Soft stabilization assemblies with off-set connector

A spinal longitudinal connecting member includes a soft stabilization assembly segment having a tensioned cord and a hard rod segment. A connector in fixed engagement with the hard rod also captures the tensioned cord of the soft segment, the connector being in fixed or sliding relation with the tensioned cord. The connector places the soft assembly segment in lateral or off-set and staggered relation to the hard rod segment. The connector may be integral to a bone anchor.

BACKGROUND OF THE INVENTION

The present invention is directed to soft or dynamic fixation assemblies for use in bone surgery, particularly spinal surgery, and in particular to longitudinal connecting members for such assemblies, the connecting members being attached to at least two bone fasteners.

Historically, it has been common to fuse adjacent vertebrae that are placed in fixed relation by the installation therealong of bone screws or other bone anchors and cooperating longitudinal connecting members or other elongate members. Fusion results in the permanent immobilization of one or more of the intervertebral joints. Because the anchoring of bone screws, hooks and other types of anchors directly to a vertebra can result in significant forces being placed on the vertebra, and such forces may ultimately result in the loosening of the bone screw or other anchor from the vertebra, fusion allows for the growth and development of a bone counterpart to the longitudinal connecting member that can maintain the spine in the desired position even if the implants ultimately fail or are removed. Because fusion has been a desired component of spinal stabilization procedures, longitudinal connecting members have been designed that are of a material, size and shape to largely resist flexure, extension, torsion, distraction and compression, and thus substantially immobilize the portion of the spine that is to be fused. Thus, longitudinal connecting members are typically uniform along an entire length thereof, and usually made from a single or integral piece of material having a uniform diameter or width of a size to provide substantially rigid support in all planes.

An alternative to fusion, which immobilizes at least a portion of the spine, and the use of more rigid longitudinal connecting members or other rigid structure has been a “soft” or “dynamic” stabilization approach in which a flexible loop-, S-, C- or U-shaped member or a coil-like and/or a spring-like member is utilized as an elastic longitudinal connecting member fixed between a pair of pedicle screws in an attempt to create, as much as possible, a normal loading pattern between the vertebrae in flexion, extension, distraction, compression, side bending and torsion. Another type of soft or dynamic system known in the art includes bone anchors connected by flexible cords or strands, typically made from a plastic material. Such a cord or strand may be threaded through cannulated spacers that are disposed between adjacent bone anchors when such a cord or strand is implanted, tensioned and attached to the bone anchors. The spacers typically span the distance between bone anchors, providing limits on the bending movement of the cord or strand and thus strengthening and supporting the overall system. Such cord or strand-type systems have typically required specialized bone anchors and tooling for tensioning and holding the cord or strand in the bone anchors.

The complex dynamic conditions associated with spinal movement create challenges for the design of elongate elastic longitudinal connecting members that exhibit an adequate fatigue strength to provide stabilization and protected motion of the spine, without fusion, and that allow for some natural movement of the portion of the spine being reinforced and supported by the elongate elastic or flexible connecting member. A further challenge are situations in which a portion or length of the spine requires a more rigid stabilization, possibly including fusion, while another portion or length may be better supported by a more dynamic system that allows for protective movement.

