Abstract:
A tissue protector has a body structure having a longitudinal extending thin web. The body structure has an unconstrained first shape configured to form a nerve shield and is configured to shrink about a longitudinal axis to a smaller constrained second shape sized to fit into a lumen of a cannula. Preferably, the second constrained shape is oval or round having a maximum diameter equal or less than an inside diameter of the lumen. The body structure is configured to return to the first shape when the cannula is withdrawn or returned to this shape as the implant advances.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a tissue protector, or in this particular example, a tissue and nerve shield for use in minimally invasive spinal surgery. 
       BACKGROUND OF THE INVENTION 
       [0002]    When a surgeon is accessing a region to be repaired such as the disc space between adjacent vertebrae, great care must be taken to avoid injury to the exposed nerve root. 
         [0003]    Dural tears, nerve root damage, bleeding and infection, operating on the wrong level or on the wrong side are as real issues in all spinal surgeries. 
         [0004]    With thoracic approaches, pneumothorax is also a possibility. 
         [0005]    In addition, some injuries may be underestimated or even go unnoticed, such as a dural tear under the low-pressure irrigation. 
         [0006]    It is an objective of the present invention to further minimize the potential for such complications by providing a unique protective tissue protector or nerve shield made in accordance to the invention as disclosed herein. 
       SUMMARY OF THE INVENTION 
       [0007]    A tissue protector or nerve shield has a body structure having a longitudinal extending thin web. The body structure has an unconstrained first shape configured to form a nerve shield and is configured to shrink about a longitudinal axis to a smaller constrained second shape sized to fit into a lumen of a cannula. Preferably, the second constrained shape is oval or round having a maximum diameter equal or less than an inside diameter of the lumen. The body structure is configured to return to the first shape when the cannula is withdrawn from between two adjacent vertebral bodies and the body structure is held in position between the vertebral bodies. 
         [0008]    The web is configured to shield a nerve root and the surrounding tissue. Also, the unconstrained first shape of the web is sized to receive a spinal implant for insertion between the two vertebral bodies. The web forms a guide and a shield for the spinal implant. The web can have a thin oval or circular cross section in the unconstrained first shape. Alternatively, the web can have a channel or “U” cross section, rectangular or triangular cross section in the unconstrained first shape. 
         [0009]    In a preferred embodiment, the body structure further has a pair of rails on each lateral end or side of the web, the web being interposed between said rails. The nerve shield when unconstrained has at least one rail shielding a nerve root. The rails are spaced by the web, when the body structure is in the unconstrained first shape, a lateral distance or width to receive a spinal implant or surgical instrument. The pair of rails is configured to guide a spinal implant during insertion while at least one of said rails shields the nerve root or tissue of interest. The rails are enlarged longitudinally extending projections having a round or at least partially round cross section. The web can be a thin rectangular cross section in the unconstrained first shape. 
         [0010]    The invention permits a method of shielding a nerve root or tissue of interest during a spinal surgical procedure having the steps of: making an incision; inserting a cannula, wherein the cannula has a shield constrained inside the lumen of the cannula; positioning the distal end of the cannula past or beside a nerve root or tissue; withdrawing the cannula while holding the shield in position past or beside the nerve root or tissue; and freeing the shield allowing movement from a constrained shape to an unconstrained shape to protect and shield the nerve root or tissue. The method further can include inserting a spinal implant using the unconstrained shield as a guide to position the implant between two vertebral bodies. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention will be described by way of example and with reference to the accompanying drawings in which: 
           [0012]      FIG. 1  is a perspective view of a nerve shield of a first embodiment of the present invention shown in a deployed first unconstrained shape. 
           [0013]      FIG. 2  is a top view showing the end of the deployed shield. 
           [0014]      FIG. 3  is an exemplary frontal view of the device in a deployed first shape. 
           [0015]      FIG. 4  is a frontal view of the rolled or wrapped tissue protector showing a second constrained shape for insertion in a lumen of a cannula. 
           [0016]      FIG. 5  is a top view of the nerve shield of  FIG. 4  in a second constrained shape, the circular dashed lines representing the diameter of a lumen of a cannula into which the device can fit. 
