Focus on CME at the University of Calgary

Carpal Tunnel Syndrome The non-idiopathic causes of (CTS) involve intrinsic and extrinsic conditions responsible for compression. To establish a work-related association, there should be a history of excessive or unusual hand use of a nature known to be associated with CTS prior to the onset of symptoms.

By Ron Gorsché, MD, MMedSc (Occupational Health), CCFP

arpal tunnel syndrome (CTS) is responsible about CTS and it is among the most controversial C for the most time lost in the workplace, yet of disorders. This article focuses on how recent lit- there is little consensus regarding work as a erature has contributed to the theories of patho- causative factor of the syndrome. Little is known physiology and pathogenesis of CTS, and pro- vides clinicians with a more scientific approach Dr. Gorsché is clinical associate pro- to causative factors and treatment. fessor, departments of family medi- cine and community health sciences, faculty of medicine, University of Historical Perspectives Calgary, and director, Work-Related In 1860, Paget reported the first cases of median Upper Limb Disorders Research nerve compression of the wrist — one case attrib- Unit, Calgary, Alberta. He is also uted the disorder to a tight band wrapped around active staff, High River General the wrist and the other cited complications asso- Hospital, High River, Alberta. ciated with a fractured distal radius.1 In 1941,

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Woltman first postulated the possibility of nerve toms of CTS. This approach works well for the compression within the carpal tunnel as a cause of clinician attempting to explain the syndrome to a “median neuritis,” after reporting 12 cases associ- patient, but requires further classification for epi- ated with acromegaly.2 demiological study. It also is effective when con- Phalen, who reported his extensive clinical sidering treatment options. experience between 1950 and 1972, supported Although there is no gold standard case defini- active hand use as a factor in symptom aggrava- tion for epidemiological study, to simply use “arm tion, but cast doubt on work as the sole etiology.3 ” as a definition, as does the Department of Phalen raised one of the primary issues concerning Labor in the United States, grossly overestimates the definition of work-related aspects of CTS. He the prevalence. A combination of - noted the distinction between factors that aggra- specific symptoms and electrodiagnostic signs vate symptoms of CTS and factors responsible for provides the most accurate diagnostic information the development of the condition. (Table 1).4 To rely solely on positive nerve con- duction studies has a poor predictive value, since, in some populations, as few as 22% of individuals Defining found positive by (NCS) Carpal Tunnel Syndrome actually had CTS symptoms. After 17 months of follow-up with a matched cohort, this finding did CTS can be defined simply as a complex of symp- not change. Furthermore, these workers were not toms resulting from the compression of the medi- found to be at risk for future development of CTS. an nerve at the carpal tunnel. Median nerve entrap- In the presence of electrodiagnostic data, physi- ment is the pathological process that causes symp- cal findings aside from thenar muscle wasting add

Summary Carpal Tunnel Syndrome

¥ CTS occurs as a result of an increase in pressure transmitted to the median nerve within the canal. ¥Measuring carpal tunnel pressure during various hand and wrist positions allows physicians to determine optimal positioning for splints and in prescribing work restrictions. ¥To establish a work-related association, there should be a history of excessive or unusual hand use of a nature known to be associated with CTS prior to the onset of symptoms. ¥ The goal of treatment is the resolution of symptoms and preservation of hand function. A significant number of CTS patients will improve with no treatment. This is especially true for those young workers with severe initial impairment. Nonsteroidal anti-inflammatories (NSAIDs), prednisone (1 mg/kg) orally, steroid injection into the carpal tunnel, vitamin B6 (pyridoxine) and vitamin C have all been used in treatment, although not all have been proven efficacious. ¥ Surgical treatment should only be considered in the presence of ongoing symptoms or signs of thenar wasting, together with electrodiagnostic confirmation. ¥ The most successful return-to-work outcomes have occurred when the wrist is not splinted post- operatively and the patient is instructed in a graduated program of early mobilization.

