ARTIFICIAL KNEE JOINT

Technical Field

The following inventionrelates to surgical implants placed within a knee of a patient to function as an artificial knee joint. More particularly, this invention relates to artificial knee joints which include a femoral component, a tibial component and a patellar component which exhibit a simplified femoral component, femoral component sizing, bone preparation procedures, tibial component meniscal insert low wear characteristics and dual direction knee pivoting rotation function therein.

Background Art

Human knee joints endure exceptional loads and a wide variety of loading scenarios throughout the life of an individual. While the human knee joint is capable of supporting most of these typical loads under normal conditions for the life of the individual, in certain circumstances the human knee joint suffers degraded performance. For instance, injury can occur to the knee causing the knee to not fully repair itself, or not being fully repairable through medical intervention^uch that it becomes beneficial to replace the knee joint with an artificial knee joint. In other circumstances, degenerative disease can act on the natural knee jointto degrade its performance in an irreversible fashion, such that replacement of the natural knee joint with an artificial knee joint is indicated.

Artificial knee joints are well known in the literature and have come into widespread use. In general, such artificial knee joints include a femoral component, a tibial component and a patellar component. The distal end of the femur is surgically prepared to have the distal end thereof have a contour matching an internal box surface of the femoral component. The femoral component is then attached to the distal end of the femur. Similarly, the proximal end of the tibia is prepared, typically by cutting a flat proximal surface on the proximal end of the tibia, and the tibial component is attached to this proximal end of the tibia. Muscles and ligaments surrounding the knee are disturbed as littleas possible so that they can continue to function in the same manner that they do with a natural knee joint. Proximal surfaces of the tibial component and distal surfaces of the femoral component abut each other and are designed to facilitatearticulation relativeto each other in the same way that the distal end of a natural femur articulates relativeto the proximal end of a natural tibia. Typically, an insert of materials some what more flexibleand resilientthan metal is attached to a proximal end of the tibial component, with other portions of the tibial component

formed of a more rigid material, such as titanium or cobalt chrome. This insert in some ways duplicates the function of a natural meniscus within a natural knee joint, and helps to minimize friction in the articulation of the femoral component relative to the tibial component.

Numerous drawbacks have been noted with prior art artificial knee joints and for which this invention strives to provide a significant and beneficial improvement. For instance, artificial knee joints are known for being somewhat complex to implant, and most particularly the femoral component. In particular,the distal end of the femur must be extensively shaped to properly mate with facets on the internal box face of the femoral component.

In the prior art, the surgeon must make numerous very precise cuts on the distal end of the femur and these cuts vary based on the particular geometry of the facets on the internal box face of the femoral component. Because different human bodies have different sizes, various different femoral components having different sizes must be considered before selecting the particular femoral component. Typically,a cutting jig or other specialized tool must be selected that matches with the femoral component selected so that the cuts are properly made. As a result, the surgeon, manufacturer or an associated health care facility must maintain an extensive inventory of femoral cutting jigs for potential use in an artificial knee joint surgical procedure. Such extensive inventory of cutting jigs is expensive to maintain, requires additional space within the surgery room or nearby, and presents the greater possibility of problems during or after surgery. Furthermore, an increase of such cutting jigs is more difficult to clean and sterilize which increases the potential for infection, in turn resulting in a less than fully desirable outcome. U.S. Patent Nos. 5,925,049 and 5,749,876 both describe a femoral cutting instrument sizer that allows a single tool to be used for a set of femoral components of different sizes however both devices are cumbersome and complicated to use. Accordingly, a need exists for an artificial knee joint which has a femoral component which is one of a set of femoral components of different sizes which share as many shape and size characteristics as possible, as well as a single tool which can easily make the necessary cuts for all different femoral component sizes.

Another problem with known prior art artificial knee joints is that they cannot duplicate the large amount of flexion produced by a natural human knee joint and still provide sufficient contact betweenthe artificial femur and the tibial component. Conventional artificial knee joints are limited in further flexion because they typically cause the femur or structure coupled to the femur to abut the tibia or structures coupled to the tibia to preventfurther flexion. Accordingly, a need exists for an artificial knee joint which can provideas much flexion as possible to more fully mimic a natural knee joint in performance.

Another problem with known prior art artificial knee joints is their inability or difficulty in facilitating knee pivoting rotation in both clockwise and counterclockwisedirections. A natural knee joint is capable of a small amount of pivoting rotation. Such pi voting rotation is particularly desirable when a person is walking along a curving path.

Some artificial knee joints, such as those taught by Hodge (U.S. Patent No. 5,413,604) allow for pi voting rotation of the medial condyle about the lateral condyle, but not rotation of the lateral condyle. Furthermore, other artificial knee joints, such as those taught by Kaufman (U.S. Patent No. 6,013,103) and Tuke (U.S. Patent No. 5,219,362) describe pivoting rotation of the lateral condyle about the medial condyle. Accordingly, a need exists for complete replicationof function of a natural knee joint, including pivoting rotation in both directions.

Another problem with known prior art artificial knee joints is the need for the insert or other meniscal structure to exhibit a minimum thickness for suitable wear characteristics and duration, while minimizing an amount of bone required to be removed from the proximal end of the tibia. Generally speaking, bone is removed from the proximal end of the natural tibia in an amount equaling a height of portions of the tibial component of the artificial knee joint which extend beyond the proximal surface of the tibia after it has been prepared for receiving the tibial component. Typically, regulatory authorities recommend a six millimeterthickness on the insert or other meniscal wear structure, and structural portions of the tibial component need approximately four millimeters for sufficient strength, a full ten millimetersof bone must be removed from the proximal tibiato maintain proper ligament tension and maintain patient leg length. It is desirable to remove as little natural bone as possible, as natural bone is beneficial in many respects and to be preferred over artificial structures to the extent possible.

