Patent Description:
The knee is a joint with the most complex structure in the human body and more opportunities for injury. The aging of the human body and various joint diseases or traumas will cause partial or total damage to the knee motor function, resulting in joint pain and difficulty in movement. Knee prostheses are used to replace diseased or damaged knee joints of human, and use knee ligaments and soft tissues to enable patients to recover knee function and reduce pain. The knee prosthesis is usually designed into the approximate shape of a knee of human, and mimics the natural movement of the knee of human.

<CIT> proposes a femoral component of a knee prosthesis includes a bearing surface defined by a smooth, continuous surface which in one embodiment is entirely formed by a series of three segments of surfaces of revolution, the respective shapes of which are generated by rotating a common generating curve around three separate generating axes at respective pairs of major generating radii and through respective angles of rotation. The central segment of the surfaces of revolution constantly maintains the substantially same contact configuration with the superior bearing surface of a bearing insert over a range extending from full extension (<NUM> DEG of flexion) to at least <NUM> DEG of flexion and up to <NUM> DEG of flexion. The maintenance of the substantially same contact configuration ensures area, point or line contact between the articulating surfaces which reduces contact stress and wear in flexion. In a second embodiment, the bearing surface is defined by four segments of surfaces of revolution shaped for implantation in a knee where one or both cruciate ligaments are retained.

The above information disclosed in the background section is only used to enhance the understanding of the background of the present disclosure, so it may include information that does not constitute the prior art known to those of ordinary skill in the art.

The present invention is defined in independent claim <NUM>, and preferred features according to the present invention are defined in the dependent claims. The femoral prosthesis includes a medial condyle portion and a lateral condyle portion, and the medial condyle portion and the lateral condyle portion each has a condyle surface for contacting a tibial joint surface. The tibial joint surface includes a joint surface of a natural meniscus, a tibial implant or a bearing implant for contacting the femoral prosthesis.

According to a preferred embodiment of the present invention, providing a femoral prosthesis which includes a medial condyle portion and a lateral condyle portion, and the medial condyle portion and the lateral condyle portion each having a condyle surface configured to contact the tibial joint surface, the tibial joint surface comprises a joint surface of a natural meniscus, a tibial implant or a bearing implant for abutting the femoral prosthesis.

The condyle surface having a first surface section for contacting the tibial joint surface in the range of the first flexion angle, and a second surface section for contacting the tibial joint surface in the range of the second flexion angle ;.

The range of the first flexion angle is from a first flexion angle to a second flexion angle; the range of the second flexion angle is from the second flexion angle to a third flexion angle; wherein the first flexion angle is in a range of -<NUM> to <NUM> °, the second flexion angle is in a range of <NUM> to <NUM> °, the third flexion angle is in a range of <NUM> to <NUM> °, the third flexion angle is greater than the second flexion angle.

The first curvature radius of the first surface section in the sagittal plane have the same length, and the length of a curvature radius of the second surface section in sagittal plane decreasing from the front end to the rear end.

In a further preferred embodiment of the present invention, the third flexion angle may exceed the second flexion angle by an amount in the range of <NUM>° to <NUM>°.

In a further preferred exemplary embodiment of the present invention, the second flexion angle may be in the range of <NUM>° to <NUM>°, and the third flexion angle may be in the range of <NUM>° to <NUM>°.

In a further preferred exemplary embodiment of the present invention, the first flexion angle is about <NUM>°, the second flexion angle is about <NUM>° and the third flexion angle is about <NUM>°.

In a further preferred exemplary embodiment of the present invention, the second surface section includes a plurality of curved surfaces in which the curvature radius in the sagittal plane decreasing sequentially from the front end to the rear end.

According to the present invention, a difference between curvature radii of any two adjacent curved surfaces in the sagittal plane is not greater than <NUM>.

According to the present invention, a curvature radius of a curved surface at the rear end of the second surface section is a second curvature radius, the second curvature radius is the smallest curvature radius of the second surface section.

A ratio of the first curvature radius to the second curvature radius is <NUM>-<NUM>.

In a further preferred exemplary embodiment of the present invention, a ratio of the first curvature radius to the second curvature radius is <NUM>-<NUM>.

In a further preferred exemplary embodiment of the present invention, a number of the curved surfaces of the second surface section on the sagittal plane is <NUM> to <NUM>.

In a further preferred exemplary embodiment of the present invention, the number of the curved surfaces is <NUM>.

In a further preferred exemplary embodiment of the present invention, each of the curved surfaces of the second surface section is configured to have the same central angle.

