Abstract:
A telescopic strut for use with an external fixator comprising an axially extending rod; an axially extending tube moveably recurring the rod for varying the length of the rod and tube combination along a longitudinal axis; the tube having first and second ends, the second end having a pin extending therethrough; a locking system mounted on the tube first end for adjusting the position of the rod in the tube and fixing the length of the rod and tube combination; a coupling element having a tubular sleeve with a threaded outer surface mounted on an outer surface of the second end of the tube, the sleeve having two diametrically opposed slots receiving the pin and an adjustment element threadably mounted on the sleeve outer surface for axial movement along the axis, the adjustment element having a surface contacting the pin to limit the movement of the pin in the slots.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 14/549,949, filed on Nov. 21, 2014, which is a continuation of U.S. patent application Ser. No. 13/589,624 filed on Aug. 20, 2012 and issued as U.S. Pat. No. 8,906,021, the disclosures of which are both hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a telescopic strut for an external fixator, especially for use with an external ring fixator. 
         [0003]    A plurality of compression-distraction apparatus have been designed and improved by Ilizarov and his group using two external rings to be placed around the limb to be fixed. There are usually at least two such rings, one proximal and one distal ring, which are connected with a plurality of struts or rods. Preferably, these struts are linked to the rings in a way that the attachment points can be pivoted and the length of the strut can be varied to enable adjustment of the external fixation rings. 
         [0004]    Ilizarov has also provided some improvements for said systems. European Patent No. 0 377 744 shows a telescopic strut for such an external fixator. U.S. Pat. No. 4,615,338 shows a further device to control the length of such telescopic struts. 
         [0005]    A different external ring fixator having telescopic struts is shown in U.S. Pat. Nos. 5,702,389 and 6,030,386. Other telescopic struts are shown in U.S. Pat. Nos. 8,057,474 and 8,062,293 assigned to the assignee of the present invention, the disclosures of which are incorporated herein by reference. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    However, these devices, which can be used to shorten or lengthen the telescopic struts, are difficult to adjust and it is one aspect of the invention to improve the ease of adjusting the length of the rod. Furthermore, a simple method of length adjustment and dynamization for each strut is desired. 
         [0007]    Based on the prior art, it is therefore an aspect of the invention to provide a telescopic strut, which can be readily and quickly changed in its length. 
         [0008]    It is another aspect of the invention, to allow, as an alternative, fine adjustments of the struts. 
         [0009]    In view of the above mentioned aspect it is furthermore another aspect of the invention to allow a quick switch between the two functions, i.e., to allow a quick first definition of the length of the telescopic element, and additionally, to switch for a fine adjustment of said length. 
         [0010]    It is yet another aspect to provide a variable dynamization function to the strut which allows micro-motion at a fracture/fusion site to promote healing. 
         [0011]    A telescopic strut of the present invention for use with an external fixator includes an axially extending rod having a series of circumferential grooves on an outer surface of the rod; an axially extending tube is provided for receiving the rod. The tube has a first end including a plurality of holes formed in a wall of the tube and a second end having a pin extending therethrough. A plurality of balls are provided for extending through the holes in the first end of the tube. A sleeve having an eccentric bore therethrough is mounted around the tube first end for contacting the balls. The eccentric bore has a major diameter allowing the balls to be located outside the grooves of the rod and a minor diameter causing the balls to be held within the grooves on the rod. A coupling element comprising a hollow tubular member is slidably mounted on an outer surface of the tube second end, the coupling element tubular member has two axially extending diametrically opposed slots for receiving the pin and an adjustment element is mounted on an outer surface of the coupling element tubular member for movement thereon in the axial direction. The adjustment member serves as a stop to limit the travel of the pin in the two slots. The adjustment member may be threaded and mounted on a mating thread on the coupling element tubular member. 
         [0012]    A detent may be provided for holding the sleeve in a first position where the major diameter engages the balls or a second position where the minor diameter engages the balls. The means includes a spring biasing the sleeve towards the second position. 
         [0013]    The grooves in the rod may be formed by a helical thread extending along the axial extent thereof so that rotation of the rod with the balls engaged lengthens the strut. 
         [0014]    Alternately the grooves may be formed by a plurality of radial ridges. 
         [0015]    Preferably the balls are at least partially retained within the holes of the leading end when contacted by the minor diameter of the sleeve. 
