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Prosthetics And Orthotics Science

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

Hartsell, Heather D. PhD, PT; Fellner, Chris BS; Frantz, Rita PhD, RN; Saltzman, Charles L. MD

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JPO Journal of Prosthetics and Orthotics: March 2001 - Volume 13 - Issue 1 - p 4-7
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Abstract

Neuropathic foot ulcers are the most difficult to heal and the most common precursor to lower-extremity amputations among persons with diabetes. The plantar ulcer that develops is the result of repetitive trauma applied to the sole of the foot during ambulation. In this patient population, although the patient’s ability to feel pressure on the bottom of the foot is reduced and a diminished ability to perceive pain and positional feedback also exist, the repetitive pressure and shear forces applied to the foot while walking do not diminish. 1–4 Consequently, effective management of these wounds is imperative if we, as clinicians, are to have a substantial impact on the prevention of amputations in this patient population.

Although numerous devices have been researched concerning their off-loading abilities, the total contact cast (TCC) remains the gold standard. 1 The TCC employs a well-molded, minimally padded cast that maintains contact with the entire plantar aspect of the foot and lower leg. By so doing, it functions to mechanically unload the ulcer site and reduce the vertical shear stresses, 5–8 redistributing the pressure of walking over the entire foot and lower leg. The effectiveness of the total contact cast has been well documented clinically, 2,6,8–17 with favorable results (91%) demonstrating an average healing time of 6 weeks, a considerable reduction from the average healing time of 9 weeks or more without its use but with other devices such as accommodative footwear and dressing changes.

However, the TCC is still not widely used in clinical practice. 7 Perhaps its lack of popularity relates to the fact that its application requires a skilled technician, considerable application time, and numerous applications over the duration of plantar ulcer healing. 1,2,7 Baker, 2 on his review of the total contact cast, stated that “…the most favorable results have been found if the casting is applied by someone with training in cast application who will apply subsequent casts as well. This supplies the uniformity needed…”. It has been well documented that improper cast application can cause iatrogenic ulceration. 1–3,15

The comment by Baker 2 raises an interesting issue. Studies have proven the ability of the TCC to effectively reduce plantar pressures by as much as 84%, particularly in the forefoot region, which justifies its use in plantar ulcer treatment. 4,6–8,18–21 However, the majority of these studies have involved a single application of a TCC either contrasted to a standard shoe or other off-loading device and a single occasion of comparison testing. In reality, the TCC is never applied on simply one occasion for a patient with a plantar ulcer but is reapplied as many as six to eight times. 1,7 Due to the highly skilled ability required for TCC application to obtain the customized snug fit for plantar pressure relief, the question arises concerning the consistency of repeat TCC applications.

The question of repeatability is also an issue of grave concern for the clinical researcher who uses sequentially applied TCCs to treat plantar ulceration. Clinical researchers need to know conclusively, and not by conjecture, that repeat applications of the TCC across or between subjects can be done reliably over time.

The purpose of this study was to determine the repeatability of TCC application by a skilled technician using a standardized technique, with implications for clinical research. Our hypothesis was that load redistribution by total contact casting is reliable (across subjects) and repeatable (over time).

RESEARCH DESIGN

The study used a repeated measures design. The independent variables were footwear (running shoe, TCC1, TCC2) and body region (forefoot, heel). The dependent variable was plantar pressure (N/cm2).

METHODS

SUBJECTS AND INSTRUMENTATION

Nine healthy subjects (mean age 29.2 years, range 25 to 32 years), with no past or present history of pathology to the right lower extremity, gave informed consent to participate. The study was approved by the Institutional Review Board on Human Experimentation at the University of Iowa.

The running shoe (RS), TCC1, and TCC2 were the footwear devices studied. The running shoe was a shoe of the subjects’ choosing.

