Abstract:
The invention relates to an adjustable length fixation device having a head slidable along the shaft of the fixation device. The head is larger than the shaft and prevents further distal migration of the shaft and may preferably include an external surface for engaging bone to prevent proximal migration of the shaft. The head includes an engagement portion which may be deformed to securely engage the shaft to prevent removal of the head from the shaft. The invention also contemplates a method of insertion which includes inserting the shaft into the bone, sliding the head along the shaft and into engagement with the bone, securely engaging the head to the shaft, and severing the shaft proximal of the head to thereby form a fastener of the required length.

Description:
REFERENCE TO RELATED APPLICATION 
     This is a divisional application of U.S. patent application Ser. No. 09/070,332 filed Apr. 30, 1998 is now U.S. Pat. No. 6,019,762. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to surgical devices for fixation of two or more segments of tissue, and more particularly to a fixation device useful for securing two or more segments of bone in a desired spatial relation. 
     The use of both internal and external fixation devices to prevent major movement between two or more sections of bone is well known in the art. External casts and braces have commonly been employed to prevent movement between larger bone segments, and have been particularly useful in the fixation of long bone fractures in the extremities. For small bone segments and bones within the trunk of the body which may not be readily immobilized by braces and casts; plates, screws, nails, and wires have been implanted to maintain the relative position of these bones during the healing process. In some instances, a single screw with a uniform shaft is screwed between two bone segments to maintain these in place. Alternatively, a pinning device such as a nail may be driven into both of the bone segments to create fixation. In other applications, a lag screw is utilized with a first threaded portion passed through a first bone segment and threaded into a second segment of bone. A nut is then threaded onto a second machine threaded portion of the lag screw to reduce the fracture between the two bone fragments. Alternatively, a similar type of lag screw may be utilized in conjunction with a plate. Each of a series of lag screws is inserted into bone fragments and a plate is attached across the machine threaded portion of the lag screw. A nut is threaded onto each screw thereby attaching the plate to the bone and maintaining the spatial relationship of the bone fragments. 
     For smaller bones and bone fragments, small wires, commonly known as Kirschner wires (K-wires), have been inserted into the bone to immobilize the fragments. After the wires are inserted, the proximal section of the wire is cut to the desired length. While these devices have been generally successful, at least initially, in accomplishing the desired immobilization, there are a number of problems which have been encountered with their use. Specifically, it has been found that in some instances, the fixation wire can migrate from the point of its initial insertion leading to loss of fracture fixation or damage to surrounding bodily structures, such as nerves or blood vessels adjacent the entry or exit site of the wire. Moreover, cutting the wire can result in a wire end that may be sharp, leading to possible tissue irritation adjacent the wire. In an effort to limit migration of the wire, the cut end may be bent over or left protruding from the skin, also leading to possible tissue irritation and/or infection. Additionally, if the wire is trimmed too close to the bone and the wire migrates inward, the end could be lost well within the bone surface, making it impossible to retrieve without damaging the surrounding bone structure. Thus, there remains a need for an orthopedic fixation device having the beneficial affects of the above-referenced devices but offering ease of insertion, patient comfort after insertion, reduced chances for infection, and the ability to withdraw the device after a desired time period. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an adjustable length fixation device comprising an elongated shaft and a head fixable to the shaft. The head includes an internal channel with an engaging portion movable between a first position and a second position. When the engaging portion is in the first position, the internal channel defines a first configuration adapted to slidingly receive the elongated shaft. When the engageable portion is in a second position, the internal channel defines a second configuration adapted to prevent movement of the head along the elongated shaft. 
     The present invention also contemplates a method for fixing two tissue segments. The method comprises providing an elongated shaft having a proximal end and a distal end, and a head having a channel for slidably receiving the elongated shaft. The elongated shaft distal end is inserted through a first tissue segment and into a second tissue segment. The head is positioned about the proximal end of the shaft and slidingly advanced along the shaft toward its distal end. The head is positioned adjacent the first tissue segment and locked to the shaft. 
     An apparatus according to the present invention further contemplates an instrument for removing a head from an adjustable length fixation device. The removal instrument comprises an outer member having a longitudinal axis and defining a longitudinally extending internal channel. The internal channel includes an anvil surface. An inner tube is sized to be received within the internal channel and includes a longitudinally extending cutting blade. The blade is disposed adjacent the anvil and upon rotation of the inner member in relation to the outer member, the blade is urged toward the anvil to cut a head disposed between the blade and anvil. 
