Challenging The Cumulative Injury Model: Positive Effects Of Greater Body Mass On Disc Degeneration

Abstract

PURPOSE: There are differing views as to the causes of disc degeneration. One view emphasizes genetic influences, while another, which has been referred to as a cumulative and repetitive injury model, emphasizes physical loading or biomechanical forces. Perhaps paradoxically, physical loading has been thought to be generally beneficial for the structures of the musculoskeletal system, but harmful for the intervertebral disc. The goal of this study was to investigate the associations of routine physical loading from body weight with quantitative measures of disc degeneration. METHODS: We selected 44 pairs of healthy male monozygotic twins with 8 kg or more discordance in body weight (mean 13 kg), with lumbar MRIs and bone density measurements available. The main outcome of disc degeneration was assessed through quantitatively measured disc height, disc signal intensity, and signal irregularity adjusted by the intra-body reference, adjacent cerebrospinal fluid signal. Data on suspected constitutional and environmental risk factors were available for control of possible confounding factors. RESULTS: Our findings suggest that cumulative repetitive loading due to routine physical loading with higher body mass may slightly delay disc desiccation. Whether physical loading has harmful or beneficial effects may depend on the body's capacity to adapt. CONCLUSIONS: Our findings suggest that cumulative repetitive loading due to routine physical loading with higher body mass may slightly delay disc desiccation. Whether physical loading has harmful or beneficial effects may depend on the body's capacity to adapt.