Highly-versatile variable-angle bone plate system
A bone plate system for internal fixation of bone fractures includes a bone plate having a plurality of bone plate holes. The holes are constructed to receive either a non-locking, locking, or variable-angle locking bone screw. The holes have discrete columns of teeth or thread segments arranged around the inner surface of the hole for engaging threads on the heads of locking and variable-angle locking bone screws. Conventional locking bone screws engage the bone plate coaxially with the central axis of the bone plate hole. Variable-angle locking bone screws can engage the bone plate at a selectable angle within a range of selectable angles relative to the central axis of the bone plate hole. The head of the variable-angle locking screw is at least partially spherical, and the thread thereon has a profile that follows the arc-shaped radius of curvature of the spherical portion of the screwhead.
1. A bone screw that is elongate along a direction, the bone screw including a central axis that is parallel to the direction, the bone screw comprising:
a head including an outer surface, the head having a thread on the outer surface, the thread having a cross-sectional profile comprising a first plurality of peaks that each lie on a non-linear curve, a first plurality of troughs that each are positioned between adjacent ones of the first plurality of peaks, and a first plurality of flanks that each connect one of the first plurality of peaks to an adjacent one of the first plurality of troughs, the cross-sectional profile further comprising a second plurality of peaks that are opposite the first plurality of peaks with respect to the central axis, and a second plurality of troughs that are opposite the first plurality of troughs with respect to the central axis, each of the second plurality of troughs positioned between adjacent ones of the second plurality of peaks;
a threaded shaft that extends from the head along the central axis, the threaded shaft configured and dimensioned to engage a bone;
wherein the head defines a plurality of trough profile lines, each of the plurality of trough profile lines being a straight line is perpendicular to the central axis, intersects opposed ones of the first and second pluralities of troughs, and is parallel to others of the plurality of the trough profile lines, and
wherein adjacent ones of the first plurality of troughs are separated by respective thread trough-to-trough distances as measured along the direction, the respective thread trough-to-trough distances being configured to mate with a plurality of columns of protrusions arranged on an inner surface of a hole of a bone plate so as to lock the bone screw relative to the hole at a selectable angle within a range of angles at which the bone screw can mate and lock to the bone plate.
2. The bone screw of claim 1 , wherein the bone screw defines a thread pitch defined as the distance between adjacent ones of the first plurality of peaks as measured along the central axis.
3. The bone screw of claim 2 , wherein the thread pitch between a first pair of the first plurality of peaks is different than the thread pitch between a second pair of the first plurality of peaks.
4. The bone screw of claim 1 , wherein the non-linear curve defines a radius of curvature that has a center.
5. The bone screw of claim 4 , wherein the center lies on the central axis.
6. The bone screw of claim 4 , wherein the center is spaced a distance away from the central axis with respect to a direction perpendicular to the central axis, the distance being greater than zero.
7. The bone screw of claim 4 , wherein the non-linear curve forms a portion of a circle.
8. The bone screw of claim 1 , wherein the head is partially spherically-shaped.
9. The bone screw of claim 1 , wherein the non-linear curve is a first non-linear curve, and the first plurality of troughs lie on a second non-linear curve.
10. The bone screw of claim 9 , wherein the second non-linear curve forms a portion of a circle.
11. The bone screw of claim 9 , wherein the first and second non-linear curves are parallel.
12. The bone screw of claim 1 , wherein each of the plurality of trough profile lines normally intersects the one of the first plurality of troughs and the one of the second plurality of troughs.
13. The bone screw of claim 1 , wherein each of the plurality of trough profile lines bisects the opposed ones of the first and second pluralities of troughs.
14. The bone screw of claim 1 , wherein each of the first plurality of troughs is spaced from the central axis by a distance that is less than the distance the adjacent ones of the first plurality of peaks is spaced from the central axis.
15. A bone screw that is elongate along a direction, the bone screw comprising:
a head including an outer surface, the head having a thread on the outer surface, the thread having a cross-sectional profile comprising a plurality of peaks that each lie on a non-linear curve, a plurality of troughs each of which are positioned between adjacent ones of the plurality of peaks, and a plurality of flanks each of which connect one of the plurality of peaks to an adjacent one of the plurality of troughs; and
a threaded shaft that extends from the head along a central axis that is parallel to the direction, the threaded shaft configured and dimensioned to engage a bone;
wherein the plurality of troughs includes a first pair of adjacent troughs, a second pair of adjacent troughs, and a third pair of adjacent troughs, at least one of the troughs of the third pair of adjacent troughs positioned closer to the threaded shaft with respect to the direction than both of the troughs of the second pair of adjacent troughs are from the threaded shaft with respect to the direction, at least one of the troughs of the second pair of adjacent troughs positioned closer to the threaded shaft with respect to the direction than both of the troughs of the first pair of adjacent troughs are from the threaded shaft with respect to the direction,
wherein the bone screw defines a thread pitch defined as the offset between adjacent ones of the plurality of troughs as measured along the direction, and the thread pitch between the troughs of the first pair of adjacent troughs is less than the thread pitch between the troughs of the second pair of adjacent troughs, and the thread pitch between the troughs of the second pair of adjacent troughs is greater than the thread pitch between the troughs of the third pair of adjacent troughs.
16. The bone screw of claim 15 , wherein the non-linear curve defines a radius of curvature that has a center, and the center lies on the central axis.
17. The bone screw of claim 15 , wherein the non-linear curve defines a radius of curvature that has a center, and the center is spaced a distance away from the central axis with respect to a direction perpendicular to the central axis, the distance being greater than zero.
18. The bone screw of claim 15 , wherein the non-linear curve is a first non-linear curve, and the first plurality of troughs lie on a second non-linear curve.
19. The bone screw of claim 18 , wherein the first and second non-linear curves are parallel to each other.