Wrist

As a consequence of these various definitions, fractures to the carpal bones are referred to as carpal fractures, while fractures such as distal radius fracture are often considered fractures to the wrist.

Structure

The distal radioulnar joint (DRUJ) is a pivot joint located between the distal ends of the radius and ulna, which make up the forearm. Formed by the head of the ulna (the bony knob on the back of the wrist) and the ulnar notch of the radius, the DRUJ is separated from the radiocarpal (wrist) joint by an articular disk lying between the radius and the styloid process of the ulna. The capsule of the joint is lax and extends from the inferior sacciform recess to the ulnar shaft. The DRUJ works with the proximal radioulnar joint (at the elbow) for pronation and supination.

The radiocarpal (wrist) joint is an ellipsoid joint formed by the radius and the articular disc proximally and the proximal row of carpal bones distally. The carpal bones on the ulnar side only make intermittent contact with the proximal side — the triquetrum only makes contact during ulnar abduction. The capsule, lax and un-branched, is thin on the dorsal side and can contain synovial folds. The capsule is continuous with the midcarpal joint and strengthened by numerous ligaments, including the palmar and dorsal radiocarpal ligaments, and the ulnar and radial collateral ligaments.

The parts forming the radiocarpal joint are the lower end of the radius and under surface of the articular disk above; and the scaphoid, lunate, and triquetral bones below. The articular surface of the radius and the undersurface of the articular disk form together with a transversely elliptical concave surface, the receiving cavity. The superior articular surfaces of the scaphoid, lunate, and triquetrum form a smooth convex surface, the condyle, which is received into the concavity.

Carpal bones of the hand:

• Proximal: A=Scaphoid, B=Lunate, C=Triquetrum, D=Pisiform
• Distal: E=Trapezium, F=Trapezoid, G=Capitate, H=Hamate

In the hand proper a total of 13 bones form part of the wrist: eight carpal bones—scaphoid, lunate, triquetral, pisiform, trapezium, trapezoid, capitate, and hamate— and five metacarpal bones—the first, second, third, fourth, and fifth metacarpal bones.

The midcarpal joint is the S-shaped joint space separating the proximal and distal rows of carpal bones. The intercarpal joints, between the bones of each row, are strengthened by the radiate carpal and pisohamate ligaments and the palmar, interosseous, and dorsal intercarpal ligaments. Some degree of mobility is possible between the bones of the proximal row while the bones of the distal row are connected to each other and to the metacarpal bones —at the carpometacarpal joints— by strong ligaments —the pisometacarpal and palmar and dorsal carpometacarpal ligament— that makes a functional entity of these bones. Additionally, the joints between the bases of the metacarpal bones —the intermetacarpal articulations— are strengthened by dorsal, interosseous, and palmar intermetacarpal ligaments.

The earliest carpal bones to ossify are capitate bone and hamate bone in the first six months of an infant life.

Articulations

The radiocarpal, intercarpal, midcarpal, carpometacarpal, and intermetacarpal joints often intercommunicate through a common synovial cavity.

Articular surfaces

It has two articular surfaces named, proximal and distal articular surfaces respectively. The proximal articular surface is made up of the lower end of the radius and a triangular articular disc of the inferior radio-ulnar joint. On the other hand, the distal articular surface is made up of proximal surfaces of the scaphoid, triquetral and lunate bones.