Abstract:
An anchoring element with a screw ( 12 ) comprising a threaded section ( 13 ) and a head ( 15 ) designed as a spherical segment-shaped section, and with a receiving portion ( 1 ) for connecting the screw ( 12 ) to a rod ( 19 ), is provided. The receiving portion ( 1 ) comprises a first end ( 2 ) and a second end ( 3 ) opposite the latter and a longitudinal axis ( 4 ) passing through the two ends ( 2, 3 ). The receiving portion further comprises a bore ( 5 ) coaxial with the longitudinal axis ( 4 ), a first region adjoining the first end ( 2 ) with an essentially U-shaped cross-section ( 18 ) with two free arms ( 8, 9 ) comprising a thread for receiving the rod ( 19 ) to be inserted, a region adjoining the other end ( 3 ) for receiving the head ( 15 ), and an element which exerts pressure on the rod ( 19 ) or on the head ( 15 ). In order that the screws can be used in situ for very different lengths, the threaded section ( 13 ) and the head ( 15 ) are designed as separate parts.

Description:
FIELD OF THE INVENTION 
     The invention concerns an anchoring element with a screw comprising a threaded section and a head designed as a spherical segment-shaped section, and with a receiving portion for connecting the screw to a rod. An anchoring element of this kind is used in particular in vertebral column surgery, but also in accident surgery on other bones. 
     BACKGROUND OF THE INVENTION 
     Such an anchoring element is known from DE 43 07 576 C1, for example. With known anchoring elements and screws of this kind, the threaded section of the screw and its head are constructed in one piece. As the surgeon needs very different lengths of screws, he must always have different sets of such screws available. This makes a considerable stockpile necessary, resulting in considerable costs. 
     It is the object of the invention to eliminate this drawback. 
     SUMMARY OF THE INVENTION 
     This object is achieved by an anchoring element with a screw ( 12 ) comprising a threaded section ( 13 ) and a head ( 15 ) designed as a spherical segment-shaped section, and with a receiving portion ( 1 ) for connecting the screw ( 12 ) to a rod ( 19 ), wherein the receiving portion ( 1 ) comprises a first end ( 2 ) and a second end ( 3 ) opposite the latter, a longitudinal axis ( 4 ) passing through the two ends ( 2 ,  3 ), a bore ( 5 ) coaxial with the longitudinal axis ( 4 ), a firs t region adjoining the first end ( 2 ) with an essentially Us shaped cross-section ( 7 ) with two free arms ( 8 ,  9 ) comprising a thread for receiving the rod ( 19 ) to be inserted, a region adjoining the other end ( 3 ) for receiving the head ( 15 ), and an element ( 22 ,  17 ) which exerts pressure on the rod ( 19 ) or on the head ( 15 ), characterised in that the threaded section ( 13 ) and the head ( 15 ) are designed as separate parts. 
     As a r result it is possible for the surgeon during application to shorten the threaded section to a desired length before or after implanting, and then connect it to the head and the receiving portion. In this way the maintenance of stocks is substantially reduced, and at the same time the possibilities for the Burgeon to make finer adjustments are increased, as the screws can be shortened to any length. 
     Further embodiments of the invention include one or more of the following features: 
     the threaded section ( 13 ) comprises a shank ( 14 ) at the head end; 
     the head ( 15 ) comprises a spring-yielding edge on its side facing towards the threaded section ( 13 ); 
     the edge ( 34 ) facing towards the threaded section comprises one or more apertures or recesses ( 28 ,  29 ,  33 ) which are directed parallel to the axis of symmetry ( 4 ) and distributed circumferentially; 
     an aperture ( 33 ) extends over the whole wall length, seen in a direction parallel to the axis of symmetry ( 4 ); 
     the head ( 15 ) comprises a bore ( 27 ) coaxial with the axis of symmetry; 
     the bore ( 27 ) is cylindrical; 
     the shank ( 14 ) comprises a rough surface; 
     the shank ( 14 ) is polygonal; 
     the head ( 15 ) comprises an internal thread in the bore and the shank ( 35 ) comprises an external thread mating therewith; and/or 
     the head ( 15 ) is corrugated in the circumferential direction in the bore and the shank ( 37 ) comprises a corresponding corrugation on its outer side. 
