The effect of duloxetine on fusion in rats undergoing posterolateral spinal fusion

Due to neuropathic lower back pain, the drug duloxetine is frequently used and is also commonly administered postoperatively following spinal fusion surgery. This study, which investigates the effects of duloxetine on spinal fusion, received approval from the Trakya University Local Ethics Committee for Animal Experiments. Forty female Sprague-Dawley rats, aged 8 weeks and weighing 180-220 grams, were obtained from the Trakya University Faculty of Medicine Animal Research Laboratory, and the study was conducted. Group 1: This control group received no duloxetine after undergoing L5-L6 posterolateral spinal fusion surgery. Group 2: This group received 30 mg/kg duloxetine mixed into their food daily, starting on the first postoperative day following L5-L6 posterolateral spinal fusion surgery. Group 3: This group received 60 mg/kg duloxetine via gavage daily, starting on the first postoperative day following L5-L6 posterolateral spinal fusion surgery. Group 4: This group received 120 mg/kg duloxetine mixed into their food daily, starting on the first postoperative day following L5-L6 posterolateral spinal fusion surgery. The groups were named Control, D30, D60, and D120, respectively (Table 1). All rats in each group underwent surgery via a posterior midline longitudinal incision. The posterolateral regions of the L5-L6 spinal segments were decorticated, and spinal fusion surgery was performed. The groups were followed up for 6 weeks postoperatively as planned. At the end of the 6 weeks, radiographs were taken under anesthesia for all rats, after which the rats were sacrificed. The spinal fusion segments were surgically removed from all rats for manual palpation scoring and histopathological examination. Statistical analysis of the manual palpation examination revealed no significant differences between the groups. Radiological studies also showed no significant differences in terms of fusion between the groups. Histological statistical analysis found that the number of inflammatory cells in the control group was significantly higher than in the D30 and D60 groups. In terms of neovascularization scores, the control group had significantly higher scores compared to the D30, D60, and D120 groups. According to our study, there is a weak indication that duloxetine, used for treating neuropathic pain in patients undergoing spinal fusion for any reason, may have a negative impact on fusion. The lack of significant differences observed in manual palpation examination, radiological studies, and histopathological assessments regarding new bone formation suggests that duloxetine does not have a clinically significant positive or negative effect on fusion. Considering the pathologist's interpretation that inflammation and repair phases in the fusion areas may have been accelerated in the drug-treated groups, resulting in reduced inflammation cells, which could explain the absence of differences in new bone formation among the groups, it may also be concluded that the drug use positively influences healing and fusion maturation. The results obtained in this study indicate that further research is needed to clarify this topic. Keywords: duloxetine, spinal fusion, neuropathic pain, rat