SUMMARY OF THE INVENTION

Longitudinal connecting member assemblies according to the invention for use between at least two bone anchors provide soft or dynamic, protected motion of the spine and may be extended to provide additional soft or dynamic sections or more rigid support along an adjacent length of the spine, with fusion, if desired. An illustrated longitudinal connecting member assembly according to an embodiment of the invention includes a soft portion or segment connected to a more rigid or hard portion or segment by a transversely oriented connector structure, the connector structure placing the soft portion of the assembly in parallel but lateral or off-set and staggered relationship with the hard portion of the assembly. Stated in another way, when implanted onto a patient's spine, the assembly generally runs along a portion of the spine with a connector attaching a soft elongate segment with a hard elongate segment; however, the soft and hard elongate segments of the assembly are not directly in line with one another but rather are positioned medial/lateral or lateral/medial with respect to one another. The soft portion of the assembly includes an inner segment or core, typically a tensioned cord or cords, the core being fixed at either end thereof to substantially rigid segments or structures, the rigid segments including but not limited to the off-set connector structure, bone anchors (typically bone screws, such as mono-axial or poly-axial screws), or end blocking structures or stops that are not part of a bone anchor or screw structure. The core is also usually surrounded by a spacer that may be elastomeric or hard and rigid. Furthermore elastomeric bumpers may be used at locations along the soft portion of the assembly and about the tensioned cord or core to provide a continuous axial load. The tensioned inner core or cord of the soft portion of the assembly and one or more compressed spacers and/or bumpers cooperate dynamically, such features also having some flexibility in bending, but also protecting and limiting flexing movement of the inner core. The rigid or hard portion of the assembly is typically a hard rod or bar that is attached to both the off-set connector structure and to one or more bone anchors. The off-set connector may be closed or open at a top thereof, having structure for mating cooperation with set screws or other closure tops that in turn have structure for fixing to the soft portion inner core or to the hard rod portion located within the off-set connector structure. In some embodiments, the off-set connector is integral with a bone anchor. Assemblies of embodiments of the invention may include mono- and/or poly-axial bone anchors, both open and closed. Typically open mono- or poly-axial bone anchors are fixed to the hard rod portion of the assembly, while either open or closed bone anchors may be used to capture, and if desired, fix the inner core of the assembly soft portion against the respective bone anchor. In certain embodiments it may be desirable to allow the soft core or cord to be in sliding engagement with the off-set connector and also with one or more bone anchors.

A variety of embodiments according to the invention are possible. Rods or other substantially rigid structures having different measures of rigidity may be connected according to embodiments of the invention. Either rigid lengths or flexible cords may be of greater or lesser lengths for attaching to one and up to a plurality of bone anchors.

It is an object of the invention to provide apparatus and methods that are easy to use and especially adapted for the intended use thereof and wherein the apparatus are comparatively inexpensive to make and suitable for use. Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. It is also noted that any reference to the words top, bottom, up and down, and the like, in this application refers to the alignment shown in the various drawings, as well as the normal connotations applied to such devices, and is not intended to restrict positioning of the connecting member assemblies of the application and cooperating bone anchors in actual use.

With reference toFIGS. 3-7, a longitudinal connecting member assembly according to an embodiment of the invention, generally1, is shown that includes a connector structure2that attaches a soft segment or assembly portion, generally3, with a hard segment or portion, generally3′ in a staggered and offset orientation to one another. As best shown inFIG. 5, the soft non-fusion segment3is elongate and extends substantially along a central axis A. The hard segment portion3′ is also elongate and extends substantially along a central axis A′ that is substantially parallel to the axis A. The elongated segments3and3′ are in a lateral/medial or medial/lateral relationship to one another when the assembly1is connected to a spine (not shown) utilizing bone anchors, such as open and closed mono-axial and polyaxial bone screws and hooks.

The illustrated soft segment3of the assembly1includes the following components: an elongate bendable and soft, flexible core in the form of a tensioned cord4; a cannulated spacer6that may be compressible; two elastic bumpers8; and a fixing structure or blocking member in the form of a blocker10with cooperating set screw11sized and shaped for pressing against and/or into the cord4and fixing the cord with respect to the blocker10. The hard portion or segment3′ is illustrated as a cylindrical rod14.

