AU2015203508A1 - Orthopaedic knee prosthesis having controlled condylar curvature - Google Patents

Abstract

An orthopaedic knee prosthesis includes a femoral component having a condyle surface. The condyle surface is defined by one or more radii of curvatures, which are controlled to reduce or delay the onset of anterior translation of the femoral component relative to a tibial bearing. 2 - ~ ~ 10 Fig. 1

Description

1 ORTHOPAEDIC KNEE PROSTHESIS HAVING CONTROLLED CONDYLAR CURVATURE [0001] This Application is a divisional of the present applicant's Australian Patent Application No.2009202631 and the whole contents thereof are included herein by reference. TECHNICAL FIELD [0002] The present disclosure relates generally to orthopaedic prostheses, and particularly to orthopaedic prostheses for use in knee replacement surgery. BACKGROUND [0003] Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged natural joint is replaced by a prosthetic joint. A typical knee prosthesis includes a tibial tray, a femoral component, and a polymer insert or bearing positioned between the tibial tray and the femoral component. Depending on the severity of the damage to the patient's joint, orthopaedic prostheses of varying mobility may be used. For example, the knee prosthesis may include a "fixed" tibial bearing in cases wherein it is desirable to limit the movement of the knee prosthesis, such as when significant soft tissue loss or damage is present. Alternatively, the knee prosthesis may include a "mobile" tibial bearing in cases wherein a greater degree of freedom of movement is desired. Additionally, the knee prosthesis may be a total knee prosthesis designed to replace the femoral-tibial interface of both condyles of the patient's femur or a uni-,compartmental (or uni-condylar) knee prosthesis designed to replace the femoral-tibial interface of a single condyle of the patient's femur. [0004] The type of orthopedic knee prosthesis used to replace a patient's natural knee may also depend on whether the patient's posterior cruciate ligament is retained or sacrificed (i.e., removed) during surgery. For example, if the patient's posterior cruciate ligament is damaged, diseased, and/or otherwise removed during surgery, a posterior stabilized knee prosthesis may be used to provide additional support and/or control at later 2 degrees of flexion. Alternatively, if the posterior cruciate ligament is intact, a cruciate retaining knee prosthesis may be used. [0005] Typical orthopaedic knee prostheses are generally designed to duplicate the natural movement of the patient's joint. As the knee is flexed and extended, the femoral and tibial components articulate and undergo combinations of relative anterior- posterior motion and relative internal-external rotation. However, the patient's surrounding soft tissue also impacts the kinematics and stability of the orthopaedic knee prosthesis throughout the joint's range of motion. That is, forces exerted on the orthopaedic components by the patient's soft tissue may cause unwanted or undesirable motion of the orthopaedic knee prosthesis. For example, the orthopaedic knee prosthesis may exhibit an amount of unnatural (paradoxical) anterior translation as the femoral component is moved through the range of flexion. [0006] In a typical orthopaedic knee prosthesis, paradoxical anterior translation may occur at nearly any degree of flexion, but particularly at mid to late degrees of flexion. Paradoxical anterior translation can be generally defined as an abnormal relative movement of a femoral component on a tibial bearing wherein the contact "point" between the femoral component and the tibial bearing "slides" anteriorly with respect to the tibial bearing. This paradoxical anterior translation may result in loss of joint stability, accelerated wear, abnormal knee kinematics, and/or cause the patient to experience a sensation of instability during some activities. SUMMARY [0007] According to one aspect, an orthopaedic knee prosthesis may include a femoral component and a tibial bearing. The femoral component may have a condyle surface curved in the sagittal plane. The tibial bearing may be a bearing surface configured to articulate with the condyle surface of the femoral component. The condyle surface of the femoral component may be configured to contact the bearing surface at a first contact point on the condyle surface at a first degree of flexion less than about 30 degrees. The condyle surface of the femoral component may be also be configured to contact the bearing surface at a second contact point on the condyle surface at a second degree of flexion greater than 3 about 45 degrees. Additionally, the condyle surface of the femoral component may be configured to contact the bearing surface at a third contact point on the condyle surface at a third degree of flexion greater than the second degree of flexion. In some embodiments, the first degree of flexion may be in the range of 0 degrees to 10 degrees, the second degree of flexion may be in the range of 60 degrees to 70 degrees, and the third degree of flexion may be in the range of 80 degrees to 110 degrees. For example, in one particular embodiment, the first degree of flexion is about 5 degrees, the second degree of flexion is about 65 degrees, and the third degree of flexion is about 90 degrees. [0008] The condyle surface in the sagittal plane may have a first radius of curvature at the first contact point, a second radius curvature at the second contact point, and a third radius of curvature at the third contact point. In some embodiments, the third radius of curvature may be greater than the second radius of curvature by at least 0.5 millimeters. Additionally, the condyle surface in the sagittal plane between the first contact point and the second contact point may include a plurality of curved surface sections. Each curved surface section may have a different radius of curvature. [0009] The plurality of curved surface sections may include an anterior-most curved surface section. In some embodiments, the radius of curvature of the anterior-most curved surface section may have a length greater than the radius of curvature of any other curved surface section of the plurality of curved surface sections. Additionally, in some embodiments, the length of the radius of curvature of each curved surface section posterior to the anterior-most curved surface section may be less than the length of the radius of curvature of an anteriorly-adjacent curved surface section. For example, in some embodiments, the length of the radius of curvature of each curved surface section posterior to the anterior-most curved surface section is less than the length of the radius of curvature of an anteriorly-adjacent curved surface section by a distance in the range of 0.1 millimeters to 5 millimeters, in the range of 1 millimeters to 3 millimeters, and/or about 1 millimeter. [0010] Each of the plurality of curved surface sections may subtend a corresponding angle. In some embodiments, each angle subtended by the plurality of curved surface sections being approximately equal. In other embodiments, the angle 4 subtended by each of the curved surface sections posterior to the anterior-most curved surface section may be less than the angle subtended by an anteriorly-adjacent curved surface section. For example, in some embodiments, the angle subtended by each of the curved surface sections posterior to the anterior-most curved surface section may be less than the angle subtended by the anteriorly-adjacent curved surface section by an amount in the range of 0.5 degrees to 5 degrees. Additionally, in other embodiments, the angle subtended by each