Abstract:
A computer aided system of orthopedic surgery is disclosed and omnidirectional osteogenesis is provided as an example thereof. To perform this surgery a craniofacial anatomic surgical simulator (CASS) is described, in which simulator a stereolithographic medical model is mounted. The medical model hereof is modified for this purpose so that pre-operative intra-oral devices, including custom-fitted fixation plates, can be crafted. An occlusal splint formed on the stereolithographic model acts as an armature for a docking bar which is, during the surgical operation, rigidly affixed to the fixation plate(s). The CASS, in one embodiment hereof, includes an indexing means for alignment of the stereolithographic model. The CASS also simulates the temporomandibular joint and fixedly mounts segments of the model in a post-operative condition.

Description:
CROSS REFERENCE TO RELATED 
     This is a non-provisional of Provisional Application No. 60/871,441 filed Dec. 21, 2006, entitled Articulator for Patient Generated CAT Scan Craniofacial Stereolith Model; of Provisional Application 60/885,570 filed Jan. 18, 2007 entitled Craniofacial Maxillary Custom Intra-Oral Distraction Device; and of Provisional Application 60/899,441 filed Feb. 6, 2007, entitled Intra-Oral Mandibular Distraction Device, said provisional applications incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to methods, devices, and computer generated models for a system of orthopedic surgery and more particularly for surgical employment of distraction osteogenesis using intra-oral omnidirectional distraction devices. This invention is implemented using medical imaging; medical modeling; computer-aided design and manufacturing; a novel craniofacial anatomic surgical simulator, a custom-fitted, removable fixation device with distractor; and, a precision docking mechanism that allows omnidirectional positioning of skeletal segments. 
     2. Description of the Related Art 
     In the past, computerization for surgical preplanning purposes has provided stereolithographic models of the anatomic site. These are three-dimensional models constructed using digitized information from scanning devices such as laser and acoustic reflection apparatus and various types of transmission apparatus including X-ray, magnetic resonance imaging (MRI), positron emission (PET or SPECT) as well as ultrasonic radiation. 
     Upon data being captured by scanning a series of spaced parallel planes, the scans are combinable by computed-tomographic (CT) techniques to construct a three dimensional projection of the scan in the form of a medical model such as a stereolithographic representation. Anatomical modeling using CT-scan data is well known and is widely accepted in pre-operative planning, rehearsal of surgical procedures, and the manufacture of prosthetic devices. 
     U.S. Pat. No. 6,112,109 of D&#39;urso and U.S. Patent Application Publication 2005/0133955 both describe the use of CT-scan data for constructing prosthetic devices that are custom-fit to provide a better relationship between the remaining healthy bone and the orthopedic implant. 
     To implement the inventor&#39;s system of orthopedic surgery several heretofore unknown devices needed to be developed. A craniofacial anatomic surgical simulator is described, infra, for mounting and working the stereolithographic model. As background to this development, Krause et al. in U.S. Pat. No. 6,701,174 comment that in the complex area of bone distraction surgery “it is difficult, if not impossible, to make accurate surgical plans based solely on a limited number of two-dimensional renderings of bone geometry. This is because of the complex and inherently three-dimensional nature of bone deformities as well as of fixator geometry. Furthermore, two-dimensional depictions of surgical plans may not accurately portray the complexities involved in accessing the target positions of the osteotome and fixator pins surrounding the operated bone. Lack of three-dimensional modeling of these geometric complexities makes it difficult to accurately mount the fixator on the patient according to the presurgical plan”. 
     The computer-assisted preplanning of Krause et al. made an early attempt to resolve this long-felt need through the use of a Taylor Spatial Frame—a collection of fixator struts and associated software; however, they found that the apparatus did not provide visual feedback on how the fixator frame and bone fragments should be moved over time. 
