Electromyostimulation influences the mechanical properties and microarchitectures of bones beyond the stimulation site

Abstract

Electromyostimulation is a nonpharmacological prevention method for osteoporosis that is safe and feasible for the elderly and people with physical disabilities. Our previous study demonstrated that random pulse train (RdPT) electromyostimulation of rat quadriceps induces an increase in the mechanical properties of the contralateral unstimulated femoral neck. However, the efficacy of this stimulation on other untested bones is still unclear. The objective of this research is to investigate the response of previously unstimulated bones to single-site electromyostimulation. The left quadriceps of rats were stimulated electrically by periodic pulse train (PrPT) or RdPT with 2 mA-magnitude pulses at 552 μs and a 50% duty ratio. The stimulation effect was examined on the diaphysis of long bones and lumbar vertebrae (L2–L5) by quasi-static mechanical tests and microcomputed tomography analysis. RdPT increased the strain energy at the stimulated left femur but did not change the properties of the other long bones. For the lumber vertebrae, on the other hand, both stimulations showed similar results. The stiffness of lumbar vertebra increased in L2, and the stiffness and the maximum load decreased in L4. Additionally, the BMC (bone mineral content), BV (bone volume), and TV (tissue volume) were reduced in L2, but not changed in L4. The other vertebrae were not affected by the stimulations. In conclusion, RdPT influences not only the stimulated femur, but also the lumbar vertebrae site-dependently as well as PrPT. These findings suggest the whole-body scale effect of electromyostimulation, however, which is not positive in all the bones, requiring further investigations for its clinical applications.