of the curved surface sections posterior to the anterior-most curved surface section may be greater than the angle subtended by an anteriorly-adjacent curved surface section. For example, in some embodiments, the angle subtended by each of the curved surface sections posterior to the anterior-most curved surface section may be greater than the angle subtended by the anteriorly-adjacent curved surface section by an amount in the range of 0.5 degrees to 5 degrees. [0011] According to another aspect, an orthopaedic knee prosthesis may include a femoral component and a tibial bearing. The femoral component may have a condyle surface curved in the sagittal plane. The tibial bearing may be a bearing surface configured to articulate with the condyle surface of the femoral component. The condyle surface of the femoral component may be configured to contact the bearing surface at a first contact point on the condyle surface at a first degree of flexion in the range of 0 to about 30 degrees. The condyle surface of the femoral component may be also be configured to contact the bearing surface at a second contact point on the condyle surface at a second degree of flexion in the range of 45 degrees to 90 degrees. The condyle surface in the sagittal plane between the first contact point and the second contact point may include at least five curved surface sections. Each curved surface section may have a radius of curvature having a length different from any other curved surface section. [0012] The plurality of curved surface sections may include an anterior-most curved surface section. The radius of curvature of the anterior-most curved surface section may have a length greater than the radius of curvature of any other curved surface section of the plurality of curved surface sections. Additionally, the length of the radius of curvature of each curved surface section posterior to the anterior-most curved surface section may be less than the length of the radius of curvature of an anteriorly-adjacent curved surface section. For example, the length of the radius of curvature of each curved 5 surface section posterior to the anterior-most curved surface section maybe less than the length of the radius of curvature of an anteriorly-adjacent curved surface section by a distance in the range of 1 millimeters to 3 millimeters. [0013] Each of the plurality of curved surface sections may subtend a corresponding angle. In some embodiments, the angle subtended by each of the curved surface sections posterior to the anterior-most curved surface section may be less than the angle subtended by an anteriorly-adjacent curved surface section. In other embodiments, the angle subtended by each of the curved surface sections posterior to the anterior-most curved surface section may be greater than the angle subtended by an anteriorly-adjacent curved surface section. [0014] According to another aspect, an orthopaedic knee prosthesis may include a femoral component and a tibial bearing. The femoral component may have a condyle surface curved in the sagittal plane. The tibial bearing may be a bearing surface configured to articulate with the condyle surface of the femoral component. The condyle surface of the femoral component may be configured to contact the bearing surface at a first contact point on the condyle surface at a first degree of flexion in the range of 0 to about 30 degrees. The condyle surface of the femoral component may be also be configured to contact the bearing surface at a second contact point on the condyle surface at a second degree of flexion in the range of 45 degrees to 90 degrees. The condyle surface in the sagittal plane between the first contact point and the second contact point may include at least five curved surface sections. Each curved surface section may subtend a corresponding, substantially equal angle and may have a radius of curvature different from any other curved surface section. BRIEF DESCRIPTION OF THE DRAWINGS [0015] The detailed description particularly refers to the following figures, in which: [0016] FIG. 1 is an exploded perspective view of one embodiment of an orthopaedic knee prosthesis; [0017] FIG. 2 is an exploded perspective view of another embodiment of an orthopaedic knee prosthesis; 6 [0018] FIG. 3 is a cross-sectional view of one embodiment of a femoral component and tibial bearing of FIG. 1 taken generally along section lines 2-2 and having the femoral component articulated to a first degree of flexion; [0019] FIG. 4 is a cross-sectional view of a femoral component and tibial bearing of FIG. 3 having the femoral component articulated to a second degree of flexion; [0020] FIG. 5 is a cross-sectional view of a femoral component and tibial bearing of FIG. 3 having the femoral component articulated to a third degree of flexion; [0021] FIG. 6 is a cross-sectional view of another embodiment of the femoral component of FIG. 1; [0022] FIG. 7 is a cross-sectional view of another embodiment of the femoral component of FIG. 1; [0023] FIG. 8 is a graph of the anterior-posterior translation of a simulated femoral component having an increased radius of curvature located at various degrees of flexion; [0024] FIG. 9 is a graph of the anterior-posterior translation of another simulated femoral component having an increased radius of curvature located at various degrees of flexion; [0025] FIG. 10 is a graph of the anterior-posterior translation of another simulated femoral component having an increased radius of curvature located at various degrees of flexion; and [0026] FIG. 11 is a graph of the anterior-posterior translation of another simulated femoral component having an increased radius of curvature located at various degrees of flexion. DETAILED DESCRIPTION OF THE DRAWINGS 7 [0027] While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the concepts of the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. [0028] Terms representing anatomical references, such as anterior, posterior, medial, lateral, superior, inferior, etcetera, may be used throughout this disclosure in reference to both the orthopaedic implants described herein and a patient's natural anatomy. Such terms have well-understood meanings in both the study of anatomy and the field of orthopaedics. Use of such anatomical reference terms in the specification and claims is intended to be consistent with their well-understood meanings unless noted otherwise. [0029] Referring now to FIG. 1, in one embodiment, an orthopaedic knee prosthesis 10 includes a femoral component 12, a tibial bearing 14, and a tibial tray 16. The femoral component 12 and the tibial tray 16 are illustratively formed from a metallic material such as cobalt-chromium or titanium, but may be formed from other materials, such as a ceramic material, a polymer material, a bio-engineered material, or the like, in other embodiments. The tibial bearing 14 is illustratively formed from a polymer material such as a ultra-high molecular weight polyethylene (UHMWPE), but may be formed from other materials, such as a ceramic material, a metallic material, a bio-engineered material, or the like, in other embodiments. [0030] As discussed in more detail below, the femoral component 12 is configured to articulate with the tibial bearing 14, which is configured to be coupled with the tibial tray 16. In the illustrative embodiment of FIG. 1, the tibial bearing 14 is embodied as a rotating or mobile tibial bearing and is configured to rotate relative to the tibial tray 16 during use. However, in other embodiments, the tibial bearing 14 may be embodied as a fixed tibial bearing, which may be limited or restricted from rotating relative the tibial tray 16.

