Abstract:
A bone distraction device having a ratchet and pawl mechanism such that incremental rotation is allowed in one direction and prevented in the other, and further having a quick release mechanism such that the ratchet and pawl mechanism can be released to allow free rotation in both directions.

Description:
[0001]    This application claims the benefit of U.S. Non-Provisional patent application Ser. No. 12/284,679, filed Sep. 24, 2008, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to the field of medical distraction devices in the field of bone fixation, repair and regeneration, and more particularly relates to such devices and methods utilized in mandibular and maxillary craniofacial repair, facial reconstruction, and treatment for congenital, developmental and traumatic, defects. 
         [0003]    It is often desirable or necessary to effect reconstruction or repair of the craniofacial bones defining the face of a person, such as the midface, the mandible and/or the maxilla. This need may arise from congenital conditions, developmental disorders or trauma. In many circumstances the abnormalities are corrected by first dividing a bone through osteotomy, i.e., cutting or fracturing a bone to create two segments separated by a gap or space. In some instances the bone segments will be shifted into the proper orientation and alignment, and then fixed in place relative to each other until bone growth across the gap results in the formation of a unitary bone member. In other instances it is necessary to lengthen the original bone member, in which case devices known as distractors are utilized. A distractor is a device that has affixation means, such as bone plates, that are joined to each of the bone segments on opposite sides of the osteotomy using mechanical fasteners such as bone screws. The device further includes distraction means that allows the distance between the bone plates to be slowly increased over time, thereby allowing new bone growth to occur between the bone segments. The distraction means may comprise for example a threaded rod contained within a framework or elongated housing, the rod being in connection with one or two translatable shoe or mounting members to which are connected a proximal bone plate and a distal bone plate, whereby the bone plates affixed on either side of the osteotomy gap to the bone to be extended can be gradually separated in a controlled and precise manner by rotating the threaded rod to separate the plate mounting members. The new bone growth increases in dimension until the proper bone length is achieved, at which time the distraction process is halted and the distractor is removed. U.S. Pat. No. 6,752,808 issued to Schumacher illustrates and describes a distraction device of the type referenced above. 
         [0004]    A typical example of this procedure is when the mandible or jawbone fails to fully develop in the anterior-posterior direction, a condition known as mandibular hypoplasia, which is manifested as a severely fore-shortened chin. To correct this anomaly, osteotomies are performed on each side of the mandible and a pair of distraction devices are affixed to the mandible. Extension of the distractors is performed in unison to lengthen the mandible until the desired position of the mandible relative to the midface is achieved. After sufficient regeneration and healing, the distractors are removed. 
         [0005]    For another example, it is often desired to advance the midface or maxillary region relative to the jaw and skull to correct for maxillary hypoplasia, where the upper lip and/or nose are depressed relative to the remainder of the face structure. In this case the osteotomy may be performed across the maxilla to the nasal cavity, and a pair of distractors are affixed across the osteotomy gap, or an external distraction apparatus is mounted to the skull with affixed means to distract the anterior maxillary segment. Gradual extension of the distractors in unison advances the anterior maxillary segment relative to the posterior maxillary segments while bone regeneration fills in the osteotomy gap. When the proper position is achieved, distraction is halted. After sufficient regeneration and healing, the distractors are removed. 
         [0006]    It is desirable that the distraction be performed in a controlled or incremental manner, whereby the advancement distance can be accurately accounted for, and it is further desirable that the apparatus allow for rotation in only one direction to insure that the bone plates are separated rather than contracted. This may be accomplished by utilizing a ratchet and pawl mechanism or having mating teeth, such that rotation of the drive head joined to the threaded rod and relative movement of the bone plates can only occur in the distraction direction. Examples of distraction devices utilizing ratchet and pawl mechanisms or mating teeth are seen in U.S. Pat. No. 5,681,309 to Ross, Jr. et al., U.S. Pat. No. 5,704,938 to Stawhlin et al., U.S. Pat. No. 6,033,412 to Losken et al., and U.S. Pat. No. 6,277,124 to Haag. 