Prior art attempts have been made to nest the insert into the tibial component somewhat, but only with joints that prevent twisting. See for instance patent to Aubriot (U.S. Patent No. 5,326,358) and Johnson (U.S. Patent No. 4,568,348). Accordingly, a need exists for a tibial component of an artificial knee joint which can maintain the regulatory recommended thickness of an insert or other wear structure while minimizing a height of other portions of the tibial component of the artificial knee joint,and still allowtwisting,to minimizethe amount of required bone removal from the proximal end of the tibia.

Disclosure of Invention

With this invention, an artificial knee joint is provided which includes a femoral component and a tibial component that together satisfy the needs and shortcomings of the prior art identified above. The joint includes a femoral component surgically affixable to a distal end of a femur and a tibial component surgically affixable to a proximal end of a tibia. An insert is also provided as a portion of the tibial component which is removably attachable to the tibial component. With this inventiona jig is also provided to assist in making the cuts necessary to form surfaces on the distal end of the femur appropriate to mate with facets on an internal box face of the femoral component. This jig includes slots or other guides for a cutting tool so that the jig helps the

surgeon who is wielding the cutting tool to cut the proper portions of the distal end of the femur away to provide the required surfaces on the distal end of the femur.

The jig is provided to make appropriate cuts for multipledifferent sizes of femoral components. In particular, slots or other cutting tool guide structures are provided which are the same for each size femoral componentto be surgically implanted,exceptfor an anterior surface cut which is made at a variabledistance from a posterior surface cut, depending on a size of the femoral componentto be implanted. Other slots or other structures within the jig are the same for other cuts to be made to form the surfaces on the distal end of the femur for proper fit with the selected femoral component. Adjustability of the jig for cutting of the anterior surface is in one embodiment provided by a plurality of separate anterior slots withinthejig. In another embodiment,thejig is provided with an anterior slot on a moving portion of the jig that can slide relative to fixed portions of the jig to a desired position for making the necessary cut to form the anterior surface on the distal end of the femur. The femoral component is generally in the form of a surfacing structure providinga new wear surface on the distal end of the femur. As such it includes a patellar flange portion adapted to be placed adjacentthe anterior surface of the distal end of the femur and a medial condylar leg and a lateral condylar leg, both extending down from the patellarflange portion generally parallel to each other. The condylar legs curve posteriorly as they extend from the patellar flange portion. A distal and posterior face of the femoral component is provided primarily upon the medial condylar leg and lateral condylar leg and is adapted to abut with the insert of the tibial component of the artificial knee joint. The internal box face of the femoral component includes an anterior facet, a distal facet, a posterior facet, and preferably a pair of diagonal facets at either side of the distal facet. The posterior facet is angled back toward a centerline of the femoral component as the posterior facet extends away from the distal facet. Such a negative angle for the posterior facet of the internal box surface and corresponding forming of the posterior surface on the distal end of the femur, allows the distal face of the two condylar legs to wrap around the posterior side of the distal end of the femur sufficiently farther to allow an increase of contactand flexion in operation of the knee joint when compared to prior art knee joint femoral components. The tibial component includes a substantially planar plate oriented substantially perpendicular to a shaft which is adapted to pass down into a marrow of the tibia and substantially coaxial with a centerline of the tibia. The insert is supported upon a proximal side of the plate. A dovetail rib extends in an anterior to posterior direction from the proximal surface of the plate. The insert includes a dovetail recess sized to be aligned with the dovetail rib on the plate so that the insert can be slid onto the dovetail rib and held tightly to the proximal surface of the plate.

To minimize a thickness of the plate and an overall height of the combination of the insert and the plate, the proximal surface of the plate includes depressions therein and a distal surface of the

insert includes lobes therein that drop down into the depressions in the proximal surface of the plate. In this way, a maximum thickness of the insert is maintained, especially beneath wells in a proximal surface of the insert, without adding height to the overall insert and plate of the tibial component. Two wells in the proximal surface of the insert have a curvature matching a curvature of the condylar legs of the femoral component. Thus, the condylar legs of the femoral component can reside within these generally spherical wells in the insert and the joint can experience flexion while maintaining surface contact between the wells of the insert and the condylar legs of the femoral component. The wells have valleysthat extend arcuatelyand mostly in an anterior directionaway from low points of the wells. These valleys are of lesser depth in a distal direction as the valleys extend anteriorly away from low points of the wells. The valleys curve about a center point axis aligned with the low point of the other of the pair of wells. Side walls of the valleys are appropriately gradual so that cross-sections of the valleys perpendicular to centerlines of the valleys contain a curvature similar to that of the condylar legs of the femoral component. In this way, one of the condylar legs can remain at a low point within one of the wells while the other condylar leg can rotate along a valley of one of the wells away from the low point and moving slightly upwardly in a proximal direction. As the elevationof the valleys increase, tension on ligaments and muscles of the knee joint tighten to resist further pivoting rotation of the knee joint. Gravity loads tend to encourage the condylar legs back to the low points of the wells, as well as forces applied by the ligaments and muscles themselves. Such pivoting rotation can occur in either direction with one of the condylar legs remaining in a low point of one of the wells while the other condylar leg can move arcuately within its well. In this way, a small amount of knee pivoting rotation action is providedby the artificial knee joint of this invention,mimickingperformanceof a natural knee joint being replaced.

Brief Description of Drawings

Figure 1 is a side elevation view of a distal end of a femur before cuts are made thereto to form surfaces on the distal end of the femur for receipt of the femoral component of the artificial knee joint, and with cut lines to be made shown in broken lines thereon.

