Applied anatomy of the hip and buttock

The hip joint is a ball-and-socket joint, formed by the femoral head and the acetabulum (Fig. 1, see Standring, Fig. 80.15). The articular surfaces are spherical with a marked congruity; this limits the range of movement but contributes to the considerable stability of the joint. In the anatomical position, the anterior/superior part of the femoral head is not covered by the acetabulum. This is because the axes of the femoral head and of the acetabulum are not in line with each other. The axis of the femoral head points superiorly, medially and anteriorly, while the axis of the acetabulum is directed inferiorly, laterally and anteriorly. The cup-shaped acetabulum is a little below the middle third of the inguinal ligament. The acetabular articular surface is an incomplete cartilaginous ring, thickest and broadest above, where the pressure of body weight falls in the erect posture, narrowest in the pubic region. The rough lower part of the cup, the acetabular notch, is not covered by cartilage. The centre of the cup, the acetabular fossa, is also devoid of cartilage but contains fibroelastic fat. The acetabular labrum, a fibrocartilaginous ring attached to the acetabular rim, deepens the cup and enlarges the contact area with the femoral head (see Standring, Fig. 81.5). The part of the labrum that bridges the acetabular notch does not have cartilage cells and is called the transverse acetabular ligament. If forms a foramen through which vessels and nerves may enter the joint. The acetabular labrum is triangular in section. The base is attached to the acetabular rim and the apex is free. The femoral head is ovoid or spheroid but not completely congruent with the reciprocal acetabulum. It is covered by articular cartilage except for a rough pit for the ligamentum teres, a flattened fibrous band, embedded in adipose tissue and lined by the synovial membrane (Figs 2, 3). The ligament connects the central part of the femoral head with the acetabular notch and its transverse acetabular ligament. The ligament is extra-articular and contains a tiny branch of the obturator artery partly responsible for the vascular supply of the femoral head. The femoral head and neck also receive arterial supply from the capsular vessels, arising from the medial and lateral circumflex arteries (see Fig. 3).