Date of Award
Doctor of Philosophy (PhD)
Developmental dysplasia of the hip (DDH) is characterized by abnormal bony anatomy, causes pain and functional limitations, and is a prominent risk factor for premature hip osteoarthritis. Although the pathology of DDH is believed to be mechanically-induced, little is known about how DDH anatomy alters hip biomechanics during activities of daily living, partly due to the difficulties with measuring hip muscle and joint forces. Musculoskeletal models (MSMs) are useful for dynamic simulations of joint mechanics, but the reliability of MSMs for DDH research is limited by an accurate model representation of the unique hip anatomy. To address such challenges, this research used subject-specific MSMs to identify how DDH hip biomechanics are influenced by the abnormal bony anatomy. First, to determine the importance of model specificity, personalized MSMs using image-based bony anatomy and muscle paths were compared against MSMs with generic anatomy. MSMs with subject-specific anatomy estimated significantly different hip muscle and joint forces compared to generic models, thus are necessary for delineating DDH-specific pathomechanics. Next, image-based MSMs were used to calculate hip muscle moment arm lengths and lines of action during gait, to determine how DDH alters dynamic muscle force production. Hips with DDH had reduced abductor moment arms, which elevated muscle and joint forces in the medial direction. Results confirmed hip muscles’ contributions to joint overloading, which could in turn interact with the abnormal anatomy to induce pathomechanics at the articular level. To verify this phenomenon, hip loading estimated from MSMs was projected to the pelvis anatomy to predict acetabular edge loading during two movement tasks, gait and double-legged squat. Results showed that edge loading was elevated by the shallow acetabulum of DDH, and was highly dependent on the kinetics and muscle demand of task-specific movements. These findings could help explain the prevalence of region-specific labral tears in DDH. Overall, this research provided new insights into the relationships among bony anatomy, muscle function, and joint biomechanics in hips with DDH. The outcomes can refine our understanding of mechanically-induced DDH pathology, and inform patient-specific clinical assessments and treatments to improve long-term hip joint health.
Michael D. Harris
Spencer P. Lake, Philip V. Bayly, Marcie Harris-Hayes, Cecilia Pascual-Garrido,