Impact of movement sequencing on sciatic and tibial nerve strain and excursion during the straight leg raise test in embalmed cadavers.

STUDY DESIGN: Laboratory study, repeated-measures design.

OBJECTIVES: To quantify differences in sciatic and tibial nerve biomechanics (strain and excursion) during common variations of the straight leg raise (SLR) test.

BACKGROUND: Hip flexion and ankle dorsiflexion are the primary movement components of the SLR. It has been suggested that the nervous system is loaded differently when ankle dorsiflexion is added before or after hip flexion. There are, however, no data to either support or refute this suggestion.

METHODS: Strain and excursion in the sciatic and tibial nerve were measured in the hip, knee, and ankle regions during 2 movement sequences for the SLR test in 10 embalmed cadavers. The proximal-to-distal sequence consisted of hip flexion followed by ankle dorsiflexion; the distal-to-proximal sequence consisted of ankle dorsiflexion followed by hip flexion.

RESULTS: In the SLR end position, strain and excursion were comparable for both sequences for the sciatic and tibial nerve at the knee (P>.24). Strain in the tibial nerve at the ankle was greater with the proximal-to-distal sequence (P = .008), but the actual difference was small (0.8%). The pattern of strain increase and nerve excursion varied between sequences (P≤.009), with nerve strain increasing earlier and being maintained longer in regions closest to the joint that was moved first in the movement sequence.

CONCLUSION: Varying the movement sequence does not substantially impact excursion and strain in the end position of the SLR. Therefore, if neurodynamic test sequencing is useful in the differential diagnosis of neuropathies, it is not likely due to differences in strain in the end position of testing.