Connection assembly for spinal implant systems

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'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'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'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's size to be reduced without sacrificing the assembly'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's size, that allow the assembly to approximate a final installed position early in the installation process while the assembly'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'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]FIG. 1 is a plan view of a connection assembly for a spinal implant device according to the illustrated embodiment of this invention.

[0009]FIG. 2 is a plan view in exploded form.

[0010]FIG. 3 is a front elevation view.

[0011]FIG. 4 is a front elevation view in exploded form.

[0012]FIG. 5 is a front elevation of a first interface element according to the illustrated embodiment of this invention.

[0013]FIG. 6 is a side elevation.

[0014]FIG. 7 is a plan view.

[0015]FIG. 8 is an opposite side elevation.

[0016]FIG. 9 is a front elevation of a second interface element according to the illustrated embodiment of this invention.

[0017]FIG. 10 is a side elevation.

[0018]FIG. 11 is a plan view.

[0019]FIG. 12 is an opposite side elevation.

[0020]FIG. 13 is a perspective view of a rod connection member with its interface element in place.

[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]FIG. 15 is a plan view, partially in cross section and nearly secured.

[0023]FIG. 16 is a sectional view as at line <b>16</b>-<b>16</b> 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]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]FIG. 18 is a plan view, partially cut away, of a connection assembly showing the compressible member, the member in a compressed state.

[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 <b>10</b> 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 <b>12</b> and a bolt connecting member <b>22</b>. The rod connecting member <b>12</b> has an aperture <b>14</b> for receiving a spinal implant rod and a threaded aperture <b>32</b> for receiving a securing member such as the set screw for urging the rod within the aperture <b>14</b>. The bolt connecting member <b>22</b> has an aperture <b>24</b> for receiving a spinal implant bolt or screw.

[0029] The rod connecting member <b>12</b> and the bolt connecting member <b>22</b> 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 <b>22</b> having a male protrusion <b>27</b> symmetrical about its long or connection axis <b>13</b> and a rod connecting member <b>12</b> having a female cavity <b>19</b> (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 <b>30</b> a threaded female cavity <b>20</b> (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 <b>12</b> has a first interface element <b>40</b> fixed against rotation relative to the rod connecting member <b>12</b> and the bolt connecting member <b>22</b> similarly has a second interface element <b>41</b> fixed against rotation relative to the bolt connecting member <b>22</b>. Interface elements, <b>40</b> and <b>41</b> are positioned on seats <b>17</b> and <b>26</b> (FIG. 4), respectively, between the rod and bolt connecting members and are moveable on the seats <b>17</b> and <b>26</b> between connecting members <b>12</b> and <b>22</b>. External stops <b>16</b> and <b>28</b> prevent removal of the interface elements <b>40</b> and <b>41</b>. Suitable external stops can include, but are not limited to, a backing face as illustrated by external stop <b>16</b> or a surface disruption as can be formed by peening as illustrated by external stop <b>28</b>.

[0031] Different views of interface elements <b>40</b> and <b>41</b> according to this invention are shown in FIGS. <b>5</b>-<b>12</b>. The interface elements can be of any suitable shape including round as shown. The preferred first interface element <b>40</b> has an engagement surface <b>44</b> and an engagement groove <b>46</b> thereon, running diametrically through the interface element <b>40</b>. The engagement groove <b>46</b> is sized and positioned to engage the spinal implant rod <b>60</b> as illustrated in FIG. 14. Similarly the preferred second interface element <b>41</b> has an engagement surface <b>45</b> similarly having an engagement groove <b>47</b> thereon running diametrically through the second interface element <b>41</b>. Engagement groove <b>47</b> is sized and shaped to accept a spinal implant bolt <b>62</b> as illustrated in FIG. 15. Preferred interface elements <b>40</b> and <b>41</b> have generally square or rectangular central openings <b>48</b> and <b>49</b> which correspond to the size and shape of the cross-section of the respective seats <b>17</b> and <b>26</b> where interface elements <b>40</b> and <b>41</b> are positioned. The size and shape of the openings <b>48</b> and <b>49</b> as well as the size and shape of the cross-sections of seats <b>17</b> and <b>26</b> can vary as long as both interface elements <b>40</b> and <b>41</b> are fixed against rotation relative to their respective connecting members <b>12</b> and <b>22</b>, and at least one of the interface elements <b>40</b> or <b>41</b> is free to move between the connecting elements <b>12</b> and <b>22</b> on its respective seat <b>17</b> or <b>26</b>.

