Apparatus for preventing screw backout in a bone plate fixation system
First Claim
1. A bone fixation apparatus comprising:
- a bone fixation plate having a bottom surface adapted to engage a portion of the bone being fixated, an opposite top surface and a bore defined therethrough;
a bone screw having an elongated shaft and an enlarged head portion engaging said bore at said top surface of said plate when said shaft extends therethrough, said shaft defining a first diameter non-threaded portion adjacent said head portion and bone engaging threads having a second larger diameter remote from said head portion; and
an annular collar substantially surrounding said non-threaded portion of said bone screw shaft, said collar having an initial inner diameter greater than said second diameter, said collar being formed of a material such that said inner diameter shrinks in response to a change in temperature thereof to a final diameter smaller than said second diameter to thereby trap said collar between said head portion and said second diameter bone engaging threads of said bone screw.
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Accused Products
Abstract
A system for internal fixation of bone includes a fixation plate having a number of bores therethrough, a corresponding number of screws each having an enlarged head portion and an elongated shaft portion defining bone engaging threads thereabout and a non-threaded portion between the head and threaded portions, and a corresponding number of screw anti-backout members each having a bore therethrough. The screw anti-backout members are positioned within the bores of the fixation plate and are initially sized to slidingly receive an elongated shaft therethrough. The screws are advanced through the plate bores and screw anti-backout members so that the fixation plate is secured to the underlying bone with the bores of the screw anti-backout members surrounding a non-threaded portion of the shafts. The system is thereafter heated sufficiently to shrink the bores of the screw anti-backout members, thereby trapping the non-threaded portions of the screw shafts between the fixation plate and the threaded portions.
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Citations
25 Claims
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1. A bone fixation apparatus comprising:
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a bone fixation plate having a bottom surface adapted to engage a portion of the bone being fixated, an opposite top surface and a bore defined therethrough; a bone screw having an elongated shaft and an enlarged head portion engaging said bore at said top surface of said plate when said shaft extends therethrough, said shaft defining a first diameter non-threaded portion adjacent said head portion and bone engaging threads having a second larger diameter remote from said head portion; and an annular collar substantially surrounding said non-threaded portion of said bone screw shaft, said collar having an initial inner diameter greater than said second diameter, said collar being formed of a material such that said inner diameter shrinks in response to a change in temperature thereof to a final diameter smaller than said second diameter to thereby trap said collar between said head portion and said second diameter bone engaging threads of said bone screw. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A fixation system for use with a fixation member having a top surface, a bottom surface and a bore defined therethrough, said fixation system comprising:
- a fastener having an elongated shaft, a headed portion engagable with the bore at the top surface of the fixation member when the shaft extends therethrough, a first diameter non-threaded portion adjacent said headed portion, and a second larger diameter threaded portion remote from said headed portion; and
an apparatus for preventing the fastener from backing out of said bore when said shaft extends therethrough including an annular collar having an initial inner diameter deformably sizable to slidingly receive the elongated shaft therethrough and an outer diameter sized to engage said bottom surface of said fixation member, said collar being formed of a material such that said inner diameter shrinks to a final diameter less than the second diameter threaded portion of the fastener in response to a change in temperature thereof to thereby trap said fixation member between said collar and the headed portion of the fastener. - View Dependent Claims (16, 17, 18, 19, 20)
- a fastener having an elongated shaft, a headed portion engagable with the bore at the top surface of the fixation member when the shaft extends therethrough, a first diameter non-threaded portion adjacent said headed portion, and a second larger diameter threaded portion remote from said headed portion; and
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21. A method for securing a fixation plate having a number of bores therethrough to a bone with a corresponding number of bone screws wherein each of the screws have a headed portion and an elongated shaft extending therefrom defining a first diameter non-threaded portion adjacent the head portion and a second larger diameter bone engaging threaded portion remote from the head portion, the method comprising the steps of:
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(1) forming a number of annular collars constructed of a shape memory alloy to have a final inner diameter less than the second diameter while the crystal structure of said alloy is in the austenite phase; (2) cooling said collars sufficiently so that the crystal structure of said alloy shifts to the martensite phase; (3) increasing the inner diameter of each of said annular collars while maintaining said collars in the martensite phase to permit passage therethrough of an elongated bone screw shaft; (4) mounting the fixation plate to the bone by advancing each of the number of bone screws through a corresponding fixation plate bore, through one of said annular collars and into the bone; and (5) heating said number of collars sufficiently to cause said inner diameters of said collars to shrink to their final diameters thereby trapping the number of collars between the head. portions and the threaded portions of the corresponding number of bone screws. - View Dependent Claims (22, 23, 24, 25)
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Specification