Abstract:
Ankle prosthesis ( 400 ) comprising a tibial component ( 100 ), a talar component ( 200 ) and an intermediate component ( 300 ) interposed between said tibial component ( 100 ) and said talar component ( 300 ). The prosthesis has an anatomical shape and enables restoration of articular functionalities. Also described are a tool for the shaping of a talus, which shaping is aimed at the implant of the talar component ( 200 ) of said prosthesis ( 400 ), and a surgical tool for enabling a shaping of the tibia aimed at the implantation of the tibial component ( 100 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an ankle prosthesis. 
         [0002]    The present invention also relates to a tibial component for said prosthesis. 
         [0003]    The present invention also relates to a talar component for said prosthesis. 
         [0004]    The present invention moreover relates to a tool for the shaping of a talus aimed at the application of said prosthesis. 
       BACKGROUND ART 
       [0005]    As is known there exist several circumstances, of traumatic and/or pathological nature, which involve the application of a prosthesis of the ankle. 
         [0006]    This prosthesis is set between the terminal part of the tibia and the upper part of the talus, to replace the original articulation in all respects. 
         [0007]    The ankle prostheses typically comprise a tibial component, which is fixed to the terminal part of the tibia, and a talar component, which is fixed to the upper part of the talus. Between the tibial component and the talar component a third component is interposed, suitably shaped so as to enable the first two components to move reciprocally and hence provide, from the mechanical viewpoint, functionalities similar to those typically provided by a natural articulation. 
         [0008]    Applicants have noted that the prostheses available nowadays imply surgical operations of application which are considerably complicated, both in terms of access to the area at which the operation is required, and in terms of machining/shaping of the bones to which the components of the prosthesis have to be secured. 
         [0009]    For example, some prostheses require a lateral-type operation, which involves removal of some intact and functional bone portions (e.g. fibula), which otherwise would not be affected by the surgical operation. 
         [0010]    These prostheses also require forming a pair of grooves (imagining the patient in a standing position, these grooves are arranged horizontally and transversely to the direction in which the patient would walk) in the terminal part of the tibia. Also this machining operation, besides being complex from the viewpoint of its execution, causes a very in-depth machining of a portion of a substantially healthy bone. 
         [0011]    From the viewpoint of the talar component, it often requires a multiplicity of steps of cutting/shaping of the talus, which renders the surgical operation further complex and risky. 
         [0012]    In fact, the drawbacks mentioned above, besides impacting on the difficulty of the operation in general, also involve risks both for the patient (in case of a defective result of the intervention) and for the surgeon who performs the surgical intervention, from the viewpoint of his/her professional responsibility. 
         [0013]    It should also be noted that, often, surgeons are not able to deal with an operation of this nature (which, moreover, requires a long learning curve), such that they fall back to the alternative consisting of the arthrodesis, i.e., the “joining” or “fusion” of the articulation. This leads to the permanent loss of the articular functionality and the ensuing condition of permanent disability. It is clear that this type of solution penalizes in an unacceptable way the patient, to whom a treatment of a completely different nature should be offered. 
       AIMS AND SUMMARY OF THE INVENTION 
       [0014]    Therefore, the aim of the present invention is to provide an ankle prosthesis, and related components, which can be installed in a simpler manner, hence reducing the risks for the patient and for the surgeon. 
         [0015]    In particular, the aim of the invention is to provide a prosthesis which can be installed using the so-called “frontal operation” technique, so as to avoid removal and subsequent reconstruction of bony portions not strictly related to the operation. In greater detail, the invention enables to implant an ankle prosthesis while maintaining intact the posterior malleolus of the tibia, also called Volkmann&#39;s Triangle or third malleolus. 
         [0016]    Another aim of the invention is to enable installation of an ankle prosthesis by increasing—with respect to the state of the art—the stability and the optimal support of the system, while preserving the integrity of the trabecular structure of the bone. 
