Symmetry in Kinetics Variables in Total Hip Arthroplasty Patients during Unilateral vs. Bilateral Tasks
1
Varin, D; + 1Lamontagne, M; 1Reynolds, S; 2Beaulé, P E
+1University of Ottawa, Ottawa, ON, Canada, 2The Ottawa Hospital, Ottawa, ON, Canada
[email protected]
METHODS
Fifty-one patients that had unilateral THA were recruited (22 men,
age: 65 ± 7 yrs, Body Mass Index (BMI): 28 ± 5 kg/m2, assessed 299 ±
104 days after surgery). Exclusion criteria included prior lower-limb
surgery, presence of joint degeneration at other lower-limb joints and
any other condition that could alter their gait. Informed written consent,
approved by the institution’s research ethics board, was obtained. They
performed three trials of and standing on a bench adjusted to their tibial
plateau height, as well as three trials of walking at a self-selected natural
pace. Twenty lower limb markers were tracked with a nine-camera
motion analysis system and ground reaction forces were collected with
two force plates. Kinematic data were calculated using Euler angle
convention and kinetics were obtained with inverse dynamics. The four
variables of interest included peak hip and knee extension moment, as
well as peak hip and knee power. A symmetry index (S) was calculated
using the following formula:
S = │Vno - Vo│/ (│Vno│+│Vo│) * 100%
(1)
where Vno is the kinetic variables of the non-operated limb and Vo
of the operated limb. This formula, adapted from Talis et al. [3],
measures the symmetry regardless of direction. Paired t-tests were
performed on the symmetry indices and alpha was set at 0.05. It was
decided that, based on data previously obtained from a cohort of 19
healthy control participants with similar age and BMI, a symmetry index
under 10 would indicate symmetry for the specific variable. Each
participant was then categorized, based on their mean differences, in one
of three groups: no-side favouring (SYM), favouring the operated (OP)
or the non-operated (NO) limb; for each variable.
RESULTS
It was found that THA patients had significantly greater asymmetry
indices during standing for their peak hip power generation (Table 1).
While the other t-tests did not achieve significance, the same trend was
observed in peak knee power and peak hip extension moment. Inversely,
THA patients showed greater asymmetry during walking for the peak
knee extension moment.
Table 1. Average symmetry indices and paired t-test results.
Variable
Walk
Stand
P-value
Peak hip power
13.5 ± 10.6
19.5 ± 15.5
.024
Peak knee power
11.9 ± 7.7
16.0 ± 12.7
.058
Peak hip moment
13.3 ± 15.3
18.5 ± 15.6
.102
Peak knee moment
22.6 ± 26.6
16.1 ± 11.0
.083
When looking at the distribution of the symmetry categories (SYM, OP
and NO), most THA patient favoured their NO side to produce the
extension moment and power at the hip and knee during both the
standing and walking tasks. When looking only at those who had an
index below 10, thus that had a symmetrical pattern, we can observe
more patients were in this category for the walking task compared to the
standing task, for all the variables analyzed (Figure 1).
30
Walk
25
Frequency
INTRODUCTION
Several studies showed improvements in activities of daily living
such as walking and stair climbing [1], but some abnormalities persist
long after the primary total hip arthroplasty (THA)[2]. A certain level of
asymmetry was shown in THA patients when looking at the vertical
ground reaction force amplitude during a standing task. We
hypothesized that THA patient would exhibit more symmetry in a
unilateral task (walking) than a bilateral task (standing). The proposed
mechanism is that patients would prefer to use their non-operated limb
for a bilateral task whereas a unilateral task would force the patient to
use the operated limb.. In order to verify this, we measured the level of
symmetry in kinetics variables in a cohort of 51 THA patients. The
purpose of this study is therefore to compare the level of symmetry
exhibited by THA patients during a unilateral and a bilateral task.
Stand
20
15
10
5
0
Peak hip
power
Peak knee
power
Peak hip
moment
Peak knee
moment
Figure 1. Frequency of THA patient that had a symmetry index under 10
for peak hip and knee extension moment and power during walking and
standing.
DISCUSSION
We hypothesized that the THA group would show more asymmetry
in lower limb kinetics during the bilateral task of standing compared to
the unilateral task of walking. The rationale being that when they can
use both limbs for a task, patients would naturally prefer their sound
limb over their operated one. However, when they do not have a choice
to use the operated limb, such as during the single-legged stance phase
of gait, they would have kinetic patterns closer to their sound limb. As
expected from prior studies [3], most THA patients preferred their sound
limb during standing for producing for all hip kinetic variables. When
looking at the mean symmetry index, only the hip power generation was
found to be significantly different between tasks. Contrary to what we
expected, a greater level of asymmetry was observed in knee extension
moment during walking, and an equal number of participants preferred
either side for knee power. This might be explained by the compensation
that the knee must perform in response to the reduced moment and
power at the ipsilateral hip.
An important finding is that more THA patients were classified in
exhibiting a symmetrical pattern (an index under 10) in the walking task
(24.8 on average for the 4 variables) compared to the standing task (18
on average) for all variables examined. This finding is in line with our
hypothesis and could be explained by the mechanism that patients
cannot rely on their sound side when in single-legged stance.
It is therefore suggested that, when evaluating the functional
performance of patient that had hip replacement, as well as any other
unilateral lower limb surgical procedure, both bilateral and unilateral
tasks should be evaluated. Also, rehabilitation protocols might want to
avoid bilateral training (such as squats), as patient would probably
compensate with the other limb.
SIGNIFICANCE
The findings of this study will differentiate the differences observed
in kinetic variables between a unilateral and bilateral task and help better
understanding how THA patients compensate when they can or cannot
rely on their sound side.
ACKNOWLEDMENTS
The authors would like to thank Sarah Leduc-Gaudet and Julie
Gamarnik from the University of Ottawa, as well as Anna Fazekas from
the Ottawa Hospital for their efforts. This research was supported, in
part, by the Canadian Institutes of Health Research.
REFERENCES
1. Shrader et al. 2009. Clin Orthop Relat Res. 467(6): p. 1476-84.
2. Beaulieu et al. 2010. Gait Posture. 32(2): p. 269-273.
3. Talis et al. 2008. Clin Biomech. 23(4): p. 424-433.
Poster No. 1883 • ORS 2012 Annual Meeting