Abstract:
A femoral component of an artificial knee joint is configured with multiple different facets which are similar in size and shape for many different sizes, to simplify an associated method for forming a distal end of the femur to receive the femoral component. Jig embodiments are provided to form surfaces on a distal end of a femur to correspond with facets of the femoral component, with the same jig usable for femoral components of differing size. The femoral component includes medial and lateral condylar legs with a posterior facet of the femoral component exhibiting a negative angle relative to a central axis of the femur, to maximize contact and increase flexion of the artificial knee joint.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The following patent application is being filed in coordination with another patent application having a very similar disclosure and related to other portions of a common artificial knee joint. This other corresponding application is entitled “TIBIAL COMPONENT OF AN ARTIFICIAL KNEE JOINT,” has the same inventor, was filed on the same day and has Ser. No. 12/148,366. 
     FIELD OF THE INVENTION 
     The following invention relates 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 OF THE INVENTION 
     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, such 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 joint to 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 little as 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 facilitate articulation relative to each other in the same way that the distal end of a natural femur articulates relative to the proximal end of a natural tibia. Typically, an insert of materials somewhat more flexible and resilient than 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. Pat. 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 between the 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 prevent further flexion. Accordingly, a need exists for an artificial knee joint which can provide as 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 counterclockwise directions. A natural knee joint is capable of a small amount of pivoting rotation. Such pivoting 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. Pat. No. 5,413,604) allow for pivoting 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. Pat. No. 6,013,103) and Tuke (U.S. Pat. No. 5,219,362) describe pivoting rotation of the lateral condyle about the medial condyle. Accordingly, a need exists for complete replication of 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 millimeter thickness 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 millimeters of bone must be removed from the proximal tibia to 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. Pat. No. 5,326,358) and Johnson (U.S. Pat. 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 allow twisting, to minimize the amount of required bone removal from the proximal end of the tibia. 
     SUMMARY OF THE 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 invention a 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 multiple different sizes of femoral components. In particular, slots or other cutting tool guide structures are provided which are the same for each size femoral component to be surgically implanted, except for an anterior surface cut which is made at a variable distance from a posterior surface cut, depending on a size of the femoral component to 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 within the jig. In another embodiment, the jig 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 providing a new wear surface on the distal end of the femur. As such it includes a patellar flange portion adapted to be placed adjacent the anterior surface of the distal end of the femur and a medial condylar leg and a lateral condylar leg, both extending down from the patellar flange 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 contact and 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 valleys that extend arcuately and mostly in an anterior direction away 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 elevation of 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 provided by the artificial knee joint of this invention, mimicking performance of a natural knee joint being replaced. 
     OBJECTS OF THE INVENTION 
     Accordingly, a primary object of the present invention is to provide 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 invention is to provide a 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 component of 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 tibia for 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 provide an 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 invention is to provide an 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 available for wear that exhibits a low profile such that a minimum amount of natural tibia bone is required to be removed. 
     Other further objects of the present invention will become apparent from a careful reading of the included drawing figures, the claims and detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 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. 
         FIG. 2  is a side elevation view similar to that which is shown in  FIG. 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. 
         FIGS. 3 and 4  are perspective views of an adjustable jig attachable to the distal surface of the femur similar to the fixed jig of  FIG. 2 , but which adjustable jig features an adjustable portion for moving one of the slots to different distances adjustably spaced from other slots within fixed portions of the jig. 
         FIG. 5  is a side elevation view similar to that which is shown in  FIG. 2 , but illustrating use of the adjustable jig of  FIGS. 3 and 4  thereon. 
         FIG. 6  is a perspective view of the distal end of the femur with a femoral component of the artificial knee joint exploded therefrom, and illustrating how the femoral component is oriented and configured to fit upon the distal end of the femur. 
         FIG. 7  is a side elevation view of the distal end of the femur including a femoral component attached thereto. 
         FIG. 8  is a perspective view of the femoral component of  FIGS. 6 and 7 . 
         FIG. 9  is a top plan view of that which is shown in  FIG. 8 . 
         FIG. 10  is a front elevation view of that which is shown in  FIG. 8 . 
         FIG. 11  is a rear sectional view of that which is shown in  FIG. 8 . 
         FIG. 12  is a side elevation view of that which is shown in  FIG. 8 , and illustrating in 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. 
