Hand

The hand constitutes the distal part of the upper limb and provides the fine, precise movements needed in activities of daily living. It consists of 5 metacarpal bones and 14 phalanges, as well as numerous muscles innervated by the median and ulnar nerves. The muscles of the hand are classified as extrinsic (forearm-based) or intrinsic (hand-based) depending on the location of the muscle belly. These muscles are also grouped by area or type: thenar, hypothenar, lumbricals, and interossei.

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Bones of the Hand

The bones of the hand consist of the following:

  • Metacarpals
    • There are 5 metacarpal bones corresponding to each of the fingers.
    • The proximal portion is called the base.
    • The middle portion is called the shaft.
    • The distal portion is called the head.
  • Phalanges 
    • Digits 2–5 have 3 phalanges: proximal, middle, and distal.
    • The 1st digit or the thumb only has 2 phalanges: proximal and distal.

Joints of the Hand

The joints of the hand and fingers consist of:

  • Metacarpal-phalangeal joints, connecting the metacarpals to the fingers
  • Interphalangeal joints, the hinge joints between the phalanges of the fingers
Table: Joints of the hand
TypeComponentsFunctionClinical relevance
InterphalangealHinge joint
  • Between the phalanges of each digit
  • Proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints
  • The thumb has an interphalangeal (IP) joint.
  • Flexion
  • Extension
  • Distal: swan neck deformity, Heberden’s nodes
  • Proximal: boutonniere deformity, Bouchard’s nodes
MetacarpophalangealThumb: hinge jointHead of the 1st metacarpal and the proximal end of the proximal phalanx
  • Flexion
  • Extension
Affected early by rheumatoid arthritis
2nd–5th digits: ellipsoid jointsHeads of the 2nd–5th metacarpals and the proximal end of the proximal phalanges
  • Flexion
  • Extension
  • Abduction
  • Adduction
Joints of the digits

Joints of the digits, featuring the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints

Image by BioDigital, edited by Lecturio

Intrinsic Muscles of the Hand

The muscles of the hand are divided into 2 groups based on muscle belly location:

  1. Extrinsic: Muscle bellies are in the forearm; they provide strength and grip. (See the following section.)
  2. Intrinsic: Muscle bellies are within the hand and are responsible for fine movement of the fingers.
    • Thenar muscles
      • Form the thenar eminence
      • Responsible for multiple motions of the thumb
      • All innervated by the median nerve (except for the adductor pollicis, which is innervated by the ulnar nerve)
    • Hypothenar muscles
      • Form the hypothenar eminence
      • Responsible for multiple motions of the 5th digit (“little finger”)
      • All innervated by the ulnar nerve
    • Lumbricals: 
      • Link the flexor and extensor tendons of the fingers
      • Flex the MCP joints and contribute to the extension of the interphalangeal joints
      • Lumbricals I and II (lateral side of the hand) are innervated by the median nerve.
      • Lumbricals III and IV (medial side of the hand) are innervated by the ulnar nerve.
    • Interossei
      • 4 dorsal interossei abduct the 2nd–5th fingers.
      • 3 palmar interossei adduct the 2nd–5th fingers.
      • Are innervated by the ulnar nerve
Anterior view of the right hand, featuring the palm, thenar and hypothenar muscles

Anterior view of the right hand, featuring the palm, thenar, and hypothenar muscles making up the thenar and hypothenar eminences, and the palmar aponeurosis

Image by BioDigital, edited by Lecturio.

Thenar muscles

MuscleOriginInsertionInnervationFunction
Opponens pollicisFlexor retinaculum and trapeziumLateral side of the 1st metacarpal boneRecurrent branch of median nerve (C8)Opposes thumb
Abductor pollicis brevisFlexor retinaculum and tubercles of scaphoid and trapeziumLateral side of proximal phalanx of 1st digit
  • Abducts thumb
  • Supports the opposition
Flexor pollicis brevisFlexor retinaculum and trapezium
  • Superficial head: median nerve
  • Deep head: deep branch of ulnar nerve (C8, T1)
Flexes thumb
Adductor pollicis
  • Oblique head: base of 2nd–3rd metacarpals and capitate
  • Transverse head: palmar surface of 3rd metacarpal
Medial side of proximal phalanx of thumbDeep branch of ulnar nerve (C8)Adducts thumb
Thenar muscles in hand

Thenar muscles of hand

Image by Lecturio.

