KNEE PROSTHESIS

Abstract: This invention is a knee prosthesis (11) including a tibial component (47) for mounting to the proximal end of a tibia, and a femoral component (23) for mounting to the distal end of a femur. At least the face surface (31) of the medial condylar portion of the femoral component (23) may be preferably substantially congruent with the face surface (45) of a medial cavity in the upper surface of the tibial component so that substantially complete surface to surface contact between the face surface (45) of the medial cavity in the upper surface of the tibial component (47), and the face surface (31) of the medial condylar portion of the femoral component (23), is provided throughout a significant portion of the range of flexion of the knee joint. The tibial component (47) may include a base member (53), an articular bearing member (67) movably positioned on the upper surface of the base member (53), and structure (61) for restricting the movement of the lateral portion of the articular bearing (67) member relative to the base member, to allow a swinging motion thereof relative to the medial portion of the articular bearing member.

Description: KNEE PROSTHESIS BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates in general to an improved knee prosthesis for replacing at least a portion of a knee joint. 2. Information Disclosure Statement: A knee prosthesis for partially or totally replacing a knee joint which has been damaged due to trauma or disease typically includes a femoral component for attachment to the distal end of a femur, and a tibial component for attachment to the proximal end of a tibia. The tibia component often includes a base or tray for being implanted in the tibia, and an insert or meniscal plate on the face of the tray for articulating with the condyles of the femoral component. Murray et al., U.S. Patent 4,224,696, issued September 30, 1980, discloses a prosthetic knee including a femoral component for being attached to a femur, a tibial base for being attached to a tibia, and an insert or meniscal plate disposed between the distal plateau or face of the femoral component and the proximal plateau or face of the tibial base. The proximal plateau or face of the tibial component has a concave, co poundly curved surface while the distal face of the insert has a convex surface shaped complementary to the proximal plateau or face of the tibial component so as to permit substantially unrestrained relative sliding motion between the proximal plateau or face of the tibial component and the distal face of the insert when the two are biased against each other. Brooks et al., U.S. Patent 4,714,474, issued December 22, 1987, discloses a knee joint prosthesis including a tibial component with a base for being attached to a tibia, and a removable articulating surface insert that is locked to the tibial base when implanted. Lacey, U.S. Patent 4,759,767, issued July 26, 1988, discloses a tibial component of a knee prosthesis that includes a base for being attached to a tibia without bone cement, and a replaceable plateau insert for being non-movably attached to the base by the use of undercut flanges extending upward from the plateau of the base which coact with appropriate grooves in the lower face of the insert. Jones et al., U.S. Patent 5,071,438, issued December 10, 1991, discloses a prosthetic knee with a tibial prosthesis comprising a baseplate and an articulating surface which pivots on the baseplate about an axis within a medial condylar compartment. Tuke et al., U.S. Patent 5,219,362, issued June 15, 1993, discloses a knee prosthesis including a femoral component having a medial condyle and a lateral condyle, and a tibial component having a proximal plateau or face with a medial condyle receiving recess and a lateral condyle receiving recess. The medial condyle and medial condyle receiving recess are generally spherical. The lateral condyle receiving recess is in the form of an arcuate groove, and the curvature of the lateral condyle in the sagittal plane is formed about a pair of parallel axes such that as the knee is straightened, the lateral tibial condyle recess is cammed anteriorly, thereby allowing the tibia to rotate medially slightly about its axis as the knee is straightened from a flexed position. Nothing in the known prior art discloses or suggests the present invention. More specifically, nothing in the known prior art discloses or suggests a knee prosthesis that provide substantially complete surface-to-surface contact between the face surface of a medial cavity in the upper surface of a tibial component and the face surface of a medial condylar portion of a femoral component throughout a significant portion of the range of flexion of the knee joint, or a knee prosthesis with a tibial component that restricts the movement of an articular bearing member thereof on the upper surface of a base member thereof to a pivotal movement about one or more axes extending generally perpendicular to the medial portion of the upper surface of the base member. SUMMARY OF THE INVENTION The present invention provides an improved knee prosthesis for replacing at a least portion of a knee joint between the distal end of a femur and the proximal end of a tibia. One object of the present invention is to provide a knee prosthesis specifically designed to provide substantially complete surface-to-surface contact between the face surface of a medial cavity in the upper surface of a tibial component and the face surface of a medial condylar portion of a femoral component throughout a significant portion of the range of flexion of the knee joint. One concept of such a knee prosthesis is to provide a medial articular bearing member and a lateral articular bearing member with the medial articular bearing member positioned and aligned with the primary center of pressure of the medial condylar joint reaction load and designed to transmit high contact pressure at low velocity and permit flexion-extension rotation, varus-valgus rotation and a small but minimal anterior- posterior translation; and with the lateral articular bearing member designed for internal/external rotation about the translationally constrained medial articular bearing member and to translate to positions in the anterior-posterior and superior/inferior directions as it rotates about the medial articular bearing member and to permit physiological velocities under conditions of low contact pressure due to the transmission of high contact pressure on the medial condyle. Such a knee prosthesis may include a tibial component having a medial cavity and a lateral cavity in the upper surface thereof, and a femoral component with a lateral condylar portion for pivotally coacting with the lateral cavity in the upper surface of the tibial component and a medial condylar portion for pivotally coacting with the medial cavity in the upper surface of the tibial component, the distal coronal and distal sagittal curvatures of the face surface of the medial condylar portion being substantially congruent with the coronal curvature and sagittal curvature, respectively, of the medial cavity in the upper surface of the tibial component so that substantially complete surface-to-surface contact between the face surface of the medial cavity in the upper surface of the tibial component and the face surface of the medial condylar portion of the femoral component is provided throughout a significant portion of the range of flexion of the knee joint. Another object of the present invention is to provide a knee prosthesis specifically designed to restrict the movement of an articular bearing member on the upper surface of a base member to a pivotal movement about one or more axes extending generally perpendicular to the medial portion of the upper surface of the base member. One concept of such a knee prosthesis is to provide a sliding insert or meniscus that is permitted to rotate generally about the medial side of the tibial tray (e.g., about an actual axis or axes of rotation comprising a bundle of parallel axes that extend normal to the tibial tray and are positioned in the medial said of the prosthesis) , and to provide femoral and tibial condylar surfaces that conform readily to one another such that only a single axis of movement in extension/flexion is provided as the knee is flexed and extended. Such a knee prosthesis may include a base member having an upper surface, an articular bearing member movably positioned on the upper surface of the base member, and restriction means for restricting the movement of the lateral portion of the articular bearing member relative to the base member to allow a swinging motion thereof relative to the medial portion of the articular bearing member. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded perspective view of a right knee prosthesis, illustrating a first preferred embodiment of the present invention, the left knee prosthesis being a substantial mirror image thereof. Fig. 2 is a top plan view of a femoral component of the knee prosthesis of Fig. 1. Fig. 3 is a sectional view substantially as taken on line 3-3 of Fig. 2, with portions omitted for clarity. Fig. 4 is a sectional view substantially as taken on line 4-4 of Fig. 2. Fig. 5 is a sectional view substantially as taken on line 5-5 of Fig. 2. Fig. 6 is a top plan view of an articular bearing member of the tibial component of the knee prosthesis of Fig. 1. Fig. 7 is a sectional view substantially as taken on line 7-7 of Fig. 6, with portions thereof omitted for clarity. Fig. 8 is a front or anterior elevational view of an articular bearing member of Fig. 6. Fig. 9 is a sectional view substantially as taken on line 9-9 of Fig. 6, with portions thereof omitted for clarity. Fig. 10 is a bottom plan view of the articular bearing member of Fig. 6. Fig. 11 is a sectional view substantially as taken on line 11-11 of Fig. 6, with portions thereof omitted for clarity. Fig. 12 is a sectional view substantially as taken on line 12-12 of Fig. 6, with portions thereof omitted for clarity. Fig. 13 is a top plan view of a base member of the tibial component of the knee prosthesis of Fig. 1. Fig. 14 is a sectional view substantially as taken on line 14-14 of Fig. 13, with portions thereof omitted for clarity. Fig. 15 is a front or anterior elevational view of the base member of Fig. 13, with portions thereof broken away for clarity. Fig. 16 is a medial side elevational view of the base member of Fig. 13. Fig. 17 is a bottom plan view of the base member of Fig. 13. Fig. 18 is a somewhat diagrammatic sagittal sectional view of the knee prosthesis of Fig. 1, shown implanted in a knee joint with the knee joint substantially fully extended. Fig. 19 is a somewhat diagrammatic sectional view substantially as taken on line 19-19 of Fig. 17 with portions thereof omitted for clarity. Fig. 20 is similar to Fig. 18 but shows the knee joint partially flexed. Fig. 21 is similar to Fig. 18 but shows the knee joint flexed substantially 90 degrees. Fig. 22 is a somewhat diagrammatic sectional view substantially as taken on line 22-22 of Fig. 21 with portions thereof omitted for clarity. Fig. 23 is a somewhat diagrammatic sectional view substantially as taken on line 23-23 of Fig. 19, showing the articular bearing member of the tibial component substantially fully rotated in an anterior direction with respect to the base member of the tibial component, and with portions omitted for clarity. Fig. 24 is a somewhat diagrammatic sectional view substantially as taken on line 24-24 of Fig. 22, showing the articular bearing member of the tibial component substantially fully rotated in a posterior direction with respect to the base member of the tibial component, and with portions omitted for clarity. Fig. 25 is an exploded perspective view of a right knee prosthesis, illustrating a second preferred embodiment of the present invention, the left knee prosthesis being a substantial mirror image thereof. Fig. 26 is a bottom plan view of an articular bearing of the tibial component of the knee prosthesis of Fig. 25. Fig. 27 is a sectional view substantially as taken on line 27-27 of Fig. 25, with portions thereof omitted for clarity. Fig. 28 is a somewhat diagrammatic sectional view similar to Fig. 23 but showing the articular bearing member of the tibial component of the knee prosthesis of Fig. 25 substantially fully rotated in an anterior direction with respect to the base member of the tibial component, and with portions omitted for clarity. Fig. 29 is a somewhat diagrammatic sectional view similar to Fig. 24 but showing the articular bearing member of the tibial component of the knee prosthesis of Fig. 25 substantially fully rotated in a posterior direction with respect to the base member of the tibial component, and with portions omitted for clarity. Fig. 30 is an exploded perspective view of a right knee prosthesis, illustrating a third preferred embodiment of the present invention, the left knee prosthesis being a substantial mirror image thereof. Fig. 31 is a top plan view of the tibial component of the knee prosthesis of Fig. 30. Fig. 32 is a sectional view substantially as taken on line 32-32 of Fig. 31, with portions thereof omitted for clarity. Fig. 33 is a sectional view substantially as taken on line 33-33 of Fig. 32, with portions thereof omitted for clarity. Fig. 34 is a sectional view substantially as taken on line 34-34 of Fig. 32, with portions thereof omitted for clarity. Fig. 35 is a somewhat diagrammatic medial sagittal sectional view of the knee prosthesis of Fig. 30, shown implanted in a knee joint with the knee joint substantially fully extended. Fig. 36 is a somewhat diagrammatic lateral sagittal sectional view of the knee prosthesis of Fig. 30, shown implanted in a knee joint with the knee joint substantially fully extended. Fig. 37 is similar to Fig. 35 but shows the knee joint partially flexed. Fig. 38 is similar to Fig. 36 but shows the knee joint partially flexed. Fig. 39 is similar to Fig. 35 but shows the knee joint flexed substantially 90 degrees. Fig. 40 is similar to Fig. 36 but shows the knee joint flexed substantially 90 degrees. Fig. 41 is an exploded perspective view of a right knee prosthesis, illustrating a fourth preferred embodiment of the present invention, the left knee prosthesis being a substantial mirror image thereof. Fig. 42 is a top plan view of a base member of the tibial component of the knee prosthesis of Fig. 41. Fig. 43 is a sectional view substantially as taken on line 43-43 of Fig. 41, with portions thereof omitted for clarity. Fig. 44 is a somewhat diagrammatic sectional view similar to Figs. 23 and 28 but showing the articular bearing member of the tibial component of the knee prosthesis of Fig. 41 substantially fully rotated in an anterior direction with respect to the base member of the tibial component, and with portions omitted for clarity. Fig. 45 is a somewhat diagrammatic sectional view similar to Figs. 24 and 29 but showing the articular bearing member of the tibial component of the knee prosthesis of Fig. 41 substantially fully rotated in a posterior direction with respect to the base member of the tibial component, and with portions omitted for clarity. Fig. 46 is an exploded perspective view of a right knee prosthesis, illustrating a fifth preferred embodiment of the present invention, the left knee prosthesis being a substantial mirror image thereof. Fig. 47 is a bottom plan view of a lateral articular bearing of the tibial component of the knee prosthesis of Fig. 46. Fig. 48 is a sectional view substantially as taken on line 48-48 of Fig. 46, with portions thereof omitted for clarity and with the lateral articular bearing shown in broken lines. Fig. 49 is a somewhat diagrammatic sectional view similar to Figs. 23 and 28 but showing the lateral articular bearing member of the tibial component of the knee prosthesis of Fig. 46 substantially fully rotated in an anterior direction with respect to the base member of the tibial component, and with portions omitted for clarity. Fig. 50 is a somewhat diagrammatic sectional view similar to Figs. 24 and 29 but showing the lateral articular bearing member of the tibial component of the knee prosthesis of Fig. 46 substantially fully rotated in a posterior direction with respect to the base member of the tibial component, and with portions omitted for clarity. DESCRIPTION OF THE PREFERRED EMBODIMENTS A first preferred embodiment of the knee prosthesis of the present invention is shown generally in Figs. 1-24 and identified by the numeral 11. The knee prosthesis 11 is designed to replace at least a portion of a knee joint 13 between the distal end 17 of a femur 15 and the proximal end 21 of a tibial 19. The knee prosthesis 11 includes a femoral component 23 for mounting to the distal end 17 of the femur 15, and a tibial component 25 for mounting to the proximal end 21 of the tibia 19 and for articulating with the femoral component 23. The femoral component 23 preferably includes a medial condylar portion 27, a lateral condylar portion 29, and a patellar flange portion 31 joining the anterior ends of the medial and lateral condylar portions 27, 29 together with the medial and lateral condylar portions 27, 29 substantially parallel to and spaced apart from one another to form an intercondylar notch or recess 33 therebetween as clearly shown in the drawings. Each condylar portion 27, 29 has an outer or face surface 35 for articulatingly engaging a portion of the tibial component 25 as will hereinafter become apparent. The face surface 35 of each condylar portion 27, 29 preferably has a distal portion 37 for articulatingly engaging a portion of the tibial component 25 when the knee joint 13 is extended and partially flexed as shown in Figs. 18 and 20, and a posterior portion 39 for articulatingly engaging a portion of the tibial component 25 when the knee joint 13 is flexed substantially 90' as shown in Fig. 21. The distal portion 37 of the face surface 35 is defined by a precise distal sagittal curvature formed by the radius Rl shown in Figs. 3 and 4, and a precise distal coronal curvature formed by the radius R2 shown in Fig. 5. The posterior portion 39 of the face surface 35 is defined by a precise posterior sagittal curvature formed by the radius R3 shown in Figs. 3 and 4 and a posterior coronal curvature shown in Fig. 22. The radius Rl is preferably the same size as the radius R2 so that the distal portion 37 of the face surface 35 forms a semispherical shape. The radius R3 is preferably smaller than the radii Rl, R2. Thus, for example, the radii Rl, R2 may be 1.25 inches (3.175 