8 [0031] The tibial tray 16 is configured to be secured to a surgically-prepared proximal end of a patient's tibia (not shown). The tibial tray 16 may be secured to the patient's tibia via use of bone adhesive or other attachment means. The tibial tray 16 includes a platform 18 having a top surface 20 and a bottom surface 22. Illustratively, the top surface 20 is generally planar and, in some embodiments, may be highly polished. The tibial tray 16 also includes a stem 24 extending downwardly from the bottom surface 22 of the platform 18. A cavity or bore 26 is defined in the top surface 20 of the platform 18 and extends downwardly into the stem 24. The bore 26 is formed to receive a complimentary stem of the tibial insert 14 as discussed in more detail below. [0032] As discussed above, the tibial bearing 14 is configured to be coupled with the tibial tray 16. The tibial bearing 14 includes a platform 30 having an upper bearing surface 32 and a bottom surface 34. In the illustrative embodiment wherein the tibial bearing 14 is embodied as a rotating or mobile tibial bearing, the bearing 14 includes a stem 36 extending downwardly from the bottom surface 32 of the platform 30. When the tibial bearing 14 is coupled to the tibial tray 16, the stem 36 is received in the bore 26 of the tibial tray 16. In use, the tibial bearing 14 is configured to rotate about an axis defined by the stem 36 relative to the tibial tray 16. In embodiments wherein the tibial bearing 14 is embodied as a fixed tibial bearing, the bearing 14 may or may not include the stem 22 and/or may include other devices or features to secure the tibial bearing 14 to the tibial tray 16 in a non-rotating configuration. [0033] The upper bearing surface 32 of the tibial bearing 14 includes a medial bearing surface 42 and a lateral bearing surface 44. The medial and lateral bearing surfaces 42, 44 are configured to receive or otherwise contact corresponding medial and lateral condyles of the femoral component 12 as discussed in more detail below. As such, each of the bearing surface 42, 44 has a concave contour. [0034] The femoral component 12 is configured to be coupled to a surgically prepared surface of the distal end of a patient's femur (not shown). The femoral component 12 may be secured to the patient's femur via use of bone adhesive or other attachment means. The femoral component 12 includes an outer, articulating surface 50 having a pair of medial and lateral condyles 52, 54. The condyles 52, 54 are spaced apart to define an 9 intracondyle opening 56 therebetween. In use, the condyles 52, 54 replace the natural condyles of the patient's femur and are configured to articulate on the corresponding bearing surfaces 42, 44 of the platform 30 of the tibial bearing 14. [0035] The illustrative orthopaedic knee prosthesis 10 of FIG. 1 is embodied as a posterior cruciate-retaining knee prosthesis. That is, the femoral component 12 is embodied as a posterior cruciate-retaining knee prosthesis and the tibial bearing 14 is embodied as a posterior cruciate-retaining tibial bearing 14. However, in other embodiments, the orthopaedic knee prosthesis 10 may be embodied as a posterior cruciate sacrificing knee prosthesis as illustrated in FIG. 2. [0036] In such embodiments, the tibial bearing 14 is embodied as a posterior stabilizing tibial bearing and includes a spine 60 extending upwardly from the platform 30. The spine 60 is positioned between the bearing surfaces 42, 44 and includes an anterior side 62 and a posterior side 64 having a cam surface 66. In the illustrative embodiment, the cam surface 66 has a substantially concave curvature. However, spines 60 including cam surfaces 66 having other geometries may be used in other embodiments. For example, a tibial bearing including a spine having a substantially "S"- shaped cross-sectional profile, such as the tibial bearing described in U.S. Patent Application Serial No. 12/165,582, entitled "Posterior Stabilized Orthopaedic Prosthesis" by Joseph G. Wyss, et al., which is hereby incorporated by reference, may be used in other embodiments. [0037] Additionally, in such embodiments, the femoral component 12 is embodied as a posterior stabilized femoral component and includes an intracondyle notch or recess 57 (rather than an opening 56). A posterior cam 80 (shown in phantom) and an anterior cam 82 are positioned in the intracondyle notch 57. The posterior cam 80 is located toward the posterior side of the femoral component 12 and includes a cam surface 86 configured to engage or otherwise contact the cam surface 66 of the spine 60 of the tibial bearing 14 during flexion. [0038] It should be appreciated that although the orthopaedic knee prosthesis 10 may be embodied as either a posterior cruciate-retaining or a cruciate-sacrificing knee prosthesis, the femoral component 12 and the tibial bearing 14 of the knee prosthesis 10 10 are discussed below, and illustrated in the remaining figures, in regard to a posterior cruciate-retaining knee prosthesis with the understanding that such description is equally applicable to those embodiments wherein the orthopaedic knee prosthesis 10 is embodied as a posterior cruciate- sacrificing (posterior stabilized) orthopaedic knee prosthesis. [0039] It should be appreciated that the illustrative orthopaedic knee prosthesis 10 is configured to replace a patient's right knee and, as such, the bearing surface 42 and the condyle 52 are referred to as being medially located; and the bearing surface 44 and the condyle 54 are referred to as being laterally located. However, in other embodiments, the orthopaedic knee prosthesis 10 may be configured to replace a patient's left knee. In such embodiments, it should be appreciated that the bearing surface 42 and the condyle 52 may be laterally located and the bearing surface 44 and the condyle 54 may be medially located. Regardless, the features and concepts described herein may be incorporated in an orthopaedic knee prosthesis configured to replace either knee joint of a patient. [0040] Referring now to FIGS. 3-5, the femoral component 12 is configured to articulate on the tibial bearing 14 during use. Each condyle 52, 54 of the femoral component 12 includes a condyle surface 100, which is convexly curved in the sagittal plane and configured to contact the respective bearing surface 42, 44. For example, in one embodiment as shown in FIG. 3, when the orthopaedic knee prosthesis 10 is in extension or is otherwise not in flexion (e.g., a flexion of about 0 degrees), the condyle surface 100 of the condyle 52 contacts the bearing surface 42 (or bearing surface 44 in regard to condyle 54) at one or more contact points 102 on the condyle surface 100. [0041] Additionally, as the orthopaedic knee prosthesis 10 is articulated through the middle degrees of flexion, the femoral component 12 contacts the tibial bearing 14 at one or more contact points on the condyle surface 100. For example, in one embodiment as illustrated in FIG. 4, when the orthopaedic knee prosthesis 10 is articulated to a middle degree of flexion (e.g., at about 45 degrees), the condyle surface 100 contacts the bearing surface 42 at one or more contact points 104 on the condyle surface 100. Similarly, as the orthopaedic knee prosthesis 10 is articulated to a late degree of flexion (e.g., at about 70 degrees of flexion), the condyle surface 100 contacts the bearing surface 42 at one or more contact points 106 on the condyle surface 100 as illustrated in FIG. 