Effects of bone deformation on patient-specific finite element predictions of hip chondrolabral mechanics

Patient-specific finite element models of hip cartilage and labrum (chondrolabral) mechanics have improved the understanding of form-function relationships underpinning hip osteoarthritis. While these models often assume the pelvis and femur are rigid bodies to reduce development and computational time, contact stresses may be overestimated when the pelvis and femur cannot deform. Recent advancements in element formulations, constitutive models, and integration of patient-specific boundary/loading conditions warrant a re-examination of this rigid body assumption. We assessed the influence of material representations for the pelvis and femur on finite element predictions of chondrolabral mechanics during level walking and squatting. Four material representations were evaluated: (1) rigid bodies, (2) deformable-inhomogeneous with CT-derived material properties, (3) deformable-two-material with distinct trabecular and cortical bone materials, and (4) deformable-one-material model. Patient-specific kinematics and joint reaction forces for level walking and squatting were derived from motion capture and musculoskeletal models, respectively. During level walking, there were no significant differences between bone material representations for maximum cartilage contact pressure, contact area, shear stress, or first principal strain. During squatting, rigid and one-material models produced significantly higher maximum contact pressures, while other metrics remained unaffected. Rigid models required significantly less computational runtime and memory than deformable models. Our findings indicate rigid bone assumptions suffice for level walking, improving efficiency in large cohort studies, but deformable bone models are likely warranted for activities that produce larger bone deformations such as squatting. This study provides guidance for selecting bone material representations that balance accuracy and computational efficiency in hip biomechanical analyses.