Abstract:
A harness for attachment about a knee femur of a subject, said harness comprising two abutment members, said abutment members being oriented against a skin outer surface at predetermined medial and lateral sites relative to a femur so as not to limit motion of the knee, and a strap operatively interconnecting the two abutment members such that the harness is adapted to be used on different knee sizes with the strap surrounding the knee and with the abutment members being urged against the skin outer surface at the predetermined medial and lateral sites by the strap, at least one of the abutment members supporting at least one femoral trackable member adapted to be tracked. The harness may be used for the pivot shift test.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority on U.S. Provisional Patent Application No. 60/990,074, filed on Nov. 26, 2007. 
     
    
     FIELD OF THE APPLICATION 
       [0002]    The present application 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 application measures precisely and non-invasively the relative 3D position and orientation, velocity and acceleration of the tibia in respect with the 3D position and orientation, velocity and acceleration of the femur during time and the relative 3D movement, velocity and acceleration of the tibia in respect of the femur. 
       BACKGROUND OF THE ART 
       [0003]    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 the knee allow the computation of relative movement 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 prostheses, evaluating diagnostic methods for ligament injuries and studying the injury mechanism in a knee joint. 
         [0004]    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. 
         [0005]    One test used to obtain such information is known as the pivot shift test. The pivot shift test is used for dynamically assessing the instability of the deficient knee following anterior cruciate ligament (ACL) injuries for example. The pivot shift test involves the patient lying down in supination, while a clinician performs movements and applies forces on the knee. With these manipulations, the clinician subjectively establishes the degree of instability of the knee. Due to the absence of non-invasive in vivo knee systems enabling the capture of objective data, the results of the pivot shift test as assessed by the clinician remain highly subjective. 
         [0006]    The pivot shift is a complex, dynamic displacement between the tibia and the femur and no measurement tool or technique are currently commercially available to objectively assess the pivot shift. Rather, the clinician must subjectively attribute a grade of 0 (none), 1 (glide), 2 (clunk) or 3 (gross) to the shift on the basis of her/his experience. It is this grade which gives an appreciation of knee function. However, it has been well documented that different clinicians, especially less experienced ones, attribute grades differently for a same knee 
         [0007]    In order to produce objective data during the pivot shift test, Hoshino et al. (“In Vivo Measurement of the Pivot-Shift Test in the Anterior Cruciate Ligament-Deficient Knee Using an Electromagnetic Device”, AJSM Preview, Mar. 9, 2007, doi: 10.1177/0363546507299447) describe the use of motion sensors on the leg to capture motion signals by which the movement of the leg is quantified. However, perhaps due to the nature of the motion sensors used and the fixation of these sensors on a simple elastic strap, or to an absence of normalization for the subjective assessment of the clinician, the results lacked accuracy. 
         [0008]    U.S. Pat. No. 7,291,119, issued to De Guise et al. on Nov. 6, 2007, describes a harness that is used in 3D kinematic analysis of the knee. The harness is secured to predetermined sites on the knee, at which sites there is relatively little movement between the skin/soft tissue and the bone elements, whereby the harness is used non-invasively. The harness has a pair of abutment members that are interrelated by a rigid arch, with the arch supporting a trackable member. The harness does not impede the normal movement of the knee. One of the issues with the harness is that with its construction, it cannot be used with a patient in supination as the harness is maintained in position by abutment on a femoral condyle. 
       SUMMARY OF THE APPLICATION 
       [0009]    It is therefore an aim of the present application to provide a novel harness for kinematic analysis of the knee. 
         [0010]    It is a further aim of the present application that the harness be used in the pivot shift test. 
         [0011]    It is a still further aim of the present application to provide a method for normalizing the subjective results of the pivot shift test, for instance using the harness of the present application. 
         [0012]    Therefore, in accordance with the present application, there is provided a harness for attachment about a knee of a subject, said harness comprising two abutment members, said abutment members being oriented against a skin outer surface at predetermined medial and lateral sites relative to a femur so as not to limit motion of the knee, and a strap operatively interconnecting the two abutment members such that the harness is adapted to be used on different knee sizes with the strap surrounding the knee and with the abutment members being urged against the skin outer surface at the predetermined medial and lateral sites by the strap, at least one of the abutment members supporting at least one femoral trackable member adapted to be tracked. 
         [0013]    Further in accordance with the present application, each abutment member has at least one plate and an abutment projecting from the plate, the abutment made of a rigid material and being adapted to contact the skin outer surface at the predetermined site, with the plate contacting the skin outer surface in the periphery of the predetermined site. 
         [0014]    Still further in accordance with the present application, each abutment member comprises two of said plate, with a first plate supporting the abutment, and a second plate connected to the first plate to define a gap therewith to accommodate the strap. 
