WO1997018770A1 - Shoulder implant - Google Patents

Abstract

There is described a titanium implant (40) for fixing parts (11, 12) of an acromion (7). Implant (40) comprises a bone plate (41) and a base plate (42) substantially perpendicular to the bone plate (41), wherein bone plate (41) and base plate (42) meet according to an intersecting line (43). Bone plate (41) comprises a bone plate base portion (51) adjoining the intersecting line (43) and an elongated bone plate fixation portion (52) extending from the bone plate base portion (51), of which bone plate fixation portion (52) a center line (54) includes an angle α with the intersecting line (43) of about 60°. Provided in the bone plate fixation portion (52) are openings (55; 55'; 55'') for passing a screw (62) therethrough. Base plate (42) comprises two base plate portions (44, 45), wherein provided in each base plate portion (44, 45) is an opening (46, 47) for passing a screw (61) therethrough, and wherein at the end of each base plate portion (44, 45), a triangular hook portion (48, 49) is formed that is perpendicular to the base plate (42).

Description

Title: Shoulder implant

The invention relates to an implant for fixing parts of a human shoulder blade.

The shoulder joint is a joint enabling a movement of the am relative to the body. More in particular, the shoulder joint is a ball joint, with the substantially spherical extremity of the humerus resting in a bowl-shaped space defined by the shoulder blade (scapula). That bowl-shaped space is, viewed relative to the body, substantially open outwards and downwards, and has on its inside a wall defined by the glenoid, while an upper wall is defined by the tip of the shoulder blade (acromion).

If the continuity of this bone piece is interrupted by an artificial sectioning of the bone, a so-called osteotomy, or by a fracture, the healing process is rendered more difficult in that it is not properly possible, if at all, to fix the broken parts relative to each other in a stable manner.

It is an object of the invention to improve and

accelerate the healing process of such a fracture or osteotomy by providing an implant whereby the fracture parts of the acromion can be fixed relative to each other.

A problem involved is that the deltoid (musculus

deltoides) extends over the shoulder joint, which muscle should be passed during the fixing of the acromion for fitting an implant. Hence, it is a further object of the present invention to provide an implant as mentioned above, which, during use, damages the deltoid muscle as little as possible.

To that end, an implant according to the invention has the features as described in claim 1.

These and other aspects, features and advantages of the present invention will be specified by the following

specification of a preferred embodiment of an implant

according to the invention, with reference to the accompanying drawings, wherein:

Fig. 1 is a schematic perspective view of a right shoulder of a human, in rear view; Fig. 2 is a more schematic section of some parts of the shoulder joint;

Fig. 3 is a schematic top plan view of the right shoulder;

Fig. 4A is a top plan view of an embodiment of an implant according to the invention;

Fig. 4B is a bottom view of this embodiment;

Fig. 4C is a side elevation of this embodiment;

Fig. 4D is a front view of this embodiment; and

Fig. 5 is a section, comparable with Fig. 2, to illustrate the action of the implant according to the invention.

Fig. 1 schematically shows a right shoulder joint, generally designated by reference numeral 1, of a human, in rear view. The shoulder joint 1 can be interpreted as a ball joint, with the substantially spherical extremity 2 of the humerus 3 resting in a bowl-shaped space 5 defined by the shoulder blade (scapula) 4. The bony part of this bowl-shaped space 5 is on its inside defined by the glenoid 6 and at its upper side by the tip (acromion) 7 of the shoulder blade 4. The acromion 7 can be considered a roof-shaped extremity of a bone ridge 8 which is an integral part of the shoulder

blade 4.

In Fig. 2, only the acromion 7 and the spherical

extremity 2 of the humerus 3 are sketched. In the acromion 7, a fracture has occurred, as designated by reference

numeral 10; the fracture halves will hereinafter be referred to as acromion body 11 and acromion fracture part 12. The acromion body 11 is the portion of the acromion 7 which is still an integral part of the shoulder blade 4; the acromion fracture part 12 is the broken-off, extreme portion of the acromion 7.

Fig. 3 schematically shows the (broken) acromion 7 from the top. Fig. 3 illustrates that the bone ridge a of the shoulder blade 4, viewed from the acromion 7, is directed obliquely backwards, and that the collarbone (clavicle) 9 is directed obliquely forwards but not connected, or at least not by bone, to the shoulder blade 4. In Fig. 3, it is indicated in dotted lines that the deltoid (musculus deltoides) 20 attached to the collarbone⁹ overlies the acromion fracture part 12. This deltoid 20 disturbs the position of the acromion fracture part 12

relative to the acromion body 11 in that on the extremity of the acromion fracture part 12 remote from the fracture 10, a downwardly directed force is exerted, which force is in Fig. 2 designated by Fl. Consequently, the healing of the

fracture 10. i.e. adhesion of the acromion fracture part 12 to the acromion body 11 through bone growth, is rendered

difficult not only because the acromion fracture part 12 can move relative to the acromion body 11, but also because the acromion fracture part 12 assumes a wrong, downwardly hinged position relative to the acromion body 11.

