JP4127619B2 - Artificial knee joint - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an artificial knee joint that replaces a living knee joint.
[0002]
[Prior art]
When the knee joint suffers from osteoarthritis of the knee, rheumatoid arthritis, bone tumor, or suffers trauma or the like, it is replaced with an artificial knee joint. This knee prosthesis consists of a combination of a femoral component having two inner and outer condyles and a tibial component having two inner and outer joint surfaces that respectively support the two condyles. The shape is close to the joint. That is, when the condyle is viewed from the side, it is substantially circular, and when viewed from the front-rear direction, the outline is convex, and the joint surface is concave.
[0003]
[Problems to be solved by the invention]
By the way, in the living body knee joint, when the knee joint is extended, the tibia side is externally rotated (the ankle side is rotated outward), and when it is bent, it is accompanied by the rotational motion of internal rotation. Therefore, this movement is also required in the artificial knee joint, and this movement is induced by the shape of the contact surface formed by the inner and outer condyles and the inner and outer joint surfaces. On the other hand, in this configuration, if the components cannot be turned, excessive stress is applied to the joint surface side made of polyethylene or the like due to the above-described turning action, causing uneven wear or peeling. Further, the same thing occurs even if the rotation alignment is incorrectly adjusted in the replacement operation of the artificial knee joint.
[0004]
For this reason, in many cases, the joint surface side can be swiveled around the bone axis, but if it is allowed to swivel indefinitely, the joint surface has a horizontally long shape. Occasionally, it protrudes from the tibial tip and damages the surrounding tissue. Further, when the turning angle is increased, the turning operation itself becomes unstable. Therefore, even in the conventional artificial knee joint, the turning angle is restricted to a certain range. As a general structure of this restriction structure, a protrusion formed on one of the insert or base plate of the tibial component formed by the insert forming the inner and outer joint surfaces and the base plate attached to the tibia and supporting the insert is formed on the other. In addition to being guided by being inserted into a groove, the method depends on a method of restricting turning by restricting the section of the groove.
[0005]
However, according to this, the surface pressure is excessively increased at the portion where the projection hits the dead end of the groove, and the groove and the projection are broken and damaged, thereby reducing the durability. In addition, backlash occurred in the protrusion and the groove, and the turning was blurred. Of course, in the living knee joint, the joint surface cannot turn, but the stress due to the rotating action is absorbed by deformation of the meniscus interposed between the joints. However, when the artificial knee joint is worn, these meniscuses are excised, so such an action cannot be expected.
[0006]
On the other hand, the pivot center of the joint surface in the conventional knee prosthesis has been set to the center of its shape, that is, the midpoint of the inner and outer joint surfaces. The reason is not clear, but to simplify the movement and facilitate control, to ensure the ease of manufacturing, so that it can be applied to either the left or right knee with a single thing, etc. I think that the. However, the center of the rotational action in the living knee joint is closer to the inside than the center of the shape, forming a so-called medial pivot. In this respect as well, the conventional artificial knee joint moves differently from the living knee joint, and lacks natural movement. In the present invention, this medial pivot is applied to an artificial knee joint so that the artificial knee joint can move close to a living knee joint. In addition, a turning control mechanism that does not require excessive force is employed to improve durability.
[0007]
[Means for Solving the Problems]
Under the above-mentioned problems, the present invention provides an artificial joint that supports the inner and outer condyles of the femoral component attached to the femur so as to be pivotable back and forth on the inner and outer joint surfaces of the tibial component attached to the tibia. In the knee joint, the tibial component is hollowed in the lower surface of the flat plate, the base plate is provided with a peg inserted into the bone marrow of the tibia toward the bone axis direction, and the dish-like body placed on the flat plate The shaft portion provided on the lower surface is composed of an insert that is inserted into the peg so as to be pivotable within a certain range while being tightly fitted to the peg, and the shaft portion of the insert and the peg of the base plate are formed on the upper surface of the dish-shaped body. The present invention provides an artificial knee joint characterized in that it is displaced inward from the left and right midpoints of the inner and outer joint surfaces .
[0008]
The tibial bone axis is offset inwardly from the midpoint of the medial and external articular surfaces at its proximal end and tilted inward on the upper side, so that The center of gravity, such as weight, is deviated inward rather than at its midpoint. Therefore, deviating the turning center of the insert toward this side causes the inner and outer condyles of the femoral component to turn at the center of gravity, thereby making this turning operation smooth. That is, a medial pivot can be formed to make the movement closer to a living knee joint.
[0009]
This alleviates the stress applied to the inner and outer joint surfaces of the insert, thereby contributing to the improvement of durability by preventing uneven wear and peeling. In addition, when the turning center is displaced inward, the amount of slide in the front-rear direction of the inner and outer condyles during turning is larger on the outer side than on the inner side, so that the rotational motion during flexion and extension in the living knee joint This makes the movement smooth and contributes to an increase in the bending angle.
