US20100222819A1 - Integral Spring Junction - Google Patents

Abstract

Spinal stabilization devices, systems and methods are provided that include a spring junction wherein a structural member is mountable to a spine attachment fastener and a resilient element is affixed to the structural member along an attachment region of the resilient element. The attachment region is disposed physically separately with respect to an active region of the resilient element. The attachment region can include a weld region produced via an E-beam welding process involving temperatures of 1000° F. or greater, wherein a heat-affected zone adjacent the weld region is disposed physically separately with respect to the active region. The resilient element may be a coil spring including bend regions adjacent its outermost (i.e., last) coils wherein the material of the coil spring initially bends away from the last coil, then bends back toward the last coil before terminating near the last coil.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• The present application is a continuation application that claims priority benefit to a co-pending and commonly assigned non-provisional patent application entitled “Spring Junction and Assembly Methods for Spinal Device,” which was filed on Aug. 3, 2005, and assigned Ser. No. 11/196,102.
BACKGROUND
• 1. Technical Field
• The present disclosure relates to advantageous devices, systems and methods for spinal stabilization. More particularly, the present disclosure relates to devices, systems and methods for providing dynamic stabilization to the spine with systems/devices that include one or more enhanced spring junctions so as to provide clinically efficacious results.
• 2. Background Art
• Each year, over 200,000 patients undergo lumbar fusion surgery in the United States. While fusion is effective about seventy percent of the time, there are consequences even to these successful procedures, including a reduced range of motion and an increased load transfer to adjacent levels of the spine, which may accelerate degeneration at those levels. Further, a significant number of back-pain patients, estimated to exceed seven million in the U.S., simply endure chronic low-back pain, rather than risk procedures that may not be appropriate or effective in alleviating their symptoms.
• New treatment modalities, collectively called motion preservation devices, are currently being developed to address these limitations. Some promising therapies are in the form of nucleus, disc or facet replacements. Other motion preservation devices provide dynamic internal stabilization of the injured and/or degenerated spine, e.g., the Dynesys stabilization system (Zimmer, Inc.; Warsaw, Ind.) and the Graf Ligament. A major goal of this concept is the stabilization of the spine to prevent pain while preserving near normal spinal function.
• To provide dynamic internal spinal stabilization, motion preservation devices may advantageously include dynamic junctions that exhibit multiple degrees of freedom and commonly include active force-absorbing/force-generating structures. Such structures may include one or more resilient elements, e.g., torsion springs and/or coil springs, designed and deployed so as to contribute strength and flexibility to the overall device. While the flexibility afforded by such resilient elements is plainly critical to the effectiveness of the respective devices of which they faun a part, the elevated force levels associated with the use of such resilient elements can result in such resilient elements developing significant levels of internal stress. Depending on the magnitude and location thereof, internal stresses may pose the potential for stress-induced fatigue, material deformation and/or cracks. The FDA has promulgated rules (e.g., Title 21, Subchapter H, Part 888, Subpart D, Section 888.3070 regarding pedicle screw spinal systems) that, in relevant part, require manufacturers to demonstrate compliance with special controls, including but not limited to applicable mechanical testing standards geared toward high reliability and durability.
• With the foregoing in mind, those skilled in the art will understand that a need exists for devices, systems and methods for motion-preserving spinal stabilization devices and systems having reliable, durable constructions. In addition, a need exists for manufacturing processes and/or techniques that may be used to reliably and efficiently produce motion-preserving spinal stabilization devices and systems. These and other needs are satisfied by the disclosed devices and systems that include advantageous spring junctions, as well as the associate methods for manufacture/assembly thereof.
SUMMARY OF THE PRESENT DISCLOSURE
• According to the present disclosure, advantageous devices, systems and methods for spinal stabilization are provided. According to exemplary embodiments of the present disclosure, the disclosed devices, systems and methods include a spring junction that promotes reliable and efficacious spinal stabilization. The disclosed spring junction includes a structural member that is mounted or mountable with respect to a spine attachment fastener such as a pedicle screw, and a resilient element affixed to the structural member. The resilient element has an attachment region, along which the resilient element is affixed to the structural member, and an active region. The attachment region of the resilient element is physically separately disposed with respect to the active region thereof.
