Abstract:
An interdiscal tensiometer comprises a load measuring means for measuring load between two points and a distance measuring means for measuring distance between the two points. A method of use is also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation-in-part of co-pending U.S. utility patent application entitled, “Interdiscal Tensiometer Apparatus and Method of Use,” having Ser. No. 10/666,502, filed on Sep. 19, 2003, which is entirely incorporated herein by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     The invention generally relates to systems, devices, and methods related to grafting interbody segments and, more particularly, to interdiscal tensiometer apparatus and methods of use.  
       DESCRIPTION OF RELATED ART  
       [0003]     The human spine is composed of a column of thirty-three bones, called vertebra, and their adjoining structures. The twenty-four vertebrae nearest the head are separate bones capable of individual movement and are generally connected by anterior and posterior longitudinal ligaments and by discs of fibrocartilage, called intervetebral discs, positioned between opposing faces of adjacent vertebrae. The twenty-four vertebrae are commonly referenced in three sections. The cervical spine, closest to the head and often referenced as the “neck,” comprises the first seven vertebrae of the spine. The thoracic spine and the lumbar spine are below the cervical spine. Each of the vertebra include a vertebral body and a dorsal arch, which enclose an opening, called the vertebral foramen, through which the spinal cord and the spinal nerve pass. The remaining nine vertebrae below the lumbar spine are fused to form the sacrum and the coccyx and are incapable of individual movement.  
         [0004]     Fusion of vertebral bodies may be required for any number of reasons. Most often, such fusion is necessitated when an intervertebral disk is damaged, degenerates, or otherwise becomes diseased, causing great discomfort by way of impinging on the spinal cord and/or nerve roots. When more conservative treatments and minimally invasive procedures have been exhausted, it may become necessary to surgically remove the damaged disk and fuse the associated vertebral bodies in order to restore the original spatial relationships, as well as desired stability.  
         [0005]     Once the damaged disk has been removed, a bone graft or fusion cage packed with grafting material, or autograft bone, is placed in the intervertebral space in order to fuse the vertebral bodies together. The grafting material typically comprises bone fragments taken from the iliac crest of the patient. For the individual fragments to become one mass that will eventually fuse the vertebral bodies, the mass of fragments needs to be placed in an environment that will exert adequate force on the fragments. Research has shown that a physiologic pre-load measured in Newtons is desirable to achieve a desirable fusion outcome. As such, the size of the fusion device chosen is important to achieving fusion.  
         [0006]     Currently, surgeons venture an educated guess when determining the size fusion device to use during such procedures. However, where the pre-load is less than the preferred range, such as when the fusion device is too small, non-union or delayed union of the fusion device can result. Where the pre-load is excessive, such as when the fusion device is too large or as can occur in a severely degenerative spine, subsidence can result. Both results are undesirable and render the surgery unsuccessful.  
         [0007]     Similarly, the fibrocartilage discs, or intervetebral discs, can also need replacement. Total disc replacement is facilitated by removal of the degenerated or diseased disc and replacement with a new material. As with graft material for fusion, it is important to select a size of implant that will result in a desirable load being exerted on the replacement disc once in position. For example, while it is desirable for a total_disc replacement disc to experience physiologic loads measured in Newtons, it is currently difficult to determine the size replacement disc that will result in such desired loading. Despite the difficulties surrounding the selection of the proper size replacement disc, sizing is critical to the success of the surgery.  
         [0008]     As with fusion surgeries, currently surgeons employ an educated guess when determining the size of the disc replacement to be used in such procedures.  
         [0009]     Therefore there is a need for improved devices, systems, and/or methods that address these and/or other shortcomings of the prior art.  
       SUMMARY  
       [0010]     Interdiscal tensiometer apparatus and methods of use are provided. An embodiment of an interdiscal tensiometer briefly described, in architecture, comprises a load measuring means for measuring load between two points and a distance measuring means for measuring distance between the two points.  
         [0011]     Methods of use of an interdiscal tensiometer are also provided. In this regard, one embodiment of such a method, among others, can be broadly summarized by the following steps: providing a pair of primary members being hingedly fixed together, each one of the pair of primary members having a contact tine; measuring a load on the contact tines; and measuring a distance between the contact tines. The contact tines are adapted to engage a pair of intervertebral bodies such that the load measuring means can measure a load therein and the distance measuring means can measure a distance therebetween.  
