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Offloading Diabetic Foot Ulcers With the Next Generation of Pressure Relief

Effective offloading of lower extremity ulcers can mitigate one of the direst consequences of diabetes. These authors take a look at the future of offloading using an innovative device. 

Diabetic foot ulcers (DFUs) are among the most common preventable complications in patients with diabetes, yet patients with diabetes have a 15–25% lifetime incidence of foot ulcers.1,2 Approximately 20% of hospitalizations among the diabetic population are due to DFU, and 65% of patients will have a recurrence within 5 years.3 Complications from DFUs are a leading cause of lower extremity amputations.4 It is estimated that up to 85% of all non-traumatic lower extremity amputations are a direct result of DFUs.4 

Diabetic foot ulcer formation is often multi-factorial. It is well established that increased blood glucose levels contribute to neuronal damage, which causes a decrease in the ability of nerve fibers to transmit adequate signals and results in neuropathy.5 When patients develop sensory neuropathy and lose their protective response mechanisms to pain, they are unable to detect minor trauma such as blisters or abrasions.5-7 

Decreased motor nerve fiber densities can detrimentally affect patients’ balance and spatial awareness, impacting gait and ambulation. As a result, this abnormal cadence can create additional areas of pressure on already vulnerable tissue, leading to callus and subsequent ulcer formation. Microvascular dysfunction contributes to reduced tissue perfusion, causing a reduction in oxygenation of the tissues, which may result in an increased vulnerability to mechanical stress.3 All of these pathophysiologic changes can contribute to the development of DFUs and their subsequent failure to heal. 

The current standard of care for DFUs includes adequate wound bed preparation with appropriate debridement and application of specialized dressings to provide the wound with a moist environment. Offloading the DFU is of paramount importance in their treatment. No advanced therapeutic options will succeed without sufficient pressure reduction on the DFU.

Taking a Load Off Plantar Foot Ulcers

Plantar foot ulcers are a direct result of increased pressure in the presence of neuropathy. For successful wound healing to occur, repetitive stresses must be eliminated and plantar pressures must be decreased. These goals can be achieved through offloading the plantar foot through such means as bed rest, crutches, wheelchairs, roll-a-bout scooters, walkers, total contact casts (TCC), removable cast walkers, custom splints, Charcot restraint orthotic walkers (CROW), extra-depth shoes, half-shoes, surgical shoes, felted foam, and bulky bandages. The effectiveness of these devices varies significantly, but the most effective offloading is achieved when forces are spread over a wide area of contact while ensuring compliance.8–10

Numerous trials have validated the efficacy of the TCC in offloading. TCCs offload by not only reducing plantar pressures, but by eliminating ankle joint motion. By prohibiting plantarflexion, force is reduced in the forefoot and midfoot, and weight is transferred to the lower leg. Due to the conical shape of the tibial segment of the lower extremity, weight is also transferred to the hard cast. Further benefits to TCCs are that they mold to the leg, helping to decrease edema; and they are cumbersome, which can cause the patient to take fewer steps a day, thus reducing repetitive stresses. However, perhaps the single most important attribute of this offloading technique is forced patient compliance. Patients cannot easily remove the device on their own, which ensures that weight and pressure are adequately controlled.  

Is TCC the Gold Standard?

TCC has been referred to as the gold standard in DFU offloading—but should it be if clinicians are reluctant to adopt TCC into their wound care practices? 

The 2019 International Working Group on the Diabetic Foot’s (IWGDF) practical guidelines for diabetic ulcer care note that offloading is the cornerstone in treatment of diabetic foot ulcers.11 The IWGDF recommends a non-removable, knee-high offloading device in the treatment of neuropathic plantar ulcers. 

Yet a retrospective analysis of the U.S. Wound Registry from January 2, 2007 to January 6, 2013, found that only 2.2% of the 221,192 plantar ulcers registered were offloaded.12 Of those patients who did receive offloading, only 16% received a TCC; 36.8% were simply placed in a surgical shoe. It was also noted that there were significantly more amputations in the non-TCC-treated patients than in those patients treated with TCCs.12 Only 61% of the clinics participating in the registry used TCC, and of those, only 3.7% of patients with a “TCC-eligible” wound seen in those clinics received a TCC.

