Polyaxial bone anchor with pop-on shank, friction fit retainer and lateral alignment feature
A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in a one piece receiver, the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. A down-loadable compression insert and a friction fit split retainer are located in the receiver providing pop- or snap-on assembly of the shank with the receiver either prior to or after implantation of the shank into a vertebra. Laterally located, spaced crimping apertures in the receiver press receiver walls into engagement with the insert to prohibit rotation of the insert with respect to the receiver.
1 . In a bone anchor, the improvement comprising:
a) a shank having a body for fixation to a bone and an integral upper portion having a first curved surface;
b) a receiver having a base and a pair of opposed upstanding arms, the arms defining an open channel, the base defining a chamber and a lower opening, the chamber communicating with both the channel and the lower opening, each arm having a non-centrally located crimping aperture, each crimping aperture partially defined by a crimp wall;
c) an insert disposed within the receiver with each crimp wall being pressed into frictional engagement with the insert for substantially prohibiting rotation of the insert with respect to the receiver, each crimp wall located near one of a front and rear surface of the insert, the insert further having a second curved surface sized and shaped for frictional mating engagement with the shank upper portion first curved surface; and
d) a resilient open retainer having a base, the retainer captured within the chamber and expandable about at least a portion of the shank upper portion and wherein expansion-only locking engagement occurs between the shank upper portion and the retainer base and between the retainer base and the receiver.
2 . The improvement of claim 1 wherein each crimping aperture is a first crimping aperture and each receiver arm further includes a second crimping aperture spaced from the respective first crimping aperture, each second crimping aperture partially defined by a crimp wall for a total of four crimp walls being pressed against the insert to substantially prohibit rotation of the insert with respect to the receiver.
3 . The improvement of claim 1 wherein the insert has an outer face releasably frictionally locked against the receiver.
4 . The improvement of claim 1 wherein the receiver channel is a first channel and the insert has a second channel, the insert being top loaded into the receiver and then rotated into a position above the retainer with the second channel aligned with the first channel.
5 . The improvement of claim 1 wherein the retainer base has at least a first planar surface seated on a second planar surface partially defining the receiver chamber.
6 . The improvement of claim 1 wherein the retainer base has an outer non-tapered surface in engagement with a second surface partially defining the receiver chamber.
7 . The improvement of claim 1 wherein the retainer has a third inner curved surface in a friction fit with the shank upper portion first curved surface during temporary manipulation of the shank with respect to the receiver prior to the final expansion-only locking engagement, the shank upper portion being movable with respect to the retainer with some resistance when a force is applied to the shank to pivot the shank with respect to the receiver.
8 . In a bone anchor, the improvement comprising:
a) a shank having a body for fixation to a bone and an integral upper portion having a first curved surface;
b) a receiver having a base and a pair of opposed upstanding arms, the arms defining an open channel, the base defining a chamber and a lower opening, the chamber communicating with both the channel and the lower opening, each arm having a pair of spaced crimping apertures, each crimping aperture located near a perimeter of the respective arm, each crimping aperture partially defined by a crimp wall;
c) an insert disposed within the receiver with each crimp wall being pressed into frictional engagement with the insert substantially prohibiting rotation of the insert with respect to the receiver, the insert having a second curved surface sized and shaped for frictional mating engagement with the shank head; and
d) a resilient open retainer having a base, the retainer captured within the chamber and expandable about at least a portion of the shank upper portion, the retainer having a third curved surface in a friction fit with the shank upper portion during temporary manipulation of the shank with respect to the receiver, the shank upper portion being movable with respect to the retainer with some resistance when a force is applied to the shank to pivot the shank with respect to the receiver, and wherein the retainer is in an expanded state when final locking engagement occurs between the shank upper portion and the retainer base and between the retainer base and the receiver.
9 . The improvement of claim 8 wherein the retainer further comprises a pair of opposed outwardly extending resilient tabs and the retainer base has at least a first planar surface and each receiver arm has a lower centrally located through aperture and the receiver base has a second planar surface partially defining the receiver chamber and wherein after the shank head is received through the retainer base, the retainer base first planar surface is seated on the receiver second surface and the resilient tabs expand to a neutral state and are captured within the through apertures.
10 . The improvement of claim 8 wherein the insert has an outer projected portion releasably frictionally locked against the receiver.
11 . In a bone anchor, the improvement comprising:
a) a shank having a body for fixation to a bone and an integral upper portion having a substantially spherical surface;
b) a receiver having a base and a pair of opposed upstanding arms, the arms defining an open channel, each arm having an outer surface, the base defining a chamber and a lower opening, the chamber communicating with both the channel and the lower opening, each arm having a substantially centrally located through aperture and a pair of spaced lateral crimping apertures formed in the arm outer surface and located on either side of the through aperture, each crimping aperture defined in part by a crimp wall;
c) an insert disposed within the receiver with each crimp wall being pressed into frictional engagement with the insert allowing the insert to be moved vertically with some force but substantially prohibiting rotation of the insert with respect to the receiver, the insert having a curved surface portion sized and shaped for frictional mating engagement with the shank spherical surface, the insert further having a pair of outwardly extending arm portions, each arm portion partially extending through one of the centrally located receiver through apertures, the arm portions being engageable by manipulation tools located at the receiver arm outer surface for movement of the insert both downwardly into contact with the shank head and upwardly away from the shank head; and
d) a resilient open retainer having a base, the retainer captured within the chamber and expandable about at least a portion of the shank upper portion, the retainer having a second curved surface in a friction fit with the shank upper portion spherical surface during temporary manipulation of the shank with respect to the receiver, the shank upper portion being movable with respect to the retainer with some resistance when a force is applied to the shank to pivot the shank with respect to the receiver, and wherein the retainer is in an expanded state when final locking engagement occurs between the shank upper portion and the retainer base and between the retainer base and the receiver.
12 . The improvement of claim 11 wherein a shallow groove is formed in each receiver arm outer surface, each groove communicating with one of the through apertures, each groove extending from the respective aperture to a top surface of the receiver arm, each groove having a width for receiving a manipulation tool.
13 . The improvement of claim 11 wherein the insert has an outer face releasably frictionally locked against the receiver.
14 . The improvement of claim 11 wherein the insert is top loaded into the receiver and then rotated into a position above the retainer.
15 . The improvement of claim 11 wherein the retainer base has at least a first planar surface seated on a second planar surface partially defining the receiver chamber.
16 . The improvement of claim 11 wherein the retainer base has a first outer non-tapered surface in engagement with a second surface partially defining the receiver chamber.
17 . The improvement of claim 11 wherein the retainer further comprises a pair of opposed outwardly extending resilient tabs and the retainer base having at least a first planar surface and the receiver having a second planar surface partially defining the receiver chamber and a second pair of opposed apertures and wherein after the shank head is received through the retainer base, the retainer base first planar surface is seated on the receiver second surface and the resilient tabs expand to a neutral state and are captured within the second pair of receiver apertures.