Abstract:
A pediatric mandibular distractor comprising a housing member elongating along a longitudinal axis, the housing member having at least one elongated slot elongating along at least a portion of the longitudinal axis and opening laterally through at least a side portion of the housing member; at least one fixed footplate attached to the housing member; a drive rod; and at least one moveable footplate engageable with the drive rod through the elongated slot by a connector. Wherein, when the fixed and moveable footplates are attached to the respective first and second bone surfaces, a bottom portion of the housing member is proximate to the first and second bone surfaces, and the side portion is further from the bone surfaces than the bottom portion in a direction transverse to the longitudinal axis. Methods of assembling and installing the exemplary pediatric mandibular distractor summarized above are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/730,194 filed Nov. 27, 2012, the disclose of which is hereby incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to a distractor, in particular a pediatric internal mandibular distractor for distracting bone surfaces. 
         [0003]    The obstruction of the airway due to micrognathia is a frequent complication in infants and young children with congenital craniofacial syndromes such as Nager syndrome, Treacher Collins syndrome, and Goldenhar syndrome. These syndromes, along with specific secondary conditions such as maxillary hypoplasia in the setting of cleft lip and palate, hemifacial, microsomia, and Pierre Robin sequence, may require mandibular distraction. The small mandible causes prolapse of the tongue base against the posterior pharyngeal wall leading to respiratory distress. Particularly in young infants, airway obstruction is also commonly associated with feeding difficulties resulting in failure to thrive. 
         [0004]    Mandibular distraction osteogenesis provides an alternative to traditional methods of airway management in infants with Pierre Robin Sequence. This approach consists of lengthening of the mandible, which allows the tongue base to move forward by its anterior muscular attachments to the mandible. Furthermore, this approach has allowed avoidance of tracheostomy as well as early decanulation in infants with Pierre Robin sequence. Tracheostomy in neonates is associated with perioperative and postoperative morbidity such as hemorrhage, pneumothorax, and tracheal stenosis. 
       SUMMARY OF THE INVENTION 
       [0005]    This application discloses a pediatric mandibular distractor and related methods for assembly and installation. 
         [0006]    An aspect of the present invention provides a pediatric mandibular distractor. The distractor in accordance with this aspect of the invention desirably comprises a housing member elongating along a longitudinal axis. The distractor may have at least one fixed footplate attached to the housing member. A drive rod may be arranged within the housing member along the longitudinal axis. 
         [0007]    The housing member desirably has at least one elongated slot elongating along at least a portion of the longitudinal axis. The slot may open laterally through at least a side portion of the housing member. Desirably, the drive rod may be engageable with at least one moveable footplate through the elongated slot by a connector. 
         [0008]    The fixed and moveable footplates are preferably attachable to respective first and second bone surfaces. When so attached, the bottom portion of the housing member may be proximate to the first and second bone surfaces while the side portion of housing member may be further from the bone surfaces than the bottom portion. 
         [0009]    A number of additional aspects of the invention are also disclosed within this application. For example, each of the fixed footplate and moveable footplate may include a planar portion having a plurality of holes for receiving at least one bone screw; and each of the planar portions of the fixed and moveable footplates may be co-planar. 
         [0010]    Another aspect of the invention is that a distal interface of the drive rod may be rotatably secured to a distal end of the housing member. Many aspects of being rotatably secured are contemplated. For example, the distal interface of the drive rod may have a channel for rotatably securing the drive rod to the housing member when a retaining pin is received in the channel. In another aspect, the distal end of the housing member may have a hole for receiving the retaining pin therein. In yet another aspect, the distal interface of the drive rod may be enclosed within the distal end of the housing member. 
         [0011]    Aspects regarding the actuation of the pediatric mandibular distractor are also disclosed in this application. For example, a distractor in accordance with this aspect of the invention may be configured so that rotation of the drive rod advances the moveable footplate along the longitudinal axis. The drive rod may have a threaded portion and the connector of the moveable footplate may be engageable with the threaded portion of the drive rod through the elongated slot. 
         [0012]    In another aspect, the connector may include a threaded bore and a bent portion, the threadable bore may be rotatably engageable with the drive rod, and the bent portion may extend laterally through the elongated slot. In still yet another aspect, the bent portion may comprise two substantially perpendicular bends that offset a bone attachment portion of the moveable footplate from the longitudinal axis in a direction transverse to the longitudinal axis. 
         [0013]    Other aspects of the invention regarding the housing member are also disclosed. For example, a proximal interface of the drive rod may have an exterior dimension that is less than an interior dimension of the housing member, such that the proximal interface is receivable within the housing member to restrict lateral movement of the drive rod. In some aspects of the invention, the exterior dimension of the proximal interface may be larger than a diameter of a threaded portion of the drive rod. 
