Emerging Insights On Ex-Fix Offloading For Diabetic Foot Ulcers

William P. Grant, DPM, FACFAS, Lisa M. Grant, and Bryan R. Barbato, BS

It is well understood that unremitting pressure is a major etiologic factor in both the creation and persistence of diabetic foot ulcers. Sensory neuropathy in combination with autonomic and motor neuropathy readily produces foot deformities with bony prominences and skin lacking normal protective sensibility. Further complicating the problem, alteration in tendon morphology and its function produces increased plantar pressures as well as temporal alteration in the phasic gait cycle that can destroy the protective barrier of the skin beneath the foot.

   Historically, researchers have embraced total contact casting (TCC) as a gold standard of treatment for neuropathic diabetic foot ulcerations. Multiple studies have demonstrated healing rates ranging between 77 to 100 percent.1-12

   Alternatively and more recently, researchers have studied the use of controlled ankle motion (CAM) walker boots as an offloading modality for diabetic foot ulcers.13 Authors have demonstrated that CAM Walker boots are virtually equivalent to TCC in terms of efficacy and far easier and safer.13 Interestingly, some authors advocate wrapping the CAM walker boots with cast tape between visits, emphasizing enforced adherence and continuous use as being integral to the success of these modalities.

   As with any other treatment modality, however, TCC has its limitations and complications.

   Perhaps the greatest limitation of the TCC or the casting tape wrapped CAM walker boot is the inability of the physician or home health nurse to examine the wound, or the foot for that matter, between office visits. This can result in deterioration of the ulcer, infection, new ulcerations or ischemic changes without awareness in the neuropathic patient. Disastrous consequences including limb loss can occur with this modality, particularly when inexperienced practitioners attempt to use this offloading option. Use of the CAM walker boot can negate this issue to some extent but not entirely.

   Another issue for TCCs is the indication is limited to grade 1A diabetic foot ulcers as per the University of Texas Wound Classification System.14 In other words, one would not use TCCs for wounds beyond non-infected, non-ischemic superficial ulcerations that do not extend to tendon, bone or capsule.

   When the reality is that 20 percent of diabetic foot ulcers are ischemic, approximately 56 percent become infected and 50 percent are neuropathic, this significantly limits the population appropriate for total contact casting. In fact, 30 percent of all patients with DFUs have at least two of these conditions.15

   In fact, the wound characteristics most often associated with failure to heal are the size of the wound, its grade and its duration.16

Could External Fixation Be A Viable Offloading Alternative To TCC And CAM Walker Boots For Complex Diabetic Foot Wounds?

An alternative to TCC or CAM walker boots for the offloading of diabetic foot wounds is external fixator frames. Traditionally, surgeons have utilized Ilizarov skinny wire and hybrid half-pin fixators for Charcot reconstruction of the midfoot, hindfoot or ankle in patients with diabetes.

   Bent tension wire fixation reportedly offers better compression of a midfoot osteotomy then either Kirschner wires or lag screws.17 This fixation also provides synergistic compression when surgeons combine these fixation options. When it comes to using this modality for offloading, the wires do not need to be bent, only tensioned.

   Typically, external fixation with multiplanar frames permits some weightbearing as the body load is shared by the external fixator with the limb and the foot. Often, incorporating a surgical shoe helps facilitate offloading with external fixation.

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