Ankle-foot orthoses: Effect on gait abnormalities in tibial nerve paralysis

To study the biomechanical effects of gastrocnemius-soleus dysfunction and its potential remediation, the gait patterns of six able-bodied young adults were analyzed before and after induced temporary tibial nerve paralysis. Ambulation with the tibial nerve block was performed with and without the assistance of an ankle-foot orthosis (AFO) with a rigid anterior stop adjusted to either 5° plantarflexion or 5° dorsiflexion. The gait abnormalities resulting from tibial nerve paralysis include delayed advancement of the center of pressure, delayed ipsilateral heeloff and early contralateral heelstrike, decreased steplength, decreased ankle dorsiflexion moment, and increased knee flexion moment. This study provides quantitative information on the degree to which these abnormalities were corrected by appropriately adjusted AFOs. When using an AFO with an anterior stop, subjects with tibial nerve paralysis had improved advancement of the center of pressure (p<0.01). The body's ground reactive force line moved forward more normally, pivoting over the metatarsal head area and raising the heel earlier than observed with uncorrected tibial nerve paralysis, thus approximating the normal ankle dorsiflexion moment, normal timing of gait events, normal advancement of the hip, and normal steplength. The AFO with the anterior stop set at 5° plantarflexion was more effective in restoring the values to normal than the AFO with the anterior stop set at 5° dorsiflexion, but still did not consistently achieve the normal values. Only by using the AFO with the anterior stop set at 5° plantarflexion was the increased knee flexion moment observed during the block reduced to normal levels (p<0.01). The restoration was due to the reduction of the moment arm of the vertical force with respect to the knee to normal values.