FIELD OF THE INVENTION

The present invention generally relates to pivotal bone anchor assemblies for use in bone surgery, particularly spinal surgery.

BACKGROUND

Bone screws are utilized in many types of spinal surgery in order to secure various implants to vertebrae along the spinal column for the purpose of stabilizing and/or adjusting spinal alignment. Although both closed-ended and open-ended bone screws are known, open-ended screws are particularly well suited for connections to rods and connector arms, because such rods or arms do not need to be passed through a closed bore, but rather can be laid or urged into an open channel within a receiver or head of such a screw.

Typical open-ended bone screws include a threaded shank with a pair of parallel projecting branches or arms which form a yoke defining slot or channel having different shapes, such as U-shaped and square shaped, for example, to receive a rod. Hooks and other types of connectors, as are used in spinal fixation techniques, may also include open ends for receiving rods or portions of other structure.

A common mechanism for providing vertebral support is to implant bone screws into certain bones which then in turn support a longitudinal structure such as an elongate rod, or are supported by such a rod. Bone screws of this type may have a fixed head or receiver relative to a shank thereof. In the fixed bone screws, the rod receiver head cannot be moved relative to the shank and the rod must be favorably positioned in order for it to be placed within the receiver head. This is sometimes very difficult or impossible to do. Therefore, pivotal or polyaxial bone screws are commonly preferred. Open-ended polyaxial bone screws typically allow for pivoting and rotation of the separate receiver about the shank in one or more planes until a desired rotational position of the receiver is achieved by fixing such position relative to the shank during a final stage of a medical procedure when an elongate rod or other longitudinal connecting member is inserted into the receiver, followed by a locking set screw or other closure.

SUMMARY

Briefly described, one embodiment of the present disclosure comprises a pivotal bone anchor assembly for securing an elongate rod to patient bone. The pivotal bone anchor system generally includes a shank having a head and an anchor portion, a receiver having an axial bore and an open channel for receiving the elongate rod, and a collet insert that is top loadable into a first upper position within the axial bore of the receiver. The collet insert includes a lower collet-type chamber or pocket for receiving the shank head. The bone anchor assembly also includes a pressure ring that is uploadable into the collet pocket prior to the shank head, and having an upper surface for engaging the elongate rod. After receiving the shank head within the collet pocket below the pressure ring, the collet insert and pressure ring are downwardly deployable together with the shank head into a second position within the axial bore to capture the shank head within the bone anchor assembly. With the collet insert in the second position, the pressure ring is operable to transfer an applied pressure from the elongate rod positioned in the open channel to the shank head to lock an angular position of the shank relative to the receiver.

The invention will be better understood upon review of the detailed description set forth below taken in conjunction with the accompanying drawing figures, which are briefly described as follows.

