AU708718B2 - Shoulder implant - Google Patents

Description

WO 97/18770 WO 9718770PCT/NL96/00448 Title; Shoulder implant Thae invention relates to an implant for fixing parts of a human shoul.der blade.

The shoulder joint is a joint enmabling a movement of the arm relative to the body. M~ore in particular, the shoulder joint is a ball joint, with thle substantially spherical extremity of the humterus 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, tile 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 thie acrooion can be fixed relative to each other.

A problem involved is that the deltoid (mu~sculus delzoides) 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 obj ect 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 L.

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; WO 97/18770 WO 9718770PCT/NL96/00448 2 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 a~n 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 hiuman, in rear view. The shoulder joint I 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 acramion 7 and the spherical extremity 2 of the humerus 3 are sketched. In the acroznion 7, a fracture has occurred, as designated by reference numeral 10O; the fracture halves will herei nafter be referred to as acromion body 11 and acromion fracture part 12. The acromion body 11 is the portion of the acrortion 7/ which is still an integral part of the shoulder blade 4; the acrou'ion fracture part 12 is the broken-off, extreme portion of the acromion 7.

Fig. 3 schematically shows the (broken) acrcuLion 7 from the top. Fig. 3 illustrates that the bone ridge 8 of the shoulder blade 4, vi.ewed 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.

WO 97/18770 PCT/NL96/00448 3 In Fig. 3, it is indicated in dotted lines that the deltoid (musculus deltoides) 20 attached to the collarbone 9 overlies the acramion fracture part 12. This deltoid disturbs the position of the acromion fracture part 12 relative to the acromion body 11 in that on the extremity of the acramion fracture part 12 remote from the fracture 10, a downwardly directed force is exerted, which force is in Fig. 2 designated by FI- Consequently, the healing of the fracture 10, i.e. adhesion of the acratnion 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 Ii.

The irplant 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 i, 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, bit preferably titanium is used, because in that case, it is still possible to produce an image, by means of X-radiation, of the set acramion 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 m. In a simple form, the two plates 41 and 42 are manufactured fron 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 WO 97/18770 WO 97/ 8770PCT/NL96/00448 4 the material, because in that case, the resulting implant 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 acrcaiion 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 L 4 2 based on the corresponding dimension of the acromion 7. A Suitable length L42 is about 26 mm. The width E 1 4 2 of the base plate 42, measured perpendicularly to the plane of the bone plate 41. is about 7-10 mmn. A suitable width is about mmi. A central portion of the base placte 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 L" and L 4 S respectively (measured in the direction of the abovementioned intersecting line 43) of about 6 mmn. 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 zrmoie 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 Ste, B 45 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 =m.

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 Ls. measured along the intersecting line 43, which length corresprnda to the length "2 of the base Plate 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 WO 97/18770 WO 9718770PCT/NL96/00448 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 S2 is at least one hole 55S for passing a Screw 62 (Fig. 5) therethrough. In the exemlaxy embodiment shown, three of such holes 55, 55', and 551, 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 a with the intersecting line 43, which angle ar is adapted to the direction of the bone ridge 8. N~omally, this angle a is in the range of 400-800. A suitable value for this angle a is about 600.

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 Ls 2 f or the bone plate fixation Portion 52, measured along the center line 54 from the end to the intersection S, is about 50 mm.

In this warner, 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 It will be understood that an implant for a left shoulder is of mirror- syumetrical 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 is slid over the acrczuion 7 from aside, with the hook Portions 48, 49 being stuck under the extremity of the acrCmiOn fracture part 12, while the bone plate 41 comes to lie on the acromion body 11. and the bone ridge a. Horizontal screws 61 are provided through the holes 46, 47 in the base WO 97/1 8770 PCTINL96/00448_ portions 44, 45 of the base plate 42, which horizontal screws 61 preferably extend into the acramion body 11. vertical screws 62 are provided through the holes 55, 55', 5511 in the bone plate fixation portion 52, which vertical screws 62 extend into the acromion body 11 and/or the bone ridge B.

Preferably, at least one of those holes (551") 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 acroinion 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 r-he above-mentioned force Fl. This force, however, is tak~en 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 hereinaboe the deltoid uscle 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 implant 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 ch~annel extending theretkzrough, along the body axis thereof, are preferably used, which screws can be fitted by means of a guide wire. This technique is kniown per se.

WO 97/18770 WO 9718770PCT/NL96/00448 7 The implant according to the invention provides maximu st-ability while involving a minimum of fastening material and a miniimum 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 mo~dify the embodim~ent 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 IS so that its shape is more properly adapted to the shape of the bone parts of die 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 diff ers f rom three

Claims (1)

1. 8- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. An implant for fixing parts of an acromion, including: a bone plate; at least one opening provided in the bone plate for passing a screw therethrough; a base plate substantially perpendicular to the bone plate, wherein the bone plate and the base plate meet according to an intersecting line; at least one opening provided in the base plate for passing a screw therethrough; at least one hook portion perpendicular to the base plate. 2. An implant according to claim i, wherein a central portion of the base plate is removed to define two base plate portions, wherein, at the end of each base plate portion, a hook portion is formed that is perpendicular to the base plate, and wherein in each base plate portion an opening is 20 provided for passing a screw therethrough. o 3. An implant according to claim 1 or 2, wherein each hook portion has a substantially triangular shape. 25 4. An implant according to any one of the preceding claims, b oo*.: wherein the base plate has a length of about 26mm, measured along the intersecting line. An implant according to any one of the preceding claims, wherein the bone plate includes a bone plate base portion which adjoins the intersecting line and whose length, measured along the intersecting line, is substantially equal to the corresponding length of the base plate, and wherein the bone plate further has an elongated bone plate fixation portion extending from the bone plate base portion. Q:\OPER\GCP\75083.SPE- 15/6/99 9 6. An implant according to claim 5, wherein the bone plate fixation portion has a centre line which includes an angle a with said intersecting line in the range of 40°-800, preferably about 7. An implant according to any one of the preceding claims, manufactured from titanium. 8. An implant substantially as hereinbefore described with reference to the accompanying drawings. DATED this 15th day of June, 1999 PETRUS MARIA ROZING By his Patent Attorneys DAVIES COLLISON CAVE 4 4 0 4. 4 4 4* 4*44 4 4 0 Pa 'V