Normative sciatic nerve excursion during a modified straight leg raise test

Minimal data exists on how much sciatic nerve motion occurs during straight leg raise (SLR). The purpose of this study was to report preliminary normative ranges of sciatic nerve excursion using real time ultrasound during a modified SLR. The sciatic nerve was scanned in the posterior thigh in sixteen asymptomatic participants (age range 19-68 years). Nerve excursion was measured in transverse and longitudinal planes during knee extension from 90° to 0°, with the hip flexed to 30° and 60°. The ultrasound data was analysed off-line using cross correlation software. Results demonstrated that most nerves moved superficially during knee extension, a large proportion (10/16) moved laterally. Longitudinal excursion ranged from 6.4 to 14.7 mm (mean (SD) 9.92 mm (2.2)) in 30° hip flexion, and 5.1-20.2 mm (mean (SD) 12.4 mm (4.4)) in 60° hip flexion. Mean nerve excursion was significantly greater in 60° hip flexion (p = 0.02). There is a large between-subject variation in sciatic nerve excursion during this modified SLR in asymptomatic subjects. Mean nerve excursion was found to be higher with the hip pre-positioned in greater flexion, suggesting that pre-loading may not consistently reduce excursion.