Timing of Frontal Plane Trunk Lean, Not Magnitude, Mediates Frontal Plane Knee Joint Loading in Patients with Moderate Medial Knee Osteoarthritis
Timing of Frontal Plane Trunk Lean, Not Magnitude, Mediates Frontal Plane Knee Joint Loading in Patients with Moderate Medial Knee Osteoarthritis
Dan K. Ramsey 0
Allen L. Carl
0 Faculty of Medicine, School of Health Sciences, University of Iceland , Saemundargata 2, 101 Reykjav ??k , Iceland
1 Department of Health Professions Education, D'Youville College , 220 Koessler Administration Building (KAB), 320 Porter Ave, Buffalo, NY 14201 , USA
The purpose of this study was to examine the influence of trunk lean and contralateral hip abductor strength on the peak knee adduction moment (KAM) and rate of loading in persons with moderate medial knee osteoarthritis. Thirty-one males (17 with osteoarthritis, 14 controls) underwent 3-dimensional motion analysis, strength testing of hip abductors, and knee range of motion (ROM) measures, as well as completing the knee osteoarthritis outcome score (KOOS). No differences were found between groups or limbs for gait cycle duration, but the osteoarthritis group had longer double-limb support during weight acceptance ( < 0.001) and delayed frontal plane trunk motion towards the stance limb ( < 0.01). This was reflected by a lower rate of loading for the osteoarthritis group compared to controls ( < 0.001), whereas no differences were found for peak KAM. Trunk angle, contralateral hip abductor strength, and BMI explained the rate of loading at the involved knee ( < 0.001), an association not found for the contralateral knee or control knees. Prolonged trunk lean over the stance limb may help lower peak KAM values. Rate of frontal plane knee joint loading may partly be mediated by the contralateral limb's abductor strength, accentuating the importance of bilateral lower limb strength for persons with knee osteoarthritis.
Osteoarthritis (OA), knee OA in particular, is a large and
growing public health concern. Notable increases in
estimated years lived with disability owing to OA has been
observed over the last 15 years [
] with concomitant activity
limitations projected to increase [
]. Moreover the economic
burden associated with knee OA is expected to rise
concurrently with the ageing population, resulting in increased
demand for primary and revision knee joint arthroplasty
]. Therefore, emphasis has been focused on investigating
whether conservative biomechanical modalities mediate
disease progression [
Frontal plane trunk movements have recently garnered
increased attention, with evidence suggesting patients with
severe medial compartment OA exhibit greater ipsilateral
peak trunk lean as opposed to persons with less severity [
This may be an effective strategy for mediating pain relief
], evoked by redirecting the ground reaction force more
laterally and lowering medial compartment load as inferred
by lower external knee adduction moments (KAM) observed
among healthy controls [
] and persons with medial knee
] during gait. Perhaps this may be an effective strategy,
particularly for persons with mild to moderate knee OA, to
attenuate KAM magnitudes similar to that of the uninvolved
knee and/or controls, despite varus deformity [
It is during the first 10% of the gait cycle when
transitioning from double- into single-limb support and weight
acceptance (from initial contact (IC) of the stance limb until
contralateral toe-off ) when the first peak KAM typically occurs
]. Yet the rate of loading throughout weight acceptance
(WA), as ref lected by the positive slope of the KAM prof ile,
has been associated with medial knee joint degeneration,
independent from the peak and KAM impulse [
plane pelvic stability and, thereby, trunk and hip joint motion
are regulated by the hip abductor muscles. Ef fective control
of hip and pelvis frontal plane movement calls for good
eccentric control, not just of the hip abductors on the affected
side but also on the contralateral side for stabilizing the pelvis
prior to IC. The rate and magnitude of knee loading during
WA may therefore be in part mediated by contralateral hip
abductor strength, which has not been well studied. While
recent studies have investigated the relationship between
hip abductor function and gait parameters, none report
an association between contralateral hip abductor strength,
neuromuscular activation patterns, or ipsilateral peak KAM
magnitudes after accounting for body size [
]. A recent
meta-analysis on studies of hip strength in people diagnosed
with symptomatic knee OA demonstrated weaker isometric
and isokinetic hip abduction strength . Contralateral hip
abductor strength would affect control of contralateral pelvic
drop during stance, and greater pelvic drop has been shown to
increase knee adduction moments [
]. Better understanding
of the relationship between hip strength, trunk lean, and knee
joint loading in people with knee OA may help clinicians
design targeted rehabilitation programs for those affected
by knee OA. Therefore, the purpose of this study was to
examine whether frontal plane knee joint loading was related
to temporal-spatial parameters and to determine whether
contralateral hip abductor strength mediates loading in
addition to trunk lean. We hypothesized that greater trunk
lean would be evident in persons with symptomatic moderate
medial compartment OA compared to matched controls, and
that either ipsilateral or contralateral hip abductor strength
might be inversely associated with loading parameters at the
index knee of OA patients during the WA phase of gait.