• According to exemplary embodiments of the present disclosure, the spring junction includes a weld region. A heat-affected zone of the resilient element and associated with the weld region is disposed adjacent the weld region, but is physically separately disposed with respect to the active region of the resilient element. The active region of the resilient element is generally subjected to cyclical stress, e.g., during in situ use of the disclosed spinal stabilization device. In exemplary embodiments, the weld region is produced via a welding process, such as electron-beam welding, and accordingly may be subjected to welding temperatures of about 1000° F. or higher. In addition, in exemplary embodiments of the present disclosure, the resilient element takes the form of a spring, e.g., a coil spring or helical spring, which extends into the weld region and which is mounted with respect to the structural member to form the spring junction.
• According to further exemplary embodiments of the present disclosure, the resilient element includes a bend region disposed between the weld region and an adjacent coil of the resilient element that extends along a helically-shaped path. The bend region is sized and shaped so as to initially bend away from the helically-shaped path before bending back toward the helically-shaped path and terminating at or in the weld region. In some such embodiments, the direction of the initial bend away from the helically-shaped path includes an axial component, but does not include a radial component. The bend region may further be sized and shaped so as to remain substantially peripherally aligned with such helically-shaped path when viewed in an axial direction with respect to the helically-shaped path. Of note, such spring junctions may be formed at opposite ends of the resilient element such that the resilient element/spring is mounted between spaced-apart structural members that are permitted to move relative to each other.
• According to further exemplary embodiments of the present disclosure, a rod is mounted with respect to (or integrally formed with) the structural member. The rod may be advantageously adapted to mount with respect to an upwardly-extending structure associated with a pedicle screw. The rod/pedicle screw may be mounted with respect to each other such that relative movement of the rod relative to the pedicle screw is permitted in at least one plane.
• In a still further embodiment, a method is disclosed for producing a spring junction in which a resilient element is welded to a structural member such that an active region of the resilient element is disposed physically separately with respect to the heat-affected zone associated with such welding. In some such embodiments, a further step is disclosed in which a resilient element is provided that defines an active region and a bend region, and wherein such welding results in the bend region being disposed between the active region and the heat-affected zone. Such a resilient element can include a coil extending along a helically-shaped path, and in which the bend region is configured so as to initially bend away from such helical path defined before bending back toward such helical path.
• In a still further embodiment, a combination is provided that includes a structural member having a first end, a second end opposite the first end, an aperture between the first end and the second end, and a notch formed in the second end. The combination also includes a resilient element having a bend region at an end thereof, the bend region terminating at a termination. The resilient element is secured to the first end of the structural member such that the bend region extends through the aperture and the termination is lodged in the notch. In some such embodiments, the resilient element is further affixed to the structural member via a weld formed with respect to the termination and the structural member at the notch. In other such embodiments, the termination is configured and dimensioned so as to extend at least partially in the direction of the first end of the structural member, and the bend region is configured and dimensioned such that the termination can be threaded through the aperture, and thereby rotated toward and into the notch. In some such cases the structural member includes a helical groove formed in the first end and terminating adjacent the aperture, and the resilient element includes an active region adjacent the bend region and spaced apart from the termination, and the active region includes a coil threaded along the helical groove to an extent of the aperture.
