419
JRRD
Volume 47, Number 5, 2010
Pages 419–430
Journal of Rehabilitation Research & Development
JRRD
Volume 47, Number 5, 2010
Pages 419–430
Journal of Rehabilitation Research & Development
ANALYSIS OF BIOMECHANICA EFFECTIVENESS OF VALGUS-INDUCING KNEE BRACE FOR OSTEOARTHRITIS OF KNEE
Thomas Schmalz, PhD;
1*Elmar Knopf, MD;
2Heiko Drewitz, CPO;
1Siegmar Blumentritt, PhD
1–2Bock Healthcare, Department of Research, Duderstadt, Germany;
2Orthopaedic Department, Georg August
University, Göttingen, Germany
Abstract—The biomechanical effectiveness of a valgus-inducing knee brace was investigatedfor 16 patients with knee
osteoarthritis (mean +/– standard deviation age 56 +/– 10 yr,
height 172 +/– 9 cm, mass 83 +/– 7 kg, body mass index 27.6 +/–
4.5 kg/m
2
). At the time of investigation, all subjects had been
wearing the brace for at least 4 weeks. In addition to conduct-ing standard gait analysis, we calculated the valgus moment
generated by the brace by using a novel system that measured
the actual deformation of the brace during stance phase and
determined the reaction force created by the brace on the leg.
The mean maximum value of the orthotic valgus moment was
0.053 Nm/kg, which represents approximately 10% of the
external genu varus moment without the brace. This finding
may explain the pain relief reported by patients using such
braces in clinical studies. Use of the tested brace also
decreased the magnitude of gaitasymmetry between the braced
and contralateral legs during walking (horizontal ground reac-tion force, external knee flexion moment), presumably because
the subjects’ need to walk abnormally to shield the knee from
pain was reduced.
Key words: biomechanics, gait analysis, knee loading, knee
osteoarthritis, orthopedics, orthotics, pain, rehabilitation, val-gus bracing, visualanalog scale.
INTRODUCTION
Osteoarthritis of the knee isone of the most common
joint diseases. The incidence of painful arthritic knees
increases significantly from the third decade onward [1].
Epidemiological studies showthat approximately 5 to
6 percent of the population present clinically with painful
knee osteoarthritis [1]. Treatment may be by operative
and nonoperative methods. In addition to arthroscopy,
operative treatments includejoint replacements and
osteotomies. Nonoperative treatments are usually offered
in mild to moderate cases or when surgery is not feasible,
and may include drug therapies, physiotherapeutic mea-sures, and orthopedic devices (walking aids, orthopedic
inserts, shoe sole elevations, knee braces). According to
the most recent analysis, less than 1 percent of all
patients with knee osteoarthritis are fitted with a knee
brace [2].
The clinical effectiveness of this medical device has
been reported in previous studies (i.a., [3–8]). However,
studies published to date show conflicting results regard-ing the biomechanical mechanism of the knee brace.
Many studies have shown that the external varus
moment is a suitable indicator of knee joint loading,
Abbreviations: BW = body weight, SD = standard deviation,
VAS = visual analog scale, WB= with brace, WOB = without
brace.
*
Address all correspondence toThomas Schmalz, PhD;
Otto Bock HealthCare GmbH, Forschungs-und Entwick-lungswerkstatt, Labor für Biomechanik, Hermann-Rein-Straße 2a, D-37075 Göttingen, 0551 3075131 Germany;
fax: 0049-551-3075134. Email: schmalz@ottobock.de
DOI:10.1682/JRRD.2009.05.0067
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JRRD, Volume 47, Number 5, 2010
which is increased in the majority of cases with varus
deformities secondary to knee osteoarthritis [9–13]. Sci-entific investigations of the effect of a knee brace on the
external varus moment report either a reduced varus
moment [14–16] or no significant change in this biome-chanical parameter [17–19]. These contradictory results
raise questions about whether or not forces produced by
knee braces are sufficient to significantly alter the exter-nal moment.
A number of researchers have suggested that braces
for treating varus knee osteoarthritis generate a valgus
moment, partially compensating for the external varus
moment [15,20] and, therefore,reducing the need for the
muscles and ligaments to counteract the pathological
forces [21]. This mechanism isalso believed to result in
reduced joint force within the medial compartment,
reducing pain symptoms [20–21].
Given the contradictory theories and findings, ana-lyzing the external varus moment in the gait laboratory
appears to be inadequate to provide evidence about the in
vivo function of a knee osteoarthritis brace. For this rea-son, previous studies have used specially designed test
braces with highly precise integrated sensors to directly
measure the valgus moment created by the brace
[16,20,22].
In contrast, this article introduces a method for deter-mining the valgus moment without an instrumented test
brace. The approach presented here uses each patient’s
individual brace without modification. Using the pre-scribed, fitted brace worn by each person provides more
direct evidence about the actual effect of the brace in
vivo. The overall goal of this study is to add to the body
of knowledge regarding the biomechanical basis for val-gus-inducing knee braces.
METHODS
Patients
Sixteen patients (eight male, eight female) diagnosed
with medial knee osteoarthritis by orthopedists were
recruited for this study (Table 1). The clinical criteria for
Table 1.
Data for participants with knee osteoarthritis wearing valgus-inducing brace.
Patient Sex Age (yr) Height (cm) Mass (kg) BMI
Wearing
Duration
(wk)
Wearing
Time (h/d)
Walking
Distance
(km/d)
1 M 60 148 78 23.1 4 12.0 6.0
2 M 48 160 94 36.5 4 12.0 7.0
3 F 45 157 57 23.0 6 9.0 6.0
4 F 41 178 72 22.7 4 9.0 8.5
5 F 43 169 77 27.1 4 6.0 4.5
6 F 62 158 67 26.8 6 11.0 2.0
7 F 65 172 65 22.1 164 10.0 7.5
8 F 59 167 100 35.8 4 12.0 7.5
9 F 67 171 94 32.0 4 8.0 5.5
10 M 61 170 92 31.8 8 6.0 3.5
11 M 45 171 93 31.7 4 8.0 7.5
12 M 57 173 84 28.2 6 11.0 3.0
13 M 54 180 91 28.0 7 12.0 4.0
14 M 50 192 92 25.0 21 16.0 6.5
15 F 67 176 82 26.6 60 10.0 5.0
16 M 64 179 86 26.8 52 2.0 1.0
Mean — 56 172 83 27.9 22 9.6 5.3
SD — 9 9 12 4.5 42 3.2 2.2
Min — 41 157 57 22.1 4 2.0 1.0
Max — 67 192 100 36.5 164 16.0 8.5
BMI = body mass index, F = female, M = male, Max = maximum, Min = minimum, SD = standard deviation.
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SCHMALZ et al. Biomechanical effectiveness of valgus-inducing knee brace
diagnosis of osteoarthritis included radiological assess-ment combined with patient reports of knee swelling,
morning stiffness, pain duringambulation, or joint stiff-ness. An experienced orthopedist grouped the patients
according to the osteoarthritis classification system
developed by Kellgren and Lawrence [23]. One patient
was assigned to level 1, five patients to level 2, seven
patients to level 3, and three patients to level 4.
All patients had been previously prescribed by their
treating physician the knee brace used in this study for
treatment of their osteoarthritis and had worn it daily for
a minimum of 4 weeks at the time of testing. The 4-week
period was considered sufficient to verify wearing com-pliance and permit adequate acclimation to the brace
(Table 1). Exclusion criteria for the study included recent
injuries, skin disorders, varicosities, and diseases other
than knee osteoarthritis influencing the gait pattern.
All patients signed an informed consent to participate
in this study. Each recruited patient traveled to the gait
laboratory for one measurement session. In addition to
the biomechanical measurements, they were asked to give
a short subjective assessment of the effect of the brace.
Functional Description and Fitting Procedure of
Tested Knee Brace
The patients used the Genu Arthro knee brace, which
has a unilateral sidebar design (Otto Bock; Duderstadt,
Germany [Figure 1]). The Genu Arthro brace is a prefab-ricated system that is individually adjusted to each
patient’s body measurements. All brace fittings were con-ducted by the same qualified and experienced orthotist.
The pain-relieving function of this brace is based on
the classic three-point pressure principle. Thigh and
shank segments are connected by a single axis joint on
the lateral side of the leg. An adjustment mechanism per-mits variable positioning of the thigh segment in the
coronal plane while the patient is standing (Figure 2).
