Polyaxial bone screw with increased angulation
A polyaxial bone device includes a screw, a screw housing, and a spring. The screw includes a screw head and a shaft that extends from the screw head. The screw housing defines a longitudinal axis and a bore that extends along the longitudinal axis. The screw housing includes a basewall and opposed sidewalls that extend from the basewall. The basewall defines a notch that receives the shaft to increase pivotal movement between the screw and the screw housing relative to the longitudinal axis of the screw housing. The opposed sidewalk define a rod-receiving channel. The screw housing defines a transverse hole in communication with the bore. The spring is supported in the transverse hole and extends therethrough. The spring extends into the bore to frictionally engage the screw head while the screw head is seated in the bore.
1. A polyaxial bone screw device comprising:
a screw including a screw head and a shaft extending from the screw head;
a screw housing defining a longitudinal axis and a bore that extends along the longitudinal axis, the screw housing including a basewall and opposed sidewalls that extend from the basewall, the basewall defining a notch configured to receive a portion of the shaft therein, the notch configured to increase pivotal movement between the screw and the screw housing relative to the longitudinal axis of the screw housing, the opposed sidewalls defining a rod-receiving channel, the screw housing further defining a transverse hole that is in communication with the bore;
a spring supported in the transverse hole of the screw housing and extending therethrough, the spring extending into the bore of the screw housing to frictionally engage the screw head of the screw while the screw head is seated in the bore of the screw housing; and
a pin disposed within the transverse hole and in engagement with the spring.
2. The polyaxial bone screw device of claim 1 , wherein the spring is configured to maintain the shaft at an angular position relative to the longitudinal axis of the screw housing while frictionally engaged with the screw head.
3. The polyaxial bone screw device of claim 1 , wherein the screw head includes an outer surface that is configured to facilitate flictional engagement with the spring.
4. The polyaxial bone screw device of claim 1 , further including an anvil disposed within the screw housing and positioned to support a spinal rod seated within the rod-receiving channel.
5. The polyaxial bone screw device of claim 4 , wherein the anvil is seated on the screw head while a portion of the anvil is configured to engage the spring.
6. The polyaxial bone screw device of claim 4 , wherein the spring is frictionally engaged with the screw head while engaged to the portion of the anvil to support the screw in a position relative to the screw housing.
7. The polyaxial bone screw device of claim 1 , wherein the screw housing is pivotable in a first direction relative to the screw to a first angle and pivotable in a second direction relative to the screw to a second angle, the first angle different than the second angle, the shaft of the screw positioned within the notch of the screw housing while disposed at the first angle.
8. The polyaxial bone screw device of claim 7 , wherein the first angle is about 60 degrees relative to the longitudinal axis of the screw housing and the second angle is about 45 degrees relative to the longitudinal axis of the screw housing.
9. The polyaxial bone screw device of claim 1 , further including a set screw configured to be threadably received within the screw housing to secure a spinal rod within the screw housing.
10. A method of securing a spinal rod to a polyaxial bone screw device, the method comprising:
inserting a polyaxial bone screw into bone, the polyaxial bone screw having:
a screw having a head and a shaft extending therefrom, the shaft insertable into bone;
a screw housing including opposed sidewalls defining a U-shaped rod-receiving channel, the screw housing further defining an opening for receiving the head of the screw, a notch for receiving a portion of the shaft, and a transverse hole; and
a spring extending through the transverse hole and maintained by a pin disposed within the transverse hole;
positioning the screw housing relative to the screw, the screw housing movable in a first direction relative to the screw to a first angle and movable in a second direction relative to the screw to a second angle, the first angle greater than the second angle, wherein the portion of the shaft of the screw is received in the notch of the screw housing at the first angle when the screw housing is moved in the first direction;
supporting the portion of the shaft in at least one of the first and the second angles through frictional engagement between the spring and the head of the screw; and
coupling the spinal rod to the polyaxial bone screw by inserting a portion of the spinal rod into the U-shaped rod-receiving channel of the screw housing of the polyaxial bone screw.
11. The method of claim 10 , further including selectively pivoting the screw along a longitudinal axis of the spinal rod in the first direction relative to the screw housing to the first angle.
12. The method of claim 11 , wherein positioning the screw housing includes positioning the portion of the shaft within the notch such that the first angle is about 60 degrees.
13. The method of claim 12 , further including selectively pivoting the screw along a longitudinal axis of the spinal rod in the second direction relative to the screw housing to the second angle.
14. The method of claim 13 , wherein positioning the screw housing includes positioning the portion of the shaft within another region of the screw housing separate from the notch such that the second angle is about 45 degrees.
15. The method of claim 10 , further including securing the spinal rod to the polyaxial bone screw by attaching a set screw to the screw housing.
16. A polyaxial bone screw device comprising:
a screw including a screw head and a shaft extending from the screw head;
a screw housing defining a longitudinal axis and a bore that extends along the longitudinal axis, the screw housing including a basewall and opposed sidewalls that extend from the basewall, the basewall defining a notch configured to receive a portion of the shaft therein, the notch configured to increase pivotal movement between the screw and the screw housing relative to the longitudinal axis of the screw housing, the opposed sidewalls defining a rod-receiving channel, the screw housing further defining a transverse hole that is in communication with the bore;
an anvil disposed within the screw housing; and
a spring supported in the transverse hole of the screw housing, the spring extending into the bore of the screw housing and being in engagement with the anvil and the screw head.
17. The polyaxial bone screw of claim 16 , wherein the anvil is positioned to support a spinal rod seated within the rod-receiving channel.
18. The polyaxial bone screw of claim 16 , wherein the anvil defines a slot and the spring is engaged within the slot to rotatably lock the anvil relative to the screw housing.