         [0016]    A telescopic strut of the present invention for use with an external fixator may also comprise an axially extending rod, an axially extending tube moveably receiving the rod for varying the length of the rod and tube combination along a longitudinal axis. The tube has first and second ends, the second end having a pin extending therethrough. An adjustment system is mounted on the tube first end for adjusting the position of the rod in the tube. A connector element is provided having a tubular sleeve with a threaded outer surface mounted on an outer surface of the second end of the tube. The connector element can include a ball joint which can be locked when the connector is fixed in a hole in a ring of an external fixation frame. The sleeve has two axially extending diametrically opposed slots for receiving the pin and an adjustment element threadably mounted on a threaded portion of the tubular sleeve outer surface for axial movement along the axis. The adjustment element has an annular surface contacting the pin to limit the movement of the pin in the slots. 
         [0017]    The rod is threaded and is mounted in the end of the tube such that relative rotation therebetween causes a length variation of the rod and tube combination along the longitudinal axis. 
         [0018]    The adjustment system may include radially moveable elements which selectively engage and disengage the threaded rod to allow axial sliding when disengaged and fine adjustment by the relative rotation of the tube and rod when engaged to vary the strut length. 
         [0019]    The tubular sleeve is coupled to an opening in an external fixation ring by releasable connectors which allow rotation of the sleeve and tube about the axis of the rod and tube to vary the axial length of rod and tube when the radially moveable elements are engaged. 
         [0020]    The two slots in the connector sleeve each have a first end and the adjustment element can move the pin into contact with the slot first end to prevent the pin from moving in the two slots. The sleeve outer surface includes markings showing the distance between the slot first end and the pin wherein the markings are in 1 mm increments. 
         [0021]    The pin may include a pair of protruding ends for receiving a tool for rotating the tubular sleeve and tube relative to the rod for varying the length of the strut. 
         [0022]    An additional telescoping strut of the present invention for an external fixator comprises a threaded rod, a tube threadably receiving the rod with the tube and rod extending along a longitudinal axis. The tube has a first end with a pin extending therethrough. An adjustment element is provided for fixing the relative axial position of the tube and rod; and a dynamization system mounted on the first end of the tube, the system comprising a sleeve slidably mounted on the tube with the pin extending through a pair of diametrically opposed slots on the sleeve such that the pin can move in the axial direction with respect to the slots; an adjustable stop element mounted on the sleeve movable to limit the level of the pin in the slots. The adjustable stop element is a nut mounted on a threaded outer surface of the sleeve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The invention is now described with reference to the enclosed drawings, showing preferred embodiments of the telescopic strut: 
           [0024]      FIG. 1  is an elevation view of a telescopic strut according to the invention; 
           [0025]      FIG. 2  is an exploded view of the length adjusting portion of the telescopic strut according to  FIG. 1 ; 
           [0026]      FIG. 3  is a side view in cross-section of the telescopic strut according to  FIG. 1 ; 
           [0027]      FIG. 4  is a cross section of the rod along line- 4  in  FIG. 3 ; 
           [0028]      FIG. 5  is an elevation view of the coupling element connected to the threaded rod of the strut for coupling the strut to a ring of an external fixation system; 
           [0029]      FIG. 6  is a cross-sectional view of the connector of  FIG. 5 ; 
           [0030]      FIG. 7  is an elevation view of a coupling element connected to the tubular portion of the strut of the present invention for connecting the strut to a second ring element of an external fixation system; 
           [0031]      FIG. 8  is a cross-sectional view of the connection element of  FIG. 7 ; 
           [0032]      FIG. 9  shows an adjustment wrench for adjusting the dynamization of the strut of the present invention; 
           [0033]      FIG. 10  shows the same adjustment wrench adjusting the length of the strut of the present invention; and 
           [0034]      FIG. 11  is an isometric view of the wrench shown in  FIGS. 9 and 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    Referring to  FIG. 1  there is shown a perspective view of a telescopic strut according to the invention generally denoted as  10 . The telescopic strut comprises two free ends  11  and  12 , which include coupling elements  100  and  200  being attachment points for connecting the strut to two external rings to be placed around the limb to be treated. The attachment coupling elements  100  and  200  according to this embodiment preferably comprise ball joints as will be discussed below, but this entirely depends on the kind of fixation element for which the rod is used. 