         FIG. 13  is a side elevation view of that which is shown in  FIG. 12  without the femurs shown and depicting nine sizes of femoral components and how they relate together. 
         FIG. 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. 
         FIG. 15  is a side elevation view of the tibial component shown in place upon the proximal end of the tibia. 
         FIG. 16  is an exploded parts view of the entire artificial knee joint shown in perspective and from below. 
         FIG. 17  is a perspective view of the completed artificial knee joint in extension and with the femur and tibia brought together. 
         FIG. 18  is a sectional side elevation view of that which is shown in  FIG. 17 . 
         FIG. 19  is a side elevation view of that which is shown in  FIG. 17 , and with a knee joint in a state of partial flexion. 
         FIG. 20  is a side elevation view similar to  FIG. 19 , but showing full flexion of the knee joint. 
         FIGS. 21 and 22  are perspective views similar to that which is shown in  FIG. 17 , but illustrating pivoting rotation of the knee joint in both a clockwise and counterclockwise direction. 
         FIG. 23  is a top plan view of the insert of the tibial component of this invention. 
         FIG. 24  is a perspective view of the plate and shaft of the tibial component of this invention. 
         FIG. 25  is a side elevation view of the tibial component showing the insert portion in the process of being slid onto the plate. 
         FIG. 26  is a perspective view similar to that which is shown in  FIG. 25  but after the insert has been almost fully attached to the plate of the tibial component. 
         FIG. 27  is a perspective view similar to that which is shown in  FIG. 26 , but after the insert has been completely attached to the plate of the tibial component. 
         FIG. 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. 
         FIG. 29  is a perspective view of an alternative tibial component with an augment removably attachable thereto and shown exploded away from the tibial component and with a second position for the augment shown in broken lines. 
         FIG. 30  is a perspective view of the alternative tibial component of  FIG. 29  with the augment attached to the tibial component. 
         FIG. 31  is a full sectional view of the alternative tibial component and augment taken along line  31 - 31  of  FIG. 30 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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 tibia T. The invention includes 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 invention also includes methods for preparing the distal end of the femur to receive an appropriately sized femoral component. 
     In essence, and with particular reference to  FIGS. 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 tibial T 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  ( FIGS. 18-20 ). 
     More specifically, and with particular reference to  FIGS. 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 C 1  is made to the distal end of the femur ( FIG. 1 ). This cut is typically approximately perpendicular to the centerline L of the femur F, but most preferably slightly angled, as shown in  FIG. 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 C 1  ( FIGS. 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 particular, a 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 C 2  ( FIGS. 1 and 2 ). Diagonal slots  7 ,  9  are separately utilized to form cuts C 3  and C 4 . 
     The fixed jig  2  also includes an anterior slot array  8  aligned with cut lines C 5 -C 13 . 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  ( FIG. 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 C 5  ( FIG. 1 ) or one of the other cut lines C 6 -C 13  ( FIG. 2 ) 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 adjustable jig  12  provides an alternative to the fixed jig  2 . The adjustable jig  12  ( FIGS. 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 C 1  ( FIG. 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  FIG. 5 ) relative to other portions of the adjustable jig  12  that are 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  within the groove  18 , such as a “cross” form ( FIG. 3 ). Thus, the guide  13  and adjusting slot  16  can slide relative to 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 ( FIG. 5 ) a user can see which graduation adjacent which indicia is aligned with the set line  19  ( FIG. 4 ). This indicia, such as a number or letter, corresponds with the size of femoral component ( FIG. 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 have a similar size, shape and relative orientation to other surfaces on the distal end of the femur, with the exception of the anterior surface. This anterior surface maintains the same orientation relative to 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 component  20  within a set of femoral components  20  of different sizes ( FIG. 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 implantation site. Thus, overall a surgeon need only have one jig, one cutting tool for use with the jig and one set of femoral components associated with the left or right knee that is receiving the artificial knee joint. Simplicity and freedom from potential error results from such a simplified system. 
     With particular reference to  FIGS. 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 ( FIG. 12 ), with details of other femoral components  20  within a set of different fixed sizes of femoral components  20  being similar, except for size adjustability as depicted in  FIG. 12 . 
