Patent Description:
A knee joint is a joint formed of a femur, a tibia, and a patella. In the knee joint, joint cartilages of a distal end of the femur and of a proximal end of the tibia and a meniscus present therebetween function as cushions, whereby the knee joint can move smoothly.

However, when such knee cartilages wear and the meniscus is damaged due to fatness, aging and the like, not only cushioning between the distal end of the femur and the proximal end of the tibia is lost, but also deformation of the knee joint occurs and progresses with the elapse of time. Further, also when rheumatoid arthritis develops, the knee is injured, and so on, the knee joint is deformed. When the knee joint is thus deformed (causes knee osteoarthritis), the knee joint is disabled to move smoothly, and a patient feels a severe pain when walking and so on, and further, sometimes has difficulty walking.

As a treatment for such knee osteoarthritis, total knee arthroplasty (TKA) is adopted. This total knee arthroplasty is a technique for resecting the distal end of the femur and the proximal end of the tibia and replacing such resected portions by an artificial knee joint. A large number of patients undergo the total knee arthroplasty at present. The total knee arthroplasty has effects that the pain can be removed, that the patients are enabled to walk usually, and the like, and gives a high satisfaction to the patients. Further, a large number of artificial knee joints for use in the total knee arthroplasty are also developed (refer to Patent Documents <NUM> and <NUM>).

Moreover, in recent years, there has also been adopted unicompartmental knee arthroplasty (UKA) that replaces only a part of a knee joint by an artificial knee joint. In Patent Document <NUM> that follows, a partial unicompartmental system for the unicompartmental knee arthroplasty is disclosed. Patent Documents <NUM>, <NUM> and <NUM> are also known and discloses other arthroplasty components.

However, in the current total knee arthroplasty and the current the unicompartmental knee arthroplasty, the meniscus cannot be preserved in principle. Further, in the total knee arthroplasty, a joint surface is entirely cut out and replaced by the artificial knee joint, and therefore, it is difficult to reproduce a height of the original joint surface. The height of the original joint surface changes, whereby many reports on unexpected pains and on limitations of a movable range are made after surgeries, and the patients have not been fully satisfied.

In this connection, it is an object of the present invention to provide an artificial knee joint capable of acquiring characteristics closer to those of a normal knee joint, and to provide a bridge member, an insert member and a base plate, which are used therein.

An assembly for artificial knee joint according to the present invention is defined in claim <NUM>.

With this configuration, the insert member is embedded in only a part of the joint surface, whereby a surface of the insert member can be matched with a joint surface that has remained therearound, and therefore, it is possible to reproduce a height of an original joint surface. Moreover, the height of the original joint surface is reproduced, thus making it possible to preserve a meniscus. As a result, in accordance with the artificial knee joint according to the present invention, the characteristics closer to those of the normal knee joint can be acquired.

An assembly for an artificial knee joint according to an embodiment of the present invention will be described below with reference to the drawings. The assembly for an artificial knee joint according to the present invention is an artificial knee joint for use in total knee joint replacement in a treatment for knee osteoarthritis, rheumatoid arthritis and the like, characterized in adopting a structure capable of preserving a meniscus and a ligament.

<FIG> illustrates a use state of an assembly for an artificial knee joint <NUM>. <FIG> illustrate constituent members of the artificial knee joint <NUM>. In the following description of the artificial knee joint <NUM>, a direction where a tibia T extends will be referred to as an up-down direction, and a front-rear direction and left-right direction of a patient in the tibia T will be referred to as a front-rear direction and a left-right direction, respectively.

The assembly for an artificial knee joint <NUM> includes: an insert member <NUM> embedded in a part of a joint surface of a medial condyle MC or lateral condyle LC of the tibia T; and bridge members <NUM> disposed underneath the insert member <NUM>. The assembly for an artificial knee joint <NUM> according to the invention further includes a base plate <NUM> disposed between the insert member <NUM> and the bridge members <NUM>. In <FIG>, the insert member <NUM> is embedded in a part of a joint surface of the lateral condyle LC.

A part of the joint surface of the medial condyle MC or lateral condyle LC of the tibia T, specifically, a damaged portion (or worn portion) of the joint surface is resected, and the insert member <NUM> is embedded in a portion subjected to the resection. The insert member <NUM> is embedded while a height and surface shape thereof are being adjusted so that an upper surface of the insert member <NUM> smoothly connects to such a surrounding original joint surface.

