Abstract:
The invention relates to an implantable orthopaedic device comprising a load-bearing element, such as a bone plate, for fixing elements, such as bone screws, that can be oriented polyaxially. The load-bearing element is equipped with at least one opening for the passage of the fixing elements. A two part insert is provided in the opening, the insert having an external form that complements the internal form of the receiving opening and permits the polyaxial rotation of the insert in the opening. The insert is equipped with a central bore for receiving the body of the fixing element. The first insert element part has a central inner hollow chamber, into which the second insert element part can be introduced. The first insert element is flexible or has at least one slit, in such a way that when the two insert elements are displaced axially in relation to one another, the first insert element in the plate can be expanded at least partially in order to block the position and alignment of the fixing element in the device in a polyaxial manner.

Description:
The invention concerns an implantable orthopedic device with a load-bearing element, such as a bone plate, with at least one polyaxially-oriented fixation element such as a bone screw. In the load-bearing element there is at least one opening for the passage of the polyaxially oriented fixation element. A first insert is provided that can be inserted in the opening into a mounting, such that the insert exhibits an external shape that is complementary to the internal shape of the mounting. This allows a polyaxial rotation of the insert in the mounting. The first insert exhibits a central through-bore for receiving the body of the fixation element. In addition the implantable orthopedic device has a second insert for holding the first insert in the mounting. 
   An alternate device is known, for example, from U.S. Pat. No. 5,954,722. There is at least one opening provided in the plate that defines a mounting, in which a one-piece insert equipped with a slit going all the way through a wall thereof can be inserted. The insert has inner threading, in which a threading of the fixation element can engage. The opening of the plate is shaped like a partial hollow sphere, so that it forms a mounting for the insert which exhibits a spherical outer surface. In this way, the insert may be polyaxially oriented with a fixation element that is screwed into it. When the fixation element is screwed into the insert, it spreads the insert apart, which now, in the mounting, fixes the element into position. 
   U.S. Pat. No. 5,607,426 shows another solution for the polyaxial positioning of a fixation element. There is also at least one opening provided in the plate, which defines a mounting, in which a two-part insert may be inserted, the outer portion of which exhibits external threading which is able to engage with an interior threading in the plate provided on the side away from the bone. On the side near the bone, the plate is equipped with a conical tapering of the opening. Against this conical tapering the complementarily-shaped inner portion of the insert is supported. The inner portion of the insert has multiple slits, is hollow, and is equipped to hold a spherical head of the fixation element. Thus the fixation element may be polyaxially oriented. The screwing in of the outer part of the insert causes it to press on the inner part of the insert, which, as a consequence of its displacement in a perpendicular direction to the plate surface through the conical tapering, reduces the hollow space and thus fixes the spherical head of the fixation element in its position. It is clear that the polyaxial fixation of the spherical head of the fixation element must occur first and may be effected through the insertion of a tool in a groove provided in its head. 
   SUMMARY OF THE INVENTION 
   The invention has as one aspect improving a device of the type described in such a way that it is simpler, faster and more secure for the surgeon to handle. 
   This objective is achieved pursuant to the invention by the fact that the insert consists of two insert elements with a through bore wherein the first insert element exhibits the spherical outer shape, which allows its polyaxial rotation in the mounting. Additionally, the first insert element exhibits a central inner hollow space in which the second insert element may be inserted. The first insert element exhibits at least one slit of such a type that in an axial displacement of the two insert elements against each other the first insert element may be at least partially spread out in the plate, in order to block the position and orientation of the fixation element polyaxially when inserted in the device. 
   Through the fact that a two-part insert element is provided, a polyaxial locking may be secured in a simple manner, without this necessitating a higher expenditure in the insertion of such specially-designed bone plates. 

