AU2004201647B2

AU2004201647B2 - Total metatarso-phalangeal prosthesis, and ancillary devices for fitting this prosthesis

Info

Publication number: AU2004201647B2
Application number: AU2004201647A
Authority: AU
Inventors: Marc Augoyard; Michel Benichou; Thibaut Leemrijse; Michel Maestro; Jacques Peyrot; Didier Poncet; Mathieu Ragusa; Bernard Valtin
Original assignee: Pied Innovation 2 P I 2; DePuy Ireland ULC
Current assignee: Pied Innovation 2 "pi2"; DePuy Ireland ULC
Priority date: 2003-08-06
Filing date: 2004-04-20
Publication date: 2010-08-19
Anticipated expiration: 2024-04-20
Also published as: NZ531099A; EP1508316B1; DE602004006471D1; FR2858545B1; JP2005052629A; AU2004201647A1; EP1508316A1; FR2858545A1; ES2285370T3; DE602004006471T2; ATE362352T1

Abstract

The prosthesis has a metatarsal implant (1) including head (6) whose inclined rear plane side (7) forms preset angle with a plane normal to an axis of an anchoring rod. An articular surface of the head and the rear side meet at a lower point of the implant. A distance between the axis of the rod and the lower point is determined, such that the head does not extend in the sesamoid grooves arranged on a lower base of a metatarsal. - Independent claims are also included for the following: (a) an identification supplementary for implementing metatarsal phalange prosthesis (b) a guiding supplementary of a metatarsal phalange (c) a phalange cut supplementary for implementing a metatarsal phalange prosthesis.

Description

AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S):: DePuy France AND Pied Innovation 2"P.I.2" ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Nicholson Street, Melbourne, 3000, Australia INVENTION TITLE: Total metatarso-phalangeal prosthesis, and ancillary devices for fitting this prosthesis The following statement is a full description of this invention, including the best method of performing it known to me/us: 5102 -la The present invention relates to a new total metatarso phalangeal prosthesis of the type involving surface rejection, and also to ancillary devices for fitting this prosthesis . 5 It also relates to a set of. metatarsal implants and to a set of such prostheses of different dimensions. Total metatarso-phalangeal prostheses are already known 10 which comprise a metatarsal implant having an osseous anchoring rod and an articular body arranged at the end of this rod, a phalangeal implant, and an intermediate plateau or plug intended to be arranged on the phalangeal implant and having an articular surface complementing the articular 15 surface of the metatarsal implant. Such a prosthesis is described, for example, in the patent FR-B-2 737 013. 20 According to a first aspect of the present invention, there is provided a total metatarso-phalangeal prosthesis comprising a metatarsal implant comprising an anchoring rod intended to be arranged longitudinally in the metatarsal, and a head situated at the end of the rod, intended to be applied against the resected 25 surface of the end of the metatarsal, and having an articular surface, and a phalangeal implant having a body intended to be introduced axially into the phalanx, and a rim situated at the proximal end of said body and capable of presenting an articular surface complementing the articular surface presented by the body 30 of the metatarsal implant, wherein the head of the metatarsal implant has, opposite the articular surface, an inclined and plane rear face intended to bear against a resected surface of -2 the metatarsal, said rear face forming, with the plane perpendicular to the axis of the anchoring rod, an angle of 200 + So so as to extend rearwards towards the top, starting from the lower base of the metatarsal, and wherein the 5 articular surface of said head and said inclined rear face meet at a lower point, forming the lowest point of the metatarsal implant, the distance between the axis of the anchoring rod and said lowest point being determined in such a way that the head does not extend into the sesamoid 10 grooves disposed on the lower base of the metatarsal. Preferred embodiments of the invention provide a prosthesis for the articulation between the first metatarsal and the first phalanx of the great toe. 15 The rear face of the head of the metatarsal implant can, when the foot is placed flat on the ground, be situated in a position substantially perpendicular to the ground. Furthermore, the freedom left in the area of the sesamoid 20 grooves can make it possible to preserve the functionality. of the ligaments and of the articulation. Preferably, said articular surface of the phalangeal implant is able to be carried by a separate plug which can be 25 introduced into and held in the phalangeal implant. In a preferred embodiment, the articular surface of the body of the implant has only a single radius in the sagittal plane. In other words, a sagittal cross section of this 30 surface forms an arc of a circle. It is likewise highly advantageous if said surface can also have just a single radius in the horizontal plane.