In a further preferred exemplary embodiment of the present invention, each of the curved surfaces of the second surface section is configured to have different central angle respectively.

According to a further aspect of the present invention, a knee prosthesis which includes the femoral prosthesis as described above, wherein the knee prosthesis further includes a tibial base and a tibial bearing. The tibial base is connected to a tibia; the tibial bearing is located between the femoral prosthesis and the tibial base, an upper surface of the tibial bearing is articulated with the femoral condyle joint surface of the femoral prosthesis, a lower surface of the tibial bearing is connected with the tibial base.

In the femoral prosthesis provided in the present invention, the first surface section is a contact surface between the femoral prosthesis and the tibial joint surface during the gait movement of the human body, and has the curvature radius of the same length in the sagittal plane to avoid abnormal relative movement of the joint surface caused by curved surface changes and to ensure the stability of joint motion. The second surface section is the part of the condyle surface that contacting with the tibial joint surface, when the knee is in high flexion, and the gradual decrease of the curvature radius in the sagittal plane can maintain the stability of the movement of the knee under high flexion, and when the difference between the curvature radius of the first surface section and the curvature radius of the rear end of the second surface section can be larger, which can make the curvature radius in the sagittal plane of the condyle surface (that is, the first surface section) that is in contact with the tibial joint surface during gait movement be larger, and maximize the contact area between the condyle surface and the tibial joint surface, reduce the contact stress between the condyle surface and the tibial joint surface, thereby effectively reducing joint wear. Walking is the most frequent movement of the knee joint (prosthesis), reducing the wear of the knee prosthesis during the walking can effectively increase the life of the prosthesis.

The above described and other features and advantages of the present invention will become more apparent by describing the example embodiments in detail with reference to the accompanying drawings.

The reference numerals of the main components in the drawings are described as follows:.

femoral prosthesis; <NUM>. condyle surface; <NUM>. first surface section; <NUM>. second surface section; <NUM>. curved surface; <NUM>. osteotomy surface; <NUM>. fixing columns; <NUM>. tibial bearing; <NUM>. tibial base; A. first contact point; B. second contact point; C. third contact point; D. fourth contact point; E. fifth contact point; z. coronal plane. reference contact point; O. first circle center; P. second circle center; Q. third circle center; θ1. first flexion angle; θ2. second flexion angle; θ3. third flexion angle; R1. first curvature radius; R2. second curvature radius; R3', R4', R5', R6', R7'. curvature radius; G, H, I, K, L. contact point.

Preferred embodiments will now be described more fully with reference to the accompanying drawings. However, the embodiments can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable
manner in one or more embodiments. In the following description, many specific details are provided to give a full understanding of the embodiments of the present disclosure.

The terms "first" and "second" are used only as markers, not as a limitation on the number of objects.

An embodiment of the present invention provides a femoral prosthesis, as shown in <FIG>, the femoral prosthesis <NUM> includes a condyle surface <NUM> for contacting a tibial joint surface, the condyle surface <NUM> has a first surface section <NUM> for contacting the tibial joint surface in the range of a first flexion angle, and a second surface section <NUM> for contacting the tibial joint surface in the range of a second flexion angle. The range of the first flexion angle is from a first flexion angle θ1 to a second flexion angle θ2; the range of the second flexion angle is from the second flexion angle to a third flexion angle; In one embodiment, the first flexion angle θ1 is any flexion angle from -<NUM> to <NUM> °, the second flexion angle θ2 is any flexion angle from <NUM> to <NUM> °; the third flexion angle θ3 is any flexion angle from <NUM> to <NUM> °, the third flexion angle θ3 is greater than the second flexion angle θ2; the first surface section <NUM> on the sagittal plane has the first curvature radius of the same length, and the curvature radius in the sagittal plane of the second surface section <NUM> decreases from the front end to the rear end.

Specifically, the femoral prosthesis includes a medial condyle portion and a lateral condyle portion, and the medial condyle portion and the lateral condyle portion each have a condyle surface <NUM> for contacting a tibial joint surface, the tibial joint surface includes the joint surface of the natural meniscus, tibial implant or bearing implant for contacting the femoral prosthesis <NUM>.

