Journal of Biomechanics 43 (2010) 2164–2173
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Journal of Biomechanics
journal homepage: www.elsevier.com/locate/jbiomech
www.JBiomech.com
Loading of the knee joint during activities of daily living measured in vivo in
five subjects
I. Kutzner a,n, B. Heinlein a,b, F. Graichen a, A. Bender a,c, A. Rohlmann a, A. Halder d,
A. Beier d, G. Bergmann a
a
Julius Wolff Institute, Charité – Universitätsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany
ZHAW Zurich University of Applied Science, Biomechanical Engineering, Winterthur, Switzerland
c
Berlin-Brandenburg Center for Regenerative Therapies, Charité – Universitätsmedizin Berlin, Germany
d
Hellmuth-Ulrici-Kliniken, Klinik für Endoprothetik, Sommerfeld, Germany
b
a r t i c l e in f o
a b s t r a c t
Article history:
Accepted 26 March 2010
Detailed knowledge about loading of the knee joint is essential for preclinical testing of implants,
validation of musculoskeletal models and biomechanical understanding of the knee joint. The contact
forces and moments acting on the tibial component were therefore measured in 5 subjects in vivo by an
instrumented knee implant during various activities of daily living.
Average peak resultant forces, in percent of body weight, were highest during stair descending
(346% BW), followed by stair ascending (316% BW), level walking (261% BW), one legged stance (259%
BW), knee bending (253% BW), standing up (246% BW), sitting down (225% BW) and two legged stance
(107% BW). Peak shear forces were about 10–20 times smaller than the axial force. Resultant forces
acted almost vertically on the tibial plateau even during high flexion. Highest moments acted in the
frontal plane with a typical peak to peak range 2.91% BWm (adduction moment) to 1.61% BWm
(abduction moment) throughout all activities. Peak flexion/extension moments ranged between
0.44% BWm (extension moment) and 3.16% BWm (flexion moment). Peak external/internal torques
lay between 1.1% BWm (internal torque) and 0.53% BWm (external torque).
The knee joint is highly loaded during daily life. In general, resultant contact forces during dynamic
activities were lower than the ones predicted by many mathematical models, but lay in a similar range
as measured in vivo by others. Some of the observed load components were much higher than those
currently applied when testing knee implants.
& 2010 Elsevier Ltd. All rights reserved.
Keywords:
Knee
Forces
Moments
Telemetry
In vivo
Measurements
Load
Implant
1. Introduction
The knee joint is loaded by external forces (ground reaction
force, masses and acceleration forces of foot and shank). Their
sum is counterbalanced by the forces acting across the joint, i.e.
the tibio-femoral contact forces, muscle forces and forces in soft
tissue structures. The ‘net moment’, caused by the external forces,
is additionally counterbalanced by the moments exerted by
muscles, soft tissues, contact forces and frictional forces. Muscle
and joint contact forces can be analysed using gait data together
with musculoskeletal modelling techniques e.g. inverse dynamics
and static optimization. However, large variations of reported
loading exist. Using gait analysis and a mathematical model,
Morrison calculated joint forces of 200–400% BW (percent of
body weight) during level walking (Morrison, 1970). Whilst more
n
Corresponding author. Tel.: + 49 30 450 559678; fax: + 49 30 450 559980.
E-mail address: [email protected] (I. Kutzner).
0021-9290/$ - see front matter & 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jbiomech.2010.03.046
recently forces of approximately 310% BW were reported using a
similar computational approach (Taylor et al., 2004), other studies
calculated contact forces of up to 710% BW during level walking
and even 800% BW for downhill walking (Costigan et al., 2002;
Kuster et al., 1997; Seireg and Arvikar, 1975).
To overcome uncertainties of mathematical models, telemetrized implants were developed to measure the joint contact
forces in vivo. Taylor and co-workers measured loads in the shaft
of a distal femoral replacement (Taylor et al., 1998). The estimated
forces in the knee joint of 220–250% BW during level walking
were smaller than those determined analytically. Recently, load
data measured by instrumented total knee replacements during
activities of daily living in vivo became available (D’Lima et al.,
2005, 2006, 2007; Mündermann et al., 2008). One year postoperatively peak tibial forces were 280% BW (level walking), 290%
BW (stair ascending), 330% BW (stair descending) and 264% BW
(chair rise). Most data is restricted, however, to total compressive
forces measured in one subject. Complete six component load
data during walking and stair climbing, measured in two subjects
I. Kutzner et al. / Journal of Biomechanics 43 (2010) 2164–2173
in vivo, was only published by Heinlein et al. (Heinlein et al.,
2009). Peak axial forces of 208–276% BW (level walking) and
327–352% BW (descending stairs) were reported.