     The present invention further contemplates an orthopedic fixation system including a plate in combination with an adjustable length fixation device according to the present invention. A fixation plate having at least one aperture, may be placed along the tissue to be fixed. An elongated shaft may extend through the aperture in the plate and into the tissue to be fixed. A head having an outer surface for engagement with the plate and an internal channel, is positioned on the shaft with the shaft extending through the internal channel. The head may then slide along the shaft until it engages the plate and is fixed in position to engage the plate and the shaft. In one preferred embodiment, the head includes a series of external threads to mate with a similar internal thread pattern in the plate. In another preferred embodiment, the aperture of the plate includes at least a partially spheroidal surface which is engaged by a corresponding surface on the head to permit non-perpendicular orientation of the shaft with respect to the plate. 
     One object of the present invention is to provide an adjustable fixation device. Another object of the present invention is to provide a K-wire fixation device with a head slidable along the shaft. A further object of the present invention is to provide a method for fixation of two or more bone segments with an elongated shaft and an adjustable head. Yet a further object of the invention is to provide a plate and adjustable length fixation device, the fixation device having angular freedom of movement with respect to an opening in the plate. Still a further object is the provision of an instrument to remove a head locked to a shaft according to the present invention. These and other objects of the present invention will become apparent to those skilled in the art, based on the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the adjustable length fixation device in accordance with the present invention. 
     FIG. 2 is a top view of the fixation device of FIG.  1 . 
     FIG. 3 is a partial cross-sectional view showing insertion of the fixation device of FIG.  1 . 
     FIG. 4 is a partial end view of an insertion device. 
     FIG. 5 is a partial side view of the insertion device of FIG.  4 . 
     FIG. 6 is a cross-sectional view of the device of FIG. 1 surrounded by a crimping device. 
     FIG. 7 is a cross-sectional view showing the crimping device engaging the fixation device of FIG.  1 . 
     FIG. 8 is a cross-sectional view of the fixation device of FIG. 1 after crimping. 
     FIG. 9 is a side view of the fixation device of FIG. 1 after crimping and cutting. 
     FIG. 10 is a top view of the device of FIG.  9 . 
     FIG. 11 is an end view of a socket of a removal tool. 
     FIG. 12 is a partial side view of the socket of FIG.  11 . 
     FIG. 13 is a side view of an alternative embodiment of a head according to the present invention. 
     FIG. 14 is a top view of the head of FIG.  13 . 
     FIG.  15 ( a ) is a cross-sectional end view of a head removal instrument according to the present invention. 
     FIG.  15 ( b ) is an end view of the removal instrument of FIG.  15 ( a ) with the cutting blade engaging the head. 
     FIG. 16 is a partial cross-sectional view showing insertion of a fixation system in accordance with the present invention. 
     FIG.  17 ( a ) is a partial cross-sectional view of a head in engagement with a plate. 
     FIG.  17 ( b ) is a partial cross-sectional view of an alternative embodiment of a head in engagement with a plate. 
     FIG. 18 is a partial cross-sectional view of a further embodiment of a head in engagement with a plate. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated devices, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     An adjustable length fixation device according to the present invention, is shown in FIG.  1 . The fixation device includes an elongated shaft  10  having a proximal end  18  and a distal end  16 . Adjacent distal end  16  is externally threaded portion  14 . Elongated shaft  10  has a diameter  20  which extends over substantially the entire length of the elongated shaft. While the present invention is shown having a uniform diameter along the entire length of the elongated shaft  10 , it is contemplated that the shaft could include varying diameters depending on the application in the body and the tool used to drive the shaft into position. In the preferred embodiment, elongated shaft  10  includes a longitudinal axis  22  which extends from the proximal end to the distal end. 
     In the embodiment of FIG. 1, threaded area  14  is shown having a diameter less than or equal to the diameter  20  of the entire shaft. Although this is shown in a preferred embodiment, it should be understood that the shaft may have a bayonet point, a trocar point, or a threaded portion  14  formed such that the threads have a diameter greater than diameter  20 . Moreover, while threads are shown as a bone engaging surface on shaft  10 , it is contemplated that the shaft may be smooth or utilize other bone engaging surfaces, such as ridges, knurling, barbs, etc. Additionally, the bone engaging surface could extend over a much longer segment of elongated shaft  10 . 
