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J Am Dent Assoc, Vol 132, No 2, 163-170.
© 2001 American Dental Association | ![]() |
DENTISTRY & MEDICINE |
| ABSTRACT |
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Methods. In a cross-sectional study, dentists (n = 1,079) were screened during the American Dental Associations Annual Health Screening Program in 1997 and 1998 by means of standard electrodiagnostic measures in the dominant hand and a self-reported symptom questionnaire. The authors diagnosed a median mononeuropathy from a 0.5- or 0.8-millisecond, or ms, prolongation of the median sensory-evoked peak latency compared to the ulnar latency. They diagnosed CTS if the subject also had accompanying symptoms of numbness, tingling or pain.
Results. Thirteen percent of screened dentists were diagnosed with a median mononeuropathy (using a 0.5-ms prolongation as the criterion), but only 32 percent of these had symptoms consistent with CTS (4.8 percent overall). When the 0.8-ms prolongation was used as the electrodiagnostic criterion, only 2.9 percent (overall) were diagnosed with CTS. People with diabetes, rheumatoid arthritis and obesity were more likely to have a median mononeuropathy.
Conclusions. The prevalence of symptoms consistent with CTS in the dominant hand among dentists was higher than the prevalence in the general population. However, when electrodiagnostic confirmation is added, the prevalence of CTS was nearly the same as that among the general population.
Clinical Implications. Early recognition of CTS can lead to more effective management. Education regarding ergonomic risk factors can be an effective preventive measure.
Carpal tunnel syndrome, or CTS, is one of a number of muscle-, tendon- and nerve-related disorders that affect people performing intensive work with their hands. There has been a tremendous increase during the last 20 years in the numbers of reported cases of CTS.13 Both dentists and dental hygienists have been reported to have a high prevalence of upper-extremity musculoskeletal disorders, including CTS.48 A 1997 American Dental Association survey reported that 9.2 percent of dentists had been diagnosed by a physician as having some type of repetitive motion disorder.9 The prevalence was higher among female and older dentists. Within this group of dentists who had a diagnosed repetitive-motion disorder, approximately 19 percent required surgery and more than 40 percent shortened their work hours.
CTS is characterized by numbness, tingling or pain in the distribution of the median nerve in the hand. The palmar surface of the thumb, index and middle finger are the primary areas involved (FigureThis study of carpal tunnel syndrome is the largest in the literature to feature both a clinical symptom survey of and electrodiagnostic testing in dentists.
). The symptoms typically are worse at night and with repetitive activity. Although CTS is a clinical diagnosis based on history and symptoms, tests of median nerve function can be used to confirm injury to the median nerve at the wrist. The use of nerve conduction studies adds objective evidence to what can be a confusing clinical picture. If conduction of the median nerve across the wrist is prolonged as compared with conduction of another nerve in the hand that does not go through the carpal tunnel (for instance, the radial or ulnar nerve), this abnormality is referred to as a median mononeuropathy. Although many people complain of hand pain and tingling, only 20 percent are diagnosed with a concomitant median mononeuropathy.1012
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The ergonomic risk factors associated with CTS include repetitiveness of work, forceful exertions, mechanical stress, posture, temperature and vibration.13 These risk factors are present for dentists and dental hygienists: dental instruments may cause contact stress over the carpal tunnel, and wrists may be held in awkward positions for prolonged periods. In a 1998 study of a small cohort of dental hygienists, Bramson and colleagues14 evaluated several potential risk factors using hand-surface goniometry and electromyography. They concluded that hygienists exposure to high-risk postures was minimal and that the force they exerted during work was of medium risk (11 to 20 percent maximum voluntary contraction, based on surface electromyography data). In addition to repetitive work and contact stresses, hygienists and dentists may be exposed to other potential risk factors, such as the use of potentially restrictive ambidextrous gloves.15
In addition to ergonomic risk factors, there are several anthropometric factors and medical conditions associated with an increased risk of developing CTS.16 There is a higher prevalence of CTS among women and among people with diabetes, rheumatoid arthritis and thyroid disease.17 Obese people are four times more likely to have an entrapment of the median nerve at the wrist, but the mechanism of injury is not known; other peripheral nerves do not seem to be affected.
In the study described here, we attempted to quantify the prevalence of CTS among dentists using an objective assessment of the health of the median nerve across the wrist, using nerve conduction measures. We attempted to compare these results with the prevalence of CTS in the general population. Additionally, we explored the association of the various known risk factors for CTS within this population.
| SUBJECTS, MATERIALS AND METHODS |
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Questionnaire. The HSP questionnaire included questions on CTS-related symptoms, medical history, and demographic and anthropometric datathat is, age, sex, hours worked per week and weeks worked per year. Each dentist also was weighed and his or her height was measured; these values were recorded on the questionnaire. Height and weight were converted to body mass index, or BMI (in kilograms per square meter), as a measure of obesity (defined as a BMI > 29).
