This part of the bone structure marks the transition area between the forearm and the hand.
The wrist joint (also known as the radiocarpal joint ) is a synovial joint in the upper limb.
Structures of the wrist joint
The wrist joint is made up of:
- Distally: the proximal row of the carpal bones (except the pisiform).
- Proximally: the distal end of the radius and the articular disc.
The ulna is not part of the wrist joint; articulates with the radius just proximal to the wrist joint at the distal radioulnar joint. It is prevented from articulating with the carpal bones by a fibrocartilaginous ligament, called the articular disc , which lies on the upper surface of the ulna.
Together, the carpal bones form a convex surface, which articulates with the concave surface of the radius and the articular disc.
Like any synovial joint, the capsule has two layers. The fibrous outer layer adheres to the radius, ulna, and proximal row of the carpal bones. The inner layer is made up of a synovial membrane that secretes synovial fluid that lubricates the joint.
There are four ligaments in the wrist joint, one for each side of the joint:
- Palmar Radiocarpal – Found on the palmar (anterior) side of the hand. It passes from the radius to both rows of carpal bones. Its function, in addition to increasing stability, is to ensure that the hand follows the forearm during supination.
- Dorsal Radiocarpal – Found on the dorsal (posterior) side of the hand. It passes from the radius to both rows of carpal bones. It contributes to the stability of the wrist, but also ensures that the hand follows the forearm during pronation.
- Ulnar collateral: it runs from the ulnar styloid to the pyramidal and pisiform. It works in conjunction with the other collateral ligament to prevent excessive lateral joint displacement.
- Radial collateral: runs from the radial styloid process to the scaphoid and trapezius. It works in conjunction with the other collateral ligament to prevent excessive lateral joint displacement.
The wrist joint receives blood from the branches of the dorsal and palmar palmar arches, which are derived from the ulnar and radial arteries.
The innervation of the wrist is produced by branches of three nerves:
- Median nerve: anterior interosseous branch.
- Radial nerve: posterior interosseous branch.
- Ulnar nerve : deep and dorsal branches.
Movements of the wrist joint
The wrist is an ellipsoid-type synovial joint, allowing movement along two axes. This means that flexion, extension, adduction, and abduction can occur at the wrist joint.
All movements of the wrist are performed by the muscles of the forearm.
- Flexion: produced mainly by the flexor carpi ulnaris, flexor carpi radialis, with the help of the superficial flexor of the fingers.
- Extension : mainly produced by the extensor carpi radialis longus and carpi radius, and the extensor carpi ulnaris, with the help of the digital extensor.
- Adduction: produced by the extensor carpi ulnaris and the ulnar flexor ulnaris.
- Abduction: produced by the abductor pollicis longus, flexor carpi radialis, extensor carpi radialis longus, and extensor carpi radialis brevis.
Injuries to the wrist joint
In the case of a blow to the wrist (for example, falling onto an outstretched hand), the navicular takes most of the force. A fractured scaphoid is more common in the younger population.
The main clinical sign of a scaphoid fracture is tenderness in the anatomical snuffbox.
Anterior dislocation of the Lunate
This can occur when landing on a dorsiflexed wrist. The lunate is forced forward and compresses the carpal tunnel, causing the symptoms of carpal tunnel syndrome.
This manifests clinically as paresthesia in the sensory distribution of the median nerve and weakness of the thenar muscles. The lunate may also undergo avascular necrosis, for which immediate clinical attention is needed for the fracture.
Colles’ fracture is the most common fracture that affects the wrist and occurs when landing on an outstretched hand.
The radius fractures, with the distal fragment being displaced posteriorly. The ulnar styloid process can also be damaged and avulsed in most cases.
This clinical condition produces what is known as the “supper fork deformity.”