Abstract:
A bone distractor for distracting bone on opposite sides of an osteotomy of the bone. Included are a first affixation member for affixation to the bone on one side of the osteotomy and a second affixation member for affixation to the bone on another side of the osteotomy. A screw means has a rotatable member engaging the first and second affixation members for distracting the first and second affixation members relative to each other in response to rotation of the rotatable member. An extension member is removably connectable to the rotatable member of the screw means for imparting torque to the screw means when connected thereto and rotated. The extension member can be flexible to permit elastic bending while imparting torque.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of U.S. patent application Ser. No. 09/394,609 filed on Sep. 13, 1999, which is incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to apparatus for correction of craniofacial abnormalities, and more particularly to apparatus for affixation to maxillary or mandibular bones to effect distraction of the bones relative to a fracture or osteotomy.  
         BACKGROUND OF THE INVENTION  
         [0003]    Various developmental disorders of the human skull result in craniofacial abnormalities in which certain bones fail to grow in proper proportion to other bones, or in which certain bones fuse prematurely, causing malformation of the midface or mandible. It is known to correct such abnormalities by separating the bones through osteotomy or fracture, and then slowly distracting the bones relative to each other, thereby inducing bone growth at the separation line. As the bones are distracted, the newly formed bone at the growth surfaces adjacent the separation fills in the increasing gap between the bones. By this method, the midface of the cranium can be advanced forward, or the mandible can be lengthened, for example.  
           [0004]    Apparatus for effecting distraction can involve two affixation members, in which each affixation member is temporarily affixed to the bone on opposite sides of the osteotomy, such as by bone screws, and a screw drive member that threadedly engages at least one of the affixation members. By rotating the screw drive member incrementally and periodically, the two affixation members are driven apart, and hence the bones on either side of the osteotomy are distracted relative to the location of the osteotomy. Typically, after the desired amount of distraction is achieved and the new bone growth is sufficiently consolidated, the distraction apparatus is removed.  
           [0005]    While the distraction apparatus is in place, the screw drive member must be accessed periodically, typically via the oral cavity, so that a driver can be engaged with the screw drive member to apply torque thereto. Often the location and orientation of the distraction apparatus are such that access to the driven end of the screw drive member is difficult or awkward. To address this problem, universal joints have been used to permit alignment of the driving end of the driver with the driven end of the screw drive member of the distraction apparatus, while permitting the handle of the driver to be oriented at a convenient angle, often outside the oral cavity. Such universal joints can be bulky and do not always provide the desired degree of angular adjustment between the handle of the driver and the driving end of the driver.  
           [0006]    It would be advantageous to provide an improved distractor apparatus having a driven member that is more easily accessed by an external driver through the oral cavity. The present invention, an embodiment of which is described below with reference to the drawings, provides this and other advantages.  
         SUMMARY OF THE INVENTION  
         [0007]    In accordance with one aspect of the present invention, a bone distractor is provided for distracting bone on opposite sides of an osteotomy of the bone. The bone distractor includes a first affixation member for affixation to the bone on one side of the osteotomy, and a second affixation member for affixation to the bone on another side of the osteotomy. A screw means has a rotatable member that engages the first and second affixation members for distracting the first and second affixation members relative to each other in response to rotation of the rotatable member. An extension has means for removably connecting the extension to the rotatable member of the screw means and for imparting torque to the rotatable member when connected thereto and the extension is rotated.  
           [0008]    According to another aspect of the present invention, the extension includes a flexible shaft capable of bending elastically while imparting torque.  
           [0009]    It is an object of the present invention to provide an improved bone distractor that is readily accessible for incremental distraction while emplaced in a patient.  
           [0010]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0012]    [0012]FIG. 1 is a perspective view of a bone distractor in accordance with the present invention.  
         [0013]    [0013]FIG. 2 is a plan view of the bone distractor of FIG. 1.  
         [0014]    [0014]FIG. 3 is a side view of the bone distractor of FIG. 2.  
         [0015]    [0015]FIG. 4 is a side view of a flexible extension useful in combination with the bone distractor of FIG. 1.  
         [0016]    [0016]FIG. 5 is a side view of a driver tool useful in combination with the bone distractor of FIG. 1 and/or the flexible extension of FIG. 4.  