The aim of this study was to examine the tibio-femoral contact
forces and moments in the knee joint during daily life in vivo
in a more representative cohort of 5 subjects and to examine
inter-individual differences. All six load components (3 forces,
3 moments) acting on an instrumented tibial tray were measured.
2.2. Subjects
After obtaining approval of the ethics committee and the subjects’ informed
consent to participate in the study and have their images published, the prosthesis
was implanted in 4 male and 1 female subjects with osteoarthritis (Table 1).
A medial parapatellar approach was used; the cruciate ligaments were sacrificed.
Femoral and tibial component were cemented. The mechanical axis angles
between the tibial axis and an axis connection knee and hip joint centers were
determined by radiographs during two legged stance (Specogna et al., 2007;
Colebatch et al., 2009). No subject had further joint replacements except K2L,
whose contralateral knee had been replaced 6 months previously.
2.3. Activities investigated and data evaluation
2. Materials and methods
2.1. Instrumented implant
Various forces and moments act across the knee joint, caused by external
forces, active muscles, soft tissue deformations and the contact forces and
moments acting directly between the condyles and the tibial plateau. The
instrumented knee implant measures the 3 contact forces and 3 contact moments,
acting on the tibial component, with a typical error below 2% (Heinlein et al.,
2007). Its design is based on the INNEX FIXUC total knee system (Zimmer GmbH,
Winterthur, Switzerland) with an ultra-congruent tibial insert and a standard
femoral component. From the load-dependent deformations of its stem, which are
measured by 6 semi-conductor strain gages (KSP 1-350-E4, Kyowa), the 6 load
components are calculated. All signals are sensed and transmitted by a custommade, inductively powered telemetry circuit (Graichen et al., 2007).
2.1.1. Coordinate system and nomenclature
The centre of the coordinate system is fixed at the right tibial component on
the extended stem axis at the height of the lowest part of the polyethylene insert
(Fig. 1). Forces and moments measured in left knees were transformed to the right
side. Force components +Fx, +Fy and +Fz act in lateral, anterior and superior
direction on the tibial component. Moments +Mx, +My and + Mz act in the sagittal,
frontal and horizontal plane of the tibial component and turn right around their
respective axes. From the components, the resultant forces F and moments M were
calculated.
The moments are termed, according to clinical conventions, after the tibial
rotation they counterbalance. To give an example: if external or muscle forces act
as to abduct the tibia, the moment +My counteracts this rotation. This moment is
termed ‘abduction moment’ (although it tries to adduct the tibia). In this sense all
moments are named: flexion/extension moment¼ + Mx/ Mx, abduction/adduction
moment¼ + My/ My, external/internal rotation moment¼ + Mz/ Mz.
The contact moments can be caused by a distance between the resultant force
and the centre of the coordinate system, by friction between femoral and tibial
component or by both factors and are only a fraction of the total knee moments.
The coordinate system is fixed to the tibial tray and not to the instantaneous
axis of the knee joint. Magnitudes of the flexion/extension moments around the
knee axis, for example, may differ substantially from the ones acting around the
prosthesis’ x-axis (Heinlein et al., 2009).
Fz
Mz
Mx
2165
My
Fx
Fy
Fig. 1. Coordinate system of the instrumented tibial component.
Eight most frequent and strenuous activities of daily living were investigated
(Table 2, Fig. 2) and are further named by their abbreviations. Every activity was
repeated 5 to 25 times by each subject. Average time courses of resultant forces
from several trials were calculated using a dynamic time warping procedure
(Wang and Gasser, 1997). During 2LegSt, StUp, SitD and KneeB ground reaction
forces were measured to control an even body weight distribution. KneeB was
performed to self-selected flexion angles: K1L (90–1001), K2L (100–1051), K3R
(90–951), K4R (80–851) and K5R (90–951).
Ranges of forces and moments during complete loading cycles are stated by
their maximal (and minimal, if applicable) peak values. In different subjects these
peak values may occur at different time points. Peak forces during walking, for
example, can act either during the instants of contralateral toe off (CTO) or prior to
contralateral heel strike (CHS).
