Method of assembling a bottom-loaded pivotal bone anchor assembly with compression insert and two-part shank retainer
View Patent ↗A method of assembling a pivotal bone anchor assembly includes positioning an insert and a two-part retainer into a central bore of a receiver having a seating surface proximate a bottom opening, a closure mating structure proximate a top opening, and integral engagement structures protruding inwardly between the closure mating structure and the seating surface. The insert includes an upper surface for engaging a rod and side surfaces engageable with the integral engagement structures to restrict motion of the insert with the central bore. The retainer includes two separable retainer parts together defining outer retainer surfaces engageable with the seating surface and inner retainer surfaces. The method also includes uploading a shank head of a shank through the bottom opening and into the retainer, with the two retainer parts operable to separate and then move back together to capture the shank head, after which a downwardly-directed force is configured to drive the outer retainer surfaces into frictional engagement with the seating surface to lock the angular orientation of the shank with respect to the receiver.
1. A method of assembling a pivotal bone anchor assembly configured to secure an elongate rod to a bone of a patient via a closure, the method comprising:
positioning an insert and a two-part retainer into an axial bore of a receiver,
the receiver comprising a base defining a cavity centered about a vertical axis and communicating with a bottom surface of the base through a bottom opening, and a pair of upright arms extending upward from the base defining an open channel configured to receive the elongate rod, the cavity including a seating surface proximate the bottom opening and extending upward through the open channel to tops of the upright arms to define the axial bore, the axial bore including a discontinuous closure mating structure proximate the tops of the upright arms and integrally formed opposite engagement structures, where prior to the positioning of the insert into the axial bore, the opposite engagement structures protrude inwardly between the closure mating structure and the seating surface,
the insert comprising an upper curvate surface configured to engage the elongate rod and outer side surfaces configured to engage the opposite engagement structures of the axial bore to restrict the motion of the insert relative to the receiver, and
the two-part retainer comprising two separable retainer parts together defining an inner retainer surface, each retainer part having an outer retainer surface engageable with the seating surface; and
uploading an upper capture portion of a bone anchor through the bottom opening and into the two-part retainer that has been pre-loaded into the cavity, the bone anchor comprising the upper capture portion having an outer capture surface complementary with the inner retainer surface and a lower attachment portion opposite the upper capture portion configured for attachment to the bone,
wherein the two retainer parts are configured to at least partially move away from each other and then back toward each other upon the uploading of the upper capture portion into the cavity to operably engage and capture the upper capture portion within the receiver with the bone anchor extending downwardly through the bottom opening, and
wherein a force directed downwardly onto the two-part retainer in operable engagement with the upper capture portion is configured to drive the outer retainer surfaces of the retainer parts into frictional engagement with the seating surface of the cavity to lock the angular orientation of the bone anchor with respect to the receiver.
2. The method of claim 1 , wherein the bone anchor is movable polyaxially with respect to the receiver prior to application of the downwardly directed force.
3. The method of claim 1 , wherein positioning the insert into the axial bore of the receiver further comprises downloading the insert through an upper opening.
4. The method of claim 1 , wherein positioning the insert into the axial bore of the receiver further comprises uploading the insert through the bottom opening.
5. The method of claim 1 , wherein the outer side surfaces of the insert further include elongate grooves configured to engage the opposite engagement structures of the axial bore to restrict the motion of the insert relative to the receiver.
6. The method of claim 1 , wherein the upper capture portion of the bone anchor further comprises an external spherical surface.
7. The method of claim 6 , wherein the external spherical surface of the upper capture portion is engageable by a lower spherical surface of the insert.
8. The method of claim 1 , wherein the seating surface of the cavity decreases in diameter toward the bottom opening.
9. The method of claim 8 , wherein each retainer part has a top surface, a bottom surface, and at least a lower portion of the outer retainer surface that decreases in diameter toward the bottom surface.
10. The method of claim 1 , wherein the at least partial movement of the two retainer parts away from each other further comprises a pivoting and moving apart of the two retainer parts with respect to each other within the cavity so as to capture the upper capture portion of the bone anchor therein.
11. The method of claim 1 , wherein each retainer part further comprises end walls in spaced parallel relation with the respective end walls of the other retainer part when the two-part retainer is in operable engagement with the bone anchor upper capture portion within the cavity of the receiver.