   
     PRELIMINARY DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in two embodiments referencing the drawings. They show: 
       FIG. 1  is a sectional side view of a first embodiment of the device; 
       FIG. 2  is a sectional view of the first insert element from  FIG. 1 ; 
       FIG. 3  is a sectional view of the second insert element from  FIG. 1 ; 
       FIG. 4  is a sectional side view of a first modified form of the first embodiment of the device; 
       FIG. 5  is a sectional side view of a second modified form of the first embodiment of the device; 
       FIG. 6  is a sectional view in another plane of the first insert element of the first embodiment according to  FIG. 1 ; and 
       FIG. 7  is a sectional side view of a second embodiment of the device. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a sectional side view of a first embodiment of the device. A plate identified as  1  is generally intended for implantation on a bone. Plate  1  normally has a number of holes  2  at an angle to its principle plane. The main axis of the holes  2  is identified as  3 . The bone material is in the area marked  4  when inserting the device. Instead of the plate  1 , one may also speak more generally of a load-bearing element, since besides plates, other load-bearing element such as, for example, rods, in particular, may be provided for the insertion of the invention. 
   The holes  2  may (not illustrated) be shaped as hollow cylinders near the opening, so that outer walls parallel to the main axis  3  result. The openings themselves may be rounded off or shaped so as to form spheres facing outward. These parallel outer walls may, however, also be shaped differently, for example with the opening widening conically, or narrowing conically, to name only two simple rotation-symmetrical possibilities. What is essential is the existence of projections  7  or  8 . This means that between these projections  7  or  8  a mounting  9  is created, which is shaped like a hollow sphere. The diameter of this hollowed out mounting  9  is larger than the cylindrically-shaped space formed by the projections  7  or  8 . This assures that flange-like rotating projections  7  or  8  exist, that securely hold an insert element  10 , which is at least in some parts spherical, in the mounting  9 . 
   This first spherical insert element  10  can then turn freely around its spherical mid-point, which lies in the axis  3 , which is represented in  FIG. 1  by the perpendicular orientation of the first insert element  10 . The first insert element  10 , however, cannot fall out of the mounting  9 . 
   The first insert element  10  here has partial slits at four locations at a distance of 90 degrees reciprocally from above and below, which may be seen more clearly in the detailed drawing of  FIG. 2 . The same characterizing features are given the same reference numbers in all drawings. The characterizing features of the first insert element  10  to be described below in connection with  FIG. 1  may also be seen in the detailed drawing thereof in  FIG. 2 . Two slits  6  are made from above, and two slits  6  from below in the first insert element  10 . 
   In  FIG. 1  the cutting plane lies in the two opposing open slits  6 , above. The first insert element  10  is equipped along axis  3  with a through bore  11  for the passage of a fixation element  5 , such that the passage widens on the side away from the bone into a mounting  12  for a fixation element head, and thus defines a shoulder  13 , on which the fixation element head may be supported. The shoulder  13  spans a plane that runs perpendicular to the main axis  3  of the first insert element  10 . 
   On the side near the bone, the first insert element  10  is equipped along axis  3  with a similarly widened hollow space  14  for the acceptance of a second insert element  20 . 
   The hollow space  14  of the first insert element  10 , provided to accept the second insert element  20 , it widens in the direction of the end  4  near the bone and forms a conical wall surface  16 . In place of a cone that opens up, another form may be selected, preferably one that is rotation-symmetrical to axis  3 . 
   On the end of the conical wall surface  16  near the bone a bend (or alternatively a continuous transition through a rounding)  17  is provided, with which the hollow space  14  of the first insert element  10  goes into a cone that closes in on itself with a wall surface  18 . The wall surface  18  may also be seen as a part of an inward-projecting rotating lug. Here it is sufficient for the holding function if only partial areas of the perimeter exhibit the said inward-projecting lugs  18 . 
   The second insert element  20  is essentially shaped to be complementary to the hollow space  14  of the first insert element  10 , so that it can be taken up, with some play, in the hollow space  14  of the first insert element  10 .  FIG. 3  shows a sectional view of the second insert element from  FIG. 1 , in which the largest section  21  of the second insert element  20  may be more clearly seen, which lies in the area of the passage  17  of the first insert element  10 . Through the wall surface  18  of the first insert element  10  the second insert element  20  is held in the first insert element  10 . 