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Table 1 The Likelihood of CTS Based on Clinical and EDS Findings*

Category Symptoms Electrodiagnostics(EDS) Ordinal Likelihood of CTS Classic/Probable Nocturnal Positive +++ symptoms, tingling, burning or pain in at least 2 digits of 1,2, or 3. Palm pain, wrist pain or radiation proximal to wrist.

Classic/Probable As above Negative +/- Possible Tingling, numbness, Positive + + burning or pain in at least 1 of the first 3 digits 1,2, or 3

Unlikely No symptoms in Positive __ digits 1,2,3.4

*In the absence of electrodiagnostic studies, a combination of symptoms and one positive provocative sign, such as Tinels, Phalens, wrist compression test or 3 point discrimination gives the best diagnostic information.

*Thenar muscle wasting is the only truly objective physical sign of CTS and increases the likelihood of CTS in all categories. little to the accuracy of diagnosis. All other working population in a Montreal study has been provocative diagnostic tests, such as Tinel’s, calculated to be 0.9 per 1,000 adults.6 In studies of Phalen’s, wrist compression, and two-point dis- specific groups of workers, the incidence in com- crimination, are subjective and, therefore, are not puter users is actually no different than in the gen- sensitive. In the absence of electrodiagnostic test- eral population, whereas in meat packers it is ing, however, adding one positive provocative reported as high as 11 per 100 person years.7,8 physical finding to the case definition is most accu- rate. Anatomy •This fibro-osseous U-shaped canal is made up Prevalence and Incidence of a bony floor and walls and a roof of fibrous The prevalence of CTS in the general population flexor retinaculum. The proximal edge of the has been estimated to be 5% for women and only canal is near the distal wrist crease at the level 0.6% for men.5 The surgical incidence among the of the pisiform carpal bone. The canal then

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extends distally about 2.5 cm to the level of the hook of hamate. The normal contents of the canal or tunnel include the flexor digitorum profundus and flexor digitorum superficialis tendons of digits II-V, the flexor pollicis longus and the median nerve as shown in Figure 1. •Tendon sheaths cover the tendons within the carpal tunnel. The tendon sheath for the flexor pollicis longus, also called the radial bursa, begins proximal to the carpal tunnel and extends to the base of the distal phalanx of the thumb. The ulnar bursa is larger and covers the superficial and deep tendons of digits II-V. It also begins proximal to the carpal tunnel, extending to the base of the distal phalanx of digit V and to the middle of the metacarpals. • In many individuals, the proximal ends of the lumbrical muscles that originate on the flexor Figure 1. Carpal tunnel anatomy digitorum profundus tendon enter the distal end of the carpal tunnel during flexion.9 At the opposite, or proximal end, of the carpal tunnel, the flexor muscle bellies will pass by the pisi- form carpal bone at the entrance to the canal when the wrist is extended greater than 30 degrees and intra canal pressures would exceed 30 mmHg, if fingers were extended to 0 degrees or flexed greater than 45 degrees.10 • Although the median nerve innervates the thumb, index, middle and one-half of the ring fingers, aberrant or cross-over innervation from the has been found in 30% of hands. The motor branch of the median nerve to the thumb can exit prior to the flexor retinacu- lum, in the middle, or distal to it.

Peripheral Nerve Structure and Function Figure 2. Hand diagram used to localize symptoms to median, ulnar or . Median nerve = yellow; The neuron consists of a cell body located in the ulnar nerve = blue; radial nerve = red. anterior horn (motor) or dorsal root ganglia (sen-

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Table 2 Effects of Compression on the Peripheral Nerve