In the femoral prosthesis <NUM> provided in the present disclosure, the first surface section <NUM> is a contact surface between the femoral prosthesis <NUM> and the tibial joint surface during the gait movement of the human body, and has a single curvature radius in the sagittal plane to avoid abnormal relative movement of the joint surface caused by curved surface changes and to ensure the stability of joint motion. The second surface section <NUM> is the part of the condyle surface <NUM> that contacting with the tibial joint surface in a high flexion state of the knee (for example, in a squatting state), and the gradual decrease of the curvature radius of the second surface portion <NUM> in the sagittal plane can maintain the stability of the movement of the knee under high flexion, and when the difference between the curvature radius of the first surface portion <NUM> and the curvature radius of the rear end of the second surface section <NUM> can be larger, which can make the curvature radius in the sagittal plane of the condyle surface <NUM> (that is, the first surface section <NUM>) that is in contact with the tibial joint surface during gait movement be larger, and maximize the contact area between the condyle surface <NUM> and the tibial joint surface, reduce the contact stress between the condyle surface <NUM> and the tibial joint surface, thereby effectively reducing joint wear. Gait movement is the most frequent movement of the knee joint (prosthesis), thus, reducing the wear of the knee prosthesis during the walking can effectively increase the life of the prosthesis.

The following describes the components of the femoral prosthesis <NUM> provided in the embodiments of the present disclosure in detail with reference to the drawings.

In order to better explain and illustrated the technical solutions of the present disclosure, the directions, cut planes, etc. involved in the present disclosure are explained and illustrated in combination with the conventional description methods in the art.

In the field of anatomy and medical devices, the directions and planes such as inside, outside, front, rear, far, near, sagittal plane, coronal plane, and cross section have specific meanings, and are well known to those skilled in the art. Unless otherwise specified, these terms refer to the meanings recognized by those skilled in the art.

Generally, when describing the human body, joint or prosthesis, the following three sections are usually involved: sagittal plane, coronal plane z and cross section. Among them, the sagittal plane is a longitudinal section that divides the human body or joint into left and right parts along the front-rear direction, where the sagittal plane passing through the center of the human body is the median sagittal plane, which divides the human body into two equal parts. The coronal plane z refers to a longitudinal section that divides the human body or joint into front and rear parts along the left and right directions, the coronal plane z is perpendicular to the sagittal plane. The cross section is a plane that divides the human body or joint into upper and lower parts and parallels to the ground plane, and the cross section is perpendicular to the coronal plane z and the sagittal plane.

It can be understood that when describing a knee joint or a knee prosthesis, the sagittal plane, the coronal plane z, and the cross section all refer to the sections of a upright person, and the flexion angle is <NUM> ° at this time. When the knee joint or knee prosthesis is stretched or flexed, or when the posture of the human body is adjusted, the sagittal plane, the section may change accordingly.

Generally, when describing the human body, joint, or prosthesis, three different directions are involved: near and far, inside and outside, and front and rear. Among them, the far end refers to the end of the human body or joint that is relatively far away from the trunk. The near end refers to the end of the human body or joint that is relatively close to the trunk. The inside refers to the side that is relatively close to the median sagittal plane of the human body. The outside refers to the side that is relatively far from the median sagittal plane of the human body. The front side refers to the side that is relatively close to the abdomen on the sagittal plane. The rear side refers to the side relatively close to the back on the sagittal plane.

As shown in <FIG>, at a specific flexion angle, the condyle surface <NUM> contact the tibial joint surface, and the contact surface is a contact point or multiple consecutive contact points in the condyle surface <NUM> on the sagittal plane, referred to as "contact point". It can be understood that the contact points and the flexion angles correspond one-to-one, and those skilled in the art can determine the contact point or the circle center of each of the plurality of consecutive contact points of the condyle surface <NUM> on the sagittal plane at a specific knee flexion angle.

Where, the flexion angle at any contact point refers to the angle between the curvature radius of the contact point on the sagittal plane and the coronal plane z. In other words, the condyle surface <NUM> appears as a curve on the sagittal plane, and the curve includes a contact point, and the curve has a tangent through the contact point, the angle between the perpendicular of the tangent on the sagittal plane and the coronal plane z is the flexion angle of the contact point. And when the flexion angle of the contact point is negative, it indicates that the contact point is located at the front end of the femoral prosthesis <NUM>, and when the flexion angle at the contact point is positive, it indicates that the contact point is located at the rear end of the femoral prosthesis <NUM>.

