Patent Publication Number: US-2022211509-A1

Title: Orthopaedic system with medial pivoting insert

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. patent application Ser. No. 16/802,091 entitled “ORTHOPAEDIC SYSTEM WITH MEDIAL PIVOTING INSERT”, filed Feb. 26, 2020, which is incorporated herein by reference. U.S. patent application Ser. No. 16/802,091 is a non-provisional application based upon U.S. provisional patent application Ser. No. 62/810,570, entitled “ORTHOPAEDIC SYSTEM WITH MEDIAL PIVOTING INSERT”, filed Feb. 26, 2019, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to orthopaedic systems, and, more particularly, to orthopaedic systems for performing knee replacement surgery. 
     2. Description of the Related Art 
     Orthopaedic systems are known that are used to improve functions of joints in the body, such as the knee, that have been diminished due to injury and/or disease. For repairing the knee, an orthopaedic system may include an insert that is coupled to the tibia and a femoral component that is coupled to the femur. The femoral component bears on the insert to mimic the natural movement of the knee. While many orthopaedic systems provide the patient with a functional knee, known orthopaedic systems often have dynamic characteristics that do not mimic the natural knee. 
     What is needed in the art is an orthopaedic system that can closely mimic the natural movement of the knee following implantation. 
     SUMMARY OF THE INVENTION 
     The present invention provides an orthopaedic system with an insert that is asymmetric to allow medial pivoting that closely mimics the natural movement of the knee. 
     In some exemplary embodiments provided according to the present invention, an orthopaedic system includes an insert defining an anterior-posterior centerline and including: a medial half on one side of the centerline and defining a medial shape, the medial half having a medial articular surface defining a medial dwell region; and a lateral half on an opposite side of the centerline and defining a lateral shape that differs from the medial shape, the lateral half having a lateral articular surface. A femoral component includes a medial condylar portion bearing on the medial articular surface and a lateral condylar portion bearing on the lateral articular surface. The insert is configured to substantially limit anterior-posterior translation of the femoral component and define a pivot axis that extends through the medial dwell region. The insert is configured such that rotation of the lateral articular surface follows an arcuate path about the pivot axis. The medial condylar portion and the medial articular surface define a maximum medial clearance therebetween and the lateral condylar portion and the lateral articular surface define a maximum lateral clearance therebetween that is greater than the maximum medial clearance. 
     In some exemplary embodiments provided according to the present invention, an orthopaedic system includes an insert defining an anterior-posterior centerline and including: a medial half on one side of the centerline and defining a medial shape, the medial half having a medial articular surface defining a medial dwell region; a lateral half on an opposite side of the centerline and defining a lateral shape that differs from the medial shape, the lateral half having a lateral articular surface; and an anterior stabilizing surface formed adjacent to an anterior of the insert and formed as a sloped surface that extends downwardly toward a posterior of the insert, the anterior stabilizing surface extending downwardly toward the posterior at a slope angle of between 4° and 8°. A femoral component includes a medial condylar portion bearing on the medial articular surface and a lateral condylar portion bearing on the lateral articular surface. The insert is configured to substantially limit anterior-posterior translation of the femoral component and define a pivot axis that extends through the medial dwell region. The insert is configured such that rotation of the lateral articular surface follows an arcuate path about the pivot axis. 
     One possible advantage that may be realized by exemplary embodiments provided according to the present invention is that rotation of the femoral component closely mimics the natural movement of the knee. 
     Another possible advantage that may be realized by exemplary embodiments provided according to the present invention is that the insert stabilizes the femoral component in the anterior-posterior direction to reduce the risk of implant shift. 
