Abstract:
The present application relates to connectors for coupling together two surgical members of different materials while inhibiting galvanic corrosion. The connector may include a first coupling element composed of a material with a similar galvanic potential to one of the surgical members, and a second coupling element composed of a material with a similar galvanic potential to the second surgical member. Each of the first and second coupling elements may be configured to connect to the respective surgical member. The connector may also include a coupling medium disposed between the first and second coupling elements. The coupling medium may function to connect together the two coupling elements, and isolate the coupling elements to inhibit galvanic corrosion.

Description:
BACKGROUND 
       [0001]    The present application relates to a device and methods for connecting elongated surgical members, and in particular, to methods and connectors that allow elongated surgical members of different materials to be attached together while inhibiting galvanic corrosion. 
         [0002]    It is often necessary to surgically treat disorders such as scoliosis and broken bones with two or more elongated surgical members. The elongated members, typically either rods or plates, are placed along the area to be treated, such as the broken bone or the vertebral column. The elongated members may be attached with various attachment devices, such as screws, hooks, and various other types of fasteners. 
         [0003]    It is well known that the strength and stability of a dual member assembly can be increased by coupling the members with a connector that transversely connects to the longitudinal axes of the members. Specifically, the two members are parallel to each other and may overlap, or may be in an end-to-end configuration. 
         [0004]    Biocompatible materials are used for the members but, however, due to corrosion concerns, members of different materials are rarely connected together. The corrosion resistance commonly referred to in the art is against direct chemical attack, which in the body means a slow erosion of the material by acids which dissolve the material. It is well known that most body fluids that bathe implants are acidic. The biocompatible metals dissolve extremely slowly in the body. Polymers are even more resistant to acidic attack. 
         [0005]    A second type of corrosion is electro-chemical, also called galvanic corrosion. Every metal is conductive and has a distinct electrochemical potential, i.e., voltage when immersed in an acidic or saline environment. A battery is created when two such metals are introduced in a common bath, and then connected together. One metal becomes an electron donor and dissolves, and the other becomes an electron receptor and adds material (a compound of the donor and the bath materials). Galvanic corrosion is a serious problem when metals of different galvanic potential are combined in a common medium and in close proximity to each other. 
         [0006]    Generally, galvanic corrosion is avoided by using members of only one type of metal. However, this limits the choice of a plurality of metals of different properties when desired, such as stress resistance, elasticity, hardness, and so forth. Further, if two different members are close to one another, a battery action can be made if there is some contact, such as anchors and plates and so forth. 
         [0007]    Therefore, devices and methods are needed that would allow the elongated surgical members to be connected together while inhibiting galvanic corrosion. 
       SUMMARY 
       [0008]    The present application relates to connectors for coupling together two surgical members of different materials while inhibiting galvanic corrosion. The connector may include a first coupling element composed of a material with a similar galvanic potential to one of the surgical members, and a second coupling element composed of a material with a similar galvanic potential to the second surgical member. Each of the first and second coupling elements may be configured to connect to the respective surgical member. The connector may also include a coupling medium disposed between the first and second coupling elements. The coupling medium may function to connect together the two coupling elements, and isolate the coupling elements to inhibit galvanic corrosion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic representation of a connector positioned between first and second members according to one embodiment. 
           [0010]      FIG. 2  is a perspective view of a connector constructed according to one embodiment. 
           [0011]      FIG. 3  is a perspective view of a coupling element constructed according to one embodiment. 
           [0012]      FIG. 4  is a perspective view of a coupling element constructed according to one embodiment. 
           [0013]      FIG. 5  is a side view of a connector constructed according to one embodiment. 
           [0014]      FIG. 6  is a perspective view of a connector constructed according to one embodiment. 
           [0015]      FIG. 7  is a side view of a connector constructed according to one embodiment. 
           [0016]      FIG. 8  is a section view of a connector constructed according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The present application is directed to devices and methods for connecting together surgical members of different materials and inhibiting galvanic corrosion.  FIG. 1  illustrates a schematic representation of a connector  10  that connects together first and second members  100 ,  110 . The connector  10  includes a first coupling element  20  that connects to and includes the same or similar galvanic potential as the first member  100 . The connector  10  also includes a second coupling element  30  that connects to and includes the same or similar galvanic potential as the second member  110 . A coupling medium  40  is positioned between the first and second coupling elements  20 ,  30 . The coupling medium  40  connects together the two coupling elements  20 ,  30  and insulates the two members  100 ,  110  to inhibit a galvanic couple from being established when the members  100 ,  110  are positioned within a patient. 
         [0018]    A function of the connector  10  is to connect two members  100 ,  110  of different galvanic potentials. The connector  10  performs this function by physically separating the two members  100 ,  110  with one or more inert materials, or by one or more intermediate galvanic materials. 
