Abstract:
Disclosed is a novel connection assembly for a spinal implant system having:  
     novel interface element having an internal stop that limits rotation of the spinal implant rod and associated members with regard to the spinal implant bolt and associated members allowing the implant system to initially assume a position that approximates its final adjusted position and allows the assembly&#39;s size to be reduced without sacrificing its mechanical strength;  
     a compressible member located between the interface elements that ensures free rotation of the spinal implant rod and its associated members in relation to the spinal implant bolt and its associated members until a proper position has been obtained and allows an initially secured system to be repositioned without additionally separating the interface element&#39;s locking structures;  
     and components provisionally secured to prevent disengagement during transportation and handling that can be engaged during installation utilizing minimal force with common hand tools.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Spinal implant systems provide a rod for supporting and positioning the spine in response to the specific problem being corrected by the implant and the patient&#39;s particular anatomy. The systems comprises a support rod, bolts secured to vertebrae and a connector that securely engages the support rod to the connecting bolts and allows the system to assume positions where the rod is maintained at various angles in response to the problem being corrected and the patient&#39;s particular anatomy. Although implant systems currently available satisfy these basic needs, further refinements are needed in the design of the connection assemblies utilized. Connection assemblies are needed that: minimize the assembly preparation prior to installation; can quickly assume and maintain an approximate position in the initial phase of installation, then be quickly and easily locked into position to complete the installation; have the ability to be repositioned with minimal effort after initially secured; and require minimal space in the patient&#39;s spinal region for installation.  
         SUMMARY OF THE INVENTION  
         [0002]    It is one object of the present invention to provide a connection assembly for a spinal implant system having components that limit the rotation of a spinal implant rod in respect to a corresponding spinal implant bolt, cause the initially implanted system to assume and maintain a position that approximates its final position and allow the system to be easily secured when the appropriate position has been attained. The structure limiting rotation is an interface element having an internal stop within an internal circumference or internal periphery, the internal stop positioned to contact other internal structures such as two edges of a seat maintaining a second interface element. The nature of the internal stop and its placement allow the connection assembly&#39;s size to be reduced without sacrificing the assembly&#39;s performance.  
           [0003]    In one aspect of the present invention, a connection assembly for connecting a spinal implant rod to a spinal implant bolt is provided, the assembly comprising: a rod connecting member having an opening for receiving a portion of the rod, and a first interface element on the rod connecting member; a bolt connecting member attached to the rod connecting member, the bolt connecting member having an opening for receiving a portion of the bolt, and a second interface element on the bolt connecting member; the first interface element being fixed against rotation relative to the rod connecting member and the second interface element having a disengaged condition wherein the rod connecting member and bolt connecting member are rotatable within a limited range relative to one another, the limited range defined by an internal stop element positioned within an inner periphery of one of the interface elements; and the first interface element and the second interface element having an engaged condition wherein the rod connecting member and bolt connecting member are fixed against rotation relative to one another. Connection assemblies according to this embodiment of the present invention have structural features that provide for reduction in the assembly&#39;s size, that allow the assembly to approximate a final installed position early in the installation process while the assembly&#39;s interface elements are in a disengaged condition and allow the assembly to be quickly and easily secured to maintain an appropriate position once the elements assume an engaged condition.  
           [0004]    It is a further object of the present invention to provide connection assembly for connecting a spinal implant rod to a spinal implant bolt wherein the assembly can be initially secured and subsequently re-positioned and re-secured with minimal effort as needed. In one aspect of the present invention, a connection assembly for connecting a spinal implant rod to a spinal implant bolt is provided, the assembly comprising: a rod connecting member having an opening for receiving a portion of the rod; a first interface element on the rod connecting member; a bolt connecting member having an opening for receiving a portion of the bolt; a second interface element on the bolt connecting member, the first interface element being fixed against rotation relative to the rod connecting member and the second interface element being fixed against rotation relative to the bolt connecting member, the rod connecting and the bolt connecting members rotatably attached about a connection axis, one member opposing the other; interlocking structures on opposing surfaces of the interface elements, such that when the elements are engaged with one another, the interlocking structures prevent rotational movement of the interface elements relative to one another; and a compressible member positioned between the interface elements, the compressible member in its uncompressed state preventing the interlocking structures from engaging. Connection assemblies according to this embodiment of the present invention have a compressible member positioned between the interface elements that in its uncompressed state prevents engagement of the interlocking structures, in its compressed state allows the interlocking structures to become engaged to prevent rotation of one interface element relative to another interface element, and upon returning to its uncompressed state separates the interlocking structures associated with the interface elements allowing the interface elements to once again rotate for repositioning.  