Hypothenar muscles

MuscleOriginInsertionInnervationFunction
Palmaris brevisFlexor retinaculum and palmar aponeurosisSkin of the hypothenar eminenceUlnar nerveStrengthens palmar grip by wrinkling the skin of the ulnar palm
Abductor digiti minimiPisiform and flexor carpi ulnarisMedial side of proximal phalanx of the 5th digitDeep branch of ulnar nerve (T1)Abducts the 5th digit
Flexor digiti minimi brevisHook of hamate and flexor retinaculumFlexes proximal phalanx of the 5th digit
Opponens digiti minimiMedial border of 5th metacarpalOpposes the 5th digit
Hypothenar muscles hand

Hypothenar muscles

Image by Lecturio.

Lumbrical muscles

MuscleOriginInsertionInnervationFunction
Lumbricals (I–II)Lateral 2 tendons of flexor digitorum profundusLateral surfaces of extensor expansions of the 2nd–5th digitsMedian nerve (T1)Flex metacarpophalangeal and extend interphalangeal joints of 2nd–5th digits
Lumbricals (III–IV)Medial 2 tendons of flexor digitorum profundusDeep branch of ulnar nerve (T1)
Lumbricals muscles

Lumbrical muscles

Image by BioDigital, edited by Lecturio

Interossei muscles

MuscleOriginInsertionInnervationFunction
Dorsal interossei (4 muscles)Radial and ulnar side of each pair of consecutive metacarpalsBase of proximal phalanges and extensor expansions (dorsal: 2nd–4th digits; palmar: 2nd, 4th, and 5th digits)Deep branch of ulnar nerve (T1)Abduct 2nd–4th digits
Palmar interossei (3 muscles)Sides of the metacarpals facing midlineAdduct 2nd, 4th, and 5th digits

Extrinsic Muscles of the Hand

The extrinsic muscles of the hand have their origin and muscle bellies in the forearm and are divided into flexor (anterior compartment) and extensor (posterior compartment) muscles.

Extensors (enclosed in the extensor retinaculum)Flexors (enclosed in a common synovial sheath)
SuperficialDeepSuperficialDeep
  • Extensor carpi radialis longus
  • Extensor carpi radialis brevis
  • Extensor digitorum
  • Extensor digiti minimi
  • Extensor carpi ulnaris
  • Abductor pollicis longus
  • Extensor pollicis longus
  • Extensor pollicis brevis
  • Extensor indicis proprius
  • Flexor carpi radialis
  • Palmaris longus
  • Flexor carpi ulnaris
  • Flexor digitorum superficialis
  • Flexor digitorum profundus
  • Flexor pollicis longus

Extrinsic extensor muscles: superficial layer

MuscleOriginInsertionInnervationFunction
Extensor carpi radialis longusLateral supracondylar ridge of the humerusDorsal aspect of base of 2nd metacarpalRadial nerveAbduction and extension of the wrist (dorsiflexion)
Extensor carpi radialis brevisLateral epicondyleDorsal aspect of base of 3rd metacarpal
Extensor digitorumExtensor expansion, base of middle and distal phalanges of 2nd–5th digitsPosterior interosseous nerve (C7; from deep radial nerve)
  • Extend wrist
  • Extend 2nd–5th digits at metacarpophalangeal and interphalangeal joints (5th digit for EDM)
Extensor digiti minimiExtensor expansion, middle and distal phalanges of 5th digit
Extensor carpi ulnarisLateral epicondyle of the humerus and posterior surface of ulnaDorsal aspect of base of 5th metacarpalExtends and adducts wrist
Superficial extensor muscles of the hand

Extrinsic extensor muscles of the hand: superficial layer

Image by BioDigital, edited by Lecturio.