   Referring to  FIG. 3 , the second insert element  20  does not have slits and preferably is not compressible. It has a continuous inner-threaded bore  22  into which fixation element  5  may be screwed. 
   The device functions as follows: Plate  1  is placed on the bone area  4 , is made ready in the holes  2 , in which the polyaxial fixation is provided, with the two insert elements  10  and  20  inserted. The fixation element  5 , for example a screw, is set down, directly or through a guide, and positioned so that the main axis  3  of the screw  5  is aligned with the main axis of the two insert elements  10  and  20 . Through the spherical outer shape of the first insert element  10 , a broad range of angles may be selected. The screw  5 , when screwed in, at first engages with its outer threading  25 , later to be anchored in the bone, into the inner threading  22  of the second insert element  20  and then in the bone material  4 . In this way the screw head moves from the side away from the bone towards the plate  1  and the first insert element  10 . The diameter of the bone screw  5  and the associated threading size may be selected such that the said first outer threading  25  of the bone screw  5  goes through the first insert element  10  without touching it. After a cylindrical transition area  27  the screw has a second outer threading  28 . The second outer threading  28  is cylindrical and engages with the threading  22  of the second insert element  20 . 
   Aside from the directional guiding of the screw  5  in the second insert element  20  an additional fixing of the direction and orientation occurs in the moment when the head of the fixation element  5  enters into the hollow space  12 , since then side walls of the first insert element  10  confirm the previously set orientation in the first insert element  10  as well, to the extent that the diameter of the shaft and the threading  27  and  28  of the bone screw  5  are sufficiently great. Then comes the moment when the fixation element  5  is screwed in far enough that the head lies on the shoulder  13 . From this point further turning of the fixation element  5  effects an axial movement of the second insert element  20  along the axis  3  toward the hollow space  14 . In this way the conical surfaces  16  of the two insert elements toward one another and the inner, inflexible, second insert element spreads the flexible first insert element  10  apart, so that its spherical outer surfaces at least partially press against the wall of mounting  9 . In this way it is possible, by simply pulling tight the fixation element  5 , to set the previously adjusted polyaxial orientation and to confirm it. 
   Advantageously, the plate  1  and the insert elements  10  and  20  are made of medical steel or titanium or another material used in medicine technology. In particular, PEEK may be used as a material, which—in addition to other materials—also allows another advantageous embodiment of the first insert element  10 . Then this first insert element  10  can be designed without slits, since, through the choice of materials it is in itself flexible. Such an insert element  10  is thus advantageously strengthened with carbon fibers. What is essential is that the first insert element can be deformed elastically, so the type and number of slits and/or the selection of materials are only two examples of possible embodiments. The said deformability or flexibility must allow a spreading out of the first insert element  10  in a radial direction with respect to the mounting  9 . In the embodiment portrayed, the mounting  9  is a hollow sphere centered in the thickness of the plate  1 . 
     FIGS. 4 and 5  show sectional side views of two modified forms of the first embodiment of the device. The area of the first and second insert elements  10  and  20  is designed the same way as the embodiment represented in  FIG. 1 through 3 . As stated above, it is essential that the insert is held in the mounting  9 , which is assured by means of the rotating projections  7  or  8  here in  FIG. 1 . These are the edges of the mounting  9  in  FIG. 1  near the upper surface of the plate that, due to their hollow sphere form, have a smaller diameter than the depth of the mounting  9  itself. 
   This requires an exertion of force in inserting the insert. 