Once the brace has been individually adjusted, reaction
forces will be generated on the thigh depending on the
magnitude of the adjustment.
At the beginning of the treatment phase, the brace
adjustment was optimized for each patient according to
his or her individual needs. The most important criterion
for this procedure was the patient’s tolerance of the val-gus forces resulting from the coronal plane adjustments,
as illustrated in Figure 2. After the patients were
recruited into this study, the individual adjustment of the
valgus force was evaluated and modified as needed
before the measurement session began.
Subjective Assessment
Before the biomechanical investigations, the patients
were queried about their medical history and perceptions
of the quality of brace fitting. Subjects were asked to
assess the fit of the brace, wearing comfort of the compo-nents, appearance, and ease of use on a scale ranging
from 0 (“very poor”) to 6 (“very good”). Patient self-reports of daily wearing time were recorded to assess
compliance in wearing the brace. Pain while walking was
measured with a visual analog scale (VAS) ranging from
0 (“no pain”) to 10 (“worst pain imaginable”).
Figure 1.
Patient wearing Genu Arthro valgus-inducing knee brace used in study.
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Biomechanics
Standard Gait Analysis
Gait analysis was conducted under two conditions:
without brace (WOB) and with brace (WB), in random
order. For the WB condition, an additional static mea-surement was recorded without the thigh portion of the
brace secured to the leg. Eight to ten walking trials were
recorded for each condition.
Measurement of ground reaction forces during walk-ing was conducted bilaterally with use of two force plates
(measuring frequency 1,080 Hz; Kistler; Winterthur,
Switzerland). Motion kinematics were tracked by an
optoelectronic six-camera system (120 Hz; Vicon;
Oxford, United Kingdom) with use of passive reflective
markers fixed to anatomical reference points. The marker
set used comprises seven markers for each side of the
body (acromioclavicular joint, lateral epicondyle of
elbow, wrist, greater trochanter, lateral femoral condyle,
lateral malleolus, and fifth metatarsal head). External
moments acting on the major joints of the lower limb
were calculated based on kinematic data and ground reac-tion forces with use of Vicon Body Builder 3.5 software.
Determination of Valgus Moment Produced by Brace
The moment created by the brace can be determined
from the reaction force acting on the proximal force
application point of the brace and from the effective lever
arm. The effective lever arm results from the functional
length of the thigh module (Figure 3(a)).
The first step was to determine the relationship
between the reaction force of the brace Fbr
and the result-ing frontal deformation of the brace by means of a simple,
self-developed force-measuring station (Figure 3(a)).
With this station, the force acting at the proximal edge of
the thigh piece (Pin Figure 3(a) and (c)) is transferred
directly by a cord and pulley assembly so it can be mea-sured by a spring dynamometer (SDM, Hahn-Kolb; Stutt-gart, Germany).
Before gait analysis, the displacements Xi
of the
point Presulting from the acting forces were determined
by means of a simple linear scale (Figure 3(c)). After
recording a set of 15 to18 pairs of values for Fbr
and Xi
for each brace, we found the following linear relationship
(Figure 3(b)–(c)):
where X0
= initial position in unloaded condition, Xi=
change in distance compared to unloaded condition, Fbr=
reaction force, and Cbr
= stiffness of brace, i= 1 . . . (15
. . . 18).
Based on this correlation, the stiffness of each individu-ally adjusted brace Cbr
could be defined by means of a
regression calculation (example is shown in Figure 3(b)).
Once the individual value for Cbr
has been deter-mined, the valgus moment of the brace can be determined
from gait laboratory data. Measuring the specific defor-mation of each brace during the WB gait analysis enabled
calculation of the biomechanical effect of the device in
the frontal plane.
Three additional markers wereattached to the brace
for this purpose (uniaxial hinge, proximal, and distal end
of the brace). Based on the three-dimensional coordinates
of these markers, deformation (relative to the static mea-surement taken before the thigh segment was cinched
down) was determined with use of simple trigonometric
calculations. This deformation,combined with the stiffness
COrthpermits calculation of the reaction force and associ-ated moment created by the brace. The brace valgus
moment was calculated during the first 50 percent of the
gait cycle, when knee joint loading is of particular interest.
Figure 2.
Different basic adjustments to Genu Arthro brace. Left: low
deformation = low valgus moment after cinching up thigh section;
right: strong deformation = high valgus moment after cinching up
thigh section.
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SCHMALZ et al. Biomechanical effectiveness of valgus-inducing knee brace
Data Processing
Mean values standardizedto the gait cycle were
derived for all biomechanical parameters for each subject.
Mean group values were then calculated, permitting
Figure 3.
(a) Force measuring station for defining stiffness of brace, (b) individual example demonstrating relation between reaction force of brace leading
to deformation according to equation in main text, and (c) demonstration of measurement principle. Fbr
= force on brace, P= proximal force
application point, SDM = spring dynamometer.
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comparison between both conditions and between the
arthritic and contralateral limbs. Significant differences
between the peak values of key biomechanical parame-ters were determined by the Wilcoxon test.
RESULTS
Subjective Assessment
On the basis of the mean ± standard deviation (SD)
8.9 ± 3.4 h/d duration of use reported, we consider these
subjects highly compliant in wearing the brace. The mean ±
SD pain-with-walking VAS score of 6.4 ± 1.7 for the
WOB condition was significantlyreduced to 3.3 ± 1.9 for
the WB condition (p 0.01). Subjective evaluations of
the knee brace—with the exception of wearing comfort at
the thigh—were very favorable, with average scores
ranging between 4.3 (“good”) and 4.9 (“very good”). The
average value of 3.4 for wearing comfort at the thigh may
have resulted from the intermittent feeling of slipping of
the brace reported by six subjects.
Biomechanics
Time-Distance Parameters
The mean walking speed significantly increased from
1.27 m/s WOB to 1.36 m/s WB (p 0.01). Cadence WB
increased significantly compared with WOB, from 107 to
110 steps/min (p 0.01). The step length for the arthritic
limb increased from 0.71 m WOB to 0.73 m WB, while
step length of the contralateral limb reduced from 0.75 to
0.73 m (Table 2).
Ground Reaction Force
The analysis of the vertical component of the ground
reaction force (Figure 4(a)) shows that vertical loading
decreases between 5 and 15 percent of the gait cycle on
the arthritic limb WOB when compared with the con-tralateral leg or with the WB condition. The first vertical
force maximum is also significantly decreased in the
WOB condition compared with the WB condition (104%
vs 109% body weight [BW], respectively, p 0.05).
Significant differences were also observed in the hor-izontal component of the ground reaction force during
early stance phase, sometimes referred to as the “braking
force” (Figure 4(b)). Compared with the contralateral
limb, the horizontal force was significantly reduced
WOB (14.3% vs 17.9% BW, respectively, p 0.01). In
the WB condition, the horizontalforce on the leg affected
by osteoarthritis increased by 16.4 percent BW, which is
comparable to the horizontalforce on the contralateral
limb. No systematic differencescould be identified in the
mediolateral forces under any of the investigated condi-tions (Figure 4(c)).
Biomechanical Characteristics of Knee Joint
The knee flexion moments inthe sagittal plane dur-ing the first part of stance phase are strikingly different
between conditions. The mean maximum flexion moment
for the contralateral knee was 0.45 Nm/kg under condi-tions, while the mean maximum flexion moment for
the arthritic knee WOB was significantly diminished to
0.23 Nm/kg (p 0.01). The maximum flexion moment for
the arthritic knee WB increased to 0.33 Nm/kg, although
this change was not statistically significant. (Figure 5(b)).
The limb loading characteristics of the affected limb
are associated with reduced motion of the knee joint
throughout the stance phase.Both stance phase flexion
and stance phase extension on the affected limb were
both reduced by approximately 3° compared with the
contralateral side (Figure 5(a)). This finding was true
whether or not the brace was being worn.
The mean maximum value of the external varus
moment (0.53 Nm/kg) was the same regardless of the
test condition for the contralateral limb. The mean maxi-mum loading on the arthritic knee WOB increased to
0.63 Nm/kg, although this change was not statistically
Table 2.
Mean time-distance parameters for participants with knee osteoarthritis walking with brace (WB) and without brace (WOB).
Condition Walking Speed (m/s) Cadence (steps/min)
Step Length (m)
Osteoarthritic Limb Nonosteoarthritic Limb
WOB 1.27 107 0.71 0.75
WB 1.36
*
110
*
0.73
†
0.73
†
*
Significant difference between conditions, p 0.01.
