AFO vs SMO: how to reason through the orthotic choice in pediatric PT

Your CI hands you a referral note for a four-year-old and asks a simple question before the family arrives: "SMO or AFO?"

It sounds like a product question. It is a reasoning question. The answer is not in the diagnosis on the referral, and it is not in whatever the last child with the same diagnosis wore. It is in where this child's movement breaks down, what the brace will cost them, and whether the family can make it work on a school morning.

The short answer: which joint needs the help

The difference between the two is the joint they control.

A supramalleolar orthosis (SMO) controls the foot. It improves foot alignment and stability while leaving the ankle free to move. It fits the child who needs midfoot control without restricting gait mechanics.

An ankle foot orthosis (AFO) controls the ankle. A solid AFO provides ankle stability and controls motion in the sagittal plane, which is what you want when the problem is excessive plantarflexion or poor ankle control.

So the first question is not "which brace." It is "where is the problem: the foot, the ankle, or the knee above them?"

Four questions that sort the choice

1. Is the problem at the foot or at the ankle? Flexible pronation, mild hypotonia, and ligamentous laxity point toward an SMO: the foot needs alignment, and the ankle can do its job. Excessive plantarflexion, poor ankle control, or crouch point toward an AFO.

2. Is dorsiflexion available, and does the child have the control to use it? A hinged AFO allows controlled ankle motion while preventing excessive plantarflexion. It suits equinus with available dorsiflexion and mild spasticity. But a hinge only helps a child with the motor control and strength to use it. Without that, the hinge is motion the child cannot manage.

3. What is the knee doing in stance? If the knee is the problem, an ankle-level answer may not be enough. A ground reaction AFO (GRAFO) uses ground reaction force to promote knee extension in children with crouch gait or knee instability in stance, and it only works when it is properly tuned and aligned. Significant knee instability, weakness, or contracture may call for a knee ankle foot orthosis (KAFO), at a higher energy cost and with real compliance considerations.

4. What will the brace cost this child? Every orthosis trades something. A solid AFO can reduce push-off. Any device that removes all challenge also removes the slight instability children learn from. The right brace is the least restrictive one that lets the child do the thing they are trying to do.

The orthoses side by side

Orthosis	Common indications	What it does	What to watch
SMO	Flexible pronation, mild hypotonia, ligamentous laxity	Improves foot alignment and stability while allowing ankle motion	Best when the child needs midfoot control without restricting gait mechanics
Solid AFO	Excessive plantarflexion, crouch gait, poor ankle control	Provides ankle stability and controls sagittal plane motion	Reduced push-off; confirm the alignment serves the functional goal
Hinged AFO	Equinus with available dorsiflexion, mild spasticity	Allows controlled ankle motion while preventing excessive plantarflexion	Needs adequate motor control and strength to benefit from the hinge
Ground reaction AFO	Crouch gait, knee instability in stance	Promotes knee extension through ground reaction force	Tuning and alignment, to avoid compensations
Dynamic AFO	Tone management, sensory input, mild alignment needs	Supports alignment while encouraging active movement	Skin integrity and movement quality

The diagnosis narrows the field without making the decision. The Playbook's diagnosis-to-equipment crosswalk lists "AFOs or SMOs" for cerebral palsy and "SMOs or AFOs" for Down syndrome. Both options appear for both diagnoses because the child, not the label, decides.

The five lenses every prescription passes through

Once you know which joint needs help, five considerations decide whether a specific device is right for this child:

• Function. What does the child want to do? Walk to recess, keep up on the playground, stand at the bathroom sink. The brace serves the goal, not the diagnosis.
• Tolerance. A device that stays in the closet is not working. Watch the trend in wear time, not just the first day.
• Movement variability. Children learn from slight instability. An orthosis that eliminates every challenge eliminates motor learning with it.
• Growth. Pediatric orthotics are dynamic. How soon the child will outgrow the device is part of the decision.
• Family. Wearing schedules, skin checks, donning and doffing, the car seat, the school shoes. If it is not realistic for this family, it is not the right device.

What the evidence says

The strongest evidence is in children with cerebral palsy. A 2018 systematic review and meta-analysis of 56 studies and 884 children, most with spastic CP, found that AFOs produced small improvements in gait speed and small to moderate improvements in gross motor function. In children with equinus gait, posterior AFOs (solid, hinged, supramalleolar, and dynamic designs were grouped together) produced large improvements in ankle dorsiflexion at initial contact and in swing, and they decreased ankle power generation in stance.¹

That last finding is the push-off trade-off in the table above, measured. It is the reason the "what will it cost" question belongs in every decision.

The rationale for SMOs is much less developed. A 2024 narrative review of 47 studies found that every study explained why AFOs were prescribed, while only five described a rationale for SMOs, and most of those rationales were nonspecific.² When you recommend an SMO, write down why. The literature often will not do it for you.

Common student errors

• Treating a brace as a sign of regression rather than a tool for participation
• Trying to remove support too early
• Focusing on the device instead of what the child can now do
• Not asking the orthotist about wearing schedule expectations
• Documenting the equipment without documenting the function

The last one matters most. "Child wears bilateral SMOs" tells a reviewer nothing. What changed in gait, standing, or play when the child had them on is what supports the recommendation.

The decision is shared

Orthotic prescription is collaborative. The PT brings the movement analysis, the orthotist brings the device expertise, the physician brings the medical picture, and the family brings the reality of the child's day. Your job in that conversation is to name the functional goal and the specific movement problem clearly enough that everyone is solving the same problem.

Then keep reassessing. Children grow, skills change, and a brace that was right in March can be holding a child back by October. Watch gait, posture, endurance, participation, and skin, and document the benefits and the problems. Confirm your state practice act and payer policies for how orthotic recommendations are made and documented where you work.

Drawn from Chapters 15 and 20 of the Pediatric PT Playbook: the orthoses cheat sheet, the five considerations for orthotic decision making, the diagnosis-to-equipment crosswalk, and the guidance on monitoring and family education.

References

1. Lintanf M, Bourseul JS, Houx L, Lempereur M, Brochard S, Pons C. Effect of ankle-foot orthoses on gait, balance and gross motor function in children with cerebral palsy: a systematic review and meta-analysis. Clin Rehabil. 2018;32(9):1175-1188. doi:10.1177/0269215518771824. PMID: 29714066.
2. Dailey AH, Landers J, Anderson S, Dillon MP. Exploring the rationale for prescribing ankle-foot orthoses and supramalleolar orthoses in children with cerebral palsy: a narrative synthesis of rationale statements. Prosthet Orthot Int. 2024;48(3):290-299. doi:10.1097/PXR.0000000000000282. PMID: 38857165.