The dose-response relationship between cumulative lifting load and lumbar disk degeneration based on magnetic resonance imaging findings

Background. Lumbar disk degeneration (LDD) has been related to heavy physical loading. However, the quantification of the exposure has been controversial, and the dose-response relationship with the LDD has not been established.Objective. The purpose of this study was to investigate the dose-response relationship between lifetime cumulative lifting load and LDD.Design. This was a cross-sectional study.Conclusions. The results suggest a dose-response relationship between cumulative lifting load and LDD.Methods. Every participant received assessments with a questionnaire, magnetic resonance imaging (MRI) of the lumbar spine, and estimation of lumbar disk compression load. The MRI assessments included assessment of disk dehydration, annulus tear, disk height narrowing, bulging, protrusion, extrusion, sequestration, degenerative and spondylolytic spondylolisthesis, foramina narrowing, and nerve root compression on each lumbar disk level. The compression load was predicted using a biomechanical software system.Results. A total of 553 participants were recruited in this study and categorized into tertiles by cumulative lifting load (ie, <4.0 ? 105, 4.0 ? 105 to 8.9 ? 106, and ?8.9 ? 106 N h). The risk of LDD increased with cumulative lifting load. The best dose-response relationships were found at the L5–S1 disk level, in which high cumulative lifting load was associated with elevated odds ratios of 2.5 (95% confidence interval [95% CI]=1.5, 4.1) for dehydration and 4.1 (95% CI=1.9, 10.1) for disk height narrowing compared with low lifting load. Participants exposed to intermediate lifting load had an increased odds ratio of 2.1 (95% CI=1.3, 3.3) for bulging compared with low lifting load. The tests for trend were significant.Limitations. There is no “gold standard” assessment tool for measuring the lumbar compression load. ? 2014 A merican Physical Therapy Association.