Wrist Joint

The wrist connects the forearm to the hand. It consists of 8 carpal bones, multiple joints, and various supporting ligaments, as well as the distal bones of the forearm and the proximal portion of the 5 metacarpal bones of the hand. The wrist is crucial for the functioning of the upper limb, and it provides stability while positioning the hand for intricate motions.

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Bones of the Wrist

The bones of the wrist consist of:

  • Distal radius and ulna: The distal ulna is not technically part of the wrist, as it articulates distally with the triangular fibrocartilage complex (TFCC).
  • 5 proximal metacarpals 
  • 8 carpal bones, arranged in 2 rows:
    1. Proximal row (lateral to medial): scaphoid, lunate, triquetrum, and pisiform
    2. Distal row (lateral to medial): trapezium, trapezoid, capitate, and hamate

There are many mnemonics to help memorize the order and location of the carpal bones. They are learned from lateral to medial and proximal to distal: scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, hamate.

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Proximal and distal rows of the carpal bones

The proximal and distal rows of the carpal bones

Image by Lecturio.

Joints of the Wrist

The wrist is able to move in multiple directions, as it functions as a stable platform for the hand.

JointTypeComponentsLigamentsFunction
Distal radioulnarPivot jointHead of ulna and ulnar notch on radius
  • Palmar and dorsal radioulnar ligaments
  • Articular disk
Supination-pronation
RadiocarpalSynovial ellipsoid jointDistal radius and proximal row of carpal bones (except pisiform)
  • Radial and ulnar collateral ligaments
  • Palmar and dorsal radiocarpal ligaments
  • Flexion-extension
  • Abduction-adduction (of the hand)
MidcarpalCompound synovialProximal and distal row of carpal bonesIntercarpal, volar, dorsal, radial, and ulnar ligamentsSliding and gliding
IntercarpalAmphiarthrosesAmong the carpal bones of each rowIntercarpal, dorsal, and volar ligamentsStabilize the wrist
CarpometacarpalAmphiarthroses (2nd–5th)Distal carpal and 2nd–5th metacarpalsDorsal and palmar carpometacarpal ligamentsLimited gliding
Saddle (thumb)Trapezium and 1st metacarpalIntermetacarpal, dorsoradial, collateral, and volar ligaments
  • Flexion-extension
  • Abduction-adduction
  • Opposition
  • Circumduction

Movements of the Wrist and Associated Muscles

The wrist acts as a transition between the forearm and hand. The table below summarizes the forearm muscles and their associated movements. The name of each muscle is a reflection of the action of the muscle on the wrist and hand.

Table: Forearm muscles and their associated movements
MovementMuscle
FlexionMain:
  • Flexor digitorum superficialis
  • Flexor digitorum profundus
Assisted by:
  • Palmaris longus
  • Flexor carpi radialis
  • Flexor carpi ulnaris
ExtensionMain:
  • Extensor carpi radialis longus and brevis
  • Extensor carpi ulnaris
  • Extensor digitorum
Assisted by: extensor retinaculum
AbductionThe following extensor and flexor muscles work in tandem to cause abduction:
  • Extensor carpi radialis longus and brevis
  • Flexor carpi radialis
AdductionThe following extensor and flexor muscles work in tandem to cause adduction: flexor and extensor carpi ulnaris

Notable Anatomical Features

Carpal tunnel

The carpal tunnel is formed by the following:

  • Anteriorly: the fibrous flexor retinaculum 
  • Posteriorly: the concave palmar surface of the carpal bones 
  • Contents of the carpal tunnel:
    • Median nerve
    • Tendons of the flexor digitorum superficialis (4)
    • Tendons of the flexor digitorum profundus (4)
    • Tendon of the flexor pollicis longus (in radial sheath; 1)
Structure and contents of the carpal tunnel

Structure and contents of the carpal tunnel

Image by Lecturio.

