FR2784577A1 - Replacement femoral implant for knee prosthesis has posterior wedge with extension for inserting between condyle and distal wedge - Google Patents

Abstract

The implant (1) has a trochlea (2) with a pair of condyles (3) connected to it, and distal (6) and posterior (7) wedges with a single fixing (14) for adjusting the condyle thickness. The posterior wedge has an extension (22) for insertion between the condyle surface and the distal wedge. The extension is in the form of a spade with an end recess (30) to fit round a boss (12) on the condyle surface which is covered by the distal wedge, the latter having a hole (8) for the fixing (14).

Description

 The present invention relates to a femoral implant for knee prosthesis in the context of the recovery of failed prostheses.

 More specifically, the femoral implant is of the type comprising a trochlea, a pair of condyles connected to the trochlea, as well as distal and posterior shims for adjusting the thickness of the condyles, a pair of these shims being provided to be fixed. at least one of the condyles.

 We know that the addition of wedges to the femoral part of a knee replacement prosthesis makes it possible to catch up on the femoral bone following either the ablation of the previous prosthesis, or poor bone quality, or a combination of these two causes.

 In the case of a revision prosthesis, the surgeon encounters difficulties in defining, using preoperative radiographs, the type of prosthesis that he can consider fitting. Also it must have recourse to sets of wedges intended for the distal and posterior parts of the two condyles which compose the femoral element of the knee prosthesis. In addition, the surgeon must be able to perform his intervention in easy, reliable operating conditions and allowing him to reduce the necessary operating time.

Patent EP-0 378 928 teaches the use of distal and posterior wedges in a femoral implant of knee prosthesis, namely
Independent of one another, or in one piece, the maintenance of these wedges on the condyles being ensured by clipping.

 This solution requires a large set of shims of variable thicknesses, resulting in a high manufacturing cost. In addition, the surgeon is unable to perform prior tests of the wedges, since their clipping prevents any subsequent removal after a test. Thus this embodiment, although fulfilling the intended function of catching up and adjustment, has the disadvantage of not corresponding completely satisfactorily to the needs of the surgeon.

 In essence, for femoral implants for resumption of knee prosthesis, this need of the surgeon resides in means allowing a flexible adaptation of the distal wedge and / or of the posterior wedge. This necessity implies the simplest possible means and at the same time the least expensive, easy to install, both temporarily to test the most suitable hold size on the patient, as well as definitively.

 This is not the case for the shims of the prosthesis of patent EP 0 378 928: if the shim is a single piece it is necessarily standard and therefore cannot be chosen according to a distal thickness or a thickness posterior different from the thicknesses of the distal and posterior parts of a monobloc wedge. If, on the other hand, this bone catching wedge is made up of two separate elements, it does not have the drawbacks of a monobloc wedge, but requires separate fixing means for each wedge, which results in higher production costs and handling. more important preoperative. In both cases, the wedges described by the aforementioned patent cannot be tested beforehand by the surgeon to allow him to choose the thickness most suited to the patient, and this because of their method of fixing by clipping which results in a fitting. definitive on the condyle.

 The invention aims to propose a femoral implant for knee prosthesis, fitted with bone adjustment shims arranged to avoid! es disadvantages above.

 According to the invention, one of the distal and posterior wedges is extended by an extension adapted to be able to be placed between the surface of the condyle and the second wedge, and a single means of fixing the two wedges is provided.

 This unique fixing means can be easily removed to replace one or both of the shims with one or two shims of different thickness.

 According to an advantageous embodiment, the extension is a tab extending the rear wedge.

 According to another characteristic of the invention, the tab is provided with an end adapted to at least partially surround a boss on the surface of the condyle which can be covered by the distal wedge, and in which a hole for receiving a fixing element common to the two wedges, a passage opening for this element also being formed in the distal wedge.

 Such an arrangement of wedges is particularly simple and convenient to implement by the surgeon, these two wedges being used alone or in combination, the single means of fixing the two wedges to the condyle reduces the cost price of the implant as well as the manipulations required.