         [0019]      FIG. 2  illustrates one embodiment of a connector  10  with a first coupling element  20 , second coupling element  30 , and a coupling medium  40 . The first coupling element  20  includes a body  21  with a first opening  22  sized to receive the first member  100 . A second opening  23  extends through the body  20  from a different direction and extends into the first opening  22 . A constraining member  24  is sized to fit within the second opening  23  and extend into the first opening  22  to contact against and constrain the first member  100  with the body  21 . The first section  20  is constructed of a material that includes the same or substantially the same galvanic potential as the first member  100 . 
         [0020]    Similarly, the second coupling element  30  includes a body  31  with a first opening  32  sized to receive the second member  110 . A second opening  33  extends through the body  31  from a different direction and extends into the first opening  32 . A constraining member  34  is sized to fit within the second opening  33  and extend into the first opening  32  to contact against and constrain the second member  110  with the body  31 . The second section  30  is constructed of a material that includes the same or substantially the same galvanic potential as the second member  110 . 
         [0021]    In this embodiment, the first opening  22  includes a centerline C 1  that is substantially parallel to a centerline C 2  of the first opening  32 . This configuration provides for connected together first and second members  100 ,  110  that are substantially parallel. 
         [0022]    The first and second coupling elements  20 ,  30  are constructed of material with the same or substantially the same galvanic potentials respectively as the first and second members  100 ,  110 . Examples of the materials include but are not limited to titanium, titanium alloys, stainless steels, stainless steel alloys, cobalt chrome, and cobalt chrome alloys. In one embodiment, the first coupling element  20  is constructed from stainless steel, and the second coupling element  30  is constructed from titanium. 
         [0023]    The first and second coupling elements  20 ,  30  may be separate pieces as illustrated in  FIGS. 3 and 4 .  FIG. 3  illustrates the first coupling element  20  that includes a contact side  29  that faces towards the second coupling element  30 . The contact side  29  includes an outwardly-extending tongue  24 .  FIG. 4  illustrates the second coupling element  30  with a contact side  39  that faces towards the first coupling element  20 . The contact side  39  includes a groove  34  that extends along the height of the body  31 . Groove  34  includes a shape that accommodates the tongues  24 . The tongues  24  are sized to fit within the groove  34  forming a dovetail connection between the coupling elements  20 ,  30 . In another embodiment, the tongues  24  and groove  34  do not extend along the entirety of the contact sides  29 ,  39 , but rather only along a limited length. Another embodiment includes a single tongue  24  that extends along the contact side  29 . In another embodiment (not illustrated), the coupling medium  40  includes threads that engage with threads on the coupling elements  20 ,  30 . 
         [0024]    The coupling medium  40  is positioned between and forms a barrier that separates the first and second coupling elements  20 ,  30 . Coupling medium  40  is constructed of an inert material that insulates the first and second coupling elements  20 ,  30 . Coupling medium  40  includes a thickness that prevents the direct contact between the coupling elements  20 ,  30  that could produce galvanic corrosion. In one embodiment, the thickness of the medium  40  is substantially constant throughout. In other embodiments, the medium  40  includes a varying thickness. In each various embodiment, the coupling member  40  includes a thickness and is positioned across the contacts sides  29 ,  39  to prevent direct contact between the coupling elements  20 ,  30 . 
         [0025]    In one method of manufacturing the connector  10 , the coupling elements  20 ,  30  are mated together with the tongue  24  positioned within the groove  34 . The coupling medium  40  is initially in a flowable state and is injection molded to flow into the space formed between the coupling elements  20 ,  30 . The medium  40  contacts against the contact surfaces  29 ,  39  and fills the space and eventually cures to a final state to connect together the coupling elements  20 ,  30 . 
         [0026]    In one embodiment, gaps  25  are positioned along the height of the contact surface  29 . Similarly, gaps  35  are positioned along the contact surface  39 . These gaps  25 ,  35  facilitate the insertion and flow of the coupling medium  40  during manufacturing. The coupling medium  40  fills the gaps  25 ,  35  to provide a secure attachment between the coupling elements  20 ,  30 . In one embodiment as illustrated in  FIGS. 2 and 4 , gaps  35  extend inward from the contact surface  39 . In another embodiment as illustrated in  FIG. 5 , gaps  35  are positioned inward from the contact surface  39  and extend inward into the groove (not illustrated in  FIG. 5 ). The gaps  35  in each of these various embodiments are filled by the coupling medium  40  and form struts across the dovetail connection to prevent the coupling elements  20 ,  30  from sliding apart. 
         [0027]    The coupling medium  40  may be constructed of a non-metallic material such as but not limited to PEEK (poly-ether-ether ketone), PEK, PAEK, PEKKEK, polymers, and/or ceramics and other non-conductive materials. 
         [0028]    In one embodiment, the first member  100  is constructed of titanium and the second member  110  is stainless steel. The connector  10  includes a first coupling element  20  constructed of cobalt chrome that contacts against the titanium first member  100  and a second coupling element  30  constructed of stainless steel that connects to the stainless steel second member  110 . The coupling medium  40  is constructed of PEEK that is positioned between the first and second coupling elements  20 ,  30 . 
