Patent Description:
Orthopedic procedures and prostheses are commonly utilized to repair and/or replace damaged bone and tissue in the human body. For example, a knee arthroplasty can be used to restore natural knee function by repairing damaged or diseased articular surfaces of the femur and/or tibia. An incision is made into the knee joint to expose the bones comprising the joint. Cut guides are used to guide the removal of the articular surfaces that are to be replaced. Prostheses are used to replicate the articular surfaces. Knee prostheses can include a femoral prosthesis implanted on the distal end of the femur, which articulates with a tibial bearing component and a tibial component implanted on the proximal end of a tibia to replicate the function of a healthy natural knee. Various types of procedures are known including a total knee arthroplasty (TKA), where all of the articulating compartments of the joint are repaired with prosthetic components. <CIT> describes a posterior stabilized femoral prosthesis for a knee arthroplasty having medial and lateral condyles shaped for articulation with a tibial articular surface of a bearing component. In more detail, <CIT> discloses a joint prosthesis that includes e.g., a femoral component and a tibial component. The medial and lateral condylar articular surfaces may have substantially uniform and equal radii from full extension to about <NUM>° of flexion. From <NUM>°, the lateral condylar articular surface has a smaller radius than the medial condylar articular surface such that the medial condyle gradually becomes increasingly more proud than the lateral condyle to facilitate internal rotation of the tibia at deep flexion. Also, the tibial articular component may include a post intermediate the medial and lateral compartments that engages a cam on the femoral articular component between the medial and the lateral condylar articular surfaces. The cam and post become congruent at flexion angles of approximately <NUM>° flexion and mate symmetrically during the first <NUM>°-<NUM>° of further flexion, and then mate asymmetrically at greater degrees of flexion to force internal rotation of the tibia.

This disclosure pertains generally to prostheses and systems for knee arthroplasty. The present inventors have recognized, among other things, improvements to femoral prostheses (sometimes called femoral prostheses) and tibial bearing components (sometimes called tibial bearing prostheses, tibial bearings, bearings, poly or bearing components). In particular, the present inventors have focused on posterior-stabilized (PS) prostheses, which include a spine on the tibial bearing component and a cam on the femoral prosthesis that are configured to interact together when the femoral prosthesis is in flexion to provide further stability to the knee joint. PS prostheses are typically utilized in instances where one or more of the cruciate ligaments (e. g, ACL and PCL) of the knee joint have suffered degeneration and must be eliminated. PS prostheses have particular design considerations and kinematics, which differ from other types of knee prostheses such as ultra-congruent (UC) and cruciate-retaining (CR) prostheses, for example.

Considering criteria specific to PS prostheses, the present inventors have designed femoral prostheses and tibial bearing components that allow for greater joint stability, improved kinematics during flexion of the knee joint, and increased compatibility with other known prosthesis designs. Accordingly, the invention provides a system of posterior stabilized knee prostheses for a knee arthroplasty as defined in claim <NUM>. Thus, with regard to the femoral prostheses disclosed the present inventors propose an example where the medial and lateral condyles are shaped to articulate with a tibial articular surface of a tibial bearing component through a range of motion. In a sagittal plane, the medial and lateral condyles can define medial and lateral multi-radius curves, respectively. The medial multi-radius curve can have a single common radius swept through a first angular extent to define a single arc length that extends from between substantially -<NUM> degrees flexion to substantially <NUM> degrees flexion, inclusive. A posterior portion (shown and described subsequently) of the medial and lateral condyles can have a thickness of <NUM>. In one example, the medial multi-radius curve can have a second radius swept through a second angular extent to define a second arc length that extends from between substantially <NUM> degrees flexion to beyond <NUM> degrees flexion. The medial and lateral condyles can be symmetrically shaped such that lateral condyle can have a lateral multi-radius curve of a same shape as the medial multi-radius curve. Thus, the lateral multi-radius curve can have the single common radius swept through the first angular extent to define the single arc length that extends from between substantially -<NUM> degrees flexion to substantially <NUM> degrees flexion, inclusive.

According to the invention, the femoral prosthesis and the tibial bearing component are configured such that an area of contact between the medial condyle and the tibial articular surface includes a medial dwell point of the tibial articular surface when the femoral prosthesis is in full extension. The femoral prosthesis and the tibial bearing component can be configured such that the area of contact between the medial condyle and the tibial articular surface does not shift during the range of motion between zero degrees flexion and substantially <NUM> degrees flexion and includes the medial dwell point during the range of motion between zero degrees flexion and substantially <NUM> degrees flexion. A spine of the tibial bearing component and a cam of the femoral prosthesis make initial contact when the range of motion reaches substantially <NUM> degrees flexion. A medial compartment of the tibial bearing component can be configured to have between about a <NUM>:<NUM> congruence ratio and about a <NUM>:<NUM> congruence ratio with the medial condyle through the first angular extent, the congruence ratio can comprise a ratio of the similarity between a sagittal radius of the medial compartment and the single common radius of the medial condyle.

