Asymmetric artificial knee joint

The present invention relates to an asymmetric artificial knee joint that includes a bearing member having a medial sulcus and a lateral sulcus, and a femoral component having a medial condyle and a lateral condyle and disposed on the bearing member.

TECHNICAL FIELD

The present invention relates to an asymmetric artificial knee joint and, more particularly to an asymmetric artificial knee joint including: a bearing member having a medial sulcus and a lateral sulcus; and a femoral component having a medial condyle and a lateral condyle and disposed on the bearing member. The bearing member is formed such that lateral sulcus point of the lateral sulcus is positioned more forward than a medial sulcus point of the medial sulcus, and a distance from a central plane of the bearing member to a medial sulcus-point plane including the medial sulcus point of the medial sulcus is larger than a distance from the central plane of the bearing member to a lateral sulcus point-plane including the lateral sulcus point of the lateral sulcus. The femoral component is formed such that a distance from a central plane of the femoral component to a medial peak-point plane including peak points on the medial condyle is larger than a distance from the central plane of the femoral component to a lateral peak-point plane including peak points on the lateral condyle, in order to prevent inwardly biased wear of the bearing by moving the artificial knee joint on the medial sulcus of the bearing member and the medial condyle of the femoral component and to uniformly distribute load applied to the knee to the medial and lateral sides of the knee.

BACKGROUND ART

A knee joint, which is a joint composed of three bones of the femur, the tibia, and the patella surrounding a knee, is a very important joint supporting the weight of a human body and is related to motions using the legs, such as walking or running through joint motion. There is the articular cartilage at the end of the femur and there is the meniscus at the end of the tibia, but when the cartilage is damaged due to strenuous exercise or aging, the bones come in direct contact with each other and a severe pain may be caused.

Total knee arthroplasty is an operation wherein the knee joint is removed by cutting off portions of the femur and the tibia and then an artificial knee joint is implanted by connecting a femoral component91to an end of the femur F, inserting and fixing a tibia member93in the end of the tibia T, and then installing a bearing member95on the tibia member93FIG. 1shows flexion of a knee after total knee arthroplasty and a technology related toFIG. 1has been disclosed in Korean Patent No. 10-1184905 (2012 Sep. 20).

A virtual central cut surface for dividing a human body to the left and right parts is called a sagittal plane, and with respect to any one of left and right legs, the inner side of the knee positioned at the sagittal plane is called a medial side and the outer side of the knee positioned on the opposite side of the sagittal plane is called a lateral side.

In general, a femoral component includes a lateral condyle positioned at the outer side and having an articular surface, a medial condyle positioned at the inner side and having an articular surface, and a cam connecting the lateral condyle and the medial condyle. The top at the center of the curved articular surface is called a peak.

A bearing member usually includes a lateral sulcus positioned at the outer side and having an articular surface, a medial sulcus positioned at the inner side and having an articular surface, and a post positioned between the lateral sulcus and the medial sulcus.

In the related art, the femoral component of artificial knee joints has a lateral condyle and a medial condyle symmetrically arranged with a cam therebetween and the bearing member is also symmetrically formed with a post therebetween, so abduction (external rotation) that is accompanied by rotation and roll-back around the lateral condyle of the femoral component occurs in flexion of a knee. According to clinically examined results, when a knee performs a motion, a larger load is applied to the medial side at a ratio of 1:2˜3 between the lateral side and the medial side. Accordingly, after an artificial knee joint is implanted, the medial sulcus is worn or damaged earlier than the lateral side of the bearing member, so it has been required to develop a technology for solving this problem.FIG. 2shows a knee joint in abduction, which has been disclosed in Korean Patent Application Publication No. 10-2013-0102034 (2013 Sep. 16).

Further, referring toFIG. 3, in abduction of a femoral component, it has frequently occurred that a cam911of a femoral component91hits against the edge of a post951of a bearing member95, thereby damaging the bearing member95. The reason for the damage is because the post951of the bearing member95has a left-right symmetric structure.

