Direct current electrical stimulation increases the fusion rate of spinal fusion cages

Study Design. A randomized experimental evaluation of direct current stimul ation in a validated animal model with an experimental control group, using blinded radiographic, biomechanical, histologic, and statistical measures. Objectives. To evaluate the efficacy of the adjunctive use of direct curren t stimulation on the fusion rate and speed of healing of titanium interbody fusion cages packed with autograft in a sheep lumbar interbody fusion mode l. Summary of Background Data. Titanium lumbar interbody spinal fusion cages h ave been reported to be 90% effective for Single-level lumbar interbody fus ion. However, fusion rates are reported to be between 70% and 80% in patien ts with multilevel fusions or with risk factors such as obesity, tobacco us e, or metabolic disorders. The authors hypothesized that direct current sti mulation would increase the fusion rate of titanium interbody fusion cages packed with autograft in a sheep lumbar interbody fusion model. Methods. Twenty-two sheep underwent lumbar:discectomy and fusion at L4-L5 w ith an 11- x 20-mm Bagby and Kuslich (BAK) cage packed with autograft. Seve n sheep received a BAK cage and no current. Seven sheep; had a cage and a 4 0-muA current applied with a direct current stimulator. Eight sheep bad a B AK cage and a 100-muA current applied. All sheep were killed 4 months after surgery. The efficacy of electrical stimulation in, promoting interbody fu sion was assessed by performing radiographic, biomechanical, and histologic analyses in a blinded fashion. Results. The histologic fusion rate increased as the direct current dose in creased from 0 muA to 40 muA to 100 muA (P < 0.009). Histologically, all an imals in the 100-<mu>A group had fusions in both the right and left sides o f the cage. Direct current stimulation had a significant effect on increasi ng the stiffness of the treated motion segment in right lateral bending (P < 0.120), left lateral bending (P < 0.017), right axial rotation (P < 0.004 ), left axial rotation (P< 0.073), extension (P < 0.078), and flexion (P < 0.029) over nonstimulated levels. Conclusion. Direct current stimulation increased the histologic and biomech anical fusion rate and the speed of healing of lumbar interbody spinal fusi on cages in an ovine model at 4 months.