Mechanism and Design Analysis of Articulated Ankle Foot Orthoses for Drop-Foot

Table 1

Summary of reviewed design.

AFO type	Weight	Active joint element	Locking/; assistive moment mechanism	Maximum resistive moment	Advantage	Disadvantage
Dream brace [33]	0.35 Kg	One-way frictional clutch	Resistive	1.6–1.8 Nm for small and medium size	Light weight, compact	Fixed resistance in plantarflexion direction throughout the gait cycle
AFO with oil damper [27]	0.40 Kg	Oil damper	Resistive	5–20 Nm per 10° of plantarflexion	Adjustability of; initial angle and stiffness, lightweight	Resistive torque cannot be modulated
AFO with passive pneumatic element [38]	—	Passive pneumatic element	Resistive	4 Nm	Compact, lightweight, variable motion control	Difficult to adjust the constraint force
University of Illinois AFO [10]	1 Kg	Cam lock mechanism	Locking	—	Energy harvesting capacity, variable motion control	Bulky size, no resistance during loading response
Okayama University AFO [39]	0.86 Kg	Pneumatic actuator	Assistive	2 Nm	Energy harvesting capacity, untethered	Bulky size, small assistive torque
iAFO [40]	1.3 Kg	MR damper	Resistive	5 Nm at 20°/s; angular velocity	Different modes of rigidity during gait cycle, smaller power system required, untethered	Heavy, control setting needs skilled physician
AFO with MR brake [25]	1.6 Kg	MR brake	Resistive	24 Nm	Large braking torque, modulation of stiffness in different phases of gait	Heavy, tethered and high energy consuming
Halmstad AFO [32]	—	MR damper	Resistive	—	Responds to change of surface condition, simple and untethered design, only three control parameters	Bulky, not capable of producing assisting torque
AFO with CMRFB [41]	0.99 Kg	Compact MR fluid brake and a spring unit on the ankle joint	Resistive	10 Nm	Lightweight, compact, better motion control	Tethered, complex mechanism
AFO with SEA [24]	2.6 Kg	Series elastic actuator	Assistive	—	Adjustable ankle impedance, provides both plantarflexion and dorsiflexion assistance	High weight, tethered
AAFO with SEA [42]	—	Series elastic actuator	Assistive	—	Plantarflexion and dorsiflexion motion control, adjustable impedance	Bulky size, tethered
AFO with four-bar mechanism [43]	0.625 Kg	Passive four-bar linkage mechanism	Assistive	—	Simple, lightweight, does not restrict motion other than swing phase	Uncomfortable, not adjustable, unable to prevent foot-slap, actuation depends on knee flexion
IPEC AFO [9]	0.46 Kg	Active four-bar linkage and spring mechanism	Assistive	3.51 Nm in dorsiflexion; direction and; 3.88 Nm in plantarflexion direction	Lightweight, able to provide both plantarflexion and dorsiflexion moments	Bulky,; complex mechanism