Current Concepts In Offloading Diabetic Foot Ulcers

   As the prevalence of diabetes mellitus increases worldwide, there will be a concomitant increase in the development of the lower extremity manifestations of the disease process. In the United States alone, there are currently an estimated 24 million patients living with diabetes.1,2 Given the reported 15 percent lifetime incidence for the development of lower extremity ulcerations in this patient population, this equates to approximately 3.6 million diabetic foot ulcers (DFUs).3

   Obviously, podiatrists are on the frontlines when it comes to treating ulcerations in these complex patients. It is important for the physician involved in lower extremity limb preservation to be well versed in both the surgical and conservative methods of treatment.

   The morbidity and mortality associated with the development of lower extremity ulcerations has been well established, and it is important for the clinician to recognize that greater than 80 percent of all non-traumatic lower extremity amputations are diabetes related.3,4 Those patients undergoing major amputation have a significantly diminished life expectancy. In fact, recent research has demonstrated that the morbidity and mortality associated with major limb amputation are greater than most cancers.5

Assessing The Impact Of Pressure In The Development Of Wounds

   Often patients with diabetes present with significant systemic and local factors that lead to the development and progression of lower extremity wounds. A triad of pathology exists whereby vasculopathy, neuropathy and musculoskeletal deformity in the context of increased pressures forces combine in the development of DFUs.6,7

   The literature demonstrates that diabetic neuropathy affects up to 50 percent of patients and that neuropathic ulcerations are a primary risk factor for the development of non-traumatic LEA.8,9 Patients with diabetic neuropathy commonly present with a diffuse somatic neuropathy of the distal symmetric sensorimotor type. These patients can present with mixed sensorimotor deficits, pain, paresthesia, hyperesthesia and dysesthesias. These patients often demonstrate proprioceptive deficits, autonomic dysregulation and muscle atrophy. These neurological deficits can combine to contribute to wound development in the context of increased shear and vertical forces.8,10

   In addition to neuropathy, the hyperkeratotic wound margins can increase plantar pressures due to what has been termed the “edge effect.”11 When this occurs, the wound margins roll inward, limiting migration toward the center of the wound while simultaneously creating increased pressure forces along the wound periphery. These developments lead to further tissue breakdown.

   During ambulation, ground reactive forces (GRF) exert significant force through the lower extremity. These forces can be perpendicular to the foot (vertical stress) or they can be parallel to the foot (shear stress). When working together, vertical loading and shear forces can cause repetitive stress to the tissues and lead to ulceration. This is of particular concern in those patients who suffer from diabetic neuropathy and have lost the “gift of pain.”12

   When considering the transmission of forces in the lower extremity, one must consider the gait cycle.13 During the gait cycle, research has demonstrated that the pressure imparted through one foot can be 1.2 to 1.5 times the patient’s body weight.14

   When a skeletal deformity exists, pressure can also be higher due to the development of boney prominences. Commonly, this skeletal deformity is a consequence of intrinsic muscle atrophy due to peripheral motor neuropathy.15 Often, these foot deformities present prior to the development of sensory neuropathy symptoms in what were previously described as “low-risk” patients. In fact, the American Diabetes Association (ADA) has now included foot deformity as a risk factor in its Foot Risk Classification system.3

Is Total Contact Casting Still The Gold Standard For Offloading DFUs?

   There are numerous offloading modalities available to the clinician. These vary in complexity and cost. However, each device follows the basic premise to reduce both the vertical and shear forces across the wound site in order to allow for wound healing. Of significant importance to all of these devices is patient adherence as offloading devices only work if patients are indeed wearing them. It is vital that the physician impress upon the patient the necessity of continued adherence in the use of offloading devices. Three of the most commonly utilized modalities are the total contact cast (TCC), removable cast walker (RCW) boots, and the instant total contact cast (iTCC).

