Compartments and innervation of the hand

Median and ulnar nerves (“king of the hand”)

Innervate muscles in the hand

Carpometacarpal (CMC) joint of digit 1

Joint between the carpal bones and the first metacarpal

Thumb flexion and extension

Occur in the frontal plane

Thumb abduction and adduction

Occur in the sagittal plane

CMC joint of digit 1

Synovial saddle joint that allows opposition and reposition

Flexor retinaculum

Deep to the palmar aponeurosis

Thenar compartment

Contains muscles that move the thumb

Thenar eminence

Fatty padded tissue at digit 1

Thenar muscles and their relative depths

Abductor pollicis brevis (superficial), flexor pollicis brevis (intermediate), opponens pollicis (deep)

Thenar muscle innervation

Recurrent branch of the median nerve

Recurrent branch of the median nerve

Sometimes pierces abductor pollicis brevis and flexor pollicis brevis to reach opponens pollicis

Hypothenar compartment

Contains muscles that move digit 5

Hypothenar eminence

Fatty padded tissue at digit 5

Hypothenar muscles and their relative depths

Abductor digiti minimi (superficial), flexor digiti minimi brevis, opponens digiti minimi (deep)

Hypothenar muscle innervation

Deep branch of the ulnar nerve

Palmaris brevis location

Superficial to the hypothenar compartment; not part of any compartment

Palmaris brevis attachments

Short, transversely oriented fibres attach to the palmar aponeurosis

Palmaris brevis action

Tenses the palmar aponeurosis

Palmaris brevis innervation

Superficial branch of the ulnar nerve

Central compartment

Contains the lumbricals

Lumbrical attachments

Arise from the tendons of flexor digitorum profundus and attach to the extensor tendons on the posterior side of the digits

Lumbrical actions

Flex MCP joints and extend interphalangeal joints of digits 2–5

Lumbrical innervation

Lateral two by the median nerve; medial two by the deep branch of the ulnar nerve

Adductor compartment muscle

Adductor pollicis, shaped like a 7 or triangle

Adductor pollicis action

Adducts the thumb

Adductor pollicis innervation

Deep branch of the ulnar nerve

Interosseous compartment

Contains palmar and dorsal interossei between metacarpals of digits 2–5

Palmar interossei (3 PAD)

Adduct digits 2, 4, and 5 toward digit 3

Dorsal interossei (4 DAB)

Abduct digits 2–4 away from digit 3

Digit 3 abduction

Can occur in both directions, away from the middle finger's midline

Median nerve origin

Medial cord of the brachial plexus

Median nerve pathway

Travels inferiorly and medially toward the humerus, passes between the heads of pronator teres, then between flexor digitorum superficialis and profundus

Median nerve at the wrist

Travels lateral to the palmaris longus tendon and deep to the flexor retinaculum through the carpal tunnel

Median nerve hand branches

Recurrent branch and digital branches to the lateral two lumbricals and lateral 3.5 digits

Median nerve sensory distribution

Lateral 3.5 digits, including the lateral half of digit 4

Ulnar nerve origin

Medial cord of the brachial plexus

Ulnar nerve pathway

Passes posterior and medial to the medial epicondyle, then inferior and deep to flexor carpi ulnaris

Ulnar nerve at the wrist

Passes superficial to the flexor retinaculum

Ulnar nerve branches

Divides into superficial and deep branches

Superficial branch of the ulnar nerve

Innervates palmaris brevis and supplies the medial 1.5 digits

Deep branch of the ulnar nerve

Innervates deep hand muscles, including hypothenar muscles, medial two lumbricals, adductor pollicis, and palmar and dorsal interossei