Abstract:
The present invention provides an improved orthopedic system for the modification of the distance between the maxilla and zygoma. In a preferred embodiment, the system includes proximal and distal footplates attached to an orthopedic device. The distal footplate is attached to the zygoma, with the proximal footplate being mechanically coupled to the maxilla. This mechanical coupling is achieved either through attachment directly to the maxilla or by attachment to a construct which is then wired to the patient&#39;s teeth. The orthopedic device, which may be a distractor, allows for modification of the distance between the maxilla and zygoma. The entire system can advantageously be placed intra-orally within a patient. In a preferred embodiment, the footplates are also detachable from the orthopedic device and are composed of a bioresorbable material, such that they will be absorbed by the patient&#39;s body. Methods for using this novel orthopedic system are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority rights from U.S. Provisional Application 60/294,640, filed Jun. 1, 2001. 

   BACKGROUND OF THE INVENTION 
   The present invention relates generally to a bone distractor device and more particularly, to a bone distractor device having multiple degrees of freedom. 
   Conventional bone distractor devices utilize plates fixed to different bone areas, a transport bone segment, and a fixed bone area. The transport bone segment is attached to a linear device that allows the transport bone segment to be moved along a linear path, resulting in the generation or distraction of a linear bone segment. When a bone segment is to be distracted in other than the direction in which the distractor device is connected, the distraction device usually must be removed and reattached, requiring additional medical procedures. The present invention was developed in light of these drawbacks. 
   BRIEF SUMMARY OF THE INVENTION 
   A bone distractor for distracting bone tissue includes a first bone attachment portion, a second bone attachment portion, and a linkage connecting the first bone attachment portion with the second bone attachment portion. The linkage allows at the first or second bone attachment portion to move with respect to the other along a linear path. The linkage allows the first or second bone attachment portions to rotationally move with respect to the other. 
   In another aspect of the invention, the first bone attachment portion and second bone attachment portion are inter-orally positioned on a mandible of a human jaw. Skin may generally cover the first bone attachment portion and/or second attachment portion. 
   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 
       FIGS. 1A ,  1 B,  1 C, and  1 D, are, respectively, a side elevational view in a first operating position, a front perspective view in the first operating position, a side elevational view in a second operating position and a top plan view in the second operating position of a first preferred embodiment of a device according the present invention. 
       FIG. 1E  is a top plan, detail view of a modified version of a component of the device of  FIGS. 1A–1D . 
       FIG. 1F  is a side elevational, detail view of the component shown in  FIG. 1E . 
       FIG. 2A  is cross-sectional view taken along line  2 — 2  of  FIG. 1D , showing a worm screw rack displacement mechanism. 
       FIG. 2B  is a side elevational detail view of a modified form of construction of a portion of the structure shown in  FIG. 2A . 
       FIG. 3  is a cross-sectional, detail view of the distal end of a tool used for adjusting the device of  FIGS. 1A–1D . 
       FIG. 4  is a cross-sectional view taken along a vertical plane, which can be the same plane as the view of  FIG. 2 , showing a worm gear displacement mechanism employed in the device of  FIGS. 1A–1D . 
       FIG. 5  is a perspective view showing a splint that may be used with the device of  FIGS. 1A–1D . 
       FIGS. 6A ,  6 B,  6 C and  6 D are, respectively, a side elevational view, a top plan view, a front perspective view and a rear perspective view of a second embodiment of a device according to the present invention. 
       FIG. 7  is a cross-sectional, detail view of a component of the device of  FIGS. 6A ,  6 B,  6 C and  6 D. 
       FIGS. 8 ,  9 ,  10  and  11  are, respectively, a side elevational view, a front elevational view, a bottom plan view and a side elevational, cross-sectional detail view of a third embodiment of a device according to the invention. 
       FIG. 12  is a perspective view showing a modified version of the embodiment of  FIGS. 8–11 . 
       FIG. 13  is a perspective view, partly in cross section, of another modified version of the embodiment of  FIGS. 8–11 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A first preferred embodiment of the invention is illustrated in  FIGS. 1A–1D , which will be described together. 
