WO1996005784A1

WO1996005784A1 - Unguided endoprosthesis for small limbs

Info

Publication number: WO1996005784A1
Application number: PCT/DE1995/000611
Authority: WO
Inventors: Hans-Jürgen Moje; Dieter Werner
Original assignee: Moje Hans Juergen; Dieter Werner
Priority date: 1994-08-19
Filing date: 1995-05-03
Publication date: 1996-02-29

Abstract

The invention concerns an unguided endoprosthesis for small limbs, in particular for toe and finger joints. The endoprosthesis can be used to replace, in a single operation, one side or the whole of a damaged joint. Depending on the degree of damage, only part of the joint may be replaced or the whole of it. The patient can therefore be treated rapidly and usually without having to be admitted to hospital as an in-patient. The joint surface (1) of the endoprosthesis proposed is circular or rectangular in shape with rounded edges and preferably with a conical central hole (3). A centering pin (4) passes through the hole and into the bone (8) behind it. The joint surface (1) and the centering pin (4) are preferably made of a non-allergenic high-strength ceramic material.

Description

Non-guided endoprosthesis for small joints

The invention relates to a non-guided endoprosthesis for small joints, in particular for the joints of the toes and the joints of the fingers.

Endoprostheses for small joints have been known for years to replace damaged joints. These endoprostheses mostly consist of metals that are compatible with humans and are used surgically instead of the destroyed joint.

EP-A1-0 455 929 proposes a joint prosthesis, in particular for a finger joint, which comprises a bearing body having a bearing surface in the form of a thin-walled shell element made of high-strength metallic materials, on the rear side of which a shaft to be embedded in the bone is molded.

Likewise, EP-A-0 420 794 suggests one

Finger joint prosthesis, which consists of two prosthesis halves sliding on each other, each of which is anchored in the bone ends assigned to the joint part. The prosthesis halves consist of a sintered structure of hydroxyl apatite. However, this material is not suitable for highly stressed joints because it does not provide the required high strength properties.

EP-A-0 396 519 describes a special anchoring element for anchoring a prosthesis in the bone ends. With the help of the invention, the joint prosthesis is anchored as firmly and deeply as possible in the adjacent bone. A guide bush ensures sufficient centering. This anchoring element is preferably made of titanium or is coated with titanium. There may be additional surface texture have to facilitate attachment in the bone and improve the hold.

All prostheses are made of metal. However, the use of metal has decisive disadvantages for the replacement of joints. Bad sliding properties, which lead to high stress on the joints, are particularly worth mentioning, especially if only one joint side has been replaced. Here the bone experiences a high level of abrasion from the metal part. The high allergenic pollution caused by the metal or metal alloys should also be mentioned.

Further disadvantages result from the extensive resections of the bone part to be replaced. each

Fastening in the bone necessarily requires a large length of bone in order to achieve good durability. The end joints of the fingers cannot therefore be restored with such endoprostheses.

In addition, the loads on the limbs of the toes and fingers are very different. So the joints of the toes are loaded more heavily than the joints of the fingers. Guided joints, i.e. those that are anchored in the adjacent bones, are less resilient than joints that are not guided. For this reason, attempts are increasingly being made to replace the joints of the toes in particular with non-guided endoprostheses.

A non-guided joint replacement is proposed in EP-A-0 314 593. To replace the joint, in a first operation a metal joint surface, which has the shape of a joint shell, is inserted between the bones between which the joint is to be replaced, and is held by a mandrel screwed in from the tip of the foot. The mandrel is pulled in a second operation and in one third operation, when the new formation of the joint is complete, the joint surface is removed again. This method, long practiced in France, was intended to restore the natural joint. The main disadvantage was the appearance that the joint surface was often displaced due to the lack of centering when the mandrel was pulled, and therefore the healing success was not achieved. In addition to the high load, especially the first and third operations, the patient was unable to walk for a longer period of time, but at least during the time in which the spine was needed.

The object of the invention is therefore to provide an endoprosthesis for small joints which is not guided and which replaces the destroyed joint with the aid of a single operation.

Another object of the invention is to heal the patient as quickly as possible and without inpatient treatment.

These tasks are solved by an endoprosthesis according to the main claim.

The joint surface, which is to replace at least one missing joint part, is locked in the bone with a centering pin. For this purpose, the articular surface, which has a circular or rectangular shape with rounded edges, has a preferably conical center hole. Through this the centering pin is in the one behind

Bone introduced. The joint surface and the centering pin are preferably made of a non-allergenic, high-strength ceramic material, such as, for example, a ceramic based on zirconium oxide from TOSOH CORPORATION, Japan, but they can also consist of plastics, metals or metal alloys which have the required properties possess non-allergenic properties. It is not necessary that the joint surface and the centering pin each consist of the same materials in a joint replacement.