Accordingly, it is required to develop a technology that prevents inward wear of a joint by preventing concentration of load on the medial side of a knee and prevents shock to a post edge of a bearing member by increasing the contact area between the cam of a femoral component and the post of a bearing member.

DISCLOSURE

Technical Problem

The present invention has been made in an effort to solve the problems.

An object of the present invention is to provide an artificial knee joint that can prevent damage and wear of a medial sulcus of a bearing member and accomplish anatomical knee motion of a human body by making a medial condyle of a femoral component and the medial sulcus of the bearing member as the center of motion.

Another object of the present invention is to provide an artificial knee joint in which a lateral condyle can move forwardly more than a medial condyle such that a femoral component can be adducted in flexion of a knee, thereby increasing stability of joint motion by tensioning tissues around a knee joint.

Another object of the present invention is to provide an artificial knee joint in which a lateral sulcus point that is a peak point of a lateral sulcus is positioned more forward than a medial sulcus point that is a peak point of a medial sulcus such that a lateral condyle can move forwardly more than a medial condyle and a femoral component can be adducted, thereby increasing stability of joint motion by tensioning tissues around the knee joint.

Another object of the present invention is to provide an artificial knee joint in which a posterior condyle of a lateral condyle has various curvatures in comparison to a posterior condyle of a medial condyle in a femoral component such that the lateral condyle can move forwardly more than the medial condyle and the femoral component can be adducted, thereby increasing stability of joint motion by tensioning tissues around the knee joint.

Another object of the present invention is to provide an artificial knee joint in which curvatures of a posterior condyle of a lateral condyle increase toward a posterior direction in a femoral component such that the lateral condyle can move forwardly more than the medial condyle and the femoral component can be adducted, thereby increasing stability of joint motion by tensioning tissues around the knee joint.

Another object of the present invention is to provide an artificial knee joint in which a bearing member is asymmetrically formed such that a posterior surface of the bearing member is inclined from a lateral surface to a medial surface in order that that a femoral component that is adducting can be abducted to follow the anatomical structure of human body.

Another object of the present invention is to provide an artificial knee joint in which a posterior protrusion of a lateral sulcus has a curvature smaller than a curvature of a posterior protrusion of a medial sulcus in a bearing member such that a femoral component that is adducting can be abducted to follow the anatomical structure of human body.

Another object of the present invention is to provide an artificial knee joint in which a femoral component is formed such that a distance from a central plane of the femoral component to a medial peak-point plane including peak points on a medial condyle is larger than a distance from the central plane of the femoral component to a lateral peak-point plane including peak points on a lateral condyle, whereby it is possible to prevent damage and wear of a medial sulcus of a bearing member by reducing load that is concentrated on the medial sulcus.

Another object of the present invention is to provide an artificial knee joint in which a bearing member is formed such that a distance from a central plane of the bearing member to a medial sulcus-point plane including a medial sulcus point of a medial sulcus is larger than a distance from the central plane of the bearing member to a lateral sulcus point-plane including a lateral sulcus point of a lateral sulcus, whereby it is possible to prevent damage and wear of a medial sulcus of the bearing member by reducing load that is concentrated on the medial sulcus.

Another object of the present invention is to provide an artificial knee joint in which when a central plane of a bearing member and a central plane of a femoral component are aligned, the distance from the central planes to a medial peak-point plane is the same as the distance from the central planes to a medial sulcus-point plane, and the distance from the central planes to a lateral peak-point plane is the same as the distance from the central plane to a lateral sulcus-point plane such that the femoral component is placed in position on the bearing member.

Another object of the present invention is to provide an artificial knee joint in which a bearing member is asymmetrically formed such that a posterior surface is inclined from a lateral surface to a medial surface in order that a cam surface of a femoral component comes in contact with the asymmetric posterior surface of the post of the bearing member in a wide area when a femoral component that is adducting changes into abduction following the anatomical structure of human body, whereby it is possible to prevent large shock from being applied to a post edge of the bearing member from the cam of the femoral component.

Technical Solution

The present invention has the following configuration to achieve the objects.

