Abstract:
A spiral distraction device includes anchoring means for attachment of the device to each side of a patient&#39;s existing mandible. A conjoined intermediate bar attaches to and transports moveable bone pieces on each side of the patient&#39;s mandible towards each other in a spiral vector that is larger than the patient&#39;s anatomical mandible contour.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This Application is a Continuation of Application PCT/GB03/00814 filed on Feb. 28, 2003. Application PCT/GB03/00814 claims priority for Application 0204783.5 filed on Mar. 1, 2002 in the United Kingdom.  
       FIELD OF THE INVENTION  
       [0002]     This invention relates to an osteogenesis method and device.  
       BACKGROUND OF THE INVENTION  
       [0003]     Distraction osteogenesis (“DO”) was originally described by Ilizarov in the 1950&#39;s in the lengthening of limb bones by the manipulation of callus following osteotomy, with external pins passing through the skin. DO was later adapted for advancement of the facial bones using both internal screw devices and external pin distraction devices. These devices were developed as a simpler alternative to complex composite flap reconstruction of the facial skeleton, which involve long and complex surgical multi-sited and multi-staged procedures. In particular, the area of the chin is technically very difficult to reconstruct.  
         [0004]     All distraction devices to date have a problem, with precise choice of vector leading to deformity, and malocclusion. External pins cause skin necrosis and scarring as they are pulled through the tissue with their attached bone. These devices also have a low mechanical advantage leading to bending and fracture of transcutaneous pins. Furthermore, reconstruction of the curved vector of the chin is difficult especially with external pins and the associated frames and this leads to unwarranted soft tissue damage.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     According to one aspect of the present invention, there is provided a spiral distraction device comprising anchoring means for attachment of the device to each side of a patient&#39;s existing mandible, conjoined intermediate bar means adapted to attach to and transport moveable bone pieces on each side of the patient&#39;s mandible towards each other in a spiral vector that is larger than the patient&#39;s anatomical mandible contour, and means to action the intermediate bar means to effect said transport.  
         [0006]     Preferably the spiral vector is a spiral curve vector, such a curved vector preferably produces a class 111 or mandible prognathism contour.  
         [0007]     By spiralling the moving bone in opposite rotations, the moveable bone pieces can be transported to almost overlap with each other at or near the mid-line position. Removal of the distraction device from the patient once bone-transportation is complete allows the surgeon to ‘bend’ the bone pieces back towards each other to achieve bony overlap and thereafter be conjoined in a wholly or substantially regular line across the midline.  
         [0008]     Using rapid prototyping and engineering assisted surgery techniques, preoperative planning can ensure a normal degree of mandibular prognathism. This is achieved with the conversion of a prognathic Class III mandibular profile at the endpoint of distraction to a normal Class I mandibular profile following removal of the distraction device and bending of the intervening callous to achieve bony overlap in the midline.  
         [0009]     In one embodiment of the present invention, the intermediate bar means includes a capstan means through or around which the relevant part of the bar means and/or means for attachment is wound or otherwise rotated to effect the transportation action. Also preferably, the capstan includes one or more key attachment means such as a suitable aperture in which a bar, key etc, can be permanently or removably inserted.  
         [0010]     The intermediate bar means preferably includes one or more spiral vector bars whose distal ends are attachable to the mandible attachment means. The attachment means act as anchors.  
         [0011]     According to another embodiment of the present invention, the distraction device includes one or more shuttles adapted to wholly or substantially cut or cleave through patient&#39;s tissue to assist in transportation of the moving bone pieces therethrough.  
         [0012]     The spiral action of each vector could equally result in the right hand bone pieces being transported to a position above the left hand bone piece at or near the midline position, or vice versa.  
         [0013]     The spiral curve vector of each bone piece is preferably wholly or substantially a parabolic vector shape.  
         [0014]     The method of attachment of the device to a mandible, and method of attachment of bone pieces together once transported, is well known in the art. Such means includes screws, etc.  
         [0015]     According to a second aspect of the present, there is provided a method of forming a mandible for a patient using a spiral distraction device as hereinbefore defined, comprising the steps of; 
        attaching anchoring means to each side of a patient&#39;s existing mandible;     conjoining the intermediate bar means to the anchoring means and to moveable bone pieces on each side of the patient;     activating the intermediate bar means to transport the bone pieces towards each other in a spiral vector that is larger that the patient anatomical mandible contour;     removing the distraction device at the end point of distraction; and     conjoining the bone pieces.        
 
