Abstract:
A spinal stabilization system, apparatus, and method are disclosed which include an interconnection mechanism for engaging stabilization members to one another. In one embodiment, the interconnection mechanism comprises a locking member having first and second threaded segments. An anchor member is provided having an upper segment and a lower segment, wherein the lower segment is structurally configured for engagement with a respective bone segment. A first stabilization member is connected to the upper segment of the anchor member. A locking member is engaged with the anchor member such that the first stabilization member is fixedly secured to the anchor member by a lower portion of the locking member having a first threaded segment. A second stabilization member is connected to an upper portion of the locking member by a cap that is threaded onto a second threaded segment of the locking member.

Description:
TECHNICAL FIELD 
     The present invention relates generally to stabilization systems and methods configured to stabilize at least a portion of the spinal column via the use of an interconnection mechanism for engaging two or more stabilization members to one another. 
     BACKGROUND 
     In the art of orthopedic surgery, and particularly spinal surgery, it has long been known to anchor one or more elongate stabilization members, such as spinal plates or rods, to a portion of the spinal column to provide stabilization and support across two or more vertebral levels. With regard to prior stabilization systems, in order to revise or add to an existing system, one or more stabilization components must be loosened and/or removed to allow for integration and attachment of additional stabilization members or devices to the system, thereby tending to increase the complexity and duration of the surgical procedure. 
     There remains a need for improved stabilization systems and methods. The present invention satisfies this need and provides other benefits and advantages in a novel and unobvious manner. 
     SUMMARY 
     The present invention relates generally to stabilization systems and methods configured to stabilize at least a portion of the spinal column. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms of the invention that are characteristic of the invention are described briefly as follows. 
     In one aspect of the present invention, a bone structure stabilization system is provided which is capable of stabilizing adjacent bone structures. The bone structure stabilization system includes an anchor member having an upper segment and a lower segment. The lower segment of the anchor member is structurally configured to be positioned in a respective bone segment. In one embodiment, the lower segment of the anchor member comprises an externally threaded segment that acts as a bone screw for securing the anchor member in a respective bone structure. A first stabilization member is connected to the upper segment of the anchor member. In one example, the first stabilization member comprises a rod and the upper segment of the anchor member includes a head defining a cradle portion in which a portion of the rod is positioned. 
     The bone structure stabilization system also includes a locking member that is engaged with the anchor member. The locking member is connected to the anchor member such that the first stabilization member is fixedly secured to the anchor member by a lower portion of the locking member. The lower portion of the locking member protrudes downwardly from a mounting segment of the locking member and includes an externally threaded segment. The anchor member includes an internally threaded segment within which the externally threaded segment of the locking member is threaded to engage the locking member with the anchor member. A lower surface of the externally threaded segment makes contact with a surface of the first stabilization member to thereby secure the first stabilization member to the anchor member. 
     The bone structure stabilization system also includes a second stabilization member that is connected to an upper portion of the locking member. In one example, the second stabilization member comprises a plate member having an elongated slot. The upper portion of the locking member includes an externally threaded segment about which the elongated slot is positioned. A portion of the externally threaded segment protrudes upwardly through the elongated slot and above an upper surface of the plate member. A cap is connected to the upper portion of the locking member to secure the second stabilization member to the locking member. In one embodiment, the cap includes an internally threaded segment that threads onto the externally threaded segment of the locking member that protrudes upwardly through the upper surface of the plate member to secure the plate member to the locking member. 
     Another aspect of the present invention is directed to a method of stabilizing adjacent bone structures. The method includes the step of inserting an anchor member into a portion of bone structure. The anchor member includes a threaded portion that is capable of threading into a portion of bone structure to fixedly secure the anchor member to the bone structure. A first stabilization member is then positioned within a cradle defined by the anchor member. The first stabilization member is secured in the cradle of the anchor member with a locking member that includes a lower mounting surface and an upper mounting surface. A threaded segment protrudes downwardly from the lower mounting surface and threads into an internally threaded segment of the anchor member. A second stabilization member is then placed on the upper mounting surface of the locking member. Once in place, the second stabilization member is secured on the upper mounting surface of the locking member with a locking cap. The cap threads onto a threaded segment protruding upwardly from the upper mounting surface. 
     Yet another aspect of the present invention is directed to a spinal stabilization apparatus. The spinal stabilization apparatus includes a plurality of bone anchor members positioned in respective vertebrae of a spinal column. A first stabilization member is positioned in a first set of the bone anchor members that spans from a beginning location in one vertebra to an ending location in another vertebra. A first locking member is positioned in each of the bone anchor members of the first set of bone anchor members except the bone anchor member at the ending location. The first locking member secures the first stabilization member in the first set of bone anchor members. 
