Patent Application
20100137994
The invention relates to a joint part prosthesis, particularly for a finger joint. It consists of either a proximal or a distal component, as well as a shaft that extends away from this component, to be mounted in a bone.
Artificial finger joints consist essentially of two elements, namely a proximal and a distal component. A component has a convex joint head that interacts with the other part, which demonstrates a convex joint socket.
Artificial finger joints are inserted between the metacarpal bone and the finger bone, or between individual finger bones. Such joints have to be inserted if degenerative joint diseases such as osteoarthritis, post-traumatic arthritis, or rheumatoid arthritis of the joints in question are present. Another alternative that retains mobility of the individual finger members is a total joint replacement.
From the state of the art, particularly from EP 1203569 A (FINSBURY (DEVELOPMENT) LIMITED LEATHERHEAD) Mar. 3, 2000, finger joint implants are known in the configuration of so-called PIP shaft implants. They have a proximal or a distal component, which components interact accordingly, each having a shaft that points away from these components. The shaft is generally configured to be conical and is introduced into the bone marrow of a bone. In order to allow introduction, the interior of the bone is partly cleared out using a clearing tool, and the implant is driven into the bone using a hammer-like instrument. Fixation takes place in such a manner that the diameter of the cleared bore is smaller than the outside diameter of the shaft, so that a kind of press fit is formed between the shaft and the interior of the bone.
The implant itself consists of a material having a modulus of elasticity similar to bone. This modulus of elasticity similar to bone avoids so-called stress shilding and thus promotes bone build-up. Additionally, fixation of the implant in the medullary space of the bone is improved in this manner.
Products according to the state of the art have disadvantages such as implant loosening due to insufficient fixation and insufficient connection with the bone, as well as high wear values, thereby causing corresponding friction wear. The shaft-like construction within the medullary space creates sufficient room for itself if loosened, so that an implant that was fixed in place previously is no longer functionally correct. The consequences of this are pain caused by migration or even fractures.
Furthermore, the disadvantage of the embodiments according to the state of the art consists in that the individual joint part prostheses cannot be disposed in a manner to reliably prevent twisting.
It is therefore the task of the invention to further develop a joint part prosthesis, particularly for finger joints, in such a manner that the likelihood of loosening of the implant is reduced, in contrast to the state of the art.
The core idea of the solution of the task is to provide the shaft with wing-like or fin-like configurations, so that the rotation-symmetry shape that is advantageous for production and for clearing out the medullary space of the bone is retained, but nevertheless, an anti-twist security device is provided.
One of the significant advantages of the invention is that because of the configuration of the joint part prosthesis according to the invention, it is no longer necessary to clear out the medullary space of the bone into which the implant is to be placed by means of working on it by hitting or hammering. Nevertheless, the joint part prosthesis can be fixed in place in simple and efficient manner. Since the shaft of the joint part prosthesis has rotation symmetry, it is sufficient to clear out the medullary space of the bone by means of rotational movements. In this way, damage to adjacent joints, in particular, caused by the hammering process required for clearing, is avoided.
One of the other significant advantage of the invention is that the joint part prosthesis can be inserted into the medullary space of a bone, with its shaft, and is also fixed in place there, in anti-twist manner, without additional steps being required.
The invention provides that anti-twist devices are provided on the mantle surface of the shaft of the joint part prosthesis. An anti-twist device comprises at least one fin-like element that is disposed on the mantle surface of the shaft of the joint part prosthesis, and extends in the longitudinal direction of the shaft. In this connection, it is preferably narrow and advantageously configured to be somewhat thicker toward the shaft. This brings with it the advantage that for one thing, torques/torsions that occur can be absorbed by the anti-twist element. For another thing, it has the advantage, because of the fact that the free ends are configured to be narrower, that simple insertion into the prepared cleared medullary space is possible.
A preferred embodiment of this anti-twist security device provides that it/they increase in their reaches, proceeding from the free end, in the direction of the distal or proximal component, so that twisting is still possible at insertion of the implant, and the farther the implant is introduced into the medullary space, the more likely it is that twisting is configured to be restricted.
In order to be able to install such anti-twist devices together with the shaft of a component, it is provided to clear the cavity accordingly. Aside from the dimensions of the shaft, the spaces that project away laterally are also cleared by means of a gauge, so that the implant can be inserted with precise fit. Clearing preferably takes place by means of rotating and oscillating movements, so that no hammering movements, which put stress on the joints, are required.
In one exemplary embodiment, the joint part prosthesis consists of a material that is known from the state of the art.
Preferably, the anti-twist elements form a one-piece part with the shaft.
A preferred embodiment provides that the distance from the mantle surface of the shaft decreases toward the free end of the anti-twist element, in the direction of the free end of the shaft.
Another embodiment provides that the fin-like elements extend only partly over the longitudinal expanse of the shaft. It is advantageous if they are configured only in certain sections.
Alternatives provide that a plastic can be used, particularly in order to achieve the modulus of elasticity similar to bone. This also brings with it the particular advantage that the joint part prostheses can be produced by means of injection-molding methods.
Other advantageous embodiments are evident from the following description, the drawings, as well as the claims.
The drawing shows:
In
The free end 5 of the shaft 4 is preferably configured in ball-like manner, so that no sharp edges can be formed, which can injure any marrow of the bone during insertion of the prosthesis.
Furthermore, the wall of the shaft 4 is configured to be round, particularly in the region of the free end 5.
On the mantle surface 6, the anti-twist device 7 according to the invention is disposed. This anti-twist device 7 serves to fix a joint part prosthesis 1 that has been introduced into a medullary space, which space preferably takes up at least almost the same cross-section as the shaft 4 configured together with the anti-twist device 7, in place in such a manner that turning of the joint part prosthesis 1 within the medullary space is no longer possible.
The anti-twist device 7 consists of at least one anti-twist element 8 that is configured in the longitudinal expanse of the shaft 4 and has a fin-like construction.
Particularly in the region of the free end 5 of the shaft 4, it is provided to configure the anti-twist element 8 very slightly, with regard to its distance from the mantle surface of the shaft 4, so that during introduction, corresponding positioning within the medullary space is still possible. The deeper the joint part prosthesis 1 is introduced into the medullary space, the more the fin-like anti-twist devices 7 penetrate into the medullary space and press themselves into the marrow of the bone. A corresponding wedge effect occurs.
The anti-twist element 7 prevents rotational movement of the joint part prosthesis 1 in or opposite to the arrow direction 9. It serves at least only slightly to bring about fixation of the joint part prosthesis 1 in the rotation direction, but also in the longitudinal direction.
The invention can be used for joint part prostheses in both the distal or the proximal region. Likewise, use for all types of prostheses that have a shaft-like configuration is possible, where it is important to prevent a rotational movement of the joint part prostheses from being possible.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20 2007 009 620.8 | Jul 2007 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2008/001243 | 5/9/2008 | WO | 00 | 1/8/2010 |
