Abstract:
For use in training needle techniques such as spinal anesthesia and or lumbar epidural steroid injections, a spinal model includes a complete natural bone vertebral column that is embedded in a matrix of crystal clear ballistic gel. The synthetic gel does not harbor bacteria, can be reused and does not require refrigeration. Natural bone offers significantly better image contrast over radiopaque replicas. A transparent synthetic gel matrix permits observation of needle progression by both the trainee and the trainer and provides unique opportunities for coaching and intercession to prevent poor needle placement prior to its occurrence.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 14/325,391, filed on Jul. 8, 2014, and entitled SPINAL INJECTION TRAINER AND METHODS THEREFOR, now U.S. Pat. No. 9,280,915, issued Mar. 8, 2016, which claims benefit of U.S. Provisional App. No. 61/847,564, filed on Jul. 18, 2013 and entitled SPINAL INJECTION TRAINER AND METHODS THEREFOR, the specifications of which are herein incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to medical training models and more particularly to a model that includes natural vertebrae embedded in a matrix of clear synthetic ballistic gel, and its uses. 
     BACKGROUND 
     Spinal models for injection technique practice or training have been described in the past. Computerized Imaging Reference Systems, Inc, Norfolk Va., offers a lumbosacral spine model that includes a radiopaque plastic spinal model embedded in silicone. Other models including natural gelatin based embedded spinal phantoms for ultrasound use have been described; Jia Wei et al. “Gelatin-Agar Lumbosacral Spine Phantom” J Ultrasound Med (2011) 30:263-272, describes an agar-gelatin matrix and Bellingham et al., “A Low-Cost Ultrasound Phantom of the Lumbosacral Spine” Regional Anesthesia and Pain Medicine (2010) vol. 35, no. 3, describes a concentrated gelatin matrix. While the foregoing are no doubt useful for their intended use, neither silicone models nor the described natural gelatin based matrices provide realistic tactile feedback for the trainee. 
     Natural gelatin is a material obtained from collagen and other animal by-products and is a component in numerous foods and cosmetic products. More particularly, “ballistic” gel is a formulation based on either natural gelatin or a synthetic, which is calibrated to possess ideally, characteristics similar to human muscle tissue, and is used primarily in ballistics testing. One standard calibration of ballistic gel involves firing into it a .177 caliber steel BB, from an air gun, measuring the velocity of the projectile and the depth of penetration. Ballistic gels based on natural gelatin will darken, degrade quickly, and cannot be reused. Because bacterial contamination and decay are a concern, natural gelatin based models must be refrigerated between uses. More recently, synthetic ballistic gels have been formulated to mimic the properties of natural gelatin, but are odorless and colorless, and unlike natural gelatin, can be reused by heating and reforming by melting and re-pouring into a form. Two U.S. companies that make or sell synthetic ballistic gel are Clear Ballistics LLC. P.O Box 723 Fort Smith AR, 72901, and Ballistek Gel LLC, N8547 North Rd, Ixonia, Wis. 53036. Synthetic ballistic gel is not subject to rapid decay, does not require refrigeration and does not serve as a bacterial reservoir. 
     Imaging Techniques 
     While training phantoms employing skeletal replicas are adequate for sonographically guided needle insertion, plain plastic or resin components will not show adequately in either plain x-ray or fluoroscopic imaging because they are non-radiopaque. In the case of x-rays, bone appears lighter than the surrounding tissue. In a fluoroscope, relatively more x-rays pass through soft tissue to fluoresce a phosphor screen and produce real time moving images wherein the bones appear relatively darker than the surrounding tissue. While some practice models employ plastic vertebrae made of radiopaque resin enabling it to be seen in a fluoroscope monitor, the image contrast provided by radiopaque plastic is unlike that of natural bone because of the naturally non-uniform distribution of calcium in bone which selectively absorbs more or less of the x-rays, thereby producing a more dimensional image. 
     Anatomic Training 
     While use of cadavers has been declining in U.S. Medical schools primarily due to cost of preparing and maintaining the corpus, anatomists have complained that cadavers are still the best way to teach anatomy because it provides kinesthetic reinforcement as opposed to computerized models. Although anatomical teaching models are better now than in the past, a common material used to simulate tissue, silicone, although superior to other less resilient plastics, still does not provide the tactility of human tissue. 