An artificial knee joint according to an aspect of the present invention includes a bearing member having a medial sulcus and a lateral sulcus, in which a lateral sulcus point of the lateral sulcus is positioned more forward than a medial sulcus point of the medial sulcus such that the medial sulcus is a center of motion, thereby preventing inwardly biased wear of the bearing member.

The lateral sulcus point may be positioned at a 10˜25% anterior point of an AP length connecting an anterior point to a posterior point of the bearing member.

The bearing member may be formed such that a distance from a central plane of the bearing member to a medial sulcus-point plane including the medial sulcus point of the medial sulcus is larger than a distance from the central plane of the bearing member to a lateral sulcus point-plane including the lateral sulcus point of the lateral sulcus.

In the bearing member, a posterior protrusion of the lateral sulcus may have a curvature smaller than a curvature of a posterior protrusion of the medial sulcus.

The bearing member may be asymmetrically formed such that a posterior surface of the bearing member is inclined from a lateral surface to a medial surface.

An artificial knee joint according to another aspect of the present invention includes a femoral component having a medial condyle and a lateral condyle, in which the lateral condyle moves forwardly longer than the medial condyle and the femoral component is adducted, in the femoral component, in flexion of a knee.

The femoral component may be formed such that a distance from a central plane of the femoral component to a medial peak-point plane including peak points on the medial condyle is larger than a distance from the central plane of the femoral component to a lateral peak-point plane including peak points on the lateral condyle.

In the femoral component, a lateral posterior condyle of the lateral condyle may have various curvatures in comparison to a medial posterior condyle of the medial condyle.

In the femoral component, the curvatures of the lateral posterior condyle of the lateral condyle may increase toward a posterior direction.

An artificial knee joint according to another aspect of the present invention includes: a bearing member having a medial sulcus and a lateral sulcus; and a femoral component having a medial condyle and a lateral condyle and placed on the bearing member, in which a lateral sulcus point of the lateral sulcus is positioned more forward than a medial sulcus point of the medial sulcus in the bearing member, the lateral condyle moves forwardly more than the medial condyle and the femoral component is adducted, and the medial sulcus of the bearing member and the medial condyle of the femoral component form a center of motion.

The bearing member may be formed such that a distance from a central plane of the bearing member to a medial sulcus-point plane including the medial sulcus point of the medial sulcus is larger than a distance from the central plane of the bearing member to a lateral sulcus point-plane including the lateral sulcus point of the lateral sulcus, and the femoral component may be formed such that a distance from a central plane of the femoral component to a medial peak-point plane including peak points on the medial condyle is larger than a distance from the central plane of the femoral component to a lateral peak-point plane including peak points on the lateral condyle.

When the central plane of the bearing member and the central plane of the femoral component are aligned, the distance from the central plane of the bearing member to the medial sulcus-point plane including the medial sulcus point of the medial sulcus may be the same as the distance from the central plane of the femoral component to the medial peak-point plane including the peak points on the medial condyle, and the distance from the central plane of the bearing member to the lateral sulcus point-plane including the lateral sulcus point of the lateral sulcus may be the same as the distance from the central plane of the femoral component to the lateral peak-point plane including the peak points on the lateral condyle.

The femoral component may include a cam connecting the medial condyle and the lateral condyle to each other, the bearing member may be asymmetrically formed such that a posterior surface of the bearing member is inclined from a lateral surface to a medial surface, and an inclination of the posterior surface of the post may be the same as an angle that is formed by abduction of the femoral component at the moment when the cam of the femoral component comes in contact with the post.

Advantageous Effects

According to the present invention, it is possible to achieve the following effects from the configuration, combination, and operation relationship described below.

According to the present invention, it is possible to prevent damage and wear of a medial sulcus of a bearing member and to enable anatomical knee motion of a human body by making a medial condyle of a femoral component and the medial sulcus of the bearing member as the center of motion.

Further, since the lateral condyle moves forwardly more than the medial condyle such that a femoral component can be adducted in flexion of a knee, it is possible to increase stability of joint motion by tensioning tissues around a knee joint.

