The total contact cast (TCC) is an effective intervention to reduce plantar pressure in patients with diabetes and a plantar forefoot ulcer. The walls of the TCC have been indirectly shown to bear about 30 percent of the plantar load. A method to measure inside the TCC walls with capacitance sensors has shown that the anterodistal and posterolateral-distal regions of the lower leg bear the highest load. The objective of an open access study published January 7 in the Journal of Foot and Ankle Research was to directly measure these two regions in patients with diabetes and plantar forefoot ulcers to further understand the mechanism of pressure reduction in the TCC.
Capacitance sensor strips placed at the anterodistal (a) and posterolateral-distal (b) regions of the lower leg. Figure courtesy of the Journal of Foot and Ankle Research.
For the study, a TCC was applied to 17 patients with diabetes and a plantar forefoot ulcer. TCC wall load (contact area, peak pressure, and maximum force) at the anterodistal and posterolateral-distal regions of the lower leg were evaluated with two capacitance sensor strips measuring 90cm. Plantar load (contact area, peak pressure, and maximum force) was measured with a capacitance sensor insole placed inside the TCC. Both sensors collected data simultaneously at a sampling rate of 50 Hz synchronized to heel strike. The magnitude of TCC wall load as a proportion of plantar load was calculated. The TCC walls were then removed to determine the differences in plantar loading between the TCC and the cut down shoe-cast for the whole foot, rearfoot, midfoot, and forefoot (region of interest).
According to the study, the TCC wall load was “substantial.” Plantar contact areas recorded at the anterodistal lower leg was 48 percent and 34 percent at the posterolateral-distal lower leg. Plantar peak pressure recorded at the anterodistal lower leg was 28 percent and 12 percent at the posterolateral-distal lower leg. Plantar maximum force recorded at the anterodistal lower leg was 12 percent and 4 percent at the posterolateral-distal lower leg. There were significant differences in plantar load between the TCC and the cut down shoe-cast for the whole foot, rearfoot, midfoot, and forefoot (region of ulcer).
Contact area increased by 5 percent beneath the whole foot, 8 percent at the midfoot, and 6 percent at the forefoot in the shoe-cast. Peak pressure increased by 8 percent beneath the midfoot and 13 percent at the forefoot in the shoe-cast. Maximum force increased 6 percent beneath the midfoot in the shoe-cast. The study authors called each of these increases significant.
The study states that offloading plantar neuropathic ulcers using a TCC is regarded as the gold standard in patients with diabetes. This study shows that the walls of the TCC bear considerable load when measured directly in patients with diabetes and forefoot ulceration. Reduced plantar contact area in the TCC compared to the shoe-cast suggests that the foot is suspended by the considerable load bearing capacity of the walls of the TCC, which contributes mechanically to the pressure reduction and redistribution properties of the TCC.