         [0036]      FIG. 1  shows the main components of the telescopic strut. There is an outer tube tubular element  21  having a bore in which the threaded rod  22  is partially located. Tube  21  has a bore therein for receiving rod  22  the bore can be only partially through tubular element  21  leaving a solid end adjacent coupling  200 . The outer tube  21  has mating thread elements  30  for engaging threaded rod  222  which is located within a sleeve  23  at an end of tubular element  21  and are better seen in  FIG. 2  as well as  FIG. 3  and will be described below. In the preferred embodiment sleeve  23  comprises a bayonet groove  24  for a quick change between the desired quick length change mode and the fine adjustment mode. The sleeve  23  can be switched between two rotational positions for this, i.e., to lock and unlock movement the axial direction. Therefore the groove  24  has a U-form, the ends of the groove  24  defining the two positions with the help of a bolt  26  provided within the groove  24 . The recessed ends  24   a  and  24   b  of the groove  24  are oriented in axial direction of the telescopic strut. These ends face in the same direction, towards the spring  27 , as can be seen in  FIG. 1  and the exploded view of  FIG. 2 , to allow displacement of the bolt  26  against the force of spring  27 . 
         [0037]    A security mechanism, to avoid unintentional switching, is realized by an additional nut  25 , blocking the bolt  26  in one of the free ends of groove  24 . 
         [0038]      FIG. 3  shows a view in cross-section of the telescopic strut according to  FIG. 1 . Sleeve  23  can be pushed against action of spring  27  provided on the outer tube  21  and which spring is biased with help of nut  25 . Then the sleeve  23  is turned around 90° and is arrested within the other free end  24   a  or  24   b  of the groove  24 . It is preferred that this position is fixed through nut  25 . 
         [0039]    The turning angle of 90 degrees is defined in view of the way the quick length adjustment mode is working. This can be seen in  FIG. 4  being a representation of a cross section of the rod along line  4 - 4  in  FIG. 3 . It can be seen from  FIG. 4  that the sleeve  23  has a non-cylindrical inner bore. The bore can be, e.g., elliptical. The shorter diameter of the bore is sufficient to accommodate the outer diameter of the foremost portion  25   a  of outer tube  21  shown in  FIG. 2 , which is cylindrical. Foremost portion  25   a  comprises on both sides a plurality of preferably, four holes  38  to accommodate one ball  28  each. Of course, it is also possible to provide only two balls on each side or five or more. Three or four balls have been proven to be sufficient without lengthening the sleeve  23  too much. 
         [0040]    The inner diameter of outer tube  21  is greater than the outer thread portion of the rod  22  which is cylindrical. Therefore, the rod  22  can be pushed into the outer tube  21 , when the bolt  26  is in a position which allows the sleeve  32  to be oriented as shown in  FIG. 4 . Then the balls  28  can freely move against the inner wall of sleeve  23  and the rod  22  can be axially pushed. For that the sum of the outer diameter of the rod  22  and twice the diameter of the balls  28  is less or nearly equal to the inner diameter of the sleeve  23 . 
         [0041]    Separation of the threaded rod  22  from the outer tube  21  is prevented through an abutment screw  29  which is screwed into a corresponding thread within the threaded rod  22  and which can abut on a corresponding shoulder within the tube  21  as shown in  FIG. 3   
         [0042]    By turning the sleeve  23  around the bolt  26 , i.e., by 90°, the balls  28  will be moved because of the elliptic inner shape within the sleeve  23 . In this way the balls  28  are pushed through holes  38  towards the grooves of the thread  22  for interlocking, i.e., connecting the thread with the outer tube  21 , because the balls  28  stand within both parts and leave no room to allow a direct axial movement of the threaded rod  22 . 
         [0043]    In this position the threaded rod  22  still can be moved axially through rotational movement of tube  21  being directly coupled via bolt  26  to sleeve  23  against the threaded rod  22  which can rotate in view of the balls  28  pressed in its threads. This allows for the fine adjustment. 
         [0044]    Thus the elements allow for a quick change between free axial adjustment of the telescopic strut, if the balls  28  do not engage the threaded rod  22 . If the balls do engage rod  22  then a fine adjustment through rotation of the outer tube  21 /rod  22  is allowed. The balls  28  are engaging the one or subsequent grooves of the threaded rod  22 , e.g., depending on the pitch of thread of the rod  22 . The pitch angle of the thread can be chosen, e.g., between 30 and 60 degrees and especially between 40 and 50 degrees. 
