The efficacy of direct current stimulation for lumbar intertransverse process fusions in an animal model

Study Design. Posterolateral lumbar intertransverse process fusion using a rabbit model with autologous bone graft and direct current stimulation was compared with fusion achieved by using autologous bone graft alone. Objectives. To determine the efficacy of direct current electrical stimulat ion for the posterolateral lumbar intertransverse process fusion technique by using a 20-muA current and the more recently developed 60-muA current de livered by an implantable direct current stimulator. Summary of Background Data. Previous studies have demonstrated a positive e ffect of direct current electrical stimulation on posterior spinal fusion t echniques. However, until recently, the environment of an intertransverse f usion was not well simulated. The current research examined the posterolate ral lumbar intertransverse process fusion technique with direct current ele ctrical stimulation using a rabbit model. This appears to parallel human fu sion techniques more closely and allows for lower cost and technical ease. Methods. In this study, 44 adult New Zealand white rabbits underwent an L5- L6 intertransverse process fusion. All the fusions used an autologous bone graft obtained from bilateral posterior iliac crests. A device was implante d in all the rabbits subcutaneously, and they were divided randomly into th ree groups: a sham or non-functioning group, a 20-muA low-current stimulato r group, and a 60-muA higher-current stimulator group. Spinal fusion was ev aluated radiographically, histologically, and manually as well as by biomec hanical testing 5 weeks after surgery. Results. Radiographic grades, manual palpation, biomechanical strength, and stiffness showed an increasing trend from sham or inactive stimulator grou ps to low-current and then to high-current stimulator groups. Histologic an alysis revealed that the higher-current stimulator showed that, statistical ly, the healing response of the host tissue to the autograft had increased significantly, as compared with the sham. Conclusions. Direct current electrical stimulation is efficacious in improv ing both the healing rate and strength in this posterolsteral lumbar fusion model. In addition, it appears that this effect is enhanced by increasing the stimulation current from 20 muA to 60 pA.