Pivotal bone anchor assembly and method for use thereof
View Patent ↗A pivotal bone anchor assembly is provided that includes a receiver, a shank, and a compression insert. The receiver can have a shank holding lower portion and an upper portion with a channel. The shank can have a head portion and an anchor portion attachable to bone. The compression insert can be positionable with the receiver, and can have an upper portion including at least one notch at least partially formed in an outer surface of the upper portion, and defining at least one resiliently deflectable upwardly-facing surface extending over or above the at least one notch. In one embodiment, the at least one resiliently deflectable upward facing surface being deflectable when the head portion of the shank and the compression insert are positioned in the receiver to provide a pre-lock friction fit in the assembly prior to securing a longitudinal connecting member in the channel with a closure.
1. A pivotal bone anchor assembly for securing a longitudinal connecting member to a bone of a patient via a closure, the bone anchor assembly comprising:
a receiver having a lower opening and a shank holding lower portion with a bottom surface, and an upper portion with a channel configured to receive the longitudinal connecting member and including a helically wound guide and advancement structure, the lower opening communicating with a receiver central bore centered on a receiver longitudinal axis, and the receiver central bore including an integral downwardly-facing engagement surface below the helically wound guide and advancement structure;
a shank having a head portion with an upper engagement surface and an anchor portion opposite the head portion configured for attachment to the bone, the head portion configured for being positionable within the shank holding lower portion of the receiver with the shank extending downwardly below the bottom surface; and
a compression insert positionable with the receiver having a central opening centered on an insert longitudinal axis, a lower portion with a downwardly-facing surface, and an upper portion including at least one notch at least partially formed in an outer surface of the upper portion of the compression insert and extending at least in part in a transverse direction relative to the insert longitudinal axis, and defining at least one resiliently deflectable upwardly-facing surface integral with the upper portion of the compression insert and extending over the at least one notch, the at least one resiliently deflectable upwardly-facing surface being deflectable in an axial direction relative to the insert longitudinal axis and engageable with the downwardly-facing engagement surface in the receiver central bore when the head portion of the shank and the compression insert are positioned in the receiver central bore, so as to provide an axially directed force for a pre-lock friction fit in the assembly prior to securing the longitudinal connecting member in the channel with the closure.
2. The pivotal bone anchor assembly of claim 1 , wherein the compression insert further comprises upwardly-facing concave surfaces configured to engage the longitudinal connecting member.
3. The pivotal bone anchor assembly of claim 1 , wherein the downwardly-facing surface of the lower portion of the compression insert directly engages the upper engagement surface of the head portion of the shank.
4. The pivotal bone anchor assembly of claim 1 , wherein the compression insert is twisted into position within the receiver central bore with the at least one resilient deflectable upwardly-facing surface coming into contact with the downwardly-facing engagement surface in the receiver central bore.
5. The pivotal bone anchor assembly of claim 1 , further comprising a separate retainer including an annular shape with an upper surface, a lower surface, and an interior cavity between the upper surface and the lower surface, the retainer being configured for capturing a portion of the head portion of the shank within the shank holding lower portion of the receiver.
6. The pivotal bone anchor assembly of claim 5 , wherein the retainer is positionable within in the shank holding lower portion of the receiver so as to provide for pivotal motion between the receiver and the shank.
7. The pivotal bone anchor assembly of claim 1 , wherein the shank holding lower portion and the upper portion of the receiver are integrally formed together.
8. A pivotal bone anchor assembly for securing a longitudinal connecting member to a bone of a patient via a fastener, the pivotal bone anchor assembly comprising:
a receiver having a lower opening, a bottom surface, a receiver central bore centered about a vertical centerline axis and in communication with the bottom surface of the receiver through the lower opening, and an upper portion defining a channel configured to receive the longitudinal connecting member and including a mating structure engageable with the fastener, the channel communicating with the receiver central bore, and the receiver central bore including at least one non-threaded downwardly-facing surface below the mating structure and a lower at least partially spherical seating surface adjacent the lower opening;
a shank having a head portion with a lower spherical engagement surface and an upper spherical engagement surface and an anchor portion opposite the head portion configured for attachment to the bone, the head portion configured for being positionable within a lower portion of the receiver central bore with the shank extending downwardly below the bottom surface and the lower spherical engagement surface pivotally engageable with the lower at least partially spherical seating surface; and
a compression insert having a central opening centered on an insert longitudinal axis, an upwardly-facing surface configured to receive the longitudinal connecting member, at least one notch at least partially formed in an outer surface of the compression insert and extending at least in part in a traverse direction relative to the insert longitudinal axis, and an engagement surface extending above the notch, the engagement surface being resiliently downwardly deflectable in an axial direction relative to the insert longitudinal axis;
wherein the compression insert is configured for axially biased overlapping engagement between the downwardly-facing surface of the receiver central bore and the engagement surface extending above the notch of the compression insert, so as to apply a downward frictional force on the head portion of the shank prior to locking the assembly with the fastener.
