Assessing The Use Of Ex-Fix For Offloading In Diabetic Limb Salvage

Dong Kim, DPM, Jeffrey McAlister, DPM, and Paul J. Kim, DPM

In lieu of the advancements in wound healing and innovations in surgical technique, limb salvage in the patient with diabetes remains a costly and complex endeavor. Some advocate immediate amputation for complex diabetic ulcers or gangrene.1 However, researchers have associated amputations in patients with diabetes with decreased life expectancy and an increased risk of contralateral amputation.2 The challenge with wound healing in patients with diabetes stems from the existence of comorbidities such as vasculopathy, neuropathy and propensity for infection.3

   With this in mind, a multidisciplinary team effort is warranted. This team should consist of: vascular surgeons re-establishing blood flow; podiatric and orthopedic surgeons performing debridements and ensuring skeletal stability; plastic surgeons for complex soft tissue coverage; and infectious disease specialists to stabilize the patient’s infection.4

   Despite the challenge, most superficial ulcers heal with definitive revascularization, local wound care including debridements, edema control and offloading. Final closure, however, becomes problematic when tendons, bones, joints and neurovascular structures are exposed. In such instances, viable reconstructive options for soft tissue coverage include local rotation flaps, pedicled muscle flaps and free flaps, according to the well documented reconstructive ladder.4 These flaps require strict postoperative management and offloading since known causes for flap failure may occur secondary to repetitive shear forces, pressure and premature ambulation.4,5

   Accordingly, let us take a closer look at the advantages and disadvantages of external fixation in the realm of free tissue transfer and their use in limb salvage.

What The Research Reveals About Flaps And Limb Salvage

Pedicle flaps require isolation of an identifiable, named neurovascular bundle supplying the donor tissue. They are generally more difficult to dissect and have higher complication rates than free flaps in the lower extremity.4 Pedicle flaps also have a limited coverage area due to their axis of rotation. Despite these shortcomings, there are some advantages to pedicle flaps. General anesthesia is not required, there is minimal functional deficit and the hospital stay is generally shorter.4,6

   However, free flaps (fasciocutaneous or muscle) can cover larger defects. The flaps are usually healthy muscle and work well for larger plantar wounds. The problem arises when the source vessels are calcified and difficult to anastomose. This often happens in patients with longstanding diabetes and end-stage renal patients. With free flaps, researchers have noted current limb salvage rates of 83.4 percent in a 28 month follow-up period.7 Authors have reported 77 percent survival rates at eight years following free flaps whereas survival rates at five years following amputation range between 22 and 38 percent.6,8

Addressing Potential Postoperative Concerns After Flap Reconstruction

Offloading is one of the most important factors to flap survival in the postoperative period.9 Motion along a joint, pressure and shear forces are undesirable and account for many flap failures.4 In addition, one needs to ensure elevation of the extremity for a period of time postoperatively to decrease swelling and encourage venous return.10 Authors have described many techniques, such as pillows and water mattresses, to offload the operative limb.11,12 However, these options do nothing to immobilize joints and are more suitable in simple wound care settings. Casting and external fixation are more appropriate methods to achieve immobilization and offloading during the postoperative phase.

   Researchers have shown that total contact casting is effective at offloading and ultimately healing neuropathic diabetic ulcers.13 Although options such as a removable CAM walker and polyurethane foam have eliminated some of the disadvantages of casting, they are not favorable in the management of flap reconstructed extremities.14,15 Casts do not give easy access to the flap for observation and monitoring of vascular status.5 If wound care is indicated, frequent cast changes are time consuming and uncomfortable to the patient.16 The only option to access the flap and perform vascular examinations is to create a window in the cast. However, this method is time consuming, dangerous and aesthetically displeasing.

   External fixation addresses many of the postoperative concerns following flap reconstruction. External fixation allows for strict immobilization of joints, specifically the ankle joint.17 Excessive ankle dorsiflexion and plantarflexion not only transmit shear forces to complex flaps but also increase intracompartmental pressures in the limb, which can promote venous congestion.16 Immobilization of the joints also prevents flap contractures that may be detrimental not only to flap survival but to general function of the limb.18

   Another advantage of external fixation is that it allows easy access to observe the flaps and donor sites. Frequent monitoring can identify potential complications such as dysvascularity and hematomas. For example, muscle flaps may drain heavily in the postoperative period and frequent dressing changes are required to prevent maceration and infection.16 It is also easier to perform Doppler checks of flaps through an external fixator than a cast, which initially an intensive care nurse must do every hour.

   External fixation allows offloading not only to the flaps but also other pressure areas such as the heel. Concomitantly, the external fixator allows elevation of the extremity, which is important for flap survival. One can achieve elevation via the construct alone or by hanging the external fixator by a rope tied to a crossbar over a bed.19 In regard to types of external fixation, available options for foot and ankle surgeons include ring fixation with wires, a monolateral frame or a hybrid frame. The foot and ankle surgeon and plastic surgery team should routinely meet preoperatively and decide on the type of device to use based on the anatomic location of the wound and need for offloading the flap. This will assist the pre-surgical planning team and greatly cut down on operative time and complications.

   External fixation is not without its drawbacks. Common complications with external fixation include pin tract infections, hardware failure and muscular atrophy. One can usually treat these complications with local wound care and oral antibiotics, replacement of hardware, and physical therapy.4 External fixation is also a poor choice for patients with psychiatric illnesses, non-adherence or impending mortality.16 Morbid obesity, incapacitation of the contralateral limb and spasticity are relative contraindications as well.16 There is a component of coordination among various surgical and medical teams when applying external fixators during the stages of limb reconstruction and wound coverage. The podiatric surgeon may manage the debridements, wound care and external fixation while the plastic surgeon harvests and inlays the flap.4

In Conclusion

An attempt at limb salvage is a complex and challenging task for even the most skilled surgeon. There are many factors to consider when choosing the right intervention for a patient. For those considering flap reconstruction, vascular status, renal disease and adherence are the biggest factors.3 External fixation is a valuable tool in an attempt at limb salvage. It can offload, immobilize joints, allow flap and donor site observation, permit wound care, increase adherence and improve patient comfort. In the end, limb salvage is a total team effort consisting of a multidisciplinary approach striving for one common goal.

   Dr. Dong Kim is a first-year resident at INOVA Fairfax Hospital in Falls Church, Va.

Dr. McAlister is a third-year Chief Resident at INOVA Fairfax Hospital in Falls Church, Va.

   Dr. Paul J. Kim is an Associate Professor at Georgetown University Hospital in Washington, D.C. He is a Fellow of the American College of Foot and Ankle Surgeons.

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