           [0017]      FIG. 6A  shows a first alternative embodiment end view of the device showing no rails. 
           [0018]      FIG. 6B  shows the end of  FIG. 6A  in the constrained second shape. 
           [0019]      FIG. 6C  shows a second alternative embodiment showing rails with an oval web, both devices shown in an unconstrained first shape. 
           [0020]      FIG. 6D  shows the end of  FIG. 6C  in the constrained second shape. 
           [0021]      FIG. 7A  is a solid version of the first embodiment  FIG. 1 . 
           [0022]      FIG. 7B  is a rolled rails of the lateral ends version of the first embodiment of  FIG. 1 . 
           [0023]      FIG. 8  is a perspective view of the nerve shield used as a guide for insertion of a spinal implant. 
           [0024]      FIG. 9A  is a third alternative embodiment showing a “U” shape configuration unconstrained. 
           [0025]      FIG. 9B  is the constrained view of the third alternative. 
           [0026]      FIG. 9C  is a fourth view of an alternative embodiment. 
           [0027]      FIG. 9D  is the constrained view of the fourth alternative. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    With reference to the drawings  FIGS. 1 and 2 , a unique tissue protector  10  is illustrated. The tissue protector  10  has a first unconstrained shape having a size typically much larger than an 8.5 min lumened cannula as shown by the cross sectional circle. Such cannulas are often used in spinal surgery where minimally invasive approach is taken where an incision is cut into the patient&#39;s back above a target area of the spine and the cannula is inserted. The cannula provides an access port into which tools can go in and clean out the disc space and provide a prepared surface into which a spinal implant  100  can be inserted. Ideally, the insertion of a spinal implant  100  should be conducted in such a fashion that the nerve root is protected during the insertion procedure. In order to accomplish this, the present invention provides a tissue protector  10  that can lay adjacent one side of the nerve root and provide a barrier between the spinal implant  100  and the nerve root or any tissue along the way. 
         [0029]    A unique feature of the present invention tissue protector  10  is that it is provided with a very thin web  12  as shown in  FIG. 2 . The web  12 , shown in  FIGS. 1 and 3 , extends longitudinally down the length of the tissue protector  10  in an unconstrained first shape. It is designed to be wrapped or rolled about a longitudinal axis A into a tightly compressed size sufficiently small to fit inside the lumen  22  of a small diameter cannula  20 , as shown in  FIGS. 4 and 5 . The tissue protector  10  can take a variety of cross sectional shapes as shown in  FIGS. 5, 6A, 6B, 6C, 6D, 9A and 9C . The web  12  is shown as a continuous piece of thin material having an almost fully circular shape, but open forming two ends  14  such that the web  12  can be spirally wound to compress it to a diameter d that is smaller than the lumen opening of a cannula  20  into which it will be inserted. Alternatively, shown in  FIG. 6C , is an embodiment having a cross sectional shape wherein two enlarged projections or bulbous ends  14  are provided and these ends  14  similarly can be folded inwardly to achieve the diameter d as required, as shown in  FIG. 6D . Both of these designs are such that when positioned inside a cannula  20 , they can be easily held in that position when the cannula  20  is positioned into a target region. The distal end of the cannula  20  will reach at or past the nerve root and in doing so the shield  10  which is carried inside the cannula  20  can be held in at the target location as the cannula  20  is withdrawn from the incision leaving only the tissue protector  10  in place adjacent the nerve root. The tissue protector  10 , being free of the cannula  20 , returns to the unconstrained first shape. When this occurs, a spinal implant  100  can be used to be slid down the interior surface of the tissue protector  10 . 
