Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2000-03-28
2001-06-19
Reip, David O. (Department: 3731)
Surgery
Instruments
Orthopedic instrumentation
C606S062000, C606S075000
Reexamination Certificate
active
06248109
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an implant for fixing two bone fragments to each other, in particular for fixing an axially corrected capitulum of a metatarsal bone, e.g. hallux valgus.
BACKGROUND OF THE INVENTION
Osteotomies for treating hallux valgus have already been known for decades and have the object of functionally reconstructing the axis of the 1st metatarsal. It is necessary in this context, after the osteotomy, to fix the two bone fragments in their corrected position in order to prevent mobility between the fragments and to permit reliable osseous union without dislocation.
To fix the osteotomy, it is already known to use plates which are secured to the cortical bone by means of a number of screws in order to prevent the bone fragments from buckling. A considerable surgical outlay is required for this.
Bone clamps are also known for fixing the osteoLomy, but their use involves the risk of splintering of the bone.
AT 937 U has disclosed an implant for fixing two bone fragments to each other, in particular for treating an axial deviation of a metatarsal bone, e.g. hallux valgus, which implant comprises a clasp with two arms which are connected to each other at one of their ends and in this area delimit an opening for passage of a screw which can be screwed into one of the two bone fragments and which, with their other, free ends, can be introduced into the medullary cavity of the other bone fragment and can spread apart. After osteotomy has been performed, the clasp is introduced proximally into the medullary cavity of one bone fragment via the free ends of the two arms and spreads apart in this medullary cavity, after which the clasp is anchored on the other bone fragment by means of the screw guided through the opening.
As a result of the spreading force and the frictional fit of the clasp arms, and as a result of the intermittent compression arising upon functional loading, the intramedullary part of this known implant has a high degree of stability. By contrast, however, the extramedullary part is anchored in the bone via only one screw, whereas a two-point bearing is required on account of the torque which increasingly occurs as the compression of the screw anchoring between implant and metatarsal head decreases.
SUMMARY OF THE INVENTION
The object of the present invention is to improve and stabilize the fixing of this known implant to the one of the two bone fragments connected to the implant via the screw, without in so doing having to modify the surgical procedure. To achieve this object, the invention proposes that a shim part, through which the screw is passed, be arranged between the clasp opening and the screw head, which shim part has projections which can be anchored in the bone fragment. These projections provide for fixing of the clasp to the bone fragment in addition to the screw, as a result of which the stability is considerably improved. The shim part is preferably in the shape of a circular annulus and has spikes protruding essentially at right angles from the annular plane, which spikes penetrate or are pressed into the bone fragment and are thus securely anchored in the bone fragment.
A preferred embodiment of the implant according to the invention is characterized in that the shim part has a recess receiving the clasp with form fit in the area of the opening, and a lateral slot for passage of the arms of the clasp. This embodiment affords a form fit between the shim part and the clasp and thereby reliably prevents the clasp from twisting about the screw axis. The shim part is pressed onto the bone fragment (or vice versa) by the screw, preventing a change in the position of the spikes penetrating into the bone fragment. The invention makes it possible to connect the two bone fragments to each other in a stable manner directly without special bone incision.
It is expedient for the shim part to have at least three projections.
This shim part is preferably made of a tissue-compatible material, for example stainless steel according to ISO 5832/1.
REFERENCES:
patent: 4838254 (1989-06-01), Gauthier
patent: 4915092 (1990-04-01), Firica et al.
patent: 000937 U (1996-08-01), None
patent: 0288229 (1988-10-01), None
Morrison & Foerster / LLP
Reip David O.
Waldemar Link (GmbH & Co.)
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