FR2776506A1 - Shoulder prosthesis glenoid member and ancillary components - Google Patents

Abstract

The glenoid member of the prosthesis comprises a metal or ceramic base (3) shaped to fit into the glene (2) of the shoulder blade (1) and equipped with an anchor in the form of a central keel (12) and a side lug (13) with holes, joined by a screw inserted transversely through the bone. The glenoid member is covered by a plate (6) of a synthetic material which interacts with a hemispherical head (8) on the humeral member (9).

Description

The subject of the present invention is a glenoid shoulder prosthesis, of the

  type comprising a metal base, shaped to adapt to the anatomic glenoid of the scapula, with a polyethylene plate having an articular surface for receiving the head of a humeral prosthesis, as well as means for anchoring the base in the glenoid cavity. Historically, glenoid prostheses were first proposed, only made of polyethylene, with a central fin anchoring in a hole

  of the glenoid cavity, the fixation being obtained by cementing.

  Unfortunately, a significant percentage of

  io glenoid loosening of these prostheses, at the end of variable durations.

  The most classic and most used approach is the anterior, delto-pectoral approach. According to this approach, the glenoid is seen by the surgeon in profile, the scapula being in a frontal plane, which makes it difficult for the surgeon to dig and cement the glenoid, due to the lack of

place and visibility.

  Despite numerous attempts to improve the fixation technique, the main problem remains the risk of glenoid loosening, the parameters of which it is difficult to clearly determine. These difficulties are explained in the article by Michael E. TORCHIA, Robert H. COFIELD and Curtis R. SETTERGREN from Nov-Dec. 1997

  in the journal "Journal of Shoulder and Elbow surgery".

  We therefore tried to avoid fixing by cementing, by replacing it with screwing devices, with bone rehabitation and removal of the fin. The prosthesis then comprises a metal substrate, commonly called "metal back" and a "medallion" or tray of synthetic material, usually polyethylene, the screwing being performed in the axis of the medallion. Thus, for example, patent FR-2 741 796 (95 14 454) describes a glenoid prosthesis comprising a metal substrate or seat and a plate for articulation of the head of the humeral prosthesis, the metal seat being provided with two pegs. anchor provided with elastically deformable fins and cooperating with screws. Patent FR 2 695 313 (92 11 000) also describes a glenoid implant, the metal base of which is provided with

fixing screw in the glenoid.

  In general, the screw fixing is only intended to guarantee perfect contact between the prosthesis and the bone, for the time necessary to subsequently obtain a final anchorage by bone rehabitation, favored by an osteointegrating coating. on the substrate

  metallic, in particular hydroxyapatite.

  A first problem encountered with this type of prosthesis lies in the fixing of the polyethylene plate on the metal substrate. This problem is currently resolved by prefixing the polyethylene plate to the metal base in the factory, the whole being thus delivered to the surgeon. A second problem is caused by the very large thickness of the implants thus produced, which makes the surgical intervention relatively difficult. Indeed either the surgeon must sufficiently activate the glenoid bone, thus damaging the patient's bone capital, or the humeral prosthesis

  must be lateralized, which leads to certain complications.

  Finally, the installation of the screw is difficult because of the lack of space available opposite the articular surface and the approach route,

  the direction forms an obtuse angle with the screw axis.

  Ultimately, despite all these improvements, there are still loosening after a certain time of use. Their origin lies in the stresses undergone by the prosthesis, which are distributed around the entire periphery of the articular surface. These constraints are located both in a vertical, frontal and in an anteroposterior plane causing a phenomenon of "rocking chair" also called "rocking horse effect". A relatively high percentage of glenoid prostheses thus undergoes loosening, a certain fraction of these entailing the obligation of a

resumption of surgery.

  2 5 The object of the invention is therefore to propose a humeral prosthesis

  glenoid equipped with secure and reproducible fixation means, in

  associating it with an appropriate preparation of the bone glen by avive.

  In accordance with the invention, the means for anchoring the prosthesis comprise a central keel and a lateral fin secured to the base and extending transversely with respect thereto, the fin extending from the edge of the base to be able to adapt to the anterior face of the scapula; a bone anchor screw passes through two coaxial passage holes arranged in the fin and the keel to arrange the fixing screw

  in a direction substantially transverse to the general plane of the scapula.

