Abstract
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.
Diabetes mellitus affects an estimated 16 million Americans, with
approximately 800,000 new cases reported each
year1. Children born
in the United States in 2000 have a greater than one-third lifetime
probability of diabetes mellitus
developing2. A
retrospective cohort study of patients with diabetes in a large staff-model
health maintenance organization demonstrated an incidence of foot ulcers of 2%
per year among 8905 patients with established
disease3. Related
work has suggested that a foot ulcer will develop in as much as 15% of
patients with diabetes at some point in the course of the
disease4.
Unhealed ulcers often lead to additional complications such as infection,
osteomyelitis, and
amputation3-5.
A prospective study of 776 subjects at the Seattle VA Hospital demonstrated a
11.7/1000 person-year annual risk of major lower-extremity amputation among
patients with diabetes and showed that previous ulceration increases the
relative risk of amputation 2.5
times6. In a
companion study, the same group found a greater than twofold increased risk of
death of subjects with foot ulcers after adjustment for age, type of diabetes,
duration of the disease, treatment, glycosylated hemoglobin level, history of
lower-extremity amputation, and smoking (cumulative
pack-years)7.
Of the many methods used to treat plantar ulcers in diabetic feet, total
contact casts have consistently shown the most
promise8-12.
A total contact cast is a below-the-knee walking cast that is applied with a
minimal amount of padding to fit the foot and leg intimately and to limit toe
motion. Casts are generally applied weekly or every two weeks until the
plantar ulcer has healed. The beneficial effects of total contact casts have
been documented in multiple
prospective8-10,13,14
and
retrospective11,12,15
clinical studies, with healing of an average of 80% of the ulcers. In
contrast, placebo treatment in most randomized, controlled trials resulted in
wound closure for an average of only 30% to 40% of the
ulcers16. Healing
is also substantially faster in a total contact cast. However, even though
total contact casts are the most effective method for achieving healing of
diabetic plantar ulcers, many practitioners do not use them because they are
difficult to apply and remove and patients are unwilling to comply with
non-weight-bearing after cast application.
Most protocols for treatment with total contact casts were designed with
the assumption that the cast must be completely dry prior to
weight-bearing10,11.
Patients are typically instructed not to bear any weight on the cast during
the first twenty-four to forty-eight hours after application to allow the
plaster to cure
properly9,12,17,18.
It has been suggested that failure to comply with this recommendation results
in a deformation of the intimately molded cast that will impair its efficacy.
In our practice and that of others, many patients refuse treatment with total
contact casts because of these restrictions on
activity11.
We conducted this study to evaluate patient compliance with
non-weight-bearing after application of a total contact cast and its
association with the rate of ulcer healing as measured by the weekly change in
the radius of the ulcer.
Subjects
The institutional review board on human experimentation at the University
of Iowa approved this prospective, observational study. One hundred and fifty
patients with diabetes mellitus and an active foot ulcer who were seen at a
dedicated tertiary care diabetic foot clinic were screened for inclusion in
the study between May 2001 and December 2003. Inclusion criteria included
diabetes mellitus, a Wagner grade-I ulcer on the plantar surface of the
foot19, no clinical
signs or symptoms of infection, no antibiotic therapy, Doppler toe pressure of
>30 mm Hg, an ulcer of at least 0.5 cm2 in area and 0.1 cm in
depth, and the ability to bear weight on the contralateral extremity. One
hundred and four patients with a plantar foot ulcer were excluded from the
study because of ongoing local infection (fifty-three patients), an ulcer that
measured <0.5 cm2 in area or <0.1 cm in depth (thirty-six),
refusal of the cast treatment because study participation was inconvenient or
because of the inability to be non-weight-bearing (twenty-six), Doppler toe
pressure of <30 mm Hg (six), steroid dependency (six), a history of
noncompliance with clinical care (six), and inadequate cognitive ability to
complete the study (three).
Forty-six subjects met the inclusion criteria and agreed to participate in
the study. Three of them did not subsequently enter the study: one because an
infection developed before the first study visit, one because the ulcer healed
before the first visit, and one because of unwillingness to continue
participating. Of the remaining forty-three subjects, three were excluded from
the analysis: two because the ulcer became infected before the first cast
change, and one because of a shuffling gait that prevented the step-counting
device from distinguishing discrete steps. The remaining forty patients
(twenty-five men and fifteen women) formed the core for this analysis. Eight
had Type-I and thirty-two had Type-II diabetes mellitus. The median age was
fifty-two years (range, twenty-five to seventy years). On the initial
examination, the median area of the ulcer was 1.28 cm2 (range, 1.01
to 12.80 cm2) and the median radius was 0.65 cm. Eleven of the
ulcers were in the midfoot region of feet with previous Charcot collapse and
deformity, and twenty-nine (twenty-five metatarsal ulcers and four toe ulcers)
were located under the forefoot. Of the forty feet, thirteen had
radiographically evident Charcot collapse, which was at the Lisfranc joint in
six, at the talonavicular joint in four, and at the naviculocuneiform joint in
three.