         [0012]     Other systems, methods, features and/or advantages will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description, and be protected by the accompanying claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Many aspects can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
         [0014]      FIG. 1  is a side view of an embodiment of an interdiscal tensiometer.  
         [0015]      FIG. 2  is a side view of the interdiscal tensiometer illustrated in  FIG. 1  in operation. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]      FIG. 1  illustrates one preferred embodiment of an interdiscal tensiometer (hereinafter, “tensiometer”)  10  of the present invention. The tensiometer  10  comprises a pair of substantially similar primary members  12 . Each primary member  12  comprises a handle  16  and an opposing contact tine  18 . The primary members  12  are pivotally fixed to each other in a cross-over configuration at a hinge connection  14 . The hinge connection  14  can optionally be spring-loaded. A spring-loaded hinge connection  14  urges contact tines  18  toward each other when no force is applied to the handles  16 . The spring (not shown) can be spiral, linear or any suitable configuration. As force sufficient to overcome the spring pre-load is applied to the handles  16 , the contact tines  18  are urged away from each other. It should be understood that the illustrated shape of the primary members  12  is merely an exemplar shape, however, it is preferable that the primary members  12  are shaped such as to require minimal space in which to operate. It should also be understood that various shapes other than the shape depicted may be used. The primary members  12  of the tensiometer  10  can comprise any suitable material, such as, for example, stainless steel.  
         [0017]     The primary members  12  each comprise a handle  16  disposed toward one end. It is preferable that the handles  16  provide for ease in gripping and use of the tensiometer  10 . The handle  16  can comprise any suitable material, such as hard or soft rubber, plastic, or the like.  
         [0018]     Each primary member  12  further comprises a contact tine  18  disposed opposing the handle  16 . The contact tine  18  is arranged and configured to contact a portion of a vertebral body.  
         [0019]     The tensiometer  10  further comprises a tension measure device  26 . The tension measure device  26  can comprise a strain gage, or any suitable instrument for measuring load. The tension measure device can be located in any suitable location and can comprise any suitable configuration. The tension measure device  26  measures the pre-load in the interdiscal space into which the contact tines  18  are inserted. The tension measure device  26  also measures the distance disposed between the contact tines  18  when the handles  16  are urged apart. In such a configuration, the tension measure device  26  may alternately measure the distance disposed between the handles  16  when urged apart. The distance between the handles  16  then correlates to the distance measured by the contact tines  18 . The distance between the contact tines  18  can be measured by any suitable measuring device that can be located in any suitable position on the tensiometer  10 .  
         [0020]     Turning next to  FIG. 2 , a method of use of the tensiometer  10  is illustrated. The tensiometer  10  is used to determine the appropriate size for an implant device  24  to be disposed in an interdiscal space  20  disposed between a pair of vertebral bodies  22  in order to achieve the desired force load on the implant device  24 . The implant device  24  can comprise a fusion device comprising bone graft, a fusion cage packed with grafting material, autograft bone, or any suitable material and device configuration. A fusion device is used to fuse vertebrae together to prevent movement. The implant device  24  can also comprise material suitable for a total disc replacement. The total disc replacement material can comprise any suitable metal, Polyetheline, or Peek material.  
         [0021]     The contact tines  18  of the primary members  12  are disposed within the interdiscal space  20 . A user grips the tensiometer  10  at the handles  16  disposed on each of the primary members  12 . Portions of the primary members  12  are urged apart by application of an outward force F applied to the handles  16  of the primary members  12 . The application of force F to the handles  16  pivots the primary members  12  about the hinge connection  14  causing the contact tines  18  to move apart from each other in direction A. The primary members  12  pivot about the hinge connection  14  until the contact tines  18  each engage a portion of the opposing vertebral bodies  22 . Outward force F is applied to the primary members  12  until the desired force is read on the tension measure device  26 . The tension measure device  26  further indicates the height measured by the contact tines  18  and indicates the size implant device  24  appropriate for that interdiscal space.  
         [0022]     It should be emphasized that he above-described embodiments of the present invention, particularly, a “preferred” embodiment, are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiment(s) of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein with the scope of this disclosure and the present invention and protected by the following claims.