Carpal tunnel syndrome: understanding what you may not have.

"Where the spirit does not work with the hand, there is no art. "

--Leonardo da Vinci

Da Vinci's sentiment could relate to the importance of the psyche in the creation of art. The word psyche comes via Latin from the Greek word psukhe meaning breath, life and soul. Similarly, performing the skills of a dental hygienist requires the aptitude of a great artist coupled with the knowledge of a scientist. With the high incidence of physical pain and psychological stress in the dental hygiene profession, one's spirit or psyche can be dampened from fear that a career may be cut short due to one ache or another pain.

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Carpal tunnel syndrome (CTS) is one of those aches or pains that comes to the minds of many dental hygienists who experience forearm, wrist, and/or hand pain. However, the diagnosis of this syndrome is not based on symptoms alone, and not everyone with wrist pain or paresthesias has CTS. We will explore the many facets necessary to thoroughly understand this syndrome, the associated risk factors, diagnostic criteria and tests, and the options for treatment. The powerful psychological impact of pain can impair performance in athletic, creative or professional endeavors. Seeking early intervention is key to minimizing the psychological effects and halting the progression of any physical problem, and CTS is no exception. Understanding this syndrome may help some avoid a problem once thought to be inevitable. A mind in concert with the body accomplishes great things.

History

This syndrome was first recognized in 1854 by Sir James Paget, who reported median nerve compression after a radial fracture. (1) Subsequently, the first surgical intervention came 79 years later in 1933, by Sir James Learmonth, who reportedly released the transverse carpal ligament (TCL) to relieve pressure on the median nerve at the wrist. (2) Since then, the signs, symptoms, diagnostic tests and interventions have been extensively discussed and described for this common peripheral neuropathy.

Anatomy

Many think of CTS as a wrist pathology; however, the compression of the median nerve causing the associated symptoms occurs in the hand and not in the wrist. Nevertheless, the nerve conduction velocity is measured across the wrist. The bones of the hand, known as the carpals, form the floor of a tunnel--the carpal tunnel. The proximal row of carpals includes the scaphoid, lunate, triquetrum and the pisiform; with the distal row containing the trapezium, trapezoid, capitate and hamate. Over this floor, forming the ceiling of the carpal tunnel is the TCL. Housed in the tunnel are nine tendons and one nerve. There are four tendons of the flexor digitorum superficialis muscle going to fingers 2-5, responsible for flexing the middle joint of the fingers (Figure 1A), four tendons of the flexor digitorum profundus muscle also going to fingers 2-5 responsible for flexing the distal joint of the fingers (Figure 1B), and one tendon from the flexor pollicus longus muscle going to the thumb to flex the thumb (Figure 1C). The star of the syndrome, the median nerve, sits on top of these tendons most closely situated to the TCL.

Risk Factors

So just what are the factors that influence the pressure in the carpal tunnel that can be associated with CTS? There are mechanical and nonmechanical risk factors.

Mechanical factors that increase the risk of CTS: (3-11)

* Direct pressure or a space-occupying lesion such as an acute injury including wrist trauma such as fractures, dislocations or crush injuries. (3-5)

* Additional pressure-increasing conditions include infection, degenerative and inflammatory changes in tendon sheaths, other inflammatory conditions, tumors, hypertrophic synovium and osteophytes. (5,6)

* Anatomically, a variation in the hook of the hamate bone (part of the floor in the carpal tunnel) was more often found in study subjects with CTS compared with the group without CTS. (7) While this factor is not easily changed, it may explain idiopathic CTS in those who do not possess other risk factors.

* Wrist motion and/or position. Wrist flexion and extension, especially at end-ranges, can increase the pressure in the carpal tunnel and contribute to the development of CTS. During treatment, wrist splints are designed to keep the wrist in a slightly extended position where volume of the carpal tunnel is the largest and the pressure is the least. In practice, monitor your positioning.

* Vibration (8-11)

* Occupational risk factors such as repetitive motion, force, posture and vibration are also reported to be strongly associated with CTS. To the contrary, a recent literature review supported the idea that "occupational CTS is uncommon and it is essential to exclude all other causes, particularly the intrinsic factors such as obesity before attributing it to occupation." But the article did recognize that the "risk of CTS was higher in occupations involving high pressure, high force, repetitive work, and the use of vibrating tools." (11)

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Nonmechanical factors also can increase the risk of CTS: (12-23)

* Female gender. Those with CTS tend to be of the female gender (more often than male), and between 30 and 50 years of age. (12,13,19,20)

* Pregnancy also increases the risk of developing CTS. The increase in vasculature and interstitial fluids potentially can increase the pressure in the carpal tunnel. (14)

* Systemic disorders place people at higher risks of developing CTS. (15-17) Diabetes, hypothyroidism, gout and rheumatoid arthritis are conditions where the nerves are more susceptible to compression and ischemia. Renal failure with hemodialysis has been shown to also be linked to CTS. These systemic conditions may directly or indirectly affect the microcirculation, axon transport, interstitial fluid pressures and pressure thresholds for nerve conduction. (12,13)

* Size of the carpal tunnel inlet. (18) The cross-sectional area at the carpal tunnel inlet was much larger in those with CTS than in the control group.