[0010]
According to the present invention, in the above artificial knee joint, the peg and the shaft portion fitted in each other according to claim 2 are composed of a straight portion having an elliptical cross section and a tapered portion. Means are provided wherein the straight portion of the portion is oval to allow a range of turns within the straight portion of the peg . When the insert is pivoted indefinitely, it hurts the surrounding tissue, rotation of the inner and outer condyles and the insert (rolling, sliding, sliding) from becoming unstable, but those that prevent this, by way The shaft part can swivel within the peg without any blurring, and it does not restrict turning by partially applying a small area member such as a protrusion and groove, so the surface pressure becomes too high, causing destruction etc. There is no.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings, among which FIG. 1 is a perspective view of an insert of a tibial component and a base plate constituting an artificial knee joint for a left knee showing an example of the present invention. 2 is a perspective view of a femoral component that also constitutes the artificial knee joint, FIG. 3 is a side view showing the above artificial knee joint mounted on the knee, FIG. 4 is a plan view of the insert, and FIG. 5 is a plan view of the base plate. 6 is a cross-sectional view taken along line AA in FIG. 5, and FIG. 7 is a cross-sectional view taken along line BB in FIG.
[0012]
The artificial knee joint is composed of a combination of a femoral component 1 and a tibial component 2. Of these, the femoral component 1 is made of a biocompatible metal such as a titanium alloy, and the inner surface is formed in a polygonal shape. The inner condyle 3 and the outer condyle 4 are formed in a substantially circular shape, that is, in a substantially C shape in a side view, and the distal end of the femur 5 is appropriately cut off. It is attached here (FIG. 2). Although not shown in the figure, a type called a PS type that regulates a specific mutual movement with a raised portion of a later-described tibial component 2 that is accommodated here by covering the above-described missing portion with a box is also available. This type is also included in the femoral component 1 here. In this case, when the medial condyle 3 and the lateral condyle 4 are viewed from the front-rear direction, the outer contour has a convex surface, and this convex surface continues to the streak back and forth.
[0013]
On the other hand, the tibial component 2 is composed of a base plate 7 that is cut at the proximal end of the tibia 6 and attached to the end of the tibia 6 and an insert 8 that is mounted on the base plate 7 ( FIG. 1). Of these, the base plate 7 is made of a biocompatible metal, and has a peg 10 protruding from the center of the lower surface of a flat plate 9 provided on the upper portion. By embedding the peg 10 in the bone marrow of the tibia 6 Fixed. On the other hand, the insert 8 is made of a medical resin material such as ultra-high molecular weight polyethylene, a dish-like body 11 stacked on the base plate 7, and a shaft portion protruding from the back surface and inserted into the peg 10 described above. 12.
[0014]
The peg 10 in this case is a cylindrical body having a hollow inside, and is composed of a straight portion 10a provided immediately below the center of the flat plate body 9 and a tapered portion 10b that is continuous below the straight portion 10a. . On the other hand, the shaft portion 12 is a shaft body having an upper straight portion 12a and a lower tapered portion 12b. The straight portion 12a is tightly fitted to the straight portion 10a of the peg and the tapered portion 12b is tightly fitted to the tapered portion 10b ( It is inserted so that it can turn without any play.
[0015]
Therefore, the weight applied to the insert 8 is not only the back surface of the dish-like body 11 of the insert 8 and the upper surface of the flat plate body 9 of the base plate 7, but also the mutual tapered portions 10b and 12b. As a result, the amount of wear is reduced and the durability is improved. Further, since the shaft portion 12 is tightly fitted in the peg 10, there is no backlash or blurring when the shaft portion 12 is turned, so that the movement is stable.
[0016]
On the upper surface of the dish-like body 11 of the insert 8, a low raised portion 15 is interposed between the inner articular surface 13 and the outer articular surface 14 that respectively support the inner condyle 3 and the outer condyle 4 of the femoral component 1. Is formed. Both the joint surfaces 13 and 14 are formed in a concave shape substantially along the outline shape of the medial condyle 3 and the lateral condyle 4, and this concave shape is developed back and forth.
[0017]
The femur 5 and the tibia 6 need to bend and extend relatively as the knee bends and stretches. In the above artificial knee joint, this movement is caused by the inner and outer condyles 3 and 4 on the inner and outer joint surfaces 13 and 14. This is made possible by rotating with rolling and sliding (FIG. 3). The angle of bending is −10 to 140 °, with rolling mainly in the initial stage and sliding mainly in the latter stage, but all movements are controlled by ligament groups such as the cruciate ligament and collateral ligament. The inner and outer condyles 3 and 4 do not fall off (dislocation) from the inner and outer joint surfaces 13 and 14.
[0018]
In addition to this, the insert 8 is formed on the base plate 7 in particular because the contact surface between the insert 8 and the inner and outer condyles 3 and 4 is formed so as to induce a rotational movement at the initial stage and the final stage of the bending and stretching angles. It can turn slightly in the horizontal plane. In this example, a horizontal plane U that is installed for the bottom of the plate members 9 of the base plate 7 is not parallel to the plane perpendicular V to the bone axis of the tibia 6, are provided with inclined forward by an angle α Therefore (therefore, the inner and outer joint surfaces 13 and 14 are also inclined backward by this angle α), the above-mentioned turning is made on this plane V (FIG. 6). If the plane V is inclined backward, bending becomes easy, but instability at the time of standing cannot be denied. Therefore, the backward inclination angle α is set in a range of 0 to 15 ° in consideration of these.