Preferably, plural types of the insert member <NUM> are prepared, and <FIG> illustrates insert members 2a to 2c different in shape. <FIG> illustrates perspective and cross-sectional views of the insert members 2a to 2c.

The insert members 2a to 2c have a disk shape as a whole. The insert member 2a is embedded in the medial condyle MC of the tibia T, and has an upper surface formed into a recessed curved surface. The insert member 2b is embedded in the lateral condyle LC of the tibia T, and has an upper surface formed into a protruding curved surface. Further, the insert member 2c has an upper surface formed into a flat surface.

On a lower surface of each of the insert members 2a to 2c, a concentric step portion <NUM> to which an upper end portion of the cylindrical base plate <NUM> is fitted is formed. Note that, when the base plate <NUM> is not provided, the step portion <NUM> is not formed.

A diameter of each of the insert members 2a to 2c is, for example, <NUM> to <NUM>, preferably <NUM> to <NUM>. Actually, a plurality of the insert members 2a to 2c different in diameter are prepared in advance, and the optimal-size insert members 2a to 2c are selected while referring to a patient's image of MRI or the like.

A thickness of the insert members 2a to 2c is, for example, <NUM> or more. With regard to the insert members 2a to 2c, a plurality of the insert members 2a to 2c different in thickness are prepared in advance, and the optimal-thickness insert members 2a to 2c are selected while referring to the patient's image of MRI or the like. Thus, a height of the upper surface of each of the insert members 2a to 2c can be matched with a height of the original joint surface.

Further, a recess of the insert member 2a embedded in the medial condyle MC is, for example, <NUM> to <NUM>, and a swell of the insert member 2b embedded in the lateral condyle LC is, for example, <NUM> to <NUM>. The upper surface of each of the insert members 2a to 2c is formed so as to smoothly connect to the original joint surface around the embedded portion of each.

The insert members 2a to 2c are composed of a material (for example, polymer polyethylene or the like) having high slipperiness and wear resistance.

The bridge members <NUM> are disposed below the insert member <NUM> along a substantially horizontal direction, and support the insert member <NUM> from below. The bridge members <NUM> which function as rafts in such a way are sometimes referred to as raft pins. Note that the bridge members <NUM> do not always have to come into contact with a lower surface of the insert member <NUM>. That is, the bridge members <NUM> may support the insert member <NUM> with a spongy bone in the tibia T interposed therebetween without coming into contact with the lower surface of the insert member <NUM>.

A shape of the bridge member <NUM> is not particularly limited, and <FIG> illustrates bridge members 3a to 3c different in shape. <FIG> illustrates perspective views of the bridge members 3a to 3c.

The bridge members 3a to 3c are rod-shaped members, and have a length that allows both ends thereof in a longitudinal direction to be anchored to a cortical bone of the tibia t. Thus, each of the bridge members 3a to 3c becomes a both-end fixed bridge in which both ends are fixed to the hard cortical bone. A length of the bridge members 3a to 3c is, for example, <NUM> to <NUM>. Actually, a plurality of the bridge members 3a to 3c different in length are prepared in advance, a depth of holes into which the bridge members 3a to 3c are inserted is measured by a depth gauge at the time of surgery, and the optimal-length bridge members 3a to 3c are selected. The bridge members 3a to 3c are prepared at, for example, <NUM>-mm pitch, preferably <NUM>-mm pitch. Moreover, a width of the bridge members 3a to 3c is, for example, <NUM> to <NUM>.

A cross-sectional shape of the bridge members <NUM> is not particularly limited. A cross section of the bridge member 3a is circular. However, the cross section of the bridge member 3a may be elliptical.

A cross section of the bridge member 3b is triangular. In a use state, the bridge member 3b may be disposed so as to point a vertex of the triangle upward as illustrated in <FIG>, but may be disposed so as to point a bottom of the triangle upward to form an inverted triangular cross section. The bridge member 3b is disposed so as to point the bottom of the triangle upward, whereby the function to support the insert member <NUM> increases.

A cross section of the bridge member 3c is quadrangular. Herein, the quadrangle is a concept that includes, a square, a trapezoid, a rhombus, and the like, as well as the rectangle illustrated in <FIG>.

