J Manipulative Physiol Ther. 2003 Jan; 26(1): 25-33.

Comparative analysis of low-back loading on chiropractors using various workstation table heights and performing various tasks.

Lorme KJ, Naqvi SA.

Caloundra DC, PO Box 3754, Queensland, Australia 4451.

BACKGROUND: There is epidemiologic evidence that chiropractors are a high-risk group for low-back disorders. However, to date there are no known biomechanical studies to determine whether their workstations may be a contributing factor. OBJECTIVE: To investigate whether chiropractors' workstation table height or the tasks they perform make them susceptible to low-back strain. As well as investigating low-back strain, a screening was performed to determine whether chiropractors' upper extremities were at risk for undue strain as workstation table height was varied. Study Design: Experimental pilot study. SETTING: A university ergonomic laboratory. METHODS: An adjustable manipulation table was set at 3 different heights: 465 mm, 665 mm and 845 mm.Each of the 7 volunteer chiropractors were fitted with a triaxial electrogoniometer and were videotaped and photographed for analysis while performing spinal manipulation to the cervical, thoracic, and lumbar spine of a volunteer patient at each workstation table height. Two biomechanical models, one static and one dynamic, were used to record the dependent variables. A screening of various upper extremity variables was also performed with the static model. RESULTS: For the subjects under study, a significant difference was found for the variables maximum sagittal flexion, disk compression force, and ligament strain as table height was varied. For the lumbar and thoracic manipulation tasks, the medium table height (655 mm) was found to create the least low-back strain. For the cervical manipulation task, the high table height (845 mm) was found to be the least straining on the low-back. The low height table (465 mm) was the most straining for all tasks. Upper extremities were not significantly affected by changes to table height. Significant differences were found for the task performed for axial rotational velocity, disk compression force, ligament strain, maximum sagittal flexion, dominant (right) elbow moment, and dominant (right) shoulder moment variables. There was no significant interaction between table height and task performed. CONCLUSION: Workstation table height was found to have a significant effect on low-back load of subjects under study. The results of this study demonstrate an overall unacceptably high amount of sagittal flexion, ligament strain, and disk compression force on the chiropractor subjects in the tasks performed.