5. It should be 11 appreciated, of course, that the femoral component 12 may contact the tibial bearing 14 at a plurality of contact points on the condyle surface 100 at any one particular degree of flexion. However, for clarity of description, only the contact points 102, 104, 106 have been illustrated in FIGS. 3-5, respectively. [0042] The orthopaedic knee prosthesis 10 is configured such that the amount of paradoxical anterior translation of the femoral component 12 relative to the tibial bearing 14 may be reduced or otherwise delayed to a later (i.e., larger) degree of flexion. In particular, as discussed in more detail below, the condyle surface 100 of one or both of the condyles 52, 54 has particular geometry or curvature configured to reduce and/or delay anterior translations and, in some embodiments, promote "roll-back" or posterior translation, of the femoral component 12. It should be appreciated that by delaying the onset of paradoxical anterior translation of the femoral component 12 to a larger degree of flexion, the overall occurrence of paradoxical anterior translation may be reduced during those activities of a patient in which deep flexion is not typically obtained. [0043] In a typical orthopaedic knee prosthesis, paradoxical anterior translation may occur whenever the knee prosthesis is positioned at a degree of flexion greater than zero degrees. The likelihood of anterior translation generally increases as the orthopaedic knee prosthesis is articulated to larger degrees of flexion, particularly in the mid-flexion range. In such orientations, paradoxical anterior translation of the femoral component on the tibial bearing can occur whenever the tangential (traction) force between the femoral component and the tibial bearing fails to satisfy the following equation: T < pN (1) wherein "T" is the tangential (traction) force, "p" is the coefficient of friction of the femoral component and the tibial bearing, and "N" is the normal force between the femoral component and the tibial bearing. As a generalization, the tangential (traction) force between the femoral component and the tibial bearing can be defined as T=M/R (2) 12 wherein "T" is the tangential (traction) force between the femoral component and the tibial bearing, "M" is the knee moment, and "R" is the radius of curvature in the sagittal plane of the condyle surface in contact with the tibial bearing at the particular degree of flexion. It should be appreciated that equation (2) is a simplification of the governing real-world equations, which does not consider such other factors as inertia and acceleration. Regardless, the equation (2) provides insight that paradoxical anterior translation of an orthopaedic knee prosthesis may be reduced or delayed by controlling the radius of curvature of the condyle surface of the femoral component. That is, by controlling the radius of curvature of the condyle surface (e.g., increasing or maintaining the radius of curvature), the right-hand side of equation (2) may be reduced, thereby decreasing the value of the tangential (traction) force and satisfying the equation (1). As discussed above, by ensuring that the tangential (traction) force satisfies equation (1), paradoxical anterior translation of the femoral component on the tibial bearing may be reduced or otherwise delayed to a greater degree of flexion. [0044] Based on the above analysis, to reduce or delay the onset of paradoxical anterior translation, the geometry of the condyle surface 100 of one or both of the condyles 52, 54 of the femoral component 12 is controlled. For example, in some embodiments, the radius of curvature of the condyle surface 100 is controlled such that the radius of curvature is held constant over a range of degrees of flexion and/or is increased in the early to mid flexion ranges. Comparatively, typical femoral components have decreasing radii of curvatures beginning at the distal radius of curvature (i.e., at about 0 degrees of flexion). However, it has been determined that by maintaining a relatively constant radius of curvature (i.e., not decreasing the radius of curvature) over a predetermined range of degrees of early to mid-flexion and/or increasing the radius of curvature over the predetermined range of degrees of flexion may reduce or delay paradoxical anterior translation of the femoral component 12. [0045] Additionally, in some embodiments, the condyle surface 100 is configured or designed such that the transition between discrete radii of curvature of the condyle surface 100 is gradual. That is, by gradually transitioning between the discrete radii of curvature, rather than abrupt transitions, paradoxical anterior translation of the femoral component 12 may be reduced or delayed. Further, in some embodiments, the rate of 13 change in the radius of curvature of the condyle surface in the early to mid flexion ranges (e.g., from about 0 degrees to about 90 degrees) is controlled such that the rate of change is less than a predetermined threshold. That is, it has been determined that if the rate of change of the radius of curvature of the condyle surface 100 is greater than the predetermined threshold, paradoxical anterior translation may occur. [0046] Accordingly, in some embodiments as illustrated in FIGS. 6-12, the condyle surface 100 of the femoral component 12 has an increased radius of curvature in early to middle degrees of flexion. By increasing the radius of curvature, paradoxical anterior translation may be reduced or delayed to a later degree of flexion. The amount of increase between the radius of curvature R2 and the radius of curvature R3 (see FIGS. 6 and 7), as well as, the degree of flexion on the condyle surface 100 at which such increase occurs has been determined to affect the occurrence of paradoxical anterior translation. As discussed in more detail in the U.S. patent application serial number 12/165,579, entitled "Orthopaedic Femoral Prosthesis Having Controlled Condylar Curvature", which was filed concurrently herewith and is hereby incorporated by reference, multiple simulations of various femoral component designs were performed using the LifeMOD/Knee Sim, version 1007.1.0 Beta 16 software program, which is commercially available from LifeModeler, Inc. of San Clemente, California, to analyze the effect of increasing the radius of curvature of the condyle surface of the femoral components in early and mid flexion. Based on such analysis, it has been determined that paradoxical anterior translation of the femoral component relative to the tibial bearing may be reduced or otherwise delayed by increasing the radius of curvature of the condyle surface by an amount in the range of about 0.5 millimeters to about 5 millimeters or more at a degree of flexion in the range of about 30 degrees of flexion to about 90 degrees of flexion. [0047] For example, the graph 200 illustrated in FIG. 8 presents the results of a deep bending knee simulation using a femoral component wherein the radius of curvature of the condyle surface is increased by 0.5 millimeters (i.e., from 25.0 millimeters to 25.5 millimeters) at 30 degrees of flexion, at 50 degrees of flexion, at 70 degrees of flexion, and at 90 degrees of flexion. Similarly, the graph 300 illustrated in FIG. 9 presents the results of a deep bending knee simulation using a femoral component wherein the radius of curvature of the condyle surface is increased by 1.0 millimeters (i.e., from 25.0 millimeters 14 to 26.0 millimeters) at 