Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1996-09-05
1999-12-07
Milano, Michael J.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
A61F 232
Patent
active
059975784
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a special process for the cutting production of threads, in which, at least in a part region of their extension, a more or less sliding influence on or correction of the thread profile is desired. Such a design can be advantageous for specific uses. Such a preferred use of the process is proposed.
2. Description of the Related Art
Threads are in widespread use as constructive elements in general mechanical engineering. Threads are usually made cylindrical, and in addition conical threads are also commonly used, for example for oil-field pipes. A large number of different thread profiles are known and are laid down in standards. The said profile on a workpiece is usually invariable, that is to say the thread profile at the thread start is identical to that at the thread end. Exceptions are conceivable, however, in which it could be advantageous to have a shape of the thread profile formed from thread groove and thread tooth which changes in a flowing manner at least in a part region of the thread, for example in order to make it easier to introduce a screw thread into a nut thread.
However, special geometrical conditions with respect to the thread prevail primarily in threads on curved surfaces, such as occur particularly in the case of screw-in artificial hip-joint sockets. Here, with regard to the outer shape of the shell body, for example hypospherical, hemispherical or hyperspherical, conico-spherical, parabolic, toroidal, elliptic or similar geometries are known. Metal-cutting production processes for the threads of screw sockets of this type result, sometimes necessarily, in distortions of the thread profile which vary in flowing manner and which in most cases are neither intended nor desired. Particularly the use of thread teeth having asymmetric flank angles, there is the phenomenon that, depending on the tilting direction of the resulting thread tooth, the tooth height from the socket equator towards the socket pole increases or decreases in a flowing manner, the result of this then being either much too large or virtually stunted thread teeth at the near-pole thread start. In the first case, extremely large thread teeth led to the fact that very high forces become necessary in order to screw in the socket or the implant cannot be screwed in until there is full bone contact. In the second case, only very feeble primary fixation is to be achieved. In both cases, there is the risk that the implant will work loose, and this would mean a further operation on the patient as a consequence.
SUMMARY OF THE INVENTION
The object was, therefore, to provide a hip-joint socket which can be produced by metal cutting and with a thread located on the curved outer surface and having asymmetric flank angles of the said tooth and a thread-tooth height adaptable along the thread extension, as well as a process for the production of such a special thread for this and other uses.
The object is achieved, according to the invention, in that the thread groove of a thread located on a curved outer surface is divided into at least two strip-like part surfaces of different pitch, whereas the width of the thread bottom, as measured in the radial projection, changes in a flowing manner along the extension of the thread, in such a way that the thread-tooth height which results in each case is adapted to the constructive preconditions. Furthermore, the invention makes available a process for the production of such a special thread.
Thus, it is proposed to machine the said groove along the same contour, in the region provided for the adaptation of the thread profile, at least in two production passes with at least two different pitches. For this purpose, the same tool or two or more different tools can optionally be used. If only one tool is to be employed, its two flanks must correspond to the shape of the two thread flanks. The invention here affords the possibility of choosing to use either a tool which corresponds in its profile to the profile o
REFERENCES:
patent: 4822367 (1989-04-01), Stuhmer
patent: 5336015 (1994-08-01), Stewart
patent: 5358533 (1994-10-01), Noiles
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