The assembly1is shown with two closed monoaxial bone screws16and three open monoaxial bone screws18. The closed screws16each have an upper portion or head21integral with a lower shank22having at least one helical thread form for rotating and driving the screw into a vertebra. Each head21has a cylindrical opening24formed in a top thereof that is sized, shaped and threaded for mating with a set screw, such as the set screw11′, best illustrated inFIG. 7. Each of the illustrated open bone screws18includes a head or upper portion27integral with a lower shank28having at least one helical thread form for rotating and driving the screw into a vertebra. The head27is in the form of opposed arms that form an open channel30sized and shaped to closely receive the rod14in an open or percutaneous manner and having a guide and advancement structure, illustrated as a flange form31for rotating into and mating engagement with a closure top such as a closure top35shown inFIGS. 3 and 5, for example. Details of both open and closed screws and closures, such as the screws11and11′ and the closures35for use with longitudinal connecting member embodiments of the invention are described in greater detail in Applicant's U.S. patent application Ser. No. 13/506,657 filed May 7, 2012, published as U.S. 2012/0221054, the entire disclosure of which is incorporated by reference herein (and hereafter identified as the '657 application). For example, certain open screws are shown in FIGS. 33-43 of the '657 application and certain closed bone screws are shown in FIGS. 69-71 of the '657 application. The '657 applications also discloses a variety of set screws and closure tops for use with the bone screws described therein. In the present application, although the assembly1soft segment3is shown with closed screws, it is noted that the soft segment3′ may also be used with open bone screws, both monoaxial and polyaxial, as described, for example, in Applicant's '657 application. It is also noted that although the soft segment3is shown with the cord gripping closure top11′ and another of the closed screws16is shown without a closure, in certain embodiments, the bone anchors used with the soft segment3may also be used with non-gripping closures that allow for the cord4to slip or slide with respect to the closure as described in detail in Applicant's '657 application.

The tensioned cord4, spacer6, bumpers8and blocker10with set screw11are identical or substantially similar to the longitudinal connecting member components identified by the same names and described in greater detail in Applicant's '657 application, the disclosure of which has already been incorporated by reference herein. For example, a tensioned cord 1004 is shown in FIGS. 28-32 of the '657 application and described in paragraph 146 therein that is the same or substantially similar in form and function to the tensioned cord4. Spacers 1006 and 2006, for example, are shown in FIGS. 30-32 and 44-49, respectively, of the '657 application and described in paragraphs 147 and 168-72 therein that are the same or substantially similar in form and function to the spacer6. Bumpers 1008 and 2008, for example, are shown in FIGS. 30-32 and 44-49, respectively, of the '657 application and described in paragraphs 148-49 and 168-72 therein that are the same or substantially similar in form and function to the elastic bumpers8. A blocker and set screw combination 2010, 2011 is shown in FIGS. 44-49 of the '657 application and described in paragraph 170 therein that is the same or substantially similar in form and function to the end blocker10and set screw11combination. Spacers6and bumpers8of embodiments of the invention are typically cylindrical tubes prior to assembly, but may be formed in other geometric shapes. Also, it is noted that the illustrated elastic bumpers8shown in the drawings are shown compressed in the drawing figures and thus are not shown as cylinders, but rather in a compressed form wherein the bumper bulges outwardly at a middle portion thereof.

With particular reference toFIGS. 1 and 2, the off-set connector2can also be described as a double-wide blocker, with one portion of the connector sized and shaped for receiving a tensioned cord and an adjacent portion sized and shaped for receiving another connector, such as a hard rod. The illustrated connector2includes a first through bore defined by a substantially cylindrical surface50and a second, parallel through bore formed by a substantially cylindrical surface52, both bore cylindrical surfaces50and52formed in the connector2between and through substantially planar front54and rear56surfaces. The front surface54is parallel to the rear surface56. A top surface58perpendicular to both the front surface54and the rear surface56is substantially planar and terminates at the front and rear surfaces54and56. In the illustrated embodiment, opposed side surfaces60and62are each curved and also terminate at the top surface58. A bottom substantially planar surface65spans between the curved side surfaces60and62. However, it is foreseen that in other embodiments of the invention the bottom surface65may include cut-outs and curves. The cylindrical surface50is located near the side surface60and the cylindrical surface52is located near the side surface62, the cylindrical surfaces50and52being uniformly spaced from the respective side surfaces60and62. Formed in the top surface58are a pair of spaced apertures defined by threaded cylindrical surfaces70and72. The cylindrical surface70runs from the top surface58and terminates at the bore50while the cylindrical surface72runs from the top surface58and terminates at the bore52. Thus apertures defined by the surfaces70and72communicate with and are perpendicular to the bores defined by the respective cylindrical surfaces50and52. The threaded surface70is sized and shaped for mating engagement with a set screw111, as shown for example inFIG. 3a, and the threaded surface72is sized and shaped for mating engagement with a set screw111′, shown in bothFIG. 3andFIG. 3a. It is noted that in the embodiment illustrated inFIG. 3a, the set screws11,11′ and111are identical. However, in other embodiments of the invention, set screws or closure tops of different sizes or geometries may be utilized to press the tensioned cord4into frictional engagement with other connectors, end blockers or bone screws.

