DE29810576U1 - Shaft endoprosthesis - Google Patents

Description

A 54 458 u AESCULAP AG & Co. KG

30 April 1998 At Aesculap Square

u-234 78532 Tuttlingen

■_ _._ STEMMING ENDOPROSTHESIS

The invention relates to a shaft endoprosthesis for long bones with a shaft that is circular in cross-section at least in its lower part, with a lower section and an upper section, on the upper side of which there is a neck that is inclined relative to the longitudinal axis of the upper section and forms a plane with the longitudinal axis of the upper section of the shaft, and that accommodates a joint ball, wherein the longitudinal direction of the upper section of the shaft is angled transversely to the plane relative to the longitudinal direction of the lower section.

Such a shaft endoprosthesis is known, for example, from DE 94 03 263 Ul. Such a prosthesis is suitable for achieving a large-area force transmission so that stress peaks in the bone can be avoided. When cementing such endoprostheses, the shaft should be embedded as evenly as possible in a cement socket. From a certain shaft length, this can lead to problems due to the curvature of the long bone at the distal end of the shaft.

The object of the invention is to design a generic shaft endoprosthesis in such a way that even with longer shafts, a problem-free insertion in curved long bone areas is possible.

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This object is achieved according to the invention in a shaft endoprosthesis of the type described at the outset in that the shaft has a flattening at the lower end of the lower section on its outside protruding from the plane.

The shaft is flattened on one side in such a way that the curvature of the long bone is taken into account when the shaft is inserted into the long bone. Despite this, the rest of the circumference still has a circular cross-section, so that increased stability of the shaft is guaranteed in this area, as well as very even cementing. The flattening can improve rotational stability, and the described shape also improves the possibility of explanting the shaft.

In principle, the flattening can be achieved by replacing the circular cross-section of the shaft over a part of the circumference with a less pronounced curvature, for example with an oval or elliptical cross-sectional area, but according to a particularly preferred embodiment, the flattening is formed by a flat outer surface of the shaft. The circular cross-section of the shaft is therefore replaced on one side, namely ventrally, by a flat surface, i.e. the cross-sectional circle is closed off on one side by a secant.

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It is advantageous if the flattening extends from the lower end of the lower section of the shaft over at least one third of the height of the lower section. In a preferred embodiment, the flattening is inclined relative to the longitudinal axis of the lower section of the shaft in such a way that its distance from the longitudinal axis decreases towards the lower end of the shaft. This essentially corresponds to the fact that the lower end of the shaft protrudes increasingly further ventrally from the plane spanned by the upper section of the shaft and the neck.

Preferably, the cross-section of the shaft is reduced by twenty to fifty percent by the flattening, but it can also be provided that the reduction is greater at least in the lower part of the lower section, i.e. in this area the flattening then extends beyond the middle of the shaft.

The angle of inclination of the flattening relative to the longitudinal axis of the lower section is preferably between 1° and 10°, in particular between 2° and 4°.

It is also advantageous if the lower section of the shaft tapers conically towards the bottom, for example with a cone angle of around 1°. This not only makes it easier to insert the shaft into the long bone, but also to explant it if necessary.

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In a preferred embodiment of a shaft endoprosthesis, in which four axially parallel grooves for receiving a centering element are arranged on the outside of the lower shaft in the area of its lower end, distributed over the circumference, it can be provided that the grooves lie in planes parallel to the longitudinal direction, which are rotated by 45° ym the longitudinal axis with respect to the flattening. This makes it possible to work the grooves deep enough into the shaft even in the area of the flattening, so that the centering element also has a perfect fit in the lower end of the shaft in the area of the flattening;

The following description of preferred embodiments of the invention serves to explain in more detail in conjunction with the drawing. They show:

Figure 1: a front view of a stem endoprosthesis;

Figure 2: a side view of the shaft endoprosthesis of Figure 1 with the centering element removed;

Figure 3: a sectional view along line 3-3 in Figure 2 and

Figure 4: a sectional view taken along line 4-4 in Figure 2.

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The shaft endoprosthesis shown in the drawing comprises a shaft 1 with an upper section 2 and an adjoining lower section 3. The lower section 3 has a circular cross-section and is straight-line, with the lower section 3 tapering conically towards the lower end with a conicity angle of the order of 1°. ,

The upper section 2 widens from bottom to top, forming an arched outer contour and at its upper end merges into a neck 6 that runs obliquely to the longitudinal axis of the upper section 2 and carries a clamping cone 7. A joint ball with an inner cone can be pushed onto this clamping cone in a manner known per se and not shown in the drawing and secured in the clamping seat.