¥ Pressures of 80 mmHg (10.7 kPa) interrupts all intraneural blood flow. ¥ Pressures above 30 mmHg (4.0 kPa) inhibit all antegrade and retrograde axonal transport. ¥When extraneural pressure fluctuates rapidly, the effects on nerve function are associated with the mean value of the pressure waveform. ¥ There is an increased tolerance for high pressures among those with hypertension. The critical extraneural pressure threshold above which nerve function is blocked is 30 mmHg (4.0 kPa) below the diastolic pressure. CTS often manifests itself after treatment for hypertension. ¥ Compression of 30 mmHg (4.0 kPa) led to an elevated intraneurial pressure that persisted for 24 hours. These effects are likely due to the increased vascular permeability of the epineurial and endoneurial vessels producing edema after compression. ¥A pressure of 30 mmHg applied to the median nerve appears to be the critical threshold for . sory) and an axon extending into the periphery, endoneurial space, and the tissue pressure with- and made up of myelinated and non-myelinated in the fascicle is slightly positive. fibers. These fibers are arranged in bundles, • There are no lymphatics within the endoneurial called fascicles, surrounded by membrane, called space. Any edema that develops, therefore, may a perineurium. The fascicles are organized into increase pressure within the fascicle rapidly groups held together by a loose connective tissue, and interfere with the microcirculation. called the epinerium. The endoneurium is the • The median nerve can move an average of 9.6 connective tissue that separates the individual mm during wrist flexion and slightly less so nerve fibers from their basement membrane. during extension. There are a few important properties of peripher- al nerve physiology that help explain the changes that occur during periods of increased pressure or Pathophysiology injury. CTS occurs as a result of an increase in pressure • The peripheral nerve has a well-developed transmitted to the median nerve within the canal. microvascular system that supplies the energy Two theories have been proposed to explain the for axonal transport of nutrients. Disturbances effect this increase in pressure has upon the medi- in this transport mechanism may be involved in an nerve.11 Both theories attempt to explain the the development of diabetic neuropathy, also response to pressure, but not the cause. rendering the nerve more vulnerable to injury, Microvascular insufficiency. The acute such as compression at the carpal tunnel. symptoms of pain, parasthesia and night numb- • The vessels have a coiled configuration, allow- ness are thought to be secondary to ischemia in ing for uncompromised circulation during nor- the median nerve. These cases are characterized mal gliding of the nerve. by rapid, reversible nerve conduction changes • There is a blood-nerve barrier protecting the and symptomatic improvement following carpal

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important to the clinician who is faced with deci- sions in determining causation and prescribing modifications and appropriate splints. Table 2 summarizes the outcomes of pressure studies involving peripheral nerves. In general, axonal demyelination and degeneration is rarely seen when nerves are subjected to pressures of less than 30 mmHg.

Carpal Tunnel Pressures Associated with Wrist and Hand Position Measuring carpal tunnel pressure during various hand and wrist positions allows physicians to determine optimal positioning for splints and in prescribing work restrictions. As shown in Table 3, intra canal pressures follow a U-shaped para- bolic curve, with only extremes of wrist and fin- ger flexion and extension producing pressures above the 30 mmHg threshold for injury. A wrist Figure 3. Potential anatomical sites for median nerve at neutral position, with the metacarpo-pha- entrapment. langeal joints at 45 degrees, results in the lowest tunnel release. One study found that up to 98% pressure and is most suitable for splinting.15 of CTS cases examined had vascular sclerosis.12 Mechanical compression. Persistent nerve conduction impairment is believed to be due to the The Effect of effects of nerve compression. A “tadpole” lesion, Force or Loading on characterized by thinning of the myelin, develops Carpal Tunnel Pressures because of a shearing-type of pressure phenome- non at the end of the internodal segment with a Researchers have studied the effects of various bulbous-like swelling at the facing edge. hand activities and forces on the carpal tunnel pressures (Table 4).16 Highest pressures occur with forceful grasping, and the lowest with fin- The Effects of ger-tapping. Epidemiological studies have also Nerve Compression confirmed the low incidence of CTS and protec- tive effect of keyboarding.17,18 Activities involv- A dose-response curve has been established, fol- ing forceful, repetitive and prolonged grasping lowing experiments with intra canal pressure or vibration, therefore, will increase pressures, transducers.13,14 The outcomes of such studies are whereas finger work or light repetitive grasping

