|Year : 2017 | Volume
| Issue : 3 | Page : 292-297
Influence of occupation on median nerve cross-sectional area in apparently healthy volunteers
Anthony Chukwuka Ugwu1, Benjamin Effiong Udoh2, Alhaji Modu Ali3, Mohammed Abba4, Emmanuel Buba5, Mohammed Yusuf Mohammed6
1 Department of Radiography and Radiological Sciences, Faculty of Health Sciences and Technology, Nnamdi Azikwe University, Anambra State, Nigeria
2 Department of Radiography and Radiological Sciences, Faculty of Allied Medical Sciences, University of Calaber, Calaber, Cross-River State, Nigeria
3 Department of Radiology, Federal Neuro Hospital Maiduguri, Kano State, Nigeria
4 Department of Radiography, Faculty of Allied Health Sciences, Bayero University Kano, Kano State, Nigeria
5 Department of Radiology, Federal Teaching Hospital, Gombe, Gombe State, Nigeria
6 Department of Radiology, University of Maiduguri Teaching Hospital, Maiduguri, Borno State, Nigeria
|Date of Web Publication||5-Sep-2017|
Benjamin Effiong Udoh
Department of Radiography and Radiological Sciences, Faculty of Allied Medical Sciences, University of Calaber, Calaber, Cross-River State
Source of Support: None, Conflict of Interest: None
Background: Sonographic measurement of the median nerve has been proposed as a useful alternative to the electrodiagnostic test in the diagnosis of the carpal tunnel syndrome because of its ability to reveal morphological changes.
Objective: The objective of this study was to investigate the influence of occupation, gender, and hand dominance on the median nerve cross-sectional area (MNCSA).
Methodology: One hundred and eighty apparently healthy volunteers were recruited for the study. Hand dominance was ascertained in all volunteers. The device used was Voluson P8 ultrasound system with a 12-MHz transducer, using custom preset for musculoskeletal ultrasound. The Anteroposterior (D1) and transverse (D2) diameters of the median nerve were taken bilaterally at the level of the pisiform bone at the anterior surface of the wrist joint. Using these values, the MNCSA was calculated using the ellipse Formula.
Results: The volunteers were divided into repetitive and nonrepetitive groups. The MNCSA was significantly higher (P < 0.05) in the repetitive work group than in nonrepetitive work groups. Similarly, a significant difference in mean MNCSA was noted between male and female volunteers in both groups. Again, a significant difference in mean MNCSA was observed in dominant and nondominant hands in the repetitive work group (P < 0.05). However, there was no significant difference in mean MNCSA in the nonrepetitive work groups (P < 0.05).
Interpretation and Conclusion: A statistically significant difference in MNCSA was detected between repetitive and nonrepetitive work groups, male and female gender as well as in dominant and nondominant hands. Occupation, hand dominance, and gender, therefore, affect the cross-sectional area of the median nerve.
Keywords: Area, dominant, median nerve, musculoskeletal, repetitive, sonography
|How to cite this article:|
Ugwu AC, Udoh BE, Ali AM, Abba M, Buba E, Mohammed MY. Influence of occupation on median nerve cross-sectional area in apparently healthy volunteers. Indian J Health Sci Biomed Res 2017;10:292-7
|How to cite this URL:|
Ugwu AC, Udoh BE, Ali AM, Abba M, Buba E, Mohammed MY. Influence of occupation on median nerve cross-sectional area in apparently healthy volunteers. Indian J Health Sci Biomed Res [serial online] 2017 [cited 2019 Jun 17];10:292-7. Available from: http://www.ijournalhs.org/text.asp?2017/10/3/292/214006
| Introduction|| |
The median nerve, which is popularly called “eye of the hand,” is one of the three major nerves of the forearm and hand. It courses from the brachial plexus in the axilla to innervate the intrinsic muscles of the hand. It is the only nerve that passes through the carpal tunnel, and when this nerve is compressed at the wrist region, it leads to a condition known as carpal tunnel syndrome (CTS). CTS is the most common form of peripheral nerve entrapment and the common cause of hand discomfort and functional impairment among middle-aged women, especially during pregnancy.,,, The symptoms of median nerve compression include pain, numbness, or tingling on the anterior surface of the index, middle, or radial half of the ring finger. It is often associated with weakness of hand grip or nocturnal symptoms, including hand or arm pain and numbness.
Based on the combined clinical presentation and the electrodiagnostic testing, the prevalence of CTS ranges from 1% to 5% in the general population , and up to 10% among active workers in certain occupations., CTS is the major cause of work disability among workers in some group of occupation.
