Note: Descriptions are shown in the official language in which they were submitted.
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A SYSTEM FOR THE ANALYSIS OF
3D KINEMATIC OF THE KNEE
FIELD OF THE INVENTION
The present invention relates to a knee harness and
method for the precise and non-invasive measurement of
knee motion and its analysis in 3D. Specifically, the
present invention measures precisely and non-invasively
the relative 3D position and orientation of the tibia
in respect with the 3D position and orientation of the
femur during time and the relative 3D movement of the
tibia in respect of the femur.
BACKGROUND OF THE INVENTION
Human joints are usually more complex than a single
axis. The knee joint is among the most complicated
synovial joints in the musculoskeletal system. The
kinematic studies of knee allow the computation of
force distribution during physical activities (such as
walking), evaluating surgical operations such as
ligament reconstruction, evaluating the effects of
inaccurate positioning of condylar prostheses,
evaluating the effect on the knee of the use of foot
prosthesis, evaluating diagnostic methods for ligament
injuries and studying the injury mechanism in a knee
joint.
By performing a combination of rolling and
sliding, the knee joint accommodates the small contact
area between the femur and the tibia. The anatomical
structure of the femoral condyles leads to a complex
combination of translations and rotations, which
includes components of abduction/adduction,
internal/external rotations and flexion/extension.
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Some tools are known that allow an evaluation of
the knee. Instrumented clinical tests as KT1000 [Back
et al., 1990] have been proposed, but their use is
still under debate and their reliability and inter-
s observer reproducibility are questioned [Forster et
al., 1989; Huber et al., 1997]. The Lars Rotational
Laxiometer [Beacon et al., 1996; Bleday et al., 1998]
seems to demonstrate a satisfactory inter and intra-
observer reproducibility, but the measurement is
limited to the laxity of the knee along one movement
axis. Also, considering the 3D nature of the knee's
movement, it is essential to complete this measurement
by a more global evaluation, in 3D and in movement.
To measure the rotations, localising sensors
(magnetic, optic, ultrasonic...) can be used in order to
follow the position and orientation of the femur and
the tibia in space. Experiments have been made in order
to measure the relative motion between the femur and
tine tibia using such sensors placed on the skin.
However, Macleod and Morris (1987) were the first to
study the inevitable relative movement between skin and
bone during a movement analysis. This has also been
done by Sati et al. (1996) who has reported three
general methods which address the problem of relative
skin movement: 1) use of intracortical pins to fix
rigidly but invasively the sensors to the bones, 2) use
of statistical calculations to correct the positions of
several sensors and 3) use of attachment systems in
order to reduce sensors movement in respect with the
underlying bone. Only the third method allows having
relatively precise measurements of the bone position
and orientation, non-invasively. Because these two
factors are essential during routine examinations of
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the knee, the use of an external attachment system
seems to be the best compromise.
Sati et al. (1996) proposed an attachment system
for the sensors. This mechanical fixation system
attaches the sensors onto the underlying bone non
invasively. Three attachment sites onto the condyles
are related with a mechanical bridge, which insure the
application of inward clamping pressure. A vertical bar
insures the system to accurately reflect the
orientation of the femoral long axis. Th.e tibial
attachment consists of a long bow-shaped plate strapped
at both ends to the proximal and distal ends of the
tibia. It has been shown that the system can measure
knee kinematics with acceptable precision (Sati et al.
1996). This attachment system however revealed some
problems in its use:
The mechanical bridge which relates the attachment
sites on the femoral harness is designed to be flexible
in order to provide comfort to the subject when
performing extension of the knee since biceps femoris
tendon and ilio-tibial band approach one another during
full extension, and the lateral attachment sits on the
biceps femoris muscle which has the effect of pushing
the lateral attachment away from the knee (Sati, 1996).
However, this causes a displacement of the three
femoral attachments, particularly on the lateral side,
that produces an antero-posterior force which can lead
to harness detachment. Also, the localising sensors
motion is then influenced by their location on the
attachment system.
Moreover, the mechanical bridge flexibility causes
orientation changes in part of the harness during
subject full extension, which can result in errors in
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measurements of the position and orientation of the
sensors fixed on the harness. Further, the addition of
force exerted on knee structures when performing full
extension is similar for all subjects. Although it can
be acceptable for many subjects, the force can be
unbearable for some. Finally, the adjustment and
installation is somewhat long and not precise.