     A dual thread locking member is positioned in the bone anchor member at the ending location. The dual thread locking member includes a mounting segment positioned between an upper externally threaded segment and a lower externally threaded segment. The lower externally threaded segment threads into an internally threaded portion of the bone anchor member at the ending location to secure the first stabilization member in the bone anchor member. A second stabilization member is positioned about the upper externally threaded segment of the dual thread locking member and a portion of the upper externally threaded segment protrudes above a surface of the second stabilization member. A locking cap is used to secure the second stabilization member to the upper externally threaded segment. 
     Another aspect of the present invention is directed to a method of revising an implanted spinal construct. The method includes removing a set screw from an anchor member that secures a first stabilization member to a respective bone segment. A lower portion of a locking member is then connected to the anchor member to once again secure the first stabilization member to the anchor member. A second stabilization member is then placed about an upper portion of the locking member such that a portion of a lower surface of the second stabilization member rests on an upper surface of a mounting segment of the locking member. A cap is then secured to the upper portion of the locking member to fixedly secure the second stabilization member to the upper surface of the mounting segment. This method allows constructs to be revised without requiring the removal of an existing construct, thereby reducing surgery time, recovery time, and the number of components required to perform the revision surgery. 
     Yet another aspect of the present invention is directed to a locking member for a bone stabilization apparatus having at least first and second stabilization members. The locking member includes a mounting segment having an upper engagement surface and a lower engagement surface. A lower threaded segment extends downwardly from the lower engagement surface of the mounting and is structurally configured to be connected with an anchor member to secure the first stabilization member within the anchor member. An upper threaded segment extends upwardly from the upper engagement surface of the mounting segment that is structurally configured to receive a second stabilization member such that a portion of the second stabilization member rests on the upper engagement surface. A locking cap having an internal threaded segment is structurally configured to thread onto the upper threaded segment to secure the second stabilization device to the upper engagement surface of the mounting segment. 
     It is one object of the present invention to provide stabilization systems and methods configured to stabilize at least a portion of the spinal column. Further objects, features, advantages, benefits, and aspects of the present invention will become apparent from the drawings and description contained herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a stabilization system according to one embodiment of the present invention, as engaged to a portion of the spinal column. 
         FIG. 2  is a top view of a stabilization member according to one embodiment of the present invention. 
         FIG. 3  is a side view of the stabilization member illustrated in  FIG. 2 . 
         FIG. 4  is a side perspective view of an anchor member according to one embodiment of the present invention. 
         FIG. 5  illustrates a stabilization assembly according to another embodiment of the present invention including an elongate stabilization member engaged with an anchor member by a locking member. 
         FIG. 6  is a perspective view of the locking member illustrated in  FIG. 5 . 
         FIG. 7  illustrates a stabilization assembly according to another embodiment of the present invention including first and second stabilization members engaged with an anchor member by a locking member. 
         FIG. 8  is a side perspective view of a locking cap portion of the locking member illustrated in  FIG. 7 . 
         FIG. 9  is a side view of the locking cap portion illustrated in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is hereby intended, and that alterations and further modifications to the illustrated devices and/or further applications of the principles of the invention as illustrated herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
     Referring to  FIG. 1 , illustrated therein is a spinal stabilization system  10  according to one form of the present invention. The stabilization system  10  generally includes first supports or stabilization members  12   a ,  12   b  engaged to a first portion of the spinal column via a number of bone anchors  18 , which are in turn interconnected with second supports or stabilization members  14   a ,  14   b  engaged to a second portion of the spinal column  16  via a number of bone anchors  18 . The anchor members  18  are configured to securely anchor the stabilization members  12   a ,  12   b  and  14   a ,  14   b  to respective vertebrae  22  of the spinal column  16 . As will be set forth in greater detail below, in one embodiment of the invention, the anchor members  18  comprise bone screws, with locking members provided to engage the stabilization members to the bone screws. However, it should be understood that other types and configurations of anchor members are also contemplated as falling within the scope of the present invention including, for example, spinal hooks, staples, bolts or any other suitable bone anchor device that would occur to one of skill in the art. 