         [0017]    A further aim of the invention is to provide a prosthesis that requires limited and simplified machining operations of the bony terminations to which the prosthesis has to be applied. In particular, a further aim of the invention is to enable the application of an ankle prosthesis by performing a limited number of cuts and/or millings on the bony end portions at which the prosthesis is to be positioned. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    These and still other aims are substantially achieved by an ankle prosthesis as described in the appended claims. 
           [0019]    Further characteristics and advantages will become more apparent from the detailed description of a preferred and not exclusive embodiment of the invention. 
           [0020]    This description is provided herein below with reference to the accompanying figures, also having an exemplifying and non-limiting nature, in which: 
           [0021]      FIG. 1  shows a side view of a tibial component of an ankle prosthesis in accordance with the present invention; 
           [0022]      FIG. 2  shows the component of  FIG. 1  in a perspective view; 
           [0023]      FIG. 3  shows the component of  FIGS. 1 and 2  in a plan view; 
           [0024]      FIG. 4  shows a side view of an intermediate component of an ankle prosthesis in accordance with the present invention; 
           [0025]      FIG. 5  shows an exploded view of an ankle prosthesis according to the present invention, comprising the tibial component of  FIGS. 1-3  and the intermediate component of  FIG. 4 ; 
           [0026]      FIG. 6  shows a front view of a talar component of the ankle prosthesis according to the present invention; 
           [0027]      FIG. 7  shows a side view of the talar component of  FIG. 6 ; 
           [0028]      FIG. 8  shows a top view of the talar component of  FIGS. 6-7 ; 
           [0029]      FIG. 9  shows a perspective view of the talar component of  FIGS. 6-8 ; 
           [0030]      FIG. 10  shows a frame forming part of a surgical apparatus according to the present invention; 
           [0031]      FIGS. 11, 11   a - 11   c  show schematically parts or details of the surgical apparatus according to the present invention; 
           [0032]      FIG. 11 d    shows a schematic perspective view of the surgical apparatus according to the present invention; 
           [0033]      FIG. 12  shows a side view of another embodiment of a tibial component for the ankle prosthesis in accordance with the present invention; 
           [0034]      FIG. 13  shows a perspective view of the tibial component of  FIG. 12 ; 
           [0035]      FIG. 14  shows a front view of the tibial component of  FIGS. 12 and 13 ; 
           [0036]      FIG. 15  shows a perspective view of a further embodiment of a tibial component for the ankle prosthesis in accordance with the present invention; 
           [0037]      FIG. 16  shows a top view of the tibial component of  FIG. 15 ; 
           [0038]      FIG. 17  shows a front view of the tibial component of  FIGS. 15-16 ; 
           [0039]      FIG. 18  shows a side view of the tibial component of  FIGS. 15-17 ; 
           [0040]      FIG. 19  shows a side view of another embodiment of a talar component for the ankle prosthesis according to the present invention; 
           [0041]      FIG. 20  shows a perspective view of the talar component of  FIG. 19 ; 
           [0042]      FIGS. 21-22  show two embodiments of a tool for the shaping of a talus, finalized to the implant of the talar component according to the present invention. 
           [0043]      FIG. 23  shows a terminal portion of a patient&#39;s tibia before cutting. 
           [0044]      FIG. 24  shows a flat cutting of a tibial terminal portion performed with a surgical apparatus according to prior art. 
           [0045]      FIG. 25  shows a arched shape cutting of a tibial terminal portion performed with a surgical apparatus according to the present invention. 
           [0046]      FIG. 26  shows details of a second embodiment of a surgical apparatus according to the present invention; 
           [0047]      FIGS. 27 and 28  show details of a third embodiment of a surgical apparatus according to the present invention; 
           [0048]      FIG. 29  shows a frame forming part of a fourth embodiment of the surgical apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0049]    With reference to the accompanying figures, with  400  has been generally designated an ankle prosthesis according to the present invention. 
         [0050]    The ankle prosthesis  400  ( FIG. 5 ) comprises a tibial component  100  and a talar component  200 , adapted to mutually cooperate in such a way that, after installation in a patient, they can allow movements substantially identical to those obtainable by the original bony articulation. 
