Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-10-19
2003-08-26
McDermott, Corrine (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S016110
Reexamination Certificate
active
06610089
ABSTRACT:
FIELD OF THE INVENTION
Generally, the present invention relates to spinal implant devices, surgical tools and associated techniques for promoting spinal fusion.
BACKGROUND OF THE INVENTION
It is known that when an intervertebral disc degenerates or is damaged, there is often a compression of the disc and a reduction in the normal intervertebral height. Typically, this condition results in abnormal motions that become a source of pain.
In order to treat pathologies of this type, the disc is often stabilized to eliminate the abnormal motions caused by disc disorders or injuries. Generally, one approach is to prevent articulation between the two vertebrae situated on each side of the damaged disc by bone fusion. This fusion fixes the vertebrae to each other, eliminating the relative mobility causing the pain. Various spinal implants to promote fusion between adjacent vertebrae have been proposed. It has been proposed to interconnect the two vertebrae by a kind of rigid U-shaped stirrup, which restores the discal height with a bone graft material disposed inside the stirrup. However, one drawback of this proposal is its diminishing effectiveness over a period of time.
Another proposal for promoting spinal fusion includes implanting a spinal cage to interconnect the adjacent vertebrae; the spinal cage includes a cylindrical member provided with a series of openings and provided with anchoring points. This implant is placed in a recess formed in the intervertebral disc and penetrates the opposite cortical endplates of the two vertebrae, which were previously hollowed out to receive the implant. This penetration forms openings in the sub-chondral endplates to place spongy bone of the vertebrae in contact with bone graft material placed inside the implant, facilitating bone fusion. U.S. Pat. No. 5,015,247 provides one example of this approach.
Yet another proposal for spinal fusion comprises inserting hollow tubular implants having a generally ovoidal external shape into the intervertebral space. However, these implants require both annular ribs to inhibit axial displacement and longitudinal ribs or teeth to prevent rotation of the implant about its longitudinal axis. One example of this approach is found in U.S. Pat. No. 5,683,463 issued to Godefroy et al. In another example in U.S. Pat. No. 5,888,224 issued to Beckers et al., a rotatable implant for spinal fusion is disclosed. The rotatable implant requires a linking connector to inhibit longitudinal rotation. Other rotatable implants are described in U.S. Pat. No. 5,607,424 issued to Tropiano.
However, one drawback of these proposed implants is their lack of support of the cortical bone tissue, particularly bearing against the peripheral wall of the vertebral bodies. This contributes to their diminishing effectiveness in maintaining normal disc height over a period of time.
Proper performance of a spinal implant of this type requires balancing the need to promote fusion between the spongy bone and the need to form a reliable load bearing relationship with the stronger cortical bone. As a result, the spinal implant must be neither engaged too far into the openings provided in the cortical endplates to provide a sufficiently dense load bearing surface, nor insufficiently inserted, in which case the bone fusion between the two vertebrae would be adversely affected by a poor anchorage. Thus, there is a demand for devices and techniques that facilitate attaining the proper balance between fusion and load support.
Thus, in light of the above described problems, there is a continuing need for advancements in the treatment of spinal deformities, including improved spinal implants and devices relating to spinal fusion and for surgical methods to treat spinal deformities. The present invention is such an advancement and provides a wide variety of benefits and advantages.
SUMMARY OF THE INVENTION
The present invention relates to spinal implants, surgical tools and the use thereof. Various aspects of the invention are novel, nonobvious, and provide various advantages. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms and features, which are characteristic of the preferred embodiments disclosed herein, are described briefly as follows.
According to one form of the invention, the spinal implant comprises a body having a central part arranged to allow arthrodesis and at least one terminal part for bearing against the cortical bone of the vertebral endplates. The central part is adapted to penetrate the vertebral endplates, transversely projecting from the terminal bearing part. Thus the invention achieves a separation between the end parts constituting the load bearers, and the intermediate part of the implant which permits fusion. In addition, the central part may include at least one cavity for receiving a bone graft material.
In another form of the present invention, an implant for insertion between a first vertebra having a first cortical bone endplate and a second vertebra having a second cortical bone endplate includes two terminal parts. The first terminal part defines a first bearing surface to bear against the first cortical bone endplate and a second bearing surface opposite the first surface to bear against the second cortical bone endplate. The second terminal part opposes the first terminal part and defines a third bearing surface to bear against the first cortical bone endplate and a fourth bearing surface opposite the third surface to bear against the second cortical bone endplate. The implant has an elongated central part defining an upper projection extending past the first and third surfaces, and a lower projection extending past the second and fourth surfaces. These projections correspondingly pass through openings in the first and second cortical bone endplates when the first and third surfaces bear against the first cortical bone endplate and the second and fourth surfaces bear against the second cortical bone endplate. The terminal parts are dimensioned to facilitate restoration of the natural geometry of the intervertebral space (lordosis, kyphosis, and parallel discs). Thus, the first and second surfaces may be separated by a first distance, and the third and fourth surface may be separated by a second distance greater than the first distance to accommodate a natural curvature of the spine.
In a further form of the present invention, an implant with two terminal parts also has an elongated central part that includes a pair of longitudinal walls defining a cavity. The walls defme a first edge projecting past the first and third surfaces and a second edge projecting past the second and fourth surfaces. The first and second edges correspondingly penetrate the first and second cortical bone endplates when the first and third surfaces bear against the first cortical bone endplate and the second and fourth surfaces bear against the second cortical bone endplate.
According to another form, the bearing surfaces of the terminal end parts are defined by flanges extending from opposing ends of the implant along its longitudinal axis. Preferably, the bearing surfaces are generally flat for bearing against the cortical bone of the vertebral endplates of the two adjacent vertebrae. It is also preferred that openings be cut into the cortical endplates in their central regions corresponding to the length of a central part of the implant along the longitudinal axis and leaving a region of the cortical bone endplates around the periphery of the openings. The length of the remaining peripheral endplate corresponds to the length of the bearing surfaces along the longitudinal axis. When the implant is placed in position, the edges of the walls of the central part engage the openings cut in the cortical endplates and consequently do not substantially bear against the remaining peripheral portion of the endplates. A cavity may be defined by the central part that holds bone graft material in contact with the spongy bone of the two vertebrae. In contrast, the
Chopin Daniel
Liu Mingyan
Meisel Hans-Jörg
Barrett Thomas
McDermott Corrine
SDGI Holdings Inc.
Woodard Emhardt Moriarty McNett & Henry LLP
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