Evaluation of the probability of spinal damage caused by sustained cyclic compression loading

A sensitivity analysis of two alternative models predicting damage to vertebral motion segments (VMS) in cyclic compression was performed to evaluate the relative probability of damage occurring when peak compression force, loading frequency, or duration in a lifting task is changed. The first model is based on the assumption that fatigue failure is the mechanism underlying damage to the VMS in cyclic compression. The second model is based on the assumption that the VMS damage in cyclic compression is determined by the viscoelastic deformation of the segment and that the instant of failure can be predicted on the basis of the energy stored in this process. With both models, we estimated the percentage of the population likely to incur a VMS injury when performing a repetitive lifting task with peak compression forces ranging from 1500 to 4100 N, frequencies from 2 to 12 min-1, and durations between 30 and 120 min. The results indicate a dominant influence of the peak compression force on this outcome over the domain studied. This conclusion holds qualitatively for both models, suggesting that for a comparative analysis they can be considered interchangeable. However, a considerable quantitative difference in the absolute outcomes of the two models was found, which stresses the importance of further study on the validity of these models.