• The spring junction(s) of the present disclosure are typically employed as part of a spinal stabilization system that may advantageously include one or more of the following structural and/or functional attributes:
• • Exemplary embodiments of the spring junction (and associated spring/structural member subassembly) are capable of undergoing at least approximately 10,000,000 cycles of combined extension/contraction and bending (e.g., during mechanical testing);
  • Implementation of the disclosed spring junctions have no substantial effect on the footprint of the dynamic stabilization devices in which they are incorporated, e.g., the resilient elements (e.g., springs) of such spinal stabilization devices do not extend radially inwardly or outwardly to a greater extent than the dynamic stabilization devices that do not include the disclosed spring junctions, thereby preserving compatibility with existing components and/or proven or preferred geometries;
  • An outwardly/upwardly, then inwardly/downwardly extending bend region at each end of the resilient element, combined with a notch on the external end of each spring cap plate provides a snap-fit system which positively locates the ends of the resilient element within their respective notches during pre-welding assembly, and presents a convenient face for purposes of electronic-beam welding without undue risk of annealing and/or other types of damage to the active region of the resilient element.
• Advantageous spine stabilization devices, systems and methods may incorporate one or more of the foregoing structural and/or functional attributes. Thus, it is contemplated that a system, device and/or method may utilize only one of the advantageous structures/functions set forth above, a plurality of the advantageous structures/functions described herein, or all of the foregoing structures/functions, without departing from the spirit or scope of the present disclosure. Stated differently, each of the structures and functions described herein is believed to offer benefits, e.g., clinical advantages to clinicians and/or patients, whether used alone or in combination with others of the disclosed structures/functions.
• Additional advantageous features and functions associated with the devices, systems and methods of the present disclosure will be apparent to persons skilled in the art from the detailed description which follows, particularly when read in conjunction with the figures appended hereto. Such additional features and functions, including the structural and mechanistic characteristics associated therewith, are expressly encompassed within the scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
• To assist those of ordinary skill in the art in making and using the disclosed devices, systems and methods for achieving enhanced reliability, dependability, and/or durability, e.g., in a dynamic spinal stabilization device, reference is made to the appended figures wherein:
• FIG. 1 is a perspective exploded assembly view of a spinal stabilization device/system, according to the present disclosure;
• FIG. 2 is an exploded assembly view of a spinal stabilization device/system, including pedicle screws and associated mounting structures, in accordance with an embodiment of the present disclosure;
• FIG. 3 is an unexploded assembly view of the exemplary spinal stabilization device/system ofFIG. 2;
• FIGS. 4,5 and6 are interior end, exterior end, and cross-sectional views of a structural member associated with the exemplary spinal stabilization device/system ofFIGS. 2-3;
• FIGS. 7,8 and9 are interior end, exterior end, and cross sectional views of another structural member associated with exemplary spinal stabilization device/system ofFIGS. 2-3;
• FIG. 10 is a side view of a resilient element that may be employed in forming one or more spring junctions according to the present disclosure;
• FIG. 11 is a side assembly view of the exemplary spinal stabilization device/system of
• FIGS. 2-3 illustrating assembly of the components ofFIGS. 4-9;
• FIG. 12 is a perspective detail view of the interface between the structural member ofFIGS. 7-9 and the resilient element ofFIG. 10;
• FIG. 13 is a top view of the interface between the structural member ofFIGS. 7-9 and the resilient element ofFIG. 10;
• FIG. 14 is a sectional view of the interface between the structural member ofFIGS. 7-9 and the resilient element ofFIG. 10 taken along the line14-14 ofFIG. 13; and
• FIGS. 15 and 16 illustrate various exemplary types and ranges of motion associated with exemplary spinal stabilization devices/assemblies of the present disclosure.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
• The present disclosure provides advantageous devices, systems and methods for improving the reliability, dependability and/or durability of spinal stabilization systems. More particularly, the present disclosure provides advantageous devices, systems and methods for mechanically mounting resilient elements (e.g., torsion springs and/or coil springs) to, and/or for coupling resilient elements between, structural members (e.g., plates, caps, flanges, rods, and/or bars) associated with dynamic spinal stabilization systems. The mounting and/or coupling methods/techniques of the present disclosure provide enhanced reliability, dependability and/or durability without significantly increasing material weight or volume requirements and without compromising the important functions of the dynamic spinal stabilization devices/systems of which they form a part.