         [0051]    Preferably, as it will be more readily apparent in the following, the ankle prosthesis  400  also comprises an intermediate component  300 , adapted to enable mutual cooperation and movement between the tibial component  100  and the talar component  200 . 
         [0052]    The tibial component  100  is configured to be fixed to the end of the tibia of the patient, in a position substantially facing the talus. The tibial component  100  can be a single-piece element. 
         [0053]    The tibial component  100  can be made, for example, of chromium/cobalt, possibly with a coating made of titanium/plasma/spray or a similar coating. 
         [0054]    In greater detail, the tibial component  100  ( FIGS. 1-3 ) comprises a main body  110  having a substantially plate-shape. 
         [0055]    The main body  110  has a top surface  110   a  and a bottom surface  100   b.    
         [0056]    The top surface  110   a  is adapted to engage with the end of the tibia. 
         [0057]    The bottom surface  110   b  is adapted to engage with other components of the prosthesis  400 , such as for example the aforementioned intermediate component  300  ( FIGS. 4-5 ). 
         [0058]    As schematically shown in  FIG. 3 , the main body  110  has, in a top view, a substantially quadrilateral profile, delimited by a front side  111 , a pair of flanks  112 ,  113  and a rear side  114 . 
         [0059]    The front side  111  and/or the flank  112  and/or the flank  113  and/or the rear side  111  may be substantially curvilinear. 
         [0060]    Preferably the front side  111 , the flanks  112 ,  113  and the rear side  114  are substantially curvilinear so as to give the tibial component  100  an anatomical conformation. 
         [0061]    Preferably, the front side  111  has a greater length than the rear side  114 . 
         [0062]    Preferably the development of the flanks  112 ,  113  is divergent from the rear side  114  to the front side  111 . This divergent development is represented in  FIG. 3  by a pair of dashed lines. 
         [0063]    The top surface  110   a , developing from the front side  111  to the rear side  114  has a curved profile, with its concavity facing towards the bottom surface  110   b.    
         [0064]    The bottom surface  110   b  has a development similar to that of the upper surface  110   a , being substantially and approximately parallel to it. 
         [0065]    Advantageously, the main body  110  has one or more expansions  120 ,  130 ,  140  that extend from the top surface  110   a.    
         [0066]    It should be noted that none of the expansions  120 ,  130 ,  140  comes in contact with the perimeter delimiting the top surface  110   a . This perimeter is schematically represented by the combination of the front side  111  with the flanks  112 ,  113  and with the rear side  114 . 
         [0067]    In particular the expansions  120 ,  130 ,  140  are configured so as to enable an anchoring to the terminal part of the tibia, and to prevent transverse movements (i.e., along directions substantially orthogonal to the prevailing development of the tibia itself) of the tibial component  100  with respect to the tibia. 
         [0068]    The expansions  120 ,  130   140  are adapted to be inserted in the inner part of the bony cortex of the tibia, thus ensuring stability with respect to the anterior/posterior displacement. 
         [0069]    The expansions preferably comprise one or more fins, and in particular a front fin  120  and a rear fin  130 , which extend according to profiles substantially transverse to the flanks  112 ,  113 . 
         [0070]    The front fin  120  is positioned in the front part of the main body  100 , at the front side  111 . 
         [0071]    The rear fin  130  is positioned in the rear part of the main body  100 , at the rear side  114 . 
         [0072]    Preferably the above mentioned expansions comprise one or more spikes  140 , as schematically shown in  FIGS. 1-3 , having for example the shape of small pyramids. 
         [0073]      FIGS. 12-14 and 15-18  illustrate two slightly different embodiments, in which ( FIG. 12-14 ) the fins have a different shape, and in which ( FIG. 15-18 ) the fins are substantially replaced by respective sequences of spikes. 
         [0074]    In order to engage with the aforementioned intermediate component  300 , the main body  110  can be provided with a suitable connection structure  150 . Preferably said connection structure  150  enables a removable engagement between the tibial component  100  and the intermediate component  300 . In this way it is possible to use an intermediate component  300  of appropriate dimensions, preferably adapted to the talar component  200 . 
