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Effect of anatomic realignment on muscle function during gait in patients with medial compartment knee osteoarthritis.

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Arthritis & Rheumatism (Arthritis Care & Research)
Vol. 57, No. 3, April 15, 2007, pp 389 –397
DOI 10.1002/art.22608
© 2007, American College of Rheumatology
ORIGINAL ARTICLE
Effect of Anatomic Realignment on Muscle
Function During Gait in Patients With Medial
Compartment Knee Osteoarthritis
DAN K. RAMSEY, LYNN SNYDER-MACKLER, MICHAEL LEWEK, WILLIAM NEWCOMB,
KATHERINE S. RUDOLPH
AND
Objective. Individuals with medial compartment knee osteoarthritis (OA) and genu varum use different movement and
muscle activation patterns to increase joint stability during gait. The purpose of this study was to ascertain whether
opening-wedge high-tibial osteotomy (OW-HTO) corrected pathomechancial abnormalities associated with the progression of knee OA.
Methods. Fifteen patients diagnosed with medial knee OA and genu varum who were scheduled for OW-HTO were tested
prior to and 1 year following OW-HTO. Fifteen age- and sex-matched controls were also tested. Frontal plane laxity was
measured from stress radiographs. All participants underwent quadriceps strength testing with a burst superimposition
technique and gait analysis with surface electromyography to calculate knee joint kinematics and kinetics and muscle
co-contraction during the stance phase of gait. Participants rated their knee function and instability using a self-report
questionnaire.
Results. Static alignment improved following the surgery. Medial laxity (P ⴝ 0.003) and instability (P ⴝ 0.002)
significantly improved, and statistical reductions in the adduction moment resulted in lower levels of vastus medialismedial gastrocnemius muscle co-contractions (P ⴝ 0.089). Despite improvements in global rating of knee function (P ⴝ
0.001), the OA group’s ratings remained significantly lower than those of the healthy controls (P ⴝ 0.001). Quadriceps
strength deficits and knee flexion impairments persisted.
Conclusion. Persistent quadriceps weakness and impaired knee kinematics after realignment suggest that the movement
strategy may perpetuate joint destruction and impede the long-term success of realignment. Rehabilitation should focus
on quadriceps strength and improving joint mobility to improve the long-term function of individuals with medial knee OA.
KEY WORDS. Knee osteoarthritis; Osteotomy; Gait; Co-contraction.
INTRODUCTION
Knee osteoarthritis (OA) is the most common cause of
functional disability, affecting ⬃6% of US adults over the
The contents of this report are the sole responsibility of
the authors and do not necessarily represent the official
views of the National Center for Research Resources or the
NIH.
Supported by National Center for Research Resources
grant P20-RR-016458 and NIH grants T32-HD-007490, R01HD-037985, and R01-AR-048212.
Dan K. Ramsey, PhD, Lynn Snyder-Mackler, ScD, PT,
SCS, Michael Lewek, PhD, PT, William Newcomb, MD,
Katherine S. Rudolph, PhD, PT: Research University of Delaware, Newark.
Address correspondence to Katherine S. Rudolph, PhD,
PT, 301 McKinly Lab, University of Delaware, Newark, DE
19716. E-mail: krudolph@UDel.Edu.
Submitted for publication February 10, 2006; accepted in
revised form July 21, 2006.
age of 30 (1,2). The goal of contemporary management is to
control pain and improve knee function and quality of life.
When nonoperative management fails, high-tibial osteotomies (HTO) are commonly prescribed to realign the knee
and reduce symptoms (3,4). However, mechanisms other
than malalignment that exacerbate cartilage destruction
may persist.
Excessive frontal plane joint laxity, quadriceps weakness, and high muscle co-contraction are also related to
knee OA and all have been implicated in contributing to
functional deficits and the pathogenesis of knee OA (5–
11). Recently, we reported that frontal plane laxity was
localized to the medial compartment and that greater medial laxity was related to increased muscle activity (12).
