A novel approach to mapping load transfer from the plantar surface of the foot to the walls of the total contact cast: a proof of concept study

Abstract

BackgroundTotal contact casting is regarded as the gold standard treatment for plantar foot ulcers. Load transfer from the plantar surface of the foot to the walls of the total contact cast has previously been assessed indirectly. The aim of this proof of concept study was to determine the feasibility of a new method to directly measure the load between the cast wall and the lower leg interface using capacitance sensors.MethodsPlantar load was measured with pedar® sensor insoles and cast wall load with pliance® sensor strips as participants (n=2) walked along a 9 m walkway at 0.4±0.04 m/sec. The relative force (%) on the cast wall was calculated by dividing the mean cast wall force (N) per step by the mean plantar force (N) per step in the shoe-cast condition.ResultsThe combined average measured load per step upon the walls of the TCC equated to 23-34% of the average plantar load on the opposite foot. The highest areas of load on the lower leg were located at the posterior margin of the lateral malleolus and at the anterior ankle/extensor retinaculum.ConclusionsThese direct measurements of cast wall load are similar to previous indirect assessment of load transfer (30-36%) to the cast walls. This new methodology may provide a more comprehensive understanding of the mechanism of load transfer from the plantar surface of the foot to the cast walls of the total contact cast.

Total contact cast wall load in patients with a plantar forefoot ulcer and diabetes

“…Contact area data and regional pressure patterns comparing a cushion-modified TCC and a conventional TCC have shown pressure reduction and redistribution without increasing the plantar contact area [ 34 ]. These findings support a suggested mechanism of load transfer to the walls of the TCC [ 1 , 21 , 26 , 46 ] or to the rearfoot [ 26 ].…”

“…Finally, Tanaka and colleaugues [ 45 ], assessed five healthy participants and measured plantar pressure (F-SCAN, Tekscan Inc, South Boston, Massachusetts) in a conventional Patella Tendon Bearing Cast (PTB) with a heel (used for the treatment of below knee fractures), and the contralateral side (extension shoe) and attributed a 30 % offloading to the cast walls. Direct measurement of inside the TCC walls with the use of capacitance sensors has shown that the TCC walls bear 23–34 % of the plantar load [ 46 ]. It is diffcult to compare these studies because they all report different units of measurement, cast technique, terminal devices (cast shoes and heels), TCC rigidity and cushioning materials.…”

“…TCC wall load (contact area, peak pressure and max force) at two regions of the lower leg were evaluated with two capacitance sensor strips measuring 90 cm 2 (pliance®, novel GmbH, Germany). These regions were based upon the proof of concept study identifying the areas of highest TCC wall load [ 46 ] and are defined as anterodistal lower leg (along the tibia, running distally, specifically across the top of the ankle mortise over connective tissue structures) and posterolateral-distal lower leg (on the posterolateral part of the lower leg, running distally from a line slightly posterior to the fibula head and passing posterior to the lateral malleolus, specifically at the area of the lateral malleolus) (Fig. 2 ).…”

“…The walls of the TCC have been indirectly shown to bear approximately 30 % of the plantar load in small samples of healthy participants [ 21 , 26 , 45 ]. Direct measurement to measure load inside the TCC walls with capacitance sensors has shown that the TCC walls bear 23–34 % of the plantar load [ 46 ]. Furthermore, the direct measurement method has shown that the anterodistal and posterolateral-distal regions of the lower leg bear the highest load, although this has only been evaluated in two participants without an ulcer.…”

Offloading Plantar Pressures in Healthy Adults: Stirrup Cast vs Total Contact Cast

“…8,13 It aims to relieve mechanical stress from high-pressure areas of the foot to the wall of the cast without increasing pressure elsewhere. 1,8,10,13 TCC is a custom-made, knee-high nonremovable cast made of either plaster or fiberglass rolls and an attachable protective sole that facilitates walking and protects the cast. 10,13,14 Not only are TCC more cost-effective than removable offloading devices but they also result in more rapid healing owing to a more effective redistribution of pressure over the foot and lower leg.…”