Measuring outcomes in cervical spine surgery: think twice before using the SF-36

Abstract

Study design: Psychometric evaluation of a patient-reported scale for measuring health status.

Objective: To evaluate the ability of the Medical Outcomes Study 36-item Short-Form Health Survey (SF-36) to satisfy the clinical and research needs of cervical spine surgeons.

Summary of background data: Although the SF-36 has been shown to be a reliable measure in the general population, the fundamental assumptions underpinning the generation of scale and summary scores must be rigorously tested before it can be considered a suitable measure for use in specific populations.

Methods: Data from 147 patients undergoing cervical spine surgery were examined. We examined the assumptions underpinning the generation of SF-36 scale and summary measures, targeting to the sample, and the scale's ability to detect change. RESULTS.: Evidence supports the reporting of SF-36 scale scores, but not SF-36 summary measures. Three of the 8 scales had notable floor/ceiling effects indicating poor targeting. Responsiveness was good for all scales except those with high floor/ceiling effects.

Conclusions: The SF-36 fails to satisfy the measurement needs of cervical spine surgeons. Scale scores are valid, but floor and ceiling effects mean that changes in quality of life associated with surgery are underestimated. SF-36 summary scores are not valid. Neurosurgeons need better and more sophisticated scales to measure their outcomes.