1. health and fitness
2. disease
3. arthritis

Bišèeviæ
MM 24.3
AP
AM
MG 23.3;24.3
AI
DH:
Galley: 24. 03. 2005.
Author
CLINICAL SCIENCE
Gender Differences in Knee Kinematics and its Possible
Consequences
Mirza Bišèeviæ, Davor Tomiæ 1 , Vito Starc 2 , Dragica Smrke 3
Department for Orthopedic and Traumatology, Clinical Center, University of Sarajevo; 1 BS –
Telecom, Sarajevo, Bosnia and Herzegovina; 2 Institute for Physiology and Biomechanics,
Ljubljana Medical Faculty; and 3 Department of Traumatology, Clinical Center Ljubljana, Ljubljana,
Slovenia
Aim
Methods
Results
Conclusion
To analyze anatomic and kinematic characteristics of male and female knees in the sagittal plane.
Ten healthy male and 10 healthy female participants performed extension of their right lower leg in
non-weight bearing and weight bearing conditions. The centers of knee joint motion were obtained by
videographic motion analysis, and radii of condylar curves were calculated from digitalized X-ray scan.
The Knee Roll software was made for this purpose.
The extension of the knee in non-weight loaded and weight loaded conditions is a combination of rolling and sliding joint surface motion with 6:5 ratio, in both genders. During the last 20° of the extension
of weight loaded male knee, rolling/sliding ratio changed to 8:1 (P<0.05). Average radii of condylar
curves were between 4.5 and 1.7 cm medially, and between 3.2 and 1.8 cm laterally, for 0° and 90°
flexion contact point, respectively. Gender differences in the radii of condylar curves, after the adjusting to body height were insignificant.
A higher proportion of joint surface sliding with consecutive anterior tibial displacement in women indicates more strain during knee extension, potentially making the female anterior cruciate ligament
tend and susceptible to injury. The gender differences in the knee kinematics are probably the consequence of different soft tissue structure or its activity, because no difference in the sagittal shape of femoral condyles was noted.
The knee is the largest and most complicated joint in the human body with discongruent
but very functional articular surfaces. In spite of
large forces at the ends of the two longest lever
arms in the human body, the knee becomes a fixed
straight rod in terminal extension, able to bear
body weight without muscle effort. During the
knee motions, flexion, and extension, there is a
discrepancy between non-circular leg motions
and circular motions of the cruciate ligaments and
their insertions. As one of the links rotates on the
other (Fig. 1), at any instant in time there is a point
which has zero velocity and constitutes the instantaneous center of motion (ICM).
ICM path measurements provide valuable information about characteristics of the knee
kinematics (1). If the ICM lies on the joint contact
surface, there is pure rolling, and if the ICM is infinitesimally far from the joint contact surface,
there is a pure sliding joint motion. However, a
wide ICM path is characteristic of the knee varus
and a narrow ICM path of the knee valgus. Both
wide and narrow ICM paths normalize after implantation of a knee endoprosthesis (2). The anterior cruciate ligament (LCA) injury can affect the
knee ICM pathway as well (3).
In everyday activities, the knee extension occurs almost always in the weight bearing
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Gender Differences in Knee Kinematics
Croat Med J
Bišèeviæ et al:
Figure 1. Position and "J" shape of the normal instantaneous center of motion path.
conditions. It is more likely to expect the altered
joint kinematics and knee joint symptoms during
weight loaded than non-weight loaded conditions.
Even small changes in the joint kinematics during
lifetime could make a joint susceptible to osteoarthritis or injuries.
Although males sustain harder labor and
sports activities, strong female bias in the knee
osteoarthritis (OA) and rupture of the anterior
cruciate ligament (4,5) is evident. So far, there is
no adequate explanation for this difference. A
higher percentage of sliding component during female knee extension than during male knee extension might be one of the reasons for the strong female bias in the majority of knee pathology.
The aim of this work was to analyze anatomic and kinematic characteristics of male and female knees in the sagittal plane. Videographic motion analysis was used in the determination of the
ICM path and rolling/sliding ratio during the knee
extension. Additionally, the radii of medial and
lateral condylar curves were calculated from the
knee side view X-rays.
The knee extension was analyzed in
non-weight bearing and weight bearing conditions, to reveal the influence of the weight bearing
and increased muscle activity on the patterns of
the knee joint motion.
