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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.
Graduate Student Supervision
Doctoral Student Supervision
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.
Adult spinal deformity (ASD) affects 60% of aging adults, with many researchers and clinicians acknowledging the importance of the lumbopelvic musculature. This work investigated morphometry of lumbopelvic muscle in ASD patients in upright functional postures in comparison to supine using upright magnetic resonance imaging (MRI), with foundational feasibility studies in asymptomatic individuals. A secondary aim explored markers of muscle activity from upright MRI. Subjects (asymptomatic: 6 lumbar, 6 lumbopelvic, 7 upper arm; ASD: 8 lumbopelvic), were scanned in a 0.5T upright MRI (MROpen, Paramed) in various upright and supine postures. Measures included muscle morphometry (cross-sectional area (CSA), position) for the multifidus/erector spinae, psoas major, gluteus, and iliopsoas L3/L4-S4/S5, and bony geometry. Repeatability was assessed using intraclass correlation coefficient (ICC(3,1)), effects of posture and muscle activity were evaluated by ANOVA(p
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
Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Spinal muscles play an important role in two inter-related clinical problems in the thoracolumbar spine: 1) age-related progressive kyphosis and 2) proximal junctional kyphosis (PJK) following correction surgery. Although these disorders occur largely in the thoracic spine and show symptoms in weight-bearing postures, studies have not investigated thoracic muscles in postures other than supine. Moreover, almost all the image-based thoracolumbar models are developed from muscle data obtained from supine imaging, which questions its credibility. Hence the objectives of this study were to i) analyze the effect of posture on thoracic spinal muscle parameters in different postures, and ii) develop a method for translation of MRI-derived spinal and muscle data into a thoracolumbar biomechanical model. Two regions (T4-T5 and T8-T9) of the thorax of six healthy volunteers were imaged (0.5T MROpen, Paramed, Genoa, Italy) in four postures (supine, standing, sitting, and flexion). Descriptive guidelines were developed to identify and quantify three muscles- trapezius (TZ), erector spine (ES), and transversospinalis (TS) from axial MR images. Intra- and Inter- segmentation repeatability was assessed using ICC(3,1). The effect of spinal level and posture on muscle parameters (cross-sectional area (CSA) and position (radius and angle)) was evaluated using 2-way repeated measures ANOVA (p
Introduction: Osteoarthritis (OA) is the most prevalent joint disease in Canada, affecting millions of people. OA begins with softening of cartilage and is characterized by progressive loss of the tissue resulting in joint impairment. Because cartilage’s primary function is mechanical, and because OA disrupts cartilage’s mechanical function, there is a substantial need for a non-invasive method to assess cartilage mechanics. Contrast-enhanced computed tomography (CECT) using charged contrast agents is an imaging method developed to quantify Glycosaminoglycan (GAG) content of cartilage.Since GAG is a key determinant of cartilage compressive stiffness, CECT measurements may be correlated with cartilage stiffness. The objective of this study was to determine whether CECT using a novel cationic contrast agent (CA4+) is correlated with cartilage stiffness in intact human joint surfaces.Methods: Six human femoral condyle compartments with intact healthy cartilage (ICRS grade 0 or 1) were used. Cartilage stiffness was measured across the surface in a Mach-1 testing system(Biomomentum, Montreal) using an indentation test. The samples were then immersed in CA4+ solution for 48 hours and then scanned at 41μm resolution in a hr-pQCT scanner (Xtreme CT,Scanco, Zurich). The averages of CECT attenuations at the sites of the indentation tests were computed for both superficial cartilage (600μm depth) and for the full thickness of cartilage.Correlations between stiffness and CECT attenuation were assessed with scatter plots and Pearson’s correlation coefficient.Results: A significant and positive correlation was observed between stiffness data and mean CECT attenuations in superficial cartilage across all samples, with correlation coefficients ranging fromr=0.4 to 0.72, and 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.
