In the

human body The human body is the entire structure of a Human, human being. It is composed of many different types of Cell (biology), cells that together create Tissue (biology), tissues and subsequently Organ (biology), organs and then Organ system, org ...

, the carpal tunnel or carpal canal is a flattened

body cavity A body cavity is any space or compartment, or potential space, in an animal body. Cavities accommodate organs and other structures; cavities as potential spaces contain fluid. The two largest human body cavities are the ventral body cavity, a ...

on the

flexor In anatomy, flexor is a muscle that contracts to perform flexion (from the Latin verb ''flectere'', to bend), a movement that decreases the angle between the bones converging at a joint. For example, one's elbow joint flexes when one brin ...

( palmar/volar) side of the

wrist In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...

, bounded by the

carpal bones The carpal bones are the eight small bones that make up the wrist (carpus) that connects the hand to the forearm. The terms "carpus" and "carpal" are derived from the Latin wikt:carpus#Latin, carpus and the Greek language, Greek wikt:καρπός ...

and flexor retinaculum. It forms the passageway that transmits the

median nerve The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus. The median nerve originates from the lateral and medial cords of the brachial plexus, and has cont ...

and the

tendon A tendon or sinew is a tough band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...

s of the extrinsic flexor muscles of the hand from the forearm to the

hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the Koala#Characteristics, koala (which has two thumb#O ...

. The median artery is an anatomical variant (increasingly found). When present it lies between the radial artery, and the ulnar artery and runs with the median nerve supplying the same structures innervated. When swelling or degeneration occurs in the tendons and sheaths of any of the nine flexor muscles ( flexor pollicis longus, four

flexor digitorum profundus The flexor digitorum profundus or flexor digitorum communis profundus is a muscle in the forearm of humans that flexes the fingers (also known as digits). It is considered an Muscles of the hand#Extrinsic, extrinsic hand muscle because it acts on ...

and four flexor digitorum superficialis) passing through the carpal tunnel, the canal can narrow and compress/entrap the median nerve, resulting in a compression neuropathy known as

carpal tunnel syndrome Carpal tunnel syndrome (CTS) is a nerve compression syndrome associated with the collected signs and symptoms of Pathophysiology of nerve entrapment#Compression, compression of the median nerve at the carpal tunnel in the wrist. Carpal tunn ...

(CTS). If untreated, neuropraxia, parasthesia and muscle atrophy (especially of the thenar muscles) can occur. The condition often requires surgical division of the retinaculum to relieve the pressure upon the nerve.

Structure

The

that make up the wrist form an arch which is convex on the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

side of the hand and concave on the palmar side. The groove on the palmar side, the ''sulcus carpi'', is covered by the flexor retinaculum, a rigid band of

fibrous tissue Connective tissue is one of the four primary types of animal tissue, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesode ...

, thus forming the carpal tunnel. On the side of the

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

, the flexor retinaculum is attached to the scaphoid bone, more precisely its tubercle, as well as the ridge of trapezium. On the

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

r side, it is attached to the pisiform and hook of hamate. The narrowest section of the tunnel is located a centimetre beyond the mid-line of the distal row of carpal bones where the sectional area is limited to 1.6 cm². The tendons of the flexor digitorum superficialis and profundus pass through a common ulnar sheath, while the tendon of the flexor pollicis longus passes through a separate radial sheath. The mesotendon shared by these tendons is attached to the radial and palmar walls of the carpal tunnel. Superficial to the carpal tunnel and the flexor retinaculum, the ulnar artery and ulnar nerve pass through the ulnar tunnel/Guyon's canal.

Function

Ten structures pass through the carpal tunnel, most of them flexor tendons (not the muscles themselves): *

(four tendons) * flexor digitorum superficialis (four tendons) * flexor pollicis longus (one tendon) *

Median nerve The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus. The median nerve originates from the lateral and medial cords of the brachial plexus, and has cont ...

between tendons of flexor digitorum profundus and flexor digitorum superficialis The flexor carpi radialis (one tendon) is often incorrectly stated to travel within the carpal tunnel. More precisely, it travels within the fibers of the flexor retinaculum which forms the roof of the carpal tunnel, rather than running inside the tunnel itself.

Effect of wrist movements

Movements in the wrist affect the shape and width of the carpal tunnel. The width decreases considerably during the normal range of motion in the wrist; and because the carpal bones move in relation to each other with every motion of the hand, the bony walls of the tunnel are not rigid. Both flexion and extension increase compression in the carpal tunnel. * Flexing the wrist causes the flexor retinaculum to move closer to the radius which considerably decreases the cross section of the proximal opening of the tunnel. Additionally, the distal end of the capitate presses into the opening. * In extreme extension, the lunate constricts the passage as it is pressed toward the interior of the tunnel.

Clinical significance

Carpal tunnel syndrome Carpal tunnel syndrome (CTS) is a nerve compression syndrome associated with the collected signs and symptoms of Pathophysiology of nerve entrapment#Compression, compression of the median nerve at the carpal tunnel in the wrist. Carpal tunn ...

is characterized by tingling, burning and pain (needle, pin) through the course of median nerve particularly over the outer fingers and radiating up the arm, that is caused by compression of the carpal tunnel contents. It is associated with repetitive use,

rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects synovial joint, joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and h ...

, and a number of other states. It can be detected using Tinel's sign and the Phalen maneuver. It may be treated non-surgically by splinting or

corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are invo ...

injection. Definitive management often requires surgical division of the flexor retinaculum, the aponeuroses which forms the roof of the carpal tunnel, or another carpal tunnel surgery. Symptoms of the syndrome can sometimes be caused by tight muscles in the neck and shoulder region.

Additional images

File:Slide9VVVVV.JPG, Carpal tunnel File:Slide1dsds.JPG, Wrist joint, deep dissection. Anterior palmar view. File:Hand dissection 9.jpg, Carpal tunnel

References

External links

* {{DEFAULTSORT:Carpal Tunnel Occupational hazards Wrist