     Both silicone “tissue” of costly training models and the relatively inexpensive gelatin based phantoms break down with repeated punctures rendering them unfit for training. At some point, accumulated needle tracks will interfere with both light transmission, clarity and disturb the intended path and placement of subsequent needles. It would be desirable to provide a teaching model for the human spine that provides realistic tactile feedback of the vertebral column and surrounding tissue. It would be further desirable if such a model were suitable for fluoroscopically guided spinal injection techniques. In addition to being reusable and requiring no refrigeration, the foregoing model should produce an image that reflects actual bone contour, and be transparent so that needle path and placement can be observed or practiced with or without the use of a imaging techniques such as fluoroscopy or sonography. 
     SUMMARY 
     The present invention seeks to address the shortcomings of past spinal training models by providing a spinal model that includes a complete natural bone vertebral column that is embedded in a matrix of crystal clear ballistic gel. The synthetic gel does not harbor bacteria, can be reused and does not require refrigeration. Natural bone offers significantly better image contrast over radiopaque replicas. More dimensional, i.e., contoured image contrast is obtainable with natural bone which is obtained via cadavers or antique teaching skeletons. For use in training needle techniques such as spinal anesthesia and or lumbar epidural steroid injections, a transparent synthetic gel matrix permits observation of needle progression by both the trainee and the trainer and provides unique opportunities for coaching and intercession to prevent poor needle placement prior to its occurrence. Because the matrix closely simulates the feel of human tissue, for purposes of anatomy instruction, a flexible opaque sheet of a self-healing material such as closed cell polyurethane foam or similar material, preferably having a thickness between 2 and 10 mm, is placed over the model so that the structures and regions of the spine can be taught, and later independently discerned, without benefit of visual reinforcement. 
     In one aspect of the instant invention, a model possessing a vertebral column of natural bone embedded in a clear matrix of ballistic gel is clearly visible inside the gel, and therefore suitable for injection practice with or without fluoroscopic imaging. 
     Because surgical hardware makes distinguishing spinal structures difficult as it can mask or distort adjacent regions, in an aspect of the instant invention, a vertebral column advantageously includes surgical hardware such as brackets and threaded fasteners so clinicians can develop the ability to better visualize on a monitor spinal anatomy with surgical hardware in place. 
     In yet another aspect of the present invention, a thin opaque cover simulating tactile properties of human skin is provided to enable blind injection practice or palpation of vertebral structures such as the spinous processes. 
     In still another aspect of the present invention, areas between vertebrae may include a foam disk surrounded by a silicone layer that permits a needle to be placed into the disc space. 
     In whatever aspect, the model of the instant invention may include needle track mitigation using heat or focused energy to produce localized heating of matrix regions in order to effectively fuse or reabsorb needle tracks. One preferred embodiment includes a pair of cartridge heaters, at least one on each side of that region of the vertebral column affected by needle practice. The cartridge heaters are preferably controlled by a PIO controller that can maintain a programmed temperature to within −0.5 to +0.5 degrees Celsius. PIO control permits more stable temperature range management than other types of temperature control such as on/off control, or proportional control. Suitable PIO controllers for the invention include, but are not limited to auto-tune type controllers such as the EZ-ZONE PM Temperature Controller Series from Watlow Inc. 12001 Lackland Rd. St. Louis, Mo. USA 63146, that provide for adaptive temperature sensing and learning, whereby the controller initially probes a material to determine its thermal properties which are then employed in the controller&#39;s PIO algorithm. When it is desired that the needle tracks be erased, the controller can be set to cycle to a desired temperature that is where the synthetic gel matrix starts to transition to a flowable state, whereby the tracks are fused closed, and the cartridge heaters powered off. 
     Other possible uses combining the disclosed aspects and features of the present invention will suggest themselves to those having skill in the art and benefit of this disclosure. 
     The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a preferred embodiment according to the present invention; 
         FIG. 2  is a cross-sectional view taken along lines  2 - 2  of the embodiment shown in ( FIG. 1 ) showing a needle insertion; 
         FIG. 3  is a detail view showing a needle insertion; 
         FIG. 3 a    is a detail view of a segment of spinal column showing a foam disk between vertebrae; 
         FIG. 4  is a plan view showing placement of cartridge heaters adjacent the spine; 
         FIG. 5  is a plan view of one embodiment according to the present invention having surgical hardware on the spine; and 
         FIG. 6  shows the embodiment of ( FIG. 1 ) with a sheet placed over the contoured form. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference Listing 
     
         
           100  spinal model 
           110  form 
           112  insert 
           120  synthetic gel matrix 
           121  gel matrix contour 
           125  aperture 
           130  vertebral column 
           131  spinous process 
           132  intervertebral disc 
           133  pelvic bone 
           134  spinal cord 
           136  spinal nerve 
           138  surgical hardware 
           140  foam vertebral disc 
           200  sheet 
           300  needle 
           600  localized heating means 
       
    
     DEFINITIONS 
     Unless otherwise explained, any technical or medical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The singular terms “a,” “an,” and “the” include plural referents unless the context clearly indicates otherwise. Similarly, the word “or” is intended to include “and” unless the context clearly indicates otherwise. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of this disclosure, suitable methods and materials are described below. The term “comprises” means “includes.” Publications, patent applications, patents, and other references mentioned herein, if any, are incorporated by reference in their entirety for all purposes. In case of conflict, the present specification, including explanations of terms, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     Referring generally to  FIGS. 1-6 , a spinal injection training model  100  including a form  110  containing a gel matrix  120  into which a complete vertebral column of natural bone  130  with simulated associated soft vertebral tissue structures  132 ,  134 ,  136  has been embedded. The matrix is a transparent synthetic ballistic gel having a density and feel substantially like that of human tissue in order to provide realistic haptic feedback upon needle  300  insertion and placement techniques, and spinal palpation practice which can be performed with opaque sheet  200  ( FIG. 6 ) positioned on or off the top surface of the model, and which is preferably of a silicone or other elastomer resembling the texture of human skin. 
