Patent Publication Number: US-2022218490-A1

Title: Cam stabilized knee prosthesis

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of the filing date of U.S. Provisional Patent Application No. 63/136,353 filed Jan. 12, 2021, the disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to orthopedics devices and, more particularly, to knee prostheses. 
     During articulation of a natural knee joint, flexion between the tibia and the femur takes place about a transverse axis while some relative rotation between the tibia and the femur occurs about a longitudinal axis. The rotation about the transverse axis through flexion and extension is not as simple as that of a hinge of a door in which its rotational axis remains stationary. Instead, the transverse axis of the knee moves in the anteroposterior direction during flexion and extension. In this regard, as the knee joint flexes from an extended position, the center of contact between the femur and tibial plateau moves posteriorly. This is known as femoral roll-back which is generally facilitated by the posterior cruciate ligament. Femoral roll-back is the knee&#39;s natural mechanism for maximizing the range of possible flexion and for also maximizing efficiency of the extensor mechanism. 
     Total knee arthroplasty commonly involves the sacrifice of the anterior and posterior cruciate ligaments. The cruciate ligaments, in addition to providing for femoral roll-back, also facilitate the natural internal-external rotation of the tibia relative to the femur and resist paradoxical movement between these bones during certain activities, such as those involving a heel strike. Since the removal of these ligaments has the attendant consequence of removing their kinematic functionality, it is often the objective of total knee prostheses to gain some measure of functionality back. 
     Conventional knee prostheses often utilize a cam and post mechanism to account for the elimination of the cruciate ligaments. Some tibial baseplates even include a spherical member at the end of its post to articulate with a spherical cavity in a femoral component to help facilitate internal-external rotation. However, in prostheses such as these, the post member must have a considerable height to articulate with the femoral component which can result in the post bearing significant cyclic loads. Moreover, femoral roll-back may be precluded by being constrained. 
     Although several knee prostheses have been developed over the years, improvements are still possible. A need exists for knee prostheses capable of more closely imitating the natural knee. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     A total knee prosthesis described in this disclosure includes a femoral component and a tibial component. The femoral component includes a spherical member and a cam member disposed within an intercondylar notch. The tibial component includes a post defining a recess thereon. The recess is sized to receive the spherical member. The spherical member is adapted to articulate with the recess of the post, thus allowing the femoral component to articulate relative to the tibial component. The spherical member may rotate within the recess until a degree of flexion in which the cam member contacts the post of the tibial component, wherein further flexion may cause the spherical member to translate within the recess. The articulation between the spherical member and the post occurs at a distal portion of the spherical member and the cam member contacts the post at a height such that a moment force may be applied to the tibial most that may not require additional support to withstand. 
     In certain embodiments, a total knee prosthesis may include a femoral component having an anterior flange, a first femoral condyle, a second femoral condyle, a spherical member and a cam member. The first and second femoral condyles may extend from the anterior flange and at least partially defining an intercondylar recess therebetween. The spherical member and cam member may be positioned within the intercondylar recess such that the cam member is offset from the spherical member in a posterior direction. The total knee prosthesis may further include a tibial component having a bone contact side and an articular side. The articular side may have first and second tibial condyles and a post extending therefrom. The post may have a post recess extending into an end thereof and may be sized to receive the spherical member. The post recess may define an anterior spherical portion and a posterior runout portion. The anterior spherical portion may have a radius of curvature in a sagittal plane extending from the post. The posterior runout portion may be linear and tangent to the anterior spherical portion in the sagittal plane. 
     The tibial component may include a baseplate and an insert connectable to the baseplate. The baseplate may define the bone contact side of the tibial component. The insert may define the articular side of the femoral component. The insert may have the post and first and second tibial condyles. The insert may include a base configured to connect to the tibial baseplate. The post may extend from the base. The post and the base may form a monolithic structure. The baseplate may include a plurality of pegs extending from the bone contact side. 
