http://www.medscape.com/viewarticle/558600
From Spine
A Randomized Controlled Trial Evaluating the Effects of New Task Chairs on Shoulder and Neck Pain Among Sewing Machine Operators: The Los Angeles Garment Study
Posted: 06/25/2007; Spine. 2007;32(9):931-938. © 2007 Lippincott Williams & Wilkins
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· Abstract and Introduction
· Results
Abstract and Introduction
Abstract
Study Design: This is a 4-month randomized controlled trial to evaluate the effect of chair design on neck/shoulder pain among sewing machine operators.
Objective: Determine whether a chair with a curved seat pan leads to improved changes in monthly neck/shoulder pain scores compared with a control intervention.
Summary of Background Data: Sewing machine operators experience a high prevalence and severity of neck and shoulder pain in comparison to other working populations probably due to the sustained shoulder abduction and neck and upper back flexion required of the task. An adjustable height task chair that supports a forward sitting posture may reduce these posture-related risk factors and reduce neck/shoulder pain.
Materials and Methods: A total of 277 sewing machine operators with neck/shoulder pain were assigned to receive 1) miscellaneous items (control group), 2) a chair with a flat seat pan plus miscellaneous items, or 3) a chair with a curved seat pan plus miscellaneous items. Participants completed a monthly questionnaire assessing neck/shoulder pain severity.
Results: Based on estimates of pain score changes from a repeat-measures linear regression, participants who received the flat seat chair experienced a decline in pain of 0.14 (95% confidence interval, 0.07-0.22) points per month compared with those in the control group, while those who received the curved seat experienced a decline of 0.34 (95% confidence interval, 0.28-0.41) points per month compared with those in the control group. These estimates did not change after adjustment for potential covariates.
Conclusions: These findings demonstrate that an adjustable height task chair with a curved seat pan can reduce neck and shoulder pain severity among sewing machine operators.
Introduction
It has been reported that sewing machine operators experience more chronic neck or shoulder pain than other working populations.[1-5] In a cross-sectional study of 224 sewing machine operators, 67% reported neck or shoulder pain; based on physical examinations, 24% were diagnosed with tension neck syndrome and 20% with cervical syndrome.[6] In another study, physical examinations were performed on sewing operators and hospital workers randomly sampled from age-matched strata. Sewing machine operators received diagnoses of cervical syndrome, cervicobrachial fibromyalgia, and rotator cuff syndrome more often than hospital workers.[7]
In 2000, the garment industry employed 11 million workers worldwide with approximately 350,000 workers in the United States.[8] The Los Angeles basin is home to the largest garment production center in the United States. Most of the work is done by minimum wage, nonunion, immigrant women in shops that employ fewer than 20 people.[9] Sewing machine operators perform precision tasks at a relatively fast pace with work cycles of 30 to 60 seconds. This repetitive, stereotyped work is typically performed on nonadjustable workstations and chairs. The task demands and the lack of adjustability of the workstations may lead to sustained awkward postures, such as cervical and thoracic spine flexion and shoulder elevation and abduction (Figure 1), which may result in elevated rates of neck and shoulder pain.[6,7,10-13]
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| Figure 1. Typical posture of sewing operator with a conventional chair. Note flexed postures of thoracic and cervical spine and abduction of shoulder. Note also that the operator increased the height of the chair with paper cones. |
A pilot study by our group, carried out at sewing shops in Oakland, CA, evaluated a variety of workstation interventions with the goal of reducing neck, thoracic and lumbar spine flexion, shoulder elevation, and shoulder abduction during garment work. Examples of the workstation changes we studied were: sloping of the work surface toward the operator; adding side tables to support the material and reduce reach; providing reading glasses; adding task lamps; providing a foam wedge for the seat; providing a new chair; and adding a foot rest. Ultimately, the intervention that appeared most likely to reduce risk factors for neck and shoulder pain was a new task chair with a curved, 2-part seat pan (Figure 2) based on principles proposed for industrial work.[14-16] Theoretically, the 2-part seat pan supports the forward leaning posture by allowing a more open thigh-torso angle, thereby retaining the lumbar curvature and a less kyphotic thoracic spine. The pelvis is supported on the more horizontal rear part of the seat to prevent forward sliding associated with a forward sloping seat pan. The seat was also adjustable in height and slope to accommodate different task demands and employees of different stature.
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| Figure 2. Design concept for a task chair with a 2-part, curved seat pan, which supports forward leaning by allowing a more open thigh-torso angle and preserving lumbar lordosis. |
The purpose of the intervention study we are reporting here was to compare the impact of this new task chair, a conventional task chair, and a placebo intervention on neck and shoulder pain in industrial sewing operators. The primary outcomes evaluated were monthly neck and shoulder pain severity. The null hypothesis was that the change in neck and shoulder pain scores would be the same in all 3 intervention groups over a 4-month period.
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