Carpal tunnel syndrome

Carpal tunnel syndrome (CTS) or Median Neuropathy at the Wrist occurs when the median nerve becomes pressed or squeezed as it travels from the forearm (antebrachium) through the wrist into the hand. The median nerve controls sensations to the palm side (anterior) of the thumb and fingers (although not the little finger), as well as impulses to some small muscles in the hand that allow the fingers and thumb to move. The pressing or squeezing often results from repetitive stress injury (RSI) in an occupational context, such as using a keyboard and mouse without proper wrist support, or an assembly line job where the same tool is used in the same way for hours. Prevention of CTS, and RSI in general, is often more cost-effective than disability and not-always-successful treatment.

On the anterior side of the wrist is a sheath of connective tissue that forms a transverse carpal ligament, the flexor retinaculum. It is attached, medially, to the pisiform and the hamulus of the hamate bone; laterally, to the tubercle of the scaphoid, and to the medial part of the volar surface and the ridge of the trapezium. This ligament is superficial to the flexor tendons for the Phalanges (fingers). The carpal tunnel is the space posterior to (deep to) the flexor retinaculum and anterior to (superficial to) the carpal bones, through which the tendons slide during hand and particularly during finger movement. These tendons include the flexor digitorum profundi, and flexor digitorum superficiali groups, as well as the flexor pollicis longus. The median nerve also travels through the carpal tunnel.

If an inflammation exists which causes any of the structures associated with the carpal tunnel to swell appreciably (resulting in a positive Tinel's sign, where gently tapping the nerve produces tingling or pain), or if the size of the canal is reduced (such as when bending the wrist at a 90 degree angle, testing for Phelan's sign), the median nerve can become compressed causing symptoms of pain, paresthesias, and muscle weakness in the forearm and hand. The value of these and other findings on physical examination, however, has been questioned. Nerve conduction velocity and electromyography are valuable tools, and increasing value is seen in magnetic resonance imaging and high-resolution ultrasonography. Plain X-ray radiographs tend not to give useful information.

The differential diagnosis should rule out more general peripheral neuropathy. Especially if there are symptoms in both hands and wrists, genetic testing for hereditary neuropathy with liability to pressure palsy (HNPP) can be informative and give guidance for prevention in the patient and the patient's blood relatives

In terms of treatment, the underlying cause can offer some guidance. Hypothyroidism for instance is implicated in some cases when the reduced thyroid hormone levels cause synovial swelling. Treatment of the root cause disorder can offer relief from symptoms. Other treatments for CTS include anti-inflammatory medications (steroidal and non-steroidal), restriction/limitation of hand/wrist motion where RSI is involved, and "carpal tunnel release" surgery. In carpal tunnel release surgery a surgeon physically severs the flexor retinaculum ligament to release the pressure on the median nerve.