Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2000-01-12
2001-09-18
Philogene, Pedro (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S064000, C606S064000
Reexamination Certificate
active
06290703
ABSTRACT:
The present invention relates in general to a fixing device, in particular for fixing to the sacrum and usable during osteosynthesis of the backbone.
BACKGROUND OF THE INVENTION
It is commonplace to perform osteosynthesis of the backbone by using fixing devices that are fastened to the sacrum. This makes it possible to perform reduction movements between the various fixed stages, which movements can be contractions, distractions, or indeed reversals of vertebrae that have slipped forwards relative to the backbone, where the latter condition is known as “spondylolisthesis”.
Distraction is often performed for reduction of spondylolisthesis. Partial reduction is thus obtained by putting the fibers of the patient's ligament and disk apparatus back under tension. Reduction is completed by using equipment in accordance with the operating technique associated therewith. Except under exceptional circumstances, the operation is performed bilaterally. Throughout the description below, only one side of the treatment is described.
Most blocks or plates known in the prior art for fixing to the sacrum suffer from certain drawbacks. One of these drawbacks lies in that the orientation of the bone-fastening screws is fixed, which means that the device clearly lacks flexibility in use, given variations from one patient to another concerning the configuration of the sacrum and the neighborhood thereof.
Another drawback of known plates or blocks for fixing to the sacrum lies in the risk of the fastening screws becoming unscrewed, particularly under the effect of relative micromovements that occur between the equipment and the sacrum. This can result in failure of the fixing to the sacrum.
Also, backbone osteosynthesis can be performed by using equipment serving to fix various functional units of the spinal column, often in a very rigid manner. This gives rise to a sudden change in the distribution of forces, and thus to resulting stress and deformation states for the disks underlying and overlying the fixing. At some stage in the long term, this modification gives rise to degeneration of the disks. This condition is known as the “hinge syndrome”.
Document EP-A-0 625 337 discloses a bone fixing device, in particular for fixing the sacrum for osteosynthesis of the backbone, the device comprising elongate link means receiving at least one bone-fastening screw, which screw passes through an orifice formed in the link means, in which the link means include in the bottom region thereof a bearing surface of essentially circular cross-section, in which the head of the screw has a surface that is essentially spherical for bearing against said bearing surface, and in which the link means include a first thread in the orifice, the device also including a plug having a second thread suitable for co-operating with the first thread and for coming into clamping contact with said screw head to hold it in a desired angular position. That device enables the inclination of the screws relative to an elongate link element to be varied, and it also enables the spacing between the screws to be varied.
Nevertheless, that known device is disadvantageous in that the elongate link means are constituted by a plurality of components, specifically an elongate member of cup-shape and a plurality of fixing blocks distributed along the elongate member, each receiving the head of a screw, and at the bottom, a zone corresponding to the elongate member.
This means that it is extremely fiddly for the surgeon to handle the device and put it into place, and in particular it is necessary to slide a series of fixing blocks along the elongate member, and to hold them in position thereon.
OBJECTS AND SUMMARY OF THE INVENTION
A first object of the present invention is to mitigate that drawback.
To this end, the invention provides a bone fixing device of the type defined above, wherein the link means are constituted by a single-piece plate-shaped element having the orifice and the first thread formed therein, and wherein said bearing surface is essentially spherical.
Preferred, but non-limiting aspects of the device of the invention are the following:
the first thread is a tapping formed internally in the orifice at a distance from said bottom, and the plug has an outside thread;
the screw head also has a generally spherical top, and the plug has a complementary internal spherical cavity;
said plate includes a series of orifices in alignment that are interconnected by a slot enabling a bone-fastening screw to be moved from one orifice to another before tightening;
said screw head and said plug have identical tightening sockets;
said plate is designed to be fixed to a first bone and forms an integral portion of an element that also includes an eyelet for another bone-fastening screw for fastening to a second bone, together with a rod interconnecting said plate and said eyelet;
the device further includes a bone-fastening device for fastening to another bone, to which said rod is fixed;
the device includes at least two bone-fastening screws passing through respective orifices formed in said plate, and the two screws are suitable for taking up two different angular positions;
the device further includes means for attenuating the stiffness of the assembly between at least one of the bone-fastening screws and said element;
said means for attenuating stiffness comprise at least one piece of flexible material interposed and compressed between said screw head and the associated plug;
the device is associated with a plurality of pieces of flexible material having different flexibilities, thereby enabling different degrees of stiffness attenuation to be provided without requiring action to be taken on the torque with which the plug is tightened;
said piece is an O-ring;
said piece is a pellet;
said stiffness attenuation means comprise a thixotropic fluid interposed between and compressed between the plug and said screw head;
said spherical bearing surface of said orifice is formed by deforming an O-ring placed in a bottom region of said orifice;
said spherical bearing surface of said orifice is constituted by a surface of a rigid ring fitted in a bottom region of said orifice;
said rigid ring is made of a material selected from the group comprising: ceramic-coated titanium alloys, titanium alloys treated by ion bombardment, and solid ceramics;
the stiffness attenuation means further include a surface coating suitable for reducing friction between said essentially spherical bearing surface and said complementary surface of the screw head; and
said surface coating is made by nitrogen ion bombardment.
REFERENCES:
patent: 4696290 (1987-09-01), Steffee
patent: 5324290 (1994-06-01), Zdeblick et al.
patent: 5443467 (1995-08-01), Biedermann et al.
patent: 5520690 (1996-05-01), Errico et al.
patent: 5531746 (1996-07-01), Errico et al.
patent: 5607426 (1997-03-01), Ralph et al.
patent: 5669911 (1997-09-01), Errico et al.
patent: 6022350 (2000-02-01), Ganem
Blakely & Sokoloff, Taylor & Zafman
Philogene Pedro
Stryker France S.A.
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