A Guide To Orthotic Therapy For Adult-Acquired Flatfoot

Paul R. Scherer, DPM

Orthotic Therapy Recommendations For Stage I AAF

Negative cast: neutral suspension cast
Positive cast correction: perpendicular
Material: rigid polypropylene
Heel cup: deep 18 mm to 22 mm
Width: wide with medial flange
Cast fill: standard
Heel skive: 4 mm to 6 mm medial skive determined by heel eversion
Positive cast modification: no inversion; sweet spot navicular tuberosity
Rearfoot post: flat or 0/0
Top cover: full-length EVA to the toes
Forefoot extensions: none necessary

Pointers For The Orthotic Treatment Of Stage II AAF

Treatment for this more advanced pathology, which includes the hallmark of tendinosis and the attenuation of the tendon, must be more aggressive than for stage I. One must direct treatment to the dysfunction of the rearfoot ligaments as they bear the load of excessive forces and start to attenuate. Attempts to maintain this flexibility, especially of the ankle joint, must be included in the treatment plan if the patient is to maintain function and a relatively normal gait.

   Complete restriction of subtalar joint motion places a burden on the ankle joint. The subtalar joint has a small but significant function in the sagittal plane, allowing dorsiflexion of the foot on the leg. If this dorsiflexion is restricted, then ankle dorsiflexion must increase to compensate for it. This extra burden can itself produce deterioration, compensation and deformity, and the device must address this.

   The loss of function in the subtalar interosseous ligament and the spring ligament makes conventional functional foot orthoses (FFOs) of little use. Redirecting GRF is ineffective since this force cannot transfer from the calcaneus to any other bone through these ligaments. The unabated internal rotation of the leg requires some sort of mechanical intervention above the ankle to relieve symptoms and to prevent or slow the progression of further deformity.

   The motivation behind the development of podiatric ankle-foot orthoses (AFOs) like the Richie Brace was to apply forces both below the foot through the footplate and above the foot through uprights attached to the lower leg in order to control the transverse and frontal plane motions above the ankle.

   Richie Brace AFOs are created from negative casts, which capture the subtalar joint in relative neutral position and the orientation of the malleoli (and therefore the position of the ankle joint axis). The neutral cast, similar to the one used for the aforementioned functional foot orthoses, must reduce the supinatus (false forefoot varus) that almost always occurs as compensation in this pathology.

   An orthotic laboratory makes a Root-type footplate that has two stirrups with leg uprights attached, producing the lower leg component. The hinges between the stirrups and the uprights allow sagittal plane motion during gait but inhibit frontal and transverse plane motion. The concept is to provide external fixation between the rearfoot and the lower leg to compensate for the damaged and attenuated ligaments.3

   Custom-articulated AFOs, in my experience and in a case report, produce greater anatomic alignment than prefabricated or non-articulated AFOs.12 However, it is merely an assumption that anatomic realignment actually delays further deformity or produces any permanent correction. We do know that anatomic realignment, especially of the rearfoot, reduces symptoms.

   Selecting footwear for the stage II patient is as important as selecting the brace. Again, in my experience, patient adherence in treatment is primarily a function of orthotic comfort and the ability to wear culturally acceptable footwear. Rigid athletic shoes with motion control or shoes with stiff shank construction and reinforced heel counters are essential. Occasionally, persistent edema in a patient with this pathology will necessitate extra depth shoes.

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