9. The pivotal bone anchor assembly of claim 8 , wherein the compression insert further comprises inwardly positioned concave surfaces configured to engage the longitudinal connecting member.
10. The pivotal bone anchor assembly of claim 8 , wherein at least one of the downwardly-facing surface of the receiver central bore or the engagement surface of the compression insert includes a sloped portion operable to provide a cam action that urges a lower surface of the compression insert against the upper spherical engagement surface of the head portion of the shank.
11. The pivotal bone anchor assembly of claim 8 , wherein the downwardly-facing surface of the receiver central bore is downwardly inclined.
12. The pivotal bone anchor assembly of claim 8 , wherein the downwardly-facing surface of the receiver central bore is perpendicular to the vertical centerline axis of the receiver.
13. The pivotal bone anchor assembly of claim 8 , further comprising a retainer including an annular shape with an upper surface, a lower surface, and an interior cavity between the upper surface and the lower surface, the interior cavity being configured for capturing a portion of the head portion of the shank within a lower portion of the receiver.
14. The pivotal bone anchor assembly of claim 13 , wherein the retainer is positionable within the lower portion of the receiver and configured to engage the lower spherical engagement surface on the head portion to provide for pivotal motion between the receiver and the shank.
15. The pivotal bone anchor assembly of claim 8 , wherein the mating structure is a helically wound guide and advancement structure.
16. The pivotal bone anchor assembly of claim 8 , wherein the shank includes a central axial bore extending an entire length thereof along a shank longitudinal axis, the central axial bore of the shank having a width that is less than a most narrow width of a central non-slip tool engaging aperture formed into the head portion thereof.
17. The pivotal one anchor assembly of claim 8 , wherein the upper portion of the receiver includes opposite outwardly facing recessed planar surfaces that are parallel with respect to each other and with the receiver longitudinal axis.
18. A method of using a bone anchor assembly configured to secure a longitudinal connecting member to a bone of a patient, the method comprising:
providing:
a receiver having an upper portion with a channel configured to receive the longitudinal connecting member, a shank holding lower portion including a lower opening, and a receiver central bore communicating with the lower opening and being centered on a receiver longitudinal axis and including a downwardly-facing engagement surface,
a shank having a head portion and an anchor portion opposite the head portion configured for attachment to the bone, and
a compression insert having a central opening centered on an insert longitudinal axis, a lower portion with a downwardly-facing surface, and an upper portion including at least one notch at least partially formed in an outer surface of the upper portion of the compression insert and extending at least in part transversely relative to the insert longitudinal axis, and defining at least one resiliently deflectable upwardly-facing surface integral with the upper portion of the compression insert and extending over the at least one notch, the at least one resiliently deflectable upwardly-facing surface being deflectable in an axial direction relative to the insert longitudinal axis;
positioning the compression insert in the receiver central bore, and loading the head portion of the shank into the shank holding lower portion of the receiver; and
engaging the at least one resiliently deflectable upwardly-facing surface of the compression insert with the downwardly-facing engagement surface of the receiver central bore to provide an axially directed force for a pre-lock friction fit prior to securing the longitudinal connecting member in the channel.
19. The method of claim 18 , further comprising capturing the head portion of the shank in the shank holding lower portion within the receiver central bore with a retainer including an upper surface, a lower surface, and an interior cavity, the retainer configured to capture a portion of the head portion of the shank in the shank holding lower portion of the receiver.
20. The method of claim 19 , further comprising engaging an outer spherical surface of the retainer with a spherical seating surface in the shank holding lower portion of the receiver to provide for pivotal movement of the receiver with respect to the shank.