1. Technical Field
The present disclosure relates to surgical screw systems and, more particularly, to screw systems for tethering to bone.
2. Discussion of Related Art
The spine is made up of a superposition of vertebrae that are normally aligned along a vertebral axis, extending from the lumbar vertebrae to the cervical vertebrae. When an individual's spine presents abnormal curvature, the vertebrae are inclined relative to one another and relative to said vertebral axis. The lateral edges of the vertebrae situated on one side are thus closer to one another and form a concave curve, while the lateral edges on the other side appear spaced apart from one another and form a convex curve. In order to straighten the spinal column, the lateral edges of the vertebrae on the concave side are spaced apart from one another and are taken relative to one another to a distance that is substantially equivalent to the distance between the lateral edges on the other side. Thereafter, in order to keep the vertebrae in that position relative to one another, known devices such as spinal rods, screws, and hooks are utilized.
The hooks are generally inserted in pairs in each vertebra and on either side close to the pedicles, the heads of the hooks projecting from the posterior wall of a vertebra, one on either side of the spinous process. The heads may be tulip-shaped to receive a rod that is secured by means of a setscrew inserted in the head and bearing against the rod. Rows constituted by the heads of the hooks situated on either side of the spinous processes are interconnected and held in fixed position by two rods that are parallel to each other and to the axis of the spine.
The screws also have tulip-shaped heads and are inserted in the posterior walls of vertebrae in the pedicles on either side of the spinous processes. The screws are inserted into the pedicles of the vertebrae, and under certain circumstances, the pedicles may be damaged. Wires can be used when the pedicles of the vertebrae are relatively small. However, often due to the loading on the wire and the small surface area of the wire, the wire may be pulled through the anatomy and thus become ineffective.
Therefore, a continuing need exists for an implant that can provide spinal correction to meet the needs of each patient, while maintaining the safety of the patient.