WO1998004216A1

WO1998004216A1 - Complete endoprosthesis for the shoulder

Info

Publication number: WO1998004216A1
Application number: PCT/EP1997/004079
Authority: WO
Inventors: Basim A. Fleega
Original assignee: Fleega Basim A
Priority date: 1996-07-26
Filing date: 1997-07-28
Publication date: 1998-02-05
Also published as: DE29623435U1; DE19630298A1

Abstract

The invention concerns a complete endoprosthesis for the shoulder with a shaft (10) and an interchangeable head (20) which can be affixed to the shaft (10) and which is shaped like a mushroom head and symmetrical to a center line (M) and with a connecting side (211) for the shaft (10) constructed on the underside of the head (20), whereby the connecting side (211) of the head (20) on its underside runs in a direction not perpendicular to the center line (M) of the head (20). The head (20) can be fastened to the sh aft (10) in different positions (A, B, C, D) which turn about its axis of attachment (W).

Description

description

Total shoulder arthroplasty

The object of the invention relates to a total shoulder endoprosthesis with a shaft and a head which can be exchangeably fastened to the shaft, with a mushroom-shaped shape symmetrical to a central axis M and with a connection side for the shaft formed on the underside of the head.

The total shoulder arthroplasty was developed by C.S. Neer developed. The head which replaces the removed part of the humeral head of the humerus has approximately the shape of a spherical section, also referred to as a mushroom-shaped shape. The known head, which has a symmetrical shape, is fastened on a shaft which has an insertion part for insertion into the upper arm leg and at the end a usually plate-shaped connecting side on which the head is fastened. The heads can be made of a material that is compatible with the body, such as titanium, cobalt-chrome, ceramics with or without a coating. Heads and shafts with different dimensions of the same shape are available for different body sizes.

The problem now arises that complications can arise in the implantation of the shoulder prosthesis with shaft and head if, for example, the shoulder prosthesis is at an incorrect angle with respect to the glenoid

ORIGINAL DOCUMENTS (Shoulder joint socket) or humeral head of the humerus, which leads to dislocation. In such a case, it has previously been necessary to remove the entire shoulder prosthesis and to re-implant it in order to achieve the optimal fit of the shaft and thus of the head fastened on the shaft.

The invention has for its object to enable the correction of the fit of implanted shoulder prostheses with shaft and head without removing the entire prosthesis and also to achieve an improved possibility of compensating for imperfections in the region of the shoulder joint by means of an implanted head.

To achieve the object, the invention proposes that

Design the underside of the head for the total shoulder endoprosthesis to be oblique with respect to the central axis (M) of the head. According to the invention, a head which is in principle asymmetrical for the implantation is thus obtained, which fills the space between the humeral head and the glenoid differently depending on its position on the shaft.

Advantageous embodiments of the head according to the invention can be found in the characterizing features of the subclaims.

According to the invention, the underside of the head is asymmetrical with respect to the central axis M of the head, so that the central axis M of the head is inclined at an acute angle with respect to the mounting axis of the head on the shaft. This means that when the head mounted on the shaft rotates about its fastening axis W, the axis of symmetry, namely the central axis of the head, moves on a conical surface around the fastening axis when the head rotates. This means that the head, viewed in plan view, assumes an asymmetrical position on the shaft with respect to the fastening axis and can therefore be displaced accordingly by rotation and in this way is able to fill different spaces in the shoulder joint area.

In particular, it is proposed that the underside, which forms the connection side of the head to the shaft, be inclined at an acute angle α with respect to the perpendicular position to the central axis M of the head, the angle preferably being between 5 and 20 °. In particular, it is proposed to design heads with different angles α as a modular system, for example, on the one hand, a series of mushroom-shaped heads of different sizes as a series, these being formed with an angle of 5 °, 10 ° or 15 ° inclined connection side.

According to a further proposal of the invention, the head is formed with a protruding wedge-shaped neck part, the underside of which forms the connection side which is inclined with respect to the central axis M of the head. The head and neck part are preferably made from one part, but it is also possible to produce the head and neck part in two parts and then to connect them during assembly or beforehand.

In a preferred development of the head according to the invention for a shoulder prosthesis, it is proposed that the head be formed with a neck part in the form of a crooked circular cylinder, the crooked cross-sectional area of which forms the underside and connection side of the head towards the shaft.