The bridge member 3a that has a circular cross section has a simple shape; however, considering strength, the bridge member 3b that has a triangular cross section and the bridge member 3c that has a quadrangular cross section are preferable. Moreover, the bridge member 3b or the bridge member 3c may be driven into a circular through hole drilled by a drill or the like.

The bridge members 3a to 3c are composed of a material (for example, titanium, stainless steel and the like) that has high biocompatibility and high rigidity.

The base plate <NUM> is disposed between the insert member <NUM> and the bridge members <NUM>. The base plate <NUM> has a cylindrical shape, is fitted to the step portion <NUM> formed on the lower surface of the insert member <NUM>, and supports an outer edge of the insert member <NUM> from below. A wall thickness of the cylindrical base plate <NUM> is, for example, <NUM>.

As the base plate <NUM>, a plurality of those different in height may be prepared. Thus, at the time of adjusting the height of the insert member <NUM>, the height can be adjusted not only by the insert member <NUM> itself but also by the base plate <NUM>. Further, a height adjusting plate (not shown) may be disposed separately between the base plate <NUM> and the bridge members <NUM>.

The base plate <NUM> does not always have to come into contact with the bridge members <NUM>. That is, the base plate <NUM> may allow the spongy bone of the tibia T to be interposed between the same and the bridge members <NUM> without coming into contact with the bridge members <NUM>.

According to the invention, the base plate <NUM> is cylindrical, but otherwise the shape of the base plate <NUM> is not particularly limited, and <FIG> illustrates base plates 4a to 4d different in shape. <FIG> illustrates perspective views of the base plates 4a to 4d. <FIG> is perspective and cross-sectional views illustrating a use state of the base plate 4d.

In a cylindrical portion <NUM> of the base plate 4a, fixing holes <NUM> and fixing grooves <NUM>, to which two bridge members 3c which have a quadrangular cross section are fitted, are formed. Two bridge members 3c are arranged in a cross shape. The base plate 4a and the bridge members 3c are combined with each other, whereby the base plate 4a and the bridge members 3c are integrated with each other. Therefore, the function to support the insert member <NUM> increases.

The base plate 4b has a bottomed cylindrical shape that has the cylindrical portion <NUM> and a bottom portion <NUM>. With such a configuration, the insert member <NUM> can be prevented from sinking when a large load is applied thereto.

The base plate 4c has a lattice-shaped mesh portion <NUM> formed in a lower opening of the cylindrical portion <NUM>. With this configuration, the mesh portion <NUM> can prevent the base plate 4c from sinking, and in addition, can reinforce the cylindrical portion <NUM> to maintain the cylindrical shape thereof. Further, a footprint of the base plate 4c is increased by the mesh portion <NUM>, whereby there increases such a function to support the base plate 4c by cement installation.

The base plate 4d is composed so that an upper end surface of the cylindrical portion <NUM> is inclined with respect to a plane perpendicular to a cylinder axis of the cylindrical portion <NUM>. Meanwhile, a lower end surface of the cylindrical portion <NUM> is parallel to the plane perpendicular to the cylinder axis. That is, the upper end surface of the base plate 4d is formed diagonal with respect to the lower end surface thereof. The base plate 4d is used in combination with an insert member 2d illustrated in <FIG>. Like the upper end surface of the base plate 4d, the upper surface of the insert member 2d is formed so as to be inclined with respect to the plane perpendicular to the cylinder axis of the base plate 4d. Further, a step portion <NUM> of the insert member 2d is parallel to the upper surface. With this configuration, the base plate 4d is rotated about the cylinder axis, whereby a height of the insert member 2d can be adjusted according to the height and shape of the joint surface of the actual tibia T. At this time, in order that the insert member 2d cannot rotate with respect to the base plate 4d, mutual contact surfaces of the step portion <NUM> of the insert member 2d and the upper end surface of the base plate 4d may be provided with protrusions and grooves fitted to this protrusion. A shape and number of the protrusions are not particularly limited, and for example, the protrusions may be at least one point protrusion, a plurality of linear protrusions which extend radially from the cylinder axis taken as a center.

<FIG> illustrate base plates <NUM> according to other embodiments. The base plate <NUM> includes the cylindrical portion <NUM> (an example of a tubular portion) and protruding portions which protrude outward from an outer circumferential surface of the cylindrical portion <NUM>. The protruding portions are provided on the outer circumferential surface of the cylindrical portion <NUM>, and can thereby suppress the base plate <NUM> from sinking.

