Polyaxial bone screw with cam connection and lock and release insert
View Patent ↗A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in a receiver, the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. A retaining member for capturing the shank in the receiver includes a sloping surface for a frictional, press fit, cammed engagement with the shank. A compression insert having a resilient structure provides non-floppy positioning of the shank with respect to the receiver and also independent locking of the shank with respect to the receiver.
1. A medical implant comprising:
a) a receiver having a lower portion with a cavity and a lower opening communicating with the cavity and an upper portion with an upper opening communicating with a longitudinal connecting member receiving channel, the channel communicating with the cavity;
b) a bone screw shank having a head and a body for fixation to bone, the head having an engagement surface;
c) a retaining member for capturing the shank head within the receiver, the retaining member having an interior surface sized and shaped for a locking press-fit with respect to the shank, thus fixing engagement with the shank head engagement surface; and
d) a compression insert positioned in the receiver and operatively locking the shank head with respect to the receiver.
2. The implant of claim 1 wherein the shank and retaining member cooperate in such a manner that a partial rotation between the retaining member and the shank brings the shank and retaining member into the locking press-fit engagement.
3. The implant of claim 2 wherein the shank has a central axis and the partial rotation between the shank and retaining member is about the central axis.
4. The implant of claim 1 , wherein the shank head engagement surface is located on an outwardly extending projection, the projection frictionally mating with the retaining member interior surface.
5. The implant of claim 4 , wherein the projection is a plurality of projections.
6. The implant of claim 5 wherein the shank head has three outwardly extending projections.
7. The implant of claim 1 wherein the shank head has a lower spherical surface having a radius and the retaining member has an outer spherical surface, a radius of the outer spherical surface being the same as the radius of the shank head lower spherical surface, the outer spherical surface and the retaining member lower spherical surface being adjacent.
8. The implant of claim 7 wherein the shank head lower spherical surface terminates at a shelf, the retaining member being seated on the shelf.
9. The implant of claim 8 , wherein the shelf is a first shelf and the shank has a projection with a first inclined surface and the retaining member has a second shelf with a second inclined surface, the first and second inclined surfaces being in frictional engagement with a portion of the retaining member being located between the first shelf and the first inclined surface.
10. The implant of claim 1 wherein the compression insert has first and second positions with respect to the receiver, and wherein in the first position, the insert engages the upper portion of the receiver, the shank head being in movable frictional engagement with the insert, and in the second position, the insert frictionally engaging a lower inner surface of the receiver with the insert being in locked engagement with the shank head.
11. The implant of claim 10 wherein the shank head has a top surface and the insert exclusively engages the top surface and remains spaced from the retaining member in all articulations of the shank with respect to the receiver.
12. The implant of claim 1 , wherein the receiver channel is a first channel and the insert further comprises:
a) a pair of opposed arms forming a second channel, the arms being substantially non-resilient, the second channel in alignment with the first channel; and
b) an outer resilient structure located near and slightly spaced from a respective arm, the resilient structure being compressible toward the respective arm, the structure, when compressed, resiliently pressing against the receiver during manipulation of the shank with respect to the receiver with the shank head being in frictional, but movable engagement with the insert.
13. The implant of claim 12 wherein the resilient structure is locked against the receiver when the resilient structure is in a neutral to near neutral substantially non-compressed state and the insert is operatively frictionally locked against the shank.
14. The implant of claim 12 , wherein the compressible resilient structure and the respective arm form a slit.
15. The implant of claim 12 , wherein the outer compressible resilient structure and the respective arm form a through slit running from a top surface to a lower surface of the insert.
16. The implant of claim 12 , wherein the outer compressible resilient structure is located at a top surface of the insert.
17. The implant of claim 12 , having first and second compressible resilient structures, one structure located at each arm.
18. The implant of claim 1 , wherein the receiver includes two inner cylindrical walls of different diameters.
19. A polyaxial bone screw assembly comprising:
a) a shank having a body for fixation to a bone and an upper portion with a top surface, the upper portion having an engagement structure, the upper portion further having a lower partial spherical surface having a first radius;
b) a receiver defining an open channel and having a base with a seating surface partially defining a cavity, the open channel communicating with the cavity, the cavity communicating with an exterior of the base through an opening sized and shaped to receive the shank upper portion therethrough;
c) a retainer for capturing the shank within the receiver, the retainer being sized and shaped for press fit locking engagement with the shank engagement structure, the retainer having an external partial spherical surface having a second radius, the retainer partial spherical surface and the shank lower partial spherical surface sized and shaped for initial pivoting such that the first radius is substantially the same as the second radius; and
d) a compression insert positioned in the receiver, the insert operatively locking the shank head with respect to the receiver seating surface.
20. The assembly of claim 19 wherein the retainer has an interior structure configured to engage and fix against the shank engagement structure, the shank and retainer cooperating in such a manner that a partial rotation between the retainer and the shank brings the shank and retainer structures into locking engagement.
21. The assembly of claim 20 wherein the shank has a central axis and the partial rotation between the shank and retaining member is about the central axis.
