Background: Changes in intervertebral disc (IVD) morphology and biochemistry have been characterized only incompletely in the rat hindlimb unloading (HLU) model. Here we present preliminary data on the differential effects of short periods of weight-bearing with or without low-level whole-body vibrations (WBV) on the lumbar rat IVD during HLU.
Methods: Rats were subjected to HLU and exposed to daily periods (15 min x d(-1)) of either ambulatory activities (HLU+AMB) or whole body vibrations superimposed upon ambulation (HLU+WBV; WBV at 45 Hz, 0.3 g).
Results: At the end of the 4-wk experimental period and compared to age-matched control rats (AC), the lumbar IVD of HLU+AMB had a 22% smaller glycosaminoglycans/collagen ratio, 12% smaller posterior IVD height, 13% smaller cross-sectional area, 9% greater ratio of height/area, and a 24% smaller volume of the surrounding muscle tissue. Compared to HLU+AMB rats, the addition of low-level vibratory loading did not significantly alter IVD biochemistry, posterior height, area, or volume but normalized muscle volume (-8% vs. AC) and the IVD height/area ratio (-3% vs. AC) to levels similar to normal controls. Relative to AC, superposition of the vibratory stimulus onto ambulation had a greater effect on IVD area than on IVD height. IVD volume and IVD posterior height of HLU+WBV rats remained 13% and 16% smaller than in normal controls.
Conclusion: Even though neither intervention was successful in preventing hindlimb unloading induced changes in IVD volume, compared to ambulation alone, very low-level whole-body vibrations resulted in greater total back and abdominal muscle volume and directionally altered IVD geometry.