The carpal tunnel is an osteofibrous canal, the boundaries of which are the scaphoid and pisiform bones proximally, the trapezium and hamate bones distally, and thus lies toward the ulnar aspect at the heel of the hand. Within the carpal tunnel are found the median nerve, the tendons of the flexor carpi radialis, the flexor pollicis longus in separate sheets, and the superficial and deep flexors of the digits within a common tendon sheath. Carpal tunnel syndrome (CTS) is the most common peripheral entrapment neuropathy.

Etiology¹

Compression of the median nerve eventually can be triggered by factors that provoke an increase in volume of a structure within the carpal tunnel. These are:

• Traumatic, as in the case of wrist fractures (Colles' or subluxation of the lunate).
• Occupational activities, such as repeated use of some tools, and certain jobs that require repeated strong wrist motions. Injuries of this type are referred to as "repetitive stress" injuries, and are more frequent among people involved with excessive typing, using the mouse, working at computer keyboards or cash registers, factory workers, and some musicians. Once irritation of the median nerve has occurred, very little provocation is enough to offset symptoms.
• Inflammatory conditions such as rheumatoid arthritis, gout, and hematoma lead to thickening of the transverse carpus ligament and the tendons of the carpal tunnel.
• Other factors are endocrine (hypothyroidism, pregnancy, acromegaly, and menopause); the tunnel can also become compressed by a ganglion or a tumor.
• Generalized peripheral neuropathy can occur in diabetics. Hemophiliacs and patients on anticoagulants are also at a greater risk of developing CTS.
• Partial syndromes where symptoms occur in only a part of the nerve's territory have been observed as a result of an injury, incorrect use of a walking stick, or a trigger finger.

Pathologic Anatomy and Staging of Compression³

• In early compression, there is decreased axonal transport. However, morphologic changes are absent. The patient complains of intermittent symptoms, tests positive for provocative tests, and can be found to be hypersensitive to 256 cps. These patients do best with conservative therapeutic management.
• In moderate compression, persistent interference of intraneural microcirculation is present with intrafascicular edema. However, wallerian degeneration has not taken place. There is decreased vibratory sensation, positive findings on provocative tests, thenar weakness, and abnormal sensory findings.
• In severe compression, fibrosis occurs. Electromyography (EMG) studies show denervation potentials in the muscles supplied by the median nerve. Persistent sensory changes, abnormal two-point discrimination greater than 4 mm, and thenar atrophy are present.

History and Symptoms^1,2,4,12,13

With carpal tunnel syndrome, the symptoms are primarily distal to the wrist and include "pins and needles" and numbness into the median nerve distribution (the palmar aspect of the thumb, index, middle and radial half of the ring finger, as well as the dorsal aspect of the distal phalanges of these fingers). These symptoms are experienced especially on exertion, and rest brings temporary relief. Nocturnal paresthesia is not uncommon. Pain develops in about few months in about 15% of patients but need not necessarily precede the above symptoms, and is felt in the palm of the hand and may even be referred to the forearm in severe cases. Symptoms are often aggravated by repeated activity of the wrists, and long-standing cases show atrophy and weakness of the thenar muscles and the lateral two lumbricals, following which there is inability to use the hand.

Inspection and Examination^1,2,3,5

Inspection can reveal structural changes—post fracture, deformities, ganglia, bony subluxations, conditions that could be relevant when the overall clinical picture is considered. In long-standing cases, muscular atrophy and the flattening of the thenar eminence give rise to the ape hand deformity. The most accessory tests are the Phalen's test (most sensitive) and the Tinel's tests (most specific). A positive result gives a useful clinical indication of the CTS, but the diagnosis is not excluded when the tests turn out to be negative.

Test of sensation: pin-prick, light touch, and two-point discrimination show if sensation is impaired.

Tourniquet test: inflation of the tourniquet for 1 minute gives rise to pins and needles.