2. Materials and Methods
Data for this cross-sectional laboratory study were collected
during baseline measurements of patients who had been
referred by orthopedic specialists for a fitting and trial
treatment with an unloader (valgus) brace [
]. Due to limited
number of female patients at the clinic who were inclined
to try an unloader brace, a decision was made to include
only males in this study. Seventeen male patients (aged 40?60
years) with confirmed medial knee OA, Kellgren Lawrence
(KL) grade 2 or 3 radiographic changes [
], and clinical
history of pain and functional impairments fulfilled the
inclusion criteria. In cases where bilateral radiographic knee
OA was diagnosed, the more symptomatic knee denoted
the affected one. Patients were excluded if they had joint
replacement surgery, periarticular fracture, osteotomy, knee
ligament reconstruction, or arthroscopic surgery to any lower
limb joint within 6 months of the study. Exclusion criteria
also included radiologically confirmed OA in the ankle or hip
joints, intra-articular corticosteroid or viscosupplementation
injection to either knee joint within 3 months of study
participation, or any musculoskeletal or neurological
impairment, dermatological or circulatory problems in the lower
extremities that might affect ambulation. Fourteen
asymptomatic male subjects were recruited from the university
community to serve as controls (CTRL) and were matched
to the OA cohort by age (to within 5 years), weight (to within
5 kilograms), and height (to within 5 centimeters).
The protocol of this study was approved by the National
Bioethics Committee and Data Protection Authority
(VSNb2011100025/03.07). Participants signed an informed
consent form and then completed the knee osteoarthritis
outcome score (KOOS) questionnaire [
]. Passive knee
joint range of motion (ROM) was measured bilaterally
from full extension to flexion by a single physical therapist
with over 10 years of clinical experience. The same physical
therapist also conducted hip abductor isometric strength
testing with a hand-held dynamometer (Lafayette Manual
Muscle Tester, Lafayette, USA) placed 5 cm proximal to the
lateral femoral condyle with participants laying supine .
Straps were used to secure the pelvis and each lower limb
during strength testing (Figure 1). After a single, submaximal
practice trial, participants performed three maximal trials of
5 s duration, separated by 15 s of rest. The strongest trial was
used for analysis, normalized by the participant?s body mass
During motion capture, kinematic and kinetic data were
collected at 100 Hz as participants walked across the lab floor
at a brisk self-selected pace wearing their own comfortable
low top walking shoes. Data were collected until 5 successful
foot strikes per foot on force plate were obtained. A total of 47
retroreflective markers were used during three-dimensional
gait analysis using 8 Oqus 300 infrared cameras (Qualisys AB,
Gothenburg, Sweden) synchronized with two AMTI force
plates (American Management Technology, Inc., Watertown,
USA), embedded into the lab floor. Markers were placed
over specific anatomic landmarks of participants in order
to define proximal and distal trunk, pelvis, thighs, shanks,
and feet as rigid segments, while clusters of 4-5 markers per
segment were used for tracking purposes during walking
trials (Figure 2). A static measurement was used to define
segments and joint centers based on anatomical markers,
as well as the relative position of tracking markers and
each participant?s body mass. Markers were autotracked
and labeled using Qualisys Track Manager software while
commercial software (Visual3D , C-Motion, Germantown,
USA) was used for further data processing.
Marker and force data were low-pass-filtered using a
Butterworth filter with a cut-off frequency at 6 and 20 Hz,
respectively. A model template was applied to define body
BMI: body mass index; INV: involved side; UN: uninvolved side; ROM: passive range of motion; ADL: activities of daily living. ?Significantdifference between
groups (? < 0.001). ?Significantdifference between knees (? < 0.01).
50.4 (6.2); 40?59
28.3 (3.1); 23.0?34.6
1.04 (0.28); 0.72?1.69
1.05 (0.25); 0.77?1.81
127.3 (10.2); 107?139??
133.8 (9.6); 106?148
64.1 (16.6); 33?94?
segments and their local reference systems, as well as joint
centers. Rigid-body analysis and inverse dynamics
postprocessing were conducted to obtain kinematic variables
between segments of the lower limbs based on an
-Cardan ordered sequence. Frontal plane trunk motion was
calculated with respect to the lab?s coordinate system, in order
to derive trunk position without the influence of pelvic tilt.
Joint moments for the lower limbs were derived by inverse
dynamics, resolving the joint moment into the proximal
segment, using the software default settings for normalization
to body mass (Nm/kg). Specific gait events (IC and TO) were
defined by utilizing a force plate data threshold of 15 N, and
those events then used for analysis related to the gait cycle,
examining trunk lean during stance and specifically at the
end of WA. Rate of loading (slope of the moment curve) was
calculated as the change in frontal plane external knee joint
moment from IC to the first peak KAM over time (seconds)
]. Data were exported into Microsoft Excel and SPSS
statistical software for data compilations and further analysis.
