BACKGROUND CONTEXT Pseudarthrosis or failure-to-fuse occurs in approximately 70% of lumbar interbody fusion procedures. To improve the success of fusion, various surgical adjuncts such as bone grafts and bone morphogenic protein (BMP) are commonly used. Unfortunately, BMP has been associated with serious complications including local inflammation and ectopic bone formation in the spinal canal. To overcome the challenges of BMP, direct current electric stimulation (DCES) has been examined as a nonpharmacologic means of inducing local bone formation and spinal fusion. Direct current electric stimulation has been demonstrated to up-regulate osteoinductive factors which govern new bone formation and lead to fusion. The principal innovation behind the technology is the concept of using existing metallic spinal instrumentation (pedicle screws, rods, etc.) to focally deliver bone forming DCES directly to the fusion site. The system of instrumentation thereby functions simultaneously as both conventional mechanical fixation and internal osteogenic stimulator. PURPOSE The present study was designed to determine whether novel osteogenic spinal instrumentation is capable of improving mechanical stabilization and bony interbody fusion of the lumbar spine in a large animal model. METHODS A posterolateral interbody fusion across L4–L5 was performed on 36 skeletally mature sheep. The treated functional spinal unit (FSU) was stabilized posteriorly using four osteogenic pedicle screws and connecting bars (INDOSTM, OsteoVantage, Inc. Fayetteville, AR, USA), with a PEEK interbody device (IBD), placed via a lateral approach, across the disc space. Three treatment groups were studied: (Group 1) IBD filled with tricalcium phosphate (TCP), (Group 2) IBD filled with TCP with DCES, and (Group 3) IBD filled with BMP (InfuseTM, Medtronic Spine, Memphis, TN). Active osteogenic spinal instrumentation (ie, Group 2) consisted of standard titanium pedicle screws and rods that have been modified with proprietary anodization patterns and power supplies to conduct and deliver therapeutic DCES to the fusion site (ie, the disc space). Eighteen (n=18) animals were sacrificed at 13 and 26-weeks. Following euthanasia, kinematic, radiographic and histological analyses were performed on explanted FSUs. RESULTS No in-life complications were observed, and all osteogenic spinal instrumentation were confirmed to be in operation over the study period. For all 3 kinematic loading cases Group 2 and Group 3 demonstrated significantly lower ROM compared to Group 1 at the 13-week sacrifice time point. Reduction in ROM magnitudes was observed in all directions for Group 2 as compared to Group 1 at the 13-week time point; these reductions were significant in lateral bending and flexion–extension. For all treatment groups, the ROM results from the 26-week group were significantly less than the 13-week data. The significant differences at the 13-week time point between Group 2 and Group 1 clearly demonstrate that DCES causes increased reduction in ROM during the early healing cascade. Histomorphometric data demonstrated a significant increase in the percent (%) bone within the IBD graft window between the 13 and 26-week time points for Group 2 only (p CONCLUSIONS Previous research has demonstrated that DCES up-regulates osteoinductive factors which govern new bone formation and fusion. It has been shown to enhance normal physiologic expression of BMP-2, BMP-6 and BMP-7 in osteoblasts. In addition, DCES stimulates macrophages to release VEG-F. This study indicates that DCES can have a significant effect on local bone formation and spinal fusion as measured by ROM kinematics and bony response as measured by radiographic analysis and histopathology. In total, osteogenic spinal instrumentation delivering focused DCES at the fusion site promoted both mechanical stabilization of the spine and osteogenic stimulation of new bone formation and bony fusion.
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Jan 1, 2020
Eiji Nakamachi + 4
Open Access