     As further background to the surgical simulator hereof, in the medical literature Cheung et al. In a 2007 article entitled,  Vector Guidance Splint for Internal Maxillary Distraction  (IL Oral Maxillofacial Surgery, pp. 1852 et seq.) reports using a Hanau Engineering Articulator, developed in the 1920&#39;s. 
     Taking dental articulators as the forebears of the Craniofacial Anatomic Surgical Simulator hereof leads one to view the articulator patent art starting with Hanau, U.S. Pat. No. 1,586,739 and leading patents to Tradowsky, U.S. Pat. No. 4,365,955; El Hadary, U.S. Pat. No. 5,073,109; Federici, U.S. Pat. No. 5,533,896; and Shih, U.S. Pat. No. 5,720,612. None of these devices fulfill the simulation requirements of the disclosure at hand. 
     SUMMARY 
     This disclosure describes a craniofacial anatomic surgical simulator (CASS) for mounting a medical model such as a stereolithographic medical model. The framework of the CASS includes a fixed base and a pair of columns arising therefrom, which columns are adjustable to raise and lower a mounting plate on which the craniomaxillary portion of the medical model is mounted. The CASS also provides fixtures to mount the mandibular portion within the glenoid fossae and simulates the temperomandibular joint. The CASS facilitates the formation of pre-operative intra-oral devices required for omnidirectional distraction osteogenesis. 
     The description of the preferred embodiments, infra, describes two models of the CASS which differ in the manner in which segmented portions of the medical model are held in place. Both describe mounting mandibular portions with three degrees of freedom. In the first embodiment this is accomplished with a movable base for mandibular mounting and in the second embodiment manipulators or “helping hands” are used in place thereof. It is further noted that the medical model is specific to the application at hand in that the truncated upper portion is replaced with a cranial mounting plate. Also, mounting nodes or connectors are placed about the medical model and the CASS framework to facilitate management of the medical model. 
     The CASS is constructed to enhance the measurement of cephalometric points by providing a grid on the fixed base. Additionally the stereolithographic model may be indexed within the CASS framework by having a computer generated midline reproduced on the cranial mounting plate of a model and matched to a similar midline of the upper mounting plate. Other details of the construct are described in the specification which follows. 
     OBJECTS AND FEATURES OF THE INVENTION 
     It is an object of the present invention to provide for prefitting or custom fabrication of internal devices for omnidirectional distraction, such as, for craniofacial surgery intra-oral distractors, docking bars, and modified occlusal splints. 
     It is another object of the present invention to provide a medical model, such as a computed tomographic (CT) generated stereolithographic facial skeleton, to optimize planning and preparation phase of craniofacial surgery. 
     It is yet another object of the present invention to provide a computer-aided system of surgery whereby through simulation information is gained as to anatomic variables, including the contour and surface mapping of the bone, the quality of the bone, and the location of neurovascular structures. 
     It is a further object of the present invention to provide in the pre-planning phase the most favorable osteotomy and ostectomy design and the analysis of possible anatomical interferences upon segmental movement. 
     It is yet another object of the present invention to provide a medical model suitable for mounting in an craniofacial anatomic surgical simulator therefor and facilitating the pre-fitting of internal devices. 
     It is a feature of the present invention that the craniofacial anatomic surgical simulator hereof has a medical model mounting arrangement with an accurate and functional temperomandibular joint for suitably positioning the maxillofacial and mandibular segments so as to enhance surgical planning. 
     It is another feature of the present invention that the omnidirectional distraction with the anatomically contoured fixation plates prevents the difficulties of prior intra-oral devices which resulted in the undesired rotation of the maxilla. 
     Other objects and features of the invention will become apparent upon review of the drawings and the detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in more detail below with reference to the embodiments shown in the drawing in which like elements are labeled similarly. 
