Microscopic analysis of the iliofemoral and ischiofemoral ligaments in the hip joint: collagen fiber direction and crimp distribution

Since no previous studies have described the functional significance of the iliofemoral and ischiofemoral ligaments on the basis of microscopic analyses, we examined the direction of collagen fiber alignment and crimp distribution of the collagen fibers in sections cut in different directions. Polarized microscopic images of sections along the longitudinal (L) and transverse (T) planes of each ligament were obtained from 20 cadavers (8 males and 12 females, age at death 81.7 ± 9.4 years old). Results showed that the microscopic direction of collagen fibers in the iliofemoral ligament was parallel to the macroscopic direction, suggesting that this ligament may play a part in restricting extension of the hip joint. In contrast, the microscopic direction of collagen fibers in the ischiofemoral ligament was not parallel to the macroscopic direction, suggesting that this ligament may contribute not only to the restriction of medial rotation but also retstriction of flexion of the hip joint. From the low density of the crimp distribution in the L plane, the iliofemoral ligament may contribute to stability of the hip joint in the standing position in the living body. In conclusion, the microscopic observations of the direction of collagen fibers as well as the crimp distribution shown in the present study provide a better understanding of the functional significance of the iliofemoral and ischiofemoral ligaments.