Wrist (radiocarpal) joint

Location: Between the distal end of the forearm and the proximal row of carpal bones, at about the level of the proximal skin crease of the wrist.

Bones taking part

• Radius (distal articular surface)
• Ulna (separated from the carpus by the articular disc)
• Scaphoid
• Lunate
• Triquetrum
• Pisiform (not part of the radiocarpal joint)
• Trapezium (distal row; midcarpal joint)
• Trapezoid (distal row; midcarpal joint)
• Capitate (distal row; midcarpal joint)
• Hamate (distal row; midcarpal joint)

Articulating surfaces

• Proximal (concave) side: the distal articular surface of the radius and the inferior surface of the articular disc of the distal radioulnar joint
• Distal (convex) side: the proximal surfaces of the scaphoid, lunate and triquetrum, joined by interosseous ligaments into one smooth oval surface
• The scaphoid and lunate meet the radius; the triquetrum lies against the articular disc (and makes fuller contact with it when the hand is adducted).
• The ulna does not articulate with the carpal bones; the pisiform does not take part either.

Structural

Synovial joint (ellipsoid / condyloid type).

Functional

Diarthrosis (freely movable).

Synovial subtype

Ellipsoid (condyloid): an oval convex surface in an oval concave socket.

Axes

Biaxial: flexion-extension and abduction-adduction, which combine as circumduction; no active rotation.

Capsule & cavity

A fibrous capsule surrounds the joint, attached to the distal ends of the radius and ulna above and to the proximal row of carpal bones below. It is strengthened by the palmar and dorsal radiocarpal and ulnocarpal ligaments and by the radial and ulnar collateral ligaments. The synovial membrane lines it; the joint cavity is normally separated from the distal radioulnar joint by the articular disc.

• Positions the hand for grasping and fine work by flexing, extending and deviating it.
• Transmits forces from the hand to the radius (and, through the interosseous membrane, to the ulna).
• Slight extension of the wrist puts the long finger flexors at a better length for a strong grip.

Stability vs mobility: Fairly stable for a biaxial joint: the oval surfaces fit well and many ligaments surround it, and the tendons crossing the wrist support it further. Its mobility is shared with the midcarpal joint.

• Fall on the outstretched hand (FOOSH) commonly fractures the distal radius; a Colles fracture has the distal fragment displaced dorsally (the 'dinner-fork' deformity).
• Scaphoid fracture is the commonest carpal fracture: tenderness in the anatomical snuffbox. Its blood supply enters distally, so the proximal fragment can undergo avascular necrosis.
• Anterior dislocation of the lunate can press on the median nerve in the carpal tunnel.
• Tears of the articular disc (triangular fibrocartilage) cause pain on the ulnar side of the wrist.

• Say 'radiocarpal joint' and define its surfaces: radius + articular disc above; scaphoid, lunate, triquetrum below.
• State clearly that the ulna does not articulate directly with the carpus and that the pisiform is not part of the joint.
• Classify it as an ellipsoid (condyloid) synovial joint, biaxial.
• Explain why adduction has a greater range than abduction (the radial styloid reaches further distally).
• Mention the midcarpal joint (between the proximal and distal carpal rows) as contributing to wrist movement.
• Do not place pronation and supination here.

• Saying the ulna articulates with the carpal bones.
• Including the pisiform among the bones of the radiocarpal joint.
• Listing pronation and supination as wrist movements.
• Calling the wrist a hinge joint; it is ellipsoid and biaxial.
• Confusing the ulnar collateral ligament of the wrist with that of the elbow.