A second version of the harness was produced, with
a bridge that is rigid in expansion but flexible in
torsion, relating one lateral and two medial supports.
No lateral expansion is possible during knee extension
because of the bridge's rigidity in expansion, which
produces an unbearable pressure on both sides of the
knee for most of the subjects and causes errors in
measurements.
Due to these disadvantages, there is a need to
provide a new harness design in order to improve the
precision, the sensibility and the reproducibility of
the knee analysis system without affecting the
subject's comfort.
SUMMARY OF THE INVENTION
It is therefore a feature of the present invention
to overcome the disadvantages of the prior art and
provide a harness and method of use which permits
precise measurements and analysis of the knee movement,
i.e. the description during time of the tibial and
femoral three-dimensional positions and orientations,
one with respect to the other.
It is a further feature of the present invention
to provide a harness which can obtain a non-invasive
attachment for the localising sensors on the femur,
which is composed of orthoplasts, not related by a
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flexible mechanical bridge, and which is comfortable
for the subject, especially during full extension.
It is a still further feature of the present
invention to provide an attachment system that can be
5 installed on a subject's knee rapidly and precisely.
In accordance with the above features, from a
broad aspect, the present invention provides a knee
movement analysis system composed of a rigid harness
which fixates, in a non-invasive manner, localising
sensors on the femur, and an attachment system which
fixates, in a non-invasive manner, localising sensors
onto the tibia, and a program analysing the location
measurements, therewith providing results on kinematic
or posture of the knee.
The present invention differs from the prior art
in that it consists of a three-dimensional knee
movement analysis system, which uses a rigid attachment
system for localising sensors on the femur and on the
tibia. The rigidity of the femoral harness is
compensated by a new design of the two orthoplasts,
which absorb by mean of springs, the lateral pressure
forces due to knee expansion when performing a full
range of motion.
The harness rigidity provides improvements in
sensors stability and precision in respect with the
femur, in rapidity of installation on the knee and in
comfort for the subject and thus, improvements in the
precision, the quality, and the reproducibility of knee
evaluation.
According to a further broad aspect of the present
invention there is provided a harness for attachment
about a knee femur of the subject. The harness
comprises a rigid and non-flexible frame supporting two
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resiliently mounted clamping means. The clamping means
are urged under pressure outwardly for application
against a skin outer surface at predetermined medial
and lateral sites relative to a femur. A non-resilient.
adjustable stabilising element is connected to the
rigid frame and disposed at a predetermined location
with respect to the medial clamping means in spaced
relationship therewith and adjustable for clamping
contact on a skin outer surface and in alignment with
the centre of a medial condyle of the femur whereby to
stabilise the rigid frame about a knee. An attachment
means is secured to the harness and has means for
securement above the knee.
According to a further broad aspect of the present
invention the harness attaches about the knee femur of
a subject in a non-invasive system for precise and
reproducible three-dimensional movement analysis of the
knee. The system also comprises attachment means
associated to a knee tibia in a fixed relationship.
Localising sensors are secured to the harness and to
the tibial attachment means. The sensors provide
position and orientation indications associated with
the femur and the tibia in space. A means is also
provided to generate data corresponding to the position
and orientation of the sensors, in time.
According to a further still broad aspect of the
present invention there is provided a method of
determining the kinematic of a knee in a non-invasive
manner. The method comprises the harness as above
described attached about the knee femur and the tibial
attachment means is secured to the knee tibia in a
fixed relationship. Data is generated by localising
sensors secured to the harness and the tibial
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attachment means. The data localises the sensors in
space and in time. The location of the sensors is
detected at specific time intervals to provide location
data at the time intervals. The data is treated,
analysed and resulting data is generated for use in the
description of a knee to which the harness and tibial
attachment means is secured.