centimeters) while the radius R3 may be 0.75 inches (1.905 centimeters). The curvatures of the distal portions 37 of the face surface 35 of the medial and lateral condylar portions 27, 29 of the femoral component 23 in a substantially sagittal plane are formed about a center point on a distal or first transverse axis Tl that passes through the center of curvature of both distal portions 37. Similarly, the curvatures of the posterior portions 39 of the face surface 35 of the medial and lateral condylar portions 27, 29 of the femoral component 23 in a substantially sagittal plane are formed about a center point on a posterior or second transverse axis T2 that passes through the center of curvature of both posterior portions 39. As clearly shown in Fig. 2, the first and second transverse axes Tl, T2 preferably extend parallel to one another with the second transverse axis T2 preferably located posteriorly of the first transverse axis Tl. As illustrated in Figs. 3 and 4, the second transverse axis T2 is also preferably located distally of the first transverse axis Tl. Each condylar portion 27, 29 may be substantially identical, or symmetric, to one another. That is, the distal sagittal and coronal curvatures Rl, R2 of the lateral condylar portion 29 of the femoral component 23 preferably matches the distal sagittal and coronal curvatures Rl, R2 of the medial condylar portion 27 of the femoral component 23, with the transverse axis Tl extending along a transverse plane, etc. On the other hand, the condylar portions 27, 29 may be asymmetric to one another. That is, face surface 35 of the lateral condylar portion 29 of the femoral component 23 may be designed so that it does not match of the face surface 35 of the medial condylar portion 27 of the femoral component 23. For example, the distal sagittal and/or coronal curvatures Rl, R2 of the lateral condylar portion 29 of the femoral component 23 may be larger than the respective distal sagittal and/or coronal curvatures Rl, R2 of the lateral condylar portion 29 of the femoral component 23, or may be formed about a center point that is not on the same transverse plane as the center point about which the respective distal sagittal and/or coronal curvatures Rl, R2 of the lateral condylar portion 29 of the femoral component 23 are formed, etc. Thus, the distal sagittal curvature Rl' of an alternative lateral condylar portion 29 as shown in broken lines in Fig. 3 may be based on a larger radius than the distal sagittal curvature Rl of the medial condylar portion 27 as shown in Fig. 4. The patellar flange portion 31 may be asymmetric as clearly shown in Figs. 1, 2, and 5, or may be symmetric as will now be apparent to those skilled in the art. The femoral component 23 may include typical attachment aids for helping to secure the femoral component 23 to the distal end 17 of the femur 15. Such attachment aids may include one or more pegs, fins, surface treatments, etc. , as will now be apparent to those skilled in the art. The femoral component 23 may be constructed in various manners and out of various materials as will now be apparent to those skilled in the art. Thus, for example, the femoral component 23 can be machined, cast, forged or otherwise constructed as a one-piece, integral unit out of a medical grade, physiologically acceptable metal such as a cobalt chromium alloy or the like, in various sizes to fit a range of typical patients, or may be custom-designed for a specific patient based on data provided by a surgeon after physical and radiography examination of the specific patient, etc. The tibial component 25 includes a base or tray member 43 for being secured to the proximal end 21 of the tibia 19, and an articular bearing, insert or superstructure member 45 for being movably mounted on the base member 43. The base member 43 has an upper or proximal surface 47, a lower or distal surface 49, a medial side 51, a lateral side 53, an anterior or front side 55, and a posterior or rear side 57. The upper surface 47 may be substantially flat and planar as shown in the drawings. The base member 43 preferably includes attachment aids 59 for helping to secure the base member 43 to the proximal end 21 of the tibia 19. Such attachment aids 59 may include one or more pegs, fins, screws, surface treatments, etc., on the lower surface 49 thereof as will now be apparent to those skilled in the art. As clearly shown in Figs. 14 and 16, a peg-like attachment aid 59 thereof may have an aperture therein for allowing extensions to be attached thereto for extending into the intramedullary canal of the tibia 19, etc., as will now be apparent to those skilled in the art. The base member 43 may include a boss or pin 61 extending upward from the upper surface 47 thereof substantially centrally of the upper surface 47 as clearly shown in Figs. 1 and 12, a medial ledge or wall 63 extending upward from the upper surface 47 thereof adjacent the medial side 51 thereof and extending generally from substantially the midportion of the anterior side 55 around the medial side 51 and to substantially the midportion of the posterior side 57 thereof (i.e., along the posterior/medial quadrant, the medial side, and the anterior/medial quadrant of the upper surface 47 of the base member 43), and a lateral fin 65 extending upward and outward from the upper surface 47 thereof adjacent the lateral side 53 thereof and extending generally from substantially the midportion of the lateral side 53 and to substantially the midportion of the posterior side 57 thereof (i.e., along the posterior/lateral quadrant of the upper surface 47 of the base member 43) . The lateral fin 65 preferably has a rounded upper edge to form a lip and coacts with the lateral side 53 of the base member 43 to form a groovelike outer surface 66 (see Fig. 13) to provide a bearing or articulating surface against which the popliteus muscle of the leg can ride after the knee prosthesis 11 is implanted as will now be apparent to those skilled in the art. The base member 43 may be constructed in various manners and out of various materials as will now be apparent to those skilled in the art. Thus, for example, the base member 43 can be machined or otherwise constructed as a one-piece, integral unit out of a medical grade, physiologically acceptable metal such as a cobalt chromium alloy or the like, in various sizes to fit a range of typical patients, or may be custom- designed for a specific patient based on data provided by a surgeon after physical and radiography examination of the specific patient, etc. The upper surface 47 may be polished for reasons which will hereinafter become apparent. The articular bearing member 45 has an upper or proximal surface 67, a lower or distal surface 69, a medial side 71, a lateral side 73, an anterior or front side 75, and a posterior or rear side 77. The lower surface 69 may be substantially flat and planar as shown in the drawings for matingly and confrontingly contacting the upper surface 47 of the base member 43. The sides 71, 73, 75, 77 of the articular bearing member 45 preferably generally angle upward and outward from the lower surface 69 to the upper surface 67 thereof. The upper surface 67 of the articular bearing member 45 preferably has a medial concavity 79 for pivotally receiving and coacting with the face surface 35 of the medial condylar portion 27 of the femoral component 23, and a lateral concavity 81 for pivotally receiving and coacting with the face surface 35 of the lateral condylar portion 29 of the femoral component 23. The medial and lateral concavities 79, 81 are similar to one another and each has a face surface 83 for articulatingly receiving a portion of the face surface 35 of the respective condylar portion 27, 29 of the femoral component 23 as will hereinafter become apparent. The face surface 83 of each concavity 79, 81 is preferably defined by a precise proximal sagittal curvature formed by the radius R4 shown in Figs. 7 and 9, and a precise proximal coronal curvature formed by the radius R5 shown in Fig. 12. The radius R4 is preferably the same size as the radius R5 so that the face surface 83 forms a semispherical shape. In addition, the radii R4, R5 are preferably substantially congruent with or approximately the same size as the radii Rl, R2, with appropriate clearances, so that there is substantially complete surface-to-surface contact between the face surfaces 35, 83 throughout a significant portion of the range of flexion of the knee joint 13, e.g., between full extension of the knee joint 13 as shown in Fig. 18 and approximately 60 * of flexion of the knee joint 13 as illustrated in Fig. 20. The articular bearing member 45 preferably has a slot 87 in the lower surface 69 thereof for receiving the pin 61 of the base member 43. The slot 87 is preferably dimensioned to loosely receive the pin 61 to thereby allow the articular bearing member 45 to pivot and slide on the base member 43 and may be curved somewhat about a center on the lateral side of the articular bearing member 45 as shown in Figs. 23 and 24. The articular bearing member 45 preferably has a medial groove 89 for guidingly receiving the medial ledge 63 of the base member 43. The medial groove 89 preferably extends upward from the lower surface 69 thereof adjacent the medial side 71 thereof and extending generally