Figure 2 is a side elevation viewsimilar to that which is shown in Figure 1 , but after making a first cut to the femur to form the distal surface of the femur, and after attachment of a fixed jig to the distal surface for guiding of cutting tools for the making of other cuts to form other surfaces on the distal end of the femur.

Figures 3 and 4 are perspective views of an adjustable jig attachable to the distal surface of the femur similar to the fixed jig of Figure 2, but which adjustablejig features an adjustable portion for moving one of the slots to different distances adjustably spaced from other slots within fixed portions of the jig. Figure 5 is a side elevationview similar to that which is shown in Figure 2, but illustrating use of the adjustablejig of Figures 3 and 4 thereon.

Figure 6 is a perspective view of the distal end of the femur with a femoral component of the artificialknee joint exploded therefrom, and illustratinghow the femoral component is oriented and configured to fit upon the distal end of the femur. Figure 7 is a side elevationview of the distal end of the femur including a femoral component attached thereto.

Figure 8 is a perspective view of the femoral component of Figures 6 and 7.

Figure 9 is a top plan view of that which is shown in Figure 8.

Figure 10 is a front elevation view of that which is shown in Figure 8. Figure 1 1 is a rear sectional view of that which is shown in Figure 8.

Figure 12 is a side elevationview of that which is shown in Figure 8, and illustratingin broken lines how two other femoral components of larger and smaller sizes share common surfaces with each other, except for an anterior facet and portions of a distal face of the femoral component to allow for simple size adjustability. This view also shows the femurs of different sizes matching those of the femoral components.

Figure 13 is a side elevation view of that which is shown in Figure 12 without the femurs shown and depicting nine sizes of femoral components and how they relate together.

Figure 14 is an exploded parts view of a tibial component of the artificial knee joint of this invention showing an insert portion of the tibial component exploded away from a plate and shaft portion of the tibial component, and exploded from a proximal end of a tibia.

Figure 15 is a side elevationview of the tibial component shown in place upon the proximal end of the tibia.

Figure 16 is an exploded parts viewof the entire artificial knee joint shown in perspective and from below. Figure 17 is a perspective view of the completed artificial knee joint in extension and with the femur and tibia brought together.

Figure 18 is a sectional side elevation view of that which is shown in Figure 17.

Figure 19 is a side elevation viewof thatwhich is shown in Figure 17, and with a knee joint in a state of partial flexion. Figure 20 is a side elevation view similar to Figure 19, but showing full flexion of the knee joint.

Figures 21 and 22 are perspective views similar to that which is shown in Figure 17, but illustrating pivoting rotation of the knee joint in both a clockwise and counterclockwise direction.

Figure 23 is a top plan view of the insert of the tibial component of this invention.

Figure 24 is a perspective view of the plate and shaft of the tibial component of this invention. Figure 25 is a side elevation view of the tibial component showing the insert portion in the process of being slid onto the plate.

Figure 26 is a perspective view similar to that which is shown in Figure 25 but after the insert has been almost fully attached to the plate of the tibial component.

Figure 27 is a perspective view similar to that which is shown in Figure 26, but after the insert has been completely attached to the plate of the tibial component.

Figure 28 is a full sectional elevation view of the tibial component including the insert portion and the plate and shaft portion, with the insert portion exploded away from other portions of the tibial component to most clearly show complementally formed contours thereof.

Figure 29 is a perspective view of an alternativetibial component with an augment removably attachablethereto and shown exploded away from the tibial component and with a second position for the augment shown in broken lines.

Figure 30 is a perspective view of the alternative tibial component of Figure 29 with the augment attached to the tibial component.

Figure 31 is a full sectional view of the alternativetibial component and augment taken along line 31-31 of Figure 30.

Best Modes for Carrying Out the Invention

Referring to the drawings, wherein like reference numerals represent like parts throughout the various drawing figures, reference numeral 10 is directed to an artificial knee joint for replacing a natural knee joint between a femur F and a tibiaT. The inventionincludes a femoral component 20 and a tibial component 40, as well as tools 2, 12 for forming a distal end of the femur F to receive the femoral component 20. The inventionalso includes methods for preparing the distal end of the femur to receive an appropriately sized femoral component.

In essence, and with particular reference to Figures 15 and 16, the basic details of the artificial knee joint 10 are described, according to a preferred embodiment. The joint 10 includes the femoral component 20 adapted to be coupled to an appropriately shaped distal end of the femur F. The joint 10 also includes a tibial component 40. The tibial component 40 primarily includes a shaft 42 for insertion into the proximal end of the tibialT and a plate 50 of generally planar form perpendicular to the shaft 42. An insert 70 provides a removable portion of the tibial component 40 which attaches to the plate 50. This insert 70 cooperates with a dovetail rib 60 on the plate 50 to

secure the insert 70 tightly to the plate 50. The insert 70 can then act somewhat as a meniscal component within the joint 10 for interfacing with the femoral component 20 in an articulating fashion during operation of the joint 10 (Figures 18-20).

More specifically, and with particular reference to Figures 1-5, details of jigs 2, 12 for use in forming surfaces of the distal end of the femur F to receive the femoral component 20, are described according to a preferred embodiment. Before using either of the jigs 2, 12, a cut Cl is made to the distal end of the femur (Figure 1). This cut is typicallyapproximatelyperpendicularto the centerline L of the femur F, but most preferably slightly angled, as shown in Figure 1. The fixed jig 2 provides one form of tool for assisting a surgeon in properly forming surfaces on the distal end of the femur F to receive the femoral component 20. The fixed jig 2 is generally in the form of a thick rigid structure which has an abutting face 4 which is caused to abut a distal surface of the femur F formed by cut line Ci (Figures 1 and 2). Pins or pegs 3 provide one form of means to temporarily secure the fixed jig 2 to the distal surface of the femur F.

