Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2001-10-06
2004-02-17
Milano, Michael J. (Department: 3731)
Surgery
Instruments
Orthopedic instrumentation
C606S079000
Reexamination Certificate
active
06692501
ABSTRACT:
BACKGROUND
Present methods of forming an implantation space between adjacent vertebral bodies in the human spine generally include the use of one or more of the following: hand held biting and grasping instruments known as rongeurs; curettes; drills and drill guides; rotating burrs driven by a motor; and osteotomes and chisels. Sometimes the vertebral end plate must be sacrificed as occurs when a drill is used to drill across the disc space and deeper into the vertebral bodies than the thickness of the bony end plate region. Such a surgical procedure necessarily results in the loss of the hardest and strongest bone tissue of the vertebral bodies located in the bony end plate region and thereby removes from the vertebral bodies that portion of its structure best suited to absorbing and supporting the loads placed on those vertebral bodies by an interbody spinal implant. Nevertheless, the surgeon must work upon the adjacent end plates of the adjacent vertebral bodies to access the underlying vascular bone that is capable of participating in the fusion by allowing active bone growth, and also to attempt to obtain an appropriately shaped surface in the vertebral bodies to receive the implant. Because the end plates of the adjacent vertebral bodies are not flat, but rather have a compound curved shape, and because the implants, whether made of bone or any other suitable implant material, when fabricated or manufactured, tend to have a geometric rather than a biologic shape, it is generally necessary to conform at least a portion of the vertebral bodies to the shape of the implant to be received therebetween.
It is important in forming the space between the adjacent bone structures to provide a surface contour that closely matches the contour of the implants so as to provide an adequate support surface across which the load transfer between the adjacent bone structures can be evenly applied. In instances where the surgeon has not been able to form the appropriately shaped space for receiving the implants, those implants may slip or be forcefully ejected from the space between the adjacent vertebral bodies, or lacking broad contact between the implant and the vertebral bodies, a failure to obtain fusion may occur.
Prior devices having a plurality of rotating cutting elements for removing bone with a drive mechanism between the cutting elements had limitations in certain applications. For example, if the bone to be cut was thicker than the individual thickness of each of the cutting elements, then the portion of the device between the cutting elements could hit the uncut bone and stop the bone removal device from advancing deeper into the bone being cut. Further, the presence of the drive member between the cutting elements kept the cutting elements spaced apart and thus could prevent the placement of the bone removal device into very narrow spaces such as, but not limited to, disc spaces as might be found in some instances in the cervical spine.
There remains therefore a need for an improved spinal interspace shaper that does not have such limitations so as to achieve the desired purposes as described herein.
SUMMARY OF THE INVENTION
The present invention relates to a bone removal device for insertion into and at least in part across the height of a disc space between adjacent vertebral bodies in the human spine, and a guard for providing protected access to the disc space and for maintaining a desired positioning of the adjacent vertebral bodies relative to each other, and to a method of working on those portions of the vertebral bodies adjacent that disc space to remove bone material sufficient to form a desired contoured end plate and to thereby access the underlying vascular bone. For purposes of this application, the bony “end plate region” of the vertebral bodies is defined as the outer shell of compact bone (the bony end plate) adjacent to the spinal disc and the underlying subchondral zone.
The apparatus and associated method of the present invention is adapted to form a surface on or into each of the vertebral body surfaces that are adjacent the intervertebral disc space. The prepared spaces are formed through the inert outer bone of the vertebral bodies to get to the vascularized underlying bone, preferably, without generally removing all of the thickness of the end plate region. The formed surface(s) have a defined shape and a contour corresponding to a preferred interbody spinal implant to be implanted in the disc space.
The bone removal device of the present invention is useful in the cervical, thoracic, and lumbar spine from anterior to the transverse processes of the vertebrae, lateral or anterolateral in the thoracic and lumbar spines, or from posterior in the lumbar spine. The bone removal device, in a preferred embodiment, generally includes a cutting element movably and preferably replaceably mounted on the distal end of a shaft. A depth limiting mechanism preferably controls the depth of insertion of the cutting element into the intervertebral space (i.e., the disc space). The device also includes a handle that may be detachable from the shaft. As used herein, the term “handle” refers to a portion of the device that a surgeon may grip or otherwise manipulate to guide the working end of the device. That “handle” may in fact have multiple purposes. For example, the handle may be a portion of the shaft on which the working end is mounted at one end. Alternatively, the handle may be part of a segment that connects the device to a power source. For example, the handle may be part of a power source that supplies pressurized gas to the power source if turbine driven, or the handle may be a drill, but the term “handle” is used herein in its broadest context to refer to that which the surgeon grasps to use the present invention.
Additionally, the shaft may be detachable from the working end. The device also includes a drive mechanism that transmits power to activate, i.e., move, the cutters. The drive mechanism connects to an energy source, e.g., a rechargeable battery that further may be but need not be housed within the handle of the device. By way of example only, the drive mechanism may include an electric motor or an electromagnetic oscillating mechanism. Or, again by way of example only, the drive mechanism and handle in which it may be disposed may include the head unit of a gas powered turbine of a type commonly used in other surgical instruments.
In a preferred embodiment, the working end is generally as wide as the spinal implant to be implanted or the width of a combined plurality of implants adapted for side-by-side use between the adjacent vertebral bodies adjacent the disc space. The receiving bed, i.e., the prepared surface of the vertebral bodies, when formed by the device, will correspond in shape, size, and contour to the corresponding surfaces of a preferred spinal implant or combined width of implants to be implanted. The surface produced by the bone removal device is generally flat or concave to correspond to the upper or lower vertebral body contacting surfaces of the implant that will be implanted between the vertebral bodies. In an embodiment of the present invention having domed or convex upper and lower cutters or cutting members the device may be inserted into the spine and then turned on to form to desired shape into the adjacent vertebral bodies. The cutters have a leading end that is capable of cutting through bone and/or disc material to form a pocket or socket having a contour corresponding to the forward aspect of the leading end, as well as at least a portion of the side surfaces of the preferred implant to be implanted. These sidewalls assist in restraining the implant from lateral movement.
The working end of the present invention includes a pair of opposed, outwardly facing cutters which lie in planes that may be either parallel to each other or, alternatively, convergent to each other. The present invention saves time by simultaneously preparing both of the vertebral end plates adjacent a disc space. The bone removal device shapes the
Davis D. Jacob
Martin & Ferraro LLP
Milano Michael J.
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