         FIG. 1  is a schematic diagram of the new system of orthopedic surgery for which the craniofacial anatomic surgical simulator is designed; 
         FIG. 2  is a perspective view of the first embodiment of the craniofacial anatomic surgical simulator of this invention having a uniquely positionable mandibular mounting arrangement; and, 
         FIG. 3  is a perspective view of the second embodiment of the craniofacial anatomic surgical simulator of this invention utilizing transfer assemblies to hold segments of the stereolithographic model. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This disclosure describes a new system of orthopedic surgery, which changes present-day craniofacial procedures and is particularly applicable to distraction osteogenesis. In order to work within this new surgical milieu, an initial trio of inventions were required. While the following introductory discussion uses distraction osteogenesis as exemplary, it should be borne in mind that certain devices, such as the craniofacial anatomic surgical simulator (CASS), may be more broadly applied. 
     Surgical Preplanning 
     Referring to the schematic diagram of the system  FIG. 1 , a general overview of the new system of orthopedic surgery is now provided. Three principal divisions are apparent, namely, (1) surgical preplanning; (2) pre-operative device construction; and, (3) patient procedures. 
     Upon initializing the process, an IMAGING  22  of the patient is first undertaken. The IMAGING  22  step may obtain digitized data from scans of magnetic resonance imaging (MRI), X-ray, computed tomography (CT), ultrasound, laser interferometry or position emission technique (PET). From the collected data, accurate anatomic information as to the bone formation and bone malformation is available. 
     A medical model, preferably stereolithographic, is formed using MODELING  24  techniques presently extant. Typical of the available modeling techniques are those described in a Christensen, U.S. Patent Application Publication 2005/0133955 for custom prosthesis development. In preparation for the mounting of the model on the craniofacial anatomic surgical simulator which follows, the segments of the stereolithographic model are carefully evaluated. 
     The inventor&#39;s craniofacial anatomic surgical simulator, described in detail herebelow, is now used to mount the parts of the stereolithographic model in the pre-operative positions thereof. The MOUNTING ON CASS  26  process is key to the extreme accuracy of the omnidirectional distraction. The MOUNTING ON CASS  26  process provides the facility for accurately forming the docking bar and the surface mapping required for the anatomically contoured fixation plates and the process does so without the need for vector determination or vector guides. 
     The mounted stereolithographic medical model also provides, during surgical preplanning, for the SIMULATING  28  phase. Here any osteotomy required and the incisions for installing the custom-fitted fixation plates are preplanned. Upon receipt of the customized contoured anchor from the laboratory, the casting is fitted to the model and, with the docking bar in place, the day-to-day distraction movement and adjustment is planned. 
     Pre-Operative Device Construction 
     Using omnidirectional distraction osteogenesis as an example, the surgeon, either alone or with the support team, forms a wax model for lost-wax casting of ANATOMICALLY CONTOURED FIXATION PLATES device  30 . In the example described below, the medical model, being an accurate representation of the cranial skeletal structure, custom fits the ANATOMICALLY CONTOURED FIXATION PLATES  30  so as to follow the surface map of the bone contours at the site of installation. In this manner, the device is pre-operatively precision fitted to the patient and, unlike some prior art intra-oral devices, does not require bending at the time of installation. Besides the preciseness of custom-fitting and the removal of the bending requirement, the ANATOMICALLY CONTOURED FIXATION PLATES  30  are rigid devices which eliminate vector requirements, including vector alignment and vector guides. 
     Again using omnidirectional distraction osteogenesis as an example, the surgeon either alone or with the support team, places all the segments of the stereolithographic model in the post-operative position and forms an OCCLUSAL SPLINT/DOCKING BAR ARMATURE  32 . With the segments of the model assembled on the CASS in the final position to be attained, the preforming of the DOCKING BAR  34  and designing and forming of the CONNECTING RODS  36  completes the pre-operative device construction. These devices enable the surgical procedure in which full distraction in all directions becomes feasible. 
