Introduction: Degenerative lumbar spondylolisthesis (DS) patients are treated with instrumented fusion, following EBM guidelines, and typically have excellent clinical outcomes. However, not all lumbar fusion procedures adhere to EBM guidelines, typically due to a lack of prospective data. Objective: This retrospective study compared outcomes of DS lumbar fusion patients treated according to EBM guidelines (EBM concordant) to lumbar fused patients with procedures that did not have clear EBM literature that supported this treatment, the goal being to examine the value of present EBM to guide clinical care. Methods: A total of 125 DS patients were considered EBM concordant, while 21 patients were EBM discordant. Pre- and postsurgical ODI scores were collected. Clinical outcomes were stratified into substantial clinical benefit (SCB ΔODI >10 points), minimal clinical importance benefit (MCID ΔODI ≥ 5 points), no MCID (ΔODI < 5 points), and a group that showed no change or worsening ODI. Fisher’s exact and χ2 tests for categorical variables, Student’s t-test for continuous variables, and descriptive statistics were used. Statistical tests were computed at the 95% level of confidence. Results: Analysis of 125 degenerative spondylolisthesis patients was performed comparing preoperative and postoperative (6 months) ODI scores. ODI improved by 8 points in the EBM concordant group vs. 2.1 points in the EBM discordant group (p = 0.002). Compliance with EBM guidelines was associated with an odds ratio (OR) of 2.93 for achieving MCID ([CI]: 1.12–7.58, p = 0.027). Conclusions: Patients whose lumbar fusions met EBM criteria had better self-reported outcomes at six months than those who did not meet the requirements. A greater knowledge set is needed to help further support EBM-guided patient care.