-3 Of course, the opposite articular surface of the phalangeal implant is a complementary surface. In a particularly preferred embodiment, the complementary 5 articular surface is formed by an intermediate plug, carried by the phalangeal implant, and free in terms of rotation about the axis of the phalanx. Perfect congruence can thus be obtained in all positions, 10 the rotary plug permanently adapting in all the angular positions. The articular surface of the plug can advantageously have on its periphery, and more precisely on a substantial part of 15 the periphery of the lower half and/or of the periphery of the upper half, an indentation determining a convex edge for the clearance of the articulation in the position of flexion and/or of extension. 20 In a preferred embodiment of the invention, and particularly in the case where the phalangeal articular surface is formed by a plug turning freely in the phalangeal implant, the latter has a hollow frustoconical anchoring body continued, at its proximal end, by a head in the shape of a peripheral 25 frustoconical rim, the plug having a corresponding shape, namely a frustoconical distal portion whose conicity corresponds to that of the body, and continued by a plateau having a peripheral distal surface whose conicity corresponds to that of the rim of the implant, which also 30 means the plug can be given a particularly robust form. At the periphery, the rim can come into contact with the C:Wonb\1DCCdL\030I8S I.DOC-27O07/201 -4 cortical bone of the phalanx and bear thereon. Preferably, the proximal face, inclined at 200 + 50, of the head of the metatarsal implant is continued, towards the 5 top, by an upper face forming, with the preceding one, a dihedron, preferably with an obtuse angle of 1450 ± 20Q, intended to be applied against an upper resected plane inclined by the same angle in relation to the resected surface receiving the proximal face. 10 According to a second aspect of the present invention, there is provided a set of metatarsal implants comprising a plurality of metatarsal implants of different sizes, designed to form part of the prosthesis defined above, the 15 distance between the axis of the anchoring rod and the lowest point being substantially constant for all the implants of the set. The sesamoid grooves can thus remain free, whichever 20 metatarsal implant is used. In this set, the articular faces of the heads of the metatarsal implants are preferably dimensioned so as to meet the corresponding upper face at an upper point, at different 25 predetermined respective distances from the axis of the anchoring rod. Sets as described above may allow the surgeon to choose the dimensions of the various components of the prosthesis 30 during surgery. During fitting of the prosthesis, it is also possible to -5 choose a metatarsal implant whose upper part is best adapted to the ligament state of the upper level of the articulation. These ligaments are in fact often deformed, stiffened or hardened by the disease which necessitated 5 fitting the prosthesis. The metatarsal implant will in particular be chosen so as not to interfere with the lateral ligaments upon dorsal flexion of the articulation. Advantageously, the diameter of the rod of the metatarsal 10 implant can be substantially constant, irrespective of the implant chosen from the set, and it may be possible simply to vary the length of this rod from one implant to another in the set. 15 According to a third aspect of the present invention, there is provided a set of prostheses which comprises a set of metatarsal implants as defined above, a plurality of phalangeal implants of different sizes, and a plurality of plugs also of different sizes, wherein the plug whose 20 articular surface is congruent with the articular surface of a given metatarsal implant can be received in at least two phalangeal implants of consecutive sizes in order to form a prosthesis as defined above. 25 This can additionally permit the same dihedral resection to be carried out using the same ancillary devices, irrespective of the size of the metatarsal. The phalangeal implant can have a frustoconical body having 30 the same dimension for all the implants in the set, this cone being followed by the frustoconical rim, only the diameter of the periphery of this rim being variable from one C:WFLRPonbPDCC\IL3'f3*1 LDOC-2/07/201iI -6 implant to another in the set, preferably so as to bear against the cortical bone of the phalanx, while nonetheless being set back in relation to the external size of the phalanx in the area of the resection, 5 It is possible to define several plugs within the set, all of them having the same frustoconical plug part adapted to the frustoconical body of the phalangeal implant and having different peripheral diameters and/or plateau thicknesses within the set 10 The set of implants is preferably presented in sterile kits. In a particular embodiment of the set according to the invention, there are three or four sizes of metatarsal implants having rods with 15 a diameter of 5 mm. For example, for a set comprising three metatarsal implants, the radii of curvature of the articular surface 10 are, respectively, 7 + 0.5, 8 ± 0.5 and 9 ± 0.5 mm in the sagittal plane and 14 1, 16 ± 1 and 18 + 1 rm in the horizontal plane, and the lowest points in the sagittal plane (the implant axis being 20 horizontal) are situated at a comn distance of between about 2 and 6 rm from the axis. In such a set, it is preferable to have four sizes of phalangeal implants, each implant having an implant body with a distal end 25 diameter of 4.7 ± 2 mm and a diameter at the periphery of the rim of 12 ± 1, 13. 3 1, 14 -6 + 1 and 16 + 1 mm. It is thus possible to provide three or four plugs of different sizes, namely plugs with a diameter of 12 * 0.5, 13 ± 0-5 and 14 + 0.5 mm for 30 a set of three plugs.