Ulcer Treatment
All study subjects were treated with total contact casts until healing of
the ulcer or for thirteen weeks. After the initial application, the casts were
reapplied at one week and at three, five, seven, nine, and eleven weeks or
until the ulcer had completely epithelialized. After each cast was removed, an
experienced clinician evaluated the ulcer. Débridement was performed as
necessary. Devitalized tissue and the external rind build-up of callus,
unsupported by an underlying matrix, were removed with a sharp instrument. All
casts were applied with use of a standard technique as described
previously20. The
cast includes a thin layer of padding, foam placed around the toes, felt over
osseous prominences, well-molded plaster inner layers, and a fiberglass outer
carapace. To ensure consistency in the application of the casts, all were
applied by the same orthotist, who had applied more than 100 total contact
casts annually in each of the previous ten years. The reliability of this cast
application technique was reported previously in a comparative study of
subjects alternately fitted with plaster-based and all-fiberglass total
contact
casts20.
Following each cast application, a nurse educator verbally reinforced a
clearly written set of instructions detailing the need to remain absolutely
non-weight-bearing during the first forty-eight hours after each cast
application (see Appendix). Immediately after the initial cast application, a
physical therapist instructed the patients about the use of crutches or a
walker without bearing weight on the involved extremity and monitored their
ability to comply.
Activity Measurement
A StepWatch step activity monitor (Cyma, Seattle, Washington) was
incorporated into the exterior of the cast to record the number of steps that
each subject took on an hourly basis between each cast change. The use and
accuracy of this device in a cast has been previously
described21. The
StepWatch data for all steps between cast changes (at one week or two weeks)
were downloaded at the time of each cast removal, and the data were converted
to the number of steps per day.
Measurement of Ulcers and Determination of Rate of Ulcer Healing
At each clinic visit, the ulcer area was measured by placing a clear piece
of acetate over it and tracing the edge with an indelible marker with a 1-mm
tip. The ulcer edge was defined as the line dividing the healed portion from
the unhealed portion. Thus, the reference surface consistently defined the
unhealed portion of the ulcer. The surface area and perimeter were determined
with use of a Lasico Planimeter/Digitizer (Lasico, Los Angeles, California),
which has an accuracy of ±0.1% according to the manufacturer.
Four investigators were trained to perform the measurements, and two of the
four performed the measurements at each study visit. The interrater and
intrarater reliability of the measurements made on twenty subjects
(eighty-four ulcer measurements) over the course of the treatment protocol was
assessed with use of interclass correlation coefficients. The results showed
an interrater reliability of 0.99 and an intrarater reliability of 0.98 among
the four investigators, which are consistent with findings in other studies of
wound measurement reported in the
literature22-24.
The rate of ulcer healing (the dependent variable) was expressed as the
linear advance of the wound edge (the change in radius), as this technique has
been shown to reduce bias from disparate ulcer sizes or shapes within the same
study cohort25. In
an extensive analysis of secondary-intention wound closure, Snowden concluded
that wounds tend to close by a constant linear rate of advance perpendicular
to the wound
margin26. This
finding was validated by analysis of both wounds healing by epithelialization
and those healing by contraction. The parameter used to measure ulcer healing
in this study was direct measurement of the linear advance of the wound
margin. The area and perimeter measurements, as determined from digitized
wound tracings, were used to quantify the linear advance of the wound margin
with use of the formula: d = ?A/p, where ?A is the difference in
the area of the wound from one measurement point to the next, p is the average
of the wound perimeter from one measurement point to the next, and d is the
distance of the advance of the wound margin toward the wound center from one
measurement point to the next. The mathematical proof for this formula has
been described in detail by
Gilman25.
Data Analysis
The association between the number of steps per day after each cast change
and the change in the radius of the ulcer during the cast-wear interval was
tested with use of a linear mixed-model analysis. The mixed model included the
number of steps per day as the independent variable and the change in the
ulcer radius per week as the dependent variable. Since the change in the ulcer
radius and the steps per day were measured at multiple time-points for each
subject (until healing of the ulcer or thirteen weeks after cast application),
use of a linear mixed-model analysis enabled us to account for the correlation
between the data points from the same subject.
