US-20260123964-A1 - MEDICAL IMPLANT THREADED PLUG HAVING A LEADING FACE START STRUCTURE WITH CONCAVE AND CONVEX SURFACES

US20260123964A1US 20260123964 A1US20260123964 A1US 20260123964A1US-20260123964-A1

Abstract

A medical implant assembly including a receiver and a fastener. The receiver having helically wound thread form. The fastener having an axis of rotation and a continuously helically wound thread form. The continuously helically wound thread form having a start structure and an upper loading 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 loading surface. The leading face including a partial concave and convex surface extending between the root and the crest. The start structure being configured as a single lead start structure and a dual lead start structure.

Inventors

Roger P. Jackson
James L. Surber

Assignees

Roger P. Jackson

Dates

Publication Date: 20260507
Application Date: 20251231

Claims (20)

1 . A medical implant assembly comprising: a receiver having an upper portion with an inner surface at least partially configured as a helically wound thread form extending up towards a top surface of the receiver, and a channel configured to be attached to an elongate member; and a plug being threaded and configured to be positioned within the upper portion of the receiver, the plug having an axis of rotation, a continuously helically wound thread form, and a bottom surface with an annular outer edge, 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 surface of the start structure, the leading face extending between the root and the crest and having a concave surface portion adjacent the root and a convex surface portion adjacent the crest, the lower surface of the start structure being spaced apart and above the annular outer edge of the bottom surface of the plug so as to not be connected with the annular outer edge thereof.
2 . The medical implant assembly of claim 1 , wherein the plug comprises an internal drive socket.
3 . The medical implant assembly of claim 1 , wherein the start structure is a first start structure disposed at a diametrically opposite location on the plug from a second start structure.
4 . The medical implant assembly of claim 1 , wherein the upper portion of the receiver includes a first arm and a second arm spaced apart from each other by the channel, the helically wound thread form of the receiver being a discontinuously helically wound thread form and formed on the first and second arms, the top surface of the receiver being formed on the first arm and the second arm.
5 . The medical implant assembly of claim 1 , wherein the leading face of the start structure includes at least a partial planar surface.
6 . The medical implant assembly of claim 4 , wherein the first arm includes a first breakoff extension coupled to the top surface of the first arm, and the second arm includes a second breakoff extension coupled to the top surface of the second arm, each of the first and second breakoff extensions including the inner surface having the discontinuously helically wound thread form, the discontinuously helically wound thread form of the first breakoff extension configured to cooperate with the discontinuously helically wound thread form of the first arm, and the discontinuously helically wound thread form of the second breakoff extension configured to cooperate with the discontinuously helically wound thread form of the second arm to rotatably transfer the plug therebetween prior to the first and second breakoff extensions being separated from the first and second arms, respectively.
7 . The medical implant assembly of claim 6 , wherein a first outer radiused notch is located at a convergence of the first breakoff extension and the first arm at the top surface thereof, and a second outer radiused notch is located at a convergence of the second breakoff extension and the second arm at the top surface thereof, the first outer radiused notch being located opposite a first inner radiused recess, and the second outer radiused notch being located opposite a second inner radiused recess.
8 . The medical implant assembly of claim 1 , wherein the lower surface of the start structure includes a bottom beveled surface.
9 . The medical implant assembly of claim 1 , wherein the upper surface of the continuously helically wound thread form of the plug slopes rearward from the root towards the crest relative to a line drawn perpendicular to the axis of rotation of the plug and a tangent line drawn along the upper surface.
10 . The medical implant assembly of claim 1 , wherein the lower surface of the continuously helically wound thread form of the plug slopes rearward from the root towards the crest relative to a line drawn perpendicular to the axis of rotation of the plug and a tangent line drawn along the lower surface.
11 . The medical implant assembly of claim 1 , wherein the plug is a breakoff plug.
12 . A medical implant assembly comprising: a receiver having an upper portion with an inner surface at least partially configured as a helically wound thread form extending up towards a top surface of the receiver, and a channel configured to be attached to an elongate member; and a plug being threaded and configured to be positioned within the upper portion of the receiver, the plug having an axis of rotation, a continuously helically wound thread form, and a bottom-most surface configured to be engaged by the elongate member, the bottom-most surface including an annular outer edge, the continuously helically wound thread form configured with a terminal start structure having an upper surface extending between a root and a crest of the continuously helically wound thread form, and a leading face extending below the upper surface, the leading face having a curvate and concave surface portion adjacent the root and a convex surface portion adjacent the crest, the leading face being spaced apart and above the annular outer edge of the bottom-most surface of the plug so as to not be connected with the annular outer edge thereof.
13 . The medical implant assembly of claim 12 , wherein the plug further comprises a central opening extends entirely through the plug.
14 . The medical implant assembly of claim 12 , wherein the terminal start structure is a first start structure disposed at a diametrically opposite location on the plug from a second start structure.
15 . The medical implant assembly of claim 12 , wherein the upper portion of the receiver includes a first arm and a second arm spaced apart from each other by the channel, the helically wound thread form of the receiver being discontinuous and formed on the first and second arms, the top surface of the receiver being formed on the first arm and the second arm.