For example, as shown in <FIG>, the first circle center <NUM> is the circle center of the curvature radius of the first contact point A, the second circle center P is the circle center of the curvature radius of the second contact point B, the third circle center Q is the circle center of the curvature radius of the third contact point C. The line segment AO is the curvature radius of the first contact point A, and the angle θ1 between the line segment AO on the sagittal plane and the coronal plane z is the flexion angle of the first contact point A. The line segment BP is the curvature radius of the second contact point B, and the angle θ2 between the line segment BP on the sagittal plane and the coronal plane z is the flexion angle of the second contact point B. The line segment CQ is the curvature radius of the third contact point C, and the angle θ3 between the line segment CQ on the sagittal plane and the coronal plane z is the knee flexion angle of the third contact point C.

Define the contact point F with flexion angle <NUM>° as the reference contact point F, define the coronal plane z passing through the reference contact point F as the reference coronal plane z, the reference coronal plane z divides the femoral prosthesis <NUM> into two parts, the front part and the rear part. Where the front end of the femoral prosthesis <NUM> is located at the front side of the reference coronal plane z, and the rear end of the femoral prosthesis <NUM> is located at the rear side of the reference coronal plane z. When the contact point is located at the front end of the femoral prosthesis <NUM>, the flexion angle of the contact point is negative; when the contact point is located at the rear end of the femoral prosthesis <NUM>, the flexion angle of the contact point is positive.

It can be understood that any contact point refers to the point on the condyle surface <NUM> contacting with the tibial joint surface on the sagittal plane, and it does not means that the condyle surface <NUM> and the tibial joint surface are necessarily already in contact at this contact point. In a single sagittal plane, the contact point may be point-shaped; and on the entire condyle surface <NUM>, each of corresponding contact points may be connected into a line. In other words, the condyle surface <NUM> can be at least in line contact with the tibial joint surface, and the line becomes a contact point on the sagittal plane.

In the femoral prosthesis <NUM> provided in the present disclosure, as shown in <FIG>, the condyle surface <NUM> is a smooth curve on the sagittal plane, and the smooth curve includes at least a first contact point A, a second contact point B and a third contact point C. The first surface section <NUM> is a curve between the first contact point A and the second contact point B on the sagittal plane; the second surface section <NUM> is a curve between the second contact point B and the third contact point C on the sagittal plane.

The first flexion angle θ1 is corresponded to the first contact point and in the range of -<NUM>° to <NUM>°. The second flexion angle θ2 is corresponded to the second contact point and in the range of <NUM>° to <NUM>°. The third flexion angle θ3 is corresponded to the third contact point and in the range of <NUM>° to <NUM>°. And the third contact point C is located on the rear side of the second contact point B, so that the third flexion angle θ3 is greater than the second flexion angle θ2. The first curvature radius of the first surface section <NUM> has the same length on the sagittal plane, and the curvature radius on the sagittal plane of the second surface section <NUM> decreases from the front end to the rear end.

In one embodiment, the second flexion angle θ2 is in the range of <NUM>° to <NUM>°, and the third flexion angle θ3 is in the range of <NUM>° to <NUM>° to ensure the stability of the knee prosthesis under gait movement and increase curvature radius of the contact surface on the sagittal plane during the walking to reduce the wear caused by frequent gait movement.

In one embodiment, the difference between the third flexion angle θ3 and the second flexion angle θ2 is <NUM>° ~ <NUM>°, so as to ensure that the curvature of condyle surface <NUM> between the second contact point B and the third contact point C is gentle and avoid abnormal movement of the joint surface caused by sudden curvature.

Further, the difference between the third flexion angle θ3 and the second flexion angle θ2 is <NUM>° ~ <NUM>°, so as to increase the change of curvature of the second surface section <NUM>, and further ensure the stability of the knee joint in a high flexion state, so that the first surface section <NUM> can be set with a larger curvature radius, thereby further reducing the contact stress between the condyle surface <NUM> and the tibial joint surface during the walking.

For example, in one embodiment of the present disclosure, the flexion angle corresponding to the first contact point A is <NUM>°; the flexion angle corresponding to the second contact point B is <NUM>°; and the flexion angle corresponding to the third contact point C is <NUM>°. In the gait movement of the human body, the movement angle of the knee joint is generally in the range of <NUM>° ~ <NUM>°, and the knee joint is generally under the greatest pressure at this time. Therefore, walking is the most important and frequent movement of the knee joint, in this embodiment, the performance of the femoral prosthesis <NUM> is optimal in walking state.