         [0030]    With reference to  FIGS. 1-5 , a preferred embodiment of the present invention is illustrated. This preferred embodiment tissue protector  10  of the present invention has the web  12  as a straight or flat rectangular thin material extending longitudinally wherein the ends have two enlarged bulbous features or projections  14  that are positioned at a lateral distance creating a space between the enlarged ends forming a shallow channel  16 . As shown in  FIGS. 2 and 3 , the unconstrained shape has a fairly large width. This width can be as high as 16 mm. However, as shown in  FIG. 4 , when the shield body structure  11  is folded or wrapped or rolled about a longitudinal axis A into a tightly constrained second shape, the nerve shield  10  occupies a space which will fit within an  8 . 5  mm diameter lumen of a cannula  20 . This is fully illustrated in  FIG. 5 . When in this constrained second position, the tissue protector  10  can be positioned inside a cannula  20  and can be held there until the cannula  20  is positioned in the proper location or target region between two adjacent vertebral bodies in the disc space at or past the nerve root. At this point, the cannula  20  can be withdrawn while holding the tissue protector  10  into position at the location. As the tissue protector  10  is freed from the constraint of being inside lumen  22  of the cannula  20  it is free to regain its unconstrained first shape. When the tissue protector  10  is fully deployed free of the cannula  20 , it achieves the appearance as illustrated in  FIGS. 1 and 2 . To better appreciate what happens when the tissue protector  10  is in this unconstrained position deployed between the adjacent vertebrae, a handle  200  is illustrated in  FIG. 8  having a spinal implant  100  positioned at a distal end of the handle  200  fixed at a proximal end of the implant  100  such that the implant  100  can be positioned onto the tissue protector  10  in the channel  16  between the enlarged ends  14  and slid into position. As shown, the tissue protector  10  provides at least one enlarged projection  14  to be adjacent or next to the nerve root and as long as the spinal implant maintains its position within the trough or channel  16  created by the two enlarged ends  14 , the nerve root is protected. The implant  100  will slide freely into its desired implant location without any concern of hitting any nerve tissue or other tissue in the immediate area. This feature eliminates any risk of tissue or nerve tears. 
         [0031]    While the implant  100  is shown on the flat web  12  of the body structure  11 , it is appreciated that the spinal implant  100  similarly could be placed within the unconstrained first shapes of the other alternative embodiments having either a simple thin web  12  without any enlarged projections  14 , shown in  6 A, wherein the implant can be positioned inside the unconstrained first shape after the nerve shield  10  has been freed of the cannula  20  or similarly can be placed inside the other alternatives shown in  FIG. 6C, 9A and 9C  to allow the implant to be basically encapsulated by a tissue protector  10  as it is being passed through to its target location. 
         [0032]    Alternatively, the implant can help or cause the tissue protector to achieve unconstrained final shape. So, as the implant advances, the tissue protector goes from constrained to unconstrained. 
         [0033]    With reference to  FIGS. 9A-9D , another alternative cross section is shown wherein the circular shape of  6 A without any enlarged bulbous ends  14  is shown, however, in this case the web  12  has a somewhat “U” shape configuration that allows it to be rolled up and wrapped into a second tightly sized second shape to fit inside the cannula. This alternative embodiment similarly can have the enlarged bulbous ends  14  as previously discussed. However, in this shape, the unconstrained first shape of the device will take that approaching a “U” shaped central web  12 . The alternatives provide a much deeper channel  16 . 
         [0034]    With reference to  FIGS. 7A and 7B , the preferred embodiment shown in  FIG. 1 , can be formed as a solid piece of material molded or alternatively can be made from a thin piece of material having the ends rolled. When formed as a thin piece of material, it is likely that the material can be a thin nitinol or other thin metal material or any other material that can easily rolled into a tight configuration. As illustrated, the preferred embodiment achieves the shape somewhat similar to a partially unopened scroll and is commonly referred to as a scroll shield. 
         [0035]    Since this is only one of the shapes that the tissue protector  10  can take, the alternative embodiments show variations in that shape. The thickness of the web  12  will be adapted to any size necessary to achieve an adequate wrapping. The primary objective is to ensure that the tissue protector  10  can be sufficiently constrained to fit easily and be held easily in a cannula  20  having an 8.5 mm diameter by way of example. Larger and smaller diameter cannulas could be used. 
         [0036]    Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described, which will be within the full intended scope of the invention as defined by the following appended claims.