Quantification of overload injuries to thoracolumbar vertebrae and discs in persons exposed to heavy physical exertions or vibration at the work-place: Part 1 - The shape of vertebrae and intervertebral discs — study of a young, healthy population and a middle-aged control group

The ongoing search for causes (and strategies for prevention) of low back trouble in sub-groups of the population exposed to heavy physical exertions or whole body vibration requires reliable data on the prevalence of lower-spine overload damage. Because published reports on this topic are rare and mostly qualitative, the present study was initiated to assess, objectively and quantitatively, overload damage to vertebrae and intervertebral discs. Part I of the work has involved the establishment of a normative database of shape parameters from measurements of 683 (539 male, 144 female) lateral radiographic views of the thoracolumbar spine of young (17–30 years), healthy subjects. In addition, age-related shape alterations were explored from measurements of 364 male middle-aged (31–57 years), non-exposed controls. Advanced methods for shape analysis and shape parameter construction were required, and duly developed, in order to minimise the influence of confounding factors such as radiographic magnification, image distortion, axial rotation or lateral tilt. The results revealed that the variation in shape parameters varies between 2% and 10% within the group of normals (this being largely biological variability as opposed to measurement error). Within this normal group subtle but statistically significant differences due to gender and geographic origin were observed. Comparison of the normals with the controls revealed only slight, but clearly demonstrable differences. The narrow range of ‘normal shape’ together with the high accuracy of shape analysis are the foundation for Part II of this study which will involve a comparison of exposed cohorts with the normal standard (adjusted for ageing effects). This will, for the first time, enable objective quantification of the prevalence of overload damage to the spines of persons exposed to heavy physical stresses and whole body vibration, and thus form the basis of a scientific rationale for recommendation of safety guidelines.