Establishing simulation-derived acetabular targets for walking and deep squat: a musculoskeletal modeling study

Abstract

Background Deep squats are required for basic activities of daily life, such as toileting and floor work, but the Lewinnek acetabular safe zone was based on static supine radiographs and did not account for dynamic pelvic positioning during functional activities. Consequently, quantitative positioning targets that integrate walking with deep-squat biomechanics remain poorly defined. Methods Simulations were performed in the AnyBody Modeling System using a generic adult musculoskeletal model. Angular Impingement Distance and Angular Edge-loading Distance (AED) were computed at 1° increments across 10,201 acetabular component positions during walking and deep squat. A dual-activity feasible zone was defined as component positions simultaneously satisfying AID- and AED-based criteria for both activities. Sensitivity to femoral head diameter (28, 32, and 36 mm) was evaluated. Results In the normal spinal-mobility scenario, the dual-activity feasible zone contained 231 positions, with a target position at radiographic anteversion (RA) 24° and radiographic inclination (RI) 46°. Only 21.6% of these feasible positions fell within the Lewinnek zone; most required higher anteversion or inclination than the Lewinnek target. In the reduced lumbopelvic-mobility scenario, the feasible zone contained 209 positions with a target position shifted toward higher anteversion and inclination (RA 36°, RI 56°) and no overlap with the Lewinnek zone. Sensitivity to femoral head diameter was substantial: compared with the 28-mm head, the 36-mm head increased the feasible zone 4.2-fold (375 vs. 89 positions), with the 32-mm default yielding 231 positions. Conclusion We present a computational framework for deriving activity-specific acetabular positioning targets from dynamic musculoskeletal simulations of walking and deep squat. The resulting targets are biomechanically grounded but remain simulation-derived hypotheses pending clinical validation.