Wrist joint Anatomy and Biomechanics

Wrist Joint Anatomy and Biomechanics

The human hand has a complex mechanism to perform functional capabities. its integrity is essential for daily functions. The Wrist Joint also, known as the Radiocarpal joint is a Synovial joint of Ellipsoid variety, in the upper limb, marking the area of transition between the forearm and the hand.

Structures of the Wrist Joint:

Articulating Surfaces 

The wrist joint is formed by:
• Distally – The proximal row of the carpal bones (except the pisiform).
• Proximally – The distal end of the radius, and the articular disk.

The ulna is not part of the wrist joint – it 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 disk, which lies over the superior surface of the ulna.
Together, the carpal bones form a convex surface, which articulates with the concave surface of the radius and articular disk.

Joint Capsule
Like any synovial joint, the capsule is dual layered. The fibrous outer layer attaches to the radius, ulna and the proximal row of the carpal bones. The internal layer is comprised of a synovial membrane, secreting synovial fluid which lubricates the joint.
Ligaments
There are four ligaments of note in the wrist joint, one for each side of the joint.

• Palmar radiocarpal – It is found on the palmar (anterior) side of the hand. It passes from the radius to both rows of carpal bones. Its function, apart from increasing stability, is to ensure that the hand follows the forearm during supination.

• Dorsal radiocarpal – It is found on the dorsum (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 – Runs from the ulnar styloid process to the triquetrum and pisiform. Works in union with the other collateral ligament to prevent excessive lateral joint displacement.

• Radial collateral – Runs from the radial styloid process to the scaphoid and trapezium. Works in union with the other collateral ligament to prevent excessive lateral joint displacement.

Neurovascular Supply

Innervation to the wrist is delivered by branches of three nerves:
• Median nerve – Anterior interosseous branch.
• Radial nerve – Posterior interosseous branch.
• Ulnar nerve – deep and dorsal branches.

Muscles of the wrist joint:

• EXTENSOR CARPI RADIALIS LONGUS.

• EXTENSOR CARPI RADIALIS BREVIS.
• EXTENSOR CARPI ULNARIS.
• FLEXOR CARPI RADIALIS.
• FLEXOR CARPI ULNARIS.
• PALMARIS LONGUS.

Movements of the Wrist Joint

The wrist is an ellipsoidal (condyloid) type synovial joint, allowing for movement along two axes. This means that flexion, extension, adduction and abduction can all occur at the wrist joint.
All the movements of the wrist are performed by the muscles of the forearm.

Flexion –  Produced mainly by the flexor carpi ulnaris, flexor carpi radialis, with assistance from the flexor digitorum superficialis.

Extension – Produced mainly by the extensor carpi radialis longus and brevis, and extensor carpi ulnaris, with assistance from the extensor digitorum.

Adduction – Produced by the extensor carpi ulnaris and flexor carpi ulnaris

Abduction – Produced by the abductor pollicis longus, flexor carpi radialis, extensor carpi radialis longus and brevis

Osteokinematics and Arthrokinematics

Osteokinematics

flexion /Extension :

• Axis – Coronal axis
• Plane – sagittal  plane
• ROM for flexion – 65 -85 degree
• Rom for extension – 55-80 degree

Ulnar / radial deviation –

• Axis – Anteroopostrior axis
• Plane -coronal plane
• ROM – 0-30 ulnar radiation , 15-20 degree radial deviation

ARTHROKINEMATICS

 Wrist Flexion / Extension:

• It follows CONVEX - CONCAVE rule.
• Roll and Slide will be in opposite direction.
• Dorsal Roll - during extension.

Ventral Slide - lunate moves on styloid process of radius.

* Extension at RadioCarpal joint :
• The convex surface of lunate rolls dorsally on radius and slides ventrally.

*Flexion at RadioCarpal joint :
•The convex surface of lunate rolls centrally and slides dorsally.

Clinical

COLLES FRACTURE :

Colles fracture most common fracture involving the wrist , caused by falling onto outstretched hand. The radius fractures, with the distal fragment being displaced postiorly. In this radius bone breaks.

The ulnar styloid process can also be damaged in majority of cases.
This condition is called Dinner fork deformity

Scaphoid fracture :

 The Scaphoid  bone of the hand is most commonly fractured bone – typically fall on an outstretched hand ( FOOSH).
Clinical features is pain and tenderness  in the anatomical Snuff box .
Patient with missed Scaphoid fracture are likely to develop osteoarthritis of the wrist in later life.