Common concerns regarding TCC among practitioners are that total contact casting is expensive, messy, takes too much time, or has too great a risk for complications. Additional drawbacks to TCC application must be considered. TCCs are contraindicated in patients who have signs of osteomyelitis or acute wound infection. Adequate perfusion must be present in the lower extremity; most manufacturers suggest an ankle brachial index (ABI) of ≥0.7. Weekly cast changes are the standard of care; therefore, patients should be compliant with appointments. 

Prefabricated removable cast walkers (RCW), which were originally designed for the treatment of fractures and sprains, can be effective in offloading diabetic foot ulcers. Fleischli and colleagues performed a study evaluating the effectiveness of five different offloading devices in reducing peak plantar foot pressures.13 Using the DH Pressure Relief Walker (Ossur) as their representative removable walking cast (RWC), the authors found it was as effective or more effective than the TCC at reducing plantar pressures. 

Lavery and colleagues found similar results in a separate trial in which mean peak pressure measurements were obtained at the level of the plantar metatarsal heads and great toe to compare offloading in several commonly used devices.9 Among the studied shoegear, the highest peak plantar pressures were found under the second and fifth metatarsal heads in those wearing canvas oxfords at 51.6 N/cm2. Diabetic extra-depth shoes performed only slightly better at 38.2 N/cm2. However, TCC and the DH Pressure Relief Walker measured significantly lower mean peak pressures at 8.5 N/cm2 and 8.3 N/cm2, respectively. The same held true for mean peak pressures under the great toe: there was no significant difference between the TCC and the DH Walker, but there were significant differences between the TCC and DH Walker and all the other shoegear tested. It would therefore behoove clinicians to consider this evidence prior to employing shoe-based offloading in the treatment of DFUs.

Removable cast walkers have some tangible advantages over total contact casts. A removable walker allows clinicians, patients and caregivers access to the wound to perform more frequent dressing changes. This access is especially important in cases of wound infection or excessive exudate, a situation in which a TCC would be contraindicated anyway. Patients may also remove the cast walkers to sleep and shower, reducing the impingement on their activities of daily living that a TCC can cause. However, this final advantage of RCWs may also be its biggest downfall as patients often remove and not replace the RCW, failing to comply fully with the specified offloading regimen, negatively affecting healing.

Armstrong and colleagues found that patients wear their removable offloading device for less than 30% of their daily activity.14 A subsequent study by Armstrong and colleagues examined 63 patients with superficial non-infected wounds randomly assigned to wear a TCC, removable cast walker (RCW) or half shoe.15 Wound healing in each subset was tracked over the course of 12 weeks. The results showed a significant difference in healing between patients wearing TCC, 89.53%, and patients wearing RCW, 65.0%, or patients wearing half shoes 58.32%. The median time to heal was also significantly different between the TCC group (4.8 weeks), and the RCW (7.2 weeks) and the half shoe (8.7 weeks) groups. Although studies have shown similar decreases in plantar pressures in both TCCs and RCWs, it’s possible that this seemingly greater overall efficacy of TCCs in healing is due to the forced compliance that being non-removable ensures.9,13 

A Closer Look at the Next Generation in Offloading Devices

For clinicians reluctant to implement TCC in their practices, there is now another option in removable cast walkers. OPED Medical Inc. has developed what perhaps could be the best of both worlds: the VACOcast Diabetic (Figure 1). 

This cast boot device offloads forefoot and midfoot ulcers with the effectiveness of a TCC. One of the many advantages of this device is the rocker sole, which allows the patient a safer and more normal gait pattern than other offloading devices. The VACOcast lining is composed of a bead-filled insert that re-molds under a vacuum at each fitting to conform to the foot like fiberglass. The device comes with two washable low-friction wicking synthetic velour liners that can be easily exchanged for increased hygiene if soiled. The liner also covers the toes to prevent debris from entering the boot. An added foam bed layer allows for increased shock absorption and optimal pressure distribution.16 The VACOcast has a locking mechanism that provides forced compliance and control similar to that of a TCC (Figure 1). However, unlike with a TCC, a health care worker can easily access the wound for treatment by unlocking the boot.  

