CZ233793A3 - Joint prosthesis - Google Patents

Abstract

A joint prosthesis (3) has two extensions (4, 5) that can be linked to bones and swivel with respect to each other around an axis bolt (6). One of the extensions (5) has a claw shaped head and the other extension (4) has a head part provided with a bearing eye that enters the claw-shaped head. The axis bolt of the joint extends through the mutually aligned bores of the claw-shaped head and bearing eye. The axis bolt (6) of the joint tapers towards one end and/or its outer diameter is reduced towards said end, which is designed as a ring-shaped snapping element that cooperates with corresponding ring-shaped snapping elements arranged on one of the mutually aligned openings of the claw-shaped head.

Description

Joint prosthesis

Technical field

BACKGROUND OF THE INVENTION The present invention relates to articulated prostheses with two bones attachable to one another relative to one another relative to one axis, one of which is provided with a jaw-shaped head and the other is provided with a bearing-bearing head and engaging the jaw-shaped head. it passes through the matching holes in the jaw-shaped head and through the bearing eye.

BACKGROUND OF THE INVENTION

For example, prostheses of the aforementioned kind are described in US-PS 4,193,139. Another articulated endoprosthesis, as described, for example, in DE-A 2 351 912, is primarily intended for the elbow joint because of its structure. Overall, most of the prior art prostheses are more or less suitable for a particular use case or for replacing a totally certain joint.

In addition to the aforementioned US-PS 4193 139, articulated prostheses which, like the articulated prosthesis according to the invention, are primarily intended for replacing the toe joint, are also particularly described in EP-B1 214 773. they are intended for the joints of the fingers, limited to the uniaxial bend of the rotatably connected bone portions, the use of the second joint from the tip of the finger obviously being considered first and foremost. However, due to the known design of such prostheses, it is necessary to remove a relatively long portion of the bone on the front surface on which the joint is to be fitted in order to create a location for the joint. In such operations, a part of the bone to which the articular connective tissue may initially have been removed is thus removed and a new location for attaching the connective tissue to the bones must be sought. Experience has shown that a new increment of bone connective tissue at a site other than the original natural site is associated with major problems.

In addition to the high mechanical strength, mechanical articulated prostheses must also be easy to assemble in order to allow a correspondingly short time to perform the operation during their operative use or deployment.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION It is an object of the invention to provide a joint, i.e. a joint prosthesis, particularly for use as a metatarsal joint which, by virtue of its construction, allows only small areas of mutually opposite faces to be hinged to each other to be removed. only to the extent that natural sites of connective tissue accretion can remain intact. Another object is to provide a joint prosthesis of the above type, which is distinguished by its simple construction and assembly without the use of expensive tools. The object is solved by a joint prosthesis, which consists in that the axis of the joint is formed by a pin which tapers towards one end and / or is offset to a smaller diameter, this end being formed as a circular stop together with the respective circular stops of one of mating through holes of the jaw-shaped head. By making the joint axis in the form of a connecting pin, it is possible to make the joint itself relatively small and to ensure a secure anchoring of the extensions in the respective bones before the assembly of the joint is performed in a simple manner in a minimal space. In order to assemble the joint, it is sufficient to push the stop pin into the respective through holes, which requires a relatively small space, which in turn means that only small lengths must be removed from the bones to be joined by such an artificial joint. In addition to this particularly advantageous connection, the end of the pin can be tapered to facilitate centering and insertion of the pin, and in any case the definitive bearing is made by driving the free end of the pin against the corresponding jaw-shaped head stops. The assembly can still be greatly facilitated by having a pivot in the joint axis having a blind hole for gripping the tool on its face facing away from the stop, while allowing a particularly simple mounting of the tool for handling a relatively small pivot in the joint axis if the blind hole is internally threaded. . Overall, relatively small pins in the axis of the hinge with correspondingly small hinges can also be securely assembled in a minimal space in such a construction, due to the possibility of using a correspondingly easier to handle tool.

