Anatomic Study of Hip Pericapsular Muscle Arrangement on the Joint Capsule.

Background: Despite the recognized importance of pericapsular muscles in hip stability, their specific roles in stability remain debated. For anatomically elucidating how the pericapsular muscles can act on the femoral head and neck through the joint capsule, this study aimed to investigate pericapsular muscle arrangement on the joint capsule with a positional relation to the femoral head and neck and their histological relationships.

Methods: Eight hips of 7 anatomic donors (average age, 72.5 years) fixed with 8% formalin were analyzed. Five hips were macroscopically assessed to determine the arrangement of the pericapsular muscles (iliopsoas, gluteus minimus, gemelli muscles, obturator internus, and externus) on the joint capsule, and 3 were analyzed histologically.

Results: When viewed from the side of the greater trochanter (posterolateral aspect), the pericapsular muscles were macroscopically arranged spirally and ran clockwise around the femoral neck axis on the joint capsule of the right hip. The gluteus minimus had histological continuity to the joint capsule through the tendon. The other pericapsular muscles, including the iliopsoas, obturator externus, and complex of the obturator internus, had histological continuity to the joint capsule through their perimysium.

Conclusions: The pericapsular muscles were arranged on the joint capsule in a spiral pattern, with histologically close continuity to the joint capsule through the perimysium or tendon.

Clinical relevance: The contraction force of the pericapsular muscles may be generated spirally with their centripetal force because they maintain their spiral running course through histological continuity. The pericapsular muscles may be vital in maintaining the centric position of the femoral head by balancing their centripetal forces through the joint capsule.