- BACKGROUND: The diagnosis and management of acquired lumbar spinal stenosis (ALSS) is an area of growing interest with an increase in its prevalence and detection in the older population. OBJECTIVES: To investigate the diagnostic accuracy of a modified extension test (MExT) for diagnosing ALSS in subjects aged fifty or over. METHODS: Symptomatic response of the bi-component MExT was evaluated and compared against magnetic resonance imaging (MRI) findings in 30 subjects. Estimates of sensitivity, specificity, likelihood ratios (LRs) and post-test probabilities were all calculated, and the capability of the test to discriminate between grade and location of stenosis was also appraised. RESULTS: MExT sensitivity was high at 92% (95% confidence intervals (CI), 72-99%) leading to a significant negative likelihood ratio at -LR 0.2 (95% CI, 0.03-1.36); conversely, specificity was low at 40% (95% CI, 7-82%) with only a small positive likelihood ratio of +LR 1.53 (95% CI, 0.74-3.16). All correlations between the MExT and concurrent grade, or location of stenosis appeared weak and insignificant. CONCLUSIONS: The MExT was found to demonstrate acceptable criterion validity in relation to ruling-out a diagnosis when a negative result was observed; however, further validation appears warranted.