Abstract Background Continuous injection of local anesthetics by using surgical wound catheters for postoperative pain relief has gained acceptance in recent years. However, whether this method can be alternatively used instead of systemic opioids in different surgical procedures has not yet been elucidated. Objectives The aim was to investigate the effect of continuous injection of bupivacaine through a catheter inside the surgical wound on reducing the postoperative pain of lumbar spine fusion surgeries. Methods In this clinical trial, 31 patients undergoing non-traumatic lumbar spine stabilization surgery were randomly assigned to receive (n = 15) or do not receive (n = 16) bupivacaine through a catheter inside the surgical wound, postoperatively. Pain intensity (NRS), dose of required morphine, and drug-related complications within 24 hours of intervention were assessed and compared by the Mann-Whitney and independent t-test. Results Mean pain intensity was significantly lower in the case group over the first postoperative hour in the recovery room (p < 0.001), which continued for the first 2 hours after entering the ward. The mean morphine intake was lower in the bupivacaine group during the first postoperative 24 hours (16 ± 0.88 vs. 7.33 ± 0.93 mg, p < 0.001). The two groups were not significantly different regarding drug-related complications. Conclusion Continuous intra-incisional infusion of bupivacaine helped better pain reduction during the early postoperative hours while sparing morphine consumption in the first postoperative day.