Forearm, wrist, and hand

Overview

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
  • Type: realtively immobile compound synovial joint
  • Components: proximal and distal carpal bones
  • Movements
    • Sliding and gliding
Intercarpal joints
  • Type: amphiarthroses
  • Components: joints between the individual carpal bones of a row
  • Function: stabilizes the wrist
Carpometacarpal joint
  • 2nd–5th carpometacarpal joints: amphiarthroses between the carpal bones and metacarpal bones that stabilize the structure of the wrist
    • Movement: minimal gliding
  • Carpometacarpal joint of the thumb: a saddle joint between the trapezium and first metacarpal bone
    • Movements: a multiaxial joint, unlike the other carpometacarpal joints
      • Flexion
      • Extension
      • Abduction
      • Adduction
      • Opposition
      • Circumduction
    • Clinical significance: Trapeziometacarpal osteoarthritis (or osteoarthritis at the base of the thumb)
Joints of the hand Metacarpophalangeal joint (MCP)
  • 2nd–5th MCP joints: ellipsoid joints between the 2nd–5th metacarpals and the proximal phalanges of the medial 4 fingers
    • Movements
      • Flexion
      • Extension
      • Abduction
      • Adduction
  • 1st MCP joint: hinge joint between the 1st metacarpal and the proximal phalanx of the thumb
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

(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
  • Median nerve
  • Forearm: pronation
  • Elbow: flexion (weak)
  • Pronate against resistance and palpate muscle belly
Flexor carpi radialis
  • Forearm: flexion
  • Wrist: flexion and abduction
  • Flex the wrist against resistance and palpate muscle belly
  • Abduct the wrist against resistance
Flexor digitorum superficialis
  • Wrist, MCP, and PIP joints: flexion
  • Flex the specific digit with the other fingers held in extension
Palmaris longus
  • Wrist: flexion (weak)
  • Wrist flexion against resistance makes the tendon taut
Flexor carpi ulnaris
  • Ulnar nerve
  • Wrist: flexion and adduction (strong)
  • 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)
  • Medial half (to the ring and little fingers): ulnar nerve
  • Lateral half (to the index and middle fingers): median nerve
  • Wrist, MCP, and DIP joints: flexion
  • Hold the PIP in extension, and flex the DIP
Flexor pollicis longus
  • Interosseous membrane, shaft of the radius (anterior surface)
  • Base of the distal phalanx of the thumb
  • Median nerve
Pronator quadratus
  • Anterior surface of distal ulnar shaft
  • Anterior surface of distal radial shaft
  • Pronation of the forearm
  • 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
  • Lateral supracondylar ridge of the humerus
  • Proximal to the radial styloid
  • Radial nerve
  • Muscle belly becomes prominent on flexing the elbow against resistance, with the forearm in half-pronation

Extensor carpi radialis longus

ECRL

  • Lateral supracondylar ridge of the humerus
  • Base of 2nd metacarpal (dorsal aspect)
  • Wrist: extension (dorsiflexion) and abduction

  • 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

  • Dorsal base of the middle and distal phalanges of the fingers
  • Wrist, MCP, PIP, and DIP: extension
  • Extension of the fingers against resistance

Extensor digiti minimi

EDM

  • Middle and distal phalanges (extensor expansion) of the little finger
  • 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
  • Wrist: extension and adduction
  • Adduction of the wrist against resistance makes the tendon taut
Anconeus
  • Cannot be independently tested

Deep extensor compartment

Abductor pollicis longus

APL

  • Interosseus membrane and posterior surface of the radius and ulna
  • Base of the 1st metacarpal
  • 1st MCP (of the thumb): abduction
  • Wrist: abduction
  • Abduction of the thumb against resistance makes the tendon taut

Extensor pollicis longus

EPL

  • Interosseus membrane and posterior surface of the ulna
  • Distal phalanx of the thumb

Extensor pollicis brevis

EPB

  • Interosseous membrane and posterior surface of the radius
  • Proximal phalanx of the thumb
Extensor indicis
  • Interosseous membrane and posterior surface of the ulna
  • 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
  • Lateral surface of the proximal radius
  • Supinate against resistance with the elbow extended

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 (radial fossa)

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 of the palm and exert their action mainly on the 1st MCP.
Muscle Origin Insertion Innervation

Function

Testing

Abductor pollicis brevis

  • First proximal phalanx
  • Median nerve
  • Abduction
  • Abduct the thumb against resistance
  • Pen test

Opponens pollicis

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

Flexor pollicis brevis

  • First proximal phalanx
  • Median and ulnar nerves
  • Flexion
  • Flexion of the 1st MCP against resistance, with IP in extension
  • Capitate, base of the 2nd and 3rd metacarpals
  • First proximal phalanx (ulnar sesamoid bone)
  • Ulnar nerve

Adductor pollicis

  • Adduction
  • 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
  • Proximal phalanx of 5th finger
  • Ulnar nerve
  • Abduction
  • Abduct the 5th finger against resistance
Flexor digiti minimi brevis
  • Proximal phalanx of 5th finger
  • Flexion
  • 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
  • Skin of the hypothenar eminence
  • 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

  • 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.
Muscle Origin Insertion Innervation Function Testing

Lumbricals

(I–IV)

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

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)

  • Definition: Fibrous thickening of the palmar deep fascia located at the proximal part of the palm
  • Attachments
  • Structures superficial to the flexor retinaculum (medial to lateral): ulnar nerve, ulnar artery, palmar cutaneous branch of ulnar nerve, palmaris longus tendon, palmar cutaneous branch of median nerve
  • Function
    • Forms the roof of the carpal tunnel
    • Holds the flexor tendons in place

Extensor retinaculum

(dorsal carpal ligament)

  • Definition: fibrous thickening of the deep fascia of the forearm that is located on the dorsal aspect of the wrist
  • Attachments
  • Structures superficial to the extensor retinaculum: superficial branch of radial nerve
  • Function: holds the extensor tendons in place
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
  • The medial terminal branch of the brachial artery
  • Originates just below the cubital fossa and lies in the medial aspect of the forearm
  • Passes superficial to the flexor retinaculum
  • Ends by forming the ulnar part of superficial and deep palmar arches
  • Is most superficial at the wrist, below the tendon of the flexor carpi ulnaris in a supine forearm
  • The median nerve lies medial to the proximal part of the artery
  • The ulnar nerve lies medial to artery in the wrist and distal part of the forearm
  • Supplies: elbow joint, medial forearm muscles, medial carpal bones, medial three fingers, and the median and ulnar nerves
  • Branches
    • Anterior and posterior ulnar recurrent arteries
    • Common interosseus artery
    • Palmar and dorsal carpal branches
    • Terminal superficial and deep branches to the superficial and deep palmar arches
Deep palmar arch
Superficial palmar arch

Veins

Superficial veins

Vein Characteristics
Cephalic vein
  • Origin: radial side of the dorsal venous network of the hand at the anatomical snuffbox
  • Course: lies on the lateral side of the forearm and arm
  • Tributaries: median cubital vein
  • Termination: drains into the axillary vein at the deltopectoral groove
  • Drains the palm, lateral forearm, and lateral arm
Basilic vein
Median antebrachial vein
  • Origin: palmar venous network of the hand
  • Course: lies in subcutaneous tissue in the middle of the ventral forearm
  • Termination: median cubital vein (most common)
  • Drains: superficial structures of ventral mid-forearm and wrist

Deep veins

  • 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

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)

  • Origin: musculocutaneous nerve
  • Innervates: skin over the lateral arm

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)

  • Origin: radial nerve
  • Innervates: skin over the posterior arm
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