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Table 3 Table 4 Carpal Tunnel Pressures The Effect of Force or Loading Associated with Wrist and Hand on Carpal Tunnel Pressures Position 1. Loading and unloading one pound cans ¥ Mean pressure at rest is 8 mmHg (2.4 kPa). failed to raise pressures greater than ¥With wrist movement, peak pressures greater 18 mmHg. than 40 mmHg occur at full flexion and 2. Making a fist increased extraneural pressure extension. within the carpal tunnel to 234 mmHg. ¥With wrist extension highest pressures 3. Pinching a load between index finger and (greater than 50 mmHg) were recorded with thumb increased pressure to 50 mmHg. MCP joint at extremes of zero degrees or 90 4. Grasping a 10.4 cm diameter cylinder degrees and full suppination. increased the carpal canal pressure to ¥With wrist flexed the highest pressures were 75 mmHg. recorded at MCP of 0 degrees. 5. Finger pressing did not elevate carpal tunnel ¥Lowest pressures were recorded with the wrist pressures until the maximum exertion of at zero to ten degrees extension and MCP 15 Newton was applied. joints at 45 degrees and forearm pronated at 45 degrees. or purely an aggravation to an underlying condi- tion. A number of personal factors have been with a neutral wrist will not. found to be associated with CTS.19 There appears to be a marked hormonal influence in women (Table 6), whereas, in men, CTS is asso- Pathogenesis ciated with morphology, such as short stature The non-idiopathic causes of CTS involve and obesity.20 Work-related activities found to intrinsic and extrinsic conditions responsible for be associated with the onset of CTS, include the nerve compression (Table 5). To establish a following: work-related association, there should be a his- •Prolonged grasping; tory of excessive or unusual hand use of a nature • Forceful grasping; known to be associated with CTS prior to the • The use of handtools (especially vibrating); onset of symptoms. The carpal-canal-pressure • The use of the wrist in extreme flexion or studies outlined above provide a guide to those extension; activities that put patients at risk of having nerve • Activities that compress the palm; compression. The evidence suggests that neither • Repetitive impact to the base of the palm; and cumulative trauma disorder (CTD) nor repetitive • Shoulder rotation with arm elevated.21 hand use without forceful or prolonged grasping, are hazardous. The literature is not able to settle the controversy over whether work is causative Diagnosis

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Table 5 Differential Diagnosis of Median Nerve Compression

1. Space Occupying Structures or : 2. Accumulation of Fluid: A. Lumbrical muscles or flexor tendon muscle bellies A. Pregnancy B. Tumors B. Congestive heart failure C. Cysts C. Compartment syndromes D. Congenital aberrant muscle D. Local inflammatory conditions E. Fractures F. Foreign body

3. Increase in Extracellular Matrix: A. Acromegaly B. Myxedema C. Mucopolysaccharidosis D. Monoclonal gammopathies Spinal Lesion or “double crush” syndrome: The phenomenon whereby an injury to a nerve proximally such as the dorsal root renders the nerve more susceptible to compression injury distally, such as at the carpal tunnel.

Signs and symptoms. CTS, by definition, is a in up to 30% of cases, and cervical radiculopa- clinical syndrome and the clinician must decide thy, often referred to as double crush syn- which patients are the best candidates for confir- drome.23 If symptoms are purely sensory, the matory electrodiagnostic study. A study examin- theory of interruption to axonic flow, causing ing the various clinical criteria necessary to increased peripheral nerve susceptibility, is less achieve high-specificity (low false-positive) likely, since flow from the nerve root to the arrived at the consensus outlined in Table 1. spine and periphery is separate and indepen- Except for the presence of thenar muscle wast- dent.24 ing, the addition of find- Electrodiagnostic study. The electrodiagnos- ings offers little to the accuracy of diagnosis. tic study (EDS) consists of two components — There are no sensitive, objective, provocative the nerve conduction study (NCS) and the elec- physical examination techniques available to the tromyographic examination (EMG). These stud- clinician. A simple hand diagram has been vali- ies can be administered safely in patients with dated for identifying median nerve symptoms pacemakers and cardiac arrythmias. Patients (Figure 2).22 This hand diagram is especially with human immunodeficiency virus (HIV), useful in populations where language is a con- hepatitis or Cruetzfeld-Jacob disease can be test- cern. The use of a simple pinwheel is helpful ed with disposable needles. Patients can be reas- when mapping out areas of numbness or differ- sured that electric shocks of varying intensity ences between hands. There has been a signifi- are slightly uncomfortable, but harmless. A neu- cant association between bilateral CTS, present rologist performs the examination, with the limb