<FIG> is plan and side views of the base plate 4e, and <FIG> illustrates a perspective view of each of fins <NUM>. The base plate 4e has the fins <NUM> provided on the cylindrical portion <NUM>. The fins <NUM> of which number is four are provided on a circumferential direction of the cylindrical portion <NUM>. The fins <NUM> are plate-shaped members formed of the same material as that of the cylindrical portion <NUM>. Each of the fins <NUM> has a rectangular portion 45a and a triangular portion 45b. A part of the triangular portion 45b protrudes outward from the outer circumferential surface of the cylindrical portion <NUM>. The triangular portion 45b has a sharp tip end so to easily enter the spongy bone.

The cylindrical portion <NUM> has opening portions 40a which allow a tube inside and a tube outside to communicate with each other. A width of the opening portions 40a is slightly wider than a width of the rectangular portions 45a of the fins <NUM>. Thus, the fins <NUM> can be protruded from the cylinder inside to the cylinder outside through the opening portions 40a. Further, each of the fins <NUM> may have a stopper 45c that restricts a protrusion amount thereof from the outer circumferential surface of the cylindrical portion <NUM>. Such stoppers 45c restrict the fins <NUM> from moving by coming into contact with an inner circumferential surface of the cylindrical portion <NUM>.

Moreover, as illustrated in <FIG>, the respective fins <NUM> are differentiated in shape from one another, whereby the protrusion amounts of the triangular portions 45b which protrude from the outer circumferential surface of the cylindrical portion <NUM> may be changed. For example, the protrusion amount of the triangular portion 45b may be decreased at a place close to the cortical bone, and the protrusion amount of the triangular portion 45b may be increased at a place distant from the cortical bone.

<FIG> illustrates a plan view of a base plate 4f. The base plate 4f has four fins <NUM> provided on the cylindrical portion <NUM>. Each of the fins <NUM> has a rectangular portion 46a and a semicircular portion 46b. A part of the semicircular portion 46b protrudes outward from the outer circumferential surface of the cylindrical portion <NUM>.

<FIG> illustrates a plan view of a base plate <NUM>. The base plate <NUM> has eight fins <NUM> provided on the cylindrical portion <NUM>. Note that the number of fins <NUM> thus provided is not particularly limited; however, is preferably three or more.

<FIG> illustrates a plan view of a base plate <NUM>. The base plate <NUM> has four fins <NUM> provided on the cylindrical portion <NUM>. The fins <NUM> extend in directions inclined in a circumferential direction with respect to normal directions of the outer circumferential surface of the cylindrical portion <NUM>.

<FIG> illustrates a plan view of a base plate 4i. The base plate 4i has fins <NUM> extending in directions different from those of the base plate <NUM> illustrated in <FIG>.

<FIG> illustrates a side view of a base plate 4j. The base plate 4j has fins <NUM> extending diagonally downward from the outer circumferential surface of the cylindrical portion <NUM>.

A base plate <NUM> illustrated in <FIG> has threads <NUM> provided on the outer circumferential surface of the cylindrical portion <NUM>. The threads <NUM> are intermittently provided in the circumferential direction along the outer circumferential surface of the cylindrical portion <NUM>. Moreover, the threads <NUM> are provided in a plurality of rows in the up-down direction. Note that, though the threads <NUM> may be intermittently provided in the circumferential direction along the outer circumferential surface of the cylindrical portion <NUM>, the threads <NUM> may be provided on the entire outer circumferential surface of the cylindrical portion <NUM>. Preferably, the threads <NUM> have lower surfaces inclined upward toward tip ends thereof so as to easily drive the base plate <NUM> into the tibia when the base plate <NUM> is driven thereinto (see an enlarged view).

A base plate <NUM> illustrated in <FIG> has recessed portions <NUM> provided on the outer circumferential surface of the cylindrical portion <NUM>. The recessed portions <NUM> are intermittently provided in the circumferential direction along the outer circumferential surface of the cylindrical portion <NUM>. Moreover, the recessed portions <NUM> are provided in a plurality of rows in the up-down direction. With an elapse of time, the spongy bone enters the recessed portions <NUM>, whereby the base plate <NUM> is suppressed from sinking. Note that, though the recessed portions <NUM> may be intermittently provided in the circumferential direction along the outer circumferential surface of the cylindrical portion <NUM>, the recessed portions <NUM> may be provided on the entire outer circumferential surface of the cylindrical portion <NUM>.

