Pivotal bone anchor assembly having a threaded shank head and a threaded receiver lower opening

#The present invention relates to apparatuses and methods for use in performing spinal surgery and, in particular, to polyaxial bone screws for use in spinal surgery. Such screws have a head that can swivel about a shank of the bone screw, allowing the head to be positioned in any of a number of angular configurations relative to the shank.

#Bone screws are utilized in many types of spinal surgery in order to secure various implants to vertebrae along the spinal column. Spinal implant screws typically have a shank that is threaded and configured for implantation into a pedicle or vertebral body of a vertebra. Such a screw also includes a head designed to extend beyond the vertebra and also defines a channel to receive a rod or other implant. In bone screws of this type, the head may be open, in which case a closure member must be used to close between opposite sides of the head once a rod or other implant is placed therein. Alternatively, the head may be closed, wherein a rod-like implant is threaded through the head of the bone screw.

#When the head and shank of the bone screw are fixed in position relative to each other, it is not always possible to insert a bone screw in such a manner that the head will be in the best position for receiving other implants. Consequently, swivel head bone screws have been designed that allow the head of the bone screw to rotate or swivel about an upper end of the shank of the bone screw while the surgeon is positioning other implants and finding the best position for the bone screw head. However, once the surgeon has determined that the head is in the best position, it is then necessary to lock or fix the head relative to the shank. Different types of structures have been previously developed for such purpose.

#FIG. 1 is an exploded perspective view of a polyaxial bone screw assembly according to the present invention having a shank with a capture structure at an end thereof, a head, and a closure structure.

#FIG. 2 is an enlarged and fragmentary view of the assembly of FIG. 1, showing the head in cross-section, taken along the line 2-2 of FIG. 1, and illustrating the shank in front elevation prior to the insertion of the shank capture structure into the head according to a method of the invention.

#FIG. 3 is a reduced and fragmentary cross-sectional view of the head and shank, taken along the line 2-2 of FIG. 1, showing the shank capture structure partially screwed into the head.

#As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure.

#With reference to FIGS. 1-9, the reference number 1 generally represents a polyaxial bone screw apparatus or assembly according to the present invention. The assembly 1 includes a shank 4 and a head 6. The shank 4 further includes a body 8 integral with an upwardly extending capture structure 10. The shank 4 and head 6 are often assembled prior to implantation of the shank body 8 into a vertebra 13, as seen in FIGS. 3 and 4. However, in a method of the invention shown in FIGS. 10 and 11, the shank body 8 is first implanted in the vertebra 13, followed by joining the head 6 to the shank 4.

#FIG. 1 further shows a closure structure 16 of the invention for biasing a longitudinal member such as a rod 19 against the capture structure 10 which in turn biases the structure 10 into fixed frictional contact with the head 6, so as to fix the rod 19 relative to the vertebra 13. The head 6 and shank 4 cooperate in such a manner that the head 6 and shank 4 can be secured at any of a plurality of angles, articulations or rotational alignments relative to one another and within a selected range of angles both from side to side and from front to rear, to enable flexible or articulated engagement of the head 6 with the shank 4 until both are locked or fixed relative to each other near an end of an implantation procedure.