     Yet another possible advantage that may be realized by exemplary embodiments provided according to the present invention is that both internal and external rotation can occur over a defined rotation range without impingement by the insert on the condylar portions of the femoral component. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view from a lateral side of an orthopaedic system including an insert and a femoral component bearing on the insert, provided in accordance with the present invention; 
         FIG. 2  is a perspective view from a medial side of the orthopaedic system of  FIG. 1 ; 
         FIG. 3  is a posterior perspective view of the orthopaedic system of  FIGS. 1-2 ; 
         FIG. 4  is a perspective view from the anterior of the orthopaedic system of  FIGS. 1-3 ; 
         FIG. 5  is another perspective view of the orthopaedic system of  FIGS. 1-4 ; 
         FIG. 6  is a perspective view of the posterior of the insert of the orthopaedic system of  FIGS. 1-5 ; 
         FIG. 7  is an anterior view of the insert of  FIGS. 1-6 ; 
         FIG. 8  is a posterior view of the insert of  FIGS. 1-7 ; 
         FIG. 9  is a top view of the insert of  FIGS. 1-8 ; 
         FIG. 10  is a bottom view of the insert of  FIGS. 1-9 ; 
         FIG. 11  is a lateral view of the insert of  FIGS. 1-10 ; 
         FIG. 12  is a medial view of the insert of  FIGS. 1-11 ; 
         FIG. 13  is a top view of the insert of  FIGS. 1-12  with arrows illustrating pivoting movement of the insert provided according to the present invention compared to an insert configured for center pivoting movement of a femoral component; 
         FIG. 14  is a medial view of the orthopaedic system of  FIGS. 1-5 ; 
         FIG. 15  is a lateral view of the orthopaedic system of  FIGS. 1-5 and 14 ; 
         FIG. 16  is a cross-sectional view of the orthopaedic system of  FIG. 14  taken along line  16 - 16 ; 
         FIG. 17  is a cross-sectional view of the orthopaedic system of  FIG. 15  taken along line  17 - 17 ; 
         FIG. 18  is a perspective view of various inserts for an orthopaedic system; 
         FIG. 19  is a close-up posterior view of the orthopaedic system of  FIGS. 1-5 and 14-17 ; 
         FIG. 20A  is a perspective view of the orthopaedic system of  FIGS. 1-5, 14-17, and 19  in a neutral, non-pivoted position; 
         FIG. 20B  is a perspective view of the orthopaedic system of  FIG. 20A  after 13° of external pivoting; and 
         FIG. 20C  is a perspective view of the orthopaedic system of  FIG. 20A  after 10° of internal pivoting. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to  FIGS. 1-5 , there is shown an exemplary embodiment of an orthopaedic system  100  for repairing a knee that generally includes an insert  200  and a femoral component  300  bearing on the insert  200 . The insert  200  and the femoral component  300  may both comprise one or more biocompatible materials including, but not limited to, titanium, stainless steel, cobalt chrome, ultra-high molecular weight polyethylene, and polyether ether ketone. As can be seen, the femoral component  300  includes a pair of condylar portions  310 ,  320  that bear on the insert  200 . The condylar portion  310  is, for example, a medial condylar portion that bears on a respective medial half  210  of the insert  200 , as will be described further herein. Similarly, the condylar portion  320  may be a lateral condylar portion that bears on a respective lateral half  220  of the insert  200 . Many different types of femoral components  300  are known, and any suitable configuration of femoral component may be incorporated in the orthopaedic system  100  provided in accordance with the present disclosure. With further reference to  FIGS. 1-5 , and referring now to  FIGS. 6-13  as well, it can be seen that the insert  200  defines an anterior-posterior centerline CL (most clearly illustrated in  FIGS. 6  and  9 ) that extends from an anterior  230  of the insert  200  to a posterior  240 . The medial half  210  of the insert  200  is located on a medial side of the centerline CL and the lateral half  220  of the insert  200  is located on an opposite, lateral side of the centerline CL. As illustrated in, for example,  FIG. 6 , the halves  210 ,  220  of the insert  200  are asymmetrical, i.e., the medial half  210  and the lateral half  220  are not mirror images of each other. 
     The medial half  210  has a medial articular surface  211  and the lateral half  220  has a lateral articular surface  221 . When the orthopaedic system  100  is formed, the medial condylar portion  310  of the femoral component  300  has a medial condylar surface  312  that bears on the medial articular surface  211  and the lateral condylar portion  320  has a lateral condylar surface  322  that bears on the lateral articular surface  221 . The medial articular surface  211 , the medial condylar surface  312 , the lateral articular surface  221 , and the lateral condylar surface  322  may each be generally flat in the medial-lateral direction. As used herein, “generally flat” corresponds to a radius in the medial-lateral direction ML of at least 45 mm, as illustrated in  FIG. 8 . Further, each of the surfaces  211 ,  312 ,  221 ,  322  may be dished in an anterior-posterior direction AP in the sense that the surfaces  211 ,  312 ,  221 ,  322  define a radius in the anterior-posterior direction AP that is less than 45 mm. In other words, the medial curvature of the surfaces  211 ,  312 ,  221 ,  322  in the medial-lateral direction ML is less than the anterior curvature in the anterior-posterior direction AP because the radius in the medial-lateral direction is greater than the radius in the anterior-posterior direction AP. Further, both condylar portions  310 ,  320  may be non-spherically curved and instead be, for example, cylindrically curved. 
