Direct Current Electrical Stimulation to Enhance Arthrodesis: Optimal Stimulation Parameters in a Rodent Model of Lumbar Intertransverse Fusion

Introduction: Despite existing adjuncts, pseudoarthrosis remains a significant problem in spine fusion surgery, leading to disease recurrence and revision surgeries. Finding novel strategies that enhance bony fusion is a major challenge. The study objective was to determine the optimal dose of direct current stimulation for maximal arthrodesis in a rat model of intertransverse fusion.

Methods: Three groups of Sprague-Dawley rats underwent L4-L5 posterolateral intertransverse fusion with iliac autograft packed in titanium electrodes: 1) Sham, without stimulation, 2) 20µA stimulation, and 3) 40µA stimulation. Animals were sacrificed for micro computed-tomography (micro-CT) of the fusion mass. For analysis, each side was treated as an independent sample. Micro-CT parameters of bone volume, total tissue volume, and bone volume to total tissue volume ratio were compared using ANOVA with post-hoc Tukey’s multiple comparisons.

Results: 21 animals underwent the procedure, 2 died intraoperatively, 1 had postoperative complication, and 2 had a device malfunction. Final analysis included 5 animals in sham, 6 in 20µA, and 5 in 40µA groups. There was no statistically significant difference in bone volume among the sham, 20µA and 40µA stimulation groups (49.6 ±22.7, 50.5 ±11.9, and 45.9 ±10.3 respectively, p=0.78). There was no statistically significant difference in total tissue volume (274.6 ±109.5, 257.8 ±76.6, and 250.6 ±56.6, p=0.80). Bone volume to total tissue volume ratio was 0.177 ±0.015, 0.199 ±0.017, and 0.184 ±0.024 in the sham, 20µA and 40µA stimulation groups (p=0.038). Pairwise comparisons revealed bone volume to total volume ratio for the 20µA group was significantly higher than sham (p=0.011) and higher but not statistically significant compared to 40µA group (p=0.069).

Conclusion : 20µA direct current stimulation performs better than sham, and appears to perform better than 40µA in terms of bone volume to total tissue volume ratio. This is consistent with previous studies which noted an upper limit on direct current for promoting osteogenesis.