 Of course, the femoral implant can be used either with one or two wedges for one of the condyles or both condyles, or without wedge as required.

 Other features and advantages of the invention will become apparent during the description which follows, given with reference to the appended drawing which illustrates an embodiment thereof by way of nonlimiting example.

 Figure 1 is an exploded perspective view, substantially to scale, of an embodiment of the femoral implant for knee prosthesis according to the invention.

 FIG. 2 is a bottom view of the distal wedge visible in FIG. 1.

 Figure 3 is a side elevational view, on an enlarged scale of the femoral implant of Figure 1 equipped with its distal and posterior thickness adjustment shims.

 The femoral implant 1 illustrated in the drawings is intended for a knee replacement prosthesis, and comprises a trochlea 2 forming the anterior part of the implant, as well as a pair of condyles 3 having convex articular surfaces 4 adapted to cooperate with a tray of a tibial implant not shown. The implant 1 is completed by a central tubular base 4 disposed on a central portion 5 of connection between the condyles 3 on the side opposite to their articular surfaces 4. The base 4 is adapted to receive an intramedullary femoral stem not shown.

 The femoral implant 1 is completed by at least one pair of compensating and bone adjustment wedges adapted to be able to be fixed on the internal surface of a condyle 3, namely a distal wedge 6 and a posterior wedge 7. Each surface the interior of the condyles 3 is designed to be able to receive either only one of these two wedges 6,7, or both in combination according to the needs observed by the surgeon for adjusting the thickness of the condyles 3.

 The wedge 6 is constituted by a plate whose contour is adapted to the conformation of the associated condyle 3: thus the body of the wedge 6 consists of a first part of rectangular contour 6a extended in the direction of the trochlea 2 by a trapezoidal part 6b. In the wedge 6 is drilled a hole 8 with a conical wall 9 which can be placed coaxially with a hole 11 of a boss 12 projecting from an imprint 13 arranged in the distal and posterior inner surface of each condyle 3. A flat head screw or milled depending on whether the wedge 6 is used alone or associated with the posterior wedge 7, can be screwed into the tapped hole 11, which is extended in the condyle 3 by a blind hole, in order to secure the distal wedge 6 with the implant femoral 1. The wedge 6 is completed, on its bearing face on the condyle 3, by studs 16, 17 and 20 arranged on either side of the bore 8 to facilitate the correct positioning of the distal wedge 6 Thus the two chamfered studs 16 are formed at the angles of the rectangular part 6a of the wedge 6, the central stud 20 is formed between the studs 16 and the hole 8, and the stud 17 is positioned to rest on the boss. annular 12 when the wedge 6 is in place, in app ui on the edges of the imprint 13 from which it projects.

 The posterior wedge 7 is formed by a plate 19 of suitable thickness, of substantially rectangular outline with two rounded vertices 21 provided to come to be positioned facing the free end of the corresponding condyle 3. The posterior plate 19 is extended by an extension consisting of a tab 22 profiled to adapt to the conformation of the inner surface of the condyle 3. The latter thus has, in the impression 13, a flat posterior surface 23, a flat distal surface 24 and a flat surface 25 of connection between surfaces 23 and 24. These three surfaces 23,24,25 correspond to bone cuts made by the surgeon.

 Correlatively, the tab 22 comprises a first flat part 22a fixed to the surface of the wafer 19 so as to be able to be housed in the cavity 13 bearing on the surface 23, a second flat part 22b adapted to be placed opposite the chamfer surface 25, and a third end portion 22c placed in the cavity 13 on the distal surface 24. The end portion 22c present in the example described a semi-circular wall 30 adapted to be able to surround the boss 12, cylindrical in the example shown.

 The tab 22 with its end portion 22c thus ensures correct positioning of the posterior wedge 7 on the condyle 3, only this tab 22 being housed inside the cavity 13 while the plate 19 projects from the plane defined by the edges of the imprint 13.

 Two or more pairs of shims 6, 7 of variable thickness can thus be provided. Each wedge 6,7 can be used in isolation, the two wedges also being able to be used in combination as illustrated in FIG. 3.

