Forces Involved with Ankle Foot Orthoses

Open Kinetic Chain Forces Sagittal Plane

• Dorsiflexion weakness - Swing phase or Plantarflexion contracture prevention

  • Corrective force: instep strap/shoe closure directed posterior/plantar

  • Counter forces: distal plantar surface directed superiorly and proximal posterior calf directed

• Plantarflexion weakness - Dorsiflexion contracture prevention

  • Corrective force: Posterior heel directed anteriorly and superiorly

  • Counter forces: Dorsum of the metatarsal heads directed toward plantar surface and anterior calf strap or shell directed posteriorly

Closed Kinetic Chain Forces - Sagittal Plane

• Knee Hyperextension Control

  • Corrective force: At instep of ankle with instep strap/shoe closure directed plantar/posteriorly

  • Counter forces: At distal plantar surface directed dorsally and proximal posterior calf directed anteriorly

• Crouch (flexion) Control

  • Corrective force: At posterior heel directed anteriorly and superiorly

  • Counter forces: Dorsum of the metatarsal heads directed toward plantar surface and anterior calf strap or shell directed posteriorly

Coronal Plane Forces

Internal Rotary Deformity (IRD) AKA Pronation

• Foot:

  • Corrective force: Laterally directed at medial longitudinal arch and sustentacular tali modification

  • Counter forces: Medial directed forces at lateral calcaneus and distal 5th metatarsal

• Ankle:

  • Corrective force: Laterally directed force at medial supramalleolar area (with or without Sabolich Modification) and medial talus area (and sustentacular tali modification)

  • Counter forces: Medially directed force at lateral calcaneus and proximal medial calf

Sabolich Flange Modification

• Medial for pronation condition support

• Lateral for supination condition support

Applied Forces

Modifications:

• Decide on areas to modify and assure proper 3-point force systems before describing on work ticket and modifying

• 1-5 mm of plaster removal on positive model in desired areas to apply force on patient/consider counter reliefs on opposite side of model

• Avoid removing plaster on prominent boney anatomy - plaster should be removed around those areas

• Compare your measurements before and after modifications

• During fitting - additional padding may be applied in the desired pressure areas if needed

Ground Reaction Force Modifications

• Shoe heel shape and density

• Anterior rocker shape

• Posterior rocker shape

• Shank plate

• AFO toe plate length and stiffness

• Heel height/posting to change shank to vertical angle

Straps

• Layover

• Figure 8

• Slot strap

• Chafe and loop

• T-strap

• Spiral strap

• BOA strap

Strapping Requirements

• Appropriate contact/support for function

• No plastic bridging/maximize contact

• Material strength/wear and tear

• Appropriate design to assist with 3-point force systems

• Easy in donning/doffing

• Cognitive abilities

• Cosmesis

Normal Gait Cycle

Gait with SAFO

Gait with AAFO with PF stop free DF