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.
A different situation exists if there is a wound on the weightbearing surface. In this case, one can construct an offloading external fixator to completely remove all pressure from the plantar foot. The surgeon can accommodate this by simply adding an additional ring below the foot plate after applying post-op dressings.
Be aware though that adding this offloading ring has consequences, both positive and negative.
In terms of benefits, the offloading frame absolutely removes all weight from the wound, permitting an environment that is conducive to wound healing 24 hours per day. This eliminates surface tension on the plantar foot.
Surgeons can incorporate split thickness skin grafts, local flaps or free flaps without any interference due to unremitting pressure from a cast or accidental partial weightbearing. Using external fixation for offloading also allows one to examine the wound daily. Podiatrists can manage draining wounds and deal with post-op complications in real time. Surgeons can also perform reconstruction or limb salvage simultaneously, including an arthrodesis osteotomy or partial amputation.
Conversely, offloading external fixation has a variety of limitations specific to its nature. First, application of an external fixator requires a surgeon confident of having the skills necessary to apply and maintain an external fixator. The procedure to apply a frame typically requires approximately 30 to 60 minutes of OR time. All of the skinny wires must be tensioned for the frame to function. Aftercare requires cleansing of the pin sites and application of an antibacterial dressing at the pin-skin interface. Pin sites can become irritated or infected, or the pins may fail. These complications would require a prompt return to the operating room for a pin exchange.
In our experience, the offloading frame typically has a slightly higher complication rate with pin breakage, irritation and pin site infection. This is likely due to the frame now carrying the entire body load and not sharing it with the foot. Typically, we see the most proximal pin above the ankle as the most likely pin to become irritated or break.
Recommended Indications For Using External Fixator Offloading Frames
1. Ulcer greater than grade IIA (University of Texas Wound Classification System)
2. Ulcer occupies a large portion of the plantar foot
3. The ulcer location precludes appropriate offloading
4. The ulcer is infected or ischemic
5. The ulcer is associated with a complex deformity
6. The ulcer requires a flap or graft
7. Non-weightbearing not possible
(e.g. amputation of opposite limb)
What One Preliminary Study Revealed
A preliminary study initiated in our office included 11 consecutive patients with complex diabetic wounds. We utilized offloading external fixation in all of these patients, who additionally had multiple surgical procedures. Seventy-seven percent of the patients had deep wounds, 92 percent of the wounds were infected and 39 percent of the wounds were ischemic.
Prior to our intervention, the average ulcer duration was 281 days and 100 percent of the wounds were neuropathic. In regard to adjunctive procedures, we utilized 25 acellular matrices, seven skin grafts and four local flaps prior to ex-fix application. We utilized five skin grafts and seven local flaps in combination with ex-fix application. All of the wounds healed and the average number of days to ulcer healing was 59. There was a 15 percent complication rate with two pin site infections. There was no ulcer recurrence.
In comparison, other studies utilizing TCC had averages of 43 days of therapy duration, a 90.3 percent healing rate, a 23.4 percent complication rate and a 32 percent ulcer recurrence rate.1-12
Offloading external fixation is a valuable and beneficial tool for the podiatrist to employ in limb salvage. Just as TCC has become a gold standard for less complex diabetic foot ulcers, the external fixator may in fact become acknowledged as a gold standard in complex diabetic wound repair.
Dr. Grant is a Fellow of the American College of Foot and Ankle Surgeons, and is board-certified by the American Board of Podiatric Surgery. He is an instructor in the Department of Surgery at Eastern Virginia Medical School and is in private practice in Virginia Beach, Va.
Ms. Grant is a third-year podiatric medical student at Des Moines Medical University.
Mr. Barbato is a graduate of James Madison University and a current applicant to colleges of podiatric medicine.
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Editor’s note: For further reading, see “External Fixation: Is It The Answer For Diabetic Limb Salvage?” in the July 2004 issue of Podiatry Today or “Assessing The Use Of Ex-Fix For Offloading In Diabetic Limb Salvage” in the February 2012 issue.