Elevated Frequency Loading of Facet Joints

With disc degeneration and height loss, facet joints may become susceptible to damage when exposed to elevated frequency loading. The investigators hypothesized that elevated frequencies alter normal mechanical response of facet joints which may be a mechanical predisposition for low back pain. Facet joints from six bovine L4-L5 vertebra were subjected to 520 loading cycles from -15N to -60N at 1Hz, 5Hz, 20Hz, 40Hz and 80Hz. Net deformation, strain, cumulative strain, and elastic stiffness were computed for each cycle, averaged across frequencies and subjected to non-linear exponential regression. Regression parameters were examined with a Tukey post-hoc test. Asymptotic limits of deformation were statistically significant (P<0.005) while elevated frequencies displayed significant decreases with respect to deformation change per cycle as compared to 1Hz. (P<0.005) Initial strain data indicated all frequency comparisons were statistically significant (P<0.01. The strain change per cycle indicated 1Hz loading was statistically equivalent to both 40Hz and 80Hz loading (P>0.05). The 5Hz frequency was statistically elevated compared to other frequencies (P<0.01). Initial stiffness indicated all frequency comparisons were statistically different (P<0.05). This study represents mechanical evidence for the predisposition of individuals exposed to high frequency loading toward increased incidence of load back pain.