         [0021]     Preferably, the bone pieces are transported towards each other by bending the bone pieces backwards so as to achieve bony overlap. This is facilitated by virtue of the malleability of adjacent callous in the area of distraction.  
         [0022]     The distraction device is removed at the end point of distraction, i.e. when the shuttles reach their end point of movement by contact with the capstan.  
         [0023]     Preferably, the bone pieces are transported through a number of discrete steps.  
         [0024]     The spiral distraction device of the present invention provides; 
        accurate presurgical planning with selection of a predetermined vector using rapid prototyping reverse engineering and Engineering Assisted Surgery Principles which facilitate the translation of the surgical plan into the patient;     improved Mechanical Advantage, with less force required for distraction and less soft tissue injury;     an internal device using cord or chain distraction techniques and an external capstan/key mechanism;     easy assembly and disassembly;     a mechanism to facilitate bony union between the distracted segments with bony overlap using a lag/position screw system which may also double as an overdenture attachment system; and     spiral distraction vectors which permit easy removal of the device from the patient with a ring hammer device.        
 
         [0031]     The use of the present device is also associated with the reduced surgical trauma and operating time and has applications in other areas of the skeleton.  
         [0032]     The present invention is useable to reconstruct any bit of the lower jaw, i.e. the body of the mandible, as well as the chin. In that regard, the spiral vector may be a ‘straight’ spiral vector, i.e. the bone spirals along a substantially straight line, as well as a curved spiral vector for the front of the chin. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]     An embodiment of the present invention will now be described by way of example only and with reference to the accompanying photographic drawings in which:  
         [0034]      FIG. 1  shows anchoring devices planted on a stereoscopic lithographic model;  
         [0035]      FIG. 2  shows parts of a distraction device of the present invention;  
         [0036]      FIGS. 3 and 4  show assembly of the device;  
         [0037]      FIG. 5  shows the assembled device on a lithographic model from below.  
         [0038]      FIGS. 6   a  and  6   b  show front and side views of  FIG. 5 ;  
         [0039]      FIG. 7  shows activation of the device of previous Figures; and  
         [0040]      FIG. 8  shows extraction of the device after use. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0000]     Referring to the Drawings:  
         [0000]      FIG. 1 :  
         [0000]     Disassembled System  
         [0000]     Anchorage to Mandibular Ramus (A)  
         [0041]     Two custom made devices are manufactured using rapid prototyping and reverse engineering techniques. These devices are screwed to the outside of the mandibular ramus with 2.7 mm screws or another appropriate screw system. The design may be planned on a stereoscopic lithographic model (or other engineered model from biological scan data) and loop under the lower border of the mandible to the lingual side of the mandible. Located on the lingual side of the anchorage device is a female part of an attachment device (B) which fits into the male attachment part of the spiral vector bar. This device provides skeletal anchorage for the distraction mechanism. It is possible that this anchorage device could be mass produced.  
         [0000]      FIG. 2 :  
         [0000]     The Spiral Vector Bar (c)  
         [0042]     The spiral vector bar is custom made (but could be mass produced) and consists of an implantable metal bar which slots into the anchorage; as shown later. The principle of this device is that it produces a curved shape that is larger than the patient&#39;s anatomical mandible contour, so that when the device is removed the right and left sides of the regenerated bone, the bone can be bent backwards to produce an overlap of bone which may be lag screwed or otherwise fixed to achieve bony union. The lag screw mechanism could incorporate an overdenture abutment attachment which penetrates the oral mucosa for attachment of an overdenture.  
         [0043]     The spiral vector bar (D) receives runner bars from one or more mobile shuttles, into one or more spiral channels which will be attached to mobilised osteotomised fragments of the posterior mandible. This permits smooth passage of the shuttle around a predetermined vector. A modification of attachment of the shuttle involves the incorporation of a ring which surrounds the spiral vector bar guiding the shuttle on a spiral thread.  
         [0044]     The shuttles are sharp to provide a cutting mechanism to facilitate the transport the bone pieces of the shuttle through the body tissues.  
         [0045]     A capstan device is located anteriorly (E) with two optional removable key attachments. These are inserted into the capstan using the key (G) and an angled screwdriver (H). The key attachments penetrate through the skin below for daily cranking with a predetermined traction distance. The cranking rod is designed to pull the contralateral shuttle round the spiral to the end point using a traction cord of dacron or other suitable implantable material wire or chain.  
         [0046]     A variation of the capstan device includes one or more intra oral key attachments attached directly into the capstan in cases with adequate access and good mouth opening.  
         [0047]     An elastic band (I) is shown connecting the shuttles. This is only to stabilise movement of the device in the photographic demonstration of vector dynamics. The elastic band is not included in the device for implantation.  
         [0000]      FIGS. 3 and 4 :  
         [0000]     Key Attachments  
         [0048]     The removable key attachments are fixed to the device as illustrated. In this case the capstan is exposed and located in the floor of the mouth.  
         [0049]     The key attachments penetrate the skin below the chin.  
         [0050]     (I)—indicates the elastic band, (used for photographic illustration of vector dynamics only).  
         [0051]     One or more,(in the case illustrated two) traction cords (J) run in a groove within the spiral vector bar and then pass backwards through a hole.  
         [0000]      FIG. 5 :  
         [0000]     The Assembled System  
         [0052]     The device is designed to grow the mandible with a greater anterior projection so that on removal of the device the jaw can be bent backwards to achieve bony contact between the two distracted segments so that the end point is the correct contour of the chin and lower jaw. 
        A—Skeletal Anchorage Device to mandibular ramus     B—Female attachment part for spiral vector bar (hidden by elastic band I)     C—Spiral distractor bar for choice of selective vector     D—Shuttle     E—Capstan     F—Removable Key attachments     I—Elastic Band (for photographic demonstration of vector dynamics only). 
 
