ASSOCIATION BETWEEN SPINOPELVIC PARAMETERS AND PATIENT-REPORTED OUTCOMES AFTER LUMBAR FUSION: A PROSPECTIVE COHORT STUDY

Abstract

Objectives: To determine whether postoperative spinopelvic parameters are associated with patient-reported disability and pain after instrumented lumbar fusion for degenerative lumbar disease, with postoperative PI–LL mismatch analysed primarily as a continuous exposure and secondarily using a prespecified 10° threshold. Methods: Adults undergoing one to three level instrumented lumbar fusion will be assessed with standardized standing radiographs including the pelvis before surgery and at the prespecified postoperative assessment. Pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), lumbar lordosis (LL), and PI–LL mismatch will be measured independently by two observers. The primary clinical outcome will be postoperative Oswestry Disability Index (ODI). Secondary outcomes will include postoperative back- and leg-pain VAS and change from baseline. Multivariable regression will assess whether postoperative PI–LL remains associated with postoperative ODI after adjustment for clinically relevant baseline factors. Results: Of 100 patients assessed, 8 were excluded (3 prior spine surgery, 2 deformity >30° Cobb angle, 2 incomplete radiographs, and 1 declined consent), leaving 92 enrolled and operated. Six patients were lost to follow-up, leaving 86 patients for the final analysis. The mean PI–LL mismatch improved from 16.8° ± 6.3° preoperatively to 7.5° ± 4.1° postoperatively (P<0.001). Lumbar lordosis increased from 38.6° ± 9.1° to 47.9° ± 7.4° (P<0.001), pelvic tilt decreased from 27.6° ± 6.0° to 19.8° ± 5.2° (P<0.001) and sacral slope increased from 27.1° ± 6.8° to 34.6° ± 5.9° (P<0.001). ODI improved from 52.3% ± 10.4% to 22.6% ± 9.8% (mean change 29.7 percentage points, P<0.001). Back-pain VAS improved from 7.2 ± 1.3 to 2.4 ± 1.1 and leg-pain VAS from 6.5 ± 1.6 to 1.9 ± 1.2 (both P<0.001). The postoperative PI–LL correlation coefficients of 0.65 with ODI and 0.58 with VAS, both P<0.001. In the threshold analysis, 55 patients were reported in the ≤10° group and 31 in the >10° group; postoperative ODI, back-pain VAS, leg-pain VAS, and satisfaction were all reported as better in the ≤10° group. Multivariable analysis reported postoperative PI–LL mismatch (β=0.62, 95% CI 0.41–0.83, P<0.001) and pelvic tilt (β=0.28, 95% CI 0.05–0.51, P=0.018) as independent predictors of postoperative ODI. Conclusions: In the cohort, postoperative improvement in lumbar lordosis and reduction in PI–LL mismatch were accompanied by improvement in ODI,pain scores and residual PI–LL mismatch was positively associated with postoperative disability. Pre-operative radiographic planning using pelvic parameters may help optimise the choice of fusion levels and lordosis restoration, reducing the risk of mechanical complications and unsatisfactory outcomes.