Application of extracorporeal shock wave treatment to enhance spinal fusion: a rabbit experiment

Background: Extracorporeal shock wave treatment has been used to treat many orthopedic disorders. However, the effect of extracorporeal shock waves on spinal fusion has not been reported. Methods: Fifteen rabbits were used in this study. Spinal fusion was performed with decortication of bilateral L5 and L6 transverse processes, and placement of the bone chips onto the ipsilateral L5-L6 intertransverse space. The right L5 and L6 transverse processes in all animals were treated with 1000 impulses of ESWT at 14 kV (equivalent to 0.18 mJ/mm²) at 3 and 6 weeks after surgery. The left transverse processes did not receive ESWT, and were served as controls. Radiographic examinations of the spines were performed at 3, 6, and 12 weeks. Computed tomography was performed at 12 weeks. The rabbits were killed at 12 weeks, and the spinal segments were harvested for histomorphological examination. Results: Radiographs of the tested rabbits taken at different post-ESWT stages demonstrated repairing effect of ESWT on the fusion gap of the treated (right) sides. Statistical analysis of the image studies indicated that 11 (73%) of 15 rabbits showed superior fusion mass on the ESWT (right) side than that of control (left) side (P < .001). The remaining 4 (27%) rabbits showed no discernable fusion difference between the ESWT side and the control side. Histomorphological examination showed good new bone formation in 9 fusion masses. All of these cases were noted on the ESWT (right) sides. Statistical analysis showed that ESWT sides had better new bone formation than the control sides (P = .001). Conclusions: Results of this study demonstrated that ESWT is effective in promoting spinal fusion in rabbits.