Removable gripping set screw
First Claim
1. A set screw comprising:
- a) a body having an axis of rotation and a radially outer threaded surface, an upper surface and a lower surface;
b) said body having a multi-diameter bore extending axially from said upper surface;
c) said bore having a first diameter upper portion adjacent said upper surface and forming a first circumferential edge with said upper surface;
said bore lower portion having a second diameter smaller than said first diameter and beginning at a shoulder spaced from said upper surface;
said bore lower portion having a second circumferential edge at the inner side of said shoulder; and
d) said first and second edges being sized and spaced so as to be adapted to simultaneously engage an outer surface of an easy out for purposes of removal.
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Accused Products
Abstract
A medical implant set screw having a base joined to a head by a breakaway region. The set screw has a longitudinally and axially extending bore that passes through the head and into the base. The bore has a stepdown within the base so as to produce a first circumferential edge. The base breaks away from the head at a predetermined torque during installation so as to expose an upper surface. The portion of the bore in the base intersecting with the upper surface forms a second edge that is spaced above the edge formed by the step and which has a somewhat greater diameter than the edge formed by the step. The two edges of the bore are sized, positioned and spaced so as to allow an easy-out to simultaneously engage both to improve gripping by the easy-out of the base during removal thereof. The set screw base also includes a threadform having a leading edge and a trailing edge that both intersect with a plane passing through an axis of rotation of the set screw so as to form intersections that both slope rearwardly from an inner edge to an outer edge thereof.
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Citations
9 Claims
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1. A set screw comprising:
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a) a body having an axis of rotation and a radially outer threaded surface, an upper surface and a lower surface;
b) said body having a multi-diameter bore extending axially from said upper surface;
c) said bore having a first diameter upper portion adjacent said upper surface and forming a first circumferential edge with said upper surface;
said bore lower portion having a second diameter smaller than said first diameter and beginning at a shoulder spaced from said upper surface;
said bore lower portion having a second circumferential edge at the inner side of said shoulder; and
d) said first and second edges being sized and spaced so as to be adapted to simultaneously engage an outer surface of an easy out for purposes of removal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
a) a head for gripping and driving during installation.
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3. The set screw according to claim 2 wherein:
a) said head is initially secured to said body by a breakaway region and said head separates from said bore upon the application of a preselected torque.
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4. The set screw according to claim 3 wherein:
a) said breakaway region is located at the position having the least cross-sectional area between said head and body in a plane perpendicular to an axis of rotation of said screw.
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5. The set screw according to claim 4 wherein:
a) said breakaway region and said first edge are both in a common plane perpendicular to said axis of rotation.
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6. The set screw according to claim 1 wherein:
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a) said threaded outer surface has a helically wound threadform thereon;
said set screw has a direction of normal advancement along said axis of rotation;
b) said threadform has a leading surface and a trailing surface; and
c) both said leading surface and said trailing surface slope rearwardly relative to said direction of advancement from inner edges to outer edges thereof.
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7. The set screw according to claim 6 in combination with an open headed bone screw having a pair of spaced arms with facing threaded surfaces that mate with the thread on said set screw during use such that said set screw closes between said arms.
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8. The set screw according to claim 1 in combination with a medical implant having a first element and a second element wherein said set screw is received in a threaded bore of said first element and has a bottom that abuts against said second element during use to lock the second element in fixed position relative to said first element.
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9. In a set screw having a body with a threaded outer surface and an axially aligned bore;
- the improvement comprising;
a) said bore having an upper first edge and a stepdown shoulder with a second edge;
said first and second edges being positioned and spaced to be adapted to both simultaneously engage an easy-out for removal.
- the improvement comprising;
Specification