In order to secure the inserted implant against rotation, which can occur in particular at the joints of the fingers, it is also possible to form the flattened portion on the opposite side of the articular surface. The bone to which the endoprosthesis is to be fitted must then have a corresponding wedge-shaped recess into which this wedge-shaped part of the endoprosthesis is fitted.

The implantation of these endoprostheses consists of the following steps: In a first step, the through the

Bone part to be replaced resected, in a second step the articular surface is adapted to the bone, in a third step the articular surface is centered with a centering pin which is pressed through the center hole of the articular surface into the underlying bone. The wound is then closed.

If a complete joint is to be implanted, steps 1 to 3 are repeated on the opposite joint part and the wound is then closed.

This makes it possible for the first time to completely restore the end joints of the fingers and toes with an endoprosthesis. The defective joint is replaced in a single operation, in which either only one joint part or both are replaced. The endoprosthesis remains in the body. The main advantages of the proposed endoprosthesis are the low burden on the patient. The bone only has to be resected to a very small extent. The centering pin has no task of anchoring, it locks only the articular surface against slipping sideways until it is surrounded by the newly formed bone tissue. The depth of penetration of the centering pin into the adjacent bone is therefore very small. The endoprosthesis preferably consists of a non-allergenic ceramic. This has much more favorable properties in terms of compatibility with humans than the metal parts used to date.

The invention allows inexpensive restoration of destroyed joints both with regard to the implant and with regard to the operation and the aftercare of the operated patient.

The invention is based on

Embodiments are explained, reference being made to the accompanying drawings.

1A to IC show possible shapes of the articular surface in a view from above and as sectional views;

Fig. 1d shows possible shapes of the centering pins;

Fig. Le to lg show further embodiments of the

Invention;

Fig. 2 shows a unilateral replacement of the finger end joint of the third finger;

Fig. 3 shows a one-sided replacement of a joint of the first toe;

Fig. 4 shows the replacement of a complete joint of the first

Toe. 5a to 5c show examples of endoprostheses according to the invention with a wedge-shaped

Fitting in finger bones.

The same parts are designated with the same reference numbers in all drawings. In Figs. la to lc and FIGS. le to lg show some forms of articular surfaces 1 for small joints as views from above and as sectional views along lines II to VI-VI. Fig. La shows a circular joint surface 1 for the replacement of the joint of a toe with the center hole 3. This center hole 3 preferably has a smaller diameter on the side lying on the bone 8 than on the joint side. The circular surface here has a concave curvature 5 for the replacement of a proximal joint part. The side abutting the bone 8 has a flattened portion 2.

FIG. 1b shows a joint surface 1 with a convex curvature 5 for the replacement of the distal joint part, which supplements the joint surface 1 according to FIG. 1 to form a complete joint for a toe joint.

In Fig. Lc an articular surface 1 is shown for the replacement of a finger joint. According to the anatomy of the finger joint, the joint surface 1 has a rectangular shape with rounded edges.

In Figs. le and lf the joint surface of the endoprosthesis for the last finger joint is also equipped with a concave (5) and a convex curvature (6). As with the other endoprostheses, the concave curvature (5) is assigned to the proximal joint part and the convex curvature (6) to the distal joint part.

Fig. 1 g also represents an endoprosthesis for the last finger joint. With this embodiment, the entire last bone member can be replaced. This form is particularly advantageous when the end member is so badly damaged that it can no longer offer the endoprosthesis an attachment. Some forms of the centering pins 4 are shown in FIG. The centering pin 4 preferably has a conical shape and it can have certain configurations known per se in order to enlarge the surface of the shaft. In addition, the cross section of the centering pin 4 can be shaped differently. Furthermore, a rounded head 9 can also be formed, which offers additional advantages for both insertion and centering. The use of centering pins 4, which have a rounded head 9, is particularly advantageous when replacing finger joints.

FIG. 2 shows a schematic illustration of a one-sided replacement of a finger joint with the aid of the joint surface 1 shown in FIG. 1c. It can be clearly seen that the centering pin 4 penetrates the adjacent bone 8 only slightly. It can also be seen that the bone 8 has been resected only very slightly. This makes it possible for the first time to surgically restore the end joint of a finger. Since the articular surface 1 made of ceramic remains in the finger after the healing process, there are no further stresses. The newly formed bone tissue encloses the extremely compatible ceramic body and thus gives it the necessary support.