   This embodiment includes an upper plate  12  composed of two wings  14  and  16 . Plate  12  is secured to, and forms a unit with, an upper housing  18 . All of the components of the device illustrated in  FIGS. 1A–1D  may be made of metal and wings  14  and  16  and housing  18  may be formed as a single cast unit, or wings  14  and  16  may be formed separately from housing  18  then welded to the side of walls of housing  18 . An upper drive track  22  extends through a passage in housing  18 . This passage may be formed directly in the cast unit constituting housing  18 . A shaft  26  carries a threaded element (not visible) that also extends into the opening in housing  18 . The threaded end of shaft  26  engages threading, or teeth,  28  on track  22  in such a manner that rotation of shaft  26  will produce movement of housing  18  along the length of track  22 . Thus, track  22  cooperates with the threaded element to form a worm screw rack mechanism. The internal structure of housing  18  will be described in further detail below. 
   A rotational adjustment gear housing  34  contains a gear wheel that is coupled to the lower end of track  22  and a screw  38  having threads that engage the gear wheel. Rotation of screw  38  produces a rotation of the gear wheel, and a corresponding pivotal movement of track  22 , for example between the position shown in  FIGS. 1A and 1B , on one hand, and the position shown in  FIGS. 1C and 1D , on the other hand. The structure within housing  34  will be described in greater detail below. 
   In the illustrated embodiment, track  22  has two successive bent portions that extend at right angles to one another. Track  22  has a lower end mounted in housing  34 . These portions serve to offset the upper portion of track  22 , along which housing  18  can be displaced, from the axis of rotation of the gear wheel, so that the upper portion of track  22  extends along a line that will intersect a lower drive track  42  at a point between the proximal and distal ends of track  42 . 
   A lower drive track  42  is rigidly fixed to housing  34  and carries, at its upper surface in the figures, a threading, or teeth,  46  similar to threading  28 . Drive track  42  extends through an opening in a lower housing  52 . This opening further receives the threaded end of second shaft  56 , which threaded end engages threading  46 . Rotation of shaft  56  effects a movement of housing  52  along track  42 . The mechanism within housing  52  is identical to that within housing  18  and will be described in greater detail below. 
   Secured to housing  52 , below drive track  46 , is an anterior lower plate  60  provided with a plurality of bone screw holes  62 . 
   Referring specifically to  FIG. 1B , each wing  14 ,  16  of upper plate  12  is composed of a longitudinal strip  64 ,  66  provided with a plurality of bone screw holes  68 . Extensions  72 ,  74  extend laterally from either side of each strip  64 ,  66  and each extension  72 ,  74  is provided with at least one bone screw hole  68 . Depending on the exact conformations of the bone regions to which wings  14  and  16  are to be secured, one or more of extensions  72 ,  74  of each wing can be broken off prior to implantation. 
   As shown particularly in the top plan view of  FIG. 1D , wings  14  and  16  extend from housing  18  along a plane that is inclined with respect to the longitudinal axis of track  42  and shaft  56 , and wing  14  is initially given a curved configuration. These orientation features of wings  14  and  16  are selected to conform to the facial skeleton portions to which wings  14  and  16  are to be attached for an individual having an average facial skeleton conformation. Models having different dimensions may be produced for pediatric patients, on the one hand, and adult patients, on the other. Since there will be variations in conformation from one individual to another, wings  14  and  16  are made of a material that is capable of being bent to conform to the individual patient. 
   In the embodiment shown in  FIGS. 1A–1D , wings  14  and  16  form a one-piece unit with housing  18 . However, according to an alternative embodiment shown in  FIGS. 1E and 1F , wings  14  and  16  may be formed as a one-piece unit separate from a housing  18 ′. Here, housing  18 ′ still receives track  22  and shaft  26 , but is provided with a plate portion  75  carrying an upstanding pin  76 . The unit providing wings  14  and  16  has a cylindrical portion  77  presenting a through bore that seats over pin  76 . Pin  76  may be provided at its upper end with a retaining member  78 , such as a locking clip, to hold portion  77  in place on pin  76 . With this arrangement the unit that includes wings  14  and  16  and portion  77  can be rotated around pin  76  to facilitate positioning wings  14  and  16  relative to the bone surface to which they are to be secured. Wings  14  and  16  and portion  77  are not shown in  FIG. 1F  to allow the form of housing  18 ′ to be viewed more clearly. 
