INTRODUCTION
Carpal tunnel syndrome (CTS) occurs due to overuse of the hand, a tumor, or external injury, and it results in narrowing of the carpal tunnel which puts pressure on the median nerve. CTS is one of the most common entrapment neuropathies of the upper limb [
1,
2,
3]. In particular, it is highly related to occupations involving repeated movements and upper limb strength [
4]. Accordingly, work-related CTS is a major cause of work-time restrictions and economic loss [
5,
6,
7]. Previous studies reported a 0.6%–4.9% prevalence of CTS among typical workers [
8,
9]. However, the prevalence among agricultural workers is higher than that in office workers [
10]. In Korea, the prevalence rates were 6.5%, 23.5%–26%, 29.4%, and 16.9% among telephone exchange operators, meat-processing workers, workers in the wood-processing industry, and residents working in agricultural areas, respectively [
11,
12,
13,
14]. However, despite numerous studies relating CTS to various occupations, no studies have assessed CTS among orchardists in Korea.
CTS is diagnosed based on patients' subjective signs and symptoms, physical examination results, and electrodiagnostic tests. In particular, electrodiagnostic tests have high sensitivity and specificity [
15], but they are limited by the fact that they are time-consuming and need an appointment to be performed, making them difficult to implement in all patients; they also cause discomfort in patients and have high costs [
16]. As a result, when physicians suspect CTS based on clinical symptoms and other physical test results, the most commonly used tests to confirm the diagnosis are Tinel's sign, Phalen's test, and Durkan's carpal compression test (CCT). Among these physical examinations, Phalen's test and Tinel's sign highly correlate with electrodiagnostic test results [
17]. However, Tinel's sign and Phalen's test showed false-positive results in 25% of healthy people, and had sensitivities and specificities of 25%–75% and 70%–90%, respectively, for CTS diagnosis, suggesting that physical examination findings may not always be concordant with electrodiagnostic test results [
18,
19]. No clear conclusions have been made about the relationship between electrodiagnostic test results and physical examination findings for detecting CTS, and studies on the quantitative relationships between electrodiagnostic tests and physical examinations are insufficient.
Therefore, this study investigated the prevalence of CTS in typical orchardists and identified related characteristics. The study group was expected to show a high prevalence of CTS owing to the nature of their work, which involves repeated use of the hands and wrist. Moreover, the quantitative relationships between electrodiagnostic tests and physical examination results were analyzed to assess their use in CTS diagnosis. Furthermore, the relative diagnostic values of various physical examinations were also assessed.
DISCUSSION
This epidemiological study revealed a higher prevalence of CTS in orchardists than in other occupational groups in the Gyeongsangnam-do region. Lee et al. [
24] diagnosed CTS when patients satisfied all 6 items in the Final List of Clinical Diagnostic Criteria (2006), which was described by Graham et al. [
25], and reported a CTS prevalence of 0.75% in the general Korean population. However, no specific diagnostic criteria, domestic or international, have been established for CTS in the general population.
The incidence and prevalence of CTS in typical adults are 0.125%–1% and 5%–16%, respectively, and they may vary according to diagnostic criteria [
4]. However, increased incidence of work-related CTS leads to a gradual increase in the prevalence. The incidence and prevalence of work-related CTS, both international and domestic, have been reported. The reported domestic prevalence rates of work-related CTS are 21.4% in rayon factory packing workers, 12.8% in condom industrial workers, 10.8% in telephone operators, and 73.9% in meat and fish processing workers. In addition, some studies reported that the CTS prevalence in farmers is 16.9% [
11,
12,
13,
14]. Based on a comparative analysis of occupational characteristics associated with CTS under surveillance from 2001 to 2004, the high-risk occupational groups for CTS included agriculture, forestry and fishery workers, simple labor workers, machine operators, and assembly workers. Among these high-risk occupational groups, agriculture-associated workers had the highest risk of developing CTS at 25.7% [
26].
Compared with other occupations, orchardists use scissors with a strong grip for pruning and repeatedly flex their wrists during harvest. These repeated movements expose them to a high risk of developing CTS. In this study, 51.5% of orchardists were suspected of having CTS based on abnormal electrical diagnostic test results. Compared with other studies on high-risk workrelated CTS, this study obtained a 51.5% CTS prevalence, which is a meaningful result that shows a relatively high prevalence. However, the differences in the prevalence rates reported by several domestic studies may be due to differences in diagnostic criteria, study design, research, regions, and population size unique to each study.
The present study only used findings from electrodiagnostic tests for the diagnosis of CTS. Therefore, selection bias might have resulted in the increased prevalence in this study, as the subjects were selected randomly from among those who participated in health screening, irrespective of the presence or absence of symptoms.
Based on previous studies that identified risk factors and characteristics related to CTS, the present study also analyzed sex, age, body mass index, waist circumference, and total work time of orchardists in the Gyeongsangnam-do region. The results showed that age and total work time significantly contributed to the development of CTS. These results support previous observations that the risk of developing CTS generally increases in middle-aged women [
4]. The mean total work time until undergoing tests among orchardists in the CTS group was 32.1±13.2 years, which was significantly longer than that in the normal group. According to the Human Development Report of the United Nations Development Programme, on a global scale, the daily work time of agricultural workers in Korea is long, and it is 10 hours 35 minutes for men and 11 hours 11 minutes for women. Thus, these long work hours of Korean agricultural workers, in addition to the year-round farming season, may support the results of the present study [
27].
