Summary
The wrist is comprised of the carpus and the radiocarpal joint. The carpus is the complex of eight carpal bones (scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, and hamate), while the radiocarpal joint is the region of articulation between the carpus and radius. Distally, the carpus articulates with the metacarpal bones, which, together with the phalanges, make up the bones of the hand. The forearm (lower arm or antebrachium) has an anterior compartment, which consists of the flexor group of muscles and is innervated by the ulnar and median nerve, and a posterior compartment, which consists of the extensor group of muscles and is innervated by the radial nerve. The flexor group of muscles is involved in pronation of the forearm and flexion of the wrist and fingers, while the extensor group of muscles is involved in supination of the forearm and extension of the wrist and fingers. Both groups of muscles are also involved in the abduction and adduction of the wrist. The intrinsic muscles of the hand are responsible for hand and finger movement and consist of the thenar, hypothenar, lumbrical, and interossei muscles. The forearm, the wrist, and the hand are perfused by the radial and ulnar artery and their branches. They are drained by the superficial cephalic and basilic veins and the deep radial and ulnar veins.
Overview
Bones and joints
Ulna
Radius (bone)
Radioulnar joint
Injury to the radial or ulnar diaphysis can disrupt the proximal or distal radioulnar joints.
Interosseous membrane of the forearm
Bones of the wrist (carpal bones)
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“Stubborn Larry Tried Pills That Triumphantly Cured Him:” Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate (carpal bones from lateral to medial and proximal to distal).
Anatomical snuffbox
Pain and tenderness in the anatomical snuffbox after trauma to the wrist suggest a scaphoid fracture. These fractures can be difficult to see on plain x-ray.
Muscles and fascia
Muscles of the forearm [1]
The median nerve innervates all the forearm flexors, with the exception of the flexor carpi ulnaris and the ulnar portion of the flexor digitorum profundus, which are innervated by the ulnar nerve.
De Quervain syndrome involves inflammation of the tendons on the radial side of the wrist, the extensor pollicis brevis, and the abductor pollicis longus.
Supinator syndrome is a relatively rare entrapment syndrome in which the deep branch of the radial nerve is trapped in the supinator tunnel between the heads of the supinator muscle, resulting in weak finger extension. Causes include trauma or overuse of the supinator muscle.
The forearm extensors are innervated by the radial nerve or by its branch, the posterior interosseous nerve.
The superficial flexors originate from the medial epicondyle of the humerus, and the superficial extensors from the lateral epicondyle of the humerus.
Thenar muscles
These muscles form the thenar eminence (the muscular prominence on the palmar aspect at the base of the thumb) of the palm and exert their action mainly on the 1st MCP.
Hypothenar muscles
These form the hypothenar eminence (the muscular prominence located on the palmar aspect at the base of the 5th finger) and exert their action mainly on the 5th MCP.
The muscles of the hypothenar eminence are innervated by the ulnar nerve.
Lumbricals and interossei
PAD: Palmar interossei ADduct the fingers. DAB: Dorsal interossei ABduct the fingers.
Fascia and retinacula of the wrist and hand [1]
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The palmar aponeurosis is the structure that hypertrophies and contracts in Dupuytren disease.
Vasculature and lymphatic drainage
Innervation
The forearm and hand are innervated by branches of the brachial plexus. The median, radial, and ulnar nerves are terminal branches of the brachial plexus that provide motor and sensory innervation.
Motor innervation
- For further information on motor innervation of the forearm and hand, see “Neurovasculature of the upper limbs.”
Sensory innervation
- The sensory innervation of the hand is provided by the median nerve, radial nerve, and ulnar nerve.
- The sensory innervation of the forearm is provided by the lateral cutaneous nerve of the forearm, medial cutaneous nerve of the forearm, and posterior cutaneous nerve of the arm.
- For further information on sensory innervation of the forearm and hand, see “Neurovasculature of the upper limbs.”
Dermatomal distribution of the forearm and hand
- C6: posterolateral forearm, thumb, and lateral side of the index finger
- C7: ventral forearm, middle finger, medial side of the index finger, and lateral side of the ring finger
- C8: distal third of the medial forearm, the little finger, and medial side of the ring finger
- T1: proximal two-thirds of the medial forearm
Clinical significance
Bones and joints
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Ulna
- Ulnar fractures
- Ulnar styloid fracture (associated with distal radius fractures)
- Radius
- Distal radius fractures (e.g., Colles fracture, Smith fracture)
- Radial head subluxation
- Radioulnar joint
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Carpal bones
- Scaphoid fracture
- Lunate dislocation
- Metacarpal bones: boxer's fracture (metacarpal neck fracture)
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Joints of the wrist and hand
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Trapeziometacarpal osteoarthritis
(rhizarthrosis)
- The saddle joint of the thumb is susceptible to cartilaginous degeneration, resulting in osteoarthritis.
- Approximately 8–12% of the population is affected by carpometacarpal osteoarthritis. [2]
- Clinical features: pain and swelling at the base of the thumb
- Diagnostics [2]
- Thumb grind test: performed by applying axial compression along the plane of the metacarpal bone and rotating the thumb metacarpal base. Pain or crepitus indicates a positive grind test, suggesting carpometacarpal osteoarthritis.
- Thumb lever test: performed by grasping the first metacarpal just distal to the base and moving it back and forth in the lateral and medial directions. Pain or crepitus indicates a positive lever test, suggesting carpometacarpal osteoarthritis.
- MCP extension test: performed by placing one finger on the interphalangeal joint and applying resistance against extension while the patient tries to extend the thumb. Pain or crepitus indicates a positive MCP extension test, suggesting carpometacarpal osteoarthritis.
- Treatment: may involve excision of the trapezium.
- Metacarpophalangeal joint: 1st MCP joint is affected early by rheumatoid arthritis
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Interphalangeal joints
- Bouchard nodes (in osteoarthritis) and Boutonniere deformity (in rheumatoid arthritis) affect the PIP.
- Heberden nodes (in osteoarthritis) and Swan neck deformity (in rheumatoid arthritis) affect the DIP.
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Trapeziometacarpal osteoarthritis
(rhizarthrosis)
Muscles and fascia
- De Quervain tenosynovitis
- Dupuytren contracture
- Carpal tunnel syndrome
- Guyon canal syndrome
- Supinator syndrome
Innervation
- Ulnar nerve entrapment
- Median nerve neuropathy
- Radial neuropathies
Other
- Finger injuries
- Volkmann ischemic contracture
- Compartment syndrome
References
- Standring S. Gray's Anatomy: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences ; 2016
- Model Z, Liu AY, Kang L, Wolfe SW, Burket JC, Lee SK. Evaluation of Physical Examination Tests for Thumb Basal Joint Osteoarthritis. Hand. 2016; 11 (1): p.108-112. doi: 10.1177/1558944715616951 . | Open in Read by QxMD