Further, since the lateral sulcus point that is a peak point of a lateral sulcus is positioned more forward than the medial sulcus point that is a peak point of a medial sulcus such that the lateral condyle can move forwardly more than the medial condyle and the femoral component can be adducted, it is possible to increase stability of joint motion by tensioning tissues around the knee joint.

Further, since the posterior condyle of the lateral condyle has various curvatures in comparison to the posterior condyle of the medial condyle in a femoral component such that the lateral condyle can move forwardly more than the medial condyle and the femoral component can be adducted, it is possible to increase stability of joint motion by tensioning tissues around the knee joint.

Further, since the curvatures of the posterior condyle of the lateral condyle increase toward a posterior direction in a femoral component such that the lateral condyle can move forwardly more than the medial condyle and the femoral component can be adducted, it is possible to increase stability of joint motion by tensioning tissues around the knee joint.

Further, since the bearing member is asymmetrically formed such that the posterior surface of the bearing member is inclined from the lateral surface to the medial surface, a femoral component that is adducting can be abducted to follow the anatomical structure of human body.

Further, since the posterior protrusion of a lateral sulcus has a curvature smaller than a curvature of the posterior protrusion of the medial sulcus in the bearing member, a femoral component that is adducting can be abducted to follow the anatomical structure of human body.

Further, since the femoral component is formed such that the distance from the central plane of the femoral component to the medial peak-point plane including peak points on the medial condyle is larger than the distance from the central plane of the femoral component to the lateral peak-point plane including peak points on the lateral condyle, it is possible to prevent damage and wear of a medial sulcus of a bearing member by reducing load that is concentrated on the medial sulcus.

Further, since the bearing member is formed such that the distance from the central plane of the bearing member to the medial sulcus-point plane including the medial sulcus point of the medial sulcus is larger than the distance from the central plane of the bearing member to the lateral sulcus point-plane including the lateral sulcus point of the lateral sulcus, it is possible to prevent damage and wear of a medial sulcus of a bearing member by reducing load that is concentrated on the medial sulcus.

Further, since when the central plane of a bearing member and the central plane of a femoral component are aligned, the distance from the central planes to the medial peak-point plane is the same as the distance from the central planes to the medial sulcus-point plane, and the distance from the central planes to the lateral peak-point plane is the same as the distance from the central plane to the lateral sulcus-point plane, the femoral component can be placed in position on the bearing member.

Further, since the bearing member is asymmetrically formed such that the posterior surface is inclined from the lateral surface to the medial surface in order that the cam surface of the femoral component comes in contact with the asymmetric posterior surface of the post of the bearing member in a wide area when the femoral component that is adducting changes into abduction following the anatomical structure of human body, it is possible to prevent large shock from being applied to a post edge of the bearing member from the cam of the femoral component.

BEST MODE

Hereinafter, preferred embodiments of an asymmetric artificial knee joint according to the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, well-known functions or constructions will not be described in detail since they may unnecessarily obscure the understanding of the present invention. Unless specifically defined, all terms used herein are the same as the general meanings of corresponding terms that those skilled in the art understand, and if they conflict with the meanings of terms used herein, they follow the definition used herein.

It should be noticed that the drawings for illustrating the present invention show an artificial knee joint that is inserted into the left knee from the sagittal plane.

FIG. 4is a perspective view of a bearing member of the present invention. Referring toFIG. 4, a bearing member10of the present invention is a component that is disposed on a tibial component connected to femur-sided end of the tibia in total knee arthroplasty to support a femoral component30. Preferably, the bearing member10is a part having an articular surface that allows for translation, rotation, and roll-back of the femoral component30on the bearing member10, depending on motions of the femur in knee motion. The material of the bearing member10is not specifically limited, but may be preferably polyethylene.

The bearing member10has a top surface6that extends between an anterior edge7and an opposing posterior edge8. Recessed into top surface6is a medial sulcus11and a lateral sulcus13. A post15centrally upstands from top surface6.

