Abstract:
An orthopedic device having a support structure provided with at least an orifice for a fixing screw associated with a nut; the head of the screw to be pressed on one side of the support, and the nut adapted to be pressed on the other side of the support, in a housing enabling its being integrated at least partly, so as to enable the support structure to be clamped between the screw head and the nut when the screw body has been completely screwed in the receiving bone material. The implantable device includes elements for maintaining the nut in its housing opposite the orifice, and elements for locking the nut in rotation. The contours of the housing and of the nut are dimensioned to provide at least one degree of freedom to the nut in the housing enabling self-centering of the screw and nut.

Description:
BACKGROUND OF THE INVENTION 
   1. Summary of the Invention 
   The present invention relates to a new orthopaedic implant system of the type formed of a supporting structure fitted with at least one orifice to let through a fastening screw associated with a nut. 
   2. Description of the Related Art 
   Generally speaking, orthopaedic implants, in particular osteosynthesis implants, include a supporting structure in the form of a plate, a shell or other, fitted with one or of several orifices intended to let through fastening screw able of being anchored in the receiving bone material. 
   The general shape and the dimensions of this supporting structure are adapted to the implantation constraints. 
   There exist a very large number of types of implants which differ in particular by the presence or not of an interconnection between the screw head and the supporting structure, to optimise retention of the screw over a long period of time, and/or the presence of means conferring to the fastening screw a possibility of angular orientation relative to the axis of its reception orifice, to enable the practician position at best said screw relative to the site of implantation and to the corresponding spatial constraints. 
   Good holding quality of the implant is obtained when the supporting structure is sandwiched between the screw head and a nut, as known from the document WO-A-99/09903. But in such a case, the particular interconnection of the nut with the supporting structure requires accurate introduction of the fastening screw so as not to damage the thread of the nut during the screwing operation; and the practician has no possibility of orienting the screws spatially. 
   SUMMARY OF THE INVENTION 
   The present invention provides a new implantable orthopaedic device, simple in its structure, convenient, exhibiting good locking and holding qualities, and allowing certain possibility of spatial orientation of the fastening screw relative to the axis of the reception orifices laid out in the supporting structure. 
   This orthopaedic implant is of the type formed of a supporting structure fitted with at least one orifice to let through a fastening screw associated with a nut, the head of said screw being intended for resting on one side of said support, and said nut being intended for resting on the other side of said support, in a housing which enables at least partial integration, to allow clamping said supporting structure between the screw head and the nut, upon complete clamping of the screw body in the receiving bone material; this implantable device also includes means for holding said nut in its reception housing facing the orifice of the supporting structure, and for locking said nut in rotation. 
   According to the present invention, the contours of the housing of the supporting structure and the contours of the nut are sized to confer at least one degree of freedom to said nut in said housing, thereby enabling self-centring of the fastening screw and of the associated nut, regardless of the admissible orientation of the axis of said screw relative to the axis of the orifice of the supporting structure. 
   According to a first possible embodiment, the holding means of the nut in its reception housing are composed of a material rebound closing partially said housing. 
   According to another embodiment, these holding means are formed of an added-on clip closing partially the reception housing of nut. 
   In the latter embodiment, the clip for holding a nut is advantageously in the form of an open circular loop; this loop comprises a snap-on groove which co-operates with a throat of appropriate shape provided in the integration housing of the nut. 
   According to another characteristic, the means for locking the nut in rotation in the reception housing of the supporting structure are formed of at least one relief laid out on one of said parts (nut or supporting structure), co-operating with an adapted notch, provided on the other part (supporting structure or nut). 
   According to a particular embodiment, the implant includes cylindrical contact surfaces between the screw head and the supporting structure, on the one hand, and between the supporting structure and the nut, on the other hand. These cylindrical contact surfaces are adapted to confer to the fastening screw a possibility of orientation relative to the supporting structure, while keeping contacts between surfaces (cylindrical contacts) enabling to optimise the connection during clamping. 