Extrinsic extensor muscles: deep layer

MuscleOriginInsertionInnervationFunction
Abductor pollicis longusPosterior surface of radius and ulna, interosseous membraneBase of 1st metacarpalPosterior interosseous nerve (C7 and C8) from deep radial nerve
  • Extends wrist
  • Abducts thumb
  • Extends thumb at carpometacarpal joint
Extensor pollicis longusPosterior surface of ulna, interosseous membraneDorsal surface of distal phalanx of thumb
  • Extend wrist
  • Extend distal (longus) and proximal (brevis) phalanx of thumb at interphalangeal joint
  • Extend metacarpophalangeal and carpometacarpal joints
Extensor pollicis brevisPosterior surface of radius, interosseous membraneDorsal surface of proximal phalanx of thumb
Extensor indicisPosterior surface of the ulnaExtensor expansion of 2nd finger
  • Extends 2nd digit
  • Assists with wrist extension
Deep extensor muscles of the hand

Extrinsic extensor muscles of the hand: deep layer

Image by BioDigital, edited by Lecturio.

Extrinsic flexor muscles: superficial layer

MuscleOriginInsertionInnervationFunction
Flexor carpi radialisMedial epicondyle of humerusBase of 2nd–3rd metacarpalsMedian nerve (C7)Flexes and abducts wrist
Palmaris longusFlexor retinaculum and palmar aponeurosisFlexes wrist weakly and tenses palmar aponeurosis
Flexor carpi ulnarisMedial epicondyle of the humerus, olecranon, and posterior ulnaPisiform, hook of hamate, base of 5th metacarpalUlnar nerve (C8)Flexes and adducts wrist
Flexor digitorum superficialisMedial epicondyle of the humerus, proximal shaft of the radiusMiddle phalanges of the medial 4 fingersMedian nerve (C7)
  • Flexes the proximal interphalangeal joints
  • Assists in flexing the metacarpophalangeal and wrist joints
Extrinsic Flexor Muscles of the hand - Superficial layer

Extrinsic flexor muscles of the hand: superficial layer

Image by BioDigital, edited by Lecturio.

Extrinsic flexor muscles: deep layer

MuscleOriginInsertionInnervationFunction
Flexor digitorum profundusProximal end of the ulna (medial and anterior surfaces) and interosseous membraneDistal phalanges of the 2nd–5th digits
  • Digits 2 and 3: median nerve (C7, C8, T1)
  • Digits 4 and 5: ulnar nerve (T1)
  • Flexes wrist
  • Flexes distal interphalangeal joint
  • Holds proximal interphalangeal joint in extension
Flexor pollicis longusShaft of radius (anterior surface) and interosseous membraneDistal phalanx of thumbAnterior interosseous nerve (branch of median) (C8)
  • Flexes wrist
  • Flexes interphalangeal and metacarpophalangeal joints of thumb
Extrinsic Flexor Muscles of the Hand - Deep layer

Extrinsic flexor muscles of the hand: deep layer

Image by BioDigital, edited by Lecturio.

Movements of the Fingers

Extensor expansion

Also known as the extensor hood, dorsal expansion, dorsal hood, or dorsal aponeurosis of the hand and/or fingers. The extensor expansion comprises the tendons of the extensor muscles of the fingers and how these insert into the phalanges:

  • At the distal end of the metacarpal, these tendons expand and merge to form an aponeurosis (“hood”), which covers:
    • Head of the metacarpal (dorsal and lateral sides)
    • Proximal phalanx (dorsal and lateral sides)
  • At the proximal phalanx, the tendons divide into bands:
    • Lateral bands (2 per finger): pass on either side of the middle phalanx and insert into the distal phalanx, receiving tendons from the lumbricals, extensor indicis, and dorsal and palmar interossei muscles
    • Central band (1 per finger): passes down the center of the proximal phalanx to insert into the base of the middle phalanx
    • Retinacular bands (2 per finger): pass obliquely on the lateral sides of the middle phalanx to connect the aponeuroses of palmar and dorsal sides of the finger
Extensor expansion of the digits

Schematic of a finger, featuring the extensor expansion or dorsal aponeurosis and insertion of the tendons of the flexor digitorum muscle

Image by Lecturio.

Flexor pulley system

Comprises the tendons of the flexor muscles of the fingers and how these insert into the phalanges, supported by a system of ligaments:

  • Palmar aponeurosis
  • 5 annular pulleys: made by transverse retinacular ligaments
  • 3 cruciform pulleys: made by oblique cruciate ligaments
  • Flexor muscles of the fingers:
    • Flexor digitorum superficialis tendons split at the proximal phalanx and insert laterally into the middle phalanx.
    • Flexor digitorum profundus tendons pass centrally and insert into the distal phalanx.

