Value of the bell test and the hyperextension test for diagnosis in sciatica associated with disc herniation: comparison with Lasègue's sign and the crossed Lasègue's sign

Abstract

Objectives: To evaluate the reliability, sensitivity, specificity and positive (PPV) and negative (NPV) predictive values for the diagnosis of sciatica associated with disc herniation of the bell test (BT) and the hyperextension test (HT).

Methods: According to magnetic resonance imaging, computed tomography scanning or myelography findings, patients were classified as having sciatica associated with disc herniation (group A) or sciatica without disc herniation or sciatica of other mechanical origin (group B). Four clinical manoeuvres [bell test (BT), hyperextension test (HT), Lasègue's sign (LS) and the crossed Lasègue's sign (CL)] were tested by three investigators. Intra- and interobserver reliabilities were calculated using the kappa correlation coefficient or the intraclass correlation coefficient (ICC). The sensitivity, specificity, PPV and NPV of the four manoeuvres were calculated. Stepwise logistic regression analysis was performed to determine the best set of variables predicting sciatica caused by disc herniation.

Results: Seventy-eight patients (43 in group A, 35 in group B; 33 males) with a mean age of 50+/-16 yr were included. Interobserver reliabilities ranged from 0.58 to 0.64 for the BT, 0.35 to 0.50 for the HT, 0.27 to 0.47 for LS and 0.43 to 0.72 for CL. LS had the best sensitivity (0.77-0.83) and CL the best specificity (0.74-0.89), while PPV and NPV were equivalent for the four manoeuvres (0.55-0.75 for PPV and 0.45-0.59 for NPV). The best PPV was observed for the association of HT with CL (0.67-0.85). Stepwise logistic regression analysis did not allow us to propose a set of variables predicting sciatica caused by disc herniation.

Conclusion: This study suggests that clinical values of the BT and HT are of interest, and are similar to those of LS and CL.