     The femoral component  20  generally is formed of a common mass of material and includes a medial condylar leg  22  and a lateral condylar leg  24  which each extend from a patellar flange 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 over the 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 component  20  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 centerline of the femur F when the femoral component  20  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 similarly formed. 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 facet  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 facet  35  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 laterally an entire width of the internal box face  30  of the femoral component  20  ( FIG. 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  FIGS. 6 ,  8 - 11  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 ( FIGS. 2 and 19 ) relative to a centerline of the femoral component  20  and a centerline of the femur F when attached to the femur F. As best depicted in  FIG. 18 , this negative angle 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 negative angle. By providing such a negative angle, a greater amount of flexion and contact can be obtained (along arrow B of  FIG. 18 ) between the tibia T and femur F. 
     Cut line C 2  associated with posterior slot  6  in the fixed jig  2  ( FIG. 2 ) provides the internal box surface of the distal end of the femur F with a negative angle relative to a centerline of the femur F which corresponds with the negative angle of the posterior facet  35  relative to a centerline of the femoral component  20  ( FIG. 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 split facets  32 ,  35 ,  38  are coplanar, they are often referred to as a single plane and a single facet for simplification. 
     The anterior diagonal facet  36  maintains a common position for each size of femoral component  20  ( FIG. 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  at a fixed transition line between the anterior diagonal facet  36  and the distal facet  32 . Other facets preferably maintain their size and relative orientation for the different sized femoral components  20 . 
     With particular reference to  FIGS. 14-26 , 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 tibia T. 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  FIG. 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  exhibit an overall lesser distal height to 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  ( FIGS. 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 dovetail cross-section. The beveled walls  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 , without the 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  FIG. 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  FIGS. 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  FIG. 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 conceivable that 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  FIG. 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 particular contour to allow both flexion of the femoral component  20  relative to the tibial component  40 , and also a degree of pivoting rotation (about arrows D and E of  FIGS. 19 and 20 ) in both a clockwise and counterclockwise direction. 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 curvature of 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  FIG. 18 ). However, if pivoting rotating loads are applied (such as along arrows D and E of  FIGS. 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 ( FIGS. 19 and 21 ) along a left valley  82  within the left well  77  in a generally anterior direction, but following an arc maintaining a constant distance from the low point  81  of the right well  78 , depicted by arrow H ( FIG. 21 ). 
     Alternatively, if 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 ( FIGS. 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 ( FIG. 21 ). 
     The valleys  82 ,  83  slope proximally away from the low points  80 ,  81  slightly. Thus, as such pivoting rotation action occurs, the condylar legs  22 ,  24  are moving anteriorly and 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 proximally 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 pivoting rotation 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 maintained for 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 typically recommend a minimum amount of wear height within the insert  70  or other meniscal structure, having a flat distal surface  72  on the insert  70  would require the insert  70  to exhibit a 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 minimum of six millimeters must be maintained within the insert  70 , upon implantation, and if the wells  77 ,  78  have three millimeters of 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 millimeters thick, 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 vertically from 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  FIGS. 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 volume deficiency is limited to only a portion of the tibia T. With this invention, as shown in the embodiment of  FIGS. 29-31 , an augment  170  can be added to the alternative tibial component  140  on at least one half of the alternative tibial component  140  and a portion of the tibia T cut away to accommodate this augmented alternative tibial component  140 . 
     In particular, the alternative tibial component  140  is similar to the tibial component  40  of the preferred embodiment, described above, except that the shaft  142  is depicted in this embodiment as tapering somewhat in diameter as it extends towards a tip, and is shown somewhat elongated. 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  have a slightly different shape than that of the gussets  44  of the preferred embodiment described above. The alternative tibial 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  ( FIGS. 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  have a pointed tip  162  and threads  164  on a cylindrical side thereof. When the alternative tibial 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 attachment of the tibia T to the alternative tibial component  140 . If the alternative tibial component  140  requires augmentation, the augment  170  can be utilized on either side of the alternative tibial 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 between the 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 entire augment  170  is generally thin in form, it can be reversed to fit on either a left or right side of the alternative tibial 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 embodiment shows two of these threaded prongs  160 , it is conceivable that the 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 lower end 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 diameter similar 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 alternative to 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 alternative tibial component  140 , the augments  170  become part of the alternative tibial component  140  for implantation within the knee joint  10 . 
     Referring to  FIG. 31 , a gap can be seen between the augment  170  and the plate  150  of the alternative tibial 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 relative to the alternative tibial 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 reversibility for the augment  170 . One particular place 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 embodiment of 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 invention disclosure. 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 invention are identified as 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 permanent or temporary and either in 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.