Forearm, wrist, and hand

Summary

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

Injury to the radial or ulnar diaphysis can disrupt the proximal or distal radioulnar joints (see Monteggia fracture, Galeazzi fracture).

Ulna

Radius

Joints of the forearm

Radioulnar joints

Interosseous membrane of the forearm

Bones of the wrist (carpal bones)

Rows Carpal bones Characteristics

Proximal row

(lateral to medial)

Scaphoid
Lunate

Triquetrum

(Cuneiform)

Pisiform

Distal row

(lateral to medial)

Trapezium
Trapezoid
Capitate
Hamate

The carpal bones, from lateral to medial and proximal to distal can be remembered with the phrase "Some Lovers Try Positions That They Can't Handle."

Bones of the hand

Joints of the wrist and hand

Joint Characteristics
Joints of the wrist

Radiocarpal joint

(Wrist joint)

Midcarpal joint
Intercarpal joints
Carpometacarpal joint
Joints of the hand Metacarpophalangeal joint (MCP)
Interphalangeal joint

Muscles and fascia

Muscles of the forearm

Flexor compartment of the forearm

(Anterior compartment)

Compartments Muscle Origin Insertion Innervation Function

Testing

Ask the patient to perform the muscle's functions against resistance

Superficial flexor compartment

All have a common origin in the medial epicondyle of the humerus

Pronator teres
  • Pronate against resistance and palpate muscle belly
Flexor carpi radialis
  • Flex the wrist against resistance and palpate muscle belly
  • Abduct the wrist against resistance
Flexor digitorum superficialis
  • Flex the specific digit with the other fingers held in extension
Palmaris longus
  • Wrist flexion against resistance makes the tendon taut
Flexor carpi ulnaris
  • Flex the wrist against resistance and palpate the tendon
  • Adduct the wrist against resistance
Deep flexor compartment Flexor digitorum profundus
  • Interosseous membrane and the ulnar shaft (medial and anterior surfaces)
  • Hold the PIP in extension, and flex the DIP
Flexor pollicis longus
Pronator quadratus
  • Pronation against resistance with the wrist and fingers in neutral position

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

(Posterior compartment)

Compartment Muscle Origin Insertion Innervation Function Testing

Superficial compartment

Brachioradialis
  • Muscle belly becomes prominent on flexing the elbow against resistance, with the forearm in half-pronation

Extensor carpi radialis longus

ECRL

  • Base of 2nd metacarpal (dorsal aspect)
  • Muscle bellies become prominent on extending the wrist against resistance, with the forearm in pronation

Extensor carpi radialis brevis

ECRB

  • Base of 3rd metacarpal (dorsal aspect)

Extensor digitorum

Main extensors of all digits except the thumb

  • Wrist, MCP, PIP, and DIP: extension
  • Extension of the fingers against resistance

Extensor digiti minimi

EDM

  • Extension of the little finger (MCP, PIP, and DIP)
  • Extend the little finger with other fingers held in flexion

Extensor carpi ulnaris

ECU

  • Base of 5th metacarpal
  • Adduction of the wrist against resistance makes the tendon taut
Anconeus
  • Cannot be independently tested

Deep extensor compartment

Abductor pollicis longus

APL

  • Base of the 1st metacarpal
  • Abduction of the thumb against resistance makes the tendon taut

Extensor pollicis longus

EPL

Extensor pollicis brevis

EPB

Extensor indicis
  • Extensor expansion of index finger.
  • Extension of the index finger (MCP, PIP, and DIP)
  • Extend the index finger with other fingers held in flexion
Supinator muscle

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!

The superficial flexors originate from the medial epicondyle of the humerus and the superficial extensors from the lateral epicondyle of the humerus!

Anatomical snuffbox

Pain and tenderness in the anatomical snuffbox after trauma to the wrist is suggestive of a scaphoid fracture. These fractures can be difficult to see on plain x-ray.