     Referring now to FIGS. 1 and 2, there is shown a fixation device head  30  in accordance with the present invention. In a preferred embodiment of the present invention, head  30  is a ferrule including a series of external threads  32  adjacent distal end  34 . Threads  32  terminate adjacent distal end  34  in a taper  42 . Head  30  has a proximal end  44  with a taper  38  connected to the threads  32  by a crimping zone  36 . In a preferred embodiment, crimping zone  36  is substantially cylindrical. However, it is contemplated that the crimping zone could be formed in a variety of shapes including, but not limited to, cylindrical, conical, triangular, rectangular, hexagonal, or any other geometric shape desired by the user. It will be understood that these shapes could be utilized by a driving tool to drive the head into the bone or for subsequent removal. In a preferred embodiment of head  30 , slots  40  are formed within tapered area  38  to receive a corresponding driving tool. A driving tool (FIG. 3) may engage slots  40  to thread head  30  into surrounding bone. An additional feature of the present invention, is that threads  32  of head  30  and threads  14  of shaft  10  have substantially identical pitches. Thus, once head  30  has been joined with shaft  10 , rotation of the shaft advances or withdraws the head and shaft in unison. While the use of substantially identical thread pitches is shown in a preferred embodiment, it is contemplated that the pitch of the threads adjacent the head and those adjacent the distal end of the shaft could be formed such that threads have different pitches. With threads of different pitches, rotation of shaft  10  with head  30  fixed thereto, may tend to compress a fracture line. 
     Head  30  further includes a substantially cylindrical internal channel  46  having a diameter  48 . The diameter  48  is slightly larger than diameter  20  of shaft  10  to permit head  30  to slide freely along shaft  10 . Channel  46  includes a deformable portion within crimping zone  36 . It will be understood that diameter  48  may be altered by deforming the ferrule, particularly within crimping zone  36 . It will be understood that the crimping may deform the internal channel  48  from the substantially cylindrical shape shown, to an irregular shape engaging shaft  10 . The exterior surface of crimping zone  36  has a diameter  50 . The outermost diameter  52  of threads  32  is larger than the crimping zone diameter  50 . While this arrangement of diameters is shown in the preferred embodiment, it is contemplated that it may be desirable to have the diameter of crimping zone  36  larger than the diameter of threads  52  to prevent over insertion of the device into the bone. 
     Referring now to FIG. 3, a shaft  11  is shown inserted into a first bone fragment  60  and a second bone fragment  62  across fracture  64 . A head  31 , identical to head  30  of FIGS. 1 and 2, has been crimped to the proximal portion of shaft  11  and the proximal portion of shaft  11  removed. 
     Elongated shaft  10  is similarly shown inserted into first bone segment  60  and second bone segment  62  fracture  64 . An insertion tool  70  is shown engaging head  30 . Insertion tool  70  includes a cannula  80  adapted to receive shaft  10  along its entire length and allow the proximal end  19  of shaft  10  to extend beyond insertion tool  70 . Insertion tool  70  includes a handle  72  which may be gripped by the user to transmit both rotational and compressive force to head  30 . Insertion tool  70  has a driving end  74  adapted to engage proximal end  44  of head  30  to transmit rotational and compressive force to head  30 . Referring now to FIGS. 4 and 5, the driving end  74  of insertion tool  70  includes projection  76  sized to be received within slots  40  of head  30 . 
     Head  30  may be locked to shaft  10  by deforming at least a portion of the ferrule to engage shaft  10  and prevent movement of head  30  along shaft  10 . In a preferred embodiment of the present invention, crimping is performed by a longitudinally extending crimping tool  90  as disclosed in U.S. application Ser. No. 09/013,434, which is incorporated herein by reference. While the description of the preferred embodiment discloses use of a longitudinal crimping tool, use of conventional crimping tools is within the scope and spirit of the present invention. Moreover, although a portion of head  30  is shown as being moveable to a locked position by deformation, it is contemplated that other locking mechanisms on head  30  may be utilized to hold shaft  10 . 
     As shown in FIG. 6, longitudinal crimping tool  90  is positioned over shaft  10  and head  30 . Longitudinal crimping tool  90  includes an outer member  92  defining an interior channel  94 . Shaft  10  and head  30  are positioned within interior channel  94 . Additionally extending within interior channel  94  is an inner crimping member  96 . Inner crimping member  96  includes a crimping surface  100 . Outer member  90  includes a crimping surface  98  defined within inner channel  94 . Although both crimping surfaces  98  and  100  are shown as substantially planar, it is contemplated that the surfaces could be formed of other cooperating configurations to provide alternative crimping patterns. 
     Referring now to FIG. 7, inner member  96  is moved in relation to outer member  92  to force crimping surfaces  100  and  98  toward one another. Movement of inner member  96  and outer member  92  deforms at least a portion of head  30  and in a preferred embodiment, a portion of shaft  10 . In this manner, head  30  may lockingly engage shaft  10  to prevent further sliding movement along the longitudinal axis of shaft  10 . 