         [0014]    Another aspect of this invention provides a method for assembling a pediatric mandible distractor. The assembly method in accordance with this aspect of the invention desirably includes providing a housing member with a fixed footplate, a moveable footplate with a connector, and a drive rod with a distal interface, the housing member elongating along a longitudinal axis. The assembly method may also include placing the connector into the housing member so that the moveable footplate extends laterally through an elongated slot in the housing member. Another aspect of the assembly method may include inserting the distal interface of the drive rod into a proximal end of the housing member. Yet another aspect of the assembly method may include engaging the connector with the drive rod. Still yet another aspect of the assembly method may include securing the distal interface of the drive rod within a distal end of the housing member. Desirably, once the distractor is assembled, actuation of the drive rod advances the moveable footplate along the longitudinal axis. 
         [0015]    Additional aspects of the assembly method are also disclosed. For example, the elongated slot may elongate along at least a portion of the longitudinal axis and open laterally through at least a side portion of the housing member. In another aspect of the invention, the distal interface of the drive rod may have a channel; wherein the step of securing the distal interface of the drive rod within the distal end of the housing member may comprise receiving a retaining pin in the channel. In yet another aspect, the distal end of the housing member may also have a hole; wherein the step of securing the distal interface of the drive rod within the distal end of the housing member may also comprise receiving the retaining pin in the hole. In still yet another aspect, the distal interface of the drive rod may be received within an enclosed portion of the distal end of the housing member. 
         [0016]    A further aspect of the present invention provides a method of distracting bone. The method in accordance with this aspect of the invention desirably includes attaching a fixed footplate of a distractor to a first bone surface, attaching a moveable footplate of the distractor to a second bone surface, and actuating the drive rod to advance the moveable footplate along the longitudinal axis. 
         [0017]    In accordance with this aspect of the invention, the fixed footplate may be attached to a housing portion of the distractor. The housing portion may elongate along a longitudinal axis with at least one elongated slot elongating along at least a portion of the longitudinal axis. The elongated slot may open laterally through at least a side portion of the housing member. In another aspect, the distractor may have a drive rod, and the moveable footplate may have a connector engageable with the drive rod through the elongated slot. In another aspect, actuating the drive rod may advance the moveable footplate along the longitudinal axis. 
         [0018]    Desirably, when the fixed and moveable footplates are attached to the respective first and second bone surfaces, a bottom portion of the housing member is proximate to the first and second bone surfaces, and the side portion is further from the bone surfaces. In some aspects of the invention, the bone may be a mandible, and the method of installation may further comprise the step of performing an osteotomy in a body, ramus, or angle of the mandible prior to attaching the fixed and moveable footplates to the respective first and second bone surfaces. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1A  is a bottom plan view and  FIG. 1B  is a side plan view of a distractor according to aspects of the invention. 
           [0020]      FIG. 2  is a perspective view of the distractor of  FIGS. 1A and 1B  with a cross-section of the housing removed along A-A. 
           [0021]      FIG. 3  is a view of the drive rod for use with the distractor of  FIGS. 1A-1B . 
           [0022]      FIG. 4  is a cross-section of the housing for use with the distractor of  FIGS. 1A-1B  along A-A. 
           [0023]      FIG. 5  is a top plan view of the distractor in an open configuration. 
           [0024]      FIG. 6  is a cross-sectional view of the second footplate. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIGS. 1A and 1B  illustrate a distractor  100  according to aspects of the invention and  FIG. 2  illustrates a perspective view of the distractor of  FIGS. 1A and 1B  with a cross-section of the housing removed along A-A. 
         [0026]    The distractor  100  may include a housing  110  that is generally cylindrical and extends along a longitudinal axis of the distractor  100 . The housing  110  may be hollow and may include a slot  112  that extends longitudinally along the housing  110 , at least partially between a proximal end  110   a  and a distal end  110   b  of the housing  110 . In one example, the slot  112  may extend to the edge of the housing  110  at the proximal end  110   a , but may not extend to the edge of the housing  110  at the distal end  110   b . The slot  112  may have any width, and in one example may have a width sufficient to accommodate a footplate and/or footplate attachment, as will be described in greater detail below. Advantageously, the slot  112  may be positioned along a side of the housing  110  rather than along the bottom of the housing proximate the underlying bone. Desirably, the location of the slot  112  along the side of the housing reduces the risk of tissue bone ingrowth into the distractor via the slot. 
         [0027]    The housing  110  may also include one or more holes  114 . In one example, the holes  114  may be configured to receive one or more pins  150 , as will be described below. The holes  114  may be formed through at least one wall of the housing  110  such that the one or more pins  150  may be inserted into the housing  110  in a direction perpendicular to the longitudinal axis. In one example, the one or more pins  150  may be inserted in a direction perpendicular to the attachment portion of one or more footplates. 
