Carpometacarpal thumb joint prosthesis

p0001The invention relates to a thumb saddle joint. It is intended to be after resection of the natural joint metacarpal I implanted between the trapezium and the Os.

p0002Artificial finger joints are known. For example, pointed to the finger joint described in DE 195 12 854 C. This has a first and a second anchoring stem which are settable in the finger bones. Between the anchoring stems of a hinge joint is arranged in the form of a ball joint. The first anchoring stem is connected to a ball cage of the hinge joint, in which a is provided with a stem ball joint is mounted, wherein the stem the ball cage passing through a provided therein slit and is in communication with the second anchoring stem. The slot in the ball cage expands from the point at which the stem passes through the ball cage in the extended position of the joint, to the point at which the stem passes through the ball cage in flexion of the joint, on continuously.

p0003With this finger joint, the target has been tracked to provide a finger joint which achieves a high accuracy of reproduction of the natural physiological movement of a natural finger joint. For this purpose, is responsible primarily the ever-widening slot.

p0004The known hinge can be as metacarpophalangeal joint or implanted between his knuckles. For implantation as carpometacarpal joint, the known joint is not suitable. Moreover, it is difficult due to the relative isolation of the function simple to manufacture in the case of advanced wear of the joint components again, that is to replace the worn components.

p0005Against this background, the object of the present invention to remedy this situation. So it is a carpometacarpal joint specify whose worn parts can be replaced in a simple manner, without the anchoring of the implant would be attacked in the bony material.

p0006This object is achieved by the inventive carpometacarpal joint, comprising<ul><li>into the trapezium (12) implantable first stem part (1),</li><li>a metacarpal in the Os 1 (13) implantable second stem part (2),</li><li>a handle connected to the second part (2) releasably connected receiving part (3) with a spherical cap-shaped recess (4), and</li><li>a stem with the first part (1) detachably connected to the joint ball (5) in the recess (4) of the receiving part (3) and rolls on bending of the joint therein,</li><li>wherein the base edge (11) of the recess (4) engages over the equator of the joint ball (5).</li></ul>

p0007The carpometacarpal joint of the invention is basically constructed as a hip replacement in kinematic reversal. Comparing the trapezium with the natural basin there is a kinematic reversal is that the trapezium, the joint ball is connected which engages into a recess in the receiving part, which is detachably connected to the second stem part. The second stem portion would correspond to the hip stem with a artificial hip joint. This measure is selected for reasons of space and allows for a greater range than when the pivot joint ball would be connected to the second stem part which would then engage in a recess in the first stem part.

p0008Luxationsneigungen be prevented in that the base edge of the recess engages over the equator of the joint ball. The receptacle part preferably consists of polyethylene, whereas the joint ball preferably made of a metal. The joint parts are thereby joined together by exerting a antiluxatorischen effect by the metal ball, the recess in the receiving part briefly spreads, which then, after the base edge is snapped over the equator of the sphere, this includes springs back due to the restoring forces in the initial position and so the ball safely ,

p0009Preferably, the handle parts are formed as hollow shafts with grid structured outer wall. This means that the hook parts are, figuratively speaking, is formed of a molded into a tube open mesh-like network. This design not only allows ingrowth of bone trabeculae, but a veritable Durchwachsen the surface of the implant with the bone trabeculae, thereby providing a very firm hold of the implant in the bone.

p0010The hook parts are left at a possible revision become necessary in the bone and only the wearing parts such as the receiving part and possibly the joint ball to be replaced and the joint assembled thereupon again.

p0011The stability of the seat of the first stem portion in the Trapezium is further increased, if advantageous to the Trapezium is to face side of the first handle portion is at least partially provided with an open-meshed three-dimensional network structure. In this network structure in and through it again can grow trabecular bones and so ensure a stable long-term fixation.

p0012It is particularly preferred, if on the joint ball, a conical connecting pin is formed, which sits with a molded in the first handle part conical clamping sleeve in a conical clamping fit. In case of revision, the conical clamping can be canceled and the ball joint to be replaced along with the pin with a new part.

p0013According to an advantageous development it is provided that the first stem portion is provided on its the Trapezium made facing side with at least one anti-rotation plate. This anti-rotation plate is driven into the Trapezium, serving the rotation lock.

p0014More preferably, the receiving part of polyethylene, high density polyethylene and indeed. It is connected to the second shaft part in a kind of snap connection, but it can be solved with the use of appropriate tools in revision again, so that this part can easily be replaced, leaving the stem parts in the bone.

p0015The invention is illustrated with reference to an embodiment according to the drawing figures. In the drawing:<dl id="dl0001"><dt>Fig. 1</dt><dd>schematically the location of the implanted carpometacarpal joint in the hand bones,</dd><dt>FIG. 2</dt><dd>an enlarged view of the implanted carpometacarpal joint, and</dd><dt>Fig. 3</dt><dd>exploded thumb saddle joint in a view (a), in an opposite (a) rotated by 90 ° position (b) and a schematic sectional view.</dd></dl>

p0016Hereinafter, like parts are provided with the same reference numerals.

p0017A first overview gives Fig. 1. Fig. 1 schematically shows a hand skeleton.

p0018Between the 12 and the trapezium metacarpal 13 is the carpometacarpal joint implanted. This essentially consists of a first stem part 1, which has been implanted in the trapezium 12, from the second post part 2, which is seated in the first metacarpal 13 and a receiving part and a ball joint, as is clear from the following considerations.

p0019Reference is made to FIG. 2. In addition to the already mentioned parts of a releasably connected to the first shaft part 1 the joint ball 5 is provided. With the second shaft part 2 is releasably connected to a receiving part 3. The ball joint 5 is situated in a dome-shaped recess in the receiving part 3, which in Fig. 3 (c) is apparent.

p0020The handle parts 1 and 2 are embodied here as a hollow stems with lattice-structured outer wall. 6 This allows turning on and grow through the hollow stem with bone material to long-term fixation.

p0021Further details are the representations of FIG. 3 (a) to refer to (c). Below is only a reference to the embodiments, the subject of the above were not already description.

p0022The Trapezium the 12 to be directed towards side of the first stem part 1 is here present fully equipped with an open-meshed, three-dimensional spatial network structure 7, into and through which trabecular bones to further promote the long-term stability waxing.

p0023In the illustrated embodiment, the first shaft part 1 is provided on the trapezium 12 is to face side with two anti-rotation shields 10th These are in the trapezium 12 driven (Fig. 2) so as to ensure a rotation safety of the stem part 1 in 12 Trapezium. Thus, the driving of the rotation plates 10 can be made easily as possible, instructing the rotary blades 10 is a knife-like contour (Fig. 3 (b)).

p0024In the schematic sectional view of FIG. 3 (c) the recess 4 in the receiving part 3 is clearly visible. The joint ball 5 comes in the recess 4 lie and roll upon exercise of the joint function in the receiving part 3 from. The dimensions are chosen so that the base edge 11 of the recess 4 engages over the equator of the ball joint 6, to the extent to exert a luxation.

p0025The receiving part 3 is connected to a type of snap closure and the complementarily shaped head of the second post part 2 that it can be removed in a revision case again and replaced with a new recording part. 3

p0026The interchangeability of the joint ball 5 is ensured by an integrally formed conical connecting pins 8 provided with a molded in the first shaft part 1 the conical clamping sleeve 9 (Fig. 3 (c)) sits in a conical clamping fit.