The Repeatability of Total Contact Cast Applications: Implications for Clinical Trials:

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

BACKGROUND

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 approximately 30 % of the plantar load. A new direct 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 this study was to directly measure these two regions in patients with Diabetes and a plantar forefoot ulcer to further understand the mechanism of pressure reduction in the TCC.

METHODS

A TCC was applied to 17 patients with Diabetes and a plantar forefoot ulcer. TCC wall load (contact area, peak pressure and max force) at the anterodistal and posterolateral-distal regions of the lower leg were evaluated with two capacitance sensor strips measuring 90 cm(2) (pliance®, novel GmbH, Germany). Plantar load (contact area, peak pressure and max force) was measured with a capacitance sensor insole (pedar®, novel GmbH, Germany) placed inside the TCC. Both pedar® and pliance® collected data simultaneously at a sampling rate of 50Hz synchronised 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).

RESULTS

TCC wall load was substantial. The anterodistal lower leg recorded 48 % and the posterolateral-distal lower leg recorded 34 % of plantar contact area. The anterodistal lower leg recorded 28 % and the posterolateral-distal lower leg recorded 12 % of plantar peak pressure. The anterodistal lower leg recorded 12 % and the posterolateral-distal lower leg recorded 4 % of plantar max force. 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 significantly increased by 5 % beneath the whole foot, 8 % at the midfoot and 6 % at the forefoot in the shoe-cast (p < 0.05). Peak pressure significantly increased by 8 % beneath the midfoot and 13 % at the forefoot in the shoe-cast (p < 0.05). Max force significantly increased 6 % beneath the midfoot in the (shoe-cast p < 0.05).

CONCLUSION

In patients with diabetes and a plantar forefoot ulcer, the walls of the TCC bear considerable load. 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.

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

BACKGROUND

Total 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.

METHODS

Plantar 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.

RESULTS

The 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.

CONCLUSIONS

These 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.

Effect of initial weight-bearing in a total contact cast on healing of diabetic foot ulcers

BACKGROUND

Although total contact casts are highly effective in the treatment of plantar ulcerations in patients with diabetes mellitus, they are not widely used. One reason for this lack of acceptance may be the difficulty in complying with an initial period of non-weight-bearing, as is generally recommended by physicians. We performed this study to assess the effects of early weight-bearing on the healing rates of plantar ulcers in patients with diabetes who were wearing a total contact cast.

METHODS

Forty patients with diabetes mellitus who had a noninfected forefoot or midfoot ulcer were treated with total contact casts until healing or for thirteen weeks. The patients were instructed to bear no weight on the cast for forty-eight hours after it was applied. Using an embedded step counter, we measured the number of steps taken during the first twenty-four and forty-eight hours, the first week, and each subsequent two-week period after application of the cast. We removed the cast, measured the radius of the ulcer, and then reapplied the cast at the end of the first week and of each subsequent two-week period after cast application until the ulcer healed or for thirteen weeks. We then determined the effect of the number of steps during various time intervals on the rate of ulcer healing (defined as a change in the ulcer radius).

RESULTS

Most patients walked on the cast in the immediate postoperative period. The effects of modest amounts of early weight-bearing on ulcer healing rates appear negligible. Only excessive walking during the first twenty-four or forty-eight hours after cast application is likely to prolong the duration of cast treatment.

CONCLUSIONS

Moderate early weight-bearing retards healing of plantar ulcers only minimally in patients with diabetes mellitus treated with total contact casts. Allowing patients to walk immediately after placement of a total contact cast may improve their acceptance of this form of therapy.

LEVEL OF EVIDENCE

Therapeutic study, Level II-1 (prospective cohort study). See Instructions to Authors for a complete description of levels of evidence.

The effects of total contact casting materials on plantar pressures

The plaster-based total contact cast (TCC) is effective at reducing high plantar pressures associated with foot ulceration in the patient with diabetes. However, the weight and the lengthy drying time which require nonweightbearing create an inconvenience for the patient. Fiberglass has been commonly used as a substitute for plaster due to the quicker drying time, although little is known about the effects of fiberglass on plantar pressures. The purpose of the study was to compare a plaster-based TCC (PB-TCC) and an all-fiberglass TCC (AF-TCC) using selected plantar pressure parameters for commonly ulcerated regions of the foot. Using a repeated measures design, 10 healthy subjects consented to walk, for four consecutive trials, along a 25-m corridor while wearing a running shoe, PB-TCC, and AF-TCC. For each of the footwear conditions, parameters of peak pressure, pressure-time integral, and contact time for the forefoot, lateral midfoot, and heel regions were recorded using the Pedar trade mark system of plantar pressure measurement. Both the PB-TCC and AF-TCC produced similar peak plantar pressures that were significantly lower (p =.001) than the running shoe. Pressure-time integrals were similar for all footwear conditions and contact time was not altered with footwear type. In summary, the AF-TCC appears to be an effective alternative to the PB-TCC for plantar pressure reduction in the management of neuropathic foot ulceration.

Total contact casting: its effect on contralateral plantar foot pressure

Total contact casts (TCC) are commonly used in the treatment of neuropathic ulcers of the foot related to diabetes. However, casts may alter the gait pattern and increase loading parameters of the contralateral foot. We determined the effects of total contact casting on plantar pressure parameters for the contralateral extremity. Ten healthy subjects consented to walk, for four consecutive trials, along a 25-meter corridor while wearing a running shoe (RS), fiberglass TCC and a traditional TCC. Parameters of peak pressure, contact time and pressure-time integrals for the contralateral forefoot, metatarsal V area and heel were recorded using the novel Pedar system of plantar pressure measurement. Repeated measures analyses of variance (footwear x region) were used to analyze the recorded parameters with post-hoc Tukeys selected for follow-up analysis. Each of the measured parameters for the forefoot, lateral foot over metatarsal V and heel regions on the contralateral foot were similar regardless of footwear worn. Use of a TCC does not appear to affect contralateral foot contact pressure parameters and likely does not increase the risk of contralateral ulceration.