Carpal tunnel

Carpal tunnel

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Encyclopedia
In the human body
Human body
The human body is the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs.By the time the human reaches adulthood, the body consists of close to 100 trillion cells, the basic unit of life...

, the carpal tunnel or carpal canal is the passageway on the palmar
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...

 side of the wrist
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;...

 that connects the forearm to the middle compartment of the deep plane of the palm. The tunnel consists of bones and connective tissue. Several tendon
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...

s and a nerve pass through it.

The canal is narrow and when any of the nine long flexor tendons passing through it swells or degenerates, the narrowing of the canal often results in the median nerve
Median nerve
The median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus....

 becoming entrapped or compressed, a medical condition known as carpal tunnel syndrome
Carpal tunnel syndrome
Carpal Tunnel Syndrome is an entrapment idiopathic median neuropathy, causing paresthesia, pain, and other symptoms in the distribution of the median nerve due to its compression at the wrist in the carpal tunnel. The pathophysiology is not completely understood but can be considered compression...

.

Contents


A total of nine flexor tendons (not the muscles themselves) pass through the carpal tunnel:
  • flexor digitorum profundus
    Flexor digitorum profundus muscle
    - References :...

     (four tendons)
  • flexor digitorum superficialis (four tendons)
  • flexor pollicis longus
    Flexor pollicis longus muscle
    The flexor pollicis longus is a muscle in the forearm and hand that flexes the thumb...

     (one tendon)

A single nerve passes through the tunnel: the median nerve
Median nerve
The median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus....

 between tendons of flexor digitorum profundus and flexor digitorum superficialis

Structure


The carpus
Carpus
In tetrapods, the carpus is the sole cluster of bones in the wrist between the radius and ulna and the metacarpus. The bones of the carpus do not belong to individual fingers , whereas those of the metacarpus do. The corresponding part of the foot is the tarsus...

, the bony elements of the wrist, form an arch which is convex on the dorsal 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
Flexor retinaculum of the hand
The flexor retinaculum is a strong, fibrous band that arches over the carpus, converting the deep groove on the front of the carpal bones into a tunnel, the carpal tunnel, through which the Flexor tendons of the digits and the median nerve pass.It is attached, medially, to the pisiform and the...

, a sheath
Sheath
Sheath may refer to:* Scabbard, a sheath for holding a sword, knife, or other large blade, as well as guns, such as rifles.* The outer covering of a cable* Condom, a kind of contraception* Debye sheath, a layer of a plasma in physics...

 of tough connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...

, thus forming the carpal tunnel. The flexor retinaculum is attached radially to the scaphoid tubercle and the ridge of trapezium, and on the ulna side to the pisiform and hook of hammate.

The narrowest section of the tunnel is located a centimetre beyond the mid-line of the distal
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...

 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 ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...

r sheath, while the tendon of the flexor pollicis longus passes through a separate radial
Radius (bone)
The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...

 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
Ulnar artery
The ulnar artery is the main blood vessel, with oxygenated blood, of the medial aspect of the forearm. It arises from the brachial artery and terminates in the superficial palmar arch, which joins with the superficial branch of the radial artery...

 and ulnar nerve
Ulnar nerve
In human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest unprotected nerve in the human body , so injury is common...

 pass through the ulnar tunnel.

Effect of wrist movements


Movements in the wrist affects the shape and width of the carpal tunnel. The width decreases considerably during 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.

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