[0032] As shown in FIGS. <b>5</b>-<b>12</b>, interface elements <b>40</b> and <b>41</b> have interlocking structures <b>50</b> and <b>51</b> on the surfaces opposite the engagement surfaces <b>44</b> and <b>45</b>. As shown in FIGS. 1 and 2, the interlocking structures <b>50</b> and <b>51</b> oppose each other in the completed connection assembly <b>10</b> and become engaged when pressed together between the rod connecting member <b>12</b> and the bolt connecting member <b>22</b>. When interlocking structures <b>50</b> and <b>51</b> 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. <b>5</b>-<b>12</b> 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, <b>12</b> and <b>13</b>) novel interface element <b>41</b> has an internal stop <b>52</b> in the form of a tab located on an inner periphery. The internal stop <b>52</b> is sized and positioned to cooperate with two adjacent edges <b>21</b> and <b>23</b> (FIG. 13) of the seat associated with the rod connecting member to restrict rotation of interface element <b>40</b> and rod connecting member <b>12</b> in relation to interface element <b>41</b> and bolt connecting member <b>22</b> to less than about <b>90</b> degrees. When assembled, internal stop <b>52</b> is positioned between edges <b>21</b> and <b>23</b> (FIGS. 3, 4 and <b>13</b>) or any other combination of adjacent edges. Rotation of interface element <b>41</b> in either direction causes the internal stop <b>52</b> to contact a limiting element, either edge <b>21</b> or edge <b>23</b>, thereby limiting rotation to the arc defined by the two edges <b>21</b> and <b>23</b>. In the present embodiment rotation is limited to less than about 90 degrees. Rotation can be increased by increasing the arc defined by edges <b>21</b> and <b>23</b> or decreased by decreasing the arc defined by edges <b>21</b> and <b>23</b>. Utilization of the novel internal stop <b>52</b> 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'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 <b>70</b> fixed to seat <b>17</b> (FIGS. 3 and 13) in the region of groove <b>54</b> between and in contact with at least the inner face <b>38</b> of interface element <b>41</b> to maintain a sufficient distance between the interlocking structures <b>50</b> and <b>51</b> to prevent their engagement while the compressible member <b>70</b> is in an uncompressed state. As illustrated in FIG. 18 when set screw <b>18</b> is engaged within aperture <b>32</b> spinal implant rod <b>60</b> is moved toward connecting member <b>22</b>. Interface elements <b>40</b> and <b>41</b>, positioned between the implant rod <b>60</b> and connecting member <b>22</b> are forced in the direction of connecting member <b>22</b> and toward each other, compressing member <b>70</b> against the inner face <b>38</b> of interface element <b>41</b> and causing interlocking structures <b>50</b> and <b>51</b> engage. As a result, rotation of interface elements <b>40</b> and <b>41</b> and their respective connecting elements <b>12</b> and <b>22</b> is prevented. When the force behind interface element <b>40</b> is removed, member <b>70</b> resumes its uncompressed state forcing interface elements <b>40</b> and <b>41</b> apart, causing the interlocking structures to disengage. As a result rotation of the interface elements <b>40</b> and <b>41</b> and their respective connecting elements <b>12</b> and <b>22</b> is again possible without any additional effort to separate the interface elements.

