The hip, a synovial ball-and-socket joint, is vital to static and dynamic postural control as it supports the weight of the trunk and facilitates load transmission between the trunk and lower extremities. During ambulation, the hip is subject to significant ground reaction forces. When standing on one leg, three to four times the body weight is transmitted through the hip,1 and, when jogging, up to eight times the body weight is transmitted through each joint.2
The pelvic girdle forms the structural base of support between the lower extremities and the trunk. A relatively immobile structure, the pelvis is formed by pairs of three fused bones joined anteriorly by the pubic symphysis and posteriorly by the sacrum. The hip articulation, formed by the femoral head and acetabulum, is the strongest and most stable joint in the body. However, stability is gained at the expense of range of motion (ROM).
The anterior and lateral portion of the pelvis is formed by two innominate bones, each consisting of the ilium, ischium, and pubis (Fig. 12-1). These bones fuse during the teenage years, but their two primary bony prominences, the ischial tuberosity and anterior superior iliac spine (ASIS), may not fuse until the third decade of life.2 The posterior junction of the pelvic girdle is formed and stabilized by its articulation with the sacrum, a broad, thick bone that fixates the spinal column to the pelvis.
Anterior view of the bony pelvis. A total of seven bones form the pelvis: Two ischial, two pubic, and two ilial bones form each half, and the sacrum, forming the posterior border. The pubic, ilium, and ischial bones fuse to form the acetabulum.
On the lateral aspect of the pelvis, the acetabulum, a downwardly and outwardly directed depression, accepts the femoral head within its fossa. The superior wall of the acetabulum is formed by the ilium, the inferior wall by the ischium, and the internal (medial) wall by the pubis, with discontinuity inferiorly. This space is spanned by the transverse ligament.3 A depression for the ligamentum teres is centered within the fossa. The labrum, a thick ring of fibrocartilage with more substantial superior and inferior areas, lines the outer rim of the acetabulum and deepens the acetabulum by approximately 21% (Fig. 12-2).4
Lateral view of the pelvis showing the acetabulum. The acetabular fossa is bordered by the fibrocartilaginous acetabular labrum.
The femoral head is globular, with an articular surface that is slightly over a 180-degree arc in diameter. Its articulating surface is thickly covered with hyaline cartilage except for a ...