Ligament of head of femur

At a glance

English

Ligament of head of femur

Latin (TA2)

Ligamentum capitis femoris

System

Ligament

Region

Lower limb

Side

Paired, left and right

About the ligament of head of femur

Also called the round ligament or ligamentum teres, this band lies inside the hip joint. It is a flattened band roughly triangular in outline. Its narrow end is fixed to the front and upper part of the fovea, the small pit near the centre of the femoral head. Its broad end splits into two bands that attach to the two margins of the acetabular notch, the gap at the lower rim of the socket, and between them it merges with the transverse acetabular ligament.

The ligament lies in the fat-filled acetabular fossa and is wrapped in a sleeve of synovial membrane, so it sits within the joint cavity but outside its synovial space. Its strength varies widely: in some people it is substantial, in others little more than a synovial fold, and occasionally even the fold is missing. It carries a small artery to the femoral head, a branch that the obturator artery sends into the acetabulum.

The ligament tightens when the thigh is half bent and then drawn inwards or rotated outwards, and it slackens when the limb is moved away from the midline. It was long thought to add little to the stability of the adult hip, where the three capsular ligaments do most of the work against dislocation. More recent studies suggest it does help to stabilise the joint, especially in the extreme ranges of movement.

Its artery matters for nourishing the femoral head during childhood, but in most adults it is too small to keep the head alive alone, which is why a displaced fracture of the femoral neck can lead to avascular necrosis of the head. Tears of the ligament are recognised as a cause of deep hip pain and are found and treated at hip arthroscopy. In infants with developmental dysplasia of the hip, a thickened ligament can block the head from returning to the socket.

Attachments and function

Attaches from

The upper front part of the fovea on the femoral head.

Attaches to

Both margins of the acetabular notch, blending with the transverse acetabular ligament.

Function

Carries a small artery to the femoral head and adds some stability at the extremes of hip movement; taut in flexion with adduction or external rotation.

Blood supply

The obturator artery's acetabular branch, which runs within it to the femoral head.