Pertinent Pointers On Offloading Diabetic Foot Ulcerations

Offloading plays a key role in the management of diabetic foot ulcerations. With this in mind, these authors review the literature and discuss a variety of modalities ranging from non-weightbearing options and therapeutic half-shoes to removable cast walkers and total contact casts.

   The combination of sensory neuropathy and high plantar pressures is the main factor responsible for plantar foot ulcer development in patients with diabetes mellitus.1,2 Neuropathic foot ulcers affect up to 15 percent of patients with diabetes and neuropathic foot ulcers are the primary factor leading to lower extremity amputations.3 Among the diabetic population, amputation is associated with re-amputation, contralateral limb amputation, placement in an extended care facility, a decrease in the quality of life and death.4-8

   Diabetic foot ulcers occur due to a combination of isolated pressure and repetitive stress. Researchers have shown that two key forces act on the foot. Vertical mechanical forces act perpendicular to the skin surface and shear forces act parallel to the skin surface.9 These forces act in tandem in the pathogenesis of diabetic foot wounds.

   Several studies have shown that vertical and shear forces are highest at the edge, not the center, of pressure application and that this is the area of maximum soft tissue damage. This tissue damage, resulting from both vertical stress and shear forces, is described as the “edge effect.”10,11

   Various researchers have described increased plantar foot pressures in patients with diabetic neuropathy and have shown they are related to the development of plantar foot ulcers.12-15 A recent multicenter prospective clinical trail showed that high peak plantar pressures > 6 kg/cm2 have high specificity in identifying patients at risk of developing plantar foot ulcers.16 Researchers have reported multiple factors that lead to high plantar pressures. These factors include obesity, sensory impairment, foot deformities, limited joint mobility, callus formation and reduced plantar soft tissue thickness.9,17-22

   In addition to peak plantar pressure, researchers have shown the forefoot to rearfoot peak plantar pressure ratio (F/R ratio) to be a predictor of foot ulceration. A F/R ratio >2 is reportedly as specific as a peak pressure >6 kg/cm2 in identifying patients who will develop foot ulceration.12 Motor impairment, functional shortening of the Achilles tendon (by way of advanced glycosylation of soft tissues) and possible rupture of the plantar fascia all have the potential to produce equinus deformity and subsequently increase the pressure under the forefoot area.23-26 Additionally, limited dorsiflexion of the ankle results in earlier heel rise in the gait cycle and subsequent earlier and extended loading of the forefoot.

   Healing ulcerations requires adequate blood supply, control of infection, appropriate wound care, debridement and offloading. One can best achieve offloading by spreading force over a wide area of contact, thus decreasing pressure.

   In addition to decreasing plantar pressures, ensuring patient adherence is another key component of offloading devices. There are numerous modalities clinicians can choose from when it comes to offloading diabetic foot ulcers. The ideal device reduces plantar pressures, both vertical and shear, while ensuring patient adherence. With this in mind, let us take a closer look at several of the currently available offloading modalities.

What About Non-Weightbearing Options Or Gait Modification?

   Complete offloading of diabetic foot ulcers with bed rest, crutches, walkers, Roll-A-Bouts (Roll-A-Bout Corp.) and wheelchairs is very effective for wound healing. However, there are several disadvantages, particularly significant alteration of patient lifestyle. There are multiple reported complications associated with prolonged bed rest including infection, deep vein thrombosis, pulmonary embolus, thrombophlebitis and decubitus ulceration.27 Crutches and walkers require upper body strength, endurance and balance precluding use by many patients, especially those who are obese and elderly. Wheelchairs are rarely used as few homes and workplaces are designed to accommodate their use.

   Researchers have shown that gait modifications, specifically decreasing propulsion and speed, decrease plantar pressures.9 As a result, alteration in walking style can be a therapeutic intervention. Zhu and Brown have demonstrated that plantar pressures, particularly in the forefoot, are considerably reduced during a shuffling gait or a “step-to” gait.28,29 However, alteration of walking speed requires tremendous discipline from the patient and is highly unreliable as a voluntary treatment modality. A propulsive gait and slower walking speed are additional benefits of several offloading devices including removable cast walkers (RCWs) and total contact casts (TCCs).

