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Portrait of Hip joint

Anatomy · Joints & cartilage

Hip joint

The deepest ball-and-socket joint

Lower limb · pelvis to thigh

The hip joint is a multiaxial ball-and-socket joint between the spherical head of the femur and the deep cup of the acetabulum of the hip bone. Where the shoulder trades stability for mobility, the hip favours stability: a deep socket, a fibrocartilage labrum and some of the strongest ligaments in the body hold it in place while still allowing flexion, extension, abduction, adduction and rotation.

How to spot them

  • ▸A spherical femoral head, angled inwards on a neck, seats deeply in the acetabulum
  • ▸The acetabular labrum, a fibrocartilage rim, deepens the socket further
  • ▸Three capsular ligaments (iliofemoral, pubofemoral and ischiofemoral) spiral round the joint
  • ▸A small ligament of the head of the femur runs from the acetabular notch to a pit on the head

What to know

A ball-and-socket joint whose socket is so deep that the ball is more than half enclosed

Hip joint — the acetabulum and femoral head.

Its Y-shaped ligament, running from the anterior inferior iliac spine to the intertrochanteric line, is often called the strongest in the body

Hip joint — the iliofemoral ligament.

A fibrocartilage rim deepens the cup, and a small round ligament carries an artery to the head

Hip joint — acetabular labrum and ligament of the head of femur (ligamentum teres).

A break through the neck of the femur can cut off the blood supply to the ball, risking death of the bone

Hip joint — avascular necrosis after femoral neck fracture.

Sir John Charnley's low-friction arthroplasty at Wrightington made replacement of this joint a routine operation

Hip joint — total hip replacement.

Key ideas

  • Stable by design: deep bony socket, labrum, capsule and three strong ligaments make dislocation much rarer than at the shoulder.
  • Blood supply to the femoral head comes mainly from retinacular branches running up the neck, so femoral neck fractures endanger it.

Quick-fire facts

  • •The hip is a multiaxial ball-and-socket synovial joint between the head of the femur and the acetabulum of the hip bone.
  • •The acetabular labrum is a fibrocartilage lip on the outer margin of the acetabulum that deepens the socket (OpenStax).
  • •The iliofemoral ligament (Y ligament of Bigelow) is generally described as the strongest ligament in the human body.
  • •The ligament of the head of the femur (ligamentum teres) carries a small artery to the femoral head, more important in children.
  • •Developmental dysplasia of the hip is a shallow acetabulum, screened for in newborns.
  • •Sir John Charnley pioneered the modern total hip replacement in the 1960s.
  • •Hip dislocation is usually posterior and needs great force, such as a car dashboard injury.

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Sources