The Hand and Wrist
last authored: Sept 2009, David LaPierre
related pages: hand & wrist history and physical exam
Introduction
The hand has a palmar or volar surface, a dorsal surface, and radial (thumb) and ulnar (small finger) sides.
The thenar area has the thumb muscles, while the hypothenar area has muscles of the small finger.
The palm is composed of thick skin, with dense connective tissue joining it to fascia. This provides protection and limits mobility of the skin during work. The dorsal skin is looser, with a greater degree of areolar tissue. This provides space for lymphatic and venous drainage, as well as swelling during inflammation or injury.
The palmar fascia is the site of insertion of the palmaris longus tendon, responsible for wrist flexion.
Bones and Joints
Each finger has a proximal, middle, and distal phalanx, and three joints, the metacarpophalangeal (MCP) proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints. The thumb has only two joints, an MCP and an interphalangeal joint.
The joints are protected from sideways motion by collateral ligaments and from hyperextension by a volar plate.
The wrist is composed of eight bones arranged in two rows. Proximally, there is the scaphoid, lunate, triquetrum, and pisiform, while distally, there is the trapezium, trapezoid, capatate, and hamate. The bones are held together by interosseous ligaments, and no tendons attach to them.
Musculature and Tendons
Muscles and tendons can be intrinsic, originating in the hand, or extrinsic, originating in the forearm. Extrinsic extensor muscles travel along the dorsum and are contained within the extensor retinaculum, a 2-cm band acting as a pulley. The retnaculum is anchored to the bone by septations.
The carpal tunnel contains nine flexor tendons and the median nerve and is bordered by the carpal bones as walls and by the transverse carpal ligament (TCL) as a roof. Primary wrist flexors travel outside the carpal tunnel.
Thenar muscles include opponens pollicis, flexor pollicis brevis, and abductor pollicis brevis, all innervated by the median nerve.
Flexor digitorum superficialis tendons attach to the middle phalanx, while profundus insert at the distal phalanx. The flexors enter at the MCP joint under the flexor sheath, which runs along the finger. It is thickened at various points to provide pulley function, keeping the finger close to the bone. The tendon sheath is lined by fibroblasts, which secrete lubricating fluid.
The hand contains the interossei, lumbricals, and adductor pollicis, all innervated by the ulnar nerve.
Dorsal interossei abduct the finger, while volar (palmar) interossei adduct it (DAB, PAD).
Motion of the Hand and Wrist
The hand can pronate and supinate, (supinate = palm up; ie carrying a bowl of soup)
Finger extension and flexion is self-explanatory, but the thumb is somewhat harder to describe. Abduction creates a 90 degree angle with the extended fingers, with the thumb brought in towards the centre of the palm. Extension is also at right angles to the fingers, though in the same plane as the palm and fingers. Opposion brings the thumb and small finger together.
Innervation
The hand is innervated by the radial, median, and ulnar nerves.
The radial nerve divides into the posterior interosseous nerve, which innervates the wrist, finger, and thumb extensor muscles, and the radial sensory nerve, which provides sensation to the dorsum of the thumb, index, and middle finger.
The median nerve travels between the flexor digitorum muscles to enter the carpal tunnel. It is the source of parasthesias, pain, and weakness in carpal tunnel syndrome. The anterior interosseous nerveinnervates flexor pollicis longus, index finger flexor digitorum profundus, and pronator quadratus. The median nerve itself innervates flexor carpi radialis, pronator teres, flexor digitorum superficialis, palmaris longus, and flexor digitorum profundus to the middle finger. The median nerve also provides sensation to the palmar surface of the first four fingers.
The ulnar nerve innervates flexor carpi ulnaris and flexor digitorum profundus to the ring and small fingers. It also innervates the interossei, ulnar lumbricals, flexor pollicis brevis, and adductor pollicis. It provides sensation to the ring and small fingers.
Get Mike to present on the embryology of the thumb...
Blood Supply
The hand is vascularized by the radial and ulnar arteries, which branch into a series of arches. Digital arteries run alongside each finger. Further information required here.
Nails
Nails begin in the germinal nail matrix, approx. 0.5 cm from the nail fold.
Fingertips
Fibrous septae join the fingertip to underlying structures, providing traction during gripping. The bone here forms a tuft to further improve grip. Flexor and extensor tendons join the distal phalanx before the nailbed.
Clinical Vignette 1
A man with no previous problems falls through a window and cuts his wrist. He loses sensation to the dorsum of his thumb and is unable to extend his fingers. What nerve
This happens.
How do you respond?
Clinical Vignette 2
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