High-frequency loading of lumbar ligaments increases proinflammatory cytokines expression in a feline model of repetitive musculoskeletal disorder.

BACKGROUND CONTEXT Cumulative (repetitive) lumbar disorder is common in the workforce, and the associated epidemiology points out high risk for lifting heavy loads, performing many repetitions, and performing movements at high velocity. Experimental verification of viscoelastic tissue degradation and a neuromuscular disorder exist for cyclic work under heavy loads. Experimental validation for a disorder because of cyclic loads under high-velocity movement is missing. PURPOSE Obtain experimental verification that high-velocity lumbar flexion-extension results in significant increase of proinflammatory cytokines in the viscoelastic tissues. STUDY DESIGN Laboratory experiments using two in vivo feline model groups subjected to cyclic flexion-extension at low and high velocity. METHODS Seven hours after cumulative 60 minutes of cyclic flexion-extension at moderate load of 40 N and 0.25 Hz for first group and 0.5 Hz for the second group, the supraspinous ligaments of L3-L4 to L5-L6 were harvested and subjected to cytokines (interleukin [IL]-1β, IL-6, IL-8, tumor necrosis factor-α, and transforming growth factor-β1) analysis. Two-way mixed model analysis of variance with a post hoc analysis were used to assess any significant differences (p<.05) in cytokines expression level between the two groups as well as main effect and interaction with lumbar levels. RESULTS Expression levels of the five cytokines were significantly increased in the group subjected to the high-frequency loading. CONCLUSIONS Exposure of the lumbar spine to high-velocity flexion-extension triggers a significant increase in proinflammatory cytokines, indicating pronounced changes consistent with an acute inflammation. Further exposure to activity over prolonged periods may trigger chronic inflammation and tissue degeneration as the source of cumulative lumbar disorder.