   Preferably these cylindrical contact surfaces have the same axis. 
   According to a preferred embodiment, the implant includes spherical contact surfaces between the screw head and the supporting structure, on the one hand, and between the supporting structure and the nut, on the other hand, which are adapted to confer to the fastening screw a possibility of orientation relative to the supporting structure, while keeping contacts of surfaces (spherical contacts). This particularity confers important possibilities for angular adjustment of the screw and optimises the mechanic connection during clamping. 
   Preferably these spherical contact surfaces, in form of spherical caps have the same centre. 
   To obtain a compact assembly and having an interesting capacity of angular adjustment of the screws, the axis or the centre of the cylindrical or spherical contact surfaces, is situated in the vicinity of the upper plane of the supporting structure, or is confused with this plane. 
   According to still another particularity, the orthopaedic implant complying with the invention includes a nut containing a cylindrical shaft exhibiting a female thread and a spherical cap or crown situated at the periphery of said cylindrical shaft. 
   According to still another particularity, the fastening screw is fitted with a body thread able to co-operate with the receiving bone material, and of a head thread able to co-operate with the associated nut, the outer diameter of the body thread being smaller than or equal to the outer diameter of the head thread to let the screw through the nut. 
   For optimised clamping, the fastening screw(s) are advantageously fitted with a head thread composed of n threads offset by 1/n turns, and whereof the pitch co-operates with that of the thread of the nut and to that of the body thread. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be further illustrated, without being limited thereto, by the following description of several particular embodiments, given solely for exemplification purposes and represented on the appended drawings whereon: 
       FIG. 1  represents generally an orthopaedic plate positioned at the surface of a fractured bone, and intended to receive fastening screws; 
       FIG. 2  is a functional flow chart of a first possible embodiment of an implant of the present invention; 
       FIG. 3  illustrates a top view of a possible embodiment of an orifice laid out in the supporting structure to let through a fastening screw; 
       FIGS. 4 to 7  illustrate four different functional flow charts of implants of the present invention, authorising angular adjustments of the axis of the screw relative to the supporting structure; 
       FIG. 8  is an exploded sectional view, of a preferred embodiment of implant of the functional flow chart of  FIG. 7 ; 
       FIG. 9  shows the implant of  FIG. 8 , upon complete straight screwing, i.e. the screw is centred on the axis of the orifice of the support; 
       FIG. 10  shows the same implant as  FIG. 9  but upon complete tilting clamping, i.e. the screw forms an angle with the axis of the orifice of the support; 
       FIG. 11  is a large-scale partial view, of the underside of the supporting structure showing the reception housing of the nut; 
       FIG. 12  is a sectional view according to  12 - 12  of  FIG. 11 ; 
       FIG. 13  is also a large-scale perspective view, of a nut for the implant illustrated on  FIGS. 8 to 10 ; 
       FIG. 14  is a view of the upperside of the nut illustrated on  FIG. 13 ; 
       FIG. 15  is a diametrically sectional view according to  15 - 15  of  FIG. 14 ; 
       FIG. 16  is a lateral view of the nut illustrated on  FIGS. 13 to 15 ; 
       FIG. 17  is a large-scale perspective view of the circular clip enabling to hold the nut in the housing of the supporting structure; 
       FIG. 18  is a top view of the clip illustrated on  FIG. 17 ; 
       FIG. 19  is a diametrically sectional view of the clip according to  19 - 19  of  FIG. 18 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows the orthopaedic implant  0  formed of a supporting structure in the form of an osteosynthesis plate  1  positioned on a fractured bone  2 , for example, an epiphysis of the radius, and exhibiting four circular orifices  3  for accommodating the fastening screws  5 . Each screw  5  includes a screw head  6  and a screw body  8 . 
     FIG. 1  also illustrates the drilling gun  9  which is used before placing the screws  5  in order to drill positioning holes in the bone material, through the orifices  3 . 
