Ankle Foot Orthoses (AFO) Comprehensive Study Notes

Ankle Foot Orthoses (AFOs) are lower extremity biomechanical devices designed to control joint motion, assist weak muscle groups, enhance gait efficiency, and provide joint stability throughout the stance and swing phases of walking.

Structural Characteristics:
- Lightweight and streamlined design.
- Fabricated from a plastic insert.
- Available in both prefabricated and custom-made options.
- Possesses posterior trimlines behind the malleoli to allow dynamic ankle flexibility.
Biomechanical Function:
- Bends backward during early stance phase.
- Recoils during swing phase to lift the foot and assist with dorsiflexion.
- Offers slight plantarflexion at heel contact to prevent sudden knee flexion.
Material Modifications and Adjustments:
- Plastic material can be trimmed away to weaken the spring action.
- Material cannot be added back to increase rigidity.
Stability Characteristics:
- Provides no medial-lateral stability.

Structural Characteristics:
- Features a steel spring mechanism integrated into the ankle stirrup.
- Tightness is adjustable via a screw positioned directly on the spring mechanism.
- Bulkier design compared to the posterior leaf spring AFO.
Biomechanical Function:
- Spring compresses during the stance phase.
- Spring rebounds during the swing phase to assist dorsiflexion.
- Provides slight plantarflexion at heel contact, comparable to the posterior leaf spring AFO.
Clinical Precautions and Contraindications:
- Must be avoided in patients presenting with spasticity.

Structural Characteristics:
- Utilizes a metal ankle hinge equipped with a posterior stop mechanism.
Biomechanical Function:
- Limits plantarflexion motion.
- Prevents toe drag during the swing phase.
- Imposes a flexion force at the knee during early stance, which prevents knee hyperextension.

Structural Characteristics:
- Utilizes a metal ankle hinge equipped with an anterior stop mechanism.
Biomechanical Function:
- Limits dorsiflexion motion.
- Assists individuals with paralysis of the triceps surae muscle group to achieve propulsion during late stance.

Solid AFO Features and Function:
- Constructed of rigid plastic with trimlines positioned anterior to the malleoli.
- Limits all foot and ankle motion.
Hinged AFO Modification:
- Solid AFO designs are occasionally divided transversely at the ankle joint level, joining the lower foot piece and upper calf section with a hinge.
- Permits slight sagittal plane motion.
- Facilitates progression to the foot-flat position during early stance.

Structural Characteristics:
- Double-upright metal ankle joint featuring anterior and posterior channels.
- Accommodates combinations of springs and pins/pegs inside the channels.
Functional Principles:
- Pins/pegs function to limit movement.
- Springs function to assist movement.
Specific Channel Mechanics:
- Pin / peg in anterior channel: Limits dorsiflexion (DF).
- Pin / peg in posterior channel: Limits plantarflexion (PF).
- Spring in anterior channel: Causes / assists plantarflexion (PF).
- Spring in posterior channel: Causes / assists dorsiflexion (DF).

Structural Characteristics and Function:
- Wraps spirally around the lower leg.
- Limits all foot and ankle movements.
Clinical Precautions and Contraindications:
- Contraindicated in the presence of moderate to severe spasticity.
- Contraindicated in the presence of moderate to severe edema.

O’Sullivan SB, Schmitz TJ, Fulk GD. Physical Rehabilitation. F.A. Davis Company; 2019.