Polyaxial bone screw assembly
View Patent ↗A polyaxial bone screw assembly includes a shank body having an upper head portion with a mating segment and a first partial spherical surface, a retainer structure being mateable with the mating segment of the upper head portion, the retainer structure having a second partial spherical surface such that when mated, the first and second partial spherical surfaces form a spherical ball member, a receiver defining an open channel and having a base with a seating surface partially defining a cavity, the open channel communicating with the cavity, the cavity communicating with an exterior of the base through an opening sized and shaped to receive the shank upper head portion therethrough, and a bushing sized and shaped to fit within open channel and cavity, the bushing having a lower rounded surface engageable with a top surface of the spherical ball member formed by the shank and retainer structure.
1. In a polyaxial bone screw assembly for fixation to a bone, the assembly including a shank with a threaded body and an upwardly extending head portion, a retainer structure sized and shaped to matingly engage and pivotally rotate with the head portion, and a receiver pivotally engaging the head portion, the improvement comprising:
a) a shank having a body for fixation to a bone, an upper head portion, a central cannulation bore extending the entire length of the body and upper head portion along a first axis the upper head portion defining a first partial sphere;
b) a retainer structure, having a second central cannulation bore along a second axis and defining a second partial sphere, the first partial sphere mating in the receiver to with the second partial sphere so as to form a ball that polyaxially rotates within the receiver and wherein the second central bore aligns with the first central bore.
2. The improvement according to claim 1 including:
a) a bushing operably positioned above the shank and allowing polyaxial movement of the ball relative to the receiver during positioning and applying a downward force to the shank when the assembly is fully assembled to bias the shank against the receiver and thereby lock the position of the shank relative to the receiver.
3. The improvement according to claim 1 wherein the first partial sphere has a concave region and the second partial sphere has a convex region that is operably received in the concave region of the first partial sphere.
4. The improvement according to claim 1 wherein the first partial sphere has upper and lower portions and the first cannulation bore extends separately through both portions.
5. A polyaxial bone screw assembly for fixation to a bone, the assembly including a shank with a threaded body and an upwardly extending head portion, a retainer structure sized and shaped to matingly engage the head portion, a receiver pivotally engaging the head portion and having two spaced apart arms each being internally threaded and defining gaps therebetween, and an upper pressure insert receivable in the receiver and pivotally engaging the head portion, the assembly comprising:
a) a shank having a body for fixation to a bone, an upper head portion, a central cannulation bore extending the entire length of the body and upper head portion the upper head portion defining a first partial sphere;
b) a retainer structure, having a second partial sphere the first and second partial spheres mating n the receiver to form a ball like structure that polyaxially rotates in the receiver during position.
6. The assembly according to claim 5 wherein the first partial sphere has a concave region and the second partial sphere has a convex region that mates with the concave region.
7. The assembly according to claim 6 wherein the bone is a first bore and the second partial sphere has second bore that aligns with the first bore.
8. In a polyaxial bone screw assembly for fixation to a bone, the assembly including a shank with a threaded body and an upwardly extending head portion, a retainer structure sized and shaped to matingly engage the head portion, a housing having a first opening and a second lower opening, the lower opening pivotally engaging the head portion of the shank and an upper pressure insert receivable in the receiver and pivotally engaging the head portion, the improvement comprising:
a) a shank having a body for fixation to a bone, an upper head portion, a central bore extending the entire length of the body and upper head portion the upper head portion having a first partial spherical surface;
b) a retainer structure, having a second partial spherical surface such that when the retainer and shank mate in the retainer the first and second partial spherical surfaces join to form a generally special combined surface.