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Table 6 Gender Differences in Personal Risk Factors Associated with CTS

Risk Factor OR 95% CI Prior musculoskeletal complaint 1.98 1.61 to 2.42 for which consultation sought Obesity 1.68 1.29 to 2.18 Prior oral contraceptive use 1.38 1.08 to 1.76 (but not current use) in women over 40 years old History of consultation for any 1.36 1.11 to 1.66 menstrual disorder Lower socioeconomic class 1.23 1.02 to 1.50 Current use of hormone replacement therapy Respiratory complaints Pregnancy

Males: Obesity, age, short stature and history of stenosing flexor tenosynovitis.

warmed to at least 32 degrees, and will follow SNAP is recorded traveling to the distal the guidelines set out by the American limb (antidromically or against the normal Association for Electrodiagnostic Medicine. direction) and returning from the distal limb (orthodromically or the direction nomally taken). The Electrodiagnostic Glossary of Terms -Distal sensory latency, or onset latency, is the length of time it takes for a stimulus to The nerve conduction study (NCS). The pur- travel a set distance to initiate a SNAP. pose of the NCS is to determine if there is a time - Sensory amplitude: The amplitude of the delay, a change in intensity, or a reduction in SNAP is not determined by the number of velocity of a nerve impulse between one section axons, but by the cross-sectional density of a peripheral nerve and another. In the case of of the conducting sensory axons within the CTS, any delay of motor and sensory impulses nerve. traveling across the carpal tunnel is of interest. • The Motor Axons are assessed by placing an • The Sensory Axon. electrode on the skin overlying a muscle inner- - Sensory nerve action potential (SNAP): vated by the median nerve, such as the thenar When sensory axons are examined, the eminence.

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occurs, and the recorded SNAP and CMAP will be absent or abnormally small. This is due to a loss of impulse conduction or a conduction block. The reference laboratory should deter- mine the normal ranges for any electrodiagnostic study. The normal range has traditionally been established as the mean +/- 2 standard deviations.25 The electromyogram (EMG). A needle elec- trode inserted into muscle can be used to assess the electrical stability of the muscle membrane and the electrical properties of a muscle undergo- ing voluntary contraction. Pathological changes in nerves and muscle, plus many metabolic abnor- malities, may be detected. The needle electrode examination begins by recording the muscle at Figure 4. Example of a custom molded night splint. rest, searching for spontaneous potentials, such as: • Fibrillation potentials and positive sharp waves. These are assessed by recording the muscle at rest, while looking for spontaneous - Compound muscle action potential potentials from a single muscle fiber. These (CMAP): The summated depolarization of findings indicate underlying muscle denerva- the muscle fibers underlying an electrode tion. Whole motor units can be assessed next by produces a waveform, called the com- looking for the presence of: pound muscle action potential. - . Whole motor units can be -Distal motor latency (DML): The length evaluated, regardless of the presence of den- of time between stimulation at a standard ervation, because fasciculations may site and the onset of the CMAP is termed originate in the spinal cord or anywhere thedistal motor latency. along the length of the motor axon. - Motor conduction velocity: By stimulating - The motor unit action potential (MUAP) is a the nerve at two different sites, the motor summated, large single waveform, which nerve conduction velocity can be calculated. results from the near simultaneous discharge The distal motor latency and motor nerve con- of the muscle fibers supplied by an anterior duction velocity are mainly dependent on the horn cell, stimulated during a voluntary integrity of the myelin sheath, whereas the muscle contraction. Disease processes amplitude and shape of the CMAP offer infor- affecting the motor unit can be detected mation about the number of functioning axons more readily with this measurement. A supplying the muscle. In demyelinating disor- neurologist may decide that an electromyo- ders, therefore, there will be abnormally pro- gram (EMG) is unnecessary in a straightfor- longed distal latencies and reduced conduction ward case of CTS. If, however, the velocities, due to slowed impulse transmission. symptoms are atypical or a concomitant If the entrapment continues, axonal degeneration cervical lesion is present, an EMG may be

