What The Literature Reveals About AFOs And Adult-Acquired Flatfoot

I read with interest a recent Orthotics Q&A column in Podiatry Today entitled “Expert Insights For Prescribing AFOs.”¹ Four panelists gave opinions about when they prescribe certain styles of ankle foot orthotic (AFO) devices, specifically articulated, solid non-articulated and custom gauntlet devices. One of the panelists suggested that a certain branded brace, which is a custom gauntlet brace, could provide enhanced stability for “unstable biomechanical conditions, whether they involve soft tissue, bone or both.” He also called this brace his “go-to” brace for patients with chronic posterior tibial tendon dysfunction (PTTD).

For disclosure, I own an AFO company. More importantly, my company fabricates and sells all types of AFO devices including articulated AFOs, solid AFOs and custom gauntlet braces. As a consultant and teacher of AFO therapy, I am frequently placed in a position of recommending a certain style of brace for a specific pathologic condition. My recommendations are based upon sound science rather than financial bias since my company provides all types of braces.

Adult-acquired flatfoot secondary to posterior tibial tendon dysfunction is a complex disorder. It represents a broad range of clinical presentations and various levels of deformity that are now classified according to clinical findings.² Surgical approaches to PTTD are based upon the stage of deformity, magnetic resonance imaging (MRI) findings, the extent of ligamentous disruption and the presence of arthritic involvement. It would be ludicrous to propose that one single surgical procedure was effective for all for stages of adult-acquired flatfoot. 

Why then do I continue to hear my colleagues proclaim they use the same brace to treat each and every patient with PTTD? If stage 2 PTTD is a flexible and reduceable deformity and stage 3 is a rigid deformity, why would you treat both patient groups with the same solid gauntlet AFO?

A general rule when bracing patients with PTTD is to preserve mobility of the ankle joint. When the ankle joint motion is restricted, it places a greater demand for motion of the midfoot joints. The midtarsal joint and tarsometatarsal joints are most critical for offloading and stability in patients with PTTD. In the surgical setting, it is well known that when one surgically fuses the joints of the hindfoot, it places a greater load on adjacent joints.   

Kitaoka and coworkers demonstrated a shift of load with solid AFO braces in a kinematic study comparing solid with articulated AFO braces in two patients with flatfoot.³ The authors concluded that the articulated AFO would be more comfortable and provide more stability than the solid AFO. In their summary, the authors stated:  

“The articulated AFO limited midfoot sagittal motion more than the solid AFO. One explanation for this phenomenon is that by allowing more motion to occur at the talocrural joint, less motion was required at the midfoot joint to advance the tibia during gait.”

Neville and Houck studied three different AFO designs in the treatment of a patient with stage 2 PTTD.⁴ Articulated devices performed better and corrected deformity better than the solid AFO. The articulated AFOs corrected hindfoot deformity by providing more inversion, corrected the medial longitudinal arch and provided more forefoot adduction in comparison to the solid AFO. The authors concluded:

“The most appropriate of the 3 orthoses considered for the correction of flatfoot deformity in this patient was the custom articulated orthosis.”

In another study of AFO devices treating PTTD, Neville and Lemley again demonstrated the advantage of articulated AFOs over solid AFO braces.⁵ Two articulated AFOs showed more hindfoot inversion than a solid AFO. During midstance, the two articulated AFOs showed greater changes in forefoot plantarflexion in comparison to the solid AFO. Across all phases including loading response, midstance and terminal stance phases, the articulated AFO had more forefoot adduction than the solid AFO, which had minimal effect.

When considering the averages across all of the aforementioned phases, the custom articulated device limited eversion better than the solid AFO (3.3 degrees for the articulated device in comparison to 2.3 degrees for the solid AFO and 2.2 degrees for the off-the-shelf device).⁵ This outcome is consistent with a previous case study in which the articulated device was the most successful in limiting hindfoot eversion.⁴
 
The design of the articulated device has a close-fitting heel cup, which may improve inversion control. Another hypothesis is that greater muscle function may allow ankle motion to aid with greater inversion motion.

In stage 3 and 4 adult acquired flatfoot, the rigid deformity and pain of degenerative arthritis often requires arthrodesis of hindfoot joints to correct deformity. Similarly, a more rigid non-articulating gauntlet would be indicated for these patients. Whether planning surgical intervention or AFO bracing, each and every patient must be evaluated to determine level of deformity, range of motion of major joints and presence of arthritis. In every case, preservation of joint motion and restoration of normal gait are the ultimate goals. Articulated AFO devices have proven to achieve this outcome better than solid non-articulated gauntlet braces.

References

1. DeHeer P, Mirkin G, Volpe R, Williams B. Expert insights for prescribing AFOs. Podiatry Today. 2019; 32(2):24-26.

2. Johnson KA, Strom DE. Tibialis posterior tendon dysfunction. Clin Orthop Rel Res. 1989; 239:196-206.

3. Kitaoka HB, Crevoisier XM, Harbst K, Hansen D, Kotajarvi B, Kaufman K. The effect of custom-made braces for the ankle and hindfoot on ankle and foot kinematics and ground reaction forces. Arch Phys Med Rehabil. 2006;87: 130-5.

4. 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.

5. Neville C, Lemley FR. Effect of ankle-foot orthotic devices on foot kinematics in Stage II posterior tibial tendon dysfunction. Foot Ankle Int. 2012; 33(5):406–414.