* Obesity. An obese worker is more likely to develop CTS than their slimmer counterpart. In the obese, the sensory conduction velocity of the median nerve across the wrist is slower. Studies have shown that higher levels of fitness and healthy lifestyles lowered the risk of developing CTS. (11,19,20)

* Psychological factors. Poor mental health was associated with more severe symptoms and lower satisfaction with treatment outcomes. A weak mind lends to a weak body. (21-23)

* Alcoholism. (22)

Symptoms of CTS

The classic hallmark symptoms of CTS are

* Nocturnal pain. (22,24)

* Numbness, tingling, and/or burning along the median nerve's sensory distribution in the hand. (Figure 2). (11,24)

Wrist pain itself is not necessarily a symptom that would immediately indicate the presence of CTS, as many tend to think. Other associated symptoms include grip weakness and uncoordinated hand motion. In more severe stages of the syndrome, the motor portion of the median nerve becomes involved. As a result, precision movements such as approximating the tip of the thumb and the opposing fingertips may prove difficult (Figure 3). Equally, there may be visible wasting of the thenar muscles of the hand.

Diagnosing CTS

Diagnosing CTS can include taking a thorough history, performing a physical exam (including provocation tests such as Phalen's and Tinel's, or vibration perception threshold), and ordering electrophysiological studies. Unfortunately, findings show that the physical exam alone had poor test-retest and inter-rater reliability for the most common tests performed and therefore should not be used to diagnose CTS. (25) Nerve conduction studies are the gold standard according to some, but Electromyography (EMG) is also used. (18,20,24) Recently, the accuracy of sonography has been found similar to that for EMG. "Sonography is probably preferable because it is painless, easily accessible and preferred by the patients." (18) Whichever electrodiagnostic test results are used, they cannot be used alone to accurately diagnose CTS. In a recent review article, (26) several authors concluded that the combination of electrodiagnostic findings, combined with the presence of the characteristic distribution of symptoms of CTS, were the most accurate means of establishing the diagnosis, but cautioned that there is no gold standard. Still, 10 percent to 15 percent of those with clinical CTS will have normal nerve conduction studies.

Interventions

Conservative management of CTS includes physical therapy, bracing/splinting of the wrist(s), anti-inflammatory medications and activity modifications. Physical therapy may include modalities such as ultrasound or low-level laser, soft tissue mobilization, joint mobilization, tendon gliding exercises and eccentric exercises when appropriate. Traction or stretch to the median nerve should be avoided, as it can change intraneural circulation. Should these methods not prove successful, a steroid injection into the tendons/tendon sheaths may be performed if indicated by the physician to decrease the inflammation that may be causing the increased pressure on the median nerve. Finally, surgery is indicated in two basic situations: first, if conservative treatment has failed to relieve the symptoms; and second, if the motor portion of the median nerve becomes involved. This would manifest with muscle atrophy in the thenar muscles and/or difficulty approximating the tip of the thumb with the opposing fingertips (Figure 3). The goal of the surgery is to release the pressure in the carpal tunnel by dissecting the TCL. This relieves the pressure in the carpal tunnel and theoretically resolves the problem.

Summary

Know the risk factors and eliminate those you can. Be familiar with the hallmark symptoms. If you do present with the classic signs of CTS, seek medical intervention immediately. Early diagnosis and treatment can improve your outcome. CTS should never go untreated, as it can cause permanent nerve damage. Remember, not all wrist pain is CTS, but pain usually does not go away on its own. So be intent on obtaining medical advice for the management of any symptoms before your symptoms manage you.

References

(1.) Paget J. Lectures on surgical pathology. Philadelphia, Pa.: Lindsay and Blakiston; 1854.

(2.) Learmonth JR. The principle of decompression in the treatment of certain diseases of peripheral nerves. Surg Clin North Am. 1933; 13: 905-13.

(3.) Roquelaure Y, Ha C, Pelier-Cady NC, et al. Work increases the incidence of carpal tunnel syndrome in the general population. Muscle Nerve 2008; Jan 30. [Authors: could this be Apr;37(4):477-82.?]

(4.) Violante FS, Armstrong TJ, Fiorentini C, et al. Carpal tunnel syndrome and manual work: a longitudinal study. J Occup Environ Med. 2007; 49(11): 1189-96.

(5.) Bugajska J, Jedryka-Goral A, Sudol-Szopinska I, Tomczykiewicz K. Carpal tunnel syndrome in occupational medicine practice. Int J Occup Saf Ergon 2007; 13 (10): 29-38.