Preferably, the design of the articulated prosthesis according to the invention is such that the stops are formed by circular grooves and / or circular ribs. In order to allow the elastic drive of such annular grooves against the annular ribs, physiologically harmless plastics can be advantageously used, whereby the assembly or manufacture of the hinge can be substantially simplified by matching the jaw-shaped orifices of the jaw having substantially the same internal diameter and the stops are arranged in a housing which is inserted in one of the two holes of the jaw-shaped head and secured against falling out. The arrangement of matching holes with substantially the same inner diameter makes it possible to select simple manufacturing tools for jaw-shaped extensions and heads, where the necessary small tolerances can then be ensured by correspondingly high-precision inserts, in particular a sleeve. Furthermore, it is possible in this way to select the corresponding high-strength materials, in particular metal materials, for the extensions and the head structure, and since bushings with correspondingly small manufacturing tolerances are used, and in particular bushings made of physiologically harmless plastics. between metal parts. Such undesirable friction between the metal parts of the joint while using the self-lubricating capabilities of various physiologically acceptable plastics occurs even if the structure is such that the sleeve is provided with a circular flange with an inner diameter of holes exceeding the outer diameter which abuts on the inner side of the head jaw. in the form of a jaw, thereby allowing lateral stabilization of the joint with a correspondingly low tolerance, seen in the direction of the bearing axis. This effect can be further improved by inserting a bearing bush in the bearing eye of the head of the second extension having a circular flange having an outer diameter exceeding the inner diameter of the bearing bushing bore hole, thereby ensuring that the bearing eye of the bearing on both sides friction on the metal parts of the inner walls of the jaws embracing the head may be removed.

With regard to the use of the articulated portes according to the invention as a joint in the area of the metacarpals or toes, it is necessary to mimic only the articulation of the articulated joint, for which the head is provided with at least one stop arm which acts together with a jaw-shaped head of the second extension. In this way, at least one of the limit positions, for example the joint extension position, can be clearly delimited by the stop, without the need for additional space occupying the component for this purpose.

In order to ensure secure anchoring of the extensions even in such small joints, the construction is preferably such that the extensions are substantially centrally symmetrical to their longitudinal axis intersecting the axis of the bearing, preferably on the extensions on their outer side preferably circumference in the direction of their longitudinal axis. Such ribs, particularly sharp-edged, improve the respective anchoring effect in the end region of the bones and offer a number of advantages when fitting the bones in the bone. While the known, very asymmetric inserts have high accuracy requirements for the respective bone recesses for fast and secure adhesion, such very centrally symmetrical inserts impose considerably less requirements on the maximum allowable tolerances of these recesses without significantly reducing the degree of adhesion. In order to ensure that the anchoring effect is sufficient immediately after the indentation, the design is preferably such that the sharp-edged ribs decrease in the direction towards the free end, and for this reason the necessary connection to the bone material is covered with a biologically degradable ceramic. The compression of the extensions into the more easily produced recesses on the ends of the hinged bones is thereby greatly simplified and, with less force, allows the extensions to taper substantially towards their free end.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail by way of example with reference to the accompanying drawings, in which: FIG. 1 schematically shows a cross-section of, for example, a metatarsal joint with an articulated prosthesis according to the invention; FIG. 2 shows a plan view of a jaw-shaped head carrying extensions; Fig. 1 shows a side view of the extension or part of the joint in the direction of arrow III in Fig. 2, Fig. 4 shows a view in the direction of the arrow IV in Figures 2 and 3, Fig. 5 shows a side view of a second, non-split bearing Fig. 6 shows a plan view of the second extension in the direction of the arrow VI of Fig. 5; Fig. 7 shows a view of the joint axis forming the pin of the joint prosthesis according to the invention; 8 is a cross-sectional view of a sleeve displaceable in the jaw of a jaw-shaped head on which they are disposed at the jaw clippers for coaction with the pin of FIG. 7 and FIG. 9 shows a section of another bearing pouz8 Dre which is insertable into the bearing eye of the head portion of the second extension joint prosthesis according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In Fig. 1 two bones 1 and 2 planted joint prosthesis 2 P ^ro replace a natural joint, wherein the joint prosthesis comprises three two extensions 4 and 5, which is inserted into a selected or hollow shaft of the bone and which are shown below in detail. The two extensions 4 and 5, respectively the joint parts, are rotatably articulated to each other, the axis of rotation being shown schematically in FIG. 1 under the number 6. The axis of rotation is formed by a pin which can be inserted into the matching holes of the extensions 4 and 5. Fig. 7. The actual joint regions of the articular prosthesis, that is, those partial regions that protrude from bones 1 and 2, are so short due to the use of the pin as the joint axis that the natural growth sites 7 for the ligaments at the end regions of the bones .