FIG. 3 shows a replacement of the proximal joint part of a joint of the first toe with the aid of the joint surface 1 shown in FIG. 1a. In this embodiment, the shallow depth of penetration of the centering pin 4 into the adjacent bones is also visible. The concave curvature 5 runs against the healthy joint part. Experience shows that not only the functionality of the joint is restored, but also the natural joint side is stabilized again.

Fig. 4 shows the use of a complete joint in the first toe. Both an articular surface 1 according to FIG. 1 a and an articular surface 1 according to FIG. 1 b are used instead of the destroyed joint.

The figures 5a to 5c show endoprostheses according to the invention with wedge-shaped fits into the bones 8 of the end joints of the fingers. 5a shows the replacement of the proximal joint part of the end member, 1 denoting the implant, 5 the concave curvature of the implant 1, 3 the center hole, 4 the centering pin and 7 the wedge-shaped recess. Fig. 5b shows the replacement of the distal part of the end joint and Fig. 5c shows the replacement of the complete joint. The wedge is perpendicular to the direction of movement of the joint. This embodiment of the invention is particularly advantageous when replacing finger joints because the risk of twisting is relatively great in the case of the finger joints.

The exemplary embodiments serve only for explanation. In the same way, the joints of the 1, 2, 4 and 5th fingers and the 2nd to 5th toes can be treated with the appropriate endoprostheses.

After resection of the destroyed joint parts, the flattening 2 of the joint surface 1 or the wedge-shaped opposite side of the joint surface is adapted to the bone 8 during operation and centered on the bone 8 located behind it with a centering pin 4. As already stated, this centering pin 4 is not used for fastening. The required fixation of the implant takes place solely through the healing process, in which the newly formed bone tissue Encloses endoprosthesis. The operation is ended after the wound is closed.

These examples are intended to make it clear that these are small implants, with the help of which even the smallest joints of the human hand and toes can be inexpensively restored. The operation to insert the endoprostheses can also be done on an outpatient basis under certain conditions.

Although the present invention has been described and explained in detail, it is clearly evident that the examples are only intended to be illustrative and are not to be seen as a limitation. The scope of the present invention is limited only by the claims.

Claims

CHANGED CLAIMS [received at the International Office on February 5, 1996 (February 5, 1996), original claims 1-11 replaced by new claims 1-7 (2 soaps)]

1. Non-guided endoprosthesis for small joints consisting of an endoprosthesis body with an articular surface, characterized in that the articular surface (1) is modeled on the natural joint, that the endoprosthesis body has a flattened portion (2) on the opposite side to the articular surface and a central hole (3 ), by means of which the endoprosthesis body can be locked with the aid of a centering pin (4) on the bone (8) behind it.

2. Non-guided endoprosthesis according to claim 1, characterized ge indicates that the centering pin (4) has a straight or conical shaft and a rounded head (9).

3. Non-guided endoprosthesis according to claim 1, characterized ge indicates that the articular surface (1) has a circular shape with a concave curvature (5) for the proximal articulated part or a convex curvature (6) for the distal articulated part.

4. Non-guided endoprosthesis according to claim 1, characterized in that the joint surface (1) has a rectangular shape corresponding to the joint part and is rounded at the corners.

5. Non-guided endoprosthesis according to one of claims 1 to 4, characterized in that the center hole (3) to the bone (8) is conical.

6. Non-guided endoprosthesis according to one of claims 1 to 5, characterized in that the body and the centering pin (4) consist of a non-allergenic ceramic material, a non-allergenic plastic or a non-allergenic metal of high strength, the body and the centering pin (4) consist of the same or different materials. SPARE BLADE (RULE 26) 7. Non-guided endoprosthesis according to claim 1, characterized ge indicates that the flattened portion (2) is formed wedge-shaped to secure against rotation, and is placed against a corresponding wedge-shaped depression in the bone (8).

REPLACEMENT BLAπ (RULE 26) Declaration under Article 19 (1)

1. The claim 1 is replaced by the amended claim 1 of the same numbering.

2. Claims 2 and 3 are replaced by amended Claim 2.

3. Claim 4 is replaced by claim 3 of the same name.

4. Claim 5 is replaced by claim 4 of the same name.

5. Claim 6 is replaced by claim 5 of the same name.

6. Claims 7 to 10 are replaced by the amended claim 6.

7. Claim 11 is replaced by claim 7 of the same name.