Bone plate with form-fitting variable-angle locking hole
A bone plate includes at least one variable angle locking hole that is configured to threadedly mate with a variable angle locking screw oriented so as to define any angle among a range of angles with respect to a central axis of the VA locking hole at which a threaded head of the locking screw is configured to threadedly purchase with the bone plate in the variable angle locking hole.
1 . A system comprising:
a bone plate comprising:
an inner surface configured to face the underlying bone, and an outer surface opposite the inner surface; and
an internal surface that extends from the outer surface to the inner surface so as to define a hole that is oriented along a central hole axis, wherein the internal surface includes threading that is interrupted by a recess that is recessed with respect to the threading in a radially outward direction away from the central hole axis, and the threading extends along only three sides of the internal surface; and
a variable angle locking screw having a threaded head, the variable angle locking screw extending along a central screw axis
wherein the bone plate is configured to mate with the threaded head of the variable angle locking screw in the hole at any angle within a range of angles defined by the central screw axis and the central hole axis, such that the threaded head threadedly purchases with the threading at all three sides of the internal surface, wherein all angles within the range of angles are oblique to the central hole axis, and the range of angles comprises fifteen degrees.
2 . The system of claim 1 , wherein the three sides of threading comprise columns of thread segments that are spaced from each other by respective recesses.
3 . The system of claim 1 , wherein the recess is unthreaded.
4 . The system of claim 1 , wherein the recess defines a recessed surface, and the recess has a radial depth sufficient such that the recessed surface is recessed with respect to the internal surface along the radially outward direction.
5 . The system of claim 4 , wherein the recessed surface defines a curvature along a plane that is oriented normal to the central hole axis.
6 . The system of claim 5 , wherein the recessed surface comprises a circular path.
7 . The system of claim 5 , wherein the curvature is defined by a radius that is smaller than a radius from the central hole axis to the internal surface.
8 . The system as recited in claim 1 , wherein the internal surface defines a lead-in surface that is tapered radially inward from the outer surface to the threading.
9 . The system as recited in claim 8 , further comprising an undercut surface that is tapered radially outward as it extends from the threading to the inner surface.
10 . The system as recited in claim 9 , wherein the recess extends from the lead-in surface to the undercut surface.
11 . The system as recited in claim 1 , wherein the outer surface defines a perimeter of an opening to the hole, and the perimeter defines a circle.
12 . The system as recited in claim 1 , wherein the outer surface defines a perimeter of an opening to the hole, and the perimeter is non-circular.
13 . The system as recited in claim 12 , wherein the threading at the three sides defines a triangular profile in a plane that is perpendicular to the central hole axis.
14 . The system as recited in claim 1 , wherein the threading is tapered toward the central hole axis as it extends axially in a direction that is defined from the outer surface toward the inner surface.
15 . The system as recited in claim 14 , wherein the threading is tapered toward the central hole axis at an angle between approximately 5 degrees and approximately 30 degrees as the threading extends axially in the direction.
16 . The system as recited in claim 15 , wherein a recessed surface of the recess is tapered toward the central hole axis at the angle as the threading extends axially in the direction.
17 . The system as recited in claim 1 , wherein the range of angles is within a thirty degree cone that is centered about the central hole axis.
18 . The system as recited in claim 1 , wherein the thread angle of the thread segments of the bone plate and the thread angle of the threaded head of the variable angle locking screw define a ratio between 1.1:1 and approximately 1.8:1.
19 . The system as recited in claim 1 , wherein the hole is configured such that when the threading is mated with the threaded head of the variable angle screw at the angle, the threaded head is spaced from the recessed surface in a radially inward direction that is opposite the radially outward direction.
20 . The system as recited in claim 1 , wherein the outer surface defines a perimeter of an opening to the hole, and the perimeter defines a triangular profile.