Exploring The Potential Of AFO Devices

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A Review Of Neuromuscular Disorders Of The Lower Extremity

Ankle foot orthoses have traditionally been prescribed to treat neuromuscular disorders of the lower extremity. The California Classification provides an overview of common disorders (spastic, coordination, flaccid and weakness) you may see in your practice.

Spastic disorders include cerebral palsy, post-cerebral vascular accident (CVA) and post-brain injury. These are primarily upper motor neuron lesions. From a podiatric standpoint, the spastic condition usually results in equinus and equinovarus. These conditions are not easy to categorize as their natural course can vary between spasticity and weakness or both.

Coordination disorders include Friedrick’s Ataxia, cerebellar ataxia and Parkinson’s Disease. These conditions are least likely to require AFO interventions.

Flaccid disorders include polio, radiculopathy, Charcot-Marie-Tooth (CMT) and peroneal muscular atrophy. Flaccid conditions are perhaps the simplest pathologies to evaluate and treat with AFOs. When there is no contracture or equinus, choosing a proper AFO design is simplified.

You may see muscle weakness in patients who have multiple sclerosis and muscular dystrophy. Muscle imbalance inevitably results in the lower extremity with acquired deformity and altered gait pattern. When treating these patients, you must consider stability of the knee when prescribing the appropriate AFO.

While understanding the pathomechanics of these neuromuscular disorders is critical for any practitioner prescribing AFOs, your biomechanical assessment of the patient will ultimately determine what type of orthotic device is most appropriate. Performing gait analysis, a range of motion exam and muscle testing are critical for determining the appropriate prescription.

The Arizona AFO is popular among podiatrists for treating Charcot deformities and adult-acquired flatfoot.
When treating patients who have dropfoot conditions and flexion instability of the knee, the author recommends using a full length AFO. He says you can choose between the posterior leaf spring AFO (see photo on left) or the solid ankle AFO (see photo on r
A custom-molded AFO should not be contraindicated when there is sensory neuropathy, according to the author. He says you can line the shell and foot plate with laminated multi-density foam to protect the skin (as seen above).
By Douglas Richie Jr., DPM

While several large orthotic laboratories have offered AFOs for over 20 years, the increasing demand for the devices has become a significant phenomenon in the podiatric field. Why have podiatrists turned to AFOs more and more in recent years? There are three key reasons that have caused this shift in treatment.
First, there has been a meteoric rise in the number of patients who have challenging foot and ankle pathologies. Two of these pathologies, adult acquired flatfoot secondary to posterior tibial tendon insufficiency and diabetic Charcot’s arthropathy, have disappointing treatment results with traditional orthotic devices alone. Secondly, there has been increased inclusion of AFO, bracing and pedorthics topics into the curriculum of podiatric medical education and educational seminars. New “podiatric AFO” technologies have also emerged. These technologies are not only user-friendly, but tend to embody the traditions of podiatric biomechanics.

Know The Differences Between AFOs And Traditional Foot Orthoses
AFOs do provide mechanical advantages over traditional foot orthoses. AFOs provide a force system both above and below the major joint axes of the rearfoot and ankle. Depending on the AFO design , you can apply these forces in either the frontal, sagittal or transverse planes.

Orthoses apply force to stabilize a joint via a three-point pressure system, which is defined as two forces applied to a body part opposed by a third force applied between the first two. In the majority of AFOs, multiple three-point force systems provide stability to one or more joints in one or more planes throughout the gait cycle.
Traditional foot orthoses, particularly the Root Functional Orthosis, rely on ground reaction forces to stabilize a joint. You cannot establish a three-point force system with foot orthoses to control any of the major joints of the rearfoot. While the combination of proper footwear and a functional foot orthosis can potentially provide adequate three-point force systems, this is not always predictable and the effects of such a shoe-foot orthotic system are limited to certain phases of the gait cycle.
The efficacy of functional foot orthoses to treat common lower extremity pathologies has been primarily validated by anecdotal reports in the medical literature. Today, there is considerable debate about how foot orthoses actually work. There is little evidence that these devices actually realign the skeleton and change joint position.
Realizing the necessary design of an orthotic to change a joint position allows you to understand why traditional foot orthoses have demonstrated minimal ability to significantly change the position of the subtalar joint in gait. Foot orthoses may work by redirecting forces and changing neuromuscular patterns of the lower leg. Benno Nigg, et. al., are conducting research at the University of Calgary that will shed further light on this fascinating subject.

Which Pathologies Can You Treat With AFOs?
Podiatrists see several lower extremity pathologies in which changing a joint position is desirable in achieving a satisfactory treatment outcome. These conditions include adult acquired flatfoot secondary to posterior tibial tendon dysfunction, Charcot’s arthropathy and dropfoot. All of these pathologies require you to apply force to the tibia to adequately control rotation of both the ankle and the subtalar joints.
Years ago, DPMs initially began using cam-walker style boots to treat these pathologies with great success. Yet once they reduced the acute symptoms, there was a reluctance to consider long-term treatment with a foot and ankle brace. Now it is recognized that the same stabilization provided by a cast-boot can be accomplished by an AFO with better function and patient compliance.

How You Can Use AFOs To Treat Dropfoot
In the case of dropfoot, there are many considerations in patient evaluation and AFO prescription, which can be confusing to the average practitioner. Critical assessment factors include range of motion, muscle weakness, spasticity, knee stability and the patient’s size and weight. Another critical concern is activity level and lifestyle of the patient.

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