• The exemplary embodiments disclosed herein are illustrative of the advantageous spinal stabilization devices/systems and surgical implants of the present disclosure, and of methods/techniques for implementation thereof. It should be understood, however, that the disclosed embodiments are merely exemplary of the present invention, which may be embodied in various forms. Therefore, the details disclosed herein with reference to exemplary dynamic spinal stabilization systems and associated methods/techniques of assembly and use are not to be interpreted as limiting, but merely as the basis for teaching one skilled in the art how to make and use the advantageous dynamic spinal stabilization systems and alternative surgical implants of the present disclosure.
• With reference toFIG. 1, components of adynamic stabilization element10 disclosed in commonly assigned U.S. Non-Provisional patent application Ser. No. 11/027,270, filed Dec. 31, 2004 (hereinafter “the '270 Application”), are shown in an exploded view. The disclosure of the '270 Application is hereby incorporated herein by reference in its entirety. As shown inFIG. 1, thedynamic stabilization element10 includes two structural elements in the form of aspring cap12 and aspring cap14, and two resilient elements in the form of aninner spring16 and anouter spring18. Thespring cap12 is affixed to anattachment member20 that is configured to be coupled to the head of a pedicle screw (not shown) via a dynamic joint (not shown). Thespring cap14 is affixed to arod22 that is configured to be attached to another attachment member (not shown) that is in turn coupled to the head of another pedicle screw (not shown) via another dynamic joint (not shown). Thedynamic stabilization element10 permits relative axial/longitudinal motion, as well as angular/rotational motion, of therod20 relative to theattachment member20, as part of a larger spinal stabilization system (shown only in relevant part).
• Thespring cap12 includes aninterior end24, anexterior end26 opposite the interior end, apost28 axially positioned on theinterior end24, anannular channel30 formed in theinterior end24 around thepost28, a helically-shapedgroove32 formed in theinterior end24 around theannular channel30, and anaperture34 passing through thespring cap12 between the interior and exterior ends24,26 thereof at anend36 of the helically-shapedgroove32. Thespring cap14 includes aninterior end38, anexterior end40 opposite theinterior end38, apost42 axially positioned on theinterior end38 around thepost42, a helically-shapedgroove46 formed in theinterior end38 around theannular channel44, and anaperture48 passing through thespring cap14 between the interior and exterior ends38,40 thereof at anend50 of the helically-shapedgroove46.
• Theinner spring16 consists ofcoils52 sharing a common diameter and arranged sequentially about a common axis between a coil termination54 (obscured) at anend56 of theinner spring16 and acoil termination58 at anotherend60 thereof opposite theend56. Theouter spring18 consists ofcoils62 sharing a common diameter and arranged sequentially about a common axis between a coil termination64 (obscured) at anend66 of theouter spring18 and acoil termination68 at anotherend70 thereof opposite theend66.
• In the assembled state of thedynamic stabilization element10, theinner spring16 is positioned within theouter spring18. Thecoil52 at theend56 of theinner spring16 is positioned on or around thepost28 of thespring cap12, and against theinterior end24 of thespring cap12 so as to occupy (at least in part) theannular channel30 formed therein. Thecoil52 at theend60 of theinner spring16 is positioned on or around thepost42 of thespring cap14 and against theinterior end38 of thespring cap14 so as to occupy (at least in part) theannular channel44 formed therein. In this way, theinner spring16 is effectively captured between thespring cap12 and thespring cap14 and effectively floats relative to the opposingposts28,42. Thecoil62 at theend66 of theouter spring18 is threaded into theinterior end24 of thespring cap12 along the helically-shapedgroove32 at least until thecoil termination64 reaches theaperture34 of thespring cap12. Theouter spring18 is fixed with respect to thespring cap12, e.g., by welding, and may be trimmed so as to be flush relative to an edge formed at the interface between theaperture34 and theexterior end26 of thespring cap12. Thecoil62 at theend70 of theouter spring18 is threaded into theinterior end38 of thespring cap14 along the helically-shapedgroove46 at least until thecoil termination68 reaches theaperture48 of thespring cap14. Theouter spring18 is fixed with respect to thespring cap14, e.g., by welding, and may be trimmed so as to be flush relative to an edge formed at the interface between theaperture48 and theexterior end40 of thespring cap14.