†
No significant difference between conditions.
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SCHMALZ et al. Biomechanical effectiveness of valgus-inducing knee brace
significant (Figure 5(c)). Averaged values from gait analy-sis WB did not demonstrate any measurable changes for
this parameter, similar to several prior studies.
Effect on Knee Joint of Moments Created by Brace
The mean curve presented in Figure 6illustrates the
moment created by the braces during the first half of the
gait cycle. The SD reflects important differences between
individual results. The time during stance phase when
maximum loading occurs alsovaried between subjects.
Figure 4.
Mean ground reaction force (F): (a)vertical component (z), (b)horizontal
component (x), and (c)mediolateral component (y). Gray = nonar-thritic contralateral limb (without brace [WOB]), thick black =
arthritic limb with brace, and thin black = arthritic limb WOB. BW =
body weight, t (%GC) = time (% gait cycle).
Figure 5.
Mean biomechanical knee parameters: (a)flexion-extension (Flex-Ext) angle, (b)stance phase external sagittal knee moment (My
), and
(c)stance phase external varus knee moment (Mx
). Gray = nonarthritic
contralateral limb (without brace [WOB]), thick black = arthritic limb
with brace, and thin black = arthritic limb WOB. t (%GC) = time (%
gait cycle).
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Overall, the valgus moment generated by the brace
increased during stance phase but only moderately so.
The increase was most obvious between 0 and 10 percent
of the gait cycle, decreasingbetween 10 and 30 percent
of the gait cycle, i.e., during stance phase knee flexion.
Between 30 and 50 percent of the gait cycle, the valgus
effect of the brace increased once again.
Maximum and mean values of the orthotic moment
during stance phase were used as quantitative evaluation
parameters (Table 3). The mean maximum value of
0.053 Nm/kg and the mean value of 0.040 Nm/kg pro-vided by the brace represent 9 and 10 percent, respec-tively, of the external knee moment. Minimum and
maximum percentages fell between 2 and 28 percent for
both parameters, indicating thatthe actual forces applied
to the patient’s leg were quite variable.
DISCUSSION
Measurement of the external genu varus moment of
patients with medial knee osteoarthritis—the standard
parameter for assessing knee loading—very often dem-onstrates an abnormal increase in the varus loading, even
without associated changes in the knee axis [10,13,18]. In
theory, this parameter could be useful for estimating the
prognosis for osteoarthritis inthe future and monitoring
the effectiveness of various treatment methods. The
results in this study correspond to those of earlier studies
that did not show any significant influence on the exter-nal varus moment created by the knee braces [17–19],
supporting the conclusion that the effect of the brace in
the real world is insufficientto significantly reduce this
moment. We believe that the main effect of an unloader
brace, in most cases, is compensation for a portion of the
external load. The consequences of such an effect are
decreased internal moments (those created by the mus-cles and ligaments) resulting indecreased forces on the
medial portion of the knee joint.
Contradictory results from other studies [14–16] may
be an artifact of different investigation approaches (e.g.,
use of instrumented braces, unrealistically tight adjust-ments of the braces). Results from previous studies on
the effect of braces on knee axis movements are also
equivocal. While several studies report positive results
[24–25], Hamann’s study investigating 20 knee osteoar-thritis patients found no relationship between X-ray find-ings and mode of action of the tested knee braces [18].
In our study, the valgus moments created by the
braces were measured for the first time while in use by
the patients. The mean value of 0.040 Nm/kg and the
mean maximum value of 0.053 Nm/kg for this cohort
correlate well with prior studies using different instru-mented braces. Self et al. indicated values of 0.038 and
0.050 Nm/kg [16], the values reported by Pollo et al.
were 0.071 and 0.133 Nm/kg [20], and the latest study
conducted by Fantini Pagani et al. identified values of
0.030 and 0.102 Nm/kg [22]. These absolute values sug-gest that the moment created by the brace varies, with
Self at al. between 7 and 12percent of the external
moment, Pollo et al. between 6 and 20 percent, and Fan-tini Pagani et al. between 7 and 20 percent. These results
Figure 6.
Mean valgus moment of brace (Mbr
) for first 50 percent of gait cycle.
Thick black = mean, thin black = mean ± 1 standard deviation.
t (%GC) = time (% gait cycle).
Table 3.
Moment generated by knee brace (Mbr
) and percentage of external genu varus moment (Mx
).
Evaluation Parameter
Mbr
(N·m/kg) Mbr
(% Mx
)
Mean Min Max Mean Min Max
Max 0.053 0.009 0.121 9 2 28
Mean (10%–50% GC) 0.040 0.001 0.111 10 2 28
GC = gait cycle, Max = maximum, Min = minimum.
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SCHMALZ et al. Biomechanical effectiveness of valgus-inducing knee brace
compare favorably with the value of 10 percent found in
this study. Larger effects with the brace calculated in
some studies may reflect orthoses tightened so snugly
that they would not be well tolerated by the patients in
real world use.
We therefore suggest that inrealistic situations, the
valgus moment produced by the brace during walking
may compensate on average for approximately 10 per-cent of the external varus moment at the knee despite
considerable deviations from this mean value in individu-al cases. Biomechanical-model calculations suggest that
a moment from the brace of this magnitude would result
in a reduction of joint forceswithin the medial compart-ment on the order of 80 to 100 N [20]. A reduction in
internal knee forces of this magnitude supports the
hypothesis that the pain relief and functional improve-ments reported by osteoarthritis patients may be the
result of the reduction in internal joint loading that the
brace provides.
Alterations in the gait pattern between the WOB and
WB conditions can be influenced by changes in walking
speed. The increase in the vertical ground reaction force
for the affected limb WB could be due to the observed
mean difference of 0.09 m/s in walking speed [26]. This
relatively small change in velocity did not result in sig-nificant differences in most kinetic and kinematic gait
parameters as compared with the unaffected limb. Other
differences between the WB and WOB conditions for the
affected limb, such as the horizontal ground reaction
force and external flexion moment in the first 30 percent
of the gait cycle, cannot be attributed to a walking speed
difference of 0.09 m/s [27]. Therefore, walking without
the brace can be characterized by reduced walking speed
accompanied by significant step-length asymmetry,
reduced brake force of the arthritic limb immediately
after weight acceptance, and reduced sagittal loading
throughout stance phase. These findings correlate well
with the results of an earlier extensive study reporting on
the gait pattern of 139 knee osteoarthritis patients [28].
Gait pattern changes of this sort appear to be a protective
mechanism to reduce joint pain, as illustrated by the
reduction in external flexion moment, which correlates
directly with a reduction in joint contact forces [28]. The
present study shows that a brace can also contribute to a
more symmetrical gait pattern if deviations from normal
in the arthritic limb can besignificantly reduced. Objec-tive measurements of this reduction in asymmetry may
correlate with the pain-reducing effect of these medical
devices.
CONCLUSIONS
The results from this study show that the studied val-gus-inducing knee brace can compensate for approxi-mately 10 percent of the external genu varus moment.
This compensation appears to be the main biomechanical
mechanism that results in a reduction of joint force
within the medial joint compartment. This biomechanical
effect is an essential requirement for the reduced pain and
improved overall function (such as a more symmetrical
gait pattern) that result from the use of such braces.
Orthotic treatment can effectively manage patients at
early and middle stages of osteoarthritis or when other
treatment methods are not applicable.
ACKNOWLEDGMENTS
Author Contributions:
Study concept and design:S. Blumentritt, T. Schmalz, E. Knopf.
Acquisition of data:T. Schmalz, E. Knopf.
Analysis and interpretation of data:T. Schmalz, E. Knopf.
Drafting of manuscript:T. Schmalz.
Critical revision of manuscript for important intellectual content:
T. Schmalz, S. Blumentritt.
Statistical analysis:E. Knopf, T. Schmalz.
Administrative, technical, or material support:H. Drewitz.
Study supervision:S. Blumentritt, T. Schmalz.
Financial Disclosures: The authors have declared that no competing
interests exist.
Funding/Support: This material was unfunded at the time of manu-script preparation.
Additional Contributions: We gratefully acknowledge Annett Elsner
and John W. Michael for preparation of the manuscript.
Institutional Review: This study was approved by the Medical Fac-ulty on the Research Ethics Committee of the University of Göttingen,
and all investigations were performed in accordance with the
approved protocol to ensure that ethical and humane principles were
followed. Written informed consent was obtained from all participants
for participation and publication, including publication of photo-graphs and other visual depictions of subjects.