CNR?ortb\DCCiL3(.l J IDO %M -6a According to a fourth aspect of the present invention, there is provided an ancillary position-marking device for fitting a prosthesis as defined above, having a body equipped with a cylindrical inner passage allowing it to slide and to turn 5 about a broach implanted axially in the metatarsal, and, starting from said body, two bent arms whose ends are arranged spatially so as to be able to substantially lock in the sesamoid grooves, towards their distal end at the lower part of the metatarsal, in such a way as to maintain the 10 body in a suitable axial and angular position in relation to said two sesamoid grooves, said body additionally having a means for receiving and positioning of an ancillary metatarsal resecting device, extending parallel to the axis of the implant and hence to the broach, and at a distance 15 from the metatarsal in the alteral direction towards the sagittal plane of the patient. According to a fifth aspect of the present invention, there is provided an ancillary device for guiding the resecting of 20 the metatarsal, used for fitting a prosthesis as defined above, having a body with a passage allowing it to slide on the receiving means of an ancillary position-marking device according to either of Claims 15 and 16, said body having means for fixing it relative to the bone, said body additionally having at least one 25 resection slit for the passage of an oscillating saw, said slit being inclined by an angle of 700+ 200 with respect to the axis of the broach when the assembly is mounted on the metatarsal. According to a sixth aspect of the present invention, there is 30 provided an ancillary device for phalangeal resection, for fitting a prosthesis as defined above, having a body allowing it to be fixed laterally on the cortical bone of the phalanx, at least one slit for C: RParW\CCL\30BRl59,LDO C-27/07/2010 - 6b phalangeal rejection, and an extension intended to bear against a corresponding end of the ancillary device for metatarsal resection according to either of Claims 17 and 18, in such a way as to exactly define the relative 5 positions of the two resecting assemblies, the metatarsal and phalangeal resection slits being substantially parallel when the two ancillary resenting devices are combined. According to a preferred embodiment of the invention, there 10 is provided a set of ancillary devices permitting fitting of a prosthesis according to the invention. Embodiments of the present invention may provide simplified metatarso-phalangeal prostheses having anatomical properties 15 which enhance the functionality of the metatarso-phalangeal articulation established by a prosthesis, and also provide for the adaptation of this prosthesis within the anatomical environment of this articulation. Embodiments of the present invention provide ancillary devices permitting precise 20 fitting of the implants, in all the situations encountered.

