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Forearm, wrist, and hand

Last updated: April 18, 2021

Summarytoggle arrow icon

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 of the forearm

Ulna

Radius (bone)

Joints of the forearm

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)

Rows Carpal bones Characteristics

Proximal row

(lateral to medial)

Scaphoid (bone)
Lunate (bone)

Triquetrum

(formerly cuneiform)

Pisiform

Distal row

(lateral to medial)

Trapezium
Trapezoid (bone)
Capitate
Hamate

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.

Bones of the hand

Joints of the wrist and hand

Characteristics of the joints of the wrist and hand
Joints Type Components Movements/function
Joints of the wrist

Radiocarpal joint

(wrist joint)

Midcarpal joint
  • Sliding and gliding
Intercarpal joint
  • Stabilizes the wrist
Carpometacarpal joint (CMC) 2nd –5th CMC joints
  • Minimal gliding
  • Stabilizes the structure of the wrist
Carpometacarpal joint of the thumb
Joints of the hand
Metacarpophalangeal joint(MCP)

2nd–5th MCP joints

1st MCP joint
Interphalangeal joint
  • Proximal interphalangeal joint (PIP) and distal interphalangeal joint (DIP)

Muscles of the forearm [1]

Flexor compartment of the forearm (anterior compartment) [1]

Superficial flexor compartment

Muscle Origin Insertion Innervation Function

Testing

Pronator teres
  • Pronate the patient's forearm against resistance, while palpating the muscle belly.
Flexor carpi radialis
  • Flex the patient's wrist against resistance, while palpating the muscle belly.
  • Abduct the wrist against resistance.
Flexor digitorum superficialis
  • Middle phalanges of the digits, except the thumb
  • Flex the patient's specific digit while holding the other fingers in extension.
Palmaris longus [1]
  • Flexing the patient's wrist against resistance will make the tendon taut.
Flexor carpi ulnaris
  • Flex the patient's wrist against resistance, while palpating the tendon.
  • Adduct the patient's wrist against resistance.
Deep flexor compartment
Flexor digitorum profundus
  • Interosseous membrane and the ulnar shaft (medial and anterior surfaces)
  • Hold the patient's PIP in extension, and flex the DIP.
Flexor pollicis longus
Pronator quadratus
  • Pronate the patient's forearm against resistance, while holding 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, which are innervated by the ulnar nerve.

Extensor compartment of the forearm (posterior compartment)

Superficial compartment
Muscle Origin Insertion Innervation Function Testing
Brachioradialis
  • Muscle belly becomes prominent on flexing the patient's elbow against resistance, with the forearm in half-pronation.

Extensor carpi radialis longus

(ECRL)

  • Muscle bellies become prominent on extending the patient's wrist against resistance, with the forearm in pronation.

Extensor carpi radialis brevis

(ECRB)

Extensor digitorum

(ED)

  • Extend the patient's fingers against resistance.

Extensor digiti minimi

(EDM)

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

Extensor carpi ulnaris

(ECU)

  • Adducting the patient's wrist against resistance makes the tendon taut.
Anconeus
  • Cannot be independently tested
Deep extensor compartment

Abductor pollicis longus

(APL)

  • Abducting the patient's 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

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.

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.

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.

Characteristics of the thenar muscles
Muscle Origin Insertion Innervation

Function

Testing

Abductor pollicis brevis

Opponens pollicis

  • Thumb opposition
  • Touch the tip of the patient's little finger with the thumb, against resistance.

Flexor pollicis brevis

  • Flex the patient's 1st MCP against resistance, while holding the IP in extension.

Adductor pollicis

  • Adduct the patient's thumb against resistance.

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.

Characteristics of the hypothenar muscles
Muscle Origin Insertion Innervation Function Testing
Abductor digiti minimi
  • Abduct the patient's 5th finger against resistance.
Flexor digiti minimi brevis
  • Flex the patient's 5th MCP against resistance with the IP in extension.
Opponens digiti minimi
  • Opposition
  • Touch the patient's tip of the thumb against resistance.
Palmaris brevis
  • Strengthens palmar grip by wrinkling skin on the ulnar side of the palm
  • The skin should pucker on the medial border of the palm when the tips of the patient's 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

Characteristics of the lumbricals and interosseous muscles
Muscle Origin Insertion Innervation Function Testing

Lumbricals I–IV

  • Extensor apparatus of the fingers
  • With the PIP and DIP held in extension, flex the patient's MCP against resistance.

Palmar interossei muscles I–III

  • Extensor apparatus of digits 2, 4, 5
  • Adduct the fingers toward the midline
  • Adduct the patient's 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 patient's 2nd, 3rd, and 4th fingers against resistance.

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

Fascia and retinacula of the wrist and hand [1]

Characteristics of the fascia and retinacula of the wrist and hand
Structure Definition Attachments Structures/contents Function

Flexor retinaculum of the hand

(flexor retinaculum; transverse carpal ligament)

  • Forms the roof of the carpal tunnel
  • Holds the flexor tendons in place

Extensor retinaculum

(dorsal carpal ligament)

  • Fibrous thickening of the deep fascia of the forearm that is located on the dorsal aspect of the wrist
  • Holds the extensor tendons in place
Palmar aponeurosis
  • A triangular thickening of the palmar deep fascia that invests the muscles of the hand
  • The apex: continuation of the palmaris longus tendon
  • The base: divides into 4 slips that insert into the skin overlying the MCP joints of the fingers
  • Consists of fibers in multiple directions that distally go on to form the pretendinous bands
  • Creates a semirigid barrier between the skin and the neurovascular and tendon structures
  • Forms part of the flexor tendon pulley
Carpal tunnel
  • Passageway from the forearm to the anterior hand

Ulnar canal

(Guyon canal)

  • An osteofibrous channel on the medial aspect of the palm

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

Arteries

Veins

Lymphatic drainage

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

Motor innervation of the forearm and hand
Forearm Hand Deficit
Median nerve
  • Pronation of the forearm
  • Opposition of thumb
Ulnar nerve
Radial nerve
  • -
  • Extension of the wrist

Sensory innervation

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

Muscles and fascia

Innervation

Other

  1. Standring S. Gray's Anatomy: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences ; 2016
  2. 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