     The posterior runout portion may define a posterior extent of the recess. The anterior spherical portion may define an anterior extent of the recess. The post may have a sidewall extending in an inferior-superior direction and defining a perimeter thereof. The spherical member may articulate with the anterior spherical portion and posterior runout portion. The cam may articulate with a posterior aspect of the sidewall through flexion and extension of the total knee prosthesis. The cam may engage the posterior aspect of the sidewall at 90 degrees of flexion. The spherical member may articulate with the spherical portion at −15 to 90 degrees of flexion and may articulate with the runout portion at 90 to 150 degrees of flexion. The spherical member may both rotate and translate in an anteroposterior direction relative to the spherical and runout portions of the post cavity. The spherical member may have a radius of curvature of 7.6 mm. The radius of curvature of the spherical portion may be 7.6 mm. 
     The femoral component may be adapted to define a first position in which the spherical member is positioned within the anterior spherical portion of the post and the cam member does not contact the post. The femoral component may be adapted to define a second position in which the spherical member is positioned within the anterior spherical portion of the post and the cam member contacts that post. The femoral component may be adapted to define a third position in which the spherical member is positioned within the posterior runout portion and the cam member contacts the post. The femoral component may be adapted to define a fourth position in which the spherical member does not contact the recess of the post and the cam member contacts the post. A distal portion of the spherical member may contact and articulate with the recess of the post of the tibial component. The posterior runout portion may include medial and lateral portions curving in a superior direction forming a cylindrical shape within the recess. The radius of curvature of the medial and lateral portions of the posterior runout portion may be substantially equal to the radius of curvature of the spherical member. 
     In certain alternative embodiments, a total knee prosthesis may include a femoral component having an anterior flange, a first femoral condyle, a second femoral condyle, and a spherical member, the first and second femoral condyles extending from the anterior flange and at least partially defining an intercondylar recess therebetween. The spherical member may be positioned within the intercondylar recess. The total knee prosthesis may further include a tibial component having a bone contact side and an articular side. The articular side may have first and second tibial condyles and a post extending therefrom. The post may have a post recess extending into an end thereof and sized to receive the spherical member. The post recess may define an anterior spherical portion and a posterior runout portion. The anterior spherical portion may be concavely formed in the post. The posterior runout portion may be linear and tangent to the anterior spherical portion in the sagittal plane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional side view of a knee prosthesis taken along a midline thereof and according to an embodiment of the disclosure. 
         FIGS. 2A-B  are perspective superior and inferior views, respectively, of a femoral component of the knee prosthesis of  FIG. 1 . 
         FIG. 3A  is a perspective superior view of a tibial component of the knee prosthesis of  FIG. 1 . 
         FIG. 3B  is perspective superior view of an insert of the tibial component of  FIG. 3A   
         FIG. 3C  is a perspective side view of the insert of  FIG. 3B . 
         FIGS. 4A-E  illustrate the knee prosthesis of  FIG. 1  in first, second, third, fourth and fifth positions of flexion, respectively. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, when referring to bones or other parts of the body, the term “proximal” means closer to the heart and the term “distal” means more distant from the heart. The term “inferior” means towards the feet and the term “superior” means towards the head. The term “medial,” when used in connection with a component or a patient&#39;s anatomy, refers to a side or region facing the center of the patient. The term “lateral,” when used in connection with a component or a patient&#39;s anatomy, refers to a side or region facing toward the patient&#39;s side, i.e., away from the center of the patient. The term “anterior,” when used in connection with a component or a patient&#39;s anatomy, refers to a side or region facing the front of the patient. The term “posterior,” when used in connection with a component or a patient&#39;s anatomy, refers to a side or region facing the rear of the patient. As used herein, the terms “substantially,” “generally,” “approximately,” and “about” are intended to mean that slight deviations from absolute are included within the scope of the term so modified. 
