Anoosha Pai S
Master of Applied Science in Biomedical Engineering (MASc)
Investigation of Level and Posture Effects on the Thoracic Spinal Muscle Morphology with Upright Open MRI
Dr. David Wilson is a Professor in the Department of Orthopaedics at UBC. He received his D. Phil. in Engineering Science from the University of Oxford for work on the 3-dimensional kinematics of the knee, followed by a fellowship in orthopaedic biomechanics. His research interests include sports medicine, joint reconstruction/replacement, and medical imaging. Dr. Wilson is renowned for his research on the links between joint mechanics, clinical symptoms, and the success of orthopaedic procedures. His team has expertise in non-invasive assessments of cartilage health, including the use of emerging MRI techniques, such as delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), to detect changes in osteoarthritic joints much earlier than conventionally possible. Dr. Wilson was awarded a Canadian Arthritis Network New Investigator award.
Osteoarthritis (OA) is a prevalent disease with mechanical risk factors. One risk factor, varus knee alignment, is associated with medial tibiofemoral (TF) OA. High tibial osteotomy (HTO) is a surgical treatment for younger patients with varus malalignment that aims to reduce medial TF loading by realigning the mechanical axis. Post-HTO MR investigation of cartilage health is complicated by metal artifact from surgical implants. Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) is a validated assessment of cartilage health sensitive to early OA. Techniques to reduce metal artifact in dGEMRIC were tested in phantom and in vivo. Saturation recovery reduced the extent of metal artifact, allowing dGEMRIC measurement near metal. The mechanical change caused by HTO may increase lateral TF or patellofemoral (PF) loads, which may damage cartilage. Fourteen knees were examined before and after HTO using dGEMRIC. No significant differences were found between pre-operative and either 6- or 12-month results (TF or PF). These results indicate that cartilage may not be degenerating in the short term with HTO. Clinical measures of mechanical changes with HTO are often frontal radiographs obtained in one joint position. Three-dimensional kinematic changes associated with HTO are unknown. Using a validated MR kinematics method, fourteen knees were examined before and after HTO. Seven of 11 kinematic parameters (TF and PF) showed significant differences between pre-operative and both 6- and 12-month follow-ups. These 3D changes may relate to clinical success; identifying these relationships may lead to improvements in HTO. Knee kinematics are often assessed from a series of static positions. However, differences may exist between kinematics estimated from static poses and those from movement. A new dynamic method was developed to evaluate differences between static and dynamic kinematics in normal knees (n = 10). Eight of 11 kinematic parameters showed significant differences between dynamic and static kinematics. Dynamic 3D kinematics are often different from static results, and may provide information not obtainable from static scans. In conclusion, numerous changes in knee joint kinematics and no apparent changes in cartilage health are associated with HTO within one year. Methods developed may help answer important questions about other orthopaedic disorders.
Osteoarthritic (OA) subchondral bone is marked by mechanical and morphological alterations which are thought to influence cartilage integrity, leading to degeneration. The exact role of subchondral bone in OA etiology is, however, unclear and much of our understanding of OA-related subchondral bone changes has come from animal models or cadaveric specimens as opposed to in vivo assessments of people living with OA. The objectives of this thesis were to 1) develop a noninvasive clinical imaging tool capable of measuring proximal tibial subchondral bone density—a surrogate measure of bone stiffness, 2) compare subchondral bone density differences between normal and OA knees using this novel imaging technique with an existing maximum intensity projection technique, 3) determine the ex vivo and in vivo precision of proximal tibial subchondral bone density measures using this novel imaging technique, and 4) determine whether this novel imaging technique can be used to predict bone stiffness values obtained using mechanical indentation testing. We developed the novel imaging tool: computed tomography topographic mapping of subchondral density (CT-TOMASD), which characterizes and maps 3D subchondral bone mineral density (BMD) in relation to depth from the subchondral surface. Ex vivo comparisons between OA and normal knees revealed significantly higher density (17-36%) in OA knees. CT-TOMASD was more proficient than the maximum intensity projection technique at distinguishing density pattern differences between OA and normal knees. CT-TOMASD precision errors were
Mechanical-based treatment strategies for patellofemoral osteoarthritis (OA) have had limited success. This is likely because the magnitude of mechanical change required to improve clinical symptoms has not been quantified because, until recently, the tools required to do so were not available. The aim of this thesis was to develop and characterize MRI-based assessments of in vivo joint mechanics (three-dimensional patellar kinematics and contact areas) that can be used in studies of patellofemoral OA. Three studies of three-dimensional patellar kinematics were carried out. Study 1 examined the effect of load on kinematic measurements. The results showed that increased load caused patellae to flex, tilt medially and translate proximally and posteriorly (p
Cam femoroacetabular impingement (FAI) is a mechanical process thought to cause of hip osteoarthritis (OA). In cam FAI, it is thought that a ‘cam deformity’ on the femoral head-neck junction intrudes into the intra-articular joint space, inducing elevated mechanical force on acetabular cartilage. However, few experimental studies have measured contact mechanics in FAI. Open MRI in functional positions has potential to directly and non-invasively assess cam FAI, but MRI measures have not been related to mechanics. This thesis asked, in cadaver hips positioned in a simulated anterior impingement posture: (1) Does open MRI show intrusion of a cam deformity into the intra-articular joint space? (2) Is a cam deformity associated with elevated acetabular contact force? (3) Are MRI measures of cam FAI related to acetabular contact force?Cadaver hips (cam, n=9; controls, n=3) were positioned in a simulated anterior impingement posture, then imaged using open MRI with multi-planar reformatting. The β-angle was measured at 72 locations about the circumference of the femoral neck, and a binary ‘MRI cam-intrusion sign’ was defined (positive if βmin20N) defined elevated contact force.Minimum β-angle ranged from 1.4° to -28.5° in cams versus 4.6° to -0.2° in controls. Cam hips were significantly more likely than controls to have a positive MRI cam-intrusion sign (p=0.0182, Fisher’s exact test) and positive contact-force sign (p=0.0083). There was a significant relationship between the MRI cam-intrusion sign and contact-force sign (p=0.033).This thesis established that open MRI measures of cam FAI relate to contact mechanics, indicating that open MRI has significant potential to investigate the biomechanics of cam impingement. Open MRI can be used to establish treatment guidelines and understand why some hips develop OA and some do not.