Iliolumbar ligament

At a glance

English

Iliolumbar ligament

Latin (TA2)

Ligamentum iliolumbale

System

Ligament

Region

Abdomen

Side

Paired, left and right

About the iliolumbar ligament

The iliolumbar ligament ties the lowest lumbar vertebra to the pelvis and is one of the main restraints of the lumbosacral junction. It starts at the outer end of the L5 transverse process and fans out as it runs laterally. A small extra band from the fourth lumbar transverse process to the crest, behind the main ligament, is sometimes present; fibrous strands are often found there, but they count as a true ligament only when they are dense.

The ligament usually splits into two main parts as it reaches the pelvis. The upper band reaches the iliac crest near its rear end, on its inner lip, just in front of the sacro-iliac joint, and above it is continuous with the thoracolumbar fascia, of which it forms the thickened lower edge. The lower band, sometimes called the lumbosacral ligament, runs down and outwards onto the sacral base and ala, where it merges with the anterior sacro-iliac ligament.

Psoas major lies in front of it, quadratus lumborum takes part of its origin from its upper surface, and the deep back muscles of the vertebral groove lie behind it. The lumbosacral trunk passes down just medial to the lower band.

Together with the lateral lumbosacral ligament and the ordinary ligaments of the spine, such as the longitudinal ligaments, yellow ligaments (ligamenta flava) and the bands between and over the spinous processes, it steadies the joint between L5 and the sacrum. It limits bending to the side and rotation of L5 and resists the vertebra sliding forwards on the sloping top of the sacrum. Strain of the ligament is a recognised cause of low back pain felt at the back of the iliac crest, and it can be a source of pain in spondylolisthesis.

Attachments and function

Attaches from

The tip and front of the fifth lumbar transverse process, occasionally with a slip from L4.

Attaches to

The posterior part of the iliac crest, on its inner lip, in front of the sacro-iliac joint, and, by its lower band, the sacral base, where it merges with the anterior sacro-iliac ligament.

Function

Anchors L5 to the pelvis, limiting side bending, rotation and forward slip at the lumbosacral joint.

Nerve supply

Small branches of the posterior rami of the lower lumbar nerves.

Blood supply

The iliolumbar artery, a branch of the internal iliac artery, runs close to it.