Effects of high-frequency, low-magnitude mechanical stimulus on bone healing.

Recent studies have shown osteogenic effects of high-frequency mechanical stimuli. The purpose of this study was whether externally applied, high-frequency, low-magnitude interfragmentary movements affect the process of bone healing. In 12 sheep, a transverse osteotomy with a 3 mm gap was created in the right metatarsus and externally stabilized by a rigid circular fixator. External stimulation was performed in six sheep with the use of ground-based vibration. The sheep were standing with their hind limbs on a platform that produced vertical movements resulting in interfragmentary movements of approximately 0.02 mm magnitude at 20 Hz frequency. The other six sheep remained rigidly stabilized by external fixation during the 8-week study and served as a control group. Healing was assessed postmortem by densitometric and mechanical examinations. No significant differences were found between the two groups, although callus formation was slightly enhanced (11%) in the stimulated group compared with the control group. Mechanical stimuli attributable to weightbearing in the control group were sufficient enough to initiate callus formation even under rigid, external fixation. Thus, external mechanical stimulation with the stimulation design described in the current study might not be indicated for improvement of bone healing.