Radiocarpal joint

The radiocarpal joint is a major synovial joint of the wrist and is an example of a condyloid joint. 

Gross anatomy

Location

The joint occurs proximally between the concave surface of the distal end of the radius and the articular disc of the distal radioulnar joint, and distally by the oval shaped convex surface of the proximal carpal row (the scaphoid, lunate and triquetral bones).

Movement

• flexion
  • flexor digitorum superficialis
  • flexor digitorum profundus
  • palmaris longus
  • flexor carpi radialis and ulnaris (when contracting in unison)
• extension
  • extensor carpi radialis longus and brevis
  • extensor carpi ulnaris
  • extensor digitorum
• adduction / ulnar deviation
  • flexor carpi ulnaris and extensor carpi ulnaris (when contracting in unison)
• abduction / radial deviation
  • extensor carpi radialis longus and brevis as well as flexor carpi radialis (when contracting in unison)
• circumduction
  • combinations of the above-mentioned muscles are used to create circular hand motions about the wrist

Articulation

Key features of the radiocarpal joint:

• condyloid joint (ellipsoidal) 
• distal radius articulates with the scaphoid, lunate, and triquetrum (carpal bones)
• normal ulnar slant 15-25º
• normal palmar inclination 15-20º

The distal radius broadens to possess a large articular surface and has a radial styloid process that usually extends 9-12 mm distal to the articular surface of the ulnar. This results in an ulnar slant and palmar inclination at the radiocarpal joint.

Ligaments

Multiple separate ligaments stabilise the adjacent carpal bones to the distal radius.

Volar surface

• radial collateral ligament: attach to the styloid process
• radioscaphocapitate ligament
• radiolunate ligament
• radioscapholunate ligament

Dorsal surface

• radioscaphoid ligament
• radiolunate ligament
• radiotriquetral ligament

Tendons

Volar surface

• flexor digitorum superficialis and profundus tendons
• flexor carpi radialis and ulnaris tendons
• flexor pollicis longus tendons
• palmaris longus tendon

Dorsal surface

• extensor carpi radialis longus and brevis tendons
• extensor pollicis longus tendon
• extensor digitorum tendons
• extensor indices tendon
• extensor digiti minimi tendon
• extensor carpi ulnaris tendon

Radial surface

• abductor pollicis longus tendon
• extensor pollicis brevis tendon

The tendon of the brachioradialis muscle attaches to the styloid process of the distal radius. In turn, it does not pass over the radiocarpal joint.

Innervation

• anterior interosseous nerve arising from median nerve (C5-T1)
• posterior interosseous nerve arising from radial nerve (C7-C8)

Arterial Supply

• palmar carpal arch
  • formed by palmar carpal branches of radial and ulnar arteries
  • reinforced by the anterior interosseous artery and penetrating deep branches of the deep palmar arch
• dorsal carpal arch
  • formed by dorsal carpal branches of the radial and ulnar arteries
  • reinforced by the anterior and posterior interosseous arteries

Variant anatomy

Ulnar variance refers to the relative positioning of the ulnar and radial articular surfaces at the level of the radiolunate articulation.

• neutral: same level
• positive: ulna is distal to the radius
• negative: ulna is proximal to the radius