Articular capsule of hip joint

At a glance

English

Articular capsule of hip joint

Latin (TA2)

Capsula articularis coxae

System

Joint

Region

Lower limb

Side

Paired, left and right

About the articular capsule of hip joint

The articular capsule of the hip joint is a dense cylinder of fibrous tissue enclosing the ball-and-socket joint of femoral head and acetabulum. On the pelvis it attaches just outside the acetabular labrum, to the bone of the rim and to the transverse acetabular ligament across the notch, so the labrum lies inside the joint. On the femur it reaches the intertrochanteric line in front, but behind it stops partway along the neck, about a finger's breadth above the intertrochanteric crest. The distance from the cartilage of the head to the capsular attachment is much the same all round, which leaves a larger bare area of neck behind than in front.

The capsule has two layers of fibres. Longitudinal fibres run from pelvis to femur and are thickest above and in front, where the joint is most loaded; behind and below the capsule is thinner and looser. Deep circular fibres form the zona orbicularis, a collar that grips the narrowest part of the neck. Some longitudinal fibres turn back along the neck as retinacula, carrying the vessels that nourish the femoral head.

Three ligaments blend with the capsule and greatly strengthen it: the Y-shaped iliofemoral ligament in front, among the strongest in the body, the pubofemoral ligament below and in front, and the ischiofemoral ligament behind. All three wind round the neck and tighten when the hip is extended, so a standing person can lean back on them with little muscle effort. They loosen when the hip is flexed, which is why the joint rotates more freely in that position. Inside the capsule runs the round ligament, from the acetabular notch to the femoral head.

Fractures of the femoral neck that lie inside the capsule can tear the retinacular vessels and leave the femoral head short of blood, risking avascular necrosis. A tight, swollen capsule causes the hip to be held flexed and slightly rotated, the position of least tension.

Attachments and function

Formed by

Attached to the rim of the acetabulum outside the labrum and to the transverse acetabular ligament.

Joins

Attached to the intertrochanteric line in front and to the back of the femoral neck above the intertrochanteric crest.

Movements

Encloses the hip joint, holds the femoral head in the socket, and with its ligaments limits extension and excess rotation while bearing body weight.

Nerve supply

Articular branches of the femoral, obturator and sciatic nerves, and the nerve to quadratus femoris.

Blood supply

The medial and lateral circumflex femoral arteries, with branches of the obturator and gluteal arteries; retinacular branches run along the neck to the head.