  The prosthesis is therefore screwed in an antero-direction

  posterior, in a relatively sagittal plane, this screwing being much more

  as easy as in a frontal plane by the delto-pectoral approach.

  The base must be well adapted to the surface of the bone glenoid to avoid any tilting and must therefore have excellent congruence

  with this, the screwing must be additionally very precise.

  According to an additional characteristic of the invention, the keel extending in a plane containing the axis of the articular surface of revolution of the base, the coaxial holes for passage of the glenoid anchoring screw are made along an axis which defines, with a plane orthogonal to the plane of the keel and to the axis of the articular surface, an angle between zero and 40

  degrees, and preferably between about 20 and 35 degrees.

  Thanks to this angle, the anchor screw crosses not only the lateral fin and the central keel, but also the anterior and posterior cortex on the opposite edges of the glenoid, namely the anterior cortex in the vicinity of the glenoid rim and the cortex. posterior at a certain distance from the glenoid cavity, which ensures the solidity of the fixation. Thanks to this arrangement of the screw through holes, the latter passes relatively far from the base at the central keel, which also promotes

better bone rehabitation.

  The ancillary device for placing this prosthesis comprises in particular a device for supporting and aiming the axis of screwing of the bone anchoring screw; this device comprises a block adapted to receive laterally in abutment the fin of the prosthesis, a rod secured to this block, a plate which can be mounted on this rod transversely to the latter and in an adjustable manner in position relative to the block, and an element integral with the wafer, provided with a head which can come to bear on the articular surface of the prosthesis tray. Thus the latter can be rigidly assembled to the

  aimed when the aileron is engaged in abutment on the block.

  Other features and advantages of the invention will become apparent during

  of the description which follows, made with reference to the accompanying drawings which

  illustrate an embodiment by way of nonlimiting example.

  FIG. 1 is a view of the anterior face of a scapula and in exploded perspective of a humero-glenoid prosthesis according to the invention.

  Figure 2 is a side view of the scapula of Figure 1.

  FIG. 3 is a view of the bone contact face of the base, in plan on an enlarged scale of the glenoid prosthesis of FIG. 1 provided with

  its bone anchor screw in the glenoid.

  Figure 4 is an elevational view on an enlarged scale of the assembly of the glenoid prosthesis of Figures 1 and 3 and an apparatus

  support and sighting of the screwing axis.

  FIG. 4A is a partial elevation view of the aiming device of

Figure 4.

  Figure 5 is an elevational view in partial section on scale

  enlarged of the prosthesis of figures 1, 3 and 4.

  Figure 6 is an exploded perspective view from below of the

  glenoid prosthesis of figures 1 and 3 to 5.

  t0 Figure 7 is a perspective view of the prosthesis of Figures 1 and

  3 to 6 taken above its articulation plate.

  We see in Figures 1 and 2 a human scapula 1 with its glenoid cavity 2, which can receive a humero-glenoid prosthesis constituted

as follows.

  The prosthesis comprises a concave metal base 3, approximately oval, of which a face 4, preferably convex, is shaped to adapt with excellent congruence to the anatomical glen after sharpening. Its second surface 5, preferably concave, is profiled to receive a plate 6 made of a material with a low coefficient of friction, namely a synthetic material such as polyethylene. The base 3 is metallic or made of a porous material such as

  porous ceramic, allowing bone rehabitation.

  The plate 6 has a concave articular surface 7, for example of revolution, adapted to allow articulation on this surface, of the spherical head 8 of a humeral prosthesis 9 (FIG. 1) arranged so

known in the humerus 1 1.

  The base 3 is provided with means for anchoring in the glenoid cavity 2.

  These anchoring means comprise a central keel 12 and a lateral fin 13 integral with the base 3, preferably made in one piece with the latter. The keel 12 extends along the axis XX of the articular surface of revolution 7 (FIG. 5) over an appropriate length, in order to be able to come

  fit into a notch 14 prepared by milling the bottom of the cavity 2.

  The lateral fin 13 extends parallel to the keel 12, the periphery 12a of which is advantageously semi-circular (FIG. 6). Fin 13 can thus come

  adapt to the anterior aspect of the scapula.