from substantially the midportion of the anterior side 75 around the medial side 71 and to substantially the midportion of the posterior side 77 thereof (i.e., along the posterior/medial quadrant, the medial side, and the anterior/medial quadrant of the lower surface 69 of the articular bearing member 45) . The articular bearing member 45 may be constructed in various manners and out of various materials as will now be apparent to those skilled in the art. Thus, for example, the articular bearing member 45 can be machined, molded or otherwise constructed as a one-piece, integral unit out of a medical grade, physiologically acceptable plastic such as an ultra high molecular weight polyethylene or the like, in various sizes to fit a range of typical patients, or may be custom-designed for a specific patient based on data provided by a surgeon after physical and radiography examination of the specific patient, etc. With the articular bearing member 45 constructed out of ultra high molecular weight polyethylene or the like, it will freely slide on the polished upper surface 47 of the base member 43. The tibial component 25 includes restriction means for restricting the slidable movement of the articular bearing member 45 relative to the base member 43 to allow a swinging motion of the lateral portion of the upper surface 67 of the articular bearing member 45 and a pivotal motion of the medial portion of the upper surface 67 of the articular bearing member 45. The restriction means may be designed to restrict the pivoting motion of the articular bearing member 45 to approximately 20 degrees of internal/external rotation of the knee joint 13 as will now be apparent to those skilled in the art. The restriction means may be constructed or formed by various structure. For example, the articular bearing member 45 may have a spherical dome or boss (not shown) extending inferiorly from the lower surface 69 substantially beneath the medial concavity 79 in the upper surface 67 thereof, and the base member 43 may have a matching depression (not shown) in the upper surface 47 thereof on its medial side, thereby permitting the articular bearing member 45 to pivot about the axis of the medial dome and depression. However, it should be understood that such specific construction of the restriction means can be reversed by forming the dome on the upper surface 47 of the base member 43 and by forming the mating recess in the lower surface 69 of the articular bearing member. Alternately, the restriction means can be formed or defined by two small diameter pins (not shown) extending upwardly from the upper surface 47 of the base member 43, each post being centered generally beneath one of the medial or lateral concavities 79, 81 of the upper surface 67 of the articular bearing member 45, a cylindrical recess (not shown) on the medial side of the lower surface 69 of the articular bearing member 45 for pivotally receiving one of the posts, and a curved slot (not shown) on the lateral side of the lower surface 69 extending generally in the anterior/posterior direction and formed on a radius from the center of the cylindrical recess for pivotally receiving the other post. The cylindrical recess and curved slot both preferably have a width greater than the diameter of the respective posts for slidably receiving the posts. This construction allows the medial portion of the articular bearing member 45 to slide in a substantially coronal or horizonal plane with respect to the base member 43 by an amount permitted by the respective width differences of the post and cylindrical recess and/or slot, and allow the lateral portion of the articular bearing member 45 to slide with respect to the base member 43 in the medial/lateral direction by the respective width differences of the post and cylindrical recess and/or slot, and in the anterior/posterior direction by the length of the slot. However, it should be understood that such specific construction of the restriction means can be reversed by providing the pins on the lower surface 69 of the articular bearing member and by forming the mating cylindrical recess and slot in the upper surface 47 of the base member 43. Preferably, however, the restriction means is formed or defined by the coaction of the pin 61, medial ledge 63, and lateral fin 65 of the base member 43, and the slot 87 and medial groove 89 of the articular bearing member 45. This design allows a general swinging motion of the lateral portion of the articular bearing member 45 anteriorly and posteriorly while the medial portion of the articular bearing member 45, although permitted some translational movement with respect to the base member 43, is more stationary. However, it should be understood that such specific construction of the restriction means can be reversed by forming the slot 87 in the upper surface 47 of the base member 43, by providing the pin 61 on the lower surface 69 of the articular bearing member 45, by providing the medial ledge 63 and lateral fin 65 on the lower surface 69 of the articular bearing member 45, and by forming the medial groove 89 in the upper surface 47 of the base member 45, etc. The method of replacing a knee joint 13 using the joint prosthesis 11 of the present invention typically starts with standard preoperative planning to estimate the size of the prosthesis to be implanted. The knee joint 13 can then be exposed in any typical manner. The distal end 17 of the femur 15 and the proximal end 21 of the tibia 19 can then be resected and prepared, and a trial reduction of the knee joint 13 performed using appropriate trial implants. Upon successful trial reduction, an appropriate femoral component 23 is implanted on the prepared distal end 17 of the femur 15, and an appropriate base member 43 is implanted on the prepared proximal end 21 of the tibia 19. An appropriate articular bearing member 45 is mounted on the base member 43. After final testing for motion and stability, the surgical site can be closed in any typical manner. The joint prosthesis 11 thus provides a tibial base member 43 bearing a tibial articular bearing member 45 that is permitted a degree of movement on the base member 43. By shaping the curvatures of the medial and lateral condylar portions 27, 29 to precisely match the curvatures of the medial and lateral concavities 79, 81, respectively, of the upper surface 67 of the articular bearing member 45, the medial and lateral condylar portions 27, 29 and the medial and lateral concavities 79, 81, respectively, will stay in perfect surface-to- surface contact when the knee joint 13 is flexed such that only a single axis of movement in extension/flexion is provided as the knee joint 13 is flexed and extended. By sizing the pin 61 of the base member 43 somewhat smaller than the slot 87 in the lower surface 69 of the articular bearing member 45 [e.g., by sizing the pin 61 with a 0.250 inch (6.35 millimeters) diameter and by sizing the slot 87 with a 0.300 inch (7.62 millimeters) width] , and by slightly curving the slot 87 in the anterior/posterior direction (e.g., about a radius of 0.689 inches (approximately 17.5 millimeters), the lateral portion of the articular bearing member 45 is permitted a general swinging motion anteriorly and posteriorly while the medial portion of the articular bearing member 45, although permitted some translational movement with respect to the base member 43, is more stationary. The coaction between the medial ledge 63 of the base member 43 and the medial groove 89 of the articular bearing member 45, and between the lateral fin 65 of the base member 43 and the lateral and posterior sides 73, 77 of the articular bearing member 45 will further restrict and define the free movement of the articular bearing member 45 relative to the base member 43. As thus constructed and used, the knee prosthesis 11 provides a prosthesis in which the movement of the tibial articular bearing member 45 with respect to the tibial base member 43 is restrained by three constraints. The first is a pin and slot arrangement between the articular bearing member 45 and the tibial base member 43. The second is an upstanding ledge formed along the medial edge of the tibial base member 43 and against which the tibial articular bearing member 45 may abut in its movement. The third restraint is an upstanding and outwardly slanting ledge provided along the posterior lateral quadrant of the tibial base member 43 the inner surface of this ledge extends superiorly and laterally from its attachment to the tibial base member 43, and the tibial articular bearing member 45 is similarly configured so as to come into substantial surface-to- surface contact with the inner surface of the ledge. The knee prosthesis 11 provides such a prosthesis having an upstanding and outwardly slanting ledge provided along the posterior lateral quadrant of the tibial base with an upper edge that is rounded to form a lip, and with an outside surface that is grooved slightly below the lip to thus configure the lip to be a bearing surface or articulating surface against which rides the popliteus. A second preferred embodiment of the knee prosthesis of the present invention is shown generally in Figs. 25- 29 and identified by the numeral 2.11. The knee prosthesis 2.11 is also designed to replace at least a portion of a