The effect of local steroid application on bony fusion in a rat posterolateral spinal arthrodesis model

INTRODUCTION: Local steroid administration during anterior cervical spine surgery has been shown to improve postoperative dysphagia. However, concerns over potential complications remain. This study aims to evaluate the effect of local steroid administration on bone regeneration and spine fusion in a preclinical model, as well as the impact on osteogenic differentiation of human bone marrow‐derived mesenchymal stem cells (hBM‐MSCs) in a 3D culture system. MATERIALS AND METHODS: Forty‐five rats underwent bilateral L4‐L5 posterolateral lumbar fusion (PLF) utilizing local delivery of low‐dose recombinant human bone morphogenetic protein‐2 (rhBMP‐2; 0.5 μg/implant). Rats were divided into three groups: no steroid (control), low dose (0.5 mg/kg), and high dose (2.5 mg/kg) of triamcinolone. Bone growth and fusion were assessed using radiography, blinded manual palpation, and micro‐CT analysis and were visualized by histology. The impact of triamcinolone exposure on osteogenic differentiation of hBM‐MSCs was evaluated by gene expression analysis, alkaline phosphatase activity assay, and alizarin red staining. RESULTS: No significant differences in fusion scores or rates were seen in the low‐ or high‐dose steroid treatment groups relative to untreated controls. Quantification of new bone formation via micro‐CT imaging revealed no significant between‐group differences in the volume of newly regenerated bone. Triamcinolone also had no negative impact on pro‐osteogenic gene transcript levels, and ALP activity was enhanced in the presence of triamcinolone. Mineral deposition appeared comparable in cultures grown with and without triamcinolone. CONCLUSIONS: Local steroid application does not seem to inhibit rhBMP‐2‐mediated spine fusion in rats, though our study may not be adequately powered to detect differences in fusion as measured by manual palpation or bone volume as measured by micro‐CT. These findings suggest that local triamcinolone may not increase pseudarthrosis in spine fusion procedures. Further large animal and clinical studies to verify its safety and efficacy are warranted.