Abstract:
Internal pedicle insulator implants, assemblies and related methods are provided. A representative method includes: placing an implant at least partially about an intermediate portion of the fixture, the implant having an inner surface; driving a distal end of the implant into tissue into which the fixture is inserted; and dispensing cement such that the cement is located between the inner surface of the implant and an exterior of the fixture.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation-in-Part application, which claims priority to U.S. Patent application entitled, “Internal Pedicle Insulator Apparatus and Method of Use,” having Ser. No. 11/712,257, filed on Feb. 28, 2007, which claims priority to U.S. Patent application entitled, “Internal Pedicle Insulator Apparatus and Method of Use,” having Ser. No. 11/110,005, filed on Apr. 20, 2005, which claims priority to U.S. provisional application entitled, “Internal Pedicle Insulator Apparatus” having Ser. No. 60/563,797, filed on Apr. 20, 2004, each of which is entirely incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to surgical instruments and tools, and in particular, relates to an internal pedicle insulator apparatus. 
     DESCRIPTION OF THE RELATED ART 
     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. 
     The degeneration of any portion of the lumbar spine can result in instability of the spine, which can lead to impingement or damage to the spinal cord or nerve roots. Impingement of the spinal column or nerve root can result in pain. Damage to spinal cord or nerve roots can result in reduced motor skills or even paralysis. Degeneration of the lumbar spine can be a result of fractures, tumors or other various degenerative diseases. 
     It is well known that utilization of pedicle screws for posterior lumbar stabilization procedures. These procedures typically include inserting a pedicle screw posteriorly into the pedicle or pillar of the lumbar spine. The screw is then connected to plates or rods for stabilization of the lumbar spine. A bone graft also can be added to help solidify the stabilization. The pedicle screw may be inserted off center, such as, for example, too medial, which may impinge on the associated nerve root causing pain. This requires a repositioning of the screw. However, even after repositioning there may be an effect on the pedicle wall, which can still cause nerve root irritation. Such procedures are also susceptible to loosening of the screw. 
     SUMMARY 
     Internal pedicle insulator implants, assemblies and related methods are provided. In this regard, an exemplary embodiment of an internal pedicle insulator implant comprises: a cylindrical wall having a first end and a second end, the second end exhibiting an annular taper; a slot extending between the first end and the second end such that, when viewed in plan view, the implant is generally C-shaped; and a first fin extending outwardly from an outer surface of the wall, the fin being operative to reduce a tendency of the implant to rotate after insertion into tissue 
     An exemplary embodiment of an implant assembly comprises: an implant having a wall defining an interior cavity and having a first end and a second end, and a first fin extending outwardly from an outer surface of the wall, the fin being operative to reduce a tendency of the implant to rotate after insertion into tissue. 
     An embodiment of a method for stabilizing a surgical fixture comprises: placing an implant at least partially about an intermediate portion of the fixture, the implant having an inner surface; driving a distal end of the implant into tissue into which the fixture is inserted; and dispensing cement such that the cement is located between the inner surface of the implant and an exterior of the fixture. 
     Other systems, methods, features, and advantages of the present invention will be or 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 advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a side view of an embodiment of the internal pedicle insulator apparatus of the present invention. 
         FIG. 1A  is a cross-sectional top view of an embodiment of the internal pedicle insulator apparatus illustrated in  FIG. 1 . 
         FIG. 1B  is a perspective view of an embodiment of an internal pedicle insulator implant of the internal pedicle insulator apparatus illustrated in  FIG. 1 . 
         FIG. 2  is a perspective view of an embodiment of an internal pedicle insulator implant of the internal pedicle insulator apparatus illustrated in  FIG. 1 . 
         FIG. 2A  is a cross-sectional top view of an embodiment of an internal pedicle insulator implant illustrated in  FIG. 2 . 
         FIG. 3  is a side view of the internal pedicle insulator apparatus illustrated in  FIG. 1  in use. 
         FIG. 4  is a top view of the internal pedicle insulator implant of the internal pedicle insulator apparatus illustrated in  FIG. 1  in use. 
         FIG. 5  is a top view of another embodiment of an internal pedicle insulator implant of the internal pedicle insulator apparatus in use. 
         FIG. 6  is a schematic diagram depicting another embodiment of an implant. 
         FIG. 7  is a schematic diagram depicting a degraded vertebral body. 
         FIG. 8  is a schematic diagram depicting the vertebral body of  FIG. 7  with an embodiment of an implant and pedicle screw fixed therein. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates one preferred embodiment of an internal pedicle insulator apparatus  10 . The internal pedicle insulator apparatus  10  comprises an inner insertion rod  12 , an outer insertion rod  14 , and an internal pedicle insulator implant  16 . 
