Kinematic analysis of ankle joint during gait in drop foot patients wearing passive Ankle-Foot Orthosis *

Abstract

The term ‘drop-foot’ refers to an uncommon presentation of degenerative diseases, derived from neurological, muscular or anatomical complications, resulting in difficulties in performing foot dorsiflexion. This causes an abnormal gait pattern, characterized by two complications: the ‘foot slap’ at the initial contact with the ground, and the ‘toe-drag’ during the swing phase. In order to support gait, a common non-surgical treatment is the use of lightweight ‘L’ shaped ankle-foot orthosis (AFO). In this study we combine gait analysis and biomechanical modeling tools to analyse the kinematics of ankle joint in gait with and without the support of a passive AFO, namely the ‘Codivilla’ spring. The study was conducted on a population of eighteen adult subjects suffering from unilateral drop-foot (7 females, age 58.1 ± 14.5 years, BMI 23.4 ± 4.60). The infrared multicamera system SMART DX by BTS Bioengineering (Milan, Italy), was used to acquire data relating the 3D position of 22 markers placed on patient’s body, following the Davis protocol, during walking trials performed in two conditions: barefoot and with the AFO mounted on the affected limb. Data were then imported in OpenSim (SimTK software) and used to solve an inverse kinematic problem in order to reproduce walking and compute the evolution of body joints angles. Ankle dorsiflexion and subtalar inversion signals were analysed using MATLAB (2022a) to compute the following metrics for each angle: Range of Motion (RoM), angle at Heel Strike (HS) and angle at Toe Off (TO). The two-way ANOVA statistical test was used to analyse the effects of two factors: walking condition (with versus without AFO) and limb (affected versus contralateral). The interaction factor (condition*limb) was also analysed. Fig. 1 shows the evolution over the gait cycle of the ankle and subtalar angles in the two walking conditions for each foot. Solid lines are obtained as the mean value of subjects’ averaged step. Shaded areas represent the variability among subjects. Table 1 reports the results of the two-way ANOVA test in terms of p-value. Results show that the AFO ‘Codivilla’ spring acts on the kinematics of ankle by reducing the RoM during walking, as it limits the plantar flexion of drop foot. However, it does not significantly affect the ankle angle at HS and TO, although the first is lower in the affected foot. Results also show that the evolution of subtalar angle in the affected foot is altered, not in the RoM, rather in values, in particular at the initial phases of gait cycle. However, the considered orthosis does not produce improvements in the kinematics of subtalar angle. This is probably due to the L-shape of the device, which does not limit ankle inversion/eversion. In conclusion our study confirms the alterations of the drop foot in the kinematics of the ankle joint, particularly at Heel Strike in which both the ankle and the subtalar angle are altered compared to the contralateral foot. The use of Codivilla spring results in a more physiological dorsiflexion of the ankle but has no significant effect on the kinematics of the subtalar joint.