- 7 This set of ancillary devices advantageously comprises the following components: - an ancillary position-marking device having a body 5 equipped with a cylindrical inner passage allowing it to slide and to turn about a broach implanted axially in the metatarsal, and, starting from said body, two bent arms whose ends are arranged spatially -so as to be able to substantially lock in the sesamoid grooves, 10 towards their distal end at the lower part of the metatarsal, in such a way as to maintain the body in a suitable angular position in relation to said two sesamoid grooves, said body additionally having a means for receiving and positioning of an ancillary 15 metatarsal resecting device, this means possibly advantageously being a preferably non-circular rod extending parallel to the axis of the implant and hence to the broach, and at a distance from the metatarsal in the lateral direction towards the sagittal plane of the 20 patient; - an ancillary device for guiding the resecting of the metatarsal, having a body with a passage allowing it to slide on the receiving means of the ancillary position 25 marking device, said body having means for fixing -it relative to the bone, preferably transverse passages through which it is possible to pass small lateral fixation broaches which are screwed into the lateral cortical bone of the metatarsal, said body additionally 30 having at least one resection slit, preferably two, for the passage of an oscillating saw, said at least one slit being inclined by an angle of 700 + 200 with respect to the axis of the broach when the assembly is mounted on the metatarsal, the second slit being more 35 inclined, so that said two slits thus make it possible to form firstly the resected surface receiving the rear face of the head of the implant, and the second resected surface forming an obtuse angle, preferably of 145o + 200, with the aforementioned resected surface; - an ancillary device for phalangeal rejection, having a body allowing it to be fixed laterally, likewise by small broaches, on the cortical bone of the phalanx, at 5 least one slit, preferably two parallel slits, for phalangeal resection, and an extension intended to bear, pre-ferably by interlocking, against a corresponding end .of ~ the ancillary device for metatarsal resection; in such a way as to exactly 10 define the relative positions of the two resecting assemblies, the metatarsal and phalangeal resection slits being substantially parallel when the two ancillary resecting devices are combined. 15 Disclosed herein is a surgical method for fitting a total metatarso-phalangeal prosthesis according to the invention, said method comprising the following steps, after access has been made via the lateral metatarso phalangeal access route: 20 - luxation of the phalanx, - placement of an axial broach in the metatarsal, placement of an ancillary position-marking device on the broach by means of sliding and rotation 25 until said ancillary device is immobilized by means of the ends of the bent arms being lodged in the two sesamoid grooves, - placement of the ancillary metatarsal resecting device on the ancillary position-marking device, 30 - fixation of said ancillary resecting device by means of broaches screwed into the metatarsal, - 200 rejection of the end of the metatarsal, then resection of the second face of the dihedron, - placement of the ancillary phalangeal rejecting 35 device, preferably by fixing it first on the metatarsal ancillary device, then reducing the luxation, phalangeal rejection, placement of the ancillary devices, - determination of the external diameter of the rim of the phalangeal implant, for example using a template, placement of the trial metatarsal implant, 5 - after renewed luxation of the phalanx, axial drilling of the phalanx using a cutter with a form corresponding to the phalangeal implant, - placement of the trial phalangeal implant, - withdr-awal of the trial phalangeal implant ahd 10 impaction of the phalangeal implant, - withdrawal of the trial metatarsal implant and impaction of the metatarsal implant, - determination of the thickness of the plug carrying the phalangeal articular surface and 15 introduction of the plug into the phalangeal implant, - reduction then closure of the incisions. Other advantages and characteristics of the invention 20 will become clear from the following description which is given solely by way of non-limiting example and with reference to the attached drawings, in which: Figure 1 is a diagrammatic perspective view of an implant 25 according to a preferred embodiment of the invention when fitted, Figure , 2 is a diagrammatic sagittal cross section - of the position of three metatarsal implants of a set in relation to a metatarsal, 30 Figure 3 is a diagrammatic cross section through a metatarsal implant with its plug, Figures 4 to 9 show respective top and side views of 35 three metatarsal implants of different sizes, Figures 10 to 12 show side elevations of three plugs of different sizes, - 10 Figures 13 to 16 show side elevations of four phalangeal implants of different sizes, Figure 17 shows a diagrammatic side elevation of the 5 ancillary position-marking device, Figure 18 shows a bottom view of this ancillary device, Figure 19 shows a diagrammatic view of an end of the 10 metatarsal with different angular positions of the ancillary position-marking device in relation to the sesamoid grooves, Figure 20 shows a side elevation of the ancillary 15 metatarsal resecting device when it is being fitted in place, Figure 21 shows a bottom view during fixation of this ancillary device, 20 Figure 22 shows a side view of the ancillary phalangeal resecting device positioned on the ancillary metatarsal resecting device, 25 Figure 23 shows a bottom view of the assembly from Figure 22. Referring to Figure 1, this shows a metatarsal M and a phalanx P which, after corresponding resected surfaces 30 have been formed, have received a metatarsal implant 1, and a phalangeal .implant 2 with a plug 3 forming the articulation surface. Referring to Figure 2, the solid lines show a 35 diagrammatic cross section of the metatarsal implant 1. The dotted lines and the broken lines, respectively, represent two other sizes of metatarsal implants arranged in the same position on the metatarsal M, the three metatarsal implants forming an example of a set - 11 of metatarsal implants according to the invention. As will also be seen by referring to Figures 4 to 9, each metatarsal implant 1 has a cylindrical rod 4 which 5 terminates in a beveled, then rounded end 5. The diameter of this rod is intended to permit fixation of the implant in a drilled hole which has been formed beforehand axially in the metatarsal. 10 The metatarsal implant also has a head 6 with two faces forming a dihedral angle. One is the rear face 7, which forms an angle of about 200 with the axis of the rod 4, so that the rear face is inclined upwards and rearwards. At approximately the level of the upper 15 limit of the rod 4, the plane face 7 is continued by a face 8 which is inclined by an angle of about 1450 with respect to the face 7. In the example shown, the rod 4 is joined integrally to the face 7, but it will be appreciated that the axis 9 of the dihedron could also 20 be lower or higher. At the distal end, the head 6 has an articular surface 10 which, shown in the sagittal plane, has a single radius of curvature to form an arc of a circle. In the 25 perpendicular plane, that is to say in the horizontal plane, the surface 10 also has a single radius of curvature. The articular surface 10 meets up with the rear face 7, in the sagittal plane, at a lower point 11 situated at a distance h from the axis of the rod 4. 30 In the context of the invention, this distance h is preferably chosen between 2 and 6 mm. This distance h is identical or substantially identical for all the metatarsal implants of a same set. The distance h is 35 such that when the implant is positioned on the metatarsals, as is shown in Figure 2, the position of the point 11 is such that the articular surface, in its lower part, does not encroach upon the opening of the sesamoid grooves S shown in Figure 19.

