Patent Publication Number: US-2013245777-A1

Title: Knee system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional patent application No. 61/407,691 filed 28 Oct. 2010, which is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a surgically implantable knee system. 
     BACKGROUND 
     Despite the advancements in implant design and surgical technique, total knee replacements still have certain limitations, and postoperative results can be less than desired. One issue that may arise is pain associated with movement of the knee, especially at deep flexion. There can be any number of causes for this, including inflammation of the soft tissue in and around the knee area. The inflammation may be caused by impingement of the tissue by the implant as it articulates, particularly when it articulates at the extremes of its range, such as during deep flexion. Therefore, it would be desirable to provide a knee replacement system that overcomes the problems described above, and allows a more anatomic range of motion for the patient without the pain associated with movements such as deep flexion. 
     SUMMARY 
     Embodiments of the invention overcome at least some of the problems described above and provide a greater range of motion without the pain associated with some implant designs. 
     Embodiments of the invention include a knee system having separate medial and lateral tibial inserts. In at least some embodiments, the one of the medial or lateral insert is fixed, while the other insert is movable. Embodiments of the invention provide an anterior cruciate ligament (ACL) retaining design that allows for medial translation and roll back of the femoral component as it moves during flexion. If the tibial insert was a single-piece design, and was mobile on both sides—i.e., one full mobile unit rotating on a central axis—the lateral side could roll forward as the medial side translates posteriorly, causing more pressure to the lateral soft tissue envelope, which becomes in some instances inflamed and fibrotic leading to failure of implant satisfaction. Embodiments of the invention having a separate mobile insert and a separate fixed insert, help to avoid the problem of increased pressure to the lateral soft tissue envelope. 
     If both medial and lateral inserts are separate, and both are mobile, paradoxical anterior translation of the femoral component on tibia components could impinge the soft tissue envelope, causing repetitive trauma, bleeding, swelling, inflammation, scar contracture and possible failure. Embodiments of the invention having a separate mobile insert and a separate fixed insert, help to avoid this problem as well. In at least some embodiments, the tibial insert will be rounded, smooth and will have no greater a forward sagittal radius than the front of the tibial edge. This reduces or eliminates the soft tissue impingement. Also by fixing the one of the tibial inserts, bearing spit-out is inhibited. 
     Some embodiments include a circular undercut on the tibial tray that allows for a high interface contact and ease of obtaining a high polish. The surface of the tibial tray, which interfaces with the bottom of the tibial insert on the medial side, can either be flat or curvilinear in both the sagittal and coronal radii to control the bearing motion in the natural glide pattern. This can mimic the directional effect of the tibial spline to the femoral component. Also, a relief can be provided in the central concavity of the tibial tray increases the allowable thickness of the tibial insert. 
     Embodiments of the invention include a knee prosthesis for implantation in a knee. The knee prosthesis includes a tibial arrangement including a tibial tray configured for attachment to a surgically-prepared surface of a proximal end of a tibia, and a tibial insert system including a lateral tibial insert and a medial tibial insert. One of the lateral tibial insert or the medial tibial insert is a movable tibial insert configured to move in a generally anterior-posterior (A-P) direction relative to the tibial tray, and the other of the lateral tibial insert or the medial tibial insert is a fixed tibial insert configured for fixed attachment to the tibial tray. Each of the tibial inserts has a respective tibial articular surface. The knee prosthesis also includes a femoral component configured for attachment to a surgically-prepared surface of a distal end of a femur. The femoral component has a femoral articular surface. The femoral articular surface and the tibial articular surfaces are configured to contact each other and to articulate relative to each other during flexion and extension of the knee. 
     Embodiments of the invention also include a knee prosthesis for implantation in a knee having a tibial arrangement, which includes a tibial tray configured for attachment to a surgically-prepared surface of a proximal end of a tibia, and a tibial insert system configured for attachment to the tibial tray and including a tibial articular surface. The knee prosthesis also includes a femoral component configured for attachment to a surgically-prepared surface of a distal end of a femur. The femoral component includes a femoral articular surface configured to contact and articulate relative to the tibial articular surface during flexion and extension of the knee. The femoral component further includes a medial condyle and a lateral condyle narrower than the medial condyle for at least a portion of the condyles. 
