Bone screw
A threaded fastener for embedment into bone is disclosed. Threads are formed on cylindrical stock. The thread pattern features upper and lower surfaces. The upper surface includes (in section) two facets which intersect to form a “V” shaped contour and a lower surface which is undercut below an upper facet nearest a root of the fastener thread. The fastener includes a self-tapping cutter at a distal extremity and a driving head at its proximal extremity. The cylindrical stock contemplates two variants: it may be hollow from the proximal end to the self-tapping cutter or from the self-tapping cutter to its distal end. The self-tapping cutter is configured to feed bone shards into the hollow.
1. A threaded fastener for embedment into bone, comprising:
an elongate, cylindrical shaft having a distal end for embedment and a proximal end having means to rotate said fastener for advancement and retraction,
a thread wound about said cylindrical shaft such that said thread spirals along at least a portion of said shaft, and space interposed between said spiral thread defines a cylindrical spiral,
said thread having means for interlocking with adjacent bone into which said fastener is embedded defined by:
a surface facing said proximal end defining an upper flank and formed from first and second facets, said first facet appearing substantially planar when viewed in section and emanating from said cylindrical shaft and sloping downwardly, towards said distal end, said first facet terminating at said second facet, said second facet appearing substantially planar when viewed in section and sloping upwardly, towards said proximal end, a juncture between said first and second facets appearing as a sharp crease when viewed in section, said first and second facets collectively approximating a “V” shaped profile when viewed in section;
a surface facing said distal end defining a lower flank and including a third facet emanating from said cylindrical shaft and declined towards said distal end such that an area below said third facet and bound by the third facet and a plane perpendicular to a long axis of said fastener and terminating at an outboard extremity of said third facet defines a material void constituting an undercut, and
a fourth facet on said lower flank and extending away from said third facet, not constituting an undercut.
2. The fastener of claim 1 wherein a self-tapping cutter disposed adjacent said distal end and further including a pilot disposed at a distal extremity of said fastener such that said self-tapping cutter is interposed between said pilot and said thread, said pilot constraining said fastener to track a predrilled pilot hole.
3. The fastener of claim 2 wherein at least one portion of said cylindrical shaft is hollow and open adjacent said self-tapping cutter to receive bone shards therein.