‘Individual’ forces or moments of each subject refer to the average peak values
from all investigated trials. ‘Typical’ forces or moments are the averages of the
individual loads from all five subjects. ‘Absolute’ maxima/minima refer to the
highest/lowest value from all investigated subjects and trials.
In the following, peak forces are stated in percent of the body weight (%BW),
peak moments in percent body weight times meter (%BWm).
3. Results
3.1. Typical peak loads
During most activities (except static positions), shear forces and
moment components changed their sign during a loading cycle.
Forces in the transverse plane, for example, changed from a
laterally directed force +Fx to a medially directed force Fx. This
sign inversion becomes obvious in Fig. 3 if all large symbols are
above zero and the small symbols are below zero. In the following,
all values refer to typical peak loads if not stated otherwise.
3.1.1. Resultant forces F (Fig. 3A)
Smallest peak resultant forces of 107% BW were measured
during 2LegSt. During SitD the values were about two times higher
(225% BW). StUp, KneeB, 1LegSt and LevWalk caused nearly the
same forces (246–261% BW). The highest forces acted during AscSt
(316% BW) and DesSt (346% BW). The absolute maximum of F
from all subjects and trials was 400% BW, measured in K5R during
DesSt. Peak axial forces Fz were of similar magnitude as the
stated resultant forces F.
3.1.2. Shear forces Fx and Fy (Fig. 3B and C)
Shear forces in the transverse plane were about 10–20 times
smaller than the axial force Fz. In most subjects the largest shear
forces Fx and Fy were found during LevWalk, AscSt and DesSt.
Medial shear forces ( Fx) ranged between 1% and 18% BW,
forces in lateral direction (+ Fx) between + 1% and +16% BW.
Highest medial forces were mainly observed in K4R, highest
lateral forces mainly in K2L.
Shear forces Fy in posterior direction were highest for
LevWalk ( 26% BW), AscSt ( 32% BW) and DesSt ( 34% BW).
In K4R, however, high flexion activities (SitD, StUp, KneeB) led to
individual posterior forces Fy of 46% BW. Shear forces in
anterior direction ( + Fy) typically lay between + 2% and + 18% BW.
During 1LegSt, Fy always acted in the posterior direction.
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Table 1
Subject data.
Subject
K1L
K2L
K3R
K4R
K5R
Sex
Age at implantation (years)
Body weight (kg)
Height (cm)
Time of measurement (months post-operatively)
Mechanical axis angle (deg.) preoperative
Mechanical axis angle (deg.) postoperative
Male
63
100
177
10
8 varus
3 varus
Male
71
90
171
22
8 varus
5 varus
Male
70
92
175
16
9 varus
4 varus
Female
63
97
170
7
3 varus
5 valgus
Male
60
100
175
11
11 varus
1 varus
Table 2
Activities investigated.
Activity
Abbreviation
Trials
Conditions
Two legged stance
Sitting down
Standing up
Knee bend
One legged stance
Level walking
Ascending stairs
Descending stairs
2LegSt
SitD
StUp
KneeB
1LegSt
LevWalk
AscSt
DesSt
5
5
5
5
5
25
10
10
Equal load distribution
Seat height 45 cm, no support at armrest
Seat height 45 cm, no support at armrest
Self-selected flexion angle
No or minimal support at fingertip
Self-selected comfortable speed on level ground
Stair height 20 cm, no support at handrail
Stair height 20 cm, no support at handrail
Fig. 2. Subject K5R during the investigated activities. Body positions at peak resultant forces; A: one legged stance, B: standing up/sitting down, C: knee bend, D: level
walking, E: ascending stairs, F: descending stairs
3.1.3. Flexion–extension moments Mx (Fig. 4A)
In the sagittal plane high flexion moments + Mx ( + 0.53% to
+ 3.16% BWm), but only small extension moments Mx ( 0.14%
to 0.44% BWm) acted. Flexion moments + Mx were highest
during DesSt (3.16% BWm), followed by AscSt (2.29% BWm),
LevWalk (1.92% BWm) and 1LegSt (1.81% BWm). Slightly lower
flexion moments occurred during high flexion and two-legged
activities: StUp (1.24% BWm), SitD (1.35% BWm) and KneeB (1.39%
BWm). With an absolute maximum of 6.00% BWm the highest
flexion moment ( +Mx) was seen in K3R during DesSt.