30 degrees of flexion, at 50 degrees of flexion, at 70 degrees of flexion, and at 90 degrees of flexion. The graph 400 illustrated in FIG. 10 presents the results of a deep bending knee simulation using a femoral component wherein the radius of curvature of the condyle surface is increased by 2.0 millimeters (i.e., from 25.0 millimeters to 27.0 millimeters) at 30 degrees of flexion, at 50 degrees of flexion, at 70 degrees of flexion, and at 90 degrees of flexion. Additionally, the graph 500 illustrated in FIG. 11 presents the results of a deep bending knee simulation using a femoral component wherein the radius of curvature of the condyle surface is increased by 5.0 millimeters (i.e., from 25.0 millimeters to 26.0 millimeters) at 30 degrees of flexion, at 50 degrees of flexion, at 70 degrees of flexion, and at 90 degrees of flexion. [0048] In the graphs 200, 300, 400, 500, the condylar lowest or most distal points (CLP) of the medial condyle ("med") and the lateral condyle ("lat") of the femoral component are graphed as a representation of the relative positioning of the femoral component to the tibial bearing. As such, a downwardly sloped line represents roll-back of the femoral component on the tibial bearing and an upwardly sloped line represents anterior translation of the femoral component on the tibial bearing. [0049] As illustrated in the graphs 200, 300, 400, 500, anterior sliding of the femoral component was delayed until after about 100 degrees of flexion in each of the embodiments; and the amount of anterior translation was limited to less than about 1 millimeter. In particular, "roll-back" of the femoral component on the tibial bearing was promoted by larger increases in the radius of curvature of the condyle surface at earlier degrees of flexion. Of course, amount of increase in the radius of curvature and the degree of flexion at which such increase is introduced is limited by other factors such as the anatomical joint space of the patient's knee, the size of the tibial bearing, and the like. Regardless, based on the simulations reported in the graphs 200, 300, 400, 500, paradoxical anterior translation of the femoral component on the tibial bearing can be reduced or otherwise delayed by increasing the radius of curvature of the condyle surface of the femoral component during early to mid flexion. [0050] Accordingly, referring back to FIGS. 6 and 7, the condyle surface 100 in the sagittal plane is formed in part from a number of curved surface sections 102, 104, 106, 15 108, the sagittal ends of each of which are tangent to the sagittal ends of any adjacent curved surface section of the condyles surface 100. Each curved surface section 102, 106, 108 is defined by a radius of curvature. In particular, the curved surface section 102 is defined by a radius of curvature R1, the curved surface section 106 is defined by a radius of curvature R3, and the curved surface section 108 is defined by a radius of curvature R4. In addition, as discussed in more detail below, the curved surface section 104 is designed to provide a gradual transition from the first radius of curvature R1 to a second radius of curvature R2. To do so, the curved surface section 104 is defined by a plurality of curved surface sections 110, 120, each of which is defined by a separate radius of curvature R5. [0051] As discussed above, the condyle surface 100 of the femoral component 12 is configured such that the radius of curvature R3 of the curved surface section 106 is greater than the radius of curvature R2 of the curved surface section 104. In one embodiment, the radius of curvature R3 is greater than the radius of curvature R2 by 0.5 millimeters or more. In another embodiment, the radius of curvature R3 is greater than the radius of curvature R2 by 2 millimeters or more. In another embodiment, the radius of curvature R3 is greater than the radius of curvature R2 by 2 millimeters or more. In a particular embodiment, the radius of curvature R3 is greater than the radius of curvature R2 by at least 5 millimeters or more. It should be appreciated, however, that the particular increase of radius of curvature between R2 and R3 may be based on or scaled to the particular size of the femoral component 12 in some embodiments. [0052] Each of the curved surface sections 102, 104, 106, 108 contacts the bearing surface 42 (or 44) of the tibial bearing 14 through different ranges of degrees of flexion. For example, the curved surface section 102 extends from an earlier degree of flexion 91 to a later degree of flexion 92. The curved surface section 104 extends from the degree of flexion 92 to a later degree of flexion 93. The curved surface section 106 extends from the degree of flexion 93 to a later degree of flexion 94. [0053] For example, in one embodiment, the curved surface section 102 may extend from a degree of flexion 01 of about -10 degrees (i.e., 10 degrees of hyperextension) to a degree of flexion 02 of about 5 degrees of flexion. The curved surface section 104 extends from the degree of flexion 02 of about 5 degrees of flexion to a degree 16 of flexion 03 of about 65 degrees of flexion. The curved surface section 106 extends from the degree of flexion 03 of about 65 degrees of flexion to a degree of flexion 04 of about 90 degrees of flexion and the curved surface section 108 extends from the degree of flexion 04 of about 90 degrees of flexion to a degree of flexion 05 of about 104 degrees of flexion. [0054] It should be appreciated, however, that each of the curved surface sections 102, 104, 106, 108 may extend from degrees of flexion different from those discussed above. For example, the particular degrees of flexion through which the curved surface sections 102, 104, 106, 108 extend may be based or otherwise determined based on the type of femoral component 12 (e.g., cruciate-retaining or posterior stabilized), the size of the femoral component 12, and/or the like. [0055] As discussed above, the curved surface section 104 is designed to gradually transition from the radius of curvature R1 to the radius of curvature R2. To do so, in one embodiment as illustrated in FIG. 5, the curved surface section 104 is defined by a plurality of curved surface sections 110. In the illustrative embodiment of FIG. 5, the curved surface section 104 is defined by six curved surface sections 1 10A, 110B, 1 10C, 1 10D, 1 10E, 1 10F, but may be defined by or otherwise include more or less curved surface sections 110 in other embodiments. The particular number of curved surface sections 110 used may be based on, for example, the size of the angle subtended by the curved surface section 104. [0056] Each of the curved surface sections 110 of the condyle surface 100 contacts the bearing surface 42 (or 44) of the tibial bearing 14 through different ranges of degrees of flexion. For example, the curved surface section 1 10A extends from the degree of flexion 02 to a later degree of flexion OC1, the curved surface section 11 OB extends from the degree of flexion OC1 to a later degree of flexion 0C2, the curved surface section 11C extends from the degree of flexion 0C2 to a later degree of flexion 0C3, the curved surface section 1 10D extends from the degree of flexion 0C3 to a later degree of flexion 0C4, the curved surface section 1 10E extends from the degree of flexion 0C4 to a later degree of flexion 0C5, and the curved surface section 1 1OF extends from the degree of flexion OC5 to the later degree of flexion 03.

