Foot & Ankle International - June 2017 - 691

Miller et al

Figure 1. The weight-bearing measurement setup. A scale is
placed under the radiograph plate and the contralateral foot is
placed on a platform to equalize the height.

apply when standing radiographs were obtained for common conditions of the foot and ankle. We also sought to test
if giving basic instructions at the time of radiograph acquisition would improve standardization of weight bearing.

Methods
Institutional review board approval was obtained for this
study. Adult patients who required weight-bearing radiographs of the foot or ankle as part of their routine clinical
care were eligible for inclusion. Exclusion criteria included
a history of recent lower extremity surgery, polytrauma
patients with significant concurrent injuries, patients who
were unable to stand safely, and those who were unable to
give informed consent because of cognitive or neurologic
impairment. Fifty subjects were enrolled, including 23
males (46%) and 27 females (54%). The average age was
48.9 years (range 18-74, SD 14.3). Twenty-seven subjects
had ankle radiographs, whereas the remaining 23 cases had
foot radiographs obtained.
A digital scale was placed under the image receiver cassette. To allow the patient to stand on a level surface, the
contralateral foot was placed on a raised platform at the
same height as the foot being imaged (Figure 1). Patients
removed their socks and shoes and were instructed to stand
on the cassette overlying the scale. No specific instructions
were given prior to the first trial other than what the radiology technician would normally do in the regular clinical
scenario.
The amount of weight applied was blinded to the patient
and recorded at the time of the initial radiograph (trial 1).
The patient was then specifically instructed to place "half
[his or her] weight" on the affected limb, and the weight

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was again recorded in blinded fashion for the second radiograph (trial 2). Following completion of the radiographs,
the total body weight of each subject was recorded. The
weight of the protective lead apron worn by each patient
was subtracted from these measurements.
The percentage of total body weight applied when radiographs were obtained was then calculated and compared to
50% of the patient's body weight. The absolute value of the
difference between the observed percentage and 50% body
weight was calculated in order to evaluate the accuracy of
weight bearing during the image acquisition. Given that
standing foot and ankle radiographs are typically obtained
with patients applying half their weight on the imaged
extremity,1,6 the "ideal" amount of applied weight for the
purposes of this study was defined, arbitrarily, as 45% to
55% total body weight. In the authors' view, accurate
assessment of true bony alignment would be more adversely
affected if an inadequate amount of weight was placed, but
should be acceptable if "too much" weight was applied; we
defined "appropriate" weight bearing, arbitrarily, to be
greater than 45% body weight.
One-sample, 1-sided t test was used to compare the absolute value of the difference in percentage body weight compared to 50%. Two-sample and paired t tests between trials
1 and 2 and chi-square tests were used to compare continuous and categorical variables, respectively, as appropriate.
Statistical significance was defined as an alpha error of less
than 5% (P < .05). Statistical analysis was performed using
IBM SPSS Statistics version 23.0 (IBM, Armonk, NY).

Results
The mean and 95% confidence intervals of percentage body
weight in trials 1 and 2 was 45.7% ± 3.2% (P = .012 compared to the 50% mark) and 49.2% ± 2.4%, respectively (P
= .428 compared to 50%). Comparison of trial 1 and trial 2
as above with a paired t test yielded a P = .0313 (Figures 2
and 3). Figure 2 demonstrates the scatter plot distribution of
each patient's weight bearing during image acquisition for
trial 1 and trial 2. The dashed lines mark the 45% and 55%
limits used to define "ideal" weight bearing. Figure 3 demonstrates the proportion of patients who had "ideal" (45%55%) and "appropriate" (>45%) weight bearing. For trial 1,
18/50 subjects were within the "ideal" range for weight
bearing compared to 32/50 on trial 2 (P = .005). In trial 1,
24/50 subjects had "appropriate" weight bearing compared
to 39/50 on trial 2 (P = .002).
The mean (and 95% CI) absolute difference in percentage weight bearing compared to 50% in trials 1 and 2 was
9.3% ± 2.3% and 5.8% ± 1.8%, respectively (P = .005). The
mean improvement toward ideal 50% weight bearing was
3.6% ± 2.4% between trial 1 and 2. Thirty-four of 50 subjects improved their weight bearing closer to 50%, whereas

Table of Contents for the Digital Edition of Foot & Ankle International - June 2017