There has been a six-fold increase in diabetes mellitus over the last four decades in the United States.1 Indeed, 798,000 new diabetic patients are diagnosed each year in the U.S.2,3 The statistics are particularly disturbing when it comes to lower extremity amputation among people with diabetes. Lower extremity amputation among the diabetic population increased from 67,000 in 1994 to 140,000 in 2000.4 While amputation in the diabetic population is a viable option in the presence of significant peripheral arterial disease and gangrene, life expectancy after major lower extremity amputation is appalling with only a 40 percent five-year survival rate.2,3 However, many of these lower extremity amputations can be prevented via diabetic limb salvage. Granted, one must consider a realm of potential complications and the general health of the individual before proceeding with diabetic limb salvage (see “Why Appropriate Patient Selection Is Essential” below). Salvaging the diabetic foot has challenged many expert surgeons to provide a stable, predictable and reproducible method for fixating an unstable diabetic limb. However, one technique that is proving to be reliable for diabetic limb salvage is external ring fixation. Why Appropriate Patient Selection Is Essential The goals for limb salvage should be simple, focused and presented clearly to the patient. The goal is not just to prevent amputation but to provide a stable, ambulatory limb which, combined with education and glycemic control, will improve the quality of life for the patient. Optimizing patient compliance via the involvement of other specialty medical professionals will produce predictable results while achieving preset goals. One must address optimizing the diabetic patient’s emotional, psychological and physical well-being prior to surgical intervention for limb salvage. Indeed, patient selection is an extremely important factor when considering the use of external ring fixation for patients with diabetes. Discovering physical, psychological and emotional limitations during an interview process long before surgery can prevent early and profound failure. A difficult aspect of the interview process is determining the level of the patient’s intellect when discussing external fixation. Assessing the patient requires experience by the surgeon and possibly multiple interview sessions in order to ensure the patient fully understands all aspects of external ring fixation. Also keep in mind that a patient’s personal hygiene is often an under-evaluated factor during the interview process. However, a patient’s personal hygiene may play a large role in the development of pin tract infections during external ring fixation. People with poor hygiene and/or incontinence are poor candidates for external fixation and predictably experience higher rates of infection. How External Fixation Addresses The Failures Of Traditional Internal Fixation Traditional techniques of fixation in diabetic limb salvage can be unreliable.5 The use of internal screws, plates, staples coupled with a patient’s inability to remain non-weightbearing often yields inconsistent and undesirable results. For many diabetic patients, Charcot deformity is the pathological entity requiring surgical limb salvage intervention. However, two key factors lead to the failure of traditional internal fixation for reconstruction. These factors include poor bone quality and the inability to achieve adequate compression; and a deformity that limits access for proper, accurate fixation with appropriate anatomic reconstruction. External ring fixation does produce predictable and reproducible results in diabetic limb salvage.5 By using tensioned wires in external fixation adjacent to either the corrective osteotomy of the joint or the portion of the foot that you will be stabilizing, the compression you obtain will exceed that which is possible with internal fixation. There are applications for external ring fixation that cannot be addressed with internal fixation. For example, many patients have physical handicaps that prevent them from being non-weightbearing after surgery. Using an external ring fixator allows guarded weightbearing immediately after the procedure. The ability to bear weight is limited by painful stimulus so it stands to reason that neuropathic patients are often noncompliant. One must show these patients how much weight they can place on the operative foot as the degree of patient compliance will have an impact on results. Weighing The Pros And Cons Of External Fixation The evolution of the external ring fixation principles developed by Ilizarov facilitates extremely stable, predictable results for the reconstruction of the diabetic foot.6 However, it’s important to bear in mind that applying external fixation can be technically difficult without proper training, and has advantages and disadvantages. Advantages include extremely stable fixation, uniform compression and the ability to reduce noncompliance complications by allowing the patient partial weightbearing immediately after surgery. The main disadvantage of using external ring fixation is the potential for infection at the pin sites. Meticulous pin care minimizes the risk of infection in this immune-compromised group of patients. There are many indications for external fixation and they include: Charcot reconstruction, ankle/rearfoot arthrodesis and fractures, delayed/non-unions, congenital deformity correction, pes cavus/pes planus correction, and tumor/neoplasm correction. There are also a few contraindications that include: severe to moderate peripheral arterial disease without vascular surgical intervention; mental incompetence; and when patients have a history that potentially suggests the development of “frame fever” (severe anxiety/panic resulting in early removal of the ring fixator). How To Solve Potential Minor Complications Of External Fixation As with all forms of fixation, complications do occur with the use of external fixation. Minor complications include pin tract irritation, pin tract infection, fractured trans-osseous wires or half pins, and pain secondary to positioning of the wires.7 Minor complications of the skin-wire interface are what differentiate external fixation from forms of internal fixation. It is normal for postoperative edema to occur around surgical sites and the nature of external fixators prevents adequate compression in most circumstances. While the pin sites allow for drainage of serous and hemorrhagic fluids, postoperative drainage promotes the risk of infection and pin site irritation. Intermittent swelling around pin sites can lead to more significant infections into deeper layers of tissue. In order to address these issues, we emphasize using sterile sponges with a pin cut that helps prevent edema around pins while absorbing excessive drainage immediately after the procedure. Postoperative dressing changes include cleaning the fixation wires with antiseptic from the skin-pin interface out toward the frame. This technique prevents iatrogenic infection during dressing changes. Pain secondary to pin placement and orientation is a common minor complication. There may be pain when one places the