EP9.6 Dynamic Hip Capsule Ligament Strain Throughout the Gait Cycle: A Biomechanical Analysis and Correlation with Radiographic Parameters

Abstract Background/Purpose The hip capsule—comprising the iliofemoral, ischiofemoral, and pubofemoral ligaments—is a critical stabilizing structure contributing to joint congruency across varying positions and functional demands. Prior work has demonstrated that capsular ligaments adapt dynamically during gait; however, the phase-specific strain behavior of each distinct ligament and its relationship to bony morphology remains poorly characterized. The purpose was to quantify dynamic strain patterns of the three primary hip capsular ligaments at discrete gait cycle phases and correlate peak strain with radiographic parameters including acetabular version and lateral center-edge angle (LCEA). Methods Synchronized biplane radiographs (100 images/second) were collected during treadmill walking in 24 asymptomatic participants. CT-derived 3D bone models were segmented and marked at insertion sites for the medial and lateral bands of the iliofemoral ligament, as well as the pubofemoral and ischiofemoral ligaments. Dynamic strain was calculated from inter-insertion distances referenced to static standing. A wrapping surface defined by femoral head radius, fixed to the femoral head center and aligned along the head-neck axis, was incorporated to prevent lateral iliofemoral band penetration of bony surfaces during motion. Multivariable mixed-effects linear regression correlated peak strain with femoral version, acetabular version, and LCEA across four discrete gait phases: heel strike (0%), contralateral toe-off (25%), contralateral heel strike (50%), and swing phase (75%). Statistical significance was set at p<0.01 following Bonferroni correction. Results Mean peak iliofemoral strain (9.5%; SD 4.08) occurred at 51.5% of the gait cycle; ischiofemoral peak strain (4.7%; SD 8.73) at 35.5%; and pubofemoral peak strain (5.7%; SD 4.14) at 57.4%. Iliofemoral strain was significantly reduced with hip flexion at the 25%, 50%, and 75% phases, and with internal rotation and adduction across all phases. Smaller LCEA correlated with higher peak iliofemoral strain (r = 0.42, P<0.01). Conclusion Individual hip capsular ligaments experience distinct strain patterns at specific gait cycle phases, with the iliofemoral ligament most substantially loaded during terminal stance. The correlation between reduced acetabular coverage and greater ligament strain underscores the role of bony morphology in capsular loading. These findings can guide clinicians in identifying high-risk hip positions and informing phase-specific rehabilitation following capsular injury or repair.