Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
1999-11-16
2001-06-19
Smith, Jeffrey A. (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
Reexamination Certificate
active
06248105
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a device for the connection of a longitudinal rod with a bone anchoring element.
BACKGROUND OF THE INVENTION
The prior art teaches a number of spinal fixation systems which allow the spinal rod to be inserted after the pedicle screw is implanted with the angle between the rod and pedicle screw variable. An example of such systems is disclosed in European patent 330,881 of Sherman and European patent 441,729 of Vignaud. The disadvantage of these and similar systems is that the rod still must frequently be bent after coupling to the pedicle screw because of anatomical considerations. German patent 19,509,332 of Harms minimizes this disadvantage. Specifically, because relative movement of the screw head with respect to the rest of the screw is possible, the rod need only be bent in one plane after coupling with the pedicle screw.
The disadvantages of this known pedicle screw consist therein that the head part and the threaded part are not apt to be separated, the head part and the longitudinal rod are not apt to be fastened separately with respect to the threaded part, the reachable solidity is low because of the one-sided alignment of the longitudinal slots in the pressure element according to the DE-C 195 09 332 and it is difficult to remobilise the head part once it is fastened. The separability of the head part and the threaded part is a necessity to use different head parts according to the need and that the view is not impeded through the head part during the screwing in of the screw part into the bone. A separate fastening of the head part and the longitudinal rod and a high solidity between head part and threaded part enable the application of distraction and compression without a loss of angle between the pedicle screw and the longitudinal rod and the conservation of the anatomical bending of the stabilized vertebral segments. Remobilization is especially important in case of explantation or new adjustment of the fixation.
A further such connection device is disclosed in WO 97/02786 ERRICO which allows in a simple manner to connect a pedicle screw or more generally a bone anchoring element with a longitudinal rod and which permits a great freedom regarding the angle between the two elements. In case of this known connection device the disadvantage consists therein that the spring chuck is part of the connection element and therefore consists of the same material impairing the choice and pairing of the material with the bone screw to improve the solidity.
SUMMARY OF THE INVENTION
The object of the invention lies therein to provide a device for the connection of a longitudinal rod with a pedicle screw having the following qualities:
simple handling;
screwing in the threaded part of the device even without the
connection part;
possible later snap-on of the connection part;
depending on the situation and the preference of the surgeon the free choice of or combination of sidewardly open, upwardly open or closed connection parts. For instance an upwardly open connection part facilitates the insertion of the longitudinal rod while a sideward opening enables sideward corrections and thanks to the possibility of the sideward removing of the connection part each pedicle screw may any time be fastened at the longitudinal rod or be removed again without the necessity of demounting the whole fixation system.
The present invention relates to a vertebral fixation system connector for connecting a longitudinal rod with a bone anchoring element, such as a pedicle screw. The connector includes a connecting member having upper and lower ends, a bore hole through the lower end with a central axis, and a through hole running transversely to the central axis for receiving the longitudinal rod. The connector also has a tensioning member configured and dimensioned for insertion in the upper end of the connecting member for securing the bone anchoring element to the connector at a surgeon selected angle, a radially compressible spring chuck arranged within the connecting member coaxial to the central axis with an upper end and a lower end provided with a cavity for receiving the head of the bone anchoring element, and an insert slidable in the bore hole of the connecting member and having a recess complementary in shape to an outer surface of the spring chuck. The spring chuck is axially supported in the bore hole without impeding radial movement of the spring chuck therein.
The present invention also relates to a vertebral fixation system. The system includes a longitudinal rod, a bone anchoring element, and a connector for connecting the rod to the bone anchoring element. The connector includes a connecting member having upper and lower ends, a bore hole through the lower end with a central axis, and a through hole running transversely to the central axis for receiving the longitudinal rod. The connector also has a tensioning member configured and dimensioned for insertion in the upper end of the connecting member for securing a bone anchoring element having a head and a shaft to the connector at a surgeon selected angle, a radially compressible spring chuck arranged within the connecting member coaxial with the central axis and having an upper end and a lower end that includes a cavity for receiving the head of the bone anchoring element, and an insert slidable in the bore hole of the connecting member and having a recess complementary in shape to an outer surface of the radially compressible spring chuck. The spring chuck is axially supported in the bore hole without impeding radial movement of the spring chuck therein.
The device according to the invention consists of a connection part accepting the longitudinal rod wherein a pedicle screw having a preferably spherical head may afterwards be snapped-on and fastened. The connection part may be simply snapped-on in the desired number and variant onto the pedicle screws already implanted in the vertebral bodies so that a primary connection between longitudinal rod and pedicle screw is produced. Via the screw-in of the tension means into the fixation device the longitudinal rod is axially and rotatively fastened and simultaneously the device is fastened at a stable angle. Thereby the adjusting screw serving as a tension means presses on the longitudinal rod inserted in the device, this one presses on hollow cylinder which encompasses a hollow truncated cone which is alternatingly slotted and radially not fastened and which is itself compressed because of its conically shaped outer surface and wedging the preferably spherical head of the pedicle screw.
The device according to the invention such offers the advantage compared to the known devices that the pedicle screws are not only fastenable exactly perpendicularly to the longitudinal rod but allows an angle of up to ±25° and because of the distance between the rotating center of the connection part and the axis of the longitudinal rod sideward deviations between longitudinal rod and pedicle screw may be compensated to a certain degree depending on the thickness of the longitudinal rod having an amount of between 4 to 10 mm. This qualities enable the application of longitudinal rods standardizedly prebent at the production site what causes serious difficulties by the mounting of conventional systems. A further advantage of a variant of the device according to the invention consists therein that depending on the embodiment of the hollow cylinder and the tension means respectively on the embodiment of the device the longitudinal rod and the preferably spherical head of the bone screw may be fastened separately.
The angular stability may be improved such that the head of the screw consists of a relatively hard material (e.g. Titanium-Aluminium-Niobium-alloy) and the alternately slotted hollow truncated cone consists of a relatively soft material (e.g. Titanium in its soft state).
Another possibility for the improvement of the angular stability consists therein to provide the preferably spherical head of the pedicle screw and/or the complementa
Hess Martin
Schlapfer Fridolin
Pennie & Edmonds LLP
Robert Eduardo C.
Smith Jeffrey A.
Synthes (U.S.A.)
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