     FIG. 2  is a functional flow chart which shows schematically the assembly of a screw  5  on the supporting plate  1 . 
   On this figure, one may note the presence of un nut  10  positioned in a housing  12  laid out in the supporting plate  1 , so that upon complete screwing of said plate  1  is sandwiched between the head  6  of the screw  5  and said nut  10 . The female thread of the nut  10  co-operates with the male thread of the screw body  8  to lock the assembly upon complete screwing. 
   To this end, the screw  5  may include a single thread, on the one hand for anchoring in the bone material, and on the other hand for co-operation with the nut; but it may also be fitted with two different threads each ensuring one of the functions aforementioned. 
   The nut  10  may be simply integrated partially in the housing  12 . It is held in place in said housing  12 , facing the orifice  3 , by appropriate holding means  13 , and it is also locked in rotation by appropriate means represented in the form of a simple line marked  14 . 
   The holding means  13  may be in the form of a material rebound or of an added-on structure detailed below, of the locking clip type, implemented, after positioning the nut  10  in the housing  12 . 
   The rotation of the nut  10  is locked either by the general relative shapes of the nut  10  and of the reception housing  12 , or by co-operation of complementary members such as relief(s) and notch(es), laid out on the surfaces facing the nut and of the housing. 
   According to the invention, the contours of the housing  12  and the contours of the nut  10  are adapted and sized to confer to the latter, in said housing, at least one degree of freedom, greater than that of a simple functional clearance, thereby enabling self-centring of the screw  5  and of the nut  10 , and this regardless of the admissible orientation of the axis of said screw relative to the axis of the housing  3 . 
     FIG. 2  shows both lines of axes  15  illustrating the amplitude of possible corresponding inclinations of the screws. The middle position, normal to the supporting plate  1  is represented by the axis  16 , which axis  16  corresponds to the axis of the housing  3 . 
   As represented on  FIG. 3 , the supporting plate  1  may include elongated orifices  3 ′ thereby giving a possibility of additional longitudinal adjustment of the screws  5  with respect to the support  1 . These elongated orifices  3 ′ may have a general rectilinear or curvilinear shape. 
     FIGS. 4 ,  5 ,  6  and  7  are functional diagrams derived from that of  FIG. 2 , illustrating the screwed assembly of the invention, but with cylindrical or spherical contact surfaces between the screw head  6  and the supporting plate  1 , on the one hand, and between the supporting plate  1  and the nut  10 , on the other hand, authorising a degree of freedom and relatively important angular adjustment possibilities of the screw  5 , while keeping a significant contact surface promoting good cohesion of the assembly after screwing. 
   In all cases, the different parts are shaped as well as possible to obtain significant angular adjustment possibilities and to keep the best possible contacts between surfaces. In the case of cylindrical contact surfaces, the angular adjustment is possible in a plane if the orifice  3  is circular, or in different parallel planes corresponding to a prismatic volume if an oblong orifice  3 ′ as illustrated on  FIG. 3  is available.
 
In the case of spherical contact surfaces, there is preferably a circular reception orifice and the angular adjustment of the screw is then possible within a conical volume whereof the axis is confused with that of the circular orifice  3 .
 
   On  FIG. 4 , the head  6  of the screw  5  is en contact with an intermediate member  18  which comprises a slipping surface in contact with the supporting plate  1 . The contact surfaces between the head  6  and this added-on member  18  correspond to a cylindrical portion centred on an axis  19 , or to a spherical cap centred at a point  19 , as the case may be. The axis or the centre  19  is here positioned on the outside, above the supporting plate  1 . 
   On the other hand, the nut  10  and the supporting plate  1  are also in contact on cylindrical or spherical surfaces, as the case may be. The axis or the centre  20  of the cylindrical portion or of the corresponding portion of spherical cap is here positioned on the inside, i.e. on the bone structure side. 
   The nut  10  is held in place by the means  13  and it is locked in rotation by means  14  schematised in the form of a simple line. 