The implant according to the invention, of which

Figs. 4A-D show an embodiment 40, promotes the healing

process, on the one hand in that the acromion fracture part 12 is fixed relative to the acromion body 11, and on the other in that the above-mentioned forces are taken up.

The implant 40 is manufactured from a material that is strong and biocompatible. The material used can for instance be stainless steel, but preferably titanium is used, because in that case, it is still possible to produce an image, by means of X-radiation, of the set acromion 7, the glenoid and the humerus.

In side elevation (Fig, 4C), the implant 40 has a

substantially L-shaped cross section, and comprises a bone plate 41 and a base plate 42 substantially perpendicular thereto. The intersecting line between the plane defined by the bone plate 41 and the plane defined by the base plate 42 is designated by 43. The thickness of the bone plate 41 and the base plate 42 is relatively small, and is preferably about 1 mm. in a simple form, the two plates 41 and 42 are

manufactured from a flat strip, by bending that strip over the line 43. However, the two plates 41 and 42 are preferably manufactured from a solid block, by cutting away portions of the material, because in that case, the resulting implant 40 is stronger.

The implant 40 is intended to be fitted on the

acromion 7, with the bone plate 41 on top of the acromion 7 while the base plate 42 is downwardly directed and rests against the extremity of the acromion 7, as sketched in

Fig. 5. As is clearly shown in the front view of Fig. 4D, the base plate 42, measured along the intersecting line 43, has a length L₄₂ based on the corresponding dimension of the acromion 7. A suitable length L₄₂ is about 26 mm. The width B₄₂ of the base plate 42, measured perpendicularly to the plane of the bone plate 41. is about 7-10 mm. A suitable width is about 8.5 mm. A central portion of the base plate 42 has been removed over a length of about 14 mm. Accordingly, the base plate 42 comprises two base portions 44 and 45 substantially perpendicular to the bone plate 41, each having a length L₄₄ and L₄₅ respectively (measured in the direction of the above-mentioned intersecting line 43) of about 6 mm. Provided in each of these base portions 44, 45 is a hole 46, 47 for passing a screw 61 (see Fig. 5) therethrough.

Located at the end of each base portion 44, 45 remote from the bone plate 41 is a substantially triangular hook portion 48, 49, which is substantially perpendicular to the base plate 42 and hence directed substantially parallel to the bone plate 41. A suitable width B₄₈, B₄₉ for each triangular hook portion 48, 49, measured from the free end to the corresponding base portion 44, 45, i.e. perpendicular to the above-mentioned intersecting line 43, is about 7 mm.

The bone plate 41 comprises a bone plate base portion 51 and a bone plate fixation portion 52. The bone plate base portion 51 adjoins the intersecting line 43, and has a length L51, measured along the intersecting line 43, which length corresponds to the length L₄₂ of the base place 42. The bone plate base portion 51 can extend as an uninterrupted whole along the intersecting line 43 or, as shown in the top plan view of Fig. 4A, be provided with a central recess 53 having for instance a semicircular or semi-elliptic contour, which recess 53 is a continuation of the removed central portion of the base plate 42.

The bone plate fixation portion 52 has an elongated shape with a center line 54. This center line 54 intersects the intersecting line 43 at an intersection S about halfway the bone plate base portion 51. Provided in the elongated bone plate fixation portion 52 is at least one hole 55 for passing a screw 62 (Fig. 5) therethrough. In the exemplary embodiment shown, three of such holes 55, 55', and 55" are present.

Because the bone ridge 8 is directed obliquely backwards, as mentioned hereinabove, the center line 54 of the elongated bone plate fixation portion 52 makes an angle α with the intersecting line 43, which angle α is adapted to the

direction of the bone ridge 8. Normally, this angle α is in the range of 40°-80°. A suitable value for this angle α is about 60°.

A suitable width B₅₂ for the bone plate fixation

portion 52, measured perpendicularly to the center line 54, is about 8 mm. A suitable length L₅₂ for the bone plate fixation portion 52, measured along the center line 54 from the end to the intersection 5, is about 50 cm.

