OBJECTIVETo validate the hypothesis that there exists an optimal axial compression stress range to enhance tibial fracture healing.

METHODSRabbits with a surgically induced V-shaped tibial fracture were separated into 2 main groups: the control group (C Group, n equal to 6) without application of any axial compression stress stimulation postoperatively and the stimulation group (S Group, n equal to 90). The S Group was further divided into 20 subgroups (S11 to S54) in terms of 5 axial compression stress stimulation levels (112.8 kPa, 289.8 kPa, 396.5 kPa, 472.7 kPa, and 602.3 kPa) and 4 experimental endpoints (1, 3, 5 and 8 weeks after operation). A custom made circular external fixator was used to provide the axial compression stress of the fracture sites. Based on X-ray observation, a fracture healing scoring system was created to evaluate the fracture healing process.

RESULTSAt 8 weeks after operation, there existed a "arch shape" relationship between healing score and axial compression stress stimulation level of fracture site. The optimal axial compression stress stimulation ranged from 289.8 kPa to 472.7 kPa, accompanying the best fracture healing, i.e. the fracture line became indistinct or almost disappeared, and a lot of callus jointed the two fracture ends. Meanwhile, at 5 weeks after operation, corresponding to the relatively low healing scores, there was a fracture healing performance similar to that at 8 weeks. Besides, at 1 or 3 weeks after operation, for all the axial compression stress levels (0-602.3 kPa), no obvious healing effect was found.

CONCLUSIONSIt is implied from the stated X-ray observation results in this study that the potential optimal axial compression stress stimulation and optimal fracture healing time are available. The axial compression stress level of 289.8-472.7 kPa and fracture healing time of more than 8 weeks jointly comprise the optimal axial compression stress stimulation conditions to enhance tibial fracture healing.