     FIG. 2A  is a cross-sectional view taken along line  2 — 2  of  FIG. 1D . As stated above, housing  52  is provided with an opening, or through bore, that receives a screw, or threaded element,  86  having a male thread that is configured to mate with threading  46  on drive track  42 . Screw  86  has a free end provided with an annular recess into which is inserted a retaining pin  88  to prevent longitudinal movement of screw  86  relative to housing  52 , while allowing screw  86  to rotate within the opening provided in housing  52 . The opposite end of screw  86  is secured to the distal end of shaft  56 . 
   As further illustrated in  FIG. 2A , shaft  56  may be composed of a tightly wound wire coil enclosing a core  92  that may be rigid or bendable. Core  92  can be a solid rod or a stranded, twisted wire capable of applying tensile forces to thread  86  and housing  52 . By making shaft  56  deformable, it can be bent to conform to the portion of the patient&#39;s oral cavity in which the device is installed, thus promoting wearer comfort. 
   As shown in  FIGS. 1A–1D , the outer, or proximal, end of shaft  56  may be provided with a square head  94  that is engageable with a socket of a hand tool to allow shaft  56  to be rotated. When shaft  56  is rotated, screw  86  is rotated along therewith so that the engagement of the threads on screw  86  with threading  46  causes relative longitudinal movement between housing  52  and plate  60 , on the one hand, and track  42 , on the other hand. 
   Housing  18  may have the same internal structure as housing  52 , and shaft  26  may be identical to shaft  56 . 
   In the embodiment shown in  FIGS. 1A–1D  and  2 A, plate  60  is not bendable, or is only slightly bendable. Alternatively, as shown in  FIG. 2B , plate  60  can be replaced by a malleable bone screw plate  96  provided with bone screw holes. Plate  96  can be fabricated according to principles known in the art to be sufficiently malleable to allow the plate to by bent manually to surface where it is to be affixed. This may be a bone surface or, as will be described below, a surface of a surgical fixation splint. 
   As will be described in greater detail below, the device according to the invention will be implanted internally, so that shafts  26  and  56 , as well as housings  34  and  52  and tracks  22  and  42  will be located within the patient&#39;s mouth or oral cavity. When implanted, housing  18 ,  18 ′ can be located above the oral mucosa (submucosa) against the anterior surface of the zygomatic buttress. 
   When housing  18  is to be displaced along track  22 , shaft  26  can be rotated with the aid of a special tool having an operating end that may have the form shown in  FIG. 3 . This tool may include a handle (not shown) and a housing  102  that extends to a point at which it can be grasped by the person making the adjustment. The handle is secured to a shaft  104  that is rotatably mounted in bearings  106  mounted within housing  102 . The free, or distal end of shaft  104  is secured to a first bevel gear  110  that engages a second bevel  112  having an axis of rotation perpendicular to that of gear  110 . Bevel gear  112  is mounted on a shaft  114  that passes through a circular opening in housing  102 . The outer end of shaft  114  carries a tool head that includes a member  118  providing a square socket for engagement with the square head at the end of shaft  26 . Secured to member  118  is a guide funnel  120  that can be placed around the square head of shaft  26  in order to easily guide that head into the socket provided by member  118 . Then, when the user rotates the handle that is fixed to shaft  104  while holding housing  102  stationary, gear  112 , shaft  114 , member  118  and funnel  120  can be rotated in order to rotate shaft  26  and thus displace housing  18  relative to track  22 . 
     FIG. 4  shows one exemplary embodiment of a rotational adjustment gear that may be provided in housing  34 . The upper end of screw  38  is provided with a reduced diameter threaded portion  122  that engages teeth on gear wheel  124  to form a worm gear mechanism. Gear wheel  124  is pivotally mounted on housing  34 . Screw  38  is provided with an annular recess into which is inserted a retaining pin  126  to prevent longitudinal movement of screw  38  relative to housing  34 , while allowing screw  38  to rotate within housing  34 . Rotation of screw  38  produces a corresponding rotation of gear wheel  124  about its pivot axis, thereby rotating track  22  relative to track  42 . 