Persons with medial knee OA commonly experience knee
instability, the sensation of buckling, shifting, and giving
way, which was related to higher muscle co-contraction in
muscles that cross the knee (12). Co-contraction may be a
response to weak quadriceps muscles. Individuals with
389
390
weak quadriceps walk with less knee flexion during
weight acceptance, which can interfere with the knee’s
ability to dissipate loads (6,11,13). Individuals with medial knee OA demonstrate reduced knee flexion excursions during weight acceptance and increased lower extremity muscle co-contraction during gait (12,13). Higher
co-contraction can lead to high joint contact forces that
could be detrimental to articular cartilage. However, how
alignment of the knee influences muscle co-contraction
remains unknown.
Although HTO outcomes are generally good, with reported improvements in pain and function, Machner et al
(14) and Oberg and Oberg (15) found quadriceps strength
deficits 1 year after closing-wedge osteotomies. Whether
realignment improves knee stability or affects movement
and muscle activation patterns is unknown. The purpose
of the present study therefore was to examine the effect of
anatomic tibial realignment on abnormal knee joint kinetics, kinematics, and muscle function during gait among
patients with medial knee OA and moderate genu varum.
We postulated that quadriceps strength, joint moments,
movement patterns, and muscle activity patterns would
improve significantly from preoperative levels and would
be similar to those of healthy age-matched controls following opening-wedge high-tibial osteotomy (OW-HTO).
Moreover, knee instability and mediolateral joint laxity, as
measured by patient self-report questionnaires and stress
radiography, would be normalized.
PATIENTS AND METHODS
Participants. Fifteen patients (9 men: mean ⫾ SD age
53.1 ⫾ 6.4 years, mean ⫾ SD body mass index [BMI]
30.4 ⫾ 4.4 kg/m2 and 6 women: mean ⫾ SD age 49.3 ⫾ 7.9
years, mean ⫾ SD BMI 29.2 ⫾ 4.3 kg/m2) diagnosed with
medial knee OA and genu varum were referred from a
local orthopedic practice. Patients were being treated for
pain and were scheduled for OW-HTO. Inclusion criteria
were based on clinical history, physical examination, severity of malalignment, Kellgren and Lawrence radiographic grade 2 or higher, joint space narrowing as observed from standing posteroanterior radiographs with the
knee flexed 30° (16), and difficulty with at least 1 item of
the American College of Rheumatology clinical and radiographic criteria for the classification and reporting of knee
OA (17). Skeletal alignment was measured from bilateral
long cassette radiographs from the hip joint to the feet in
the anteroposterior standing position. The weight-bearing
line (center of the femoral head to the center of the ankle
mortise) was ⬍35%, calculated as the perpendicular distance from the weight-bearing line to the medial edge of
the proximal tibia (18). A ratio ⬍50% denotes varus angulation. Persons with history of ligament deficiency; cardiovascular disease; diabetes; neurologic impairment; impaired balance; rheumatoid arthritis; total knee
replacement in either knee; other orthopedic problems in
the hips, ankles, or spine; or a BMI ⱖ40.0 were excluded.
Patients were tested prior to OW-HTO (preoperative)
and 12 months later (postoperative). Fifteen healthy ageand sex-matched controls (9 men: mean ⫾ SD age 52.0 ⫾
Ramsey et al
5.2 years, mean ⫾ SD BMI 28.8 ⫾ 2.4 kg/m2 and 6 women:
mean ⫾ SD age 47.5 ⫾ 5.6 years, mean ⫾ SD BMI 29.8 ⫾
7.7 kg/m2) with neutral alignment (norm) and no knee
pain or radiographic evidence of knee OA were recruited
from the community. All participants signed an informed
consent, which was approved by the Human Subjects Review Board.