     Referring to  FIG. 1 , a plan view of a preferred embodiment according to the present invention shows form  110  containing matrix  120  with a complete vertebral column  130  embedded therein. The form has an opening  125  that exposes a top surface of the gel matrix for needle practice. Preferably, the vertebral column is obtained from cadaverous specimens, or from antique skeletal models. The vertebrae are first cleaned and treated with a sealant that is non-reactive with the petroleum based matrix and placed in a contoured form (mold) with the spinous processes  131  pointing down, with the vertebral body facing up. The vertebral column can be secured from shifting by any means that would be appreciated by those skilled in the art and benefit of this disclosure. Because the bottom inside surface of the mold is contoured to resemble the curves of the human back, a uniform distance of about 2 cm will exist between the tops of the spinous process and the mold bottom. A block of synthetic ballistics gel is pieced and placed into the mold void containing the vertebral column which is then heated in an oven to melt and fuse the gel. Once liquefied, the matrix is subjected to vibration to raise trapped air to the surface. In this manner, after the gel cools and firms, the top can be trimmed with a knife or wire to remove any bubbles, and finally, the form is inverted so the top of the cast now has the contouring. It is possible, of course to apply a vacuum for degassing the matrix to draw out trapped air preferably prior to pouring the matrix, or prior to curing. 
       FIG. 1  is a top plan view of the model having a torso shape. As can be seen in  FIG. 2 , the contour of the exposed portion  121  of the gel matrix corresponds to the typical contours of a human back and follows the spinous process  131 .  FIG. 3  is a detail view of needle being inserted into the lumbar region of the spine surrounded by transparent gel so that injection technique can be observed form any direction. Also depicted are synthetic spinal nerves  136  which can be made of silicone or other suitable pliant material. While the embodiments shown herein depict a torso shape, in cases where the spinal column is embedded in a rectangular slab, the sides of the enclosure or shell, can be a rigid material such as acrylic to facilitate transporting the model when necessary. 
       FIGS. 3 and 3   a  show respectively, needle insertion between vertebrae, and the section of vertebral column with artificial foam discs. The discs  140  can be made of foam urethane, silicone, or other suitable material that simulates the density of a human vertebral disc. Preferably, the foam disc has a silicone layer at each end. The foam disc may alternately be embedded in a silicone or urethane of a different density. 
       FIG. 4  is a plan view of the spinal model of the invention in which cartridge heaters  600  have been placed just adjacent to the spinal region where needle practice occurs. The cartridge heaters are preferably controlled by a PIO controller so that the cartridge heater temperature will not exceed the melting point of the synthetic gel matrix. It is possible to raise the temperature to a point at which the needle tracks fuse and are reabsorbed into the transparent matrix. 
       FIG. 5  is a plan view of a model having surgical hardware installed on the embedded vertebral column. Because the vertebral column is natural bone, the contrast produced during a fluoroscopically guided procedure will realistically simulate that of an actual in vivo procedure. 
       FIG. 6  is a plan view of a model according to the present invention with an opaque sheet sized and shaped, and of a thickness that simulates skin. Palpation and discernment of the spinous process  131  can be performed “blind” to simulate a clinical setting. 
     The model of the present invention can be supplied in various sizes corresponding to different body types including obese body types, in which case the tissue possesses a relatively greater thickness over the spinous process. This is particularly useful in chiropractic training. 
     In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Therefore, this disclosure is intended to cover such alternatives, modifications, and equivalents as may be included in the spirit and scope of the description in view of the appended drawings and claims.