P.Brinckmann¹, W.Frobin¹, M.Biggemann², AK.Burton³, KM.Tillotson³

1Institut für Experimentelle Biomechanik, Universität Münster, D-Münster, ²Radiologische Klinik, Bethesda Krankenhaus, D-Duisburg, ³Spinal Research Unit, University of Huddersfield, GB-Huddersfield.

Epidemiological studies point to heavy and repeated spinal loading as well as to whole body vibration as potential causes of low back problems. The hypothetical cause-and-effect relationship between spinal loading and injuries to vertebrae and discs is supported by biomechanical model calculations and results from in-vitro tests on spine specimens. Regulations on manual handling/lifting and exposure to vibration have been issued and considerable effort is spent on a reduction of loads as well as ergonomic improvements, but surprisingly direct proof on work-related, primary mechanical overload damage to lumbar vertebrae and discs has not been demonstrated. Few previous studies have actually investigated the prevalence of overload damage to the lumbar spine in those at risk; these few studies were only qualitative. No previous study has been found that objectively and quantitatively assessed the prevalence of work-related overload damage to the lumbar spine.

Archive lateral radiographic views of the lumbar spine of 278 subjects with documented long-term exposure to heavy physical exertions or whole-body vibration were collected from 8 cohorts in the mining and steel industries. The cohort means for length of exposure were between 10 and 21 years. Height and sagittal plane displacement of lumbar vertebrae as well as height of lumbar discs were measured from the radiographs and compared with normative, age-appropriate data derived from 749 radiographs of non-exposed subjects. (The scientific tools developed to precisely measure the height of vertebrae and discs have been described in a previous report.* The measurement uses advanced methods of image analysis when processing radiographs taken in different, generally unknown geometric settings. Compensation for distortion in central projection as well as compensation for variation in radiographic posture were achieved; a prerequisite for performing a retrospective analysis on archive material.)

In virtually all cohorts selected, and irrespective of exposure to heavy spinal loading or whole-body vibration, the height of lumbar vertebrae did not deviate from normal. Only a cohort of press operators, working in a bent-forward posture, showed evidence of vertebral damage (wedge- or crush-fractures of T12 and L1). In all cohorts, sagittal plane displacement of lumbar vertebrae exhibited only very small, irregular deviations from normal. Disc height at all lumbar levels was severely and significantly decreased in 2 cohorts that had been exposed to extremely heavy spinal loading while carrying and lifting, and in one cohort that had been exposed to vibration and shock loading while working on unsprung mining machinery. Morphology of vertebrae and discs did not deviate from normal in cohorts exposed to whole-body vibration in earth moving machinery equipped with damped seats.

For the first time, this study presents quantitative data on the prevalence of overload damage to lumbar vertebrae and discs in subjects potentially at risk. The prevalence of overload damage was generally low, except for three cohorts from plants where workloads had been much higher than current regulations would permit. This suggests that strict enforcement and adherence to present regulations on lifting and handling is justified. The comparison of the results from the vibration-exposed cohorts (damped seats vs unsprung seats on unsprung machines) impressively demonstrates the effect of workplace re-design in reducing a health risk to the labour force.

* Frobin et al. Precision measurement of disc height, vertebral height and sagittal plane displacement from lateral radiographic views of the lumbar spine. Clin Biomech 1996; 12 (Suppl. 1): S4-S63.

This work is conducted under a research contract from The Health & Safety Executive, UK.

Kim Burton, 30 Queen Street, Huddersfield HD1 2SP, UK.

Phone: +44 1484 535200, Fax: +44 1484 435744, E-mail: kburton@cix.co.uk