Anatomy of the Hand

The movements of the hand are accomplished by two sets of muscles and tendons: the flexors, for bending the fingers and thumb, and the extensors, for straightening out the digits. The flexor muscles are located on the anterior (volar) surface of the forearm and are attached by tendons to the phalanges of the fingers. The extensor muscles are on the dorsal surface of the forearm and are similarly connected. The thumb has two separate flexor muscles that move the thumb in opposition and make grasping possible.

The Skeleton of the Hand

The hand has 27 bones: the 8 bones of the carpus (wrist), arranged in two sets of four; the 5 bones of the metacarpus, one to each digit; and the 14 digital bones, or phalanges, 2 in the thumb and 3 in each finger. The carpal bones fit into a shallow socket formed by the bones of the forearm.  Each metacarpal bone has a proximal base, a shaft, and a distal head.  The base of each metacarpal contacts the distal row of carpal bones to form thecarpometacarpal joint.  The head of each metacarpal contacts the proximal

at a metacarpophalangeal (MP) joint.

The proximal row of phalanges articulates with the middle row of phalanges at the proximal interphalangeal (PIP) joints, the middle and distal rows of phalanges articulate at the distal interphalangeal (DIP) joints.

The carpal bones can be remembered using the mnemonic “Some Lovers Try Positions That They Can’t Handle”

Proximal Row (Radial to ulnar wrist) Scaphoid or Carpal Navicular (Some) Links proximal to distal carpal row Lunate (Lovers) Triquetrum (Try) Pisiform (Positions) Distal Row (Radial to ulnar wrist) Trapezium/Greater multangular (That) Trapezoid/Lesser multangular (They) Capitate (Can’t) Hamate (Handle)

Muscles of the hand

Intrinsic (Originate in hand) The intrinsic muscles of the hand are involved in delicate finger movements. They include the Thenar and Hypothenar muscles, which function in positioning of the thumb and small finger for pinching; and the Interossei and Lumbricals, which insert into proximal phalanges and extensor hoods, function in metacarpal phalangeal joint flexion and interphalangeal joint extension. See the table below for a summary of the individual intrinsic muscles and their function

• Intrinsic Muscles of the Hand
  Muscle	Origin	Insertion	Action	Innervation
  Muscles acting on the Second through Fifth Digits
  Dorsal interossei (4)	ulnar side of 1st MC; both sides of 2nd-4th MC; radial side of 5th MC	Tubercle of proximal phalanx and dorsal aponeurosis: radially on 2nd and 3rd digits, ulnarly on 3rd and 4th digit	Abduct 2nd-4th digits from midline; flex MCP joint, extend PIP and DIP joints	Ulnar nerve (C8-T1, anterior)
  Palmar interossei (3)	ulnar side of 2nd and radial side of 4th-5th MC	Tubercle of proximal phalanx and dorsal aponeurosis: ulnarly on 2nd digit, radially on 4th and 5th digits	Adduct 2nd, 4th, and 5th digits to the midline of the hand. Flex MCP joint and extend PIP and DIP joints	Ulnar nerve (C8-T1, anterior)
  Lumbricals (1 and 2)	Tendons of FDP in deep palm	radial side of dorsal expansion of 2nd and 3rd digits	Flex MCP, extend DIP, PIP	Median nerve (C8-T1, anterior)
  Lumbricals (3 and 4)	Tendons of FDP in deep palm	radial side of dorsal expansion of 4th and 5th digits	Flex MCP, extend DIP, PIP	Ulnar nerve (c8-T1, anterior)
  Palmaris brevis	ulnar border of palmar aponeurosis	Skin over hypothenar region	Corrugates palmar skin	Ulnar nerve (C8-T1, anterior)
  Abductor digiti minimi	Pisiform bone	Ulnar side of base of 5th proximal phalanx	Abduct 5th digit	Ulnar nerve (C8-T1, anterior)
  Flexor digiti minimi brevis	Flexor retinaculum and hamulus	Ulnar side of base of 5th proximal phalanx	Flex 5th MCP joint	Ulnar nerve (C8-T1, anterior)
  Opponens digiti minimi	Flexor retinaculum and hamulus	Ulnar side of base of 5th MC	Flexion and opposition	Ulnar nerve (C8-T1, anterior)
  Muscles acting on the Thumb
  Abductor pollicis brevis (APB)	Anterior surface of trapezium, scaphoid	radial aspect of base of proximal phalanx	Abducts thumb	Median n. (C8-T1, anterior)
  Opponens pollicis	Trapezium	Anterolateral surface of 1st MC	Medially rotates (opposes) thumb	Median n. (C8-T1, anterior)
  Flexor pollicis brevis
  Superficial head	Transverse carpal ligament and trapezium	radial side of base of proximal phalanx	Flexes thumb	Median n. (C8-T1, anterior)
  Deep head	radial side of 2nd MC			Ulnar nerve (C8-T1, anterior)
  Adductor pollicis
  Oblique head	Anterior surface of capitate and 2nd and 3rd MC	ulnar side of base of proximal phalanx	Adducts thumb	Ulnar nerve (C8-T1, anterior)
  Transverse head	Distal half of 3rd MC

  Extrinsic (Originate in forearm)The extrinsic muscles of the hand include the wrist flexors and extensors, which stabilize the wrist in slight dorsiflexion, the Finger Flexors (five deep and four superficial), and the finger extensors

