CH632923A5 - Implant for partial replacement of a sliding surface of a human joint - Google Patents

Description

The invention relates to an implant according to the preamble of claim 1.

In recent times, efforts have been made to provide prosthetic restoration only in these partial areas for articular surfaces whose cartilage layer is damaged or destroyed only in partial areas. It is often difficult to adapt the mostly nail-like implant, consisting of an anchoring pin and a plate-like or disc-like head, to the shape and size of the parts of the articular surface in which the sliding surface and in particular the cartilage layer must be replaced.

The object of the invention is therefore to provide implants with which a partial replacement in shape, size and position of different areas of the articular surfaces is possible. This object is achieved according to the invention with the help of the features mentioned in claim 1. The partial implants of the invention make it possible to assemble several individual elements provided with relatively small plate-like heads in a plaster-like manner in order to obtain a prosthetic surface of practically any shape and size that is largely adapted to the part of the sliding surface of the joint to be replaced; With the aid of their anchoring means, the partial implants can be fixed in a simple manner by driving them in or screwing them into the cortical and cancellous layer of the bone.

With their plate-like sliding surface, the partial implants can be adapted for use in certain joints, for example in an acetabular cup or on the femoral condyles, larger plates possibly being equipped with two or more anchoring pins. However, if there are a large number of partial implants, it is also possible to provide circular or elliptical heads of different sizes for the individual partial implants, or to form them as polygons which are put together in a mosaic-like manner.

Suitable materials for the new implant are all materials that have been customary in implant technology, such as metals, metal alloys, bioceramics, pyrolytic carbon and plastic, especially polyethylene of the qualities HDPE and UHMW.

The invention is explained in more detail below on the basis of exemplary embodiments in conjunction with the drawing.

1 schematically shows a top view of an implant according to the invention for an acetabular cup;

2 and 3 show a multi-part implant for a femoral conyle in a view from the rear and from the side, FIG. 3 being shown partly in section;

FIG. 4 is a top view of the articular surface of the tibia bone, which are provided with two different embodiments of the implant according to the invention.

5 is a view of a femoral condyle covered with a number of equal-sized partial implants, during

FIG. 6 shows a view of a single partial implant on a larger scale in a detail from FIG. 5.

The implant according to FIG. 1, which is intended to replace a part of the sliding surface of an acetabular cup 4, is composed of three individual partial implants 1-3, which have different shapes and sizes; the partial implants are matched to one another in such a way that they form a practically closed, artificial sliding surface for the non-degenerated femoral head along the outer lateral and upper regions of the natural acetabular cup 4 embedded in the pelvic bone. Each partial implant 1-3 has at least one anchoring pin 5 as its own anchoring means.

The partial implants 7 and 8 shown in FIGS. 2 and 3 replace part of the condylar surface of a femur 9; they are also of different sizes, but each consist of a rectangular plate which is essentially identical in its basic shape. Each of the plates in turn has at least one anchoring pin 5.

The left tibia sliding surface 15 according to FIG. 4 is covered with partial implants 10 of the same shape and size with polygon-shaped heads which are fitted into one another in such a way that a practically closed, artificial sliding surface is created again.

Such an artificial sliding surface, which corresponds in its effect to a closed prosthesis shell, can also be achieved with two or three circular partial implants 11-13 of different diameters, as indicated schematically on the right sliding surface 14 of the tibia bone.

The sliding surface of the femoral head 21 according to FIG. 5 is partially covered with a number of partial implants 22 which, as shown in FIG. 6, have a slightly convexly curved outer surface and a circular cross section, and are all of the same size.

All of the partial implants mentioned are advantageously designed such that they are hammered or screwed into the corresponding bone without cement or at least with little cement. You then prefer to rely on the

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relatively dense and hard, cortical tissue layer, as indicated in FIGS. 3 and 5.

A particularly advantageous exemplary embodiment for anchoring a partial implant 22 is therefore described in connection with FIG. 6.

The basic shape of an anchoring pin 24 consists in a part close to the head of the partial implant 22 from a conical region 25, the length of which corresponds essentially to the thickness of the cortex layer 26 of the bone. An area 27 with a “cylindrical” basic shape then adjoins the conical basic shape toward the free end of the pin 24, the “generating” surface line of this extending parallel to its longitudinal axis. The basic shape of the areas 25 and 27 can have any cross section, for example circular, elliptical or polygonal, e.g. Be 3, 4 or polygonal; However, oval or other cross-sectional areas that do not correspond to a simple geometric surface are also conceivable for this.

