Biomechanical testing of spinal fusion segments enhanced by extracorporeal shock wave treatment in rabbits.

BACKGROUND Extracorporeal shock wave treatment (ESWT) has been proven effective in enhancing spinal fusion in a preliminary animal study. However, biomechanical tests were not performed. METHODS All 12 rabbits in this study underwent decortication at the bilateral L5 and L6 transverse processes. Bone was chipped off and placed onto the intertransverse space. The rabbits were divided into two groups, a study group (n = 6) and a control group (n = 6). In the study group, the bilateral L5 and L6 transverse processes were treated with 1000 impulses of ESWT at 14 kilovolts (KV) (equivalent to 0.18 mJ/mm(2)) at 12 and 18 weeks after surgery. The control group rabbits did not undergo ESWT. A series of radiographic examinations on each rabbit were subsequently performed. All rabbits were killed at 21 weeks, and their spines were harvested for biomechanical tests. RESULTS Radiographic examination showed 5 of the 6 rabbits in the study group had callus formation in the fusion masses. Biomechanical tests of the fusion segments showed that the mean flexion stiffness (with internal control) in the study group was 2.11 +/- 0.46, while that in the control group was 1.17 +/- 0.19. The mean extension stiffness (with internal control) in the study group was 1.70 +/- 0.39, while that in the control group was 1.23 +/- 0.29. Statistical analysis showed that the fusion segments in the study group had significantly better flexion and extension stiffness than those in the control group (p < 0.05). CONCLUSION In this animal study, radiographic examinations showed that ESWT stimulated new bone growth. Biomechanical tests showed that ESWT significantly increased the flexion and extension stiffness of spinal fusion segments.