A community podiatry service in the U.K. conducted an expanded case series evaluating the VACOcast Diabetic boot on 20 patients.17 The cohort studied consisted of 17 male and 3 female patients with an age range of 41–80 years. Of the patients enrolled, 19 had type 2 diabetes. Over 8 weeks 85% of patients either healed or improved. No device related injuries were reported, and the device was highly rated by patients for comfort, safety, stability, and the ability to ambulate.   

Case Examples of Offloading

In the authors’ experience the OPED device has provided very favorable patient outcomes. 

Case 1. A 48-year-old male with a 6-month history of a neuropathic ulcer plantar to the first metatarsal head on the right foot presented to the clinic (Figure 2). His past medical history was positive for non-insulin dependent diabetes mellitus, diabetic neuropathy, and structural changes consistent with hallux hammertoe. The patient had tried and failed multiple advanced wound care therapies including Neosporin, gentian violet, collagen and TCC. 

At this visit the TCC was removed due to patient complaints of pain and discomfort. Marked peri-wound maceration was noted at this visit. The patient’s wound, measuring 2.8 cm x 2.5 cm x 0.1 cm was treated with alginate and foam, and transitioned to the VACOcast Diabetic locking boot. The wound appearance after 4 days of VACOcast offloading shows the wound measurement decreased to 1.9 cm x 1.7 cm x 0.1 cm and the maceration had completely resolved (Figure 3). At week two of therapy the wound measurements were 1.5 cm x 0.3 cm x 0.1 cm (Figure 4). By week 3 the patient’s wound had a thin layer of epithelial coverage (Figure 5). By week 4, slightly less than 28 days in the OPED Diabetic locking boot, the patient’s wound had completely resolved (Figure 6).

The patient tolerated the walking boot very well and related no issues with pain or discomfort. Patient compliance was not an issue due to the locking mechanism. Functional status and the ability to perform activities of daily living were not negatively impacted.

Case 2. A 45-year-old female with a surgical wound dehiscence present on the plantar left midfoot for 9 weeks presented to the clinic. Her past medical history was positive for insulin dependent diabetes mellitus and diabetic neuropathy. She was status/post 26 weeks from a right sub-first metatarsal incision and drainage, and status/post 19 days from a right first metatarsal I&D of osteomyelitis with bone excision (Figure 7). The patient had tried and failed several advanced wound therapies including betadine packing, collagen and TCC. 

Wound measurements were 1.68 cm x 1.01 cm x 0.07 cm. A continuous oxygen therapy device was applied to the wound and then covered with alginate, foam, Kerlix and Coban. The patient was transitioned into the VACOcast Diabetic locking boot due to complaints of leg cramping in the TCC. Figure 8 depicts the significant improvement made in the total wound area reduction after 2 weeks of VACOcast offloading. The wound now measured 0.86 cm x 0.77 cm x 0.1 cm, a 61.19% reduction from baseline. The patient continued to progress well wearing the VACOcast and went on to complete healing in 6 weeks with no complaints of discomfort or difficulties in activities of daily living (Figure 9).

Conclusion

Offloading is a crucial component of the standard of care algorithm for diabetic foot ulcer treatment. Although researchers and consensus bureaus alike have long considered TCC to be the gold-standard offloading device, there is still a gap in clinical use—fewer than 2% of wound clinics in the U.S. utilize TCC for offloading diabetic foot ulcers.18 Numerous reasons cause wound care clinicians to be unwilling to implement TCC therapy into their practice. Limited access to the wound in order to assess healing progress or perform dressing changes is one of these. In comparison, removable cast walkers permit access to the wound for more frequent evaluations and bandage changes, but patients tend to not be fully compliant in their use. The lack of forced compliance remains the top reason healing rates for RCW are less than seen in TCC. 

The OPED VACOcast Diabetic locking cast boot may be the answer to bridging this gap by providing the ease of use of a RCW, but the benefit of forced compliance of a TCC.  Randomized, controlled trials in a larger sample of patients are required to validate the authors’ preliminary findings. 

Windy Cole is an Adjunct Professor and the Director of Wound Care at Kent State University College of Podiatric Medicine in Independence, Ohio. 

Stacey Coe is a Clinical Research Coordinator at Kent State University College of Podiatric Medicine.

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Windy Cole, DPM; Stacey Coe, BA, CCRP
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References

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17. Bowen G, Spruce P. Unpublished data, May 2018)

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