pins through the muscle belly or through areas of the leg and foot of obese patients. Surgeons can prevent this pain from soft tissue irritation by placing wires or half pins through areas in which there is less potential for tissue movement around the portion of the wire that is below the skin. However, it may be impossible at times to avoid placing wires through areas of muscle. Fractured wires and half pins are minor complications if one avoids the loss of surgical correction. Fractured pins and wires result from the stress of repetitive motion during weightbearing gait. This complication is often unavoidable. We recommend modifying the weightbearing expectations with some patients. Many obese patients, particularly patients with diabetic neuropathy, have poor proprioception and are therefore at risk for hardware failure if they can tolerate excessive or inappropriate weightbearing. In our experience, obtaining a consult with physical therapy for preoperative gait training has led to a decrease in hardware failure for most patients. A Guide To Addressing Potential Major Complications Major complications of using external fixation include non-union, osteomyelitis, neurovascular injury, joint subluxation and bone fracture.8 Major complications such as nonunion in diabetic limb salvage can be secondary to either a poor frame construct, using an insufficient number of wires and pins necessary to produce the stiffness and rigidity necessary for fusion, or both. Many cases involving diabetic limb salvage require the patient to use the fixator for a prolonged period of time in order to achieve fusion. Adequate rigidity and stiffness are needed throughout the healing time. Constant inspection of wires for loosening during postoperative visits with re-tensioning of wires helps to prevent a loss of compression across fusion sites. Being able to readjust the position of external fixators is a major advantage over internal fixation as it assists in preventing non-unions and malunions. Osseous fracture after the removal of the external fixator is a rare but major complication in diabetic limb salvage. Our experience has shown a higher incidence of tibial fracture when we have used half pins for fixation in the upper rings of external fixators. When using half pins for fixation of the external fixator to the tibia, there are key techniques one can use to avoid possible fracture. First, never use only one half pin for stabilizing an upper ring to the tibia. Second, one should use two or more half pins at different levels and angles per ring in order to avoid the possibility of developing stress risers that can lead to fracture. Our experience with osteopenic bone in diabetic limb salvage has taught us to avoid the use of half pins and rely on the use of two or three crossing skinny wires per ring in order to stabilize the upper rings. Keep in mind that using trans-osseous wires can lead to neurovascular injury, particularly when they are used to fixate the upper rings to the tibia. One should place wires across the tibia in areas that are void of neurovascular structures. You usually need to use a drill to drive the trans-osseous wire across the tibia. We recommend using the drill just to penetrate the second cortex. Then one should use a mallet to gently tap the remainder of the necessary wire through the skin opposite the entry point. This prevents twisting of the neurovascular structures around the wire when using a drill. Case Study One: Treating A Patient With Ankle Instability Secondary To Charcot Neuroarthropathy A 59-year-old obese female with a history of type 2 diabetes mellitus presented with ankle instability secondary to Charcot neuroarthropathy of nine months duration. Other physicians had suggested amputation. The patient had been evaluated and managed by endocrinology, vascular surgery, cardiology and had a prosthetic intervention to maintain as much independent living as possible. Her medical comorbidities were managed well. The patient underwent thorough counseling in order to prepare for surgical intervention in an attempt to salvage her leg. She did not have open ulcers or infection of the involved limb. Radiographs revealed severe destruction of the talus with only the talar dome apparent radiographically. We used the radiographs during our consultation with the patient. We discussed the plan to resect the remaining talus and attempt to fuse the tibia to the calcaneus. We were able to achieve an acceptable tibio-calcaneal arthrodesis (see photos above at left). The patient continued to achieve ambulation with an extra-depth shoe and ankle-foot orthosis (AFO) without further complication. Case Study Two: Achieving Acceptable Union At Six Months A 48-year-old male with a history of type 2 diabetes mellitus, Charcot neuroarthropathy and chronic ulceration presented to our clinic for surgical consultation after seven months of failed conservative therapy with wound care, custom-molded shoes and intermittent antibiotic therapy for occasional infection. An endocrinologist has managed him well for the past five months. The patient had no cardiac history and no acute renal disease. The ulcer on the affected foot was small, shallow and not infected. Radiographs revealed Charcot neuroarthropathy of the mid-tarsus with a prominence of the cuneiforms adjacent to the ulcer. The foot had a mild rocker bottom appearance and is slightly abducted at the mid-tarsus. Local wound care and total contact casting resolved the ulcer. We subsequently discussed surgical intervention as an attempt to avoid possible amputation of his foot. Our surgical intervention focused on reducing the deformity and stabilizing the hypermobile joints. We performed a bi-plane midfoot osteotomy and achieved fixation with internal screw fixation (beaming the medial column) and an external three-ring fixator. The patient was able to achieve an acceptable union at six months (see photos at right). He now has a stable foot and can ambulate without difficulty in an AFO and custom-molded shoe. Final Notes One can use external fixation successfully for salvage of the at-risk diabetic limb. It provides excellent stability for the fixation of complex deformities and allows patients to participate in their own care. However, external fixation is not the universal answer for fixation of bone. The use of external fixation is based on the present deformity and the fixation requirements necessary for stabilization. There are many variations for osseous fixation in the world of external fixation. Thorough knowledge of the characteristics unique to each type of external fixator is required in order to achieve the best result. Dr. Pupp is Clinical Director of the Foot and Ankle Clinic at the Southeast Michigan Surgical Hospital in Warren, Mich. He is a Fellow of the American College of Foot and Ankle Surgeons, and is also the Clinic Director at the Sinai Grace Diabetic Foot Center in Detroit. Dr. Wilusz is a surgical fellow at the Foot and Ankle Clinic at the Southeast Michigan Surgical Hospital in Warren, Mich. He has had extensive training in diabetic limb salvage and rearfoot reconstructive surgery.
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