   Long considered the gold standard for offloading of the lower extremity, the TCC reduces plantar pressures while allowing ambulation. The contact nature of the cast allows for even distribution of pressure away from the ulcer site, which facilitates healing. An abundance of literature demonstrates the efficacy of TCC.16,17 This is largely due to TCC forcing the patient adherence with offloading.16,17 Despite the benefits of TCCs, these casts are cumbersome to the patients and can be difficult and time consuming to apply.

   More recently, TCC modifications have been developed to increase the speed and efficiency of applying these devices. The TCC-EZ (MedEfficiency) is a product that provides the offloading potential of traditional TCC while significantly increasing the speed and efficiency of application.

   One study demonstrated that application time for the TCC-EZ was 75 seconds in comparison to 452 seconds (7 minutes and 32 seconds) for application of a traditional TCC.17 Proponents for this product relate that utilization of the TCC-EZ significantly reduces traditional barriers to TCC usage by reducing the learning curve in TCC-EZ placement and increasing the speed of application.

Can Removable Walking Boots Have An Impact?

   In light of the challenges posed by TCC application, many clinicians have opted to utilize RCW boots to offload their patients with DFUs. There is literature to suggest that RCW boots can provide plantar pressure reduction and there are now a number of devices on the market for this application. Notable devices are the DH Pressure Relief Walker (Ossur), the Conformer Boot (Bledsoe Brace Systems) and the AirCast XP Diabetic Walker (DJO).16-18

   The DH walker creates plantar pressure relief via removable shock-absorbing hexagons that offer specific ulcer offloading and a reduction of vertical and shear forces in the area of the wound. The Conformer Boot provides DFU offloading via a unique dual density foot bed that evenly distributes forces across the plantar aspect and sides the foot much like a traditional TCC. The XP Diabetic Walker utilizes an aircell-lined shell that maximizes plantar offloading, thus reducing vertical and shear stress while providing protection and immobilization.

   While these modalities are easy to apply and allow for easy removal to facilitate wound evaluation and debridement, each of these devices has a similar limitation. Since patients can remove the devices, they are limited in their effectiveness.

What About The iTCC?

   To address this issue, Armstrong and colleagues presented a randomized, prospective study that evaluated the use of “instant total contact casts” (iTCC) in comparison to TCC in the offloading of diabetic ulcerations.19 The iTCC device is a removable walking boot, which has been modified to be “irremovable” via wrapping with a cohesive bandage. The thinking is the modification would increase patient adherence while maintaining the overall benefits of RCW boots, which include ease and speed of application.18

   This study found that healing rates in patients with lower extremity ulcerations were 80 percent in the iTCC group and 74 percent in the TCC group. These findings suggest that modification of standard RCW boots to increase patient adherence with pressure offloading may increase the proportion and rate of healing of DFUs with greater efficiency of application than traditional TCCs.19

In Conclusion

   Advances in wound healing technology have greatly expanded the physician’s ability to effectively manage DFUs and thus prevent lower extremity amputations. However, one must not neglect the importance of simple offloading to reduce pressure forces at the wound site. Excess shear and vertical forces, particularly in the context of sensorimotor neuropathy, can create a repetitive stress injury that leads to ulceration in the lower extremity.

   Advances in offloading techniques can reduce the aforementioned forces at the wound site and have increased efficiency. It is also important to remember that proper wound debridement with a particular emphasis in appropriately managing the wound margins to reduce the “edge effect” is necessary prior to the utilization of an offloading device.

   With any of these therapies, patient adherence is of supreme importance. Considering the significant morbidity and mortality associated with the development of lower extremity ulcerations, it is vital that patients understand the risks and consequences of non-adherence.

Dr. Fitzgerald is a Diabetic Limb Salvage Fellow at Georgetown University Hospital in Washington, DC.

Dr. Steinberg is an Assistant Professor in the Department of Plastic Surgery at the Georgetown University School of Medicine in Washington, D.C. Dr. Steinberg is a
Fellow of the American College of Foot and Ankle Surgeons.

References:

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