Participant Follow-Up: The authors do not plan to inform partici-pants of the publication of this study.
REFERENCES
1. Felson DT, Lawrence RC, Dieppe PA, Hirsch K, Helmick
CG, Jordan JM, Kington RS, Lane NE, Nevitt MC, Zhang
Y, Sowers M, McAlindon T, Spector TD, Poole AR,
Yanovski SZ, Ateshian G, Sharma L, Buckwalter JA,
Brandt KD, Fries JF. Osteoarthritis: New insights. Part I:
428
JRRD, Volume 47, Number 5, 2010
The disease and its risk factors. Ann Intern Med. 2000;
133(8):635–46. [PMID: 11033593]
2. Hutchins S, Jones R. Orthotic intervention in the treatment
of medial compartment osteoarthritis of the knee. In: Pro-ceedings of the 12th World Congress of the International
Society for Prosthetics and Orthotics; 2007 Jul 29–Aug 3;
Vancouver, Canada. Ottawa (Canada): ISPO; 2007.
3. Katsuragawa Y, Fukui N, Nakamura K. Change of bone
mineral density with valgus knee bracing. Int Orthop. 1999;
23(3):164–67. [PMID: 10486029]
DOI:10.1007/s002640050337
4. Horlick SG , Loomer RL. Valgus knee bracing for medial
knee gonarthrosis. Clin J Sports Med. 1993;3(4):251–55.
5. Draper ER, Cable JM, Sanchez-Ballester J, Hunt N, Robin-son JR, Strachan RK. Improvement in function after valgus
bracing of the knee. An analysis of gait symmetry. J Bone
Joint Surg Br. 2000;82(7):1001–5. [PMID: 11041589]
DOI:10.1302/0301-620X.82B7.10638
6. Kirkley A, Webster-Bogaert S, Litchfield R, Amendola A,
MacDonald S, McCalden R, Fowler P. The effect of brac-ing on varus gonarthrosis. J Bone Joint Surg Am. 1999;
81(4):539–48. [PMID: 10225800]
7. Hillström HJ, Brower DJ, Bhimji S, McGuire J, Whitney
K, Snyder H, Zonay l, Clayburne G, Sieck M, Schumacher
H. Assessment of conservative realignment therapies for
the treatment of varus knee osteoarthritis: Biomechanics
and joint pathophysiology. Gait Posture. 2000;11:170–71.
8. Finger S, Paulos L. Clinical and biomechanical evaluation
of the unloading brace. J Knee Surg. 2002;15(3):155–59.
[PMID: 12152976]
9. Baliunas AJ, Hurwitz DE, Ryals AB, Karrar A, Case JP,
Block JA, Andriacchi TP. Increased knee joint loads during
walking are present in subjects with knee osteoarthritis.
Osteoarthritis Cartilage. 2002;10(7):573–79.
[PMID: 12127838]
DOI:10.1053/joca.2002.0797
10. Hurwitz DE, Ryals AB, Case JP, Block JA, Andriacchi TP.
The knee adduction moment during gait in subjects with
knee osteoarthritis is more closely correlated with static
alignment than radiographic disease severity, toe out angle
and pain. J Orthop Res. 2002;20(1):101–7.
[PMID: 11853076]
DOI:10.1016/S0736-0266(01)00081-X
11. Gök H, Ergin S, Yavuzer G . Kinetic and kinematic charac-teristics of gait in patients with medial knee arthrosis. Acta
Orthop Scand. 2002;73(6):647–52. [PMID: 12553511]
DOI:10.1080/000164702321039606
12. Weidenhielm L, Svensson OK, Broström LA, Mattsson E.
Adduction moment of the knee compared to radiological
and clinical parameters in moderate medical osteoarthrosis
of the knee. Ann Chir Gynaecol. 1994;83(3):236–42.
[PMID: 7857069]
13. Goh J, Bose K, Khoo BC. Gait analysis study on patients
with varus osteoarthrosis of the knee. Clin Orthop Relat
Res. 1993;(294):223–31. [PMID: 8358919]
14. Lindenfeld TN, Hewett TE, Andriacchi TP. Joint loading
with valgus bracing in patients with varus gonarthrosis.
Clin Orthop Relat Res. 1997;(344):290–97.
[PMID: 9372780]
DOI:10.1097/00003086-199711000-00029
15. Gaasbeek RD, Groen BE, Hampsink B, Van Heerwaarden
RJ, Duysens J. Valgus bracing in patients with medial com-partment osteoarthritis of the knee. A gait analysis study of
a new brace. Gait Posture. 2007;26(1):3–10.
[PMID: 16962329]
DOI:10.1016/j.gaitpost.2006.07.007
16. Self BP, Greenwald RM, Pflaster DS. A biomechanical
analysis of a medial unloading brace for osteoarthritis in
the knee. Arthritis Care Res. 2000;13(4):191–97.
[PMID: 14635273]
DOI:10.1002/1529-0131(200008)13:4<191::AID-ANR3>3.0.CO;2-C
17. Hewett TE, Noyes FR, Barber-Westin SD, Heckmann TP.
Decrease in knee joint pain and increase in function in
patients with medial compartment arthrosis: A prospective
analysis of valgus bracing. Orthopedics. 1998;21(2):131–38.
[PMID: 9507265]
18. Hamann R. Klinische Studie mit ganganalytischer Untersu-chung über die Wirksamkeit einer valgisierenden Knieorthese
bei dem Krankheitsbild der Varusgonarthrose [Dissertation].
[Göttingen, Germany]: Georg-August-University Göttingen;
2003.
19. Otis JC, Backus SI, Campbell DA, Furman GL, Garrison G,
Warren RF, Wickiewicz TL. Valgus bracing for knee
osteoarthritis: A biomechanical and clinical outcome study.
Gait Posture. 2000;11(2):116–17.
20. Pollo FE, Otis JC, Backus SI, Warren RF, Wickiewicz TL.
Reduction of medial compartment loads with valgus bracing
of the osteoarthritic knee. Am J Sports Med. 2002;30(3):
414–21. [PMID: 12016084]
21. Schipplein OD, Andriacchi, TP. Interaction between active
and passive knee stabilizers during level walking. J Orthop
Res. 1991;9(1):113–19. [PMID: 1984041]
DOI:10.1002/jor.1100090114
22. Fantini Pagani CH, Potthast W, Brüggemann GP. The effect
of valgus bracing on the knee adduction moment during
gait and running in male subjects with varus alignment.
Clin Biomech (Bristol, Avon). 2010;25(1):70–76.
[PMID: 19758735]
DOI:10.1016/j.clinbiomech.2009.08.010
23. Kellgren JH, Lawrence J. Atlas of standard radiographs.
Oxford (UK): Blackwell; 1963.
24. Komistek RD, Dennis DA, Northcut EJ, Wood A, Parker
AW, Traina SM. An in vivo analysis of the effectiveness of
429
SCHMALZ et al. Biomechanical effectiveness of valgus-inducing knee brace
the osteoarthritic knee brace during heel-strike of gait.
J Arthroplasty. 1999;14(6):738–42. [PMID: 10512447]
DOI:10.1016/S0883-5403(99)90230-9
25. Matsuno H, Kadowaki K, Tsuji H. Generation II knee brac-ing for severe medial compartment osteoarthritis of the
knee. Arch Phys Med Rehabil. 1997;78(7):745–49.
[PMID: 9228878]
DOI:10.1016/S0003-9993(97)90083-6
26. White S, Tucker C, Brangaccio J, Lin H. Relation of verti-cal ground reaction force to walking speed. Gait Posture.
1996;4(2):206. DOI:10.1016/0966-6362(96)80655-2
27. Lelas JL, Merriman GJ, Riley PO, Kerrigan DC. Predicting
peak kinematic and kinetic parameters from gait speed.
Gait Posture. 2003;17(2):106–12.
[PMID: 12633769]
DOI:10.1016/S0966-6362(02)00060-7
28. Kaufmann KR, Hughes C, Morrey BF, Morrey M, An KN.
Gait characteristics of patients with knee osteoarthritis. J Bio-mech. 2001;34(7):907–15. [PMID: 11410174]
DOI:10.1016/S0021-9290(01)00036-7
Submitted for publication May 18, 2009. Accepted in
revised form February 4, 2010.
This article and any supplementary material should be
cited as follows:
Schmalz T, Knopf E, Drewitz H, Blumentritt S. Analysis
of biomechanical effectiveness of valgus-inducing knee
brace for osteoarthritis of knee. J Rehabil Res Dev.