     Patient Procedures 
     Referring again to  FIG. 1 , the operative steps are now described. First, the step of inserting the devices fabricated pre-operatively is completed. The INSERTING ANATOMICALLY CONTOURED FIXATION PLATE(S) WITH CONNECTING RODS AND DOCKING BAR  28  is accomplished with the ends of the fixation plates anchoring the plates by wrapping around and undercutting the bones at the installation sites. The occlusal splint upon which the docking bar  34  was formed is inserted at INSERTING OCCLUSAL SPLINT  40 . 
     With this accomplished, a distractor, such as a Dynaform distractor (as manufactured by Stryker Leibinger BmbH &amp; Co., Freiburg, Germany) is employed, and emplaced on the docking bar at INSTALLING DISTRACTOR  42 . 
     With the device installation completed, what remains is ADJUSTING DISTRACTORS FOR OMNIDIRECTIONAL VECTOR-FREE MOVEMENT  44  and REMOVING ANATOMICALLY CONTOURED FIXATION PLATE(S) WITH CONNECTING RODS AND DOCKING BAR AND OCCLUSAL SPLINT  46 . 
     Craniofacial Anatomic Surgical Simulator 
     Referring now to  FIG. 2 , the craniofacial anatomic surgical simulator (CASS) is now described. The CASS is referred to generally by the reference designator  60  and provides a framework  62  for accommodating the stereolith model  64 . The framework  62  is constructed with an upper mounting plate  66  for attaching the craniomaxillary portion  68  of the stereolithographic model  64  and a base mounting plate  70  for attaching the mandibular portion  72  of the stereolith model  64 . 
     The framework  62  of the CASS  60  further comprises a crossbar or strut  74  to which the upper mounting plate  66  is connected. While in the present embodiment the strut  74  upper mounting plate  66  is fixed, it is within the contemplation of the present invention that this connection could swivel for right-to-left adjustment or be hinged for forward/back adjustment. The framework  62  of the CASS  60  further comprises adjustable posts or retaining elements  80  and  82  that maintain the upper mounting plate  66  at the selected elevation. 
     The medical model  64  consisting of the craniomaxillary portion  68  and the mandible or mandibular portion  72  is adapted for mounting on the CASS  60 . The craniomaxillary portion  68  is modified for the purpose of the above-described surgery by having the uppermost cranial portion removed and replaced by a cranial attachment plate  84  which is mounted to the upper mounting plate  70  by an adhesive layer  86 . 
     An artificial temporomandibula joint (TMJ)  88  and  90  is constructed to attach the mandible  72  between the base  70  and the craniomaxillary portion  68 . As the stereolithographic model  64  does not represent the soft tissue component of the TMJ  88  and  90 , the opening in the glenoid fossae  92  is filled with soft resilient dental liner or reline  94  (such as COE-SOFT Resilient Dental Liner manufactured by GC America, Inc., Alsip, Ill. 60803 or equivalent). This enables the mandible  72  to rotate during simulated surgery in an accurate manner. 
     The mandible  72  is also attached through a mandibular mounting mechanism  100  to the base mounting plate  70 . The mounting mechanism  100  is constructed with a mandibular base plate  102  and intermediate plates  104  and  106 . In the embodiment shown, plate  106  is attached to mandibular base plate  102  with three positioning screws  108  enabling the removal and remounting of the mandible  72  without losing the original location or orientation. 
     The mandibular mounting mechanism  100  is attached to the base  70  of the CASS  60  with two posts (not shown) and three universal movement lock joints  110 . During simulated surgery, this mounting arrangement enables the movement of the mandible  72  vis-á-vis the craniomaxillary portion into the desired post-operative position. 
     When the CASS  60  is used to simulate mandibular ramus surgery, it is necessary to configure the device so that the proximal segment of the mandibular ramus is fixed. To accomplish this, a ramus pin  112  is disposed on both sides of the stereolith model  64  and a ramus pin lock joint  114 , similar to lock joint  110 , is secured thereto. Depending from lock joint  114  is upper guide rod  116 , which, in turn, is secured to intermediate lock joint  118  and to lower guide rod  120 . The lower guide rod  120  is secured to mandibular base plate  102  through base plate lock joint  122 . With this structure in place, the mandible  72  relation to the craniomaxillary portion  68  is adjusted by a change in elevation at posts  76  and  78  being locked in place at clamps  80  and  82  and by unlocking the previously described lock joints sliding and rotating the segments to the desired position and locking the joints. 