         [0075]    In one embodiment the connection structure  150  comprises a pair of constraining elements  151 ,  152 , each positioned at a respective flank  112 ,  113 . 
         [0076]    In particular, each constraining element  151 ,  152  may comprise a respective plate  151   a ,  152   a  with a respective slot  151   b ,  152   b  suitable for housing a corresponding expansion  310 ,  320  of the intermediate component  300 . 
         [0077]    It should be noted, for example, that the intermediate component  300  may be made of polyethylene. 
         [0078]    Advantageously the top surface  330  of the intermediate component  300  is shaped substantially complementary to the bottom surface  110   b  of the main body  100  of the tibial component  100 . 
         [0079]    The talar component  200  ( FIGS. 6-9 and 19-20 ) is configured to be fixed to the talus of the patient, in a position substantially facing the aforementioned end of the tibia. The talar component  200  can be a single-piece element. 
         [0080]    The talar component  200  comprises a main body  210  having a top surface  210   a  and a bottom surface  210   b.    
         [0081]    The bottom surface  210   b  is substantially flat and substantially quadrilateral. 
         [0082]    The bottom surface  210   b  is delimited by a front side  211 , a first and a second flanks  212 ,  213  and a rear side  214 . 
         [0083]    At each side  211 ,  214  and at each flank  212 ,  213  there extends, from the bottom surface  210   b , a respective expansion  221 ,  222 ,  223 ,  224  adapted to engage directly with a talus of a patient. 
         [0084]    In one embodiment, the expansions  221 ,  222 ,  223 ,  224  are connected to one another in a substantial continuous fashion, as shown in  FIG. 9 . 
         [0085]    In a different embodiment, the expansions  221 ,  222 ,  223 ,  224  are separated from each other, as shown in  FIGS. 19-20 . 
         [0086]    In addition to the cited expansions, the main body  210  can further comprise one or more spikes  230  which extend from the bottom surface  210   b  in a region more central with respect to the expansions  221 ,  222 ,  223 ,  224 . 
         [0087]    Said one or more spikes may have, for example, the shape of small pyramids. 
         [0088]    As schematically shown in  FIG. 7 , the top surface  210   a  has a curved shape developing from the front side  211  to the rear side  214 , with its concavity facing towards the bottom surface  210   b.    
         [0089]    The top surface  210   a  is also curved, developing from the first flank  212  to second flank  213 , with its convexity facing towards the bottom surface  210   b.    
         [0090]    In summary, the talar component  200  can present a substantially “saddle” shape, as regards its top surface  210   a , so as to be perfectly anatomical and replace in an optimal manner the original upper portion of the talus. 
         [0091]    As schematically shown in  FIG. 8 , the first flank  212  has a curvature larger than the second flank  213 . 
         [0092]    Preferably the front side  211  has a length greater than the rear side  214 . 
         [0093]    Advantageously, the upper surface  210   a  of the main body  210  of the talar component  200  is shaped substantially complementary to the bottom surface  340  of the intermediate component  300 . 
         [0094]    The talar component  200  can be made, for example, of chromium/cobalt, possibly with a coating in titanium/plasma/spray or similar coating. 
         [0095]    In order to appropriately shape the top part of the talus, so as to enable a proper application of the above described talar component  200 , a suitable tool  500  can be advantageously used. 
         [0096]    Such a tool  500  for shaping a talus comprises an active portion  510 , preferably mounted at one end  531  of a handle  530 , the latter having a substantially elongated shape to enable easy use of the tool  500  itself. 
         [0097]    The active portion  510  is substantially plate-shaped and has a top surface  510   a  and a bottom surface  510   b , which are substantially parallel to each other and substantially parallel to the planar development of the active portion  510 . 
         [0098]    Preferably, the bottom surface  510   b  is corrugated to promote an engagement of the active portion  510  to the talus that is to be shaped. 
