DE20011728U1 - Tripolar ball head for hip endoprostheses - Google Patents

Description

Merete Management GmbH

Fasanenstrasse 51

10719 Berlin Berlin 29.06.00

ana-ag-gb499

Tripolar ball head for hip endoprostheses

The innovation concerns a tripolar ball head for hip endoprostheses, whose spherical and hollow sphere-like shells can be pivoted and rotated on several sliding planes within each other and around a common or eccentrically arranged pivot point.

Bipolar ball heads from various manufacturers are known, also known as duo heads, in which a metal ball with a cone snaps into place and slides freely in a plastic insert or inlay that is larger than a hemisphere, and this hemisphere is covered with a metal shell. These ball heads are inserted directly into the hip, almost as a socket replacement, without being attached themselves, and can roll directly on the acetabulum with a certain degree of freedom. For this, see H.-G. Breyer, "Bipolar hip joint endoprostheses", Einhorn-Presse Verlag 1996, and also "Unfällchirurg" 1992, Springer Verlag, pages 224-229.

DE-PS 43 36 552 discloses a duo-head joint socket for an artificial hip joint that can be fixed in a pelvic bone socket. Here, a duo-head is to be covered with yet another outer cap, which is provided with fixation spikes, which are to anchor this outer cap in the patient's acetabulum. After this construction of a duo-head, however, only the ball can rotate freely in its intermediate shell; an additional sliding plane between the intermediate shell and the outer cap is not provided, and the already known design of the duo-head is not recognizable.

There have already been reports of partial impairment of the freedom of movement of duo acetabular cups, both in the acetabulum and between the ball and the plastic inlay.

A particular disadvantage of this type of dual-head endoprosthesis is that in patients with limited mobility, the outer shell of the head forms a certain connection with the acetabulum, by growing or sticking, and additional oxidation between the ball and the inlay causes a greater friction moment, which in turn can lead to increased pain and loosening of the entire prosthesis. Surgical doctors have therefore already suggested first attaching a thin metal shell to the acetabulum, into which the head of a bipolar hip endoprosthesis is then inserted, allowing the usual freedom of movement to be used.

The innovation therefore sets itself the task of improving previously known bipolar ball head hip endoprostheses by distributing the total friction force of such a head not only to the rolling of the outer shell in the acetabulum and a sliding plane in the head, but also to further, additional sliding planes.

As a solution, it is proposed to design the ball head of a hip joint endoprosthesis with at least two variable sliding planes that run towards and into each other.

This object is achieved by a ball head for hip endoprostheses with the features of claim 1. Advantageous further developments emerge from the subclaims.

The aim of ball-head joint prostheses, especially the previously known duo-head joint sockets, is to make the freedom of movement of the entire prosthesis, also known as the so-called RoM (range of motion), as large as possible.

In an example embodiment, we start with a ball head for hip endoprostheses that has an eccentric structure, i.e. the ball and the first inlay have a common center, the outer half-shell or second inlay has a different center, but this is on a common vertical axis. The inner ball, as the first sliding plane, into which the prosthesis shaft is inserted directly or via an adapter, can be rotated in a first inlay, with a second shell arranged above the first inlay as the second sliding plane. After implantation, with the ball head as a joint socket lying directly in the acetabulum without being attached, the outer shell essentially represents the third sliding or movement plane.

This makes it possible to achieve a large deflection of the femoral-side prosthesis shaft without accelerating or inducing the luxation of the inner ball, particularly in the case of long-term use and the possible adhesion of the outer shell in the acetabulum. The adhesion forces that occur there are often underestimated and represent an undeterminable quantity. Although the maximum deflection angle is given by the structural design of the prosthesis shaft to the hemispherical shell, the design according to the invention enables a deflection range that is several degrees larger. Another advantage is that the friction forces are distributed more effectively across several sliding planes.

Such a structure can now be optimally constructed using the appropriate implant materials, which have the best sliding properties and, on the other hand, also a high level of abrasion resistance.

Furthermore, this solution allows the system to be given a positive or negative eccentricity by shifting the respective center points of the individual sliding planes. It is also possible to expand the system to include one or more sliding planes in the area of this innovation.

Further advantageous embodiments emerge from the following description of an exemplary embodiment and from the drawings. It shows:

Fig. 1 in section a tripolar ball head,

Fig. 2 the ball head with a first deflection of the ball, Fig. 3 the ball head with the largest deflection of the ball.

Fig. 1 shows a tripolar ball system 10, which is positioned in the indicated acetabulum 20.

The ball 1 has an inner cone 2 for receiving the shaft of a prosthesis or a corresponding adapter (not shown in detail).

