Patent Abstract:
A malleolar implant for partial or total ankle prosthesis which includes a head having a surface to bear against an astragalus or astragalian prosthetic component and from which head extends a shank adapted to be inserted through a bore in a fibula wherein the shank is provided with means for hooking a traction member which is adapted to be inserted through the bore in the fibula in order to apply a force to pull the implant into the bore such that the implant is seated within the bore of the fibula.

Full Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a malleolar implant for a partial or total prosthesis of the ankle and to an ancillary tool for placing, such an implant. 
     DESCRIPTION OF THE RELATED ART 
     It is known, for example from EP-A-0 864 304, to fit an ankle prosthesis with a malleolar implant intended to bear against an articular surface at the level of the astragalus, whether it be question of a natural surface or of a surface of a prosthetic component. During an operation on an ankle, access to the internal articular surfaces is limited by the ligamentary system which does not necessarily allow a sufficient dislocation of the joint. In particular, access to the internal surface of the fibular malleolus may be insufficient, which induces difficulties in positioning the implant, particularly by impaction. 
     With reference to the embodiments of FIGS. 4 and 5, it is envisaged in EP-A-0 864 304 to introduce an implant from the outer face of the fibula. However, this necessarily limits the surface of the head of this implant, which must be less than or equal to the surface of the orifice provided in the bone, so that it is necessarily of relatively small dimensions with the result of substantially fragilizing the malleolus. 
     For the foregoing reasons, the positioning of the malleolar implants in the known prostheses is not entirely satisfactory. 
     It is a particular object of the present invention to overcome these drawbacks by proposing a novel malleolar implant which may be positioned precisely, even though access to the internal surface of the fibular malleolus may be limited and whereas its articular head presents dimensions allowing it to perform its function efficiently. 
     SUMMARY OF THE INVENTION 
     To that end, the invention relates to a malleolar implant comprising a head, intended to bear against the astragalus or an astragalian prosthetic component and a shank provided to be introduced in a bore in the fibula, characterized in that the shank is provided with means for hooking a traction member adapted to be maneuvered from the outer side of the fibula, in order to position the shank in the bore. 
     Thanks to the invention, the implant may be pre-positioned towards the inner face of the fibular malleolus and pulled through the through bore provided in the malleolus, with the result that the surgeon does not have to manipulate the implant with precision inside the joint, i.e. between the fibula and the tibia or between the fibula and the astragalus. The surgeon may exert an efficient effort on the traction member, which may be a flexible tie such as a suture thread, without being hindered by the surrounding bones. As a result, the positioning of the shank of the implant in the bore in the fibula may be precise, in particular due to the fact that the outer diameter of the shank may be substantially equal to the inner diameter of this bore, as the effort of traction which may be exerted from the outside of the fibula may be intense. 
     According to an advantageous aspect of the invention, the shank is provided with at least one orifice for passage of a flexible tie adapted to be engaged through the bore. In particular, the shank may comprise a plurality of orifices for passage of a flexible tie, such orifices being distributed over the length of this shank. 
     According to another advantageous aspect of the invention, the shank is provided with means for axial hold inside the bore. These means, which may be formed by outer radial flanges distributed over the length of the shank, make it possible efficiently to immobilize the shank inside the bore after it has been introduced therein by traction on the flexible member or tie. 
     The invention also relates to an ancillary tool for placing a malleolar implant as described hereinabove and, more specifically, a tool which comprises a spacer-block adapted to be inserted between the tibia and the astragalus of an ankle, and a lug fast with this spacer block and extending up to the vicinity of the outer surface of the fibular malleolus when the spacer block is in place between the tibia and the astragalus, this lug supporting a guide for boring the malleolus from its outer surface. 
     Thanks to the invention, the bore of the fibular malleolus may be effected from its outer surface and in the direction of its inner surface, with a determined relative positioning with respect to the tibia and the astragalus, with the result that the position of the malleolar implant in place in this bore is determined with precision with respect to the respective articular surfaces of the astragalus or of the tibia or of corresponding prosthetic components. The spacer block may be provided to cooperate with natural articular surfaces of the tibia and/or of the astragalus or with surfaces created by resection of these bones, in the case of placing a total ankle prosthesis. 
     According to an advantageous aspect of the invention, the spacer block is provided with a housing for receiving a shim of thickness adapted to the distance between the lower surface of the tibia and upper surface of the astragalus. This aspect of the invention makes it possible to maintain a distance corresponding to that which will be subsequently created by the prosthetic elements mounted in the lower part of the tibia and in the upper part of the astragalus, when the position of the malleolar implant is determined. 
     According to another advantageous aspect of the invention, the lug is articulated on the spacer block, with a limited possibility of pivoting. This makes it possible to adjust the position of the malleolus bore guide about the pivot axis of the lug with respect to the spacer block. In that case the spacer block and the lug are advantageously provided with orifices for passage of a common pivot pin. 
     It is also possible for the bore guide to be associated with a device for clamping the malleolus against a bearing surface formed on the lug or the spacer block. This allows a firm immobilization of the fibular malleolus during boring and thus ensures precision of the boring operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more readily understood on reading the following description of an embodiment of a malleolar implant and its ancillary tool according to the invention, given solely by way of example and with reference to the accompanying drawings, in which: 
     FIG. 1 is a view in perspective of an implant according to the invention. 
     FIG. 2 is a view in perspective of the implant of FIG. 1 during positioning in a fibular malleolus, shown with parts torn away. 
     FIG. 3 schematically shows, with parts torn away, an ancillary tool for placing the implant of FIG. 1, in the course of use. 