 The thickness of the terminal part 22c of the tab 22 is approximately equal to the height of the boss 12 above the bottom of the cavity 13, so that when the rear wedge 6 is put in place, the surface of the end portion 22c is flush with that of the boss 12. Therefore, when the surgeon wants to use only a posterior wedge 7 of appropriate thickness, he ensures the fixation of this wedge 6 by means of a flat head screw not shown, dimensioned to apply to the surface of the boss 12 and to the end portion 22c.

 On the other hand, if the surgeon wants to use only the distal wedge 6 or this wedge in combination with the posterior wedge 7, he ensures the fixation of the wedge 6 or of the two wedges 6,7 by a screw 14 with a countersunk head 15, the surface of which conical comes to bear on the conical wall 9 of the wedge 6.

Correlatively, the end part 22c is placed between the distal surface 24 and the central stud 20 of the wedge 6, which thus rests on said part 22c and keeps the rear wedge 7 in place.

 Of course, the femoral implant 1 can also be used without one of the shims 6, 7 as required, the arrangement of the imprints 13 in the condyles 3 then not constituting an annoyance. Because the femoral implant 1 is generally fixed using an orthopedic cement, the depth of the imprint 13 constituting the housing of the wedges 6,7 corresponds to the thickness necessary to make a reserve of cement and obtain thus a satisfactory connection of the implant 1 to the femoral bone.

 The set of shims 6.7 required is very small in number for each condyle 3: thus two sets of shims having two different thicknesses, of 4mm and 8mm respectively for the distal shim 6 and the posterior shim 7, may be sufficient.

 The invention is not limited to the embodiment described and may include various variant embodiments. Thus, the end portion 22c instead of having a substantially semi-circular bearing 30 as shown, could be annular and completely surround the boss 12, the radial connections 12a of which at the edge of the cavity 13 would then be eliminated. It is also possible to make an extension from the distal wedge 6, fulfilling the role of the connecting lug 22, to connect this wedge to the rear wedge 7, in which case the common means of fixing the two wedges would be arranged in the posterior end of condyle 3.

Claims (8)

 1. Femoral implant (1) of recovery for knee prosthesis, comprising a trochlea (2), a pair of condyles (3) connected to the trochlea, as well as distal (6) and posterior wedges (7) for adjusting the thickness of the condyles, a pair of these wedges being provided to be fixed to at least one of the condyles characterized in that one (7) of the wedges is extended by an extension (22) adapted to be able to be placed between the surface of the condyle (3) and the second wedge, and in that a single means (14) for fixing the two wedges is provided.  2. Implant according to claim 1, characterized in that said extension is a tab (22) extending the posterior wedge (7).  3. Implant according to claim 2, characterized in that the tab (2) is provided with an end portion (22c) adapted to at least partially surround a boss (12) of the surface of the condyle (3) which can be covered by the distal wedge (6) which also covers said end portion, and in which is drilled a hole (11) for receiving a fixing element (14) common to the two wedges, an opening (8) for passage of this element being also provided in the distal wedge (6).  4. Implant according to claims 2 and 3, characterized in that an impression (13) for positioning the wedges (6,7) is arranged in each condyle (3).  5. Implant according to claim 4, characterized in that the distal wedge (6) is provided with a stud (17) for positioning the wedge in the impression (13) and a stud (20) bearing on the tab (22) of the posterior wedge (7), the two wedges (6,7) projecting from the planes defined by the edges of the imprint.  6. Implant according to one of claims 3 to 5, characterized in that the fixing element common to the two wedges (6,7) is a countersunk head screw (15).  7. Implant according to claim 5, characterized in that the distal wedge (6) is provided with chamfered corner studs (16) which can come to bear on the inner surface (25) of the condyle (3).  8. Implant according to any one of claims 3 to 7, characterized in that it is provided with a flat head screw suitable for fixing only the rear wedge (7), said head being able to bear on the boss (12) and on the terminal part (22c).