Interosseous sacro-iliac ligament

At a glance

English

Interosseous sacro-iliac ligament

Latin (TA2)

Ligamentum sacroiliacum interosseum

System

Ligament

Region

Abdomen

Side

Paired, left and right

About the interosseous sacro-iliac ligament

Behind the ear-shaped joint surfaces of the sacro-iliac joint, the sacrum and ilium face each other across a narrow, rough-walled cleft. This space is filled by the interosseous sacro-iliac ligament, sometimes called the axial interosseous ligament. It lies deep to the posterior sacro-iliac ligament, which covers it from behind, and above and behind the synovial part of the joint. Few ligaments anywhere in the body are as strong.

Its fibres are short and dense and run between the tuberosity of the sacrum, the roughened area behind the auricular surface on the lateral part of the sacrum, and the iliac tuberosity, the matching area on the inner surface of the ilium above and behind its auricular surface. Most fibres lie almost horizontal, crossing the gap at right angles to the two bones. Fat and small vessels lie between its bundles, and the posterior rami of the sacral nerves run near its back surface.

The ligament chiefly serves to hold sacrum and ilium firmly against each other. It prevents the joint surfaces being pulled apart, so that the sacrum, wedged between the hip bones, can carry weight without slipping. The weight of the head, upper limbs and trunk passes down the vertebral column into the sacrum, and from there through these fibres into the ilia and on to the lower limbs. Because the fibres hang the sacrum between the iliac tuberosities, load tends to tighten them and press the joint surfaces together.

Seen on CT scans, the ligament region is often where the joint first fuses in older age. Its strength means that injuries usually involve fractures of the nearby bone rather than tearing of the ligament itself.

Attachments and function

Attaches from

The sacral tuberosity, the rough area behind the auricular surface of the sacrum.

Attaches to

The iliac tuberosity, on the inner surface of the ilium above and behind the auricular surface.

Function

Holds the sacrum and ilium together, prevents distraction of the sacro-iliac joint and carries the weight of the upper body from the sacrum into the hip bones.

Nerve supply

Lateral branches of the posterior rami of the upper sacral nerves.

Blood supply

Branches of the lateral sacral and superior gluteal arteries.