The Effects Of Ankle-Foot Orthosis Stiffness On Gait At Constant Speed

Objective: When neurological diseases or musculoskeletal injuries may cause lower limb dysfunction,it will seriously reduce the patient’s quality of life.Ankle-foot orthosis(AFO)can be used clinically for treatment.Meanwhile,the treatment effect is closely related to the mechanical characteristics of AFO.Therefore,the purpose of this paper was to investigate the effects of AFO stiffness on gait biomechanical characteristics at constant speed,aiming to provide scientific references for optimizing structural design and improving function of AFO.Methods: 30 healthy adults(age: 21.35±0.24 years old;height: 171.38±5.34 cm;weight:65.37±8.34 kg)were recruited.Firstly,the orthosis evaluation device was used to quantify the mechanical properties of AFO.Secondly,lower limb joint kinetics and kinematics parameters under the three different conditions of normal and two types of AFO with different stiffness(AFO1,AFO2)were recorded by using Vicon 3D motion analysis system,AMTI 3D force measurement platform,Noraxon wireless surface electromyography.Finally,biomechanical musculoskeletal model was used to simulate the impact of AFO stiffness on the biomechanics of gait.In addition,the angle,moment and muscle force of lower limb joints were analysed.Results:(1)The stiffness value of the AFO1 and AFO2 conditions were 1.16?0.94 Nm/? and2.01?1.13 Nm/?.There was a significant difference in stiffness between AFO1 and AFO2 at 5°plantar flexion and 5° dorsiflexion of ankle.(2)Compared with those without AFO,peak dorsiflexion angle of ankle,peak knee flexion angle and peak hip extension angle were increased significantly,while peak plantarflexion of ankle and peak hip flexion were significantly reduced when wearing AFO1 and AFO2.Compared with wearing AFO1,peak dorsiflexion of ankle was observably increased,while peak knee extension angle was significantly decreased when wearing AFO2.(3)Compared with those without AFO,peak hip flexion moment was observably reduced when wearing AFO1 and AFO2.Particularly,the peak knee flexion moment also significantly reduced when wearing AFO2.Compared with wearing AFO1,there was a significant difference in peak knee flexion moment.(4)Compared with those without AFO,the muscle strength of tibial anterior muscle failed to change,the peak muscle strength of soleus and gastrocnemius muscles were increased,but peak muscle strength of biceps femoris was decreased when wearing AFO1 and AFO2.Conclusions: This study demonstrates that human adopts different adaptive strategies on gait when wearing different AFO stiffness.AFO stiffness may has varying degrees of effects on the angle,moment,and muscle force of the lower limbs.Particularly,it mainly affects the motion of ankle joints.Furthermore,AFO stiffness is a key factor for recovery of walking function of user.In addition,with the help of Open Sim platform to build a musculoskeletal simulation model with AFO to realize co-simulation.It is very effectively used to AFO optimization design and rehabilitation effect evaluation.Besides,it also provides a valuable reference for optimizing other assistive devices.