     Further characteristics and suitabilities of the invention are apparent from the description of practical examples with the aid of the figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The figures show: 
     FIG. 1 a side view of a first embodiment in section; 
     FIG. 2 the embodiment shown in FIG. 1 in an exploded view; 
     FIG. 3 a corresponding exploded view of a second embodiment; 
     FIG. 4 a side view of the first bone screw used in both embodiments; 
     FIG. 5 a top view of the bone screw in FIG. 4; 
     FIG. 6 a side view of a second embodiment of the bone screw used in the first two practical examples; 
     FIG. 7 a top view of the bone screw shown in FIG. 6; 
     FIG. 8 a side view of a third embodiment of a bone screw shown in the first two practical examples; 
     FIG. 9 a side view of a further embodiment in section; 
     FIG. 10 a side view of a further embodiment in section; and 
     FIG. 11 an enlarged view of the detail X of FIG.  10 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the first embodiment shown in FIGS. 1 and 2, the anchoring element comprises a receiving portion  1  of cylindrical construction with a first end  2  and an opposed second end  3 . The two ends extend perpendicularly to an axis of symmetry or longitudinal axis  4 . Coaxially with the longitudinal axis  4  is provided a first coaxial bore  5  which extends from the first end  2  and which extends as far as a predetermined distance from the second end  3 . At the second end  3  is provided a second bore whose diameter is smaller than the diameter of the first bore. In the practical example shown, the second bore is designed as an opening whose edge is shaped as a hollow spherical segment-shaped section whose centre is directed towards the first end  2 . 
     The receiving portion  1  comprises, starting from the first end  2 , a U-shaped recess  7  extending perpendicularly to the longitudinal axis  3 , with two free arms  8 ,  9  ending towards the first end  2 . Adjoining the first end  2 , the arms comprise an internal thread  10 . The bottom of the U-shaped recess extends as far as a predetermined distance from the second end  3 . Adjoining the first end  2 , the arms  8 ,  9  comprise on the outside a section  11  whose outside diameter is smaller than the outside diameter of the adjoining section of the receiving portion. 
     The screw  12  cooperating with the receiving portion  1  comprises a threaded section  13  designed as a bone screw and a spherical segment-shaped head  15  which is connected thereto in the assembled view shown in FIG.  1 . The head has a radius which is such that, when the head  15  is received in the second bore  6  as shown in FIG. 1, the head mates with a hollow spherical segment-shaped wall section formed there, wherein the hollow spherical segment-shaped section is designed in such a way that the centre  16  of the sphere is offset towards the first end  2  to such an extent that the section forms an abutment and the sphere or the head  15  is held in the hollow spherical segment-shaped section of the second bore  6 . 
     There is further provided a pressure element  17  which is of cylindrical construction and has an outside diameter which is so large that the pressure element can be introduced into the first bore  5  and moved to and fro in the axial direction in the latter. On its lower side facing towards the second end  3  the pressure element  17  comprises a hollow spherical segment-shaped section which is constructed symmetrically to the longitudinal axis  4  and whose radius corresponds to the radius of the head  5 . The pressure element comprises a U-shaped recess  18  which extends transversely to the longitudinal axis  4  and whose free arms extend towards the first end  2 . The lateral diameter of this U-shaped recess is selected so that a rod  19  to be received can be inserted in the recess and guided laterally in the latter. The depth of the hollow spherical segment-shaped recess is selected so that it ends at a distance from the second end  3  which is greater than the distance from the centre  16  corresponding to the radius of the head  15 , looking towards the first end  2 . At the bottom of the U-shaped recess  18  is an adjoining coaxial bore  20  whose diameter is smaller than the diameter of the rod  19  to be received. 
     As can be seen from FIG. 1, the U-shaped recess  18  comprises, at its end directed towards the first end  2 , a section  21  whose inside width is greater than the diameter of the U-shaped recess  18 . 