         [0029]      FIG. 6  illustrates another embodiment of the device  10 . In this embodiment, coupling element  20  includes a different shape than coupling element  30 . Coupling element  20  includes an elongated first opening  22  to receive a first member such as a plate. A constraining mechanism  72  is positioned adjacent to the first opening  22  to constrain the first member  100 . In this embodiment, constraining mechanism  72  includes a fastener that extends through an opening in the body  21 . The constraining mechanism  72  contacts against the first member  100  positioned within the first opening  22  to prevent escape. Second coupling element  30  includes a substantially circular second opening  32  sized to receive the second member  110  in the form of a rod. In this embodiment, the first opening  22  is substantially perpendicular to the second opening  32 . 
         [0030]    The coupling medium  40  spaces apart the first and second coupling elements  20 ,  30 . In one embodiment, the coupling medium  40  is attached to the coupling members  20 ,  30  with an adhesive. In another embodiment, fasteners  52  connect the coupling medium  40  to the coupling members  20 ,  30 . In one embodiment as illustrated in  FIG. 6 , fasteners  52  extend between the coupling medium  40  and each of the coupling members  20 ,  30  for the attachment. 
         [0031]      FIG. 7  illustrates another embodiment of the device  10 . This embodiment features the coupling medium  40  positioned directly between the first and second coupling members  20 ,  30 . A width w of the coupling medium  40  is greater than a width f of the first coupling member  20  and a width s of the second coupling member  30 . 
         [0032]    In one embodiment, such as  FIG. 5 , coupling medium  40  is constructed from a single material. In another embodiment as illustrated in  FIG. 7 , coupling medium  40  is constructed of multiple different materials, such as first and second materials  40   a,    40   b.  The different materials may be oriented to segregate the coupling members  20 ,  30 . 
         [0033]      FIG. 8  illustrates another embodiment with the coupling medium  40  substantially surrounding the first and second coupling members  20 ,  30 . This construction again isolates the coupling members  20 ,  30  and inhibits galvanic corrosion. The coupling medium  40  surrounds the coupling members  20 ,  30  and forms and exterior of the device  10 . Portions of the bodies  21 ,  31  may be exposed to the exterior to facilitate insertion of the first and second members  100 ,  110 , or constraining elements  24 ,  34 . In one embodiment, the coupling medium  40  is attached to the coupling members  20 ,  30  in an over-mold process. The bodies  21 ,  31  may be shaped to facilitate the molding process. One over-mold embodiment includes the coupling medium  40  being PEEK. 
         [0034]    In one method of using the connector  10 , the first member  100  is already implanted within a patient in a previous surgical procedure. A subsequent surgical procedure includes implanting the second member  110  and connecting the second member  110  to the first member  100 . In some instances, the material of the first member  100  is unknown, or it is discovered during the subsequent surgical procedure to be constructed of a different material than originally expected. In these instances, the device  10  is connected between the first and second members  110 ,  110  to inhibit galvanic corrosion and provide a secure connection. 
         [0035]    In another embodiment, the first and second members  100 ,  110  may be purposefully constructed of different materials. This occurs when the first member  100  includes one or more physical characteristics (e.g., stiffness, stress resistance, elasticity, hardness) for attachment within the patient at a first location, and the second member  110  includes one or more different physical characteristics for attachment at a second location. The device  10  allows for the two different members  100 ,  110  to be implanted within the patient. 
         [0036]    The connector  10  may be used for connecting together a variety of different first and second members  100 ,  110 . In one embodiment, first and second members  100 ,  110  are rods. Rods may include a variety of cross-sectional shapes, and may include a variety of lengths. One use of rods includes attachment to vertebral members to treat spinal deformities. Another use includes attachment to a broken bone, such as a femur, to support the broken bone and facilitate healing. First and second members  100 ,  110  may also include plates. Plates may include a working surface with a length and width that aligns with and contacts against bone. One or more apertures may extend through the plates to receive a fastener for securing to the bone. One example of a plate is a vertebral plate sized to fit against a vertebral member. In addition to the examples given above, connector  10  may also connect together cables and bars, and combinations of these various examples. 
         [0037]    The embodiments of  FIGS. 2 ,  3 , and  4  include the openings  22 ,  32  extending through the bodies  21 ,  31  respectively. Other embodiments include one or both openings  22 ,  32  that do not extend completely through the bodies  21 ,  31 . 
         [0038]    The connector  10  may position the members  100 ,  110  at a variety of angular orientations including but not limited to parallel, perpendicular, and at non-perpendicular intersecting angles. Further, the connector  10  may position the members  100 ,  110  at various positional orientations including but not limited to end-to-end and overlapping. 
         [0039]    Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description. 
         [0040]    As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. 
         [0041]    The present embodiments may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the embodiments. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.