In the illustrated embodiment, the through bores defined by the cylindrical surfaces50and52are substantially the same size, allowing a user to laterally connect any two longitudinal connecting member assembly segments, either soft or hard without concern of how to orient the connector2with respect to such segments. Thus, the connector2may be used with or without a hard rod. For example, two soft connector segments, possibly having spacers or bumpers of different durometer or segments that differ only in length may be medially/laterally connected in a staggered manner by the connector2. Similarly, both the threaded bores70and72are shown having the same diameter and thus only the closures or screws would need to be different in height to adequately fix against a hard rod14or a soft tensioned cord4. As shown inFIGS. 6 and 7, for example, the set screws11and11′ shown inFIG. 7each include a central projection12and12′ respectively, for pressing downwardly against the cord4while the set screw111′ shown inFIG. 6is of a shorter length than the screws11and11and includes an edge or shallow rim112′ for gripping and penetrating the hard rod14. In other embodiments, the screw111may include other surfaces, points or edges for gripping the rod14or may have a planar bottom surface.

It is foreseen that in other embodiments of the invention, the cylindrical surface50that slidingly receives the cord4may have a diameter that is smaller than a diameter of the surface52that slidingly receives the rod14. Also, the set screw receiving surfaces70and72may have different diameters, thus requiring various set screws of not only different heights but also different diameters for cooperating with either side of the connector2.

With further reference toFIGS. 3 and 4-7, the assembly1is shown wherein the cord4is fixed to the end blocker10at a first end thereof, the set screw11pressing the cord4into frictional engagement with the blocker10. The cord4is then threaded through one of the elastic bumpers8and then through the head21of one of the bone screws16. The cord4is then threaded through the inelastic spacer6and the connector2, followed by another elastic bumper8and finally the head21of the bone screw16that also includes the set screw11′ that fixes the cord4to the bone screw16. The cord4is in sliding relation with both bumpers8, the bone screw16that is located between one of the bumpers8and the spacer6. The cord4is also in sliding relation with the connector2, the threaded cylindrical surface70being shown without a set screw. The soft segment3of the assembly1is shown in a nominal state, as, for example, the assembly would be in after the cord4is tensioned (in some embodiments, after the cord4has had some extension after creep and wherein the cord4may have been re-tensioned and recaptured at either the bumper10or the set screw11′. As shown, tensioning of the cord4results in some compression placed on the bumpers8. As best shown inFIG. 7, the cord4is in tension between the blocker10and the end screw16that has the set screw11′ pressing against the cord4. The cord4is free to slide with respect to all the soft segment components located between the blocker10and the end screw16, allowing the soft segment3to respond to compressive and extension forces on vertebrae (not shown) attached to both of the bone screws16. As shown inFIG. 3andFIGS. 4-7, the hard rod14is fixed to the connector2by the set screw111′ and is fixed to three bone screws18by three closure tops35.

With reference toFIG. 3a, the assembly1has been modified to create an assembly1′ wherein a soft segment3″ has the cord4fixed at one end by the blocker10and at an opposite end thereof by the set screw111rotatingly mated with the threaded cylindrical surface70of the connector2. Thus, the connector2is also a termination of the soft segment3″, the connector2functioning as an end blocker for the tensioned cord4. The tensioned cord4is in sliding relation with a bumper8, a bone screw16and a spacer6. The bone screw16is shown with the opening24empty, similar to what is shown inFIG. 3. However, in some embodiments of the invention, it may be desirable to insert a set screw11′ in the bone screw head21to fix the cord4to the bone screw16. In such an embodiment, a bumper8may be placed on an opposite side56of the connector2and the cord threaded through an additional end blocker10located adjacent such bumper8. Thus, a wide variety of combinations of bumpers, blockers, spacers and bone screws for a soft segment can be visualized. In the embodiment illustrated inFIG. 3a, the connector2is fixed to the hard rod segment3′ identical to what is shown inFIG. 3. However, it is foreseen that hard rod segments of different lengths or other hard or soft segments may be slidingly captured by the connector2or fixed to the connector2by a set screw111or111′ in lieu of the rod segment3′ shown.