3.1.4. Abduction–adduction moments My (Fig. 4B)
In the frontal plane, abduction moments +My were highest during
KneeB (1.61% BWm) followed by StUp (1.39% BWm), AscSt (1.26%
BWm), DesSt (1.04% BWm), SitD (1.14% BWm) and LevWalk (1.0%
BWm).
High adduction moments My were observed during
all activities which include temporary single legged stance.
AscSt/DesSt led to moments of 2.58/ 2.57% BWm. During
1LegSt/LevWalk slightly higher values of 2.88/ 2.91% BWm
were measured. Smaller moments acted during StUp ( 0.97%
BWm), KneeB ( 0.91% BWm) and SitD ( 0.77% BWm). With an
absolute maximum of 4.62% BWm, the highest adduction
moment My was observed in K2L during DesSt. As seen for Fy
the component My did not change its sign during 1LegSt.
Throughout all activities, highest adduction moments ( My)
were observed in K2L, highest abduction moments ( +My) in K4R.
3.1.5. External–internal rotation moment Mz (Fig. 4C)
Highest rotation moments acted during LevWalk. They
typically changed from +0.53% BWm during the early stance
phase to 1.1% BWm at late stance. AscSt also caused high
internal rotation moments Mz of 0.92% BWm. For all other
activities internal rotation moments Mz lay between 0.22%
and 0.66% BWm. External rotation moments + Mz were typically
smaller, and reached values between 0.07% and 0.53% BWm.
I. Kutzner et al. / Journal of Biomechanics 43 (2010) 2164–2173
2167
450
Resultant Force F
400
350
F [%BW]
300
250
K1L
200
K2L
K3R
150
K4R
K5R
100
Absolute Max
50
Absolute Min
Average
0
Two legged
stance
Sitting
down
Standing
up
Knee bend One legged
stance
Level
walking
Ascending Descending
stairs
stairs
Level
walking
Ascending Descending
stairs
stairs
Level
walking
Ascending Descending
stairs
stairs
40
Lateral Shear Force +Fx
30
20
Fx [%BW]
10
0
-10
-20
-30
Absolute Max
Absolute Min
Average(Max)
Average(Min)
-40
Medial Shear Force -Fx
-50
Two legged
stance
Sitting
down
Standing
up
Knee bend One legged
stance
50
Anterior Shear Force +Fy
40
30
20
Fy [%BW]
10
0
-10
-20
-30
-40
-50
-60
Posterior Shear Force -Fy
-70
Two legged
stance
Sitting
down
Standing
up
Knee bend One legged
stance
Fig. 3. Peak forces during investigated activities. Data from 5 subjects. A ¼resultant force F, B¼ medio-lateral force Fx, C ¼antero-posterior force Fy. Large/small
symbols¼ average maximum/minimum from several trials of 1 subject (‘individual’ forces). Thin lines ¼average values from all subjects and trials (‘typical forces’). Thick
lines ¼absolute maximum/minimum values from all subjects and trials. Peak values of component Fz are nearly identical to those of F.
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I. Kutzner et al. / Journal of Biomechanics 43 (2010) 2164–2173
7
Flexion Moment +Mx
6
5
Mx [%BWm]
4
K1L
K3R
K5R
Absolute Min
Average(Min)
K2L
K4R
Absolute Max
Average(Max)
3
2
1
0
-1
-2
Extension Moment -Mx
-3
Two legged
stance
Sitting
down
Standing
up
5
Knee bend One legged
stance
Level
walking
Ascending Descending
stairs
stairs
Level
walking
Ascending Descending
stairs
stairs
Level
walking
Ascending Descending
stairs
stairs
Abduction Moment +My
4
3
My [%BWm]
2
1
0
-1
-2
-3
-4
-5
Adduction Moment -My
-6
Two legged
stance
Sitting
down
Standing
up
Knee bend One legged
stance
1.5
External Torque +Mz
1.0
Mz [%BWm]
0.5
0.0
-0.5
-1.0
-1.5
Internal Torque -Mz
-2.0
Two legged
stance
Sitting
down
Standing
up
Knee bend One legged
stance
Fig. 4. Peak moments during investigated activities. Data from 5 subjects. A ¼ flexion/extension moment Mx, B ¼ abduction/adduction moment My, C¼ external/internal
rotation moment Mz. Large/small symbols¼ average maximum/minimum from several trials of 1 subject (‘individual’ moments). Thin lines ¼average values from all
subjects and trials (‘typical’ moments). Thick lines ¼ absolute maximum/minimum values from all subjects and trials.