- 12 Moreover, it will be seen that, depending on the dimensions of the articular faces 10 of the metatarsal implants of the set shown in Figures 4 to 9, the upper 5 point 12 of the implant, formed where the surfaces 8 and 10 meet, by virtue of the choice of the dimension of the implant, may or may not extend beyond the upper limit of the metatarsal M and thus best adapt -to the local ligament state. 10 In order to prevent risks of rotation of the metatarsal implant in the metatarsal, the rod of the implant can further comprise means for immobilizing it in terms of rotation, for example radial wings 13 situated on the 15 face 8. It will also be seen from Figure 2 that when the implant is placed at the end of the metatarsal, the rear face 7 comes to bear against the corresponding 20 resected face, of the same inclination, at the end of the metatarsal, while the inclined face 8 comes to bear against another, correspondingly inclined resected face at the end of the metatarsal. 25 Referring to Figure 3, this shows the phalangeal implant 2 which comprises a frustoconical body 14 having a small distal base 15 and continued, at its proximal end, by a conical rim 16. A frustoconical recess 17 is formed in the body 14 and in the 30 continuation of the proximal face of the rim 16. The diameter of the part 15 is advantageously small, for example of the order of 4.7 mm. At this level, in the opening of the recess 17, the internal diameter is 35 advantageously 6 cm, the frustoconical recess in the body 14 making it possible to receive plugs of 6 mm, for example. The maximum diameter of the rim 16 can also vary - 13 depending on the size of the phalangeal implant. This phalangeal implant can receive the plug 3 comprising a plateau 18 and a tail 19. The distal face 5 of the plateau 18 is congruent with the internal conical face of the rim 16, while the outer surface of the tail 19 is congruent with and of the same conicity as the recess 17 in the implant body 14. It will be appreciated that, in this way, the plug 3 is received 10 in the implant and has a shape giving it particular strength. With plugs made of polyethylene, for example, it is possible to achieve a resistance to shearing of approximately 42 daN. 15 The tail of the plug always has the same dimension, whereas the diameter and/or thickness of the plateau 18 can vary. As can be seen from Figure 1, the proximal articular 20 face of the plug is concave and congruent with the articular surface of the metatarsal implant, that is to say this face has, in perpendicular planes, constant radii of curvature identical to those of the surface of the metatarsal implant. 25 Finally, it will be seen that two indentations or bevels have been formed at the periphery of the articular face of the plug, namely a lower bevel 20 and an upper bevel 21, these bevels extending over almost 30 the full half of the peripheral arc of a circle concerned and permitting additional clearance in flexion and in extension respectively. Referring more specifically to Figures 4 to 16, these 35 show a complete set comprising three metatarsal implants 1, four phalangeal implants 2, and three plugs 3. For each metatarsal implant, the diameter of the rods 4 - 14 is about 5 mm, for example more or less 2 mm. As has been indicated in the drawings, the radii of curvature are, in the sagittal plane, in ascending size, 7 + 0.5, 8 + 0.5 and 9 + 0.5 mm and, in the frontal plane, 14, 5 16, and 18 mm. The sizes in the horizontal plane are 16, 18 and 20 mm. The four phalangeal implants 2 of the set have external rim diameters of, respectively, 12 + 1, 13.3 + 1, 14.6 .10 + 1 and 16 + 1 mm. The seats and surfaces receiving the plugs are identical. Finally, the set comprises three plugs 3 whose maximum plateau diameters are, respectively, 12 + 0.5, 13 + 0.5 15 and 14 + 0.5 mm. All combinations of metatarsal implant, plug and phalangeal implant are possible by virtue of the adaptability of the components. On the page featuring 20 Figures 4 to 16, the arrows drawn in broken lines represent the medically preferred links between the three components, namely metatarsal implants, plugs and phalangeal implants. 25 Reference is now made to Figures 17 to 19. To fit a prosthesis according to the invention, after luxation of the phalanx, the distal end of the metatarsal M is approached and an axial hole is made in 30 the centre of the pathological articular surface using a threaded broach 30 which is left in place. An ancillary position-marking device 31 is then engaged on the broach, said ancillary device 31 being able to 35 slide and turn about the broach and having, for this purpose, a body 32 equipped with a corresponding passage. At its proximal end, the body 32 has two arms 33 and 34 which are first bent laterally downwards, then forwards, their ends being tapered off and - 15 extending obliquely downwards. The spacing between the two ends of the arms 33 and 34 corresponds substantially to the distance between the two sesamoid grooves S when they open out at the anterior articular 5 face of the metatarsal. Also extending from the body 31 there is another bent and elongate arm 35, the greater part of which extends parallel to the broach 30 and at a certain distance from the lateral surface of the metatarsal. 10 The component 31 is engaged on the broach 30 and is slid and turned in order to bring it into the position in which the two ends of the arms 33 and 34 penetrate into the start of the sesamoid grooves S, until all 15 rotation is prevented, which at one and the same time fixes the axial position and the rotational position of the ancillary device 31. Reference is now made to Figures 20 and 21. 