   It will be appreciated that the mechanisms shown in  FIGS. 2 ,  3  and  4 , as well as in  FIG. 7 , to be described below, are only exemplary. A variety of alternative mechanisms can easily be devised by those skilled in the mechanical mechanism arts. 
   The device shown in  FIGS. 1 and 2  would be implanted in accordance with the procedure described below. Appropriate portions of the facial skeleton would be exposed surgically and the required osteotomy would be performed. By way of example, this could be a Lefort I or II osteotomy. Plate  12  will be secured above the osteotomy separation by securing wing  14  to the anterior maxilla and securing wing  16  to the malar eminence and/or the zygomatic arch, using an appropriate number of bone screws in each case. As noted above, where possible or desired, various ones of extensions  72 ,  74  may be remove, by being broken off from strip  64 ,  66 , before plate  12  is fastened in place. 
   Plate  60  will be secured to the upper jaw or the teeth, or to a splint that has been fabricated beforehand and that is secured to the upper teeth.  FIG. 5  shows an occlusal splint  140  that was made by molding an acrylic material to a mold of the patient&#39;s upper teeth and then fitted securely thereto. A plurality of fixation wires  142  are embedded in splint  140 . Wires  142  may be inserted through holes  62  in plate  60  and then twisted together in pairs in order to firmly secure plate  60  to splint  140 . 
   Alternatively, orthodontic appliances may be affixed to the patient&#39;s upper teeth and provided with wires similar to wire  142  for fixation to plate  60 . 
   Then, screw  38  is adjusted, if necessary, by the operating clinician to establish the desired angular relation between tracks  22  and  42 . In this embodiment, screw  38  is accessible for subsequent adjustment by the clinician. 
   Thus, the entire device will be disposed internally, with housing  34 , a portion of track  22 , the entirety of track  42 , housing  52  and shafts  26  and  56  disposed in the oral cavity. As a result, the device will not be readily observable and will subject the patient to minimum discomfort. 
   Subsequent to implantation, the spacing between plates  12  and  60  can be varied by the patient, or by a family member of the patient, simply by rotating shaft  26  and/or  56  according to the clinician&#39;s instructions, with appropriate hand tools. 
   In the illustrated embodiment, wings  14  and  16  are secured directly to housing  18  and extensions  64  and  66  are centered on a plane that passes approximately mid-way between the ends of housing  18  perpendicular to the longitudinal direction of track  22 . This provides a desirable positioning with respect to the facial skeleton and a reliable connection between wings  14  and  16 , on the one hand, and housing  18 , on the other hand. 
   It will also be noted that in the embodiment shown in  FIGS. 1A–1D , and particularly in  FIG. 1B , housings  18 ,  34  and  52 , tracks  22  and  46 , shafts  26  and  56  and screw  38  are all centered on a common vertical plane. This provides a compact arrangement that results in reduced patient discomfort. 
   The embodiment illustrated in  FIGS. 1A–1D  allows a full range of adjustment in the spacing between plates  12  and  60  by allowing three different adjustments, two of which are linear and one of which is angular. After the device has been implanted, the spacing between plate  12  and  60  will be varied progressively and gradually as the osteotomy heals. However, for certain treatments, three adjustments may not be required. For example, the embodiment illustrated in  FIGS. 1A–1D  can be modified by fixing housing  18  to track  22  or forming those components as a single component, and/or by eliminating the rotational adjustment gear assembly and rigidly connecting tracks  22  and  42  together, or forming those tracks of a single piece. However, the advantage of the embodiment shown in  FIGS. 1A–1D  is that it offers the possibility of any combination of adjustments and thus provides a single model that will meet the needs of all mid-face distraction procedures. 
   A second embodiment of the invention is illustrated in  FIGS. 6A–6D . Since this embodiment shares many of the features of the embodiment of  FIGS. 1A–1D , only the difference is therebetween will be described. 