         [0045]    It is clear that this fine adjustment is only possible, if at least one free end  11  or  12  of the telescopic strut can be rotated while fixed within an external fixator ring. 
         [0046]    Within another embodiment (not shown) a helically threaded rod is replaced by a rod having a plurality of radial grooves. Each of these grooves has dimensions to accommodate one of the balls  28 . In other words, the threaded rod having a groove providing a pitch is replaced by a sequence of separated adjacent radial grooves. It is thus possible to use such a rod with a flank lead to block the device in a plurality of positions. However, with radial grooves it is not possible to allow a fine tuning through rotation of tube  21 . 
         [0047]    Referring to  FIGS. 5 and 6 , there is shown a first coupling element adapted to engage a bore in a ring of an external fixation system. Typically the rings of an external fixation system are circular or part circular and have a plurality of through holes located between inner and outer diameters of the rings.  FIGS. 5 and 6  show first coupling element  100 , including a shaft  102  with a threaded portion  104  and a pivoting tubular end portion  106  adapted to thread on an end of rod  22  of strut  10 . As can be seen in cross-sectional view  FIG. 6 , the inner bore  108  of end  106  includes threads  110  adapted to be screwed onto the end of rod  22 . Pivot end  106  includes an end portion  112  having an outer part-spherical surface  114  and an inner part spherical surface  116 . Outer part-spherical surface  114  may include roughened areas or ridges  118  so that it may be locked against a part spherical recess  120  on shaft portion  102  when the assembly is tightened. Pivot portion  106  is coupled to shaft portion  102  via a threaded nut  122  having a part spherical surface  124  adapted to engage inner part spherical surface  116  of pivot end  106 . Nut  122  includes a threaded inner bore diameter  126 . Nut  122  also includes a generally cylindrical leading end  128 , which slidably engages a bore  130  within shaft  102 . Shaft  102  includes a further bore portion  132  for receiving a screw  134 , which bore has a smaller diameter than bore portion  130  so that leading end  128  of nut portion  122  may slidably engage the larger diameter bore  130  and still receive a threaded shaft  133  of a screw or tightening element  134  mounted in bore portion  132 . Bore portions  130 ,  132  and shaft  133  extend along an axis  140 . Screw element  134  may be threaded into the threaded bore  126  of nut  122  via an outer threaded portion  136  thereon. Tightening element  134  includes a drive head  138 , which may be square or hexagonal so that a tool may be applied to rotate element  134  thereby moving surface  124  of nut  122  into tight engagement with inner surface  116  of pivot end  106 . Portion  112  of pivot element  106  may have two or more longitudinal slits therein so that it may flex outwardly into engagement with part-spherical surface  120  upon movement of nut  122  toward surface  116  resulting from rotation of threaded tightening element or screw  134 . 
         [0048]    In use threaded portion  104  of coupling  100  is inserted through a hole in the external fixation system ring (not shown) and a nut is threaded onto thread  104  of shaft  102  to attach coupling element  100  to the ring. When this is done axis  140  of end  102  is co-axial with a central axis of the bore in the ring. When the end of rod  22  is threaded into pivot end  106 , it can be selectively locked in position or rotated about the ball joint in any direction about axis  140  of coupling  100  on part-spherical surfaces  114  and  120  depending on whether screw element  134  and nut  122  are either in a loosened position or a tightened down position. When tightened roughened surface  118  engages inner surface  116  which ensures no movement of rod  22  with respect to the axis  140  of the hole in the ring and of portion  102 . 
