Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-01-08
2001-03-27
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S016110, C623S023630, C623S919000
Reexamination Certificate
active
06206923
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to implantable fusion devices and methods for their use. More particularly, the present invention relates to interbody fusion devices formed of bone that may be utilized in spinal fusions.
A variety of interbody fusion implants are available for spinal fusion procedures. These implants have been manufactured of various materials including steel, titanium, composites, allograft, xenograft or other biocompatible materials. These implants may be inserted using fixed protective tubes to protect surrounding neurological and vascular structures or through an unprotected open procedure. One limitation on the size of a device inserted into the disc space is the size of the opening through surrounding tissue that is available to gain access to the disc space. From a posterior approach to the spine, the dura and nerve roots must be mobilized to gain access to the disc space. Similarly, from an anterior approach, the aorta and vena cava must be mobilized to gain access to the disc space. Such mobilization is often limited by the anatomical structures, thus resulting in a relatively small access site in comparison to the size of the disc space. Removal of additional ligaments and bone to enlarge an entrance to the disc space may de-stabilize and weaken the joint between two adjacent vertebra. Moreover, excessive retraction of vessels and neural structures to create a large access opening may result in damage to these tissues. Thus, prior procedures have been limited to placing a first device passable through the available opening on one side of the spine and mobilizing the tissue or vessels to place another similar implant on the opposite side of the spine. Each implant being limited in size by the available access site.
In response, expandable implants have been developed from biocompatible materials such as titanium and composites. These devices rely on hinges or selective deformation of the implant material to permit expansion after they are positioned in the disc space. While such devices have a reduced insertion configuration and an expanded spacing configuration, the materials utilized to form the implants are synthetic and will not incorporate into adjacent bony tissues. While bone offers much improved incorporation, the inherent brittle nature of bone resulting from a high mineral content, particularly load-bearing cortical bone, severely limits its potential deformation. Typically, for example, cortical bone consists of approximately 70% mineral content and 30% non-mineral matter. Of this non-mineral matter, approximately 95% is type I collagen, with the balance being cellular matter and non-collagenous proteins.
Bone grafts, in conjunction with other load-bearing implants, have commonly been used in a fixed shape, pulverized, or as pliable demineralized bone. One form of a pliable bone graft is a demineralized bone material typically in the form of a sponge or putty having very little structural integrity. While a demineralized bone segment may retain properties suitable to support bone ingrowth, the structural properties of the bone are altered by removal of its mineral content. Thus, such bone sponges and putties may not typically be used in load-bearing applications.
Therefore, there remains a need for a strong bone implant having an area of flexibility.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a flexible bone implant. The bone implant of the present invention comprises a first bone portion, a second bone portion, and a flexible bone portion joining the first and second bone portions. The intermediate flexible bone portion permits movement of the first bone portion in relation to the second bone portion. In a preferred embodiment, the movement of the first and second bone portions would be between a reduced size insertion configuration and an expanded configuration suitable for maintaining two bony structures in a spaced relation and permitting bone ingrowth, if desired. Optionally, the movement between the first and second bone portions may be utilized as an elastic damper when the device is positioned between adjacent bony structures.
In accordance with another aspect of the invention, the bone implant comprises a bone segment having at least one partially demineralized area creating a flexible segment of the demineralized bone segment. In one embodiment, an opposite portion of the cortical femoral ring segment is severed such that the ring segment may be expanded once it has been inserted into an intervertebral disc space. In yet another embodiment, the device includes at least two partially demineralized bone portions on substantially opposing portions of the bone segment. In this configuration, the substantially rigid portions are placed in contact with the load bearing surfaces between two adjacent bony structures such that the flexible portions perform an elastic function, allowing more normal motion or to better load bone adjacent the disc space.
In yet a further aspect of the present invention, there is provided a method for the preparation of a bone implant. The method includes providing a rigid bone segment and delineating an intermediate portion of that segment. The central portion is then at least partially demineralized to create a flexible segment between two adjacent sections of bone. The method of at least partially demineralizing a segment of bone between two adjacent rigid bone segments may be repeated as often as necessary to create the desired structure for implantation.
The present invention further contemplates a method of inserting a device formed in accordance with the present invention. Specifically, the method includes providing an insertion tube and an implant formed of bone having a first and second portions joined by a flexible central portion. The insertion tube is positioned adjacent a disc space formed by adjoining vertebrae. The first and second portions of the bone implant are then positioned into a reduced size configuration for insertion into the insertion tube. The implant is then inserted into the tube and advanced until it is positioned in the disc space. Once the implant is in the desired position, the first and second portions are moved with respect to one another by flexing of the flexible portion into an expanded implantation configuration. In a preferred embodiment of the insertion method, bone ingrowth material is placed between the first and second portions to encourage further bone ingrowth into and around the fusion devices.
These and other objects of the present invention will be apparent to those skilled in the art based on the following descriptions of the preferred embodiment of the present invention.
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University of Florida Tissue Bank, Inc. “MD-I™ and MD-II™ Custom Machined Cortical Dowels”.
Sofamor Danek—The Spine Specialist “Surgical Technique Using Bone Dowel Instrumentation For Posterior Approach” ©1996.
University of Flo
Boyd Lawrence M.
Pafford John A.
Koh Choon P.
SDGI Holdings Inc.
Willse David H.
Woodard Emhardt Naughton Moriarty & McNett
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