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Abstract

Objectives: Legg–Calvé–Perthes disease (LCPD) is a pediatric hip disorder that can result in a permanent residual deformity of the hip, which is associated with poor long-term outcomes such as early-onset osteoarthritis (OA). However, the connections between radiographic deformity measures and long-term outcomes are unclear, as three-dimensional (3D) LCPD morphology and its impacts on joint function, cartilage health, and hip biomechanics during activity have not been characterized. Overall goal: to characterize the role of residual deformity in the development of poor long-term outcomes after LCPD. Specific objectives: review the use of statistical shape modelling (SSM) in the hip, develop a framework for SSM in LCPD, determine how hip asphericity affects anterior clearance, determine how cartilage health changes with age in hips with and without LCPD deformity, develop a biomechanical model to predict shear stress during motion. Methods: I performed a scoping review of SSM in the hip and developed a framework for incremental SSM in LCPD patients aged 6-12 years. I scanned adolescents and young adults with LCPD deformity using upright open magnetic resonance imaging (MRI) to measure hip clearance, and assessed cartilage health using T₁𝝆 MRI. I developed a combined finite-element and multibody model and estimated shear stress during walking in both hips of a patient with unilateral LCPD deformity. Results: My SSM framework could represent 3D LCPD morphology accurately using only four modes (compactness 87.5%, generalization 0.99mm, specificity 1.12mm). Hip clearance was lower in hips with aspherical vs spherical deformity (-39.1°; 95% confidence interval (CI) -71.9° to -6.2°). T₁𝝆 decreased with age in hips without LCPD deformity but not in LCPD hips, which had significantly higher projected T₁𝝆 at age 25 (+5.64ms, 95% CI 2.83 to 8.46). Peak maximum-shear stress was influenced by joint motion as well as morphology during gait. Conclusions: SSM is a promising tool to accurately describe 3D pathomorphology in LCPD. Hip joint asphericity is associated with a greater potential for anterior impingement, a key cause of early OA. Changes in T₁𝝆 during adolescence and young adulthood suggest that cartilage degradation is progressive. Including motion improves biomechanical simulations of stress in aspherical LCPD deformity.