Vessels of the Hand

Arterial supply

The arterial blood supply of the hand is provided by:

  • Radial artery: palpated immediately lateral to the flexor carpi radialis tendon and just proximal to the wrist crease
  • Ulnar artery: palpated anterior medially on the wrist and passes into the hand through Guyon’s canal
  • Together, the radial and ulnar artery form 2 arterial arches:
    • Superficial palmar arch: ulnar artery + superficial palmar branch of the radial
    • Deep palmar arch: radial artery + deep palmar branch of the ulnar

Venous drainage

The venous drainage of the hand is the origin of the veins of the upper extremity and begins in the dorsal and palmar venous network of the hand.

  • Cephalic vein originates from the dorsal venous network in the area of the anatomical snuffbox.
  • Basilic vein originates from the ulnar side of the dorsal venous network of the hand.
  • Median antebrachial vein originates from the palmar venous network of the hand.
Venous drainage of the hand

Venous drainage of the hand featuring the dorsal venous arch and digital veins

Image by BioDigital, edited by Lecturio.

Innervation of the Hand

The innervation of the hand is primarily via the median and ulnar nerves, with the radial nerve only contributing a small area of sensory innervation on the radial dorsal aspect of the hand.

Motor innervation

Median nerve
  • Thenar muscles (except adductor pollicis)
  • Lateral 2 lumbricals of the hand
Ulnar nerveRemaining muscles except those supplied by the median nerve

Sensory innervation

Median nerve
  • Radial ⅔ of the palm
  • Palmar aspect of the thumb, 2nd–3rd fingers, and radial side of the 4th finger
  • Dorsal aspect of the distal phalanges of the thumb, 2nd–3rd fingers, and radial side of the 4th finger
  • Autonomous sensory zone: the tip of the index finger
Ulnar nerve
  • Ulnar ⅓ of the palm
  • Palmar and dorsal aspects of the 5th finger and ulnar side of the 4th finger
  • Autonomous sensory zone: the tip of the 5th finger
Radial nerve
  • Radial ⅔ of the dorsal aspect of the hand
  • Dorsal aspect of the thumb, 2nd–3rd fingers, and radial side of the 4th finger (except the distal phalanges)
  • Autonomous sensory zone: space between the thumb and index finger on the dorsal aspect of the hand
The innervation of the hand

Sensory innervation of the hand

Image by Lecturio.

Clinical Relevance

The following are common problems associated with the hand:

  • Boxer’s fracture: fracture of the distal portion of the 5th metacarpal bone. Usually due to hitting an object with a closed fist. Symptoms include pain and a depressed knuckle. Diagnosis is suspected based on the clinical exam and confirmed by X-rays.
  • Rheumatoid arthritis: a majority of rheumatoid diseases affect the hand and finger joints. The synovial proliferation results in skeleton erosion, destruction of the capsular ligamentous structures, and changes to tendon structure and function. Physical exam of the hand classically presents with ulnar deviation and subluxation of the metacarpal phalangeal (MCP) joints, swan neck deformities of the fingers, and Z deformity of the thumb.
  • Swan neck deformity: characterized by flexion of the DIP joint and hyperextension of the PIP joint. Associated with rheumatoid arthritis, trauma, and laceration.
  • Boutonniere deformity: characterized by DIP joint extension and PIP joint flexion. Secondary to rupture of the central slip of the extensor mechanism over the PIP joint. Associated with trauma (PIP joint dislocation) and rheumatoid arthritis.
  • Osteoarthritis: a degenerative disorder of the articular cartilage, subchondral bones, and other joint structures. Osteoarthritis is the most common type of joint disease and the leading cause of disability in older adults. The main risk factors are family history, female gender, past trauma to the involved joint, aging, and obesity.
    • Heberden’s nodes (DIP): usually secondary to primary osteoarthritis of the DIP joints. Associated with mucous cysts of the DIP joint and nail deformities. May contribute to joint contracture and deformity.
    • Bouchard’s nodes (PIP): hard, bony outgrowths or gelatinous cysts on the PIP joints. Less commonly, Bouchard’s nodes may be seen in rheumatoid arthritis. May contribute to joint contracture and deformity.

References

  1. Drake, R.L., Vogl, A.W., & Mitchell, A.W.M. (2014). Gray’s Anatomy for Students (3rd ed.). Philadelphia, PA:  Churchill Livingstone.

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