         [0049]    Referring to  FIGS. 7 and 8 , a second coupling element  200  is shown. Coupling element  200  includes many of the features of coupling  100 , including a shaft  102   a  with a threaded portion  104   a . Likewise, a screw  134   a  with drive head  138   a  is coupled to a nut  122   a  having the part spherical outer surface  124   a . Also likewise, the coupling element  200  includes a pivoting tubular end portion  106   a  extending along an axis  203 , which has a leading end  112   a  with part spherical surface  114   a  for contacting an inner surface  120   a  of element  102   a . Tubular end  106   a  is slidably mounted on end  21   a  of shaft  21 . End portion  106   a  includes a hollow end portion  108   a  fixedly receiving shaft  21  or an extension thereof such that pivot end portion  106   a  and shaft  21  cannot rotate relative to one another. Portion  106   a  now includes a threaded outer portion  202  upon which a rotatable internally threaded nut  204  is mounted. Rotation of nut  204  on threaded portion  202  moves the nut  204  along axis  203  either away from or toward end  108   a  and shaft  21 . An O-ring  206  is mounted in a groove  208  within nut  204  to hold nut  204  in a particular axial location upon rotation of nut  204  on threaded portion  202 . Tubular element  106   a  further includes a pair of slots  210  diametrically opposite one another in a wall of tubular element  106   a . Shaft portion  21  includes a pin  212  extending therethrough which pin  212  is fixed to the end of shaft  21  such as by a press fit. Upon assembly, pin  212  extends through both slots  210  in  106   a  and extends outwardly beyond the outer surface on each side of tubular member  106   a , a distance preferably approximately equal to the diameter of nut  204 . Since tubular end portion  106   a  is slidable on end  21   a  of shaft  21  the engagement of slot  210  and pin  212  hold the tubular end portion  106   a  on end  21   a . As will be discussed below, the engagement of end surface  214  of nut  204  with pin  212  as it moves within slot  210 , provides for dynamization within the strut  10  by allowing the surgeon to set a dynamization distance of, for example, 0 mm to 5 mm by rotation of nut  204 . This distance would be set by rotating nut  204  on thread  202 . Typically, 1 mm spaced markings placed on the outer surface of tubular element  106   a  would indicate the distance. 
         [0050]    In use, the telescopic strut would be used as described above and in U.S. Pat. No. 8,057,474, the teachings of which are hereby incorporated by reference, with the exception of the dynamization system discussed above. The surgeon connects strut  10  with coupling elements  100  and  200  to respective first and second external fixation frame members such as rings or plates with the threadable elements  134 ,  134   a  loosened so that the part-spherical ball joints are free to rotate. The surgeon adjusts the length of the strut initially using the quick length adjustment mode and then the fine adjustment mode until the fractured bones are in the desired alignment. At this point, the screws  134 ,  134   a  are both tightened thereby locking the strut in the desired angular and length position with respect to both the first and second ring members. A further finer adjustment is needed then one of the ball joints must be loosened by rotating a screw  134   a  which allows for rotating the tubular shaft  21  or rod  22 . Preferably the ball joint  200  is loosened by rotating screw  134   a . The surgeon then sets the dynamization system by rotating nut  204 . If no dynamization is required surface  214  of nut  204  is placed against pin  212 . Obviously multiple struts  10  may be used in the frame system. 
         [0051]    Referring to  FIGS. 9-11 , there is shown the use of a wrench  300  used to both make the fine adjustments of the length of strut  10 , as well as set the dynamization distance between pin  212  and surface  214  of nut  204 . Wrench  300  includes a first end  302  with a curved opening  304  defining first lobe  306 , second lobe  308 , and third lobe  310  adapted to respectively engage one of a plurality of grooves  215  on the outside of nut  204 . As seen in  FIG. 9 , lobes  306 ,  308 , and  310  engage three different grooves  215 . Thus rotation of wrench  300  can move nut  204  on thread  202  either toward or away from pin  212 . Tubular member  106   a  includes a series of markings  217  either cut or etched into the outer surface of tubular element  106   a  at 1 mm increments. Thus, the surgeon can set the dynamization by turning nut  204  thereby moving surface  214  with respect to pin  212 . Preferably markings  217  are spaced 1 mm so that the exact amount of dynamization can be determined by counting the number of markings  217  between surface  214  and the under surface of pin  212 . 
         [0052]    Wrench  300  has a second end  320  with a pair of hook shaped elements  322  and  324 , which each include a U-shaped recessed opening  326 , which receives the ends of pin  212  which extend beyond the outer surface of tubular element  106   s . As shown in  FIG. 10 , when end  320  is hooked over both ends of pin  212 , wrench  320  can be used to rotate shaft  21 . End  21   a  is slidably mounted within tubular element  106   a  however rotation of end  21   a  via pin  212  rotates tubular portion  106   a  via the engagement of pin  212  and slot  210  thus providing fine tuning of the length of strut  10 . As discussed above, in order to accomplish this, the ball joint within coupling element  200  must be released by appropriately turning screw  134   a . Once the correct length is achieved, the ball joint is again locked via rotation of screw  134   a . Locking end  112   a  of sleeve  106   a  against surface  120   a  via threaded element  134   a  prevents rotation of shaft  21  about any axis 
         [0053]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.