17 [0057] In the illustrative embodiment of FIG. 6, each of the curved surface sections 110 extend substantially equal degrees of flexion. That is, the degrees of flexion between 02 and OC1, OC1 and 0C2, between 9C2 and 0C3, between 9C3 and 0C4, between 9C4 and 0C5, and between 9C5 and 03 are substantially equal. In one particular embodiment, each curved surface section 110 extends for about 10 degrees. However, in other embodiments, each curved surface section 110 may extend a greater or lesser amount. In particular, in one embodiment, each curved surface section extend (i.e., subtend an angle) from about 1 degree to about 15 degrees. [0058] Each of the curved surface sections 110 is defined by a radius of curvature R5. That is, the curved surface section 1 10A is defined by a radius of curvature R5A, the curved surface section 1 10B is defined by a radius of curvature R5B, the curved surface section 1 10C is defined by a radius of curvature R5C, the curved surface section 1 10D is defined by a radius of curvature R5D, the curved surface section 1 10E is defined by a radius of curvature R5E, and the curved surface section 11 OF is defined by a radius of curvature R5F. Each radius of curvature R5 is smaller (i.e., has a shorter length) than the anteriorly-adjacent radius of curvature R5. That is, R5F is smaller than R5E, R5E is smaller than R5D, R5D is smaller than R5C, R5C is smaller than R5B, and R5B is smaller than R5A. For example, in one embodiment, each radius of curvature R5 may have a length shorter than the anteriorly-adjacent radius of curvature R5 by an amount in the range of about 0.1 millimeters to about 5 millimeters. However, in other embodiments, each radius of curvature R5 may have a length shorter than the anteriorly- adjacent radius of curvature R5 by an amount greater or less than such values. The particular length of each radius of curvature R5 may be determined based on the particular application, the length of the curved surface section 104, a defined equation, and/or the like. [0059] Referring now to FIG. 7, in another embodiment, the curved surface section 104 may be formed by a plurality of curved surface sections 120, each of which may extend a different amount of degrees (i.e., subtend angles of different sizes). For example, in the illustrative embodiment of FIG. 7, the curved surface section 104 is defined by ten curved surface sections 120A, 120B, 120C, 120D, 120E, 120F, 120G, 120H, 1201, 120J. The curved surface section 120A extends from the degree of flexion 01 to a later degree of flexion OC1, the curved surface section 120B extends from the degree of flexion 9C1 to a 18 later degree of flexion 0C2, the curved surface section 120C extends from the degree of flexion 0C2 to a later degree of flexion 0C3, the curved surface section 120D extends from the degree of flexion 0C3 to a later degree of flexion 0C4, the curved surface section 120E extends from the degree of flexion 0C4 to a later degree of flexion 0C5, the curved surface section 120F extends from the degree of flexion 0C5 to a later degree of flexion 0C6, the curved surface section 120G extends from the degree of flexion 9C6 to a later degree of flexion 9C7, the curved surface section 120H extends from the degree of flexion 9C7 to a later degree of flexion 9C8, the curved surface section 1201 extends from the degree of flexion 9C8 to a later degree of flexion 9C9, and the curved surface section 120J extends from the degree of flexion 9C9 to the later degree of flexion 03. [0060] As discussed above, each of the curved surface sections 120 extend different degrees of flexion. That is, the degrees of flexion between 02 and OC1, OC1 and 0C2, between 0C2 and 0C3, between 0C3 and 0C4, between 0C4 and 0C5, between 0C5 and 0C6, between 0C6 and 0C7, between 0C7 and 0C8, between 0C8 and 0C9, and between 0C9 and 03 are different from each other. In some embodiments, each curved surface section 120 subtends an angle that is less than the angle subtended by the anteriorly adjacent section 120. For example, in the illustrative embodiment of FIG. 7, the curved surface section 120A extends for about 10 degrees, the curved surface section 120B extends for about 9 degrees, the curved surface section 120C extends for about 8 degrees, the curved surface section 120D extends for about 7 degrees, the curved surface section 120E extends for about 6 degrees, the curved surface section 120F extends for about 5 degrees, the curved surface section 120G extends for about 4 degrees, the curved surface section 120H extends for about 3 degrees, the curved surface section 1201 extends for about 2 degrees, and the curved surface section 120J extends for about 1 degree. [0061] Although each curved surface section 120 subtends an angle 1 degree less than the anteriorly-adjacent section 120 in the illustrative embodiment of FIG. 7, the curved surface sections 120 may subtend angles that are less than the anteriorly adjacent section 120 by an amount greater than 1 degree in other embodiments. Additionally, in other embodiments, each curved surface section 120 may subtend an angle that is greater than the angle subtended by the anteriorly-adjacent section 120. For example, each curved surface section 120 may subtend an angle that is greater than the angle subtended by the 19 anteriorly-adjacent section 120 by about 0.5, 1, or more degrees in some embodiments. Further, in some embodiments, each of the curved surface sections 120 may subtend angles of various sizes. That, each curved surface section 120 may be greater than or less than the anteriorly-adjacent curved surface 120 in some embodiments. [0062] The overall shape and design of the condyle surface 100 of the femoral component 12 has been described above in regard to a single condyle 52, 54 of the femoral component 12. It should be appreciated that in some embodiments both condyles 52, 54 of the femoral component 12 may be symmetrical and have similar condyle surfaces 100. However, in other embodiments, the condyles 52, 54 of the femoral component 12 may be asymmetrical. That is, each condyle 52, 54 may have a condyle surface 100 having the features described herein but being asymmetrical to the other condyle 52, 54. [0063] While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such an illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. [0064] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. [0065] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge. [0066] There are a plurality of advantages of the present disclosure arising from the various features of the devices and assemblies described herein. It will be noted that alternative embodiments of the devices and assemblies of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of 20 such features. Those of ordinary skill in the art may readily devise their own implementations of the devices and assemblies that incorporate one or more of the features of the present invention and fall within the spirit and scope of the present disclosure as defined by the appended claims.