     The medial articular surface  211  may include a medial valley  214  with a medial dwell region  216  defining a medial minimum thickness MT and the lateral articular surface  221  may include a lateral valley  224  defining a lateral minimum thickness LT that is less than the medial minimum thickness MT, which may be seen in  FIGS. 6 and 8 . It should be appreciated that the shapes of the articular surfaces  211 ,  221  may be adjusted, as desired and/or necessary, to accommodate differently shaped femoral components and/or patient anatomy, as is known in the art. Thus, it should be appreciated that the insert  200  and the femoral component  300  provided according to the present invention can be modified in a large variety of ways. 
     The insert  200  is configured to substantially limit medial anterior-posterior translation in the anterior-posterior direction AP. In other words, the orthopaedic system  100  is stabilized in the anterior-posterior direction AP so little, if any, translation of the insert  200  and femoral component  300  occur in the anterior-posterior direction AP until deeper flexion angles of the knee. The shape of the insert  200  is provided so a pivot axis PA (illustrated in  FIG. 13 ) extends through the medial dwell region  216  in the medial articular surface  211 . By placing the pivot axis PA through the medial dwell region  216  on the medial half  210 , rotation of the lateral articular surface  221  follows an arcuate path A about the pivot axis PA while still allowing translation of the lateral articular surface  221  about the medial dwell region  216 . In this respect, rotation of the orthopaedic system  100  closely mimics that of the natural knee, which exhibits a medial pivot a majority of the time. 
     One known implant system, commercially sold as the TRIATHLON® system by STRYKER®, is commonly used for knee repair. While the TRIATHLON® system provides stability in the medial-lateral direction, there is minimal stability in the anterior-posterior direction. The lack of stability in the anterior-posterior direction increases the feel of instability to the patient. 
     To substantially limit medial anterior-posterior translation, an anterior portion of the medial articular surface  211  of the insert  200  provided according to the present invention is shaped to closely conform with a corresponding anterior portion of the medial condylar surface  312 . This conformity between the surfaces  211  and  312  limits medial anterior-posterior translation and thus provides significant stability in the anterior-posterior direction AP without having to utilize, for example, a post. The lateral articular surface  221 , on the other hand, may be less conforming to the lateral condylar surface  322  to promote pivoting along the arcuate path A. 
     Referring specifically now to  FIGS. 11 and 12 , anterior stabilizing surfaces  215 ,  225  formed in the halves  210 ,  220  of the insert  200  are illustrated in further detail. The anterior stabilizing surfaces  215 ,  225  may be formed as sloped surfaces that extends downwardly toward the posterior  240  at a slope angle of between 4° and 8° such as, for example, a 6° slope angle. The anterior stabilizing surfaces  215 ,  225  may be formed adjacent to the anterior  230  of the insert  200  and brace the femoral component  300  against anterior-posterior movement, as can be appreciated from  FIGS. 1 and 2 . This further stabilization against anterior-posterior translation can reduce the risk of the implant system  100  failing following implantation. 
     Referring still to  FIGS. 1-13 , the medial half  210  may be formed with a raised medial surface  212  that defines a peak of the insert  200 . The raised medial surface  212  may, for example, extend generally vertical relative to a bottom  202  of the insert  200  and conform to the medial condylar portion  310 . The raised medial surface  212  may be located adjacent to the centerline CL near the anterior  230  of the insert  200 . Material may be removed from the medial half  210 , as illustrated in  FIG. 9 , to avoid impingement with the femoral component  300  during rotation, as will be described further herein. The raised medial surface  212  may define a height H, relative to the medial minimum thickness MT of the medial valley  214 , that is at least 10 mm, i.e., the raised medial surface  212  extends at least 10 mm above the lowest point of the medial valley  214 . The raised medial surface  212  defining the height H can satisfy the “jumping distance” requirement of 10 mm, as is known, to prevent anterior dislocation of the insert  200  and the femoral component  300 . The medial half  210  may also include a dished surface  213  adjacent to the posterior  240  of the insert  200  that has a curved dish formed therein. 