   Firstly, the embodiment of  FIGS. 6A–6D  includes an upper drive track  22 ′ that differs from track  22  in that track  22 ′ is linear, rather then having any right angle bends. 
   Upper housing  18  is associated with an elongated, flexible shaft  26 ′ that corresponds functionally to shaft  26  of  FIGS. 1A–1D . However, shaft  26 ′ extends forwardly from housing  18  so as to be more readily accessible to a tool inserted from outside the patient&#39;s mouth. Track  42  is provided with a drive shaft guide  146 , essentially in the form of a stirrup, to guide the free end of shaft  26 ′. 
   A rotation adjustment gear housing  34 ′ is provided with a shaft  150  that allows the adjustment mechanism to be adjusted in the same manner as the other shafts. Thus, with this arrangement, the angle between tracks  22 ′ and  42  can be adjusted subsequent to implantation, by the patient or an assistant, pursuant to instructions provided by the attending clinician. 
   One suitable form of construction of the rotational adjustment gear in housing  34 ′ is shown in  FIG. 7 . 
   In  FIG. 7 , one side of housing  34 ′ has been removed to expose the interior thereof, which contains a screw, or threaded element,  170  secured to shaft  150  in order to rotate therewith. Housing  34 ′ also contains a gear wheel  174  provided on at least a portion of its outer surface with gear teeth that will mesh with the thread of screw  170 . Gear wheel  174  is fixed to housing  34 ′ via a pivot shaft  176  and is secured to track  22 ′. Screw  170  is provided, at its distal end, with an annular groove in which a pin  180  is inserted to prevent movement of screw  170  in the direction of its longitudinal axis, while permitting screw  170  to be rotated with shaft  150 . Rotation of shaft  150  and screw  170  produces a corresponding rotation of gear wheel  174  in order to vary the angular orientation of track  22 ′ relative to track  42 . 
     FIGS. 6A–6D  also show an upper plate  12  that is shown only generally. In practical implementations of the device, plate  12  can have the structure and orientation shown in  FIGS. 1A to 1D , or in  FIGS. 1E and 1F . Lower plate  60  will be secured in the manner described above with reference to  FIGS. 1A–1E . 
   The embodiment shown in  FIGS. 1A–1D  can be modified to include any one or more of these differing features of the embodiments shown in  FIGS. 6A–6D . 
   A further embodiment of the invention is shown in  FIGS. 8 ,  9 ,  10  and  11  and differs from the embodiments previously described essentially by the elimination of separate drive tracks and the connection of the various housings directly to threaded elements. 
   The basic components of this embodiment are an upper plate  212  composed of two wings and corresponding essentially to plate  12  of  FIGS. 1A–1D , a housing  218  that forms a unit with plate  212 , a threaded element  226  having an end secured in housing  218 , an internally threaded sleeve  230  in threaded engagement with element  226 , a housing  234  pivotally connected to sleeve  230 , a threaded element  256  rotatably supported by housing  234 , a sleeve  258  that is internally threaded and in threaded engagement with threaded element  256  and an anterior lower plate  260  that is secured to sleeve  258  and that corresponds to lower plate  60  of the embodiment shown in  FIGS. 1A–1D . 
   One possible form of construction of the interior of housing  234  is shown in  FIG. 11 . Threaded element  256  is supported by cylindrical bearings  270  and  272  that are fixed to housing  234  and that engage with recessed portions of threaded element  256  in order to allow threaded element  256  to be rotated about its axis, while being fixed against axial movement relative to housing  234 . 
   Sleeve  230  carries a gear wheel segment  280  that is pivotally mounted to housing  234  at a pivot pin  282 . Housing  234  further includes a threaded element  286  having a recessed portion via which threaded element  286  is retained in a cylindrical bearing  290  that is fixed to housing  234 . The engagement between bearing  290  and threaded element  286  allows threaded element  286  to rotate about its axis while preventing axial movement of threaded element  286  relative to housing  234 . The threads of threaded element  286  engage gear teeth on segment  280  so that rotation of element  286  will cause housing  234  to pivot relative to sleeve  230  about the axis of pivot  145  pin  282 . 
