Abstract:
A total hip prothesis comprises a cotyloid implant consisting of a metal cup to be anchored in the acetabulum, a polyethylene insert which provides an intermediate implant inserted into the cavity of the cup, and a femoral implant consisting of a cap having an outer convex surface which is slidably positionable within the insert cavity. An inner concave surface of the femoral implant is implantable on the head of the femur. The prothesis is particularly suitable for endo-articular implantation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a total hip prostheses adapted to be implanted endo-articularly and its auxiliary device. Upon deterioration of the articulation of the hip, for example in the case of arthrosis or rheumatoid arthritis, it may be necessary to replace the coxo-femoral articulation by a prosthesis. 
     2. Description of the Related Art 
     Certain prostheses now known comprise: 
     a cotyloid implant constituted by a metallic cup provided with primary anchoring means in the acetabulum and having externally an overall hemispheric surface and internally a concave recess, 
     an insert forming an intermediate implant generally of plastic, such as polyethylene, provided with means for connection with the cup and having externally a surface complementary to that of the recess of the cup in which it is received and internally a substantially hemispherical recess, and 
     a metallic femoral implant constituted by a femoral rod implanted in the medullar channel of the femur and a prosthetic neck surmounted by a spherical femoral head which will be articulated in the recess of the insert. 
     Implanting such a prosthesis requires an expensive total arthroplasty technique of the hip, which is subject to a number of requirements. 
     Thus, it is necessary to provide an ablation of the femoral head and a portion of the femoral neck to implant the femoral rod in the midportion of the femur, even if the degeneration of the articulation hasn&#39;t reached the neck or head of the femur. 
     In addition to ablation of the head of the femur, it is necessary to do the same for all of the articular capsule. 
     On the other hand, in this open surgery, it is necessary to provide access of about ten centimeters and to dislocate the articulation to be able to introduce the various instruments for cutting and the various implants. 
     SUMMARY OF THE INVENTION 
     The present invention therefore has for its object to provide a new total hip prosthesis permitting limiting the resection to only the injured articular surfaces so as to preserve the integrity of the head of the femur and of the capsule, and to carry out minimal arthrotomy. 
     To this end, the invention has for its object a total hip prosthesis comprising: a cotyloid implant constituted a metallic cup provided with primary anchoring means in the acetabulum and having externally an overall convex surface and internally a generally concave recess, 
     an insert forming an intermediate implant for example of a plastic such as polyethylene, provided with connection means with the cup and having externally a shape complementary to the recess of the cup in which it is received and internally a concave bearing recess, and 
     a metallic femoral implant adapted to be received slidably in the bearing recess of the insert and implanted ill the femoral bone, 
     characterized in that the femoral implant is constituted by a cap having externally a convex surface adapted to come into sliding bearing engagement in the recess of the insert and internally a concave surface adapted to implant itself in the spongy bone of the femoral head. 
     According to another characteristic of the invention, the femoral implant comprises a small screw-threaded rod which projects perpendicularly to the center of its concave surface and a separate element forming a screw-threaded nut internally for screwing on said screw-threaded rod and externally screw-threaded to screw into the femoral head along the axis of the femoral neck. 
     Preferably, the pitch of the external screw-threading of the nut is greater than that of its internal screw-threading. 
     According to another characteristic of the invention, the cotyloid implant is pierced at its center for the passage of a screw-threaded lug for primary anchoring in the acetabulum. 
     On the convex surface of the cotyloid implant and the concave surface of the femoral implant can be provided asperities or small points to improve the anchoring respectively in the acetabulum and the femoral head. 
     According to still another characteristic, the mentioned connection means are snap-in means of the mortise and tenon type at the periphery of the base of the cup and of the insert. 
     According to another characteristic, each implant comprises at its periphery a local coupling means such as substantially radial female thread, to permit its coupling to a carrying arm. 