     Although the embodiment of the invention shown in  FIG. 1  illustrates the stabilization system  10  engaged to a lateral aspect of the spinal column  16 , it should be understood that the stabilization system  10  may be engaged to other portions of the spinal column  16 , including posterior or anterior portions. Additionally, it is also contemplated that the present invention may have application in other parts of the human body including, for example, other types of joints or long bones. The particular arrangement of the stabilization members  12   a ,  12   b  and  14   a ,  14   b  is determined by the surgeon before and/or during the surgical procedure to conform the stabilization system  10  to the patient&#39;s anatomy and to provide relief for the patient&#39;s diagnosed medical condition. It should be understood, however, that the particular arrangement of the first and second stabilization members  12   a ,  12   b  and  14   a ,  14   b  is exemplary, and may be adjusted or changed to provide any desired stabilization arrangement or configuration. 
     In the illustrated embodiment of the invention, the first stabilization members  12   a ,  12   b  comprise elongate spinal rods. Although a conventional circular-shaped spinal rod is illustrated, it should be appreciated that other shapes and configurations are also contemplated, including square, rectangular, hexagonal, diamond and elliptical shaped rods, or any other suitable shape that would occur to one of skill in the art. The spinal rod  12   a ,  12   b  may be formed from stainless steel, titanium, polyethertherketone (PEEK), or any other suitable biocompatible material known to those of skill in the art. In the illustrated embodiment, the stabilization system  10  includes a pair of spinal rods  12   a ,  12   b  running substantially parallel to one another along the spinal column  16 . However, in other embodiments, a single spinal rod may be used. Additionally, it should be understood that the stabilization members  12   a ,  12   b  may take on other configurations including, for example, plates, wires, tethers, or any other suitable configuration known to those of skill in the art. 
     Referring collectively to  FIGS. 2 and 3 , in one embodiment of the invention, the second stabilization members  14   a ,  14   b  comprise plate members. The plate members  14   a ,  14   b  include an elongate body  26  extending along a longitudinal axis  28 . In the illustrated embodiment, the elongate body  26  includes at least one opening in the form of an elongate slot  30  extending generally along the longitudinal axis  28 . The elongate slot  30  extends through the elongate body  26  between upper and lower surfaces  32 ,  34 , thereby defining side rails  36  extending longitudinally along opposite sides of the elongate slot  30 , and a pair of end rails  38  extending transversely between the side rails  36  adjacent the ends of the elongate body  26 . The plate members  14   a ,  14   b  further include a flange portion  39  extending downwardly from one of the end rails  38 . As illustrated in  FIG. 7 , the flange portion  39  includes a lower engagement surface  40  configured to conform to an outer surface of the spinal rods  12   a ,  12   b . In the illustrated embodiment, the engagement surface  40  has a curved or concave configuration which conforms with an outer curved surface of the spinal rods  12   a ,  12   b . However, other shapes and configurations are also contemplated. In the illustrated embodiment, the plate member  14   a ,  14   b  include a curved or angled section  42  which interconnect first and second portions of the body  26  that are offset from one another by a distance d. In other embodiments, the plate member  14   a ,  14   b  need not include a curved or angled section, but may instead be provided with a generally flat or planar configuration. 
     Although a particular configuration of the stabilization members  14   a ,  14   b  has been illustrated and described herein, it should be appreciated that other plate configurations are also contemplated as falling within the scope of the present invention. Additionally, it should be understood that the stabilization members  14   a ,  14   b  may take on other configurations including, for example, rods, wires, tethers, or any other suitable configuration known to those of skill in the art. The stabilization members  14   a ,  14   b  may be formed from stainless steel, titanium, polyethertherketone (PEEK), or any other suitable biocompatible material known to those of skill in the art. In the illustrated embodiment, the stabilization system  10  includes a pair of plate members  14   a ,  14   b  running substantially parallel to one another along the spinal column  16 . However, in other embodiments, a single plate member may be used. 
     The spinal rods  12   a ,  12   b  and the plate members  14   a ,  14   b  are engaged to the spinal column  16  via a plurality of anchor members  18 , which as indicated above may be configured as bone screws. Referring to  FIG. 4 , shown therein is one embodiment of an anchor member  18  suitable for use in association with the present invention. The anchor member  18  extends generally along a longitudinal axis and includes a distal segment  40 , an intermediate threaded segment  42 , and a proximal fixation or connection segment  44 . The distal segment  40  may be provided with self-cutting or self-drilling capabilities, including a tip  46  defining a cutout or flute  50  providing a cutting edge  52 . The threaded segment  42  defines a helical thread  54  configured for anchoring in bone, and more particularly in cancellous bone. In the illustrated embodiment, the fixation segment  44  comprises a head  60  having a pair of generally parallel arms  62   a ,  62   b  that provide a cradle  68  defining a generally U-shaped channel  70  between the arms  62   a ,  62   b  for receiving the first stabilization member or spinal rod  12   a ,  12   b . An interior surface  72  of the arms  62   a ,  62   b  defines inner threads  74  for receiving a set screw such as, for example, a conventional set screw  19  ( FIG. 1 ) for capturing the spinal rod  12   a ,  12   b  within the cradle  68  and U-shaped channel  70  of the bone anchor  18 . Although a particular configuration of a bone anchor  18  has been illustrated and described herein, it should be understood that other types and configurations are also contemplated. 
