work of this dissertation has the potential to help establish links between FAI and dysplasia with osteoarthritis and to improve patient care
Geometric Parameterisation in Finite Element Models of Femoroacetabular Impingement
Abnormal bony morphology is a factor implicated in hip joint soft tissue damage and an increased lifetime risk of osteoarthritis. One geometric feature causing impingement and thus resulting in such damage is a bony lump on the femoral neck, known as a cam deformity.
A three-dimensional geometric parameterisation system was developed to capture key variations in the femur and acetabulum of subjects with clinically diagnosed cam deformity. Novel quantitative measures of the size and position of cams were taken and used to assess differences in morphological deformities between males and females. The precision of the measures was sufficient to identify differences between subjects that could
not be seen using two-dimensional imaging; cams were found to be more superiorly located in males than in females. As well as providing a means to distinguish between subjects more clearly, the geometric hip parameterisation facilitated flexible and rapid
automated generation of a range of hip geometries including cams. These were used to develop finite element models. Patient-specific parametric finite element models of hips under impingement conditions were verified with comparison to their patient-specific segmentation-based equivalents. The parameterisation system was then used to generate further models to investigate the effects of bone morphology on tissue strains. This demonstrated that a combination of cam location and extent affect impingement severity, highlighting the importance of reporting the full three-dimensional geometry used for
parametric models
Biomechanical importance of proximal human femur morphology and mechanics in orthopaedic purposes
Bone morphology is essential in orthopedic surgery to perform precise preoperative planning and surgery as well as to appropriately design optimal medical implants. In this study we provided a database of surgically important morphological parameters of proximal human femur for orthopedic and biomedical research purposes (study 1), indicated accuracy of the 3D reconstructed images in comparison with the optical 3D scan of real human femur (study 2), and reported the accuracy and reliability of the developed image-based finite element model in comparison with the experimental results (study 3)
Pelvic kinematics as confounding factor for cam hip impingement
The purpose of this thesis was to explore a range of biomechanical factors linked to the development of symptoms and potentially early onset hip OA in people with cam hip impingement. This was achieved through shape analysis on 3D bone models (segmented from medical images), and motion analysis performed during walking and squatting. Following ethical approval, kinematic and morphological variables were obtained from 19 pre-operative hip impingement patients and 18 healthy controls, and these were compared between groups. Patients demonstrated reduced neck-shaft-angles (-6.0°, p<.01) and increased anterior pelvic tilt during gait (+3.2°, p=.04) which are thought to predispose to impingement by decreasing the proximity between the cam and acetabular rim and making abutment more likely. The transverse pelvic plane is used to measure pelvic tilt during motion analysis, it is therefore interesting that the angle between the transverse and anterior pelvic plane is increased (+4.6°, p=.03) in patients, emphasising that the interplay between shape and function is a priority for further research. Avoidance of hip extension (-5.9°, p<.01) was also observed, which could be a compensatory mechanism to prevent further damages to the hip. Furthermore, large cams are thought to act as a mechanical constraint and limit rotation movement allowed within the acetabulum, as demonstrated by reduced peak hip internal rotation (during squat, -8.5°, p=.03). Controls were regrouped based on morphology to allow comparison between asymptomatic (CAM-; n=11) and symptomatic (CAM+, n=16) cams. Symptomatic cams have an increased width (+41.4°, p<.01), and start more superiorly (-29.4°, p<.01). Increased sagittal pelvic mobility (e.g. during a squat; -11.2° for CAM+, p<.01) is thought to be protective against hip impingement symptoms, as during high flexion angles the pelvic tilts backwards reducing the risk of abutment. These findings highlight the need to establish thresholds taking confounding factors into account.Open Acces
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A Novel Approach for the Visualisation and Progression Tracking of Metastatic Bone Disease
Metastatic bone disease (MBD) is a common secondary feature of cancer that can cause significant complications, including severe pain and death. Current methods of diagnosis require a highly trained radiologist capable of interpreting medical images and recognising the sites of MBD. These medical images are often noisy, two dimensional, greyscale and usually have a poor resolution.
In order to help assist with these issues, several studies have shown that computer aided methods can locate MBD within medical images. However these methods are limited in scope, accuracy, sensitivity, explainability and do not improve upon the poor visualisations of the underlying medical imaging data.
To address these limitations, I have developed a novel method of automatic MBD assessment and visualisation using computed tomography (CT) imaging data as the input. The method is fully automated and does not require any human interaction -- although users can interact with a viewer that visualises the results. This method has been tested on CT data from prostate cancer patients as prostate cancer is one of the most common sources of MBD.
The method described in this thesis has a sensitivity of 0.871 when detecting sclerotic and lytic lesions within a single data set. This sensitivity is comparable to existing methods, however the scope in detecting these lesions was limited to the vertebrae in previous studies. My method significantly expands this scope to include the ribs, vertebrae, pelvis and proximal femurs.
The work in this thesis also provides novel visualisations of the disease and does not suffer from explainability issues that plague modern machine learning algorithms.
In addition, I developed a novel method of tracking the spread of MBD at multiple time points using longitudinal CT data. This method is capable of calculating the change in lesion volume size across multiple time points, providing a novel numerical assessment.The Armstrong Trus
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