Measurement of joint laxity. Joint laxity was measured
using stress radiographs. With participants lying supine
and the knee flexed 20°, a 150-newton varus and valgus
force was applied to the knee using a TELOS stress device
(Austin & Associates, Fallston, MD). Joint space was measured with precision calipers (0.05-mm accuracy) at the
narrowest points on the medial and lateral compartments
for both varus and valgus stresses. Medial and lateral joint
laxity were computed as follows (19): medial laxity ⫽
medial joint opening minus medial joint closing; and lateral laxity ⫽ lateral joint opening minus lateral joint closing. This method has excellent reliability, as demonstrated
by intraclass correlation coefficients (ICCs) (3, 1) of 0.95
and 0.97 for lateral and medial laxity, respectively, using
repeated measurements on 8 healthy participants (12).
Surgery. All participants underwent OW-HTO, performed by 1 experienced orthopedic surgeon (WN), a mean
of 25 days (range 2– 62 days) after preoperative testing.
Patients used crutches and were non–weight bearing for 4
weeks and subsequently began slow progression from partial to full weight bearing over the ensuing 4 weeks. One
participant received formal physical therapy.
Measurement of pain and functional status. Functional
status and the influence of pain were assessed using the
Knee Outcome Survey Activities of Daily Living Scale
(KOS-ADLS) (20). Instability was assessed using the question, “To what degree does giving way, buckling or shifting
of the knee affect your level of daily activity?” which was
taken from the KOS-ADLS. Reliability of the self-reported
measure of knee instability question demonstrated moderate test–retest reliability, with an ICC (2, 1) of 0.72 (11).
Participants also rated their global knee function on a scale
from 0% to 100% where 100% indicates no disability.
Quadriceps femoris strength and central activation ratio. Quadriceps strength was assessed with the participant
seated in an isokinetic dynamometer (KINCOM; Chattanooga Group, Chattanooga, TN) with the hips and knees
flexed to 90o and the back supported. The axes of rotation
of the knee and dynamometer were aligned and the distal
shank was affixed to the arm 5.0 cm proximal to the lateral
malleolus. Velcro straps secured both the thigh and waist
for stabilization. The thigh was cleansed with isopropyl
rubbing alcohol. Two pre-gelled, 3 ⫻ 5–inch self-adhesive
electrodes (ConMed Corporation, Utica, NY) were placed
over the proximal vastus lateralis and distal vastus medialis to deliver a supramaximal train of electrical stimulation. Participants performed 2 submaximal and 1 nearmaximal voluntary isometric contraction (MVIC) lasting
2–3 seconds for familiarization and to potentiate the mus-
Anatomic Realignment and Muscle Function During Gait
cle. Visual feedback was used to set the target force during
warm up. If the target was surpassed, force limits were
increased incrementally. After 5 minutes of rest, participants were instructed to maximally contract the quadriceps femoris muscle for ⬃4 seconds. Intense verbal encouragement and visual feedback of force output were
used to motivate the participants to produce an MVIC.
Approximately 2 seconds into the test, the supramaximal
burst (100 pulses/second, 600-␮second pulse duration, 10
pulse tetanic train, 130 volts; Grass S88 stimulator, Grass
Technologies, West Warwick, RI) was delivered to fully
activate the quadriceps. Knee extension force was measured and evaluated at 200 Hz using custom-written software (Labview; National Instruments, Austin, TX). If a
maximal voluntary force output was achieved (no increase
in torque during the stimulation), the quadriceps was considered fully activated and testing ceased. The test was
repeated up to 3 times, with 5-minute rest intervals between tests to minimize fatigue, if the participant did not
generate a volitional force within 95% of the electrically
elicited force. The volitional force that immediately preceded the electrical stimulus was normalized to the participant’s BMI (kg/m2) to allow for comparison between
participants and groups. The highest volitional force
achieved during the 3 attempts was used for analysis.
Testing was performed on the involved limbs of the OA
group and the test limb randomly assigned for the control
group.
As a measure of activation, the central activation ratio
(CAR) was calculated according to the following equation:
CAR⫽
Fvolitional
Felectrical
where Fvolitional is the volitional force produced by the
quadriceps immediately prior to the electrical stimulus,
and Felectrical is the peak force produced when the electrical stimulus was superimposed on the volitional effort. A
CAR of 0.95 was considered complete activation of the
muscle (no inhibition).