         [0017]    [0017]FIG. 6 is a cross-sectional view of the driver tool of FIG. 5, taken in plane  6 - 6  and viewed in the direction of the arrows. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0019]    Referring to FIGS. 1, 2 and  3 , a preferred embodiment of a bone distractor apparatus  10 , constructed in accordance with the present invention, is illustrated. Bone distractor apparatus  10  includes a first affixation member  12 , and a second affixation member  14  that is moveable relative to first affixation member  12 . A pair of wing elements  16  and  18  extend transversely from a central bridge portion  20  of first affixation member  12 . Each wing element  16  and  18  is substantially planar and includes a plurality of screw holes  22  for receiving bone screws therethrough to secure wing elements  16  and  18  to bone, with wing elements  16  and  18  lying flat adjacent to the bone surface. Extending longitudinally, generally parallel to the plane in which wing elements  16  and  18  lie, are a pair of parallel rods  24  and  26 . First ends  28  and  30  of rods  24  and  26 , respectively, are friction fitted within corresponding holes in bridge portion  20  of first affixation member  12 . An end member  32  has holes spaced the same as the rod holes in bridge element  20  for receiving second ends  34  and  36  of rods  24  and  26  in similar friction fit. A threaded screw rod  38  has a first non-threaded end  40  received for free rotation within a corresponding hole in bridge member  20  located between the holes in which rods  24  and  26  are received. Screw rod  38  has a second non-threaded portion  42  received for free rotation within a corresponding hole in end member  32  located between the holes in which rods  24  and  26  are received. Non-threaded portion  42  includes an annular groove disposed within the corresponding hole in end member  32 . A pin  44  received through a cross-bore in end member  32  lies perpendicular to screw rod  38  and engages the annular groove in non-threaded portion  42  to restrain screw rod  38  against axial movement relative to end member  32 , and hence (via rods  24  and  26 ) against axial movement relative to bridge member  20  of first affixation member  12 . A driven end  46  of screw rod  38  extends outwardly beyond end member  32 . Driven end  46  has a square cross-section for engaging a driving tool. A pair of wing elements  48  and  50  extend transversely from a central bridge portion  52  of second affixation member  14 . Each wing element  48  and  50  is substantially planar and includes a plurality of screw holes  54  for receiving bone screws therethrough to secure wing elements  48  and  50  to bone, with wing elements  48  and  50  lying flat adjacent to the bone surface. Holes  56  and  58 , spaced to receive rods  24  and  26  therethrough, extend longitudinally through bridge portion  52  and are sized for a free sliding relationship between second affixation member  14  and rods  24  and  26 . A threaded hole  60  extends longitudinally through bridge portion  52  between holes  56  and  58 , and screw rod  38  is threadedly received in threaded hole  60 .  
         [0020]    In use, distraction apparatus  10  is emplaced with wing members  16  and  18  of first affixation member  12  on one side of an osteotomy of the mandible, for example, and wing members  48  and  50  of second affixation member  14  on the other side of the osteotomy. Each of wing members  16 ,  18 ,  48  and  50  are bent as necessary to lie flat adjacent the bone, and bone screws are inserted through screw holes  22  and  54  to secure first and second affixation members  12  and  14  to respective bones on each side of the osteotomy. Distraction is effected by engaging square driven end  46  of screw rod  38  with a suitable driver tool. Torque applied to screw rod  38  causes screw rod  38  to turn, rotating freely relative to first affixation member  12  and with respect to end member  32 , but in threaded engagement with second affixation member  14 . Consequently, second affixation member  14  is caused to move longitudinally relative to first affixation member  12 , sliding on rods  24  and  26 . By rotating screw rod  38  in the appropriate direction, the respective bones to which first and second affixation members  12  and  14  are affixed are distracted relative to one another. The amount of distraction per rotation of screw rod  38  is determined by the pitch of the thread.  
         [0021]    Referring to FIG. 4, a flexible extension  70  is illustrated. Flexible extension  70  includes a driver connector  72  at one end, a driven connector  74  at the other end, and a flexible shaft portion  76  therebetween. Driving connector  72  includes a body  78  crimped onto one end of flexible shaft portion  76  for rotation therewith. Extending longitudinally from body  78  is a split barrel  80  having a recess therein open to the end of barrel  80  and having a square internal cross-section sized to receive in driving engagement driven end  46  of screw rod  38  of distractor apparatus  10 . Split barrel  80  is externally threaded. An externally knurled sleeve  82 , internally threaded, is received in threaded engagement on barrel  80 . Split barrel  80  includes a non-threaded exterior portion adjacent the free end thereof that tapers to a larger diameter toward the free end. As sleeve  82  is rotated relative to split barrel  80 , such that sleeve  82  is displaced toward the free end of barrel  80 , sleeve  82  engages the tapered free end of split barrel  80  and urges split barrel  80  to contract diametrically. Driven connector  74  includes a body  84  crimped onto the other end of flexible shaft portion  76  for rotation therewith. Extending longitudinally from body  78  is a square cross-section driven portion  86 , sized similarly to driven end  46  of screw rod  38  of distractor apparatus  10 . Flexible shaft portion  76  comprises a closely wound wire spiral, preferably stainless steel, configured for elastic bending and flexing, yet capable of transmitting torque without undue torsional displacement. Alternatively, shaft portion  76  can be a non-flexing rod for use in applications in which an extension is desired, but angular realignment is not needed.  