2010;47(5)419–30.
DOI:10.1682/JRRD.2009.05.0067
Thomas Schmalz, PhD;
1*Elmar Knopf, MD;
2Heiko Drewitz, CPO;
1Siegmar Blumentritt, PhD
1–2Bock Healthcare, Department of Research, Duderstadt, Germany;
2Orthopaedic Department, Georg August
University, Göttingen, Germany
Abstract—The biomechanical effectiveness of a valgus-inducing knee brace was investigatedfor 16 patients with knee
osteoarthritis (mean +/– standard deviation age 56 +/– 10 yr,
height 172 +/– 9 cm, mass 83 +/– 7 kg, body mass index 27.6 +/–
4.5 kg/m
2
). At the time of investigation, all subjects had been
wearing the brace for at least 4 weeks. In addition to conduct-ing standard gait analysis, we calculated the valgus moment
generated by the brace by using a novel system that measured
the actual deformation of the brace during stance phase and
determined the reaction force created by the brace on the leg.
The mean maximum value of the orthotic valgus moment was
0.053 Nm/kg, which represents approximately 10% of the
external genu varus moment without the brace. This finding
may explain the pain relief reported by patients using such
braces in clinical studies. Use of the tested brace also
decreased the magnitude of gaitasymmetry between the braced
and contralateral legs during walking (horizontal ground reac-tion force, external knee flexion moment), presumably because
the subjects’ need to walk abnormally to shield the knee from
pain was reduced.
Key words: biomechanics, gait analysis, knee loading, knee
osteoarthritis, orthopedics, orthotics, pain, rehabilitation, val-gus bracing, visualanalog scale.
INTRODUCTION
Osteoarthritis of the knee isone of the most common
joint diseases. The incidence of painful arthritic knees
increases significantly from the third decade onward [1].
Epidemiological studies showthat approximately 5 to
6 percent of the population present clinically with painful
knee osteoarthritis [1]. Treatment may be by operative
and nonoperative methods. In addition to arthroscopy,
operative treatments includejoint replacements and
osteotomies. Nonoperative treatments are usually offered
in mild to moderate cases or when surgery is not feasible,
and may include drug therapies, physiotherapeutic mea-sures, and orthopedic devices (walking aids, orthopedic
inserts, shoe sole elevations, knee braces). According to
the most recent analysis, less than 1 percent of all
patients with knee osteoarthritis are fitted with a knee
brace [2].
The clinical effectiveness of this medical device has
been reported in previous studies (i.a., [3–8]). However,
studies published to date show conflicting results regard-ing the biomechanical mechanism of the knee brace.
Many studies have shown that the external varus
moment is a suitable indicator of knee joint loading,
Abbreviations: BW = body weight, SD = standard deviation,
VAS = visual analog scale, WB= with brace, WOB = without
brace.
*
Address all correspondence toThomas Schmalz, PhD;
Otto Bock HealthCare GmbH, Forschungs-und Entwick-lungswerkstatt, Labor für Biomechanik, Hermann-Rein-Straße 2a, D-37075 Göttingen, 0551 3075131 Germany;
fax: 0049-551-3075134. Email: schmalz@ottobock.de
DOI:10.1682/JRRD.2009.05.0067
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JRRD, Volume 47, Number 5, 2010
which is increased in the majority of cases with varus
deformities secondary to knee osteoarthritis [9–13]. Sci-entific investigations of the effect of a knee brace on the
external varus moment report either a reduced varus
moment [14–16] or no significant change in this biome-chanical parameter [17–19]. These contradictory results
raise questions about whether or not forces produced by
knee braces are sufficient to significantly alter the exter-nal moment.
A number of researchers have suggested that braces
for treating varus knee osteoarthritis generate a valgus
moment, partially compensating for the external varus
moment [15,20] and, therefore,reducing the need for the
muscles and ligaments to counteract the pathological
forces [21]. This mechanism isalso believed to result in
reduced joint force within the medial compartment,
reducing pain symptoms [20–21].
Given the contradictory theories and findings, ana-lyzing the external varus moment in the gait laboratory
appears to be inadequate to provide evidence about the in
vivo function of a knee osteoarthritis brace. For this rea-son, previous studies have used specially designed test
braces with highly precise integrated sensors to directly
measure the valgus moment created by the brace
[16,20,22].
In contrast, this article introduces a method for deter-mining the valgus moment without an instrumented test
brace. The approach presented here uses each patient’s
individual brace without modification. Using the pre-scribed, fitted brace worn by each person provides more
direct evidence about the actual effect of the brace in
vivo. The overall goal of this study is to add to the body
of knowledge regarding the biomechanical basis for val-gus-inducing knee braces.
METHODS
Patients
Sixteen patients (eight male, eight female) diagnosed
with medial knee osteoarthritis by orthopedists were
recruited for this study (Table 1). The clinical criteria for
Table 1.
Data for participants with knee osteoarthritis wearing valgus-inducing brace.
Patient Sex Age (yr) Height (cm) Mass (kg) BMI
Wearing
Duration
(wk)
Wearing
Time (h/d)
Walking
Distance
(km/d)
1 M 60 148 78 23.1 4 12.0 6.0
2 M 48 160 94 36.5 4 12.0 7.0
3 F 45 157 57 23.0 6 9.0 6.0
4 F 41 178 72 22.7 4 9.0 8.5
5 F 43 169 77 27.1 4 6.0 4.5
6 F 62 158 67 26.8 6 11.0 2.0
7 F 65 172 65 22.1 164 10.0 7.5
8 F 59 167 100 35.8 4 12.0 7.5
9 F 67 171 94 32.0 4 8.0 5.5
10 M 61 170 92 31.8 8 6.0 3.5
11 M 45 171 93 31.7 4 8.0 7.5
12 M 57 173 84 28.2 6 11.0 3.0
13 M 54 180 91 28.0 7 12.0 4.0
14 M 50 192 92 25.0 21 16.0 6.5
15 F 67 176 82 26.6 60 10.0 5.0
16 M 64 179 86 26.8 52 2.0 1.0
Mean — 56 172 83 27.9 22 9.6 5.3
SD — 9 9 12 4.5 42 3.2 2.2
Min — 41 157 57 22.1 4 2.0 1.0
Max — 67 192 100 36.5 164 16.0 8.5
BMI = body mass index, F = female, M = male, Max = maximum, Min = minimum, SD = standard deviation.
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SCHMALZ et al. Biomechanical effectiveness of valgus-inducing knee brace
diagnosis of osteoarthritis included radiological assess-ment combined with patient reports of knee swelling,
morning stiffness, pain duringambulation, or joint stiff-ness. An experienced orthopedist grouped the patients
according to the osteoarthritis classification system
developed by Kellgren and Lawrence [23]. One patient
was assigned to level 1, five patients to level 2, seven
patients to level 3, and three patients to level 4.
All patients had been previously prescribed by their
treating physician the knee brace used in this study for
treatment of their osteoarthritis and had worn it daily for
a minimum of 4 weeks at the time of testing. The 4-week
period was considered sufficient to verify wearing com-pliance and permit adequate acclimation to the brace
(Table 1). Exclusion criteria for the study included recent
injuries, skin disorders, varicosities, and diseases other
than knee osteoarthritis influencing the gait pattern.
All patients signed an informed consent to participate
in this study. Each recruited patient traveled to the gait
laboratory for one measurement session. In addition to
the biomechanical measurements, they were asked to give
a short subjective assessment of the effect of the brace.
Functional Description and Fitting Procedure of
Tested Knee Brace
The patients used the Genu Arthro knee brace, which
has a unilateral sidebar design (Otto Bock; Duderstadt,
Germany [Figure 1]). The Genu Arthro brace is a prefab-ricated system that is individually adjusted to each
patient’s body measurements. All brace fittings were con-ducted by the same qualified and experienced orthotist.
The pain-relieving function of this brace is based on
the classic three-point pressure principle. Thigh and
shank segments are connected by a single axis joint on
the lateral side of the leg. An adjustment mechanism per-mits variable positioning of the thigh segment in the
coronal plane while the patient is standing (Figure 2).
Once the brace has been individually adjusted, reaction
forces will be generated on the thigh depending on the
magnitude of the adjustment.
At the beginning of the treatment phase, the brace
adjustment was optimized for each patient according to
his or her individual needs. The most important criterion
for this procedure was the patient’s tolerance of the val-gus forces resulting from the coronal plane adjustments,
as illustrated in Figure 2. After the patients were
recruited into this study, the individual adjustment of the
valgus force was evaluated and modified as needed
before the measurement session began.