       FIG. 1  illustrates an embodiment of a stabilized knee prosthesis  100  for replacing a natural knee joint. Knee prosthesis  100  includes a femoral component  110  and a tibial component  160 . In operation, femoral component  110  may articulate relative to tibial component  160 . Femoral component  110  is adapted to be attached to a distal end of a femur, whereas tibial component  150  is adapted to be attached to a proximal end of a tibia in a well-known manner. Both the distal end of the femur and the proximal end of the tibia may be resected or prepared before implantation of knee prosthesis  100 . In some embodiments, knee prosthesis  100  is wholly or partly made of a substantially rigid material, such as titanium, titanium alloy, chrome-cobalt alloy, cobalt-chrome-molybdenum alloys (e.g., cobalt-chromium-molybdenum alloy sold under the trademark Vitallium®), polyethylene, polyether ether ketone (PEEK), or any suitable metal or polymer. 
       FIGS. 2A-B  illustrate femoral component  110  in greater detail according to an embodiment of the disclosure. Femoral component  110  extends from an anterior end  112  to a posterior end  114  defining a length of the femoral component  110 . Femoral component  110  further extends from a medial edge  116  to a lateral edge  118  defining a width of the femoral component  110 . Femoral component  110  includes an anterior flange  120  which extends along the width of femoral component  110  and defines an anterior and superior terminal end of the femoral component. Femoral component  110  further includes a medial condyle  122  that extends from flange  120  on a medial side of the femoral component. More specifically, medial condyle  122  has a central portion  124  that extends from flange  120  generally in a posterior direction from anterior flange  120 , and a posterior portion  126  which extends from central portion  124  generally in a posterior and superior direction. Femoral component  110  further includes a lateral condyle  132  that extends from anterior flange  120  on a lateral side of femoral component  110 . Lateral condyle  132  has a central portion  134  that extends from flange  120  generally in a posterior direction, and a posterior portion  136  extending from central portion  134  generally in a posterior and superior direction. It is noted that the posterior portions  126 ,  136  of the medial and lateral condyles  122 ,  132  respectively define posterior and superior terminal ends of femoral component  110  opposite that of anterior flange  120 . 
     Medial condyle  122  and lateral condyle  132  define an intercondylar notch  140  therebetween. Anterior flange  120  extends from anterior end  112  to the anterior-most point of intercondylar notch  140 . In this regard, anterior flange  120  defines an anterior extent of intercondylar notch  140 . Medial and lateral condyles  122 ,  132  begin extending from anterior flange  120  at the length of femoral component  110  where intercondylar notch  140  begins. That is, anterior flange  120  ends and condyles  122 ,  132  begin along an axis extending across the width of femoral component  110  tangential to the anterior-most point of intercondylar notch  140 . 
     Femoral component  110  further includes a spherical member  142  and a cam member  146  positioned within the intercondylar notch  140 . Spherical member  142  is connected to condyles  122 ,  132  via flanges  125 ,  135  that extend superiorly from an inner edges of condyles  122 ,  132 , respectively, and a horizontal post  127  that extends from the flanges  125 ,  135 . Spherical member  142  is positioned on post  127  so that its spherical curvature is positioned within the intercondylar notch  140  and pointing in an inferior direction. Spherical member  142  is also positioned superior to the condyles  122 ,  132 . Spherical member  142 , as shown, is a partial sphere such that a superior side defines a planar surface  144 . This allows femoral component  110  to be placed directly against a planar resected surface of a femur. In some examples, the spherical member  142  may have a radius of curvature of 5-10 millimeters. In one particular example, such as the example depicted in the figures, spherical member  142  may have a radius of curvature of 7.6 millimeters. 
     The cam member  146 , as in the example shown, may be offset from the spherical member  142  in a posterior direction. In other words, the cam member  146  may be disposed within the intercondylar notch  140  nearer the posterior terminal end formed by the medial and lateral condyles  122 ,  132  than the spherical member  142 . Spherical member  142  and cam member  146  may contact and articulate with components of tibial component  160  when knee prosthesis  100  is in an assembled configuration, as described in greater detail below. In this regard, cam member  146  includes a concavely curved anterior face that matches the convex posterior curvature of post  180  of tibial component  160 . 
       FIG. 3A  illustrates tibial component  160  in greater detail according to an embodiment of the disclosure. Tibial component  160  generally includes a baseplate  162  coupled to an insert  163 . Baseplate  162  defines a bone contact side configured to contact the tibia when in an implanted configuration. The baseplate may include a plurality of pegs (not shown) extending from the baseplate on the bone contact side to anchor the tibial component into a bone when in the implanted configuration. 
