Effect of Spinal Fixation in Rabbits With Metastatic Tumor Using a Novel Spinal Fusion Model

Abstract

An experimental assessment of the impact of spinal stabilization on metastasis growth using a rabbit model. To investigate the influence of spinal stabilization on the growth of metastatic spinal tumors in rabbits using a novel method of spinal fusion. For spinal metastasis patients, gait disturbances caused by back pain or paraplegia correlates with their prognosis. Palliative surgeries are good options for some patients; however, the appropriate timing and method of spinal surgery remains controversial. The biomechanical properties of a novel spinal fixation model with a locking plating system were first examined on the L2-L4 fixed vertebrae of 18 Japanese white rabbits. Biomechanical and radiographic examinations were performed at 0, 4, and 8 weeks as compared with controls. After this, another 31 rabbits were then inoculated with VX2 carcinoma cells into the L3 vertebral body and divided into fixation (N=16) and sham (N=15) groups to assess the impact of spinal stabilization on tumor growth. The time to paraplegia, and tumor cell growth and proliferation were evaluated by rabbit behavior, computed tomography, myelogram, and cell proliferation marker (MIB-1 index). In the biomechanical loading test, fixed segments showed one eighth of the range of motion and 15 times bending stiffness as compared with controls at each timepoint. No pathologic fractures were observed in the rabbits inoculated with VX2 carcinoma cells before paraplegia, and there was no difference in the time to paraplegia between the fixation and sham groups (26.7 and 28 d, respectively). Similarly, no differences were observed in osteolytic area expansion or tumor cell proliferation (MIB-1 index; 38.1% and 38.0%, respectively). Our locking plate fixation of rabbit spines exhibited sufficient biomechanical properties. Spinal fixation had little influence on the growth of the aggressive carcinoma and the time to paraplegia. However, further investigation is needed to determine the influence of spinal stabilization on slow-growing tumors.