Technical Investigation¹

Electrophysiological examination to confirm or exclude the diagnosis is necessary. In entrapment neuropathy, nerve-conduction velocity is generally thought to be a sensitive indicator of the severity of demyelination and ischemia at the entrapment point. Thus, conduction velocity measurement in CTS is of diagnostic significance.

Further, since conduction velocity measurement can identify subclinical lesions, it has particular value in initial diagnosis. However, in segment nerve injuries where a nerve is compressed locally, electrophysiological findings do not necessarily reflect the disease state of the entire nerve (the median nerve, in the case of CTS). The results of an electrophysiological study will therefore not always be consistent with clinical findings when CTS is advanced and varying stages of impairment in differing nerve fibers are present.

Although false negatives and positives do occur, EMG may not only confirm the diagnoses but may also be interesting from the prognostic point of view: When the distal motor latency between the wrist and the thumb is more than 7ms, conservative treatment will probably give only temporary relief. Computed tomography (CT) is a useful tool for evaluating the abnormalities in the wrist. Abnormalities on CT have been found in 78.2% of recent CTS, as opposed to 53.1% of positive EMGs in the same cases. High-resolution sonography is a low-cost alternative to MRI and has gained increasing popularity. A much more reliable diagnostic approach is by infiltration of 20 mg triamcinolone suspension into the carpal tunnel. If diagnosis is right, all symptoms should disappear for at least a few weeks.

Differential Diagnosis

CTS must be differentiated from the cervical disk protrusion that compresses a nerve root and from thoracic outlet syndrome with compression of a part of the brachial plexus. Symptoms in a cervical disk lesion are not activity specific, and the patient cannot localize the paresthesia exactly as in CTS. Decompression tests of the thoracic outlet are positive, and the paresthesia is felt in all fingers and does not have any specific distribution.

Treatment

Conservative treatment of CTS comprises wrist splinting, injections, medications, and physical therapy.

Splinting the wrist in neutral position, especially at night, has led to symptom reduction but has shown temporary results in about 70% of the patients. More recent studies have shown best results with a full-time splint for 3 to 4 weeks.

Injections with triamcinolone acetonide, which are diagnostic as well as therapeutic, have been shown to give temporary relief in mild to moderate cases. Medications such as oral cortico-steroids, anti-inflammatory drugs, diuretics, and pyridoxine (vitamin B6) are known to provide short-term benefit.

Physical Therapy

Myofascial release^5-8: Recent studies have found myofascial release techniques to be successful in treating CTS. These remove the "fibrous adhesion" wherever it might be along the nerve pathway. These adhesions may be caused by almost any recent or past trauma to the area, and may result in a traction neuropathy and fixation of the nerve. The eventual loss of normal gliding of the nerve could result in localized nerve tension and damage to myofascial structures, resulting in fibrous adhesions.

In the use of MRT in a carpal tunnel involvement, it is necessary to trace the median nerve at any area where it can be found to be entrapped. The most common areas are at the thoracic outlet at the costoclavicular interval; in front of the subscapularis in the axilla; under the ligament of Struthers, proximal and medial to the elbow; between the heads of the pronator teres; under the anterior interosseous membrane in the forearm; and the carpal tunnel area. Overall, the mobility of the tissue is altered and tension is reduced, helping to normalize circulation and reduce tissue tension.

Neural mobilization¹¹: techniques can be applied when there is evidence of an entrapment of the median nerve at the wrist and there is a positive neurodynamic test. These neuromobilization techniques include repetitive motions of the segment that produces the symptoms as well as a combination of movements in the more distal and proximal segments. The treatment position used is identical to the testing position. Treatment should involve all segments of the neural tissue with focus on respecting the continuity of the neural tissue.

Nerve and tendon gliding exercises: These have proven to be effective in preventing muscle tension and maintaining the elasticity of the nerves.

Joint mobilization^3,4,9: Mobilization of the carpals, especially the capitate for increased carpal tunnel space, is useful. Joints like the shoulder, the sternoclavicular joint, and the wrist are typically mobilized followed by stretching to prevent nerve scarring and strengthening exercises, which help to reinforce correct position and movement patterns.