It has been estimated that the annual incidence rate of CTS ranged from 0.5 to 5.1/1000 people and the workplace incidence rate has reached an epidemic proportions, comprising 40.8% of all upper limb repetitive motion disorders. The relationship between CTS and some occupations was documented as far back as 1947 where 6 cases of work-related CTS in repetitive work was reported. Barnhart et al. observed CTS in either or both hands in 15.4% of those workers with repetitive stress, but only in 3.1% of those workers with nonrepetitive stress.
Several studies have shown that gender, as well as occupational factors such as hand force and exposure to vibration, was related to CTS3. It has also been reported that women had greater risk developing CTS than men, though other studies concluded that women are more likely to report symptoms earlier than men. Occupation induced CTS is a major cause of lost work days and increased workers' compensation costs. Other risk factors include traumatic injury, diabetes mellitus, rheumatoid Arthritis, acromegaly, hypothyroidism, encroaching conditions, pregnancy, and lactation, lack of aerobic exercise and use of walking aids.
Sonographic evaluation of the median nerve for the diagnosis of CTS has been proposed as a useful alternative to electrodiagnostic test.,,, The effect of occupation on the median nerve has been studied base on clinical presentation and electrodiagnostic test. However, there has been no local study that sonographically compared the median nerve cross-section area (MNCSA) between repetitive and nonrepetitive work group subject. This study aimed at assessing the effect occupation on MNCSA.
| Methodology|| |
The volunteers were apparently healthy adults drawn from various occupational groups. Volunteers with an inflammatory condition of the distal forearm or wrist joint, chronic systemic problem associated with neuromuscular or musculoskeletal system, history of major wrist trauma and surgery or amputated hand, pregnant or lactating women were excluded from the study.
To ascertain whether the volunteers met the aforementioned criteria, a brief interview was conducted before all scanning and measurement. The volunteers were grouped into repetitive and nonrepetitive work groups based on their occupation, and each group consisted of ninety apparently healthy volunteers. The repetitive work group consists of sixty-one male and twenty-nine female volunteers (age range, 18–60 years; mean age ± standard deviation [SD], 35.07 ± 9.96 years) and comprises mainly of volunteers that are repeatedly involved in activities requiring hand grip or forceful flexion and extension of the wrist as part of the occupation. These include farmers, blacksmith, carpenter, bricklayers, plumbers, and construction workers. The nonrepetitive work group consisted of fifty-one male and thirty-one female volunteers (age range, 18–57 years; mean age ± SD, 29.06 ± 9.87 years) comprise mainly of volunteers that are not repeatedly involved in activities requiring repeated hand grip, flexion, and extension of wrist joint as part of their occupation or daily activities. These include students, homemakers, administrators, accountants, and clinical staff.
During the scanning, the volunteers sat and faced the examiner with the ipsilateral hand fully supinated and placed on a rectangular foam pad with the hand relaxed and slightly tilted backward. Depth, gain, and dynamic range was adjusted appropriately for optimal differentiation between nerves, tendons, and other soft tissue structures. Ultrasound gel was applied to the anterior aspect of the distal end of the forearm (carpus) at the level of pisiform bone with little or no pressure on the skin to avoid deformation of the nerve [Figure 1]., Axial images of the median nerves were obtained on both hands and image optimal definition of the borders of the median nerve was selected after transducer manipulation. The flexor tendons were seen in compartments, and they appeared as echogenic ovoid structures on transverse scan [Figure 2]. The median nerve is more superficial to the flexor pollicis longus tendon and distinguishable by identifying its pinpoint internal echoes, i.e., “starry night” or “honeycomb” description and also flexing and extending the fingers where it moves side to side rather than up and down movement being exhibited by flexor digitorum tendons. The indirect measurement method was adopted because of its high accuracy and reliability. The following median nerve dimensions were measured bilaterally at the level of pisiform bone: antero-posterior (D1) and transverse (D2) diameters of the median nerve. Measurements were taken from the leading edge hyperechoic rim of the nerve to another leading edge on the opposite direction. These values were used to calculate the MNCSA using ellipsoidal formula (CSA = D1 × D2 π/4) as described by Buchberger et al. All the nerve measurements were repeated at least twice, and the mean values were recorded to ensure reproducibility of the calculated distance.
|Figure 1: Position of the transducer for axial scanning of the median nerve at the level of the pisiform bone|
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|Figure 2: Axial sonogram of the right wrist joint at the level of the pisiform bone of a 32-year-old male volunteer|
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All sonographic examinations were performed using a sonographic scanner (Voluson P8, GE medical systems, New York, USA) and a linear array transducer (12 MHz; contact area, 9 mm × 43 mm) with custom preset for musculoskeletal ultrasound. To assess intraobserver reliability on the measured distance, the sonographic measurements were repeated on the first fifty volunteers, and there was no significance difference in both measurements. The study was carried out in Radiology Department, Federal Neuropsychiatric Hospital, Maiduguri, Borno State, Nigeria between March 2015 and August 2016.
