Measuring the clinical validity of the nerve root sedimentation sign in magnetic resonance imaging for the diagnosis of lumbar spinal stenosis

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Background: Lumbar spinal stenosis is a common degenerative disorder of the spine in elderly patients that can be effectively treated with decompression surgery. Patient history, clinical examination and imaging tests are used for diagnosis. Radiological findings in the diagnostic work-up of the patients do not always correlate well with clinical symptoms, and guidance about when to proceed to surgery is inconsistent. The recently described nerve root sedimentation sign in magnetic resonance scans is proposed to detect clinically relevant stenosis. It has been shown to discriminate well between selected patients with and without lumbar spinal stenosis but the performance of this new test, when used in a broad patient population, is not yet known. There is no accepted reference standard for the diagnosis of lumbar spinal stenosis. Methods/Design: The aim of this study is to assess the clinical validity of the sedimentation sign by evaluating its association with patient outcomes in patients with suspected lumbar spinal stenosis, and to define the role of the sedimentation sign in clinical practice. It is a single-centre retrospective chart review of patients referred to an orthopaedic spine unit for the investigation of suspected lumbar spinal stenosis. The sedimentation sign will be cross-classified with decisions for surgery based on existing tests and patient outcomes in 24 month follow-up examinations. The results will be used to estimate: i) how well the sedimentation sign can distinguish between patients that do or do not benefit from surgery, and ii) the concordance between the sedimentation sign and existing tests to explore its possible value as a triage test. In addition, the agreement in sedimentation sign ratings of two observers will be measured. Discussion: In the absence of a reference standard, the study design presented here will provide data to estimate the potential impact of the sedimentation sign on patient outcomes. The observed proportion of discordant test results will help inform the design of future randomised trials of the sedimentation sign.