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Extending the straight leg raise test for improved clinical evaluation of sciatica: The IAMMM story

BACKGROUND: The straight leg raise test (SLR) is one of the most utilized and studied physical tests in patients with low back pain (LBP) for the detection of lumbar disc herniation (LDH), showing high sensitivity and heterogeneous or low specificity. The high incidence of asymptomatic ‘pathologic’ findings in the magnetic resonance imaging (MRI) scans may cause verification bias to these results. Based on in-depth knowledge from previous studies on phenomena occurring during the SLR, we were able to add location-specific structural differentiation movements to the traditional SLR for it to better differentiate neural symptoms from musculoskeletal. The idea was presented in the IAMMM conferences for expert opinions on both reference standard and methodology in order to improve our study. METHODS: 40 subjects comprised the study population, 20 in sciatic group and 20 in control group. The study controller allocated the patients to these groups. The ESLR was performed ‘blinded’ to the subjects and judged positive/negative. For the reliability part of the study, the IAMMM protocol for reliability studies was followed. Cohen’s Kappa was calculated by cross-tabulating the ESLR results of blinded examiners. The ESLR results were also compared to the group allocation. After the blinded ESLR testing, each subject’s lumbar MRI was evaluated. The MRIs were analyzed independently by 2 senior radiologists and a spine specialist clinician. Then also the ESLR and MRI results were cross-tabulated. To obtain the odds ratio (OR) with positive ESLR or SLR results for LDH or nerve root compression (NC), a binary logistic regression analysis with subjects’ age, gender, height and weight was performed. ESLR’s validity was assessed by combination of interrater agreement and percentage prevalence of both LDH and NC. RESULTS: The extended straight leg raise test (ESLR) showed almost perfect interrater reliability between examiners and ability to detect sciatic patients: Cohen’s Kappa was 0.85 between blinded examiners, and 0.90 and 0.95 when compared to group allocation. In the MRI scans, 85% of sciatic (ESLR+) patients had LDH and 75% NC in the MRI. Not surprisingly, MRI showed a very high incidence of ‘false-positive’ findings with the ESLR negative group. The ESLR showed 0.85 sensitivity and 0.45 specificity for LDH and 0.75 sensitivity and 0.50 specificity for NC. A positive result in the ESLR was found to be highly predictive for both LDH and NC: the OR was 8.0 (p=0.028) and 5.6 (p=0.041), respectively. CONCLUSION: The ESLR showed high repeatability, reliability and validity in detecting neural symptoms and pathology seen in the MRI when judged positive. The results have been published in two separate publications In BMC musculoskeletal disorders. The IAMMM community helped in designing the study design enormously.

SLR, Sciatica, low back pain, MR, Spinal cord, nerve root

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