Iliocapsularis muscle in human fetuses

Purpose To determine the incidence of the iliocapsularis muscle in fetal period and its relationship with the hip joint capsule. Methods Twenty-one formalin-fixed fetuses (12 female and 9 male) with a mean gestational age of 29 ± 3.89 weeks (range 25–36) were dissected to reveal morphological properties of iliocapsularis muscle. Results Iliocapsularis muscle was observed in 39 out of 42 sides (92%). Its proximal attachment was detected either below the proximal attachment of rectus femoris muscle in 21 out of 39 sides (54%), or it was forming a common tendon with rectus femoris on the anterior inferior iliac spine in 10 out of 39 sides (26%), or it was forming an arch along the superior–medial–inferior sides of the proximal attachment of rectus femoris muscle in 8 out of 39 sides (20%). Muscle fibers originating from the anteromedial part of hip joint capsule were also constant in all sides. Distal attachment of iliocapsularis muscle was distal to the lesser trochanter in all specimens. Its form was as a broad muscle in 32 out of 39 sides (82%) and as a thin rectangular muscular slip in 7 out of 39 sides (18%). Iliopsoas and iliocapsularis muscles had their particular fascia in 34 out of 39 sides (87%), and in the other 5 sides, there was no fascia which prominently separated the two muscles. Its length was longer in females than males ( p = 0.031) and it was wider on the right side ( p = 0.029). Linear functions were y = 0.49 + 0.17 × weeks and y = 6.94 + 0.89 × weeks for width and length, respectively. Conclusion Data obtained with the present study about iliocapsularis muscle in fetal period revealed that it is an individual and constant muscle. Its dimension, location, and course over the hip joint capsule support the idea that it tightens the hip capsule and stabilizes the femoral head.