Can Therapeutic Shoes Or Half-Shoes Be Effective?

   Researchers have shown that extra-depth shoes with multi-density inserts are not effective in the treatment of diabetic foot ulcers. Lavery and colleagues showed up to 900 percent increased pressure in the area of the metatarsal heads with extra-depth shoe gear in comparison to TCCs and RCWs.30 A study by Gentzkow and co-workers showed that only 50 percent of foot ulcerations treated with extra-depth shoes healed at 12 weeks.31

   Half-shoes consist of a surgical shoe with a modified wedge-shaped base that ends proximal to the metatarsal heads. Half-shoes were originally designed for post-surgical use to decrease forefoot pressure by preventing forefoot ground contact. In addition to decreasing forces acting on the forefoot, half-shoes decrease vertical and shear forces by creating an apropulsive gait.

   When they compared half-shoes to local wound care, Chantelau and co-workers showed faster healing (70 days versus 118 days) and a lower incidence of serious infection in the half-shoe group.32 Additional benefits of half-shoes for diabetic foot ulcer treatment is that they are inexpensive and easy to apply. The disadvantage of half-shoes is inferior offloading ability. A study by Lavery and colleagues showed half-shoes to be less effective than TCCs and RCWs at reducing plantar pressures.30

Assessing The Pros And Cons Of Removable Cast Walkers

   Removable cast walkers (RCWs) are pressure reduction devices that provide offloading similar to the TCC, the gold standard offloading device for diabetic foot ulcers.30,33 Removable cast walkers offer several advantages including:

   • easy removal for wound inspection, dressing changes and topical therapy;
   • removal for sleeping and bathing; and
   • easy application requiring minimal time and training.

   Physicians may also employ RCWs in the treatment of infected wounds as they allow frequent wound monitoring.

   Disadvantages of RCWs include lack of adherence and variable offloading depending on the device. A randomized clinical trial comparing RCWs and TCCs showed a 65 percent healing rate with the RCW (Aircast) versus a 90 percent healing rate with TCCs.34 The authors hypothesized that the inferior healing rate in the RCW group was due to lack of adherence with the offloading device.

   Lavery and colleagues showed that pressure at the metatarsal heads ranged from 8.0 N/cm2 to 19.9 N/cm2 depending on the type of RCW physicians employed. The RCWs that reportedly provide the greatest plantar pressure reduction are the DH Pressure Relief Walker (Ossur), Conformer Boot (Bledsoe Brace Systems) and the Aircast XP Diabetic Foot Walker (DJO).30 These devices achieve pressure reduction via various modifications including removable shock absorbing hexagons (DH Walker), a dual density foot bed (Conformer Boot) and an aircell lined shell (AirCast).

Key Considerations With The Instant Total Contact Cast

   The greatest disadvantage of the RCW remains the potential for non-adherence. A study by Armstrong and colleagues showed that patients wear their offloading device during less than 30 percent of their total daily activity.34

   As a result of this, researchers developed the Instant Total Contact Cast (iTCC), which involves wrapping the RCW with adhesive bandage, plaster or fiberglass to make the device non-removable in order to ensure patient adherence.35

   However, this modification removes the ability to take off the device, prohibits frequent wound monitoring and dressing changes, and precludes the device’s use in the treatment of infected wounds. The iTCC does retain the benefit of quick application with minimal training required and little risk of iatrogenic wounds.

What The Research Reveals About The Total Contact Cast

   Total contact casts are considered the gold standard for offloading diabetic foot ulcerations.36,37 The TCC technique uses a well-molded, minimally padded cast that maintains intimate contact with the entire plantar aspect of the foot and lower leg. The molding of the cast to the lower leg redistributes pressure over a larger surface area. The TCC is effective because it evenly distributes forces across the entire plantar aspect of the foot while still allowing weightbearing and ambulation. Additionally, the “cone effect” places the cone shaped leg into a smaller conical cast receptacle, further decreasing plantar foot pressures. Furthermore, ambulation in the TCC alters patient gait, resulting in shorter stride length, decreased walking velocity and inhibition of ankle joint plantarflexion and propulsion.