     The inner insertion rod  12  has a bottom end  18  and an opposing top end  20 . It is preferable that the inner insertion rod  12  has a substantially round cross-section. However, it should be noted that the inner insertion rod  12  can comprise any suitable configuration. The inner insertion rod  12  can comprise any suitable material, such as titanium, as merely one example. 
     The outer insertion rod  14  has a lower end  11  and an opposing upper end  13 . An opening  15  is disposed at the lower end  11 . An optional handle  17  can be disposed toward the upper end  13  of the outer insertion rod  14  to facilitate use of the internal pedicle insulator apparatus  10 . An opening at the upper end  13  of the outer insertion rod  14  through which the inner insertion rod  12  can pass can also be included (not shown). It is preferable that the outer insertion rod  14  has a substantially round cross-section. It should be noted, however, that the outer insertion rod  14  can comprise any suitable cross-section. The outer insertion rod  14  can comprise titanium, however, it should be understood that the outer insertion rod  14  can comprise any suitable material. 
     The outer insertion rod  14  is arranged and configured to receive the inner insertion rod  12  through the opening  15  disposed at the lower end  11  of the outer insertion rod  14 . The inner insertion rod  12  is preferably slidably inserted into the outer insertion rod  14  such that the upper end  13  of the outer insertion rod  12  substantially corresponds to the top end  20  of the inner insertion rod  12 . Similarly, the lower end  11  of the outer insertion rod  14  substantially corresponds with the bottom end  18  of the inner insertion rod  12 . The inner insertion rod  12  is laterally slidable within the outer insertion rod  14 . 
     Referring next to  FIG. 1A , in one embodiment it is preferable that the outer insertion rod  14  is defined by a diameter D.sub.o. The inner insertion rod  12  is defined by a diameter D.sub.i. It is preferable that D.sub.o is greater than D.sub.i to facilitate the inner insertion rod  12  being slidably disposed within the outer insertion rod  14 . It is further preferable that D.sub.o is less than D.sub.i such as to leave a space  22  having a thickness T.sub.s when the inner insertion rod  16  is disposed within the outer insertion rod  14 . 
     As shown in  FIG. 1B , in one embodiment the internal pedicle insulator implant  16  is substantially rectangular in shape and curved. It should be understood, however, that the internal pedicle insulator implant  16  can comprise any suitable shape and configuration. In this embodiment it is preferable that the internal pedicle insulator implant  16  is curved as defined by a radius R.sub.i. It is preferable that the radius R.sub.i of the internal pedicle insulator implant  16  substantially corresponds to a pedicle screw  104  with which the internal pedicle insulator implant  16  is to be used. The internal pedicle insulator implant  16  is also defined by a thickness T.sub.i. It is preferable that the thickness T.sub.i is greater than the thickness T.sub.s of space  22 . The internal pedicle insulator implant  16  preferably comprises Poly Ether Ether-Ketone, but can comprise any suitable material. 
       FIGS. 2 and 2A  illustrate another embodiment of an internal pedicle insulator implant  30 . The internal pedicle insulator implant  30  is substantially tubular in shape and comprises a wall  34 . The internal pedicle insulator implant  30  has a substantially circular cross-section, defined by a diameter D.sub.i. The diameter D.sub.i is preferably arranged and configured to substantially correspond to a pedicle screw  104  with which the internal pedicle insulator implant  30  is to be used. Although a substantially circular cross-section is illustrated, it should be understood that the internal pedicle insulator can have any desired cross-sectional shape. 
     The internal pedicle insulator  30  optionally comprises at least one anti-rotation fin  32  extending outward from the wall  34 . The anti-rotation fins  32  can extend the length of the wall  34  of internal pedicle insulator  30  or only a portion of the length. The anti-rotation fins  32  can comprise any configuration that discourage rotation of the internal pedicle insulator  30  when disposed in a desired position. In one embodiment, a thickness T.sub.w of the wall  34  of the internal pedicle insulator implant  30  in addition to a height T.sub.h of an anti-rotation fin  32  extending from the wall  34  is greater than thickness T.sub.s of the space  22  between the inner insertion rod  12  and the outer rotation rod  14  when the inner insertion rod  12  is disposed within the outer rotation rod  14 . 
     In another embodiment the internal pedicle insulator implant  30  includes no anti-rotation fin  32  (not shown). In this embodiment, it is preferable that a thickness T.sub.w of a wall of the internal pedicle insulator implant  30  is greater than the thickness T.sub.s of the space  22  formed by the inner insertion rod  12  and the outer insertion rod  14  when the inner insertion rod  12  is disposed inside the outer insertion rod  14 . 