Modalities¹¹: A randomized controlled study reported a significant decrease of CTS symptoms after the application of red-beam laser (continuous wave, 15mW, 632.8 nm) on shallow acupuncture points on the affected hand, infrared laser (pulsed, 9.4W, 904 nm) on deeper points on upper-extremity and cervical paraspinal areas, and micro amps TENS on the affected wrist. Ultrasonography and phonophoresis have shown to be helpful in the initial stages for localized symptomatic relief.

Biomechanical analysis⁴ to identify faulty wrist or upper-extremity motions and ergonomic measures play a crucial role in preventing further damage. Ergonomic workstation assessment and modification with correct postural biomechanics should be emphasized.

Surgery

Surgery can be an effective treatment for CTS, but prediction on its outcome depends on the accuracy of the diagnosis before the surgical intervention and the timing of surgery with regard to the onset of symptoms. Rapid recurrence in less than 6 weeks, or symptoms lasting for more than 6 months, moderate to severe compression evidenced by muscular atrophy, or sensory deficits necessitate surgery. Surgical division of the transverse carpal ligament has shown good results in patients who do not show objective neurological deficit. The long-term results of an endoscopic release are similar to open release, but the former leads to quicker functional recovery. Postoperative rehabilitation comprises scar and joint-mobilization techniques as well as a stretching versus a strengthening program.

Santhoshini Hiremagalur, PT, specializes in hand therapy at Hands on Healing Physical Therapy in Allentown, Pa.

References

1. Ombregt, Pierre Bisschop, Herman ter Veer. A System of Orthopaedic Medicine. 2nd ed. Amsterdam, the Netherlands: Elsevier; 1995, 568–573.
2. Magee DJ. Orthopedic Physical Assessment. 3rd ed. Amsterdam, the Netherlands: Elsevier; 1987, 307,311–315,318,326.
3. Burke SL, Higgins J, McClinton MA, Saunders R, Valdata L. Hand and Upper Extremity Rehabilitation, a Practical Guide. 3rd ed. Amsterdam, the Netherlands: Elsevier; 1993, 87–95.
4. Burnett C, Glenn T, Konkler C, Therapeutic Exercise. 3rd ed. 372–374. (MFR 5678)
5. Papaioannou TT, Rushworth G, Atar D, Dekel S. Carpal canal stenosis in men with idiopathic carpal tunnel Ludwig syndrome. Clin Orth & Rel Res. 1992;285:210–213.
6. Leahy PM, Mock LE. Altered biomechanics of the shoulder and the subscapularis. Chiropractice Sports Med. 1991;5:62–70.
7. Leahy PM, Mock LE. Synoviochondrometaplasia of the shoulder: a case report. Chiropractice Sports Med. 1992;6:5–15.
8. Leahy PM, Mock LE. Myofascial release technique and mechanical compromise of peripheral nerves of the upper extremity. Chiropractice Sports Med. 1991;6:139–150.
9. Hammer W. Carpal tunnel exercises that work. Dynamic Chiropractic. 2001;19(14).
10. Goodyear-Smith F., Arroll B. What can family physicians offer patients with carpal tunnel syndrome other than surgery? A systematic review of nonsurgical management. Ann Fam Med. 2004;2:267–273.
11. Kostopoulos D. Treatment of carpal tunnel syndrome: a review of the non-surgical approaches with emphasis in neural mobilization. J Bodywork and Movement Therapies. 2004;8,2–8
12. Viera AJ. Management of carpal tunnel syndrome. Amer Fam Physician. 2003Jul15;68(2):265-272.
13. Carson-DeWitt RS. Carpal tunnel syndrome. Encyclopedia of Medicine. Available at: findarticles.com/p/articles/mi_g2601/is_0002/ai_2601000270. Accessed: December 13, 2007.
14. Greer BG, Jenkins WM, Roberts R. Carpal tunnel syndrome: a challenge for rehabilitation. J Rehabil. 1992;58(2):43-46.