knee joint 13 between the distal end 17 of a femur 15 and the proximal end 21 of a tibial 19. The knee prosthesis 2.11 includes a femoral component 2.23 for mounting to the distal end 17 of the femur 15, and a tibial component 2.25 for mounting to the proximal end 21 of the tibia 19 and for articulating with the femoral component 2.23. The femoral component 2.23 may be identical to the femoral component 23 and includes, in general, a medial condylar portion 2.27, a lateral condylar portion 2.29, and a patellar flange portion 2.31. Reference should be made to the above disclosure of the femoral component 23 for a complete and thorough understanding of the construction and function of the femoral component 2.23. The tibial component 2.25 is preferably similar to the tibial component 25 and includes a base or tray member 2.43 for being secured to the proximal end 21 of the tibia 19, and an articular bearing, insert or superstructure member 2.45 for being movably mounted on the base member 2.43. The base member 2.43 has a substantially flat and planar upper surface 2.47, a lower or distal surface 2.49, a medial side 2.51, a lateral side 2.53, an anterior or front side 2.55, and a posterior or rear side 2.57, and is otherwise similar to the base member 43. However, as clearly shown in Fig. 25, the base member 2.43 does not include a boss or pin extending upward from the upper surface 2.47 thereof such as the pin 61 of the base member 43. The base member 2.43 has a medial ledge or wall 2.63 extending upward from the upper surface 2.47 thereof adjacent the medial side 2.51 thereof and extending generally from substantially the midportion of the anterior side 2.55 around the medial side 2.51 and to substantially the midportion of the posterior side 2.57 thereof (i.e., along the posterior/medial quadrant, the medial side, and the anterior/medial quadrant of the upper surface 2.47 of the base member 2.43), similar to the medial ledge 63 of the base member 43. However, the base member 2.43 additionally has a lateral ledge or wall 2.64 extending upward from the upper surface 2.47 thereof adjacent the lateral side 2.53 thereof and extending generally from substantially the midportion of the anterior side 2.55 around the lateral side 2.53 and to substantially the midportion of the posterior side 2.57 thereof (i.e., along the posterior/lateral quadrant, the lateral side, and the anterior/lateral quadrant of the upper surface 2.47 of the base member 2.43. The ends of the medial ledge 2.63 and the lateral ledge 2.64 at the anterior side 2.55 of the base member 2.43 may be joined together so that the medial and lateral ledges 2.63, 2.64 form a single, continuous ledge from the posterior/lateral quadrant around the anterior side 2.55 to the posterior/medial quadrant as clearly shown in Fig. 25. While the base member 2.43 is not shown in the drawings as including a lateral fin similar to the lateral fin 65 of the base member 43, such a lateral fin could be included if desired. The base member 2.43 may be constructed in various manners and out of various materials as will now be apparent to those skilled in the art. Thus, for example, the base member 2.43 can be machined or otherwise constructed in the same manner hereinabove described relative to the base member 43 and reference should be made to that disclosure for a full and complete understanding thereof. The articular bearing member 2.45 has an upper or proximal surface 2.67 with a medial concavity 2.79 and a lateral concavity 2.81 for pivotally receiving and coacting with the face surfaces of the respective medial and lateral condylar portions 2.27, 2.29 of the femoral component 2.23, a lower or distal surface 2.69, a medial side 2.71, a lateral side 2.73, an anterior or front side 2.75, and a posterior or rear side 2.77, and is otherwise substantially similar to the articular bearing member 45. However, the articular bearing member 2.45 does not include in the lower surface 2.69 thereof corresponding to the slot 87 in the lower surface 69 of the articular bearing member 45. The articular bearing member 2.45 preferably has a medial groove 2.89 similar to the medial groove 89 of the articular bearing member 2.45 for guidingly receiving the medial ledge 2.63 of the base member 2.43. Thus, the medial groove 2.89 preferably extends upward from the lower surface 2.69 thereof adjacent the medial side 2.71 thereof and extending generally from substantially the midportion of the anterior side 2.75 around the medial side 2.71 and to substantially the midportion of the posterior side 2.77 thereof (i.e., along the posterior/medial quadrant, the medial side, and the anterior/medial quadrant of the lower surface 2.69 of the articular bearing member 2.45). In addition, the articular bearing member 2.45 preferably includes a lateral groove 2.91 for guidingly receiving the medial ledge 2.64 of the base member 2.43. The lateral groove 2.91 preferably extends upward from the lower surface 2.69 thereof adjacent the lateral side 2.73 thereof and extending generally from substantially the midportion of the anterior side 2.75 around the lateral side 2.73 and to substantially the midportion of the posterior side 2.77 thereof (i.e., along the posterior/lateral quadrant, the lateral side, and the anterior/lateral quadrant of the lower surface 2.69 of the articular bearing member 2.45). The ends of the medial groove 2.89 and the lateral groove 2.91 preferably met at the midportion of the anterior side 2.75 of the articular bearing member 2.45 so that the medial and lateral grooves 2.89, 2.91 form a single, continuous groove from the posterior/lateral quadrant around the anterior side 2.75 to the posterior/medial quadrant as clearly shown in Fig. 26. The articular bearing member 2.45 may be constructed in various manners and out of various materials as will now be apparent to those skilled in the art. Thus, for example, the articular bearing member 2.45 can be machined or otherwise constructed in the same manner hereinabove described relative to the articular bearing member 45 and reference should be made to that disclosure for a full and complete understanding thereof. The tibial component 2.25 includes restriction means for restricting the slidable movement of the articular bearing member 2.45 relative to the base member 2.43 to allow a swinging motion of the lateral portion of the upper surface 2.67 of the articular bearing member 2.45 and a pivotal motion of the medial portion of the upper surface 2.67 of the articular bearing member 2.45. The restriction means may be designed to restrict the pivoting motion of the articular bearing member 2.45 to approximately 20 degrees of internal/external rotation of the knee joint 13 as will now be apparent to those skilled in the art. The restriction means may be constructed or formed by various structure. Preferably, however, the restriction means is formed or defined by the coaction of the medial and lateral ledges 2.63, 2.64 the base member 2.43 with the medial and lateral grooves 2.89, 2.91 of the articular bearing member 2.45. This design allows a general swinging motion of the lateral portion of the articular bearing member 2.45 anteriorly and posteriorly while the medial portion of the articular bearing member 2.45, although permitted some translational movement with respect to the base member 42.3, is more stationary. The method of replacing a knee joint 13 using the joint prosthesis 2.11 is substantially the same as hereinabove described relative to the joint prosthesis 11, and reference should be made to that disclosure for a full and complete understanding thereof. A third preferred embodiment of the knee prosthesis of the present invention is shown generally in Figs. 30- 40 and identified by the numeral 3.11. The knee prosthesis 3.11 is also designed to replace at least a portion of a knee joint 13 between the distal end 17 of a femur 15 and the proximal end 21 of a tibial 19. The knee prosthesis 3.11 includes a femoral component 3.23 for mounting to the distal end 17 of the femur 15, and a tibial component 3.25 for mounting to the proximal end 21 of the tibia 19 and for articulating with the femoral component 3.23. The femoral component 3.23 may be identical to the femoral component 23 and includes, in general, a medial condylar portion 3.27, a lateral condylar portion 3.29, and a patellar flange portion 3.31. Reference should be made to the above disclosure of the femoral component 23 for a complete and thorough understanding of the construction and function of the femoral component 3.23. The tibial component 3.25 is preferably similar to the tibial component 25 and includes a base or tray member 3.43 for being secured to the proximal end 21 of the tibia 19, and an articular bearing, insert or superstructure member 3.45 for being fixedly mounted on the base member 3.43. The base member 3.43 preferably includes a head portion 3.46 and attachment aids 3.59 for helping to secure the head portion 3.46 to the proximal end 21 of the tibia 19. The attachment aids 3.59 may include one or more pegs, fins, screws, surface treatments, etc., on the lower surface of the head portion 3.46 as will now be apparent to those skilled in the art. In addition, the upper surface of the head portion 3.46 may include articular bearing attachment aids (not shown) for