         [0099]    The active portion  510  has a front recess  511 , a rear recess  514 , as well as first and second side recesses  512 ,  513 . These recesses  511 ,  512 ,  513 ,  514  preferably have an elongated shape; should the active portion  510  have a substantially quadrilateral shape, then each recess  511 ,  512 ,  513 ,  514  would be advantageously substantially parallel to a respective side of said substantially quadrilateral shape. 
         [0100]    Conveniently the recesses  511 ,  512 ,  513 ,  514  define a substantially quadrilateral profile. 
         [0101]    In one embodiment, schematically shown in  FIG. 21 , the first side recess  512  comprises a front portion  512   a  and a rear portion  512   a  separated from each other; similarly, the second side recess  513  comprises a front portion  513   a  and a rear portion  513   b  separated from each other. 
         [0102]    The front portion  512   a  of the first side recess  512  and the front portion  513   a  of the second side recess  513  are connected in a continuous fashion to the front recess  511 , so as to form a first slot which is substantially “U”-shaped. 
         [0103]    The rear portion  512   a  of the first side recess  512  and the rear portion  513   b  of the second side recess  513  are connected in a continuous fashion to the rear recess  514 , so as to form a second slot which is substantially “U”-shaped and opposite to said first slot. 
         [0104]    This embodiment can be advantageously used for shaping a talus before applying the talar component shown in  FIG. 9 . 
         [0105]    In a different embodiment ( FIG. 22 ), the front recess  511 , the first and the second side recess and the rear recess  514  are separated from each other. In particular the recesses  511 ,  512 ,  513 ,  514  can be separated from each other by respective angular portions of the active portion  510 . 
         [0106]    This embodiment can be advantageously used for shaping a talus before applying the talar component shown in  FIGS. 19-20 . 
         [0107]    Preferably, the active portion  510  may have a cavity  520  which is located inside the region delimited by the substantially quadrilateral profile formed by the four recesses  511 ,  512 ,  513 ,  514 . 
         [0108]    This cavity  520  can have, for example, a hemispherical shape. 
         [0109]    The cavity  520  is advantageously adapted to engage with a distractor. 
         [0110]    In order to apply the ankle prosthesis  400  to a patient, a suitable apparatus  600  can be used. The surgical apparatus  600  is preferably configured for ensuring a cutting of a tibia of a patient by a frontal approach. 
         [0111]    The surgical apparatus  600  comprises firstly a frame  610  having a first portion  610   a  and a second portion  610   b  ( FIG. 10 .  11   a ,  11   d ). 
         [0112]    The first portion  610   a  is adapted for the support of a leg of a patient, in particular in such a way that the leg remains stretched in a substantially horizontal direction. 
         [0113]    The second portion  610   b  is adapted for the support of the patient&#39;s foot, in particular in a transverse direction with respect to the floor. 
         [0114]    In practice, the first and the second portions  610   a ,  610   b  may be implemented as respective plate-shaped supports, for example having a substantially rectangular shape, suitably inclined one relative to one another. Advantageously, the inclination between the two plate-shaped supports can be adjustable, so as to enable an adaptation to different positions required by the specific operational circumstances. 
         [0115]    The second portion  610   b  may be pivotably mounted on the first portion  610   a  about a rotation axis A extending transversally to the prevailing direction of development D 1  of the leg of the patient. 
         [0116]    Preferably the first and/or the second portion  610   a ,  610   b  have retaining means  611  for keeping the leg and/or the foot in the proper position. 
         [0117]    As shown by way of example in  FIG. 10 , the retaining means  611  can be obtained by suitable bands, which prevent the leg and the foot of the patient to move from the respective first and second portions  610   a ,  610   b  of the frame  610 . 
         [0118]    Preferably the retaining means  611  associated with the first portion  610   a  are configured to operate with corresponding adjustment means, which enable an axial/longitudinal movement of the retaining means, so as to make it possible to adapt the position of the retaining means to the size of the patient&#39;s leg, and in particular to the length of the latter. 
         [0119]    For example, the adjustment means may enable for a mutual displacement, along the first portion  610   a  of the frame  610 , of a pair of retaining bands being part of the aforementioned retaining means. 