2 and 3 show in detail the extension 5 or the part of the joint carrying the jaw-shaped head. Immediately on the extension 5, tapering towards its free end 8, two jaws 9 adjoin each other, in each case aligned holes 10 of substantially the same cross-section with the axis of rotation 6. On the extension 5, particularly sharp ribs 12 are arranged on its periphery in the direction of its longitudinal axis 11, as is also clear from FIG. 4. Further, the conically tapering shape of the extension is clearly visible from FIG.

In the assembled state, the jaws 9 embrace the bearing eye 13 of the second extension 4, which is shown in detail in FIGS. 5a 6. In the extension 4 or in the bearing eye 13, a hole 14 is aligned with the holes or holes 10 of the second extension 5. In the assembled state, the pin shown in Fig. 7 passes through. Also, the attachment shown in Figs. 5 and 6 has a tapering cross-section conically towards the free end 15 and is also provided with sharp-edged ribs.

12. Overall, the extensions 4 and 5, or the joint portions, are not only centrally symmetrical but also identical in their partial areas extending into the bones, so that the joint can be inserted in both positions.

The circumferentially spaced ribs 12 are arranged in such a way that, when inserted into bones, only one rib is arranged on the inner side, i.e. on the bend side of the joint, while the other two ribs 12 shown in the figure are correspondingly arranged on the outer The ribs protrude from the respective free end 8 and 15, respectively, in order to facilitate the drive of the respective extensions into the recesses in the bones. Generally, the ribs are used to anchor the bones in the bones and in particular to prevent the bones from rotating. Furthermore, due to the presence of the ribs, the geometric shape of the recesses formed in the bones need not be too high, since the ribs can compensate for correspondingly irregular recesses in the bones by their different height.

In one of the jaws 9, a sleeve 16, shown in FIG. Similarly, the bearing bush 18 shown in FIG. 9 is inserted into the opening 14 of the bearing eye 13 of the second extension, which also has a circular flange 19 adjacent to the inner side of the bearing eye and thus disposed between the bearing eye 13 and the adjacent jaw 9. The sleeve 16 is naturally fitted onto the second jaw 9.

In order to assemble the articulated prosthesis, a pin 20, shown in FIG. 7, which forms the axis of the joint, is inserted into the openings 10 and 14 in the extensions 5 and 4, respectively into the openings in the sleeves 16 and 18. In this case, the pin 20 tapers to one end 21 and is offset to a smaller cross-section, whereby a free end 21 of the pin 20 forms a circular stop 22 in the form of a circular rib. When inserting a member 20 from that side of the articulated prosthesis that is opposite the jaw 9 with the sleeve 16, the pin first passes through the first opening of the first jaw 9 and then passes through the opening 23 of the bearing bush 18 into the bearing eye and then into the bush 16 arranged in the second jaw. . As can be seen in FIG. 8, a sleeve 16 is provided with a circular stop 24 dimensionally aligned with the diameter of the sleeve stop 22 so that when the knuckle or coupling pin is fully inserted, the stop 22 is locked into the sleeve 16 and sleeve 16. Thus, the two extensions 4 and 5 or the hinge parts are hinged to each other in a simple manner.

For insertion of the tools, a pin hole 25 is provided in the pin 20, which is provided with an internal thread in the part region 26, so that, for example, a screw or the like can be arranged therein for easy manipulation of the pin or for application of necessary forces. removed after simple assembly.

When using the articulated prosthesis in the area of the fingers or metacarpals, only a single-axis articulation is required, for which the end position of the articulated prosthesis is shown in FIG. In order to prevent excessive stretching or bending in the opposite direction, a stop arm 27 is provided on the bearing eye 13 shown in FIGS. 5 and 6, which in the extended position abuts the inner surface 28 of the extension 5 between the jaws 9 and prevents excessive bending beyond the extended position. The bending angle beyond the extended position is limited to about 10 ° by this stop.

