Aagaard, P.

Jensen, C.

Overgaard, S.

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Abstracts / Osteoarthritis and Cartilage 20 (2012) S54–S296 S99related to high articular cartilage TF T1r- and T2. Peak external extension
moment was related to low articular cartilage T1r- and T2 and high
T1r- and T2 in 4 of 6 meniscus compartments.
Greater Q:H CSA ratio was related with greater TF T1r (r ¼ 0.327) and T2
(r ¼ 0.401). Greater M:L Q ratio was associated with greater M:L ratio of
meniscus T1r (r ¼ 0.337). Greater M:L Q ratio was associated with greater
KAM peaks (r¼0.357) and impulse (r¼0.461), and greater frontal ROL
(r¼ 0.303). Greater Q:H ratio was associated with greater peak frontal
(r¼ 0.645) and sagittal moments (r ¼ 0.360) and greater dynamic frontal
malalignment (r ¼ 0.330
Conclusions: These are the 1st results to show relationships between
static/dynamic alignment, muscle balance and cartilage composition in
young health subjects. Based on these data, young subjects with varus
show worse medio-lateral balance of cartilage composition likely pro-
gressing to OA. The impact of static and dynamic loading is more
pronounced on the meniscus than the articular cartilage indicating a more
important role of meniscus in pathogenesis of knee OA than previously
thought. These data also show for the 1st time that muscular imbalance
(high Q:H and M:L CSA ratios) is related to high knee loads (high KAM
impulse) and worse cartilage composition (high T1r- and T2). Overall,
these data suggest the need for development of preventive programs that
emphasize muscle retraining and strategies to alter medio-lateral balance
of cartilage composition. We continue to process the data to assess rela-
tionship of functional mechanics with articular cartilage laminar T1r- and
T2 relaxation times and texture values. We are also in the process of doing
subregional analysis of articular cartilage in light of the ﬁndings of
different relationship of ﬂexion and extension moments with T1r- and T2
relaxation times.
184
RECOVERY IN HORIZONTAL GAIT AFTER HIP RESURFACING VS. TOTAL
HIP ARTHROPLASTY AT 6-MONTH FOLLOW-UP - A RANDOMIZED
CLINICAL TRIAL
C. Jensen 1, P. Aagaard 2, S. Overgaard 1. 1Orthopaedic Res. Unit, Odense,
DENMARK; 2 Inst. of Sports Sci. and Clinical Biomechanics, Odense, Denmark
Standard total hip arthroplasty (THA) is the established surgical treatment
for patients older than 65 years with progressive osteoarthritis. However,
implant survivorship curves decline more rapidly in patients younger than
50 years. Resurfacing hip arthroplasty has therefore been suggested as an
alternative for younger more active patients. Walking ability is one of the
most common and useful outcome measures used in hip replacement
patients, and the ability to safely ambulate is considered a pre-requisite for
discharge frommost orthopedic facilities. Improvements inwalking ability
and kinematics have been suggested after hip resurfacing, but no study
sofar has objectively assessed this aspect in a randomized trial including
standard THA.
Purpose: To test the hypothesis that (i) a superior recovery in gait would
be observed following resurfacing total hip arthroplasty compared to
standard total hip arthroplasty and (ii) to investigate the hypothesized
relationship between mechanical hip and knee muscle performance and
horizontal gait function in patients with total hip replacement.
Methods: Forty-three patients were randomized into either standard or
resurfacing THA. Three-dimensional gait data were collected at self-
selected normal and maximal walking speed. Primary outcome was gait
speed while secondary outcomes comprised selected temporospatial and
kinematic parameters obtained during horizontal walking. Explorative
outcome was the relationship between isolated mechanical hip and knee
muscle performance and horizontal gait function in younger THA patients
56  6 years (range 44-64). Data was collected pre-operatively, 2 and 6
months post-operatively
Results: There was no effect of treatment on horizontal self-selected
normal speed, however an effect of treatment was observed on maximal
walking speed where standard THA subjects walked faster than the hip
resurfacing subjects (P ¼ 0.03). No differences in the recovery of spatio-
temporal parameters were observed. Also, peak hip ﬂexion and peak hip
adduction angles recorded during the stance phase were similar in bothgroups. Maximal isometric knee and hip muscle strength were positively