• As described in the '270 Application, theouter spring18 is typically shorter than theinner spring16, such that as thespring cap12 and thespring cap14 are brought toward each other (i.e., to permit theouter spring18 to be mounted on both), theinner spring16 is placed in compression. The degree to which theinner spring16 is compressed is generally dependent on the difference in length as between the inner andouter springs16,18. Thus, the preload compression of theinner spring16 may be controlled and/or adjusted in part through selection of the relative lengths of the inner andouter springs16,18. In addition to the preload compression of theinner spring16, the mounting of theouter spring18 with respect to the spring caps12,14 includes placing theouter spring18 in tension. The overall preload of thedynamic stabilization element10 corresponds to equal and opposite forces experienced by and/or contained within the inner andouter springs16,18.
• Theinner spring16 reaches its free length (i.e., non compressed state) at or about the point at which a patient's movement exceeds a “neutral zone” (as described more completely in the '270 Application). Beyond this point, theinner spring16 is free floating (e.g., on the opposingposts28,42), while theouter spring18, already in tension, extends in length even further.
• In the overall design of the disclosed spinal stabilization system, optimization of the attachment between theouter spring18 and thespring cap14 is desirable. In experimental studies associated with spinal stabilization devices of the type disclosed herein, it has been noted that direct welding of theouter spring18 and thespring cap14 may not provide an optimal means of attachment. While not intending to be bound by theory, it is believed that a “heat-affected” zone may be created in thecoil62 at theend70 of theouter spring18 as a result of the process of welding theouter spring18 to thespring cap14. More particularly, such heat-affected zone is believed to arise as a result of an annealing effect brought about by the migration of excess heat arising from an electronic-beam welding process. In accordance with such electronic beam or E-beam welding processes, elevated temperatures in a range of approximately 1000° F. or higher are used to affix theouter spring18 to thespring cap14 by essentially melting such components together. The heat-affected zone so produced can be at least 0.005″-0.030″ in axial length, and is located immediately adjacent the weld formed at theend70 of theouter spring18, and along the active region of theouter spring18. (As used herein in reference to a spring or resilient element, the term “active region” or “active portion” refers to a region, portion, or part of the spring or resilient element which, during normal in-situ use and/or representative mechanical testing of the spring or resilient element, actively contributes to the characteristic stiffness of the spring or resilient element, and/or actively participates in the axial travel and/or lateral bending thereof.) The heat-affected zone can include a soft or weak point on thecoil62 at which a Rockwell hardness of the material of theouter spring18, ordinarily falling within a range of from approximately 46 to approximately 54, dips sharply; e.g., to a value in a range of from approximately 20 to approximately 24.
• According to the present disclosure, geometric/structural modifications to theouter spring18 and thespring cap14 have been found to advantageously enhance the reliability and durability ofdynamic stabilization element10. Exemplary embodiments of the advantageous geometric/structural modifications to theouter spring18 and thespring cap14 are described hereinbelow with reference toFIGS. 2-14, as is a beneficial cooling/supercooling step involving the modified outer spring and the modified spring caps associated therewith. As a result of these geometric/structural modifications, and/or of the cooling/supercooling step, a durability standard of 10,000,000+failure-free cycles has been achieved with apparatus in which an outer spring has been welded to its associated spring caps to form a dynamic stabilization device as described herein.
• According to exemplary embodiments of the present disclosure, the geometric/structural modifications include the creation of a substantial physical separation of the active portion of the outer spring from the heat-affected zone associated with the E-beam welding process, and/or from the actual site of the weld formed between the attached components. As a result of this separation, to the extent that any region of the outer spring becomes significantly annealed, and/or is brought to a significantly lowered Rockwell hardness value as a result of E-beam welding, the amount of cyclic stress to which that softened or annealed portion is exposed is substantially reduced and/or brought to such a low level that the respective junctions between the outer spring and its associated spring caps can exhibit very high levels of reliability/durability.