In this manner, the bone plate 41 has a shape which, in top plan view (see Fig. 4A) substantially corresponds to the shape of a hockey stick or to the shape of the Greek letter λ. it will be understood that an implant for a left shoulder is of mirror-symmetrical design in respect of the implant shown for the right shoulder.

Presently, the use of the implant 40 according to the invention will be explained. The fitting of the implant 40 is effected through surgery, as will be appreciated. The implant 40 is slid over the acromion 7 from aside, with the hook portions 48, 49 being stuck under the extremity of the acromion fracture part 12, while the bone plate 41 comes to lie on the acromion body 11 and the bone ridge 8. Horizontal screws 61 axe provided through the holes 46, 47 in the base portions 44, 45 of the base plate 42, which horizontal screws 61 preferably extend into the acromion body 11. vertical screws 62 are provided through the holes 55, 55 P 55" in the bone plate fixation portion 52, which vertical screws 62 extend into the acromion body 11 and/or the bone ridge 8.

Preferably, at least one of those holes (55") is slightly elongated (with the long axis of the ellipse being

substantially perpendicular to the base plate), to be able to take up some play during fitting.

By virtue of the horizontal screws 61, the acromion fracture part 12 is at first positioned in the right place relative to the acromion body 11. However, these screws 61 alone would not be able to withstand the above-mentioned force F1. This force, however, is taken up by the hook portions 48, 49, which form a support under the extremity of the acromion fracture part 12, and transmit that force to the acromion body 11 and/or the bone ridge 8 by means of the vertical screws 62. Because of the relatively great length of the bone plate fixation portion 52, those vertical screws 62 are loaded relatively slightly.

As mentioned hereinabove, the deltoid muscle extends over the extremity of the acromion fracture part 12, and that deltoid muscle actually sits in the way during the fitting of the fixation means. However, during the fitting of the inhalant 40, it suffices to provide relatively small incisions in the longitudinal direction of the deltoid muscle fibers to enable the base portions 44, 45 with the associated hook portions 48, 49 and screws 61 to pass, which incisions heal relatively quickly over the implant.

For the horizontal screws 61, cannular screws, i.e.

screws having a channel extending therethrough, along the body axis thereof, are preferably used, which screws can be fitted by means of a guide wire. This technique is known per se. The implant according to the invention provides maximum stability while involving a minimum of fastening material and a minimum of "operation damage" (to the deltoid muscle).

It will be readily understood by anyone skilled in the art that it is possible to alter or modify the embodiment shown of the device according to the invention without departing from the inventive concept or protective scope of the invention, as defined in the claims. For instance, it is possible that the above-mentioned measurements and angles are adapted to the build and/or age of the person for whom the implant is intended.

It is also possible that the bone plate fixation

portion 52 has a bent center line 54.

Further, it is possible that the implant is slightly bent so that its shape is more properly adapted to the shape of the bone parts of the patient in question. This adaptation can be performed by the surgeon himself directly before the fitting of the implant.

Further, it is possible that the number of base portions is larger than two, or that the number of screw holes (55) differs from three.

Claims

1. An implant (40) for fixing parts (11, 12) of an acromion (7), comprising:

a bone plate (41);

at least one opening (55; 55'; 55") provided in the bone plate (41) for passing a screw (62) therethrough;

a base plate (42) substantially perpendicular to the bone plate (41), wherein the bone plate (41) and the base

plate (42) meet according to an intersecting line (43);

at least one opening (46, 47) provided in the base plate (42) for passing a screw (61) therethrough;

at least one hook portion (48, 49) perpendicular co the base plate (42).

2. An implant according to claim 1, wherein a central portion of the base plate (42) is removed to define two base plate portions (44, 45), wherein, at the end of each base place portion (44, 45), a hook portion (48, 49) is formed that is perpendicular to the base plate (42), and wherein in each base plate portion (44, 45) an opening (46, 47) is provided for passing a screw (61) therethrough.

3. An implant according to claim 1 or 2, wherein each hook portion (48, 49) has a substantially triangular shape.

4. An implant according to any one of the preceding claims, wherein the base plate (42) has a length of about 26 mm, measured along the intersecting line (43).

5. An implant according co any one of the preceding claims, wherein the bone plate (41) comprises a bone plate base portion (51) which adjoins the intersecting line (43) and whose length, measured along the intersecting line (43), is substantially equal to the corresponding length of the base plate (42), and wherein the bone plate (41) further has an elongated bone plate fixation portion (52) extending from the bone plate base portion (51).

6. An implant according to claim 5, wherein the bone plate fixation portion (52) has a center line (54) which includes an angle α with said intersecting line (43) in the range of 40º-80°, preferably about 60°.

7. An implant according to any one of the preceding claims, manufactured from titanium.

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