DE4137383C2 - Endoprosthesis - Google Patents

Description

The invention is based on an endoprosthesis with a shaft, one Metal or a composite material proximal shaft section, the at least partially an open-cell or open-pore Has surface structure.

Endoprostheses with a shaft are e.g. B. as thigh parts of artificial hip joints or as artificial knee joints or the like known. In these known endoprostheses The stem is usually made of metal, which is used during implantation cement-free or with the interposition of bone cement in one Bone cavity is used to make the endoprosthesis this way to anchor. The metallic one can be used for cement-free anchoring Shaft have a metallic surface to which the renewable  Bone tissue should grow closely. Alternatively, the Surface of the metallic shaft z. B. an open cell structure, into which the renewable bone tissue grows and thereby creates a tight microstructured bone / metal bond. Because of the elasticity of the natural bone and the given Properties of the metal shaft are after the implantation Endoprosthesis, however, micro movements between the bone tissue and the Shaft cannot be excluded and therefore it cannot be excluded that the presence in particular in the distal end portion of the shaft of the shaft permanent mechanical disturbances and irritations in the surrounding bone tissue.

The cement-free shaft anchor is an alternative to cemented shaft anchoring and is used particularly in the USA, but also in Europe using different, more biocompatible smooth, roughened or porous implant surfaces, some with additional, so-called bioactive calcium phosphate ceramic layers applied.

Previous clinical and experimental work with cement-free To a large extent, however, shaft anchors showed so-called proximal "stress shielding" phenomena. The latter join High rigidity prostheses, d. H. large cross section and / or Material with a high modulus of elasticity, piled up. Requirement for a Such stress shielding is a stress bypass that occurs in the Usually done through a distal stress concentration.

DE 31 06 917 C2 describes a method for producing endoprostheses of the type mentioned above, which is used to manufacture of open-cell or open-pore surfaces of anchoring parts of endoprostheses. In the open cell or open pore Surface can ingrow renewable bone tissue and thereby create a tight microstructured bone / metal bond. The Bone tissue has grown into the open cell structure  as a result that a stable and intimate firm bond between Bone tissue and prosthesis is realized.

A multi-part prosthesis is known from DE 34 14 924 A1, in which a prosthesis section clamped with a shaft via a clamping system is, this shaft either completely or partially resorbable material exists, but does not have the task in a section to take care of the anchorage itself. Such Prostheses can only be used where, after a certain There is no longer any power transmission via the shaft and the The shaft is then superfluous.

A shaft of an endoprosthesis is known from DE 34 20 035 A1, which a layer of calcium compound on its entire surface possesses, which should stimulate the bone growth and is resorbable, after the absorption of this coating the entire shaft takes over the anchoring in the known manner.

The object of the invention is an endoprosthesis of the aforementioned Kind in such a way that after the implantation of the endoprosthesis especially in the distal end region of the shaft mechanical disturbance and irritation of the bone tissue avoided and particularly firm, intimate ingrowth in the proximal section of the shaft is guaranteed.

This task is the endoprosthesis of the type mentioned solved according to the invention in that a middle and / or distal Section of the shaft consists of bioabsorbable material.

Because of the viscous elastic properties of cancellous bone and the metal-porous or open-cell surface, despite proximal ingrowth from bone tissue distally to pendulum-like Micro-movements come that initially form a connective tissue boundary layer induce and possibly also bone remodeling processes in the distal  Shank area that thinning the existing there Corticalis corresponds. A distally bioresorbable shaft portion would also rule out this problem. The advantages of The invention now lies particularly in the fact that the shaft is not one has resorbable, proximal section, which for long-term anchoring serves in the bone tissue and with a suitable shape of the Surface structure firmly anchored by ingrowth of the bone tissue can be during the other shaft sections or which is especially useful for long-term use for unwanted load transfers are responsible or by distal micromovements lead to connective tissue formation in the distal shaft area would be made of bioresorbable material, which in human body, for example, gradually degraded through hydrolysis becomes.

Known materials, for example, can be used as bioabsorbable material Polymers based on organic acids, for example derivatives of Use lactic acid, glycolic acid and their copolymers etc., compare, for example, the book publication "Macromoleculare Biomaterials ", CRC Press 1984, pp. 119 to 142" Bioresorbable Plastic Materials for Bone Surgery "or" Clinical Materials "1986, 1, p. 233 to 257.

The open cell surface structure is particularly preferred in those areas of the non-absorbable, proximal shaft section provided in which the force transmission from the endoprosthesis in the natural bones. Is the endoprosthesis for example a thigh part of a hip joint, so becomes a neck section carrying the joint ball, and at least the subsequent shaft section made of a non-absorbable material, for example made of metal or a composite material, and this non-absorbable proximal shaft section bears in part or in full at an amount of one One third to two thirds of its proximal portion is an open cell  metal porous surface structure, so that the firm anchoring between bone tissue and shaft in the proximal shaft section over a sufficient length of the shaft. Of the the shaft section adjoining this distally is opposed at least partially made of bioabsorbable material, which is after the implantation for a predetermined time space (between 12 and 16 weeks) in the bone. The bioabsorbable In this way, the shaft section serves for primary stabilization the endoporothesis immediately after its implantation. While then - after implantation - the proximal, non-absorbable Ingrown shaft section and a firm anchorage bond to Bone is generated, the bioresorbable shaft section becomes simultaneously reduced.

According to a preferred embodiment of the invention, the non-absorbable, proximal shaft section to its distal Continue at the end as a core with a reduced cross-section. The bioresorbable shaft section is then a sleeve formed, which surrounds the shaft core over the entire circumference.