[0035] Compressible member <b>70</b> 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 <b>70</b> can be maintained in position within assembly <b>10</b> either with a biocompatible adhesive or by sizing and shaping member <b>70</b> appropriately. An adhesive is unnecessary provided member <b>70</b>, in its uncompressed form, fits between and contacts the inner faces of interface elements <b>40</b> and <b>41</b>, has a shape that causes it to be secured and prevents engagement of elements <b>50</b> and <b>51</b>. Cured forms of <b>70</b> 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 <b>40</b> and <b>41</b> according to this invention are shown in FIGS. <b>5</b>-<b>12</b>. The interface elements can be of any suitable shape including round as shown. Preferred interface elements <b>40</b> and <b>41</b> have an engagement surfaces <b>44</b> and <b>45</b> which have engagement grooves <b>46</b> and <b>47</b>, running diametrically through the interface element, the engagement grooves for engaging either a spinal implant rod <b>60</b> or a spinal implant bolt <b>62</b> in an installed spinal implant assembly illustrated in FIGS. 14 and 15. Preferred interface elements have a generally square or rectangular central opening <b>48</b> or <b>49</b> that correspond to the cross-sectional shape of the respective seat <b>17</b> and <b>26</b> to which the interface element is engaged. The size and shape of the openings <b>48</b> and <b>49</b> can vary as can the size and shape of seats <b>17</b> and <b>26</b>, provided the size and shape of the opening in the first interface element <b>48</b> coincides with the size and shape of seat <b>17</b> associated with the rod connecting member <b>12</b> and provided the size and shape of the opening in the second interface element <b>41</b> coincides with the size and shape of seat <b>26</b> associated with the bolt connecting member <b>22</b>.

[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 <b>12</b> utilized in connection assembly <b>10</b> having a set screw <b>18</b> provisionally secured by a material <b>75</b> surrounding the threads <b>29</b> of set screw <b>18</b> and the internal threads <b>31</b> within aperture <b>32</b> (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 <b>10</b> to a spinal implant rod <b>60</b> and a spinal implant bolt <b>62</b> is shown in FIGS. 14 and 15. The spinal implant rod <b>60</b> and spinal implant bolt <b>62</b> are properly positioned within the connecting member <b>10</b>. Set screw <b>18</b>, provisionally secured within aperture <b>32</b>, is threaded into aperture <b>32</b> (FIG. 14) where it contacts a side of the spinal implant rod <b>60</b>, forces rod <b>60</b> toward the bolt connecting member <b>22</b>. The rod <b>60</b> contacts the first interface element <b>40</b> through its engagement groove <b>46</b>. As torque is applied to set screw <b>18</b>, material <b>75</b> (FIG. 16) is disrupted allowing set screw <b>18</b> to engage aperture <b>32</b>. As set screw <b>18</b> is further threaded into aperture <b>32</b>, interface element <b>40</b> is urged toward interface element <b>41</b>; member <b>70</b> is compressed between interface elements <b>40</b> and <b>41</b>; interlocking structures <b>50</b> and <b>51</b> are engaged preventing further rotation of rod connecting member <b>12</b> and bolt connecting member <b>22</b> and interface element <b>41</b> engages implant bolt <b>62</b> through engagement groove <b>47</b>. When set screw <b>18</b> has been sufficiently engaged, the entire assembly will be locked against movement.

[0040] Adjustments can be made by loosening set screw <b>18</b> whereby member <b>70</b> will become uncompressed, causing interface elements <b>40</b> and <b>41</b> to move away from each other. As interface elements <b>40</b> and <b>41</b> are separated, interlocking structures <b>50</b> and <b>51</b> disengage allowing free rotation of the interface element <b>40</b> and rod connecting member <b>12</b> with regard to interface element <b>41</b> and connecting member <b>22</b>. After a preferred position has been attained, the assembly can be re-secured by re-tightening set screw <b>18</b>.

[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.