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Table 7 Classification of the Severity of the Electromyogram

Mild Moderate Severe Motor Latency 4.0 to 5.0 msec 5.0 to 7.0 msec Above 7.0 msec or negative Sensory Latency 3.0 to 4.0 msec 4.0 to 6.0 msec Above 6.0 msec or negative Sensory Amplitude Below 20uV Below 20 uV Below 20 uV or negative Denervation Negative Negative Positive

Adapted from Choi SJ, Ahn DS: Correlation of clinical history and electrodiagnostic abnormalities with outcome after surgery for carpal tunnel syndrome. Plastic and reconstructive surgery 1998; 102:2374-80.

helpful. The clinician must remember that and preservation of hand function. A significant there are at least six regions proximal to the number of CTS patients will improve with no treat- carpal tunnel where the median nerve may ment. This is especially true for young workers with be entrapped (Figure 3). severe initial impairment.27 This helps explain why many unproven, alternative therapies claim success. For those patients who fail to resolve spontaneously, Laboratory Investigations early intervention is the key to successful outcomes. All cases of CTS that fail to improve with conser- Conservative: 50% to 75% improvement. Work vative treatment should undergo a baseline inves- Restrictions. Patients should be instructed to avoid tigation to rule out other associated diseases. This activities associated with CTS, both at work and at should include tests for s-thyroid stimulating hor- home. Such activities include using hand tools, mone (s-TSH), fasting blood sugar, protein elec- forceful grasping, prolonged grasping, placing pres- trophoresis, B12, rheumatoid factor, antinuclear sure against the palm and awkward positions of antibody (ANA) and erythrocyte sedimentation extreme flexion or extension. rate (ESR). If there is a history of previous trauma Night splints. A custom, molded night splint to the wrist or hand an x-ray should be ordered.26 should be fashioned by an occupational therapist (Figure 4). Using carpal canal pressure princi- ples, as outlined previously, the splint should The Stages of CTS maintain the wrist in a near-neutral position with With the foregoing knowledge of pathophysiolo- a few degrees of ulnar deviation and with gy, three stages of CTS have been proposed (Table metacarpophalangeal (MP) joints at 45 degrees. 7). Treatment is based on the severity determined Night splints prevent the incursion of the lum- by both clinical and electrodiagnostic assessment. brical muscles into the distal carpal tunnel, which occurs with wrist flexion during sleep. Daytime working splints are of little value. Treatment Although one recent article found improvement The goal of treatment is the resolution of symptoms in one aspect of sensory conduction, there was

