Short applications of very low-magnitude vibrations attenuate expansion of the intervertebral disc during extended bed rest.
BACKGROUND CONTEXT
Loss of functional weightbearing during spaceflight or extended bed rest (BR) causes swelling of the lumbar intervertebral discs (IVDs), elongates the spine, and increases the incidence of low back pain (LBP). Effective interventions for the negative effects of unloading are critical but not yet available.


PURPOSE
To test the hypothesis that high-frequency, low-magnitude mechanical signals (LMMS) can attenuate the detrimental morphologic changes in the lumbar IVDs.


STUDY DESIGN/SETTING
Volunteers were subjected to 90d of BR and 7d of reambulation. While retaining this supine position, 18 random subjects received LMMS (30Hz) for 10min/d, at peak-to-peak acceleration magnitudes of either 0.3g (n=12) or 0.5g (n=6). The remaining subjects served as controls (CTRs).


PATIENT SAMPLE
Eighteen males and 11 female (33+/-7y) healthy subjects of astronaut age (35+/-7y, 18 males, 11 females) and without a history of back pain participated in this study.


OUTCOME MEASURES
A combination of magnetic resonance imaging and computed tomography scans of the lumbar spine of all subjects were taken at baseline, 60d, 90d, and 7d post-BR. Back pain was self-reported.


METHODS
IVD morphology, spine length, and back pain were compared between CTR and LMMS subjects.


RESULTS
Compared with untreated CTRs, LMMS attenuated mean IVD swelling by 41% (p<.05) at 60d and 30% (p<.05) at 90d. After 7 days of reambulation, disc volume of the CTR group was still 8% (p<.01) greater than at baseline, whereas that for the LMMS group returned the disc volume to baseline levels. In contrast to BR alone, LMMS also retained disc convexity at all time points and reduced the incidence of LBP by 46% (p<.05).


CONCLUSIONS
These data indicate that short daily bouts of LMMS can mitigate the detrimental changes in disc morphology, which arise during nonweightbearing, and provides preliminary support for a novel means of addressing spinal deterioration both on earth and in space.