The fixed jig 2 includes a face 5 opposite the abutting surface 4. Slots pass from the face 5 to the abutting surface 4 for guiding of a cutting tool through the fixed jig 2, then into bone of the femur F to form the surfaces required on the distal end of the femur F to receive the femoral component 20. In particulars posterior slot 6 is provided passing from the face 5 through to the abutting surface 4. This posterior slot 6 is utilized to form cut C2 (Figures 1 and 2). Diagonal slots 7, 9 are separately utilized to form cuts C3 and C4. The fixed jig 2 also includes an anterior slot array 8 aligned with cut lines Cs-Cl 3. In this embodiment nine separate anterior slots are provided within the slot array 8. Each separate slot corresponds with one particular size for the femoral component 20 (Figure 12). The surgeon makes a determination as to which femoral component 20 would best be utilized with the patient. The surgeon then makes one cut through one of the anterior slots in the anterior slot array 8 to form the surface corresponding with cut Cs (Figure 1) or one of the other cut lines Ce-Ci 3 (Figure T) to form the anterior surface of the distal end of the femur F as desired to fit with the femoral component 20 that has been selected.

An adjustablejig 12 provides an alternativeto the fixed jig 2. The adjustable jig 12 (Figures 3- 5) is generally similar to the fixed jig 2 except where particularly described herein. An abutting surface 14 is thus provided for temporary attachment adjacent to the distal end of the femur F formed by cut line Ci (Figure 1). Once the adjustable jig 12 is attached to the distal end of the femur F, a guide 13 is utilized which slides (along arrow A of Figure 5) relativeto other portions of the adjustablejig 12 thatare fixed to the femur F. When the guide 13 is touching the femur F, an adjustable slot 16 is positioned where desired for forming of a cut to form the anterior surface of the femur F.

This guide 13 is coupled to a structure in which the adjustable slot 16 is formed, along with a mast 17. The mast 17 is adapted to slide within a groove 18 formed in fixed portions of the

adjustable jig 12. A cross-sectional contour of the mast 17 and groove 18 are preferably selected to prevent rotation of the mast 17 withinthe groove 18, such as a "cross" form (Figure 3). Thus, the guide 13 and adjusting slot 16 can slide relativeto other slots within the adjustable jig 12 to place the adjustable slot 16 where desired to form the cut associated with the anterior surface for the distal end of the femur F.

Most preferably, the face 15 of the adjustable jig 12 includes a set line 19 thereon and the mast 17 includes a series of numbers and associated graduation marks thereon. These indicia and graduation marks could be placed on the face 15 with the set line 19 formed on the mast 17 if desired. When the guide 13 abuts the femur F (Figure 5) a user can see which graduation adjacent which indicia is aligned with the set line 19 (Figure 4). This indicia,such as a number or letter, corresponds with the size of femoral component (Figure 12) that will properly fit upon the distal end of the femur F after making cuts through the various slots of the adjustable jig 12.

Utilizing one of the jigs 2, 12 of this invention, each of the surfaces of the distal end of the femur are formed to havea similarsize, shape and relativeorientationto other surfaces on the distal end of the femur, with the exception of the anterior surface. This anterior surface maintains the same orientation relativeto other surfaces on the distal end of the femur, but exhibits a variable distance away from the posterior surface of the distal end of the femur. Thus, each femoral component20 within a set of femoral components 20 of different sizes (Figure 12) can be similar in size and shape, except for portions which are to be located adjacent the anterior surface of the distal end of the femur. Such anterior portions of the femoral component 20 are each slightly modified for different sizes within the set of femoral components. To achieve this similarity between femoral components of different sizes, one of the diagonal cuts exhibits variable length, with this anterior diagonal cut being almost non-existent for the smallest femur F, and largest to accommodate the largest femurs F. In addition, the femoral component 20, while it could be made generic and suitable for use on either a left or right knee, is most preferably optimized to be slightly asymmetrical to be provided either on a left knee or a right knee implantationsite. Thus, overall a surgeon need only have one jig, one cuttingtool for use with the jig and one set of femoral components associated with the left or right knee that is receivingthe artificial knee joint. Simplicity and freedom from potential error results from such a simplified system.

With particularreference to Figures 6-17, details of the femoral component 20 of the artificial knee joint 10 are described, according to a preferred embodiment. These details are described with regard to a femoral component 20 of midsize (Figure 12), with details of other femoral components 20 within a set of different sizes of femoral components 20 being similar, except for size adjustability as depicted in Figure 12.

The femoral component 20 generally includes a medial condylar leg 22 and a lateral condylar leg 24 which each extentfrom a patellarflange portion 26. Legs 22, 24 exhibit a curvature which

allow them to wrap around the distal end of the femur F from the anterior surface to the posterior surface and overthe distal surface of the femur F. A distal face 28 of the femoral component 20 is a generally curving surface optimized to abut and articulate against the insert 70 of the tibial component 40 described in detail below. Each condylar leg 22, 24 has a separate (same) curvature on the distal face 28 which is preferably substantially spherical, and most importantly has a curvature which matches that of the wells 77, 78 on the proximal surface 76 of the insert 70, described in detail below.

An internal box face 30 defines that portion of the femoral component20 which abuts against the distal end of the femur F. This internal box face 30 is divided into separate facets to which an adhesion medium can engage, or other fastening structures can be connected. The internal box face 30 includes a distal facet 32 which is close to perpendicular to a centerline of the femoral component 20, with a centerline of the femoral component 20 defined as a line aligned with a centerlineof the femur F when the femoral component20 is attached to the distal end of the femur F. However,the distal facet 32 preferably extends slightly further distally on a side of the distal facet 32 closest to the posterior diagonal facet 38. The distal facet 32 can support an axial structure which can penetrate into the femur F, or other attachment structures can be provided to extend generally proximally into the femur F. The distal facet 32 preferably maintains its size and shape for all sizes of femoral components 20.