I. Kutzner et al. / Journal of Biomechanics 43 (2010) 2164–2173
300
Forces [%BW]
Fx
Fy
Fz
300
F
2169
Fx
Forces [%BW]
Fy
Fz
F
200
200
100
100
2 legs
2 legs
1 leg
0
0
Sitting down
Standing up
Two & one legged
stance
-100
-100
-200
-200
Time [s]
Time [s]
4.0 Moments [%BW*m]
Mx
My
Mz
Moments [%BWm]
M
My
Mz
M
2.0
2.0
0
0
-2.0
Time [s]
0
1
2
Forces [%BW]
3
4
5
Fx
Fy
Fz
6
7
0
F
max.
Flexion
100
Descending
Ascending
0
Knee bend
-100
-200
Time [s]
Moments [%BW*m]
Mx
My
250
200
150
100
50
0
-50
-100
-150
-200
M
Mz
2.0
0
0
Time [s]
-2.0
400
1
2
3
Fx
Forces [%BW]
4
Fy
Fz
1
2
3
Fx
Forces [%BW]
Fy
5
F
CHS
Level Walking
Time [s]
Mx
My
Mz
M
Time [s]
0
400
F
Fz
5
-2.0
6
300
4
HS CTO
Moments [%BW*m]
2.0
0
Time [s]
-2.0
8
200
0.2
0.4
Forces [%BW]
0.6
0.8
Fx
Fy
1
1.2
Fz
1.4
1.6
F
300
200
200
CTO
CSC
100
Ascending stairs
-100
100
0
CTO
CSC
0
-100
-200
Descending stairs
-200
-300
4.0
Mx
Time [s]
Moments [%BWm]
Mx
My
Mz
-300
Time [s]
4.0
M
2.0
Moments [%BWm]
Mx
My
Mz
M
2.0
0
0
Time [s]
-2.0
0
0.25
0.5
0.75
1
1.25
1.5
1.75
2
Time [s]
-2.0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Fig. 5. Load patterns during investigated activities. Upper diagrams ¼ forces, lower diagrams¼ moments. Exemplary trials from K5R. HS: heel strike; CTO: contralateral toe
off; CHS: contralateral heel strike; CSC: contralateral stair contact.
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I. Kutzner et al. / Journal of Biomechanics 43 (2010) 2164–2173
3.2. Load patterns
3.4. Load variations
The force- or moment-time courses for each activity were
similar amongst the subjects. In the following, typical load
characteristics are described using exemplary trials from K5R
(Fig. 5).
Load variation within one subject was moderate. The intraindividual range of peak resultant forces F was typically around
50% BW during LevWalk (Fig. 7A), AscSt and DesSt. Smaller ranges
of about 30% BW were observed during all other activities
(Fig. 7C), which implies an overall intra-individual variation of
peak resultant forces of about 10–20%.
Inter-individual variation of F was highest during KneeB
(Fig. 7D). Peak values differed between 182% BW (K4R) and
300% BW (K1L), reflecting the variation of performing this
movement. With variations of about 70% BW, inter-individual
variation was moderate for StUp, SitD and LevWalk (Fig. 7B),
smaller differences of about 50% BW were observed during AscSt,
DesSt, 1LegSt and 2LegSt.
Even though the peak to peak range of shear forces and
moments were comparable between most subjects, the load
magnitudes varied considerably (Figs. 4, 5). During most activities
the highest medial shear forces Fx, posterior shear forces Fy,
extension moments Mx and abduction moments + My were
measured in K4R. Highest lateral shear forces + Fx, adduction
moments My and external rotation moments +Mz were mostly
found in K2L. Highest flexion moments +Mx were measured in
K3R.
3.2.1. Two/one legged stance (Fig. 5A)
Changing from 2LegSt to 1LegSt led to about 2.5 times
increased axial forces Fz as well as an increase of the adduction
moment My and flexion moment +Mx. Shear forces Fx, Fy
remained small during one and two legged stance.
3.2.2. Knee bend, standing up and sitting down (Fig. 5B and C)
During high flexion activities, highest peak forces were
observed at the instant of large flexion (KneeB, Fig. 2C), shortly
after loosing contact with the chair (StUp, Fig. 2B) and prior to the
seated position (SitD, Fig. 2B). During high flexion especially the
abduction moments +My, but also the flexion moments + Mx were
high. These high values of + My indicate a pronounced load shift to
the lateral compartment.