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no improvement in symptoms.28 cessful return-to-work outcomes have occurred . when the wrist is not splinted post-operatively • Nonsteroidal anti-inflammatories (NSAIDs) and the patient is instructed in a graduated pro- improve pain, but have not been shown to be gram of early mobilization.31 Most patients can effective treatment for long-term resolution. return to light-hand use following the removal of •Prednisone (1 mg/kg) orally often provides sutures, but may not tolerate the use of hand symptomatic relief in an acute onset. tools for an average of six to eight weeks. All • Steroid injection into the carpal tunnel pro- cases of surgical failure should undergo a com- duces short-term relief of symptoms, but risks plete examination and repeat electrodiagnostic include median-nerve damage. There is one assessment to rule out other, less common, caus- randomized controlled trial reporting sympto- es of . matic improvement with injection of 40 mg of methylprednisilone into the volar forearm, 4 cm proximal to the wrist crease.29 Conclusion • There is no evidence to date of an association In summary, compression of the median nerve between CTS and vitamin B deficiency. within the carpal tunnel at the wrist is responsi- •Vitamin C has not been shown to be effective ble for the symptoms,CME signs and electrodiagnos- for this purpose. Be aware that supplementing tic findings in CTS. Modifications in hand use, with vitamin C in the presence of vitamin B6, as well as night splints to reduce intra-canal or ingesting more than 500 mg per day of vit- pressure, are the most effective conservative amin B6, may injure the nerve.30 interventions, and, failing that, surgery is more Alternative therapies. There is insufficient than 90% successful. evidence to support the use of physiotherapy, ultrasound, magnets, lasers or manipulation in the treatment of CTS. Surgical treatment (90% improvement). Surgical treatment should only be considered in References 1. Paget J: Lectures in Surgical Pathology. Lindsay and the presence of ongoing symptoms or signs of Blackiston, Philadelphia, 1860, pp. 42. thenar wasting, together with electrodiagnostic 2. Woltman HW: Neuritis associated with acromegaly. confirmation. The use of the short 2 cm to 3 cm Archives of Neurological Psychiatry 1941; 45:147-52. palmar incision to release the flexor retinaculum 3. Phalen GS: The carpal tunnel syndrome. J Bone Joint Surgery 1966; 48A:211-28. is the method preferred by most reports in the lit- 4. Rempel D, Evanoff B, Amadio PC, et al: Consensus cri- erature. Complications include injury to the teria for the classification of carpal tunnel syndrome in thenar motor branch, injury to the median nerve epidemiologic studies. Am J Public Health 1998; 88:1447-51. itself, , bleeding and failure to resolve 5. de Krom M, Knipschild P, Kester A, et al: CTS: symptoms. A tender surgical scar is the post- Prevalence in the general population. J Clinical operative complication that most often hampers Epidemiology 1992; 45:373-6. return to work. Endoscopic surgical release, 6. Rossignol M, Stock S, Patry L, et al: Carpal tunnel syn- drome: What is attributable to work? The Montreal however, has been largely abandoned because of Study. Occupational and Environmental Medicine 1997; a higher surgical complication rate. 54:519-23. Post-operative return to work. The most suc- 7. Stevens JC, Witt JC, Smith BE, et al: The frequency of carpal tunnel syndrome in computer users at a medical

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facility. 2001; 56(11):1568-70. cases of carpal tunnel syndrome). J of Hand Surgery 1985; 8. Gorsche RG, Wiley JP, Renger RF, et al: Prevalence and 10(2):202-4. incidence of carpal tunnel syndrome in a meat packing 24. Wilbourn AJ, Gilliatt RW: Double crush syndrome: A critical plant. Occupation and Environmental Medicine 1999; analysis. Neurology July 1997:21-9. 56:417-22.