[0019]
In the present invention, the pivot center of the insert 8 is displaced inward from the midpoint of the inner and outer condyles 3 and 4 (FIG. 4). In other words, the turning point is an intermediate point between the inner and outer joint surfaces 13 and 14, specifically, a point R displaced inward from the shape center S by a predetermined distance δ. Therefore, this means that the shaft portion 12 of the insert 8 pivots about the center of the peg 10 of the base plate 7, so that the pivot center R of the insert 8 is displaced inward from the shape center S by a distance δ. This means that the center of rotation of the insert 8 set on the pace plate 7 is also shifted by this distance δ (FIG. 5).
[0020]
By the way, although this distance (delta) is determined suitably, about 1-10 mm is suitable like a living body knee joint. On the other hand, the insert 8 of this example is inserted so that the shaft portion 12 is tightly fitted into the peg 10 of the base plate 7 and can be turned. It does not occur, and the surrounding tissue is not damaged. Further, in the present invention, in order to make this more thorough, this rotation is not limited, but is regulated within a certain range.
[0021]
As a specific configuration of this regulation, in this example, the straight section 10a of the peg 10 has a fan-shaped cross-sectional shape, and the straight section 12a of the shaft section 12 fitted to the straight section 10a is replaced with the straight section 10a. On the other hand, the ellipsoid is allowed to turn by a certain angle (FIG. 7). Therefore, even at the turning limit point, there is no situation where an excessive pressure is applied to a small area portion such as a stopper or a groove, and the specific portion is not broken or damaged. By the way, the range in which the shaft portion 12 can turn in the peg 10 is the maximum turning angle β. In the present invention, the turning angle β is set to 20 ° or less like the living body knee joint. The turning angle β can be adjusted by changing the shape of the straight portion 12a.
[0022]
As described above, the rotational movement between the inner and outer condyles 3 and 4 and the inner and outer joint surfaces 13 and 14 derived from the bending and stretching of the knee is centered on the turning center R which is closer to the inside than the shape center S by the eccentric distance δ. Therefore, a medial pivot similar to that of a living knee joint is formed, so that excessive stress is not applied to the insert 8 and the turning motion is smoothly performed, and uneven wear and peeling are not caused on the surface, thereby improving durability. . In addition, when the center of rotation R is displaced inward, the distance R ₁ from here to the center of the medial condyle 3 is larger than the distance R ₂ to the center of the lateral condyle 4, so The amount of movement of the lateral condyle 4 before and after becomes larger than that of the medial condyle 3, and the rotational movement of the tibia during bending and stretching becomes smooth and contributes to an increase in the bending angle.
[0023]
【The invention's effect】
As described above, according to the present invention, the insert of the tibial component that supports the femoral component can be swiveled, and the swivel center is provided by being displaced inward from the center of the inner and outer joint surfaces formed in the insert. Therefore, a medial pivot similar to a living knee joint is formed on the artificial knee joint to make the movement smooth. This alleviates the stress applied to the joint surface, thereby preventing uneven wear and peeling and improving durability. In addition, deviating the center of rotation to the inside will increase the amount of movement of the internal and external condyles in the anteroposterior direction at the time of turning, so that the rotational movement of the tibia during knee flexion and extension is greater. Becomes smooth and contributes to an increase in the bending angle.
[Brief description of the drawings]
FIG. 1 is a perspective view of a tibial component insert and a base plate showing an example of the present invention.
FIG. 2 is a perspective view of a femoral component showing an example of the present invention.
FIG. 3 is a side view showing a state where an artificial knee joint according to an embodiment of the present invention is mounted on a knee.
FIG. 4 is a plan view of an insert showing an example of the present invention.
FIG. 5 is a plan view of a base plate showing an example of the present invention.
6 is a cross-sectional view taken along the line AA in FIG.
7 is a cross-sectional view taken along the line BB in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Femoral component 2 Tibial component 3 Medial condyle 4 Lateral condyle 5 Femur 6 Tibia 7 Base plate 8 Insert 9 Flat plate 10 Peg 11 Dish-shaped body 12 Shaft part 13 Inner joint surface 14 Outer joint surface R Rotation center

Claims (2)

In an artificial knee joint that supports the internal and external condyles of the femoral component attached to the femur so that it can be rotated back and forth by the internal and external joint surfaces of the tibial component attached to the tibia, the tibial component is hollow on the bottom surface of the flat plate The base plate provided with a peg that is inserted into the bone marrow of the tibial bone in the direction of the bone axis, and the shaft provided on the lower surface of the dish-like body placed on the flat plate turn in a certain range while being tightly fitted to the peg. The insert shaft portion and the base plate pegs are displaced inward from the left and right midpoints of the inner and outer joint surfaces formed on the upper surface of the dish-shaped body. A prosthetic knee joint. The section where the peg and shaft part fit together consists of a straight part with an elliptical shape and a taper part, and the straight part of the shaft part has an elliptical shape that allows a certain range of turning within the straight part of the peg. claim 1 of the artificial knee joint with Te.

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