           [0005]    It is a further object of the present invention to provide a medical assembly comprising first and second assembled components, wherein the components are provisionally secured in their assembled configuration by a biocompatible material, and wherein the biocompatible material is disruptable during installation of the medical assembly. Additionally, the biocompatible material may also be capable of being resorbed by the body. Preferred embodiments of the present invention maintain their configuration during normal shipping and handling and during installation allow disruption of the provisionally secured component utilizing hand tools and forces reasonable within a surgical environment.  
           [0006]    It is a still further object of the present invention to provide for an interface element having structural features that cooperate with other structural features of a connection system to restrict rotation of the interface element and any associated component about a central axis. In one aspect of the present invention, an interface element for use in a connection assembly is provided, the interface element comprising: a structure having at least one face; a central opening for receiving a structural element of a rod connecting member or a bolt connecting member and resist rotation relative thereto; and at least one internal stop element located about an inner periphery of the interface element. The utilization of interface elements of the present invention in connection assemblies allows the size of the assembly to be reduced without sacrificing the assembly&#39;s mechanical strength. Connection assemblies utilizing the novel interface element take up less space within a patient while still facilitating installation by providing restricted rotation of the rod connecting and bolt connecting members. As a result, a spinal implant system utilizing the assembly can be smaller without sacrificing performance.  
           [0007]    It is a still further object of the present invention to provide a method to provisionally secure a component of a medical device therein, but allow the secured component to be subsequently engaged or removed. In one aspect of the present invention, a method is provided for provisionally securing components of a medical device, the method comprising: providing at least two components of a medical assembly to be provisionally secured, the components having surfaces suitable for engagement; applying a biocompatible material to at least one of the surfaces; contacting the surfaces to be secured; and maintaining contact of the surfaces until the components have been provisionally secured. Components of medical devices secured by this method remain in place after manufacture and during shipment and subsequent handling and can be engaged as necessary with minimal effort utilizing common hand tools and forces appropriate to a surgical environment to effect installation of the device in the usual manner.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a plan view of a connection assembly for a spinal implant device according to the illustrated embodiment of this invention.  
         [0009]    [0009]FIG. 2 is a plan view in exploded form.  
         [0010]    [0010]FIG. 3 is a front elevation view.  
         [0011]    [0011]FIG. 4 is a front elevation view in exploded form.  
         [0012]    [0012]FIG. 5 is a front elevation of a first interface element according to the illustrated embodiment of this invention.  
         [0013]    [0013]FIG. 6 is a side elevation.  
         [0014]    [0014]FIG. 7 is a plan view.  
         [0015]    [0015]FIG. 8 is an opposite side elevation.  
         [0016]    [0016]FIG. 9 is a front elevation of a second interface element according to the illustrated embodiment of this invention.  
         [0017]    [0017]FIG. 10 is a side elevation.  
         [0018]    [0018]FIG. 11 is a plan view.  
         [0019]    [0019]FIG. 12 is an opposite side elevation.  
         [0020]    [0020]FIG. 13 is a perspective view of a rod connection member with its interface element in place.  
         [0021]    [0021]FIG. 14 is a front elevation, partially in cross section, of a spinal implant assembly according to the illustrated embodiment of this invention in a nearly secured mode.  
         [0022]    [0022]FIG. 15 is a plan view, partially in cross section and nearly secured.  
         [0023]    [0023]FIG. 16 is a sectional view as at line  16 - 16  in FIG. 15 and viewed in the direction of the arrows but showing only the rod connecting member and a provisionally secured setscrew according to the illustrated embodiment of this invention.  