The above described method is further
characterised in that the resulting data consists of
steps of defining a coordinate system relativ~=.~ to the
group of sensors fixed to the harness, defining a
coordinate system relative to the group of sensors
fixed on the tibial attachment means and calculating
the mathematical relationship between the coordinate
systems one to another.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a perspective view of the harness
constructed in accordance with the present invention;
Figs. 2a and 2b are sectional views of the
clamping means located on the lateral and medial side
of the knee, respectively;
Fig. 3 is a perspective view of tibial attachment
means;
Figs. 4a and 4b are respectively medial and
lateral views of the anatomical structures of the knee,
permitting the identification of installation sites of
the harness on the knee;
Fig. 5 is a schematic and block diagram
representing the system for analysis of the three
dimensional kinematic of the knee;
Figs. 6a and 6b are perspective views, of the
localising sensor secured against the harness,
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respectively, for contact with the anterior and lateral
side of the knee;
Fig. 7a is a fragmented side view of a leg showing
the harness and tibia attachment bar secured thereto
with ultrasound localising sensors; and
Fig. 7b is a perspective view of an ultrasound
localising sensor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Figures 1 and 2, the harness 100 of
the present invention is described. This harness 100
comprises a rigid and non-flexible frame 101 which is
formed as a rigid arch. At each end of the frame there
is provided a medial rigid support 103 and a lateral
rigid support 102. The distance between the ends is
fixed or adjustable.
The harness 100 further comprises two resilient
clamping means, 116 and 117 as shown in Figs . 2a and
2b, each of them comprising a rigid housing 104 and 105
in which there is retained two rigid abutment elements
106 and 107 each having an outer end configured to fit
the shape of a condyle. Springs 118 and 119, or any
other resilient means, apply an outward force on the
abutment elements. At least one of the clamping means
116 or 117 could be secured to rigid supports 102 or
103 by adjustable means, e.g. in sliding fit adjustment
in a cavity 120 formed in rigid support 102. This
adjustable means is hereinshown as being an adjustment
screw 121 having a finger gripping head 122. The
springs 118 and 119 are also interchangeable to vary
the force of the abutment elements 106 and 107.
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The harness 100 further comprises a non-resilient
adjustable stabilising element 123 comprising a
threaded rod 113 having an abutment pad 111 at an outer
end thereof. This stabilising element 123 is being
secured to a support frame 112, which support frame 112
is connected to the rigid frame 103 by adjustable means
herein a screw attachment 115. The position of the pad
111 is adjusted by an adjustment wheel 114.
The harness 100 further comprises an attachment
means in the form of a bar 108. This attachment bar 108
is in the form of a long narrow flat plate and could be
formed of two sections interconnected by a hinge 109 or
by a pivot. The attachment bar 108 could be secured by
a VelcroTM strap 110 or by other attachment means above
the knee of the wearer.
Referring now to Figure 3, the tibial attachment
means is described. This attachment means comprises a
tibia attachment bar 124 secured below the knee by
means of two adjustable Velcro straps 125 and 126, or
by other attachment means. This attachment bar 124 is
also in the form of a long narrow flat plate.
Referring to Figs. 1, 4a and 4b, the installation
of the harness 100 on knee 127 is described. The
harness 100 is installed on the knee 127 by urging the
abutment elements 105 and 107 of the clamping means 116
and 117 against the skin at predetermined sites 128 and
129 on the knee. These predetermined sites are located
medially between the vastus medialis 130 and the
sartorius tendon 131 of the knee and laterally between
the ilio-tibial band 132 and the biceps femoris tendon
133 of the knee. The harness 100 is thereafter secured
proximally, rigidly attaching the attachment bar 108
against the medial side of the thigh and securing this
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attachment bar by means of the VelcroT"~ strap 110.
Without affecting subject's comfort, the harness
stability is adjusted by means of the adjustable screw
wheel 114 as well as the adjustment of the abutment
5 element 106 by rotating the head 122. The abutment pad
111 of the stabilising element 123 is urged against
skin in alignment with the centre of the medial condyle
128.
Referring to Figs. 3, 4a and 4b, the installation
10 of the tibial attachment on the knee 127 is described.
The tibia attachment bar 124 is installed by adjusting
its position so that the bar 124 urges on the anterior
side of the tibia, below the tuberosity 134 of the
tibia 135, securing the tibia attachment bar 124 below
this tuberosity by means of the adjustable straps 125
and 126.