The independent variables of (1) average number of steps per day in the
first twenty-four hours, (2) average number of steps per day in the first
forty-eight hours, (3) average steps per day in the first twenty-four hours as
a percentage of the daily average number of steps during the cast-wear
interval excluding the first forty-eight hours, (4) average steps per day over
the first forty-eight hours as a percentage of the daily average number of
steps during the cast-wear interval excluding the first forty-eight hours, and
(5) average number of steps per day during the cast-wear interval excluding
the first forty-eight hours were each tested in separate models to assess
their association with the change in the ulcer radius per week. Another model
was fitted that included age as a covariate.
We also calculated the reduction in healing rate due to the average number
of steps taken per day in the first twenty-four and forty-eight hours that
could be detected by the statistical test at the 0.05 significance level with
0.80 power for the sample size used in our study.
Ulcer Healing
We collected data on forty subjects, with an average of four data points
(range, one to seven data points) per subject. In the intent-to-treat
population, thirty-two (80%) of forty ulcers healed in the cast during the
thirteen-week study period, five did not heal, cast treatment was stopped for
one at seven weeks because of infection, and two patients declined to continue
participating in the study after having been treated with the cast for a
period of time. Of the thirty-two ulcers that healed in thirteen weeks or
less, half healed by five weeks and half healed between seven and thirteen
weeks; the median time to healing was six weeks (range, one to thirteen
weeks).
Number of Steps
Despite being instructed to maintain strict non-weight-bearing while
wearing the cast, most patients walked on the cast during the first
forty-eight hours. In the entire group of forty patients, the median number of
steps per day was 523 in the first twenty-four hours, 808 in the first
forty-eight hours, and 2083 during the period of cast treatment excluding the
first forty-eight hours. Step activity was also defined as a ratio of the
number of steps per day in the first twenty-four or forty-eight hours to the
number of steps per day in the remainder of the cast-treatment interval (i.e.,
excluding the first forty-eight hours) preceding each study visit. In the
first twenty-four hours after cast application, the median step activity was
34% of the unrestricted daily step activity. In the first forty-eight hours,
the median was 50% of the unrestricted daily step activity.
Association of Number of Steps with Rate of Ulcer Healing
The healing rates over the entire thirteen weeks were not significantly
affected by the average number of steps per day in the first twenty-four
hours, the average number in the first forty-eight hours, or the daily average
in the entire period of cast treatment
(Table I). A model that
included age as a covariate showed no significant effect of age (p > 0.36),
with estimates for the regression coefficients being very similar to those
obtained in the first model.
With the number of observations used in this study, 0.0018 cm was the mean
reduction in the change in the wound radius per week for every 100 steps
taken, on average, per day in the first twenty-four hours (or in the first
forty-eight hours) that could be detected at the 0.05 significance level with
0.80 power. The estimated time to wound closure of an ulcer with a 0.65-cm
radius (the observed median radius), on the basis of an estimated healing rate
of 0.0915 cm per week if no steps are taken, is 7.10 weeks
(Table II). The detectable
slope corresponds to an increase in time to wound closure of one to 8.10 weeks
with an average of 627 steps or an increase of at least two to 9.10 weeks with
an average of 1116 steps per day in the first twenty-four hours (or first
forty-eight hours). For a wound with a radius of 0.94 cm (a radius in the
observed seventy-fifth percentile), the estimated time to wound closure with
no steps taken is 10.27 weeks, with the detectable slope corresponding to an
increase in time to wound closure of one to 11.27 weeks with an average of 450
steps or an increase of two to 12.27 weeks with an average of 828 steps per
day in the first twenty-four hours (or first forty-eight hours).
In this prospective observational study, we found that plantar ulcers in
patients with diabetes mellitus treated with total contact casts and partially
restricted walking healed at rates equal to those in subjects who completely
restricted initial weight-bearing. Since standard clinical practice is to
change the total contact cast every two weeks, the effects of modest early
walking do not appear to have a clinically relevant impact on the rate of
ulcer healing. In particular, failure to comply with our strict admonitions to
refrain from weight-bearing in the first forty-eight hours after cast
application seemed to have no clinically relevant effect on the rate of
healing.
Lack of research on the relationship between activity in a total contact
cast and rates of healing has perpetuated the belief that patients need to
remain non-weight-bearing during the first twenty-four to forty-eight hours
after cast application. On the basis of this suspected relationship,
clinicians routinely inform patients of this restriction when recommending the
use of a total contact cast. This sometimes leads the patient to refuse the
treatment despite its well-documented benefits with regard to healing. The
results of our study suggest that restriction of weight-bearing immediately
following application of a total contact cast is not necessary.