  The plate 6 includes means for fixing to the metal base; it may for example be provided with a central tab 15 for snapping into a corresponding hole 16 formed in the central zone of the base 3. Coaxial holes 17, 18 for passage of an anchor screw 19 are arranged respectively in the lateral fin 13 and in the central keel 12, in order to allow the screw 19 for fixing the prosthesis to be placed in a substantially antero posterior plane (plane of FIGS. 3 and 5). The distance dl between the hole 17 and the surface 4 of the base 3 is less than the distance d2 between the hole 18 of the keel 12 and said surface 4 and the length of the fin 13 is less than that of the keel 12 The holes 17 and 18 are made along an axis YY which delimits, with a plane P orthogonal to the plane of the keel 12 and to the axis XX of the articular surface 7, an angle A of between 0 and 40 degrees. Preferably the angle A is between approximately 20 and degrees, this value being optimized to approximately 30 degrees (it is

20 degrees in Figure 4).

  The prosthesis for placing the prosthesis (3, 6) comprises a device comprising a block 21 adapted to receive laterally as a stop.

  the fin 13 of the base 3 (FIG. 5) resting on a shoulder 31.

  The apparatus also comprises a rod 22 integral with this block 21 and a plate 23, pierced with a through hole for a threaded portion 24 of the rod 22 so as to be able to slide thereon. The plate 23 extends transversely to the rod 22 and the apparatus comprises an element 25 integral with the plate 23 and provided with a head 26 which can come to bear on the articular surface 7 of the plate 6. The element 25 can be consisting of a bolt on the rod of which is threaded a one-piece tube 27 with the head 26 and made of plastic. The tube 27 passes through an oblong hole 20 arranged in the plate 23 and which allows the element 25 to travel in one direction

perpendicular to the rod 22.

  The threaded part 24 of the rod 22 cooperates with a nut 28 for fixing the plate 23 in a determined position on the rod 22, and a spring 29 for returning the plate 23 is arranged coaxially with the rod 22, in

press on block 21.

  The implementation of the device which has just been described takes place in the following manner. The fin 13 is placed in abutment on the shoulder 31, the base 3 and the plate 6 being assembled, then the plate 23 is made to slide on the threaded rod 24 until the head 26 comes to bear on the articular surface 7. The plate 23 is blocked in this position by screwing the nut 28, the plate 23 being held in position by force

  return spring 29. The device is then secured to prosthesis 3, 6.

  The prosthesis is placed as follows, by the way

first delto-pectoral.

  The surgeon performs, if necessary, a section of the humeral head or otherwise releases it from the glenoid cavity 2. He performs a pilot hole in the middle of the glenoid, in order to be able to center and guide a bur 'a known way. Then the surgeon uses a milling system (not shown), making it possible to sharpen the glenoid 2 precisely, in order to adapt it to the conformation of the surface 4 of the base 3 to obtain excellent congruence. The surgeon then cuts if necessary in the anterior edge of the glenoid 2 the housing for receiving the aileron 13, which must have a very precise position, and digs the notch 14 centro-glenoid. This advantageously has a radius and a thickness which can be equivalent to

  the thickness and radius of the keel 12.

  After these preparatory operations, the surgeon sets up the prosthesis with the help of the sighting device or guide illustrated in FIGS. 4 and 4A. The glenoid being fixed to the device, it pushes the keel 12 into the notch 14 and has the fin 13 in its glenoid housing. He then uses the sighting device to perform a precise drilling along the YY axis, through the anterior cortex of the glenoid and, beyond the keel 12, through the cortex.

  posterior. Finally the surgeon performs the installation of screw 19.

  The glenoid prosthesis and its fitting ancillary present the

following advantages.

  * fixation of the prosthesis by screwing in a sagittal plane or relatively close to this plane is easy by the delto-pectoral route, conventional in the fitting of shoulder prostheses. It eliminates the difficulties previously encountered by surgeons in proceeding to screwing in the axis of the polyethylene medallion 6

  by the delto-pectoral approach.