     Optionally, at an angle mimicking the massateric sling, on both sides of the stereolithographic model  64 , upper pegs  122  and  124  are placed in the zygomatic arch  126  and lower pegs  128  and  130  are placed in the mandible  72  with elastics  132  and  134  therebetween. 
     In operation the CASS  60  fulfills numerous pre-surgical functions. Specific to craniofacial surgery, the CASS  60 , because of its extreme accuracy, facilitates the collection of cephalometric data. This is aided when a grid  136  is provided on base  102  for use in positioning measuring instruments. 
     For the craniofacial surgical technique described above, the CASS  60  provides a form for modeling the 
     Referring now to  FIG. 3 , a second embodiment of the craniofacial anatomic surgical simulator (CASS) is shown and is now described. The CASS device is referred to generally by the reference designator  160 . In this embodiment, similar parts to those of the first embodiment are referred to by reference designators 100 units higher than a similar part in the first embodiment. 
     The CASS device  160  provides a framework  162  for accommodating the stereolithographic model  164 . The framework  162  is constructed with an upper mounting plate or extension arm  166 . Optionally, the mounting plate  166  is constructed to include a universal swivel joint (not shown) for freely adjusting the same. The upper mounting plate  166  attaches the craniomaxillary portion  168  of the stereolithographic model  164 . The framework  162  further includes a base mounting plate  170  for attaching the mandibular portion or mandible  172  of the stereolithographic model  164 . 
     The framework  162  of the CASS  160  further comprises a crossbar or strut  174  to which the upper mounting plate  166  is connected. Adjustable posts  176  and  178  are held by retaining elements  180  and  182  to maintain upper mounting plate  166  at the selected elevation. 
     As previously mentioned, the stereolithographic model  164  consists of two basic parts, namely, the craniomaxillary portion  168  and mandible  172  is modified slightly differently from that of the first embodiment. Here, at each ramus segment  181  and  183 , corresponding male attachment node or ramus connector  185  and  187  is emplaced. Similarly an attachment node or mandible connector  189  is emplaced on mandible  172 . For easy management of the stereolithographic model  164 , the framework  162  is constructed with a male attachment node or column connector  191  and  193  on each adjustable post  176  and  178 , respectively, and at least one base connector  195  on base  170 . Between ramus connector  185  and column connector  191 , a manipulator or transfer device  197  (such as Kronus Helping Hands Model HD23, Catalog #64-2991, Radio Shack Corporation, Fort Worth, Tex. 76102 or equivalent) holds the ramus segment  181  (which has been separated from mandible  172 ). 
     As shown in  FIG. 3 , a manipulator or transfer device  199  (such as Axiomatic Transfer Fork Assembly Model 050-155 of SAM—Präzisionstechnik Gmble, Gauting, Germany or equivalent) holds the mandibular segment  172  between base connector  195  and mandibular connector  189 . Completing the mounting arrangement for the model  164 , the ramus segment  183  in a manner analogous to segment  181 , is held by a transfer device  201  between ramus connector  187  and column connector  193 . 
     The stereolithographic model  164  is truncated by having the uppermost cranial portion removed and replace by a cranial mounting plate  184 . In this embodiment the midlines of the cranial mounting plate  184  and the upper mounting plate  166  form a reference means with, for example, the midline  203  of cranial mounting plate  184  being raised and midline  205  of upper mounting plate  166  being indented. Thus, upon mounting, midline  203  interengages with midline  205  resulting in the positive indexing of stereolithographic model  164  on framework  162 . 
     Because many varying and different embodiments may be made within the scope of the inventive concept herein taught and because many modification may be made in the embodiments herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.