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:
- Proximal row (lateral to medial): scaphoid, lunate, triquetrum, and pisiform
- 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.
- So Long To Pinky, Here Comes The Thumb
- Some Lovers Try Positions That They Can’t Handle
- Sam Likes To Push The Toy Car Hard
Joints of the Wrist
The wrist is able to move in multiple directions, as it functions as a stable platform for the hand.
|Distal radioulnar||Pivot joint||Head of ulna and ulnar notch on radius||Supination-pronation|
|Radiocarpal||Synovial ellipsoid joint||Distal radius and proximal row of carpal bones (except pisiform)|
|Midcarpal||Compound synovial||Proximal and distal row of carpal bones||Intercarpal, volar, dorsal, radial, and ulnar ligaments||Sliding and gliding|
|Intercarpal||Amphiarthroses||Among the carpal bones of each row||Intercarpal, dorsal, and volar ligaments||Stabilize the wrist|
|Carpometacarpal||Amphiarthroses (2nd–5th)||Distal carpal and 2nd–5th metacarpals||Dorsal and palmar carpometacarpal ligaments||Limited gliding|
|Saddle (thumb)||Trapezium and 1st metacarpal||Intermetacarpal, dorsoradial, collateral, and volar ligaments|
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.
|Abduction||The following extensor and flexor muscles work in tandem to cause abduction:|
|Adduction||The following extensor and flexor muscles work in tandem to cause adduction: flexor and extensor carpi ulnaris|
Notable Anatomical Features
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)
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
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
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.
- Drake, R.L., Vogl, A.W., & Mitchell, A.W.M. (2014). Gray’s Anatomy for Students (3rd ed.). Philadelphia, PA: Churchill Livingstone.