Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-04-16
2001-02-20
Mancene, Gene (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C606S064000
Reexamination Certificate
active
06190413
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to vertebral implant. More particularly this invention concerns such an implant positioned between two vertebrae, normally in the place of a removed vertebra or intervertebral disk.
BACKGROUND OF THE INVENTION
When a vertebra is broken or crushed it is frequently necessary to ablate the body of the crushed or broken vertebra or vertebrae. In order, however, to prevent the spinal column from collapsing with damage to the fragile spinal cord running in the vertebral foramen forward of the vertebral body, it is necessary to employ an implanted spacer. This device is braced vertically between the bodies of the adjacent vertebra and holds them apart at the desired spacing. It may even serve to distract two vertebrae which have become too closely spaced due to crushing of a vertebra or disk.
In U.S. Pat. No. 5,571,192 a spinal implant is described for engagement in a space left by ablation of a vertebral body between a pair of adjacent vertebrae. It has a tubular center element extending along an axis and a pair of end elements. The center element is formed with upper and lower screwthreads of opposite hand and with a plurality of radially throughgoing apertures. The upper and lower tubular end elements are each formed with a plurality of radially throughgoing apertures, each have a circular-section inner end threaded onto a respective one of the screwthreads, and each have an outer end adapted to bear on a respective one of the adjacent vertebrae.
Thus such an implant can be set in an area where the body or bodies or one or more vertebra have been ablated. The length of the implant is then increased by rotating the center element to force out the end elements and bring their outer ends into solid engagement with the confronting vertebral surfaces. The screwthreads offer sufficient mechanical advantage so that the system can even be used to distract the vertebrae, as is frequently necessary in the event of a crushing injury. The tubular elements of the implant can be filled with bone cement and/or bone fragments to ensure that the implant becomes anchored in place in living bone. Since the outer elements surround the screwthreads of the inner element, once installed the screwthreads will be largely covered so that their sharp edges do not impair healing.
Such an arrangement serves very well to maintain the axial spacing between the vertebrae it is installed between, but must normally be used in conjunction with a separate bone plate and or external dorsal appliance secured by bone screws to the flanking vertebrae. This extra equipment is needed to prevent any relative lateral shifting of the vertebrae and to prevent the implant from moving out of position.
Not only is the plate or appliance difficult to install, but it is extremely inconvenient for the patient whose wound must often be left open. In addition the plate or appliance often block access to the implant so if same needs to be adjusted, for instance lengthened, it must be removed and reinstalled.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an improved intervertebral implant.
Another object is the provision of such an improved intervertebral implant which overcomes the above-given disadvantages, that is which eliminates the need for substantial additional hardware.
SUMMARY OF THE INVENTION
An implant for insertion between a pair of spaced vertebrae has according to the invention a center element and a pair of end elements fitted to the center element and each adapted to engage a respective one of the vertebrae. The center and end elements have formations for varying the spacing between the end elements. According to the invention respective brackets fixed to the end elements are each fixable to the respective vertebra.
Thus it is possible to secure the implant in place by fixing its end brackets to the respective vertebrae. This leaves the center element exposed for adjustment. Thus during the operation the core assembly formed by the center and end elements can be set in place, then the end elements are secured to the respective vertebrae, and finally the center element is turned to separate the end elements and perform the desired amount of distraction of the flanking vertebrae. The brackets leave the center of the assembly completely exposed for adjustment or filling with bone fragments.
In accordance with the invention the formations includes screwthreads engaged between the center and end elements. The end elements are formed as caps engaged over ends of the center element.
According to the invention each bracket is generally L-shaped and has a long leg attached to the respective vertebrae and an arcuate short leg attached to the respective element. The long leg is also arcuate in section and each long leg is formed with at least one elongated slot. A bone screw is engaged through the slot with the respective vertebra. Furthermore each slot is formed with seats for a head of the bone screw and each short leg is formed with two holes and the respective end element is formed aligned therewith with two holes. Respective bolts each engage through a respective one of the holes of the short leg and into the respective hole of the respective end element.
Each short leg is split according to the invention between the respective holes into a pair of halves. A respective screw is engaged between each pair of halves for pulling same together and clamping the bolts in the holes of the respective end element. Each bracket is formed with a slot between the halves and with a rounded hole at an end of the slot and the long leg is formed with an elongated slot to each side of and generally parallel to the slot.
The elements are at least partially tubular and are each formed with an array of holes spaced so that the holes of the center element overlap with the holes of the end elements. This facilitates bone growth through the implant to lock it in place and in effect incorporate it in the patient's spinal column.
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Dubno Herbert
Mancene Gene
Priddy Michael B.
Ulrich GmbH & Co. KG
Wilford Andrew
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