In one embodiment, the curvature radius of the condyle surface is the same in the range of the flexion angle of <NUM>° ~ <NUM>°, the curvature radius on the sagittal plane corresponds to the first curvature radius R1 in the above embodiment. When the flexion angle is <NUM>°, the curvature radius of the condyle surface on the sagittal plane corresponds to the second curvature radius R2 in the above described embodiment. In the embodiment, there are <NUM> different curvature radii in the range of the flexion angle of <NUM>° ~ <NUM> °, as shown in <FIG>, for example, the curvature radii of R3', R4', R5', R6', R7' correspond to the contact points on the sagittal plane are G, H, I, K, L respectively, the five different curvature radii and the second curvature radius are gradually reduced, and the curvature radius of the condyle surface on the sagittal plane is gradually changed from the first curvature radius R1 to the second curvature radius R2.

For another example, the flexion angle corresponding to the first contact point A is <NUM>°, the flexion angle corresponding to the second contact point B is <NUM>°, and the flexion angle corresponding to the third contact point C is <NUM>°. In this way, the difference between the two ends of the second flexion angle range is <NUM>°, which is beneficial to set more curved surfaces with gradually curved in the condyle surface <NUM> between the second contact point B and the third contact point C, and further, it is more conducive to achieving a smoother curvature transition; it is also conducive to increasing the first curvature radius R1, thereby increasing the contact area of the femoral prosthesis <NUM> with the tibial joint surface during the walking, reducing contact stress, and improving the life of the femoral prosthesis <NUM>.

According to above design, a relatively large R1 can be used to ensure that the knee joint maintains the maximum contact area during the walking (within a flexion range of <NUM>°~<NUM>°), reduces contact stress, and effectively reduces the amount of wear during the walking. The multi-radius design of the second surface section at <NUM>°~<NUM>° can avoid the abnormal forward movement of the femoral condyle caused by the mutation of the curvature radius from R1 to R2. The design of multiple curvature radii can achieve a gradual change from a large curvature radius to a small curvature to avoid abnormal forward movement.

In another embodiment of the present disclosure, the flexion angle θ1 of the first contact point A is <NUM>°; the flexion angle θ2 of the second contact point B is <NUM>°; and the flexion angle of the third contact point C θ3 is <NUM>°.

The second surface section <NUM> includes a plurality of curved surfaces <NUM> in which the curvature radius on the sagittal plane decreases sequentially from the front end to the rear end. Correspondingly, on the sagittal plane, the second surface section <NUM> may has a plurality of curves that are sequentially arranged from the front end to the rear end and the curvature radius is sequentially reduced.

For example, as shown in <FIG>, on the sagittal plane, the condyle surface <NUM> further has a fourth contact point D and a fifth contact point E between the second contact point B and the third contact point C, where the curved surface <NUM> between the second contact point B and the fourth contact point D has a third curvature radius R3, and the curved surface <NUM> between the fourth contact point D and the fifth contact point E has a fourth curvature radius R4. The curved surface <NUM> between the fifth contact point E and the third contact point C has a second curvature radius R2. The first curvature radius R1, the third curvature radius R3, the fourth curvature radius R4, and the second curvature radius R2 decrease sequentially.

According to the invention, the curvature radius of the curved surface <NUM> at the rearmost end of the second surface section <NUM> is the second curvature radius, that also is the shortest curvature radius. The value of the difference between the curvature radii of two adjacent curved surfaces <NUM> can be determined according to the difference between the first curvature radius R1 and the second curvature radius R2. The larger the difference between the first curvature radius R1 and the second curvature radius R2 is, the larger the difference between the curvature radii of the two adjacent curved surfaces <NUM> may be; otherwise, the smaller the difference between the first curvature radius R1 and the second curvature radius R2 is, the smaller the difference between the curvature radii of the two adjacent curved surfaces <NUM> may be. Of course, the difference between the curvature radii of the two adjacent curved surfaces <NUM> can also be determined according to the number of curved surfaces <NUM> of the condyle surface <NUM> between the second contact point B and the third contact point C; the more of curved surfaces <NUM> of the condyle surface <NUM> between the second contact point B and the third contact point C is, the smaller the difference between the curvature radii of two adjacent curved surfaces <NUM> may be; conversely, the less of curved surfaces <NUM> of the condyle surface <NUM> between the second contact point B and the third contact point C is, the larger the difference in curvature radii between two adjacent curved surfaces <NUM> may be.

According to the invention, in the sagittal plane, the difference between the curvature radii of the two adjacent curved surfaces <NUM> is not greater than <NUM>, so as to avoid abnormal movement of the joint surface caused by the large difference between the curvature radii of two adjacent curved surfaces <NUM>.

