Pivotal bone anchor assembly with resiliently biased friction fit insert

1. A pivotal bone anchor assembly for securing a longitudinal connecting member to a bone of a patient via a closure, the pivotal bone anchor assembly comprising:

a receiver comprising a base portion defining a lower portion of a central bore centered about a vertical centerline axis and communicating with a bottom surface of the base portion through a bottom opening, and an integral upper portion defining a channel configured to receive the longitudinal connecting member, the central bore extending upward from the bottom opening through the channel to a top of the upper portion and including a helically wound guide and advance structure adjacent the top of the upper portion, an integral non-threaded downward-facing surface below the helically wound guide and advance structure, and a seating surface adjacent the bottom opening;

a shank comprising a head portion and an anchor portion opposite the head portion configured for attachment to the bone, the head portion being positionable within the lower portion of the central bore with the shank extending downwardly through the bottom opening;

a compression insert comprising a lower insert portion defining a center opening and an upper insert portion having at least one slot formed therein to define at least one resiliently downwardly compressible structure extending over the at least one slot, the compression insert being positionable within the central bore of the receiver with the at least one resiliently downwardly compressible structure being engageable with the downward-facing surface,

wherein when the head portion of the shank and the compression insert are positioned together in the central bore of the receiver, the engagement between the at least one resiliently downwardly compressible structure and the downward-facing surface is configured to provide an axially directed resilient biasing force for a pre-lock friction fit of the pivotal bone anchor assembly prior to securing the longitudinal connecting member in the open channel with the closure.

2. The pivotal bone anchor assembly of claim 1 , wherein the compression insert further comprises an upwardly-facing partial cylindrical surface alignable with the channel of the receiver and configured to receive the longitudinal connecting member.

3. The pivotal bone anchor assembly of claim 2 ,

wherein the upper insert portion further comprises a pair of insert arms extending upward from the lower insert portion to define the partial cylindrical surface therebetween, and

wherein the at least one slot further comprises a pair of notches formed into the pair of insert arms to define a pair of resiliently downwardly compressible structures opposite from one another across the center opening of the compression insert.

4. The pivotal bone anchor assembly of claim 2 , wherein the compression insert is configured for positioning into the central bore of the receiver in a first position and then for rotation about the vertical centerline axis toward a second position with the at least one resiliently downwardly compressible structure being rotated into engagement with the downward-facing surface of the central bore.

5. The pivotal bone anchor assembly of claim 4 , further comprising at least one inner pocket formed into the central bore of the receiver between the at least one downward facing surface and the seating surface and at least one protuberant interference structure projecting radially outward from a side of the compression insert,

wherein the at least one inner pocket is configured to receive the at least one protuberant interference structure upon rotation of the compression insert about the vertical centerline axis into the second position so as to inhibit further rotation of the compression insert with respect to the receiver in at least one direction.

6. The pivotal bone anchor assembly of claim 1 ,

wherein the head portion of the shank further comprises a spherical upper surface, and

wherein the lower insert portion further comprises a downwardly-facing spherical inner surface configured to directly engage the spherical upper surface of the head portion of the shank.

7. The pivotal bone anchor assembly of claim 1 , wherein the compression insert is downloadable into the central bore through the upper portion of the receiver.

8. The pivotal bone anchor assembly of claim 1 , wherein the head portion of the shank is uploadable into the lower portion of the central bore through the bottom opening of the receiver.

9. The pivotal bone anchor assembly of claim 1 and further comprising a retainer configured for positioning within the lower portion of the central bore, the retainer having a lower outer surface configured to engage the seating surface of the axial bore and an inner surface configured to capture and hold the head portion of the shank within the base portion of the receiver.

10. The pivotal bone anchor assembly of claim 9 , where the retainer is positionable within the lower portion of the central bore prior to the head portion of the shank.

11. The pivotal bone anchor assembly of claim 9 ,

wherein the seating surface of the central bore further comprises a spherical seating surface adjacent the bottom opening, and

wherein the lower outer surface of the retainer further comprises a spherical surface configured to pivotably engage with the spherical seating surface to provide for pivotal motion between the receiver and the shank.

12. The pivotal bone anchor assembly of claim 1 , wherein the channel of the receiver further comprises an open channel defined by a pair of upright arms extending upwardly from the base portion.

13. The pivotal bone anchor assembly of claim 12 and further comprising the longitudinal connecting member and the closure, wherein the closure is configured for positioning entirely within the open channel of the receiver above the longitudinal connecting member and in engagement with the helically wound guide and advance structure to apply a downward pressure to a top of the longitudinal connecting member, so as to secure the longitudinal connecting member to the bone of the patient.

14. A pivotal bone anchor assembly for securing a longitudinal connecting member to a bone of a patient via a closure, the pivotal bone anchor assembly comprising:

a receiver comprising a base portion defining a lower portion of a central bore centered on a vertical centerline axis and communicating with a bottom surface of the receiver through a bottom opening, and a pair of upstanding arms integral with the base portion defining a channel configured to receive the longitudinal connecting member, the central bore extending upward through the channel to tops of the upstanding arms and including a discontinuous helically wound thread form adjacent the tops of the upstanding arms and threadably engageable with the closure, at least one non-threaded downward-facing surface below the helically wound thread form, and a spherical seating surface adjacent the bottom opening;

a shank comprising a head portion with a lower spherical surface and an upper spherical surface and an anchor portion opposite the head portion configured for attachment to the bone, the head portion configured for positioning within the central bore with the lower spherical surface pivotally engageable with the spherical seating surface of the receiver and the shank extending downwardly through the bottom opening; and

a compression insert having a central opening, an upward facing surface configured to receive the longitudinal connecting member, a downward-facing spherical surface configured to directly engage the spherical upper surface of the head portion of the shank, and at least one horizontally extending notch formed into an upper portion of the compression insert to define at least one resiliently downwardly compressible structure extending over the at least one notch and having an upper engagement surface,

wherein the compression insert is positionable into the central bore of the receiver above the head portion of the shank, with the upper engagement surface of the at least one resiliently downwardly compressible structure in overlapping engagement with the at least one downward-facing surface of the central bore, so as to apply a resilient biasing frictional force onto the head portion of the shank prior to locking the assembly with the closure.