Claims (20)

1. An orthopaedic knee prosthesis including: a femoral component having a condyle surface that is curved in the sagittal plane, the condyle surface including: an inferior-most point, a distal surface extending posteriorly from the inferior-most point to a superior- most point, the distal surface defining an arc having a magnitude of about 30 degrees between the inferior-most point of the condyle surface and the superior-most point of the distal surface, a first posterior surface connected to the superior-most point of the distal surface, the first posterior surface extending superiorly and posteriorly away from the distal surface to define an arc having a magnitude of about 15 degrees, and a second posterior surface having an inferior point connected to a superior most point of the first posterior surface, the second posterior surface extending superiorly from the inferior point to a superior-most point, wherein (i) the condyle surface in the sagittal plane has a first radius of curvature at a first point on the distal surface, (ii) the condyle surface in the sagittal plane has a second radius of curvature at a second point on the second posterior surface, and (iii) the condyle surface in the sagittal plane has a third radius of curvature at a third point on the second posterior surface positioned between the second point and the superior-most point of the second posterior surface, the third radius of curvature being greater than the second radius of curvature by at least 0.5 millimeters, wherein the condyle surface in the sagittal plane between the first point and the second point includes a plurality of curved surface sections, each curved surface section having a different radius of curvature. 22

2. The orthopaedic knee prosthesis of claim 1, wherein the plurality of curved surface sections include an anterior-most curved surface section, the radius of curvature of the anterior-most curved surface section having a length greater than the radius of curvature of any other curved surface section of the plurality of curved surface sections.

3. The orthopaedic knee prosthesis of claim 2, wherein the length of the radius of curvature of each curved surface section posterior to the anterior-most curved surface section is less than the length of the radius of curvature of an anteriorly-adjacent curved surface section.

4. The orthopaedic knee prosthesis of claim 3, wherein the length of the radius of curvature of each curved surface section posterior to the anterior-most curved surface section is less than the length of the radius of curvature of an anteriorly-adjacent curved surface section by a distance in the range of from 0.1 millimeters to 5 millimeters.

5. The orthopaedic knee prosthesis of claim 4, wherein the length of the radius of curvature of each curved surface section posterior to the anterior-most curved surface section is less than the length of the radius of curvature of an anteriorly-adjacent curved surface section by a distance in the range of from 1 millimeters to 3 millimeters.

6. The orthopaedic knee prosthesis of claim 5, wherein the length of the radius of curvature of each curved surface section posterior to the anterior-most curved surface section is less than the length of the radius of curvature of an anteriorly-adjacent curved surface section by about 1 millimeter.

7. The orthopaedic knee prosthesis of any one of claims 1 to 6, wherein each of the plurality of curved surface sections subtends a corresponding angle, each angle subtended by the plurality of curved surface sections being approximately equal.