     FIG. 4  shows a design in which in the area near the bone, plate  1  exhibits a ring-shaped recess  31 . The insert elements  10  and  20  are then first inserted in the mounting  9  and set in such a way that a third insert element  30  may subsequently be inserted as a ring in the corresponding recess  31  in the plate  1 . Here the fixing action may be provided by pressing, screwing, bonding or another process commonly used in medical technology. This third insert element  30  then is provided with a spherical inner surface, which continuously fills in the mounting  9  of the plate  1 , so that the first insert element may now be supported on the side near the bone before the implantation by the rotating tapered edge  8 ′. The implantation itself takes place in the same way as with the first embodiment, i.e. through the interaction of both the first and the second insert elements  10 ′ and  20 ′ on the complementary surfaces  16 , without the third insert element  30  exercising an essential function here. It only takes up the forces exerted on the half near the bone in spreading out the first insert element  10 . 
   For the description of the first insert element  10 ′ according to the second modification of the first embodiment, reference is made to the description of  FIG. 1 . The difference between the two first insert elements  10  and  10 ′ consists of the fact that the first insert element  10 ′ according to this modification has no area  17 , which exhibits a bend or a continuous transition through a rounding of a widening section into a tapering section. Rather, the conical wall surface  16  ends or may, for example, transition into a surface parallel to the principle plane of the plate  1 . 
   The second insert element  20 ′, on the other hand, exhibits an area of large diameter. In this way, the first insert element  10 ′ and the second insert element  20 ′ may be freely inserted from the underside into opening  2  of plate  1 . They are positioned in mounting  9  by means of a third insert element  30 ′, which is inserted as a ring in a corresponding recess  31  in the plate  1 . In this way, the fixing may be provided by pressing, screwing, bonding or another process commonly used in medical technology. This third insert element  30 ′ then is equipped with a conical surface  18 ′ tapering toward the bone  4 , against which the second insert element  20 ′ may be supported before the implantation. The implantation itself takes place in the same way as with the above-cited embodiments, i.e. through the interaction of both the first and the second insert elements  10  and  20 ′ on the complementary surfaces  16 . 
   In place of the complementary surfaces  16  shown in the drawings as conical surfaces, other surface forms that allow a frictional connection may be provided, which may tighten against each other, if a fixation element is pushed forward by the insert elements  10 ′ and  20 ′. 
   In this way, both insert elements  10  and  20  or  10 ′ and  20 ′ are each held firmly against the against the spherical inner walls of the plate  1  through spreading out of the side areas  41  ( FIG. 2 ) of the first insert element  10 ,  10 ′, which happens as a result of the axial pressure of the underside of the fixation element head on the shoulder  13  and against the central area  42  of the first insert element  10 ,  10 ′. This holding action is exerted by the axial counter-movement of the second insert element  20  or  20 ′ in the direction of its longitudinal axis  3 , which thus spreads the wing areas  41 , the inner surfaces  16  of which engage in a grip complementary to the tapering of the central area  42  with the corresponding surfaces of the second insert element  20  or  20 ′. 
     FIG. 6  shows a side view cut in another plane of the first insert element  10  of the first embodiment according to  FIG. 1 , such that the cut goes through the solid material of the first insert element  10  and thus no slits are visible. This figure therefore corresponds to an embodiment with a first insert element that is in itself flexible, for example, one made of PEEK. 
   Alternatively to the threading  22 , the second insert element  20  may also be provided with a smooth inner boring, so that there is no direct contact between the screw  5  and the second insert element  20 . Then the function of the axial movement of the second insert element  20  can be realized through underside  29  of the second insert element  20  being guided correspondingly closer to the bone, as when placed in the lower position presses against the first insert element  10  and spreads it. 
     FIG. 7  finally shows a sectional side view of a second embodiment of the device. The same characterizing features appearing in the figures are always given the same reference numbers. Here the shoulder  13 ″ is provided for support in the inner insert element, which is pressed by means of the head of the screw  5  against the outer insert element (and spreads it). For this to succeed, inner threading  22 ″ is provided in the outer insert element. The design of the lug  18 ″ and the conical engagement surfaces  16 ′ can be executed as in the first embodiment.