Regarding the tibial bearing component, the medial compartment can be configured to have the medial dwell point a distance between about <NUM>% and about <NUM>% of a total anterior-posterior extent of the tibial bearing component as measured from an anterior most point to a posterior most point of the tibial bearing component. The lateral compartment can be configured to have a lateral dwell point a distance between about <NUM>% and about <NUM>% of a total anterior-posterior extent of the tibial bearing component as measured from an anterior most point to a posterior most point of the tibial bearing component.

Additionally, there is also described a family of tibial bearing components that can have at least eleven different stock sizes so as to achieve more compatible combinations when used with a family of tibia prostheses that can have at least nine different stock sizes and a family of femoral prostheses that can have at least twelve different stock sizes. Due to the number of components and the designed compatibility between various sizes in the respective families, thirty three combinations of the at least eleven different stock sizes of the family of tibial bearing components can be compatible for operable use with the at least twelve different stock sizes of the family of femoral prostheses.

To further illustrate the apparatuses and systems disclosed herein, the following non-limiting examples are provided:
The invention provides, a system of posterior-stabilized knee prostheses for a knee arthroplasty, the system comprises:
a tibial bearing component having a tibial articular surface with a medial compartment and a lateral compartment, wherein the tibial bearing component has a spine extending proximally from the tibial articular surface and positioned between the medial and lateral compartments, and wherein the medial compartment has a medial dwell point; a femoral prosthesis having a cam and medial and lateral condyles spaced to either side of the cam, wherein the medial condyle is configured for articulation with the medial compartment and lateral condyle is configured for articulation with the lateral compartment, and wherein femoral prosthesis is configured to articulate through a range of motion relative to the tibial bearing component, such range of motion includes a full extension that corresponds to zero degrees flexion of a knee joint and positive flexion that corresponds to greater than zero degrees flexion of the knee joint, wherein an area of contact between the medial condyle and the medial compartment includes the medial dwell point when the femoral prosthesis is in full extension, and wherein the spine and cam are both configured to make initial contact when the range of motion reaches substantially <NUM> degrees flexion.

Optionally, the area of contact between the medial condyle and the tibial articular surface does not shift during the range of motion between zero degrees flexion and substantially <NUM> degrees flexion and can include the medial dwell point during the range of motion between zero degrees flexion and substantially <NUM> degrees flexion.

Optionally, in a sagittal plane the medial and lateral condyles define medial and lateral multi-radius curves, respectively, and wherein the medial multi-radius curve can have a single common radius swept through a first angular extent to define a single arc length that extends from between substantially -<NUM> degrees flexion to substantially <NUM> degrees flexion, inclusive.

Optionally, the medial compartment is configured to have the medial dwell point a distance between about <NUM>% and about <NUM>% of a total anterior-posterior extent of the tibial bearing component as measured from an anterior most point to a posterior most point of the tibial bearing component.

Optionally, the system comprises a posterior portion of the medial and lateral condyles having a thickness of <NUM>.

Optionally, the systems of any one or any combination of the above can be configured such that all elements or options recited are available to use or select from.

These and other examples and features of the present apparatuses and systems will be set forth in part in the following Detailed Description. This Overview is intended to provide non-limiting examples of the present subject matter - it is not intended to provide an exclusive or exhaustive explanation. The Detailed Description below is included to provide further information about the present apparatuses and systems.

In the drawings, which are not necessarily drawn to scale, like numerals can describe similar components in different views. Like numerals having different letter suffixes can represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various examples discussed in the present document.

The present application relates femoral prostheses, tibial bearing components and systems including such prostheses and components.

The invention is defined in the claims. Any subject-matter that is disclosed herein, but which is not defined in the claims, does not form part of the invention.

In a TKA, both of the medial and lateral condyles of the femur can be resected. Similarly, the tibia can be resected to remove the medial articular surface and the lateral articular surface using a cutting apparatus. Other portions of the knee, e.g., the intercondylar eminence, can also be removed. Depending on the type of TKA, features such as the ligaments can be spared or can also be removed. As discussed above, in a PS TKA, the ligaments such as the posterior cruciate ligament PCL are removed. Prostheses can be implanted on the femur and the tibia and a bearing component can be placed between the femoral prosthesis and the tibial prosthesis to provide for the replaced articular surfaces.

<FIG> shows a system <NUM> that includes a femoral prosthesis <NUM> and a tibial bearing component <NUM>. The femoral prosthesis <NUM> includes a lateral condyle <NUM>, a medial condyle <NUM>, bone interfacing surfaces <NUM>, and a cam <NUM>. The tibial bearing component <NUM> includes an articular surface <NUM>, an intercondylar region <NUM>, a periphery <NUM> and a distal surface <NUM>. The articular surface <NUM> includes a lateral compartment <NUM> and a medial compartment <NUM>. The intercondylar region <NUM> includes a spine <NUM>.

