General Description - Ankle-Foot Orthotics PDF Print E-mail

1. AFO

An ankle-foot orthosis (AFO) is commonly prescribed for weakness or paralysis of ankle dorsiflexion, plantar flexion, inversion, and eversion. AFOs are used to prevent or correct deformities and reduce weight bearing. (See images below.)

Flesh colored plastic Gelett joint with dorsiflex...

Flesh colored plastic Gelett joint with dorsiflexion assist ankle-foot orthosis.

 

 

Carbon plastic ankle-foot orthosis with footplate.

Carbon plastic ankle-foot orthosis with footplate

The position of the ankle indirectly affects the stability of the knee with ankle plantar flexion providing a knee extension force and ankle dorsiflexion providing a knee flexion force. An AFO has been shown to reduce the energy cost of ambulation in a wide variety of conditions, such as spastic diplegia due to cerebral palsy, lower motor neuron weakness of poliomyelitis, and spastic hemiplegia in cerebral infarction.4,5

2. Thermoplastic AFO

Thermoplastic AFOs - These devices are plastic molded AFOs, consisting of the following 3 parts: (1) a shoe insert, (2) a calf shell, and (3) a calf strap attached proximally. The rigidity depends on the thickness and composition of the plastic, as well as the trim line and shape. Thermoplastic AFOs are contraindicated in cases of fluctuating edema and insensation. (See image below.)

Thermoplastic molded ankle-foot orthosis (posteri...

Thermoplastic molded ankle-foot orthosis

3. Posterior leaf spring (PLS)

Posterior leaf spring (PLS) - The PLS is the most common form of AFO with a narrow calf shell and a narrow ankle trim line behind the malleoli. The main function of this AFO design is to limit plantarflexion range of motion during swing phase when an individual has weakness of the ankle dorsiflexors. Unfortunately, the inherent flexibility of this design will not control excessive subtalar eversion, midtarsal pronation, and forefoot abduction. The placement of the mechanical axis of the AFO posterior to the anatomic axis leads to migration of the orthosis during plantarflexion and dorsiflexion range of motion and the potential for skin irritation or ulceration on the leg.

Figure 49.13. Custom fabricated posterior leaf spring ankle foot orthosis.Custom fabricated posterior leaf spring ankle foot orthosis.
  • Spiral AFO - This AFO consists of a shoe insert, a spiral that starts medially, passes around the leg posteriorly, then passes anteriorly to terminate at the medial tibial flare where a calf band is attached. The spiral AFO allows for rotation in the transverse plane while controlling ankle dorsiflexion and plantar flexion, as well as eversion and inversion.
  • Hemispiral AFO - This AFO consists of a shoe insert with a spiral starting on the lateral side of the shoe insert, passing up the posterior leg, and terminating at the medial tibial flare where the calf band is attached. This design is used for achieving better control of equinovarus than the spiral AFO can.
  • Solid AFO - The solid AFO has a wider calf shell with trim line anterior to the malleoli. This AFO prevents ankle dorsiflexion and plantar flexion, as well as varus and valgus deviation.
  • AFO with flange - This AFO has an extension (flange) that projects from the calf shell medially for maximum valgus control and laterally for maximum varus control.
  • Hinged AFO - The adjustable ankle hinges can be set to the desired range of ankle dorsiflexion or plantar flexion.
  • Tone-reducing AFO (TRAFO) - The broad footplate is used to provide support around most of the foot, extending distally under the toes and up over the foot medially and laterally to maintain the subtalar joint in normal alignment. The TRAFO is indicated for patients with spastic hemiplegia

4. Metal and metal-plastic AFOs

This type of AFO consists of a shoe or foot attachment, ankle joint, 2 metal uprights (medial and lateral), with a calf band (application of force) connected proximally. The stirrup anchors the uprights to the shoes between the sole and the heel. The caliper is a round tube placed in the heel of the shoe, which connects to the uprights and also allows for easy detachability of the uprights. A molded shoe insert is another alternative to fit the stirrup into the shoe, which also allows maximum control of the foot and aligns the anatomic and mechanical ankles. (See image below.)

Plastic shell and metal uprights molded knee-ankl...

Plastic shell and metal uprights molded knee-ankle-foot orthosis with drop lock joints.

5. Ankle Joints

  • Ankle joints - The mechanical ankle joints can control or assist ankle dorsiflexion or plantar flexion by means of stops (pins) or assists (springs). The mechanical ankle joint also controls mediolateral stability. Knee extension moment is promoted by ankle plantar flexion, and knee flexion moment is promoted by ankle dorsiflexion.
    • Free motion ankle joint - The stirrup has a completely circular top, which allows free ankle motion and provides only mediolateral stability.
    • Plantar flexion ankle joint stop - This ankle joint stop is produced by a pin inserted in the posterior channel of the ankle joint or by flattening the posterior lip of the stirrup's circular stop. The plantar flexion stop has a posterior angulation at the top of the stirrup that restricts plantar flexion but allows unlimited dorsiflexion and promotes knee flexion moment. This design is used in patients with weakness of dorsiflexion during swing phase and flexible pes equinus.
    • Dorsiflexion ankle joint stop - The stirrup has a pin inserted in the anterior channel of the ankle joint or by flattening the anterior lip of the stirrup's circular stop. The dorsiflexion stop has an anterior angulation at the top of the stirrup that restricts dorsiflexion but allows unlimited plantar flexion and promotes a knee extension moment in the meantime. This design is used in patients with weakness of plantar flexion during late stance.
    • Limited motion ankle joint stop - This ankle joint stop has anterior and posterior angulations at the top of the stirrup with restricted dorsiflexion and plantar flexion ankle motion. The limited motion ankle joint stop has a pin in the anterior and the posterior channel, and it is used in ankle weakness affecting all muscle groups.
    • Dorsiflexion assist spring joint - This joint has a coil spring in the posterior channel and helps to aid dorsiflexion during swing phase.
    • Varus or valgus correction straps (T-straps) - A T-strap attached medially and circling the ankle until buckling on the outside of the lateral upright is used for valgus correction. A T-strap attached laterally and buckling around the medial upright is used for varus correction.

 

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Article reference : http://emedicine.medscape.com/article/314838-overview

 

 

Comments  

 
0 #1 hira shamim 2012-09-30 08:35
this was really helpful thankz ..!!
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