16 . The medical implant assembly of claim 12 , wherein the leading face of the terminal start structure includes at least a partial planar surface.
17 . The medical implant assembly of claim 15 , wherein the first arm includes a first breakoff extension coupled to the top surface of the first arm, and the second arm includes a second breakoff extension coupled to the top surface of the second arm, each of the first and second breakoff extensions including an inner surface having a discontinuously helically wound thread form, the discontinuously helically wound thread form of the first breakoff extension configured to cooperate with the discontinuously helically wound thread form of the first arm, and the discontinuously helically wound thread form of the second breakoff extension configured to cooperate with the discontinuously helically wound thread form of the second arm to rotatably transfer the plug therebetween prior to the first and second breakoff extensions being separated from the first and second arms, respectively.
18 . The medical implant assembly of claim 17 , wherein a first outer radiused notch is located at a convergence of the first breakoff extension and the first arm at the top surface thereof, and a second outer radiused notch is located at a convergence of the second breakoff extension and the second arm at the top surface thereof, the first outer radiused notch being located opposite a first inner radiused recess, and the second outer radiused notch being located opposite a second inner radiused recess.
19 . The medical implant assembly of claim 12 , wherein a lower surface of the terminal start structure includes a bottom beveled surface.
20 . The medical implant assembly of claim 12 , wherein the upper surface of the continuously helically wound thread form of the plug extends perpendicularly relative to the axis of rotation of the plug.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of U.S. patent application Ser. No. 19/377,497, filed Nov. 3, 2025, which is a continuation of U.S. patent application Ser. No. 18/980,342, filed Dec. 13, 2024, now U.S. Pat. No. 12,458,409, which is a continuation of U.S. patent application Ser. No. 18/188,855, filed Mar. 23, 2023, now U.S. Pat. No. 12,251,136, which is a continuation of U.S. patent application Ser. No. 17/808,438, filed Jun. 23, 2022, now U.S. Pat. No. 11,911,075, which is a continuation of U.S. patent application Ser. No. 17/476,652, filed Sep. 16, 2021, now U.S. Pat. No. 11,399,873, which is a continuation of U.S. patent application Ser. No. 17/123,499, filed Dec. 16, 2020, now U.S. Pat. No. 11,129,646, which is a continuation of U.S. patent application Ser. No. 16/779,304, filed Jan. 31, 2020, now U.S. Pat. No. 10,898,233, which is a continuation of U.S. patent application Ser. No. 15/964,502, filed Apr. 27, 2018, now U.S. Pat. No. 10,548,641, which is a continuation of U.S. patent application Ser. No. 15/469,076, filed Mar. 24, 2017, now U.S. Pat. No. 9,956,004, which is a continuation of U.S. patent application Ser. No. 14/566,356, filed Dec. 10, 2014, now U.S. Pat. No. 9,636,146, which is a continuation of U.S. patent application Ser. No. 13/694,849, filed Jan. 10, 2013, now U.S. Pat. No. 8,911,479, which claims the benefit of U.S. Provisional Application No. 61/631,746, filed Jan. 10, 2012 and U.S. Provisional Application No. 61/634,361, filed Feb. 28, 2012, all of which are incorporated by reference in their entireties herein and for all purposes. BACKGROUND OF THE INVENTION The present invention is directed to structure for joining together parts of a medical implant, in particular to closure mechanisms for use with open bone anchors in spinal surgery, and in some embodiments thereof, for use with spinal bone anchors such as polyaxial screws. Bone anchors, such as bone screws and hooks are utilized in many types of spinal surgery in order to secure various implants to vertebrae along the spinal column for the purpose of stabilizing and/or adjusting spinal alignment. For example, the most common mechanism for providing vertebral support is to implant bone screws into certain bones which then in turn support a rod or are supported by the rod. Although both closed-ended and open-ended bone anchors are known, open-ended anchors are particularly well suited for connections to longitudinal connecting members such as hard, soft or deformable rods, dynamic or elastic connectors and connector arms, because such rods or other connector members do not need to be passed through a closed bore, but rather can be laid or urged into an open channel within a receiver or head of such a bone anchor. Generally, the anchors must be inserted into the bone as an integral unit or a preassembled unit, in the form of a shank or hook and connected pivotal receiver. In some instances, a portion of such a preassembled unit, such as a shank of a polyaxial bone screw assembly, may be independently implanted into bone, followed by push- or pop-on assembly of a receiver portion of the unit. Typical open-ended bone screws include a threaded shank with a head or receiver having a pair of parallel projecting branches or arms which form a yoke with a U-shaped slot or channel to receive a rod or other longitudinal connecting member. Hooks and other types of connectors, as are used in spinal fixation techniques, may also include similar open ends for receiving rods or portions of other fixation and stabilization structure. The open-ended head or rod receiver portion of such implants typically includes a pair of spaced arms forming a channel closed by a closure member after the rod or other longitudinal connecting member is placed in the channel. Known closures include slide-on types, twist-on varieties that are rotated ninety degrees to a locked in position, and a variety of single start helically wound guide and advancement structures including, for example, thread forms having v-thread, reverse-angle buttress or square thread forms, to name a few, as well as other non-threadlike helically wound forms. Sometimes threaded plugs are utilized with outer threaded nuts to prevent splaying of the receiver arms. As indicated above, the force required to press a closure structure down onto a rod or other connector located between arms of an open implant is considerable. Even though a head or receiver portion of an open polyaxial bone anchor may be pivoted in a direction to make it easier for the arms of the open implant to receive a rod or other connector, spinal misalignments, irregularities and the placement of other surgical tools make it difficult to place the rod or other connector between the arms of the implant while a closure structure is mated with the open implant as well as used to push the rod or other connector downwardly into the implant. For example, when the closure is a cylindrical pl