         [0120]    With reference to the frame  610 , a main operative plane is defined, which is the plane on which there lie the prevailing direction of development D 1  of the leg of the patient and the prevailing direction of development D 2  of the patient&#39;s foot. 
         [0121]    In other words, the main operative plane can be identified as a plane substantially orthogonal to the planar development of the first portion  610   a  and the planar development of the second portion  610   b  of the frame  610 . 
         [0122]    The apparatus  600  comprises a blade  620  ( FIGS. 11 b , 11 c , 11 d   ) mounted on the frame  610  and configured to cut an end of the tibia of the patient. 
         [0123]    The blade  620  has, in a projection on the main operative plane, a determined curvature C 1 . This determined curvature C 1  has its concavity facing towards the second portion  610   b  of the frame  610 . 
         [0124]    In practice, the curvature C 1  of the blade  620  corresponds to the shape that must be given to the terminal portion of the tibia of the patient through the cutting operation performed using the blade  620   
         [0125]    The apparatus  600  also comprises a first guide  630  and a second guide  640 , associated to the blade  620  to enable the same to operate the desired cut. 
         [0126]    The first guide  630  is mounted on said frame  610  and is adapted to impose to the blade  620  a movement according to a first trajectory T 1 . This first trajectory T 1 , defined on a plane parallel to said main operative plane, comprises at least one line having a curvature C 2  substantially equal to the determined curvature C 1 , i.e., the curvature presented by the blade  620 . 
         [0127]    In more detail, the first guide  630  comprises a pair of guide elements  631 ,  632 , each having a respective groove  631   a ,  632   a  defining at least said first trajectory T 1 . In other words, each groove  631   a ,  632   a  comprises a portion shaped in a manner substantially identical to the curvature C 1  of the blade  620 . 
         [0128]    Preferably the guide elements  631 ,  632  are longitudinally movably mounted on the first portion  610   a  of the frame  610 , and the frame  610  includes at least one immobilization means  637  configured for immobilizing the guide elements  631 ,  632  on the frame  610 . The first portion  610   a  of the frame  610  may for example include two longitudinal elements  638  each configured for supporting a respective guide element. 
         [0129]    Preferably each groove  631   a ,  632   a  also has additional portions, which extend from one end or from both ends of the portion defining the trajectory T 1 . 
         [0130]    In the preferred embodiment, each groove  631   a ,  632   a  has a first substantially straight portion, followed by the portion that defines the first trajectory T 1 , in turn followed by a further substantially straight portion. 
         [0131]    Preferably one of the guide elements or both the guide elements  631 ,  632  is/are equipped with one or more movable end-of-stroke elements  633 ,  634 ,  635 ,  636 . In this way it is possible to precisely adjust the beginning and the end of the first trajectory T 1 , depending on the specific needs of each intervention. 
         [0132]    Advantageously a pair of movable end-of-stroke elements  633 ,  634 ;  635 ,  636  is provided for each guide element  631 ,  632 . 
         [0133]    In the preferred embodiment, the guide elements  631 ,  632  have an elongated shape extending from the first portion  610   a  of the frame  610 . 
         [0134]    The second guide  640  is mounted on the frame  610 ; preferably the second guide  640  can be mounted on the retaining means prearranged at the first portion  610   a  of the frame  610 . The second guide  640  is configured to be disposed above a frontal part of the tibia of the patient when the leg of the patient is supported on the first portion  610   a  of the frame. 
         [0135]    The second guide  640  imposes to the blade  620  a second trajectory T 2  on a plane substantially orthogonal to the main operative plane and parallel to the prevailing direction of development of the leg D 1  (i.e., in practice, a substantially horizontal plane or parallel to the floor). 
         [0136]    The second trajectory T 2  is arc-shaped and has a concavity facing towards the second portion  610   b  of the frame  610 , i.e., towards the patient&#39;s foot. 
         [0137]    Preferably the second guide  640  comprises a guide body  641 , for example of a substantially parallelepiped shape, having a slot  642  defining the second trajectory T 2 . 
