Abstract:
A harness for attachment about a knee femur and comprised of a rigid and non-flexible frame support two resiliently mounted clamping means and sensors is described for the non-invasive measurement of knee motion and its analysis in 3-D is described. The clamping means elements 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 stabilizing element is connected to the rigid frame and disposed at a predetermined location with respect to the medial clamping element in spaced relationship therewith and adjustable for clamping contact on a skin outer surface and in alignment with the center of a medial condyle of the femur whereby to stabilize the rigid frame about a knee. An attachment rod is secured to the harness and has straps for securing the rod above the knee.

Description:
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. 
   Some tools are known that allow an evaluation of the knee. Instrumented clinical tests as KT1000 [Bach et al., 1990] have been proposed, but their use is still under debate and their reliability and inter-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&#39;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 the 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 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. The 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 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&#39;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&#39;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 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 installed on a subject&#39;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 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 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 relative 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. 2   a  and  2   b  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. 4   a  and  4   b  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. 6   a  and  6   b  are perspective views, of the localising sensor secured against the harness, respectively, for contact with the anterior and lateral side of the knee; 
       FIG. 7   a  is a fragmented side view of a leg showing the harness and tibia attachment bar secured thereto with ultrasound localising sensors; and 
       FIG. 7   b  is a perspective view of an ultrasound localising sensor. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 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. 2   a  and  2   b , 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 . 
   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 Velcro™ strap  110  or by other attachment means above the knee of the wearer. 
   Referring now to  FIG. 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 ,  4   a  and  4   b , 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 attachment bar by means of the Velcro™ strap  110 . Without affecting subject&#39;s comfort, the harness stability is adjusted by means of the adjustable screw wheel  114  as well as the adjustment of the abutment 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 ,  4   a  and  4   b , the installation 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 ,  7   a  and  7   b , 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.  FIG. 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 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 posture is adopted or movement of the knee 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, helicoïdal 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 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 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 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 helicoïdal 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 helicoïdal axis of the knee but also angle of rotation around the helicoïdal axis and translation along the helicoïdal axis described at predetermined time intervals. 
   The tibial attachment bar  124  is composed of a rigid rod approximately 3 cm wide, 25 cm long and 3 mm thick. 
   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.