Polyaxial bone screw with helically wound capture connection

Abstract

A polyaxial bone screw assembly includes a threaded shank body having an upper capture structure, a head and a closed retainer ring. The external capture structure surface and retainer ring internal bore surface are both threaded for rotatable attachment within a cavity of the head. The head has a U-shaped cradle defining a channel for receiving a spinal fixation rod. The head channel communicates with the cavity and further with a restrictive opening that allows for loading the capture structure into the head but prevents passage of the closed retainer ring out of the head. The retainer ring has an external substantially spherical surface that mates with an internal surface of the head, providing a ball joint, enabling the head to be disposed at an angle relative to the shank body. The threaded capture structure or the closed retainer structure includes a tool engagement formation and gripping surfaces for non-slip engagement by a tool for driving the shank body into bone.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a divisional of U.S. application Ser. No. 10 / 986,377, filed Nov. 10, 2004.BACKGROUND OF THE INVENTION[0002]The present invention is directed to polyaxial bone screws for use in bone surgery, particularly 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.[0003]Many spinal surgery procedures require securing various implants to bone and especially to vertebrae along the spine. For example, elongate rods are often utilized that extend along the spine to provide support to vertebrae that have been damaged or weakened due to injury or disease. Such rods must be supported by certain vertebrae and support other vertebrae.[0004]The most common mechanism for providing vertebral support is to implant bone screws into certain bones which then in turn support the rod or are supported by the r...

AI Technical Summary

Benefits of technology

The invention is a polyaxial bone screw assembly that solves various problems in the prior art. It provides a screw that can be securely fastened to bone and easily assembled with a tool. The assembly includes a shank with a capture structure and a head with a cavity that securely holds the capture structure. The assembly also includes a retainer structure that securely holds the shank and is easily assembled with the capture structure. The retainer structure includes a threaded portion that securely attaches to the capture structure. The assembly is designed to prevent unintentional disassembly and provides a lightweight, low-profile solution. The technical effects of the invention include improved grip for bone implantation tools, secure attachment of the capture structure to the retainer structure, and secure attachment of the retainer structure to the bone.

Problems solved by technology

This is sometimes very difficult or impossible to do.

Consequently, heavy, bulky implants are undesirable and lighter implants with a relatively small profile both in height and width are more desirable.

However, a drawback to smaller, lighter implants is that they may be more difficult to rigidly fix to each other and into a desired position.

Lack of bulk may also mean lack of strength, resulting in slippage under high loading.

A further drawback of smaller components is that they may be difficult to handle during surgery because of their small size, failing to provide adequate driving or gripping surfaces for tools used to drive the shank into bone.

One undesirable attribute of some of the swivel-head implants is the need for a multitude of components that may loosen or even disassemble within the body.

It is most undesirable for components to be free to move around in the body after the completion of surgery.

Loosening of components relative to each other may result in related undesirable movement of the bone or vertebra that the implant was intended to stabilize.

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