Although a number of physical examinations and signs have been shown to be useful for diagnosing CTS, the most well-known methods are Tinel's sign, Phalen's test, and Durkan's CCT. However, the effectiveness of these provocative tests for CTS diagnosis is controversial. These well-known physical examinations show varied results. For example, Tinel's sign has a sensitivity and specificity of 23%–67% and 55–100%, respectively, compared with 10%–91% and 33%–100%, respectively, for Phalen's test, and 28%–68% and 33%–74% for Durkan's CCT [
4]. Christopher et al. [
28] analyzed the literature related to CTS clinical symptoms and reported limited or no diagnostic value for Tinel's sign and Phalen's test. Conversely, Szabo et al. [
29] reported high sensitivity (89% and 83%, respectively) of Durkan's CCT and Phalen's test, and a specificity of 71% for Tinel's sign. In this study, the sensitivities of Tinel's sign, Phalen's test, and Durkan's CCT were 64.9%, 60.0%, and 59.2%, respectively, and their specificities were 52.0%, 50.5%, and 52.1%, respectively. These results show that all physical examinations performed in this study, in addition to clinical symptoms and EMG, have sufficient diagnostic value for CTS. However, in the physical examinations, low specificities were observed for Tinel's sign, Phalen's test, and Durkan's CCT (38.4%, 36.1%, and 40.9%) in the subjects aged ≥65 years. The diagnostic values of the physical examinations decreased in the elderly population. Therefore, further diagnostic tests for CTS should be performed depending on the age of the population tested.
The typical electrodiagnostic test has a reported sensitivity of approximately 77% and a false-negative rate of 10%–35% [
30]. Although other reports indicated that electrodiagnostic testing is not useful for diagnosing CTS [
31], it is generally considered essential for clinical diagnosis of CTS and is typically used in combination with several diagnostic methods to increase its sensitivity [
30]. In the present study, the diagnosis and severity of CTS in orchardists from the Gyeongsangnam-do region were classified by using only the electrodiagnostic test, irrespective of the symptoms. However, the CTS severity grades suggested by Bland [
23], determined by using electrodiagnostic testing, have been reported to accurately reflect clinical symptoms. As the 377 subjects had similar ages and working environments, the prevalence results of this study are highly reliable. The low sensitivity and specificity of the physical examinations in relation to the prevalence can be explained by the slight differences in the testing methods used, as the physical examinations were performed by several examiners during the course of the 1-year study.
Opinions differ regarding the correlation between physical examination and electrodiagnostic test results in the diagnosis of CTS. Hwang et al. [
32] reported a correlation of electrodiagnostic tests with Tinel's sign and Phalen's test. In contrast, Mondelli et al. [
17] reported that the diagnostic values of physical tests, including Tinel's sign and Phalen's test, became limited or nonexistent as CTS severity increased. In addition, Priganc and Henry [
15] investigated the correlation of CTS severity with Tinel's sign, Phalen's test, and Durkan's compression test, and they reported that the positive rate with Phalen's test increased significantly with greater severity. Jeong and Kim [
33] reported that Phalen's and hand elevation tests were significantly correlated with CTS severity, with Phalen's test showing a higher correlation than the hand elevation test.
According to the results of the present study, the positive rate with the physical examinations did not increase with increased severity of CTS diagnosed by using electrodiagnostic tests. Nevertheless, the results of Tinel's sign, Durkan's CCT, and Phalen's test showed significant differences as the severity of CTS increased. Moreover, a weak but significant positive correlation was found between CTS severity and both Tinel's sign and Durkan's CCT. Of these tests, Durkan's CCT showed a significant odds ratio, which suggests that physical examination accurately reflects CTS severity. These results are not consistent with those reported by Priganc et al. [
15] and Jeong and Kim [
33]. However, these differences can be explained by variation in (1) study subjects, (2) study design, and (3) diagnostic criteria for CTS severity. In particular, previous studies investigated subjects with symptoms such as hand paresthesia, sensory impairment, or myasthenia, whereas the subjects in the present study consisted of orchardists with or without symptoms. This may have resulted in a low positive rate in the physical examinations and consequent discrepancies in the correlation with CTS severity.
Electrodiagnostic testing is an essential method for the diagnosis of CTS. The diagnostic characteristics include reduced conduction speed in the palm-wrist or finger-wrist segments of the median sensory nerve, and prolonged latency of the median motor nerve [
34]. However, as described earlier, the present study evaluated the severity based on prolonged latency of the median sensory and motor nerves [
22,
23]. Comparison of the mean median nerve latency in the electrodiagnostic tests according to the results of the 3 physical examinations revealed the median sensory and motor nerves. This suggests that out of the 3 physical examinations, Durkan's CCT best reflects the results of the electrodiagnostic test.
This study investigated the prevalence of CTS among healthy orchardists in the Gyeongsangnam-do region by analyzing clinical symptoms and EMG results. This is one of the first prevalence studies performed in domestic fruit farmers. However, this study is biased in terms of both the size and representativeness of the samples of the target population. These facts cannot be ruled out. In addition, although the prevalence reported in this study may be meaningful, the study has limitations; the value of physical examination may be relatively low because the subjects were restricted to the Gyeongsangnam-do region and the consistency in the examination is relatively inadequate because of multiple inspectors.
The CTS prevalence among orchardists from the Gyeongsangnam-do region was 51.5%, which was far higher than that among the other occupational groups that use their hands and arms. Electrodiagnostic testing produced more reliable results, demonstrating a significant correlation with the results of physical examinations for CTS diagnosis. In terms of physical examinations, Durkan's CCT showed a significant quantitative correlation with the results of electrodiagnostic testing. Therefore, in addition to the well-known Tinel's sign and Phalen's test, Durkan's CCT is another reliable examination method for CTS.