   Rotation of threaded element  256  will produce a displacement of sleeve  258  and lower plate  260  along the axis of element of  256 . 
   Threaded element  226  is retained in housing  218  by a structure that can be similar to components  270  and  272  shown in  FIG. 11 , whereby element  226  can rotate about its axis relative to housing  218 , but is restrained from undergoing axial movement relative thereto. Thus, rotation of element  226  will produce a displacement of sleeve  230  along the axis of element  226 . 
   The outer, or proximal, end of each element  226 ,  256  and  286  may be provided with a square head, similar to the square head  94  shown in  FIG. 1C , that is engageable with a socket of a hand tool to allow the element to be rotated. 
   The embodiment illustrated in  FIGS. 8–11  will be installed in the same manner as the embodiment of  FIGS. 1A–D . At least threaded elements  256  and  286  can be rotated by insertion of a tool through the patient&#39;s mouth. Threaded element  226  might be rotated by the use of a special tool similar to that illustrated in  FIG. 3 . 
     FIG. 12  is a perspective view showing a modified version of the embodiment of  FIGS. 8–11 , which differs only in that anterior lower plate  260 ′ is mounted above sleeve  258 ′ in position to be fastenable to bone above the patient&#39;s upper teeth. 
     FIG. 13  shows another modified version of the embodiment of  FIGS. 8–11 . In the embodiment shown in  FIG. 13 , threaded element  256  is supported in a housing  234 ′ by two pins  270 ′ that engage at diametrically opposed sides of an annular recess in element  256  in order to allow threaded element  256  to be rotated about its axis, while being fixed against axial movement relative to housing  234 ′. Sleeve  230  is provided with two holes for receiving pivot pins  282  and  292 . Housing  234 ′ is pivotally mounted on pivot pin  282 . Threaded element  286  is held in place in housing  234 ′ by two pins  290 ′ that engage at diametrically opposed sides of the annular recessed portion of element  256  that allow threaded element  256  to be rotated about its axis, while being fixed against axial movement relative to housing  234 ′. A connecting element  291  is pivotally mounted on pivot pin  292  and is provided with a bore having a female thread that mates with threaded element  286 . Rotation of threaded element  286  causes element  286  to move axially relative to element  291 , resulting in pivotal movement of housing  234 ′ about pin  282 . This causes element  256  to pivot relative to element  226 . 
   Embodiments of the invention can be employed for performing segmental distraction of the alveolar ridge in order to close a cleft defect of alveolar bone and lower maxilla. For this purpose, subsequent to an osteotomy, a device according to the invention would be implanted in the manner described earlier herein and the anterior lower plate unit could be progressively advanced in the anterior direction during the course of bone regeneration at the osteotomy. This could be accompanied by a progressive vertical displace that increases the vertical spacing between the upper plate unit and the lower plate unit. 
   Devices according to invention can also be employed to effect vertical elongation of the alveolar ridge. In this case, after osteotomy, the lower plate unit can be secured to the alveolar ridge, at a location above and posterior to the patient&#39;s upper teeth, and progressive adjustments can be made to increase the vertical distance between the upper and lower plate units. 
   Devices according to the invention are well adapted for treatment of children whose adult teeth have not yet erupted, with lower plate  60  secured to an occlusal fixation splint. 
   The devices illustrated in the attached drawings will be implanted at the left side of the patient&#39;s face. In a complete mid-face distraction procedure, a device that is mirror symmetrical to those illustrated will be implanted in a mirror symmetrical manner at the right side of the patient&#39;s face. 
   The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without undue experimentation and without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. The means, materials, and steps for carrying out various disclosed functions may take a variety of alternative forms without departing from the invention. 
   Thus the expressions “means to . . . ” and “means for . . . ”, or any method step language, as may be found in the specification above and/or in the claims below, followed by a functional statement, are intended to define and cover whatever structural, physical, chemical or electrical element or structure, or whatever method step, which may now or in the future exist which carries out the recited function, whether or not precisely equivalent to the embodiment or embodiments disclosed in the specification above, i.e., other means or steps for carrying out the same functions can be used; and it is intended that such expressions be given their broadest interpretation.