Ligamenta flava

At a glance

English

Ligamenta flava

Latin (TA2)

Ligamenta flava

System

Ligament

Region

Neck

Side

Single, on the midline

About the ligamenta flava

The ligamenta flava, or yellow ligaments (one is a ligamentum flavum), bridge the gaps between the vertebral arches. A pair lies at every level from the junction of the axis with the third cervical vertebra down to the lumbosacral gap between L5 and S1. Their colour comes from a very high elastic content, rare among ligaments.

Each ligament has a right and a left half. A half begins next to the root of the articular process, where it blends with the capsule of the facet joint, and runs back to the midline, where the laminae unite at the base of the spine. The two halves meet there and are partly fused, with small gaps left for veins that link the internal and external vertebral venous plexuses. The fibres run almost vertically: above, they attach to the front (inner) surface of the lamina some way up from its lower edge; below, to the top edge and outer face of the next lamina. For this reason the ligaments are best seen from inside the canal, while from behind the overlapping laminae hide most of them.

Their thickness changes along the column. Cervical ligaments are thin yet wide and lengthy, and they lengthen towards the lower cervical levels as the laminae spread further apart. They thicken in the thorax and are thickest in the lumbar region. Between atlas and axis the equivalent tissue is thin and may be missing altogether.

Because they are elastic, the ligaments are under tension even when the back is straight. They resist excessive bending forwards, help the column spring back to the upright position, and, crucially, do not crumple inwards when the spine extends, which would otherwise press on the spinal cord and nerve roots. With age they can lose elastin, become fatty or calcify, and they may thicken; a thickened ligamentum flavum is a common contributor to lumbar and cervical spinal stenosis, notably in diffuse idiopathic skeletal hyperostosis. In an epidural or spinal injection the needle passes through the ligament, and the sudden loss of resistance as it emerges tells the operator that the epidural space has been reached. Surgeons removing a prolapsed disc often trim or lift part of it, using a hook to keep it clear of the dura.

Attachments and function

Attaches from

The anterior (inner) surface of the lamina of the vertebra above, a little above its lower border.

Attaches to

The upper edge and back surface of the next lamina below.

Function

Limits forward flexion, assists the return to the upright posture, and keeps the back of the vertebral canal smooth so that it does not fold in on the cord during extension.

Nerve supply

Branches of the meningeal (sinuvertebral) and dorsal rami of the spinal nerves.

Blood supply

Small branches of the spinal arteries of each segment; veins pass through gaps in the midline.