Group data were expressed as mean ± SD. To investigate the influence of occupation, gender and hand dominance on MNCSA, as well as comparisons between repetitive and nonrepetitive work groups of male and female volunteers, the Mann–Whitney U test was applied while matched sample t-test was used to compare the mean MNCSA of dominant and nondominant hand. Differences were considered statistically significant at P < 0.05.
| Results|| |
[Table 1] shows the frequency of the volunteers based on occupation. Farmers constituted more than half of the repetitive workgroup while the blacksmith had the least proportion. In the nonrepetitive work group, students constitute the largest proportion while clinical staff had the least proportion.
There was a significant positive relationship between the mean MNCSA with age, weight, and body mass index in both groups. However, there was no significant relation between MNCSA and height [Table 2]. Repetitive work group volunteers had a higher value of MNCSA than nonrepetitive work group irrespective of their gender (P< 0.05) [Table 2], [Table 3], [Table 4]. Similarly, mean MNCSA of the dominant hand was significantly higher than nondominant hands in the repetitive work group. However, there was no significant difference in mean MNCSA of the dominant and nondominant hands of the nonrepetitive work group [Table 5].
|Table 3: Comparison of the median nerve cross-sectional area in repetitive and nonrepetitive work groups|
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|Table 4: Comparison of median nerve cross-sectional area in male and female volunteers|
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|Table 5: Comparison of median nerve cross-sectional area in dominant and nondominant hands|
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| Discussion|| |
High-resolution sonography of the median nerve allows the nerve to be readily visualized and makes its morphological assessment possible. Using this technique, the dimensions, main pathological changes including nerve swelling and reduced echogenicity can be evaluated. Sonography is also capable of providing morphological information of median nerve, including the exact location, course, and extent of the nerve.
Our results show that the mean MNCSA was higher in male when compared to female, 8.89 ± 1.37 mm 2 versus 7.18 ± 1.69 mm 2. This was observed in both dominance and nondominance hands as well as in repetitive and nonrepetitive work groups. This finding agrees with that of Becker et al. and Kim et al. who reported higher values of MNCSA in males when compared to females. On the contrary, a study by Duncan et al. has shown no significant difference in mean MNCSA between males and females. This variation in findings among different authors may be attributed to the differences in equipment used, patient populations, and sonographic techniques. The increased mean MNCSA among the male gender observed in the present study is likely due to the fact that a greater number of males is involved in physically demanding occupations such as farming, construction works, and brick making, than the females.
The results of the study of Armstrong et al. show an increase in MNCSA among apprentice construction workers when compared to newly hired workers. The above findings suggest that forceful upper extremity works and occupations with high-force, high repetition physical demands which affects the cross-sectional area of the median nerve may pose an increased risk of CTS  and works involving typing and computer use may present the least risk. Several studies have associated median nerve compression to vibration exposure and occupation with high repetition and force in the hands., Similarly, Palmer, et al. also reported that repetitive and prolonged hand intensive activities, forceful exertions, awkward or static posture, vibration, and localized mechanical stress are associated with CTS.
Repetitive flexion and extension of the wrist and grasping motions of the hand are thought to repeatedly compress the median nerve between the tendons and carpal bones, leading to injury to the median nerve.
In the present study, the mean MNCSA among volunteers in the repetitive work group showed a statistically significant difference between the dominant and nondominant hands on each image. However, there was no statistically significant difference in the mean MNCSA in the nonrepetitive work group. Hammer et al. reported no significant difference in MNCSA between dominant and nondominant hands in the control group.
The mean cross-wise differences in this study were 1.40 mm 2 and 0.24 mm 2 in the repetitive work group and nonrepetitive work groups, respectively. The cross-wise difference is greater in repetitive work group than nonrepetitive work group. Wong et al. reported a crosswise difference of 1 mm 2 among patient with a normal range of MNCSA.
Our study suggests that the crosswise difference in MNCSA between the two hands might need to be taken into account among healthy volunteers when a sonographic comparison of the median nerve is to be performed bilaterally. These results might be useful during the assessment of the wrist when the interested is in knowing the actual cause of wrist pain.
| Conclusion|| |
Statistically significant difference in MNCSA was observed between repetitive and nonrepetitive work groups; male and female volunteers; and dominant and nondominant hands. Occupations involving too frequent hand grip, pinch, flexion, and extension of wrist increase the MNCSA. Occupation, gender, and hand dominance should, therefore, be considered during sonographic evaluation of median nerve, especially in CTS.
Members of staff of the Radiology Department, Federal Neuropsychiatric Hospital Maiduguri, Nigeria for their support in this research work.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]