Different effects of mechanical vibration on bone ingrowth into porous hydroxyapatite and fracture healing in a rabbit model

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Abstract
The effects of mechanical vibration on bone ingrowth into porous hydroxyapatite implants and fracture healing were examined radiographically, histomorphometrically, and biomechanically in a rabbit model. Fifty‐three female NZW rabbits were used in this study. These rabbits were divided into four separate studies to assess the effects of 20 and 60 min of vibration/day in both implant and osteotomy models as compared with the respective nonvibrated controls. For the implant model, coral hydroxyapatite goniopora rods were implanted bilaterally into tibiae and for the osteotomy model, bilateral fibulae were osteotomized. A resonant frequency of 25 Hz mechanical vibration was used. After periods of 2, 3, 4, and 6 weeks of vibration, the rabbits were killed and examined. For the implant model, there was no significant difference between control, 20, or 60 min of vibration/day with respect to the rate or amount of new bone ingrowth. For the fracture model, 60 min of vibration/day produced a significantly larger callus as compared with the nonvibrated controls (p < 0.05), whereas 20 min of vibration/day did not. Although biomechanical testing demonstrated a general trend for increased strength in the vibrated animals, it failed to reach significance. These results suggest that the mechanical vibration used in the present study had a beneficial effect on callus volume, possibly due to the stimulation of secondary bone healing processes, but does not appear to promote bone ingrowth into a porous hydroxyapatite implant.