     Embodiments of the invention further include a knee prosthesis for implantation in a knee. The knee prosthesis includes a tibial arrangement including a lateral tibial insert, a medial tibial insert, and a tibial tray configured for attachment to a surgically-prepared surface of a proximal end of a tibia. One of the lateral tibial insert or the medial tibial insert is a movable tibial insert configured to move relative to the tibial tray along an arcuate track in a generally anterior-posterior (A-P) direction. The other of the lateral tibial insert or the medial tibial insert is a fixed tibial insert configured for fixed attachment to the tibial tray. Each of the tibial inserts has a respective tibial bearing surface proximally disposed thereon. The knee prosthesis also includes a femoral component configured for attachment to a surgically-prepared surface of a distal end of a femur and having a femoral bearing surface configured to contact the tibial bearing surfaces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a knee prosthesis system in accordance with embodiments of the present invention; 
         FIG. 2  shows a top plan view of a lateral tibial insert in accordance with embodiments of the invention; 
         FIG. 3  shows a top plan view of a tibial tray in accordance with embodiments of the invention; 
         FIG. 4  shows a back view of the tibial tray shown in  FIG. 3 ; 
         FIGS. 5A-5D  show different views of a medial tibial insert in accordance with embodiments of the invention; 
         FIG. 6  shows a side view of a tibial tray in accordance with embodiments of the invention; 
         FIG. 7  shows an auxiliary view of the tibial tray shown in  FIG. 6 ; 
         FIG. 8  shows a back view of a femoral component in accordance with embodiments of the invention; 
         FIG. 9  shows a top plan view of the knee system shown in  FIG. 1 ; 
         FIG. 10  shows a cross-sectional view of a medial side of the knee system shown in  FIG. 9 ; and 
         FIG. 11  shows a cross-sectional view of a lateral side of the knee system shown in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
       FIG. 1  shows a knee system  10  in accordance with embodiments of the present invention. The knee system  10  is a knee prosthesis configured for implantation in a mammalian knee. The knee prosthesis  10  includes a femoral component  12  and a tibial arrangement  14 . The tibial arrangement includes a tibial tray  16  and a tibial insert system  18 . In the embodiment shown in  FIG. 1 , the tibial insert system  18  includes separate medial and tibial inserts,  20 ,  22 , with the medial tibial insert  20  being a movable tibial insert, and the lateral tibial insert  22  being a fixed tibial insert. As explained in more detail below, the medial tibial insert  20  is configured to move in a generally anterior-posterior direction relative to the tibial tray  16 , and the lateral tibial insert  22  is configured for fixed attachment to the tibial tray  16 . In other embodiments, a tibial insert system in accordance with the present invention may include separate medial and lateral inserts, each of which is fixed, or alternatively, a single tibial insert having medial and lateral portions integrated into a single unit. 
     The knee prosthesis  10  is a right knee, with the medial-lateral (M-L) and anterior-posterior (A-P) directions being indicated by the arrows shown in  FIG. 1 . The tibial tray  16  is configured for attachment to a surgically-prepared surface of a proximal and of the tibia, and in particular, a distal side  24  of the tibial tray  16  is configured to contact the prepared surface of the tibia. Similarly, the femoral component  12  is configured for attachment to a surgically-prepared surface of a distal end of a femur, and in particular, a proximal surface  26  of the femoral component  12  is configured to contact the prepared surface of the femur. Also shown in  FIG. 1  is a patellofemoral groove  27 , configured to provide a surface over which the patient&#39;s patella can articulate. As explained below, the patellofemoral groove  27  is configured such that the patella tracks more anatomically, which can result in a greater range of motion without pain. 
       FIG. 2  shows a top plan view of the lateral tibial insert  22 . Lateral tibial insert  22  includes a tibial articular surface  28 , which is configured to act as a bearing surface and to articulate relative to a femoral articular surface described below. As shown in  FIG. 2 , the articular surface  28  is generally arcuate, forming a curve  30  that moves medially at the A-P extremes, and moves laterally near the center of the insert  22 . An A-P axis  32  shows that the arcuate curve  30  of the articular surface  28  is not symmetric, but rather, is offset by an angle  34 . In the embodiment shown in  FIG. 2 , the angle  34  is approximately 2.5°; however, an angle between 2°-4° may be used, or even an angle between 1°-10°. Other angles, or indeed no offset angle, may be used depending on the desired geometric configuration. 
