Polyaxial pedicle screw with increased angulation
View Patent ↗A polyaxial bone anchor including a housing and a bone screw. A bottom surface of the housing includes an aperture that defines an angulation limit of the bone screw for each azimuthal angle around a longitudinal axis of the housing. The aperture is V-shaped, with the V-shape having converging side walls that define a low-angulation direction near their intersection and a high-angulation direction opposite the low-angulation direction. In some cases, the angulation limit of the bone screw is generally constant over a range of azimuthal angles centered around the high-angulation direction. The housing may be modular, including tabs on one component that are plastically deformed to engage a lip on another component. During assembly, a mandrel advances longitudinally along a bore in the housing, and forces the tabs radially outward toward the lip to a radially outward plastically deformed state.
1. A polyaxial bone anchor, comprising:
a housing having an upper end, a lower end and a bore extending through the housing from the upper end to the lower end, the bore opening out at the lower end at a lower opening, the housing including a channel configured for receiving an elongate stabilization member therethrough which extends from a first side surface of the housing to a second side surface of the housing opposite the first side surface transverse to the bore; and
a bone screw including a head and a shank extending from the head, the head of the bone screw positionable in the housing with the shank extending from the lower end of the housing;
wherein the lower opening of the bore defines an angulation limit of the bone screw for each azimuthal angle around a longitudinal axis of the bore; and
wherein the lower opening of the bore is generally V-shaped, the V-shape having a closed end proximate the longitudinal axis, an open end distal to the longitudinal axis, and angled side walls connecting the closed end and open end that define a low-angulation direction proximate their intersection at the closed end and define a high-angulation direction opposite the low-angulation direction at the open end.
2. The polyaxial bone anchor of claim 1 , wherein the housing comprises an upper housing and a lower housing rotatably coupled to the upper housing, the lower housing including the lower opening of the bore.
3. The polyaxial bone anchor of claim 2 , wherein the housing is configured to provide limited rotational movement between the upper housing and lower housing through less than 360 degrees.
4. The polyaxial bone anchor of claim 3 , wherein one of the upper housing and the lower housing includes a groove and the other of the upper housing and the lower housing includes a protuberance, the groove having a first end surface and a second end surface and the protuberance traveling in the groove between the first end surface and the second end surface, wherein rotation between the upper housing and the lower housing is limited by the protuberance contacting either the first end surface of the groove or the second end surface of the groove.
5. The polyaxial bone anchor of claim 4 , wherein the protuberance travels in the groove through at least 180 degrees, but less than 360 degrees.
6. The polyaxial bone anchor of claim 1 , wherein the angulation limit of the bone screw is generally constant over a range of azimuthal angles centered around the high-angulation direction.
7. The polyaxial bone anchor of claim 6 , wherein the range of azimuthal angles is greater than 60 degrees.
8. The polyaxial bone anchor of claim 6 , wherein the range of azimuthal angles is greater than 70 degrees.
9. The polyaxial bone anchor of claim 6 , wherein the angulation limit in the range centered around the high-angulation direction is greater than 35 degrees.
10. The polyaxial bone anchor of claim 6 , wherein the angulation limit in the range centered around the high-angulation direction is greater than 40 degrees.
11. The polyaxial bone anchor of claim 1 ,
wherein the lower end of the housing comprises a generally spherical surface; and
wherein the lower opening of the bore comprises an aperture in the generally spherical surface.
12. The polyaxial bone anchor of claim 11 , wherein proximate the high-angulation direction, the aperture comprises an intersection of the generally spherical surface with a plane perpendicular to the longitudinal axis of the bore.
13. The polyaxial bone anchor of claim 11 , wherein proximate the high-angulation direction, the aperture further extends along a lateral side of the housing.
14. The polyaxial bone anchor of claim 1 , wherein the lower opening of the bore is left-right symmetric about a plane that includes the longitudinal axis of the bore.
15. The polyaxial bone anchor of claim 1 , wherein the housing is a unitary structure.
16. The polyaxial bone anchor of claim 1 , wherein the V-shape extends all the way through the lower opening of the housing in a direction of the longitudinal axis.
17. A polyaxial bone anchor, comprising:
a housing having an upper end, a lower end and a bore extending through the housing from the upper end to the lower end along a longitudinal axis, the bore opening out at the lower end at a lower opening, the housing including a channel configured for receiving an elongate stabilization member therethrough which extends from a first side surface of the housing to a second side surface of the housing opposite the first side surface transverse to the bore; and
a bone screw including a head and a shank extending from the head, the head of the bone screw positionable in the housing with the shank extending from the lower end of the housing;
wherein the lower opening of the bore includes opposing converging side walls that define an angulation limit of the bone screw for each azimuthal angle around a longitudinal axis of the bore;
wherein the converging side walls are further apart from each other away from the longitudinal axis to define a maximum value of the angulation limit in a high-angulation direction;
wherein the angulation limit is generally constant over an azimuthal range of at least 50 degrees centered about the high-angulation direction; and
wherein the converging side walls are closer to each other nearer the longitudinal axis to define a minimum value of the angulation limit in a low-angulation direction, wherein the minimum value is less than the maximum value.
18. The polyaxial bone anchor of claim 17 , wherein the angulation limit achieves a minimum value at an azimuthal angular position between the high-angulation direction and the low-angulation direction.
19. The polyaxial bone anchor of claim 17 , wherein the angulation limit achieves a minimum value at the low-angulation direction.
20. The polyaxial bone anchor of claim 17 ,
wherein the maximum value of the angulation limit is greater than 45 degrees; and
wherein the azimuthal range is greater than 80 degrees.