In the area 25, the conical basic shape has a relatively fine toothing 28, which penetrates only a little into the cortical tissue 26 when it is driven in, but engages barb-like in this tissue with its fine teeth, so that migration out of the tissue 26 against the direction of impact is reliably prevented .

The area 27 of the pin 24 is anchored in the cancellous tissue 29 when the implant is inserted; it is therefore provided with at least one - but in the example shown several - tooth-like displacement bodies 30, the volume of which is advantageously at least about 20% of the volume of the associated basic shape 27. The teeth 30 have the task of displacing cancellous tissue when the pin 24 is driven in, which is deposited, for example, in compressed form in the “notch” behind the preceding pin 30.

As can be seen in FIG. 6, the cylindrical end region 27 is stepped at the transition point 31 with respect to the cone 5. The purpose of this step 31 is to make the smallest final diameter of the cone 25 essentially at least so large that the displacement bodies 30 of the cylindrical region 27 practically free the conical basic shape bore in the cortex 26 when driven in, 5 i.e. penetrate if possible without damaging cortical tissue.

The fine toothing 28, based on its conical basic shape 25, the length of which advantageously corresponds practically to the thickness of the cortical tissue layer 26, has a relatively small volume, which is advantageously only a few percent of the basic shape volume 25. The tissue displacement in the cortex 26 triggered by it is therefore considerably less than that in the cancellous bone 29.

The density differences between cortical and spongy tissue, which are known to be about 20: 1, can be taken into account roughly when dimensioning the volumes of the displacement bodies 28 and 30 if the ratio of these volumes to one another is at least 1:10 or less.

20 When anchoring the partial implants, after removing the damaged and therefore replaceable cartilage layer, the bone is first drilled with the help of a form drill, which corresponds in size and shape to the basic shapes of the two cone areas, and then the cone 24 is hammered in or screwed in, if necessary. The tooth-like displacement body 30 of the pin region 27 penetrating into the cancellous bone displaces, as mentioned, due to its volume which is relatively much larger than the volume of its basic shape 27 when the pin 24 is driven in, comparatively much of the tissue surrounding the drilled basic shape 27 and thereby compress it, as is known the ingrowth of the pin 24 is accelerated and improved. Because of the greater density of the cortex and - based on the associated basic volume 25 - the considerably smaller volume of the fine toothing 28 present in the conical region 25, this effect is significantly less in the cortical tissue.

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Claims (7)

632923 PATENT CLAIMS 1. Implant for an at least partial replacement of a coherent sliding surface of a human joint, characterized in that at least two independent, plate-like partial implants (1-3; 7, 8; 10; 11-13; provided with their own anchoring means (5, 24); 22) are intended for at least the partial replacement of the cartilage layer in the relevant joint area. 2. Implant according to claim 1, characterized in that the partial implants (1-3; 7, 8; 10; 11-13; 22) are coordinated in shape and size in such a way that by assembling at least some of them an at least largely complete Coverage of the supporting part of the sliding surface to be replaced is achieved. 3. Implant according to claim 2, characterized in that the individual partial implants (1-3; 7, 8; 10; 11-13; 22) are plates of different shape and / or size. 4. Implant according to claim 3, characterized in that the partial implants (11-13) consist of a number of circular disks of different diameters. 5. Implant according to claim 3, characterized in that the partial implants (1-3; 7, 8; 10) have the shape of polygons. 6. Implant according to claim 5, characterized in that the corners of the polygons (1-3; 7, 8) are rounded. 7. Implant according to claim 1, characterized in that the anchoring pins (24) of the partial implants have a conical basic shape (25) of any cross-section with an at least part of the circumference extending in a first region of the length similar to the plate-like head (22) Have fine toothing (28), and in addition that the adjoining area, which runs from the conical area to the free end of the pins (24), has a basic shape (27) of any cross-section with a surface line parallel to its longitudinal axis, and at least one over at least part of the Circumferential, tooth-like displacement body (30) is provided.