   Studies have shown that the TCC transmits force from the forefoot (where peak plantar pressures are typically the highest) to the rearfoot and cast wall.38,39 Researchers have shown that the TCC achieves 31 percent load transfer to the cast wall, which reduces forefoot load to 5 percent of that of control shoes.38 Several mechanisms contribute to the offloading ability of the TCC.

   Various researchers have repeatedly shown that TCC is an effective treatment modality for non-infected, non-ischemic, plantar diabetic foot wounds.40-49 Reported healing rates for the TCC range from 72 to 100 percent, and the average time required for wound healing with TCC is five to seven weeks.41-44

   In comparing the treatment of non-infected neuropathic foot ulcers with TCCs, RCWs and half-shoes, Armstrong and colleagues showed an 89.5 percent healing rate for TCCs, a 65 percent healing rate for RCWs and a 58.3 percent healing rate for half-shoes at 12 weeks.47 Mueller and co-workers compared TCCs to wet-to-dry wound dressings and the avoidance of weightbearing for the treatment of plantar diabetic foot ulcers.48 They showed that 90 percent of the TCC group healed within 42 days while only 67 percent of the non-TCC group healed in 65 days.

   Myerson and co-authors reviewed the treatment of neuropathic plantar foot ulceration with TCC and found an average healing rate of 75.5 percent after an average of 39 days and 90 percent of ulcerations healed at five weeks.49

   The TCC has several benefits in addition to its ability to offload plantar foot ulcerations. The TCC acts as a compressive device to control lower extremity edema, which can be an impediment to wound healing.48 Additionally, TCCs act as a barrier to infection and the irremovable nature of the TCC forces patient adherence.48

   Negative attributes of the TCC include: application time; the potential for iatrogenic applications from improper cast application or removal; inability to monitor wounds; and exacerbation of postural instability.50 Use of the TCC is contraindicated for treatment of patients with infected wounds due to the inability to frequently monitor wounds for the progression of infection. Additionally, researchers have cited vascular compromise as a contraindication to TCCs.3 Active dermatoses, contact allergies to cast material, blindness, ataxia and claustrophobia are other relative contraindications to total contact casting.

Is The TCC-EZ A Viable Alternative Option?

   Recently, physicians have made modifications that overcome some of the disadvantages of the standard TCC. The TCC-EZ (MedEfficiency) consists of a fiberglass fishnet mesh cast supported by an outer shell that provides additional support and stability for weightbearing.

   This device provides comparable offloading to standard TCCs while significantly decreasing the time of cast application. On average, clinicians can apply the TCC-EZ in one-third less time than it takes to apply a traditional TCC. Additionally, the TCC-EZ design decreases cast weight and improves patient balance.

Final Notes

   Evidence-based medicine demonstrates that the TCC is the best treatment modality to offload diabetic foot ulcerations. Further research is needed to standardize TCC cast application and increase its clinical use. Several other treatment modalities are available for patients in whom TCCs are contraindicated or for clinicians who are not properly trained in TCC application and removal technique.

Dr. Hoffman is a third-year resident with the North Colorado Podiatric Surgical Residency in Greeley, Colo.

Dr. Jensen practices at the Diabetic Foot and Wound Center at Rose Medical Center in Denver. He is the Research and Externship Director for the North Colorado Podiatric Surgical Residency program in Greeley, Colo.

Dr. Jaakola practices at the Diabetic Foot and Wound Center at Rose Medical Center in Denver. He is the Education Chair for the North Colorado Podiatric Surgical Residency program in Greeley, Colo.

For further reading, see “Current Concepts In Offloading Diabetic Foot Ulcers” in the September 2009 issue of Podiatry Today, “A Guide To Offloading The Diabetic Foot” in the September 2005 issue or “Key Insights On Offloading Diabetic Neuropathic Ulcers” in the July 2009 issue.

References:

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