         [0015]    Still further in accordance with the present application, the plate supporting the abutment is sized 5 cm×6 cm. 
         [0016]    Still further in accordance with the present application, the femoral trackable member is connected to a lateral one of the abutment members. 
         [0017]    Still further in accordance with the present application, the femoral trackable member is at least one of a passive detectable device, an active detectable device, an accelerometer and a gyroscope. 
         [0018]    Still further in accordance with the present application, the strap is made of an elastic material. 
         [0019]    Still further in accordance with the present application, a first end of the strap has a loop surrounding the second plate of the medial abutment member so as to be connected thereto, with a second end of the strap passing through the gap of the lateral abutment member to be overlaid on the first end of the strap to surround the knee. 
         [0020]    Still further in accordance with the present application, complementary Velcro™ strips are respectively provided on the first end and the second end of the strap to secure the ends of the strap to one another. 
         [0021]    In accordance with another aspect of the present application, there is provided a harness system for tracking knee movements for a leg, comprising the harness as described above; and a tibial component comprising a support member adapted to be positioned against the skin on an anterior side of the tibia of the leg, the support member supporting at least one tibial trackable member adapted to be tracked, and a second strap for securing the tibial component to the tibia with the support member positioned against the skin on the anterior side of the tibia of the leg. 
         [0022]    Still further in accordance with the present application, the support member comprises a rigid plate. 
         [0023]    Still further in accordance with the present application, the second strap is connected at a first end to a first edge of the rigid plate, the second strap being looped through a channel at a second edge of the rigid plate to be overlaid on the first end of the strap to surround the tibia. 
         [0024]    Still further in accordance with the present application, the tibial component further comprises a cushioning member on the rigid plate, the cushioning member oriented toward the tibia for interfacing the rigid plate to the tibia. 
         [0025]    Still further in accordance with the present application, the rigid plate has a housing to accommodate the tibial trackable reference. 
         [0026]    Still further in accordance with the present application, the tibial trackable member at least one of a passive detectable device, an active detectable device, an accelerometer and a gyroscope. 
         [0027]    In accordance with yet another aspect of the present application, there is provided a harness for attachment about a knee of a subject, said harness comprising one abutment member, said abutment member being oriented against a skin outer surface at a predetermined lateral site relative to a femur so as not to limit motion of the knee, and a strap operatively interconnecting the abutment member such that the harness is adapted to be used on different knee sizes with the strap surrounding the knee and with the abutment member being urged against the skin outer surface at the predetermined lateral site by the strap, the abutment member supporting at least one femoral trackable member adapted to be tracked, the abutment member having at least one plate and an abutment projecting from the plate, the abutment made of a rigid material and being adapted to contact the skin outer surface at the predetermined site, with the plate contacting the skin outer surface in the periphery of the predetermined site. 
         [0028]    In accordance with yet another aspect of the present application, there is provided a method for normalizing a pivot shift test on a knee, comprising tracking trackable members secured to the femur and to the tibia of a knee; measuring at least an orientation of the femur and of the tibia over time using tracking data from the trackable members during a pivot shift test; calculating a displacement of the femur with respect to the tibia and an angular velocity of flexion from the measured orientation; normalizing the measured displacement of the femur from a value related to said angular velocity of flexion of the knee; and grade the pivot shift test using the normalized displacement. 
         [0029]    Further in accordance with the present application, calculating a displacement of the femur with respect to the tibia comprises calculating an acceleration of the knee, and normalizing the measured displacement of the femur comprises normalizing the measured displacement from a value related to said angular velocity of flexion of the knee and to said acceleration. 
         [0030]    Still further in accordance with the present application, normalizing the measured displacement comprises calculating the value as: 
         [0000]      log [(accel AP +accel ML +accel PD )/ω flexion ] 
         [0031]    in which: 
         [0032]    accel AP  is the anterior-posterior acceleration 
         [0033]    accel ML  is the medio-lateral acceleration 
         [0034]    accel PD  is the proximal-distal acceleration 
         [0035]    ω flexion  is the mean angular velocity flexion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]      FIG. 1A  is a schematic view of a knee, from a medial standpoint; 
           [0037]      FIG. 1B  is a schematic view of the knee of  FIG. 1A , from a lateral standpoint; 
           [0038]      FIG. 2  is a perspective view of a harness constructed in accordance with an embodiment of the present application; and 
           [0039]      FIG. 3  is a perspective view of a tibial component used in combination with the harness of  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    Referring to  FIGS. 1A and 1B , parts of the knee  10  are described for reference, as the installation of the harness system of the present application will be related to the knee  10 . The harness system features a harness that will be abutted against predetermined sites  11  and  12  on opposite sides of the knee. A first one of the predetermined sites  11  is located medially between the vastus medialis  13  and the sartorius tendon  14  of the knee  10 . The predetermined site  12  is located laterally between the ilio-tibial band  15  and the biceps femoris tendon  16  of the knee  10 . The sites  11  and  12  have been identified as locations on the knee  10  at which the relative movement between the skin/soft tissue and the bone elements is minimal, and negligible for the purposes of kinematic analysis. 
