Augmentation of bone healing by specific frequency and amplitude compressive strains

A considerable proportion of bone fractures show signs of delayed or impaired healing. A novel device that applies interfragmentary compressive forces to the fracture site was developed and evaluated for its effect on fracture healing. The midshafts of the right tibias of 16 rabbits were osteotomized, leaving a 2-mm gap. A 4-pin, double-bar external fixator was fixed to the tibias. Interfragmental compressive displacement of 0.5 mm with a frequency of 1 Hz was applied 15 minutes per day. Mechanical stimulation began 1 week postoperatively and continued for 2 and 3 weeks. Control animals received no stimulation. Callus quality and area were assessed by radiographs. Maximum force and total energy absorbed up to failure of the healed bones were determined using a standard 3-point bending test. Postmortem radiographic examinations showed that mean radiographic measures in both anteroposterior and mediolateral views was significantly larger in experimental groups than controls (P=.029). Mechanical measures of the healed bones demonstrated that mean values of maximum force and absorbed energy were significantly higher in the experimental groups than in the control groups (P=.029). Both radiographic and mechanical measures were significantly higher after 3 weeks compared to 2 weeks of receiving stimulation (P<.05).