Anterior sacro-iliac ligament

At a glance

English

Anterior sacro-iliac ligament

Latin (TA2)

Ligamentum sacroiliacum anterius

System

Ligament

Region

Abdomen

Side

Paired, left and right

About the anterior sacro-iliac ligament

The sacro-iliac joint links the side of the sacrum to the inner face of each hip bone, and three ligaments hold it together: anterior, interosseous and posterior. The anterior sacro-iliac ligament is by far the weakest of the three. It is little more than a thickening of the front of the joint capsule, made of many thin, flat bands that run across the joint line on its pelvic surface.

The bands begin on the pelvic face of the sacrum's lateral part, the region formed by the ala and the lateral mass beside the sacral foramina. They pass outwards and slightly downwards to the ilium, where they attach along the edge of the ear-shaped auricular surface and into the preauricular (paraglenoid) sulcus, a shallow groove just below the joint. Above, the lowest fibres of the iliolumbar ligament blend with its upper part.

Being on the pelvic side, the ligament has important neighbours. The psoas major and iliacus lie in front of its upper part, and the lumbosacral trunk and the first sacral ventral ramus descend across it into the pelvis. The internal iliac vessels and their branches lie close by. Because of these relations, inflammation or injury of the front of the joint can irritate the nerves passing over it, and pain may be felt in the buttock or thigh.

The ligament resists the joint opening at the front and helps keep the auricular surfaces in contact, but most of the joint's strength comes from the much heavier interosseous and posterior ligaments behind. In ankylosing spondylitis the front of the sacro-iliac joint, including this ligament, is often among the first places to show inflammation and later bony fusion.

Attachments and function

Attaches from

The pelvic face of the sacrum's lateral part, beside the sacral foramina.

Attaches to

The ilium along the front margin of the auricular surface and in the preauricular (paraglenoid) sulcus.

Function

Binds the front of the sacro-iliac joint and resists its anterior surfaces separating, a minor support compared with the ligaments behind.

Nerve supply

The front of the joint receives small branches from the lumbosacral trunk and upper sacral ventral rami.

Blood supply

Branches of the iliolumbar and lateral sacral arteries.