Note that, though each of the cylindrical portions <NUM> illustrated in <FIG> has a cylindrical shape with open upper and lower portions, the cylindrical portion <NUM> may have a form in which the bottom portion <NUM> as illustrated in <FIG> is provided, or may have a form in which the lattice-shaped mesh portion <NUM> as illustrated in <FIG> is provided.

<FIG> illustrates an example of a surgery procedure. In the tibia T illustrated in <FIG>, the joint surface of the lateral condyle LC is worn. First, in a portion of the tibia T, which is located underneath the joint surface of the lateral condyle LC, through holes which extend along the front-rear direction are formed by using a drill or the like. Two through holes are formed in line in the left-right direction. Subsequently, as illustrated in <FIG>, the bridge members <NUM> are driven into the through holes. Subsequently, in a portion of the lateral condyle LC, which is located above the bridge members <NUM>, a round hole that has a diameter corresponding a diameter of the insert member <NUM> is formed. Subsequently, as illustrated in <FIG>, the base plate <NUM> is inserted into the round hole formed above the bridge members <NUM>. Finally, as illustrated in <FIG>, the insert member <NUM> is fitted to the upper end of the base plate <NUM>.

As described above, the assembly for the artificial knee joint <NUM> includes: the insert member <NUM> embedded in a part of the joint surface of the medial condyle MC or lateral condyle LC of the tibia T; and the bridge members <NUM> disposed underneath the insert member <NUM>, and having a length that allows both ends thereof to be anchored to the cortical bone of the tibia T.

In accordance with the assembly for the artificial knee joint <NUM>, the insert member <NUM> is embedded in only a part of the joint surface, whereby the surface of the insert member <NUM> can be matched with the height and shape of the joint surface that has remained therearound, and therefore, it is possible to reproduce the height of the original joint surface. Moreover, the height of the original joint surface is reproduced, thus making it possible to preserve the meniscus.

Moreover, in the assembly for the artificial knee joint <NUM>, a part of the joint portion is replaced, and therefore, the surgery is easy, surgical invasion is less, and a bleeding risk is also reduced. It is possible to preserve an anterior cruciate ligament (ACL), and when a damage is recognized in the anterior cruciate ligament, it is also possible to simultaneously rebuild the same. Further, all the ligaments can be reserved as well as the meniscus, and preservation of a deep medial collateral ligament (dMCL), which has been particularly difficult heretofore, is also possible.

The insert member <NUM> may be in contact with the bridge members <NUM>. With this configuration, the insert member <NUM> is surely supported from below by the bridge members <NUM>.

The insert member <NUM> may be in no contact with the bridge members <NUM>. With this configuration, some play can be provided between the insert member <NUM> and the bridge members <NUM>, and therefore, a destruction when a large load is applied thereto can be suppressed.

Preferably, the outer edge portion of the insert member <NUM>, which is adjacent to the meniscus, is formed into a circular arc shape. With this configuration, interference of the insert member <NUM> with the meniscus is prevented, and the meniscus can be preserved.

The bridge members <NUM> may be arranged only along the front-rear direction. If the bridge members <NUM> are arranged along the left-right direction, when a large load is applied to either one of the medial condyle MC and the lateral condyle LC, it is apprehended that the other one of the medial condyle MC and the lateral condyle LC may be adversely affected through the bridge members <NUM>.

assembly for the artificial knee joint <NUM> according to the present invention further includes the cylindrical base plate <NUM> disposed between the insert member <NUM> and the bridge members <NUM>, and supporting the outer edge of the insert member <NUM>. With this configuration, the insert member <NUM> is surely supported from below by the base plate <NUM> and the bridge members <NUM>.

The base plate <NUM> may be in contact with the bridge members <NUM>. With this configuration, the base plate <NUM> is surely supported from below by the bridge members <NUM>.

The base plate <NUM> may be in no contact with the bridge members <NUM>. With this configuration, some play can be provided between the base plate <NUM> and the bridge members <NUM>, and therefore, the base plate <NUM> sinks, and the height of the insert member <NUM> can be adjusted appropriately.