         [0028]    The housing  110  may also include a channel  116 . The channel  116  may be disposed at the distal end  110   b  of the housing  110 . The channel  116  may have an internal diameter that is less than an overall internal diameter of the housing  110 , as shown in  FIG. 4 . The channel  116  may be positioned adjacent one or more of the holes  114  such that, when pins are inserted into the holes  114 , the pins extend at least partially into the channel  116 . 
         [0029]    The distractor  100  may also include a first footplate  120 . The first footplate  120  may be attached to the distal end  110   b  of the housing  110 , and in one example may be fixed to, or integrally formed with, the housing  110 . An attachment portion  122  of the first footplate  120  may be substantially planar and may include a plurality of holes  120   a  there through. The plurality of holes  120   a  may be aligned with a bone surface and screws (not shown) may be passed there through. This may allow the first footplate  120 , and the distractor  100 , to be secured to the bone surface of the patient. In one example, the plurality of holes  120   a  may be configured to receive resorbable screws. The holes  120   a  may be countersunk as shown in  FIGS. 2 and 6 , so that the heads of the screws may be at least partially received within the holes  120   a , and, more preferably, so that the top surfaces of the screw head may be substantially flush with the top surface of the attachment portion  122 . 
         [0030]    The distractor  100  may also include a second footplate  130 . The second footplate  130  may be movable with respect to the housing  110  within a slot  112 , as will be explained in greater detail below. The second footplate  130  may include a footplate attachment  132  positioned within the housing  110  and a connector portion  134  extending through the slot  112  of the housing  110  from the engagement portion  136  to an attachment portion  132 . The engagement portion  136  may include a threaded bore formed there through configured to threadably engage with a drive rod  140 , as will be described below. An outer surface of the engagement portion  136  may be substantially cylindrical and may conform to an inner surface of the housing  110 . The attachment portion  132  of the footplate  130  may be substantially planar and may include a plurality of holes  130   a  there through, as described above with respect to footplate  120 . 
         [0031]    As shown in  FIG. 1B , the attachment portion  132  of the second footplate  130  may be positioned coplanar to the attachment portion  122  of the first footplate  120 . In this arrangement, the connector portion  134  of the second footplate  130  may include two substantially perpendicular bends  134   a, b  in order to connect the engagement portion  136  to the attachment portion  132 . In other examples, the attachment portions  122 ,  132  of the first and second footplates  120 ,  130  may be positioned orthogonal with respect to one another, or at any other desired angle suitable for the circumstances. 
         [0032]    The distractor  100  may also include a drive rod  140  arranged longitudinally within the housing  110 . The drive rod may include a threaded portion  142 , a projection  144 , and a connection interface  146 . 
         [0033]    The threaded portion  142  may be substantially cylindrical and disposed between the projection  144  and the connection interface  146 . The threaded portion may have a diameter less than an internal diameter of the housing such that the threaded portion  142  may be received within the housing  110 . 
         [0034]    One end of the drive rod  140  may include a projection  144  that extends axially with respect to the drive rod  140 . The projection  144  may be cylindrical and may have a tip  144   a  and a channel  144   b . The tip  144   a  may have a diameter that is larger than a diameter of the channel  144   b . In this regard, the projection  144  may be secured within a corresponding channel  116  of the housing  110  by way of one or more pins  150 . For example, the projection  144  may be positioned within the channel  116  such that the one or more pins  150  may partially extend into the channel  116 . The one or more pins  150  may align with and engage the channel  144   b  of the drive rod  140 , and since a clearance between the pins  150  is less than a diameter of the tip  144   a  of the projection  144 , the drive rod  140  is restricted from moving longitudinally with respect to the housing  110 . This configuration advantageously allows the distal end  110   b  of the housing  110  to be sealed, as the drive rod  140  does not extend through an opening at the distal end  110   b  of the housing, which prevents any bone or tissue from being introduced into the housing  110  through such opening. 
         [0035]    The drive rod  140  may also include a connection interface  146  disposed at an end of the drive rod  140 . The connection interface  146  may include one or more prongs  146   a, b  configured to interface with a connection member  160 . The connection interface  146  may be at least partially cylindrical and may have a diameter greater than a diameter of the threaded portion  142 . As shown in  FIG. 2 , the connection interface  146  may be at least partially received within the housing  110 . 
         [0036]    The diameter of the connection interface  146  may also be smaller than an interior diameter of the housing  110  such that the connection interface  146  may rotate freely about a longitudinal axis. In one example, the diameter of the connection interface  146  may be slightly less than the interior diameter of the housing  110  so as to constrain the orientation of the longitudinal axis of the drive rod  140  with respect to the housing  110 . In one example, the connection interface  146  is 0.5 mm less than the interior diameter of the housing  110 . As a result, the drive rod  140  may rotate freely about the longitudinal axis, but its lateral movement is restricted by the connection interface and its longitudinal movement is restricted by the pins  150 , as described above. 