15. The pivotal bone anchor assembly of claim 14 ,

wherein the upper portion of the compression insert further comprises a pair of insert arms extending upward from the lower insert portion, and

wherein the upward facing surface of the compression insert further comprises an upwardly-open partial cylindrical surface extending between the pair of insert arms.

16. The pivotal bone anchor assembly of claim 15 , wherein the compression insert is configured for positioning into the central bore of the receiver in a first position and then for rotation about the vertical centerline axis toward a second position to align the partial cylindrical surface with the channel of the receiver, with the upper engagement surface of the at least one resiliently downwardly compressible structure being rotated into engagement with the downward-facing surface of the central bore.

17. The pivotal bone anchor assembly of claim 16 , further comprising at least one inner pocket formed into the central bore of the receiver between the at least one downward facing surface and the bottom opening and at least one protuberant interference structure projecting radially outward from a side of the compression insert,

wherein the at least one inner pocket is configured to receive the at least one protuberant interference structure upon rotation of the compression insert about the vertical centerline axis into the second position so as to inhibit further rotation of the compression insert with respect to the receiver in at least one direction.

18. The pivotal bone anchor assembly of claim 14 , wherein the compression insert is downloadable into the central bore through the channel of the receiver.

19. The pivotal bone anchor assembly of claim 14 , wherein the head portion of the shank is uploadable into the lower portion of the central bore through the bottom opening of the receiver.

20. The pivotal bone anchor assembly of claim 14 and further comprising a retainer configured for positioning within the lower portion of the central bore and for capturing the head portion of the shank within the base portion of the receiver.

21. The pivotal bone anchor assembly of claim 20 , where the retainer is positionable within the lower portion of the central bore prior to the head portion of the shank.

22. A method of assembling a pivotal bone anchor assembly configured to secure a longitudinal connecting member to a bone of a patient with a closure, the method comprising:

positioning a compression insert into a central bore of a receiver,

the receiver comprising a base portion defining a lower portion of the central bore centered about a vertical centerline axis and communicating with a bottom surface of the base portion through a bottom opening, and an upper portion defining a channel configured to receive the longitudinal connecting member, the central bore extending upward from the bottom opening through the channel to a top of the upper portion and including a helically wound guide and advance structure adjacent the top of the upper portion, an integral non-threaded downward-facing surface below the helically wound guide and advance structure, and a support surface adjacent the bottom opening,

the compression insert comprising a lower insert portion defining a center opening and an upper insert portion having at least one horizontal notch formed therein to define at least one resiliently downwardly compressible structure extending over the at least one notch, with the at least one resiliently downwardly compressible structure being engageable with the downward-facing surface in the central bore of the receiver; and

positioning a head portion of a shank into the lower portion of the central bore of the receiver, the shank comprising the head portion and an anchor portion opposite the head portion configured for attachment to the bone,

wherein when the head portion of the shank and the compression insert are positioned together in the central bore of the receiver, the engagement between the at least one resiliently downwardly compressible structure and the downward-facing surface is configured to provide an axially directed resilient biasing force for a pre-lock friction fit of the pivotal bone anchor assembly prior to securing the longitudinal connecting member in the channel with the closure.

23. The method of claim 22 ,

wherein the compression insert further comprises an upper partial cylindrical surface alignable with the channel of the receiver and configured to receive the longitudinal connecting member, and

wherein positioning the compression insert into the central bore of the receiver further comprises rotating the compression insert about the vertical centerline axis from a first position in which the upper partial cylindrical surface is non-aligned with the channel toward a second position in which the upper partial cylindrical surface is aligned with the channel, and with the at least one resiliently downwardly compressible structure being rotated into engagement with the downward-facing surface of the central bore.

24. The method of claim 23 , further comprising at least one inner pocket formed into the central bore of the receiver between the at least one downward: facing surface and the bottom opening and at least one protuberant interference structure projecting radially outward from a side of the compression insert,

wherein rotating the compression insert about the vertical centerline axis from the first position toward the second position further comprises rotating the at least one protuberant interference structure into the at least one inner pocket so as to inhibit further rotation of the compression insert with respect to the receiver in at least one direction.

25. The method of claim 22 , further comprising positioning a retainer into the lower portion of the central bore of the receiver, the retainer having a lower outer surface configured to engage the seating surface of the axial bore and an inner surface configured to capture and hold the head portion of the shank within the base portion of the receiver.

26. The method of claim 25 , further comprising positioning the retainer into the lower portion of the central bore prior to the head portion of the shank.

27. The method of claim 25 , wherein positioning the head portion of the shank into the lower portion of the central bore further comprises uploading the head portion of the shank through the bottom opening.