       FIG. 3  illustrates the internal pedicle insulator apparatus  10  in use. A pedicle screw with which the internal pedicle insulator implant  16  is to be used is first removed from its position within the vertebral body. The inner insertion rod  12  is positioned as desired in the vertebral body  100 , such as in a channel created by the pedicle screw  104 . The internal pedicle insulator implant  16  is positioned adjacent the inner insertion rod  12 . The outer insertion rod  14  is positioned around the inner insertion rod  12  via the opening  15  disposed at the lower end  11  of the outer insertion rod  14 . The outer insertion rod  14  is moved in direction C toward the bottom end  18  of the inner insertion rod  12 . As the outer insertion rod  14  is moved in direction C, the outer insertion rod  14  is moved toward the internal pedicle insulator implant  16  until the outer insertion rod  14  engages the internal pedicle insulator  16 . Pressure is applied to the outer insertion rod  14  in direction C to slide the internal pedicle insulator  16  along the inner insertion rod  12  toward the vertebral body  100  until the internal pedicle insulator  16  is appropriately positioned within the vertebral body  100 . The internal pedicle insulator implant  16  is held in position by friction applied to its curved configuration when properly inserted into position. After the internal pedicle insulator implant  16  is disposed in a desired position, the pedicle screw  104  is returned to its position within the vertebral body. 
       FIG. 4  illustrates one embodiment of an internal pedicle insulator implant  16  in a desired position. As shown, the internal pedicle insulator implant  16  is positioned between an affected nerve root  102  and a jagged hole  106  in the vertebral body  100  resulting from a compromised pedicle screw  104 . 
       FIG. 5  illustrates another embodiment of an internal pedicle insulator implant  16 . In this example, however, the implant is located to prevent cement, e.g., PMMA, from contacting the nerve root  102 . Notably, the cement  110  is provided to anchor the pedicle screw  104 . In other embodiments, various other types of materials can be prevented from contacting a nerve by using an implant. Such a material can be an injectable biological substance, for example. 
     Although cement can be provided externally with respect to the screw, the embodiment of  FIG. 5  involves a screw that incorporates holes or fenestrations e.g., fenestration  112 . As such, the cement can be injected into the screw and then a portion of that cement can be pass through the fenestrations and into the surrounding tissue. Thus, the implant  16  serves as a physical barrier to prevent the cement from impinging upon the nerve root. 
       FIG. 6  schematically depicts another embodiment of an implant. In particular, implant  160  of  FIG. 6  incorporates a wall  162 . The wall is generally cylindrical in shape. The wall includes an outer surface  164 , an inner surface  166 , and opposing first and second ends  168 ,  170 . Notably, the second end exhibits an annular taper  172  that can assist in driving of the implant into tissue. 
     The embodiment of  FIG. 6  also incorporates fins  174 ,  176  that extend longitudinally along at least a portion of the length of the wall. Specifically, the fins extend from the first end and terminate at the annular taper. Although depicted with two opposing fins, other embodiments can incorporate various other numbers, sizes, shapes and locations of fins. 
     Note also that the embodiment of  FIG. 6  includes a longitudinal slot  180 . That is, although generally cylindrical, this embodiment of the implant does not exhibit a continuous annular surface. In operation, the slot enables the implant to be placed about a fixture, e.g., a screw, which is already mounted to tissue. That is, the slot enables the implant to be “snapped” around the screw by inserting the screw through the slot. 
       FIG. 7  depicts a vertebral body  190  that has a degraded pedicle  192 . In  FIG. 8 , an implant assembly that includes a fixture  194 , in this case a pedicle screw, is inserted into vertebral body  190  such that approximately a distal ⅓ of the screw is engaged within the tissue. Unfortunately, such a pedicle screw could exhibit toggle, which can degrade fixation of the screw within the tissue over time. 
     Also shown in  FIG. 8  is an implant  196  of the implant assembly that is positioned about an intermediate portion of the screw. That is, the implant is positioned such that a portion of the screw is located in a cavity  198  defined by the inner surface of the implant. 
     The implant  196  is driven such that the second (in some embodiments, tapered) end  202  of the implant becomes anchored with the tissue into which the pedicle screw also is mounted. In this embodiment, a material  204  (e.g., cement) is used to fill at least a portion of the cavity formed between the inner surface of the implant and the screw. For instance, when the fixture is a fenestrated pedicle screw, cement can be injected into the screw for filling the cavity. In this manner, the implant not only reduces toggle by limiting pivot of the proximal end of the screw, the implant serves as a shield for limiting the ability of the cement to impinge upon adjacent tissue, such as nerves. 
     It should also be noted that use of an implant also can improve the pullout strength of a screw. This increase in pullout strength can be promoted by improving the structural integrity of the structure supporting the screw and/or providing increased frictional engagement with the surrounding tissue. 
     It should be emphasized that the above-described embodiments of the present invention are merely possible examples of implementations set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiments 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.