     The present invention also relates to an auxiliary device for endo-articular implantation of the prosthesis mentioned above, characterized in that it comprises: 
     a plurality of instruments adapted to be introduced along the axis of the femoral neck from the region of the trochanter base toward the coxo-femoral articular space such that their free distal end serves to center and guide the prosthesis during its implantation, 
     a carrying arm that can support removably at its distal end the mentioned implants or a drill for introducing them by a lateral access route in the mentioned articular space, and 
     a support structure adapted to be positioned parallel to the axis of the femur and at the lower end of which is selectively ensleeved or introduced freely in rotation and/or slidably one of the mentioned instruments and at the upper end of which is ensleeved the carrying arm slidably and inclinably to engage the implant or the drill on the distal end of an instrument opening into the articular space. 
     The distal end of the instruments defines a point of intersection with the drills or the implants and gives the central working point in the coxo-femoral articulation. 
     In a particular embodiment, the distal end of the carrying arm is screw-threaded to screw into a female thread provided at the periphery of the implant or of the drill to be supported. 
     According to another characteristic, the device can comprise a hemispheric femoral drill whose internal surface is adapted to grind down the head of the femur, said drill being pierced at its center to receive secured in rotation therewith the distal end of an instrument which is adapted to be connected at its proximal end to a rotatable drive motor. 
     In this case, the device can comprise moreover a bearing arm ensleeved parallel to the carrying arm at the upper end of the support structure and constituted by a rod whose distal portion is in the form of an arc of a circle matching the shape of a meridian from the external surface of the femoral drill and of which the distal end is adapted to bear in a pivotal manner on the center of said drill. 
     The support structure can thus also comprise a means forming a vise whose movable jaw is constituted by the bearing arm and the fixed jaw is secured to said structure, the two jaws being adapted to be selectively brought together so as to press the femoral drill against the head of the femur. 
     According to another characteristic of the invention, the device can comprise a hemispheric cotyloid drill whose external surface is adapted to grind down the cotyloid cavity, said cotyloid drill being pierced at its center to receive and be secured to in rotation the distal end of an instrument which is adapted to be connected at its proximal end to a rotatable drive motor. 
     In this case, the device can moreover comprise an instrument forming a bit adapted to traverse the central hole of the cotyloid drill to hollow in the acetabulum bone a central cotyloid hole for reception of a screw-thread lug of the cotyloid implant. 
     According to still another characteristic, the distal end of the instrument has a shape complemental to the head of the screw-threaded lug mentioned above, for screwing into the centro-cotyloid hole. 
     In a particular embodiment, the device comprises a cotyloid impactal element temporarily secured in the recess of the insert by frangible peripheral points. The impact element can be provided with a recess of a shape complementary to the distal end of the instrument or a small screw-threaded rod which projects perpendicularly to the center of its lower surface. 
     The device thus comprises preferably an instrument whose distal end is internally screw-threaded in a manner complementary to the screw-threaded rod of the femoral implant and/or the impactor element. 
     According to still another characteristic, the device of the invention comprises an instrument whose distal end supports removably and is secured in rotation to the nut of the femoral implant to screw this latter into the head of the femur and on the screw-threaded rod of the femoral implant. 
     It can be provided that in the engaged position of the drill or the implant on an instrument, this latter and the carrying arm define between them an angle of about 60°. 
     To this end, the support structure can have an elbowed shape whose upper and lower branches define an angle of about 120°. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood, and other objects, details, characteristics and advantages of it will become more clearly apparent in the course of the description which follows, of a particular embodiment of the invention which is at present preferred, given solely by way of illustration and not limitatively, with reference to the accompanying schematic drawings, in which: 
     FIGS. 1 to  3  are fragmentary schematic views showing the successive steps of the resection of a cartilaginous surface of the head of the femur with the auxiliary device of the invention. 
     FIGS. 4 and 5 are detailed views respectively of the proximal end and of the distal end of the bearing arm shown in FIG.  3 . 
     FIGS. 6 to  8  are views analogous to FIG. 1, which show the successive steps of the resection of the acetabulum. 
     FIGS. 9 and 10 are views similar to FIG. 1 but showing the emplacement of the cotyloid implant. 
     FIGS. 11 and 12 are views similar to FIG. 9, but showing the emplacement of the insert of polyethylene. 
     FIG. 13 is an enlarged view in axial cross-section of the cotyloid implant provided with its insert and of the impactor element. 
