P13. Effect of intraoperative steroid treatment on spinal fusion capacity in rat spinal arthrodesis model

Abstract

BACKGROUND CONTEXT Local steroid administration during cervical spine surgery has been shown to improve postoperative dysphagia. Due to concerns for complications like pseudarthrosis, however, widespread acceptance of intraoperative local steroid administration has not been adopted for such procedures. Previous literature in a rabbit posterolateral lumbar fusion (PLF) model demonstrated inhibition of graft incorporation and consequent pseudarthrosis following postoperative intramuscular dexamethasone administration. Nevertheless, the potential complications of intraoperative local steroid administration on bone healing and spine fusion have yet to be directly investigated. PURPOSE This study aims to evaluate the effect of intraoperative local steroid administration on spinal fusion capacity in a rat model. STUDY DESIGN/SETTING Preclinical. PATIENT SAMPLE Female Sprague-Dawley rats, ages 12-16 weeks. OUTCOME MEASURES The outcome measures for this pre-clinical study are radiography, manual palpation fusion scoring, microCT and histological sectioning. METHODS Forty-five female Sprague-Dawley rats underwent bilateral posterolateral lumbar spinal fusion at L4-L5 using 0.5 mg recombinant human BMP-2 (rhBMP-2) delivered on an absorbable collagen sponge (INFUSE™; 1 mg rhBMP-2 per animal). Either no steroid (vehicle control), 0.5mg triamcinolone (low-dose steroid), or 2.5mg triamcinolone (high-dose) was added directly to the implant. (The sub-therapeutic 1 mg dose of rhBMP-2 per animal was chosen in order to avoid saturation of the fusion response and capture any potential inhibitory effect that might exist. Rats were radiographed alive at four weeks, and after euthanasia at eight weeks post-operative. Spines were then harvested and underwent manual palpation-based fusion scoring, microCT imaging, and histological sectioning. Fusion scoring was performed by three blinded observers using an established scoring system whereby 0 = no bridging bone, 1 = unilateral bridging bone, and 2 = bilateral bridging bone, with an average score of >1 considered fused. Mean fusion scores were compared using one-way ANOVA. Fusion rates were compared using Fischer's exact test. RESULTS The mean fusion scores of the control, low-dose steroid, and high-dose steroid groups were 0.61 (SD=0.59), 1.09 (SD=0.81), and 0.58 (SD=0.58), respectively. Fusion rates of the three groups were 38%, 57%, and 33%, respectively. At p>0.05, neither fusion scores nor rates were significantly different among groups (Figure 1). Data processing from MicroCT images to quantify the volume of new bone growth in fusion masses is in progress, as is histological analysis of fusion beds. CONCLUSIONS The results demonstrate that steroid delivered intraoperatively within the INFUSE™ implant during spinal fusion surgery had no adverse impact on fusion capacity in the clinically relevant rat model. Considering that intraoperative steroid use during human cervical spine surgery has been shown to minimize dysphagia, these results open the door for higher-order investigations into the potential for similar steroid use in human spine surgery patients. FDA DEVICE/DRUG STATUS Unavailable from authors at time of publication.