The Functional Role of Orthotic Devices in the Foot and Ankle



  • An orthosis is a device that imparts an external force on the musculosketal system.
  • The name has replaced terms such as calipers, braces and splints.


Mechanism of action

  • External forces on the musculoskeletal system are normally resisted by the internal forces of passive and active tissues
  • Injury, disease or disorders which affect the musculoskeletal system cause loss of normal resistance to external forces leading to deformity, contractures and loss of function
  • Orthoses modify the system of external forces and moments acting about one or more joints of the body


Main functions of orthoses

  • Restoration of function
  • Provision of support
  • Limitation or assistance of motion
  • Correction of deformity
  • Relief of pain
  • Reduce or transfer load
  • Combination of the above


Ground Reaction force (GRF)

To understand how certain orthoses work, it is essential to have an undersanding of the concept of GRF. 

  • GRF is the force exerted by the ground on the body (figure 1)
  • It is equal in magnitude - but opposite in direction - to the force exerted on the ground by the body
  • This is Newton’s third law which states that: for every reaction there is an equal and opposite reaction
  • During gait, if the GRF does not pass through the centre of a joint, it produces a moment (turning force) on that joint
  • During pre-swing phase of gait, the GRF passes behind the knee and acts as a flexion moment
  • The GRF in mid to terminal stance also falls anterior to the knee, causing a knee extension moment
  • In mid-stance, the GRF is posterior to the hip, resulting in a hip extension moment
  • During mid to terminal stance phase, the GRF will fall anterior to the ankle, resulting in an ankle dorsiflexion moment; this is resisted by contraction of the gastrocnemius–soleus muscle complex

Hip, knee and/or ankle orthoses are often utilised on weak or abnormal joints to counteract the GRF, thus providing support, stability, pain relief and improved function. 

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Figure 1. Red arrow denotes point of contact and direction of GRF at different stages of gait 


Orthoses classification

  • American Academy of Orthopaedic Surgeons (1960)
  • Nomenclature is based around the joint(s) upon which the orthosis is acting, e.g. Ankle-Foot Orthosis (AFO), Knee-Foot-Ankle Orthosis (KAFO)


Materials used for orthoses

  • Thermoforming plastics soften when heated and harden when cooled, allowing for reshaping by application of pressure
  • Thermosetting plastics can be moulded into permanent shape after heating and do not return to their original consistency, even after being reheated
  • Leather, such as cattle hide, is used for shoe construction; it conducts heat and absorbs water well
  • Rubber has resilient and shock-absorbing qualities and is still used for padding in body jackets and limb orthoses
  • Metals, such as stainless steel and aluminium alloys, are adjustable and can be used for joint components, metal uprights and bearings
  • Plaster of Paris continues to be used as the initial mould taken from the patient for the preparation of orthoses
  • Composite materials continue to be developed all the time, allowing for more resilient products that conform better to biological tissues, while reducing stress or shear forces


Complications of orthoses

  • Psychosocial and concordance issues
  • Circumferential or focal pressure leading to skin breakdown, ulceration, nerve and vessel compression
  • These problems can be addressed with orthotic design, appropriate application force, accurate fitting, contouring, sufficient padding and large contact surface areas
  • Heat and water retention can lead to skin maceration and infection


Foot and ankle orthoses

  • Understand that most orthoses are designed to be either:
    • Accommodative or
    • Corrective
  • Used as primary treatment for a wide spectrum of conditions and disorders
  • Redistribute load in areas of the foot during gait
  • Reduce risk of developing further deformity
  • Are used to help correct flexible deformity (corrective orthoses will not work on a fixed deformity)
  • Soft and well padded designs aim to accommodate fixed deformities especially in the presence of arthropathy
  • Ankle Foot Orthoses (AFOs) can be used to address deformities involving the hindfoot
  • Custom-made shoes can be used in conjunction with other foot orthoses


Commonly used insoles

  • Insoles can be simple, total contact or functional design
  • Insoles reduce the tensile stresses on ‘at-risk’ soft tissues in the foot and ankle eg. medial soft tissues in pes planus
  • Flexible pes planus:
    • stiff insole with medial arch support and medial heel wedge  - this is corrective

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Figure 2. Typical insole for pes planus, with medial arch support, medial heel wedge

  • Pes cavus
    • soft insoles with excavations for plantar prominences (accommodative) to reduce load under painful points
    • lateral heel wedge to correct varus heel (corrective) 
  • Metatarsal domes:
    • used in forefoot pain to transfer load from painful metatarsal heads to shaft
    • used to spread metatarsals on standing, thus relieving Morton's neuroma compression
    • can help with claw toes - via the 'reverse windlass' mechanism - by exerting pressure on the plantar fascia 
  • Wedged insoles aim to generate supination (medial based) and pronation (lateral based) moments around the mid/hindfoot (corrective)
  • Heel lifts are used to accommodate equinus deformities of the hindfoot and minor leg length discrepancies


Commonly used custom-made shoes

  • Extra-depth shoes with a high toe box; accommodates claw toes, reduces pressure over bony prominences for diabetic patients
  • Accommodative shoes can be used for forefoot deformities eg. severe hallux valgus and associated lesser toe hammer or claw toe deformities
  • Rocker-sole shoes are used to reduce the bending forces on a stiff and arthritic forefoot during late stance of gait eg. 1st MTPJ arthritis; the position of the rocker can be modified to also help midfoot or ankle arthritis 


Ankle Foot Orthoses (AFOs)

  • AFOs can reduce the energy cost of ambulation and exert triplanar control of the foot and ankle complex 

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Figure 3. AFO example

  • Indications include neuromuscular disorders, spinal / brain injuries leading to diplegic or hemiplegic spasticity, arthritis and complex hindfoot deformities
  • Posterior leaf spring
    • consists of a narrow calf shell and ankle trim line behind the malleoli to permit some flexibility
    • compensates for weak ankle dorsiflexors and decelerates plantarflexion at heel-strike or drop-foot in swing
  • Solid AFOs
    • have a trim line anterior to the malleoli
    • prevent ankle dorsiflexion and plantarflexion, as well as varus and valgus deviation
  • Hinged AFOs have an adjustable ankle hinge which can be set to a desired range of ankle motion
  • Ground Reaction AFOs (GRAFO)
    • to exert a knee extension moment to decelerate knee flexion
    • can compensate for a weak triceps surae and quadriceps
    • constructed with a solid ankle, incorporating the anterior portion of the proximal tibia


Total contact casting (TCC), modified casts and walker boots

  • A true TCC is comprised of Plaster of Paris and reinforced fibreglass tape with very limited padding with a drying time of 48hrs
  • They can be used to stabilise an active charcot arthropathy and prevent further deformity
  • A modified cast is made from synthetic polyester tape with a drying time of 30-60 mins

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Figure 4. Example of a modified TCC

  • Both casting techniques are recognised for the treatment of non-infected diabetic ulcers
  • Contraindications for casting techniques include the presence of infection and critical limb ischaemia
  • A walker boot with a total contact insole is an alternative treatment with comparable outcomes to TCC in diabetic patients

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Figure 5. Walker boot for Charcot arthropathy

  • CROW - Charcot Restraint Orthotic Walker
  • For more details, see Hyperbook > Systemic Disorders > Diabetic Foot > Total Contact Casting 


Viva Questions

  • How do orthoses work?
  • What orthoses would be appropriate in the management of forefoot pain?
  • Describe the Ground Reaction Force during gait?
  • A patient presents with a foot drop post total hip replacement; what type of orthosis would be appropriate for managing the pathology?