3.2.3. Level walking (Fig. 5D)
Two main force peaks occurred at the instant of contralateral
toe off (CTO) and shortly before contralateral heel strike (CHS)
(Fig. 2D). In K1L, K3R, K4R and K5R the second peak at CHS was
higher than the first one; in K2L both were of similar height. A
much smaller force peak was furthermore seen immediately
before heel strike (HS). At CTO small shear forces Fy were acting
in posterior and +Fx in lateral directions in most subjects. A shear
force Fx in medial direction was only observed in K4R.
In contrast to the high flexion activities and similar to 1LegSt
and 2LegSt, an adduction moment My acted in the frontal plane
during stance phase, indicating a medial load shift. Flexion
moments +Mx reached their peak values around CTO and CHS.
The axial torque changed from initial external rotation moments
+ Mz at CTO to pronounced internal rotation moments Mz at
CHS.
3.2.4. Ascending/descending stairs (Fig. 5E and F)
Peak forces occurred at CTO and during or shortly after
contralateral stair contact (CSC). In most subjects maximum
forces acted around CSC when AscSt (Fig. 2E) and at CTO during
DesSt (Fig. 2F). In the sagittal plane flexion moments + Mx acted
throughout the whole stance phase with peak values at CTO and
CSC. In the frontal plane, adduction moments My acted between
CTO and CSC, but abduction moments + My after CSC. The two
peak values of My occurred subsequently to CTO and CSC. The
signs of My indicate an initially predominant force transfer by the
medial compartment and a final shift to the lateral side. During
AscSt and DesSt mainly internal rotation moments Mz acted at
the tibia.
3.3. Force directions
Since both shear forces Fx and Fy were small for all activities
and in all subjects, resultant forces in general acted almost
vertically on the tibial plateau (Fig. 6). This was especially the case
for high resultant forces and surprisingly also seen to be the case
during the high flexion activities KneeB, StUp and SitD. Only in K4R
considerable shear forces in posterior direction at high flexion
were apparent. In the frontal plane only small direction
differences within subjects and activities were observed. In K2L
Fx was directed slightly laterally, in K4R slightly medially during
most activities.
4. Discussion
The knee joint is highly loaded during daily life. For most
activities, resultant forces lay typically in the range 220–350% BW.
Similar values were reported in other in vivo studies using
instrumented implants (D’Lima et al., 2007; 2005; Mündermann
et al., 2008; Taylor et al., 1998). Greater discrepancies exist
between the forces actually measured and those obtained
analytically. Many models overestimate the loads during dynamic
activities. For AscSt axial forces between 425% and 540% BW were
calculated (Morrison, 1969; Taylor et al., 2004), exceeding the
measured values by up to 40%. On the other hand models tend to
underestimate the loading during static activities due to the lack
of co-contraction in the models. The impact of co-contractions
becomes obvious if a subject looses balance during 1LegSt. Forces
of more than 550% BW were observed on that occasion. During
2LegSt the joint force is also higher than required statically.
Whereas only about 44% BW would be required to support the
body weight by both legs, additional 60% BW act due to the
muscle activities required to maintain equilibrium. In vivo load
measurements in combination with gait analyses are underway to
improve the existing models.
During high flexion activities (StUp, SitD, KneeB) typical forces
between 210% and 260% BW were measured although the body is
supported by both knee joints. Lower forces during KneeB in K4R
with a flexion angle of only 80–851 indicate that the force level
depends on the maximum flexion. During high flexion, mainly
abduction moments + My acted in the frontal plane whereas
adduction moments My prevailed during all activities which
include temporary single legged stance. Negative My values
indicate that the contact force is predominantly transferred by
the medial compartment and vice versa.
The limited data of our 5 subjects support the assumption that
abduction adduction moments and knee alignment are related.
Highest adduction moments My and thus a more medial load
transfer were observed in K2L with a varus alignment (Fig. 4).