The medial sulcus11, which is intended to support the medial condyle31of the femoral component30in contact therewith, forms an articular surface. Preferably, the medial sulcus11is a recess for receiving the medial condyle of the femoral component30having a convex surface, in which the maximally recessed portion is referred to as a sulcus point and the sulcus point on the medial sulcus11is referred to as a medial sulcus point111to be discriminated from a lateral sulcus13to be described below (seeFIG. 7).

FIG. 5is a side view showing the medial sulcus. Referring toFIG. 5, the side of the medial sulcus11is generally formed in a concave shape and the medial sulcus11can be divided into a medial anterior section113and a medial posterior section115due to different side curvatures.

The medial anterior section113is a part having a predetermined curvature and protruding forward from the medial sulcus11and the medial posterior section115is a part having a predetermined curvature and protruding rearward from the medial sulcus11. The large curvatures ahead of and behind the medial sulcus point111of the medial sulcus11prevent a medial condyle31of the femoral component30(described below) that is placed on the medial sulcus11from being disjointed forward and rearward, help the medial condyle31of the femoral component30that is placed on the bearing member10be placed in position, and limit the distance of translation of the medial condyle31of the femoral component30, so it is possible to accomplish the objective knee motion of the present invention around the medial sulcus11and the medial condyle31.

The anterior curvature of the medial anterior section113allows for rotation of the femoral component30through the medial anterior section113in the flexion of the knee, and as shown in the figure, it is preferable that the curvature at the anterior portion of the medial sulcus11is larger than the curvature at the posterior portion (the radius of curvature Rm1at the anterior portion is smaller than the radius of curvature Rm2at the posterior portion).

The lateral sulcus13, which is intended to support the lateral condyle33of the femoral component30in contact therewith, forms an articular surface, similar to the medial sulcus11. Preferably, the lateral sulcus13is a recess for receiving the lateral condyle33of the femoral component30, in which the maximally recessed sulcus point of the lateral sulcus13is referred to as the lateral sulcus point131(seeFIG. 7).

FIG. 6is a side view showing the curvature of the lateral sulcus. Referring toFIG. 6, in the lateral sulcus13of the bearing member10, the anterior portion may have a positive (+) side curvature and the posterior portion may have a negative (−) side curvature. Due to the different side curvatures, the lateral sulcus13is divided into a lateral anterior section113and a later posterior section135.

The later anterior section133is a part having a predetermined positive (+) side curvature (a radius of curvature R11) and protruding forward from the lateral sulcus13and the lateral posterior section135is a part inclined with a negative (−) side curvature (a radius of curvature R12) at the posterior portion of the lateral sulcus13. By this shape, the lateral condyle33of the femoral component30(described below) that is placed on the lateral sulcus13can perform translation and rotation over a longer distance than the medial condyle31, so it is possible to achieve the objective knee motion of the present invention around the medial sulcus11and the medial condyle31.

Longer distance translation of the lateral condyle33may be considered as conflicting with the anatomical structure of human body in which abduction (external rotation) occurs in flexion of a knee, but adduction (internal rotation) occurs around the medial sulcus11and the medial condyle31, the tissues around the joint are tightened, stability of the artificial knee joint can be increased. Further, since the curvature (radius of curvature R12) of the lateral posterior section135is smaller than the curvature (radius of curvature Rm2) of the medial posterior section115(radii of curvature R12>Rm2), adduction of the femoral component30that is converted into abduction following the anatomical structure of human body.

FIG. 7is a view showing the positions of the lateral sulcus point and the medial sulcus point on the bearing member. Referring toFIG. 7, the lateral sulcus point131is positioned more forward than the medial sulcus point111on the bearing member. This is for preventing medially biased wear of the bearing member10by making the medial sulcus11be the center of motion.

In detail, it may be preferable that the lateral sulcus point131is positioned at a 10˜25% anterior point of an AP length connecting the anterior point to the posterior point of the bearing member10.