         [0041]    The harness system of the present application also features a tibial component. Referring to  FIGS. 1A and 1B , the position of the tibial component on the knee  10  is on the anterior side of the tibia  17 , below the tuberosity  18 . 
         [0042]    Referring to  FIG. 2 , the harness is generally shown at  20 . The harness  20  is designed to be secured to the knee  10  ( FIGS. 1A and 1B ) at the predetermined sites  11  and  12 , or other suitable locations on the knee  10 . 
         [0043]    The harness  20  has a pair of abutment members  21 . The abutment members are illustrated as  21 A and  21 B, and their respective components will be appropriately affixed with “A” or “B” in the Figs. 
         [0044]    Each abutment member  21  has an abutment  22  that will contact the knee  10  ( FIG. 1 ) at the predetermined site  11  or  12 . The abutments  22  are made of a material having a relatively high rigidity. For instance, the abutments  22  are made from a vulcanized rubber. 
         [0045]    The abutments  22  each project normally from a support plate  23 . The support plates  23  are made of a rigid material, such as polyvinyl chloride (PVC). Although there are numerous suitable dimensions considered for the support plates  23 , a thickness of 0.3 cm for dimensions of 5 cm by 6 cm are suitable (i.e., approximately ⅛ in thickness, and 2×2⅜ inch). The dimensions of the support plates  23  are such that the support plates  23  contact the skin in the periphery of the predetermined sites  11  or  12 . The combination of the abutments  22  and the support plates  23  contacting the knee ensures a suitable stability of each abutment member  21  with respect to the sits  11  and  12 . 
         [0046]    Each support plate  23  may be paired with a strap plate  24 . The plates  24  are similar in construction to the plates  23 . Each pair of support plate  23  and strap plate  24  defines a gap between plates. In the illustrated embodiment, the pairs of plates  23  and  24  are assembled to one another by fasteners  25  at the corners of the plates  23  and  24 . Other configurations are also considered, as the fasteners  25  represent only solution amongst others. The fasteners  25  are typically nuts and bolts, with a spacer between the plates  23  and  24 . In the illustrated embodiment, the fasteners  25  include a wing nut. This configuration is a possibility among numerous others to provide a gap between plates  23  and  24 . 
         [0047]    A strap  26  has an end looped about one of the abutment members  21  (i.e., abutment member  21 A in  FIG. 2 ). The other end of the strap  26  is therefore free and is passed through the gap of the other abutment member  21 B, to then pass on an exterior of the abutment member  21 A. The abutment member  21 B is free to translate along the strap  26 . The end of the strap  26  features a Velcro™ portion  27  so as to be secured to a complementing Velcro™ portion  28  elsewhere on the strap  26 . 
         [0048]    The strap  26  is made of a strip of material having a given level of elasticity, such as Neoprene. Accordingly, with the Velcro™ portions  27  and  28 , and the translation between the strap  26  and the abutment member  21 B, the harness  20  is securable to different knee sizes. 
         [0049]    Either one of the abutment members  21  of the harness  20  supports one or more trackable members (not shown) for the 3D tracking of the harness  20 , and thus of the femur. The femoral trackable member is any of active and passive trackable units, such as optical patterns of retro-reflective members or emitters (e.g., electromagnetic, RF, etc.). The trackable device is preferably positioned on the lateral one of the abutment members  21 , namely the abutment member  21 B. Other components may be provided on the abutment members  21 , such as an accelerometer and a gyroscope. 
         [0050]    It is pointed out that the oversizing of the strap plates  24  when compared to the abutments  22  reduces the area of contact between the knee  10  and the strap  26 . The harness  20  may be provided with a single one of the abutment members  21 . More specifically, in an embodiment, the harness  20  only features the lateral abutment member  21 B. 
         [0051]    Referring now to  FIG. 3 , the tibial component is illustrated at  30 . The tibial component  30  comprises a tibial support member  31  secured below the knee by means of an adjustable strap  32 , or by other attachment means. As a non-restrictive example, the strap  32  has a width of 3.5 cm (i.e., approximately 1⅜ in). The strap  32  is preferably provided with appropriate Velcro™ strips to facilitate the installation of the tibial component  30  to the lower leg. 