helping to fixedly secure the articular bearing member 3.45 to the base member 3.43. Such articular bearing attachment aids may include one or more undercut flanges extending upward from the upper surface of the head portion 3.46 for coacting with coacting grooves in the lower surface of the articular bearing 3.45 such as disclosed at column 2, lines 46-52 of Lacey, U.S. Patent 4,759,767, issued July 26, 1988, incorporated herein by reference. The base member 3.43 may be constructed in various manners and out of various materials as will now be apparent to those skilled in the art. Thus, for example, the base member 3.43 can be machined or otherwise constructed in the same manner hereinabove described relative to the base member 43 and reference should be made to that disclosure for a full and complete understanding thereof. The articular bearing member 3.45 has an upper or proximal surface 3.67 with a medial concavity 3.79 and a lateral concavity 3.81 for pivotally receiving and coacting with the face surfaces of the respective medial and lateral condylar portions 3.27, 3.29 of the femoral component 3.23, and a lower or distal surface for being fixedly secure to the upper surface of the head portion 3.46 of the base member 3.43 as described above. The medial concavity 3.79 is preferably identical to the medial concavity 79 of the upper surface 67 of the articular bearing member 45 and has a face surface 3.83 for articulatingly receiving a portion of the face surface of the medial condylar portion 3.27 of the femoral component 3.23 with the face surface 3.83 preferably defined by a precise proximal sagittal curvature formed by the radius R6 shown in Fig. 33, and a precise proximal coronal curvature formed by the radius R7 shown in Fig. 32. The radius R6 is preferably the same size as the radius R7 so that the face surface 3.83 forms a semispherical shape. In addition, the radii R6, R7 are preferably substantially congruent with or approximately the same size as the radii Rl, R2, with appropriate clearances, so that there is substantially complete surface-to-surface contact between the face surface of the medial condylar portion 3.27 of the femoral component 3.23 and the face surface 3.83 of the medial concavity 3.79 of the articular bearing member 3.45 of the tibial component 3.25 throughout a significant portion of the range of flexion of the knee joint 13, e.g., between full extension of the knee joint 13 as shown in Fig. 35 and approximately 60' of flexion of the knee joint 13 as illustrated in Fig. 37. The lateral concavity 3.81 has a face surface 3.84 for articulatingly receiving a portion of the face surface of the lateral condylar portion 3.29 of the femoral component 3.23 with the face surface 3.84 preferably defined by a precise proximal coronal curvature formed by the radius R8 shown in Fig. 32, a precise anterior sagittal curvature formed by the radius R9 shown in Fig. 34, and a precise posterior sagittal curvature formed by the radius RIO shown in Fig. 34. The radii R8, R9, RIO are preferably substantially congruent with or approximately the same size as the radii Rl, R2, with appropriate clearances, so that there is substantial surface-to-surface contact between the face surface of the lateral condylar portion 3.29 of the femoral component 3.23 and the anterior end of the face surface 3.84 of the lateral concavity 3.81 of the articular bearing member 3.45 of the tibial component 3.25 during full extension of the knee joint 13 as shown in Fig. 36 and between the face surface of the lateral condylar portion 3.29 of the femoral component 3.23 and the posterior end of the face surface 3.84 of the lateral concavity 3.81 of the articular bearing member 3.45 of the tibial component 3.25 during partial extension or extension of the knee joint 13 as shown in Fig. 38. The lateral concavity 3.81 is preferably curved about an axis extending generally perpendicular to the center of the medial concavity 3.79 when viewed in plan as shown in Fig. 31 so that flexion of the knee joint 13 will cause both the medial condylar portion 3.27 and the lateral condylar portion 3.29 to pivot about that axis as will now be apparent to those skilled in the art. The articular bearing member 3.45 may be constructed in various manners and out of various materials as will now be apparent to those skilled in the art. Thus, for example, the articular bearing member 3.45 can be machined or otherwise constructed in the same manner hereinabove described relative to the articular bearing member 45 and reference should be made to that disclosure for a full and complete understanding thereof. The method of replacing a knee joint 13 using the joint prosthesis 3.11 is substantially the same as hereinabove described relative to the joint prosthesis 11, and reference should be made to that disclosure for a full and complete understanding thereof. A fourth preferred embodiment of the knee prosthesis of the present invention is shown generally in Figs. 30- 40 and identified by the numeral 4.11. The knee prosthesis 4.11 is also designed to replace at least a portion of a knee joint 13 between the distal end 17 of a femur 15 and the proximal end 21 of a tibial 19. The knee prosthesis 4.11 includes a femoral component 4.23 for mounting to the distal end 17 of the femur 15, and a tibial component 4.25 for mounting to the proximal end 21 of the tibia 19 and for articulating with the femoral component 4.23. The femoral component 4.23 may be identical to the femoral component 23 and includes, in general, a medial condylar portion 4.27, a lateral condylar portion 4.29, and a patellar flange portion 4.31. Reference should be made to the above disclosure of the femoral component 23 for a complete and thorough understanding of the construction and function of the femoral component 4.23. The tibial component 4.25 is preferably substantially similar to the tibial component 2.25 and includes a base or tray member 4.43 for being secured to the proximal end 21 of the tibia 19, and an articular bearing, insert or superstructure member 4.45 for being movably mounted on the base member 4.43. The base member 4.43 and articular bearing member 4.45 are substantially similar to the base member 2.43 and articular bearing member 2.45 of the tibial component 2.25 and reference should be made to the above disclosure of the base member 2.43 and articular bearing member 2.45 for a complete and thorough understanding of the construction and function of the base member 4.43 and articular bearing member 4.45. However, the tibial component 4.25 further includes guide means 4.91 for guiding the movement of the articular bearing member 4.45 on the base member 4.43. More specifically, the guide means 4.91 preferably includes a guide finger 4.93 on the upper surface 4.47 of the base member 4.43 and extending inwardly from the medial ledge 4.63 as clearly shown in Fig. 41, and a guide groove 4.95 in the lower surface 4.69 of the articular bearing member 4.45 and extending inwardly from the posterior side 4.77 thereof as clearly shown in Fig. 42 for receiving and coacting with the guide finger 4.93 to cause the articular bearing member 4.45 to pivot about one or more axes extending generally perpendicular to the medial portion of the upper surface 4.47 of the articular bearing member 4.45. The base member 4.43 may be constructed in various manners and out of various materials as will now be apparent to those skilled in the art. Thus, for example, the base member 4.43 can be machined or otherwise constructed in the same manner hereinabove described relative to the base member 43 and reference should be made to that disclosure for a full and complete understanding thereof. The articular bearing member 4.45 may be constructed in various manners and out of various materials as will now be apparent to those skilled in the art. Thus, for example, the articular bearing member 4.45 can be machined or otherwise constructed in the same manner hereinabove described relative to the articular bearing member 45 and reference should be made to that disclosure for a full and complete understanding thereof. The method of replacing a knee joint 13 using the joint prosthesis 4.11 is substantially the same as hereinabove described relative to the joint prosthesis 11, and reference should be made to that disclosure for a full and complete understanding thereof. A fifth preferred embodiment of the knee prosthesis of the present invention is shown generally in Figs. 46- 50 and identified by the numeral 5.11. The knee prosthesis 5.11 is also designed to replace at least a portion of a knee joint 13 between the distal end 17 of a femur 15 and the proximal end 21 of a tibial 19. The knee prosthesis 5.11 includes a femoral component 5.23 for mounting to the distal end 17 of the femur 15, and a tibial component 5.25 for mounting to the proximal end 21 of the tibia 19 and for articulating with the femoral component 5.23. The femoral component 5.23 may be identical to the femoral component 23 and includes, in general, a medial condylar portion 5.27, a lateral condylar portion 5.29, and a patellar flange portion 5.31. Reference should be made to the above disclosure of the femoral component 23 for a complete and thorough understanding of the construction and function of the femoral component 5.23. The tibial component 