Referring toFIG. 7, assuming that a virtual vertical plane including the medial sulcus point111defined as a medial sulcus-point plane Bm, a virtual vertical plane including the lateral sulcus point131defined as a lateral sulcus-point plane B1, and a virtual vertical plane including the center between the medial surface and the lateral surface of the post15(described below) of the bearing member10is defined as a central plane Bc, the distance Lm from the central plane Bc to the medial sulcus-point plane Bm is larger than the distance L1from the central plane Bc to the lateral sulcus-point plane B1in the bearing member10.

Moment of force means the product of the distance of force from a predetermined position and the magnitude of the force, and when force F is applied to a plane, force acting on a point A spaced to the left by m from the point where the force F is applied and force acting on a point P spaced to the right by n from the point where the force F is applied are respectively np/(m+n) and mp/(m+n), in which when m is smaller than n, relatively small force acts on the point B.

That is, smaller force is applied to points spaced farther from the point where reference force acts. Accordingly, the problem in the related art that two- or three-time larger force is applied to a medial portion than a lateral portion can be removed by making the distance Lm from the central plane Bc to the medial sulcus-point plane Bm larger than the distance L1from the central plane Bc to the lateral sulcus-point plane B1.

Accordingly, the present invention intends to uniformly distribute load by positioning the lateral sulcus point131more forward than the medial sulcus-point111such that the medial sulcus is the center of knee motion in the bearing member10and positioning the medial sulcus point111farther than the lateral sulcus point131from the central plane Bc of the bearing member.

The post15protrudes between the medial sulcus11and the lateral sulcus13on the bearing member10. For the convenience of description, the post33is divided into one top and four sides and the four sides can be defined as a medial surface facing the medial sulcus11, a lateral surface facing the lateral sulcus13, an anterior surface facing the anterior portion (where the patella is positioned) of the bearing member10, and a posterior surface facing the posterior portion (opposite to the position of the patella) of the bearing member10. The post15of the present invention is described on the basis of this division. The post15has an asymmetric shape in which the posterior surface is inclined from the lateral surface to the medial surface.FIG. 8shows the inclination of the posterior surface of the post. Referring toFIG. 8, it can be seen that the lower side of the top makes a predetermined angle θ from the lateral surface to the medial surface.

According to the artificial knee joint of the related art described above, when the femoral component30to be described below is adducted, as shown inFIG. 3, a cam meets the posterior surface of the post15in a narrow contact area, so stress concentration occurs and the edge of the post is strongly shocked. Accordingly, there is a need for preventing the stress concentration by increasing the contact area, and to this end, it is preferable that the bottom side of the top of the post15is inclined at an angle θ, that is, the post is asymmetrically formed such that the posterior surface is inclined from the lateral surface to the medial surface.

The inclination θ of the posterior surface of the post is made the same as the inclination generated by abduction of the femoral component30at the moment when a cam35(described below) of the femoral component30comes in contact with the post15to increase the contact area between the post15and the cam35.

FIG. 9is a perspective view of a femur component of the present invention. Referring toFIG. 9, the femoral component30of the present invention, which is intended to be coupled to the tibia-sided end of a femur in total knee arthroplasty, is placed on the top of the bearing member10to be supported by the bearing member10and makes translation, rotation, and roll-back in knee motion, and the lateral surface of the femoral component30forms an articular surface to allow for these motions. In detail, the femoral component can be considered as having a shape similar to the spherical projection at the end of the femur in the human body. The material of the femoral component is not specifically limited, but preferably, titanium may be used.

The femoral component30includes a medial condyle31, a lateral condyle33, and a cam35.

The medial condyle31means the part that is brought in contact with the medial sulcus11of the bearing member10, close to the sagittal plane, in the femoral component30, and preferably, it has a smooth convex articular surface to be stably seated in the medial sulcus11that is a recess.FIG. 10is a view showing a posterior condyle and a peak contact point of the femoral component. When the femoral component30of the present invention is placed in position on the bearing member10, the peak point being in contact with the bearing member10of peak points on the medial sulcus11is referred to as the peak contact point P, and the section from the peak contact point P to the end bending up to the posterior portion of the femoral component30is referred to as the posterior condyle. The posterior condyles are divided into a medial posterior condyle311that is the posterior condyle of the medial condyle31and a lateral posterior condyle331that is the posterior condyle of the lateral condyle33. The dark portion is the medial posterior condyle311inFIG. 10.