20 An ancillary metatarsal resecting device 40 is engaged, now in the opposite direction, onto the arm 35, this ancillary metatarsal resecting device 40 having a rectangular body 41 equipped with an elongate passage 25 receiving the arm 35 on which said ancillary device 40 can slide, but without pivoting. The body 41 has a plurality of transverse holes 42 through which small broaches 43 will be able to pass so 30 as to fix the ancillary device 40 on the metatarsal M. Towards its anterior part, the body 41 has widened areas in which there is a first transverse slit 44 inclined 700 relative to the body 40 and to the arm 35 and hence to the broach 30. Just below the last upper 35 third of the slit 44, a second slit 45 starts extending obliquely upwards and forming an obtuse angle with t-he slit 44. Finally, at its distal end, the body 41 has a surface - 16 46 with a small internal seat. The ancillary device 40 is slid on the arm 35 until the slit 44 comes into alignment, in its transverse plane, 5 with the upper part of the end of the arm 33, as can be seen in Figure 20, which determines the lower limit point 11 of the metatarsal implant which is to be fitted. In this position, the broaches 43 are screwed in and the body 41 is fixed rigidly with respect to the 10 metatarsal. The ancillary device 31 is then withdrawn, then the broach 30 whose diameter corresponds to the diameter of the rod 4 of the metatarsal implant, which will subsequently be able to be impacted into the hole left by a broach. 15 Finally, the end of the metatarsal is resected using a vibrating saw, first via the slit 44, then via the slit 45, thereby creating the two corresponding resection planes at the anterior end, which are inclined 20 according to the inclinations of the slits. A trial metatarsal prosthesis similar to the definitive metatarsal prosthesis can then be introduced, this making it possible to choose the most suitable size 25 from the set of prostheses. With the trial metatarsal implant 1 in place, the luxation is reduced and the phalanx P is brought back to the natural position with its articular surface 30 against the articular surface of the trial metatarsal implant, as can be seen in particular from Figure 23. As is shown in Figures 22 and 23, the ancillary phalangeal resecting device 50 is now put in place. The 35 ancillary device has a body 51, also equipped with a plurality of holes for the passage of small broaches for fixation on the phalanx. Towards its proximal end, this body 51 has a widened area 52 in which two parallel slits 53 and 54 are provided. The proximal end - 17 of this widened area is continued by an extremity 55 which has a short stub allowing it to penetrate into the small seat at the end 46 of the metatarsal ancillary device 40, this exactly determining the 5 respective positions of the two ancillary devices 40 and 50. As can be seen from Figure 23, in this position the body 50 is slightly inclined so as to reproduce the slight natural varus position of the first phalanx P. Then, using broaches similar to the broaches 43, the 10 body 50 can be fixed on the lateral face of the phalanx P. In this position it will be seen that the slits 53 and 54 are parallel to the slit 44 of the metatarsal implant. 15 The surgeon then uses one of the two slits 53 and 54 to form a straight cut at the end of the phalanx with the aid of an oscillating or vibrating blade. Then, by withdrawing the corresponding broaches, the 20 two resection implants 40 and 50 are removed. A luxation of the phalanx is then performed once again, and the size of the phalangeal implant is chosen. 25 For this purpose, one possible option is to use a template formed by a disc situated at the end of a sleeve in the plane of the disc, and possibly having a central hole in its inside, this disc making it possible to determine the diameter of the phalangeal 30 resection. If appropriate, this template can be put in place with the aid of a broach passed through its central hole, so that it is disposed in the correct position in the 35 phalanx. After removal of the template, the phalanx is then cut in order to form the hole which will receive the phalangeal implant. For this, a cutter is used which - 18 has an external and conical form with two stages corresponding to the two conical stages of the implant. If appropriate, this cutter can be guided by a broach which has been left in place beforehand and was used 5 for positioning the template. After this cutting, a trial phalangeal implant can be put into place, then, after the latter has been removed, the chosen phalangeal implant 2 is 10 definitively impacted. The trial metatarsal implant is then removed and is replaced by a corresponding definitive metatarsal implant which is impacted into the metatarsal M. 15 It then remains to choose the dimension of the plug and, in particular, the thickness of the plateau of the plug, in order to obtain the correct spacing between the phalanx and-the metatarsal. Once the plug has been -20 put in place in the phalangeal implant, the luxation is reduced and the anatomical incisions are closed. Various developments and alternative embodiments of the ancillary devices described above are also conceivable, 25 in particular as regards the number and arrangement of the rejection slits. Throughout this specification and the claims which follow, .unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "Comprising", Will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Claims

