Learning Objectives
By the end of this section, you should be able to:
- Describe the articulating surfaces of the wrist joint.
- Identify the major stabilising ligaments.
- Explain the movements permitted at the wrist and the muscles responsible.
- Outline the blood supply and innervation of the wrist joint.
- Recognise common clinical conditions affecting the wrist.
The wrist joint, also known as the radiocarpal joint, is the articulation between the distal radius and the carpal bones of the hand. It is a condyloid (ellipsoidal) synovial joint that forms the transition between the forearm and the hand.
This section reviews the structure, movements, neurovascular supply, and clinical relevance of the wrist joint.
Anatomical Structure
Articulating Surfaces
The wrist joint is formed by the articulation between:
- The distal end of the radius and the articular disc
- The proximal row of carpal bones (scaphoid, lunate, triquetrum; excluding the pisiform)
Together, the carpal bones form a convex surface that fits into the concave surface formed by the radius and articular disc. The ulna does not directly articulate with the carpal bones. Instead, it is separated by a fibrocartilaginous ligament known as the articular disc and articulates with the radius at the distal radioulnar joint.
Joint Capsule
The joint capsule attaches to the radius, ulna, and proximal carpal bones.
It is lined internally by a synovial membrane, which secretes synovial fluid to reduce friction during movement.
Ligaments
Four major ligaments stabilise the wrist:
- Palmar radiocarpal ligament – anterior; from radius to both carpal rows; ensures the hand follows the forearm during supination and increases stability.
- Dorsal radiocarpal ligament – posterior; from radius to carpal bones; ensures the hand follows the forearm during pronation.
- Ulnar collateral ligament – from ulnar styloid to triquetrum and pisiform; prevents excessive radial deviation.
- Radial collateral ligament – from radial styloid to scaphoid and trapezium; prevents excessive ulnar deviation.
Movements
The wrist is a condyloid synovial joint, allowing movement in two planes:
| Movement | Main Muscles |
|---|---|
| Flexion | Flexor carpi ulnaris, flexor carpi radialis, FDS |
| Extension | Extensor carpi radialis longus & brevis, extensor carpi ulnaris |
| Adduction (ulnar deviation) | Flexor carpi ulnaris, extensor carpi ulnaris |
| Abduction (radial deviation) | Abductor pollicis longus, flexor carpi radialis, extensor carpi radialis longus & brevis |
All wrist movements are produced by forearm muscles.
Mobility and Stability
The wrist is highly mobile, allowing the hand to move in multiple directions. However, this mobility increases its vulnerability to injury.
Stability is provided by:
- Intrinsic ligaments – short ligaments between carpal bones; provide fine stability but are easily damaged.
- Extrinsic ligaments – stronger ligaments connecting the radius and ulna to the carpals (radiocarpal and collateral ligaments).
Blood Supply
The wrist receives blood from branches of the palmar and dorsal carpal arches, derived from the radial and ulnar arteries.
Innervation
The wrist joint is innervated by branches of:
- Median nerve – anterior interosseous branch
- Radial nerve – posterior interosseous branch
- Ulnar nerve – deep and dorsal branches
Clinical Relevance
Scaphoid Fracture
The scaphoid is the most commonly fractured carpal bone, usually after a FOOSH injury.
Key sign: tenderness in the anatomical snuffbox.
Because its blood supply enters distally and flows proximally, fractures at the wrist can cause avascular necrosis of the proximal fragment, leading to wrist osteoarthritis.
Anterior Dislocation of the Lunate
Occurs after a fall on a dorsiflexed wrist. The lunate is displaced anteriorly, compressing the median nerve within the carpal tunnel.
Symptoms include:
- Paraesthesia in the median nerve distribution
- Weakness of the thenar muscles
This is an emergency due to the risk of avascular necrosis.
Colles’ Fracture
The most common wrist fracture is caused by a FOOSH injury.
- Fracture of the distal radius
- The distal fragment was displaced posteriorly
- Often associated with ulnar styloid fracture
Produces the classic “dinner fork” deformity.