         [0138]    The blade  620  is adapted to be inserted in the slot  642  to follow the second path T 2 . 
         [0139]    Preferably, the apparatus  600  further comprises a support element  650  to support the blade  620 . In particular, the support element  650  may be equipped with a gripping portion, to facilitate the use by the surgeon. 
         [0140]    The support element  650  is advantageously engaged with a third guide  660 . 
         [0141]    The third guide  660  has opposite ends  661 ,  662 , each engaged with a respective guide element  631 ,  632  and movable along the respective groove  631   a ,  632   a.    
         [0142]    The support element  650  is constrained to the third guide  660  and movable along the same. 
         [0143]    Preferably, the third guide  660  has an arched shape with concavity facing towards the first portion  610   a  of the frame  610 . 
         [0144]    Preferably, the apparatus  600  further comprises a feeler device  670  ( FIG. 11 ) mounted on the frame  610  and movable along the first portion  610   a  of the frame  610 . 
         [0145]    The feeler device  670  enables to identify of the area of the top of the tibia, so as to locate the starting point for carrying out the cutting of the tibia using the blade  620 . 
         [0146]    The feeler device  670  has a substantially arc-shaped shape, extending on a plane substantially orthogonal to the cited main operative plane. Advantageously, the feeler device  670  has a first end constrained to the frame  610  and a second end configured to follow the bony profile of the tibia and identify the highest point thereof (i.e., the point farthest from the first portion  610   a  of the frame  610 ). The first end, in particular, is constrained to the first portion  610   a  of the frame  610 . In this way, the feeler device  670  is sufficiently stable and can thus allow identifying in a precise and reliable way the point from where the cut is to start. 
         [0147]    Preferably, the apparatus  600  further comprises a distractor device  680  ( FIG. 11 a   ) suitable to exert a force of mutual spacing between the foot and the tibia of the patient. 
         [0148]    Preferably the distractor device  680  is applied to the talus and is gradually displaced in the direction of the foot, resulting in a gradual and measured distraction of the articulation. 
         [0149]    In this way accessibility and visibility of the area where the operation is to be carried out are ensured. 
         [0150]      FIG. 26  shows a second embodiment of the surgical apparatus  600  which differs from the first embodiment shown on  FIGS. 10 to 11   d  mainly in that the surgical apparatus  600  is devoid of the guides  630  and  660 , in that the guide  640  is directly fixed to the tibia, and in that the guide body  641  further includes a curved guiding surface  643  adjacent the slot  642  and defining at least in part the second trajectory T 2 . According to said second embodiment, the blade, and more particularly the support element  650 , can be freely manipulated by the surgeon. 
         [0151]      FIGS. 27 and 28  show a third embodiment of the surgical apparatus  600  which differs from the second embodiment shown on  FIG. 26  mainly in that the guide  640  is mounted on the frame  610  and in that the slot  642  is rectilinear. According to said the third embodiment of the surgical apparatus  600 , the guide body  641  further includes a support member  644  longitudinally movably mounted on the first portion  610   a  of the frame  610 , and configured for supporting the guide body  641 . The support member  644  may for example have an inverted U-shape, and includes two side arms  644   a  respectively mounted on the first portion  610   a  of the frame  610 , and a central arm  644   b  connected to the side arms  644   a  and configured for supporting the guide body  641 . Advantageously, the frame  610  includes at least one immobilization element configured for immobilizing the support member  644  on the frame  610 . 
         [0152]    According to the third embodiment, the guide  640  includes a movable member  645  movably mounted on the central arm  644   b  of the support member  644  along a first direction extending substantially orthogonally to the prevailing direction of development D 1  of the leg of the patient. The guide body  641  is movably mounted on the movable member  645  along a second direction extending substantially parallely to the prevailing direction of development D 1  of the leg of the patient. 
         [0153]    According to the third embodiment, the guide  640  includes an immobilization element  646  configured for immobilizing the movable member on the support member  644 , and an immobilization element  647  configured for immobilizing the guide body  641  on the movable member  645 . 