         [0024]    [0024]FIG. 17 is a plan view, partially cut away, of a connection assembly showing a compressible member according to the illustrated embodiment, the member in an uncompressed state.  
         [0025]    [0025]FIG. 18 is a plan view, partially cut away, of a connection assembly showing the compressible member, the member in a compressed state.  
         [0026]    [0026]FIG. 19 is a plan view, partially cut away, of a connection assembly showing a compressible member having a generally circular shape according to the illustrated embodiment, the member in an uncompressed state.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment 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 thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0028]    In the illustrated embodiment of the present invention there is provided a connection assembly of reduced size for a spinal implant assembly having interface elements that utilize internal structures to limit rotation of a spinal implant rod in respect to a spinal implant bolt, cause the implant assembly to assume and maintain an initial position approximating its final position, and allow the assembly to be easily secured to maintain the system in an appropriate position. There are shown in FIGS. 1 and 3, views of an assembled connection assembly  10  according to the illustrated embodiment. Corresponding exploded views are shown in FIGS. 2 and 4 illustrating internal details of selected components. The assembly comprises a rod connecting member  12  and a bolt connecting member  22 . The rod connecting member  12  has an aperture  14  for receiving a spinal implant rod and a threaded aperture  32  for receiving a securing member such as the set screw for urging the rod within the aperture  14 . The bolt connecting member  22  has an aperture  24  for receiving a spinal implant bolt or screw.  
         [0029]    The rod connecting member  12  and the bolt connecting member  22  are attached through a rotatable connection. The rotatable connection can be of any suitable design provided the connection is maintained while allowing the rotation of one member relative to the other. Suitable designs include a bolt connecting member  22  having a male protrusion  27  symmetrical about its long or connection axis  13  and a rod connecting member  12  having a female cavity  19  (FIG. 16) for receiving and engaging the male member. In a preferred embodiment, the male and female connections are provided by threaded members such as a screw  30  a threaded female cavity  20  (FIG. 13). Alternatively, the male and female connections could be provided by other suitable male and female connections capable of rotation and simple assembly such as snap-together connections. Connection would occur upon inserting the male protrusion with a flared end portion into the female cavity having a region to accept and retain the flared end portion of the male protrusion.  
         [0030]    The rod connecting member  12  has a first interface element  40  fixed against rotation relative to the rod connecting member  12  and the bolt connecting member  22  similarly has a second interface element  41  fixed against rotation relative to the bolt connecting member  22 . Interface elements,  40  and  41  are positioned on seats  17  and  26  (FIG. 4), respectively, between the rod and bolt connecting members and are moveable on the seats  17  and  26  between connecting members  12  and  22 . External stops  16  and  28  prevent removal of the interface elements  40  and  41 . Suitable external stops can include, but are not limited to, a backing face as illustrated by external stop  16  or a surface disruption as can be formed by peening as illustrated by external stop  28 .  
         [0031]    Different views of interface elements  40  and  41  according to this invention are shown in FIGS.  5 - 12 . The interface elements can be of any suitable shape including round as shown. The preferred first interface element  40  has an engagement surface  44  and an engagement groove  46  thereon, running diametrically through the interface element  40 . The engagement groove  46  is sized and positioned to engage the spinal implant rod  60  as illustrated in FIG. 14. Similarly the preferred second interface element  41  has an engagement surface  45  similarly having an engagement groove  47  thereon running diametrically through the second interface element  41 . Engagement groove  47  is sized and shaped to accept a spinal implant bolt  62  as illustrated in FIG. 15. Preferred interface elements  40  and  41  have generally square or rectangular central openings  48  and  49  which correspond to the size and shape of the cross-section of the respective seats  17  and  26  where interface elements  40  and  41  are positioned. The size and shape of the openings  48  and  49  as well as the size and shape of the cross-sections of seats  17  and  26  can vary as long as both interface elements  40  and  41  are fixed against rotation relative to their respective connecting members  12  and  22 , and at least one of the interface elements  40  or  41  is free to move between the connecting elements  12  and  22  on its respective seat  17  or  26 .  