     Referring now to FIG. 8, head  30  now includes a first planar surface  102  and a second planar surface  104  on the crimping zone of the device above the threaded area  32 . Additionally, shaft  10  has been slightly deformed to create substantially planar surfaces  101  and  103  corresponding to surfaces  102  and  104 , respectively. It will be understood that engagement of surfaces  101  and  103  with head  30  permit rotational force applied to head  30  to be effectively transmitted to shaft  10 . Deformation of shaft  10  may be enhanced by forming the shaft of a softer material than the ferrule. A portion of slots  40  have now been deformed, thus inhibiting further use of insertion tool  70 . 
     Referring now to FIGS. 9 and 10, the interconnected head  30  and shaft  10  are cut within taper  38  to remove the proximally extending portion of head  30  and shaft  10 . As shown in FIG. 9, proximal end  44  of head  30  and the proximal end  18  of shaft  10  are now co-terminous and substantially co-planar. The head and shaft have been severed within taper  38  to provide a smoother transition at the proximal end to avoid tissue irritation that might be caused by a sharp corner. 
     Referring now to FIGS. 11 and 12, there is shown a removal socket  120  for engaging the crimped head  30  of FIG. 9 for additional driving or removal of the device. Socket  120  includes interior socket  128  defining planar surfaces  122  and  124  and arcuate surface  126 . It will be understood that socket  128  is sized to engage crimped head  30  with planar surfaces  124  and  122  engaging planar surfaces  102  and  104 , respectively. 
     Referring now to FIGS. 13 and 14, there is shown an alternative embodiment of a head  140 , according to the present invention. Head  140  includes a distal end  144  and a proximal end  142 . Adjacent distal end  144  are a series of graduated conical rings  146  adapted to engage surrounding bone upon insertion. Extending between rings  146  and proximal end  142  is a crimping and cutting zone  150 . The proximal end of rings  146  further includes a shoulder  152  which may be used by an insertion tool to apply force to head  140  to slide it along shaft  10  and urge head  140  into surrounding bone. 
     Referring now to FIG. 3, in operation, shaft  10  is inserted into a first bone segment  60  and a second bone segment  62  across fracture line  64 , such that threads  14  adjacent distal end  16  secure and engage at least a portion of the second bone segment  62 . In many applications, it is desirable that threads  14  engage at least a portion of the harder cortical bone  63  of bone segment  62 . Insertion of an elongated shaft in this manner is well known in the art and will not be further explained. With the proximal end  18  of shaft  10  extending well beyond the bone, head  30  is positioned over the proximal end  18  of shaft  10  and moved along the shaft towards distal end  16 . Insertion tool  70  is likewise passed over proximal end  18  of shaft  10  and advanced along the shaft  10  until it is adjacent head  30 . The driving end  74  of insertion tool  70  is then rotated until projection  76  is received in one of the slots  40 . Once projection  76  has been securely seated in a slot  40 , insertion tool  70  is rotated to advance threads  32  into the bone of first segment  62 . It will be understood that for most applications, threads  32  are adapted to engage the harder cortical bone  61 . Once head  30  has been inserted to the desired depth, insertion tool  70  is removed from shaft  10 . 
     With head  30  inserted into bone segment  62  as desired, head  30  is then joined to shaft  10 . In a preferred embodiment, a crimping tool is utilized to deform head  30  in crimping zone  36  to secure and engage shaft  10 . While a longitudinally extending crimping tool has been described in a preferred embodiment, it is contemplated that any type of crimping tool may be utilized to perform the desired engaging function. Moreover, in a preferred embodiment, the crimping tool creates at least two planar surfaces for subsequent engagement by a driving/removal socket  120  (FIGS.  11  and  12 ). Once head  30  has been securely locked to shaft  10 , a cutting device (not shown) is positioned adjacent tapered surface  38 . The cutting tool (not shown) is operated to sever a portion of head  30  and shaft  10  extending proximal of the engagement point. In the preferred embodiment, both a portion of head  30  and shaft  10  are cut to provide a substantially co-terminous and co-planar surface on the proximal end to limit tissue irritation surrounding the protruding head and shaft. While severing of both the head and the shaft is disclosed in the preferred embodiment, it is contemplated that it is within the scope and spirit of the invention that only the shaft may be severed. 
     As an alternate method, shaft  10  may be inserted into the bone until it approaches a final location. Head  30  may be locked to shaft  10  and the head and shaft combination driven into a final position as an integral unit. 
     The device of the present invention may be removed by use of a socket  120  (FIGS. 11 and 12) positioned over the proximal end  44  of head  30 . It will be understood that the planar surfaces  124  and  122  engage planar  102  and  104 , respectively, to transmit rotational force to the head which is also transmitted to the shaft by means of the crimping engagement, to rotate the head and shaft to remove the device from bone segments  62  and  64 . 