       FIGS. 3B-C  illustrate insert  163  in greater detail. Insert  163  includes a base  164 . The base  164  defines an articular side  172  and a baseplate connection side. Base  164  includes a medial tibial condyle  174  and a lateral tibial condyle  176  on articular side  172 . Medial and lateral tibial condyles  174 ,  176  are adapted to receive and support medial and lateral femoral condyles  122 ,  132 , respectively. Femoral condyles  122 ,  132  may articulate with respective tibial condyles  174 ,  176 . Insert  163  further includes a post  180  extending from the base  164  of insert  163  on articular side  172 . In the illustrated embodiment, post  180  and base  164  are monolithic; however, it is also contemplated that post  180  and base  164  may be modular components configured to couple and decouple from each other. Post  180  defines a sidewall  181  which extends from base  164  of insert  163  in a superior direction, the sidewall  181  defining a perimeter of the post  180 . Post  180  has an ovular shape such that its posterior and anterior ends are convexly curved. When knee prosthesis  100  is in an assembled configuration, cam member  146  of femoral component  110  is configured to articulate with a posterior aspect of sidewall  181  of post  180  through flexion and extension of knee prosthesis  100 . 
     Post  180  defines a recess  182  extending into a superior end of the post  180  (i.e., an end opposite the end coupled to articular side  172 ). The recess  182  is sized to fit spherical member  142 . The post recess  182  further defines an anterior spherical portion  184  and a posterior runout portion  186 . The anterior spherical portion  184  has a radius of curvature in a sagittal plane extending through the post  180 , as best shown in  FIG. 1 . In some examples, anterior spherical portion  184  may have a radius of curvature complimentary to that of spherical member  142 . In this regard, spherical portion  184  may have the same radius of curvature, such as, for example, 5-10 millimeters, or more specifically 7.6 millimeters as in the example depicted. The anterior spherical portion  184  may define an anterior extent of the post recess  182 . The posterior runout portion  186  is linear and tangent to the anterior spherical portion  184  in the sagittal plane, as best shown in  FIG. 1 . The posterior runout portion  186  may define a posterior extent of the post recess  182 . Posterior runout portion  186  may include medial and lateral portions extending in a superior direction so as to form a cylindrical shape. Such a cylindrical shape may be sized to fit the spherical member  142  (e.g., the cylindrical posterior runout portion have a radius of curvature substantially equal to the radius of curvature of the spherical member) to allow translation in a single direction. When knee prosthesis  100  is in an implanted configuration, spherical member  142  of femoral component  110  is configured to articulate with anterior spherical portion  184  and posterior runout portion  186  of post recess  182 . Spherical member  142  may rotate and translate in an anteroposterior direction relative to anterior spherical portion  184  and posterior runout portion  186 , as described below in further detail. In this regard, prosthesis  100  provides for femoral roll-back. 
     As seen in  FIGS. 4A-E , knee prosthesis  100  substantially mimics the kinematics of the natural knee through flexion and extension. When knee prosthesis  100  is implanted in a patient, femoral component  110  is in contact with and articulates with respect to tibial component  160 . In this regard, femoral condyles  122 ,  132  contact and articulate with tibial condyles  174 ,  176 . Also, post  180  extends into intercondylar notch  140  so that spherical member  142  is positioned within cavity  182 . When prosthesis  100  is articulated through a range of motion in flexion and extension spherical member  142  articulates with spherical portion  184  and runout portion  186 . Moreover, in greater degrees of flexion, such as 90 degrees and beyond, cam member  146  contacts and articulates with post  180 .  FIGS. 4A-E  illustrate knee prosthesis  100  in various positions, each position representing the configuration of knee prosthesis  100  according to a degree of flexion of the knee. 