The bioresorbable shaft section is shaped and / or  frictionally or with suitable fasteners attached to the non-absorbable, proximal shaft section.

In a preferred embodiment of the invention the non-absorbable, proximal shaft section wears a osteoinductive coating from a calcium phosphate Ceramics such as hydroxylapatite or tricalci umphosphate and / or an osteoinductive coating using osteoinductive polypeptides as for example play Osteogenin or Bone Morphogenetic Protein. A another advantage of a coating would be seen in this be that thereby the metal ion release at least is temporarily reduced.

The bioresorbable shaft section can be according to a preferred embodiment of the invention in one given area of the non-absorbable proximal shaft cut across a given circumferential segment, while in the rest of the circumference segment the non-resor the proximal section of the shaft, the surface of the shaft forms.

Further developments of the invention are due to the features of the subclaims.

The following are exemplary embodiments of the invention explained in more detail with reference to the drawing. It shows

Fig. 1 is a side view of a femoral component of a hip joint endoprosthesis; and

Fig. 2 is a side view of another embodiment form of a prosthetic thigh part.

Figs. 1 and 2 respectively show a side view of a femoral component of a hip joint endoprosthesis. On a collar 6 is a proximal neck portion 7 is formed , which forms a plug-in cone for a prosthetic Ge joint ball. This collar 6 is not designed in the form of a support collar, so that the proximal application of force takes place exclusively via the proximal metal spongy outer surface and not via the medial cortical bone on the calcar femoral. A shaft 10 is formed on the distal side of the collar 6 and has a proximal section 12 and a distal section 16 . The distal section 16 extends to the distal end 18 of the shaft 10 .

The collar 6 , the neck section 7 and the section 12 which is positioned below the collar 6 are made of a non-absorbable material (for example metal or composite material) and - in the embodiment shown - form the so-called non-absorbable, proximal shaft section, which also has a distal section End 18 in the shaft direction extending shaft core 14 with reduced cross-section contains. Arranged around the shaft core 14 is a shaft section 16 made of bioresorbable material, which also extends to the distal end 18 of the shaft 10 .

The non-resorbable, proximal shaft section 12 is provided below the support collar 6 up to the upper edge of the bioresorbable shaft section 16 with an open-cell surface structure 13 , which allows the bone tissue to grow easily into the open pores, and thus a particularly firm form fit between bone tissue and enables non-absorbable, proximal shaft section.

The femur part of Fig. 2 has a non-resorbable, proximal shaft section 12, which is also the neck portion, the collar 6 and the accreting under the collar portion of the stem 10 includes. The non-absorbable, proximal shaft section 12 extends further distally in the medial area than in the lateral area. The non-resorbable, proximal shaft section 12 is followed by a shaft section 16 made of bioresorbable material, which extends to the distal end 18 of the shaft 10 . The bioresorbable, proximal shaft section 16 is anchored in one or more undercut recesses 15 , which are arranged on the distal boundary surface of the non-absorbable, proximal shaft section 12 . In the exemplary embodiment according to FIG. 2, the non-resorbable, proximal shaft section 12 above the bioresorbable, proximal shaft section 16 is also provided with an open-cell surface structure, which enables the bone tissue to grow firmly into this structure.

The distally extended in the medial area non-absorbable, proximal shaft section 12 has the effect that after the bioresorption of the shaft section 16 in the medial region there is sufficient shaft area available for anchoring with the bone tissue, while in the late ral area the distal zone which is particularly stressed to stretch of the shaft 10 is resorbed and as a result no load transmission or mechanical interfacial movements can arise with respect to the bone tissue there.

Claims (10)

1. Endoprosthesis with a shaft, a proximal shaft section consisting of metal or a composite material which at least partially has an open-cell or open-pore surface structure, characterized in that a central and / or distal section ( 16 ) of the shaft ( 10 ) consists of bioresorbable material . 2. Endoprosthesis according to claim 1, characterized in that the proximal shaft section ( 12 ) has a shaft core ( 14 ) running in the shaft direction with a reduced cross-sectional area, and that the bioresorbable shaft section ( 16 ) surrounds the shaft core ( 14 ). 3. Endoprosthesis according to claim 1 or 2, characterized in that the shaft core ( 14 ) extends to the distal end ( 18 ) of the shaft ( 10 ), and that the bioresorbable shaft section ( 16 ) is designed as a sleeve surrounding the shaft core ( 14 ) is. 4. Endoprosthesis according to one of the preceding claims, characterized in that the bioresorbable shaft section ( 16 ) is positively and / or frictionally attached to the proximal shaft section ( 12 ). 5. Endoprosthesis according to claim 4, characterized in that the bioresorbable shaft section ( 16 ) is anchored in at least one undercut bore ( 15 ) in the proximal shaft section ( 12 ). 6. Endoprosthesis according to one of the preceding claims, characterized in that the open-cell surface structure ( 13 ) partially or completely surrounds the proximal shaft section ( 12 ) on its circumference. 7. Endoprosthesis according to one of the preceding claims, characterized in that the proximal shaft section ( 12 ) carries an osteoconductive and / or an osteoinductive coating on its surface. 8. Endoprosthesis according to one of the preceding claims, characterized in that the proximal shaft section ( 12 ) carries a coating which reduces the release of ions. 9. Endoprosthesis according to one of the preceding claims, characterized characterized in that the endoprosthesis as a thigh part Hip joint is formed. 10. Endoprosthesis according to one of the preceding claims, characterized characterized in that the endoprosthesis as a tibial component or Femoral component of a knee joint prosthesis is formed.