FIG. 11is a side view showing the curvature of the medial posterior condyle. Referring toFIG. 11, the medial posterior condyle311may have one curvature (radius of curvature Rm). The present invention is technologically characterized in that the lateral condyle33can move forwardly more than the medial condyle31such that the femoral component30can be adducted on the bearing member10, thereby tensioning the tissues around a knee joint and increasing stability in knee motion. Accordingly, as shown in the figure, the medial posterior condyle311is given one curvature to be the center of knee motion by making uniform rotation and roll-back.

The lateral condyle33means the part that is brought in contact with the lateral sulcus13of the bearing member10, farther from the sagittal plane, in the femoral component30, and preferably, it has a smooth convex articular surface to be stably seated in the lateral sulcus13that is a recess.FIG. 12is a side view showing the curvatures of the lateral posterior condyle. Referring toFIG. 12, it can be seen that as compared with the medial posterior condyle311having one curvature, the lateral posterior condyle331has a plurality of curvatures.

Referring toFIG. 12, the radius of curvature at the peak contact point P is R11, but the radius of curvature at the posterior end of the lateral condyle33is R12. R11is larger than R12such that the curvature of the lateral posterior condyle331increases toward a posterior direction of the femoral component30.

Accordingly, adduction (internal rotation) in which the lateral condyle33moves forwardly more is generated at the early stage of flexion of a knee, and the motion is changed into abduction (external rotation) after the point where the curvature is changed. This is for preventing the present invention designed to adduct the femoral component30to prevent medial wear of a knee from causing various side effects after an operation by conflicting with the anatomical structure of human body that makes abduction.

FIG. 13is a view showing the positions of a medial peak point and a lateral peak point of the femur coupler. Referring toFIG. 13, the distance Lm from a virtual central plane Fc including the center of the cam35of the femoral component30to a medial peak-point plane Fm that is a virtual vertical plane including the peak points on the articular surface of the medial condyle31is longer than the distance L1from the virtual central plane Fc to the lateral peak-point plane F1that is a virtual vertical plane including the peak points on the lateral condyle33. This is because when force F is applied, force acting on a point A spaced left by m from the point where the force F is applied and force acting on a point P spaced right by n from the point where the force F is applied are respectively np/(m+n) and mp/(m+n), in which when m is smaller than n, relatively small force acts on the point B. Accordingly, the distance Lm from the virtual central plane Fc including the center of the cam35to the medial peak-point plane Fm is made longer than the distance L1to the lateral peak-point plane F1to prevent inwardly biased force and uniformly distribute load to the medial and lateral sides of a knee.

The cam35is disposed between the medial condyle31and the lateral condyle33to connect them and prevent dislocation of the femoral component30rotating on the bearing member10.

The cam35may connect the posterior ends of the medial and lateral condyles31and33in the femoral component10to minimize a limit in bending angle of a knee due to interference with the post15protruding on the bearing member10in flexion of the knee (seeFIG. 9).

FIG. 14is a view showing the moment when the cam and the post meet each other. Referring toFIG. 14, according to the artificial knee joint described above in the related art, the post and the cam35come in contact with each other in a narrow contact area, so large stress concentration is caused and the edge of the post is strongly shocked. Accordingly, there is a need for preventing stress concentration by increasing the contact area, and to this end, the post15is asymmetrically formed such that the posterior surface is inclined from the lateral surface to the medial surface so that the post15comes in contact with the cam35in a wide contact area. There is no need to form a predetermined inclination on the cam35like the posterior surface of the post15and it is sufficient as long as the inclination θ is formed on the posterior surface of the post the same as the inclination θ formed by abduction of the femoral component30at the moment when the cam35of the femoral component30comes in contact with the post15.

FIG. 15is a view showing that when the central plane of the bearing member and the central plane of the femoral component are aligned, the distances from the central planes to a medial sulcus-point plane and a medial peak-point plane are the same and the distances from the center to a lateral sulcus-point plane and a lateral peak-point plane are the same.

