Reliability of the Buttock Applied Strain Test to Diagnose Radicular Pain in Patients With Low Back Pain

Abstract

Background: Low-back pain (LBP) pathophysiological conditions include nociceptive back pain, somatic referred pain, radicular pain (RP), and radiculopathy. Differential diagnosis is challenging; guidance may come from patients' thorough clinical history and physical examination and, particularly for lumbar RP, from the evaluation of subjective responses of injured lumbar nerves to a strain applied at the buttock (buttock applied strain [BUAS] test). Methods: In a sample of 395 consecutive patients with LBP, sensitivity, specificity, and prior probability (positive predictive values [PPVs] and negative predictive values [NPVs]) of the BUAS test were evaluated against 2 reference tests: the straight leg raising test (SLRT) and the painDETECT (PD) questionnaire. Multinomial logistic regression (MLR) and v 2 analyses were used to evaluate the BUAS test outcomes' dependence upon independent variables (gender, age group, pain localization, SLRT outcomes, and PD outcomes). Cohen's kappa statistic was used to assess inter-rater agreement. Results: Compared with the PD questionnaire, the BUAS test showed a sensitivity of 92%, specificity of 100%, PPV of 100%, and NPV of 82%; compared with the SLRT, the BUAS test showed a sensitivity of 82%, NPV of 82%, specificity of 40%, and PPV of 40%. Inter-rater agreement of Cohen's kappa was 0.911. Significant associations were found between BUAS test outcomes and pain localization, SLRT outcomes, and PD outcomes, but not with the predictors gender or age group. MLR showed significant congruent relationships between BUAS test and PD outcomes. Conclusion: Among patients with LBP, the BUAS test showed satisfactory sensitivity, specificity, prior probability, and inter-rater reliability; thus, it may be considered a useful adjunctive tool to diagnose RP in patients with LBP. For more generalized results, more research, in clinical settings other than pain clinics, is needed. &

Reply to the Letter “Regarding Samolsky Dekel et al. Reliability of the Buttock Applied Strain Test to Diagnose Radicular Pain in Patients With Low Back Pain”

“…." 2 The latter pressure is the closest possible condition (in agreement with the commenters) for eliciting MFP when applying the BUAS test. Thus, by the definition of a positive BUAS test result, MFP could be reasonably ruled out, since eliciting pain by mere pressure would exclude a positive BUAS test result.…”

“…The sciatic nerve that the BUAS test targets arises from the L4, L5, S1, S2, and S3 spinal roots 1 . As reported in the Neurophysiological Rationale of the BUAS Test section of our article, 2 in the presence of (whichever) injured sciatic nerve roots applying pressure onto specific points along the course of this nerve or its branches may elicit or enhance the patient’s pain. Moreover “atrophic nerve fibers distal to a persistent constriction are particularly sensitive to local pressure.” 3 …”

“…Indeed, in our practice and also in our study, SLRT has never been performed alone. As stated in the study’s Methods section, “In this study the SLRT result was considered positive if both provocative and confirmative phases were shown and for either unilateral or bilateral (ie, crossed SLRT) positive responses.” 2 Consequently, the SLRT’s reliability in the study was not affected, since it was not performed alone. In the literature, 11 overall diagnostic accuracies of neurological testing procedures in detecting lumbar radicular pain have been poor.…”

<p>Combination of Gluteal Trigger Points Dry Needling and Percutaneous Endoscopic Lumbar Discectomy for Complex Low Back-Related Leg Pain</p>

“… 8 LDH occurs mainly at the L4-5 and L5-S1 levels; upper LDH (L3-4 and above) is rare. 9 Although the overall diagnostic accuracies of neurological testing procedures in detecting lumbar radicular pain is poor 10 and a novel adjunctive tool to detect lumbar radicular pain was recently reported, 11 in this patient, the numbness on the left medial calf and abnormal findings on physical examination (decline of superficial sensation in the left medial calf, tibialis anterior myodynamia and patellar tendon reflex, and a positive result of the femoral nerve traction test) could all be attributed to compression of the spinal L4 nerve root by L3-4 protruded disc materials when combined with the imaging in lumbar MRI. However, it should be noted that the patient’s pain distribution was not in an area commonly innervated by the L4 nerve root but instead by the L5 or S1 nerve root, there was no significant herniation at the L4-5 or L5-S1 levels, and the full spinal X-ray excluded the presence of transitional vertebra.…”

Regarding Samolsky Dekel et al.’s “Reliability of the Buttock Applied Strain Test to Diagnose Radicular Pain in Patients With Low Back Pain”

“…We read with great interest the article by Samolsky Dekel et al 1 on the reliability of the buttock applied strain (BUAS) test to diagnose radicular pain in patients with low back pain. The title of this study seems nonspecific and gives a false anticipation to the readers regarding coverage of a broader spectrum of low back pain due to all lumbosacral radicular pain.…”