Understanding The Impact Of Diabetic Neuropathy On Gait

Author(s): 
By Gordon Zernich, CP, BOCPO, Tomas Dowell, CPO, LPO, and Ronald B. Tolchin, DO, FAAPM&R

Weighing The Pros And Cons Of Custom And Prefabricated AFOs
Custom polypropylene plastic AFOs may also use dorsiflexion assist ankle joints. The ankle joints bisect the sagittal midline of the anatomical ankle joint and its center of rotation keyed to the distal medial malleoli. The shape of the brace provides more medial and lateral stability to the lower leg by default.
Prefabricated carbon fiber dorsiflexion assist AFOs are lighter in weight and provide a longer service life but their shape is somewhat different. These devices provide no medial lateral support to the foot and cover the half of the circumference of the proximal lower leg from the anterior aspect. They provide dorsiflexion assist and foot support by way of a serpentine shape that runs from the medial proximal part of the brace to the lateral part of the footplate between the mid- and hindfoot. A posterior Velcro strap holds it in place.
A metal AFO is attached to a stirrup or a caliper that is riveted to the heel area of the shoe. The stirrup or caliper set on the shoe reflects the amount of toe out on the contralateral side. Some metal AFOs will have a single, medial aluminum upright whereas others will have bilateral uprights that bisect the sagittal midline of the malleoli and the lower leg. The upright(s) attach to a calf band positioned approximately 7 cm distal to the fibula head. An anterior Velcro strap and a buckle attached to the uprights secure the AFO to the patient.
A metal dorsiflexion assist ankle joint AFO, which provides free range of motion to 90 degrees in the sagittal plane, is indicated for the diabetic patient with sensorimotor neuropathy and drop foot. The center of rotation and position of the ankle joint AFO is the same as the plastic type. Both ankle joint AFOs prevent footdrop while the metal AFO assists the lifting of the foot from toe off through the swing phase of the gait cycle.
The aforementioned AFOs have their own risks and potential compromises. One may mitigate some of these issues by utilizing accessory components to the AFO or to the shoe. The lateral T-strap on the shoe may be necessary to maintain the foot’s alignment with the line of progression and to counteract equinovarus of the hindfoot and the ankle. Another accessory involving a shoe modification is the solid ankle cushioned heel (SACH). The SACH modification dampens the force exerted by the foot during heel strike and approximates controlled plantarflexion to foot flat when one employs this modification with an AFO for footdrop.
Most AFOs resist, if not completely eliminate, controlled plantarflexion. While that does away with the problem of foot slapping and toe scuffing drop foot, it greatly accelerates the moment in the gait cycle between heel strike and mid-stance, virtually skipping foot flat, the intervening moment of plantarflexion between the two. Without the modification of a SACH to the shoe to compensate for the restricted or eliminated plantarflexion caused by the brace, a compromised gait pattern is still evident. Accordingly, there is further risk of pressure injuries to the sensorimotor neuropathic diabetic foot.
Other risks and compromises are limited to the specific type of brace. The PLS/AFO and its carbon fiber cousin have cosmetic appeal because both are far less noticeable when worn in public. Both function as effectively as the metal variety of AFOs and are somewhat lighter in weight than the metal brace.
However, the footplate of the polypropylene plastic AFO is hard whereas the carbon fiber composite footplate is less so with it being thinner and having more of an edge. When a hard footplate is situated inside of a shoe containing a sensorimotor neurologically impaired diabetic foot with a compromised gait pattern at best, there is a significantly increased risk of further injury to the foot.

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