Residency · Residency · Physical Medicine Rehabilitation

Lower Extremity Orthotic Prescription

Introduction

Lower extremity orthoses are external devices applied to the body to control motion, provide support, correct deformity, or improve function. Orthotic prescription is a core competency in physical medicine and rehabilitation, requiring understanding of biomechanics, pathology, and patient-specific goals.

Biomechanical Principles

Three-Point Force Systems

All orthoses function through three-point pressure systems to control joint motion. Forces applied proximal, distal, and at the joint create corrective moments. Ground reaction forces are leveraged in floor reaction AFOs.

Gait Cycle Considerations

Heel strike: Need for controlled plantar flexion. Midstance: Stability and tibial advancement control. Push-off: Energy return or rigid lever for propulsion. Swing phase: Foot clearance requirements.

Foot Orthoses (FO)

University of California Biomechanics Laboratory (UCBL): Controls hindfoot valgus/varus; rigid thermoplastic. Custom-molded insoles for pressure redistribution in diabetic feet. Metatarsal pads and bars for metatarsalgia. Heel lifts for leg length discrepancy. Total contact inserts for neuropathic feet.

Ankle-Foot Orthoses (AFO)

Solid AFO

Blocks all ankle motion (dorsiflexion and plantar flexion). Indicated for severe spasticity, ankle instability, significant weakness. Provides maximum stability but limits normal gait mechanics.

Posterior Leaf Spring (PLS) AFO

Thin, flexible posterior strut allows plantar flexion at heel strike. Primary indication: Dorsiflexor weakness (foot drop) without spasticity. Lightweight, fits in standard shoes. Does not control mediolateral instability.

Hinged AFO

Allows free or adjustable dorsiflexion; blocks plantar flexion with plantar flexion stop. Permits tibial advancement during stance; improves squat and stair mechanics. Indicated for mild-to-moderate spasticity with adequate dorsiflexion strength. Adjustable options allow progressive motion changes.

Ground Reaction AFO (Floor Reaction)

Anterior shell design with rigid ankle in slight dorsiflexion. Creates knee extension moment during stance. Indicated for quadriceps weakness or crouch gait. Contraindicated with knee flexion contractures.

Carbon Fiber AFOs

Lightweight, energy-storing designs. Dynamic response properties for active patients. Available in posterior strut and lateral strut configurations. 

Knee-Ankle-Foot Orthoses (KAFO)

Indications

Combined knee and ankle instability. Quadriceps weakness (less than grade 3 strength) with ankle weakness. Genu recurvatum requiring knee control. Progressive neuromuscular conditions (e.g., post-polio, muscular dystrophy).

Knee Joint Options

Drop-lock (ring lock): Manual lock/unlock; stable but limits function. Bail lock (Swiss lock): Spring-loaded; unlocks both sides simultaneously. Stance-control orthotic knee joints (SCO): Allow free swing phase motion while locking in stance. Offset knee joint: Alignment posterior to weight line creates extension moment.

Design Considerations

Weight minimization with carbon fiber or titanium components. Stance-control KAFOs improve gait efficiency and reduce compensatory motions. Supracondylar cuff or thigh shell for proximal support. Consider patient's upper extremity function for don/doff ability. 

Hip-Knee-Ankle-Foot Orthoses (HKAFO) and Reciprocating Gait Orthoses (RGO)

Reciprocating gait orthosis: Hip joint cables link bilateral HKAFOs. Extension of one hip assists flexion of contralateral hip. Indicated for thoracic-level paraplegia (primarily pediatric). High energy cost limits long-term ambulatory use. Often used for therapeutic standing and limited community ambulation.

Special Populations

Stroke

AFO selection based on spasticity pattern and motor recovery. Solid AFO for severe equinovarus; transition to hinged as tone decreases. Carbon fiber designs for higher-functioning patients.

Spinal Cord Injury

T12 and below: KAFO with potential for community ambulation. T6-T12: RGO or HKAFO; primarily exercise ambulation. Above T6: Standing frame for therapeutic standing only.

Pediatric Considerations

Growth-accommodating designs with adjustable straps. Supramalleolar orthosis (SMO) for flexible pes planus. Serial casting before definitive orthotic fabrication. Night splints for equinus prevention.

Orthotic Prescription Process

1. Clinical assessment: Strength, ROM, tone, sensation, skin integrity
2. Gait analysis (observational or instrumented)
3. Define biomechanical goals and functional objectives
4. Select orthotic design and components
5. Fitting, alignment, and gait training 6. Follow-up for skin checks and adjustment

Key Clinical Pearls

1. A posterior leaf spring AFO is appropriate for isolated dorsiflexor weakness without spasticity or mediolateral instability. 2. Ground reaction AFOs create a knee extension moment and are indicated for quadriceps weakness or crouch gait, but are contraindicated with fixed knee flexion contractures. 3. Stance-control KAFOs significantly improve gait efficiency compared to locked KAFOs by allowing free knee motion during swing phase. 4. Always assess skin integrity and sensation before prescribing any orthosis, especially in patients with peripheral neuropathy.

References

1. Lusardi MM, Jorge M, Nielsen CC. Orthotics and Prosthetics in Rehabilitation. 4th ed. Elsevier; 2019.
2. Fatone S, Gard SA, Malas BS. Effect of ankle-foot orthosis alignment and foot-plate length on the gait of adults with poststroke hemiplegia. Archives of Physical Medicine and Rehabilitation. 2009;90(5):810-818.
3. Yakimovich T, Lemaire ED, Kofman J. Engineering design review of stance-control knee-ankle-foot orthoses. Journal of Rehabilitation Research and Development. 2009;46(2):257-267.
4. Brehm MA, Harlaar J, Schwartz M. Effect of ankle-foot orthoses on walking efficiency and gait in children with cerebral palsy. Journal of Rehabilitation Medicine. 2008;40(7):529-534.

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