Tibial nerve dynamics during ankle dorsiflexion: Using ultrasonographic stiffness to measure excursion

Decreased nerve mobility and increased nerve stiffness have been proposed as causes of tarsal tunnel syndrome and diabetic neuropathy. The purpose of this study was to measure the stiffness of the tibial nerve (TN) at the ankle joint at positions of plantarflexion (PF) and dorsiflexion (DF) and the mobility (excursion) of the TN during dorsiflexion using shear-wave elastography ultrasonography. Twenty-one healthy adults participated in constant-velocity movements of the ankle joint from the maximum dorsiflexion angle to -20°, and the TN was imaged using an ultrasound imaging system. The maximum flow velocity value and the TN excursion distance per dorsiflexion were then calculated as indexes of excursion using the application software Flow PIV. The shear-wave velocities of the TN at PF and DF were also measured. We observed a relationship between the TN excursion and stiffness that was stronger at 25% dorsiflexion than at 75% dorsiflexion. In addition, the ultrasonographic shear-wave velocity could predict the excursion of the TN if measured under mild plantar flexion of the ankle joint (i.e., 25% dorsiflexion).