The wrist is a complex synovial joint linking the forearm to the hand, allowing fine positioning of the hand in space. It provides flexion, extension, radial deviation (abduction), ulnar deviation (adduction), and contributes to circumduction. Stability depends on intercarpal ligaments and coordinated muscle control rather than deep bony congruence. The wrist functions primarily as a link between forearm and hand, allowing flexion/extension (140° total), radial/ulnar deviation (50°), and some pronation/supination contribution via radioulnar joints. Stability relies heavily on ligaments (especially scapholunate and TFCC) and extrinsic tendons.

🦴 Bony Anatomy

The wrist joint proper (radiocarpal joint) is formed between:

Distal radius (primary articulation).
Articular disc (TFCC) separating ulna from carpus.
Proximal carpal row: scaphoid, lunate, triquetrum (pisiform does not articulate in radiocarpal joint).

Carpal Bones (8 total)

Proximal row: Scaphoid, Lunate, Triquetrum, Pisiform.
Distal row: Trapezium, Trapezoid, Capitate, Hamate.

🔗 Joint Structure

Radiocarpal joint – synovial ellipsoid joint.
Midcarpal joint – articulation between proximal and distal carpal rows.
Distal radioulnar joint (DRUJ) – allows pronation/supination.
TFCC (triangular fibrocartilage complex) – stabilises ulnar side.

🛡️ Ligaments

Palmar radiocarpal ligaments (strong stabilisers).
Dorsal radiocarpal ligaments.
Radial collateral ligament.
Ulnar collateral ligament.
Scapholunate ligament (commonly injured).

💪 Muscles Acting on the Wrist

Flexion

Flexor carpi radialis (median nerve).
Flexor carpi ulnaris (ulnar nerve).
Palmaris longus (median nerve).

Extension

Extensor carpi radialis longus & brevis (radial nerve).
Extensor carpi ulnaris (radial nerve).

Radial Deviation

Flexor carpi radialis.
Extensor carpi radialis longus/brevis.

Ulnar Deviation

Flexor carpi ulnaris.
Extensor carpi ulnaris.

🧵 Important Tendon Compartments (Dorsal Wrist)

1st: Abductor pollicis longus, extensor pollicis brevis.
2nd: Extensor carpi radialis longus & brevis.
3rd: Extensor pollicis longus.
4th: Extensor digitorum, extensor indicis.
5th: Extensor digiti minimi.
6th: Extensor carpi ulnaris.

⚡ Nerve Supply

Median nerve – anterior wrist capsule; passes through carpal tunnel.
Ulnar nerve – medial wrist (Guyon’s canal).
Radial nerve (superficial branch) – dorsal radial sensation.

🩸 Blood Supply

Radial artery – anatomical snuffbox, deep palmar arch.
Ulnar artery – superficial palmar arch.
Intercarpal arches provide collateral supply.
Scaphoid has retrograde blood supply (risk of avascular necrosis if fractured).

🔄 Function & Biomechanics

Wrist extension increases grip strength by optimising finger flexor tension (tenodesis effect). Radial and ulnar deviation allow precision grip and power grip positioning. Stability depends heavily on intact scapholunate alignment and TFCC integrity.

⚠️ Clinical Correlations

Scaphoid fracture – anatomical snuffbox tenderness; risk of AVN.
Carpal tunnel syndrome – median nerve compression.
De Quervain’s tenosynovitis – 1st dorsal compartment inflammation.
TFCC tear – ulnar-sided wrist pain.
Scapholunate dissociation – widened scapholunate gap on X-ray.

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Wrist Joint Structure and Form