The femoral prosthesis <NUM> can be implanted on a respected femur (not shown) via the bone interfacing surfaces <NUM>. The tibial bearing component <NUM> can attach to a tibial prosthesis (not shown) that is implanted on a resected tibia (not shown). The femoral prosthesis <NUM> and the tibial bearing component <NUM> are configured to articulate together through a range of motion for the femoral prosthesis <NUM>. This range of motion can include knee joint flexion and extension as will be illustrated and described subsequently.

The lateral condyle <NUM> is spaced from the medial condyle <NUM> in a medial-lateral direction by a sulcus space and in some portions of the femoral prosthesis <NUM> by a recess <NUM>. The femoral prosthesis <NUM> can have an anterior end portion <NUM> and a posterior end portion <NUM>. The cam <NUM> can be disposed at the posterior end portion <NUM> proximal of the recess <NUM>. The cam <NUM> extends between the lateral condyle <NUM> and the medial condyle <NUM>.

The lateral condyle <NUM> can be arcuate in shape having a radius of curvature along an articular surface <NUM> as will be illustrated and discussed subsequently. The lateral condyle <NUM> can be configured to be received by the lateral compartment <NUM> for articulation therewith when the femoral prosthesis <NUM> is assembled atop the tibial bearing component <NUM> such as shown in <FIG>. Similarly, the medial condyle <NUM> can be arcuate in shape along the articular surface <NUM> having a radius of curvature as will be illustrated and discussed subsequently. The medial condyle <NUM> is configured to be received by the medial compartment <NUM> for articulation therewith when the femoral prosthesis <NUM> is assembled atop the tibial bearing component <NUM> such as shown in <FIG>.

According to the example of <FIG>, the lateral condyle <NUM> can be symmetrically shaped relative to the medial condyle <NUM>. This results in the lateral condyle <NUM> and medial condyle <NUM> sharing the same radius of curvature resulting in each having a same shape for a multi-radius curve as shown and described subsequently.

For the tibial bearing component <NUM>, the articular surface <NUM> comprises a proximal surface for the tibial bearing component <NUM> and can be configured to interface with the lateral and medial condyles <NUM> and <NUM>. The articular surface <NUM> and the intercondylar region <NUM> can be opposed to and spaced from the distal surface <NUM> by the periphery <NUM>. The periphery <NUM> and/or the distal surface <NUM> can include features <NUM> for attachment to the tibial prosthesis. The features <NUM> can be shaped to mate with corresponding features of a sidewall of a tibial tray (now shown) such as to create an interference fit, for example.

As discussed above, the articular surface <NUM> includes the lateral compartment <NUM> and the medial compartment <NUM>. The lateral and medial compartments <NUM> and <NUM> can be dish shaped with a curvature in a proximal-distal and the medial-lateral directions. The lateral compartment <NUM> can be spaced in the medial-lateral direction from the medial compartment <NUM>.

The intercondylar region <NUM> can be positioned between the lateral and medial compartments <NUM> and <NUM>. The intercondylar region <NUM> can comprise a raised prominence relative to the lateral and medial compartments <NUM> and <NUM>. The spine <NUM> is part of the intercondylar region <NUM> positioned between the lateral and medial compartments <NUM> and <NUM>. The spine <NUM> can also be spaced posteriorly from an anterior edge of the periphery <NUM>. The spine <NUM> can comprise a projection extending generally proximally from the intercondylar region <NUM>. The spine <NUM> can be canted anterior-to-posterior as will be subsequently shown. The spine <NUM> can configured to be received in the recess <NUM> at <NUM> degrees flexion as shown in <FIG> and <FIG>.

Further details relating to aspects of the construct of the femoral prosthesis <NUM> and tibial bearing component <NUM> can found in <CIT>, <CIT>, <CIT>, <CIT>,<CIT> and <CIT>.

According to one example, the femoral component <NUM> can be designed to be compatible with other commercially available tibial bearing components such as those of the Zimmer Biomet Persona® knee system manufactured by Zimmer Biomet Holding, Inc. of Warsaw, Indiana. Similarly, according to one example, the tibial bearing component <NUM> can be designed to be compatible with other commercially available femoral prostheses such as those of the Zimmer Biomet Persona® knee system.

<FIG> show the femoral prosthesis <NUM> assembled atop the tibial bearing component <NUM>. In <FIG>, the knee joint is illustrated in full extension (corresponding to <NUM> degrees flexion).

