Intra-articular ligament of head of rib

At a glance

English

Intra-articular ligament of head of rib

Latin (TA2)

Ligamentum intraarticulare capitis costae

System

Ligament

Region

Thorax

Side

Single, on the midline

About the intra-articular ligament of head of rib

A typical rib (the second to the ninth) meets the spine with a head bearing two small articular facets, one above and one below, separated by a horizontal ridge, the crest of the head. The upper facet fits a demifacet on the body of the vertebra above and the lower facet one on the vertebra of the same number. Between those two demifacets lies the intervertebral disc, and so the rib head sits wedged against two bones and the disc between them.

The intra-articular ligament (formerly called the interarticular ligament) is a short band, flattened from above downwards, that runs straight from the crest of the rib head to the outer rim of the intervertebral disc. Because it reaches right across the joint, it splits the joint of the head of the rib into two separate synovial cavities, an upper and a lower, each with its own small synovial membrane. In front, it is covered by the radiate ligament, which spreads over the outside of the joint.

Where a rib meets only one vertebra the ligament is missing, and the joint has a single cavity. This applies to the first rib and to the tenth, eleventh and twelfth ribs, whose heads carry a single facet. In some other mammals a related band, the conjugate ligament, crosses behind the disc to link the heads of a right and a left rib; the human intra-articular ligament is regarded as its counterpart.

The ligament holds the rib head firmly against the disc and the vertebral bodies while still letting the head rotate slightly, the movement that underlies raising and lowering of the ribs in breathing. It contributes to the stability of the joint during twisting of the trunk. Degeneration of these small joints, with the facet joints, can be a cause of pain in the thoracic back.

Attachments and function

Attaches from

The crest of the head of the rib, between its upper and lower articular facets.

Attaches to

The disc lying between the two vertebral bodies that the rib head meets.

Function

Binds the rib head to the disc, splits the joint into upper and lower compartments and steadies it while allowing slight rotation in breathing.

Nerve supply

Branches of the dorsal rami and meningeal branches of the thoracic spinal nerves.

Blood supply

Small branches of the posterior intercostal arteries.