System for achieving selectable fixation in an orthopedic plate
View Patent ↗An orthopedic plate and fastener system is provided for fixation of bones which has an implant that can selectably be used to achieve fixed angle and variable locking of the fasteners, as well as non-locking of the fasteners. The system includes a variable locking assembly that includes a locking insert, having threads which mates with internal threads of a through opening in the implant. The system also provides for locking fixed angle fixation, and non-locking variable angle fixation, all of which can be used with the threaded holes of the plates. The locking insert is provided on a ring driver, which is similar to or acts as the drill guide used with the locking fasteners of the present. Thus, the invention also relates to a method of enabling surgery where the surgeon can select the mode of fixation of fasteners between variable axis locking, variable axis non-locking, and fixed angle locking fixation, all utilizing the same fastener opening within the implant.
1. A variable angle locking mechanism assembly for use in an orthopedic implant in bone, the orthopedic implant including a through opening having a longitudinal axis and defining an internal wall with threads, the variable angle locking mechanism comprising:
a locking insert having a body including external threads configured to mate with the threads of the through opening of the orthopedic implant, wherein the locking insert defines a fastener through hole that is further defined by an inner wall including longitudinal flat surfaces, wherein the locking insert further includes an annular flange extending radially outwardly about the through opening to form a shoulder that has an outer diameter greater than an outer diameter of said body, and is capable of mating against an external surface of the orthopedic implant; and
a fastener having a first portion for attachment in bone having a first thread and a head portion having external threads, wherein the first portion defines a fastener axis and a minor diameter and a major diameter of the external threads are tapered relative to the fastener axis, and wherein the major diameter tapers at a larger angle with respect to a proximal end of the fastener than the minor diameter tapers with respect to the proximal end of the fastener, wherein the flat surfaces of the locking insert comprise a material configured to deform relative to a material of the external threads of the head portion of the fastener to form internal threads in the locking insert as the fastener is inserted into the locking insert such that the fastener head is coupled to the locking insert in a locked relation to the implant by threads formed in the inner wall.
2. The variable angle locking mechanism assembly as set forth in claim 1 , wherein the orthopedic implant is a plate and the through opening in the plate can selectably accommodate either a fixed angle locking screw having a head with external threads that are capable of mating with the threads of the through opening of the plate or the locking insert.
3. The variable angle locking mechanism as set forth in claim 1 , wherein the locking insert is made of PEEK polymer and the fastener is made of a metal.
4. The variable angle locking mechanism assembly as set forth in claim 3 , wherein the fastener hole in the locking insert forms a torque driving recess.
5. The variable angle locking mechanism assembly as set forth in claim 1 , wherein the fastener hole in the locking insert has a cross-section that forms a polygon having from 4 to 10 sides.
6. The variable angle locking mechanism assembly as set forth in claim 1 , wherein the fastener hole of the locking insert is configured to receive a driver therein.
7. The variable angle locking mechanism assembly as set forth in claim 1 , wherein the difference in the taper angle of the major diameter to the minor diameter is from about 5° to about 15°.
8. The variable angle locking mechanism assembly as set forth in claim 6 , wherein the driver comprises a drill guide.
9. The variable locking mechanism assembly as set forth in claim 8 wherein the driver comprises a conical opening.
10. The variable angle locking mechanism assembly as set forth in claim 9 , wherein the conical opening defines a limit of an angle of the fastener when inserted in the orthopedic implant.
11. The orthopedic plate system of claim 1 , wherein the inner wall of the fastener hole is smooth.
12. The orthopedic plate system of claim 11 , wherein the fastener hole has a hexagonal cross-section.