Highest abduction moments + My and thus a more lateral transfer
were seen in K4R with a valgus alignment. The varus/valgus
alignment may furthermore influence the medio-lateral shear
forces Fx. Highest lateral forces +Fx occurred in K2L, highest
I. Kutzner et al. / Journal of Biomechanics 43 (2010) 2164–2173
K2L
K3R
K4R
K5R
223
%BW
264
%BW
297
%BW
236
%BW
313
%BW
345
%BW
298
%BW
299
%BW
325
%BW
359
%BW
337
%BW
337
%BW
323
%BW
374
%BW
289
%BW
241
%BW
261
%BW
240
%BW
265
%BW
299
%BW
261
%BW
256
%BW
185
%BW
262
%BW
270
%BW
229
%BW
227
%BW
205
%BW
247
%BW
Knee bend
One legged stance
Descending stairs
Ascending stairs
285
%BW
Sagittal Plane
Frontal Plane
Level walking
K1L
Stand up/ sit down
2171
Fig. 6. Force directions during investigated activities. Selected trials from all 5 subjects. For each activity (lines) and subject (columns) the force vectors are displayed in the
frontal (left) and the sagittal (right) plane. ‘Individual’ peak resultant forces are indicated. Different scales are used.
2172
I. Kutzner et al. / Journal of Biomechanics 43 (2010) 2164–2173
350
300
Level walking (K5R)
Level walking (all subjects)
300
250
Inter-individual range
250
Resultant Force [%BW]
Resultant Force [%BW]
Intra-individual range
200
150
100
50
200
150
K1L
K2L
K3R
K4R
K5R
100
50
Average force pattern
0
0
20
40
60
80
0
0
100
20
Normalized time
60
80
100
80
100
350
350
Knee bend (K5R)
Knee bend (all subjects)
300
Resultant Force [%BW]
300
250
Resultant Force [%BW]
40
Normalized time
200
150
100
250
200
150
K1L (max. Flexion 90-100°)
K2L (max. Flexion 100-105°)
100
K3R (max. Flexion 90-95°)
50
0
0
Average force pattern
20
40
60
K4R (max. Flexion 80-85°)
50
K5R (max. Flexion 90-95°)
80
100
Normalized time
0
0
20
40
60
Normalized time
Fig. 7. Variation of resultant force during level walking and knee bending. Left ¼intra-individual variation between several trials of K5R during level walking (A) and knee
bending (C). Thick line¼ average from all trials. Right¼ inter-individual variation between average curves of 5 subjects during level walking (B) and knee bending (D). Data
was averaged by time warping.
medial forces Fx in K4R (Fig. 3). No hint to a correlation between
the axis alignment and the axial force Fz, as expected by others
(Heller et al., 2003), was found in the present cohort.
The data presented here confirm previous findings (Heinlein
et al., 2009) that the international standard protocol for wear tests
of tibial inserts underestimates the axial torque Mz. Whereas a
peak-to-peak moment of 7 N m is defined in the ISO standard
(ISO14243-1, 2002) typical peak-to-peak moments of 15 N m
were now measured, with individual values of up to 19 N m and
an absolute range of even 29 N m. The signs of the axial torque and
all other load components change within each load cycle during
most activities. This is detrimental for bone-implant interface
stresses and polyethylene wear and should be considered when
testing knee implants.
The reported data were obtained with a specific implant
design and cannot be transferred directly to other implants or the
natural knee. The cruciate ligaments were sacrificed and
changed gait patterns are possible. Changes of passive soft
tissue structures such as the collateral ligaments may also
influence the contact loads. The axial force Fz and the resultant
force F will most likely not be affected much by the type of TKR,
however. In vivo load measurements in different, posterior
cruciate retaining TKR, indeed resulted in similar values of F
(D’Lima et al., 2007, 2005; Mündermann et al., 2008). Because of
the ultra-congruent tibial insert of our implant the largest
differences were expected for the shear forces Fx and Fy.
Surprisingly the anterior shear forces + Fy, which were measured
in the cruciate retaining implant (D’Lima et al., 2007), were also in
a similar range as those from our data. This implies that only a
small part of + Fy is transferred trough the remaining cruciate
ligament. No final conclusions, however, can be drawn due to the
limited number of subjects.
I. Kutzner et al. / Journal of Biomechanics 43 (2010) 2164–2173
The given information is the most comprehensive data set of
in vivo knee joint loading so far. Investigations in more subjects
are currently performed to even broaden this data collection and
to deepen the understanding of knee joint biomechanics.
Conflict of interest statement
This study was supported by Zimmer GmbH, Winterthur,
Switzerland. Except from funding, the sponsor was not involved
in study design, collection, analysis and interpretation of data, or
anything related to this manuscript.
Acknowledgments
The authors gratefully acknowledge the voluntary collaboration of all subjects and the technical support of Jörn Dymke. This
study was supported by Zimmer GmbH, Switzerland.
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