Learning Objectives
By the end of this section, you should be able to:
- Describe the articulating surfaces and joint type of the MCP joints.
- Identify the stabilising ligaments and supporting structures.
- Explain the movements permitted at the MCP joints and the muscles responsible.
- Outline the blood supply and innervation of the MCP joints.
- Recognise common clinical conditions affecting the MCP joints.
The metacarpophalangeal (MCP) joints are articulations between the heads of the metacarpals and the bases of the proximal phalanges.
There are five MCP joints in each hand, one for each digit.
These joints are condyloid synovial joints, allowing movement in multiple planes and forming the functional link between the palm and the fingers.
Anatomical Structure
Articulating Surfaces
Each MCP joint is formed by:
- Metacarpal head – convex, large articular surface
- Base of proximal phalanx – concave, smaller articular surface
Both surfaces are covered with hyaline cartilage.
Joint Capsule
Each MCP joint is enclosed by a loose fibrous capsule that attaches near the margins of the articulating surfaces. The capsule is thickened medially and laterally, where the collateral ligaments reinforce it.
Ligaments and Supporting Structures
Several ligaments stabilise the MCP joint:
- Proper collateral ligaments – run from the metacarpal head to the base of the proximal phalanx; limit excessive flexion.
- Accessory collateral ligaments – attach to the palmar plate; limit excessive extension.
- Palmar ligament (volar plate) – fibrocartilaginous thickening on the anterior capsule; prevents hyperextension and blends with the collateral ligaments.
- Deep transverse metacarpal ligaments – connect the palmar ligaments of digits 2–5, stabilising the metacarpal heads.
- Posterior reinforcement – provided by extensor tendons of the forearm.
Movements
The MCP joints allow movement in two planes, enabling:
- Flexion and extension
- Abduction and adduction
- Circumduction
- Limited rotation
All movements are produced by muscles of the forearm and hand.
Thumb (1st MCP Joint)
| Movement | Main Muscles |
|---|---|
| Flexion | Flexor pollicis longus & brevis |
| Extension | Extensor pollicis longus & brevis |
| Abduction | Abductor pollicis longus & brevis |
| Adduction | Adductor pollicis |
| Rotation | Flexor pollicis brevis + abductor pollicis brevis |
Digits 2–5
| Movement | Main Muscles |
|---|---|
| Flexion | FDS, FDP, lumbricals |
| Extension | Extensor digitorum, extensor indicis, extensor digiti minimi |
| Adduction | Palmar interossei |
| Abduction | Dorsal interossei, abductor digiti minimi (5th digit) |
Mobility and Stability
The primary stabilisers of the MCP joints are the collateral ligaments:
- Proper collateral ligaments limit hyperflexion
- Accessory collateral ligaments and the palmar plate limit hyperextension
The deep transverse metacarpal ligaments provide additional stability during gripping.
Blood Supply
MCP joints are supplied by branches of the radial and ulnar arteries, including:
- Princeps pollicis artery (thumb)
- Radialis indicis artery (index finger)
- Palmar and dorsal metacarpal arteries
- Common palmar digital arteries
Innervation
The MCP joints receive sensory innervation from:
- Posterior interosseous nerve (radial nerve)
- Deep branch of the ulnar nerve
- Palmar branches of the median nerve
Clinical Relevance
Skier’s Thumb
Skier’s thumb is an injury to the ulnar collateral ligament (UCL) of the 1st MCP joint. It occurs when the thumb is forcibly abducted.
Common mechanism: falling while holding a ski pole.
Diagnosis
- Physical examination: joint laxity on abduction
- Ultrasound: assessment of ligament integrity
Management
Complete ligament rupture or displaced avulsion fractures require surgical repair.