     FIGS. 14 to  16  are similar to FIG. 9, but show the successive steps of the emplacement of the femoral implant. 
     FIG. 17 is an enlarged view in axial cross-section, of the cap of the femoral implant of FIG.  16 . 
     FIG. 18 shows the total hip prosthesis of the invention, implanted in the hip. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     There will now be described a particular manner of emplacing the total hip prosthesis of the invention, with reference to the accompanying drawings. 
     The patient to be operated on is first emplaced in dorsal decubitus on an orthopedic table with traction and abduction of 60° of the lower limb to be operated on. 
     It will be noted that it will not be necessary to dislocate the coxo-femoral articulation in the course of the procedure. 
     The surgeon introduces from the trochanter base region and along the axis of the femoral neck, a guide (not shown) which opens at the level of the coxo-femoral articulation. He then hollows out along the axis of the femoral neck with the aid of tap (not shown) guided by the pin, a cylindrical longitudinal space  22  suitable for the introduction of various auxiliary instruments of which the distal end can open at the level of the coxo-femoral articulation. 
     There is shown in FIG. 1, on the one hand the upper portion of the midportion of the femur F, the large trochanter G and the small trochanter P, the femoral neck CF and the femoral head T, and, on the other hand, the cotyloid cavity C of the hip H. 
     The auxiliary device of the invention comprises an elbowed support structure  1  whose upper and lower legs  2  and  3  define between them an angle θ of the order of 120°. The lower leg  3  comprises at its free end a cylindrical sleeve  3   a,  whilst the upper leg  2  comprises at its free end an oblong sleeve  2   a  with an axial trapezoidal cross-section. 
     The auxiliary device comprises a carrying arm  4  constituted by a rod whose proximal end is prolonged by handle  4   a  and the distal end  4   b  is screw-threaded. 
     The hemispherical femoral drill  5  comprises at its periphery a radial female thread  5   a  into which is screwed the screw-threaded end  4   b  of the carrying arm  4 . The femoral drill  5  comprises on its concave surface metallic asperities  5   b  having a grinding effect, whilst its convex surface is smooth. The femoral drill  5  is pierced at its center with a hexagonal hole  5   c  into which is engaged for rotation therewith the distal end of corresponding shape  6   a  of a first instrument  6 . 
     The instrument  6  is also constituted by a rod whose distal end has a hexagonal end  6   a  and whose proximal end is prolonged by a handle  6   b  which is retained by the sleeve  3   a  of the support structure  1 . 
     The rod of the instrument  6  of course passes through the femoral neck CF along its axis, which also constitutes the axis of rotation of the rod. 
     With the carrying arm  4  is associated another arm  7 , a so-called bearing arm, constituted by a rod whose proximal end is also prolonged by handle  7   a  of a shape complementary to the handle  4   a  and whose distal portion is in the form of an arc of a circle  7   b  matching the shape of a meridian from the convex surface of the femoral drive  5 , the distal end  7   c  of this rod being provided with a rotor (see FIG. 5) to bear pivotally on the center  5   c  of said drill. 
     The instrument  6  is first introduced along the axis of the femoral neck CF until its distal end  6   a  enters the coxo-femoral articular space, so that instrument  6  being supported with its handle  6   b  by the lower leg  3  of the support structure which is positioned parallel to the axis of the femur. 
     With the assembly of the bearing and carrying arms  4  and  7  maintained parallel to each other, the femoral drill  5  is introduced through a small arthrotomy, for example of the order of 4 cm in the mentioned articular space, as is shown in FIG.  1 . 
     The two arms  4  and  7  which are guided by the sleeve  2   a  of the upper arm  2  can slide in the latter to bring the drill  5  facing the instrument  6  and to within said trapezoidal sleeve  2   a  to engage the central hole  5   c  of the drill  5  on the distal end  6   a  of the instrument  6 , as shown in FIG.  2 . 
     It will be seen, by comparing FIG. 1 to FIG. 2, that the arms  4  and  7  pass from one side to the other of the trapezoid of the sleeve  2   a,  which causes the inclination of these arms to vary. In the position shown in FIG. 2, the instrument  6  forms an angle of about 60° with the arms  4  and  7 , given that in this position the instrument  6  and the arms  4  and  7  are respectively perpendicular to the lower and upper legs  3  and  2 . 