In this study, the rate of ulcer healing (the dependent variable) was
expressed as the linear advance of the wound (the change in its radius). This
parameter can be used to measure healing ulcers regardless of their size or
shape. In addition, it is more accurate than is measurement of either the
absolute or the percent change in area between two time-points, the method
more commonly used to measure the rate of healing in clinical practice.
Although such methods can be used to document the progress of the healing of
an ulcer and to compare ulcers of the same size and shape, their validity is
compromised when ulcers of different sizes and shapes are analyzed.
Measurement of the absolute change in area inflates the progress of the
healing of large ulcers relative to that of small ulcers and gives the
impression that the rate of healing of a large ulcer decreases as time
progresses. Conversely, measurement of the percent change in area exaggerates
the progress of the healing of small ulcers relative to that of large ulcers
and suggests that the rate of healing of a small ulcer increases as time
progresses. However, as re-epithelialization occurs with wound-healing, the
wound margins advance toward closure at a nearly constant linear rate; thus,
the healing rate does not tend to change over
time26. It has been
shown that use of the linear advance of the ulcer as a measure of
healing25 minimizes
potential bias from disparate ulcer sizes or shapes within the same study
cohort27.
A major strength of this study was its prospective design, with the control
of several key variables, including the method for instructing the patients
with regard to use of the cast, the technique of applying the total contact
casts, the method of measuring the ulcers, and the documented accuracy of the
step monitor when it is used in
casts21. After each
time interval, we were able to calculate the change in the ulcer radius and to
determine whether the total number of steps taken during the cast-treatment
interval or the number of steps taken during the first twenty-four or
forty-eight hours (when weight-bearing was prohibited) had an effect on ulcer
healing. The separate calculation of each of these pairs of variables (number
of steps and change in ulcer radius) after each time interval allowed us to
compare different healing intervals for the same patient and for different
patients and permitted a careful analysis of the effects of plantar loading on
healing of diabetic plantar ulcers in a total contact cast.
A potential limitation of the study is related to the criteria for
selection of the subjects for enrollment. Patients with very small ulcers were
excluded from the study because our primary outcome measure was the
ulcer-healing rate and we wanted to include ulcers that would require a number
of cast changes to heal. Larger ulcers generally require more cast changes,
which permits more measurement time-points and thus facilitates a better
estimate of the ulcer-healing rate. In addition, we excluded five patients
with steroid dependence in order to reduce the number of known variables
affecting ulcer-healing rates. We know of no a priori reasons why the findings
of our study cannot be generalized to patients with small ulcers or steroid
dependence. We also excluded patients who had a foot infection, were unable to
comply with the cast treatment or could not use the cast safely, or were
unwilling to be non-weight-bearing during the initial use of the cast. We
believe that the practice of not treating such patients with casts is
consistent with current general medical practice and that the relatively large
number of patients who were unwilling to be treated with casts because of
concerns about non-weight-bearing speaks to the purpose of this report.
In our study, the magnitude of the minimum detectable slope was at an
acceptable level given standard clinical practice, and we found that only
truly excessive walking will prolong ulcer healing. For example, an increase
in the time to wound closure of less than two weeks for ulcers with a radius
of 0.65 cm (the median radius) as a result of an activity level of 1116 steps
in the first twenty-four hours and for ulcers with a 0.94-cm radius as a
result of an activity level of 828 steps in the first twenty-four hours is not
clinically relevant, given that the casts are usually changed at two-week
intervals. On the basis of our findings, we no longer recommend a period of
complete non-weight-bearing after application of a total contact cast for the
treatment of a plantar ulcer in a patient with diabetes mellitus. We permit
early weight-bearing but ask the patient to try to avoid extensive walking in
the first forty-eight hours after application of the cast. For these often
debilitated patients, who frequently face challenges involving the
contralateral foot or use of prostheses, the capacity for immediate
weight-bearing in casts has several potential major benefits, including better
acceptance of ulcer treatment with casts and an improved sense of balance.
The instructions for patients wearing a total contact cast used in this
study are available with the electronic versions of this article, on our web
site at
(go to the article citation and click on "Supplementary Material")
and on our quarterly CD-ROM (call our subscription department, at
781-449-9780, to order the CD-ROM). ?
Note: The authors thank Dr. Ingrid Nygaard and Dr. Richard Brand
for their careful reading and thoughtful review of the manuscript, and Mr.
Kenneth Kesserling for providing excellent orthotic support to the subjects in
this study.
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