         [0032]    As shown in FIGS.  5 - 12 , interface elements  40  and  41  have interlocking structures  50  and  51  on the surfaces opposite the engagement surfaces  44  and  45 . As shown in FIGS. 1 and 2, the interlocking structures  50  and  51  oppose each other in the completed connection assembly  10  and become engaged when pressed together between the rod connecting member  12  and the bolt connecting member  22 . When interlocking structures  50  and  51  are engaged, rotational movement of one interface element and its associated connection member relative to the other interface element and its associated connection member is prevented. Although a variety of interlocking structures can be utilized, such as for example, a plurality of variable angle ridges, circumferential spline teeth as shown in FIGS.  5 - 12  are preferred. The use of a plurality of variable angle ridges as interlocking structures is described in detail in U.S. Pat. No. 5,643,263, which is hereby incorporated herein by reference in its entirety.  
         [0033]    Referring to (FIGS. 3, 4,  12  and  13 ) novel interface element  41  has an internal stop  52  in the form of a tab located on an inner periphery. The internal stop  52  is sized and positioned to cooperate with two adjacent edges  21  and  23  (FIG. 13) of the seat associated with the rod connecting member to restrict rotation of interface element  40  and rod connecting member  12  in relation to interface element  41  and bolt connecting member  22  to less than about  90  degrees. When assembled, internal stop  52  is positioned between edges  21  and  23  (FIGS. 3, 4 and  13 ) or any other combination of adjacent edges. Rotation of interface element  41  in either direction causes the internal stop  52  to contact a limiting element, either edge  21  or edge  23 , thereby limiting rotation to the arc defined by the two edges  21  and  23 . In the present embodiment rotation is limited to less than about 90 degrees. Rotation can be increased by increasing the arc defined by edges  21  and  23  or decreased by decreasing the arc defined by edges  21  and  23 . Utilization of the novel internal stop  52  in preferred devices can allow the diameter of interface elements to be reduced from about 16 mm to about 13 mm without reducing the assembly&#39;s mechanical strength as compared to prior art devices without an internal stop. Preferred interface elements have a diameter of less than about 16 mm and more preferred interface elements have a diameter between about 15 mm to about 13 mm.  
         [0034]    In a further embodiment of the present invention, illustrated in FIG. 17, there is provided at least one compressible member  70  fixed to seat  17  (FIGS. 3 and 13) in the region of groove  54  between and in contact with at least the inner face  38  of interface element  41  to maintain a sufficient distance between the interlocking structures  50  and  51  to prevent their engagement while the compressible member  70  is in an uncompressed state. As illustrated in FIG. 18 when set screw  18  is engaged within aperture  32  spinal implant rod  60  is moved toward connecting member  22 . Interface elements  40  and  41 , positioned between the implant rod  60  and connecting member  22  are forced in the direction of connecting member  22  and toward each other, compressing member  70  against the inner face  38  of interface element  41  and causing interlocking structures  50  and  51  engage. As a result, rotation of interface elements  40  and  41  and their respective connecting elements  12  and  22  is prevented. When the force behind interface element  40  is removed, member  70  resumes its uncompressed state forcing interface elements  40  and  41  apart, causing the interlocking structures to disengage. As a result rotation of the interface elements  40  and  41  and their respective connecting elements  12  and  22  is again possible without any additional effort to separate the interface elements.  
         [0035]    Compressible member  70  can be any biocompatible material having the ability to be compressed upon the application of a force and uncompressed upon removal of the force return to its uncompressed state. The biocompatible material can be applied in an uncured form wherein adhesion to the assembly occurs upon curing or in a cured form. Cured forms of member  70  can be maintained in position within assembly  10  either with a biocompatible adhesive or by sizing and shaping member  70  appropriately. An adhesive is unnecessary provided member  70 , in its uncompressed form, fits between and contacts the inner faces of interface elements  40  and  41 , has a shape that causes it to be secured and prevents engagement of elements  50  and  51 . Cured forms of  70  having generally circular shapes have proven particularly useful in this regard (FIG. 19). Preferred compressible members are rubber materials, particularly silicone rubbers and their preferred method of application is to apply the rubber in its uncured form.  