9. Cobb TK, An K-N,Cooney WP, et al: Lumbrical muscle 25. Choi SJ, Ahn DS: Correlation of clinical history and elec- incursion into the carpal tunnel during finger flexion. J Hand trodiagnostic abnormalities with outcome after surgery for Surgery (British and European Volume) 1994; 19B(4):434-8. carpal tunnel syndrome. Plastic and reconstructive surgery 10. Keir PJ, Bach JM, Rempel DM: Effects of finger posture on 1998; 102:2374-80. carpal tunnel pressure during wrist motion. J of Hand Surgery 26. Atcheson SG, Ward JR, Lowe W: Concurrent medical dis- 1998; 23A(6):1004-9. ease in work-related carpal tunnel syndrome. Arch Intern 11. Moore SJ: Carpal tunnel syndrome. Occupational Medicine Med 1998; 158:1506-12. State of the Art Reviews 1992; 7(4):741-63. 27. Padua L, Padua R, Aprile I, et al: Multiperspective follow- 12. Fuchs PC, Nathan PA, Myers LD: Synovial histology in up of untreated carpal tunnel syndrome: A multicenter carpal tunnel syndrome. J Hand Surgery 1991; 16A:753-8. study. Neurology 2001; 56(11):1431-2. 13. Keir PJ, Bach JM, Rempel DM: Effects of finger posture on 28. Walker WC, Metzler M, Cifu DX, et al: Neutral wrist carpal tunnel pressure during wrist motion. J Hand Surgery splinting in carpal tunnel syndrome: A comparison of night- 1998; 23A:1004-9. only versus full-time wear instructions. Arch Phys Med 14. Gelberman RH, Hergenroeder PT, Hargens AR, et al: The Rehabil 2000; 81:424-9. carpal tunnel syndrome. A study of carpal canal pressures. J. 29. Dammers JW, Veering MM, Vermeulen M: Injection with Bone and Joint Surgery 1981; 63-A:380-3. methyprednisolone proximal to the carpal tunnel: 15. Weis ND, Gordon L, Bloom T, et al: Position of the wrist Randomized double blind trial. Brit Med J 1999; 319:884-6. associated with the lowest carpal tunnel pressure: 30. Franzblau A, Rock CL, Werner RA, et al: The relationship Implications for splint design. J Bone and Joint Surgery 1995; of vitamin B6 status to median nerve function and carpal 77A(11):1695-9. tunnel syndrome among active industrial workers. J Occup 16. Rempel D, Dahlin L, Lundborg G: Pathophysiology of nerve Environ Med 1996; 38(5):485-91. compression syndromes: Response of peripheral nerves to 31. Nathan PA, Meadows KD, Keniston RC: Rehabilitation of loading. J Bone and Joint Surgery 1999; 81A(11):1600-10. carpal tunnel surgery patients using a short surgical incision 17. English CJ, MacClaren WM, Court-Brown C, et al: and an early program of physical therapy. J Hand Surg Relationship between upper limb soft tissue disorders of 1993; 18A:1044-50. repetitive movements at work. Am J Industrial Med 1995; 27:1-14. Suggested Readings 18. Nathan PA, Takigawa K, Keniston RC, et al: Slowing of sen- 1. Hadler N. Occupational Musculoskeletal Disorders, Second sory conduction of the median nerve and carpal tunnel syn- Edition, 1999. Lippincott Williams and Wilkins, drome in Japanese and American Industrial Workers. Journal Philadelphia. of Hand Surgery (British and European Volume) 1994; 2. Hagberg M, Silverstein B, Wells R, et al: Work-Related 19B:30-4. Musculoskeletal Disorders, 1995, Taylor and Francis, 19. Ferry S, Hannaford P, Warskyj M, et al: Carpal tunnel syn- London,U.K. drome: A nested case-control study of risk factors in women. Am J Epidemiology 2000; 151:566-74. 20. Stevens JC, Beard CM, O’Fallon WM, et al: Conditions asso- ciated with carpal tunnel syndrome. Mayo Clin Proc 1992; 67:541-8. 21. Bernard BP (ed.) Musculoskeletal disorders and workplace Put Your Knowledge to the Test factors: A critical review of epidemiologic evidence for work- related musculoskeletal disorders of the neck, upper extremi- Answer the questions in our quiz ty, and low back. Cincinnati, Ohio: NIOSH 1997 pub. No. found on page 263 and send the 97-141. 22. Katz JN, Stirrat CR: A self administered hand diagram for the response card to the University of diagnosis of carpal tunnel syndrome. J Hand Surg 1990; Calgary for CME credits. 15A:360-3. 23. Hurst LC, Weissberg D, Carroll RE: The relationship of the double crush to carpal tunnel syndrome (An analysis of 1,000

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