Referring to Figs. 5, 6, 7a and 7b, the method for
analysing the three-dimensional kinematic of a knee
will be described. A harness 100 and the tibial
attachment bar 124 are provided with localising sensors
136, 137 or 141 on the femur of the knee and on the
tibia. The localising sensors are designated by
reference numeral 136, 137 and 141 and can be of
different types, herein illustrated are electromagnetic
sensors 137, opto-electronic sensors 136, and
ultrasonic sensors 141. These sensors are incorporated
in a system to provide data on their three-dimensional
positions or their three-dimensional positions and
orientations, with respect to an external reference, or
with respect to one another. Figure 6 illustrates an
example of the position of opto-electronic sensors 136
on the harness 100. Their positions are tracked using
a camera (not shown). When using the ultrasonic
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sensors 141, their positions are tracked by ultrasound
tx/rx methods. Their three-dimensional position and
orientation can also be determined by their
relationship to one another. When using
electromagnetic tracking sensors 137 their three-
dimensional position and orientation is tracked with
electromagnetic field emitter/receiver methods.
The harness 100 and the tibial attachment bar 124
are installed on the knee to be analysed. A knee
l0 posture is adopted or movement of the >>nee is
performed. This movement could consist of walking, or
walking on a treadmill, or bending and/or stretching
the knee... The movement could be guided by a person or
by an apparatus. Data is generated by the localising
sensors 136, 137, and 141 and the data is treated and
analysed by computerised program means 138 or
equivalent electronic means. The treatment of the data
could reside in the calculation of mathematical
relationships relating the femur with the tibia in
space during time. These relationships could be
calculated with the definition on the femur and on the
tibia of a coordinate system representing the location
of the femur and the tibia, respectively. This latter
definition could be accomplished on computerised models
which are thereafter calibrated on real bones.
The mathematical relationships, rotations,
translations, helicoldal axis, ... etc are used to
calculate knee movement indexes data 139 used in the
description of the posture, or the movement of the
knee .
Briefly summarising the method of determining the
kinematic of a knee in a non-invasive manner comprising
the harness of the present invention, the method
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comprises attaching the harness about a knee femur in
the manner as above described and securing the tibial
attachment bar to the knee tibia in a fixed
relationship. Data is generated by the localising
sensors secured to the harness and the tibial
attachment bar. This data localises the sensors in
space and in time. The location of the sensors is
detected at specific time intervals to provide location
data at the time intervals. This data is treated,
analysed and resulting data is generated which
describes the knee to which the harness and tibial
attachment means is secured.
In installing the harness about the knee care is
taken to place one of the clamping means between the
vastus medialis and the sartorius tendon of the knee.
The other clamping means is positioned between the
ilio-tibial band and the biceps femoris tendon of the
knee. The attachment rod which is connected to the
harness is placed against the medial side of thigh and
2o attached by means of straps above the knee. The
stability of the harness is verified even after the
knee has been flexed a few times. The position of the
stabilising element on the medial side is adjusted so
that one extremity urges against the skin in alignment
with the centre of the condyle when the knee is in
extension. The position of the attachment means is
adjusted so that it urges on the interior side of the
tibia below the two tuberosity of the tibia and it is
attached below the two tuberosity of the tibia.
The measurements are taken when the knee is in
movement and this is achieved by walking on a floor
surface or walking on a treadmill or jumping at least
one or a few times, or bending the knee at least once
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or stretching the knee at least one time. The movement
is guided by a person or an apparatus.
The analysis of data consists of defining a
coordinate system relative to the group of sensors
fixed to the harness, and defining a coordinate system
relative to the group of sensors fixed on the tibial
attachment rod. The mathematical relationship between
the coordinate systems one to another is then
calculated. The measurement is effected by a
computerised three-dimensional representations of the
femur and tibia and these representations are
calibrated in order to be accurately positioned and
oriented relative to real femur and tibia bones . The
mathematical relationship is defined by rotations and
translations to the femur and tibia with respect to one
another as well as a finite helicoidal axis of the
knee. The resulting data represents Euler angles and
distances described at predetermined time intervals.
The resulting data not only represents three-
dimensional orientations and positions of finite
helicoidal axis of the knee but also angle of rotation
around the helicoidal axis and translation along the
helicoidal axis described at predetermined time
intervals.
It is within the ambit of the present invention to
cover any obvious modifications of the preferred
embodiment described herein, provided such
modifications fall within the scope of the appended
claims.