     Referring to  FIG. 5 , shown therein is another embodiment of an anchor member  18 ′ suitable for use in association with the present invention. The anchor member  18 ′ is also configured as a bone screw and, like the bone screw  18 , includes a distal segment  40 , an intermediate threaded segment  42  defining a helical thread  54 , and a proximal fixation or connection segment  44  including a head  60  having a pair of generally parallel arms  62   a ,  62   b  that provide a cradle  68  defining a generally U-shaped channel  70  for receiving one of the spinal rod  12   a ,  12   b . Additionally, like the bone screw  18 , the interior surfaces of the arms  62   a ,  62   b  define inner threads for receiving a locking member or set screw for capturing the spinal rod  12   a ,  12   b  within the cradle  68  and U-shaped channel  70  of the bone anchor  18 ′. However, unlike the bone screw  18  which has a single-piece configuration, the bone screw  18 ′ has a poly-axial configuration wherein the connection segment  44  is formed separately from the threaded segment  42  and is attached thereto in a manner which allows the connection segment  44  to pivot or rotate relative to the threaded segment  42  prior to being locked at a selected angular and/or rotational position. Poly-axial bone screws are well know to those of skill in the art and need not be discussed in further detail herein. Although a particular configuration of the poly-axial bone anchor  18 ′ has been illustrated and described herein, it should be understood that other types and configurations are also contemplated. 
     Referring collectively to  FIGS. 5 and 6 , shown therein is a locking member  80  according to one embodiment of the present invention for securing one of the spinal rods  12   a ,  12   b  within the cradle  68  and U-shaped channel  70  of the bone anchor  18 ,  18 ′, and for coupling one of the plate members  14   a ,  14   b  to the bone anchor  18 ,  18 ′. In the illustrated embodiment, the locking member  80  comprises a dual-threaded member including a lower threaded segment  82  and an upper threaded segment  84  that are separated from one another by an intermediate contact or mounting segment  86 . The locking member  80  extends generally along an axis  87 , with the upper and lower threaded segments  82 ,  84  extending axially from the mounting segment  86  in generally opposite directions. 
     The lower threaded segment  82  includes external threads  88  that are configured for threading engagement with the internal threads  74  formed along the arms  62   a ,  62   b  of the bone anchor  18 ,  18 ′. The length of the lower threaded segment  82  may be sized such that a lower surface  90  of the intermediate mounting segment  86  engages an upper surfaces  66  of the arms  62   a ,  62   b  of the bone anchor  18 ,  18 ′, while at the same time exerting sufficient force against the spinal rod  12   a ,  12   b  to secure the spinal rod  12   a ,  12   b  in position relative to the bone anchor  18 ,  18 ′. The upper threaded segment  84  includes external threads  92  that are configured for threading engagement within a threaded passage formed in a locking cap or nut  110  ( FIGS. 8 and 9 ). The upper threaded segment  84  further includes a pair of opposing flat or truncated surfaces  102  that are engagable by a tool or wrench. The length of the upper threaded segment  82  is sized to extend into the elongate slot  30  defined by the plate member  14   a ,  14   b , with an upper surface  100  of the intermediate mounting segment  86  engaging a lower surface  34  of the plate member  14   a ,  14   b . Although the external threads  88 ,  92  formed along the upper and lower threaded segments are illustrated as having a particular thread configuration, it should be understood that various thread configurations are contemplated including, for example, a buttress thread, a helical thread, a square thread, a reverse-angle thread or other thread-like structures. 