For fastening the head to the shaft, it is proposed that the head for fastening to a pin formed on the connection side of the shaft has a blind hole corresponding to the pin, the central axis of the pin and the central axis of the blind hole being the fastening axis of the head on the shaft form, such that when the head is placed on the shaft, the central axis of the head is inclined at an acute angle to the fastening axis of the head. According to the invention, the head with the neck part can be fastened on the shaft in various positions rotated about its fastening axis, and since it is designed asymmetrically, it fills the space differently with respect to its constantly constant fastening axis. This makes it possible to correct the head position even with an implanted shoulder prosthesis, without the shaft having to be surgically removed and reinserted. According to the invention, it is possible, even with an implanted shoulder prosthesis, to change the position of the head with only a slight minimal intervention by rotating about the fastening axis W and thus bring about a desired correction.

With the invention, four different correction options are possible during and also after an implantation of the shoulder prosthesis by changing the head position, namely with respect to the humeral head and with respect to the pan to the front, back, up and down.

In particular, it is possible to easily correct an incorrect angular position of the implanted shoulder prosthesis by means of the head designed according to the invention even after the implantation.

The invention also makes it possible, in the case of an implanted shoulder prosthesis which has a symmetrical head, to replace said head, if necessary, and to replace it with a head according to the invention. Here, too, only minimal intervention is required and no removal of the entire prosthesis, in particular not the prosthetic shaft inserted into the humerus.

In order to enable the four correction options listed above for the seat of the same head of a shoulder prosthesis, the positions are proposed in each case to be arranged at an angle of 90 ° to one another around the fastening axis. For this purpose, the head according to the invention can have on its inclined connection side a positioning pin projecting beyond the connection side, and a number of position holes corresponding to the number of positions of the head on the shaft can be provided on the connection side of the shaft for inserting the positioning pin of the head.

In a further development of the invention, the angle between the fastening axis and the central axis of the head is preferably the same as the angle at which the connecting side of the head is inclined with respect to the perpendicular position to the central axis, and is preferably in the range from 5 to 20 °.

When designing the head according to the invention with an asymmetrical shape in the form of a connection side which is inclined with respect to the central axis, preferably by forming an approximately wedge-shaped neck part, it is proposed that the neck part tapers towards zero towards an edge side of the mushroom-shaped head part, i.e. in Cross-section considered forms a long pointed triangle.

With the head according to the invention, it is possible to correct in the case of shoulder prostheses implanted at a wrong angle in a simple manner with minimal intervention, either by replacing a normal head without asymmetry with a head according to the invention in an asymmetrical form or by replacing an already existing asymmetrical head into a other position is placed on the shaft.

The head according to the invention in the case of a high implantation of the head makes it possible to enlarge the space between the glenoid and the attachment of the rotator cuff in the shoulder area and at the same time to reduce the space between the acromyon and the humeral head. This is achieved in that the neck part forms an elevation of the head in the wedge-shaped area, so that in the end, a tension on the rotator cuff is achieved by the head according to the invention in the corresponding position in order to simultaneously reduce the space between the acromyon and the head. Changing these two levels is not possible with the previously known symmetrical heads of shoulder prostheses.

A further possibility when using the asymmetrical head according to the invention for the correction consists in that the version angle of the head in the case of an implanted shaft can be changed, in particular reduced, forwards and backwards by changing the position of the head on the shaft.

In cases in which the shoulder socket is eroded in the upper part, the

Rotator cuff compressed between the head and the shoulder joint socket, because the erosion of the shoulder joint socket creates a large space between the upper part of the head and the upper part of the shoulder joint socket. This can be corrected by the head according to the invention by inserting it into the corresponding position on the shaft, since the head in the upper part can be raised in the corresponding position by the asymmetrical design of the head according to the invention.

Lower erosion of the shoulder joint socket can lead to a loosening of the subscapilar tendon, whereby the use of a larger known head can lead to tension on the subscapilarus and infraspinatus tendon, but also to a loosening of the supraspinatus tendon. If, however, an asymmetrically sized head is used according to the invention, tension can be achieved on the subscapilarus and infraspinatus tendon without exerting pressure on the supraspinatus tendon.

The invention is explained below with reference to the drawing and examples. Show it Fig. La-c the side view, a longitudinal section and the

Bottom view of a known symmetrical head for a shoulder prosthesis

2a-c the side view, the longitudinal section and the bottom view of an inventive head in asymmetrical shape

Fig. 3 is a side view of a shoulder prosthesis with shaft and head according to the prior art

Fig. 4,5,

6.7 the side view of a shoulder prosthesis with

The shaft and head according to the invention are fastened in different positions on the shaft

Fig. 8 is a schematic representation of the top view for the different positions of the head according to the invention on the shaft

9a, b schematic representation of an implanted

Side and top view of shoulder prosthesis.

