Does the L4 nerve root extend during femoral nerve stretch test? A cadaveric study of four cases analyzing the extension rates of the lumbar nerve root.

BACKGROUND

Lumbar radicular pain is a common symptom of lumbar disc herniation and spinal canal stenosis, and L4 nerve root impingement is difficult to diagnose. This study aimed to elucidate the extension rate of L4 nerve roots in Thiel-embalmed specimens using both classic and new femoral nerve stretch test (FNST), as well as straight leg raising test (SLRT). Additionally, the extension rate of the L2 and L3 nerve roots and L5 and S1 roots were determined using FNST (both classic and new) and SLRT, respectively.

METHODS

Four Thiel-embalmed specimens were used. The extension rate data of the nerve root were obtained using a displacement sensor under the following conditions: knee joint flexed to 0°/45°/90°/135° with either the hip extension/flexion of 0° (classic FNST) or extension of 15° (new FNST); and hip joint flexed to 0°/30°/60°/90° with the knee flexion of 0° (SLRT).

RESULTS

Case A had almost no L4 nerve root lengthening at 45° and 90° knee joint flexion; however, at 135° of knee flexion, the nerve root was lengthened. In Case B, the L4 nerve root was hardly extended by the classic FNST, but it was extended at 135° of knee flexion and 15° of hip extension. In Case C, the L4 nerve root showed little change by classic FNST and it was shortened by new FNST, whereas, it was extended by SLRT. Case D showed a shortened L4 nerve root at 135° of knee flexion in classic FNST and at 0°/45°/90°/135° of knee flexion and 15° of hip extension. Further, no root shortening was observed for L2 and L3 nerve roots according to both classic and new FNST. In contrast, the extension of L2 and L3 nerve root with the new FNST was high. In all cases, nerve roots were lengthened by the SLRT. Further, as the hip flexion angle increased, the rate of nerve elongation also increased.

CONCLUSIONS

It was shown that in patients in whom L4 nerve root was extended by FNST, it was shortened by SLRT. The opposite pattern was also observed. Further, it is believed that FNST and SLRT are reliable tests for L2 and L3 radiculopathy and L5 and S1 radiculopathy, respectively, and that more tension on the femoral and sciatic nerves is better. Furthermore, we recommend that FNST should be performed with 15° hip extension and 135° knee flexion to improve the diagnostic accuracy.