Collateral metacarpophalangeal ligaments

At a glance

English

Collateral metacarpophalangeal ligaments

Latin (TA2)

Ligamenta metacarpophalangea collateralia

System

Ligament

Region

Hand

Side

Paired, left and right

About the collateral metacarpophalangeal ligaments

The collateral metacarpophalangeal ligaments are the chief stabilisers of the knuckle joints, where each metacarpal head meets the base of a proximal phalanx. Every joint has a radial and an ulnar collateral ligament, and each has two parts. The collateral ligament proper is a rounded cord on the dorsal side, and the accessory collateral ligament is a thinner fan placed further towards the palm.

The cord-like proper ligament starts in a hollow on the side of the metacarpal head, set behind the axis around which the joint turns. It runs forwards and distally at a slant to a tubercle on the side of the proximal phalanx base. The accessory part begins just in front of it, on the palmar side, and fans out to the edge of the palmar plate rather than to bone. Interosseous and lumbrical tendons pass along the sides of the joint and add to its side-to-side stability.

The metacarpal head is not a simple sphere: it is wider and projects further on its palmar side. Because the proper ligament is fixed behind the centre of rotation, it is lengthened by a few millimetres as the joint bends and becomes taut in full flexion, while the accessory part does the opposite and tightens in extension. As a result the fingers can be spread apart and slightly rotated when the hand is open, but are held firmly together, unable to spread, in a closed fist.

This is why injured hands are splinted with the knuckles bent: in that position the main ligaments stay at full length and the joint does not stiffen in extension. The ulnar collateral ligament of the thumb is a special case; its tear, known as skier's or gamekeeper's thumb, weakens pinch grip and may need surgery.

Attachments and function

Attaches from

A hollow on either flank of the metacarpal head, dorsal to the axis of rotation; the accessory part arises just palmar to it.

Attaches to

A tubercle on each side of the proximal phalanx base; the accessory part ends on the palmar plate.

Function

Stabilise the metacarpophalangeal joints against sideways force; tight in flexion so the fingers cannot spread in a fist, slack in extension so they can spread and rotate when the hand is open.

Nerve supply

Articular branches of the digital nerves from the median and ulnar nerves, with dorsal twigs from the radial and ulnar nerves.

Blood supply

Branches of the palmar metacarpal and common palmar digital arteries.