Carpal Tunnel Syndrome among Rubber Tappers: Ergonomic Risk Factors, Health-Related Quality of Life, Impairment of Work and Daily Activity, and the Effect of Using an Ergonomic Rubber Tapping Knife

Abstract

Background Rubber tapping is an occupation with a high risk for developing carpal tunnel syndrome (CTS). Exposure to forceful exertion and repetitive excessive ulnar deviation from performing tapping may be associated with CTS development, which can impair hand function, health-related quality of life (HRQoL) and productivity. We developed a new ergonomic tapping knife with the aim to reduce the need for an awkward wrist posture during rubber tapping. This study aimed to (1) evaluate the ergonomic risk factors of CTS among rubber tappers, (2) compare HRQoL and impairment in tapping and daily activities among rubber tappers with and without CTS, and (3) evaluate changes in the severity symptoms of CTS, HRQoL, and impairment in tapping and daily activities after using the ergonomically designed tapping knife. Method For the first objective, a case-control study was conducted using convenience sampling among rubber tappers who were members of the Pawong Rubber Fund Cooperative in Pawong subdistrict, Mueang district, Songkhla province, Thailand. The Boston Carpal Tunnel Syndrome Questionnaire (BCTQ) and Phalen's test and Tinel's sign were used to identify 133 cases with CTS and 401 non-CTS controls. All participants were interviewed and visited at their rubber plantation to make a video recording of their rubber tapping method, and based on the recordings Rapid Upper Limb Assessment (RULA) scores were calculated. The second objective used a cross-sectional methodology. 133 tappers with CTS (cases) and 133 tappers without CTS (controls) were selected by simple random sampling. All participants were face-to-face interviewed using the European Quality of Life Five Dimension Three Level questionnaire (EQ-5D-3L) to measure HRQOL and the Work Productivity and Activity Impairment questionnaire: General Health (WPAI:GH) was used to assess work productivity and impairment. For the third objective, we conducted a non-randomized controlled trial among 208 rubber tappers who had participated in the first part of the study. They were divided voluntarily into two groups, an intervention group (new ergonomic rubber tapping knife) and a control group (traditional knife). Each group consisted of 52 tappers with CTS symptoms and 52 without CTS symptoms. Each tapper was visited at their rubber plantation and video recordings were made to be used in scoring Rapid Upper Limb Assessment (RULA) by 2 assessors. All participants were followed for 7 months. BCTQ, EQ-5D-3L and WPAI:GH scores were assessed, plus wrist posture assessment using RULA, before and after the intervention. Results (1) Middle age, lower and higher BMI, female, underlying disease, higher number of trees tapped at or below knee level and collecting latex were independent risk factors associated with CTS. The video recordings showed that tapping at higher than chest level involved more awkward wrist postures than tapping at a lower level. Among right-handed tappers right wrist flexion and/or extension was significantly less common in the CTS group than in the non-CTS group (OR=0.4, 95% CI 0.2, 0.6). Significantly higher proportions of right wrist flexion and/or extension, left wrist radial and/or ulnar deviation, and left wrist twist were observed among right-handed tappers who tapped the rubber trees at levels higher than chest level. The relationship of hand/wrist postures and tapping height was similar in both CTS and non-CTS tappers. (2) The rubber tappers with CTS were significantly more impaired in terms of their usual activities and reported more pain and/or discomfort than the non- CTS tappers. Pain and/or discomfort was a mediator between CTS and usual activities. The CTS group had significantly higher impairment in both tapping and daily activities than the non-CTS group. In addition, the degree of symptom severity in the CTS group was related to the degree of tapping impairment. (3) The new ergonomic rubber tapping knife could significantly decrease the CTS symptom severity scores by improving wrist posture. In addition, the rubber tappers who used the new ergonomic knife had reduced HRQOL problems for usual activities and pain/discomfort compared with tappers using the traditional knife. Impairment in terms of tapping and daily activities among the CTS tappers were also significantly improved after changing from the traditional to the ergonomic knife. Conclusion The physical ergonomic risk factors for CTS among rubber tappers were the number of tapped trees at or below knee level and collecting latex. We confirmed that CTS affects both HRQOL and impairment in a dose-response pattern. Our new ergonomic rubber tapping knife would be helpful for both primary and secondary prevention of CTS among rubber tappers.