Motion capture. Participants underwent 3-dimensional
gait analysis with simultaneous surface electromyographic
measurement. Kinematic data were collected at 120 Hz
using a passive 6-camera system (VICON 512; Vicon, Oxford, UK) and ground reaction force data were recorded at
1,800 Hz from 2 Bertec force platforms (Bertec Corp.,
Worthington, OH). Motion and kinetic recordings were
synchronized for simultaneous collection.
Joint centers of the lower limb were defined using
15-mm retroreflective markers placed bilaterally over the
iliac crests, greater trochanters, lateral femoral condyles,
lateral malleolus, and fifth metatarsal heads. Rigid thermoplastic shells affixed with 4 markers were attached to an
elastic underwrap (SuperWrap; Fabrifoam, Exton, PA) surrounding the thigh and shank. Both shank and thigh shells
were placed posterolaterally and overwrapped to minimize movement (21). A marker triplet placed on the sacrum and 2 additional markers on the participant’s heel
counter along with the marker on the fifth metatarsal head
were used to track pelvis and foot movement, respectively.
391
Muscle activity was recorded concurrently at 1,800 Hz
using a 16-channel system (Motion Lab Systems, Baton
Rouge, LA) and the signals were bandpass filtered in the
hardware between 20 and 1,000 Hz prior to sampling.
Preamplified surface electrodes (20-mm interelectrode distance, 12-mm disk diameter) were placed over the midmuscle belly of the semitendinosis, biceps femoris, vastus
medialis, vastus lateralis, and medial and lateral heads of
the gastrocnemius (22). To ensure correct electrode placement, maximum voluntary isometric contractions were
performed. An MVIC and a resting baseline were recorded
for each muscle for normalization.
Participants walked along a 10-meter walkway at a selfselected pace, as measured by 2 photoelectric cells spaced
286.5 cm apart. Ten trials were collected whereby participants contacted opposing force platforms with each foot,
without targeting. Walking velocity was maintained to
within 5%, as measured during practice trials with the
photoelectric cells.
Data management and processing. Marker trajectories
and ground reaction force data were low-pass filtered (Butterworth fourth order, phase lag) at 6 and 40 Hz, respectively, using custom-written software (Labview; National
Instruments, Austin, TX). Lower limb kinematics were
calculated using rigid body analysis and Euler angles and
were referenced to the coordinate system from the standing calibration, and joint moments were derived using
inverse dynamics (Visual 3D; C-Motion, Rockville, MD)
and were normalized to body mass and height. Stance was
time normalized to 100% and averaged across the 10 trials
for each participant, condition, and group. Variables of
interest were knee flexion excursion from initial contact to
peak knee flexion and to the peak external knee adduction
moment during early stance.
The raw electromyographic (EMG) data were initially
filtered with a 350-Hz low-pass Butterworth filter, then
were full-wave rectified and filtered again with a phase
corrected eighth-order, 20-Hz low-pass Butterworth filter
to generate the linear envelope (Labview; National Instruments). Linear envelopes were normalized to peak EMG
from the MVIC. Co-contraction indices (CCIs), which we
defined as the simultaneous activation of antagonist muscles, were derived for the following muscle pairs: vastus
medialis-medial hamstrings (VMMH), vastus medialis-medial gastrocnemius (VMMG), vastus lateralis-lateral hamstrings, and vastus lateralis-lateral gastrocnemius. Muscle
responses were analyzed from 100 msec prior to initial
contact (to account for electromechanical delay [23]) to
when the first peak knee adduction moment occurred.