The ball 1 slides with its surface 3 in a first inlay 4 with an applied surface 5. Above this there is now a second inlay 6 with an applied surface 7.

This results in three sliding planes, namely the first plane 3A between ball 1 and inlay 4, the second sliding plane 5A between surface 5 and inlay 6 and the third plane of movement, plane 7A between outer shell 7 and the acetabulum 20.

The material structure is such that the ball 1 preferably consists of metal or ceramic, which slides in a first inlay 4 made of plastic, whereby the inlay 4 can have a surface 5 made of metal or ceramic that is firmly attached to it. The second inlay 6 also preferably consists of plastic, for example polyethylene (PE) and is preferably firmly connected to a metal shell or metal coating 7. The ball 1 can also be made of a corresponding plastic.

In one embodiment of the innovation, the structure of such a ball head can also be provided in such a way that instead of the second inlay 6, the outer metal shell 7 slides directly on the metal shell 5. This results in a particularly small structure of a joint socket with a sliding plane 5 A, in which metal slides on metal, whereby the particularly easy-to-manufacture metal surfaces with a low coefficient of friction represent an advantageous solution.

It goes without saying that the sliding planes 3A and 5A have no play in relation to each other, but correspond exactly with each other.

The ball head 10 shown in Fig. 1 is, as already mentioned, eccentrically constructed. All radii of the ball 1 with sliding plane 3A, inlay 4 with surface 5 and sliding plane have the common center point 12, while the outer shell 7 with sliding plane 7A has the center point 9 on the vertical axis 11.

For various reasons, it may be necessary or advantageous to assign the individual sliding planes 3A, 5A and 7A to a center point 9 other than that on the axis 11. In particular, a positive or negative displacement of the center point of the outer shell 7 can lead to a desired advantageous eccentricity of the system in order to trigger or cause self-righting moments in the acetabulum. The center point displacement of the sliding plane 5A can also produce the same results here.

Fig. 2 shows a representation of the ball head joint prosthesis 10 according to the invention without acetabulum, in a first swiveling out. In the ball 1, a possible shaft 30 of a prosthesis is indicated in dash-dot form, which is just beginning to touch the first inlay 4 and possibly to include it in a further swiveling out. The angle to one side is 35° here.

This type of swinging out can be like this, although a joint swinging out of the ball 1 with the inlay 4.5 is also possible and probable.

Fig. 3 shows the furthest pivoting of this ball head 10 to one side, namely 45°, so that a total angle of 90° is achieved. As can be seen, an even tighter construction of the outer shell 6,7 would enable even greater pivoting angles.

According to the above, a structural design of a ball head with three or four nested sliding planes is also within the scope of this innovation.

Claims (8)

1. Ball head for hip endoprostheses with a ball carrying a cone, a half-shell surrounding the ball like a dome, a sliding plane being formed between the two, characterized in that the ball head ( 10 ) consists of at least two sliding planes ( 3A , 5A ) which can be pivoted and rotated within one another and about an eccentrically or common pivot point ( 9 , 12 ). 2. Ball head according to claim 1, characterized in that a ball ( 1 ) provided with a cone ( 2 ) is surrounded by a first inlay ( 4 ) with a surface ( 5 ) in the shape of a half-shell and this in turn is surrounded by a second inlay ( 6 ) with an outer shell ( 7 ), so that two sliding planes ( 3A , 5A ) are formed. 3. Ball head according to claim 1, characterized in that all parts of the ball head ( 10 ) are arranged concentrically around a center point ( 9 ). 4. Ball head according to claim 1, characterized in that the center point for the sliding plane ( 7A ) on the vertical axis ( 11 ) is arranged above or below the center point ( 9 ). 5. Ball head according to claim 1, characterized in that the ball 1 with sliding plane 3 A, the first inlay 4 with sliding plane 5 A and the second inlay 6 with outer shell 7 A have different centers lying on a vertical axis ( 11 ). 6. Ball head according to claim 1, characterized in that the ball ( 1 ) made of metal or ceramic, the first inlay ( 4 ) made of plastic is provided with a layer ( 5 ) made of metal and the second inlay ( 6 ) made of plastic is provided with a metal shell ( 7 ). 7. Ball head according to claim 1, characterized in that instead of the second inlay ( 6 ) an external metal shell ( 7 ) is arranged and slides directly on the metal surface ( 5 ) of the first inlay ( 4 ). 8. Ball head according to one of the preceding claims, characterized in that a ball head is formed by three sliding planes with three inlays or sliding shells, which can pivot and rotate within each other and about an eccentrically or common pivot point ( 9 , 12 ).