         [0036]    Different views of the novel interface elements  40  and  41  according to this invention are shown in FIGS.  5 - 12 . The interface elements can be of any suitable shape including round as shown. Preferred interface elements  40  and  41  have an engagement surfaces  44  and  45  which have engagement grooves  46  and  47 , running diametrically through the interface element, the engagement grooves for engaging either a spinal implant rod  60  or a spinal implant bolt  62  in an installed spinal implant assembly illustrated in FIGS. 14 and 15. Preferred interface elements have a generally square or rectangular central opening  48  or  49  that correspond to the cross-sectional shape of the respective seat  17  and  26  to which the interface element is engaged. The size and shape of the openings  48  and  49  can vary as can the size and shape of seats  17  and  26 , provided the size and shape of the opening in the first interface element  48  coincides with the size and shape of seat  17  associated with the rod connecting member  12  and provided the size and shape of the opening in the second interface element  41  coincides with the size and shape of seat  26  associated with the bolt connecting member  22 .  
         [0037]    In a further feature of the illustrated embodiment of the present invention there is provided an assembly for a medical device having a selected component provisionally secured by a material that is disrupted upon installation of the assembly. Medical devices having assemblies with components provisionally secured resist disengagement of the secured components during shipping and related handling. Missing components at the time of installation or implantation are thereby avoided. Illustrated in FIG. 16 is a rod connection member  12  utilized in connection assembly  10  having a set screw  18  provisionally secured by a material  75  surrounding the threads  29  of set screw  18  and the internal threads  31  within aperture  32  (FIG. 13). Suitable materials are biocompatible materials having low to intermediate shear strength that either tear or pull loose from a bonded surface upon the application of minimal force appropriate within a surgical environment. Examples of suitable biocompatible materials are silicone rubbers.  
         [0038]    Another feature of this invention is the method for provisionally securing components of a medical device comprising providing at least two components of a medical assembly to be provisionally secured having surfaces suitable for engagement; applying a biocompatible material to at least one of the surfaces; contacting the surfaces to be secured; and maintaining contact of the surfaces until the components have been provisionally secured. An example of biocompatible materials for provisionally securing components of medical devices is silicone rubber. Preferred surfaces particularly suitable to be provisionally secured within components of medical device assemblies include the surface of a male protrusion and the inner surface of an aperture or female cavity suitable for receiving the male protrusion. More preferred surfaces include the threaded surface of a screw and the inner threaded surface of an aperture or female cavity suited for receiving the screw. The time needed for a particular biocompatible material to provisionally secure components of a medical device will vary according to the material selected. Such information is generally available from the material manufacturer or can be determined by one skilled in the art without undue experimentation.  
         [0039]    The manner of connection of the connection assembly  10  to a spinal implant rod  60  and a spinal implant bolt  62  is shown in FIGS. 14 and 15. The spinal implant rod  60  and spinal implant bolt  62  are properly positioned within the connecting member  10 . Set screw  18 , provisionally secured within aperture  32 , is threaded into aperture  32  (FIG. 14) where it contacts a side of the spinal implant rod  60 , forces rod  60  toward the bolt connecting member  22 . The rod  60  contacts the first interface element  40  through its engagement groove  46 . As torque is applied to set screw  18 , material  75  (FIG. 16) is disrupted allowing set screw  18  to engage aperture  32 . As set screw  18  is further threaded into aperture  32 , interface element  40  is urged toward interface element  41 ; member  70  is compressed between interface elements  40  and  41 ; interlocking structures  50  and  51  are engaged preventing further rotation of rod connecting member  12  and bolt connecting member  22  and interface element  41  engages implant bolt  62  through engagement groove  47 . When set screw  18  has been sufficiently engaged, the entire assembly will be locked against movement.  
         [0040]    Adjustments can be made by loosening set screw  18  whereby member  70  will become uncompressed, causing interface elements  40  and  41  to move away from each other. As interface elements  40  and  41  are separated, interlocking structures  50  and  51  disengage allowing free rotation of the interface element  40  and rod connecting member  12  with regard to interface element  41  and connecting member  22 . After a preferred position has been attained, the assembly can be re-secured by re-tightening set screw  18 .  
         [0041]    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, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.