Electrodiagnostic testing. Certified electrodiagnostic technicians measured median and ulnar sensory-evoked responses in the dominant hand using the techniques described by Kimura.18 Hands were warmed if the midpalmar temperature was below 32 C (lower hand temperatures slow nerve conduction and increase latency values).
The technicians recorded the final hand temperature. They then stimulated both ulnar and median nerves supramaximally at a distance 14 centimeters away from ring-recording electrodes placed around the second and fifth digits (Figure
), using a standard interelectrode distance of 3 cm. The transcutaneous electrical current depolarizes the median and ulnar nerves, and these depolarization waves travel down the hand to the fingers. The technicians performed all studies using either TECA TD 20 (TECA Inc.) or Viking Compass (Nicolet) electromyographic testing instruments.
The technicians recorded the peak latency and the amplitude (baseline to peak) of the median and ulnar sensory-evoked responses. Latency (in milliseconds, or ms) is defined as the time required for the impulse to travel the 14-cm distance. To control for the influences of age, disease state and limb temperature, the latency of the ulnar sensory-evoked response is subtracted from that of the median sensory-evoked response.19 This difference between median and ulnar peak latencies (median-ulnar latency) is used in the diagnosis of a median mononeuropathy. Therefore, when median nerve conduction slows, its peak latency increases, resulting in a larger median-ulnar latency value. We diagnosed CTS-screened dentists as having a median mononeuropathy if the following three criteria were met:
Although it is common to use a 0.5-ms cutoff to evaluate median ulnar latency, a more stringent criterion of 0.8 ms also has been used.1921 Therefore, of the CTS-screened dentists who met the above criteria, we diagnosed a subset that also met the more stringent requirement of a median-ulnar latency that equaled or exceeded 0.8 ms. Finally, we diagnosed the CTS-screened dentists who had a median mononeuropathy (according to either the 0.5-ms or 0.8-ms cutoff) as having CTS if they also had symptoms of numbness, tingling or pain in the fingers or hand (not limited to the median distribution).
Statistics.
We analyzed the data using statistical software (STATA Statistical Software, Release 4.0, Stata Corp.); the data consisted of descriptive statistics of the demographic, medical history, work history and electrophysiological variables. For comparisons of these results to those reported in the general population, we used
2 statistics for proportional variable and the Student t test for comparison of continuous variables. We used these same statistics for comparisons within the sample and stratified by presence or absence of a median mononeuropathy or the diagnosis of CTS.
| RESULTS |
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Of the medical conditions surveyed, rheumatoid arthritis, diabetes and obesity were additional risk factors in the CTS-screened dentists. Among the 12 dentists who had a history of rheumatoid arthritis, we found an increased likelihood of finding a median mononeuropathy compared with those who did not have the disorder (42 percent vs. 12 percent). Of the 22 dentists who had diabetes, 36 percent had a median mononeuropathy compared with 13 percent who did not have diabetes. Dentists with a median mononeuropathy were more likely to be overweightthat is, they had a higher BMI (27.5 vs. 26.0 Kg/m2, P = .001).
The type of gloves (ambidextrous vs. surgical or left/right specific) the dentists usually wore did not significantly influence the presence of a median mononeuropathy, but the vast majority of dentists used ambidextrous gloves (87 percent). However, dentists using surgical gloves (less than 4 percent of CTS-screened dentists) had slightly fewer hand and finger pain symptoms. Glove material (latex, vinyl, nitrile, neoprene or thermoplastic elastomer) also did not influence the presence of a median mononeuropathy.
Seventy-nine dentists (7.8 percent) had a prolongation of both the median and ulnar sensory latencies that would be consistent with a mild peripheral polyneuropathy. This group was older than the dentists who had no evidence of a polyneuropathy (57 vs. 49 years, P < .001), and 5 percent of this group had a history of diabetes. Symptoms of a peripheral neuropathy, sometimes confused with those of CTS, can include numbness of the hands and feet. Peripheral neuropathy often is associated with diabetes, thyroid disorders, exposure to heavy metals and nutritional disorders.