La to lc a commercially available symmetrical head for a shoulder prosthesis (total shoulder endoprosthesis) is shown, which essentially has a mushroom-shaped shape and is symmetrical to the central axis M. The height H and the diameter E of the head 20 can be chosen differently for different head sizes. On its connection side 201 for attachment to the shaft, the head 20 is flat and has the slightly conical blind hole 202 in the center. Further centering holes 203a, b, c, d can be formed around the blind hole on the connection side 201. The attachment of the head 20 according to FIGS. 1 a, b, c takes place, as can be seen in FIG. 3, on the top plate 101 of a shaft 10. In this case, a pin 102 with a pin axis is formed on the top plate 101 of the shaft 10 which defines the mounting axis W. certainly and which, in the case of the formation of a symmetrical head 20 according to the prior art, coincides with the central axis M of the head 20 during assembly, as can be seen in FIG. 3. The head 20 is plugged onto the pin 102 with its blind hole and fixed, for example, by the taper of the fits. When the head 20 is rotated about the central axis M, which is equal to the fastening axis W, according to FIG. 3, nothing changes with respect to the space which the head 20 fills.

2a, b, c shows a head 20 designed according to the invention, which has a mushroom-shaped symmetrical head part 20a and has an asymmetrical neck part 21 on its underside, namely the connection side to the shaft, for example in the form of a crooked circular cylinder. The obliquely cut surface of the neck part 21 forms the connection side 211. The angle α of the inclined connection side 211 with respect to the vertical plane 201a to the central axis M of the mushroom-shaped head part 20a of the head is between 5 to 15 °, in the example shown it is 10 ° .

Corresponding to the underside of the head 20, which is inclined with respect to the central axis M and forms the connection side 211, the fastening axis W of the head 20 according to FIGS. 2a, 2b, 2c also extends at an appropriate angle α to the central axis M.

The dimensions, namely the diameter E of the mushroom-shaped part 20a, which is symmetrical to the central axis M, and the height H can also be varied. The angle of inclination α can be varied, for example, by appropriately designing the maximum height G of the wedge-shaped neck part 21. The neck part 21 is preferably designed such that it extends from a maximum height G on one side to zero, ie to the lower edge of the symmetrical mushroom-shaped part 20a. To fasten the head 20 to the shaft, a conical blind hole 202 is again formed in the center, starting from the connection side 211, the central axis of which is perpendicular to the connection side 211 and at the same time represents the fastening axis W. As can be seen from FIG. 4, the head 20 according to FIGS. 2a, 2b, 2c is in turn placed on the shaft 10, which is formed with a projecting pin 102 for fitting the head, as described in FIG. 3. As a result of the asymmetrical design of the head according to the invention according to FIGS. 2a, b, c, the central axis M of the head 20 and the fastening axis W of the head 20 do not coincide, but are inclined towards one another in accordance with the wedge-shaped angle of the neck 21 attached.

Depending on the position in which the head 20 with the neck 21 according to the invention is now placed on the head plate 101 of the shaft, there are different fillings of space by the head above the shaft. 4, 5, 6, 7, the four positions are shown, which are formed by successively repositioning the head 20 on the shaft 10 by 90 °. By implementing the head 20 according to the invention with the neck 21 in the asymmetrical configuration, a different space filling above the head plate of the shaft is achieved, i.e. thus also a different space filling of an implanted shoulder prosthesis in the area of the shoulder joint with the same head in each case.

In the design and arrangement of the head according to FIG. 4, the lifting of the head in the lower region ensures that it is arranged in position C in the direction of the humeral head, as can also be seen from the schematic illustration according to FIG. 8.

In the arrangement according to position A according to FIG. 5, however, the head is arranged in its maximum position downward by arranging the maximum wedge of the neck 21 in the upper region of the sheep. Positions B and D show the corresponding displacements of the head 20 to the front and to the rear depending on the arrangement of the head on the head plate 101 of the shaft 10, as can also be seen from FIG. 8.

4 to 7 show. it is thus possible in a simple manner, even in the case of an implanted shaft, by means of a minimal intervention merely by changing the position of the head 20 according to the invention with the neck 21 on the shaft head plate 101

Compensate the shoulder joint in relation to the pan and / or humeral head.

