O2090: Risk Factors for Failure to Achieve SRS-22 MCID After Posterior Spinal Instrumentation and Fusion in Idiopathic Scoliosis

Background: There is a growing body of literature assessing the role of preoperative patient-reported outcome measures in predicting postoperative achievement of the minimal clinically important difference (MCID). Though this has been done for SRS-22 scores, to the best of our knowledge, there are no studies that identify risk factors for failure to achieve SRS-22 MCID. Our purpose is to identify risk factors for failure to achieve SRS-22 MCID after posterior spinal instrumentation and fusion (PSIF) in patients with idiopathic scoliosis.

Methods: SRS-22 forms were provided to all idiopathic scoliosis patients scheduled to undergo posterior spinal instrumentation and fusion from 2012-2021. Forms were provided again one year postoperatively and MCID was calculated using distribution-based methods. Binary logistic regression was used to determine the effect of this individual patient data on failure to achieve SRS-22 MCID.

Results: 348 patients met criteria. Of those, 314 had pre- and post-operative SRS-22 scores at 1 year (90% follow up). Of the 314 included in this analysis, 83% were female with average age of 14.9 ± 1.9. 289 (92%) had AIS and 25 (8%) had juvenile scoliosis. MCID was found to be 0.32. 164 (52%) of patients achieved MCID. Those who failed to achieve MCID had significantly lower preoperative SRS-22 scores (3.43 ± 0.65 vs. 3.75 ± 0.62, p< 0.001), the group was composed of significantly fewer female patients (n=115, 77% vs. n=144, 88%, p=0.02), and underwent fewer revision surgeries (n=9, 6% vs. n=21, 13%). There were no differences in age, cobb angle, kyphosis, number of levels fused, Lenke class, or lumbar modifier between groups. Male sex (OR: 2.04, 95% CI: 1.05-3.65, p=0.03, probability 67%), higher preoperative SRS-22 scores (OR: 3.63, 95% CI: 2.23-5.90, p< 0.001), and lower preoperative Cobb angle (OR: 0.97, 95% CI: 0.95-0.98, p=0.01) were all significant risk factors for failure to achieve SRS-22 MCID out to 1 year postoperatively (Table). The likelihood ratio for failure to achieve MCID with preoperative SRS-22 scores above 3.5 was 5.64 (p=0.02) and the likelihood ratio for failure to achieve MCID with preoperative Cobb angles below 63° was 5.54 (p=0.02).

Conclusion: This is the first study to date that identifies risk factors for failure to achieve SRS-22 MCID following posterior spinal instrumentation and fusion. Male sex, preoperative SRS-22 scores above 3.5, and Cobb angles below 63° were all identified as risk factors for failure to achieve MCID. Additionally, the probability of failure to achieve MCID is 67% in males and 31% in females. Preoperative SRS-22 scores have been shown to be acceptable predictors for whether patients will achieve MCID after PSIF, and, with this data, surgeons can better counsel their patients with SRS-22 scores when discussing surgical intervention.