5.25 includes a base or tray member 5.43 for being secured to the proximal end 21 of the tibia 19, and an articular bearing, insert or superstructure member 5.45 for being mounted on the base member 5.43. The base member 5.43 and articular bearing member 5.45 are substantially similar to the base member 2.43 and articular bearing member 2.45 of the tibial component 2.25 and reference should be made to the above disclosure of the base member 2.43 and articular bearing member 2.45 for a complete and thorough understanding of the construction and function of the base member 5.43 and articular bearing member 5.45. However, the articular bearing member 5.45 is divided into a separate medial articular bearing, insert or superstructure member 5.45M for being fixedly mounted on the base member 5.43, and a separate lateral articular bearing, insert or superstructure member 5.45L for being movably mounted on the base member 5.43. Also, because the medial articular bearing member 5.45H is fixedly mounted on the base member 5.43, the medial ledge may be omitted. The base member 5.43 may be constructed in various manners and out of various materials as will now be apparent to those skilled in the art. Thus, for example, the base member 5.43 can be machined or otherwise constructed in the same manner hereinabove described relative to the base member 43 and reference should be made to that disclosure for a full and complete understanding thereof. The medial articular bearing member 5.45M may be similar to the medial side of the articular bearing 45 of the tibial component 25, and may have an upper or proximal surface 5.67M with a medial concavity 5.79M for pivotally receiving and coacting with the face surfaces of the medial condylar portion 5.27 of the femoral component 5.23, and a lower or distal surface 5.69M for being fixedly attached to the medial side of the upper surface 5.47 of the base member 5.43 in any manner now apparent to those skilled in the art such as, for example, by way of articular bearing attachment aids such as one or more coacting groove and flange structures such as hereinabove disclosed relative to the knee prosthesis 3.11 as will now be apparent to those skilled in the art. The lateral articular bearing member 5.45L may be similar to the lateral side of the articular bearing 45 of the tibial component 25, and may have and upper or proximal surface 5.67 with a lateral concavity 5.79L for pivotally receiving and coacting with the face surfaces of the lateral condylar portion 5.29 of the femoral component 5.23, and a lower or distal surface 5.69L for being movably positioned on the lateral side of the upper surface 5.47 of the base member 5.43 as will now be apparent to those skilled in the art. The lateral articular bearing member 5.45L will coact with the lateral ledge 5.64 of the base member 5.43 to form or define a restriction means for allowing allows a general swinging motion of the lateral portion of the lateral articular bearing member 5.45L, while the medial articular bearing member 5.45M remains fixed and stationary. The articular bearing members 5.45M, 5.45L may be constructed in various manners and out of various materials as will now be apparent to those skilled in the art. Thus, for example, the articular bearing members 5.45M, 5.45L can be machined or otherwise constructed in substantially the same manner hereinabove described relative to the articular bearing member 45 and reference should be made to that disclosure for a full and complete understanding thereof. The method of replacing a knee joint 13 using the joint prosthesis 5.11 is substantially the same as hereinabove described relative to the joint prosthesis 11, and reference should be made to that disclosure for a full and complete understanding thereof. As thus constructed and used, the present invention provides a joint prosthesis for a knee that employs a tibial base bearing a tibial articular bearing that is permitted a degree of specifically restricted movement on the base, in which the confronting surfaces of the tibial base and the tibial articular bearing can be flat or curved, as desired. Such a joint prosthesis may include a pin and a pin-receiving slot for coacting with one another to restrict the movement of the articular bearing relative to the base. The pin could be on the upper surface of the base and the slot could be in the lower surface of the articular bearing, or vice versa. The tibial articular bearing may be permitted to rotate generally about the medial side of the tibial base with the actual axis or axes of rotation comprising a bundle of parallel axes that extend normal to the tibial base and are positioned in the medial side of the prosthesis. The prosthesis may be provided with femoral and tibial condylar surfaces that conform readily to one another such that only a single axis of movement in extension/flexion is provided as the knee is flexed and extended, and may have articulating surfaces that are congruent to provide generally surface-to-surface contact. Although the present invention has been described and illustrated with respect to a preferred embodiment thereof and a preferred use therefor, it is not to be so limited since modifications and changes can be made therein which are within the full intended scope of the invention.

Claims: We Claim: 1. A knee prosthesis for replacing at a least portion of a knee joint between the distal end of a femur and the proximal end of a tibia; the knee prosthesis comprising: (a) a tibial component for mounting to the proximal end of the tibia, the tibial component including an upper surface and having a medial cavity and a lateral cavity in the upper surface thereof; the medial cavity having a face surface with a coronal curvature and a sagittal curvature; and (b) a femoral component for mounting to the distal end of the femur, the femoral component including a medial condylar portion for pivotally coacting with the medial cavity in the upper surface of the tibial component and including a lateral condylar portion for pivotally coacting with the lateral cavity in the upper surface of the tibial component; the medial condylar portion having a face surface with a distal coronal curvature and a distal sagittal curvature that are substantially congruent with the coronal curvature and sagittal curvature, respectively, of the medial cavity in the upper surface of the tibial component so that substantially complete surface-to-surface contact between the face surface of the medial cavity in the upper surface of the tibial component and the face surface of the medial condylar portion of the femoral component is provided throughout a significant portion of the range of flexion of the knee joint. 2. The knee prosthesis of claim 1 in which complete surface-to-surface contact is maintained between the face surface of the medial cavity in the upper surface of the tibial component and the medial condylar portion of the femoral component for approximately 60" of flexion of the knee joint. 3. The knee prosthesis of claim 1 in which the lateral condylar portion of the femoral component has a face surface with a distal coronal curvature and a distal sagittal curvature that match the distal coronal and sagittal curvatures, respectively, of the face surface of the medial condylar portion of the femoral component. 4. The knee prosthesis of claim 3 in which the lateral cavity of the upper surface of the tibial component has a face surface with a coronal curvature and a sagittal curvature that are substantially congruent with the distal coronal curvature and distal sagittal curvature, respectively, of the face surface of the lateral condylar portion of the femoral component so that substantially complete surface-to-surface contact between the face surface of the lateral cavity in the upper surface of the tibial component and the face surface of the lateral condylar portion of the femoral component is provided throughout a significant portion of the range of flexion of the knee joint. 5. The knee prosthesis of claim 4 in which complete surface-to-surface contact is maintained between the face surface of the medial and lateral cavities in the upper surface of the tibial component and the medial and lateral condylar portion, respectively, of the femoral component for approximately 60' of flexion of the knee joint. 6. The knee prosthesis of claim 4 in which the medial cavity in the upper surface of the tibial component is semispherical in shape; in which the lateral cavity in the upper surface of the tibial component is semispherical in shape; in which the distal coronal curvature and distal sagittal curvature of the face surface of the medial condylar portion of the femoral component form a semispherical shape for pivotally coacting with the semispherical medial cavity in the upper surface of the tibial component; and in which the distal coronal curvature and distal sagittal curvature of the face surface of the lateral condylar portion of the femoral component form a semispherical shape for pivotally coacting with the semispherical lateral cavity in the upper surface of the tibial component. 