| DISCUSSION |
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The most recent population-based study of the prevalence of CTS in a general population was conducted in Sweden in 1997.10 This study examined the prevalence (rather than incidence) of CTS based on both electrodiagnostic and clinical criteria. Although the Swedish study also included provocative clinical examinations to further identify symptoms of hand pain and numbness, its results are directly comparable with those of our cross-sectional study of dentists (Table 4
). Based on the 0.8-ms median-ulnar latency cutoff, the prevalence of CTS among the screened dentists and that among the general population of Sweden are not remarkably different. Furthermore, the two populations were similar in age and history of diabetes or rheumatoid arthritis, which minimizes differences that could be attributed to these confounding factors. Results from the Swedish population are directly comparable with those of our cross-sectional study of dentists. Although our study population was somewhat smaller and disproportionately male, the prevalence of CTS, age and history of diabetes and rheumatoid arthritis was not significantly different in the two populations. The researchers who conducted the Swedish study used the same electrodiagnostic criteria as ours, but their clinical diagnosis included a symptom survey as well as a physical examination. In addition, their dental screening relied on both symptoms and electrodiagnostic measures, but it did not include a physical examination.10
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Women have an increased risk of the development of CTS and hand or finger pain symptoms. Because female workers have been shown to have smaller wrists and potentially smaller carpal canal volumes, they may be at greater risk of developing CTS.26 In the study by Atroshi and colleagues10 of clinical and electrodiagnostically confirmed cases of CTS in the general population in Sweden, the prevalence rate among women was 3.0 percent vs. 2.1 percent among men. Stevens and colleagues22 found the incidence rate to be three times higher among women, especially in the 50- to 70-year-old age group. Because the female dentists in our study were younger and fewer in number than the male dentists, our estimate of the prevalence among dentists may underrepresent women.
More CTS-screened dentists reported CTS-consistent hand and finger pain symptoms (28 percent) than did the Swedish population in the study by Atroshi and colleagues10 (14 percent), but less than did industrial workers in a study by Franzblau and colleagues12 (30 percent). Because CTS-screened dentists reported fewer total symptoms than did dentists who participated in the HSP, the prevalence of CTS reported in our study may be underestimated.
As we do here, earlier studies have identified several medical conditions and related prescription drug use associated with an increased risk of developing CTS and hand or finger pain symptoms: obesity, oral contraceptive use, pregnancy, diabetes, rheumatoid arthritis, thyroid disease and certain connective-tissue disorders.13 Obesity also may be associated with decreased carpal canal volumes and has been correlated with an increased prevalence of CTS.13,25 Also consistent with our observations, previous studies13,25 have associated age with the development of CTS, based on years of exposure to repetitive and forceful work. However, CTS-screened dentists were older than the national average, as reported by the ADA.9 Therefore, our findings would tend to overestimate the true prevalence of CTS in dentists overall.
A relatively high number of dentists have a prolonged median-ulnar latency, yet two-thirds of the dentists affected are asymptomatic.
Electrodiagnostic evaluation was performed only on the dominant hand and without the use of hand diagrams. It is possible that some dentists had CTS in only the nondominant hand, and thus our sample population may underestimate the conditions true prevalence. The symptom questionnaire did not include a hand diagram or any other scheme for localizing symptoms to the distribution of the median nerve. While hand diagrams may be more specific than questionnaires for identifying symptoms related to CTS, they are less sensitive than the posing of direct questions about (nonlocalizing) symptoms in the hands and fingers, as was done in this study.12
Our study is limited by its cross-sectional design and its nonrandom sample. Selection bias cannot be excluded, even though HSP-participating dentists were not drawn to the screening solely owing to hand symptoms but participated in other screening procedures as well. Our expectation was that more dentists with hand symptoms would participate in the CTS screening and lead to an overestimation of prevalence. However, when we compared the CTS screening group with the HSP group as a whole, the prevalence of hand and finger symptoms was significantly lower among CTS-screened dentists. While a random sample and longitudinal study of dentists would be ideal to assess true prevalence and incidence, this study is the largest in the literature to feature both a clinical symptom survey of and electrodiagnostic testing in dentists. Another potential factor that could bias the sample is avocational hand activity. Within our sample, dentists with the diagnosis of CTS were twice as likely to report pain symptoms (not limited to the hand) during hobby and gardening activities but not with sports activities. We did not assess this potential risk factor in enough detail to define any additional risk or protective role these activities may have had in this study.
| CONCLUSION |
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For people who have symptoms of CTS or are at an increased risk of developing the condition, early intervention can be important. When recognized early, CTS can be managed effectively with conservative and noninvasive treatment, such as the following:
There are many unproven interventions, including vitamin B6 supplements, nonsteroidal anti-inflammatory drugs and diuretics. More aggressive and invasive treatments that have been shown to be successful include steroid injections into the carpal tunnel and surgery. However, surgical management should be reserved for people with whom other treatment modalities and therapies have failed.
Early recognition of symptoms and education regarding ergonomic risk factors is important in the successful management of CTS. And although the prevalence of CTS appears no different in dentists than in the general population, implementation of some of the strategies listed here no doubt would be useful in alleviating the hand fatigue and pain reported by dentists in this study. Furthermore, because the relationship of symptoms to CTS still is not fully understood, proactive management of people at risk of developing CTS or experiencing pain is a reasonable approach to reducing the risk of future development of CTS.
| FOOTNOTES |
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| REFERENCES |
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