  * thanks to the precise arrangement of the holes 17 and 18 for the passage of the anchor screw 19 relative to the surface 4 of the base 3 (covered with hydroxapatite or microporous), the hole 17 is close to this surface 4 so that the screw 19 passes through a sufficient thickness of the anterior cortex. On the other hand, the distance of the hole 18 from this same surface 4 promotes better bone rehabitation. The solidity of the fixing by the screw 19 is increased by the fact that this screw

  crosses two cortices in addition to the keel 12 and the fin 13.

  The prior cutting of the glenoid bone 2 by milling makes it possible to perfectly adjust the articular cavity of the scapula to the conformation of the base 3. The cutting of the glenoid 2 also makes it possible to significantly reduce the thickness of the base 3 and of the plate 6, which must be as small as possible and not exceed

4.5mm approx.

  Advantageously, the design of the prosthesis according to the invention makes it possible to carry out its prior assembly at the manufacturer thus avoiding any risk of disassembly of the parts and thereby reducing the number of

  component parts to be installed successively during the operation.

  Various variants of the prosthesis can be considered. Thus the keel 15 can be removed, the plate 6 being simply clicked on the base 3. The width of the front fin 13, which is for example 8mm, can be reduced by about half. The angle between the base 3 and the fin can be reduced, so that this fin tilts towards the keel 12, the corresponding angle being, for example, 70 degrees. Tray 6 can

  substantially overlap beyond the periphery of the base 3.

  The base and the plate could be formed in one piece, in a

suitable material.

Claims (9)

  1.Genoid shoulder prosthesis, comprising a base (3), preferably concave, shaped to adapt to the anatomic glenoid (2) of a scapula (1), with a plate (6) having an articular surface ( 7) for receiving the head (8) of a humeral prosthesis (9), and means for anchoring the base in the glenoid cavity, characterized in that said anchoring means comprise a central keel (12) and a lateral fin (13) integral with the base and extending transversely thereto, the fin extending from the edge of the base so as to be able to adapt to the anterior face of the scapula and a bone anchoring screw (19) passing through coaxial holes (17, 18) for passage arranged in the fin and the keel to arrange the screw in a direction substantially transversely to the general plane of the scapula ..   2. Prosthesis according to claim 1, characterized in that, the keel (12) extending in a plane containing the axis (XX) of an articular surface (7) of revolution of the plate (6), the holes ( 17, 18) for passage of the glenoid anchoring screw (19) are made along an axis (YY) which delimits, with a plane (P) orthogonal to the plane of the keel (12) and to the axis (XX) of the articular surface, an angle (A) between zero and 40 degrees, and   preferably between 20 and 35 degrees approximately.   3. Prosthesis according to claim 2, characterized in that the distance (dl) between the hole (17) of the lateral fin (13) and the base (3) is less than the distance (d2) between the hole ( 18) of the keel (12) and the base, and   the length of the fin is less than that of the keel.   4. Prosthesis according to claim 3, characterized in that the   central keel (12) has a semi-circular outline (12a).   5. Prosthesis according to one of claims 1 to 4, characterized in   that the plate (6) is provided with a central tab (15) which snaps into   a corresponding hole (16) in the base (3).   6. Prosthesis according to any one of the claims   previous, characterized in that the base (3) is metallic or formed from a bone rehabitable material such as a porous ceramic, and the plate   (6) is made of a synthetic material such as polyethylene.   7. Ancillary for the placement of a glenoid prosthesis (3, 6)   according to one of claims 1 to 6, characterized in that it comprises a   device for supporting and aiming the axis (YY) for screwing the bone anchoring screw (19), said device comprising a block (21) adapted to receive the fin (13) of the prosthesis in abutment, a rod (22) integral with this block, a plate (23) which can be mounted on this rod in an adjustable position relative to the block and extending transversely thereto, and an element (25) mounted on the plate and provided with a head (26) which can come to bear on the articular surface (7) of the plate (6) of the prosthesis, in order to block the latter relative to said device when the flap is engaged in stop on the block.   8.Ancillary device according to claim 7, characterized in that the rod (22) has a threaded part (24), which passes through a hole in the plate (23) and cooperates with a nut (28) for fixing the plate in a determined position on the rod, and in that a spring (29) for returning the   plate is arranged coaxially with the rod, bearing on the block (21).   9. Ancillary device according to claim 8, characterized in that the block (21) has a lateral shoulder (31) for supporting the fin (13) of the prosthesis (3, 6).