Bones of the Hand
The bones of the hand consist of the following:
- 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.
- 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
|Metacarpophalangeal||Thumb: hinge joint||Head of the 1st metacarpal and the proximal end of the proximal phalanx||Affected early by rheumatoid arthritis|
|2nd–5th digits: ellipsoid joints||Heads of the 2nd–5th metacarpals and the proximal end of the proximal phalanges|
Intrinsic Muscles of the Hand
The muscles of the hand are divided into 2 groups based on muscle belly location:
- Extrinsic: Muscle bellies are in the forearm; they provide strength and grip. (See the following section.)
- 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
- 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.
- 4 dorsal interossei abduct the 2nd–5th fingers.
- 3 palmar interossei adduct the 2nd–5th fingers.
- Are innervated by the ulnar nerve
- Thenar muscles:
|Opponens pollicis||Flexor retinaculum and trapezium||Lateral side of the 1st metacarpal bone||Recurrent branch of median nerve (C8)||Opposes thumb|
|Abductor pollicis brevis||Flexor retinaculum and tubercles of scaphoid and trapezium||Lateral side of proximal phalanx of 1st digit|
|Flexor pollicis brevis||Flexor retinaculum and trapezium||Flexes thumb|
|Adductor pollicis||Medial side of proximal phalanx of thumb||Deep branch of ulnar nerve (C8)||Adducts thumb|
|Palmaris brevis||Flexor retinaculum and palmar aponeurosis||Skin of the hypothenar eminence||Ulnar nerve||Strengthens palmar grip by wrinkling the skin of the ulnar palm|
|Abductor digiti minimi||Pisiform and flexor carpi ulnaris||Medial side of proximal phalanx of the 5th digit||Deep branch of ulnar nerve (T1)||Abducts the 5th digit|
|Flexor digiti minimi brevis||Hook of hamate and flexor retinaculum||Flexes proximal phalanx of the 5th digit|
|Opponens digiti minimi||Medial border of 5th metacarpal||Opposes the 5th digit|
|Lumbricals (I–II)||Lateral 2 tendons of flexor digitorum profundus||Lateral surfaces of extensor expansions of the 2nd–5th digits||Median nerve (T1)||Flex metacarpophalangeal and extend interphalangeal joints of 2nd–5th digits|
|Lumbricals (III–IV)||Medial 2 tendons of flexor digitorum profundus||Deep branch of ulnar nerve (T1)|
|Dorsal interossei (4 muscles)||Radial and ulnar side of each pair of consecutive metacarpals||Base 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 midline||Adduct 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)|
Extrinsic extensor muscles: superficial layer
|Extensor carpi radialis longus||Lateral supracondylar ridge of the humerus||Dorsal aspect of base of 2nd metacarpal||Radial nerve||Abduction and extension of the wrist (dorsiflexion)|
|Extensor carpi radialis brevis||Lateral epicondyle||Dorsal aspect of base of 3rd metacarpal|
|Extensor digitorum||Extensor expansion, base of middle and distal phalanges of 2nd–5th digits||Posterior interosseous nerve (C7; from deep radial nerve)|
|Extensor digiti minimi||Extensor expansion, middle and distal phalanges of 5th digit|
|Extensor carpi ulnaris||Lateral epicondyle of the humerus and posterior surface of ulna||Dorsal aspect of base of 5th metacarpal||Extends and adducts wrist|
Extrinsic extensor muscles: deep layer
|Abductor pollicis longus||Posterior surface of radius and ulna, interosseous membrane||Base of 1st metacarpal||Posterior interosseous nerve (C7 and C8) from deep radial nerve|
|Extensor pollicis longus||Posterior surface of ulna, interosseous membrane||Dorsal surface of distal phalanx of thumb|
|Extensor pollicis brevis||Posterior surface of radius, interosseous membrane||Dorsal surface of proximal phalanx of thumb|
|Extensor indicis||Posterior surface of the ulna||Extensor expansion of 2nd finger|
Extrinsic flexor muscles: superficial layer
|Flexor carpi radialis||Medial epicondyle of humerus||Base of 2nd–3rd metacarpals||Median nerve (C7)||Flexes and abducts wrist|
|Palmaris longus||Flexor retinaculum and palmar aponeurosis||Flexes wrist weakly and tenses palmar aponeurosis|
|Flexor carpi ulnaris||Medial epicondyle of the humerus, olecranon, and posterior ulna||Pisiform, hook of hamate, base of 5th metacarpal||Ulnar nerve (C8)||Flexes and adducts wrist|
|Flexor digitorum superficialis||Medial epicondyle of the humerus, proximal shaft of the radius||Middle phalanges of the medial 4 fingers||Median nerve (C7)|
Extrinsic flexor muscles: deep layer
|Flexor digitorum profundus||Proximal end of the ulna (medial and anterior surfaces) and interosseous membrane||Distal phalanges of the 2nd–5th digits|
|Flexor pollicis longus||Shaft of radius (anterior surface) and interosseous membrane||Distal phalanx of thumb||Anterior interosseous nerve (branch of median) (C8)|
Movements of the Fingers
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
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
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
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.
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.
|Ulnar nerve||Remaining muscles except those supplied by the median nerve|
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.
- Drake, R.L., Vogl, A.W., & Mitchell, A.W.M. (2014). Gray’s Anatomy for Students (3rd ed.). Philadelphia, PA: Churchill Livingstone.