Muscles of the hand

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.
Muscle Origin Insertion Innervation

Function

Testing

Abductor pollicis brevis

Opponens pollicis

  • First metacarpal bone
  • Opposition
  • Touch the tip of the little finger with the thumb, against resistance

Flexor pollicis brevis

  • Flexion of the 1st MCP against resistance, with IP in extension
  • Capitate, base of the 2nd and 3rd metacarpals

Adductor pollicis

  • Adduct the thumb against resistance

Hypothenar muscles

These form the hypothenar eminence and exert their action mainly on the 5th MCP.

Muscle Origin Insertion Innervation Function Testing
Abductor digiti minimi
  • Abduct the 5th finger against resistance
Flexor digiti minimi brevis
  • Flex the 5th MCP against resistance with the IP in extension
Opponens digiti minimi
  • Ulnar border of the 5th metacarpal bone
  • Opposition
  • Touch the tip of the thumb against resistance
Palmaris brevis
  • Strengthens palmar grip by wrinkling skin on the ulnar side of the palm
  • Puckering of skin on medial border of the palm when the tips of the 5th finger and thumb are in contact with each other

The muscles of the hypothenar eminence are innervated by the ulnar nerve.

Lumbricals and interossei

Muscle Origin Insertion Innervation Function Testing

Lumbricals

(I–IV)

  • Extensor apparatus of the fingers
  • With the PIP and DIP held in extension, the MCP is flexed against resistance

Palmar interossei muscles I–III

  • Extensor apparatus of digits 2, 4, 5
  • Adduct the fingers toward the midline
  • Adduct the index and little finger against resistance

Dorsal interossei muscles I–IV

  • Extensor apparatus of digits 2–5
  • Abduct the fingers away from the midline
  • Abduct the 2nd, 3rd, and 4th fingers against resistance

PAD: Palmar interossei ADduct the fingers. DAB: Dorsal interossei ABduct the fingers.

Fascia and retinacula of the hand

Structure Characteristics

Flexor retinaculum

(transverse carpal ligament)

Extensor retinaculum

(dorsal carpal ligament)

Palmar aponeurosis
  • Definition: a triangular thickening of the palmar deep fascia that invests the muscles of the hand
  • Attachments
    • The apex is a continuation of the palmaris longus tendon.
    • The base divides into 4 slips that insert into the skin overlying the MCP joints of the fingers.
  • Clinical significance: involved in Dupuytren contracture
Carpal tunnel

Ulnar canal

(Guyon canal)

The palmar aponeurosis is the structure that hypertrophies and contracts in Dupuytren disease

References:[1][2]

Vasculature

Arteries

Artery Characteristics
Radial artery
Ulnar artery
Deep palmar arch
Superficial palmar arch

Veins

Superficial veins

Vein Characteristics
Cephalic vein
Basilic vein
Median antebrachial vein

Deep veins

Lymphatic drainage

References:[3][4]

Innervation

Motor innervation

Motor nerve Characteristics
Median nerve
Ulnar nerve
Radial nerve
  • Forearm: all extensors (posterior compartment)
  • Hand: none

Sensory innervation of the forearm and hand

Sensory nerve Characteristics
Sensory innervation of the forearm

Lateral cutaneous nerve of forearm

(lateral antebrachial cutaneous nerve)

Medial cutaneous nerve of forearm

(medial antebrachial cutaneous nerve)

  • Origin: medial cord of the brachial plexus
  • Innervates: skin over the medial forearm

Posterior cutaneous nerve of arm

(inferior lateral cutaneous nerve)

Sensory innervation of the hand Median nerve
  • Radial 2/3 of the palm
  • Palmar aspect of the radial 3.5 fingers (i.e., the thumb, index finger, middle finger, and radial side of the ring finger)
  • Dorsal aspect of skin over the distal phalanges of the radial 3.5 digits
  • Autonomous sensory zone: tip of the index finger
Ulnar nerve
  • Ulnar 1/3 of the palm
  • Palmar and dorsal aspects of the ulnar 1.5 fingers (i.e., the little finger and the ulnar side of the ring finger)
  • Autonomous sensory zone: tip of the little finger
Radial nerve
  • Radial 2/3 of the dorsal aspect of the hand
  • Dorsal aspect of the radial 3.5 fingers, except the area supplied by the median nerve
  • Autonomous sensory zone: 1st web space (between the thumb and index finger)

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

Clinical significance