Special material titanium and aluminum alloys are used as the material for the joint parts, which are distinguished by low density, high elasticity, high strength and excellent corrosion resistance. The used sleeves 16 and 18 shown in FIGS. 8 and 9 are slid onto each other not only to join the hinge parts, but also to eliminate friction between the metal parts. For this purpose, these bushings are made of a biocompatible material that has good sliding properties as well as optimum damping at minimum wear. For the rapid adhesion of the prostheses, in particular the bones 4 and 5, the bones 4 and 5 are covered with a corresponding biodegradable substance, for example by means of plasma spraying, thus allowing for earlier painlessness and thus earlier use of the operated joint. The perfect bone adhesion thus achieved with the implanted extensions 4 and 5 provides an early and good possibility of loading the artificial joint.

Of course, different outer diameters of extensions 4 and 5 may be used to accommodate different bone sizes. Conical tapering of extensions 4 and 5 is selected such that, in addition to anchoring with the ribs 12, a self-locking anchoring is performed to remove the extensions from the bones. of materials and, depending on the bone, an angle of inclination of about 5.7 ^θ, for example. If, in contrast to the illustrated embodiment, the stretching is to be carried out with a small number of ribs, the rib belonging to the bending side does not take place due to the kinematics of the joint.

Claims (13)

PATENT CLAIMS 1. An articular prosthesis with two axially pivotable, bone-attachable extensions, one of which has a jaw-shaped head and the other is provided with a bearing eye supporting the head with the jaw-shaped head, where the joint axis extends over each other jaw-shaped head holes and over the bearing eye, characterized in that the joint axis is formed by a pin (20) which tapers towards one end and / or is offset to a smaller outer diameter, the end being formed as a circular stop (22), which together with the corresponding circular stops (24) on one of the mating through holes (10) of the jaw-shaped head (9). Articulated prosthesis according to claim 1, characterized in that the pin (20) is provided with a blind hole (25) for receiving the tool on its end face facing away from the circular stops. Joint prosthesis according to claim 2, characterized in that the blind hole (25) is provided with an internal thread (26). Articulated prosthesis according to one of Claims 1 to 3, characterized in that the stops (22) are formed by circular grooves and / or circular ribs. Articulated prosthesis according to one of Claims 1 to 4, characterized in that the matching holes (10) of the jaw-shaped head (9) have substantially the same inner diameter, the stops (24) being arranged in the housing (16), which is mounted and secured against falling out in one of the two holes of the jaw-shaped head (9). Joint prosthesis according to claim 5, characterized in that the sleeve (16) is provided with a circular flange (17) with an inner diameter of the holes (10) exceeding the outer diameter which abuts on the inside of the jaw of the jaw-shaped head (9). ). Joint prosthesis according to one of Claims 1 to 6, characterized in that a bearing bush (18) is provided in the bearing eye (13) of the head of the second extension (4) and is provided with a circular flange (19) with an outside diameter exceeding the inner the diameter of the bore (14) for receiving the bearing bush (18). Joint prosthesis according to one of Claims 1 to 7, characterized in that the bearing eye (13) carrying the head carries at least one stop arm (27) which cooperates with a jaw-shaped head (9) of the second extension (5). . Joint prosthesis according to one of Claims 1 to 8, characterized in that the extensions (4,5) are made substantially centrally symmetrical with respect to their longitudinal axis (11) intersecting the bearing axis. Joint prosthesis according to claim 9, characterized in that the extensions (4,5) are provided on their outer side with preferably sharp-edged ribs (12) extending circumferentially in the direction of their longitudinal axis (11). Joint prosthesis according to claim 10, characterized in that the sharp-edged ribs (12) are lowered towards the free end of the extensions (4, 5). Joint prosthesis according to one of Claims 1 to 11, characterized in that the extensions (4, 5) are covered with a layer of biodegradable ceramics. Joint prosthesis according to one of Claims 1 to 12, characterized in that the extensions (4, 5) taper substantially towards their free end.