The distal facet 32 is preferably substantially planar, but could have a differing contour provided that the distal surface of the distal end of the femur F is similarlyformed. Because planar surfaces are most easily formed on the distal end of the femur F, the internal box face 30 of the femoral component 20 is similarly formed with planar facets such as the distal facet 32.

An anterior face 34 defines a portion of the internal box face 30 of the femoral component 20 adapted to abut against the anterior surface of the distal end of the femur F. A posterior facet 35 is similarly adapted to abut the posterior surface of the distal end of the femur F. An anterior diagonal facet 36 extends diagonally between the distal facet 32 and the anterior facet 34. This anterior diagonal facet 36 is of varying size depending on which femoral component 20 size is involved. A posterior diagonal facet 38 extends between the posterior facet35 and the distal facet 32. Each of these facets 32, 34, 35, 36, 38 are preferably each planar and joined to adjacent facets

32, 34, 35, 36, 38 along transition lines which are linear in form and extend lateral Iy an entire width of the internal box face 30 of the femoral component 20 (Figure 8). Most preferably, these transition lines include ribs thereon with other portions of the facets 32, 34, 35, 36, 38 away from these transition lines recessed slightly. Side edges of the internal box face 30 can also be raised slightly. Such ribs are depicted in Figures 6, 8-1 1 and 17, but could have a variety of different configurations or could be omitted altogether. Recesses between the ribs provide a region for adhesive or bone in-growth medial to help adhere the femoral component 20 to the femur F.

Importantly, the posterior facet 35 has a negative angle α (Figures 2 and 19) relative to a centerlineof the femoral component 20 and a centerlineof the femur F when attached to the femur F. As best depicted in Figure 18, this negativeangle α is most preferably approximately 3°, but could be increased or decreased to optimize the design. Prior art femoral components of artificial knee joints are not known to have such a negativeangle. By providing such a negative angle, a greater amount of flexion and contact can be obtained (along arrow B of Figure 18) between the tibia T and femur F.

Cut line d associated with posterior slot 6 in the fixed jig 2 (Figure 2) provides the internal box surface of the distal end of the femur F with a negativeangle relative to a centerlineof the femur F which corresponds with the negativeangle of the posterior facet 35 relative to a centerline of the femoral component 20 (Figure 18).

Note that this posterior facet 35 is in fact a pair of separate facets with each facet on one of the condylar legs 22, 24. Also, the posterior diagonal facet 38 is actually split between the two condylar legs 22, 24 and the distal facet 32 extends partially onto each of the legs 22, 24. As these splitfacets 32, 35, 38 are coplanar, they are often referred to as a single plane and a single facetfor simplification.

The anterior diagonal facet 36 maintains a common position for each size of femoral component

20 (Figure 12. However, this facet 36 varies in length to accommodate anterior facets 34 of different positions for the different femoral component sizes. For a smallest size, this anterior diagonal facet 36 is reduced to zero or near zero length so that the anterior facet is directly or almost directly adjacent the distal facet 32. Other facets preferably maintain their size and relative orientation for the different sized femoral components 20.

With particular reference to Figures 13-26, details of the tibial component 40 are described, according to a preferred embodiment. The tibial component 40 is preferably formed as a rigid construct from high strength material such as titanium or cobalt chrome. The tibial component includes a shaft 42 of elongate form adapted to be aligned with a centerline of the tibia T and to be driven down into a marrow space within the tibiaT. This shaft 42 extends down from a plate 50 which is generally planar and oriented generally perpendicular to the shaft 42. The plate 50 is adapted to abut the proximal surface of the tibia T. Gussets 44 are formed on sides of the shaft 42 and generally become thicker as the gussets 44 extend proximally toward the plate 50. These gussets 44 help to give additional strength to the plate 50 and to the shaft 42, and also to further assist the shaft 42 and tibial component 40 overall in being securely affixed to the tibia T.

Furthermore, prongs 46 preferably extend distally from the plate 50 to further engage the proximal end of the tibia T. The plate 50 is generally oval shaped and is perhaps best seen in Figure 22. The plate 50 includes a pair of spherical depressions 52 on either side of a dovetail rib 60 passing medially

between the spherical depressions 52. The spherical depressions 52 need not necessarily be spherical, but could have some other contour. These depressions 52 extend distally down into the plate 50 and help to make the tibial component 40 exhibitan overalllesser distal heightto minimize an amount of bone required to be removed from the tibia T. The plate 50 includes a posterior wall 54 extending up from a posterior edge of the plate 50.

An anterior tab 56 also extends up from the plate 50 near a lateral midpoint of the anterior edge of the plate 50. A tooth 58 extends posteriorly from the anterior tab 56. The tab 56 helps to hold the insert 70 onto the plate 50, as described in detail below. Most preferably the posterior wall 54 exhibits an overhang that extends anteriorly to some extent. This overhang helps the posterior wall 54 to hold the insert 70 securely adjacent the plate 50, as described in detail below.

The dovetail rib 60 extends proximally up from a midportion of the plate 50. This dovetail rib 60 is elongate in form extending from an anterior end 62 to a posterior end 64. The anterior end 62 stops short of the anterior tab 56, so that a gap exists between the anterior tab 56 and the anterior end 62 of the dovetail rib 60. The posterior end 64 of the dovetail rib 60 is preferably joined with the posterior wall 54 extending up from the proximal surface of the plate 50.