Of OA participants, the knee that was affected was
on the left in 8 and on the right in 9 participants, and
while 10 participants had unilateral involvement, 7 had some
degree of radiographic OA (KL 1?3) on the medial or lateral
compartment of the uninvolved side. These baseline data
were collected prior to initiation of brace use and are the
basis of this investigation. Half of the CTRL group was
randomly allocated with a left ?involved? and half with a right
Independent -tests were used to identify group
differences in age, BMI, knee ROM, and KOOS. Multivariate
analysis was used to identify differences between limbs and
groups for strength and temporal-spatial values, trunk lean
during WA, and knee joint loading (first peak KAM and rate
of loading). A mixed stepwise regression analysis was applied
for each group, with loading rate of the KAM during WA
being the dependent variable. An initial multiple regression
was run to assess the influence of contralateral hip abductor
strength values and ipsilateral trunk lean on loading rate at
the index knee, also including height and body mass based
on biomechanical rationale [
17, 26, 27
]. Significant predictors
of the loading rate were then entered into a sequential
multiple linear regression model to determine individual
contributions to the explained variance of the dependent
variable. Level of significance was set at < 0.05.
No differences were found for mean age, height, mass, BMI,
or strength between groups (Table 1). A significant deficit of
knee ROM was evident on the involved side of OA
participants as ref lected by a group by limb interaction ( = 11.824,
= 0.002). Moreover, the CTRL group scored significantly
higher on all KOOS subscales than the OA group, reflecting
expected differences in self-reported knee related symptoms,
functional abilities, and quality of life ( < 0.001).
No differences were found for mean (SD) walking speed
( = 0.316), between OA (1.58 (0.22) m/s) and CTRL (1.65
(0.16) m/s) groups. Duration of stance and swing for each
Inv: involved limb; Uninv: uninvolved limb. Significant differences between groups for relative proportion of gait cycle (% GC) spent in stance versus swing
(?interaction of group by phase; ? < 0.001). Significant group difference for WA as % GC (?main effect; ? < 0.001).
Uninv loading rate ((Nm?kg?1)?s?1)
Inv: involved limb; Uninv: uninvolved limb. Significant group difference for rate of loading (?main effect; ? = 0.019).
limb?s gait cycle (GC) is presented in Table 2 as duration
(time (sec)) and relative to the GC (% GC). No differences
were found between groups for GC duration and both groups
demonstrated interlimb symmetry. However, the OA group
demonstrated prolonged stance and a shortened swing phase
compared to controls (interaction; = 20.283, < 0.001)
and the difference in stance was mostly due to a significantly
longer double-limb support phase during WA ( = 15.323,
No main effects of group or limb and no interaction with
respect to the magnitude of the first peak KAM were found,
but for rate of loading a significant main effect of group was
found due to differences ( = 6.205; = 0.019; Figure 3 and
A significant interaction was seen due to group
differences in the magnitude of trunk lean at the beginning but
not at the end of WA ( = 7.136; = 0.012, Figure 3). Post
hoc tests revealed that at IC the CTRL group had already
initiated trunk lean towards the stance limb (mean (SD) 1.4?
(1.4?)), whereas the OA group?s trunk position was vertical
(0.0? (1.0?); < 0.001). This was further reflected in an
earlier transition of CTRL group from a lean towards the
stance limb, moving towards the contralateral limb during
midstance, which happened at a mean (SD) of 59 (17)% of the
stance phase compared to a significantly delayed transition at
71 (21)% of stance for OA participants ( = 10.186; = 0.004,
Figure 3). The overall group difference in mean peak trunk
lean values was only 0.15? (n.s.).
Multiple regression analysis demonstrated that a model
that included ipsilateral frontal plane trunk angle at the
end of WA, contralateral hip abductor strength, and BMI as
independent variables best explained the rate of loading at the
index knee. The resulting model demonstrated significance
((3, 13) = 15.486, < 0.001, adjusted 2 = .731) and
indicated that each factor added significantly to the model
towards lowering the rate of loading (trunk angle (Beta =
.635; = 0.001), contralateral hip strength (Beta = .722;
< 0.001), and BMI (Beta = .590; = 0.001)). The same
model was not successful in predicting ipsilateral PKAM ( =
0.067) or in predicting loading rate ( = 0.455) or PKAM
( = 0.333) on the contralateral side of OA participants or at
either knee of controls ( > 0.5 for both).
The main results of the study demonstrated that persons
with moderate medial knee OA exhibit different movement
patterns for frontal plane trunk lean compared to healthy
controls. This strategy may assist in maintaining the KAM for
this group to levels similar to that of controls during walking.