     Once the drill  5  is seated on the instrument  6 , the carrying arm  4  is retracted which would otherwise prevent rotation of the drill  5  (see FIG.  3 ). 
     On the other hand, the bearing arm  7  is maintained in position at its distal end  7   c  against the drill  5  and at its proximal portion by a temporary semi-rigid or resilient block  8  (shown in FIG. 4) which fills the empty space within the sleeve  2   a.    
     To apply the drill  5  against the cartilaginous surface of the femoral head T, there is used a member functioning as a vise to press the arm  7  against the drill  5 . 
     This member forming a vise is constituted by an arm  9  perpendicularly fixed to the upper leg  2  to serve as a fixed jaw and a knurled set screw  10  to bring the bearing arm  7  in, which serves as the movable jaw relative to the fixed jaw. 
     When the drill  5  is in bearing relationship against the femoral head T, the instrument  6  can then be driven in rotation by a motor (not shown) connected to its handle  6   b,  which gives rise to conjoint rotation of the drill  5 . 
     Once the drilling of the femoral head T is completed, the surgeon no longer needs to use the bearing arm  7  and the member forming a vise. 
     Extraction of the femoral drill  5  from the articular cavity is carried out by means of a gripping pliers. 
     For the resection of the cotyloid cavity C, there is used a cotyloid hemispherical drill  11  whose convex surface is provided with metallic projections  11   b  having a scraping action whose concave surface is smooth. This cotyloid drill  11  comprises also a radial peripheral internal screw-threading  11   a  in which can be screwed the distal end  4   b  of the carrier arm  4 . This latter permits engaging the cotyloid drill  11  on the distal end  4   a  of another instrument in the form of a bit  12  (see FIG.  6 ). 
     The bit  12  has a conical point at its distal end  12   a  which is prolonged by a handle  12   b  at its proximal end to be able to be ensleeved in the sleeve  3   a.  It will be seen that the handle  12   b  is connected to a rotary drive rotor  13 , shown partially and schematically in FIG.  6 . 
     The bit  12  permits hollowing a centro-cotyloid hole  14  in the bottom of the acetabulum C for reasons indicated hereinafter. 
     When the centro-cotyloid hole  14  has been hollowed out, the bit  12  is withdrawn from the support structure  1  and replaced by the mentioned instrument  6  (see FIG.  7 ). The instrument  6  will then enter the central hole of the cotyloid drill  11  and the carrying arm  4  is unscrewed to permit the rotation of said drill driven by the motor  13  (see FIG.  8 ). 
     The drilling operations are now concluded and the drill  11  is withdrawn in the same manner by a pliers (not shown) introduced through small route provided during arthrotomy. 
     The surgeon will now introduce a cotyloid implant  15  into the articular space with the aid of the carrying arm  4  whose screw-threaded distal end is screwed into a female thread provided at the periphery of said implant. 
     It will be seen in FIG. 9 that a screw or screw-threaded lug  16  has first been screwed through the central hole  15   b  of the cotyloid implant  15 , so as to be introduced simultaneously with the implant into the articular space. 
     Preferably, the head of the screw-threaded lug  16  has a peripheral rounded shape whose hollow center  16   a  is hexagonal, which permits positioning it over the hexagonal distal end of the same instrument  6  (see FIG.  13 ). 
     There can be provided on the handle  6   b  of the instrument  6  a graduated scale indicating to the operator how far he must introduce the rod  6  along the axis of the femoral neck CF for drilling of the femoral head T and then of the acetabulum C. For example, the graduation corresponding to drilling the acetabulum C will be spaced ten mm from that corresponding to drilling the femoral head T. Preferably, the central hole of the femoral drill  5  and cotyloid drill  11  and the hollow hexagonal heads  16   a  of the screw  16  are similarly dimensioned so as to be able to use the same instrument  6 . 
