The patient acceptable symptom state for the Oswestry Disability Index following single-level lumbar fusion for degenerative spondylolisthesis

Abstract

The patient acceptable symptom state (PASS) is a valuable tool for interpreting patient-reported outcomes. Previous studies have attempted to define the PASS in a heterogenous cohort with various lumbar spinal disorders and surgical procedures. We aimed to determine the PASS threshold for the Oswestry Disability Index (ODI) specifically for patients undergoing lumbar fusion for spondylolisthesis-associated functional disability. Retrospective review of prospectively collected registry data. There were 692 patients who underwent primary single-level minimally invasive transforaminal lumbar interbody fusion for degenerative spondylolisthesis between 2006 and 2014. The ODI was collected pre-operatively, at 6 months and 2 years postoperatively. An anchor question was adapted from the NASS questionnaire, "How would you rate the overall results of your treatment?" while a validation question was taken from the same questionnaire, "Has the surgery for your back condition met your expectations so far?" Responses to the anchor question were used to determine whether a PASS was achieved. Receiver operating characteristics curve analysis was performed to assess the ability of the ODI to discriminate between an acceptable/unacceptable symptom state as well as to define PASS thresholds. Sensitivity analyses were performed for different follow-up periods (6 months, 2 years), subgroups (by age, gender, BMI, and comorbidity burden), baseline ODI tertiles, and an alternate definition of PASS. In total, 529 of 692 (76%) patients completed 2-year follow-up, of which, 89% considered their symptom state to be acceptable. Areas under the curve (AUC) ranged from 0.81 to 0.90 for all receiver operating characteristics analyses, indicating that the ODI had an excellent discriminative ability. The PASS threshold was ≤18.09 at 6 months (AUC 0.81, sensitivity 77%, specificity 72%) and ≤15.27 at 2 years (AUC 0.86, sensitivity 79%, specificity 79%). These thresholds proved to be robust in the sensitivity analyses, showing minimal variation across different patient subgroups and baseline score tertiles. Patients with an ODI of ≤15.27 can be considered to have achieved a PASS after lumbar fusion for degenerative spondylolisthesis. These findings will help surgeons to contextualize a patient's functional recovery after lumbar spine surgery and enable researchers to define clinically relevant benchmarks when designing trials utilizing the ODI.