This time interval was normalized to 100 data points. CCIs
for each pair were derived using the following equation
(24):
冘 冋冉
100
CCI ⫽
i⫽1
冊
册
Lower EMGi
⫻ 共Lower EMGi ⫹ Higher EMGi兲 /100
Higher EMGi
The ratio of the lower EMGi (the level of activity in the less
active muscle) and the higher EMGi (the level of activity in
the more active muscle [to avoid, divide by zero errors])
was multiplied by the sum of the activity found in the 2
392
Ramsey et al
Table 1. Characteristics of participants’ radiographic data*
Mechanical axis, degrees
Weight-bearing line, %
Medial joint space, mm
Lateral joint space, mm
Medial laxity, mm
Lateral laxity, mm
Preoperative
Postoperative
Control
Significance
174 ⫾ 3
20.6 ⫾ 11.6
1.9 ⫾ 1.5
6.4 ⫾ 1.3
4.9 ⫾ 1.6
2.6 ⫾ 1.2
185 ⫾ 2
72.7 ⫾ 9.6
2.4 ⫾ 0.9
5.8 ⫾ 1.5
4.0 ⫾ 1.2
3.1 ⫾ 1.9
179 ⫾ 2.1
42.5 ⫾ 9.2
4.8 ⫾ 0.8
6.3 ⫾ 1.5
3.4 ⫾ 1.3
3.7 ⫾ 1.4
†
†
–
–
‡
§
* Values are the mean ⫾ SD.
† Preoperative versus postoperative, preoperative versus control, and postoperative versus control.
‡ Preoperative versus postoperative and preoperative versus control.
§ Preoperative versus control.
muscle groups. This provided a sample-by-sample estimate of the relative activation of the pair of muscles as
well as the magnitude of the co-contraction. The resulting
values were averaged to arrive at a single value representing the magnitude of co-contraction between the 2 muscles, then the mean for the 10 trials was calculated.
Statistical analysis. Statistical analysis was performed
using SPSS 13 (SPSS, Chicago, IL). Within-group comparisons (preoperative and postoperative) were assessed using paired t-tests to determine differences in joint angles
and moments, quadriceps strength, joint laxity and align-
ment, and KOS-ADLS scores. Independent t-tests were
used for group comparisons (OA and norm). A withinparticipant repeated-measures analysis of variance was
used to compare co-contraction values for both preoperative and postoperative settings. Post hoc t-tests were performed when a significant main effect for group was identified. Hierarchical regression analyses were used to assess
the influence of medial laxity, quadriceps strength, and
functional knee instability on the predicted self-reported
ratings of overall knee function (KOS-ADLS, global knee
rating score). These variables were chosen because each
has been reported to be associated with disease progres-
Figure 1. Plots depicting A, knee function during activities of
daily living, B, global rating score, and C, knee instability (giving
way, buckling, or shifting of knee) as measured by the Knee
Outcome Survey Activities of Daily Living Scale score for the
preoperative (pre-op) and postoperative (post-op) and control
groups.
Anatomic Realignment and Muscle Function During Gait
393
Table 2. Responses of osteoarthritis group to Knee
Outcome Survey Activities of Daily Living Scale question
that assessed their level of instability
Preoperative Postoperative
Experiences no giving way,
buckling, or shifting of
the knee.
Have symptom:
It does not affect my
activity.
It affects my activity
slightly.
It affects my activity
moderately.
It affects my activity
severely.
It prevents me from all
daily activities.
Patients
%
Patients
%
3
20
11
74
4
27
3
20
4
27
1
6
3
20
–
–
–
–
–
–
1
6
–
–
sion. Independent variables were entered in a stepwise
manner. Self-reported rating of knee instability was entered last so that its effect on knee function could be
determined after controlling for the other variables. Pearson’s product moment correlations were also performed to
assist in interpreting the results. Statistical significance
was set at P less than 0.05 except for muscle co-contraction
indices. An alpha level of P less than 0.1 was established
in an effort to avoid a type I error given the highly variable
nature of EMG data (25).