     As shown in  FIG. 2 , the geometry of the arcuate articular surface  28  helps to facilitate a natural movement of the knee during extension and flexion. To further facilitate normal anatomical function of the knee, the articular surface  28  of the tibial insert  22  may have a generally constant radius in a cross section taken through a sagittal plane—i.e., a cross section view in an M-L direction. Conversely, a cross section of the tibial insert  22  taken through a coronal plane—i.e., as viewed in an A-P direction—will show at least two different radii, a larger radius disposed toward the lateral edge of the tibial insert  22 , and a smaller radius disposed toward the medial edge of the tibial insert  22 . Notwithstanding the geometry of the embodiments shown in the drawing figures, embodiments of the present invention contemplate a lateral tibial articular surface of different radii in the sagittal cross section, and/or an articular surface with a single radius in the coronal cross section, depending on the desired geometry. 
       FIG. 3  shows a top plan view of the tibial tray  16 . As discussed above, the tibial insert system  18  includes separate tibial inserts on the medial and lateral sides, with the medial tibial insert  20  being movable, and the lateral tibial insert  22  being fixed. To accommodate the inserts, the tibial tray  16  includes different geometric configurations on its medial side  36  and its lateral side  38 . For example, the tibial tray  16  includes a track  40  disposed on the medial side  36 , which is oriented in a generally A-P direction. As described in detail below, the movable, medial tibial insert  20  is configured to cooperate with the track  40  to allow movement of the medial tibial insert  20  in a generally A-P direction. As shown in  FIG. 3 , the track  40  is generally arcuate in shape, which provides a natural anatomical movement for the knee during extension and flexion. 
     Illustrated for reference in  FIG. 3  is an A-P axis  41 . As shown in  FIG. 3 , the arcuate track  40  is not symmetric relative to the medial side  36 , but rather, is offset by an angle  42 . In the embodiment shown in  FIG. 3 , the angle  42  is approximately 3°; however, an angle between 2°-4° may be used, or even an angle between 1°-10°. Other angles, or indeed no offset angle, may be used depending on the desired geometric configuration. Embodiments of the invention include offset arcuate paths for a track, such as the track  40 , for an articular tibial surface, such as the articular surface  28  of the tibial insert  22 —see FIG.  2 —or for both. A patient may have a tibia that articulates along an offset arcuate path, with different patients having arcuate articulating paths offset by different angles. Indeed, the same patient may have different offset angles for each knee, and even different offset angles on the medial and lateral sides of the same knee. To facilitate a fit that is as close to anatomic as possible, radiographic information, for example, from a CT scan or MRI, can be used to choose a tray and insert combination having the right offset angles for each patient. In the embodiment shown in  FIG. 3 , the medial side  36  of the tibial tray  16  is longer in an A-P direction than the lateral side  38 . Such a configuration lends itself well to having a movable tibial insert on the medial side  36 , because the additional length provides more support for a movable insert that may overhang the anterior or posterior edge during extension and flexion of the knee. 
     The embodiment of the tibial tray  16  shown in  FIG. 3 , includes a notch  44  which acts as a cruciate cutout to accommodate the cruciate ligaments, and in fact, allows even the ACL to be preserved. To inhibit the likelihood of impingement of ligaments on the tray  16 , the notch  44  opens slightly on its medial side  46  as it goes from anterior to posterior. In particular, the notch  44  includes a tapered medial side  46  which forms an angle  48  with A-P axis  41 . In the embodiment shown in  FIG. 3 , the angle  48  is approximately 3°; however, an angle between 2°-4° may be used, or even an angle between 1°-10°. Other angles, or indeed no taper angle, may be used depending on the desired geometric configuration. In contrast to the medial side of  46 , the notch  44  includes a lateral side  50  which is generally parallel to the A-P axis  41 . Embodiments of the present invention may have a tray with a smaller notch, such that only the posterior cruciate ligament is retained, or it may have no notch, such that neither of the cruciate ligaments are retained. 
       FIG. 4  shows a back view of the tibial tray  16 . In this view, a keel  52  is shown disposed on the distal side  24  of the tray  16 . The keel  52  is configured for insertion into a tibia, and provides strength and support for a proximal portion of the tray  16 . The keel  52  includes a recessed portion, or notch  54 , which in this embodiment is generally arcuate in shape. The notch  54  provides an open area through which a replacement anterior cruciate ligament (ACL) can pass. It also provides room to pass a screw into the tibia after the implant is secured. This may be desirable, for example, in the event that a fracture appears in the tibia after the tray is cemented in place. 
     Returning to  FIG. 3 , it is shown that the tibial tray  16  includes a curved anterior surface  56  configured to provide an articular surface  40  patella, which may either be a patient&#39;s own patella, or a or a replacement or resurfaced patella making up part of a knee system such as the knee system  10 .  FIG. 3  also shows a lateral proximal portion  58  that is configured to receive the lateral tibial insert  22 , which may attach to the tibial tray  16  via a snap fit or any other convenient method of attachment. 
