Surgery – Instruments – Orthopedic instrumentation
Patent
1989-02-21
1991-08-27
Hafer, Robert A.
Surgery
Instruments
Orthopedic instrumentation
128 69, A61F 504, A61F 500
Patent
active
050429825
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a positioning device for stabilizing segments of the spinal column, comprising a threaded shaft part and a receiver part for receiving a rod at the head side, wherein the rod and the receiver part are adapted to be rigidly connected with each other by means of two fixing members engaging the receiver part. Such devices are used for stabilizing the spinal column or for stabilizing a dummy between two adjacent vertebrae.
A positioning screw is disclosed in the DE-AS No. 26 49 042. The screw comprises a threaded shaft part and a receiver part rigidly provided at the head end of the threaded shaft part. The respective receiver parts comprise receiving slots. The lateral boundaries of the slots are formed by plane surfaces with concentric depressions. The engaging nuts have plane abutment surfaces with concentric collars. The collars engage the depressions and the plane surfaces of the nuts cooperate with the plane surfaces of the receiver part. It is thereby prevented that the rod disengages from the receiver part. Furthermore, the receiver rod is fixed in a position perpendicular to the axis of the receiver part. Pressure distributing plates are adapted in shape to the vertebrae and placed below the screw heads. A disadvantage of this solution is the difficulty to on the one hand tightly screw the screws into the vertebrae and on the other hand adjust the screws in two planes exactly such that the axes of the receiving slots in the receiver parts on top of each other are aligned such that the threaded rod may be passed through the receiving slots without placing stress on the screws. Already such an attempt requires a lot of time which is a great disadvantage for an operation at the spinal column. Moreover, it is nearly impossible to obtain such an exact alignment. As a result considerable shear forces act upon the threaded rods and thus the rods may even break in the later use after the operation or do not provide the desired stabilization. In addition, the required pressure distributing plates are additional movable parts and their mounting and handling renders the operation more difficult.
It is the object of the invention to provide a positioning device of the above-described kind which facilitates the mounting operation and at the same time reduces or avoids dangers in the later use.
This object is achieved by a positioning device of the above-described kind which is characterized by the features of the characterizing part of claim 1.
Further developments of the invention will stand out from a description of embodiments with reference to the drawings. In the drawings:
FIG. 1 is a lateral view of the positioning device in a direction perpendicular to the longitudinal axis of the rod;
FIG. 2 is a lateral view normally to the view of FIG. 1 with the fixing members and the receiver part being cut;
FIG. 3 represents a second embodiment in a view corresponding to the one of FIG. 1;
FIG. 4 represents the second embodiment in a view corresponding to that of FIG. 2;
FIG. 5 is a lateral view of a third embodiment; and
FIG. 6 represents the third embodiment in the view corresponding to that of FIG. 1.
The positioning device comprises a positioning screw 1 with a threaded shaft part 2 and a receiver part 3.
The receiver part 3 comprises a spherical head which is provided with a slot 4 extending substantially perpendicular to the axis of the threaded shaft part 2. The slot receives a rod 5 which is formed as a threaded rod. Two nuts 6, 7 are provided for fixing the rod in the slot. The nuts 6, 7 are guided on the rod 5 and engage the exterior of the head.
The center plane of the slot coincides with the center of the spherical head. The slot extends into the head beyond the center of the spherical head by more than half a diameter of the rod such that it is possible to pivot or swing the rod with its center axis around the center of the sphere in a desired angular region in direction of the center plane of the slot.
The width of the slot 4 is selected larger than the diameter of the rod 5. Thi
REFERENCES:
patent: 4041939 (1977-08-01), Hall
patent: 4274401 (1981-06-01), Miskew
patent: 4611580 (1986-09-01), Wu
patent: 4611582 (1986-09-01), Duff
patent: 4658809 (1987-04-01), Ulrich et al.
Biedermann Lutz
Harms Jurgen
Brown Donald
Brown Michael
Hafer Robert A.
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