In 1996, Douglas Richie Jr., DPM, introduced the first ankle foot orthosis (AFO) to incorporate a functionally balanced foot orthosis. Podiatrists have long utilized AFOs to control ankle joint motion. However, the AFO designed by Dr. Richie was the first AFO to also provide the benefits of functional correction of the foot. These additional benefits included greater control of the subtalar joint, midtarsal joint stability and enhancement of the windlass function.
The result was a rapidly accepted new modality that became a primary treatment in the podiatric profession for pathologies including adult acquired flatfoot, ankle DJD and lateral ankle instability. These “functional AFOs” are now available from many orthotic laboratories under several brand names (see “A Guide To Available Ankle Foot Orthoses” below).
However, as with any DME item, patients wearing functional AFOs can develop comfort, fit or function problems. It is imperative that the prescribing physician be adept at troubleshooting any situation that may occur. With this in mind, let us take a closer look at two common complaints – medial malleolar irritation and talonavicular irritation – that patients may experience with functional AFOs.
Understanding The Potential Causes Of Malleolar Irritation
Irritation of the medial malleolus is the most common patient complaint with functional AFO therapy. There are several situations that can lead to this problem. These causes include improper hinge placement, medial displacement of the distal tibia, improper negative casting, improper positive castwork and lack of shoe stability.
Improper placement of the medial hinge can lead to malleolar irritation. This is most likely to occur if the physician fails to mark the malleoli appropriately or if he or she uses an improper casting position.
To avoid this problem, it is always imperative to mark the malleoli and ensure that the mark transfers to the plaster cast. If one utilizes an STS sock rather than plaster to cast the foot, then the clinician can mark the malleoli on the outside of the sock while it is still on the foot. Alternatively, one may place a piece of felt over the malleoli at the time of casting so you can capture an impression of the felt with the sock.
It is also important to ensure proper casting position. If the ankle is plantarflexed during casting, one may place the hinge too far superior to the malleolus. Be sure to maintain the foot at 90 degrees to the leg during casting. If the patient has an equinus that prevents the foot from reaching 90 degrees, then the functional AFO is contraindicated.
Pertinent Pointers For Preventing Severe Medial Displacement Of The Distal Tibia
A second cause of malleolar irritation is severe medial displacement of the distal tibia during weightbearing. The medial displacement presses the medial malleolus into the medial upright, resulting in pressure and pain.
To avoid malleolar irritation secondary to medial displacement, clinicians should:
• perform a weightbearing examination;
• plantarflex the first ray when casting;
• write an anti-pronation prescription;
• ensure proper positive castwork by the lab; and
• recommend stable shoes.
If you note a significant tibial shifting during the weightbearing examination, note it on the exam form or send a picture of the patient to the lab along with the prescription. The laboratory can adjust the medial upright to fit around the malleolus.