The Hip-Joint takes place between the head of the femur and the acetabulum of the innominate bone.

Fig. 18. Hip Joint.

It is a true ball-and-socket joint, so has movement round three axes:

Transverse - flexion and extension.

Antero-posterior - abduction and adduction.

Vertical - rotation in and out.

Ligaments

The Transverse Ligament is composed of strong fibres, which bridge across the notch in the margin of the acetabulum, leaving a gap through which vessels and nerves can pass.

The Cotyloid Ligament surrounds the margin of the acetabulum and deepens the socket. Its free edge is somewhat constricted, and grasps the head of the femur.

A capsule completely surrounds the joint. It is considerably thicker superiorly. This capsule differs from that of the shoulder-joint in not allowing the ball to be drawn from the socket to any considerable extent. The ligament is attached above to the margin of the acetabulum and below to the cotyloid and transverse ligaments. On the neck of the femur it is attached above to the root of the great trochanter, in front to the intertrochanteric line, below to the root of the small trochanter, and behind a little way above the intertrochanteric ridge. The fibres of the capsule are arranged in both the circular and longitudinal directions to give additional strength, and definite bands of longitudinal fibres are strengthened as-follows:

The Ilio-Femoral ligament (Y-shaped ligament of Bigelow) is a triangular ligament attached by its apex to the root of the anterior inferior spine and margin of the acetabulum and by its base to the intertrochanteric line. At the base the sides are thicker than the centre, hence its name.

The Pubo-Femoral ligament, attached to the acetabular end of the ramus of the pubis and the inferior aspect of the neck of the femur.

The Ischio-Capsular ligament attached above to the ischium just in front of the small sciatic notch; the lower end becomes merged in the capsule.

The Ligamentum teres is a flattened band of tissue attached by one end to the fossa on the summit of the head of the femur and by the other end to the sides of the notch in the margin of the acetabulum. A pad of fat occupies the bottom of the acetabulum.

The synovial membrane completely lines the joint and the ligaments, and hangs in loose folds between the articular margin and the attachment of the capsule on the neck of the femur.