provided the related
finding was statistically significant.
Results were unmasked following all statistical analyses.
RESULTS
Subjects
A total of 28 participants provided informed consent and
completed the protocol (i.e., no missing data). Of these,
14 were TTAs and the other 14 were members of the local
Sheriff
’s SWAT team who served as nonamputee control
subjects. The 14 TTAs included 5 Army Veterans, 3 Marine
Corps Veterans, 3 accomplished civilian athletes, 2 active
duty Army soldiers, and 1 active duty Air Force airman.
TTAs lost their limbs 8.9 ± 10.5 (mean ± SD) years before
enrollment primarily because of exposure to blasts from
improvised explosive devices. Two of the civilian TTAs lost
their limbs because of trauma and one was a congenital
amputee. TTA subjects
’ mean age (31.4 years ± 5.9) was
signi
ficantly ( p ≤ 0.05) younger than controls (38.5 years ±
5.1). The TTA
’s body mass index was 28.4 ± 6.7 kg/m
2
compared to controls
’ 26.3 ± 2.9 kg/m
2
( p > 0.05).
Although 66.7% of TTAs rated themselves as highly active,
only 35.7% of controls rated themselves as highly active
( p > 0.05). Self-reported activity (years and no. of bouts/
week) was not signi
ficantly different between TTAs and
controls, however, duration/bout was ( p
≤ 0.05). Control
subjects reported physical training of 2 to 5 bouts per week
(3.1 ± 1.1) related to their work, whereas TTAs reported
3.5 ± 1.2 (range: 1.0
–5.0) bouts per week. TTAs reported
training duration of 62.7 ± 24.3 minutes compared to 42.5 ±
16.3 reported by controls.
Prosthetic Characteristics
TTAs reported using 0.9 ± 0.9 (range: 0
–3) additional rec-
reational prostheses for the following activities; cycling,
jogging/running, skiing, snowboarding, rock climbing, swim-
ming, kayaking, soccer, and cross-
fit exercise, which consti-
tuted much of the aforementioned physical training. Sagittal
and coronal alignment of prosthetic feet setup for the study
were to manufacturer speci
fication and were not signifi-
cantly different between conditions ( p > 0.05). In terms of
prosthetic suspension, 9 subjects used a sleeve and 5 used a
pin lock. Two of the subjects using pin suspension also used
auxiliary suspension (one suction pin and one sleeve). All
subjects used a total surface bearing socket design. Re-Flex
Rotate (1.92 kg ± 1.10) made prostheses signi
ficantly
heavier ( p < 0.05; without socks/shoes) than the Vari
flex
(1.67 kg ± 0.96) and the Elite Blade (1.52 kg ± 0.96).
OC Timing Data
The OC includes 18 tasks. During the preparation period,
the
fitting and accommodation week, it became clear during
OC practice that TTAs were greatly challenged by obstacle
no. 2, the rope climb (Fig. 2, OC map). There were numer-
ous potential reasons including an inability to move the
prosthetic ankle-foot system suf
ficient to use the feet to ele-
vate the body and assist the upper limbs during climbing.
Thus, SWAT operators determined the rope climb obstacle
required elimination from further practice and evaluation for
safety reasons. Removing the rope climb obstacle reduced
the total number of tasks from 18 to 17 for both the TTAs
and the control group. Following removal of the rope climb
obstacle, total OC completion times (mean ± SD) were simi-
lar ( p > 0.05) between prosthetic feet: Elite-Blade (419 sec-
onds ± 130), Vari
flex (425 seconds ± 144), and Re-Flex
Rotate (444 seconds ± 220). Controls
’ total OC completion
time was 287.2 seconds ± 58 which was less ( p
≤ 0.05)
than TTA times. In total, controls had signi
ficantly faster
completion times ( p
≤ 0.05) compared to all 3 prosthetic
feet conditions in 13 of 17 obstacles (Table I).
The Re-Flex Rotate had two additional obstacles that
were signi
ficantly different ( p ≤ 0.05) than controls. The
Elite Blade had one additional obstacle that required more
time to complete. In terms of per-obstacle completion time
differences between prosthetic feet, only two obstacles
yielded differences: (1) climbing the chain-link fence and
(2) the sprint
finish. Climbing the chain-link fence required
greater time with the Vari
flex than it did with the Elite Blade
(14.0 seconds ± 4.9 vs. 12.4 seconds ± 4.6; p
≤ 0.05). The
sprint
finish took significantly longer ( p ≤ 0.05) to complete
with the Re-Flex Rotate (6.6 seconds ± 1.7) than it did with
either the Vari
flex (5.9 seconds ± 1.1) or the Elite Blade
(5.9 seconds ± 1.4).
Perceptive Measures
Median RPE values were signi
ficantly lower ( p ≤ 0.05) for
controls (17; range: 14
–17) than TTA regardless of foot
condition (Vari
flex 18.5[15–20], Elite Blade 18.5[13–20],
and Re-Flex Rotate 18[15-20]). Finally, when asked to rate
their preference of foot for completing the OC, 7/14 sub-
jects (50%) preferred the Elite Blade, 5/14 (36%) preferred
the Re-Flex Rotate, and the remaining 2/14 (14%) preferred
the Vari
flex.
DISCUSSION
We hypothesized that the lightest weight foot would
outperform other prosthetic foot alternatives and be the most
preferred. We further hypothesized that nonamputees would
outperform TTAs in all physical performance measures. The
Elite Blade was the foot with the lowest mass, but it was not
signi
ficantly different than the Variflex.
TTA subjects in this study are representative of combat
injured military personnel and similar to TTAs from other
studies of persons who have lost limbs in military service,
in terms of demographic and anthropometric characteris-
tics.
1,2,4,6,29
Among the more obvious results from this
study were the differences in performance between TTA and
control. TTAs were younger than controls by approximately
MILITARY MEDICINE, Vol. 181, November/December Supplement 2016
50
Energy-Storing and Shock-Adapting Prosthetic Feet in Transtibial Amputees