       FIGS. 5A-5D  show different views of the medial tibial insert  20 .  FIG. 5A  shows a medial tibial articular surface  60 , which is configured to act as a bearing surface and to articulate relative to a femoral articular surface described below. In the configuration shown in  FIG. 5A , the articular surface  60  has a generally straight orientation in the A-P direction. The tibial insert  20  itself will, however, move in a generally arcuate path in the A-P direction as it articulates within the track  40  of the tibial tray  16 . 
     As shown in  FIG. 5B , the medial tibial inserts  20  includes a tracking feature  62 , disposed on a distal side  64  of the insert  20 . In the embodiment illustrated in  FIG. 5B , the tracking feature  62  is a “key” configured to cooperate with the track  40 —see FIG.  4 —which is a “keyway”; this geometry may also be referred to as a “dovetail”. Tracking features and tracks other than keyways or dovetails are contemplated within the scope of the present invention. The tracking feature  62  has a thickness in a center portion  66  that is greater than the thickness of edge portions  68 ,  70 . This is a result of the generally curved distal surface of the tracking feature  62 , and helps to provide an overall greater thickness to the medial tibial insert in an area that would otherwise be thinner as a result of the articular surface  60 . 
     This is further illustrated in  FIG. 5C , which shows a sectional view of the medial tibial insert  20  taken through a sagittal plane.  FIG. 5C  also shows that the insert  20  includes chamfers  72 ,  74  respectively disposed at anterior and posterior ends, each of which helps to further reduce impingement on soft tissue at full extension and deep flexion.  FIG. 5D  shows another sectional view of the medial tibial insert  20  taken through a coronal plane. As shown in  FIG. 5D , the articular surface  60  includes at least two different radii  76 ,  78  as viewed in the coronal section. The first radius  76  is smaller, and provides a steeper slope toward a medial side  80  of the tibial insert  20 . Conversely, the radius  78  is larger than the radius  76 , which provides a more gradual and reduced slope toward a lateral side  82  of the insert  20 . 
       FIG. 6  shows a side view of the tibial tray  16 , and in particular, shows the angular geometry of the keel  52 . The keel  52  forms an angle  84  with a surface on the distal side  24  of the tray  16 . In the embodiment shown in  FIG. 6 , angle  84  is approximately 37°; however, different angles may be used. Toward the anterior side of the tray  16 , the keel  52  forms an angle  86  with a surface of the distal side  24  of approximately 110°. Again, this angle may change for different sizes of implants, or even for the same sized implant in different embodiments of the invention.  FIG. 7  shows the distal side  24  of the tray  22 . In this view, a thickness  88  of one portion of the keel  52  is shown, which in this embodiment is approximately 3 mm. 
       FIG. 8  shows a back view of the femoral component  12  of the knee system  10 . The femoral component  12  includes a medial condyle  90  and a lateral condyle  92 . The femoral component  12  also includes a femoral articular surface  94 , which may be conveniently divided into a medial femoral articular surface  96  and a lateral femoral articular surface  98 . The medial and lateral femoral articular surfaces  96 ,  98  are configured to respectively contact the articular surface  60  of the medial tibial insert  20  and the articular surface  28  of the lateral tibial insert  22 , such that they articulate relative to each other during extension and flexion of the knee. 
     As shown in  FIG. 8 , a width  100  of the lateral condyle  92  is less than a width  102  of the medial condyle  90 . In at least one embodiment, the width of the medial condyle is approximately 25 mm and the width of the lateral condyle is approximately 23.5 mm. This difference in width may be present for an entire articulating surface length of the condyles  90 ,  92 , or it may be present only for a portion of the articulating surface, particularly near a posterior end of the condyles  90 ,  92 . The posterior ends of the condyles will contact their respective tibial insert articulating surfaces at deep flexion. The difference in condylar width is another feature of embodiments of the present invention that helps to facilitate deep flexion of the knee without soft tissue impingement and the pain associated with it. Another feature of the femoral component  12  illustrated in  FIG. 8  is an offset, or recess  104 , near the posterior portion of the lateral side of the lateral condyle  92 . The recess  104  is another feature of embodiments of the present invention that helps to facilitate deep flexion of the knee without soft tissue impingement, and in particular, the recess  104  helps to avoid impingement with the popliteal tendon. 