7. The knee prosthesis of claim 6 in which the face surface of the medial condylar portion of the femoral component has a posterior sagittal curvature; in which the posterior sagittal curvature of the face surface of the medial condylar portion of the femoral component is based on a smaller radius than the distal sagittal curvature of the face surface of the medial condylar portion of the femoral component; in which the face surface of the lateral condylar portion of the femoral component has a posterior sagittal curvature; and in which the posterior sagittal curvature of the face surface of the lateral condylar portion of the femoral component is based on a smaller radius than the distal sagittal curvature of the face surface of the lateral condylar portion of the femoral component. 8. The knee prosthesis of claim 1 in which the lateral condylar portion of the femoral component has a face surface that does not match of the face surface of the medial condylar portion of the femoral component. 9. The knee prosthesis of claim 1 in which the tibial component includes: (a) a base member having an upper surface; (b) an articular bearing member movably positioned on the upper surface of the base member; the articular bearing member including a medial portion and a lateral portion; and (c) restriction means for restricting the movement of the lateral portion of the articular bearing member relative to the base member to allow a swinging motion thereof relative to the medial portion of the articular bearing member. 10. The knee prosthesis of claim 9 in which the restriction means includes ledge means extending upward from the upper surface of the base member for engaging a portion of the articular bearing member and for restricting the movement of the articular bearing member relative to the base member. 11. The knee prosthesis of claim 10 in which the base member has an anterior side, a medial side, and a posterior side; and in which the ledge means includes a medial ledge extending upward from the upper surface of the base member adjacent the medial side of the base member and extending generally from substantially the midportion of the anterior side of the base member around the medial side of the base member and to substantially the midportion of the posterior side of the base member. 12. The knee prosthesis of claim 10 in which the base member has a lateral side; and in which the ledge means includes a lateral ledge extending upward from the upper surface of the base member adjacent the lateral side of the base member and extending generally from substantially the midportion of the anterior side of the base member around the lateral side of the base member and to substantially the midportion of the posterior side of the base member. 13. The knee prosthesis of claim 10 in which the base member has an anterior side, a medial side, a posterior side, and a lateral side; and in which the ledge means extends substantially completely about the anterior, medial, posterior and lateral sides of the base member. 14. The knee prosthesis of claim 13 in which the tibial component further includes guide means for guiding the movement of the articular bearing member on the base member. 15. The knee prosthesis of claim 14 in which the guide means includes a guide finger on the upper surface of the base member extending inwardly from the ledge means; and in which the articular bearing member has a lower surface and has a guide groove in the lower surface thereof for receiving and coacting with the guide finger to cause the articular bearing member to pivot about one or more axes extending generally perpendicular to the medial portion of the upper surface of the articular bearing member. 16. The knee prosthesis of claim 9 in which the medial and lateral portions of the articular bearing member are separate from one another; in which the lateral portion of the articular bearing member is slidably positioned on the upper surface of the base member; and in which the medial portion of the articular bearing member is non-movably attached to the upper surface of the base member. 17. A knee prosthesis for replacing at a least portion of a knee joint between the distal end of a femur and the proximal end of a tibia; the knee prosthesis comprising: (a) a femoral component for mounting to the distal end of the femur, the femoral component including a medial condylar portion and a lateral condylar portion; and (b) a tibial component including: (i) a base member for mounting to the proximal end of the tibia, the base member including an upper surface having a medial portion and a lateral portion; (ii) an articular bearing member movably positioned on the upper surface of the base member; the articular bearing member including an upper surface having a medial portion and a lateral portion; the articular bearing member having a medial cavity in the medial portion of the upper surface thereof for receiving the medial condylar portion of the femoral component and having a lateral cavity in the lateral portion of the upper surface thereof for receiving the lateral condylar portion of the femoral component; and (iii) restriction means for restricting the movement of the articular bearing member on the upper surface of the base member to a pivotal movement about one or more axes extending generally perpendicular to the medial portion of the upper surface of the base member. 18. The knee prosthesis of claim 17 in which the articular bearing member has a lower surface; in which the restriction means includes a pin extending upward from the upper surface of the base member and a pin receiving slot means in the lower surface of the articular bearing member for movably receiving the pin and for coacting with the pin to restrict the movement of the articular bearing member relative to the base member. 19. The knee prosthesis of claim 17 in which the restriction means includes ledge means extending upward from the upper surface of the base member for engaging a portion of the articular bearing member and for restricting the movement of the articular bearing member relative to the base member. 20. The knee prosthesis of claim 19 in which the base member has an anterior side, a medial side, and a posterior side; and in which the ledge means includes a medial ledge extending upward from the upper surface of the base member adjacent the medial side of the base member and extending generally from substantially the midportion of the anterior side of the base member around the medial side of the base member and to substantially the midportion of the posterior side of the base member. 21. The knee prosthesis of claim 20 in which the base member has a lateral side; and in which the ledge means includes a lateral ledge extending upward from the upper surface of the base member adjacent the lateral side of the base member and extending generally from substantially the midportion of the anterior side of the base member around the lateral side of the base member and to substantially the midportion of the posterior side of the base member. 22. The knee prosthesis of claim 19 in which in which the base member has an anterior side, a medial side, a posterior side, and a lateral side; and in which the ledge means extends substantially completely about the anterior, medial, posterior and lateral sides of the base member. 23. The knee prosthesis of claim 22 in which the tibial component further includes guide means for guiding the movement of the articular bearing member on the base member. 24. The knee prosthesis of claim 23 in which the guide means includes a guide finger on the upper surface of the base member extending inwardly from the ledge means; and in which the articular bearing member has a lower surface and has a guide groove in the lower surface thereof for receiving and coacting with the guide finger to cause the articular bearing member to pivot about one or more axes extending generally perpendicular to the medial portion of the upper surface of the articular bearing member. 25. The knee prosthesis of claim 17 in which the medial and lateral portions of the articular bearing member are separate from one another; in which the lateral portion of the articular bearing member is slidably positioned on the upper surface of the base member; and in which the medial portion of the articular bearing member is non-movably attached to the upper surface of the base member. 26. The knee prosthesis of claim 17 in which the medial cavity of the articular bearing member conforms to a significant portion of the medial condylar portion of the femoral component to provide a single axis of rotation therebetween throughout a significant portion of the range of flexion of the knee joint. 27. The knee prosthesis of claim 17 wherein the restriction means restricts pivoting motion of the articular bearing member to approximately 20 degrees of internal/external rotation. 28. The prosthesis of claim 17 in which complete surface-to-surface contact is maintained between the lateral and medial condyles of the femoral component and the respective lateral and medial cavities of the articular bearing member between full extension of the knee joint and approximately 60 * of flexion of the knee joint.

Inventors: BLAHA J DAVID, BUCHANAN DENNIS J, PAXSON ROBERT D, WHITE STEPHEN E, BLAHA, J., DAVID, BUCHANAN, DENNIS, J., PAXSON, ROBERT, D., WHITE, STEPHEN, E.
Applicants: WRIGHT MEDICAL TECH INC, WRIGHT MEDICAL TECHNOLOGY, INC.
Application year: 1997
Main classification: A61F2
IPC codes: A61F2