         [0037]    The distractor  100  may also include a connection member  160 . The connection member  160  may include one or more prongs  160   a  at one end for forming a joint  162  with the prongs  146   a  of the connection interface  146 , establishing a connection between the connection member  160  and the drive rod  140 . In one example, the joint  162  may be a Hooke&#39;s joint, thereby allowing rotation of the drive rod  140  by rotation of the connection member  160 , or any tool attached thereto even though the connection member  160  may be angled with respect to the longitudinal axis of the drive rod  140 . At the other end, the connection member  160  may include a tool interface  164  for connecting to a tool (not shown), or extension member (not shown) connectable to a tool. 
         [0038]    The distractor  100  may be assembled by positioning the second footplate  130  within the housing  110 . In this regard, the second footplate  130  may advance toward the distal end  110   b  of the housing  110 , with the connector portion  134  advancing through the slot  112 . The drive rod  140  may be inserted at the proximal end  110   a  of the housing  110  and may be received within the threaded bore of the engagement portion  136  of the second footplate  130  and into the channel  116 . The pins  150  may then be inserted into the holes  114 , thereby restricting longitudinal movement of the rod  140  with respect to the housing  110 . 
         [0039]    The distractor  100  may be installed internally within a patient, such as an infant or young child. The first and second footplates  120 ,  130  may be secured to respective bone surfaces within the patient by way of holes  120   a  and  130   a  and one or more bone screws. In one example, the bone surfaces may be surfaces of bone comprising the mandible, which may have an osteotomy there between. Prior to installing the distractor, the osteotomy may be performed in the body, ramus, or angle of the mandible. Once installed, the connection member  160  may be rotated in a first direction about the longitudinal axis, either alone or by way of a tool or extension member. 
         [0040]    This rotation may cause the drive rod  140 , by way of the joint  142 , to similarly rotate in a first direction about the longitudinal axis. While free to rotate in this manner, the drive rod  140  is restricted from longitudinal movement, as described above, by the one or more pins  150 . The drive rod  140  is also restricted from lateral movement by the interaction between the connection interface  146  and the housing  110 . Since the drive rod  140  is rotating, but is longitudinally and laterally stationary, this causes the second footplate  130  to advance longitudinally along the drive rod  140  away from the first footplate  120  and toward the proximal end  110   a  of the housing  110 , as shown in  FIG. 5 . 
         [0041]    The threaded bore of the footplate attachment  132  is threadably engaged with the threaded portion  142  of the drive rod  140  and allows for longitudinal translation of the second footplate within the slot  112 . As the footplates  120  and  130  are slowly moved relative to one another, bone growth may be promoted between the respective bone surfaces to which they are attached. For example, the drive rod  140  may be actuated one or more times each day and rotated a specified number of times during each actuation. If the drive rod  140  is rotated in a second direction opposite the first direction, the second footplate  130  may translate back toward the first footplate  120 , thereby decreasing a distance between the two footplates  120  and  130 . 
         [0042]    The distractor  100 , as well as any components thereof, may be formed of any material, and in one example may be titanium. In one example, the distractor  100  may undergo anodization, such as type II anodization. This advantageously reduces or prevents bone or tissue of a patient from attaching or adhering to the surface of the distractor  100 . This allows for easy removal from the distractor  100  from the patient. 
         [0043]    In another implementation, the distractor  100  may include a second slot disposed longitudinally along the housing  110  on an opposite side of the housing  110  from the first slot  150 . In this example, a third footplate may be threadably engaged with the drive rod  140 , either connected to the same footplate attachment  132  as the second footplate  130  or connected to a different footplate attachment, and may translate longitudinally along the drive rod  140  via the second slot. 
         [0044]    In yet another implementation, the distractor  100  may include a plurality of fixed footplates, for example two or more fixed footplates. In one example, two fixed footplates may be positioned at a distal end of the housing  110 , and, in another example, two fixed footplates may be positioned at the proximal end of the housing, or any combination thereof. 
         [0045]    In the above examples, the planar attachment portions of the fixed first footplate  120  and the second footplate  130  are positioned on the same side of the longitudinal axis of the housing  110 . In other examples, the first and second footplates may be positioned on opposite sides of the longitudinal axis. 
         [0046]    Although the distraction is driven from the connection member  160  at the proximal end  110   a  of the housing  110  in the above examples, other implementations in accordance with aspects of the disclosure may have the distraction actuated from other locations. For example, with appropriate connections to the drive rod, the distraction may be driven from the center or at the distal end  110   b  of the distractor housing  110 . 
         [0047]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present disclosure.