The dovetail rib 60 includes a pair of substantially parallel side walls 66 adjacent to the proximal surface of the plate 50 and forming a lower portion of the dovetail rib 60 joining the dovetail rib 60 to the plate 50 (Figures 23 and 26). A top wall 65 defines a portion of the dovetail rib 60 extending most proximally from the plate 50. The top wall 65 exhibits a taper in a distal and posterior direction from the anterior end 62 toward the posterior end 64.

Beveled walls 68 extend up from the side walls 66 to the top wall 65. These beveled walls 68 provide the dovetail rib 60 with its dovetailcross-section. The beveledwalls 68 preferably maintain their form from the anterior end 62 to the posterior end 64. The side walls 66 preferably taper in height from a greatest height adjacent the anterior end 62 to a least proximal height adjacent the posterior end 64, where most preferably the side walls 66 merge into the proximal surface of the plate 50, so that adjacent the posterior end 64, the dovetail rib 60 is formed of only the beveled wall 68, withoutthe side walls 66. This tapering of the dovetail rib 60 causes a wedging action with the dovetail recess 74 of the insert 70 when the insert 70 is slid onto the dovetail rib 60 (along arrow J of Figure 23). Most preferably, the entire dovetail rib 60, anterior tab 56, posterior wall 54, plate 50, shaft 42 and prongs 46 are formed together as a unitary monolithic mass of a common material. Such forming could be by molding, machining or some combination of procedures. As an alternative, various separate parts of the tibial component 40 could be attached together, such as by welding or other bonding, or through utilization of appropriate biocompatible fasteners. The tibial component 40 also can be considered to include the insert 70 as a separately attachable portion thereof. Within the artificial knee joint 10, the insert 70 moves along with the plate 50 and shaft 40 as a single structure. However, the insert 70 can be removably attached from

and to other portions of the tibial component 40. Also, the insert 70 is typically formed of a more resilient material than that forming other portions of the tibial component 40, and particularly the plate 50 and shaft 42. For instance, the insert 70 could be formed of a biocompatible polymeric hydrocarbon material which has some degree of resilience and flexibility to best accommodate loads associated with the femoral component 20 pressing down on the insert 70 in a distal direction.

The insert 70 is itself a monolithic structure formed such as by molding or machining to have the contours shown in Figures 13-21 and 23-26. The insert 70 includes a distal surface 72 adapted to abut the plate 50. Spherical lobes 73 extend down from the distal surface 72 to reside within the spherical depressions 52 in the plate 50. These spherical lobes 73 could be a different shape, particularly if the depressions 52 are a shape different than spherical. Also, while the lobes 73 preferably fill the depressions 52, they could be smaller than or a different shape than the depressions 52.

The distal surface 72 of the insert 70 also includes a dovetail recess 74 therein. This dovetail recess 74 is interposed between engagement bars 75. The dovetail recess 74 has a contour similar to that of the dovetail rib 60. Thus, the insert 70 can have its dovetail recess 74 slid onto the dovetail rib 60 (arrow J of Figure 23) to attach the insert 70 to the plate 50.

The insert 70 includes a proximal surface 76 opposite the distal surface 72. The proximal surface 76 is adapted to support the femoral component 20 or other femoral structures thereon. For instance, it is conceivablethat the femur F might not be modified, but impact directly upon the proximal surface 76 of the insert 70, or that some other form of interface besides the femoral component 70 might be utilized. The proximal surface 76 is perhaps best seen in Figure 21. A left well 77 and right well 78 extend distally down into the proximal surface 76. A recess 79 is formed on an anterior portion of the insert 70. This recess 79 is sized to receive the tab 56 and tooth 58 therein to lock the insert 70 to the plate 50 most securely.

The wells 77, 78 exhibit a particularcontourto allow both flexion of the femoral component 20 relativeto the tibial component 40, and also a degree of pivotingrotation (about arrows D and E of Figures 19 and 20) in both a clockwise and counterclockwisedirection. In particular,the wells 77, 78 include low points 80, 81 that define most distal portions of the wells 77, 78. Side walls of the wells 77, 78 near these low points 80, 81 are preferably substantially spherical in form matching a radius of curvatureof the condylar legs 22, 24 of the femoral component 20. If these condylar legs 22, 24 exhibit a contour other than spherical, most preferably surfaces of the wells 77, 78 adjacent the low points 80, 81 would be appropriately modified to match such curvature.

By matching this curvature, surface contact is provided between the wells 77, 78 and the condylar legs 22, 24. Thus, both gravity forces and forces applied by muscles and tendons will tend to cause the condylar legs 22, 24 to remain within the wells 77, 78 adjacent the low points 80, 81 thereof. Such positioning will be maintained during flexion (rotation along arrow B of Figure

18). However, if pivoting rotating loads are applied (such as along arrows D and E of Figures 19 and 20) such pivoting rotation is accommodated.

In particular, if the medial condylar leg 22 is located within the right well 78 and the lateral condylar leg 24 is located within the left well 77, before pivoting rotation action, the medial condylar leg 22 will be aligned with the low point 81 and the lateral condylar leg 24 will be aligned with the low point 80. For pivoting rotation in a clockwise direction, the medial condylar leg 22 will remain at the low point 81. However, the lateral condylar leg 24 will rotate along arrow E (Figures 19 and 21) along a left valley 82 within the left well 77 in a generally anterior direction, but following an arc maintaininga constant distance from the low point 81 of the right well 78, depicted by arrow H (Figure 21).

