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.
Bones and joints
Bones of the forearm
- The forearm is the portion of the upper limb between the elbow and wrist joint.
- The bones of the forearm are the radius and ulna.
- They articulate with each other at the proximal and distal radioulnar joints.
- The radioulnar joints are responsible for forearm pronation and supination.
- The proximal ends of the radius and ulna articulate with the distal humerus to form the elbow joint.
- The interosseus membrane connects the shafts of the radius and ulna and stabilizes the radioulnar joints.
- Description: the medial bone of the forearm (when in anatomical position)
Parts of the ulna
- Coronoid process: an anterior-facing bony projection that forms the lower lip of the trochlear notch
- Trochlear notch: a concavity between the olecranon and the coronoid process that articulates with the trochlea of the humerus (humeroulnar joint)
- Radial notch: a lateral continuation of the trochlear notch that accommodates the head of the radius, forming the proximal radioulnar joint
- Tuberosity of the ulna: a rough area of bone just distal to the coronoid process into which the brachialis muscle inserts
- Diaphysis: triangular in shape, with three surfaces (anterior, posterior, and medial) and three borders (anterior, posterior, and interosseous)
- Distal ulna
- Proximal ulna
- Description: the lateral bone of the forearm (when in anatomical position)
Parts of the radius
- Head of radius
- Radial tuberosity
- Radial styloid: insertion site for the brachioradialis muscle and the radial collateral ligament
- Carpal articular surface of the radius
- Ulnar notch of the radius
- Dorsal tubercle of the radius (Lister tubercle)
- Proximal radius
Joints of the forearm
- General: the radius and ulna articulate with one another proximally and distally.
- Type of joint: pivot joint, allowing the distal end of the radius to move anterior and medially over the ulna (i.e., forearm pronation and supination)
- Proximal radioulnar joint: allows articulation of the head of the radius and the radial notch on the ulna
- Distal radioulnar joint: allows articulation of the ulnar head and ulnar notch on the radius
- Movement: forearm pronation and supination
Interosseous membrane of the forearm
- Definition: fibrous connective tissue that connects the lateral ulna to the medial radius
Bones of the wrist (carpal bones)
- Description: Eight carpal bones, arranged in two rows of four bones each, make up the wrist joint.
|Scaphoid (bone)|| |
- Definition: a triangular groove on the radial aspect of the dorsal wrist that becomes prominent when extending and abducting the thumb
Bones of the hand
- Metacarpal bones
Joints of the wrist and hand
|Characteristics of the joints of the wrist and hand|
|Joints of the wrist|
|Midcarpal joint|| || |
|Intercarpal joint|| || |
|Carpometacarpal joint (CMC)||2nd –5th CMC joints|| |
|Carpometacarpal joint of the thumb|
|Joints of the hand|
|Metacarpophalangeal joint(MCP)|| |
2nd–5th MCP joints
|1st MCP joint|| |
|Interphalangeal joint|| |
Muscles and fascia
Muscles of the forearm 
- The anterior (volar) compartment
- The posterior (dorsal) compartment
- Most muscles of the forearm move the wrist and hand joints (extrinsic muscles of the hand).
Flexor compartment of the forearm (anterior compartment) 
Superficial flexor compartment
|Pronator teres|| || |
|Flexor carpi radialis|| || |
|Flexor digitorum superficialis|| || |
|Palmaris longus || || |
|Flexor carpi ulnaris|| |
|Deep flexor compartment|
|Flexor digitorum profundus|
|Flexor pollicis longus|| |
|Pronator quadratus|| || |
Extensor compartment of the forearm (posterior compartment)
Extensor carpi radialis longus
Extensor carpi radialis brevis
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Extensor digiti minimi
Extensor carpi ulnaris
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|Deep extensor compartment|
Abductor pollicis longus
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Extensor pollicis longus
Extensor pollicis brevis
|Extensor indicis|| || |
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.
Muscles of the hand
- Based on where the muscle belly is located, the muscles of the hand are divided into two groups.
- Extrinsic muscles of the hand: The muscle bellies are located in the forearm (see “Muscles of the forearm” above).
- Intrinsic muscles of the hand: The muscle bellies are located within the hand.
- All hand muscles are supplied by the median nerve or ulnar nerve.
- In the resting position, there is a balance between flexors and extensors (both extrinsic and intrinsic) of the hand.
|Characteristics of the thenar muscles|
Abductor pollicis brevis
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Flexor pollicis brevis
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|Characteristics of the hypothenar muscles|
|Abductor digiti minimi|| |
|Flexor digiti minimi brevis|| |
|Opponens digiti minimi|| || || |
Lumbricals and interossei
- There are four lumbricals.
- There are seven interossei muscles: four on the dorsal side and three on the palmar side of the metacarpal bones.
- These muscles exert their actions on the fingers, but not the thumb.
|Characteristics of the lumbricals and interosseous muscles|
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Palmar interossei muscles I–III
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Dorsal interossei muscles I–IV
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Fascia and retinacula of the wrist and hand 
|Characteristics of the fascia and retinacula of the wrist and hand|
Flexor retinaculum of the hand
(flexor retinaculum; transverse carpal ligament)
|Palmar aponeurosis|| || |
|Carpal tunnel|| || |
Vasculature and lymphatic drainage
- The arterial system of the forearm originates from the brachial artery in the cubital fossa, where it bifurcates into the ulnar and radial arteries.
- The and the are the two major blood vessels that supply blood to the forearm and hand.
- These two arteries anastomose in the hand, forming the and the .
- The venous system of the forearm and hand consists of a superficial and a deep venous system.
Superficial venous system
- Located within the subcutaneous tissue
- Formed by the , , and the
Deep venous system
- Located below the deep fascia
- Formed by:
- The deep veins communicate with superficial veins via perforator veins.
- Perforating veins run between the deep and superficial veins of the upper limb, connecting the two systems.
Superficial lymphatics: accompany the superficial veins of the upper limb
- The lymphatics at the medial side (radial) of the hand and forearm accompany the cephalic vein and drain mainly into the apical group of axillary lymph nodes.
- The lymphatics at the lateral side (ulnar) of the hand and forearm accompany the basilic vein and drain first into the cubital lymph nodes (epitrochlear nodes), then terminate in the lateral group of axillary lymph nodes.
- Deep lymphatics: follow the deep veins and drain into the axillary group of lymph nodes
|Motor innervation of the forearm and hand|
|Median nerve|| |
|Ulnar nerve|| || |
|Radial nerve|| || || |
- The sensory innervation of the hand is provided by the , , and .
- The sensory innervation of the forearm is provided by the , , and .
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
Bones and joints
- (e.g., , )
- Metacarpal bones: boxer's fracture (metacarpal neck fracture)
Joints of the wrist and hand
Trapeziometacarpal osteoarthritis ( )
- 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. 
- Clinical features: pain and swelling at the base of the thumb
- Diagnostics 
- 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
- Interphalangeal joints
- Trapeziometacarpal osteoarthritis ( )