     Knee prosthesis  100  is shown in a first position in  FIG. 4A  in which the knee is fully extended (i.e., zero degrees of flexion). In the first position, spherical member  142  is located in anterior spherical portion  184  of post recess  182 . In the first position, cam member  146  does not contact post  180 . Further, anterior flange  120  is positioned anteriorly relative to other components of knee prosthesis  100  and extends in a superior direction. As knee prosthesis  100  is flexed from the first position, spherical member  142  articulates with anterior spherical portion  184  of post recess  182  and cam member  146  rotates with femoral component  110  toward post  180 , as illustrated in subsequent figures. While in this position, spherical member  142  and spherical portion  184  of recess  182  not only allows femoral component to rotate in flexion and extension, but also with internal/external rotation. 
     Knee prosthesis  100  is shown in a second position in  FIG. 4B  in which the knee prosthesis  100  is flexed at ninety degrees of flexion. In the second position, spherical member  142  is disposed in anterior spherical portion  184  of post recess  182  similar to the first position. Upon transitioning from the first position to the second position, spherical member  142  articulates with anterior spherical portion  184  of post recess  182 . In some examples, spherical member  142  may articulate within anterior spherical portion  184  between −15 degrees of flexion (i.e., hyperextension) and 90 degrees of flexion. In the second position, femoral component  110  has articulated and rotated relative to the first position, such that the anterior flange  120  is positioned superior to the other components of knee prosthesis  100  extending in a posterior direction, and cam member  146  contacts the sidewall  181  of post  180 . Due to such contact between the cam member  146  and the sidewall  181  of post  180 , additional flexion of the knee beyond ninety degrees shown in the second position may cause translation of the spherical member  142  within the post recess  182 , as will be shown in subsequent figures. 
       FIGS. 4C-E  illustrate knee prosthesis  100  in various positions greater than ninety degrees of flexion. For example,  FIG. 4C  illustrates knee prosthesis  100  in a third position in which anterior flange  120  extends in a posterior and inferior direction. Upon transitioning from the second position to the third position, spherical member  142  translates within the post recess  182 . In the third position, cam member  146  remains in contact and articulates with sidewall of post  180 , and spherical member  142  is positioned within the posterior runout portion  186  of post recess  182 . In some examples, spherical member  142  may articulate with posterior runout portion  186  of post recess  182  between 90 degrees of flexion and 150 degrees of flexion. 
       FIG. 4D  illustrates knee prosthesis  100  in a fourth position in which anterior flange  120  extends further in a posterior and inferior direction relative to the third position. Further in the fourth position, spherical member  142  is positioned further in the posterior direction along posterior runout portion  186  relative to the third position due to articulation of the spherical member  142  upon transitioning from the third position to the fourth position. In the fourth position, cam member  146  remains in contact and articulates with sidewall  181  of post  180 . 
       FIG. 4E  illustrates knee prosthesis  100  in a fifth position in which anterior flange  120  extends still further in a posterior and inferior direction relative to the fourth position. In the fifth position, cam member  146  remains in contact with the sidewall  181  of post  180 , and spherical member  142  is displaced from post  180  and no longer in contact with post recess  182  upon transitioning from the fourth position to the fifth position. It should be understood that knee prosthesis  100  may assume any and each of the above-described positions as knee prosthesis  100  transitions from full extension (as shown in  FIG. 4A ) to full flexion and vice versa. 
     The structure of the knee prosthesis  100  allows for articulation between the femoral condyles  122 ,  132  and the tibial condyles  174 ,  176  as well as between post  180  and both cam member  146  and spherical member  142 . This articulation operates to provide femoral roll-back of femoral component  110 , particularly as demonstrated between  FIGS. 4C and 4E . In this regard, contact between the condyles can translate posteriorly (i.e., roll-back) in a similar manner to that of a natural knee. This is facilitated by the similar kinematics of spherical member  142  in which spherical member  142  rolls back from spherical portion  184  to runout portion  186 . The articulation of cam member  146  on the posterior aspect of post  180  further facilitates the roll-back articulation. 
     In addition to these kinematics, the positioning of the spherical member  142  within intercondylar notch  140  of femoral component  110  minimizes the length of the post  180  needed for this sort of articulation. This is because the spherically curved surface of spherical member  142  is positioned inferior with respect to its center of curvature rather than superior to such center of curvature. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.