Ulnar canal (Guyon’s canal)

  • The ulnar canal or Guyon’s canal is formed by the following:
    • Superficially: palmar carpal ligament 
    • Floor: flexor retinaculum and hypothenar muscles
    • Medially: pisiform 
    • Laterally: hook of the hamate
  • Contents of the ulnar tunnel:
    • Ulnar nerve
    • Ulnar artery
Guyon’s canal Wrist

Cross-section of the wrist showcasing Guyon’s canal containing the ulnar artery and nerve, superior to the flexor retinaculum and carpal tunnel

Image by Lecturio.

The anatomical snuff box

  • Boundaries of the anatomical snuff box (or radial fossa):
    • Lateral/radial: tendons of extensor pollicis brevis and abductor pollicis longus 
    • Medial/ulnar: tendon of extensor pollicis longus tendon
    • Proximal: styloid process of the radius
    • Distal: apex of the triangle created by these tendons
    • Floor: trapezium and scaphoid (palpable)
  • Contents of the ulnar tunnel:
    • Radial artery
    • Superficial branch of radial nerve (meralgia paresthetica: compression or injury of this nerve at the wrist)
    • Origin of the cephalic vein
    • Scaphoid and trapezium bones
Wrist - Anatomical snuff box

Medial view of the hand and wrist, featuring the borders and contents of the anatomical snuff box

Image by Lecturio.

Clinical Relevance

Common problems associated with the wrist

  • Carpal tunnel syndrome: the most common compressive neuropathy, which may be precipitated by repetitive vibration and motions. Associated with diabetes, thyroid disease, rheumatoid arthritis, and pregnancy. Occurs from the narrowing of the carpal tunnel and subsequent compression of the median nerve and the 9 flexor tendons within it. Can lead to pain and paresthesia in the median nerve distribution and thenar muscle atrophy.
  • Scaphoid fracture: the most commonly fractured carpal bone; occurs secondary to a fall onto an outstretched hand and presents with tenderness at the anatomical snuffbox. Treatment can include prolonged wrist immobilization or surgical intervention and complications including nonunion and avascular necrosis.
  • Lunate dislocation: anterior dislocation may precipitate acute carpal tunnel syndrome. These injuries are commonly missed on initial presentation.
  • De Quervain’s tenosynovitis: a stenosing tenosynovitis of the 1st dorsal compartment, which consists of the abductor pollicis longus and extensor pollicis brevis. Usually occurs secondary to repetitive motion/overuse and may be associated with rheumatoid arthritis and mothers with toddlers. Classic physical examination test is Finkelstein’s maneuver.  
  • Ulnar nerve neuropathy or entrapment: The ulnar nerve may be compressed or traumatically injured at the wrist within the ulnar or Guyon’s canal. The injury causes paresthesias, numbness, and/or pain in the ulnar half of the hand, and in severe cases may lead to “claw hand” (4th and 5th finger hyperextension at metacarpophalangeal joints and flexion of the interphalangeal joints).  Also called “handlebar palsy” in cyclists.

Important physical examination tests of the wrist

  • Watson’s test: used to assess for ligamentous instability between the scaphoid and lunate bones. The examiner grasps the wrist in slight extension and ulnar deviation with thumb over the scaphoid tubercle on the palmar side of the wrist. Pressure is then applied to the scaphoid while the patient’s hand is deviated radially. A positive test is localized pain or laxity.
  • Finkelstein’s test: used in the assessment of de Quervain’s tenosynovitis. The patient makes a fist around their thumb and moves the hand into ulnar deviation. A positive test is sharp pain over the tendons in the first dorsal compartment along the distal radial styloid.
  • Tinel’s sign: Used in the evaluation of carpal tunnel syndrome, this test is done by lightly tapping over the median nerve on the volar surface of the wrist. A positive test elicits paresthesia in the median nerve distribution.
  • Phalen’s sign: Patient flexes both wrists and pushes the dorsal surfaces of both hands together for 30–60 seconds. A positive test elicits burning or tingling in the distribution of the median nerve, suggestive of carpal tunnel syndrome.

References

  1. Drake, R.L., Vogl, A.W., & Mitchell, A.W.M. (2014). Gray’s Anatomy for Students (3rd ed.). Philadelphia, PA:  Churchill Livingstone.

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