Alternativelyjf pivoting rotation is required in a counterclockwise direction, the lateral condylar leg 24 will remain within the low point 80 of the left well 77 and the medial condylar leg 22 within the right well 78 will move out of the low point 81 and along the right valley 83 along arrow D (Figures 20 and 21). This right valley 83 is defined by a constant distance away from the low point 80 of the left well 77 depicted by arrow G (Figure 21 ).

The valleys 82, 83 slope proximally away from the low points 80, 81 slightly. Thus, as such pivotingrotation action occurs, the condylar legs 22, 24 are movinganteriorlyand proximally along the valleys 82, 83. This adds tension to the ligaments and muscles around the knee joint 10 and require work against gravity. Preferably, the slope of the valleys 82, 83 away from the low points 80, 81 rather significantly increases in slope near an end point of the valleys 82, 83 most distant from the low points 80, 81. Thus, the legs 22, 24 would need to move proximal Iy at a significantly more rapid rate as a greater amount of pivoting rotation is encountered. Knee ligaments and muscles, as well as gravity resist such further pivoting rotation, such that the knee has stability against excessive pivoting rotation. While the condylar legs 22, 24 and the wells 77, 78 enjoy surface contact over at least portions thereof before such pivoting rotation occurs, such surface contact is maintained even during pivotingrotation for the one condylar leg 22, 24 which remains stationary within the low point 80, 81. For the other condylar leg 24, 22, that is moving along a valley 82, 83 within one of the wells 77, 78, contours of side walls of the wells 77, 78 on either side of the valleys 82, 83 are configured with a cross-section perpendicular to a centerline of the valleys 82, 83 which matches a cross- section of the condylar legs 22, 24. Thus, contact is maintainedfor the legs 22, 24 moving within the valley 82, 83 away from the low point 80, 81. Thus, point loads are avoided even during such pivoting rotation motion. By distributing loads and avoiding point loading, but rather either line loading or surface loading, a rate of wear and stress upon the insert 70 and the femoral component 20 is minimized.

Additionally, because the wells 77, 78 extend down into the proximal surface 76 of the insert 70, and because regulatory agencies typical Iy recommend a minimumamount of wear height within the

insert 70 or other meniscal structure, havinga flat distal surface 72 on the insert 70 would require the insert 70 to exhibita greater height similar to a depth of the wells 77, 78 than if the wells were not there. For instance, it is recommended that if a minimumof six millimetersmust be maintained withinthe insert 70, upon implantation,and if the wells77, 78 have three millimetersof distal depth, the proximal surface 76 of the insert 70 must be at least nine millimeters away from the distal surface 72.

By providing spherical lobes 73 on the distal surface 72 of the insert 70, such as three millimetersthick,and similar depressions 52 in the plate 50, the required thickness for the insert 70 can be maintained (i.e. six millimeters) without requiring a perimeter distance between the distal surface 72 and proximal surface 76 to be increased. Rather, thickness is maintained while shortening an overall height of the tibial component 40 of the joint 10.

Because the depressions 52 in the plate 50 reduce the strength of the plate 50 somewhat, the gussets 44 are provided to maintain sufficient plate 50 strength. In particular, the gussets 44 preferably are generally triangularly shaped planar structures oriented in substantially vertical planes radiating from the shaft 42. Preferably, four gussets 44 are provided with a widest portion of each gusset 44 adjacent the underside of the plate 50 and narrowing down to the tip of the shaft 42 most distant from the plate 50. Also, prongs 46 extend down substantially verticallyfrom the underside of the plate 50 at locations spaced from the shaft 42. Preferably, four such prongs 46 are provided with a length of about a fourth that of the shaft 42. Overall, such nesting of a portion of the insert 70 within a portion of the plate 50 can provide up to a two or three millimeter reduction in the amount of tibial bone loss in implantation of the artificial knee joint 10 according to this invention.

With particular reference to Figures 29-31 , details of an alternative tibial component 140 and associated augment 170 are described. When a natural tibia T adjacent an artificial knee joint 10 has less than fully adequate bone volume directly adjacent the tibial component, it is desirable that at least a portion of the tibial component be augmented in thickness to make up for the absence of desirable bone volume. Often such tibial bone volumedeficiency is limited to only a portion of the tibiaT. With this invention, as shown in the embodimentof Figures 29-31 , an augment 170 can be added to the alternati vetibial component 140 on at least one half of the alternati vetibial component 140 and a portion of the tibia T cut away to accommodate this augmented alternative tibial component 140.

In particular, the alternativetibial component 140 is similar to the tibial component 40 of the preferred embodiment,described above, except that the shaft 142 is depicted in this embodimentas tapering somewhat in diameteras it extends towards a tip, and is shown somewhatelongated. This shaft 142 variation is provided to illustrate the variety of different configurations for the shaft 140 that are within the scope of this invention. Similarly, the gussets 144 havea slightly different shape than that of the gussets 44 of the preferred embodiment described above. The alternativetibial

component 140 includes a plate 150 similar in form and function to the plate 50 of the tibial component 40 described above.

Uniquely, the alternative tibial component 140 (Figures 29-31) includes threaded prongs 160 extending perpendicularly in a distal direction from the underside of the plate 150, and generally parallel with the shaft 142. These threaded prongs 160 havea pointed tip 162 and threads 164 on a cylindrical side thereof. When the alternativetibial component 140 is not required to be augmented with the augment 170, these threads 164 on the threaded prongs 160 can help assist bone in-growth and secure attachmentof the tibiaT to the alternativetibial component 140. If the alternativetibial component 140 requires augmentation, the augment 170 can be utilized on either side of the alternativetibial component 140, or two augments 170 can be provided, so that both sides of the alternative tibial component 140 are augmented in thickness.