RESULTS
Radiographic data are depicted in Table 1. The weightbearing line of the knee was transferred from the medial
compartment to the lateral compartment (mean ⫾ SD
20.6% ⫾ 11.6% versus 72.7% ⫾ 9.6%; P ⬍ 0.001). Medial
laxity was significantly reduced (P ⫽ 0.003) and was
equivalent to that of healthy controls (P ⫽ 0.372). Lateral
compartment laxity was significantly lower in the preoperative group than in the control group (P ⫽ 0.035), but no
differences were observed between postoperative patients
and controls (P ⫽ 0.313).
The OA group had significant improvements in global
rating of knee function (P ⫽ 0.001) but remained significantly impaired compared with healthy controls (P ⫽
0.001) (Figures 1A and 1B). Dynamic knee stability was
also significantly improved (P ⫽ 0.002) in the OA group
and was equivalent to that of controls (P ⫽ 0.177) (Figure
1C). Twelve of 15 patients (80%) reported the presence of
instability preoperatively (Table 2). Eight (53%) of the 12
patients who had symptoms of instability indicated that
the instability affected their ability to perform activities of
daily living. Postoperatively, 4 (26%) reported the symptom of instability, but only 1 of these individuals indicated
that instability affected activities of daily living. No one in
the control group reported instability.
Medial knee laxity did not predict self-reported instability preoperatively (r2 ⫽ 0.127, P ⫽ 0.332) or postoperatively (r2 ⫽ ⫺0.262, P ⫽ 0.173). Knee instability was significantly related to self-report ratings of global knee
function (r ⫽ 0.636, P ⫽ 0.011) after realignment, with
higher knee function scores being positively associated
with greater knee stability.
Quadriceps weakness and diminished knee flexion excursions during stance persisted after surgery (Figures 2A
and 2B). When tested postoperatively, quadriceps strength
was not statistically different from preoperative strength
(P ⫽ 0.626), but the OA group had significantly lower
quadriceps strength than controls (preoperative: P ⫽
0.036, postoperative: P ⫽ 0.024). Using our operational
definition of 0.950 for the determination of full quadriceps
activation, no differences in muscle inhibition were evident, as demonstrated by similar CAR values, preoperatively and postoperatively (mean ⫾ SD CAR 0.937 ⫾ 0.052
and 0.940 ⫾ 0.028, respectively; P ⫽ 0.839) or for the
control group (0.933 ⫾ 0.066). The hierarchical regression
analyses indicated that only the addition of knee stability
accounted for a significant increase in the amount of variance explained (r2 ⫽ 0.487, r2 change ⫽ 0.481, F ⫽ 10.319,
P ⫽ 0.008); 48% of the variance in the KOS global knee
rating score was predicted by instability. Both medial laxity (r2 ⫽ 0.000, P ⫽ 0.998) and quadriceps strength (r2 ⫽
Figure 2. Plots depicting A, quadriceps strength and B, knee flexion excursions (initial
contact to peak flexion) for the preoperative (pre-op) and postoperative (post-op) and control
groups. BMI ⫽ body mass index.
394
Ramsey et al
preoperative co-contraction indices were significantly
higher, but magnitudes after surgery were not different
from controls (P ⫽ 0.135). VMMH co-contraction indices
were not statistically different across conditions (mean ⫾
SD preoperative: 14.5 ⫾ 5.7, mean ⫾ SD postoperative:
13.3 ⫾ 9.3; P ⫽ 0.660) or across groups (mean ⫾ SD norm:
12.6 ⫾ 8.7; P ⫽ 0.486 and P ⫽ 0.755, respectively). Regression analysis revealed a negative association between
quadriceps strength and medial muscle co-contraction before surgery (VMMG: r ⫽ ⫺0.599, P ⫽ 0.024; VMMH: r ⫽
⫺0.688, P ⫽ 0.006). Weaker quadriceps resulted in higher
levels of medial muscle co-contraction. Strength and medial muscle co-contractions were not correlated after surgery for the patient or the control group.