12. A method of assembling a pivotal bone anchor assembly configured to secure an elongate rod to a bone of a patient via a closure, the method comprising:
uploading an insert and a two-part retainer into an axial bore of a receiver,
the receiver comprising a base defining a cavity centered about a vertical axis and communicating with a bottom surface of the base through a bottom opening, and a pair of upright arms extending upward from the base defining an open channel configured to receive the elongate rod, the cavity including a seating surface proximate the bottom opening and extending upward through the open channel to tops of the upright arms to define the axial bore, the axial bore including a discontinuous closure mating structure integrally formed therein proximate the tops of the upright arms and opposite engagement structures, where prior to the uploading of the insert into the axial bore, the opposite engagement structures protrude inwardly between the closure mating structure and the seating surface,
the insert comprising an upper curvate surface configured to engage the elongate rod and outer side surfaces configured to engage the opposite engagement structures of the axial bore to restrict the motion of the insert relative to the receiver, and
the two-part retainer comprising two separable retainer parts together defining an inner retainer surface, each retainer part having an outer retainer surface engageable with the seating surface; and
uploading an upper capture portion of a bone anchor through the bottom opening and into the two-part retainer that has been pre-loaded into the cavity, the bone anchor comprising the upper capture portion having an outer capture surface complementary with the inner retainer surface and a lower attachment portion opposite the upper capture portion configured for attachment to the bone,
wherein the two retainer parts are configured to pivot and move at least partially away from each other upon the uploading of the upper capture portion into cavity, and then to pivot back toward each other until the inner retainer surfaces clamp around the outer capture surface to capture the upper capture portion within the receiver with the bone anchor extending downwardly through the bottom opening.
13. The method of claim 12 , wherein the outer retainer surfaces of the two retainer pieces are slidably engageable with the seating surface of the cavity after capturing the upper capture portion and prior to locking the angular orientation of the shank with respect to the receiver.
14. The method of claim 12 , further comprising applying a downwardly directed force to the upper surface of the insert to drive the outer retainer surfaces of the retainer parts into frictional engagement with the seating surface of the cavity to lock the angular orientation of the bone anchor with respect to the receiver.
15. The method of claim 12 , wherein the outer side surfaces of the insert further include elongate grooves configured to engage the opposite engagement structures of the axial bore to restrict the motion of the insert relative to the receiver.
16. The method of claim 12 , wherein the upper capture portion of the bone anchor further comprises an external spherical surface.
17. The method of claim 16 , wherein the external spherical surface of the upper capture portion is engageable by a lower spherical surface of the insert.
18. The method of claim 12 , wherein the seating surface of the cavity decreases in diameter toward the bottom opening.
19. The method of claim 12 , wherein each retainer part further comprises end walls in spaced parallel relation with the respective end walls of the other retainer part when the two-part retainer is in operable engagement with the bone anchor upper capture portion within the receiver cavity.
20. A method of assembling a pivotal bone anchor assembly configured to secure an elongate rod to a bone of a patient via a closure, the method comprising:
positioning an insert into an axial bore of a receiver,
the receiver comprising a base defining a cavity centered about a vertical axis and communicating with a bottom surface of the base through a bottom opening, and a pair of upright arms extending upward from the base defining an open channel configured to receive the elongate rod, the cavity including a seating surface proximate the bottom opening and extending upward through the open channel to tops of the upright arms to define the axial bore, the axial bore including a discontinuous closure mating structure integrally formed therein proximate the tops of the upright arms and opposite engagement structures, where prior to the positioning of the insert into the axial bore, the opposite engagement structures protrude inwardly between the closure mating structure and the seating surface,
the insert comprising an upper curvate surface configured to engage the elongate rod and outer side surfaces configured to engage the opposite engagement structures of the axial bore to restrict the motion of the insert relative to the receiver;
loading a two-part retainer into the cavity, the two-part retainer comprising two separable retainer parts together defining an inner retainer surface, each retainer part having an outer retainer surface engageable with the seating surface; and
uploading an upper capture portion of a bone anchor through the bottom opening and into the two-part retainer that has been pre-loaded into the cavity, the bone anchor comprising the upper capture portion having an outer capture surface complementary with the inner retainer surface and a lower attachment portion opposite the upper capture portion configured for attachment to the bone,
wherein the two retainer parts are configured to move at least partially away from each other upon the uploading of the upper capture portion into cavity, and then to move back toward each other to operably engage and capture the upper capture portion within the receiver with the bone anchor extending downwardly through the bottom opening.
21. The method of claim 20 , wherein the outer retainer surfaces of the two retainer pieces are slidably engageable with the seating surface of the cavity after capturing the upper capture portion and prior to locking the angular orientation of the shank with respect to the receiver.
22. The method of claim 20 , further comprising applying a downwardly directed force to the upper surface of the insert to drive the outer retainer surfaces of the retainer parts into frictional engagement with the seating surface of the cavity to lock the angular orientation of the bone anchor with respect to the receiver.
23. The method of claim 20 , wherein positioning the insert into the axial bore of the receiver further comprises uploading the insert through the bottom opening.
24. The method of claim 20 , wherein the outer side surfaces of the insert further include elongate grooves configured to engage the opposite engagement structures of the axial bore to restrict the motion of the insert relative to the receiver.