A Guide To Orthotic Therapy For Adult-Acquired Flatfoot
- Volume 24 - Issue 7 - July 2011
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The type of custom device used in one clinical report was the University of California Biomechanics Laboratory (UCBL)-type device, which is made from a neutral negative cast.10 This study demonstrated that the in-shoe device “provided superior restoration of both arch and hindfoot kinematics.” The similarly designed Root custom functional foot orthoses, with a deep heel cup, top cover and sweet spot for the navicular tuberosity, provide the same support with a much greater acceptance and adherence. This is because the Root device fits into most contemporary shoes, which is not the case with the UCBL orthosis. If the patient will not wear the device, then it cannot be effective.
The addition of a medial heel skive would improve such a device by shifting the effective ground reaction force (GRF) more medially, resisting eversion of the calcaneus and unlocking the midtarsal joint.11 Widening the midsection of the orthosis by adding a medial flange expands the surface area of the orthosis and allows better control. The flange also improves orthotic comfort by distributing force over an expanded surface area.
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.