DISCUSSION
Figure 3. Time series graphs depicting knee flexion and adduction movement patterns with knee adduction moments for the
preoperative (pre-op) and postoperative (post-op) and control
groups. The data were time normalized during stance. N*M ⫽
newton ⫻ meters; BMI*ht ⫽ body mass index ⫻ height.
0.006, P ⫽ 0.795) did not account for the explained variance.
As expected, knee adduction angles and moments were
significantly reduced throughout stance (Figure 3). Knee
flexion excursions during weight acceptance remained unchanged (Figure 2B and Figure 3) (P ⫽ 0.130) but were
significantly lower than those in the control group (preoperative: P ⫽ 0.004, postoperative: P ⫽ 0.043).
Co-contraction indices, as shown in Figure 4, revealed
that the level of VMMG co-contractions for the OA group
was significantly reduced following OW-HTO (mean ⫾ SD
preoperative: 14.2 ⫾ 7.7, mean ⫾ SD postoperative: 11.1 ⫾
5.3; P ⫽ 0.089). Comparing VMMG co-contractions with
those of the healthy group (mean ⫾ SD 7.2 ⫾ 5.6; P ⫽ 0.01),
The goal of this study was to determine whether anatomic
tibial realignment via OW-HTO corrected knee pathomechanics and muscle function associated with poor knee
function and the progression of OA. The factors that have
been shown to influence disease progression include high
knee adduction moments, excessive frontal plane laxity,
and quadriceps weakness (5–11,26,27). Less knee flexion
during weight acceptance and high muscle co-contraction
may exacerbate joint destruction by increased impact
loads (28) and increased joint contract pressures (13,29),
respectively. In spite of improvements in alignment, adduction moments, and joint laxity, realignment did not
affect quadriceps strength and knee movement patterns,
and only VMMG muscle co-contractions were reduced.
This finding suggests that some of the factors that are likely
to be involved in joint degeneration persist and could
worsen patient outcomes over time.
Postoperatively, along with the expected improvement
in frontal plane knee alignment and lower knee adduction
moments, self-reported knee instability and medial joint
laxity improved to levels comparable with controls. The
mechanism by which medial laxity improved is not entirely understood; however, we suggest that the anterior
superficial fibers of the medial collateral ligament, which
are released during the surgery, heal in a shortened position. This explanation is consistent with the work of Naudie et al (30), who demonstrated that a medial openingwedge osteotomy may tighten the capsuloligamentous
structures around the knee when used to correct hyperextension-varus thrust. Had the medial structures remained
slack, the only mechanism by which medial laxity could
be reduced is via increased medial joint width during
closing (valgus loading), which is unlikely because cartilage does not regenerate. It is logical to presume that lateral
laxity would increase with OW-HTO, and greater lateral
laxity was observed after surgery; however, the difference
was not statistically significant. Normal ligament length
and tension could increase joint integrity by improving
mechanical restraints and mediate joint stability via reflexive muscle responses elicited by mechanoreceptors originating in the periarticular joint structures (31–34). Selfreported knee instability was markedly improved after
realignment and was largely responsible for improvements
Anatomic Realignment and Muscle Function During Gait
395
Figure 4. Muscle co-contraction during gait. Co-contraction values calculated from 100
msec prior to initial contact through peak knee adduction moment for A, medial muscle
co-contractions (vastus medialis-medial hamstrings [VMMH], vastus medialis-medial gastrocnemius [VMMG]), and B, lateral muscle co-contractions (vastus lateralis-lateral hamstrings [VLLH], and vastus lateralis-lateral gastrocnemius [VLLG]). Pre-op ⫽ preoperative;
post-op ⫽ postoperative.
in self-reported knee function. The findings that medial
knee laxity did not predict self-reported knee instability
and that knee instability (not medial laxity or quadriceps
strength) predicted postoperative knee function underscore the importance of knee instability in this population.
