The Effect of Electrical Stimulation on Lumbar Spinal Fusion in Older Patients: A Randomized, Controlled, Multi-Center Trial Part 2: Fusion Rates

Study Design. Randomized, controlled, multi-center trial. Objective. To investigate the effect of direct current (DC) electrical stimulation on fusion rates after lumbar spinal fusion in patients older than 60 years. Summary of Background Data. Older patients have increased complication rates after spinal fusion surgery. Treatments which have the possibility of enhancing functional outcome and fusion rates without lengthening the procedure could prove beneficial. DC-stimulation of spinal fusion has proven effective in increasing fusion rates in younger and "high risk" patients, but little information exist on the effect in older patients. Methods. A randomized clinical trial comprising 5 orthopedic centers. The study included a total of 107 patients randomized to uninstrumented posterolateral lumbar spinal fusion with or without DC-stimulation. Fusion rate was assessed at 2 year follow-up using thin slice CT. Functional outcome was assessed using Dallas Pain Questionnaire and Low Back Pain Rating Scale pain index. Results. Available follow-up after 2 years was 89% (84 of 95 patients). Fusion rates were surprisingly low. DC-stimulation had no effect on fusion rate: 35% versus 36% in controls. Other factors associated with low fusion rates were female gender (32% vs. 42% in males, P = 0.050) and smoking (21% vs. 42% in nonsmokers, P = 0.079). Patients who achieved a solid fusion as determined by CT had superior functional outcome and pain scores at their latest follow-up. Conclusion. Thin slice CT revealed very high nonunion rates after uninstrumented spinal fusion in older patients. DC-stimulation was not effective in increasing fusion rates in this patient population. The achievement of a solid fusion was associated with superior functional outcome.