1. Total metatarso-phalangeal prosthesis comprising a metatarsal implant comprising an anchoring rod intended to be 5 arranged longitudinally in the metatarsal, and a head situated at the end of the rod, intended to be applied against the resected surface of the end of the metatarsal, and having an articular surface, and a phalangeal implant having a body intended to be introduced 10 axially into the phalanx, and a rim situated at the proximal end of said body and capable of presenting an articular surface complementing the articular surface presented by the body of the metatarsal implant, wherein the head of the metatarsal implant has, opposite the 15 articular surface, an inclined and plane rear face intended to bear against a rejected surface of the metatarsal, said rear face forming, with the plane perpendicular to the axis of the anchoring rod, an angle of 200 ± S so as to extend rearwards towards the top, starting from the lower base of the 20 metatarsal, and wherein the articular surface of said head and said inclined rear face meet at a lower point, forming the lowest point of the metatarsal implant, the distance between the axis of the anchoring rod and said lowest point being 25 determined in such a way that the head does not extend into the sesamoid grooves disposed on the lower base of the metatarsal.

2. Prosthesis according to Claim 1, wherein said articular 30 surface of the phalangeal implant is carried by a separate plug which can be introduced into and held in the phalangeal implant. C \NRPrbADCC. t, 'OC-27/07/2"I" -20

3. Prosthesis according to either one of the preceding claims, wherein the articular surface of the body of the implant has only a single radius in the sagittal plane and a single radius in the horizontal plane, the articular face of 5 the phalangeal implant being congruent and being carried by a plug which is able to turn about the axis of the phalangeal implant.

4. Prosthesis according to either one of Claims 2 and 3, 10 wherein the articular surface of the plug has on its periphery, particularly on a substantial part of the periphery of the lower half and/or of the periphery of the upper half, an indentation determining a convex edge for the clearance of the articulation in the position of flexion 15 and/or of extension.

5. Prosthesis according to any one of Claims 2 to 4, wherein the phalangeal implant has a hollow frustoconical anchoring body continued, at its proximal end, by a head in 20 the shape of a peripheral frustoconical rim, the plug having a corresponding shape, namely a frustoconical distal portion whose conicity corresponds to that of the body, and continued by a plateau having a peripheral distal surface whose conicity corresponds to that of the rim of the 25 implant, which also means the plug can be given a particularly robust form.

6. Prosthesis according to any one of the preceding claims, wherein the proximal face, inclined at 200 ± 50, of 30 the head of the metatarsal implant is continued, towards the top, by an upper face forming, with the preceding one, a dihedron, preferably with an obtuse angle of 1450 ± 200, CANRP.tbl\DCCUL\nE 5Kx OC-27m?/ja -21 intended to be applied against an upper resected plane inclined by the same angle in relation to the resected surface receiving the proximal face. 5

7. Set of metatarsal implants comprising a plurality of metatarsal implants of different sizes, designed to form part of a prosthesis in accordance with any one of Claims I to 6, the distance between the axis of the anchoring rod and the lowest point being substantially constant for all the 10 implants of the set.

8. Set of implants according to Claim 7, wherein the metatarsal implants have the characteristics of Claim 6, the particular faces of the heads of these implants being 15 dimensioned so as to meet the corresponding upper face at an upper point, at different predetermined respective distances from the axis of the anchoring rod.