         [0022]    In use, flexible extension  70  is attached to distraction apparatus  10  by connecting driving connector  72  to driven end  46  of screw rod  38  such that driven end  46  is received in driving engagement within split barrel  80 . Sleeve  82  is turned and threadedly advanced toward the free end of barrel  80 , such that barrel  80  contracts diametrically and clamps onto driven end  46 , thereby securing flexible extension  70  to distraction apparatus  10  against relative axial movement or disengagement. A suitable driving tool can be engaged with driven portion  86  and rotated, whereby torque is transmitted via flexible extension  70  to screw rod  38  of distraction apparatus  10  of FIG. 1. Flexible extension  70  is of such length as permits ready and convenient access to driven end  86  for the duration of the two to four week period during which distraction apparatus  10  is advanced. After distraction is completed, flexible extension  70  can be removed from distraction apparatus  10  to enhance the comfort of the patient for the duration of the one to three month period of bone consolidation that follows. As preferred, the length of flexible extension  70  is such that it is wholly contained within the oral cavity. Alternatively, for some applications, flexible extension  70  can extend outside the oral cavity through an incision in the cheek, for example.  
         [0023]    Referring to FIGS. 5 and 6, a driver tool  90  is illustrated. Driver tool  90  is useful for engaging and transmitting torque to the flexible extension  70  and/or screw rod  38  of distraction apparatus  10 . Driver tool  90  is also useful for determining the number of rotations imparted to flexible extension  70  and/or screw rod  38 , by emitting an audible click for each 180 degrees of rotation. Driver tool  90  includes a main handle  92 , an auxiliary handle  94 , and a drive blade  96 . Main handle  92  is affixed to drive blade  96  for rotation therewith, whereas auxiliary handle  94  is arranged for rotation about drive blade  96  relative to main handle  92 . Drive blade  96 , having a round exterior cross-section, is received in a longitudinal bore in distal end  98  of main handle  92 . A screw  100  is received in a threaded transverse bore that intersects the bore in which drive blade  96  is received in main handle  92 . Screw  100  engages drive blade  96  to secure drive blade  96  to main handle  92  against relative rotation and axial displacement. Auxiliary handle  94  includes a longitudinal bore therethrough sized to permit drive blade  96  to be received therein for relative rotation between auxiliary handle  94  and drive blade  96 . A screw  102  is received in a threaded transverse bore that intersects the bore in which drive blade  96  is received in auxiliary handle  94 . Screw  102  extends within an annular groove in drive blade  96  to prevent axial displacement of auxiliary handle  94  relative to drive blade  96 , while permitting rotation of auxiliary handle  94  relative to drive blade  96 . A bore in end face  106  of auxiliary handle  94  contains a spring biased ball detent  104  in which a ball is biased outwardly from end face  106 , yet retained against escaping. The ball detent  104  bears against end face  108  of main handle  92  when the flats  110  and  112  of auxiliary handle  94  and main handle  92  are aligned. As main handle  92  is rotated relative to auxiliary handle  94 , flat  112  moves past alignment with ball detent  104  and the ball snaps outward, free of engagement with the end face  108  of main handle  92 . Such movement of ball detent  104  results in an audible click. Another 180 degrees of rotation results in ball detent first becoming depressed by engagement with end face  108  of main handle  92 , and then snapping free again as the flat on the other side of main handle  92  aligns with ball detent  104 . Thus, for each full rotation of auxiliary handle  94  relative to main handle  92 , two audible clicks are generated. A recess in the free end of drive blade  96  has a square internal cross-section sized to engage driven end  86  of flexible extension  70  or driven end  46  of drive screw  38  of distraction apparatus  10 .  
         [0024]    In use, the recess in the free end of blade  96  is engaged with driven end  86  of flexible extension  70  or driven end  46  of drive screw  38  of distraction apparatus  10 . While holding the flats  110  of auxiliary handle  94  with the thumb and fingers of one hand to prevent auxiliary handle  94  from rotating, the main handle  92  is rotated, causing drive blade  96  to rotate and impart torque to flexible extension  70  or drive screw  38 . With each 180 degrees of rotation of main handle  92  relative to auxiliary handle  94 , an audible click is generated. Multiplying the number of clicks heard by one-half the thread pitch of screw rod  38  gives the amount by which second affixation member  14  is distracted from first affixation member  12 .  
         [0025]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.