Predictors of time to achieve clinically significant improvements following lateral lumbar interbody fusion

As lateral lumbar interbody fusions (LLIF) are increasingly performed, our understanding of postoperative clinical trajectories is important in informing preoperative patient expectations. While minimum clinically important difference (MCID) rates are widely utilized in spine surgery literature, there is less published on how long it takes for patients to achieve MCID following LLIF.

To evaluate the length of time it takes for patients to report MCID achievement for back pain, leg pain, disability, and physical function and evaluate predictors of time to achieve MCID.

Patients undergoing elective LLIF by the senior author with baseline and postoperative patient-reported outcomes (PROs) recorded were retrospectively identified. Data on potential predictors of time to MCID achievement were gathered including demographics, comorbidities, diagnostic information, and baseline PROs. MCID achievement rates for Oswestry Disability Index (ODI), Visual Analog Scale-Back (VAS-Back), VAS-Leg, and Patient-Reported Outcome Measurement Information System-Physical Function (PROMIS-PF) were calculated at six-, twelve, 6 month- 1 year- and 2-year postoperative timepoints. A Kaplan-Meier survival analysis was conducted to determine the proportion of patients achieving MCID at each time point. A multivariate Cox regression determined predictors of time to MCID achievement.

One hundred-five patients were included in the analysis. The mean time to achieve MCID for PROMIS-PF was 44.7 weeks, for VAS-Back was 38.5 weeks, for VAS-Leg was 36.7 weeks, and for ODI was 38.3 weeks. Worse baseline VAS-Back significantly predicted earlier MCID achievement for VAS-Back (HR: 1.55), while diabetes was predictive of later MCID achievement (HR: 0.21). Higher body mass index and worse preoperative ODI predicted earlier MCID achievement for ODI (HR: 1.04-1.08), and higher VAS-Leg score and two-level fusion were predictive of later MCID achievement for ODI, (HR:0.26-0.81). Worse preoperative VAS-Leg, isthmic spondylolisthesis, and three-level fusion were predictors of earlier achievement of MCID for VAS-Leg (HR: 1.27-6.47). Herniated nucleus pulposus and foraminal stenosis were early predictors (HR: 2.92-3.23) and workers' compensation was a late predictor of MCID attainment for PROMIS-PF (HR: 0.13).

Select demographic variables, comorbidities, spinal pathology, and preoperative PROs influenced the time it took for patients to report clinically significant improvements in pain, disability, and physical function scores. These findings can be used to prognosticate outcomes for patients undergoing LLIF and inform patient expectations of postoperative recovery.