Introduction: Medial opening-wedge high tibial osteotomy (HTO) is a surgical procedure intended to shift load from the medial to the lateral compartment of the knee. The 10-year success rates of HTO are variable. One factor affecting success may be how effectively the procedure corrects alignment in the coronal plane (wedge angle) and sagittal plane (slope angle). The objective of this study was to determine the effect of changing tibial slope for a range of tibial wedge angles in medial opening wedge HTO on knee joint contact pressure location and kinematics during continuous loaded flexion/extension.Methods: The accuracy and repeatability of Novel pliance capacitive pressure sensors were measured under relevant compressive forces using a materials testing system (Instron ElectroPuls E10000). Seven male cadaveric knee specimens (mean age 62 (14)) cycled through simulated squatting. Tibiofemoral and patellofemoral kinematics were measured using an infrared (Optotrak Certus) motion tracking system. Contact pressure was measured using capacitive pressure sensors (Novel Pliance). This assessment was repeated for seven clinically relevant combinations of wedge and slope. Results: The capacitive pressure sensors had a maximum error of 13 ± 2.1% when applying force across the entire sensor. Significant differences (p
Excessive or abnormal joint loading that leads to cartilage degeneration has been associated with hip osteoarthritis (OA). Before preventative measures for OA can be designed, such as physiotherapy techniques, braces, or surgical interventions, the connection between load-bearing and cartilage degeneration needs to be validated experimentally. As a first step towards such a validation, a method of measuring the load distribution across the hip joint is needed; ideally that can be used in vivo and can detect changes in the load distribution during an applied load. The objective of this study was to assess the accuracy of using biplanar radiography combined with CT imaging to estimate hip cartilage strain across the joint as an indication of the load distribution. Estimating cartilage strain using biplanar radiography and CT imaging is a multi-device multi-step measurement protocol that has error associated with each step. While biplanar radiography systems are commonly assessed on their ability to measure radio-opaque bead locations, to the author’s knowledge no studies have quantified errors in the additional steps of estimating cartilage strain. The present study used a phantom hip joint to quantify the errors in measuring bone displacement with biplanar radiography, segmenting 3D joint surfaces from a CT image, and measuring the relative proximity of joint surfaces in the biplanar radiography coordinate frame. The quantified errors were much lower than ex vivo hip cartilage deformation results in the literature, which demonstrated the potential for using this technique to estimate cartilage strain in the hip.As a proof of concept, cartilage strain was estimated in the ex vivo hip joint during a compressive load. Two hemi-pelvis/proximal femur specimens, with radio-opaque beads inserted in each bone, were loaded in compression in a materials testing machine, with biplanar radiographs acquired throughout. A small amount of cartilage deformation (0.1mm) was detected across the hip joint; however, due to the low load applied the deformation results were not comparable to the literature. The largest cartilage strains were identified in the anterior and superior regions, which was consistent with the literature. Future studies using higher loads are needed to further assess the capabilities of our system.
Cam-type femoroacetabular impingement is a painful disorder common in young adults, caused by decreased concavity of the femoral head-neck. It is associated with hip osteoarthritis, though the exact mechanism of joint damage is not fully understood. Gait analysis has shown that cam deformities cause changes to coupled motions in vivo, though it is unclear whether these changes are compensatory or due to direct bony contact. The objective of this study was to determine how cam deformities and surgical resection affect patterns of hip rotation, translation of the center of rotation, and force required to flex and abduct the hip.We assessed the relationship between deformity and coupled motions, translations of center of femoral rotation, and force required to create active unconstrained flexion and abduction ex vivo. Three deformities were simulated on each of six hemi-pelvis/proximal femur specimens. Four muscles were simulated by cables drawn from the distal tendon to the location of proximal attachment. Motion was created by actively shortening one of these cables while statically loading the others. Markers on the femur and pelvis were tracked, allowing for calculation of joint rotations and translations. A load cell on the active cable allowed for measurement of the applied force.We found that deformity resulted in increased external rotation, adduction and translation during flexion and increased internal rotation, extension and decreased translation during abduction. We also found that when a more severe deformity was present, more force was required to create both flexion and abduction to the same angle. Further, we found that resection resulted in increased internal rotation and translation during flexion and decreased internal rotation during abduction. Less force was required to create flexion and abduction following resection. Changes to motion patterns occur as a result of changed contact loads between the femoral head and acetabulum, resulting in loading of regions of articular cartilage which may not be optimized for these loads and may, therefore, begin a degenerative cascade leading to osteoarthritis. As coupled motions were observed within ranges of flexion and abduction required for daily living, it is recommended that resection be performed in an attempt to slow the progression of osteoarthritis by limiting contact between the femoral head-neck and acetabulum.
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