Subjects and Methods
Participants
Twenty healthy Caucasian participants,
10 men and 10 women, were included in the
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2005;46(2):XXX-XXX
study. They were sample of volunteers from the
student population of the city of Sarajevo. The
study was approved by the Ethics Committee of
the Ljubljana Medical Faculty. Participation in this
study was voluntary and all participants signed an
informed consent after the explanation of the test
procedure. The study was performed during September 2004 at Department for Orthopedic and
Traumatology, Clinical Center, University of Sarajevo. The inclusion criteria were: age 20-32 years;
non-obese person, body mass index (BMI) <25
kg/m2; negative history of right knee injury, complaints of patellofemoral pain, or neurological or
neuromuscular disorders; full range of right knee
active motions, and grade 5 of hamstrings and
quadriceps muscle force (6); negative Lachman’s,
posterior drawer, varus/valgus, and McMuray’s
tests (7), and the absence of any X-ray visible
changes of the right knee. The average age of the
participants was 24.45±4.56 years and there was
no statistically significant difference between genders (t test, P=0.385) (Table 1).
Table 1. Age (years), height (cm), and body mass (kg) data of
study participants
Subject
No
age
1
31
2
32
3
24
4
20
5
20
6
23
7
27
8
32
9
24
10
21
Mean±SD 25.4±4.8
Male
height mass
190
88
187
85
180
80
182
71
180
75
179
80
180
81
176
67
187
73
183
81
182±4.3 78±6.5
age
20
22
29
20
20
20
23
24
26
32
23.6±4.2
Female
height
169
175
169
178
176
165
169
168
174
169
171±4.2
mass
61
56
55
59
62
58
59
58
58
58
58±2.1
Procedure
Four photoreflective markers were
drawn on the lateral side of the naked right leg
near the greater trochanter (A), lateral condyle (B),
apex of fibula (C) and lateral malleolus (D), away
from its bony prominences to minimize skin movement artifacts (8). Markers in the regions of the
lateral condyle and lateral malleolus were X-ray
reflective.
While sitting with legs freely bending
(non-weight loaded condition/open kinetic chain),
participants extended the right lower leg (90°-0°).
The participants were instructed to hold their torso
straight and not to use their hands while elevating
the right lower leg.
Croat Med J
The part of the femur which articulates
with the tibia in a range of knee extension from
90° up to 0° is quarter of the ellipse (9-11) is mathematically defined by its wider and narrower diameters, A and B, respectively. Lines perpendicu-
Gender Differences in Knee Kinematics
Mathematical Background of Knee
Kinematics
lar on the two neighboring tangents at spots M and
N determine the center of the curve and radius of
that segment of curve – Ra (Fig. 2).
The ellipse diameters A and B, distance
between “D” marker and “B” marker, and distances between “D” marker and the tibial contact
point at 0° and 90° – (T0 and T90,) were captured
from the side view X-ray. The radii – Ra were calculated for each 10° segment of the medial and
lateral condylar curves.
Linear velocities in the directions of x
and y axes of the coordinate system (Vx, Vy), and
angular velocity (w) of the moving marker were acquired from the digitalized knee motion.
Distance from “D” marker to the ICM is
expressed as X, and distance between the ICM and
the joint contact line is expressed as Icr (Fig. 3):
Bišèeviæ et al:
Additionally, they rose from the squatting position to the standing position. During the
examination they were barefoot, with 3 cm distance between the right and the left foot and the
knees, and they were instructed not to use their
arms when rising. The motion of the right leg was
recorded by 4.2 Megapixel digital camera set on a
camera tripod at a two-meter distance. The side
view X-ray of the right lower leg, knee, supracondylar femoral area, and both X-ray reflective
markers, was reproduced on a single scan.
2005;46(2):XXX-XXX
Vx=–wz Xy and Vy=wz Xx,
X=[(Vx/wz)2+(–Vy/wz)2]1/2,
Ta=T0+[(T0–T90)(a/90)],
Icr=X–Ta
The Icr distances were calculated
through 90°-0° knee extension in non-weight and
weight loaded conditions.
Sf is the displacement (arc length) between the contact points on the femoral surface
and St is the displacement between the contact
points on the tibial surface.
The variables Sf and St are approximated by
Figure 2. The radius of condylar curve – Ra, defined with
spots M and N and angle a.
a +10
a +10
St =
ò ( Ra - Icr ) × da
a
and Sf =
ò Ra × da
a
Figure 3. Mathematical model used for the estimation of the instantaneous center of motion and Icr (distance between the
instantaneous center of motionand joint contact line).