The augment 170 preferably is a plate having a constant thickness between a substantially planar top surface 172 and a substantially planar bottom surface 174. A perimeter 176 extends betweenthe top surface 172 and bottom surface 174. This perimeter 176 follows a contour of the underside of the plate 150. Because the plate 150 is bilaterally symmetrical, and because the top surface 172 and bottom surface 174 are both planar, and oriented parallel to each other, and the entireaugment 170 is generallythin in form, it can be reversed to fit on eithera left or right side of the alternativetibial component 140, merely be reversing the top surface 172 or the bottom surface 174. The augment 170 includes slots 178 therein which can be aligned with the gussets 144 to help to stabilize the augment 170 and securely hold the augment 170 to the plate 150. Furthermore, the augment 170 preferably includes a pair of bores 175 aligning with two of the threaded prongs 160. While the preferred embodimentshows two of these threaded prongs 160, it is conceivablethatthe augment 170 could be attached with only a single threaded prong 160 and the slots 178 and gussets 144 could coact together to prevent rotation of the augment 170 relative to the plate 150 about such a single prong 160.

The bores 175 preferably include steps 177 therein both at an upper and lowerend of the bores 175. These steps 177 allow for recessing of nuts 188 as described in detail below.

The nuts 188 preferably have a generally cylindrical form with a threaded bore 182 on an interior portion thereof and with a face 186 on one end forming a flange 184 having a slightly greater diameter than other portions of the nut 180. This flange 184 has a diameter similar to that of the bores 175 at the step 177. Other portions of each nut 180 preferably have a diametersimilar to that of the bores 175 spaced from the step 177. Each nut 180 can thus be recessed into the bore 175 with the flange 184 within the step 177 for complete recessing of the nuts 180. A face 186 on each nut 180 preferably includes holes which can receive a torque applying tool so that the nuts 180 to be completely rotated into position. As an alternativeto such holes, slits could be formed in the face 186, or other engagement structures could be provided on the face 186

to facilitate rotation of the nuts 180, even as they are being recessed into the bores 175 of the augment 170. Once one or more augments 170 are attached to the alternativetibial component 140, the augments 170 become part of the alternativetibial component 140 for implantation within the knee joint 10. Referring to Figure 31, a gap can be seen between the augment 170 and the plate 150 of the alternativetibial component 140. The plate 150 has a peripheral lip extending downwardly and against which the augment 170 comes into contact when the augment 170 is attached to the plate 150. Preferably, surfaces of the augment 170, including the surface 172 and the surface 174 include a peripheral rib extending perpendicularly from the surface 172 and the surface 174. These peripheral ribs extend perpendicularly from the surface and inboard of the perimeter 176 by a distance similar to a width of the peripheral lip on the plate 150, so that the peripheral rib is located inboard of the peripheral lip on the plate 150. This peripheral rib can thus help to keep the augment 170 precisely aligned where desired relativeto the alternativetibial component 140. To further stabilize the augment 170, ribs having other patterns could also extend from the surfaces 172, 174 inboard of the peripheral rib to provide further contact between the augment 170 and the plate 150 and still maintain reversibilityfor the augment 170. One particularplace for such ribs is surrounding the bores 175 to support the augment 170 at this attachment location.

This disclosure is provided to reveal a preferred embodimentof the invention and a best mode for practicing the invention. Having thus described the invention in this way, it should be apparent that various different modifications can be made to the preferred embodiment without departing from the scope and spirit of this inventiondisclosure. When structures are identified as a means to perform a function, the identification is intended to include all structures which can perform the function specified. When structures of this inventionare identifiedas being coupled together, such language should be interpreted broadly to include the structures being coupled directly together or coupled together through intervening structures. Such coupling could be permanentor temporary and eitherin a rigid fashion or in a fashion which allows pivoting,sliding or other relative motion while still providing some form of attachment, unless specifically restricted.

Industrial Applicability

This invention exhibits industrial applicability in that it provides an artificial knee joint which mimics as closely as possible the function of a natural knee joint.

Another object of the present invention is to provide an artificial knee joint which is easy for a surgeon to size and install properly.

Another object of the present inventionis to providea method and system for preparing a distal end of a femur for receipt of a femoral component of an artificial knee joint which is easy to

perform and similar for many different sizes of artificial knee joint components.

Another object of the present invention is to provide an artificial knee joint sizing system which has multiple different size components therein but which maintain similar size for many portions thereof to simplify the forming of cuts necessary to shape the distal end of the femur. Another object of the present invention is to provide a single tool for shaping a distal end of the femur to receive a femoral componentof an artificial knee joint which can properly shape the distal end of the femur for a variety of different sizes of femoral components.

Another object of the present invention is to provide an artificial knee joint which requires a minimal amount of bone removal from the proximal end of a tibiafor receipt of a tibial component of the artificial knee joint.

Another object of the present invention is to provide an artificial knee joint which facilitates pivoting rotation in both a clockwise and counterclockwise direction.

Another object of the present invention is to providean artificial knee joint which includes many portions thereof which are symmetrical and usable for either a left or right knee. Another object of the present invention is to provide an artificial knee joint which provides a greater amount of contact between condyles and increase flexion within the artificial knee joint.

Another object of the present inventionis to providean artificial knee joint which includes a set of femoral components of different sizes for different sized femurs, with each of the components in the set having many surfaces which share a common size and shape, to simplify the different cuts required on the distal end of the femur for receipt of the femoral component thereon.

Another object of the present invention is to provide an artificial knee joint with a tibial insert for an artificial knee joint which is formed of a meniscus material that is availablefor wear that exhibits a low profile such that a minimum amount of natural tibia bone is required to be removed.

Other further objects of this invention, which demonstrate its industrial applicability, will become apparent from a careful reading of the included detailed description, from a review of the enclosed drawings and from review of the claims included herein.