Key Pearls For Prescribing AFOs

Author(s): 
Clinical Editor: Howard Dananberg, DPM

You may find that even the best of custom foot orthotics are insufficient to manage a particular patient’s problem. Either too much force is applied to the foot or perhaps the foot orthotic cannot provide the necessary support. In some of these cases, one may consider using an ankle foot orthotic (AFO). In a follow-up to last month’s cover story, a panel of experts address how and when they employ these devices in treatment. Q: In what type of situation do you consider using an AFO or similar brace? A: Alan Banks, DPM, uses an AFO in various situations, saying the device can be helpful in treating a variety of conditions. Sometimes he uses a prefabricated AFO for patients who have some type of dorsal or anterior nerve injury. Dr. Banks says plantarflexion of the foot during sleep serves as a source of traction to such nerves. He notes that this plantarflexion can aggravate or reduce the rate of healing if there is a nerve injury or neuritis. Since the AFO is typically only used at night, a custom fitted device is not required. “The prefabricated AFOs are economical and effective in this setting,” explains Dr. Banks. In some instances, they can also be employed by the patient during the day if necessary. Both Dr. Banks and Doug Richie, Jr., DPM, have found AFOs useful in treating Charcot conditions. Dr. Banks notes that he may use them to treat patients who have an early or mild Charcot deformity once the condition is quiescent. “If the device is rigid, it will alleviate much of the bending stress at the ankle,” maintains Dr. Banks. “It is this force which is the most destructive in patients with neuropathy.” In Dr. Richie’s experience, an AFO can reduce plantar pressures and resist contracture of the heel cord in the Charcot foot. More advanced Charcot conditions are a different story, according to Dr. Banks. When treating these patients, particularly those with transverse plane dominance, Dr. Banks has found the AFO “simply does not provide enough accommodation for the foot deformity.” Instead of an AFO, he typically uses a double upright brace in combination with a molded shoe or perhaps a depth oxford with an orthotic or molded plastazote liner. “This generally tends to provide better protection for the foot itself,” notes Dr. Banks. How Should You Use AFOs For Dropfoot? Howard Dananberg, DPM, most commonly uses AFOs to treat dropfoot. Dr. Dananberg notes that following conditions like CVA, problem back surgery or spinal injury, the anterior musculature of the patient’s lower leg may fail to function normally. When this specifically involves the anterior tibial muscle, the foot does not have effective dorsiflexion capacity. During swing phase, this lack of dorsiflexion causes the toes to touch the floor and patients frequently are subject to tripping, according to Dr. Dananberg. “The most usual patient accommodation for this is a steppage-type gait,” says Dr. Dananberg. “In these cases, AFOs can be quite effective.” Dr. Richie notes that when you employ the device to treat conditions such as dropfoot and lateral ankle instability, the AFO can control sagittal plane ankle rotation and also resist unwanted subtalar and midtarsal joint inversion instability if the orthotic footplate is properly contoured and balanced. Historically, bracing has been used to treat patients with dropfoot and is still “a reasonable conservative alternative for this condition,” according to Dr. Banks. However, Dr. Banks also points out that “the need for bracing of the foot and ankle has, in many circumstances, been obviated with the advancement of surgical techniques that allow patients to undergo repair of their deformities and/or with tendon transfers to provide dorsiflexion.” There are also clinical situations in which prescribing an AFO may not be the best course of action. Dr. Banks says a common problem is physicians prescribing an AFO for a patient who has a spastic equinus following a stroke. In this circumstance, the foot is often fixed in equinus and therefore the AFO is “of little benefit, except to possibly counteract some additional degree of contracture.” That said, Dr. Banks says using an AFO may be an acceptable means of controlling patients with tibialis posterior tendon dysfunction who are not surgical candidates or are waiting for a more convenient time to undergo surgery. In some instances, patients who have chronic tendonopathy at this level (or involving the Achilles tendon) may benefit from a more sustained form of immobilization which you may achieve with the AFO. Dr. Banks also notes that the AFO may provide some symptomatic relief for patients who have chronic pain secondary to arthritis and typically works better than a functional orthotic alone. Dr. Richie says one of the key benefits of the AFO is it can provide a force system both above and below the axis of rotation of the major joints of the ankle-rearfoot complex. The device also can help control position of the foot during the swing phase of gait. “These are significant advantages over standard custom functional foot orthoses,” notes Dr. Richie. “In the adult acquired flatfoot, secondary to posterior tibial tendon insufficiency, you should consider the AFO when standard foot orthoses fail or in any patient who has lost integrity of the spring ligament and deltoid ligament complex.” Q: When taking an impression for an AFO, what do you consider most important? A: When taking an impression, Dr. Dananberg says he usually makes sure the foot is positioned at 90 degrees to the lower leg. However, he cautions there are times when this is either not possible or a 90-degree device would not be appropriate due to the height of the heel the patient wears. “Several years ago, I did have a female patient who wanted to wear a high-heeled shoe,” recalls Dr. Dananberg. “She was cast in the position (mildly plantarflexed) that her foot would be in the shoe and she was very pleased with the device she received.” For Dr. Richie, the most important consideration in casting and prescribing an AFO is performing a stance evaluation of the patient and determining position of the tibia relative to the foot and floor. He emphasizes a careful assessment of ankle range of motion and reducibility of deformity when placing the foot in a corrected, “neutral” position. The cast must accurately capture the corrected foot position, according to Dr. Richie. While Dr. Banks usually refers patients to a prosthetist for molding and fabrication of the device, he will advise the prosthetist as to whether or not he wants a rigid device or one with some degree of flexibility. For the majority of patients, Dr. Banks will recommend a more rigid device in order to “maximize the level of immobilization and protection.” Q: Are there any specific problems you see with AFOs that could be considered areas to avoid during the fabrication process? A: Dr. Dananberg says he often finds the foot bed of the device is excessively long and ends in front of rather than behind the metatarsal heads. Although some who fabricate these AFOs may feel the increased length will better maintain the toes’ rectus position, Dr. Dananberg believes this increased length blocks metatarsophalangeal joint dorsiflexion and makes walking most difficult. By creating a device that ends behind the metatarsal heads and even incorporating a first ray cutout, you can achieve sufficient control of a dropfoot condition, according to Dr. Dananberg. The difference is patients can step efficiently and far more comfortably, notes Dr. Dananberg. He adds that designing a device this way “can often prevent the arch irritation so common with AFO use.” Dr. Richie says you must inform the lab about the specific limitations of the patient in terms of fixed structural deformity as well as muscle weakness or spasticity. “Patients with lateral ankle instability and high tibial varum should have their AFOs modified to fit the varus deformity of the leg. Otherwise, their lateral instability will get worse,” he contends. Dr. Richie says you cannot position a patient with dropfoot and severe equinus in a fixed solid AFO set at 90 degrees at the ankle. He also notes that one should not prescribe an articulated, full-motion AFO for a patient with spasticity. In summary, Dr. Richie says it is essential to give the lab as much biomechanical information about your patient as possible. “Certainly, this is much more important than the required information for the fabrication of standard custom foot orthoses,” he concludes. Dr. Dananberg (pictured) practices in Bedford, N.H. Dr. Richie is a Director of the American Academy of Podiatric Sports Medicine. Dr. Banks is the Director of Podiatric Medical Education and Residency Training at the Emory-Northlake Regional Medical Center in Tucker, Ga. He is a Fellow of the American College of Foot and Ankle Surgeons and is on the faculty of the Podiatry Institute.

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