associated with gait speed, step length and cadence during maximal
walking (R2¼ 0.13-0.37, P < .05).
Conclusions: The present data could not provide evidence to support the
hypothesis that resurfacing total hip arthroplasty should lead to a superior
recovery in gait and hip kinematics compared to standard 28-mm hip
arthroplasty in younger hip arthritis patients. Maximal isolated leg muscle
strength was a predictor of horizontal gait performance, and thus provides
an important and valid functional outcome measure for individuals
undergoing total hip arthroplasty.
185
WALKING WITH INCREASED FOOT PROGRESSION ANGLE CAN REDUCE
JOINT COMPRESSION IN INDIVIDUALS WITH KNEE OA
K. Manal, T.S. Buchanan. Univ. of Delaware, Newark, DE, USA
Purpose:The knee adduction moment is an often used surrogate measure
to infer joint contact force. Treatments and/or gait alterations to reduce the
magnitude of themoment are sought for thosewith knee OA, since smaller
moments are believed to be associated with less joint compression.
Previous work suggests there is little change in peak adduction moment
whenwalking with an increased foot progression angle (FPA). We propose
that greater FPA can decrease joint contact for some people, even though it
may not reduce the peak adduction moment relative to normal walking.
The purpose of this study is to present data in support of this thesis and to
suggest that walking with greater FPA may be an effective strategy for
reducing joint loading in persons with knee OA.
Methods:Ten subjects (six male, four female) with mild to moderate
medial compartment knee OA (KL-grade I-III) were referred by an area
orthopaedist. Average subject age was 64 years (8), body weight 81.8
kg (12.7), height 1.68 m (0.08), and body mass index 29.0 (5.6).
Subjects were pain free at time of testing. A six-camera motion capture
system and a force platform were used to compute joint moments and
reaction forces at the knee for normal gait and walking with a 15 degree
increase in FPA. Subjects performed 5 trials for each condition. Joint
moments and reaction forces were normalized by body weight (BW) and
height, and BW respectively. Walking speed was monitored using photo-
electric timers.
Results:Therewas no difference inwalking speed for the normal and toed-
out conditions (1.28  0.23 m/s & 1.26 0.24 m/s). The average toe-out
angle during normal walking was 2.0  6.8 degrees and 18.6  8.9 degrees
with increased FPA. The average peak adductionmoment for all 10 subjects
was almost identical for the 2 conditions, while the extensor moment was
approximately 5% smaller when walking with increased FPA. Subjects
were then grouped into those who had a larger than average decrease in
peak extensor moment and those who did not. The knee extensor moment
was smaller for 6 of 10 subjects when walking with increased FPA (0.028
vs. 0.024 N-m/(BW*Ht), p < 0.05); there was no difference in peak
adduction moment (Fig.1).
Conclusions:Peak contact force occurs at approximately 25% of stance, the
same time the extension and adduction moments reach their peak. A
decrease in peak adduction does not guarantee a reduction in peak contact
force if there is a concomitant increase in extensor moment. This has been
shown for a patient with a instrumented knee prosthesis while walking
with a medial thrust gait. We propose the opposite is also true. That is,
reduced joint compression is possible when the extension moment is
smaller and the adduction moment does not increase. This pattern was
seen for 6 of 10 subjects walking with increased FPA (Fig. 1). The clinical
relevance of this work is twofold. Firstly, we suggest that it is important to
consider the knee extension moment when inferring changes in joint
contact force estimated from the adduction moment. This is not common
practice as most studies focus on the adduction moment in isolation.
Secondly, walking with a toe-out gait may be an effective strategy to
reduce joint compressive forces in some patients with knee OA. Future
work will involve predicting joint contact force for subjects walking with
increased FPA using an EMG-driven musculoskeletal model.
Acknowledgements: NIH P20-RR016458


Recovery in horizontal gait after hip resurfacing vs. total hip arthroplasty at 6-month follow-up - a randomized clinical trial 

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Recovery in horizontal gait after hip resurfacing vs. total hip arthroplasty at 6-month follow-up - a randomized clinical trial

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