THE EFFECTS OF EXTERNAL MECHANICAL STIMULATION ON THE HEALING OF DIAPHYSEAL OSTEOTOMIES FIXED BY FLEXIBLE EXTERNAL FIXATION

Objective. The purpose of this study was to investigate the effect of an externally applied mechanical stimulus on fracture healing under fl exible fixation.Design. Stimulation of fracture healing under various conditions of interfragmentary movement in an in vivo fracture model o n 41 sheep. Background. It is generally accepted that small interfragm entary movements (IFMs) yield better bone healing results than larger IFMs (> 1 mm). However, the optimal size of IFM within the 1 mm range remains undetermined. Methods. Standardized transverse osteotomy of 3 mm gap size in the left ovine tibia was fixed with an unilateral exter nal fixator. The sheep were divided into four IFM groups of 0.0, 0.2, 0.4 and 0.8 mm and stimulated with this amplitude for 1200 cycles per day at 1 Hz. After a healing period of 6 weeks, bone mineral density a nd biomechanical stability were evaluated to determine the quality of healing. Results. The amount of callus formation increased significant ly with increasing TFM (P<0.05). However, highest biomechanical stabil ity of the healed bone and mineral density of the gap tissue was achie ved with an IFM of 0.4 mm, although the differences were not significa nt. Conclusions. These results suggest that the optimal interfragmenta ry movement for acceleration of delayed fracture healing is in the ran ge of 0.5 mm. However, the enhancement of the healing of flexibly-fixe d fractures by external application of interfragmentary movement is li mited.