All TCCs were applied by the co-investigator (CF) using a standard technique. Lamb’s wool was placed between the toes to prevent maceration. The cast sock was applied and a 1/8-inch piece of felt was placed across the tibial crest and fibular head, both malleoli, and dorsum of the foot. Cushioning 3/8-inch Sifoam (Omni Medical Specialties, San Diego, CA) was wrapped over the toes and metatarsal heads. The felt and Sifoam were retained using natural soft roll at the malleoli, tibial midshaft, and fibular head. The foot and ankle were neutrally positioned in all planes while the cast was applied to the foot and lower leg using 4-inch plaster impregnated elastic wrap. A series of 4-inch × 30-inch plaster splints reinforcing the lower leg and foot posteriorly were followed by a final 6-inch roll of fast-setting plaster. After the plaster cured, a prefabricated rocker sole was incorporated into the final layer of the casting using 4–inch fiberglass material. Subjects remained nonweightbearing for a minimum of 1 hour after TCC application to allow curing.

Plantar pressures were recorded using the Novel Pedar system (Novel GmbH, Munich, Germany), which consisted of an in-shoe array of capacitive sensors embedded in a 2.6-cm thick flexible shoe insert. The Pedar system’s operation has been previously described. 22

DATA COLLECTION PROCEDURES

Plantar pressures for each subject were recorded using three footwear devices (RS, TCC1, TCC2). Retesting of the TCC2 occurred 1 week after the TCC1 application by using a similar protocol.

The properly sized Pedar insert was placed in the subject’s running shoe, and the cable attachments secured to the Pedar sync box were clipped onto the subject’s waist belt. Ten-meter-long cables connected the Pedar sync box on the subject to the laptop computer used for data collection and storage. The subject walked on a motor-driven treadmill at a self-selected walking pace (average speed 2.5 mph; range 2.0 to 3.0 mph) and step length for approximately 5 minutes to accommodate to the protocol and develop a normal walking gait. The Pedar system was activated without the awareness of the subject, and data were collected on 84 steps before the treadmill being stopped and the subject dismounting. Only steps at a constant gait speed and step length were analyzed.

During testing and retesting of the TCCs, the subject was acclimated to the device (with Pedar insole in place) for 30 minutes or until they displayed a consistent self-selected walking pace (average speed 2.0 mph; range 1.5 to 2.5 mph) and average step length. Once accomplished, a data collection protocol similar to that described for the RS was followed.

DATA ANALYSIS

Subjects acted as their own physiologic control. Intraclass correlation coefficients determined the TCC repeatability. Mean spatially averaged peak plantar pressures were recorded for the forefoot and heel regions, separately, across 84 steps for each subject. Only steps at a constant speed and step length were analyzed using a two-way (footwear × location) analysis of variance with repeated measures and post-hoc Tukey’s tests for follow-up for significant interaction effects. The probability level of .05 was used throughout the analysis.

RESULTS

The mean spatially averaged plantar pressures and standard deviations recorded under the forefoot were 12.96 N/cm2 (1.16), 4.47 N/cm2 (1.49), and 4.47 N/cm2 (1.42) for the RS, TCC1, and TCC2, respectively Figure 1). Under the heel region, the mean spatially averaged recorded pressures were 10.35 N/cm2 (3.39), 12.77 N/cm2 (3.26), and 12.50 N/cm2 (3.46) for the RS, TCC1, and TCC2, respectively (Figure 1).

Figure 1
Figure 1:
Mean plantar pressures and SD for repeat TC versus shoe.

The main effects of footwear device (p = .001) and body region (p = .000), and the interaction effect of body region × footwear device (p = .000) were statistically significant (Table 1). When contrasted to the RS, the total contact cast applications significantly reduced plantar pressures under the forefoot region.

Table 1
Table 1:
Two-way repeated measures ANOVA for total contact cast repeatability versus a running shoe.

The repeatability for the TCC application was r = .9636 and r = .9622 for the forefoot and heel regions, respectively.

With the use of TCCs, the loads under the metatarsal heads were reduced 65.99% (9.44) for the TCC1 and 65.83% (9.19) for the TCC2. Conversely, the loads under the heel were increased 31.61% (39.90) for the TCC1 and 29.73% (43.95) for the TCC2. These changes at both the metatarsal head and heel regions were not statistically distinguishable between TCC1 and TCC2.

DISCUSSION

We found excellent repeatability of load redistribution with TCC applications spaced 1 week apart and performed by the same technician using a standardized technique. This finding is critically important for two reasons. It is necessary to maintain consistent off-loading of the foot throughout the numerous cast changes (six to eight casts on average) required over the course of plantar ulcer healing. 1,6,8,19 Second, a high level of repeatability with TCC applications is crucial in clinical research involving either a longitudinal examination of extrinsic or intrinsic factors associated with neuropathic ulcer healing, or any comparative analyses between TCC and other off-loading devices.