     Referring collectively to  FIGS. 7-9 , shown therein is a locking cap or nut  110  according to one embodiment of the present invention. The locking cap  100  is generally circular in shape and extends generally along an axis  112 . In the illustrated embodiment, the locking cap  100  includes an upper portion  114 , a lower portion  116 , and an axial passage  118  extending through the upper and lower portions  114 ,  116 . A first portion of the axial passage  118  extending through the upper portion  114  of the locking cap  110  has a hexagonal shape configured for engagement with a driving tool and terminates at a base or shoulder  120 . A second portion of the axial passage  118  extending through the lower portion  116  of the locking cap  110  has a circular shape and defines internal threads  122  configured for threading engagement with the external threads  92  formed along the upper threaded segment  84  of the locking member  80 . The first portion of the axial passage  118  extending through the upper portion  114  of the locking cap  110  may be provided with a series of notches or grooves  124  that provide frictional engagement with the driving tool and/or which aid in engaging or securing a lid or cover (not shown) to the locking cap  110  to close off the axial passage  118 . 
     As illustrated in  FIG. 9 , the upper portion  114  of the locking cap  110  defines a curved or rounded upper surface  115  devoid of sharp edges or corners to avoid injury or trauma to adjacent tissue. The lower portion  116  of the locking cap  110  includes a first cylindrical portion  126  having a diameter sized somewhat smaller than the upper portion  114  of the locking cap  110 , thereby defining a lower surface or shoulder  130 . The diameter of the first cylindrical portion  126  is preferably sized in relatively close tolerance with the width of the elongate slot  30  extending through the plate members  14   a ,  14   b . The lower portion  116  of the locking cap  110  further includes a second cylindrical portion  128  extending from the first cylindrical portion  126  and having a diameter sized somewhat smaller than the first cylindrical portion  126 . The end of the second cylindrical portion  128  may be provided with a tapered edge  132 . As shown in  FIG. 7 , when the locking cap  110  is threaded onto the upper threaded segment  84  of the locking member  80 , the lower surface or shoulder  130  of the cap  110  engages the upper surface  32  of the plate member  14   a ,  14   b , thereby forcing the plate member  14   a ,  14   b  into tight engagement against the upper surface  100  of the locking member  80 , and also firmly engaging the lower engagement surface  40  of the flange  39  against the outer surface of the spinal rod  12   a ,  12   b . Although a particular configuration of the locking cap  110  has been illustrated and described herein, it should be understood that other configurations are also contemplated as falling within the scope of the present invention. 
     In one embodiment of the invention, stabilization members  12   a ,  12   b  may comprise a stabilization system that has previously anchored to a first portion of the spinal column  16  by a number of bone anchors  18 ,  18 ′ via a prior surgical procedure. In some instances, correction or stabilization of another portion of the spinal column is required or desired. In such instances, additional stabilization members  14   a ,  14   b  may be engaged with the stabilization members  12   a ,  12   b  and anchored to another portion of the spinal column  16  by additional bone anchors  18 ,  18 ′ to provide further stabilization or support to the spinal column. Such procedures are sometimes referred to as a revision procedure or technique. During a revision procedure, benefits or advantages may be realized by avoiding removal or extensive manipulation of the previously implanted stabilization system. 
     Referring collectively to  FIGS. 1 ,  5  and  7 , in one embodiment of the invention, the conventional set screws  19  may be removed from the bone anchors  18 ,  18 ′ adjacent one end of the existing stabilization system. The removed set screws  19  are then replaced with locking members  80 , with the lower threaded segment  82  of each locking member  80  threadedly engaged along the internal threads  74  formed along the arms  62   a ,  62   b  of a respective bone anchor  18 ,  18 ′ and into engagement with the spinal rod  12   a ,  12   b  to once again securely engage the spinal rods  12   a ,  12   b  to the existing bone anchors  18 ,  18 ′. The plate members  14   a ,  14   b  are then engaged to the bone anchors  18 ,  18 ′ via insertion of the upper threaded segment  84  of the locking member  80  into the elongate slot  30 , with the lower surface  34  of the plate member  14   a ,  14   b  resting upon the upper surface  100  of the intermediate mounting segment  86  of the locking member  80 . A locking cap  110  is then threaded onto the upper threaded segment  84  of each locking member  80  until the lower surface or shoulder  130  of the cap  110  tightly engages the upper surface  32  of the plate member  14   a ,  14   b , thereby forcing the plate member  14   a ,  14   b  into tight engagement against the upper surface  100  of the locking member  80 , and also firmly engaging the lower engagement surface  40  of the flange  39  against the outer surface of the spinal rod  12   a ,  12   b . Additional bone anchors  18 ,  18 ′ are used to anchor the opposite ends of the plate members  14   a ,  14   b  to another portion of the spinal column. As should be appreciated, the plate members  14   a ,  14   b  are interconnected with the existing spinal stabilization system (including the spinal rods  12   a ,  12   b  and the existing bone anchors  18 ,  18 ′) without extensive manipulation or removal of the components associated with the existing stabilization system. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character.