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. The posterior portion of the pelvis is formed by the sacrum's wedging itself between the two halves of the pelvis. The hip articulation, formed by the femoral head and the acetabulum, is the strongest and most stable of the body's joints. However, this benefit is gained at the expense of range of motion (ROM).
The hip is subject to large 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 Tolerating these forces is possible because of the sturdy bony alignment and ligamentous arrangement of the pelvis coupled with its encompassing dynamic support.
The anterior and lateral portion of the pelvis is formed by two innominate bones, each consisting of the ilium, the ischium, and the 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 by its articulation with the sacrum, a broad, thick bone that fixates the spinal column to the pelvis. The sacrum is responsible for stabilizing the pelvic girdle.
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 posterior border is formed by the sacrum.
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. There is a 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, lines the outer rim of the acetabulum and deepens the acetabulum by approximately 21%.4 The labrum is thicker and stronger superiorly than inferiorly (Fig. 12-2).
Lateral view of the pelvis showing the acetabulum. The acetabular fossa is bordered by the fibrocartilaginous glenoid 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 ...