An upper portion of the base plate <NUM> has an inclined surface inclined with respect to the plane perpendicular to the cylinder axis thereof. With this configuration, the base plate <NUM> is rotated about the cylinder axis, whereby the height of the insert member <NUM> can be adjusted according to the height and shape of the joint surface of the actual tibia T.

Preferably, the upper surface of the insert member 2a embedded in the medial condyle MC of the tibia T is formed into a recessed curved surface. In usual, the original joint surface of the medial condyle MC is a recessed curved surface, and therefore, with this configuration, the surface of the insert member 2a smoothly connects to the surrounding original joint surface.

Preferably, the surface of the insert member 2b embedded in the lateral condyle LC of the tibia T is formed into a protruding curved surface. In usual, the original joint surface of the lateral condyle LC is a protruding curved surface, and therefore, with this configuration, the surface of the insert member 2b smoothly connects to the surrounding original joint surface.

The artificial knee joint <NUM> is not limited to the configuration of the above-described embodiments, and is not limited to the above-described functions and effects. Moreover, as a matter of course, the artificial knee joint <NUM> can be modified in various ways within the scope of the invention, which is defined by the claims.

For example, <FIG> is an example in which the insert member <NUM> is embedded in a part of each of the joint surfaces of the medial condyle MC and the lateral condyle LC. This drawing does not illustrate the base plates <NUM>; however, the base plates <NUM> may be provided, and this also applies similarly to the following drawings.

<FIG> is an example in which the insert members <NUM> have a D letter shape in plan view. <FIG> is an example in which the insert members <NUM> have a semicircular shape in plan view. <FIG> is an example in which the insert members <NUM> have an elliptical shape in plan view.

<FIG> is an example in which a bridge member <NUM> that extends along the left-right direction is disposed in addition to the bridge members <NUM> which extend along the front-rear direction.

<FIG> is an example in which one bridge member <NUM> that extends along the front-rear direction and one bridge member <NUM> that extends along the left-right direction are arranged for each of the insert members <NUM>. <FIG> is an example in which one bridge member <NUM> that extends along the front-rear direction and two bridge members <NUM> which extend along the left-right direction are arranged for each of the insert members <NUM>. <FIG> is an example in which only three bridge members <NUM> which extend along the left-right direction are arranged.

<FIG> is plan and side views of an insert member 2e according to an example that does not form part of the invention. The insert member 2e is supported from below by the bridge members <NUM> without the base plate <NUM> interposed therebetween. Therefore, the insert member 2e has a disc shape without the step portion <NUM> formed thereon. The disc-shaped insert member 2e has an outer circumferential surface provided with protrusions <NUM>. The protrusions <NUM> are intermittently provided in a circumferential direction along an outer circumferential surface of the insert member 2e. Moreover, the protrusions <NUM> are provided in a plurality of rows in the up-down direction. Preferably, the protrusions <NUM> have lower surfaces inclined upward toward tip ends thereof so as to easily drive the insert member 2e into the tibia when the insert member 2e is driven thereinto (see an enlarged view).

Claim 1:
An assembly for an artificial knee joint comprising:
an insert member (<NUM>) configured to be embedded in only a part of a joint surface of a medial condyle (MC) or lateral condyle (LC) of a tibia (T); and
a bridge member (<NUM>) configured to be disposed underneath the insert member (<NUM>), having a length that allows both ends of the bridge member (<NUM>) to be anchored to a cortical bone of the tibia (<NUM>), and supporting the insert member (<NUM>) from below,
characterized in that the assembly further comprises a cylindrical base plate (<NUM>) configured to be disposed between the insert member (<NUM>) and the bridge member (<NUM>), the baseplate (<NUM>) supporting an outer edge of the insert member (<NUM>),
wherein the cylindrical base plate (<NUM>) comprises a cylindrical portion (<NUM>), being a tubular portion,
wherein the insert member (<NUM>) comprises, on a lower surface thereof, a concentric step portion (<NUM>) to which an upper end portion of the cylindrical portion (<NUM>) is fitted,
wherein the upper end surface of the cylindrical portion (<NUM>) is inclined with respect to a plane perpendicular to a cylinder axis of the cylindrical portion (<NUM>),
wherein upper surface of the insert member (<NUM>) is formed so as to be inclined with respect to the plane perpendicular to the cylinder axis of the cylindrical portion (<NUM>), and
wherein upper surface of the insert member (<NUM>) is adjusted in height and shape so that it smoothly connects to the surrounding original joint surface.