Wrist Joint

Introduction

Introduction to the Wrist (Radiocarpal) Joint

The wrist joint, or radiocarpal joint, is a condyloid synovial articulation between the distal end of the radius and the proximal row of carpal bones (scaphoid, lunate, and triquetrum). It is the primary joint through which movements of the hand relative to the forearm occur—flexion, extension, radial deviation (abduction), ulnar deviation (adduction), and circumduction. The joint's stability is provided by a complex network of intrinsic and extrinsic ligaments, while the triangular fibrocartilage complex (TFCC) separates it from the distal radioulnar joint and articulates with the ulnar side of the carpus. The wrist is a common site of traumatic injury, including fractures of the distal radius and carpal bones, ligamentous disruptions, and overuse syndromes.

This module covers the articular surfaces, ligaments, capsule, relations, movements, blood and nerve supply, and the clinically important conditions affecting the wrist joint.

Study

1. Articular Surfaces and Joint Classification

The radiocarpal joint is a biaxial condyloid (ellipsoid) synovial joint. The proximal articular surface is formed by the concave distal end of the radius and the adjacent articular disc of the TFCC, which together create a continuous ovoid concavity. The distal articular surface is formed by the convex proximal surfaces of the scaphoid, lunate, and triquetrum bones, which are linked by the interosseous scapholunate and lunotriquetral ligaments. The ulna does not directly participate in the radiocarpal joint; it is separated by the TFCC, making the wrist a predominantly radial joint.

2. Articular Disc and TFCC

The triangular fibrocartilage complex (TFCC) articulates with the triquetrum and, in ulnar deviation, the lunate. It spans from the ulnar notch of the radius to the base of the ulnar styloid and fovea, separating the radiocarpal joint from the distal radioulnar joint. The TFCC transmits approximately 20% of axial loads across the wrist and deepens the radial articular surface.

3. Joint Capsule and Ligaments

The fibrous capsule encloses the joint and is reinforced by strong extrinsic ligaments. These are divided into palmar (volar) and dorsal groups.

Palmar radiocarpal ligaments: The strongest, they radiate from the anterior margin of the distal radius and TFCC to the proximal carpal row. Key ligaments include the radioscaphocapitate ligament, radiolunate ligament (long and short), and ulnolunate ligament. These prevent excessive extension and ulnar deviation.

Dorsal radiocarpal ligament: Arises from the dorsal rim of the distal radius and inserts on the lunate and triquetrum. It limits excessive flexion.

Radial collateral ligament: From the radial styloid to the scaphoid and trapezium, limiting ulnar deviation.

Ulnar collateral ligament: From the ulnar styloid to the pisiform and triquetrum, limiting radial deviation.

Intrinsic (interosseous) ligaments: The scapholunate and lunotriquetral ligaments connect the carpal bones of the proximal row and are crucial for carpal stability. Disruption leads to dissociative carpal instability.

4. Relations

Anteriorly, the wrist joint is crossed by the median nerve and the long flexor tendons within the carpal tunnel, and the radial and ulnar arteries. Posteriorly, the extensor tendons are arranged in six compartments deep to the extensor retinaculum. Medially, the ulnar nerve and artery pass through Guyon's canal. The radial styloid and Lister's tubercle are palpable landmarks.

5. Movements and Range of Motion

The radiocarpal joint contributes 60–70% of wrist flexion and extension, with the remainder occurring at the midcarpal joint. Normal active range: flexion 80°, extension 70°, radial deviation 20°, ulnar deviation 30°. Circumduction combines these movements. The dart-thrower's motion (radial extension to ulnar flexion) uses predominantly the midcarpal joint.

6. Blood Supply

The radiocarpal joint is supplied by the dorsal and palmar carpal arches, which receive contributions from the radial, ulnar, and anterior interosseous arteries. The scaphoid has a tenuous retrograde blood supply from the dorsal carpal branch of the radial artery, making it prone to avascular necrosis.

7. Nerve Supply

The anterior interosseous nerve (median nerve), posterior interosseous nerve (radial nerve), and dorsal and deep branches of the ulnar nerve provide articular branches to the wrist joint. The PIN is the main sensory nerve to the dorsal wrist capsule.

8. Clinical Considerations

Colles fracture: An extra‑articular fracture of the distal radius with dorsal angulation and displacement, commonly from a fall on the outstretched hand. The dinner fork deformity is characteristic.

Smith fracture (reverse Colles): A distal radius fracture with volar angulation, from a fall onto the back of the hand or direct blow.

Scaphoid fracture: The most commonly fractured carpal bone, often from a fall on the outstretched hand. At risk for nonunion and avascular necrosis due to its retrograde blood supply.

Perilunate dislocation and lunate dislocation: Progressive carpal instability patterns (Mayfield progression) resulting from disruption of the scapholunate ligament, lunotriquetral ligament, and radiocarpal ligaments. These can lead to median nerve compression.

Scapholunate ligament tear: Causes scapholunate dissociation, widened gap on radiograph (Terry Thomas sign), and dorsal intercalated segment instability (DISI).

Carpal tunnel syndrome: May be caused by increased intracarpal pressure from distal radius fractures or perilunate dislocation.

Summary

Summary of the Wrist Joint

The radiocarpal joint is a condyloid joint between the distal radius/TFCC and the scaphoid, lunate, and triquetrum. It is stabilised by palmar and dorsal radiocarpal ligaments, collateral ligaments, and the scapholunate and lunotriquetral interosseous ligaments. The joint allows flexion, extension, radial and ulnar deviation, and circumduction. Key clinical conditions include distal radius fractures (Colles, Smith), scaphoid fractures with risk of avascular necrosis, perilunate and lunate dislocations, and scapholunate ligament injuries leading to carpal instability.