Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2000-04-18
2001-05-01
Buiz, Michael (Department: 3731)
Surgery
Instruments
Orthopedic instrumentation
Reexamination Certificate
active
06224601
ABSTRACT:
DESCRIPTION
The invention relates to an osteosynthesis auxiliary for the treatment of subtrochanteric and peritrochanteric fractures as well as fractures of the neck of the femur, with a locking nail that can be introduced from the proximal end into the medullary space of a femur, which comprises a distal region having at least one transverse bore to receive a distal locking element and a proximal section through which passes a slanted passageway, and with a femoral-neck part that can be introduced from a lateral position through the slanted passageway into the neck and head of the femur, such that there can be inserted into the proximal end of the locking nail a stay-pin or the like by means of which the axial movement of the femoral-neck part within the slanted passageway in the proximal section of the locking nail can be either limited or completely blocked.
An osteosynthesis auxiliary of this kind has been disclosed, e.g. in EP 0 257 118 B1. Supplementary information can be found in EP 0 486 483 A1, EP 0 521 600 A1, EP 0 321 170 A1 or DE-U 87 01 164.6. In the known osteosynthesis auxiliaries the locking nail serves to guide and hold a femoral-neck screw. For this purpose the locking nail comprises in its proximal region a slanted bore traversing the nail, through which the femoral-neck screw can be passed. At the end of the femoral-neck screw toward the head of the femur a self-cutting thread is provided, with which anchoring in the head of the femur is achieved. In addition, into the proximal end of the locking nail a stay-pin can be inserted, by means of which the femoral-neck screw is secured against rotation. This stay-pin simultaneously cooperates with axial grooves at the circumference of the femoral-neck screw to limit the axial movement of the femoral-neck screw within the slanted bore of the locking nail. Alternatively, the stay-pin can be used to produce a rigid connection between femoral-neck screw and locking nail.
One disadvantageous feature of the known construction is that in case of a peritrochanteric fracture it is possible for the head of the femur to twist with respect to the femoral-neck screw. Here it should be kept in mind that a not inconsiderable part of the femoral-neck screw lies within the relatively soft spongiosa of the neck of the femur. Only the self-cutting thread extends into the relatively firm spongiosa of the head of the femur. Under severe stress, this thread is not Guaranteed to be rotationally stable with respect to the head-neck fragment, so that the above-mentioned twisting of the head of the femur can result.
Accordingly, it is the object of the present invention to develop an osteosynthesis auxiliary of the known kind in such a way that twisting of the head of the femur is reliably avoided in cases of peritrochanteric fractures or fractures of the neck of the femur, while retaining the known principle of sliding between locking nail and femoral-neck part. This object is achieved by the invention. By constructing the femoral-neck part as a femoral-neck blade in accordance with the invention, said blade is firstly held within the locking nail in a rotationally stable manner, and secondly it secures the head of the femur against twisting.
Because of the special construction and arrangement of the femoral-neck blade according to the invention, such that the flat sides of the femoral-neck blade extend parallel to the long axis of the locking nail or the neck of the femur, the femoral-neck blade is additionally endowed with a particularly high resistance to bending in the plane defined by the femoral-neck blade and locking nail. Accordingly, the femoral-neck blade in accordance with the present invention can sustain extremely large bending moments with no danger that the blade will be deformed in such a way as to prevent its axial movement within the slanted passageway through the locking nail with consequent loss of the above-mentioned sliding principle. In the known constructions with femoral-neck screw this phenomenon of a secondary rigid connection between femoral-neck screw and locking nail has been known to occur, with the consequence that in femoral-neck fractures and fractures in the trochanteric region (extending downward from lateral to medial: Types A1 and A2 in the AO classification of peritrochanteric fractures), the desired compression of the fractured head of the femur or head-neck fragment in the plane of fracture into the metaphyseal fragment becomes impossible and the implant perforates into the hip joint.
In a manner known per se, the locking nail is preferably made hollow throughout, so that it can be introduced into the proximal femur by way of a guide spike. The wall thickness of the hollow locking nail is about 1.5 to 2.5, in particular about 2.0 mm.
In the plane defined by the locking nail and femoral-neck blade the proximal section of the locking nail is bent laterally outward by an angle of 4° to 8°, in particular about 6°, with respect to the distal section, achieve a minimal tension-line concentration in the locking slide nail. In the known construction, the above-mentioned angle is about 12°. This distinct bend in the locking nail causes instabilities when alternating loads are imposed in the region of the bend, and the compromise in accordance with the invention avoids these. Care should also be taken that the transition between distal and proximal sections is not abrupt but constitutes a curved section. In principle, of course it would be advantageous for the locking nail to be exactly straight, because this construction would give it the greatest resistance to buckling. However, such a solution is not useful for reasons of surgical technique; that is, the bending is necessary so that the site of nail insertion can be in the region of the trochanteric tip and not in the region of the fossa. The latter would involve a considerable interference with the blood flow through the head-neck fragment, where circulation is already impeded by the fracture. Furthermore, insertion of a locking nail in the region of the trochanteric fossa is very complicated technically, so that the construction in accordance with the invention is an ideal compromise between technically simple insertion on the one hand and reduction of the tension-line concentration in the locking nail on the other.
The length of the locking nail is between 150 and 350 mm, in particular about 220 mm for the treatment of peritrochanteric fractures and about 320 mm for the treatment of subtrochanteric and pathological fractures. The somewhat shorter locking nail is straight as seen along a line parallel to the plane defined by the locking nail and femoral-neck blade. Hence the locking nail can have the same shape for both the right and the left femur. The somewhat longer design must allow for the curvature of the femur by having a ventral convexity with a radius of about 1.5 m. In this case there must be one locking nail for the right femur and a separate locking nail for the left femur.
In all cases the distal end of the locking nail is preferably rounded, so that it can be gently introduced into the medullary space of the femur.
A measure of special significance for the stability of the system in accordance with the invention is that the width of the proximal section of the locking nail in the region of the slanted passageway for the femoral-neck blade and in the direction perpendicular to this passageway is greater than the width or outside diameter of the region of the locking nail distal to this section. The transitions between the regions of different width in each case should be not abrupt but rather slightly curved, to avoid tension peaks. This construction reliably avoids breakage of the locking nail in the region of the passageway for the femoral-neck blade. This region is extremely critical with regard to stability, as it represents a weak point which furthermore is relatively heavily loaded by way of the femoral-neck blade. By means of the above-mentioned measures a sufficient resistance to breakage is achieved in the critical region around
Buiz Michael
Endocare AG
Knobbe Martens Olson & Bear LLP
Reip David O.
LandOfFree
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