As shown in the example of <FIG>, the tibial bearing component <NUM> is compatible with and configured for operable use to articulate with the femoral prosthesis <NUM>. In particular, the articular surface <NUM> of the tibial bearing component <NUM> can be configured to receive the articular surface <NUM> of the femoral prosthesis <NUM> thereon and can be configured to allow for articular movement of the femoral prosthesis <NUM> relative thereto through the range of motion in a manner that simulates the kinematics of a natural knee (e.g., allow for rollback of the femoral prosthesis <NUM> in flexion including anterior-posterior translation, engagement of the spine <NUM> with the cam <NUM> (features shown in <FIG> and <FIG>), etc.).

<FIG> shows a sagittal cross-section of the tibial bearing component <NUM> and the femoral prosthesis <NUM> with the cross-section taken through the medial condyle <NUM>. In <FIG>, the medial condyle <NUM> defines a medial multi-radius curve <NUM> that is part of the articular surface <NUM>.

As shown in <FIG>, the medial condyle <NUM> can have a high flex portion <NUM>, a posterior portion <NUM>, an extension to mid-flexion portion <NUM>, and a part of an anterior region <NUM>. As shown in the example of <FIG>, the posterior portion <NUM> and the extension to mid-flexion portion <NUM> can share a single common radius R1. Indeed, in the example of <FIG>, the posterior portion <NUM>, the extension to mid-flexion portion <NUM>, and the part of the anterior region <NUM> can share the single common radius R1.

In <FIG>, the posterior portion <NUM> extends to <NUM> degrees flexion, inclusive. The high flex portion <NUM> extends between substantially <NUM> degrees flexion to <NUM> degrees. The extension to mid-flexion portion <NUM> can extend from the posterior portion <NUM> to <NUM> degrees flexion (<NUM> degrees flexion comprising full extension). The part of the anterior region <NUM> can extend from substantially <NUM> degrees flexion to -<NUM> degrees flexion, inclusive, for example.

According to the example shown, the medial multi-radius curve <NUM> can have the single common radius R1 swept through a first angular extent to define a single arc length A that extends from between substantially -<NUM> degrees flexion to substantially <NUM> degrees flexion, inclusive. The single arc length A includes the posterior portion <NUM>, the extension to mid-flexion portion <NUM> and the part of the anterior region <NUM>. Thus, the medial multi-radius curve <NUM> can have the single common radius R1 swept through a first portion of the first angular extent to define a first part the single arc length A that extends from between substantially <NUM> degrees flexion to substantially <NUM> degrees flexion. Additionally, the medial multi-radius curve <NUM> can have the single common radius R1 swept through a second portion of the first angular extent to define a second part the single arc length A that extends from between substantially -<NUM> degrees flexion to substantially <NUM> degrees flexion.

In the example of <FIG>, the high flex portion <NUM> can have a second radius R2 that differs from that of the single common radius R1. In particular, the second radius R2 can be smaller than the single common radius R1. Such a configuration can avoid or reduce the likelihood of a kinematic conflict between the cam <NUM> (features shown in <FIG> and <FIG>) and the spine <NUM>. This can allow for a transition region in the high flex portion <NUM> of substantially <NUM> degrees of flexion (as measured from the end of the posterior portion <NUM> at substantially <NUM> degrees) as the spine <NUM> and the cam can be configured to make initial contact with the range of motion reaches substantially <NUM> degrees flexion with the tibial bearing component <NUM> positioned at a <NUM> degree anterior-to-posterior slope. If the tibial bearing component <NUM> was positioned at another angle (e.g., <NUM> degrees of slope anterior-to-posterior) as can occur in other examples, the cam and spine <NUM> would make initial contact at a different degree of flexion. For example, with the tibial bearing component <NUM> positioned at <NUM> degrees of slope anterior-to-posterior, the cam and spine <NUM> would make initial contact at an angle of flexion less than <NUM> degrees.

<FIG> shows a sagittal cross-section of the femoral prosthesis <NUM> with the cross-section taken through the lateral condyle <NUM>. In <FIG>, the lateral condyle <NUM> defines a lateral multi-radius curve <NUM> that is part of the articular surface <NUM>. As discussed previously the lateral condyle <NUM> can by symmetrically shaped with respect to the medial condyle <NUM>. Thus, the lateral condyle <NUM> can have a same shape as the medial condyle <NUM>.

As a result of the symmetry in geometry between the medial condyle <NUM> and the lateral condyle <NUM>, the lateral multi-radius curve <NUM> can have a same shape as the medial multi-radius curve <NUM>. The medial condyle <NUM> can have the high flex portion <NUM>, the posterior portion <NUM>, the extension to mid-flexion portion <NUM>, and the part of the anterior region <NUM>, as previously discussed. As shown in the example of <FIG>, the posterior portion <NUM> and the extension to mid-flexion portion <NUM> can share the single common radius R1. Indeed, in the example of <FIG>, the posterior portion <NUM>, the extension to mid-flexion portion <NUM>, and the part of the anterior region <NUM> can share the single common radius R1.