The longitudinal axis of the neck 6, together with the longitudinal axis of the upper section 2, forms a plane, relative to which the longitudinal axis of the lower section 3 is inclined, namely at an angle of between 1° and 10°, preferably at an angle of the order of between 2° and 4°. Due to this inclination of the longitudinal axis of the lower section 3 relative to the plane spanned by the longitudinal axis of the upper section 2 and the longitudinal axis of the neck 6, the lower section 3 increasingly emerges from this plane in the direction of its lower end 4. The angle between the lower section 3 and the upper section 2

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occurs approximately in the middle of the shaft 1 and occurs in a ventral direction when the prosthesis is inserted.

The circular cross-section of the lower section 3 of the shaft 1 is modified in the lower third of the lower section 3 in that the lower section 3 of the shaft 1 has a flattening 8 on its outer side, i.e. ventral, which in the embodiment shown is formed by a flat surface that begins approximately halfway up the lower section 3 and extends to the lower end 4. This flattening 8 is inclined relative to the longitudinal axis of the lower section 3. It begins at its upper end on the outer circumference of the circular shaft and penetrates deeper and deeper into the circular circumference of the shaft towards the bottom, so that the flattening widens from top to bottom (Figure 2).

In the embodiment shown, the flattening only extends so deep into the shaft that the cross-sectional area of the shaft is reduced by 30 to 50% in the lower area, but in principle it would also be possible for the flattening 8 at the lower end 4 to extend beyond the middle of the shaft, so that the cross-sectional area is reduced by more than 50% there.

At the bottom end 4 of the shaft 1, several axially parallel longitudinal grooves 9, each offset by 90° from one another, are cut into the shaft 1 from the outside.

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incorporated. The planes in which these longitudinal grooves 9 run are rotated by 45° relative to the flattening 8 (Figure 4), so that despite the flattening 8, all four longitudinal grooves 9 are clearly formed and can thus form a receptacle for a centering element 10, which is inserted into the longitudinal grooves 9 from below with corresponding longitudinal ribs 11 and thus holds the centering element 10 on the lower end 4 of the shaft 1.

Claims (10)

A 54 458 u 30 April 1998 u-234 PROTECTION OF CLAIMS 1. Shaft endoprosthesis for long bones with a shaft that is circular in cross-section at least in its lower part and with a lower
Section and an upper section, on the top of which there is a plate inclined relative to the longitudinal axis of the upper section and connected to the
Longitudinal axis of the upper section of the shaft spanning a plane, a joint ball
receiving neck, whereby the
Longitudinal direction of the upper section of the shaft compared to the longitudinal direction of the lower
section is angled transversely to the plane,
characterized in that the shaft (1) is
lower end (4) of the lower section (3) has a flattening (8) on its outer side protruding from the plane. 2. Shaft endoprosthesis according to claim 1, characterized characterized in that the flattening (8) is formed by a flat outer surface of the shaft (1). 3. Shaft endoprosthesis according to claim 1 or 2, characterized in that the flattening A 54 458 u
30 April 1998
u-234 (8) extends from the lower end (4) of the lower section (3) of the shaft (1) over at least one third of the height of the lower section (3). 4. Shaft endoprosthesis according to one of the preceding claims, characterized in that the flattening (8) is inclined relative to the longitudinal axis of the lower section (3) of the shaft (1) such that its distance from the longitudinal axis decreases towards the lower end (4) of the shaft (1). 5. Shaft endoprosthesis according to claim 4, characterized in that the flattening (8) extends beyond the middle of the shaft (1) at least in the lower part of the lower section (3) of the shaft (1). 6. Shaft endoprosthesis according to one of claims 4 or 5, characterized in that the angle of inclination of the flattening (8) relative to the longitudinal axis of the lower section (3) is between 1' and 10°. 7. Shaft endoprosthesis according to claim 6, characterized in that the angle of inclination of the flattening (8) relative to the longitudinal axis of the lower section (3) is between 2° and 4°. - 10A
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u-234 8. Shaft endoprosthesis according to one of the preceding claims, characterized in that the lower section (3) of the shaft (1) tapers conically downwards. 9. Shaft endoprosthesis according to claim 8, characterized in that the cone angle of the taper is 1°. 10. Shaft endoprosthesis according to one of the preceding claims, in which four axially parallel grooves (9) for receiving a centering element (10, 11) are arranged on the outside of the lower section (3) in the region of its lower end (4) distributed over the circumference, characterized in that the grooves (9) lie in longitudinally parallel planes which are rotated by 45° about the longitudinal axis relative to the flattened portion (8).