Polyaxial bone screw with spherical capture, compression insert and alignment and retention structures
View Patent ↗A polyaxial bone screw assembly includes a receiver, a shank, an articulation structure for retaining the shank in the receiver and a compression insert for engagement with a longitudinal connecting member such as a rod. The articulation structure includes substantially spherical convex and concave surfaces that slidably engage both shank and receiver surfaces to provide compound articulation between the receiver and the shank. The receiver includes inwardly directed spring tabs engaging the insert and prohibiting rotation of the insert within the receiver.
1. A polyaxial bone screw assembly for receiving a spinal rod, the polyaxial screw assembly comprising:
a shank for anchoring the polyaxial bone screw assembly in bone;
a receiver comprising a first channel for receiving the spinal rod;
a retainer including a slit extending through a top surface and a bottom surface, wherein the slit is disposed at an oblique angle relative to the top surface and the bottom surface;
a compression insert disposable in the receiver, the compression insert having a rod seat for contacting the spinal rod and a mating surface that pivotally mates with the shank; and
a closure structure insertable into the receiver, the closure structure configured for urging the spinal rod into engagement with the compression insert thereby urging the compression insert into engagement with the shank,
wherein the polyaxial screw assembly has:
an unlocked position in which the receiver pivots with respect to the shank and the retainer pivots with respect to both the receiver and the shank, and
a locked position in which the receiver, retainer, and shank are locked in motion relative to each other.
2. The polyaxial bone screw assembly of claim 1 ,
wherein the receiver includes a pair of opposed receiver arms defining the first channel for receiving the spinal rod; and
wherein the compression insert includes a pair of opposed insert arms extending upwards and flanking the rod seat.
3. The polyaxial bone screw assembly of claim 2 , wherein the opposed insert arms define a second channel that aligns with the first channel to receive the spinal rod.
4. The polyaxial bone screw assembly of claim 3 , wherein the compression insert is top loadable into the receiver with the second channel misaligned from the first channel and then rotatable into a position with the second channel aligned with the first channel.
5. The polyaxial bone screw assembly of claim 1 , wherein the compression insert has at least one depression formed therein and the receiver has at least one resilient structure extending therefrom, the resilient structure biasing against the compression insert at the depression.
6. The polyaxial bone screw assembly of claim 5 , wherein the at least one resilient structure is a pair of opposed spring tabs integral with the receiver and extending toward a central axis of the receiver.
7. The polyaxial bone screw assembly of claim 1 , wherein the retainer includes a first end and a second end, the retainer being compressible and expandable with the first end and second end being movable toward and away from one another.
8. The polyaxial bone screw assembly of claim 1 , wherein the oblique angle relative to the top and bottom surfaces is configured to cause the surfaces of the retainer on either side of the slit to slide and ride up on one another during assembly with other components, thereby allowing for greater compression of the retainer without increasing the space between the surfaces of the retainer on either side of the slit when the retainer is in an uncompressed state.
9. The polyaxial bone screw assembly of claim 1 , wherein the shank is cannulated.
10. The polyaxial bone screw assembly of claim 1 , wherein when the compression insert is urged into frictional engagement with the shank, the shank is urged into frictional engagement with the retainer and the retainer is urged into frictional engagement with the receiver.
11. The polyaxial bone screw assembly of claim 10 ,
wherein the receiver includes a pair of opposed receiver arms defining the first channel for receiving the spinal rod, and
wherein the pair of opposed receiver arms include engagement features formed thereon to cooperatively engage the closure structure.
12. The polyaxial bone screw assembly of claim 11 , wherein the engagement features are situated on inner surfaces of the opposed receiver arms.
13. The polyaxial bone screw assembly of claim 1 ,
wherein the retainer comprises an upper surface, a lower surface, an outer surface, and an inner surface,
the outer surface being spherical and in articulating engagement with an inner spherical surface of the receiver, and
the inner surface being spherical up to the upper surface and in articulating engagement with a spherical outer surface of an upper portion of the shank.
14. The polyaxial bone screw assembly of claim 1 , wherein:
the receiver defines a curved seat in which a curved outer portion of the retainer is configured to pivot; and
the retainer defines an inner surface having a radius sized and shaped to cooperate with the shank to form a pivoting relationship between the retainer and the shank, thereby configuring the retainer to pivot with respect to both the receiver and the shank.
15. A polyaxial bone screw assembly for receiving a spinal rod, the polyaxial bone screw assembly comprising:
a shank for anchoring the polyaxial bone screw assembly in bone;
a receiver comprising a first channel for receiving the spinal rod;
a retainer, wherein the retainer defines an outer groove configured to provide clearance when the retainer is disposed within the receiver and when the retainer is expanded about a spherical surface the shank;
a compression insert disposable in the receiver, the compression insert having a rod seat for contacting the spinal rod and a mating surface that pivotally mates with the shank; and
a closure structure insertable into the receiver, the closure structure configured for urging the spinal rod into engagement with the compression insert thereby urging the compression insert into engagement with the shank,
wherein the polyaxial screw assembly has:
an unlocked position in which the receiver pivots with respect to the shank and the retainer pivots with respect to both the receiver and the shank, and
a locked position in which the receiver, retainer, and shank are locked in motion relative to each other.
16. The polyaxial bone screw assembly of claim 1 , wherein an outer portion of the retainer is spherical segmental in shape.
17. The polyaxial bone screw assembly of claim 15 , wherein:
the receiver defines a curved seat in which a curved outer portion of the retainer is configured to pivot; and
the retainer defines an inner surface having a radius sized and shaped to cooperate with the shank to form a pivoting relationship between the retainer and the shank, thereby configuring the retainer to pivot with respect to both the receiver and the shank.
18. The polyaxial bone screw assembly of claim 15 , wherein the retainer includes a first end and a second end, the retainer being compressible and expandable with the first end and second end being movable toward and away from one another.
19. A The polyaxial bone screw assembly for receiving a spinal rod, the polyaxial bone screw assembly comprising:
a shank for anchoring the polyaxial bone screw assembly in bone;
a receiver comprising a first channel for receiving the spinal rod;
a retainer, wherein the retainer defines: a planar annular top; a bottom surface; an inner neck; a curved surface between the planar annular top and the inner neck; and an inner chamfer running between the inner neck and the bottom surface;
a compression insert disposable in the receiver, the compression insert having a rod seat for contacting the spinal rod and a mating surface that pivotally mates with the shank; and
a closure structure insertable into the receiver, the closure structure configured for urging the spinal rod into engagement with the compression insert thereby urging the compression insert into engagement with the shank,
wherein the polyaxial screw assembly has:
an unlocked position in which the receiver pivots with respect to the shank and the retainer pivots with respect to both the receiver and the shank, and
a locked position in which the receiver, retainer, and shank are locked in motion relative to each other.
20. The polyaxial bone screw assembly of claim 19 , wherein:
the receiver defines a curved seat in which a curved outer portion of the retainer is configured to pivot; and
the retainer defines an inner surface having a radius sized and shaped to cooperate with the shank to form a pivoting relationship between the retainer and the shank, thereby configuring the retainer to pivot with respect to both the receiver and the shank.