In <FIG>, the posterior portion <NUM> extends to <NUM> degrees flexion, inclusive. The high flex portion <NUM> extends between substantially <NUM> degrees flexion to greater degrees of flexion (e.g., <NUM> degrees). The extension to mid-flexion portion <NUM> can extend from the posterior portion <NUM> to <NUM> degrees flexion (<NUM> degrees flexion comprising full extension). The part of the anterior region <NUM> can extend from substantially <NUM> degrees flexion to -<NUM> degrees flexion, inclusive, for example.

According to the example shown, the lateral multi-radius curve <NUM> can have the single common radius R1 swept through a first angular extent to define a single arc length A that extends from between substantially -<NUM> degrees flexion to substantially <NUM> degrees flexion, inclusive. The single arc length A includes the posterior portion <NUM>, the extension to mid-flexion portion <NUM> and the part of the anterior region <NUM>. Thus, the lateral multi-radius curve <NUM> can have the single common radius R1 swept through a first portion of the first angular extent to define a first part the single arc length A that extends from between substantially <NUM> degrees flexion to substantially <NUM> degrees flexion. Additionally, the lateral multi-radius curve <NUM> can have the single common radius R1 swept through a second portion of the first angular extent to define a second part the single arc length A that extends from between substantially -<NUM> degrees flexion to substantially <NUM> degrees flexion.

<FIG> shows a table comparing the sagittal radii of the medial multi-radius curve <NUM> (<FIG>) of the present femoral prostheses <NUM> with the medial multi-radius curve <NUM> of various commercially available femoral prostheses of comparable size for the high flex portion <NUM>, the posterior portion <NUM>, the extension to mid-flexion portion <NUM>, and the part of the anterior region <NUM>, as previously discussed. In the table of <FIG>, the commercially available femoral prostheses are labeled "Comp. A" to "Comp. F", while the femoral prosthesis <NUM> is labeled as "Comp.

The table of <FIG> shows the single common radius R1 (illustrated in <FIG> and <FIG>) is shared by the posterior portion <NUM>, the extension to mid-flexion portion <NUM>, and the part of the anterior region <NUM> for the medial multi-radius curve as previously described. As shown in the table, none of the commercially available femoral prostheses exhibit similar geometry of the medial multi-radius curve. Indeed, all the commercially available femoral prostheses include three separate and distinct radii for the high flex portion <NUM>, the posterior portion <NUM>, the extension to mid-flexion portion <NUM>, and the part of the anterior region <NUM>.

<FIG> show aspects of the construction of the tibial bearing component <NUM> according to one example. <FIG> shows the tibial bearing component <NUM> as previously described including include the articular surface <NUM>, the intercondylar region <NUM>, the periphery <NUM> and the distal surface <NUM> as previously described in reference to <FIG>. The articular surface <NUM> can include the lateral compartment <NUM> and the medial compartment <NUM>. The intercondylar region <NUM> can include the spine <NUM>.

Unlike the lateral and medial condyles <NUM> and <NUM>, the lateral compartment <NUM> and the medial compartment <NUM> can have a different shape relative to one another as illustrated in the example of <FIG>.

<FIG> shows a sagittal cross-section through the medial compartment <NUM> of the tibial bearing component <NUM>. <FIG> shows a comparison of the articular surface <NUM> in the medial compartment <NUM> overlaid with the corresponding articular surfaces in the medial compartments of two commercially available tibial bearing components (indicated as component <NUM> and component <NUM>). Component <NUM> can comprise a cruciate retaining tibial bearing component of the Persona® knee system, for example.

As shown in <FIG>, the tibial bearing component <NUM> in the medial compartment <NUM> can have an anterior lip <NUM> at the transition between an anterior portion of the articular surface <NUM> and the periphery <NUM>, and similarly, can have a posterior lip <NUM> at the transition between a posterior portion of the articular surface <NUM> and the periphery <NUM>. As shown in <FIG>, a height of the anterior lip <NUM> and the posterior lip <NUM> exceeds those of components <NUM> and <NUM>. This configuration gives the articular surface <NUM> a steeper inclination as compared to components <NUM> and <NUM> as the articular surface <NUM> has a similar geometry to those of components <NUM> and <NUM> in a mid-portion.

<FIG> shows a sagittal cross-section through the lateral compartment <NUM> of the tibial bearing component <NUM>. <FIG> shows a comparison of the articular surface <NUM> in the lateral compartment <NUM> overlaid with the corresponding articular surfaces in the lateral compartments of component <NUM> and component <NUM>. For the articular surface <NUM> in the lateral compartment <NUM>, this configuration can be very similar to that of component <NUM>, for example. The articular surface <NUM> in the lateral compartment <NUM> can have an anterior lip <NUM> that is slightly greater in height than that of components <NUM> and <NUM>. However, a height of a posterior lip <NUM> height can be comparable to that of component <NUM>.