     Once the instrument  6  is engaged in the head of the screw-threaded lug  16 , this latter is screwed into the centro-cotyloid hole  14  hollowed out in the bottom of the acetabulum C. During this screwing operation, the carrying arm still supports the cotyloid implant  15 , by means of its distal end  4   b  which is screwed into the peripheral female thread  15   b  of the cup. 
     At the end of screwing, the carrying arm  4  is withdrawn and the screwing of the screw-threaded lug  16  is carried out with the instrument  6  to obtain good impaction of the cotyloid implant  15  in the acetabulum C. It will then be seen in FIG. 10 that the asperities or metallic points  15   a  provided on the convex surface of the implant  15  penetrate into the cotyloid bone previously drilled. 
     To emplace the polyethylene insert  17 , there is again used the carrying arm  4  which is screwed at the periphery of this insert in a manner analogous to the drills  5  and  11  and to the implant  15 , but here another instrument  18  is used in place of the instrument  6  (see FIG.  12 ). 
     Thus, as is clearly shown in FIGS. 11 to  13 , the insert or hub  17  does not engage directly on the distal end of the instrument  18 , but via an impactor  19  temporarily fixed in the concave recess of the insert  17 . 
     Although not shown, the impactor element  19  is provided by frangible peripheral points on the insert  17 . The impactor element  19  is provided on its lower surface with a small central screw-threaded rod  19   a  which is adapted to be screwed onto the female-threaded distal end  18   a  of the instrument  18 . This latter comprises in a manner similar to the instrument  6 , a handle  18   b  on its proximal portion. 
     As is more clearly seen in FIG. 13, the insert  17  is provided at the periphery of its external convex surface with several projections or lugs  17   a  which are adapted to enter the corresponding recesses or mortises  15   c  provided in the periphery of the concave internal recess of the cotyloid implant  15 . The assembly of the lugs  17   a  and the recesses  15   c  forms a connection means of the mortise-tenon type to assemble stably and rigidly the insert  17  in the cotyloid implant  15 . 
     As is seen in FIG. 11, the distal end  18   a  of the instrument  18  is first screwed onto the screw-threaded rod  19   a  of the impactor element  19 . The carrying arm  4  is withdrawn once the instrument  18  is fully screwed onto the rod (see FIG.  12 ). There is then exerted an axial pressure by striking the proximal end of the sleeve  18   b  to impact the insert  17  into the corresponding recess of the cotyloid prosthesis  15 . 
     There can be provided a metallic circle or ring ( 50 ) embedded in the insert  17  at the level of one of its parallels to eventually control, for example with an amplifier of brilliance, whether the impaction of the insert into the cup is correct. For example, if the metallic ring is exactly superposed with the peripheral edge of the metallic cup, this signifies that the impaction is correct. 
     The impactor element  19  is then disengaged from the insert  17 , by exerting a simple pull on the instrument  18  till the frangible points break. The frangible points having a resistance to traction that is less than that of the mortise-tenon assembly between the insert  17  and the cup  15 , the impactor  19  will be detached without risking loosening the insert from the cup. Instead of exerting a pull, one could also use the rotation of the instrument  18  in the direction of its screwing on the screw-threaded rod  19   a,  to give rise to rupture of the frangible points by shearing. 
     Finally, when the impactor  19  is freed, this latter is withdrawn with the help of a pliers introduced through the small lateral access root, after having unscrewed the instrument  18 . 
     There could be provided as a modification, in place of the screw-threaded rod  19   a,  a hexagonal hole corresponding to the hexagonal head of the distal end  6   a  of the instrument  6  to obtain the same result. Thus, the impaction of the insert in the cup will take place in an analogous manner and the impactor  19  will be loosened from the insert by exerting a rotative couple on instrument  18 . 
     This modification has the advantage of using the same instrument  6  for implantation also of the insert  17 . 
     Of course, the resistance to shearing of the frangible points between the impactor  19  and the insert  17  will be determined such as to be less than that of the anchoring points  15   a  of the cup  15  in the acetabulum C. 
     For example, the frangible points could be three in number and constituted by small polyethylene welds. 
