Effects of low magnitude, high frequency vibrations on bone fracture healing

Mechanical signals can stimulate bone formation cells and repair damaged bone. Recently, researchers showed that low magnitude, high frequency vibrations, common during normal daily activity, can also influence bone formation cells and create denser and stronger bones. Thus, low magnitude, high frequency vibrations may be efficacious as a non-invasive osteogenic method to mitigate osteopenia associated with disuse or postmenopause.

Fracture healing, a complex process involving numerous cells and genes, has many similarities to bone formation processes. Several mechanical methods have been shown to be successful in accelerating fracture healing rate and healing of nonunion fractures by inducing the osteogenic response.

Combining those findings, the hypothesis in the current study was that low-magnitude, high frequency vibration will enhance fracture healing processes by increasing the rate of healing and will improve the quality and quantity of the newly formed bone. Twenty-one rats underwent complete bilateral fibular osteotomy. One day after the osteotomy one of their hind-limbs was subjected to 20 min/d, 6 d/wk, low-magnitude vibrations at 45 Hz and peak acceleration of 0.6-0.7 g. The other hind-limb was used as a sham control. Both fibulas of each rat were scanned using high-resolution micro computerized tomography at days 1, 8, 15, 22, and 29. After 29 days of treatment, the rats were sacrificed, the fibulas were harvested, and the mechanical properties of the bone were tested using a nanoindentor.

Results revealed no differences in bone formation rate and bone material properties between the treated and non-treated limbs. The results suggested that indirect fracture healing was not improved by low-magnitude vibration of this frequency and amplitude, even though a number of recent studies showed evidence of increased bone regeneration associated with low-magnitude vibrations.

The rapid healing rate of bone fracture suggested that fracture healing processes can normally be very efficient. Additional studies with a larger osteotomy gap that can result in nonunion combined with longer treatment period may be needed to show any potential effects of high frequency, low magnitude vibrations on fracture healing.