Surgery – Instruments – Orthopedic instrumentation
Patent
1991-06-28
1993-05-11
Hafer, Robert A.
Surgery
Instruments
Orthopedic instrumentation
606 73, A61B 1756
Patent
active
052097536
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a bone screw comprising a threaded portion and a head, such screws being used particularly as pedicel screws.
A screw of this type is known e.g. from DE-36 14 101 C.
In some cases the bone tissue in which the screw is to be anchored is so soft that sufficiently fixing the screw is difficult.
It is an object of the invention to provide a bone screw having a threaded portion and a head which improves the anchoring in bones as compared to conventional screws. The anchoring should be precisely adjustable.
This object is attained by the bone screw as outlined in claim 1.
Additional features are indicated in the subclaims.
Further features and advantages of the invention will be apparent from the description of the figures which show:
FIG. 1 an exploded view of the bone screw, partially as sectional view, and
FIG. 2 the assembled screw together with a connecting part.
The bone screw 1 comprises a threaded portion 2 formed unitary with a head 3. The threaded portion is provided with an external thread 4 as commonly used with bone screws. As can be seen from FIG. 1, a coaxially aligned longitudinal bore extends through the interior of said screw. At the free end 6 opposite to the head a tapered conical portion 7 is provided. Slits 8 extend parallel to the longitudinal direction of said threaded portion. The axial length of said slits is at least equal to twice the length of said conical portion. Preferably, one pair of slits is provided, the slits being displaced by 180 degrees with respect to each other.
Opposite to the free end the head 3 is provided with a plane face arranged perpendicular with respect to the axis of symmetry. A recess 10 extends in axial direction which is formed to allow the screw to be screwed into a bone by a screw driver. The diameter of said recess is larger than the diameter of said longitudinal bore. Adjacent to the recess 10 a threaded portion 11 is arranged. Preferably, the length of this portion is at least twice the length of the tapered portion 7.
As can be seen from FIG. 1, the point of the bone screw is formed as a separate tip 12. A coaxially aligned bore 13 is provided at the end pointing towards the head. The opposite end has a point 14 corresponding to the tip of the bone screw. Opposite said point the exterior of said tip has a conical portion 15 tapering towards the conical portion 7 and formed to fit into said portion 7.
A shaft 16 is provided having a first threaded portion 17. The diameter and the pitch of this thread correspond to the interior thread of the portion 11 so that both threads may be joined. The diameter of the rest of the shaft 16 is dimensioned so it may be inserted into the longitudinal bore. Opposite to the first threaded portion 17 a second threaded portion 18 is provided which cooperates with an interior portion 18 and the pitch of the thread in the bore 13 are opposite to the pitch of the first threaded portion 17 and to the pitch of the corresponding interior thread in portion 11.
The length of the shaft 16 is selected such that the second threaded portion 18 extends into the tapered portion 7 and the tip 12 can be screwed onto this portion. Consequently, as shown in FIG. 2, the point 12 forms the normal point of the bone screw when the first threaded portion 17 is screwed to the end or at least close to the end of the threaded portion 11. A slit 19 is provided at the end of said threaded portion into which a screw driver may be inserted.
In operation, first the shaft 16 is screwed into the longitudinal bore 5 to the end of the threaded portion 11. Next, the tip 12 is screwed onto the second threaded portion 18 projecting into the tapered portion 7, thus forming the normal point of the screw, as shown in FIG. 2. If required, the head of the bone screw may be provided with a connecting part 20 which is movable with respect to said screw head, as described in DE 37 11 013 C. The connecting part serves to connect the screw with rods for the fixation of bone fragments, in particular spinal elements.
When the bone screw has been s
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Biedermann Lutz
Harms Jurgen
Brown Donald
Brown Michael
Hafer Robert A.
Neuner George W.
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