The NASS lumbar spine outcome assessment instrument: Large sample assessment and sub-scale identification

Background: Accurately assessing patient-reported pain and functional ability is essential to measuring quality of care. Purpose: Evaluating the instruments used in assessing quality of care is often overlooked. The North American Spine Society Lumbar Spine Outcome Assessment (NASS-LS) instrument measures patient-reported pain and function in a combined scale. We evaluated the original instrument and assessed separate pain and function subscales based on a set of the items in the original instrument. Study Design/Setting: Data were collected from seven spine clinics in the United States participating in the Spinal Surgery Consortium for Outcomes Research Project. Consenting patients were enrolled in the project and asked to complete the NASS instrument when arriving for a surgical consult. Patient Sample: Data from 811 lumbar spine patients were used. Methods: Analyses were conducted on the original instrument to determine its internal consistency and to determine the structural existence of any underlying scales. Internal consistency of the original and new scales were assessed with Cronbach's coefficient alpha. Results: The original scale was found to be a useful measure of pain and functional ability. Important subscales of pain and functional ability were also identified allowing us to report more meaningful results. Conclusion: The original instrument is useful for assessing low-back pain and function as a combined concept. The separate pain and function scales may prove useful assessing varying outcome levels and/or different decisions about subsequent follow-up care.