(6.) Sernik RA, Abicalaf CA, Pimetel BF, et al. Ultrasound features of carpal tunnel syndrome: a prospective case-control study. Skeletal Radiol 2008; 37(1): 49-53.

(7.) Chow JC, Weiss MA, Gu Y. Anatomic variations of the hook of hamate and the relationship to carpal tunnel syndrome. J Hand Surg 2005; 30(6): 1242-7.

(8.) Armstrong TJ, Fine LJ, Radwin RG, Silverstein BS. Ergonomics and the effects of vibration in hand-intensive work. Scand J Work Environ Health 1987: 13; 286-928.

(9.) Pyykko I. A longitudinal study of the vibration syndrome in Finnish forestry workers. Vibration effects on the hand and arm in industry. New York: John Wiley and Sons; 1982: 157.

(10.) Radwin RG, Armstrong TJ, Chaf?n DB. Power hand tool vibration effects on grip exertions. Ergonomics 1987; 30: 833-55.

(11.) Aroori S, Spence RA. Carpal tunnel syndrome. [Review] Ulster Med J 2008; 77(1):6-17.

(12.) Phalen G. The carpal tunnel syndrome: clinical evaluation of 598 hands. Clin Orthop Relat Res 1972; 83: 29-40.

(13.) Dieck GS, Kelsey JL. An epidemiologic study of the carpal tunnel syndrome in an adult female population. Prey Med 1985; 14: 63-9.

(14.) Massey EW. Carpal tunnel syndrome in pregnancy. Obstet Gynecol Surv 1978; 33: 145-7.

(15.) Albers JW, Brown MB, Sima AA, Greene DA. Frequency of median mononeuropathy in patients with mild diabetic neuropathy in the early diabetes intervention trial (EDIT). Muscle Nerve 1996; 19: 140-6.

(16.) Leach RE, Odon JA. Systemic causes of the carpal tunnel syndrome. Postgrad Med 1968; 44: 127-31.

(17.) Faucett J, Werner RA. Non-biomechanical factors potentially affecting musculoskeletal disorders. Washington DC: National Academy Press; 1999: 175-99.

(18.) Visser LH, Smidt MD, Lee ML. High-resolution sonography versus EMG in the diagnosis of carpal tunnel syndrome. J Neurol, Neurosurg Psychiatry 2008; 79(1): 63-7.

(19.) Moghtaderi A, Izadi S, Sharafadinzadeh N. An evaluation of gender, body mass index, wrist circumference and wrist ratio as independent risk factors for carpal tunnel syndrome. Acta Neurol Scand 2005; 112(6):375-9.

(20.) Megerian JT, Kong X, Gozani SN. Utility of nerve conduction studies for carpal tunnel syndrome by family medicine, primary care, and internal medicine physicians. J Am Board Faro Med 2007; 20(1): 60-4.

(21.) Katz JN, Losina E, Amick BC, et al. Predictors of outcomes of carpal tunnel release. Arthritis Rheum 2001; 44(5): 1184-93.

(22.) Nathan PA, Keniston RC, Lockwood RS, Meadows KD. Tobacco, caffeine, alcohol, and carpal tunnel syndrome in American industry. A cross-sectional study of 1464 workers. J Occup Environ Med 1996; 38: 290-8.

(23.) Nathan PA, Keniston RC. Carpal tunnel syndrome and its relation to general physical condition. Hand Clin 1993; 9: 253-61.

(24.) Wilder-Smith EP, Seet RC, Lim EC. Diagnosing carpal tunnel syndrome-- clinical criteria and ancillary tests. Nat Clin Pract Neurol 2006; 2(7): 366-74.

(25.) Salerno DF, Franzblau A, Werner RA, et al. Reliability of physical examination of the upper extremity among keyboard operators. Am J Ind Med 2000; 37:423-30.

(26.) Werner RA. Evaluation of work-related carpal tunnel syndrome. J Occup Rehabil 2006; 16: 207-22.

By Jacquelyn Dylla, DPT, PT, and Jane L. Forrest, EdD, RDH 

Jacquelyn Dylla, DPT, PT, is an assistant professor of clinical physical therapy in the Department of Biokinesiology and Physical Therapy at the University of Southern California (USC) and holds a part-time faculty position with USC's School of Dentistry. She serves as the director of the faculty practice on the University Park Campus, serving all students, faculty and staff. Because of the high prevalence of neck and back pain in this population, she partnered with USC's School of Cinema/Television and created a CD-ROM entitled, "Spine Tuning: a video guide to breaking back habits."

Jane L. Forrest, EdD, RDH is chair, Division of Health Promotion, Disease Prevention and Epidemiology at the University of Southern California School of Dentistry and director of the National Center for Dental Hygiene Research. Dr. Forrest has received federal funding for a series of innovative grants related to faculty development and advancing dental hygiene as a profession. One of her current interests is in increasing knowledge about body mechanics and movement so that students are prepared to begin their career pain free.