8. The orthopaedic knee prosthesis of any one of claims 1 to 7, wherein (i) the plurality of curved surface sections include an anterior-most curved surface section and (ii) each of the plurality of curved surface sections subtends a corresponding angle, the angle subtended by each of the curved surface sections posterior to the anterior-most curved 23 surface section being less than the angle subtended by an anteriorly-adjacent curved surface section.

9. The orthopaedic knee prosthesis of claim 8, wherein the angle subtended by each of the curved surface sections posterior to the anterior-most curved surface section is less than the angle subtended by the anteriorly-adjacent curved surface section by an amount in the range of 0.5 degrees to 5 degrees.

10. The orthopaedic knee prosthesis of any one of claims 1 to 7, wherein (i) the plurality of curved surface sections include an anterior-most curved surface section and (ii) each of the plurality of curved surface sections subtends a corresponding angle, the angle subtended by each of the curved surface sections posterior to the anterior-most curved surface section being greater than the angle subtended by an anteriorly-adjacent curved surface section.

11. The orthopaedic knee prosthesis of 10, wherein the angle subtended by each of the curved surface sections posterior to the anterior-most curved surface section is greater than the angle subtended by the anteriorly-adjacent curved surface section by an amount in the range of from 0.5 degrees to 5 degrees.

12. The orthopaedic knee prosthesis of any one of the preceding claims, further including: a tibial bearing having a bearing surface configured to articulate with the condyle surface of the femoral component, wherein the condyle surface of the femoral component (i) contacts the bearing surface at the first point on the distal surface at a first degree of flexion that is in the range of from 0 degrees to 10 degrees, (ii) contacts the bearing surface at the second point on the second posterior surface at a second degree of flexion that is in the range of from 60 degrees to 70 degrees, and (iii) contacts the bearing surface at the third point on the second posterior surface at a third degree of flexion that is in the range of from 80 degrees to 110 degrees. 24

13. The orthopaedic knee prosthesis of claim 12, wherein the first degree of flexion is about 5 degrees, the second degree of flexion is about 65 degrees, and the third degree of flexion is about 90 degrees.

14. An orthopaedic knee prosthesis including: a femoral component having a condyle surface that is curved in the sagittal plane, the condyle surface including: an inferior-most point, a distal surface extending posteriorly from the inferior-most point to a superior- most point, the distal surface defining an arc having a magnitude of about 30 degrees between the inferior-most point of the condyle surface and the superior-most point of the distal surface, a first posterior surface connected to the superior-most point of the distal surface, the first posterior surface extending superiorly and posteriorly away from the distal surface to define an arc having a magnitude of about 15 degrees, and a second posterior surface having an inferior point connected to a superior most point of the first posterior surface, the second posterior surface extending superiorly from the inferior point to a superior-most point to define an arc having a magnitude of about 45 degrees, wherein (i) the condyle surface in the sagittal plane has a first point on the distal surface, and (ii) the condyle surface in the sagittal plane has a second point on the second posterior surface, wherein the condyle surface in the sagittal plane between the first point and the second point includes at least five curved surface sections, each curved surface section having a radius of curvature having a length different from any other curved surface section. 25

15. The orthopaedic knee prosthesis of claim 14, wherein the at least five curved surface sections include an anterior-most curved surface section, the radius of curvature of the anterior-most curved surface section having a length greater than the radius of curvature of any other curved surface section of the at least five curved surface sections.

16. The orthopaedic knee prosthesis of claim 15, wherein the length of the radius of curvature of each curved surface section posterior to the anterior-most curved surface section is less than the length of the radius of curvature of an anteriorly-adjacent curved surface section.

17. The orthopaedic knee prosthesis of claim 16, wherein the length of the radius of curvature of each curved surface section posterior to the anterior-most curved surface section is less than the length of the radius of curvature of an anteriorly-adjacent curved surface section by a distance in the range of from 1 millimeters to 3 millimeters.

18. The orthopaedic knee prosthesis of any one of claims 14 to 17, wherein (i) the at least five curved surface sections include an anterior-most curved surface section and (ii) each of the at least five curved surface sections subtends a corresponding angle, the angle subtended by each of the curved surface sections posterior to the anterior-most curved surface section being less than the angle subtended by an anteriorly-adjacent curved surface section.

19. The orthopaedic knee prosthesis of any one of claims 14 to 17, wherein (i) the at least five curved surface sections include an anterior-most curved surface section and (ii) each of the at least five curved surface sections subtends a corresponding angle, the angle subtended by each of the curved surface sections posterior to the anterior-most curved surface section being greater than the angle subtended by an anteriorly-adjacent curved surface section.

20. An orthopaedic knee prosthesis including: a femoral component having a condyle surface that is curved in the sagittal plane, the condyle surface including: 26 an inferior-most point, a distal surface extending posteriorly from the inferior-most point to a superior- most point, the distal surface defining an arc having a magnitude of about 30 degrees between the inferior-most point of the condyle surface and the superior-most point of the distal surface, a first posterior surface connected to the superior-most point of the distal surface, the first posterior surface extending superiorly and posteriorly away from the distal surface to define an arc having a magnitude of about 15 degrees, and a second posterior surface having an inferior point connected to a superior most point of the first posterior surface, the second posterior surface extending superiorly from the inferior point to a superior-most point to define an arc having a magnitude of about 45 degrees, wherein (i) the condyle surface in the sagittal plane has a first point on the distal surface, and (ii) the condyle surface in the sagittal plane has a second point on the second posterior surface, wherein the condyle surface in the sagittal plane between the first point and the second point includes at least five curved surface sections, each curved surface section (i) subtending a corresponding, substantially equal angle having a magnitude greater than zero degrees and (ii) having a radius of curvature different from any other curved surface section.