Predictors of Early Clinically Significant Improvement Among Lumbar Fusion Patients: A Multivariate Analysis

Abstract

Background Minimum clinically important difference (MCID) achievement is a more patient-centric metric that evaluates the perception of a significant improvement in symptoms. However, few studies have investigated the factors associated with achieving this threshold earlier rather than later in a patient’s postoperative course of recovery. Objective To determine the baseline factors associated with achievement of an early MCID among patients who underwent a transforaminal, anterior, or lateral lumbar interbody fusion (TLIF, ALIF, LLIF). Methods A single-surgeon database was retrospectively reviewed for patients undergoing primary or revision, 1- or 2-level MIS TLIF, ALIF, or LLIF. Patient reported outcome measurements (PROMs) were recorded using Visual Analogue Scale (VAS) back/leg, Oswestry Disability Index (ODI), and 12-Item Short Form (SF-12) Physical Composite Score (PCS). Early achievement of MCID was defined as having a difference in pre- and postoperative PROM scores that were equal to or greater than the established values at the 6-week or 12-week timepoint. Using simple logistic regression, a cutoff of p≤0.025 was used to determine covariates correlating with early MCID achievement. Using multiple logistic regression, we then completed a post-regression analysis to assess the influence of covariates on timing of MCID achievement across VAS, ODI, and SF-12 PROMs. Results 405 patients were included, with a mean age of 53.8 years and the majority being male (64.2%) and non-obese (50.5%). Mean preoperative VAS back, VAS leg, and ODI scores were 6.4 ± 2.4, 5.6 ± 2.8, and 41.5 ± 16.8, respectively (Table 1). Majority of patients presented with degenerative spondylolisthesis (56.5%), followed by isthmic spondylolisthesis (30.5%), recurrent herniated nucleus pulposus (24.6%), and degenerative scoliosis (9.6%). Majority of procedures were primary (89.0%) in nature, with 42 cases (11.0%) being revision surgeries. Most patients received MIS TLIF (75.1%), while 16.5% received LLIF, and 8.4% received ALIF. 374 1-level procedures (92.3%) and 31 2-level procedures (7.7%) were performed. Mean operative time, blood loss, and postoperative stay was 135.1 minutes, 53.0 milliliters, and 32.7 hours, respectively (Table 2). Most patients demonstrated MCID achievement from 12-weeks to 1-year for back pain. For leg pain, disability, and physical function, majority of patients demonstrated MCID achievement at 6-months and 1-year. By 1-year following fusion and for overall, a majority of subjects (>50%) attained MCID across VAS/ODI/SF-12 PROMs (Table 3). At 6-weeks, patients with higher preoperative VAS and ODI scores demonstrated greater odds of MCID achievement (p<0.001, all). Patients with higher preoperative SF-12 PCS experienced lower odds of SF-12 PCS achievement at 6-weeks (p<0.001). Workers’ Compensation (WC) status was associated with decreased odds of MCID achievement at this timepoint across pain and disability PROMs studied (p≤0.003, all). For VAS back, degenerative spondylolisthesis increased odds for achievement (p=0.023), while for ODI, revision procedures were associated with a decreased odds for 6-week MCID achievement (p=0.034). Arthritis decreased odds of 6-week MCID achievement for SF-12 PCS (p=0.007), while history of myocardial infarction (MI) increased odds of achievement for VAS leg (p=0.034) (Table 4). For 12-weeks, MCID achievement for all PROMs was again more likely among patients with higher preoperative scores (p<0.001, all), with WC associated with decreased odds of achievement (p<0.001, all). In addition, ALIF surgery was associated with decreased odds of 12-week MCID achievement for VAS leg and ODI (p≤0.037, both), while diabetic status was associated with increased odds of attainment for SF-12 PCS (p=0.037) (Table 5). Conclusion Early MCID achievement for back pain, leg pain, disability, and physical function were more likely among patients with worse preoperative PROM values. This suggests that patients who benefit the earliest from lumbar fusion may be limited to individuals who report more severe preoperative symptoms. Furthermore, WC claimants, patients presenting for revision surgery, and those receiving ALIF (vs MIS TLIF/LLIF) are likely to experience delays in clinically meaningful recovery of pain and/or disability following lumbar fusion.