Lower extremity clinicians have known for decades that the total contact cast (TCC) is the most effective means of offloading plantar ulcers in patients with diabetes. Now research has given us a much better understanding of why—an understanding that could inspire a new generation of more effective prefabricated offloading devices.
It’s no secret that the irremovable nature of TCCs translates to superior compliance compared with removable offloading devices. We also know that restricting sagittal plane range of motion—by a TCC or any other device—leads to gait alterations, including shorter stride length and slower gait speed, that will reduce loading and limit activity. All of these things help improve ulcer-healing rates. But they have little to do with the offloading mechanism itself.
One theory has proposed that TCC offloading is accomplished by increasing plantar contact area, distributing pressure more evenly over the plantar surface of the foot and thereby eliminating high pressures at specific sites. It’s a theory that makes sense, but in 2011 researchers from the University of Sydney in Australia reported TCC-reduced pressure across each region of the foot, not just at the ulcer site, which called that theory into question.
Rather than redistributing plantar pressure, the Australian researchers hypothesized, TCC offloading is effective because the reduction in pressure across the plantar surface is offset by increased load bearing in the walls of the device. Several studies have documented this effect in healthy patients, but a new study from the Sydney group has finally demonstrated it in patients with diabetic foot ulcers. The 17-patient study, published online in January by the online Journal of Foot & Ankle Research, analyzed the offloading provided by a standard-height TCC, made with rigid and semirigid materials and modified with cellular urethane padding, and the same device with the walls removed just below the malleolus to create a shoe cast. The researchers found that for the TCC condition, significant decreases in contact area, peak pressure, and maximum force seen at the plantar surface were offset by increases within the walls of the device. They also found that plantar contact area was significantly smaller for the TCC condition than for the shoe cast condition.
The findings suggest that an important component—possibly the most important component—of effective TCC offloading is the ability of the device’s walls to suspend the foot, transferring load to the anterodistal and posterolateral-distal aspects of the lower leg.
And, although this mechanism has so far been demonstrated only in TCC devices, it’s not a huge stretch to think that strategically designed prefabricated cast walkers—perhaps even some that are already commercially available—can achieve the same type of suspension effect with a more cost-effective, patient-friendly device.
Given that only a minute fraction of patients with diabetic foot ulcers are treated with TCCs, a new generation of prefabricated alternatives with similar suspension-based offloading could drastically improve ulcer healing rates and reduce the risk of lower limb amputation. And, given the escalating incidence of diabetes worldwide, that can’t happen soon enough.