Comparison of five different methodologies for evaluating ankle–foot orthosis stiffness

Table 1 Comparison of fixture designs

Fixture name	EMPIRE	SMApp	KST	BRUCE
Fixture capabilities
Maximum Testable Dorsiflexion	25 deg	25 deg	20 deg	20 deg
Maximum Testable Plantarflexion	5 deg	25 deg	30 deg	10 deg
Tested Rotational Speed	0.75 deg/s	1 deg/s	0.75 deg/s	Manual
Fixture Speed Range	0.75 deg/s	0 to 100 deg/s	0 to 30 deg/s	Manual
Load Measurement	Six Axis load cell	Uniaxial Force Transducer	Uniaxial Torque Sensor	Uniaxial Force Transducer
Max Ankle Torque	89 Nm †	626 Nm	25 Nm	133.5 Nm
Sample rate	100 Hz	35 Hz	1000 Hz	100 Hz
AFO Mounting and Alignment
Footplate Attachment	Fixed/Clamped	Fixed/Clamped	Fixed/Clamped	Fixed/Clamped
Tibial Cuff Attachment	Fixed/Clamped	Mounted to a linear bearing	Fixed/Clamped	Mounted to a linear bearing
Transverse Alignment	Medial Border	Bisected	Medial Border	Bisected
Axis of Rotation Vertical Position	81 mm	55 mm^‡	81 mm	75 mm
Axis of Rotation Fore/Aft Position	Uncontrolled, based on surrogate shank fit	Uncontrolled, based on surrogate shank fit	Uncontrolled, based on surrogate shank fit	Uncontrolled, based on surrogate shank fit
Data processing
AFO Precycling	1st cycle discarded	Precycled once prior to recorded testing	1st cycle discarded	Precycled prior to recorded testing
Adjusted for fixture inertia?	Yes	Yes	No	No
Initial data Filtering	1 Hz LP	No	No	10 Hz LP

^†Value reported for the configuration used in this testing. Maximum testing torque at the ankle is dependent upon AFO geometry (Shuman 2021)
^‡Physical rotational axis is located at 55 mm (Totah 2021). Data were computationally adjusted to match the 81 mm rotation height in the EMPIRE

ISSN: 1743-0003