Subjective Assessment
Before the biomechanical investigations, the patients
were queried about their medical history and perceptions
of the quality of brace fitting. Subjects were asked to
assess the fit of the brace, wearing comfort of the compo-nents, appearance, and ease of use on a scale ranging
from 0 (“very poor”) to 6 (“very good”). Patient self-reports of daily wearing time were recorded to assess
compliance in wearing the brace. Pain while walking was
measured with a visual analog scale (VAS) ranging from
0 (“no pain”) to 10 (“worst pain imaginable”).
Figure 1.
Patient wearing Genu Arthro valgus-inducing knee brace used in study.
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Biomechanics
Standard Gait Analysis
Gait analysis was conducted under two conditions:
without brace (WOB) and with brace (WB), in random
order. For the WB condition, an additional static mea-surement was recorded without the thigh portion of the
brace secured to the leg. Eight to ten walking trials were
recorded for each condition.
Measurement of ground reaction forces during walk-ing was conducted bilaterally with use of two force plates
(measuring frequency 1,080 Hz; Kistler; Winterthur,
Switzerland). Motion kinematics were tracked by an
optoelectronic six-camera system (120 Hz; Vicon;
Oxford, United Kingdom) with use of passive reflective
markers fixed to anatomical reference points. The marker
set used comprises seven markers for each side of the
body (acromioclavicular joint, lateral epicondyle of
elbow, wrist, greater trochanter, lateral femoral condyle,
lateral malleolus, and fifth metatarsal head). External
moments acting on the major joints of the lower limb
were calculated based on kinematic data and ground reac-tion forces with use of Vicon Body Builder 3.5 software.
Determination of Valgus Moment Produced by Brace
The moment created by the brace can be determined
from the reaction force acting on the proximal force
application point of the brace and from the effective lever
arm. The effective lever arm results from the functional
length of the thigh module (Figure 3(a)).
The first step was to determine the relationship
between the reaction force of the brace Fbr
and the result-ing frontal deformation of the brace by means of a simple,
self-developed force-measuring station (Figure 3(a)).
With this station, the force acting at the proximal edge of
the thigh piece (Pin Figure 3(a) and (c)) is transferred
directly by a cord and pulley assembly so it can be mea-sured by a spring dynamometer (SDM, Hahn-Kolb; Stutt-gart, Germany).
Before gait analysis, the displacements Xi
of the
point Presulting from the acting forces were determined
by means of a simple linear scale (Figure 3(c)). After
recording a set of 15 to18 pairs of values for Fbr
and Xi
for each brace, we found the following linear relationship
(Figure 3(b)–(c)):
where X0
= initial position in unloaded condition, Xi=
change in distance compared to unloaded condition, Fbr=
reaction force, and Cbr
= stiffness of brace, i= 1 . . . (15
. . . 18).
Based on this correlation, the stiffness of each individu-ally adjusted brace Cbr
could be defined by means of a
regression calculation (example is shown in Figure 3(b)).
Once the individual value for Cbr
has been deter-mined, the valgus moment of the brace can be determined
from gait laboratory data. Measuring the specific defor-mation of each brace during the WB gait analysis enabled
calculation of the biomechanical effect of the device in
the frontal plane.
Three additional markers wereattached to the brace
for this purpose (uniaxial hinge, proximal, and distal end
of the brace). Based on the three-dimensional coordinates
of these markers, deformation (relative to the static mea-surement taken before the thigh segment was cinched
down) was determined with use of simple trigonometric
calculations. This deformation,combined with the stiffness
COrthpermits calculation of the reaction force and associ-ated moment created by the brace. The brace valgus
moment was calculated during the first 50 percent of the
gait cycle, when knee joint loading is of particular interest.
Figure 2.
Different basic adjustments to Genu Arthro brace. Left: low
deformation = low valgus moment after cinching up thigh section;
right: strong deformation = high valgus moment after cinching up
thigh section.
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SCHMALZ et al. Biomechanical effectiveness of valgus-inducing knee brace
Data Processing
Mean values standardizedto the gait cycle were
derived for all biomechanical parameters for each subject.
Mean group values were then calculated, permitting
Figure 3.
(a) Force measuring station for defining stiffness of brace, (b) individual example demonstrating relation between reaction force of brace leading
to deformation according to equation in main text, and (c) demonstration of measurement principle. Fbr
= force on brace, P= proximal force
application point, SDM = spring dynamometer.
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JRRD, Volume 47, Number 5, 2010
comparison between both conditions and between the
arthritic and contralateral limbs. Significant differences
between the peak values of key biomechanical parame-ters were determined by the Wilcoxon test.
RESULTS
Subjective Assessment
On the basis of the mean ± standard deviation (SD)
8.9 ± 3.4 h/d duration of use reported, we consider these
subjects highly compliant in wearing the brace. The mean ±
SD pain-with-walking VAS score of 6.4 ± 1.7 for the
WOB condition was significantlyreduced to 3.3 ± 1.9 for
the WB condition (p 0.01). Subjective evaluations of
the knee brace—with the exception of wearing comfort at
the thigh—were very favorable, with average scores
ranging between 4.3 (“good”) and 4.9 (“very good”). The
average value of 3.4 for wearing comfort at the thigh may
have resulted from the intermittent feeling of slipping of
the brace reported by six subjects.
Biomechanics
Time-Distance Parameters
The mean walking speed significantly increased from
1.27 m/s WOB to 1.36 m/s WB (p 0.01). Cadence WB
increased significantly compared with WOB, from 107 to
110 steps/min (p 0.01). The step length for the arthritic
limb increased from 0.71 m WOB to 0.73 m WB, while
step length of the contralateral limb reduced from 0.75 to
0.73 m (Table 2).
Ground Reaction Force
The analysis of the vertical component of the ground
reaction force (Figure 4(a)) shows that vertical loading
decreases between 5 and 15 percent of the gait cycle on
the arthritic limb WOB when compared with the con-tralateral leg or with the WB condition. The first vertical
force maximum is also significantly decreased in the
WOB condition compared with the WB condition (104%
vs 109% body weight [BW], respectively, p 0.05).
Significant differences were also observed in the hor-izontal component of the ground reaction force during
early stance phase, sometimes referred to as the “braking
force” (Figure 4(b)). Compared with the contralateral
limb, the horizontal force was significantly reduced
WOB (14.3% vs 17.9% BW, respectively, p 0.01). In
the WB condition, the horizontalforce on the leg affected
by osteoarthritis increased by 16.4 percent BW, which is
comparable to the horizontalforce on the contralateral
limb. No systematic differencescould be identified in the
mediolateral forces under any of the investigated condi-tions (Figure 4(c)).
Biomechanical Characteristics of Knee Joint
The knee flexion moments inthe sagittal plane dur-ing the first part of stance phase are strikingly different
between conditions. The mean maximum flexion moment
for the contralateral knee was 0.45 Nm/kg under condi-tions, while the mean maximum flexion moment for
the arthritic knee WOB was significantly diminished to
0.23 Nm/kg (p 0.01). The maximum flexion moment for
the arthritic knee WB increased to 0.33 Nm/kg, although
this change was not statistically significant. (Figure 5(b)).
The limb loading characteristics of the affected limb
are associated with reduced motion of the knee joint
throughout the stance phase.Both stance phase flexion
and stance phase extension on the affected limb were
both reduced by approximately 3° compared with the
contralateral side (Figure 5(a)). This finding was true
whether or not the brace was being worn.
The mean maximum value of the external varus
moment (0.53 Nm/kg) was the same regardless of the
test condition for the contralateral limb. The mean maxi-mum loading on the arthritic knee WOB increased to
0.63 Nm/kg, although this change was not statistically
Table 2.
Mean time-distance parameters for participants with knee osteoarthritis walking with brace (WB) and without brace (WOB).
Condition Walking Speed (m/s) Cadence (steps/min)
Step Length (m)
Osteoarthritic Limb Nonosteoarthritic Limb
WOB 1.27 107 0.71 0.75
WB 1.36
*
110
*
0.73
†
0.73
†
*
Significant difference between conditions, p 0.01.
†
No significant difference between conditions.
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SCHMALZ et al. Biomechanical effectiveness of valgus-inducing knee brace
significant (Figure 5(c)). Averaged values from gait analy-sis WB did not demonstrate any measurable changes for
this parameter, similar to several prior studies.