In order to enable a simple fixation of the head according to the invention on the head plate 101 of the shaft, it is provided to arrange four centering holes on the head plate of the shaft in a circle around the fastening axis W and at a corresponding distance on the underside, i.e. Connection side 211, the head 20 to form a projecting positioning pin 22, which is then inserted into one of the respective centering holes on the shaft plate in order to fix the positions shown in FIGS. 4 to 7.

A total shoulder prosthesis in the implanted state is shown schematically in FIG. 9a. The upper arm leg 1 with the humerus head 1 a has the cut surface 1 b, via which the shaft 10 is inserted into the upper arm leg. The head plate 101 delimits the cutting area 1b. The shoulder blade 2 with the shoulder joint socket 2a (glenoid) forms the joint space with the humeral head la. The rotator cuff is labeled 3. The head 20 according to the invention with the neck 21 is fastened in the corresponding position on the shaft plate 101 of the shaft 10 in accordance with the course of the cut surface 1b, glenoid 2a and the required angular position of the humerus. If the spatial conditions in the shoulder joint area change, it is also possible after the implantation: the position of the head 20 by rotation to change the fastening axis W and thus achieve a different space filling and improved joint function. In particular, the corrections described at the outset can be carried out with the head 20 with the neck 21 according to the invention.

Claims

claims

1. total shoulder endoprosthesis with a shaft and a head which can be exchangeably fastened to the shaft, with a mushroom-shaped shape symmetrical to a central axis M and with a connection side for the shaft formed on the underside of the head, characterized in that the connection side (211) forms the connection side Underside of the head (20) is designed to run obliquely with respect to the central axis (M) of the head.

2. total shoulder endoprosthesis according to claim 1, characterized in that the connecting side (211) forming the underside of the head (20) is asymmetrical with respect to the central axis (M) of the head (20), so that the central axis (M) of the head is inclined at an acute angle with respect to the fastening axis (W) of the head on the shaft (10).

3. total shoulder endoprosthesis according to claim 1 or 2, characterized in that the connecting side (211) forming the underside of the head (20) with respect to the perpendicular position to the central axis (M) of the head (20) inclined at an acute angle α is progressive.

4. Total shoulder prosthesis according to one of claims 1 to

3, characterized in that the head (20) is formed with a projecting wedge-shaped neck part (21), the underside of which forms the connection side (211) which is inclined with respect to the central axis (M) of the head (20).

5. total shoulder endoprosthesis according to one of claims 1 to

4, characterized in that the head (20) is formed with a neck part (21) in the form of a crooked circular cylinder, the crooked cut cross-sectional area forms the underside and connection side (211) of the head (20).

6. total shoulder endoprosthesis according to one of claims 1 to 5, characterized in that the head (20) for

Fastening to a pin (102) formed on the connection side (101) of the shaft (10) has a blind hole (202) corresponding to the pin (102), the central axis of the pin (102) and the central axis of the blind hole (202) Form fastening axis (W) of the head (20) on the shaft such that when the head (20) is placed on the shaft (10) the central axis (M) of the head (20) to the fastening axis (W) of the head (20) is inclined at an acute angle.

Total shoulder endoprosthesis according to one of claims 1 to

6, characterized in that the head (20) on the shaft (10) can be fastened in various positions (A, B, C, D) rotated about its fastening axis (W).

Total shoulder endoprosthesis according to one of claims 1 to

7, characterized in that the positions of the head (20) on the shaft (10) are arranged at an angle of 90 ° to each other.

9. shoulder total endoprosthesis according to one of claims 1 to 8, characterized in that the head (20) on its connection side (211) forming the underside has a positioning pin (22) projecting over the connection side (211) and one of the number of positions of the head (20) on the shaft (10) corresponding number of position holes (203a, b, c, d) on the connection side (101) of the shaft (10) for inserting the positioning pin (22) are formed.

10. Total shoulder prosthesis according to one of claims 1 to 9, characterized in that the angle between u

11. Total shoulder prosthesis according to one of claims 1 to

10, characterized in that the neck part (21) tapers in a wedge shape towards an edge of the mushroom-shaped head (20) towards zero.

12. Total shoulder prosthesis according to one of claims 1 to

11, characterized in that the connection side or underside (211) of the head (20) is inclined at an angle α of 5 to 20 ° from the vertical position considered with respect to the central axis (M).