Surgery – Instruments – Orthopedic instrumentation
Patent
1994-05-20
1996-08-13
Pellegrino, Stephen C.
Surgery
Instruments
Orthopedic instrumentation
606 73, A61B 1770, A61B 1786
Patent
active
055451659
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an anchoring member with a shaft to be fastened to a bone and a head for connection with a rod, the head having a substantially U-shaped cross-section which has its base connected to the shaft and comprises two free legs defining a channel for receiving the rod, wherein the legs comprise an internal thread and an external thread, and with a member embracing the legs at their outer side and having an internal thread cooperating with the external thread, and with a fastening member having a thread cooperating with the internal thread of the legs.
Such an anchoring member is known from document EP-A-0,487,830. The rod comprises a triangular cross-section and serves as a restraint from torsional motions. The longitudinal stabilisation proper is provided by plates which are curved corresponding to the intended shape correction. nature the plates are comparatively space-consuming. Further, the base between both legs is formed flat in longitudinal direction of the slit. In a practical application there is a considerable repeated alternating stress caused by the forces acted onto the rod. Hence, the rods tend to break after some time at the edges of the slit base.
It is the object of the invention to form the anchoring member in such a manner that the size of the anchor can be reduced and the anchor resists to higher continuous stresses. This is of particular importance, because such anchoring members and the rods to be connected thereto are used as components for correction implants for the human spinal column and small dimensions and an unlimited stability under load are therefore desired.
This object is achieved in that the base of the U-shaped recess has a curved portion in a direction perpendicular to the U-shaped cross-section. As a consequence, round rods which are bent corresponding to the form correction can be used in place of the plate members for the form correction proper, because even bent rods can be perfectly fastened within the anchoring members. Moreover, the stability under continuous load is considerably increased for straight rods, but in particular also for curved rods.
Further features and advantages of the invention will be evident from the description of embodiments with reference to the drawings.
In the drawings:
FIG. 1 shows a side view of a first embodiment of the anchoring member;
FIG. 2 is a front view of the apparatus shown in FIG. 1;
FIG. 3 shows a section along line III--III in FIG. 1;
FIG. 4 shows a section along line IV--IV in FIG. 2;
FIG. 5 is a side view of a second embodiment;
FIG. 6 shows a section along the plane of symmetry of a modified embodiment in exploded representation;
FIG. 8 corresponds to FIG. 7 with mounted straight rod;
FIG. 9 shows the same embodiment with a convexly curved rod; and
FIG. 10 shows the same embodiment with a concavely curved rod.
The anchoring member shown in FIG. 1 comprises a screw 1 to be introduced into a spinal column and having a threaded shaft 2 and a head 3. The head 3 comprises a U-shaped recess 4 which is symmetric with respect to the central axis of the threaded shaft 2 and which has a base 5 directed towards the threaded shaft 2. The lateral wall of the head defining the U-shaped recess 4 is formed by free legs 6, 7. As best shown in FIGS. 3, 4 and 5 a bore which 10 is coaxial with the center axis of the threaded shaft 2 and has an internal thread 8 is provided in the interior of the channel. The head 3 itself is cylindrical and comprises an external thread 9 at the region of the free legs 6, 7, as best shown in FIG. 4.
In order to allow a rod to be anchored by means of this screw a fastening member 11 formed as a threaded bolt is provided. The fastening member 11 comprises an external thread cooperating with the internal thread 8 for screwing into the U-shaped recess 4. The fastening member has a slit or any other suitable recess for engagement of a screw driver formed at its face opposite to the base 5. Further, a surrounding member embracing both U-shaped legs 6, 7 at their outer side is formed as a spigot 1
REFERENCES:
patent: 4653481 (1987-03-01), Howland et al.
patent: 5024982 (1991-08-01), Harms et al.
patent: 5176680 (1993-01-01), Vignaud et al.
patent: 5217497 (1993-06-01), Mehdian
patent: 5261913 (1993-11-01), Marnay
patent: 5312404 (1994-05-01), Asher et al.
patent: 5352224 (1994-10-01), Westermann
patent: 5360429 (1994-11-01), Jeanson et al.
Biedermann Lutz
Harms Jurgen
Shufflebarger Harry L.
Biedermann Motech GmbH
Markow Scott B.
Neuner George W.
Pellegrino Stephen C.
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