         [0154]    Such a configuration of the support member  644 , the movable member  645  and the guide body  641  allows the surgeon to adjust easily the position of the guide body  641  relative to the tibia before cutting the latter. 
         [0155]      FIG. 29  shows a fourth embodiment of the surgical apparatus  600  which differs from the previous embodiment mainly in that the second portion  610   b  is articulated relative to the first portion  610   a  about three non-parallel rotation axes. Such a configuration of the frame  610  allows the surgeon to adjust easily the position of the foot, and notably the flexion, extension, varus and valgus of the foot. 
         [0156]    From the operational point of view it should be noted the following. 
         [0157]    The patient is made to settle such that his/her leg rests on the first portion  610   a  of the frame  610  and his/her foot rests on the second portion  610   b  of the frame  610 . 
         [0158]    If necessary, the retaining means are adjusted, to ensure stability to the position of the limb. 
         [0159]    The distractor device  680  is then operated, so as to improve, as said, accessibility and visibility of the area in which the surgeon will have to operate. 
         [0160]    By means of the feeler device  670  the starting point to make the cut is located. 
         [0161]    At this point, the blade  620  is used to carry out the cut according to the desired profile. 
         [0162]    As shown in  FIG. 25 , cutting is performed in such a way to give the terminal portion of the tibia an arched shape, so as to preserve the third malleolus. The profile followed in the cutting operation is indicated in the figure by a dashed line. Otherwise, in the case of the same initial situation shown in  FIG. 23 , the cuts usually applied according to the state of the art are substantially flat ( FIG. 24 ), and therefore imply complete elimination of the third malleolus. 
         [0163]    The blade  620  is then inserted in the slot  642  of the guide body  641 , in order to enable the second trajectory T 2  to be described. This operation can be carried out by displacing the support element  650  along the third guide  660 . 
         [0164]    The blade is also moved in a way to describe the first trajectory T 1 . This operation can be carried out by moving jointly the support element  650  and the third guide  660  so that the ends  661 ,  662  of the latter slide in the grooves  631   a ,  632   a  of the guiding elements  631 ,  632 . 
         [0165]    In this way it is possible to obtain a cut as the one schematically shown in  FIG. 25 . 
         [0166]    The tibial component  100  can then be applied, in such a way that the expansions  120 ,  130 ,  140  get into the inner part of the bony cortex of the tibia. 
         [0167]    The intermediate component  300  can be simultaneously engaged with the tibial component  100 . 
         [0168]    As regards the preparation of the talus, the tool  500  is positioned on the part of the talus facing the tibia. 
         [0169]    By means of a suitable tool, in itself known, and by following the front recess  511 , the side recesses  512 ,  513  and the rear recess, it is possible to obtain a shape of the talus that is substantially complementary the talar component  200  which have to be applied. 
         [0170]    Depending on the type of component  200  that is to be applied a tool  500  of appropriate shape is used. 
         [0171]    In particular, to apply the talar component of  FIG. 9  the tool of  FIG. 21  will be used, while for applying the talar component of  FIG. 20  the tool of  FIG. 22  will be used. 
         [0172]    In the case in which the tool of  FIG. 21  is used, a further small machining may be necessary, aimed at eliminating bony residues that remained at the parts of the active portion  510  which separate the front portion  512   a  of the first side recess  512  from the rear portion  512   b  of the same first side recess  512 , and the front portion  513   a  of the second side recess  513  from the rear portion  513   b  of the same second side recess  513 . 
         [0173]    The invention achieves important advantages. 
         [0174]    First of all, by operating in accordance with a technique based on a frontal approach (rather than a later approach) removal and subsequent reconstruction of bone portions which are not directly affected by the intervention (e.g. fibula) can be avoided. 
         [0175]    Furthermore, by means of the type of curved cut herein described and claimed, it is possible to preserve the third malleolus, which would be instead removed by using a traditional flat cut. 
         [0176]    A further advantage emerges by observing that the prosthesis according to the invention has perfectly anatomical shape, and therefore allows to completely restoring the articular mobility/functionality after its installation.