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Croat Med J
2005;46(2):XXX-XXX
Gender Differences in Knee Kinematics
where, Ra is the average value of radii of medial
and lateral condylar curve (Fig. 2), Icr is the distance from the ICM to the femoral contact point
(Fig. 3), and a is the angle of extension at the observed moment (frame) with 10° successive angles. Therefore, the percentage of rolling is defined by equation
% rolling =
Sf
×100%
Sf + ( Sf - St )
The final result for each participant was
stored as txt file (Fig. 4).
(12).
Computer Data Processing – the
“Knee Roll” Software
Bišèeviæ et al:
The knee extension event was recorded
by the digital camera, and the video clip was
downloaded into the computer. After removing
the sequences out of 90° to 0° knee extension, the
Windows Media Player® (Microsoft, Seattle, WA,
USA) file was converted into the chain of
MotionBMP® (Microsoft, Seattle, WA, USA) files
(frames). This was just like creating animated cartoons where a drawing was moved a fraction of a
millimeter and every time the drawing was moved
a picture was taken. Each sequence (frame) had all
four markers visible.
Marker recognition was the most demanding part of this software. The success of auto
recognizing depended on the choice of reflective
marker size. In this system, the reflective markers
were the brightest objects and the threshold could
be set to automatically discriminate the markers.
The cluster of “pixels”, seen above the threshold,
formed the centroids of the markers, which were
automatically computed in the two dimensional
image plane of the camera. The difficulty with the
system was that every marker had to be visible in
all frames all the time. An additional problem was
the determination of marker centroid (single pixel
defined with x and y coordinates) because the software recognized the marker as a cloud of more or
less white spots (RGB more than 235). The software was able to remove small random digitizing
errors or “noise” from the transformed image sequence. Such problems are significantly reduced
with different filter options (Prewitt, Laplacian,
Gaussian, Median). Coordinate values of all markers in each frame were recalculated according to
the position of marker “B” in the first frame of each
clip (superposition). Referent line for angle and
angular velocity measurements was the direction
marker “A” to marker “B” in the first frame.
256
Figure 4. The "Knee Roll" interface – capturing of marker
coordinates.
The “Knee Roll” was developed in the
object-oriented programming language C# 2.0 for
Microsoft 9X and XP® (Microsoft, Seattle, WA,
USA). The software requires minimally 256 MB
RAM and 2.2 GHz Pentium CPU.
Statistical Methods
The independent samples t test (equal
variance, normal distribution) was used for the
analyses of differences of Ra, Icr, and the rolling
percentage between men and women, with
P=0.05 as a cut off value (13).
The collected data were processed by
Microsoft Excel® software (Microsoft, Seattle, WA,
USA).
Results
Gender Ra differences were noted for
each 10° slices at both condyles. The differences
turned out to be statistically insignificant after adjusting to body height (Table 2).
This insignificance was very close to
borderline P value of 0.05 on the lateral condyle
for segments 40°-70°.
The distances between the ICM and the
articular contact point (Icr) varied between 13 mm
and 29 mm in non-weight and weight loaded conditions. The exception was male group during terminal rising from the squat position, where Icr was
6 mm (Fig. 5).
On average, men had the ICM closer to
the articular contact point than women (19.7±8.9
mm and 20.1±6.5 mm for men and women, re-
Croat Med J
2005;46(2):XXX-XXX
Table 2. Radii of the medial and lateral condylar curves (Ra in mm, Mean±standard deviation)
Length (Ra, mean±SD mm) of condyle radii
female
16.5±2.9
17.0±3.0
17.7±3.0
19.2±2.8
21.7±2.5
25.3±2.1
30.2±2.2
36.1±3.8
42.2±6.6
46.2±8.8
male
19.5±2.6
20.1±2.7
20.6±2.6
21.5±2.4
22.9±2.2
24.7±1.9
26.7±1.6
28.9±1.8
30.6±2.3
31.7±2.6
lateral
P
0.089
0.088
0.074
0.051
0.070
0.070
0.117
0.101
0.463
0.691
female
17.3±2.8
17.8±2.9
18.3±2.8
19.2±2.5
20.6±2.0
22.3±1.3
24.5±2.4
27.0±2.9
29.3±5.3
30.7±7.1
Gender Differences in Knee Kinematics
male
17.8±2.7
18.4±2.8
19.1±2.8
20.7±2.8
23.2±2.6
26.6±2.5
31.1±2.4
36.3±3.0
41.3±4.2
44.4±5.1
medial
P*
0.293
0.296
0.279
0.250
0.227
0.212
0.364
0.884
0.729
0.590
Bišèeviæ et al:
Knee
angle
90°
80°
70°
60°
50°
40°
30°
20°
10°
0°
*Student t-test.
