Ankle strategy assistance to improve gait stability using controllers based on in-shoe center of pressure in 2 degree-of-freedom powered ankle–foot orthoses: a clinical study

Abstract

Background Although the ankle strategy is important for achieving frontal plane stability during one-leg stance, previously developed powered ankle–foot orthoses (PAFOs) did not involve ankle strategies because of hardware limitations. Weakness of movement in frontal plane is a factor that deteriorates gait stability and increases fall risk so it should not be overlooked in rehabilitation. Therefore, we used PAFO with subtalar joint for frontal plane movement and tried to confirm that the existence of it is important in balancing through clinical experiments. Methods We developed a proportional CoP controller to assist ankle strategy or stabilizing moment and enhance eversion to compensate for the tilting moment with 2 dof PAFO. It was true experimental study, and we recruited seven healthy subjects (30 ± 4 years) who did not experience any gait abnormality participated in walking experiments for evaluating the immediate effect of subtalar joint of PAFO on their gait stability. They walked on the treadmill with several cases of controllers for data acquisitions. Indices of gait stability and electromyography for muscle activity were measured and Wilcoxon signed-rank tests were used to identify meaningful changes. Results We found that subjects were most stable during walking (in terms of largest Lyapunov exponents, p < 0.008) with the assistance of the PAFO when their electromyographic activity was the most reduced (p < 0.008), although postural sway increased when a proportional CoP controller was used to assist the ankle strategy (p < 0.008). Other indices of gait stability, kinematic variability, showed no difference between the powered and unpowered conditions (p > 0.008). The results of the correlation analysis indicate that the actuator of the PAFO enhanced eversion and preserved the location of the CoP in the medial direction so that gait stability was not negatively affected or improved. Conclusions We verified that the developed 2 dof PAFO assists the ankle strategy by compensating for the tilting moment with proportional CoP controller and that wearer can walk in a stable state when the orthosis provides power for reducing muscle activity. This result is meaningful because an ankle strategy should be considered in the development of PAFOs for enhancing or even rehabilitating proprioception. Trial registration 7001988-202003-HR-833-03

Direct biomechanical manipulation of human gait stability: A systematic review

“…Preregistration of protocols and outcome measures was present in three studies [ 54 – 56 ]. Original data was made publicly available in seven studies [ 16 , 54 , 56 – 60 ], whereas seven studies mentioned data to be readily available upon request [ 61 – 67 ].…”

“…Hip flexion assistance (L2) produced indicative and limited evidence respectively for non-impaired [ 96 ] and impaired subjects [ 54 , 63 , 66 , 68 ]. The use of a powered ankle foot orthosis (AFO) (L6) shows contradictory findings for both impaired [ 55 , 97 ] and non-impaired subjects [ 67 , 98 ]. Other intervention types provided insufficient evidence.…”

Assistance force-line of exosuit affects ankle multidimensional motion: a theoretical and experimental study

“…In previous experiments conducted by Ho Seon Choi and colleagues [ 36 , 45 ], they observed that a 1-DOF powered ankle-foot orthosis, which shares structural similarity with the PTS scheme, resulted in a lateral shift of the in-shoe center of pressure during walking. Their results indicated that the 1-DOF-powered ankle-foot orthosis could generate unexpected inversion moments.…”

Assistance Force-line of Exosuit Affects Ankle Multidimensional Motion: A Theoretical and Experimental Study

“…Active inversion and eversion of the ankle joint are crucial for maintaining balance while walking [23,24]. The exosuit's unexpected non-plantarflexion moment can disrupt natural ankle movements [25][26][27], similar to muscle strength imbalances or less coordination of postural control, which have been found to exhibit a higher incidence of ankle sprains [28,29]. This can be particularly problematic for those who depend on the exosuit to compensate for impaired balance or mobility [30], as it can increase the fear of falling and the incidence of falls [31][32][33].…”

“…In this study, we primarily used the force line to describe the position and direction of the assistive force applied to the talocrural and subtalar joint axes. Several studies have recognized the importance of the position of assistance line-force and have employed double or multiple cable drives to assist multidimensional ankle motion [26,34]. These cable drives are positioned in the anterior-posterior position of the ankle joint for ankle plantar/dorsiflexion and in the medial-lateral position for inversion/eversion [35][36][37], particularly in patients with cerebral palsy and stroke [38].…”