     Reference will now be had to FIGS. 14 to  18  for the implantation of the femoral implant  20 . The femoral implant  20  here has the general shape of a spherical cap whose external convex surface is smooth to be articulated in a sliding manner within the concave recess of the insert  17 , and whose internal concave surface is provided with asperities or small points  20   b  which are adapted to anchor on the femoral head T previously drilled. The femoral implant  20  comprises also at the center of its concave surface a small screw-threaded rod  20   a  analogous to the rod  19   a  described above and a peripheral female thread  20   c  (see FIG. 16) for its connection with the carrying arm  4 . 
     Of course, the female thread could be replaced by another equivalent means permitting the connection of the implants or the drills with the carrying arm  4 . 
     It will be seen in FIG. 14 that the distal end  18   a  of the instrument  18  is screw-threaded on the small screw-threaded rod  20   a  of the femoral implant  20  which is carried at its periphery by the carrying arm  4 . 
     For implantation of the femoral implant  20 , the instrument  18  is used conjointly with a sleeve forming an abutment  21  into which is introduced the rod of the instrument  18  so as to be interposed between the trochanter base G and the sleeve  18   b  of the instrument  18 . 
     The abutment sleeve  21  is dimensioned such that the distal end  18   a  of the instrument  18  will not clear the surface of the femoral head, which permits impacting the femoral implant  20  on the femoral head T by screwing to the bottom the instrument  18  on the screw-threaded rod  20   a.    
     There is thus obtained, as seen in FIG. 15, an anchoring of the femoral implant  20  on the drilled head of the femoral head T with the screw-threaded rod  20   a  inserted into the channel  22  passing through the femoral neck CF along its axis (FIG.  18 ). 
     The screw-threaded rod  20   a  ensures centering of the femoral implant  20  on the femoral head T, but does not contribute to its primary anchoring, because its external diameter is less than that of the rod  18  and hence of the channel  22  which has been provided along the axis of the femoral neck CF (see FIG.  18 ). 
     Although this screw-threaded rod  20   a  can take place in the secondary anchoring during osseous remodeling, it is preferable to use another separate element  23  to remain fixedly in place the rod  20   a  on the femoral head T. 
     This element  23  has the shape of a nut whose internal screw-threading corresponds to that of the rod  20   a  and which comprises on its peripheral external surface another screw-thread whose thread bottom has a cross-section corresponding to that of the mentioned channel  22 . 
     The element  23  is introduced through the channel  22  from the trochanter region G with the help of another instrument  24  which supports at its distal end  24   a  the nut  23 . The distal end  24   a  of the instrument  24  comprises for example three lugs to secure in rotation the nut  23  to the instrument  24 . Thus, with the help of the instrument  24 , the nut  23  is screwed into the channel  22 , as indicated by screw-treading  25  in FIG. 18, and becomes threaded onto the rod  20   a  at the end of its movement. 
     The nut  23  is screwed to the bottom on the screw-threaded rod  20   a  to come into abutment against the concave surface of the implant  20 . The instrument  24  is then easily withdrawn because it is secured to the nut  23  only in rotation by simple contact. 
     Given that the bottom of the external screw-thread of the nut  23  has a cross-sectional diameter equal to or less than that of the channel  22 , the introduction of this element  23  will not enlarge the principal cross-section of the channel  22 . Moreover, by providing an external screw-thread on the nut  23  with a pitch which is more spaced and wider, the density of osseus spongy tissue will be substantially preserved, which avoids rendering fragile the femoral neck CF. 
     The instrument  24  can be held by the support structure  1  at the level of its proximal handle  24   b,  or else it can be used alone, as shown in FIG.  16 . 
     Of course, the relative position between the femoral head T and the acetabulum C has been shown on the drawings in a manner which does not completely reproduce the anatomical parameters, for purposes of clarity and simplification. Similarly, the overall shape of the cup  15  and of the femoral implant  20  will not necessarily be spherical, but will be dimensioned so as to reproduce the anatomical data, so as to ensure good cotyloidal covering of the femoral head. 
     It will be noted particularly that the invention preserves the osseous structure and the surrounding articular capsule. 
     Although the invention has been described in connection with a particular embodiment, it is of course evident that it is not thereby limited and that it comprises all the technical equivalents of the means described as well as their combinations if the latter enter into the scope of the claims which follow.