     Referring now to FIGS.  15 ( a ) and ( b ), there is shown an instrument for removing the head affixed to the shaft of an adjustable length fixation device according to the present invention. The removal instrument  200  includes an outer member  202  which defines an internal channel  203  that extends along longitudinal axis  215 . As with the crimping tool previously disclosed, the combination of an outer member and movable inner member is more fully disclosed in U.S. application Ser. No. 09/013,434 which is incorporated herein by reference. In this embodiment, outer member  202  further includes anvil surface  205  defined within internal channel  203 . Inner member  204  is disposed within internal channel  203  and extends along longitudinal axis  215  of outer member  202 . Inner member  204  defines a cutting blade  206  which extends longitudinally along at least a portion of the axis of inner member  204 . As shown in FIG.  15 ( b ), inner member  204  may be moved in a rotational manner about longitudinal axis  215  within internal channel  203  to urge cutting blade  206  toward anvil  205 . With shaft  210  and inner connected head  208  positioned adjacent anvil  205 , cutting blade  206  may be urged toward anvil  205  to penetrate head  208 , thereby cutting it away from shaft  210 . Once head  208  has been severed by cutting blade  206 , it may be more easily removed from the shaft for subsequent removal of the entire shaft. 
     Referring now to FIG. 16, there is shown an orthopedic fixation system according to the present invention. While the fixation system may have a number of uses, it is particularly useful in immobilizing small bone fragments and joining them to a plate. More specifically, the system includes a plate  310  having a number of apertures therethrough to receive bone engaging members. As shown in FIG. 16, bone screws  312  and  314  extend through apertures  332  and  334 , respectively, to engage the large bone segment  302 . It will be understood that the use of conventional screws through the plate provides a solid fixation point for the plate, permitting the portion extending over the plurality of smaller bone fragments to rely on the bone screw fixation for greater stability of the device. K-wires  316  and  320  are positioned through apertures  336  and  338 , respectively. K-wire  316  extends through bone segments  306 ,  302 , and  304 . K-wire  316  is joined to plate  310  by head  318 . In a similar manner, shaft  320  extends through aperture  338  and plate  310  and into bone segments  307 ,  306 , and  304 . Head  322  joins shaft  320  to plate  310 . In a similar manner, shafts  326  and  328  extend through apertures  340  and  252 , respectively, and into the bone framents, and the shafts  326  and  328  are joined to plate  310  by heads  324  and  330 , respectively. Tool  70 , further described with reference to FIG. 3, may be used to insert the heads. 
     Referring now to FIG.  17 ( a ), there is shown a partial cross-sectional view of plate  310  with internally threaded aperture  338 . Shaft  320  extends through aperture  338  and is interconnected to plate  310  by head  322 . Head  322  includes an externally threaded portion  327  which engages the internally threaded opening  336 . As previously described with other embodiments of this invention, head  322  may be joined to shaft  320  by deformation of the head in crimping area  325 . Referring now to FIG.  17 ( b ), shaft  316  extends through internally threaded aperture  336 . Head  318  joins shaft  316  to plate  310  by engagement of externally threaded portion  319  with internally threaded opening  336 . Head  318  includes an enlarged crimping area  321  having a diameter  323  larger than the minimum diameter  324  of opening  336 . Thus, movement of head  318  is limited by the enlarged crimping area  321  when shoulder  325  engages plate surface  337  adjacent opening  336 . 
     Referring now to FIG. 18, there is shown a plate and head combination permitting non-perpendicular alignment between shaft  408  and plate  402 . Specifically, plate  402  includes an opening  404  having a partially spheroidal surface  406 . In a similar fashion, head  409  includes a partially spheroidal portion  412  which extends into plate  402  and engages surface  406 . As with the previous embodiments, head  409  may be joined to shaft  408  by deformation of the crimping area  410 . As will be understood by those skilled in the art, engagement of portion  412  within opening  406  permits the longitudinal axis  422  of shaft  408  to extend in a variety of angular relations with respect to longitudinal axis  420  of plate  402 . In a perpendicular relationship, surface  414  is in alignment with the bottom surface of plate  402 . It will be understood that the combination of partially spheroidal opening  406  in plate  402  and partially spheroidal shaped body portion  412  on head  409 , enhances the uses of the plate since the fixation shaft  408  does not have to extend directly perpendicular to the plate surface. While these two structures are shown in a preferred embodiment, it is contemplated that other structures could be utilized either in the plate, in the head, or in a plate-head combination, to provide a plurality of angular relationships between shaft  408  and plate  402 . 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.