Extrinsic Muscles of the Hand
Muscle	Origin	Insertion	Action	Innervation
Muscles acting on the Second through Fifth Digits
Extensor digitorum cominus (EDC)	Lateral epicondyle of humerus	middle and distal phalanges of index, middle and ring fingers	Extends digits and wrist when fist is clenched	Radial nerve (C7-C8, posterior)
Extensor digiti minimi (EDM)	Common extensor tendon	All phalanges of fifth digit	Extends fifth digit	Radial nerve (C7-C8, posterior)
Extensor indicis proprius (EIP)	Interosseus membrane and ulna	middle and distal phalanges of index finger	extends first digit and wrist	Radial nerve (C8-T1, posterior)
Flexor digitorum superficialis (FDS)	Medial epicondyle	Base of middle phalanx of each digit	Flexes PIP, MCP, and wrist joint	Median nerve (C8-T1, anterior)
Flexor digitorum profundus (FDP)	Anterior proximal ulna and IOM	Base of distal phalanx of each digit	Flexes DIP, PIP, MCP, and wrist joints	-Median n. (C7-T1, anterior) for 2nd-3rd digit -Ulnar n. (C7-T1, anterior) for 4th-5th
Muscles acting on the thumb
Abductor pollicis longus (APL)	Posterior IOM and ulna	Base of1st MC, laterally	Abducts thumb and wrist	Radial n. (C8-T1, posterior)
Extensor pollicis brevis (EPB)	Posterior midshaft of radius and IOM	Base of proximal phalanx	Extends thumb and abducts wrist	Radial n. (C8-T1, posterior)
Extensor pollicis Longus (EPL)	Posterior surface of IOM and posteriior ulna	Base of middle phalanx	Extend thumb and abducts wrist	Radial n. (C8-T1, posterior)
Flexor pollicis longus (FPL)	Anterior mid-radius and IOM	Lateral aspect of base of proximal phalanx	Flexe thumb, MCP joint, and wrist	Median n. (C7-T1, anterior)

Blood Supply

The blood supply to the hand is via the ulnar and radial arteries. The ULNAR artery continues to the hand at the medial (ulnar) side of the wrist.The deep palmar branch arises just distal to the lateral side of the pisiform bone, where the ulnar pulse is generally palpable. This branch then passes through the hypothenar compartment to the deep palmar arch by anastamosing with the terminal branch of the radial artery.The superficial palmar branch is the major contributor to the superficial palmar arch, which lies just beneath the palmar aponeurosis. This arch is larger than the deep arch. The common digital arteries arise from this arch; each bifurcates into proper digital branches, which run on the medial and lateral side of adjacent digits in a neurovascular bundles, containing digital artery, vein, and nerve.The RADIAL artery continues to the hand at the lateral (radial side of the wrist. The superficial palmar branch of the radial artery arises at the level of the end of the radius and branches just before the radial artery passes through the “anatomic snuff box”, which is bounded by the EPL and EPB tendons and is where a radial pulse may be palpated. The superficial palmar branch then passes through the thenar compartment, and provides a minor contribution to thesuperficial palmar arch. The deep palmar branch of the radial artery is the major contributor to the deep palmar arch. It courses around the base of the thumb and passes dorsal to the 1st MC to gain access to the thenar space where it becomes the deep palmar arch.

Innervation to the Hand
The hand is innervated by three main nerves, the ulnar, medial and radial nerves.
The ULNAR nerve enters the hand with the ulnar artery Motor innervation – ulnar half of FDP most of intrinsic muscles (hypothenar muscles, interossei, lubercals 3 and 4, adductor pollicis, and the deep head of the FPB) Allows for power grip Sensation – distributed via the dorsal branch, the dorsal digital branches, and the volar digital branches. Ulnar side of dorsum of hand, 5th digit and ulnar half of 4th digit Course Passes with ulnar artery via Guyon’s Canal in wrist Test function Finger abduction against resistance Palpate belly of first dorsal interosseus muscle Conditions Cubital Tunnel Ulnar Tunnel
The MEDIAN Nerve enters the hand through the carpal tunnel Motor innervation Most of extrinsic flexors (FPL, FDS, radial half of FDP Many intrinsic flexors of the thumb (opponens pollicis, APB, supeficial head of FPB, lumbricals 1 and 2) Allows for fine control of pincer grasp Innervates thenar muscles and two radial lumbricals Sensation – distributed by palmar cutaneus branch and the volar (palmar) digital branches Palmar side of 1st-3rd digit and radial half of 4th digit, and their dorsal tips Course Passes via carpal tunnel through volar wrist Test function Opposition of thumb to each finger Observe thenar muscles for contractions
The RADIAL Nerve courses with the radial artery. Motor Innervates extrinsic hand, wrist, finger, and thumb extensors Does not innervate any intrinsic muscles Sensation – via the superficial branch Dorsalsurface of 1st – 3rd finger and radial half of 4th Test function Wrist and hand extension against resistance

Wrist structures

Carpal Tunnel Bordered by transverse carpal ligament Components of carpal tunnel Finger flexors (9 tendons) course through tunnel Median Nerve courses through tunnel Injured in Carpal Tunnel Syndrome Triangular Fibrocartilage Complex (TFCC) Articular disc Divides ulna from proximal carpal row Injured in Triangular Fibrocartilage Complex Injury