<FIG> shows a sagittal cross-section through the intercondylar region <NUM> including the spine <NUM> of the tibial bearing component <NUM>. <FIG> shows a comparison of the intercondylar region <NUM> overlaid with the corresponding intercondylar regions of component <NUM> and component <NUM>. As shown in <FIG>, an anterior facing surface <NUM> of the spine <NUM> for the tibial bearing component <NUM> can be disposed rearward of the comparable surface of components <NUM> and <NUM>.

<FIG> shows a sagittal cross-section through the cam <NUM> of the femoral prosthesis <NUM>. <FIG> shows a comparison of the cam <NUM> overlaid with the corresponding cams of components <NUM> and <NUM> (femoral prostheses designed to be operably used with component <NUM> and component <NUM>, respectively). As shown in <FIG>, the cam <NUM> can have a reduced cross-sectional area and a surface <NUM> of the cam <NUM> for the femoral prosthesis <NUM> that is configured to make contact with the spine can be disposed rearward of the comparable surface of components <NUM> and <NUM>.

<FIG> illustrate the femoral prosthesis <NUM> and the tibial bearing component <NUM> previously discussed and illustrated can provide for a more stable medial condyle in terms of laxity ranges. A sizing scheme is presented in <FIG> for sizing various of the tibial bearing components and femoral prostheses of the respective families in a manner such that they can be used in combination to better achieve the desired more stable medial condyle.

In <FIG>, the femoral prosthesis <NUM> (indicated as Comp. <NUM>) in particular the lateral condyle (<FIG>) and the medial condyle (<FIG>) are illustrated having different average anterior-posterior laxity from <NUM>° to <NUM>° flexion as shown in the graphs of <FIG>, the laxity can comprise a degree of change in the anterior-posterior position (under various applied load scenarios) of the lateral condyle and the medial condyle plotted against degrees of flexion of the femoral prosthesis. The graph <NUM> of <FIG> and graph <NUM> of <FIG>, are plots of the lateral condyle and the medial condyle, respectively, for the posterior stabilized femoral component <NUM> (Comp. <NUM>) articulating through the range of motion with the tibial bearing component previously illustrated and discussed. As exhibited by the graph <NUM> of <FIG> the medial condyle when used with the tibial bearing component's medial compartment can be relatively more stabilized (has a tighter laxity area <NUM> as indicated) when measured against commercially available PS knee system designs (as indicated by areas <NUM> and <NUM> of <FIG>), where area <NUM> indicates the envelope for a PS femoral prosthesis (previously illustrated and described as component <NUM>) and tibial bearing component (previously illustrated and described as component <NUM>) of the Persona® knee system and area <NUM> comprises the laxity of the components <NUM> and <NUM> used in combination.

<FIG> show the average width of the laxity range for the various systems of <FIG>. Again, in <FIG>, the average width of the laxity range indicated by line <NUM> for the medial condyle of the femoral prosthesis (Comp. <NUM>) with the medial compartment of the tibial bearing component as previously shown and described is lower than that of the other commercially available systems previously described in reference to <FIG>.

<FIG> is a plan view of a proximal portion of a tibial bearing component <NUM> according to an example of the present application. Tibial bearing component <NUM> can be substantially similar to tibial bearing component <NUM> previously described herein. However, <FIG> adds further detail regarding aspects of the construction of the tibial bearing component <NUM>. As shown in <FIG>, the tibial bearing component <NUM> can include an articular surface <NUM>, an intercondylar region <NUM>, a periphery <NUM>, a lateral compartment <NUM>, a medial compartment <NUM> and a spine <NUM>.

As previously described, the articular surface <NUM> can be contacted by the femoral condyles (not shown) when operably assembled in the knee. The condyles of the femoral prosthesis can contact the medial and lateral compartments <NUM>, <NUM>. More particularly, the medial compartment <NUM> and the lateral compartment <NUM> can be configured (e.g. are dish shaped) for articulation with the medial condyle and the lateral condyle of the femoral prosthesis <NUM>, respectively (as shown in <FIG> and further shown in <FIG>). The periphery <NUM> can comprise sidewalls connecting with the distal surface (not shown) and the articular surface <NUM>. The medial compartment <NUM> can differ in configuration from the lateral compartment <NUM> as will be explained in further detail subsequently. For example, the medial compartment <NUM> can have a different size and shape relative to the lateral compartment <NUM>. For example, the anterior-posterior curvature of the lateral compartment <NUM> can differ from that of the medial compartment <NUM>. A position of a medial dwell point for the medial compartment <NUM> can differ than a lateral dwell point for the lateral compartment <NUM>.