     As oriented in  FIG. 8 , the medial and lateral articular surfaces  96 ,  98  appear as lines in a coronal plane. These lines, and thus their respective articular surfaces  96 ,  98 , are made up of one or more radii to better articulate with their respective tibial articular surfaces  60 ,  28 . In the embodiment shown in  FIG. 8 , the lateral femoral articular surface  98  includes two separate radii  106 ,  108 . The first radius  106  covers approximately 75% of the lateral femoral articular surface  98 , and is disposed toward the lateral side. The second radius  108  is smaller than the first radius  106 , and covers about 25% of the lateral femoral articular surface  98 , and it is disposed toward the medial side. 
     Values of the radii  106 ,  108  may vary depending on a number of factors, including the geometric configuration of the cooperating articular surfaces of the tibial insert or inserts. Providing a smaller radius near the medial side of the lateral condyle  92  helps to reduce soft tissue impingement, particularly at deep flexion. Even so, a “radius”, such as the radius  108  may be increased significantly until it essentially becomes a straight line or chamfer, though for purposes of description herein, may still be referred to as a “radius”. In general, the second “radius” is configured to reduce the amount of material toward the medial side of the lateral articular surface  98 , which, as noted above, helps reduce soft tissue impingement. 
       FIG. 9  shows a top plan view of the knee system  10 , and in particular the femoral component  12 . A point  105  represents a center of the patellofemoral groove  27 , and as shown in  FIG. 9  it is offset from a central axis  107  of the femoral component  12 . The central axis  107  represents a center line between the outer edges of the medial and lateral condyles  90 ,  92 . In the embodiment shown in  FIG. 9 , the offset distance  109  is approximately 1-2 mm, although other offset distances may be used depending on the desired line of tracking for the patient&#39;s patella. Having the center of the patellofemoral groove  27  offset toward the lateral side works in concert with the narrower lateral condyle  92 , the combination of which helps provide a more anatomic tracking for the patient&#39;s patella. The can reduce stress on the patellar tendon and in at least some cases allow the patient&#39;s own patella to be resurfaced without the need for a patellar implant. 
     In  FIG. 9 , section lines  10 - 10  and  11 - 11  show the orientations for  FIGS. 10 and 11 , respectively.  FIG. 10  shows a side sectional view of the knee system  10 , and in particular, a section taken through the medial condyle  90  of the femoral component  12 , the medial tibial insert  20 , and the medial side  36  of the tibial tray  16 . The sectional view of the medial condyle  90 , is shown in  FIG. 10  in a sagittal plane view. In the embodiment shown in  FIG. 10 , the articular surface  96  of the medial condyle  90  has two distinct radii  110 ,  112 . The radius  110  is generally constant, and sweeps over approximately 120° of the articular surface  96 . Near the posterior side of the articular surface  96 , the radius changes and becomes much smaller to further accommodate deep flexion of the knee. 
       FIG. 11  shows a sectional view of the lateral condyle  92 , also through a sagittal plane. In this view, the lateral femoral articular surface  98  is shown as a curvilinear line  114 . In the embodiment shown in  FIG. 11 , the line  114  includes a plurality of radii which are specifically chosen to mimic the natural curvature of the articulating surface of the lateral condyle of an anatomic knee. Both the articulating surface  98  of the lateral femoral condyle  92  and the articulating surface  96  of the medial femoral condyle  90  may have a different radius or radii than those illustrated in the embodiments shown in the drawing figures. The specific selection of articulating surface geometry may depend on a number of factors, including whether one or more of the tibial inserts is movable as discussed above, what the configuration of the mating articular surface of the tibial insert or inserts is, and whether the tibial insert system is one piece or has separate medial and lateral components. 
     The components described in the knee system  10 , and the components of other embodiments of the present invention, may be made from any material having the engineering properties and physiologic compatibility desired for such an implant. For example, various metals, such as cobalt chrome and titanium alloys, can be used. One or more of the surfaces of these metal components can be porous coated or covered with hydroxyapatite, or other materials known to facilitate bone growth. Ceramic materials may also be used, as well as polymeric materials, particularly for a tibial insert system. It should also be noted that as used herein, a “sagittal” plane need not bisect the body into two equal halves; rather, it refers to a plane cuts anywhere through the body in an anterior-posterior direction. Therefore sections viewed in a sagittal plane are viewed in a medial-lateral direction. Similarly, as used herein, a “coronal” plane need not bisect the body into two equal halves; rather, it refers to a plane cuts anywhere through the body in a medial-lateral direction. Therefore sections viewed in a coronal plane are viewed in an anterior-posterior direction. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.