It can be understood that each curved surface <NUM> in the second surface section <NUM> on the sagittal plane may be a circular arc, and the central angle of each curved surface <NUM> is the same or different, as long as the difference between curvature radii of the two adjacent curved surfaces <NUM> on the sagittal plane is reasonable to avoid joint movement instability.

In general, a ratio of the first curvature radius to the second curvature radius may be <NUM> to <NUM>. The smaller the ratio of the first curvature radius to the second curvature radius is, the smaller the change of the curvature radius may be, which is beneficial to avoid abnormal movement of the joint surface caused by the large curvature of the second articular surface section <NUM>; the larger the ratio of the first curvature radius to the second curvature radius is, the longer the first curvature radius may be, which is conducive to increasing the contact surface area of the joint surface during the walking and reducing the wear of the joint prosthesis caused by frequent gait movement.

According to the invention, ratio of the first curvature radius to the second curvature radius is <NUM>-<NUM>.

In one embodiment, the ratio of the first curvature radius to the second curvature radius is <NUM>-<NUM>.

In one embodiment, on the sagittal plane, the number of the curved surfaces <NUM> of the condyle surface <NUM> between the second contact point B and the third contact point C is <NUM> to <NUM>, that is, the number of the curved surface <NUM> of the second surface section is <NUM> to <NUM>, in one embodiment, the number is <NUM> to <NUM>. In this way, different curved surfaces <NUM> are provided with different curvature radii, which can achieve a gentle transition from the first curvature radius R1 to the second curvature radius R2 of the condyle surface <NUM> and inhibit abnormal movement of the joint surface caused by a sudden change of curvature.

In another embodiment, the femoral prosthesis <NUM> of the present disclosure may further include an osteotomy surface <NUM> for connecting with the femur. The osteotomy surface <NUM> may be provided with one or more fixing column(s) <NUM> to achieve the tight connection and positioning of the femoral prosthesis <NUM> and the femur.

An embodiment of the present disclosure further provides a knee prosthesis, the knee prosthesis may include a femoral component for connecting with the femur, a tibial component for connecting with the tibia, and a tibial bearing positioned above the tibia component and articulated to the femoral component. The displacement of forward-backward and rotation of internal-external are generated between the support surface of the tibial bearing and condyle surface of the femoral component during the knee prosthesis is flexing and stretching. It is the main object in the design of knee prosthesis to ensure the stability of knee motion as much as possible and reduce the wear of knee prosthesis during the movement.

According to the invention, the knee prosthesis includes any one of the femoral prosthesis <NUM> described in the above embodiment of the femoral prosthesis. The knee prosthesis may be a posterior cruciate ligament-retaining knee prosthesis, a posterior stability knee prosthesis, or another type of knee prosthesis. Since the knee prosthesis has any one of the femoral prosthesis <NUM> described in the above embodiment of the femoral prosthesis, it has the same beneficial effects, which will not be repeated here.

Claim 1:
A femoral prosthesis (<NUM>), comprising a condyle surface (<NUM>) for contacting a tibial joint surface;
the condyle surface (<NUM>) having a first surface section (<NUM>) for contacting the tibial joint surface in a range of a first flexion angle, and a second surface section (<NUM>) for contacting the tibial joint surface in a range of a second flexion angle;
the range of the first flexion angle is from a first flexion angle (θ1) to a second flexion angle (θ2); the range of the second flexion angle is from the second flexion angle (θ2) to a third flexion angle (θ3); wherein the first flexion angle (θ1) is in a range of -<NUM>° to <NUM>°, the second flexion angle (θ2) is in a range of <NUM>° to <NUM>°, the third flexion angle (θ3) is in a range of <NUM>° to <NUM>°, the third flexion angle (θ3) is greater than the second flexion angle (θ2);
a first curvature radius (R1) of the first surface section (<NUM>) in a sagittal plane having the same length, and the length of a curvature radius of the second surface section (<NUM>) in the sagittal plane decreasing from the front end to the rear end;
wherein the second surface section (<NUM>) comprises a plurality of curved surfaces (<NUM>) in which the curvature radius in the sagittal plane decreasing sequentially from the front end to the rear end;
characterized in that a curvature radius of a curved surface (<NUM>) at the rear end of the second surface section (<NUM>) is a second curvature radius (R2), the second curvature radius (R2) is the smallest curvature radius of the second surface section (<NUM>), and:
a ratio of the first curvature radius (R1) to the second curvature radius (R2) is <NUM>-<NUM>;
wherein a difference between curvature radii of any two adjacent curved surfaces (<NUM>) in the sagittal plane is not greater than <NUM>.