22. The assembly of claim 19 wherein the retainer is a continuous closed ring.
23. The assembly of claim 19 , wherein the shank upper portion includes a lug for cammed engagement with the retainer.
24. A bone anchor comprising:
a) a receiver having a lower portion with an inner seating surface partially defining a cavity and a lower opening communicating with the cavity and an upper portion with an upper opening communicating with a longitudinal connecting member receiving channel, the channel communicating with the cavity;
b) a bone attachment structure having a head with a top surface, a first planar surface and a first partial spherical surface, the bone attachment structure also having a body for fixation to bone;
c) a retaining member having a second planar surface sized and shaped for press fit engagement with the first planar surface, such that when the first and second planar surfaces are engaged the retaining member is in fixed engagement with the bone attachment structure, the retaining member having a second partial spherical surface, the first and second spherical surfaces having substantially the same radius, both the first and second spherical surfaces receivable by the inner seating surface of the receiver; and
d) a compression insert positioned in the receiver and operatively locking the shank head with respect to the receiver.
25. The bone anchor of claim 24 wherein the bone attachment structure and the retaining member cooperate in such a manner that a partial rotation between the retaining member and the bone attachment structure results in a press fit engagement therebetween.
26. The bone anchor of claim 25 wherein the bone attachment structure has a central axis and the partial rotation between the bone attachment structure and the retaining member is about the central axis.
27. The bone anchor of claim 24 , wherein the receiver further comprises a spring tab resiliently pressing against the compression insert at an outer surface thereof, prohibiting rotation of the insert with respect to the receiver.
28. The bone anchor of claim 24 wherein the compression insert has a resilient outer surface sized and shaped to press against the receiver and temporarily hold the insert in frictional engagement with the head top surface for non-floppy positioning of the bone attachment structure with respect to the receiver.
29. The bone anchor of claim 24 wherein the compression insert has a resilient outer surface feature operatively frictionally locking against an inner surface of the receiver partially defining the cavity.
30. The bone anchor of claim 29 wherein the receiver inner surface is a cylindrical surface.
31. The retaining member of claim 24 being an integral one-piece member.
32. A bone anchor assembly comprising:
a) a receiver having a lower portion with a cavity and a lower opening communicating with the cavity and an upper portion with an upper opening communicating with a longitudinal connecting member receiving channel, the channel communicating with the cavity, a first receiver receiver downward facing seating surface partially defining the channel and a second facing surface defining the cavity;
b) a bone screw shank having a head and a body for fixation to bone, the head having an engagement surface for polyaxial motion within the receiver cavity;
c) a retaining member for capturing the shank head within the receiver; and
d) a compression insert positioned in the receiver, the compression insert having an integral resilient structure with a portion thereof partially spaced from the insert, the resilient structure being downwardly compressible toward the insert by the receiver first surface with the insert also pressing downwardly against the shank head during non-floppy articulation of the shank head with respect to the receiver and prior to locking of the assembly.
33. The bone anchor assembly of claim 32 , wherein the retaining member further comprises an interior surface sized and shaped for a locking press-fit, fixed engagement with the shank head engagement surface.
34. The bone anchor assembly of claim 32 , wherein the insert is loaded into receiver from the top of the receiver.
35. The bone anchor assembly of claim 32 , wherein the insert is loaded into receiver from the bottom of the receiver.
36. A bone anchor assembly comprising:
a) a receiver having a lower portion with a cavity and a lower opening communicating with the cavity and an upper portion with an upper opening communicating with a longitudinal connecting member receiving channel, the channel communicating with the cavity, a first receiver downward facing surface and a second receiver surface, the first and second receiver surfaces defining the cavity;
b) a bone screw shank having a head and a body for fixation to bone, the head having an engagement surface for polyaxial motion within the receiver cavity;
c) a compression insert positioned in the receiver, the compression insert having at least one integral resilient structure with a portion thereof partially spaced from the insert, the resilient structure being downwardly compressible toward the insert by the receiver first surface with the insert also pressing downwardly against the shank head during non-floppy articulation of the shank head with respect to the receiver and prior to locking of the assembly.
37. The bone anchor assembly of claim 36 , further comprising a retaining member for capturing the shank head within the receiver.
38. A bone anchor assembly comprising:
a) a receiver having a lower portion with a cavity and a lower opening communicating with the cavity and an upper portion with an upper opening communicating with a longitudinal connecting member receiving channel, the channel communicating with the cavity and a receiver downward facing surface for engaging a resilient portion of a compression insert;
b) a bone screw shank having a head and a body for fixation to bone, the head having polyaxial motion within the receiver cavity;
c) a retaining member for capturing the shank head within the receiver; and
d) the compression insert being positioned in the receiver, wherein the compression insert resilient portion is partially spaced from the insert, the resilient portion being downwardly compressible toward the insert when pressed against the receiver downward facing surface and wherein the insert also presses downwardly against the shank head so as to provide non-floppy articulation of the shank head with respect to the receiver prior to locking of the assembly.