Hand & Wrist
The hand is composed of many small bones called carpals, metacarpals and phalanges. The two bones of the lower arm -- the radius and the ulna -- meet at the hand to form the wrist.
The Median and Ulnar nerves are the major nerves of the hand, running the length of the arm to transmit electrical impulses to and from the brain to create movement and sensation.
Muscles acting on the hand (adductor pollicis, palmaris brevis, interossei, lumbricals, thenar and hypothenar muscles) can be divided into two groups: extrinsic and intrinsic muscles.
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The extrinsic muscles are located in the anterior and posterior compartments of the forearm. They control crude movements and produce a forceful grip.
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The intrinsic muscles of the hand are located within the hand itself. They are responsible for the fine motor functions of the hand.
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The flexor pulley system of the hand is a complex structure that co-ordinates flexion of the digits. It consists of:
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Long flexor tendons – and their associated synovial sheaths.
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Annular pulleys – 5 associated with each finger, 2 associated with the thumb.
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Cruciate pulleys – 3 associated with each finger.
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Oblique pulley – 1 associated with the thumb.
The main role of the flexor pulley system is to hold the flexor tendons against the phalanges; preventing them from pulling away and bowstringing. This allows efficient flexion of the individual digits by the long flexor muscles.
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The wrist joint (also known as the radiocarpal joint) is a synovial joint in the upper limb that bridges the hand to the forearm. It is actually a collection of multiple bones and joints. The bones comprising the wrist include the distal ends of the radius and ulna, 8 carpal bones (roughly arranged in two rows), and the proximal portions of the 5 metacarpal bones. Like any synovial joint, the capsule is dual layered. The fibrous outer layer attaches to the radius, ulna and the proximal row of the carpal bones. The internal layer is comprised of a synovial membrane, secreting synovial fluid which lubricates the joint.
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There are four ligaments of note in the wrist joint, one for each side of the joint
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Palmar radiocarpal – It is found on the palmar (anterior) side of the hand. It passes from the radius to both rows of carpal bones. Its function, apart from increasing stability, is to ensure that the hand follows the forearm during supination.
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Dorsal radiocarpal – It is found on the dorsum (posterior) side of the hand. It passes from the radius to both rows of carpal bones. It contributes to the stability of the wrist, but also ensures that the hand follows the forearm during pronation.
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Ulnar collateral – Runs from the ulnar styloid process to the triquetrum and pisiform. Works in union with the other collateral ligament to prevent excessive lateral joint displacement.
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Radial collateral – Runs from the radial styloid process to the scaphoid and trapezium. Works in union with the other collateral ligament to prevent excessive lateral joint displacement.
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Innervation to the wrist is delivered by branches of three nerves:
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Median nerve – Anterior interosseous branch.
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Radial nerve – Posterior interosseous branch.
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Ulnar nerve – deep and dorsal branches.
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The extensor tendon compartments of the wrist are six tunnels which transmit the long extensor tendons from the forearm into the hand They are located on the posterior aspect of the wrist. Each tunnel is lined internally by a synovial sheath and separated from one another by fibrous septa. The carpal tunnel is a narrow passageway found on the anterior portion of the wrist. It serves as the entrance to the palm for several tendons and the median nerve.
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