9. Set of implants according to either of Claims 7 and 8, 20 wherein the diameter of the rod of the metatarsal implants is substantially constant.

10. Set of prostheses which comprises a set of metatarsal implants in accordance with any one of Claims 7 to 9, a 25 plurality of phalangeal implants of different sizes, and a plurality of plugs also of different sizes, wherein the plug whose articular surface is congruent with the articular surface of a given metatarsal implant can be received in at least two phalangeal implants of consecutive sizes in order 30 to form a prosthesis in accordance with any one of Claims I to 6. C:\NRPonbl\DC\IL\30 I59_ l.DOC-27 W ,,to -22

11. Set according to Claim 9, wherein the phalangeal implant has a frustoconical body having the same dimension for all the implants in the set, this cone being followed by the frustoconical rim, only the diameter of the periphery of 5 this rim being variable from one implant to another in the set

12. Set according to either of Claims 10 and 11, comprising three metatarsal implants, wherein the radii of curvature of 10 the articular surface are, respectively, 7 ± 0.5, 8 . 0.5 and 9 + 0. 5 mm in the sagittal plane and 14 + 1, 16 + 1 and 18 + 1 mm in the horizontal plane, and the lowest points in the sagittal plane are situated at a common distance of between about 2 and 6 mm from the axis. 15

13. Set according to Claim 12, with four sizes of phalangeal implants, each implant having an implant body with a distal end diameter of 4.7 ± 2 mm and a diameter at the periphery of the rim of 12 + 1, 13-3 + 1, 146 + 1 and 20 16 2 1 mm.

14. Set according to Claim 13, wherein it comprises three plugs of different sizes, namely plugs with a diameter of 12 + 0.5, 13 + 0.5 and 14 + 0.5 mm for a set of three plugs. 25

15. Ancillary position-marking device for fitting a prosthesis according to any one of Claims 1 to 6, having a body equipped with a cylindrical inner passage allowing it to slide and to turn about a broach implanted axially in the 30 metatarsal, and, starting from said body, two bent arms whose ends are arranged spatially so as to be able to substantially lock in the sesamoid grooves, towards their -23 distal end at the lower part of the metatarsal, in such a way as to maintain the body in a suitable axial and angular position in relation to said two sesamoid grooves, said body additionally having a means for receiving and positioning of 5 an ancillary metatarsal resecting device, extending parallel to the axis of the implant and hence to the broach, and at a distance from the metatarsal in the lateral direction towards the sagittal plane of the patient. 10

16. Ancillary position-marking device according to claim 15, wherein said receiving means is a rod of non circular cross section.

17. Ancillary device for guiding the resecting of the 15 metatarsal, used for fitting a prosthesis according to any one of Claims 1 to 6, having a body with a passage allowing it to slide on the receiving means of an ancillary position marking device according to either of Claims 15 and 16, said body having means for fixing it relative to the bone, said 20 body additionally having at least one resection slit for the passage of an oscillating saw, said slit being inclined by an angle of 700+ 200 with respect to the axis of the broach when the assembly is mounted on the metatarsal. 25

18. Ancillary device according to Claim 17, wherein it comprises a second slit which is more inclined, so that said two slits thus make it possible to form firstly the resected surface receiving the rear face of the head of the implant, and the second resected surface forming an obtuse angle, 30 preferably of 1450 ± 20c, with the aforementioned resected surface. C:W ornlDCC'\1mm1s8,i.oc2fm72010U -24

19. Ancillary device for phalangeal resection, for fitting a prosthesis according to any one of Claims 1 to 6, having a body allowing it to be fixed laterally on the cortical bone of the phalanx, at least one slit for phalangeal resection, 5 and an extension intended to bear against a corresponding end of the ancillary device for metatarsal resection according to either of Claims 17 and 18, in such a way as to exactly define the relative positions of the two resecting assemblies, the metatarsal and phalangeal resection slits 10 being substantially parallel when the two ancillary resecting devices are combined.

20. Ancillary device according to Claim 19, wherein it comprises two parallel resection slits. 15

21. A prosthesis substantially as hereinbefore described with reference to the drawings and/or Examples.

22. A set of implants substantially as hereinbefore 20 described with reference to the drawings and/or Examples.

23. A set of prostheses substantially as hereinbefore described with reference to the drawings and/or Examples . 25

24. An ancillary position-marking device substantially as hereinbef ore described with reference to the drawings and/or Examples.

25. An ancillary device substantially as hereinbefore 30 described with reference to the accompanying drawings.