     On the side facing towards the first end  2 , the pressure element  17  is adjoined by a nut  22  which comprises an external thread  23  mating with the internal thread  10  and in addition an internal thread  24 . The inside dimensions of the nut  22  are selected so that the inside width is smaller than the diameter of the section  21  and larger than the diameter of the rod  19  and hence of the U-shaped recess  18 . Further, an internal nut  25  with an external thread mating with the internal thread  24  is provided. Finally, there is provided a bush  26  which encompasses the free end adjoining the first end  2  and which in the assembled state sits on the annular section  11 , as shown in FIG.  1 . 
     As can best be seen from FIG. 2, the nut  22  comprises a slot and the internal nut  25  comprises a hexagon opening for respective separate application of screwdrivers. 
     As can best be seen from FIG. 2, the head  15  is designed as a sphere flattened at its end which is to face towards the first end  2 , and comprises a bore  27  coaxial with the longitudinal axis  4 . The diameter of the bore  27  is equal to the outside diameter of the shank  14  and designed in such a way that the shank can be inserted in the bore with frictional locking. As can be seen from FIG. 2, the hollow spherical segment-shaped element shaped in this way is provided, on its side opposite the flattened end, with sections  28 ,  29  which are spaced apart from each other in the circumferential direction and extend parallel to the longitudinal axis  4  and extend as far as the end opposite the flattened side. As a result, the edge  30  facing away from the first end  2  is designed to be capable of spring yielding outwards for introduction of the shank  14 . 
     In operation, first the screw  12  is screwed into the bone or vertebra. For this purpose the shank  14  has known engagement possibilities such as a hexagon socket. Then the surgeon shortens the shank  14  to the desired length and first places the receiving portion with the second bore on the shank  14  and then guides the head from the first end  2  onto the shank  14 , so that the shank  14  is introduced into the bore  27  from the spring-yielding edge  30  and the head surrounds the shank in the manner shown in FIG.  1 . The head  15  and the shank  14  are connected to each other with frictional locking. Next the pressure element  17  is inserted and, by screwing in the nut  22 , pressed onto the head  15  in such a way that the latter undergoes desired rotational stabilisation. The bush  26  is fitted and then by means of the internal nut  25  the rod  19  is fixed. The rod  19  exerts an additional pressure on the head  15  via the pressure element  17 . 
     Due to the pressure on the head  15  exerted as seen from the first end  2 , the slotted head  15  is on the one hand connected or clamped to the shank  14 , preventing movement, and at the same time the head is locked in its rotational position. 
     The second embodiment shown in FIG. 3 differs from the embodiment described above in a modified head  31 . The latter comprises, as in the first embodiment, notches  28  which are offset from each other in the circumferential direction and which end free at the edge  34  facing away from the first end and are at a distance from the edge  32  facing towards the first end  2 . However, a notch  33  which extends fully from the edge  32  to the opposite edge  34  is provided, with the result that the spherical segment formed in this way can be compressed by an amount defined by the width of the notch  33 . The width of the slot  33  formed in this way is selected so that the head  31  first of all can be compressed to such an extent that it can be pressed in the direction shown in FIG. 3 from the second end  2  into the first bore  5  and that then the shank  14  can be inserted in the head in the same way as described above and in the same way is held in the clamped position. 
     The shank  14  of the screw preferably has the cylindrical shape shown in FIGS. 4 and 5 or a polygonal shape shown in FIGS. 6 and 7. In the latter the cross section is octagonal. A further preferred embodiment is shown in FIG.  8 . The shank is cylindrical here and comprises a rough surface which facilitates engagement between sphere  15  and shank. 
