Capsule of hip joint

The capsule of hip joint, articular capsule, or capsular ligament is strong and dense attachment of the hip joint.

Anterosuperiorly, it is attached to the margin of the acetabulum 5 to 6 mm beyond the labrum behind; but in front, it is attached to the outer margin of the labrum, and, opposite to the notch where the margin of the cavity is deficient, it is connected to the transverse ligament, and by a few fibers to the edge of the obturator foramen.

It surrounds the neck of the femur, and is attached, in front, to the intertrochanteric line; above, to the base of the neck; behind, to the neck, about 1.25 cm above the intertrochanteric crest; below, to the lower part of the neck, close to the lesser trochanter.

From its femoral attachment some of the fibers are reflected upward along the neck as longitudinal bands, termed retinacula.

The capsule is much thicker at the upper and forepart of the joint, where the most resistance is required; behind and below, it is thin and loose.

It consists of two sets of fibers, circular and longitudinal.

The circular fibers, zona orbicularis, are most abundant at the lower and back part of the capsule, and form a sling or collar around the neck of the femur.

Anteriorly they blend with the deep surface of the iliofemoral ligament, and gain an attachment to the anterior inferior iliac spine.