         [0007]    One problem with such unidirectional distraction devices is that it may be desirable or required to contract the bone plates by rotating the threaded drive rod in the direction opposite to the distraction direction. In certain circumstances, it may be necessary to allow for free rotation of the threaded drive rod rather than incremental rotation. It may also be necessary in certain circumstances to release the threaded drive rod quickly. Therefore, it is desirable and an object of this invention to provide a distraction device having a ratchet and pawl means that allows for incremental rotation of the threaded drive rod in the distraction direction, wherein a quick release disengagement means is provided such that the ratchet and pawl mechanism can be disengaged and the drive rod rotated in the opposite direction as needed. 
       SUMMARY OF THE INVENTION 
       [0008]    The invention is a bone distractor, and is especially drawn to a bone distractor used in mandibular and maxillary craniofacial repair, reconstruction and treatment that enables a surgeon to lengthen the maxilla or the mandible. In a representative illustration, osteotomies are provided on the left and right sides of the mandible or the maxilla (or both), such that the anterior portion of the mandible or the maxilla is divided from the posterior portion. This allows the anterior portions to be repositioned in a more desirable orientation. 
         [0009]    The bone distractor of the invention comprises structures for attachment of the device to a bone on opposite sides of an osteotomy gap, such as by a pair of bone plate members affixed by bone screws or similar bone attachment fasteners known in the art. The bone distractor further comprises a distraction mechanism to separate the bone plates, such that the bone portions to which the device is attached are gradually separated as well, such as by a threaded rod retained within a framework or housing, with the bone plate members mounted on one or two translatable mounting members in mechanical communication with the threaded rod, such that rotation of the threaded rod results in relative movement of one or both mounting members such that the bone plates move apart. The bone distractor device further comprises a ratchet and pawl mechanism whereby rotation of the threaded rod is allowed in only one direction while the pawl is engaged, the pawl serving to secure the threaded rod in incremental positions relative to the framework or housing, and further comprising a disengagement mechanism whereby the pawl can be quickly and easily released such that free rotation of the threaded rod in either direction is possible. 
         [0010]    In alternate language, the invention is a bone distraction device comprising a pair of bone plate members; a threaded rod retained within an elongated, linear rod housing, said threaded rod interacting with said bone plate members whereby rotation of said threaded rod within said rod housing in a distraction direction results in relative separation or contraction of said bone plate members depending upon the direction of rotation; a drive head positioned at one end of said rod housing and connected to said threaded rod, whereby rotation of said drive head rotates said threaded rod, said drive head having teeth and notches disposed annularly thereon; a pawl housing positioned on said rod housing, said pawl housing retaining a pawl biased outwardly into one of said notches on said drive head to define an engaged position, said pawl and said notches configured such that said drive head is rotatable only in said distraction direction when said pawl is in said engaged position; a slot disposed in said pawl housing and a post member connected to said pawl and extending through said slot, said slot having a longitudinal portion and an annularly oriented portion, and whereby said pawl is retracted away from said drive head notches and teeth by moving said post member within said slot longitudinally away from said drive head and then annularly to define a disengaged position, such that rotation of said drive head is allowable in either direction when said pawl is in said disengaged position. Furthermore, the invention as set forth above, wherein said pawl comprises a pawl end and wherein said pawl end is angled or curved; wherein said ratchet notches comprise an angled or curved wall.; wherein said slot is L-shaped; and/or further comprising a compressible spring member connected to said pawl, such that said spring member maintains said pawl in said engaged position. 