     The lateral half  220 , in contrast to the medial half  210 , may be formed with a generally smooth curved recess  222  that does not closely conform to the lateral condylar portion  320 . The lateral half  220  may also have a dished surface  223  adjacent the centerline CL and near the posterior  240  of the insert  200 . The lateral articular surface  221  may have a flat sagittal curvature. Thus, the lateral half  220  is shaped and configured to not conform closely with the lateral condylar portion  320 , which encourages rotation of the lateral articular surface  221  along the arcuate path A about the pivot axis PA. 
     From the foregoing, it should be appreciated that the insert  200  provided in accordance with the present disclosure has a shape that locates the pivot axis PA through the medial dwell region  216  of the medial half  210  of the insert  200  due to asymmetry of the medial half  210  and the lateral half  220 . In some embodiments, and referring now to  FIG. 13 , the insert  200  defines an anterior-to-posterior length APL between the anterior  230  and the posterior  240  and the pivot axis PA of the femoral component  300  is spaced from the posterior  240  by a pivot distance PD that is 32% to 37% of the anterior-to-posterior length APL, e.g., if the anterior-to-posterior length APL is 100 mm, the pivot axis PA may be spaced 32 cm to 37 cm from the posterior  240 . By shaping the insert  200  to place the pivot axis PA in this area of the medial half  210 , medial articulation (pivoting) can be relatively conforming and resist posterior-anterior translation following implantation. Medial pivoting of the lateral articular surface  221  along the arcuate path A about the pivot axis PA, as opposed to rotating motion about a central eminence that is common in known implants (shown on the left in  FIG. 13 ), also is similar to the natural articulation of the knee and is less prone to generating unnatural stresses in the region that can lead to tissue damage and/or implant failure. Thus, the insert  200  provided according to the present invention can be utilized in the orthopaedic system  100  to allow a movement range that closely mimics the natural movement of the knee. 
     Referring specifically now to  FIGS. 14-17 , various views of the orthopaedic system  100  provided according to the present invention are illustrated. As illustrated in  FIGS. 14 and 16 , the medial condylar portion  310  and the medial articular surface  211  define a maximum medial clearance MC therebetween. As illustrated in  FIGS. 15 and 17 , the lateral condylar portion  320  and the lateral articular surface  221  define a maximum lateral clearance LC therebetween. As can be appreciated from comparing  FIGS. 14 and 16  to  FIGS. 15 and 17 , the maximum lateral clearance LC may be greater than the maximum medial clearance MC due to the insert  200  being shaped so the medial articular surface  211  conforms closely to the shape of the medial condylar portion  310  while the lateral articular surface  221  is less conforming to the shape of the lateral condylar portion  320 . The close conforming between the medial articular surface  211  and the medial condylar portion  310  helps provide the previously described medial pivoting characteristics. 
     In some embodiments, and referring now to  FIG. 18 , an insert  1800  is provided that is similar to the previously described insert  200  but includes a post  1810  formed near a center of the insert  1800 . For comparison, the insert  200  is also illustrated in  FIG. 18 . The post  1810  may be formed, for example, by removing material from the center of the insert  1800  while maintaining asymmetry between a medial side  1820  and a lateral side  1830  of the insert  1800 . The post  1810  may be shaped to engage a corresponding cam formed in a femoral component that bears on the insert  1800 , similarly to known orthopaedic systems with posts. In other respects, the insert  1800  may be similar to the insert  200 , so further description is omitted for brevity. 
     Referring now to  FIG. 19 , a close-up posterior view of the orthopaedic system  100  is illustrated. As illustrated, each of the condylar portions  310 ,  320  of the femoral component  300  may have a corresponding concave patellar groove  311 ,  321  that extends through its respective condylar portion  310 ,  320 . As can be appreciated from  FIG. 19 , the patellar grooves  311 ,  321  may articulate and interact with the respective articular surfaces  211 ,  221  of the insert  200  throughout movement of the orthopaedic system  100 . The patellar groove  311  of the medial condylar portion  310  may closely conform to the medial articular surface  211 , to provide the medial pivot movement, while the patellar groove  321  of the lateral condylar portion  320  less closely conforms to the lateral articular surface  221  to allow pivoting along the arcuate path A. The femoral component  300  may define a sagittal curvature CS (illustrated in  FIG. 16 ) of no more than 40 mm and a coronal curvature CC (illustrated in  FIG. 19 ) of no more than 45 mm. Further, the sagittal and coronal shapes of the femoral component  300 , in some embodiments, are not spherical. By shaping the femoral component  300  in this manner, the orthopaedic system  100  can allow normal flexion while still providing medial pivoting. 