As shown in the example of <FIG>, the lateral compartment <NUM> can have a lateral articular track <NUM> having a lateral anterior-posterior extent LAP. The lateral articular track <NUM> can comprise a plurality of distal-most points along the proximal surface of the lateral compartment <NUM> that are contacted by the lateral femoral condyle during rollback of the femoral prosthesis. Similarly, the medial compartment <NUM> can have a medial articular track <NUM> having a medial anterior-posterior extent MAP that differs from the lateral anterior-posterior extent LAP. The medial articular track <NUM> can comprise a plurality of distal-most points along the proximal surface of the medial compartment <NUM> that are contacted by the medial femoral condyle during rollback of the femoral prosthesis.

As shown in <FIG>, in one example the lateral compartment <NUM> can have an anterior portion <NUM> and a posterior portion <NUM>. The anterior portion <NUM> can define the lateral articular track <NUM> as a nominally straight line when projected onto a transverse plane of the tibial bearing component <NUM>. The posterior portion <NUM> can define the lateral articular track <NUM> as a curved line toward the medial compartment <NUM> when projected onto the transverse plane of the tibial bearing component <NUM>.

In contrast, the medial articular track <NUM> can define a nominally straight line when projected onto the transverse plane of the tibial bearing component <NUM>, and the medial articular track <NUM> defined by the medial compartment <NUM> can be comprised of a uniform single curve. The nominally straight line that can be defined by the medial articular track <NUM> can be substantially parallel to the nominally straight line defined by the anterior portion <NUM> of the lateral articular track <NUM> in some cases.

For convenience, the present discussion refers to points, tracks or lines of contact between tibial bearing component <NUM> and the femoral prosthesis along the articular tracks <NUM>, <NUM>. However, it is of course appreciated that each potential point or line of contact (i.e., any of the points along one of the articular tracks <NUM>, <NUM>) is not truly a point or line, but rather an area of contact. These areas of contact may be relatively larger or smaller depending on various factors, such as prosthesis materials, the amount of pressure applied at the interface between tibial bearing component <NUM> and femoral prosthesis, relative shapes of the tibial bearing component <NUM> relative to the femoral prosthesis, and the like. Moreover, it is appreciated that some of the factors affecting the size of the contact area may change dynamically during prosthesis use, such as the amount of applied pressure at the femoral/tibial interface during walking, climbing stairs or crouching, for example. For purposes of the present discussion, a contact point may be taken as the point at the geometric center of the area of contact. The geometric center, in turn, refers to the intersection of all straight lines that divide a given area into two parts of equal moment about each respective line. Stated another way, a geometric center may be said to be the average (i.e., arithmetic mean) of all points of the given area. Similarly, a line or track is the central line of contact passing through and bisecting an elongate area of contact.

Both the medial compartment <NUM> and the lateral compartment <NUM> can include dwell points comprising the medial dwell point <NUM> and the lateral dwell point <NUM>, respectively. The medial and lateral dwell points <NUM> and <NUM> can comprise a distal-most point along the medial articular track <NUM> and the lateral articular track <NUM>, respectively. As shown in TABLE <NUM> below, the medial compartment <NUM> can be configured to have the medial dwell point <NUM> a distance between about <NUM>% and about <NUM>% of a total anterior-posterior extent T of the tibial bearing component <NUM> as measured from an anterior most point A of the tibial bearing component <NUM> to a posterior most point P of the tibial bearing component <NUM>.

As shown in TABLE <NUM>, the lateral compartment <NUM> can be configured to have the lateral dwell point <NUM> a distance between about <NUM>% and about <NUM>% of the total anterior-posterior extent T of the tibial bearing component <NUM> as measured from the anterior most point A to the posterior most point P of the tibial bearing component <NUM>.

As shown in <FIG>, the intercondylar region <NUM> can comprise an eminence or ridge of the articular surface <NUM> that can be disposed between the medial and lateral compartments <NUM>, <NUM>. The intercondylar region <NUM> can extend generally anterior-posterior and can have the spine <NUM> as previously discussed. Thus, the intercondylar ridge defined by the intercondylar region <NUM> an be disposed between the medial and lateral dished medial and lateral compartments <NUM>, <NUM> and occupies the available space therebetween.

The tibial bearing components and the femoral prostheses described herein can each be available as a family of tibial bearing components and a family of femoral prostheses, respectively. The family of tibial prostheses can be of a same design class (e.g., be shaped to be PS) and can have different stock sizes (e.g., from use with a small stature tibial component size A to a largest size J). Similarly, the family of femoral prostheses can be a same design class (e.g., be shaped to articulate with a posterior stabilized configured tibial bearing component) and can have different stock sizes (e.g., from a small stature size <NUM> to a largest size <NUM>). Different sizes of tibial bearing components can be used depending on the size of the femoral prosthesis and the tibial prosthesis selected.