         [0011]    Alternately, a bone distraction device, said device comprising: a distraction mechanism that separates a pair of bone plates divided by an osteotomy, said distraction mechanism comprising a rotating drive head positioned at one end of an elongated, linear housing and connected to a rotating threaded rod; one of said bone plates mounted to said housing in a fixed manner and the other said bone plate connected to said threaded rod in a manner allowing movement relative to said fixed bone plate; an incremental indexing mechanism that incrementally rotates said drive head and said threaded rod in a single distraction direction such that said bone plates separate, said incremental indexing mechanism comprising a ratchet and pawl assembly; said ratchet and pawl assembly comprising teeth and notches annularly disposed on said drive head and a retractable pawl member disposed in cooperative engagement with said teeth and said notches, said pawl member having an engaged position abutting said teeth and said notches allowing incremental rotation of said drive head only in said distraction direction, and said pawl member having a disengaged position separated from said teeth and said notches allowing free rotation of said drive head in either direction. Furthermore, such device wherein said pawl member comprises a pawl end and wherein said pawl end is angled or curved; wherein said ratchet notches comprise an angled or curved wall; said ratchet and pawl assembly further comprising a pawl housing, an L-shaped slot disposed on said pawl housing and having a longitudinal portion and an annularly oriented portion, and a post member connected to said pawl member and extending through said slot, whereby said pawl member is moved from said engaged position to said disengaged position by moving said post member within said slot; wherein said post is moved into said annularly oriented portion of said L-shaped slot to maintain said pawl member in said disengaged position; and/or further comprising a compressible spring member connected to said pawl member, such that said spring member maintains said pawl member in said engaged position. 
         [0012]    Alternately, a bone distraction device, said device comprising: a distraction mechanism for separating a pair of bone portions divided by an osteotomy, said distraction mechanism comprising a rotating drive head coaxially connected to a rotating threaded rod; an incremental indexing mechanism to incrementally rotate said drive head and said threaded rod, said incremental indexing mechanism comprising a ratchet and pawl assembly; said ratchet and pawl assembly comprising teeth and notches annularly disposed on said drive head and a retractable pawl member disposed within a pawl housing and acting in combination with said teeth and said notches, said pawl member having an engaged position abutting said teeth and said notches allowing incremental rotation of said drive head in one direction only, and said pawl member having a disengaged position separated from said teeth and said notches allowing free rotation of said drive head in either direction; a disengagement mechanism for releasing said pawl member such that said drive head and said threaded rod are freely rotatable in both directions, said disengagement mechanism comprising a slot disposed on said pawl housing, a post member connected to said pawl member and extending through said slot, and a compressible spring member connected to said pawl member, such that said spring member biases said pawl member in said engaged position, whereby said pawl member is moved from said engaged position to said disengaged position by moving said post member within said slot to compress said spring member. Furthermore, the device wherein said pawl member comprises a pawl end and wherein said pawl end is angled or curved; wherein said ratchet notches comprise an angled or curved wall; wherein said slot is L-shaped and comprises a longitudinal portion and an annularly oriented portion; and/or wherein said post member is disposed within said annularly oriented portion of said slot when in said disengaged position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a plan view of an illustrative embodiment of the unidirectional distraction device having a quick release disengagement mechanism. 
           [0014]      FIG. 2  is a partial view of the device of  FIG. 1 , better illustrating the quick release disengagement mechanism. 
           [0015]      FIG. 3  is a partial view illustrating an alternative ratchet and pawl mechanism. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    With reference to the drawings, the invention will now be described in detail with regard for the best mode and the preferred embodiment. 
         [0017]    The invention is a bone distractor, and is especially drawn to a linear bone distractor used in mandibular and maxillary craniofacial repair, reconstruction and treatment. In a representative procedure, osteotomies are provided on the left and right sides of the mandible or the maxilla, such that the anterior portion of the bone is divided from the posterior portion of the bone. A pair of distractor devices are utilized, one for each side of the mandible or maxilla. The distractor device is affixed to the mandible or maxilla spanning the osteotomy gap. Distraction is accomplished slowly to allow bone regeneration to occur across the osteotomy gap. When the bones are properly lengthened, the device is removed. 
