Abstract:
A bone distractor to create separation between bone segments by means of a pair of mounts respectively secured to the bone segments and interconnected by means of a drive spring which is secured to one of the mounts and threadedly interconnected to the other mount such that rotation of the drive spring creates sufficient separation of the bone segments to allow for osteogenesis to occur.

Description:
BACKGROUND OF THE INVENTION 
     Bone distractors are utilized in the field of orthodontics in connection with the repair and regeneration of craniofacial bones and in particular the mandible and maxilla. Typically, a bone is cut or fractured to create two separate segments which results in a space formed therebetween. Through the process of osteogenesis, the regeneration of bone occurs in the space between the two segments. The distance between the bone segments can be increased over time allowing additional new growth to occur. 
     One means of accomplishing distraction is to affix mounts, respectively, on the two bone segments. A drive screw is threadedly interconnected to one of the mounts and is affixed to the other mount whereby rotation of the drive screw causes separation of the bone segments. Typically, distractor drive screws are somewhat inflexible such that they are not able to bend to the degree desired in many applications and sometimes break when they are bent too far. 
     BRIEF SUMMARY OF THE INVENTION 
     According to this invention, a bone distractor is utilized to create space between two bone segments so as to achieve bone growth between the segments through the process of osteogenesis. The distractor includes a pair of mounts secured, respectively, to the bone segments with a drive spring extending through one of the segments and being threadedly interconnected to the other segment. The drive spring is disposed in a holder which is integrally joined to the first mount and the drive spring extends through the second mount. The end of the drive spring extending outwardly from the first mount is attached to a round flexible activation shaft by means of a universal mount. The activation shaft is manually rotated causing rotation of the drive spring and separation of the bone segments resulting from the threaded interconnection of the drive spring and a threaded block incorporated into the second mount. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a perspective view showing the distractor before distraction has occurred; 
         FIG. 2  is a perspective view showing the distractor after distraction has occurred; 
         FIG. 3  is an enlarged view of the distractor device; 
         FIG. 4  is an exploded view showing individual elements of the distractor; 
         FIG. 5  is a view showing details of the drive spring; and 
         FIG. 6  is an exploded sectional view taken along the line A-A in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The purpose of the bone distractor, according to this invention, is depicted in  FIGS. 1 and 2  wherein, in  FIG. 1 , bone segments  1  and  2  are in abutting relation along severance line S. Activation of the bone distractor causes bone segments  1  and  2  to separate along the severance line into the positions shown in  FIG. 2  whereby space  3  is formed therebetween. 
     The distractor, as shown in  FIG. 3 , includes mounts  4  and  5 . Mount  4  is affixed to the patient&#39;s bone by inserting bone screws through apertures  6  and  7 . Similarly, mount  5  is affixed to the patient&#39;s bone by means of attachment arms  8 ,  9  and  10  each of which has a pair of apertures  11  and  12  formed therein. Mount  5  is secured to the patient&#39;s bone by inserting bone screws through apertures  11  and  12  of each arm  8 ,  9  and  10 , as is well known in the art. 
     For the purpose of activating the distractor and separating bone segments  1  and  2 , round helical drive spring  13  is provided with flexible wire  14  extending substantially the entire internal length of drive spring  13 , as best shown in  FIG. 5 . Typical drive screws known in the art are somewhat inflexible and tend to break during use. Wire  14  enhances the stabilization properties of an inherently unstable helical drive spring  13  and aids in lessening the drive screw spring back reaction after the distractor is activated. 
     In order to complete the bone distractor, according to this invention, drive spring  13  is disposed in trough-shaped holder  15 . Holder  15  is curved and comprises bottom  16  with parallel spaced sidewalls  17  and  18  extending upwardly therefrom with the top of drive spring  13  in general alignment with the tops of sidewalls  17  and  18 . As best shown in  FIG. 3 , the proximate end of holder  15  is integrally joined to mount  4  with drive spring  13  extending through an elongated channel formed in mount  4  and with universal joint  19  affixed to the exposed free end of drive spring  13 . 
     As shown in  FIG. 6 , mount  5  contains multiple elements including base plate  20  and top plate  21  with apertures  22  and  23  formed in top plate  21 . Block  24  is secured to the underside of top plate  21  by any suitable means such as a screw threaded through an aperture formed in top plate  21  and into block  24 . The lower inner surface of block  24  includes threads  25 . 
     The assembly of mount  5  is completed by attaching top plate  21  to base plate  20  by placing top plate  21  on upstanding supports  26  and  27  which in turn are integrally joined to base plate  20 . Top plate  21  is secured in place by means of screws inserted through apertures  22  and  23  formed in top plate  21  and into threaded apertures  28  and  29  formed, respectively, in supports  26  and  27  in such manner that threaded block  24  is situated between sidewalls  17  and  18 . 
     Simultaneously with this operation, holder  15  with drive spring  13  disposed therein is positioned on base plate  20  between supports  26  and  27  and block  24  is seated between sidewalls  17  and  18  so that threaded portion  25  is threadedly interconnected with drive spring  13 . In order to secure drive spring  13  in place in holder  15 , the end of drive spring  13  extends through aperture  30  formed in the end of holder  15  with ring  31  formed on the end of drive spring  13  to prevent the withdrawal of drive spring  13  through aperture  30 . 
     Following this, the bone distractor is in condition for attachment a patient&#39;s bone, as shown in  FIG. 1 , whereby mount  4  is attached to bone segment  1  and mount  5  is attached to bone segment  2  by means of the associated bone screws. To achieve bone distraction, flexible activation shaft  32  is releasably coupled to universal joint  19  and an appropriate drive tool is attached to the free end of activation shaft  32 . Activation shaft  32  is then manipulated to cause rotation of drive spring  13 . Separation of segments  1  and  2  occurs due to a combination of the threaded interconnection between drive spring  13  and threads  25  of block  24  secured to mount  5  and the integral connection of the end of holder  15  to mount  4 .