Contraction of the Deep Hip Muscles Contributes to Hip Capsulo‐Ligamentous Complex Tension In Vivo

The anterior hip muscles, especially the iliocapsularis, reflected head of rectus femoris and gluteus minimus, attach to hip capsulo-ligamentous complex directly, and may contribute to anterior hip stability by increasing the tension of the capsulo-ligamentous complex by muscle contraction. However, it has not been verified whether the contraction of these muscles actually increases the tension of the capsulo-ligamentous complex in vivo. The objectives of our study were to clarify (1) whether deep hip muscle contractions increase the tension of the hip capsulo-ligamentous complex, and (2) which muscles most affect the changes in the tension of the capsulo-ligamentous complex. Twenty-eight healthy young individuals (22.8 ± 1.6 years) participated. The tasks included isometric hip flexion, abduction, adduction, and knee extension contraction and rest in a supine position. The shear elastic moduli (G) of the capsulo-ligamentous complex, iliocapsularis, rectus femoris, and gluteus minimus were measured using shear wave elastography. Higher G values correspond to increased muscle activity and tension of the capsulo-ligamentous complex. The G of the capsulo-ligamentous complex showed higher in hip abduction contraction than in the resting position (p = 0.008). The results of the multiple regression analysis showed that only the amount of change in G of the iliocapsularis was a significant variable, even when adjusted for maximum torque (R² = 0.412, β = 0.513, p = 0.009). The tension of the hip capsulo-ligamentous complex increased with isometric hip abduction, implying tension transfer between the muscle and the capsulo-ligamentous complex. Furthermore, the iliocapsularis has been suggested to play an important role in the transmission of tension.