Ankle Foot Orthosis (AFO)
Stiffness Optimization
The method to improve treatment outcomes with orthoses in Neuromuscular diseases
Different AFO design and their advantages
Various AFO design types exists. Three common AFO types are: dorsal AFOs, ventral AFOs, and hinged AFOs. Each design has specific indications based on the patient’s muscle strength, joint stability, and lifestyle needs.
Dorsal AFOs, or posterior leaf AFOs, have their strut positioned at the back (posterior) of the leg and foot. Dorsal AFOs bend (almost) solely in the sagittal plane. This allows for the AFO to efficiently store energy during the stance phase of gait and release it during push-off, assisting with forward propulsion. Besides providing excellent dynamic support, they are lightweight. A disadvantage is that oftentimes the shoesize nees to be 1 size larger, due to the space required at the back of the foot.
Hinged AFOs are fabricated using mechanical joints at the ankle, and are almost always custom-made. These hinges allow controlled ankle motion using springs, permitting plantarflexion and dorsiflexion within set limits. Hinged AFOs have the advantage that the stiffness towards dorsi- and plantarflexion can be different and set independently. A disadvantage is that hinged AFOs tend to be less efficient in terms of energy storing and releasing capacity and that they are heavier compared to dorsal and ventral AFOs.
Ventral AFOs, by contrast, feature an anterior support structure, lying along the front of the shin and foot. Oftentimes the strut is attached halfway the footplate, removing the need to use shoes 1 size larger. Ventral models typically offer more comfort as the pressure on the calf casing is distributed over a larger area. A disadvantage is that the AFO deforms out of the sagittal plane.
