How To Improve AFO Control Of The Adult-Acquired Flatfoot
The most popular use of ankle-foot orthotic (AFO) therapy in the podiatric profession is treatment of posterior tibial tendon dysfunction, also known as adult-acquired flatfoot. Over the past 20 years, I have learned much about this challenging pathology from my own treatment of many patients as well as consulting with practitioners to share ideas to improve outcomes with AFO therapy. Based upon these experiences, I would like to share several pearls for treating adult-acquired flatfoot with AFO therapy.
Most practitioners focus on the valgus deformity of the hindfoot as the primary concern for correction and control of the adult-acquired flatfoot. Yet research has shown that abduction of the forefoot is the dominant and unique change in the advanced stages of adult-acquired flatfoot.1
The first level of control of forefoot abduction is the shoe itself. While I always recommend proper fit of the shoe, note that too much room in the forefoot of the shoe will diminish control of lateral shifting or abduction in the adult-acquired flatfoot deformity. A snug fit against the lateral forefoot with a firm, non-forgiving upper material is desirable when treating the flatfoot with orthotic therapy. For this reason, excessively wide, extra-depth shoes are not always desirable in controlling forefoot abduction.
Take the negative cast with the foot in a non-weightbearing position. This allows you to capture a shape that almost totally eliminates the abduction deformity of the forefoot. Conversely, abduction becomes apparent the moment the adult-acquired flatfoot hits the ground and one can capture this in any semi-weightbearing or full weightbearing cast.
Research has shown that an articulated AFO is more effective in restoring alignment of stage 2 adult-acquired flatfoot than a non-articulated gauntlet style brace.2 In this study, researchers emphasized the role of preservation of ankle joint motion to stimulate activity of the flexor muscles of the lower leg.
With a non-weightbearing casting technique, the footplate portion of the AFO device will have a proper shape with minimal forefoot abduction. From here, you can also prescribe further enhancements that will prevent lateral shift of the forefoot.
An extended lateral flange is ideal for achieving this treatment goal. Lateral flanges have a reputation for being challenging for patients to tolerate, especially with irritation of the styloid process of the fifth metatarsal base. However, I have consistently observed that most patients with adult-acquired flatfoot tolerate extended lateral flanges extremely well as part of the polypropylene footplate in their AFO braces. The styloid process is rarely prominent in flatfoot deformity. Combining the lateral flange with a forefoot strap is an excellent way to control forefoot abduction (see photo above at left).
One can add a lateral “flap” of Korex and ethylene vinyl acetate (EVA) material to an already manufactured AFO device to increase control over forefoot abduction if the device is not achieving clinical results. This is easy for a practitioner to add in the office setting (see photos below).
A medial arch flange can increase the surface area of contact under the talonavicular joint. However, if the medial flange extends medial to the first metatarsal, it actually has the potential to increase forefoot abduction. In short, a lateral flange has proven to be far more effective in controlling the adult-acquired flatfoot than a medial flange.
In terms of controlling hidfoot valgus deformity, conformity of the heel cup of the AFO device is critical. Again, a non-weightbearing cast will capture the accurate contour of the calcaneus, avoiding the flattening and expansion of the fat pad that occurs with a weightbearing casting technique. One can enhance the footplate with a medial skive of the heel cup to provide a varus wedging effect under the calcaneus. Patients with adult-acquired flatfoot tolerate 6 mm and even 8 mm medial wedging of the heel cup very well.
Finally, one can control a subluxing talonavicular joint with a Medial Arch Suspender (Richie Brace), a patented device incorporating a lifting strap directly under this joint. The patient has the ability to adjust correction of medial arch collapse to the point of maximal support without irritating the sensitive area of the skin overlying the subluxing talonavicular joint (see photo below at the right).
While AFO devices of various designs have consistently shown positive treatment outcomes for adult-acquired flatfoot, certain aforementioned enhancements can further improve success and adherence with these devices.
Editor’s note: Dr. Richie is the founder and owner of Richie Technolgies, Inc., which markets the Medial Arch Suspender.
References
1. Flemister AS, Neville CG, Houck J. The relationship between ankle, hindfoot, and forefoot position and posterior tibial muscle excursion. Foot Ankle Int. 2007;28(4):448–55.
2. Neville C, Houck J. Choosing among 3 ankle-foot orthoses for a patient with stage II posterior tibial tendon dysfunction. J Orthop Sports Phys Ther. 2009;39(11):816–824.