<FIG> shows a sizing chart for the family of tibial prostheses <NUM> relative to the family of femoral prostheses <NUM>. More particularly, the sizing chart shows the family of femoral prostheses <NUM> can have at least twelve different stock sizes <NUM> to <NUM>. As previously discussed and illustrated, each femoral prosthesis can be of a same design class PS and can include a medial condyle and a lateral condyle. The family of tibial prostheses <NUM> can have at least nine different stock sizes A to J. As shown in <FIG>, the family of tibial bearing components <NUM> can be configured such that at least eleven stock sizes exist and that combinations of the at least nine different stock sizes of the family of tibial prostheses <NUM> are compatible for operable use (e.g. to facilitate a desired articulation similar to that of a natural knee) with the at least twelve different stock sizes of the family of femoral prostheses <NUM>.

This overlapping sizing and the provision of many different compatible sizes can have benefits including providing for increased stability of the medial condyle of the femoral prosthesis. For example, by having a family of tibial bearing components that can include at least eleven different stock sizes and a family of femoral prostheses that can include at least twelve different stock sizes with thirty three different possible operable combinations.

Furthermore, having overlapping sizing and the provision of many different compatible sizes (alone and/or in addition to shaping the compartments to better conform with the condyles using aspects previously discussed) can provide for an increased contact area between the medial condyle of the femoral prosthesis and the medial compartment of the tibial bearing component. As a result, the femoral prosthesis can have greater stability with respect to the medial condyle.

A medial conformity between the femoral prosthesis and the tibial bearing component can be between about <NUM>:<NUM> and about <NUM>:<NUM> through the first angular extent (previously discussed in reference to <FIG>). Put another way, the medial compartment is configured to have between about a <NUM>:<NUM> congruence ratio and about a <NUM>:<NUM> congruence ratio with the medial condyle through the first angular extent. "Conformity," (also referred to as "congruence" or "congruence ratio" in the context of knee prostheses, refers to the similarity of curvature between the convex femoral condyles and the correspondingly concave tibial articular compartments in the sagittal plane. Thus, the conformity ratio can comprise a ratio of the similarity between a sagittal radius of the medial tibial bearing compartment and a sagittal radius of the medial femoral condyle.

<FIG> shows articulation of the femoral prosthesis <NUM> with the tibial bearing component <NUM> through a range of motion between <NUM> degrees and <NUM> degrees flexion. Recall <NUM> degrees flexion comprises full extension as previously discussed and positive flexion corresponds to greater than zero degrees flexion of the knee joint. As indicated by arrows A in <FIG>, an area of contact between the medial condyle and the medial compartment does not shift position during the range of motion between zero degrees flexion and substantially <NUM> degrees flexion. Furthermore, the area of contact (as indicated by arrow A) includes the medial dwell point MD of the tibial articular surface during the range of motion between zero degrees flexion and substantially <NUM> degrees flexion. Thus, the area of contact includes the medial dwell point MD of the tibial articular surface when the femoral prosthesis <NUM> is in full extension. Recall from prior discussion that the spine and cam can make initial contact when the range of motion reaches substantially <NUM> degrees flexion with the anterior-posterior slope of the tibial bearing component of five degrees, when such initial contact occurs the area of contact (indicated as arrow A) can begin to shift position and can move off the medial dwell point MD as shown in reference to the image where the femoral prosthesis has been articulated to <NUM> degrees flexion.

As used herein the terms "substantially" or "about" means within two percent of a referenced value, within two degrees of the reference value, within <NUM> or less of the reference value, or the like, whatever, context best applies.

Claim 1:
A system (<NUM>) of posterior-stabilized knee prostheses for a knee arthroplasty, the system comprising:
a tibial bearing component (<NUM>) having a tibial articular surface (<NUM>) with a medial compartment (<NUM>) and a lateral compartment (<NUM>), wherein the tibial bearing component has a spine (<NUM>) extending proximally from the tibial articular surface and positioned between the medial and lateral compartments, and wherein the medial compartment has a medial dwell point (<NUM>);
a femoral prosthesis (<NUM>) having a cam (<NUM>) and medial and lateral condyles (<NUM>,<NUM>) spaced to either side of the cam, wherein the medial condyle (<NUM>) is configured for articulation with the medial compartment (<NUM>) and lateral condyle (<NUM>) is configured for articulation with the lateral compartment (<NUM>), and wherein the femoral prosthesis (<NUM>) is configured to articulate through a range of motion relative to the tibial bearing component (<NUM>), such range of motion includes a full extension that corresponds to zero degrees flexion of a knee joint and positive flexion that corresponds to greater than zero degrees flexion of the knee joint, wherein an area of contact between the medial condyle (<NUM>) and the medial compartment (<NUM>) includes the medial dwell point when the femoral prosthesis (<NUM>) is in full extension, and wherein the spine (<NUM>) and cam (<NUM>) are both configured to make initial contact when the range of motion reaches substantially <NUM> degrees flexion.