Sunday 3 July 2016

Injuries to the Median Nerve at the Wrist-Carpal Tunnel Syndrome-Injuries to the Median Nerve at the Elbow-Motor-Sensory-Vasomotor Changes-Trophic Changes-

Injuries to the Median Nerve at the Wrist
■■ Motor: The muscles of the thenar eminence are paralyzed and wasted so that the eminence becomes flattened. The thumb is laterally rotated and adducted. The hand looks flattened and “apelike.” Opposition movement of the thumb is impossible. The first two lumbricals are paralyzed, which can be recognized clinically when the patient is asked to make a fist slowly, and the index and middle fingers tend to lag behind the ring and little fingers.
■■ Sensory, vasomotor, and trophic changes: These changes are identical to those found in the elbow lesions.
Perhaps the most serious disability of all in median nerve injuries is the loss of the ability to oppose the thumb to the other fingers and the loss of sensation over the lateral fingers. The delicate pincer-like action of the hand is no longer possible
Carpal Tunnel Syndrome
The carpal tunnel, formed by the concave anterior surface of the carpal bones and closed by the flexor retinaculum, is tightly packed with the long flexor tendons of the fingers, with their surrounding synovial sheaths, and the median nerve. Clinically, the syndrome consists of a burning pain or “pins and needles” along the distribution of the median nerve to the lateral three and a half fingers and weakness of the thenar muscles. It is produced by compression of the median nerve within the tunnel. The exact cause of the compression is difficult to determine, but thickening of the synovial sheaths of the flexor tendons or arthritic changes in the carpal bones are thought to be responsible in many cases.
As you would expect, no paresthesia occurs over the thenar eminence because this area of skin is supplied by the palmar cutaneous branch of the median nerve, which passes superficially to the flexor retinaculum. The condition is dramatically relieved by decompressing the tunnel by making a longitudinal incision through the flexor retinaculum.

Injuries to the Median Nerve at the Elbow
Motor
The pronator muscles of the forearm and the long flexor muscles of the wrist and fingers, with the exception of the flexor carpi ulnaris and the medial half of the flexor digitorum profundus, will be paralyzed. As a result, the forearm is kept in the supine position; wrist flexion is weak and is accompanied by adduction.
The latter deviation is caused by the paralysis of the flexor carpi radialis and the strength of the flexor carpi ulnaris and the medial half of the flexor digitorum profundus. No flexion is possible at the interphalangeal joints of the index and middle fingers, although weak flexion of the metacarpophalangeal joints of these fingers is attempted by the interossei. When the patient tries to make a fist, the index and to a lesser extent the middle fingers tend to remain straight, whereas the ring and little fingers flex. The latter two fingers are, however, weakened by the loss of the flexor digitorum superficialis.
Flexion of the terminal phalanx of the thumb is lost because of paralysis of the flexor pollicis longus. The muscles of the thenar eminence are paralyzed and wasted so that the eminence is flattened. The thumb is laterally rotated and adducted. The hand looks flattened and “apelike.”

Sensory
Skin sensation is lost on the lateral half or less of the palm of the hand and the palmar aspect of the lateral three and a half fingers.
Sensory loss also occurs on the skin of the distal part of the dorsal surfaces of the lateral three and a half fingers. The area of total anesthesia is considerably less because of the overlap of adjacent nerves.

Vasomotor Changes
The skin areas involved in sensory loss are warmer and drier than normal because of the arteriolar dilatation and absence of sweating resulting from loss of sympathetic control.

Trophic Changes
In long-standing cases, changes are found in the hand and fingers. The skin is dry and scaly, the nails crack easily, and atrophy of the pulp of the fingers is present.

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