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.