CMC ligaments !

The carpometacarpal ligaments join the wrist bones to the palm bones, making the palm a stable arch; the thumb's are looser so it can move.

Official name: Carpometacarpal and metacarpal ligaments

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What it is

Ligaments joining the wrist bones to the bases of the metacarpals and the metacarpals to each other.

What it does

Make the palm a stable arch; the thumb's are looser so it can move.

Key facts

Attaches: Distal carpal bones to the metacarpal bases (dorsal, palmar, interosseous); thumb: anterior oblique (beak) and dorsoradial ligaments; intermetacarpal ligaments
Function: Lock the 2nd–3rd CMC joints (fixed central pillar); let the 4th–5th and thumb move
Tight in: Thumb abduction and extension (anterior oblique ligament)

Relations

In front: FCR tendon in the groove of the trapezium on its way to the 2nd metacarpal; the deep palmar arch and the deep branch of the ulnar nerve across the metacarpal bases
Behind: Insertions of ECRL, ECRB and ECU on the dorsal metacarpal bases; the extensor tendons to the fingers pass over them
Lateral: Radial artery, crossing the back of the first interspace and passing between the heads of the first dorsal interosseous into the palm; APL inserting on the 1st metacarpal base

How to find it

Thumb: the base of the first metacarpal stands out on the back of the hand just beyond the radial styloid; the joint line is the groove just proximal to it, which moves when the thumb is circled. Fingers: with the wrist flexed, the bump of the third metacarpal base on the back of the hand marks the 2nd–3rd CMC joints, the usual site of a carpal boss.

Examination

Grind test of the thumb CMC: axial load with rotation of the 1st metacarpal on the trapezium; pain and crepitus suggest basal thumb osteoarthritis

On imaging

The Robert view (true AP of the thumb base with the hand fully pronated) and a true lateral show trapeziometacarpal arthritis and Bennett fractures. 4th–5th CMC dislocations are easy to miss on the PA view: look for lost parallel joint lines and overlapping bones, and add a pronated oblique view or CT.

Clinical notes

Basal thumb arthritis is common in older women; laxity of the beak ligament is classically linked to it
Carpal boss: a bony bump on the back of the 2nd–3rd CMC joints, sometimes mistaken for a ganglion
CMC dislocations of the ring and little rays follow punches and high-energy falls and are often missed

Anatomical variants

An os styloideum, a separate small ossicle at the bases of the 2nd and 3rd metacarpals, may form or enlarge a carpal boss

Test yourself

Think of the answer, then tap the question to see it.

Which carpometacarpal joints are locked by the CMC ligaments, and why?

The 2nd and 3rd, a fixed central pillar that anchors the wrist movers (ECRL, ECRB, FCR); the 4th, 5th and thumb CMC can move.

In a Bennett fracture, which thumb CMC ligament holds the small fragment?

The anterior oblique (beak) ligament holds the palmar-ulnar fragment while APL pulls the shaft dorsally and radially.

Which test suggests basal thumb osteoarthritis, linked to beak ligament laxity?

The grind test: axial load with rotation of the 1st metacarpal on the trapezium; pain and crepitus are positive.

What deforming force acts in a 5th CMC fracture-dislocation (reverse Bennett)?

The ECU pulls the 5th metacarpal base ulnarly and proximally.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): ligamenta carpometacarpea dorsalia TA2 1828
Official Spanish (DeCS): Ligamentos carpometacarpianos y metacarpianos
English (TA2): Carpometacarpal and metacarpal ligaments

Sources: Terminologia Anatomica (TA2); Anatomy, Shoulder and Upper Limb, Hand Bones; Anatomy of the Human Body (20th ed.): Surface Anatomy of the Upper Extremity (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain.

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Representative model, for educational purposes only.

CMC ligaments highlighted on the Durgical 3D model