     The further embodiment shown in FIG. 9 corresponds to the preceding practical examples in all characteristics concerning the receiving portion  1 , the pressure element  17 , the rod  19  and the screws  22  and  25 . The only difference lies in that the head  15  is designed as a spherical segment which in its external dimensions corresponds to the two preceding spherical segments, but has no notches  28  or  33 . Instead, the spherical segment has an internal thread on the inside of its bore  27 . Instead of the shank  14 , there is provided a shank  35  with a thread which is designed to mate with the internal thread of the head. The bore is designed as a blind bore which ends at the end facing towards the free end  2  or comprises a stop there, so that the screw can be screwed only so far into the position shown in which it does not protrude from the spherical segment on its flattened side. As shown in FIG. 9, the internal thread of the head  15  and the corresponding external thread of the shank  35  are formed in the direction preferably opposite the direction of the thread of the threaded section  13  of the bone screw. 
     Operation takes place in the same manner as in the practical example described first, wherein after shortening of the shank  35  the head  15  is introduced into the bore  5  from the first end  2  of the receiving portion  1  and screwed onto the shank  35  introduced from the second end  3 . 
     The further embodiment shown in FIGS. 10 and 11 corresponds to the preceding practical examples in all characteristics concerning the receiving portion  1 , the pressure element  17 , the rod  19  and the screws  22  and  25 . Instead of the shank  35  and the head  15  of the embodiment according to FIG. 9, which comprises the cooperating threads, in this embodiment the shank  37  is designed as a corrugated rod in a section adjoining the end opposite the bone threaded section. The outer surface of the shank comprises valleys  38  running in the circumferential direction and ridges  39  in between them. The valleys  38  have, seen in the circumferential direction, a circle segment-shaped cross-section and their diameter halfway up or down is much larger than the corresponding diameter of the crest  39 , so that the crests  39  are pointed in relation to the bottom of the valleys  38 . The head  15  is designed as a spherical segment which in its external dimensions corresponds to the spherical segments mentioned above, but which has no notches  28  or  33 . On the inside of its bore  27 , the spherical segment of the head  15  comprises corrugations running in the circumferential direction with valleys  40  and ridges  41  which correspond to the ridges  39  and valleys  38  of the shank  37  respectively. Between the valleys  38  and the ridges  39  of the shank on the one hand and the corresponding ridges  40  and valleys  41  on the other hand is a small gap, so that the shank can be introduced into the spherical segment. 
     Operation takes place in a similar manner to the practical example according to FIG.  9 . Shortening of the corrugated shank  37  is however easier in this embodiment than shortening of the shank  35  with the thread according to FIG. 9, as the valleys  38  allow easy cutting off, whereas with the shank  35  with the thread according to FIG.  9  care must be taken that the thread is not destroyed. After shortening of the shank  37 , the head  15  is introduced into the bore  5  from the first end  2  of the receiving portion  1  and pressed onto the shank  37 . In the process the corrugations of the shank  37  and the corresponding ones of the bore  27  of the head  15  cooperate, so that the shank is held. 
     In the practical examples described above, the head  15  is in each case held by an edge designed in one piece with the receiving portion  1 . Such an abutment can also be formed in another way: for example, it is possible to drill the first bore  5  completely through the receiving portion  1  and then, adjoining the second end, to mount in it a holding element which receives the head  15 . 
     In the practical examples described above, the receiving portion always comprises the nut  22  and an internal nut  25  as well as a bush  26 . This fixing can also be designed differently in a known manner. In particular, if occasion arises only an internal nut can be provided. 
     In the practical example described above with reference to FIG. 9, the head  15  has no notches  28 ,  33 . In a further embodiment, head  15  and shank  35  have, as in the view shown in FIG. 9, threads mating with each other. The head  15  however comprises in addition the notch  33  extending over the whole length so that, as in the embodiment shown in FIG. 3, the head without the shank screwed in can be inserted in the receiving portion from the edge  3  by compression and then fitted on the shank  35  which can also be introduced from the end  3 , by screwing in, and connected to the shank  35 . As a result of the slot, when the pressure elements are applied or when the pressure is exerted on the head  15 , at the same time the head and the shank  35  are compressed more firmly than without such a slot. 
     In a further embodiment, notches  28  can be provided additionally in the manner shown in FIG. 3, in order thus to cause even greater contact pressure with the threaded shank  35 .