Table 3. Percentage of rolling (mean±SD%) during non-weight and weight-bearing knee extension
Knee
angle
90°
80°
70°
60°
50°
40°
30°
20°
10°
male
53±11
57±12
51±13
52±11
59±11
51±7
59±14
54±9
56±6
Percentage of rolling (mean±SD) during knee extension
non-weight-bearing
weight-bearing
P*
female
male
P
0.646
49±2
49±6
0.465
0.962
57±8
58±6
0.532
0.644
54±8
59±13
0.374
0.977
52±10
62±15
0.488
0.106
51±9
60±15
0.228
0.072
57±5
65±5
0.054
0.328
53±11
56±10
0.239
0.742
53±10
67±9
0.049
0.974
56±8
87±6
<0.01
female
53±8
56±10
55±7
58±7
53±13
57±8
51±8
56±11
56±1.7
*Student t-test.
spectively). This difference became statistically
significant only in the last 10° of the extension
during the closed kinetic chain (P<0.001). In
weight-bearing condition, the ICM was 6 mm
closer to the articular line than in non-weight-bear-
A
B
Figure 5. The Icr distances (mm) during non-weight loaded
(A) and weight loaded (B) knee extension at males (quadrates) and females (triangles). P<0.001, Icr distances in
male group were significantly shorter than in female group.
ing condition (22.8±8.6 mm and 17.1±6.6 mm
for non-weight and weight loaded conditions, respectively).
Rolling was a dominant joint surface
motion during knee extension. In the non-weight
bearing conditions (open kinetic chain), there was
about 54±10% of rolling, with no gender differences. In the closed kinetic chain (weight-bearing
condition), there was 58±10% of rolling (Table 3).
The rest was sliding.
During weight loaded extension from
90° to 0°, men had more rolling (62.5±9.5%)
than women (54.7±8.2%). That difference was
statistically significant only for the 20°-10° segment (P=0.049), and for 10°-0° segment
(P<0.001) of weight loaded extension.
The knee extension is a combination of
rolling and sliding with 6:5 ratio, independent of
gender or weight loaded conditions. The exception is the terminal extension weight loaded male
knee, where the ratio was 8:1. Otherwise, whereas
female knee equally rolls and slides in the terminal
extension, the male knee practically just rolls into
extended position of the weight bearing leg.
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Croat Med J
Discussion
Gender Differences in Knee Kinematics
This study found gender differences in
the radii of condylar curves, but after adjusting to
the body height these differences became insignificant. Relatively high standard deviation of Ra
within each segment, points to the differences in
the shape of the condylar curves within or between the examined groups.
Bišèeviæ et al:
On average, the ICM path in nonweight-bearing conditions was more distant to the
joint line in comparison with weight-bearing conditions. Men had the ICM path closer to the joint
contact line than women, especially during the
last 20 degrees of the loaded knee extension (Fig.
5). Due to the different Icr distances, men had
about 12%, whereas women had 44% of sliding
motion during the terminal weight-bearing extension. In all other situations the percentage of rolling remained relatively constant – about 55%
(Table 3).
There is a gender difference in the knee
kinematics – women have a higher percentage of
sliding component than men, significantly higher
only during the terminal extension phase in the
closed kinetic chain.
Rising from a sitting position is taken as
one of the most difficult and mechanically demanding functional operations for the knee. If the
standing position is to be regarded as fully functional, an individual must be able to rise without
help. Rising from a low position (squat) requires a
far greater movement in knees and a higher total
exertion of strength (14). Such activity will express
the majority of kinematic characteristics of the
knee in weight bearing condition. Even small
changes in the joint kinematics during lifetime
could make the knee joint susceptible to osteoarthritis or injuries. Some gender differences in
lower leg kinematics could be used as biomechanical explanation of higher incidence of pathological conditions in the female knees.
Many authors report about different
lower leg kinematics between men and women.
For instance, sidestepping and landing motion
analysis showed that during gait women have less
hip and knee flexion, hip and knee internal rotation, and hip abduction, higher knee valgus and
foot pronation angles and increased variability in
knee valgus, and internal rotation during sidestepping (15). Also, women land with greater knee
258
2005;46(2):XXX-XXX
flexion angles and greater knee flexion accelerations than men (16). Women demonstrate more
ankle dorsiflexion and pronation, hip adduction,
flexion and internal rotation, and less trunk lateral
flexion than men with generally higher muscle activation in a manner that could increase strain on
the LCA (17). Men generate significantly more
hamstring muscle torque (18).