  FIGS. 6   a  and  6   b:  
 
 End Point—Spiral Distraction 
       
 
         [0060]     The shuttles have been advanced to their endpoint with the creation of a neo-mandible. For illustration the shuttle related to the patient&#39;s right side of mandible (Dr) has moved superiorly and its lateral surface is now facing upwards. The Shuttle related to the patient&#39;s left side of mandible (Dl) has spiralled inferiorly with its lateral surface now facing inferiorly. This facilitates the removal of the screws into the adjacent bone and permits simple removal of the spiral distractor bar with an anterior path of removal between the regenerated pieces of new bone using a ring hammer.  
         [0000]      FIG. 7 :  
         [0000]     Spiral Vector Distraction  
         [0061]     Movement of the key provides the spiral path of distraction on the left side.  
         [0062]     The shuttle has razor sharp edges to cleave through the tissues.  
         [0000]      FIG. 8 :  
         [0000]     Removal of Device  
         [0063]     At the end point of spiral distraction, the key attachments are removed.  
         [0064]     An appropriate incision is made to expose the anterior aspect of the spiral distractor.  
         [0065]     The shuttle screws are removed from the adjacent bone in the leading edge of the neo-mandible.  
         [0066]     A specially designed ring hammer is hooked around the back of the capstan and with a sharp tap the spiral vector bar is removed with an anterior path of withdrawal.  
         [0067]     The skeletal anchorage devices to the mandibular ramus are then removed through appropriate incisions in the neck.  
         [0068]     The mandible at this stage is oversized, and the anterior free bone fragments are bent towards the midline until they overlap, at which point they are screwed together with a position screw or lag screw or screws. This fixation screw device could incorporate an overdenture attachment system which perforates the oral mucosa for denture attachment.  
         [0000]     Stabilisation  
         [0069]     Following removal of the spiral vector bar, the new chin position is stabilised using two additional dental implant precision attachment devices/overdenture attachments in the proximal mandible posterior to the osteotomy. Acting with the midline overdenture attachment this gives three point fixation until the malleable callous matures into stable bone over an estimated three month period.