Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-12-14
2001-10-09
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06299644
ABSTRACT:
The present invention relates to a vertebral replacement implant for interposition in a space left by one or more at least partially removed vertebrae between adjacent intact vertebrae, comprising a connecting body with opposite ends sized to span at least a portion of the space between the intact vertebrae; and two end pieces provided for being fixed to the opposite ends of said connecting body and comprising means for anchoring the implant into the adjacent intact vertebrae.
Such a vertebral replacement implant is already disclosed in WO 96/17564. The known implant comprises a hollow cylindrical connecting body provided at both ends with opposite screw threads onto which two endplates can be screwed. By rotating the connecting body, the two endplates can thus be drawn apart and clamped between the adjacent intact vertebrae. Set screws extending through the endplates into contact with the connecting body are provided for preventing rotation or the connecting body with respect to either of the endplates. The end faces of the endplates include a number of spikes configured to penetrate the end plate of the adjacent vertebral bodies to help maintain the position of the implant in situ.
A drawback of the known implant is that for the fixation of the adjacent intact vertebrae an additional support assembly is still required. This support assembly comprises clamps fixed laterally by means of screws to the intact vertebrae and an elongated distraction or compression rod mounted between these clamps. For applying this additional support assembly, not only the diseased or destroyed vertebra has to be dissected unilaterally but also the two adjacent intact vertebrae. This is a serious operation amongst others because during the dissection, the segmental arteries and veins have to be tied on involving an increased risk for ischemia. A complete fixation of the two adjacent intact vertebrae is however essential for fusing them by new bone growth starting from the bone grafts which are applied in the space between these two vertebrae.
An object of the present invention is now to provide a new type of vertebral replacement implant which enables to fix the two adjacent intact vertebrae sufficiently rigidly to one another that a new bone mass connecting both vertebrae may be developed, in particular without the help of any lateral support arrangements fixed laterally against the intact vertebrae.
To this end, the vertebral replacement implant according to the invention is characterized in that said anchoring means comprise a cutting screw blade provided on the end pieces for screwing these end pieces into the intact vertebrae.
According to the invention it has been found that by making use of a screw blade instead of spikes on the end pieces, the implant can be fixed sufficiently solidly into the adjacent intact vertebrae to prevent any relative movements of both intact vertebrae and hence to connect both vertebrae with new bone growth.
In an advantageous embodiment of the vertebral replacement implant according to the invention, said connecting body has first threads defined thereon at each of said opposite ends and said end pieces second threads configured to threadedly engage the first threads on said connecting body. In this way, a solid connection can easily be obtained between the end pieces and the connecting body.
Moreover, said first and second threads and said cutting screw blade have preferably a substantially equal pitch. According to the invention, it has been found that this feature enables to screw the end pieces much easier into the adjacent vertebrae. Indeed, by rotating the end pieces on the connecting body, they move apart and are thus forced to penetrate in the adjacent vertebrae at the same progression as that determined by the cutting screw blade.
In a further advantageous embodiment of the vertebral replacement implant according to the invention, said end pieces comprise a hollow cylindrical portion onto which said cutting screw blade is provided, the cylindrical portion having an open end for penetrating into a respective one of the intact vertebrae, the open end showing preferably a sharpened edge.
Due to the larger cross-section or diameter which can be achieved by means of the hollow cylindrical portion compared to for example a solid screw, a considerably more stable fixation of the end pieces in the adjacent vertebrae, more particularly against lateral bending stresses, can be realized. Moreover, also the total cross-sectional area of the cutting screw blade is larger thus providing a stronger anchoring of the end pieces, against axial stresses, in the intact vertebrae.
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patent: 9746165 (1997-12-01), None
Dykema Gossett PLLC
Pellegrino Brian E
Snow Bruce
LandOfFree
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