Surgery – Instruments – Orthopedic instrumentation
Patent
1999-03-03
2000-10-31
Buiz, Michael
Surgery
Instruments
Orthopedic instrumentation
606 73, 606104, A61B 1758
Patent
active
061395498
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a fixator for vertebrae or bone fragments, comprising a rod on which at least one pedicle screw is to be secured. The U-shaped head of the pedicle screw forms a receiving seat for the rod. The rod is held in the receiving seat by a fixing device which comprises a U-shaped clamping yoke whose legs can be connected with positive fit to the head of the pedicle screw and whose bridge holds a fixing screw. In a known spinal column fixator (DE-C 41 07 480) the fixing screw acts directly on the rod lying in the receiving seat. This has the disadvantage that the alternating forces which occur between rod and pedicle screw also act on the screw and may loosen it. This is particularly the case when the direction of the rod does not run exactly perpendicular to the longitudinal direction of the screw, and, as a result, a state of considerable looseness can arise upon relative movements, even when the screw has not moved.
The invention is therefore based on the object of making available a fixator of the type mentioned at the outset, which affords more secure connection between rod and pedicle screw and better mutual alignment to the perpendicular setting.
SUMMARY OF THE INVENTION
The solution according to the invention lies in the fact that the fixing screw does not act directly, or not exclusively directly, on the rod, and is instead used to clamp a U-shaped fixing yoke against the rod, with the ends of its legs to the sides of the clamping yoke.
The ends of the legs of the fixing yoke sit on the rod at a specific distance from the center of the fixing device and thus make it possible to exert a substantial restoring moment on this rod if it does not lie perpendicular in relation to the pedicle screw at the start of the fixing procedure. The perpendicular setting is therefore obtained very reliably during the course of the fixing procedure. This setting is also maintained very reliably under alternating forces. Relative movements between rod and fixing screw and within the fixing device do not in practice occur. Thus, the fixing screw is not acted upon by forces from alternating directions which may lead to its loosening. Rather, it is almost exclusively axial forces that act on the fixing screw.
Although the risk of loosening of the fixing screw is therefore considerably less than in the known solution, it can, in an advantageous embodiment of the invention, be provided with a securing device, in particular a locking nut. However, other known securing devices for these purposes can also be used.
In the known arrangement described at the outset, the interacting means on the head of the pedicle screw and on the clamping yoke, providing the positive fit, are designed as mutually engaging ribs and grooves running perpendicular to the direction of the pedicle screw and parallel to the rod. When, during the operation, the head of the pedicle screw is to be connected to the rod, it is often the case that these parts do not at the outset have the setting which they are intended to have; they first have to be adjusted in relation to each other by applying a certain force. Under these circumstances it can be difficult to align the fixing device with sufficient precision so that it can be pushed onto the head of the pedicle screw. The invention makes this procedure easier by making available an instrument for holding the fixing device in the correct direction. The instrument, which is equipped with a large hand grip, can be aligned easily in the desired manner, as a result of which the correct alignment of the fixing device is then also ensured. So that the fixing device is correctly aligned in relation to the instrument, according to the invention the instrument has a saddle-shaped holder part which has two rib-shaped projections which are located opposite one another and which engage under the edges of the bridge of the fixing yoke. The edges of the fixing yoke are in this way aligned with the direction of the ribs and thus also the direction of the instrument.
To ens
REFERENCES:
patent: 5702393 (1997-12-01), Pfaifer
patent: 5928233 (1999-07-01), Apfelbaum et al.
Buiz Michael
Waldemar Link (GmbH & Co.)
Woo Julian W.
LandOfFree
Spinal fixing device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Spinal fixing device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spinal fixing device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2046027