THE USE OF THE PERCENTAGE CHANGE IN OSWESTRY DISABILITY INDEX SCORE AS AN OUTCOME MEASURE IN LUMBAR SPINAL SURGERY

Study Design. A retrospective analysis of the change in the Oswestry Low Back Pain Disability Questionnaire in a heterogeneous group of 144 operatively managed patients was undertaken to examine the change in disability index as an outcome measure. Objectives. To establish the percent change in disability index as an outcome measure able to identify risk factors for poor results in lumbar spinal surgery. Methods. Epidemiologic, diagnostic, and surgical variables were examined as risk factors using step-wise multiple linear regression analysis at both follow-up times (6 months and 2 years), with percent change in disability index used as the outcome measure. Results. At 6-months follow-up, previous surgery, female gender, workers' compensation, a lower initial disability index score, increasing age, and spinal fusion alone as an operative procedure were independently and significantly negatively correlated with outcome. Further analysis revealed that for patients with spinal canal stenosis, the magnitude of the initial disability index did not correlate with outcome, whereas patients with low back pain or a prolapsed intervertebral disc fared better if they had high initial disability scores. Data at 2-years follow-up were less adequate. However, previous surgery on the spine and low initial disability score were significant negative predictors of outcome at 6-month and 2-year follow-up. Conclusions. The findings indicate that the absolute value and change in these scores after surgery vary from patient to patient, but that their percentage change is likely to be the best marker of outcome when such subjective scoring systems are used.