Spinal fusion implants and tools for insertion and revision

Abstract

An interbody fusion device in one embodiment includes a tapered body defining a hollow interior or chamber for receiving bone graft or bone substitute material. The body defines exterior threads which are interrupted over portions of the outer surface of the device. The fusion device includes truncated side walls so that on end view the body takes on a cylindrical form. In another embodiment, the tapered body is solid and formed of a porous biocompatible material having sufficient structural integrity to maintain the intradiscal space and normal curvature. The material is preferably a porous tantalum composite having fully interconnected pores to facilitate complete bone tissue ingrowth into the implant. In further embodiments, the fusion devices are provided with osteogenic material to facilitate bone ingrowth. A cap is also provided to block the opening of hollow fusion devices. The cap includes an occlusion body and an elongated anchor. In some embodiments the anchor includes a lip which is engageable to openings in the body wall. Tools are also provided for manipulating caps for interbody fusion devices. In one embodiment the tool includes a pair of prongs each having facing engagement surfaces for engaging the fusion device, and a shaft slidably disposed between the prongs. The shaft has a first end defining a cap-engaging tip for engaging a tool hole in the cap. In one embodiment the cap engaging tip defines threads. In another embodiment the prongs include a pair of releasing members on each of the facing engagement surfaces. The releasing members have a height and a width for being insertable into apertures in a body wall in the fusion device to disengage the elongate anchors from the apertures.

Description

[0001]The present application is a continuation of Ser. No. ______ (attorney docket # 4002-740), filed on Feb. 11, 1997, which is a continuation-in-part of co-pending application Ser. No. 08 / 603,674, filed on Feb. 19, 1996 which is a continuation-in-part of co-pending application Ser. No. 08 / 413,353, filed on Mar. 30, 1995 which is a continuation-in-part of co-pending application Ser. No. 08 / 411,017, filed on Mar. 27, 1995.BACKGROUND OF THE INVENTION[0002]The present invention relates to an artificial implant to be placed into the intervertebral space left after the removal of a damaged spinal disc. Specifically, the invention concerns an implant that facilitates arthrodesis or fusion between adjacent vertebrae while also maintaining or restoring the normal spinal anatomy at the particular vertebral level.[0003]The number of spinal surgeries to correct the causes of low back pain has steadily increased over the last several years. Most often, low back pain originates from damage or ...

AI Technical Summary

Benefits of technology

[0017]In another aspect a cap is provided which securely blocks the opening in a fusion device to prevent expulsion of an osteogenic material from within the device. The cap includes an occlusion body for blocking the opening and an elongated anchor for securing the occlusion body within the opening. In some embodiments the anchor includes a lip which is engageable to openings in the body wall.

Problems solved by technology

Since the damaged disc material has been removed, something must be positioned within the intradiscal space, otherwise the space may collapse resulting in damage to the nerves extending along the spinal column.

With this technique once fusion occurred the hardware used to maintain the stability of the segment became superfluous.

Moreover, the surgical procedures necessary to implant a rod or plate to stabilize the level during fusion were frequently lengthy and involved.

A number of difficulties still remain with the many interbody fusion devices currently available.

While it is recognized that hollow implants that permit bone ingrowth into bone or bone substitute within the implant are an optimum technique for achieving fusion, most of the prior art devices have difficulty in achieving this fusion, at least without the aid of some additional stabilizing device, such as a rod or plate.

Moreover, some of these devices are not structurally strong enough to support the heavy loads and bending moments applied at the most frequently fused vertebral levels, namely those in the lower lumbar spine.

In other words, if the ingrowth openings are improperly sized or configured, the autologous bone will not endure the loading that is typically found to be necessary to ensure rapid and complete fusion.

In this instance, the bone impacted within the implant may resorb or evolve into simply fibrous tissue, rather than a bony fusion mass, which leads to a generally unstable construction.

On the other hand, the bone ingrowth openings must not be so extensive that the cage provides insufficient support area to avoid subsidence into the adjacent vertebrae.

Autograft is undesirable because existing structures may not yield a sufficient quantity of graft material.

The additional surgery to extract the autograft also increases the risk of infection and may reduce structural integrity at the donor site.

Furthermore, many patients complain of significant pain for several years after the donor surgery.

Although, the supply of allograft material is not so limited, allograft is also disadvantageous because of the risk of disease transmission and immune reactions.

Furthermore, allogenic bone does not have the osteogenic potential of autogenous bone and therefore will incorporate more slowly and less extensively.

These disadvantages have led to the investigation of bioactive substances that regulate the complex cascade of cellular events of bone repair.

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