Radiographic predictors of reaching minimal clinically important difference following lumbar fusion surgery in patients with degenerative lumbar spondylolisthesis

Purpose The present study aimed to (1) compare sagittal alignment between patients with degenerative lumbar spondylolisthesis (DLS) who reached or missed the minimal clinically important difference (MCID) for clinical outcomes following lumbar fusion surgery (LFS) and (2) identify radiographic predictors associated with MCID achievement in DLS patients. Methods A total of 91 single-level DLS patients who underwent LFS and had a minimum of 1-year follow-up were enrolled in this study. The assessed radiographic parameters included thoracic kyphosis, lumbar lordosis (LL), segmental lumbar lordosis (SLL), slip percentage, sacral slope (SS), pelvic tilt (PT), pelvic incidence (PI), and sagittal vertical axis. Changes in radiographic parameters were determined by subtracting the preoperative value from the final follow-up measurement. Clinical outcomes were assessed using the Oswestry Disability Index (ODI) and the visual analog scale (VAS) for both back and leg pain. MCID values were set at 10 points for ODI, 2.1 points for VAS back pain, and 2.8 points for VAS leg pain. Patients were assigned to the reached MCID (rMCID) and missed MCID (mMCID) groups based on the postoperative (post-op) recovery of clinical outcomes. Results At the last follow-up, 68.1% (62/91), 72.5% (66/91), and 76.9% (70/91) of patients reached MCID for ODI, VAS back pain, and VAS leg pain, respectively. Concerning ODI, the rMCID group exhibited higher post-op LL (47.93° vs. 42.95°, P = 0.044), higher post-op SLL (17.08° vs. 14.41°, P = 0.032), higher post-op SS (34.46° vs. 30.63°, P = 0.027), higher ∆LL (5.90° vs. 2.44°, P = 0.017), higher ∆SLL (4.63° vs. − 1.03°, P < 0.001), higher ∆SS (4.76° vs. 1.23°, P = 0.002), lower post-op PT/PI (36.95% vs. 42.01%, P = 0.049), lower ∆PT (− 3.71° vs. 1.05°, P < 0.001), lower ∆PT/PI (− 7.45% vs. 1.97%, P < 0.001), and lower ∆PI-LL (− 5.43° vs. − 3.71°, P = 0.011) than the mMCID group. Regarding VAS back pain, the rMCID group showed higher post-op SLL (17.06° vs. 14.05°, P = 0.021), higher post-op SS (34.34° vs. 30.33°, P = 0.027), higher ∆SLL (3.93° vs. − 0.09°, P < 0.001), and lower ∆PT (− 2.91° vs. − 0.30°, P = 0.039) than the mMCID group. For VAS leg pain, higher ∆SLL (3.55° vs. 0.41°, P = 0.003) was observed in the rMCID group than in the mMCID group. Multivariate logistic regression analysis revealed that higher ∆SLL, higher ∆SS, and higher post-op SS were independent predictors for the achievement of MCID in patients with DLS. Conclusion DLS patients who reached MCID following LFS demonstrated improved post-op spinopelvic alignment. Higher ∆SLL, higher ∆SS, and higher post-op SS were the critical parameters associated with MCID achievement in patients with DLS.