JP3401132B2 - Artificial knee joint - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial knee joint that replaces a knee joint whose function is reduced or lost due to a disease such as osteoarthritis and whose pain is increased.

[0002]

2. Description of the Related Art When a knee joint with reduced or lost function and increased pain is replaced with an artificial knee joint, the femoral distal end portion and the tibial proximal end portion constituting the knee joint are separated from each other. Relative motion of both components has been realized by installing a prosthesis member and slidingly contacting these members, that is, the femoral component and the tibial component, or connecting them by a hinge coupling mechanism.

Of these, the femoral component generally has a shape in which an anterior wall and a posterior wall are connected by a bottom wall, and the femoral component is installed so that the cut distal end of the femur is sandwiched between the anterior wall and the posterior wall. To be done.

On the other hand, the tibial component is composed of a stem and a base plate fixed to the upper side of the stem, and at the time of installation, the stem is inserted into the cancellous bone of the tibia from the proximal end face of the tibial bone that is horizontally cut. The bottom edge of the base plate is brought into contact with the edge-shaped cortical bone on the proximal end face to prevent the member from sinking.

By the way, it has been reported in many literatures that the proximal end face of the tibia of the human body is not bilaterally symmetrical in terms of anatomy (for example, “Knee Morphology as a Guide to Kn”).
ee Replacement "／ Mensch and Amstutz," Clinical Or
thopaedics and Related Research "Number 112, Octob
er, 1975, pp 231-241).

Therefore, as the base plate of the femoral component, not only a bilaterally symmetrical base plate but also an asymmetrical one in plan view has been designed.

US Pat. No. 5,344,460 shows a tibial component with an asymmetric base plate and a knee prosthesis including the tibial component,
The front half of this base plate is bilaterally asymmetric, while the back half is bilaterally symmetrical.

[0008]

Background of the Invention However, in order to know more precisely what the shape of the proximal end face of the tibia is anatomically, a large number of cadaver bone samples were collected (all Japanese) and the proximal end of the tibia was removed. As in the case of an actual knee arthroplasty, the bones were cut and their shapes were sketched.
It was as shown in. That is, while the front half is substantially left-right symmetrical, the rear side is left-right asymmetrical, and the front half is left-right asymmetrical like the base plate in the above U.S. Pat. It turned out that it wasn't working.

[0009]

When such an artificial knee joint of the prior art is used, the outer edge shape of the base plate of the tibial component does not correspond to the outer edge shape of the tibial cut surface, and the outer edge of the base plate of the tibial component partially exists. Is inside the cortical bone, that is, the state where it does not rest on the cortical bone. In such a state, the load applied to the cut surface of the cortical bone is unbalanced, and the cancellous bone is also partially loaded, resulting in bone resorption due to excessive load, resulting in subsidence of the tibial component, etc. , There was a danger of causing a serious situation.

[0010]

SUMMARY OF THE INVENTION The present invention has been made on the basis of such findings, and therefore, makes the outer edge shape of the base plate of the tibial component substantially perfectly match the outer edge shape of the actual tibial cut surface. The purpose of the present invention is to provide an artificial knee joint that prevents bone resorption due to partial overload and does not cause problems such as subduction of tibial components even after long-term use after artificial knee joint installation. .

[0011]

In order to solve the above-mentioned problems of the prior art, the outer edge shape of the plate of the tibial component is substantially perfected to the outer edge shape of the actual tibial osteotomy surface based on the data collected by the osteotomy of the bone sample. We examined the shape so that As a result, the present invention provides an artificial knee joint that includes a tibial component that replaces the tibial joint surface and a femoral component that replaces the femoral joint surface. The shape is symmetrical and the posterior half is asymmetrical, and the ratio of the anterior-posterior width of the outer condyle to the anterior-posterior width of the inner condyle is 20:
Provided is an artificial knee joint characterized by being 23 to 20:30.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an artificial knee joint J of the present invention, which comprises a femoral component F fixed to the femur side and a bearing insert I which constitutes a sliding surface for the femoral component F. A base plate P formed on a fixing stem S inserted into the tibia and supporting and fixing the bearing insert I.
It is comprised from the tibia side component T provided with.

The material of each member is the femoral component F.
The base plate of the tibial component T may be made of a biocompatible metal material such as pure titanium or titanium alloy, or a biocompatible ceramic material such as alumina or zirconia, alone or in combination. As an example of the combined use of both materials, a plate-shaped ceramic member or ceramic bead appropriately formed in the portion of the femoral component F that contacts the bone is used to promote early bonding with the embedded bone. Further, as the bearing insert I of the tibial component T, it is preferable to use high-molecular polyethylene having excellent slidability, wear resistance, and elasticity.