         [0018]      FIG. 1  illustrates a representative embodiment of the distraction device comprising a distraction mechanism for separating a pair of bone portions divided by an osteotomy, the distraction device comprising structures for affixing the device to bone on either side of the osteotomy gap, such as for example a pair of bone plate members  11 , the bone plate members  11  having apertures  12  to receive mechanical fasteners such as bone screws, as is well known in the art. The distraction mechanism comprises a threaded rod  13  received within a framework or elongated, linear rod housing  14  in a manner whereby the threaded rod  13  may be rotated by turning a drive head member  15  coaxially mounted on one end of the housing  14 . The bone plate members  11  are mounted to the threaded rod  13  such that an apertured portion of each bone plate member  11  extends from each side of the threaded rod  13 , and in a manner whereby rotation of the threaded rod  13  causes the bone plates to separate or contract relative to each other, such as for example by utilizing an internally threaded mounting member or shoe (not shown) on one of the bone plate members  11  that receives the threaded rod  13 , the mounting member being able to move longitudinally along the housing  14  when the threaded rod  13  is rotated. Such mechanisms are well known in the art. Typically, the drive head member  15  is provided with a drive tool receiving bore or slot, such that rotation of the threaded rod  13  is achieved by inserting the drive tool, such as for example a hexagonal shaft, into the bore and rotating the drive tool. 
         [0019]    The distraction device further comprises an incremental indexing mechanism to rotate the drive head  15  and threaded rod  13  in a single direction via a ratchet and pawl assembly  20  that interacts with ratchet teeth  28  and notches  21  provided annularly on the drive head member  15 . The pawl member  22  is provided with a curved or angled end  23  and is biased outwardly against the ratchet notches  21  by a spring or biasing member  24 . The pawl  22  is retained within a pawl housing  25  mounted on the rod housing  14  adjacent the drive head member  15 . In this manner, the drive head  15  can be rotated in one direction relative to the housing  14 , with the rotation resulting in the depression of the biasing member  24  into the pawl housing  25  because of the angled or curved end  23 . When the drive head  15  brings the next notch  21  in alignment with the pawl  22 , the biasing member  24  forces the pawl  22  outward, locking the drive head  15  in position until further rotation force is applied because the extended portion of the pawl end  23  opposite from the angle or curve abuts the side of the teeth  28 , precluding rotation in the opposite direction. This structure results in separation of the bone plate members  11  by a defined distance with each turn of the drive head  15 . In an alternative embodiment, as shown in  FIG. 3 , the notches  21  may be provided with a curved or angled wall and the pawl end  23  presented as generally rectangular or cylindrical, in known manner, such that as before the drive head  15  can be rotated in only one direction when the pawl  22  is engaged, which in this figure is shown opposite to the direction of  FIG. 2 . 
         [0020]    The distraction device further comprises a disengagement mechanism for releasing the ratchet and pawl mechanism such that the drive head  15  can be freely rotated in either direction. The disengagement mechanism comprises an L-shaped slot  26  disposed in the pawl housing  25  and a radially extending post member  27  that is mounted on the pawl  22  and extends through the L-shaped slot  26 . To completely disengage the pawl  22  from the drive head  15 , the post member  27  is moved longitudinally within the slot  26  to depress the biasing member  24  and retract the pawl  22  a sufficient distance such that it does not contact the notches  21 . The post member  27  is then moved circumferentially into the annularly oriented portion of the L-shaped slot  26  to preclude the post member  27  from being advanced outwardly by the biasing member  24 . In this disengaged state, the drive head  15  can now be freely rotated in either direction such that the bone plate members  11  can be contracted or distracted as needed. To engage the pawl  22 , the post member  27  is simple moved from the annularly oriented portion of the L-shaped slot  26  back into the position where the biasing member  24  can push it and the pawl longitudinally within the slot  26 , thereby extending the pawl end  23  into one of the notches  21  of the drive head  15 . Alternatively, the slot  26  can be linear, such that the post member  27  must be held in the retracted position to allow for free rotation of the drive head  15  in either direction. 
         [0021]    It is contemplated that equivalents and substitutions for elements set forth above may be obvious to those of ordinary skill in the art, and therefore the true scope and definition of the invention is to be as set forth in the following claims.