Effect on Knee Joint of Moments Created by Brace
The mean curve presented in Figure 6illustrates the
moment created by the braces during the first half of the
gait cycle. The SD reflects important differences between
individual results. The time during stance phase when
maximum loading occurs alsovaried between subjects.
Figure 4.
Mean ground reaction force (F): (a)vertical component (z), (b)horizontal
component (x), and (c)mediolateral component (y). Gray = nonar-thritic contralateral limb (without brace [WOB]), thick black =
arthritic limb with brace, and thin black = arthritic limb WOB. BW =
body weight, t (%GC) = time (% gait cycle).
Figure 5.
Mean biomechanical knee parameters: (a)flexion-extension (Flex-Ext) angle, (b)stance phase external sagittal knee moment (My
), and
(c)stance phase external varus knee moment (Mx
). Gray = nonarthritic
contralateral limb (without brace [WOB]), thick black = arthritic limb
with brace, and thin black = arthritic limb WOB. t (%GC) = time (%
gait cycle).
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JRRD, Volume 47, Number 5, 2010
Overall, the valgus moment generated by the brace
increased during stance phase but only moderately so.
The increase was most obvious between 0 and 10 percent
of the gait cycle, decreasingbetween 10 and 30 percent
of the gait cycle, i.e., during stance phase knee flexion.
Between 30 and 50 percent of the gait cycle, the valgus
effect of the brace increased once again.
Maximum and mean values of the orthotic moment
during stance phase were used as quantitative evaluation
parameters (Table 3). The mean maximum value of
0.053 Nm/kg and the mean value of 0.040 Nm/kg pro-vided by the brace represent 9 and 10 percent, respec-tively, of the external knee moment. Minimum and
maximum percentages fell between 2 and 28 percent for
both parameters, indicating thatthe actual forces applied
to the patient’s leg were quite variable.
DISCUSSION
Measurement of the external genu varus moment of
patients with medial knee osteoarthritis—the standard
parameter for assessing knee loading—very often dem-onstrates an abnormal increase in the varus loading, even
without associated changes in the knee axis [10,13,18]. In
theory, this parameter could be useful for estimating the
prognosis for osteoarthritis inthe future and monitoring
the effectiveness of various treatment methods. The
results in this study correspond to those of earlier studies
that did not show any significant influence on the exter-nal varus moment created by the knee braces [17–19],
supporting the conclusion that the effect of the brace in
the real world is insufficientto significantly reduce this
moment. We believe that the main effect of an unloader
brace, in most cases, is compensation for a portion of the
external load. The consequences of such an effect are
decreased internal moments (those created by the mus-cles and ligaments) resulting indecreased forces on the
medial portion of the knee joint.
Contradictory results from other studies [14–16] may
be an artifact of different investigation approaches (e.g.,
use of instrumented braces, unrealistically tight adjust-ments of the braces). Results from previous studies on
the effect of braces on knee axis movements are also
equivocal. While several studies report positive results
[24–25], Hamann’s study investigating 20 knee osteoar-thritis patients found no relationship between X-ray find-ings and mode of action of the tested knee braces [18].
In our study, the valgus moments created by the
braces were measured for the first time while in use by
the patients. The mean value of 0.040 Nm/kg and the
mean maximum value of 0.053 Nm/kg for this cohort
correlate well with prior studies using different instru-mented braces. Self et al. indicated values of 0.038 and
0.050 Nm/kg [16], the values reported by Pollo et al.
were 0.071 and 0.133 Nm/kg [20], and the latest study
conducted by Fantini Pagani et al. identified values of
0.030 and 0.102 Nm/kg [22]. These absolute values sug-gest that the moment created by the brace varies, with
Self at al. between 7 and 12percent of the external
moment, Pollo et al. between 6 and 20 percent, and Fan-tini Pagani et al. between 7 and 20 percent. These results
Figure 6.
Mean valgus moment of brace (Mbr
) for first 50 percent of gait cycle.
Thick black = mean, thin black = mean ± 1 standard deviation.
t (%GC) = time (% gait cycle).
Table 3.
Moment generated by knee brace (Mbr
) and percentage of external genu varus moment (Mx
).
Evaluation Parameter
Mbr
(N·m/kg) Mbr
(% Mx
)
Mean Min Max Mean Min Max
Max 0.053 0.009 0.121 9 2 28
Mean (10%–50% GC) 0.040 0.001 0.111 10 2 28
GC = gait cycle, Max = maximum, Min = minimum.
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SCHMALZ et al. Biomechanical effectiveness of valgus-inducing knee brace
compare favorably with the value of 10 percent found in
this study. Larger effects with the brace calculated in
some studies may reflect orthoses tightened so snugly
that they would not be well tolerated by the patients in
real world use.
We therefore suggest that inrealistic situations, the
valgus moment produced by the brace during walking
may compensate on average for approximately 10 per-cent of the external varus moment at the knee despite
considerable deviations from this mean value in individu-al cases. Biomechanical-model calculations suggest that
a moment from the brace of this magnitude would result
in a reduction of joint forceswithin the medial compart-ment on the order of 80 to 100 N [20]. A reduction in
internal knee forces of this magnitude supports the
hypothesis that the pain relief and functional improve-ments reported by osteoarthritis patients may be the
result of the reduction in internal joint loading that the
brace provides.
Alterations in the gait pattern between the WOB and
WB conditions can be influenced by changes in walking
speed. The increase in the vertical ground reaction force
for the affected limb WB could be due to the observed
mean difference of 0.09 m/s in walking speed [26]. This
relatively small change in velocity did not result in sig-nificant differences in most kinetic and kinematic gait
parameters as compared with the unaffected limb. Other
differences between the WB and WOB conditions for the
affected limb, such as the horizontal ground reaction
force and external flexion moment in the first 30 percent
of the gait cycle, cannot be attributed to a walking speed
difference of 0.09 m/s [27]. Therefore, walking without
the brace can be characterized by reduced walking speed
accompanied by significant step-length asymmetry,
reduced brake force of the arthritic limb immediately
after weight acceptance, and reduced sagittal loading
throughout stance phase. These findings correlate well
with the results of an earlier extensive study reporting on
the gait pattern of 139 knee osteoarthritis patients [28].
Gait pattern changes of this sort appear to be a protective
mechanism to reduce joint pain, as illustrated by the
reduction in external flexion moment, which correlates
directly with a reduction in joint contact forces [28]. The
present study shows that a brace can also contribute to a
more symmetrical gait pattern if deviations from normal
in the arthritic limb can besignificantly reduced. Objec-tive measurements of this reduction in asymmetry may
correlate with the pain-reducing effect of these medical
devices.
CONCLUSIONS
The results from this study show that the studied val-gus-inducing knee brace can compensate for approxi-mately 10 percent of the external genu varus moment.
This compensation appears to be the main biomechanical
mechanism that results in a reduction of joint force
within the medial joint compartment. This biomechanical
effect is an essential requirement for the reduced pain and
improved overall function (such as a more symmetrical
gait pattern) that result from the use of such braces.
Orthotic treatment can effectively manage patients at
early and middle stages of osteoarthritis or when other
treatment methods are not applicable.
ACKNOWLEDGMENTS
Author Contributions:
Study concept and design:S. Blumentritt, T. Schmalz, E. Knopf.
Acquisition of data:T. Schmalz, E. Knopf.
Analysis and interpretation of data:T. Schmalz, E. Knopf.
Drafting of manuscript:T. Schmalz.
Critical revision of manuscript for important intellectual content:
T. Schmalz, S. Blumentritt.
Statistical analysis:E. Knopf, T. Schmalz.
Administrative, technical, or material support:H. Drewitz.
Study supervision:S. Blumentritt, T. Schmalz.
Financial Disclosures: The authors have declared that no competing
interests exist.
Funding/Support: This material was unfunded at the time of manu-script preparation.
Additional Contributions: We gratefully acknowledge Annett Elsner
and John W. Michael for preparation of the manuscript.
Institutional Review: This study was approved by the Medical Fac-ulty on the Research Ethics Committee of the University of Göttingen,
and all investigations were performed in accordance with the
approved protocol to ensure that ethical and humane principles were
followed. Written informed consent was obtained from all participants
for participation and publication, including publication of photo-graphs and other visual depictions of subjects.
Participant Follow-Up: The authors do not plan to inform partici-pants of the publication of this study.
