Influence of iliofemoral ligament laxity on hip joint contact forces during gait.

The iliofemoral ligament (ILFL) is crucial for hip joint stability, and its laxity contributes to hip joint instability. However, the effects of ligament laxity on hip kinetics remain unclear. This study aimed to develop a musculoskeletal model incorporating the ILFL and investigate the effects of ILFL laxity on hip contact forces (HCFs) during gait. Gait data were collected from 22 healthy young adults, and 21 participants with complete data were used for subsequent analyses. A musculoskeletal model incorporating the ILFL was used to investigate HCFs and muscle forces during gait. Statistical Parametric Mapping Paired t-test was used to compare HCFs and muscle forces during the stance phase of gait between a model with normal ILFL properties (normal model) and a model with ILFL laxity (laxity model). ILFL force was significantly lower in the laxity model than in the normal model. The laxity model exhibited a significant increase in the anterior HCF and a significant decrease in the medial HCF during the latter half of the stance phase. Muscle forces in the hip flexors and abductors were significantly increased. ILFL laxity increased the anterior HCF and decreased the medial HCF. These changes may contribute to instability, anterior soft-tissue injuries, and secondary hip muscle disorders.