The artificial knee joint of the present invention is characterized in that the bearing member10and the femoral component30are asymmetrically formed respectively in the medial and lateral sides such that the medial sulcus11of the bearing member10and the medial condyle31of the femoral component30are the center of motion. In this configuration, in consideration that the femoral component30makes motions on the bearing member10, when the central plane Bc of the bearing member10and the central plane Fc of the femoral component30are aligned, the distance Lm from the central planes Bc and Fc to the medial sulcus-point plane Bm including the medial sulcus point111is made the same as the distance Lm to the medial peak-point plane Fm including the peak points on the medial condyle31, and the distance L1from the central planes Bc and Fc to the lateral sulcus-point plane B1including the lateral sulcus point131is made the same as the distance L1to the lateral peak-point plane F1including the peak points on the lateral condyle33. Accordingly, the asymmetric femoral component30placed on the bearing10can stably make translation, rotation, and roll-back without being dislocated from the bearing member10.

FIGS. 16A and 16Bare a view showing the state in use of the asymmetric artificial knee joint. Referring toFIGS. 16A and 16Bto describe the operation of the present invention, the femoral component30on the bearing member10moves forward on the bearing member10in flexion of a knee.FIG. 16Ashows forward movement of the medial condyle31andFIG. 16Bshows forward movement of the lateral condyle33.

As described above, since the medial sulcus11of the bearing member10has the medial anterior section113and the medial posterior section115that each have a predetermined curvature, the distance that the medial condyle31can move forward and backward is limited.

In contrast, the lateral condyle33is preferably disposed on the lateral sulcus13including the lateral anterior section133having a curvature smaller than that of the medial anterior section113, so it can move forward a longer distance than the medial condyle31. Accordingly, a motion can be made with respect to the medial condyle31such that the movement distance of the medial condyle31is small and the movement distance of the lateral condyle33is large.

In the early stage, the medial condyle31and the lateral condyle33moved forward together on the bearing member10, but the medial condyle31can move no longer due to the medial anterior section113and only the lateral condyle33can move further forward. In this process, the surrounding tissues connected to the artificial knee joint are tightened and prevent dislocation of the artificial knee joint, thereby increasing stability. Further, since the lateral condyle33is moved with respect to the medial condyle31, inward biased wear of existing artificial knee joints can be prevented.

The lateral condyle33moves forwardly more than the medial condyle31, thereby generating adduction (internal rotation), but the forward movement is also limited by the tissues around the artificial knee joint. Further, the medial posterior condyle311has a uniform curvature, but the lateral posterior condyle331increases in curvature toward a posterior direction of the femoral component30, so it rapidly rotates, whereby the rotation is changed into abduction following the anatomical structure of human body.

Flexion at a large angle of a knee is made after the cam35of the femoral component30comes in contact with the post15of the bearing member10, but according to the related art, the contact area between the cam35and the post15is narrow and stress concentration is generated, so the post15of the bearing member10preferably made of polyethylene is quickly worn.

Accordingly, the post15of the bearing15is asymmetrically formed such that the posterior surface is inclined from the lateral surface to the medial surface and the abduction angle of the femoral component30and the inclination of the posterior surface of the post are made the same at the moment when the cam35comes in contact with the post15(seeFIG. 14), thereby increasing the contact area. Therefore, it is possible to prevent stress concentration and quick wear of the post15of the bearing member10, and to achieve more stable roll-back.

The above description exemplifies the present invention. Further, the description provides an embodiment of the present invention and the present invention may be used in other various combination, changes, and environments. That is, the present invention may be changed or modified within the scope of the present invention described herein, a range equivalent to the description, and/or within the knowledge or technology in the related art. The embodiment shows an optimum state for achieving the spirit of the present invention and may be changed in various ways for the detailed application fields and use of the present invention. Therefore, the detailed description of the present invention is not intended to limit the present invention in the embodiment. Further, the claims should be construed as being including other embodiments.