         [0052]    The support member  31  is curved in the shape of the tibia, to conform with the tibia when abutted against same. Cushioning member  33  is provided on the support member  31  to increase the comfort of the patient wearing the tibial component  30 . A suitable thickness for the cushioning member  33  is 0.5 cm (approximately 3/16 in)), although other dimensions are considered. The support member  31  supports a trackable member housing  34  (similar to that used with the harness  20 ) The housing  34  is made of a rigid material (e.g., polyvinyl chloride), and accommodates one or more trackable members or sensors, such as electromagnetic position and orientation devices, accelerometers and gyroscopes. Suitable dimensions for the housing are 4 cm×2 cm, with a height of 1 cm (1½ in×¾ in×⅜ in), although other dimensions are considered. As illustrated, the housing  35  may incorporate a strip  35  of Velcro™ for quick connection of sensors/trackable members thereto. The tibial component  30  is configured and sized so as not to interfere with the clinician when the clinician applies forces on the knee  10  during the pivot shift test. 
         [0053]    Briefly summarizing the method of determining the kinematic of a knee in a non-invasive manner comprising the harness system of the present application, the method comprises attaching the harness  20  about the knee  10 . The tibial component  30  is then secured to the tibia so as to be substantially immovable with respect to the tibia. 
         [0054]    Once the harness  20  and the tibial component are secured to the leg, data is generated by the tracking of the trackable members/sensors secured to the harness  20  and the tibial component  30  (in the trackable member housing  34 ). The data is treated, analyzed and resulting data is generated which describes the knee  10  to which the harness  20  and tibial component  30  are secured. 
         [0055]    In installing the harness  20  about the knee  10  care is taken to place the abutments  21  in the predetermined sites  11  and  12  on the knee  10  ( FIG. 1 ). The strap  26  is then manually tightened until the abutments  21  are fixed to the knee  10 , while not impeding the normal movement of the knee  10 . Once an appropriate tightness is reached, the harness  20  is secured using the Velcro™ portions  27  and  28 . 
         [0056]    The stability of the harness  20  is preferably verified after the knee  10  has been flexed a few times. 
         [0057]    The tibial component  30  is installed by the support member  31  being positioned appropriately against the tibia, as discussed above. In the appropriate position, the strap  32  is tightened and secured to the tibia, without impeding the natural motion of the leg. 
         [0058]    The analysis of data firstly involves defining a coordinate system relative to the trackable member fixed to the harness  20 , and defining a coordinate system relative to the trackable member fixed to the tibial component  30 . There are numerous prior-art ways to define such coordinate systems. For instance, one method is described in United States Publication No. 20050143676, published on Jun. 30, 2005 by De Guise et al. The coordinate systems are used to create three-dimensional representations of the femur and tibia and these representations accurately represent motions performed by the femur and tibia, relative to one another. Such tracking systems are well known. Additionally, electronic components such as accelerometers may be provided on the harness  20  and the tibial component  30 . In the pivot shift test, the tibia and femur move relatively sharply with respect to one another. Accordingly, the use of an accelerometer may provide additional useful information. 
         [0059]    The tracking of the harness  20  and of the tibial component  30  is performed when the knee  10  is in movement, for instance through the manipulations of the clinician in the pivot shift test. 
         [0060]    Using the harness  20  and tibial component  30  or like harness system, the pivot shift test results may be normalized in accordance with the present application. In particular, the sum of linear accelerations (which is mainly composed of posterior and lateral accelerations) has a very strong correlation to the grade. The main component of the pivot shift is a posterior translation and is also generally coupled with an external rotation which has a component of lateral translation. The subjective grading system has an element of suddenness (clunk vs gross clunk) which can be characterized by acceleration. 
         [0061]    As clinicians execute the pivot shift test with greater velocity of flexion generally produced kinematic parameters of greater amplitude, the normalization has all kinematic parameters related to the angular velocity of flexion produced by the clinician (e.g., mean angular velocity). For instance, the following normalization value is used for the knee: 
         [0000]      log [(accel AP +accel ML +accel PD /ω flexion ] 
         [0062]    in which: 
         [0063]    accel AP  is the anterior-posterior acceleration 
         [0064]    accel ML , is the medio-lateral acceleration 
         [0065]    accel PD  is the proximal-distal acceleration 
         [0066]    ω flexion  is the mean angular velocity of flexion 
         [0067]    all of which take into account the measurements obtained from the combination of the harness  20  and the tibial component  30 , or similar harness system. The value is then use to normalize the subjective results of grade from the clinician. 
         [0068]    This normalised parameter shows differences between all pair of grades except between grades 0 and 1. A grade 1 represents a “glide” whereas a grade 0 is an absence of pivot shift. Therefore, they both present very small linear acceleration values and are better distinguished using the amplitude of posterior translation. Simple normalisation of kinematic data to account for the clinicians&#39; different techniques allowed an improved correlation with the attributed grades.