The forearm extends from the elbow to the wrist and contains the radius and ulna. The wrist contains eight carpal bones (scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, and hamate), which articulate proximally with the radius (the radiocarpal joint) and distally with the metacarpal bones, which make up the bones of the hand together with the phalanges. The forearm has an anterior compartment, which consists of the flexor group of muscles innervated by the ulnar and median nerve, and a posterior compartment, which consists of the extensor group of muscles 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 the supination of the forearm and extension of the wrist and fingers. Both groups of muscles are furthermore involved in the abduction and adduction of the wrist. The intrinsic muscles of the hand are responsible for hand as well as finger movement and comprise 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. These 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 joints.
- 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.
- The medial bone of the forearm
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: 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 to 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
- The lateral bone of the forearm
Parts of the radius
- Head of radius:
- Radial tuberosity: distal to the medial aspect of the head; provides attachment for the biceps brachii tendon
- Radial styloid: insertion site for the brachioradialis muscle
- Carpal articular surface of the radius
- Ulnar notch of the radius: on the medial surface; articulates with the ulna, forming the distal radioulnar joint
- Dorsal tubercle of radius (Lister tubercle): palpable bony prominence of the distal radius
- Proximal radius
- Clinical significance: (including )
Joints of the forearm
- The radius and ulna articulate with one another proximally and distally.
- Type of joint: pivot joint, allowing only uniaxial rotational movement (i.e., forearm pronation and supination)
- Proximal radioulnar joint: articulation of the head of the radius and the radial notch on the ulna
- Distal radioulnar joint: articulation of the ulnar head and ulnar notch on the radius
- Clinical significance:
- Movement: forearm pronation and supination (uniaxial movement; 90°/0°/90°)
Interosseous membrane of the forearm
- Definition: fibrous connective tissue that connects the lateral ulna to the medial radius
Bones of the wrist (carpal bones)
- Eight carpal bones, arranged in two rows of four bones each, make up the wrist joint.
- Proximal row (lateral to medial): scaphoid, lunate, triquetrum, and pisiform
- Distal row (lateral to medial): trapezium, trapezoid, capitate, and hamate
- Clinical significance
Bones of the hand
- There are five metacarpal bones that are located distal to the carpal bones.
- Each has a base that articulates with the carpal bones (carpometacarpal joints), a head that articulates with the proximal phalanges (metacarpophalangeal joints), and a shaft in between.
- Clinical significance
Joints of the wrist and hand
|Joints of the wrist|| |
|Carpometacarpal joint|| |
|Joints of the hand||Metacarpophalangeal joint (MCP)|| |
|Interphalangeal joint|| |
Muscles and fascia
Muscles of the forearm
- The anterior (volar) compartment contains the flexor group of muscles that is innervated by the median and ulnar nerves.
- The posterior (dorsal) compartment contains the extensor group of muscles that is innervated by the radial nerve.
- Most muscles of the forearm move the wrist and hand joints (extrinsic muscles of the hand).
- Only pronation and supination occur at the forearm joints.
Flexor compartment of the forearm
Ask the patient to perform the muscle's functions against resistance
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|| || |
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, both of which are innervated by the ulnar nerve.
Extensor compartment of the forearm
Extensor carpi radialis longus
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Extensor carpi radialis brevis
Main extensors of all digits except the thumb
Extensor digiti minimi
Extensor carpi ulnaris
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|Anconeus|| || |
Deep extensor compartment
Abductor pollicis longus
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Extensor pollicis longus
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Extensor pollicis brevis
|Extensor indicis|| || |
The 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 its branch, the posterior interosseous nerve!
- Definition: a triangular groove on the radial aspect of the dorsal wrist that becomes prominent on extending and abducting the thumb
Muscles of the hand
- The muscles of the hand are divided into two groups based on where the muscle belly is located.
- Extrinsic muscles of the hand: Muscle bellies are located in the forearm (see “muscles of the forearm” above).
- Intrinsic muscles of the hand: 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.
- 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.
Abductor pollicis brevis
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Flexor pollicis brevis
|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.
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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 hand
Flexor retinaculum of the hand
(flexor retinaculum; transverse carpal ligament)
|Palmar aponeurosis|| |
|Carpal tunnel|| |
|Radial artery|| |
|Ulnar artery|| |
|Deep palmar arch|
|Superficial palmar arch|
|Basilic vein|| |
|Median antebrachial vein|
- Lie below the deep fascia and communicate with superficial veins via perforator veins
- Each artery has a pair of accompanying veins (venae comitantes): a radial vein and an ulnar vein.
- Brachial vein: formed by the radial and ulnar veins, which unite at the elbow
Superficial lymphatics: accompany the superficial veins of the upper limb
- The radial side of the hand and forearm accompany the cephalic vein and drain mainly into the apical group of axillary lymph nodes.
- The ulnar side 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
|Radial nerve|| |
Sensory innervation of the forearm and hand
|Sensory innervation of the forearm|| |
Lateral cutaneous nerve of forearm
Medial cutaneous nerve of forearm
Posterior cutaneous nerve of arm
(inferior lateral cutaneous nerve)
|Sensory innervation of the hand||Median nerve|
Dermatomal distribution of the forearm and hand
- C6: posterolateral forearm, the thumb and lateral side of index finger
- C7: ventral forearm, the middle finger, medial side of index finger, and lateral side of ring finger
- C8: distal 1/3 of the medial forearm, the little finger, and medial side of the ring finger
- T1: proximal 2/3 of the medial forearm