     As can be appreciated from  FIG. 19 , the insert  200  has a central ridge  250  with a medial ridge portion  251  on the medial half  210  and a lateral ridge portion  252  on the lateral half  220 . The medial ridge portion  251  has a different shape than the lateral ridge portion  252 , as will be described further herein. The concave patellar groove  311  of the medial condylar portion  310  faces the medial ridge portion  251  and the concave patellar groove  321  of the lateral condylar portion  320  faces the lateral ridge portion  252  for articulation. The medial ridge portion  251  has a region  253  formed therein that has less material than a corresponding region  254  of the lateral ridge portion  252  on the opposite side of the anterior-posterior centerline CL, i.e., the region  253  of the medial ridge portion  251  is not a mirror of the region  254  of the lateral ridge portion  252 , but has a recess or divot formed therein. 
     By forming the region  253  of the medial ridge portion  251  with less material than the corresponding region  254  of the lateral ridge portion  252 , external rotation is not undesirably prohibited by impingement between the medial condylar portion  310  and the medial ridge portion  251  of the central ridge  250 . This is in contrast to known orthopaedic systems, such as the previously described TRIATHLON® system, which have a symmetric central ridge. In such known designs, medial pivoting with combined anterior-posterior stability from close conformity would not be effective because the close conformity between the patellar groove of the medial condylar portion and the symmetric central ridge would interfere with rotation, i.e., the medial condylar portion would abut against the symmetric ridge during rotation and significantly shorten the rotation range. If the symmetric central ridge of known designs was modified to remove material that would impinge rotation, there would be a significant loss of medial-lateral stability during rotation of the lateral surfaces. The insert  200  provided according to the present invention, on the other hand, has an asymmetric central ridge  250  with material removed in the region  253  of the medial ridge portion  251 , compared to the corresponding region  254  of the lateral ridge portion  252 , so there is not impingement between the femoral component  300  and the central ridge  250  during the desired rotation range while maintaining the anterior-posterior stability from close conformity on the medial half  210 . Thus, the region  253  of the medial ridge portion  251  is configured to avoid impingement of the central ridge  250  on the medial condylar portion  310  during rotation. 
     Referring now to  FIGS. 20A-20C , the orthopaedic system  100  is illustrated in various stages of pivoting.  FIG. 20A  illustrates the orthopaedic system  100  in a neutral position where there has been no pivoting, i.e., there is 0° of pivoting.  FIG. 20B , on the other hand, illustrates the orthopaedic system  100  after 13° of posterior pivoting (which may also be called “external pivoting”). As can be appreciated from  FIG. 20B , compared to  FIG. 20A , pivoting of the lateral articular surface  321  has followed the arcuate path A about the pivot axis PA.  FIG. 20C  illustrates the orthopaedic system  100  after 10° of anterior pivoting (which may also be called “internal pivoting”). Similarly to  FIG. 20B , it can be seen in  FIG. 20C  that the lateral articular surface  221  has followed the arcuate path A about the pivot axis PA. Due to there being less material in the region  253  of the medial ridge portion  251  than the corresponding region  254  of the lateral ridge portion  252 , both internal and external rotation are allowed across the desired range of rotation. In some embodiments, the femoral component  300  is limited to 25° of rotation about the pivot axis PA, i.e., the range of rotation is 25°. As can be appreciated from  FIG. 20B , external rotation to the position in  FIG. 20B  would not be possible if the medial ridge portion  251  had the same shape as the lateral ridge portion  252 , i.e., more material in the region  253 , because the patellar groove  311  of the medial condylar portion  310  would abut against the medial ridge portion  251  and prevent further rotation. Thus, the medial ridge portion  251  being a different shape than the lateral ridge portion  252  allows close conforming between the medial condylar portion  310  and the medial articular surface  311  to provide anterior-posterior stability and medial pivoting without interfering with the natural range of rotation. 
     From the foregoing, it should be appreciated the orthopaedic system  100  provided according to the present invention provides a medial pivoting implant system that has improved anterior-posterior stability due to close conforming between the medial condylar portion  310  and the medial articular surface  211  while still allowing the natural range of rotation of the knee. The shape of the medial half  210  is different than the shape of the lateral half  220  to provide the described location of the medial dwell region  216  and close conformity for medial pivoting and also eliminates the presence of material that would obstruct external rotation. Thus, the orthopaedic system  100  provided according to the present invention allows natural movement of the knee while improving anterior-posterior stability. 
     While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.