Moreover, the rate of frontal plane knee joint loading during
WA may be mediated, in part, by the contralateral limb?s
Self-reported measures reflected distinct group
differences in symptoms, function, and quality of life as was
expected between the knee OA group and healthy
controls, whereas other parameters including body size and
hip abductor strength were not different. The OA group
had a predominantly unilateral involvement with significant
ROM deficits of the involved knee. However, although the
group demonstrated clear differences in gait patterns when
compared with CTRL group, interlimb differences were not
evident for temporal-spatial parameters, trunk lean, or knee
joint loading values within the OA group.
When temporal-spatial values were observed, the
prolonged stance of OA participants was mostly due to a longer
WA period, during which a transition is being made from
double- to single-limb support. This is in agreement with
previous reports [
] and could reflect a pain avoidance
strategy by trying to shorten the time in single stance, as
this would be the period where the GRF vector is directed
more medially and involves greater loading onto the medial
compartment than during double stance. The OA group
maintained double stance until the first peak KAM while
controls were at that point in single stance. Notably, peak
KAM values did not capture kinetic differences between
the two groups, whereas the rate of loading did. T he rate
of loading has been implicated in a more rapid rate of
]. In addition to a slightly (n.s.) slower gait
speed, a significantly prolonged WA for the OA group was
coupled with delayed transition of trunk motion, whereby
trunk lean towards the stance limb generally started af ter the
initiation of the double stance period. This may represent a
more cautious transition of weight and explain the slower rate
of loading at the knee seen in the OA group. This, in turn,
may contribute to maintaining the first peak KAM to lower
values than what might otherwise have been the case for the
OA group and thereby positively influence pain levels.
The magnitude of trunk lean has typically been reported
as the peak value of the frontal plane motion, with the peak
typically being less than 1? greater than that found at the first
peak KAM of the knee and occurring somewhat later [
Peak values of trunk lean were similar to those previously
shown for OA cohorts [
6, 13, 29
]. Group dif ferences found at
IC represent the altered timing of frontal plane trunk motion
and were not found at the end of WA or for peak values
(Figure 3). This is in accordance with the findings of Hunt et
al., where differences in peak frontal plane trunk lean were
only found between the group with severe OA and others
(with mild or moderate OA and controls) [
]. A position of
greater trunk lean at the end of WA was associated with a
slower rate of frontal plane knee joint loading at the involved
knee in our OA group. As noted previously, this likely reflects
the effects of prolonged period of double stance during WA.
Intuitively one might expect that hip abductor strength
deficiencies, which are recognized in the OA population [
would result in less eccentric control, a more rapid
contralateral pelvic drop with a resulting greater rate of loading
onto the contralateral limb during WA. The results of the
present study support this, as greater hip abductor strength
on the uninvolved side was an independent predictor of lower
rates of frontal plane knee joint loading of the affected knee
in the OA group. A cross-sectional study of an OA cohort
] showed a strong positive association between higher
hip abductor strength and better functional performance.
A recent systematic review [
] found that strengthening
programs for hip abductor muscles improved strength and
self-reported scores whereas no change in peak KAM values
occurred. Investigating possible effects of hip strengthening
exercise on frontal plane knee joint loading rate may cast a
light on this relationship.
All participants were male with K-L grade 2 and 3, which
may limit the external validity of the study, as sex dependent
biomechanical differences are recognized during gait [
and findings might differ for those with more severe OA
(K-L grade 4) [
]. An ?a priori? power analysis was not
performed, but the observed power for the interactions found
was 73% for trunk angle and greater than 90% for
temporalspatial parameters. The secondary regression analysis may
suffer from the low number of participants, in particular for
the control group, but nonetheless statistical significance was
achieved for the affected side of the OA group.
In order to maintain KAM levels near normal levels, persons
with moderate knee OA may benefit from strategies that
lower the rate of knee joint loading. Part of this strategy
may be achieved by prolonged double stance during WA and
altered timing, not degree, of frontal plane trunk motion to
affect the magnitude of knee joint loading. Strength of hip
abductors may influence their ability to maintain a prolonged
trunk position over the stance limb and provide eccentric
control while lowering the pelvis prior to contralateral WA,
which may also assist in slowing down the rate of loading and
controlling peak KAM values.
Conflicts of Interest
The authors confirm that there are no known conflicts of
interest associated with this publication.
All authors have made substantial contributions to the study
and the manuscript.
Financial support was received from the Icelandic
Physiotherapy Association. T he authors would like to thank
orthopedic surgeons at Orkuhu?si? Orthopedic Center for
assistance with recruitment. Einfr???ur A?rnado?ttir, radiologist
at Ro?ntgen Orkuhu?si?, graded radiographic changes.
Gastroenterology Research and Practice
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