The results of this study support the view that peak plantar pressures under the forefoot are significantly reduced by total contact casts compared with a running shoe. In the present study, the mean spatially averaged peak plantar pressures recorded under the forefoot region were substantially and consistently lower than those previously documented. 4,7 Whereas Lavery et al. 7 and Fleischli et al. 4 recorded averaged forefoot pressures to be 8.5 N/cm2 and 12.4 N/cm2 using the TCC, our pressures averaged 4.47 N/cm2 using the same device. Although a similar system of plantar pressure measurement was used in these studies, it is possible that differences in casting techniques, time to weightbearing, or acclimatization after application of the TCC may have altered the off-loading capacity of the TCC materials. Unlike other studies, we used 3/8” cushioning Sifoam on the forefoot and a prefabricated rocker sole, and requested that subjects remain nonweightbearing for at least 1 hour after TCC application (for materials to cure). In addition, we provided time for acclimation to the TCC before testing. Although other studies 5,18,19 also support the reduction of plantar pressures under the forefoot with use of a TCC, direct quantitative comparisons may be forbidding due to 1) reductions expressed not in standardized units of measurement but rather as percentage change from baseline (and different baseline footwear are used) or 2) different pressure systems being used for data acquisition.

In studies where reductions are expressed not in standardized units of measurement but rather as percentage change from baseline, it is absolutely essential to consider the loading environment of the baseline footwear. For example, in the present study, the average forefoot off-loading of a TCC was 65.91%. Lavery et al. 7 reported forefoot off-loading with a TCC to be 83.53%. Although the differences between our study and that of Lavery et al. may seem substantial, a reasonable explanation relates to the initial in-shoe pressures used for contrast. Subjects tested by Lavery et al. 7 were requested to wear “…thin rubber-soled canvas oxford shoes as a worst case scenario…”. to establish baseline measures. Our subjects wore contemporary running shoes with good plantar padding and a relatively thick outer sole. We wanted subjects to wear a running shoe because it would simulate a situation that is considered to be beneficial for the neuropathic foot because running shoes are designed to absorb shock, provide a firm heel counter, and conform to the sole of the foot. Most running shoes also have a slight rocker on the sole. These combinations all help to off-load the neuropathic foot, particularly the forefoot, and likely explain discrepancies between our findings and those of Lavery et al. 7

Although not statistically significant, we observed loading under the heel to have increased with TCC application when contrasted to the running shoe. The average increase in plantar pressures loading was 30.67%. It is possible that our TCC application technique (Sifoam, plaster, fiberglass, rocker external sole) redistributed some of the natural loading under the forefoot to the heel. Scant data exist regarding the effects of TCCs on heel loading; studies 18,21,23 and their comparisons are made difficult due to methodological differences. Shaw et al. 21 showed that TCCs unload the forefoot through a transference of approximately 30% of the load from the leg directly to the cast wall. They demonstrated that load-bearing is reduced under the metatarsal heads by the cavity of soft foam covering the forefoot. Shaw et al. 21 also observed pressures to increase under the heel, recorded with TCC use, by approximately 20%. This trend of redistributing plantar load from the forefoot to the heel is similar to that of the present study. The relatively small differences in average increase loading under the heel between Shaw et al. 21 and our study—20% and 31%, respectively—is likely explained by variations in casting technique (Shaw et al. used fiberglass, we used a composite) and shoes (Shaw et al. used a cast shoe, we used a running shoe).

CONCLUSIONS

We found excellent repeatability of load redistribution with TCC applications spaced 1 week apart and applied by the same technician using a standardized technique. The forefoot was substantially unloaded compared to the use of a running shoe (average 66% reduction) and some of the load seems to be redistributed to under the heel. Clinicians caring for patients with neuropathic ulcerations and clinical researchers using total contact casting can be reassured that with standardized application techniques, significant forefoot unloading may be achieved with high repeatability. Although excellent repeatability is achieved for the heel, continued research is warranted to determine effective off-loading measures for this body region.

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Keywords:

Total contact casts; plantar ulcers; insensate foot; diabetes neuropathy

© 2001 Lippincott Williams & Wilkins, Inc.