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 the carpometacarpal 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



 

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 the superficial 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