The wrist is a complex synovial joint formed by articulations of the radius, the articular disc of the distal radioulnar joint and the carpal bones.

Terminology

Somewhat confusingly, the term carpus can be used as a synonym for the wrist joint as a whole, or in a more restricted sense to refer to the eight bones of the wrist (cf. tarsus).

Gross anatomy

Articulations

The "wrist joint" is really made up of three separate joints ¹:

• radiocarpal: concave distal surface of the radius and the attached articular disc of the distal radioulnar joint proximally with the convex surface of the proximal carpal row (the scaphoid, lunate and triquetral bones) distally

• distal radioulnar: ulnar notch of the distal radius with the head of the ulna, united by the articular disc

• midcarpal: scaphoid, lunate and triquetrum proximally with the trapezium, trapezoid, capitate and hamate distally

Movements

Movements at the condyloid radiocarpal joint of the wrist include ¹:

• flexion

  • primary: flexor carpi radialis and flexor carpi ulnaris

  • secondary: palmaris longus, flexor pollicis longus, flexor digitorum superficialis and flexor digitorum profundus

• extension

  • primary: extensor carpi radialis longus and brevis, extensor carpi ulnaris

  • secondary: extensor digitorum

• adduction (ulnar deviation)

  • simultaneous contraction of flexor and extensor carpi ulnaris

• abduction (radial deviation)

  • simultaneous contraction of extensor carpi radialis longus and brevis in addition to flexor carpi radialis

• circumduction

  • the sequential occurrence of the above four movements produces circumduction

A greater proportion of the total range (60^o) of wrist extension occurs at the radiocarpal joint ¹. In contrast, a greater proportion of the total range (80^o) of wrist flexion occurs at the midcarpal joint, which is also the primary joint involved in wrist adduction and abduction ².

Ligaments

The wrist joint has intrinsic and extrinsic stabilizing structures ^1,3.

Intrinsic

• lunotriquetral ligament

• scapholunate ligament complex

• triangular fibrocartilage complex

  • triangular ligament

  • ulnomeniscal homologue

Extrinsic

• volar radioulnar ligament

• volar radiocarpal ligaments

  • radial collateral ligament of the wrist

  • radioscapholunate ligament

    • not a true ligament; does not provide mechanical strength

    • functions as a neurovascular conduit ⁴

  • radioscaphocapitate ligament

  • long radiolunate ligament

  • short radiolunate ligament

  • Vickers ligament

• volar ulnocarpal ligaments

  • ulnolunate ligament

  • ulnotriquetral ligament

  • ulnocapitate ligament

• dorsal ligaments

  • radioscaphoid ligament

  • radiolunate ligament

  • dorsal radiotriquetral ligament

  • dorsal radioulnar ligament

  • ulnar collateral ligament of the wrist

  • dorsal intercarpal ligament

​Associated structures

• flexor retinaculum

• extensor retinaculum

Joint capsule

A two-layered synovial capsule envelops the radiocarpal joint, attaching proximally to the radius and ulna, and distally to the carpal bones. The joint capsule thickens to form palmar, dorsal and collateral ligaments ¹.

Fat pads

• dorsal fat pad

• pronator quadratus fat pad

• scaphoid fat pad

Arterial supply

Arterial supply of the wrist is via the palmar and dorsal carpal arches ¹.

• dorsal carpal arch

  • supplied by dorsal carpal branches of the radial and ulnar arteries

  • Reinforced by the anterior and posterior interosseous arteries

• palmar carpal arch

  • supplied by palmar carpal branches of the radial and ulnar arteries

  • reinforced by the anterior interosseous artery, alongside penetrating deep branches of the deep palmar arch

Innervation

Multiple articular branches are derived from several nerves (Hilton's law) ¹:

• anterior interosseous nerve from the median nerve

• posterior interosseous nerve from the radial nerve

• deep and dorsal branches of the ulnar nerve

Variant anatomy

• ulnar variance

  • describes the relative position of the ulnar and radial articular surfaces at the level of the radiolunate articulation

    • neutral: ulna and radius positioned at the same level

    • negative ulnar variance: abnormally shortened ulna projects proximal to the radius

    • positive ulnar variance: abnormally lengthened ulna projects distal to the radius

• lunate morphology

• carpal boss

• carpal coalition

  • lunotriquetral coalition: most common

  • capitohamate coalition

• bifid median nerve

• persistent median artery of the forearm

• extensor digitorum brevis manus

Ossification

• ossification centers of the wrist

Related pathology

• signs

  • dinner fork deformity

  • spilled teacup sign

  • piece of pie sign

• traumatic

  • pseudo-Madelung deformity

  • gymnast wrist

  • triangular fibrocartilage complex injury

• congenital

  • Madelung deformity