     FIG. 4 is a view in perspective of the tool of FIG. 3, from underneath. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring now to the drawings, the implant  1  shown in FIGS. 1 and 2 is intended to be introduced in a bore  2  made in the lateral or fibular malleolus  3 . The implant  1  comprises a convex head  4 , substantially in the form of a spherical cap and of which the radius of curvature is substantially equal to that of the outer cheek of the astragalus of the ankle in question. The shank  5  of the implant  1  is provided with outer radial flanges  6  of which the outer diameter d 6  is substantially equal to the inner diameter d 2  of the bore  2 . 
     According to the invention, two orifices  7  are provided in the shank  5  and are capable of receiving a suture thread  8  or other flexible tie. When such a thread is engaged in one of the orifices  7 , it is possible to exert on the thread  8  an effort of T which is transmitted by the thread  8  to the shank  5  as represented by arrow T in FIG.  2 . In this way, by pulling on the thread  8 , the surgeon introduces the shank  5  in the bore  2  without having to exert an effort of thrust on the head  4  which may be difficult to access due to the surrounding ligamentary system. 
     In other words, it suffices for the surgeon to place a thread in one of the orifices  7 , to pass the two strands of the thread  8  in the bore  2  via the inner face of the malleolus, then to pull the strands via the outer side of the malleolus. The traction on the thread  8  has the effect of introducing the shank  5  of the implant  1  in the bore  2  and of applying the head  4  on the bone. The effort of traction T exerted on the thread  8  may be intense and directed parallel to the longitudinal axis X 2  of the bore  2 , with the result that the shank is efficiently drawn towards the inside of the bore  2 . In particular, taking into account the direction and intensity of the effort of traction T, the diameters d 2  and d 6  can be provided to be substantailly equal, with the result that the shank  5  is firmly maintained in place after having been positioned. 
     The shank  5  is provided with two bores  7  distributed along its axis X 5 , the bore  7  nearest the end  5   a  of the shank  5  being used. The fact that the shank  5  comprises a plurality of orifices  7  makes it possible to use an orifice  7  relatively close to the end  5   a  of the shank  5  and to avail of such an orifice including when the shank  5  is cut in order to adapt its length to the thickness e of the malleolus  3 . The number of bores  7  may, of course, be increased if necessary. 
     The bore  2  is made via the outer face  3   a  of the malleolus  3  with the aid of the ancillary tool shown in FIGS. 3 and 4. This tool  10  comprises a spacer block  11  provided to be disposed between the tibia T and the astragalus A of an ankle to be fitted with the implant  1 . The block  11  comprises a substantially planar upper surface  12  intended to cooperate with a planar surface created by resection of the distal end of the tibia. The lower surface  13  of the block  11  is formed by two planar surfaces  13   a  and  13   b  inclined with respect to each other by an angle α, the surfaces  13   a  and  13   b  being provided to bear respectively on corresponding surfaces created by resection of the upper face of the astragalus A. 
     The surface  12  of the block  11  comprises a C-shaped housing  14  intended to receive a shim  15  of which the upper surface  16  is in contact with the lower surface of the tibia T. The thickness E of the shim  15  shown in FIG. 3 is such that its upper surface  16  is flush with the upper surface  12  of the block  11 . 
     However, thicker shims may be used when the distance E′ between the lower surface of the tibia and upper surface of the astragalus is greater than in the configuration shown in FIG.  3 . 
     The block  11  defines a housing  17  for receiving the end  20  of a substantially C-shaped lug  21 . The end  20  is provided with a bore (not shown) which, in the configuration of FIGS. 3 and 4, is aligned with a bore  18  made in the block  11  and passing downwardly through this block, i.e. connecting the surfaces  12  and  13 . A screw  19  may be introduced in this bore which is at least partially tapped, this making it possible to immobilize the end  20  of the lug  21  inside the housing  17 . In practice, the clearance made when the screw  19  is tightened allows a limited pivoting about axis X 18  of the bore  18 . 
     At its end  22  opposite the end  20 , the lug  21  supports a clamping system  23  adapted to be manoevred thanks to a knurl  24  and making it possible to apply the malleolus  3  of the fibula P against a stop  25  formed on an extension  26  of the end  20  of the lug  21 . X 23  denotes the longitudinal axis of these clamping means. The clamping means  23  are hollow, with the result that a drill  30  may be introduced up to the level of the outer face  3   a  of the malleolus  3  in order to make the bore  2  from the outside towards the inside of the malleolus  3 . In this way, the surgeon may easily aim at the suitable part of the malleolus  3  thanks to the clamping means  23  which also constitute a bore guide for the drill  30 . 
     As the lug  21  is capable of pivoting about axis X 18 , the position of axis X 23  is variable in pivoting about this axis X 18 , which makes it possible optimally to adjust the orientation of the bore  2  as a function of the exact geometry of the malleolus  3 . β denotes the maximum angle of pivoting of the axis X 23  about axis X 18 . In practice, the angle β is of the order of 10°. 
     Thanks to the tool  10 , a bore  2  may therefore be formed from the outside, allowing a rapid and efficient implantation of the implant  1 . 
     When shims  15  of thickness greater than those shown in FIG. 2 are used, they can be provided to overlap the bore  18 , as the screw  19  is placed in position before positioning of the shim  15  which is effected during operation as a function of the distance E′. 
     The invention has been shown with a total ankle prosthesis, which corresponds to the geometry of the surfaces  12  and  13  of the block  11 . However, it is also applicable to a partial ankle prosthesis, without modification of the implant  1 , the ancillary tool in that case being adapted to the geometry of the anatomical articulation surfaces between the tibia and the astragalus.

Technology Classification (CPC): 0