M01.03.035 Wrist Joint

The wrist joint, also known as the radiocarpal joint, is an important structure that allows for the transition between the forearm and the hand. Understanding its anatomy, movement, and clinical relevance is crucial for medical students. Below is a detailed breakdown of the wrist joint’s structure, ligaments, blood supply, innervation, and common clinical issues associated with it.

1. Anatomical Structure

Articulating Surfaces

The wrist joint is formed by the articulation between the following structures:

• The distal end of the radius and the articular disk.
• The proximal row of carpal bones (except the pisiform).

The carpal bones form a convex surface that fits into the concave shape of the radius and the articular disk. The ulna does not directly articulate with the carpal bones; instead, it articulates with the radius at the distal radioulnar joint, separated by the articular disk.

Table 1: Articulating Surfaces of the Wrist Joint

Joint Capsule

The joint capsule surrounds the wrist joint and attaches to the:

• Radius
• Ulna
• Proximal carpal bones

Internally, the joint capsule is lined with a synovial membrane that produces synovial fluid to reduce friction during movement.

Ligaments

The wrist joint is stabilized by several key ligaments, both intrinsic and extrinsic:

Movements of the Wrist

The wrist joint is a condyloid-type synovial joint that allows movement along two axes:

• Flexion and Extension
• Adduction and Abduction

Table 2: Muscles Involved in Wrist Movements

Mobility and Stability

While the wrist joint is highly mobile, it is also prone to injury. Intrinsic carpal ligaments provide limited stability but can be damaged easily. On the other hand, extrinsic ligaments such as the radiocarpal and collateral ligaments offer stronger stabilization.

Blood Supply and Innervation

Blood Supply

The wrist joint receives blood from the dorsal and palmar carpal arches, which are derived from the ulnar and radial arteries.

Innervation

The wrist is innervated by branches of three major nerves:

• Median nerve (Anterior interosseous branch)
• Radial nerve (Posterior interosseous branch)
• Ulnar nerve (Deep and dorsal branches)

2. Clinical Relevance

Scaphoid Fracture

The scaphoid is the most commonly fractured carpal bone, usually due to a fall on an outstretched hand (FOOSH). Clinical signs include:

• Pain and tenderness in the anatomical snuffbox.
• Risk of avascular necrosis due to the retrograde blood supply to the scaphoid.

Missed fractures can lead to wrist osteoarthritis later in life.

Anterior Dislocation of the Lunate

This dislocation often occurs due to a fall on a dorsiflexed wrist. It can cause:

• Compression of the carpal tunnel, leads to carpal tunnel syndrome.
• Paraesthesia in the median nerve distribution.
• Weakness of the thenar muscles.

Immediate clinical intervention is necessary to prevent avascular necrosis.

Colles’ Fracture

A Colles’ fracture is a common wrist injury caused by a fall onto an outstretched hand. It involves:

• A fracture of the radius, with displacement of the distal fragment posteriorly.
• Avulsion of the ulnar styloid process, is often seen in these fractures.

This type of fracture is characterized by the “dinner fork deformity”.

3. Points to Remember

• The wrist joint is a condyloid synovial joint that allows movement in flexion, extension, adduction, and abduction.
• Scaphoid fractures are common and carry a risk of avascular necrosis due to the retrograde blood supply.
• Anterior lunate dislocation can lead to carpal tunnel syndrome.
• The Colles’ fracture is identified by the “dinner fork deformity”.

Understanding these clinical correlations is essential for diagnosing and treating wrist injuries effectively in medical practice.