Lower adduction moments, less knee instability, and
less medial laxity all bode well for joint integrity, but the
factors that were not improved after realignment are cause
for concern. Quadriceps weakness is a very important
factor in persons with knee OA. Although the cause remains unclear, it appears that inhibition does not substantially contribute to reductions in strength. Quadriceps
weakness has been related to worsening knee function
(7,8,35–37), the development of knee OA (9,38 – 41), and
knee OA progression (8,42). Persistent quadriceps weakness found at 12 months postoperatively is consistent with
other studies that have demonstrated long-term weakness
after knee realignment (14,15). Quadriceps weakness may
explain why the global rating of knee function remained
lower than in controls. In addition to its effect on joint
function, quadriceps weakness also has important implications to joint integrity. Quadriceps weakness is known
to accompany reduced knee flexion during weight acceptance, particularly in individuals who experience knee
instability (43). The reduced knee flexion excursion seen
postoperatively may allow higher impact loads to persist,
which exacerbate continued cartilage destruction and
eventually negate the positive outcome of the surgery.
Another factor that can influence joint contact forces is
muscle co-contraction. Despite valgus knee realignment
and reduced VMMG muscle co-contractions, VMMG muscle co-contraction remained higher than in healthy controls. By transferring the mechanical axis laterally, it is
possible that the higher magnitude of VMMG co-contraction serves to lessen lateral compartment loading after the
OW-HTO. This explanation is consistent with the work of
Schipplein and Andriacchi who proposed that the lateral
muscles may prevent lateral condylar lift off in persons
with varus alignment (29). It is plausible that medial co-
contraction might lessen load on the lateral compartment;
however, it could also cause increased joint pressure on
the diseased medial compartment, thereby contributing to
continued medial compartment destruction.
Overall, realignment improved the quality of life for
these patients by increasing knee function and mitigating
some of the factors that might lead to joint destruction, but
the knee stiffening strategy (less knee motion, higher muscle co-contraction) might have been improved had these
patients performed quadriceps strengthening activities
during rehabilitation, which was conspicuously absent.
Postoperative rehabilitation following HTO is uncommon.
Presumably because it is thought that when alignment is
restored and pain is relieved, increased use of the limb
will lead to the return of normal strength and movement
patterns. However, our data clearly show that this is not
the case. Given the importance of quadriceps strength in
mitigating OA progression, resistance training to restore
quadriceps strength 3– 6 months after surgery seems vital
to maintain the improvements caused by HTO.
Although quadriceps strengthening activities would
likely improve knee movement patterns and function in
postoperative patients, we believe that strength training
alone would be inadequate to address all of the impairments that persisted in this group. Recently, quadriceps
strength was found to increase the likelihood of knee OA
progression (42) in individuals with high frontal plane
joint laxity or varus or valgus malalignment. Although the
frontal plane laxity in this group was diminished, the
average alignment indicated a shift from varus to valgus
malalignment. It is possible that postoperative quadriceps
strength training would lead to more OA progression despite lower load on the medial compartment. Knee instability may play a role in whether strong quadriceps muscles lead to an increase or decrease in knee OA
progression. When strong quadriceps that co-contract with
antagonists (resulting in high joint compression) are coupled with high shear forces and concomitant knee instability, the cumulative effect could be highly detrimental to
396
Ramsey et al
articular cartilage. Therefore, we propose that rehabilitation to strengthen the quadriceps be accompanied by neuromuscular training to reduce knee instability so that the
cycle of destruction might be slowed or stopped.
16.
17.
ACKNOWLEDGMENT
The authors thank Laurie Andrews, RTR, for assisting with
the radiographs.
18.
AUTHOR CONTRIBUTIONS
19.
Dr. Ramsey had full access to all of the data in the study and
takes responsibility for the integrity of the data and the accuracy
of the data analysis.
Study design. Snyder-Mackler, Rudolph.
Acquisition of data. Ramsey, Lewek.
Analysis and interpretation of data. Ramsey, Snyder-Mackler,
Rudolph.
Manuscript preparation. Ramsey, Snyder-Mackler, Newcomb,
Rudolph.
Statistical analysis. Ramsey, Snyder-Mackler, Rudolph.
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