     FIGS. 5 ,  6  and  7  illustrate embodiments deprived of complementary part  18  and whereof the spherical or cylindrical contact surfaces of the screw/supporting plate and supporting plate/nut are centred on the same axis or exhibit the same centre. 
   For the embodiment illustrated on  FIG. 5 , the axis or the corresponding centre  21  is situated between both contact surfaces. 
   For the embodiment illustrated on  FIG. 6 , the axis or the corresponding centre  22  is situated on the inner face of the supporting structure  1 . 
   For the embodiment of  FIG. 7 , the axis or the corresponding centre  23  is situated on the outer face of the supporting structure  1 . 
   The embodiment illustrated on  FIG. 7  appears more compact. Preferably, the axis or the centre  23  is situated in the vicinity of the upper surface of the supporting structure  1  to enhance the possibilities of angular bottoming of the screw  5 ; the distance marked H on this figure tends then towards zero value. 
   In all cases, the nut  10  is held in its housing  12  by means  13  such as material rebound or clip as detailed below, and it is locked in rotation by means represented schematically in the form of a simple line  14  also detailed below. 
   Because of the general space requirements of the parts, the corresponding angular clearance cone always confers to the practician interesting adjustment possibilities. 
     FIGS. 8 to 19  detail an embodiment according to that represented diagrammatically on  FIG. 7 . 
     FIG. 8  represents a fastening screw  5  as a longitudinal diagrammatical section. This screw  5  shows on the one hand a screw body  8  fitted with a thread  25  and whereof the end  26  is pigtail-shaped, and on the other hand a screw head  6  fitted with one clean thread  27 . The upper section of the screw head  6  contains a cavity  29  with polygonal walls co-operating with the setting auxiliary device. 
   This screw head  6  shows at its end a collar whereof the peripheral contour is in the form of a spherical crown  7 , intended to make contact with a surface of equivalent shape provided on the supporting structure  1 . 
   The screw  5  runs through the plate  1 , seen as a sectional view, at the circular orifice  3 , as well as the nut  10  and the holding means  13 , here in the form of a locking clip, also seen as a sectional view. 
   The supporting structure  1 , the nut  10  and the locking clip  13  are represented in exploded views, separate from one another. 
   The thread  27  of the screw head  5  is adapted to that of the nut  10 . This thread is composed of n threads  28  offset by 1/n turn, whereof the pitch is able to co-operate with that of the thread  30  of the nut  10 , which pitch corresponds to that of the thread  25  of the screw body  8 . 
   The thread  25  of the screw body  8  may be anchored by screwing in the bone material; the outer diameter of this body thread  25  is smaller than or equal to the outer diameter of the head thread  27  to let the screw body  8  through the threaded orifice of the nut  10 . 
     FIG. 9  represents the fastening screw  5  upon complete screwing, in a configuration normal to the plate  1  (the bone reception structure is not represented). The plate  1  is then sandwiched between on the one hand the screw head  6 , and on the other hand the nut  10  whereof the female thread  30  co-operates with the male thread  27  of said screw head  6 . 
     FIG. 10  represents the fastening screw  5  upon complete screwing in a configuration tilted relative to the axis  16  of the orifice  3 . 
   This tilting possibility is due to the fact that the nut  10  has a degree of freedom in its reception housing  12 . On the other hand, the spherical contact surfaces of the screw head/supporting plate and supporting plate/nut enable to obtain high clamping quality regardless of the admissible tilt of the axis of the screw  5  relative to the axis  16  of the orifice  3 . 
   One may also provide a spherical contact surface between the nut  10  and the locking clip  13  for better guiding of the nut  10  when positioning the screw  5  when starting the screwing process. 
   The corresponding contact surfaces are detailed below in connection with the description of each constitutive part of the implant. 