As previously mentioned, the ICM path
measurements provide valuable information
about characteristics of the joint kinematics. For
instance, the knee with an acutely torn LCA has
the ICM path that shifts suddenly downward and
forward between 20° and 40° of flexion and shifts
back to its normal position before 90° of flexion
(19).
If the instant center lies on the surface of
the moving limb, there is rolling contact, a condition in which there is no sliding and, therefore,
minimum friction losses or wear (20). In many of
the knees in Frankel’s series, it was possible to correlate the site of wear of joint surface cartilage with
the findings in the ICM path study. The longer the
motion about an abnormal ICM path had been
present, the greater was the chance of finding wear
at arthrotomy (20). Fourfold increased sliding in
the female knee at the most loaded areas could
lead to increased wear and could be one of the
theoretical reasons for a strong female bias on the
knee osteoarthritis.
This study suggests a higher proportion
of joint surface sliding in terminal extension with
consecutive anterior tibial displacement in women than in men. This probably indicates more
strain during terminal knee extension, potentially
making the ligament tend and susceptible to injury. The gender differences in the knee kinematics are probably the consequences of different soft
tissue structure or its activity, because no difference in the bony articular shape was noted. The
majority of authors think that hamstring activation
provides deceleration and stability during the
knee extension (18,21,22). Hamstrings, by virtue
of its posterior force vector, may cause limitation
of anterior displacement of the tibia and promote
rolling in men at terminal extension (11).
Most of the above mentioned studies
were performed by computerized electronic quantification of human motion. There are several systems for such analyses such as APAS, MA, VICON,
Kinemetrix, and SIMI. Each system is based on a
Croat Med J
With the most appropriate marker selection, frame-to-frame adjusting of center position,
marker-recognizing filters, the usage of actual dimensions of both condyles, and calculation of
meaningful output usable for biomechanical and
clinical interpretation, the Knee Roll software has
been designed as a valuable tool in the analysis of
knee kinematics.
The limitation of the method and software based on it, are the 2D mathematical model
of the knee. However, this 2D mathematical
model seems to be sufficient, until 3D knee
model, which can be employed in more comprehensive analyses, becomes available.
Schwitalle’s and Frankel’s methods for
estimation of the ICM paths (2,20) offered descriptive results. Hollman’s analysis provided numerical results (11), but his study was obtained assuming equal condylar shapes. The Knee Roll software
provides numerical results based on the actual
shape of femoral condyles, and so overcomes the
main limitations of Frankel’s, Schwitalle’s, and
Hollman’s studies.
The number of participants in this study
(twenty) and their ages (20-32 years) were common for kinematic studies based on healthy participants. The authors of all other similar studies
quoted in this work (5,8,11,15-18,20,22) also analyzed between 2 and 25 healthy younger adult
volunteers. Completed bone growth after 20 years
of age (23) reduces the possible influence of
growth differences between participants. Healthy
skeletal and neuromuscular systems exclude the
The current study explains one of the
many gender differences in the knee kinematics
and relates it theoretically to the most common
knee pathology with strong female bias (anterior
cruciate ligament rupture and knee osteoarthritis).
Gender Differences in Knee Kinematics
The Knee Roll software has relatively
simple usage, and hardware components (ordinary PC and digital camera) are widely available.
A combination of videographic and X-ray techniques provides reliable data about the joint surface kinematics without violating the ethical requirements.
influence of pathology on the knee kinematics,
making the examined groups of men and women
homogenous. This allows including of a relatively
small number of participants in such studies.
Bišèeviæ et al:
digitalized video sequence which is divided into
single pictures with captions of characteristic spots
on a moving limb. The computerized hardware/software technique provides a means to objectively quantify the dynamic components of
movement. Non-invasive motion analyzing systems have been primarily used for quantification
of human activities, it has assisted medical professionals, sport scientists, and athletes to understand
and analyze movement.
2005;46(2):XXX-XXX
A new, comprehensive study based on
more participants (with and without knee pathology), matched by age, muscle activity, habits, cartilage status, and diagnosis could explore the influences of each examined factor on normal and
altered knee kinematics.
A further step for physicians, biomechanics, mathematicians, and programmers would be
the development of a system which would comprise the best features of all described types of software and relate the kinematic parameters to the
specific knee conditions, and use it as a diagnostic
tool.
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Received: February 2, 2005
Accepted: March 10, 2005
Correspoondence to:
Mirza Bišèeviæ
M. Mikuliæa 25
71000 Sarajevo, Bosnia and Herzegovina
mirzabiscevic@hotmail.com