Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Having structure to restrict rotation of threaded – mating... – Comprising a thread lock
Patent
1993-02-09
1995-04-04
Wilson, Neill R.
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Having structure to restrict rotation of threaded, mating...
Comprising a thread lock
411263, 411413, 411426, 606 73, F16B 3504, F16B 3930, A61F 504
Patent
active
054031362
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a fastener, specifically a threaded fastener especially for orthopaedic purposes.
BACKGROUND OF THE INVENTION
A generic fastener, in the form of a bolt, is already known from DE-C2 2,807,364. This previously known fastener, conceived as a bone screw, consists of a threadless middle section, to which are attached, both in the upper, proximal part and the lower, distal part, threads with differing diameters, and pitches which differ from each other but are nonetheless constant in each part. Therefore prior to inserting the bone screw, it is necessary to drill holes of differing diameters with corresponding threads having different diameters but a constant pitch, in each of the bone fragments that are to be joined together. If a thread with a smaller pitch is employed for the proximal part of the shaft, then in screwing in this previously known bone screw, the effect is to bring the two bone fragments closer together and to correspondingly compress the fracture surfaces.
A disadvantage of this previously known fastener, designed according to the principle of two threads with differing pitch, is that it has a threadless midsection, and that the differing distal and proximal threads both have constant pitches. This allows merely a compression between two loose bone fragments, but does not permit a local intraosseous pressure generation which would be desirable for a whole range of applications.
With the previously known fastener, as well as with the other bone screws, what is lacking is a differentially acting force in the proximal area, so that in the proximal area again and again we encounter a zone of small bone thickness, which results in reduced stability of the implant.
SUMMARY OF THE INVENTION
In this regard the invention will afford a remedy. At the basis of the invention is the task of creating a threaded fastener which can be screwed into a material that is at least slightly elastically compressible, such as bone material or wood. The fastener can either make its own incision or be screwed into a pre-cut thread with a constant pitch. Thus, it can create, in bone material for example, a locally differentiated intraosseous pressure, which can be made to adapt to the biological requirements concerning force application and the local loading of the material. The invention solves the problem with a fastener that demonstrates the features of claim 1.
The advantages obtained from the invention are in essence as follows. Thanks to an invention-specific pitch (which preferably diminishes constantly) of the thread in the proximal direction, a locally differentiated intraosseous pressure generation takes place in bones. In accord with the well-known Wolff's Law, this leads to controlled bone growth along the loading axes.
The good bone thickness achieved thereby in this delicate area results in a stable integration of the implant.
BRIEF DESCRIPTION OF THE DRAWINGS
An application example for the invention, which elucidates its functional principle at the same time, is depicted in the drawings, in which:
FIG. 1 depicts a cross section through the fastener of the invention.
FIG. 2 depicts a cross section through the fastener according to FIG. 1. The left half of the picture shows the initial phase of screwing in, and the right half of the picture shows the concluding phase after screwing into the bone is complete.
FIG. 3 depicts a partial cross section of the fastener of the invention with the forces present as in FIG. 2.
FIG. 4 depicts a cross section through a fastener of the invention with a conical head section.
FIG. 5 depicts a cross section of the fastener of the invention in the form of a dental implant with a cone, in which the thread shows a differentiated, diminishing pitch toward the cone.
FIG. 6 depicts a partial cross section through the thread of the fastener in accord with FIG. 4.
FIG. 7 is a schematic view illustrating the thread of a fastener according to the invention in which the depth of the thread is reduced toward the rear end.
DETAI
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patent: 5120171 (1992-06-01), Lasner
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Synthes (U.S.A.)
Wilson Neill R.
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