Medical implant thread plug having a lower rod engaging extension
View Patent ↗A receiver assembly for securing an elongate rod to a bone anchor including a receiver and a threaded plug. The receiver including an upper portion defining a channel to receive the elongate rod, an interior surface having helically wound receiver thread, and an exterior surface having in some embodiments first and second horizontal curvate extending instrument engaging grooves. The threaded plug including a longitudinal axis, a lower surface having a protrusion, and an external side surface having a continuous helically wound closure thread to rotatably mate with the helically wound receiver thread. The continuous helically wound closure thread including a lower leading surface and an upper trailing surface, both in some embodiments extending perpendicular to the longitudinal axis, and a cylindrical outer crest surface extending parallel to the longitudinal axis. When the protrusion on the threaded plug engages the elongate rod, the threaded plug does not extend overtop a top surface of the receiver.
1. A medical implant assembly for securing an elongate rod to a bone anchor, the medical implant assembly comprising:
a receiver comprising a central axis, a base portion, an upper portion defining a channel configured to receive the elongate rod, a front face, a back face opposite the front face, and a top surface, the channel extending between the front face and the back face of the receiver and extending to the top surface defining a top of the receiver, the receiver further comprising an interior surface and an exterior surface opposite the interior surface, the interior surface having a helically wound receiver thread formed therein, the exterior surface having first and second horizontal curvate extending instrument engaging grooves (HCEIEG) formed therein and being proximate the top surface of the receiver, each of the front face and back face including a planar surface extending parallel with respect to each other and the central axis, and the exterior surface including first and second outward-facing planar surfaces extending parallel with respect to each other and being positioned below the first and second HCEIEG, respectively, the first HCEIEG including a first outer end opening onto the planar surface on the front face of the receiver, the second HCEIEG including a second outer end opening onto the planar surface on the back face of the receiver; and
a threaded plug configured to be positioned within the channel to secure the elongate rod to the receiver in a locked configuration, the threaded plug comprising a cylindrical body, a longitudinal axis, a first outer diameter, a planar top surface including a central internal drive structure with a tool abutment surface defined therein, a through-bore centered around the longitudinal axis and extending below the tool abutment surface, a lower surface including a protrusion centrally positioned around the longitudinal axis and having a second outer diameter that is less than the first outer diameter, an external side surface on the cylindrical body having a continuous helically wound closure thread configured to rotatably mate with the helically wound receiver thread, the continuous helically wound closure thread including a lower leading surface, an upper trailing surface opposite the lower leading surface, and a cylindrical outer crest surface positioned between the upper trailing surface and the lower leading surface, the cylindrical outer crest surface extending parallel to the longitudinal axis, and the lower leading surface and the upper trailing surface both extending perpendicular to the longitudinal axis,
wherein, when the medical implant assembly is in a locked configuration via the threaded plug: the protrusion on the threaded plug is configured to engage the elongate rod positioned in the channel of the receiver; and the threaded plug does not extend overtop of any portion of the top surface defining the top of the receiver.
2. The medical implant assembly of claim 1 , wherein the lower surface on the protrusion includes an annular outer edge.
3. The medical implant assembly of claim 1 , wherein the protrusion includes a lower circumferential recess in communication with the through-bore.
4. The medical implant assembly of claim 1 , wherein the receiver includes breakoff extensions with internal helically wound threads.
5. The medical implant assembly of claim 1 , wherein the receiver includes a lower pressure insert having a rod-receiving channel with upright arms that flare outwardly near an upper end thereof and a lower end configured to engage a head of the bone anchor positionable in the base portion of the receiver when in the locked configuration.
6. A method of securing an elongate rod to a bone anchor using a medical implant assembly, the method further comprising:
providing the medical implant assembly of claim 1 ; and
positioning the threaded plug within the channel of the upper portion of the receiver, at least a portion of the bone anchor positioned within the receiver; and
advancing the threaded plug within the channel of the upper portion of the receiver to secure the elongate rod to the receiver in the locked configuration.
7. A medical implant assembly for securing an elongate rod to a bone anchor, the medical implant assembly comprising:
a receiver having an upper portion with an inner surface at least partially configured as a helically wound thread extending up to a top surface of the receiver, and a channel formed in the upper portion of the receiver and configured to receive the elongate rod; and
a plug being threaded and configured to be positioned within the upper portion, the plug having an axis of rotation, a continuously helically wound thread form, and a bottom surface with an annular outer edge, the bottom surface configured to engage the elongate rod, the continuously helically wound thread form having a start structure with an upper surface extending between a root and a crest of the continuously helically wound thread form, the start structure having a leading face extending below the upper surface to a lower beveled surface of the start structure extending up to the leading face, the leading face including a partial concave surface adjacent the root and a partial convex surface adjacent the crest, the partial concave and partial convex surfaces each defined by a radius of curvature that is substantially equal with respect to each other and less than a radius of curvature for the crest, the lower beveled surface of the start structure adjacent, above and spaced apart from the annular outer edge of the bottom surface so as to not be connected with the annular outer edge thereof, the bottom surface being on a centralized lower extending portion of the plug spaced below the lower beveled surface of the starting structure.
8. The medical implant assembly of claim 7 , wherein the partial concave surface blends with the partial convex surface at a location that is substantially midway on the leading face between the root and the crest of the continuously helically wound thread form.
9. The medical implant assembly of claim 8 , wherein at least a partial planar surface portion is located substantially midway on the leading face of the start structure so as to tangentially blend the partial concave surface with the partial concave convex surface therebetween.
10. The medical implant assembly of claim 7 , wherein the start structure is a first start structure disposed at a diametrically opposite on the plug from a second start structure so as to have the first start structure and the second start structure positioned 180 degrees apart from each other.