REFERENCES
1. Felson DT, Lawrence RC, Dieppe PA, Hirsch K, Helmick
CG, Jordan JM, Kington RS, Lane NE, Nevitt MC, Zhang
Y, Sowers M, McAlindon T, Spector TD, Poole AR,
Yanovski SZ, Ateshian G, Sharma L, Buckwalter JA,
Brandt KD, Fries JF. Osteoarthritis: New insights. Part I:
428
JRRD, Volume 47, Number 5, 2010
The disease and its risk factors. Ann Intern Med. 2000;
133(8):635–46. [PMID: 11033593]
2. Hutchins S, Jones R. Orthotic intervention in the treatment
of medial compartment osteoarthritis of the knee. In: Pro-ceedings of the 12th World Congress of the International
Society for Prosthetics and Orthotics; 2007 Jul 29–Aug 3;
Vancouver, Canada. Ottawa (Canada): ISPO; 2007.
3. Katsuragawa Y, Fukui N, Nakamura K. Change of bone
mineral density with valgus knee bracing. Int Orthop. 1999;
23(3):164–67. [PMID: 10486029]
DOI:10.1007/s002640050337
4. Horlick SG , Loomer RL. Valgus knee bracing for medial
knee gonarthrosis. Clin J Sports Med. 1993;3(4):251–55.
5. Draper ER, Cable JM, Sanchez-Ballester J, Hunt N, Robin-son JR, Strachan RK. Improvement in function after valgus
bracing of the knee. An analysis of gait symmetry. J Bone
Joint Surg Br. 2000;82(7):1001–5. [PMID: 11041589]
DOI:10.1302/0301-620X.82B7.10638
6. Kirkley A, Webster-Bogaert S, Litchfield R, Amendola A,
MacDonald S, McCalden R, Fowler P. The effect of brac-ing on varus gonarthrosis. J Bone Joint Surg Am. 1999;
81(4):539–48. [PMID: 10225800]
7. Hillström HJ, Brower DJ, Bhimji S, McGuire J, Whitney
K, Snyder H, Zonay l, Clayburne G, Sieck M, Schumacher
H. Assessment of conservative realignment therapies for
the treatment of varus knee osteoarthritis: Biomechanics
and joint pathophysiology. Gait Posture. 2000;11:170–71.
8. Finger S, Paulos L. Clinical and biomechanical evaluation
of the unloading brace. J Knee Surg. 2002;15(3):155–59.
[PMID: 12152976]
9. Baliunas AJ, Hurwitz DE, Ryals AB, Karrar A, Case JP,
Block JA, Andriacchi TP. Increased knee joint loads during
walking are present in subjects with knee osteoarthritis.
Osteoarthritis Cartilage. 2002;10(7):573–79.
[PMID: 12127838]
DOI:10.1053/joca.2002.0797
10. Hurwitz DE, Ryals AB, Case JP, Block JA, Andriacchi TP.
The knee adduction moment during gait in subjects with
knee osteoarthritis is more closely correlated with static
alignment than radiographic disease severity, toe out angle
and pain. J Orthop Res. 2002;20(1):101–7.
[PMID: 11853076]
DOI:10.1016/S0736-0266(01)00081-X
11. Gök H, Ergin S, Yavuzer G . Kinetic and kinematic charac-teristics of gait in patients with medial knee arthrosis. Acta
Orthop Scand. 2002;73(6):647–52. [PMID: 12553511]
DOI:10.1080/000164702321039606
12. Weidenhielm L, Svensson OK, Broström LA, Mattsson E.
Adduction moment of the knee compared to radiological
and clinical parameters in moderate medical osteoarthrosis
of the knee. Ann Chir Gynaecol. 1994;83(3):236–42.
[PMID: 7857069]
13. Goh J, Bose K, Khoo BC. Gait analysis study on patients
with varus osteoarthrosis of the knee. Clin Orthop Relat
Res. 1993;(294):223–31. [PMID: 8358919]
14. Lindenfeld TN, Hewett TE, Andriacchi TP. Joint loading
with valgus bracing in patients with varus gonarthrosis.
Clin Orthop Relat Res. 1997;(344):290–97.
[PMID: 9372780]
DOI:10.1097/00003086-199711000-00029
15. Gaasbeek RD, Groen BE, Hampsink B, Van Heerwaarden
RJ, Duysens J. Valgus bracing in patients with medial com-partment osteoarthritis of the knee. A gait analysis study of
a new brace. Gait Posture. 2007;26(1):3–10.
[PMID: 16962329]
DOI:10.1016/j.gaitpost.2006.07.007
16. Self BP, Greenwald RM, Pflaster DS. A biomechanical
analysis of a medial unloading brace for osteoarthritis in
the knee. Arthritis Care Res. 2000;13(4):191–97.
[PMID: 14635273]
DOI:10.1002/1529-0131(200008)13:4<191::AID-ANR3>3.0.CO;2-C
17. Hewett TE, Noyes FR, Barber-Westin SD, Heckmann TP.
Decrease in knee joint pain and increase in function in
patients with medial compartment arthrosis: A prospective
analysis of valgus bracing. Orthopedics. 1998;21(2):131–38.
[PMID: 9507265]
18. Hamann R. Klinische Studie mit ganganalytischer Untersu-chung über die Wirksamkeit einer valgisierenden Knieorthese
bei dem Krankheitsbild der Varusgonarthrose [Dissertation].
[Göttingen, Germany]: Georg-August-University Göttingen;
2003.
19. Otis JC, Backus SI, Campbell DA, Furman GL, Garrison G,
Warren RF, Wickiewicz TL. Valgus bracing for knee
osteoarthritis: A biomechanical and clinical outcome study.
Gait Posture. 2000;11(2):116–17.
20. Pollo FE, Otis JC, Backus SI, Warren RF, Wickiewicz TL.
Reduction of medial compartment loads with valgus bracing
of the osteoarthritic knee. Am J Sports Med. 2002;30(3):
414–21. [PMID: 12016084]
21. Schipplein OD, Andriacchi, TP. Interaction between active
and passive knee stabilizers during level walking. J Orthop
Res. 1991;9(1):113–19. [PMID: 1984041]
DOI:10.1002/jor.1100090114
22. Fantini Pagani CH, Potthast W, Brüggemann GP. The effect
of valgus bracing on the knee adduction moment during
gait and running in male subjects with varus alignment.
Clin Biomech (Bristol, Avon). 2010;25(1):70–76.
[PMID: 19758735]
DOI:10.1016/j.clinbiomech.2009.08.010
23. Kellgren JH, Lawrence J. Atlas of standard radiographs.
Oxford (UK): Blackwell; 1963.
24. Komistek RD, Dennis DA, Northcut EJ, Wood A, Parker
AW, Traina SM. An in vivo analysis of the effectiveness of
429
SCHMALZ et al. Biomechanical effectiveness of valgus-inducing knee brace
the osteoarthritic knee brace during heel-strike of gait.
J Arthroplasty. 1999;14(6):738–42. [PMID: 10512447]
DOI:10.1016/S0883-5403(99)90230-9
25. Matsuno H, Kadowaki K, Tsuji H. Generation II knee brac-ing for severe medial compartment osteoarthritis of the
knee. Arch Phys Med Rehabil. 1997;78(7):745–49.
[PMID: 9228878]
DOI:10.1016/S0003-9993(97)90083-6
26. White S, Tucker C, Brangaccio J, Lin H. Relation of verti-cal ground reaction force to walking speed. Gait Posture.
1996;4(2):206. DOI:10.1016/0966-6362(96)80655-2
27. Lelas JL, Merriman GJ, Riley PO, Kerrigan DC. Predicting
peak kinematic and kinetic parameters from gait speed.
Gait Posture. 2003;17(2):106–12.
[PMID: 12633769]
DOI:10.1016/S0966-6362(02)00060-7
28. Kaufmann KR, Hughes C, Morrey BF, Morrey M, An KN.
Gait characteristics of patients with knee osteoarthritis. J Bio-mech. 2001;34(7):907–15. [PMID: 11410174]
DOI:10.1016/S0021-9290(01)00036-7
Submitted for publication May 18, 2009. Accepted in
revised form February 4, 2010.
This article and any supplementary material should be
cited as follows:
Schmalz T, Knopf E, Drewitz H, Blumentritt S. Analysis
of biomechanical effectiveness of valgus-inducing knee
brace for osteoarthritis of knee. J Rehabil Res Dev.
2010;47(5)419–30.
DOI:10.1682/JRRD.2009.05.0067
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