With reference toFIGS. 8 and 9another embodiment of a connector2′ is shown. The connector2′ is similar to the connector2previously described herein with the exception that an open channel for a rod is formed in the connector2′ in lieu of the rod receiving through bore52and set screw aperture72combination. Thus, the connector2′ includes a cylindrical surface50′ defining a through bore, a front surface54′, a rear surface56′, a top surface58′, a curved side surface60′, a bottom surface65′ and a threaded aperture70′ substantially similar in form and function to the respective cylindrical surface50, front surface54, rear surface56, top surface58, curved side surface60, bottom surface65and threaded aperture70previously described herein with respect to the connector2. The connector2′ also includes a side portion27′ defining a rod receiving channel30′ further defined by a guide and advancement structure that is shown as a flange form structure31′ for receiving a closure top35′ that is substantially similar in form and function to the respective bone anchor upper portion or head27defining the rod receiving channel30further defined by the flange form guide and advancement structure31for receiving the closure top35previously described herein with respect to the open bone anchor18. As shown inFIG. 8, the rod14is received in the connector2′ channel30′ and the closure top35′ is rotated with respect to the flange form31′ to capture and fix the rod14within the connector2′. Similar to what has been discussed previously herein, with respect toFIG. 8, a tensioned cord4is shown fixed to the connector2′ by a set screw111inserted within the opening70′ at the top58′ of the connector2′.FIG. 8. also shows a partial spacer6disposed about the tensioned cord4and further soft connector components, including bumpers, additional bone anchors and end blockers may be connected by the tensioned cord4at an opposite side of the spacer6.

With respect toFIG. 9, the alternative connector2′ is shown with a rod14and closure top35′ similar to what is shown inFIG. 8and further shown with a tensioned cord4is sliding engagement with the connector2′, the connector aperture surface70′ not having a set screw111rotatingly mated therein. The cord4is shown in sliding engagement with a bumper8and being fixed to an end blocker10with a set screw11. Similar toFIG. 8,FIG. 9shows a partial spacer6surrounding the tensioned cord4at the back surface56′ of the connector2′. A bone screw (not shown) may be placed at an opposite end of the spacer6that may be in fixed or slidable engagement with the cord4. Further bumpers8, spacers6, bone anchors and possibly another end blocker10may be located along the tensioned cord4.

With reference toFIG. 10, another alternative connector, generally201, is shown. The connector201includes a closed connector portion202integral with a bone screw, generally218. Thus the connector portion202includes a cylindrical surface250defining a through bore, a front surface254, a rear surface256, a top surface258, a curved side surface260, a bottom surface265and a threaded aperture270perpendicular to the cylindrical surface260that is substantially similar in form and function to the respective cylindrical surface50, front surface54, rear surface56, top surface58, curved side surface60, bottom surface65and threaded aperture70previously described herein with respect to the connector2. The connector202also includes a head portion227that is integral to the connector portion202and a shank228, the head portion227defining a rod receiving channel230further defined by a guide and advancement structure that is shown as a flange form structure231for receiving a closure top235that is substantially similar in form and function to the respective bone anchor18upper portion or head27and shank28, the head27defining the rod receiving channel30further defined by the flange form guide and advancement structure31for receiving the closure top35previously described herein with respect to the open bone anchor18.

It is foreseen that a connector may also include two open channels, one for receiving a rod and the other for receiving a cord4. Furthermore, such a dual open channel embodiment could be integral with a bone screw shank.