     FIGS. 11 and 12  represent in detail the configuration of the circular orifice  3  and of the housing  12  which is laid out in the supporting structure  1 , which housing  12  is intended to receive the nut  10  detailed on  FIGS. 13 to 16 . This nut  10  is held preferably by a locking clip detailed on  FIGS. 17 to 19 , which clip enables easier disassembly of the nut than when said nut is crimped in position. 
   As represented on  FIGS. 11 and 12 , the supporting plate  1  includes a spherical ring  312  formed of a first spherical crown  31  for contact with the screw head  6 , and of a second spherical crown  32  for contact with the nut  10 . 
   The peripheral portion  313  which extends between both spherical crowns  31  and  32 , is of truncated form, with sufficient angle to allow movement of the nut  10  and hence of the screw  5  relative to the supporting part  1 . This portion  313  may form a stop for the nut  10  and in particular for its shaft  100  as detailed below. 
   On the circular periphery of the housing  12 , one may note the presence of a circular throat  33  intended for positioning and locking the retaining clip  13 . 
   The means locking the rotation of the nut  10  with respect to the support  1  are formed of at least one toe or tang.  FIG. 11  shows three tangs  34  distributed regularly in the bottom of the circular housing  12 , between the periphery of said housing and the spherical crown  32 . These tangs  34  co-operate with homologue female shapes detailed below, provided on the nut  10  for locking the latter in rotation. 
   As represented on  FIGS. 13 to 16 , the nut  10  has a spherical crown  35  intended for contact with the supporting structure  1  and in particular the spherical crown  32  of the ring  312 . One may also provide an external spherical crown  36  intended for contact with the holding clip  13 . Said spherical crowns  35 ,  36  are part of a spherical ring  356  connected to the lower periphery of a cylindrical shaft  100  serving as a nut, which shaft is fitted with the female thread  30 . 
   The external peripheral surface of the shaft  100  is accommodated with a certain clearance in the truncated portion  313  of the support  1 , so as not to alter the ball-joint spherical contacts between the nut  10  and said support. 
   The amplitude of the movement of the nut  10  with respect to the support  1  may be limited by the truncated portion  313  of said support, which acts as a stop for the shaft  100  of the nut  10 . 
   The spherical surface  36  optimises the correct spatial positioning of the nut when introducing the screw  5 . The degree of freedom of the nut  10  in its reception housing  12  enables self-centring of the fastening screw  5  and of the associated nut when fastening the implant. 
   On  FIGS. 13 and 14 , one may see the female shapes, aforementioned, in the form of cavities or notches  37  which are designed for co-operating with the tangs  34  of the supporting structure  1  in order to lock the nut  10  in rotation. The sides of these cavities or notches  37  may be parallel or slightly divergent, as illustrated on  FIGS. 13 ,  14  and  15 . 
   In the exemplary embodiment illustrated, the tangs  34  and the homologue notches  37  are three in number, laid out at 120° respectively in the bottom of the housing  12  of the supporting structure  1 , and at the periphery of the nut  10 . Cutting the spherical crown  356  using the notches  37  confers certain elasticity to the nut  10 . 
   As represented on  FIGS. 17 to 19 , the clip  13  is in the form of a circular ring fitted with a slot  38  providing thereby certain radial elasticity. On its external periphery, this clip  13  is fitted with a peripheral rib or emboss  39  which may be imbedded in the circular throat  33  of the housing  12  laid out in the support  1 . Imbedding the clip  13  on the supporting structure  1  is made possible by the presence of the slot  38 . The clip  13  is sized for holding the nut  10  in the housing  12 . 
   The clip  13  is also fitted internally with a spherical crown  40  able to co-operate with the corresponding spherical crown  36  provided on the nut  10 . 
   As mentioned before, upon complete screwing of the fastening screw  5 , the different spherical crowns: — 7  on the head  6  of the screw  5 , — 31  and  32  on the support  1 , and — 35  and  36  on the nut  10 , are concentric; one the assembly complete, the corresponding centre  23  is positioned substantially in the plane of the upper surface of the supporting plate  1 , as shown on  FIG. 9 .