Of the fixing stem S, the base plate P and the bearing insert I constituting the tibial component T, the base plate P is formed with a dovetail groove 1 formed in the front-rear direction at symmetrical positions on the upper and left sides. The groove 1 and the snap projection 2 are fitted to each other to clamp and fix the bearing insert I, while the stem S projects from the lower surface side.

FIG. 2 shows an outer edge shape of a base plate P which constitutes the tibial component T. The base plate P has a front half of a plane shape of a joint surface which is bilaterally symmetrical and a rear half of which is bilaterally asymmetrical. The ratio of the anterior-posterior width L of the outer condyle to the anterior-posterior width M of the inner condyle is 20:23 to 20:30.

The artificial knee joint J constructed as described above
Is a base plate P that constitutes the tibial component T
The planar shape of No. 2 is as described above, and matches the shape of the osteotomy of the tibia in the actual artificial knee joint J replacement. As a result, bone resorption due to partial overload that occurs when the outer edge of the base plate P partially comes inside the cortical bone, that is, when the outer edge of the base plate P does not rest on the cortical bone, is prevented, and the length after the artificial knee joint J is installed is long. Even when used for a period of time, problems such as subduction of the tibial component T do not occur.

In addition to the above, the plane shape of the joint surface of the tibial component T of the artificial knee joint J is in addition to the above,
R ₁ = 40 on the left and right front, the inner condyle side, and the outer condyle side, respectively
-80, R ₂ = 15-35, R ₃ = 10-30, R ₄ =
It is preferable to arrange 10 to 30 outline portions.
When the contour line is in this numerical range, the base plate P and the bone cutting surface of the tibia are likely to coincide with each other, and on the other hand, a slight deviation may occur between the base plate P and the tibia.

[0018]

EXAMPLES Examples of the present invention will be described below. In the artificial knee joint J of the above embodiment, the base plate P forming the tibial component T has a different planar shape, a small size,
Medium, Large, Extra Large (Small, Medium, Large, Ex-Large) 4
Type made. These are the left and right widths (M
-L) is 4mm pitch, the anterior-posterior width of the lateral condyle (Lateral AP) and the anterior-lateral width of the medial condyle (Medial AP) are different at the 3mm pitch.

More specifically, the sizes are as follows (unit: mm): Small [left / right width, anterior / posterior width of the external condyle, anteroposterior width of the internal condyle] = [62,40,44 [R ₁ , R ₂ , R ₃ , R ₄ ] Medium [left / right width, anterior / posterior width of external condyle, anterior / posterior width of inner condyle] = [66,43,47 [R ₁ , R ₂ , R ₃ , R ₄ ] large [left / right width, outer Anterior-posterior width of condyle, anterior-posterior width of inner condyle] = [70,46,50 [R ₁ , R ₂ , R ₃ , R ₄ ] Oversized [lateral width, anterior-posterior width of outer condyle, anterior-lateral width of inner condyle] = [ 74,49,53 [R ₁ , R ₂ , R ₃ , R ₄ ] An artificial knee joint J using a base plate P of each of these sizes is applied to a plurality of knee joint replacements,
When the position of the tibial component T after one year was accurately obtained and compared in detail with the position immediately after the replacement, no displacement or subduction was observed.

[0020]

As described above, according to the artificial knee joint of the present invention, the planar shape of the base plate constituting the tibial component matches the shape of the osteotomy of the tibia in the actual artificial knee joint replacement. This partially prevents the bone resorption due to partial overload that occurs when the outer edge of the base plate is inside the cortical bone, that is, when it does not rest on the cortical bone. Even when used, it has an excellent effect that problems such as sinking of the tibial component do not occur.

[Brief description of drawings]

FIG. 1 is a perspective view of an artificial knee joint according to an embodiment of the present invention.

FIG. 2 is an outer edge view of a base plate forming the artificial knee joint of FIG.

[Explanation of symbols]

J artificial knee joint F Femoral component I Bearing insert P base plate T tibia component S stem L Anterior-posterior width of the condyle Anteroposterior width of M inner condyle 1 dovetail 2 snap projection

Claims (2)

(57) [Claims] 1. An artificial knee joint comprising a tibial component replacing a tibial joint surface and a femoral component replacing a femoral joint surface, wherein the tibial component has a bilateral symmetrical front half of a plane shape of the joint surface. And the posterior half is asymmetrical, and the ratio of the anterior-posterior width of the outer condyle to the anterior-lateral width of the inner condyle is 20:23.
An artificial knee joint characterized by being ~ 20: 30. 2. In the plan-view shape of the joint surface, R ₁ = on the central anterior surface, the lateral anterior surface, the inner condyle side surface, and the outer condyle side surface, respectively.
_{40~80, R 2 = 15~35, R} 3 = 10~30, R
The artificial knee joint according to claim 1, wherein ₄ = 10 to 30 outline portions are arranged.