• With reference toFIGS. 2 and 3, a dynamicspinal stabilization system100 is shown in accordance with an exemplary embodiment of the present disclosure. Referring toFIG. 2, thespinal stabilization system100 includesattachment members102,104, pedicle screws106,108, ball/spherical elements110,112, and setscrews114,116. Theattachment member102 is configured to receive the ball/spherical element110. The ball/spherical element110 then receives the head of thepedicle screw106 such that a global/dynamic joint is formed between theattachment member102 and the head of the pedicle screw106 (see alsoFIG. 3). Theset screw114 is then inserted into the head of the pedicle screw106 (see alsoFIG. 3), thereby securing the head of thepedicle screw106 within the ball/spherical element110. Theattachment member104 is configured to receive the ball/spherical element112. The ball/spherical element112 then receives the head of thepedicle screw108 such that a global/dynamic joint is formed between theattachment member104 and the head of the pedicle screw108 (see alsoFIG. 3). Theset screw116 is then inserted into the head of the pedicle screw108 (see alsoFIG. 3), thereby securing the head of thepedicle screw108 within the ball/spherical element112.
• Thespinal stabilization system100 also includes arod118. The rod is configured to be inserted into theattachment member104, which includes atransverse aperture120 to accommodate therod118, and aset screw122 to secure therod118 at a desired position within the transverse aperture120 (see alsoFIG. 3, in which ahex driver124 is shown turning theset screw122 against the rod118).
• Thespinal stabilization system100 further includes adynamic stabilization element126 between therod118 and theattachment member102. Thedynamic stabilization element126 includesstructural members128,130, an innerresilient element132, an outerresilient element134, asheath member136, and two end clamps138. As shown inFIG. 3, the inner resilient element132 (obscured) and outer resilient element134 (partially obscured) are positioned within thesheath member136, and anend clamp138 secures thesheath member136 to each of thestructural members128,130. This prevents undesirable interaction or interference between the inner and outerresilient elements132,134 and anatomical structures in situ. Referring again toFIG. 2, the innerresilient element132 is constructed and functions in manners substantially similar to those of theinner spring16 described hereinabove with reference to thedynamic stabilization element10. The innerresilient element132 is also deployed and employed in thedynamic stabilization element126 in manners substantially similar to those in which theinner spring16 is deployed and employed in thedynamic stabilization element10 described hereinabove.
• The following components of thedynamic stabilization element126 will now be described in greater detail: the structural member128 (with reference toFIGS. 4-6), the structural member130 (with reference toFIGS. 7-9), and the outer resilient element134 (with reference toFIG. 10). Next, the manner in which thestructural members128,130 and the outerresilient element134 are assembled will be discussed (with particular reference toFIGS. 11-14). Then, the functions of thedynamic stabilization element126 will be discussed, followed by a discussion of the characteristic advantages of thedynamic stabilization element126.
• Referring now toFIGS. 4-6, thestructural member128 is affixed to (e.g., is of unitary construction with) the attachment member102 (the ball/spherical element110 is also shown within the attachment member102) and takes the form of a plate having multiple features permitting thestructural member128 to function in the manner of an end cap or spring cap with respect to the inner and outerresilient elements132,134 (FIG. 2). Thestructural member128 includes aninterior end140, anexterior end142 opposite theinterior end140, apost143 axially positioned on theinterior end140, anannular channel144 formed in theinterior end140 around thepost143, a helically-shapedgroove146 formed in theinterior end140 around theannular channel144, anaperture148 passing through thestructural member128 between the interior and exterior ends140,142 thereof at anend150 of the helically-shapedgroove146, ashort groove152 formed in theexterior end142 adjacent theaperture148, and a notch154 formed in theexterior end142 at anend156 of theshort groove152. The structure and function of thestructural member128 will be described in greater detail hereinafter.
• Referring now toFIGS. 7-9, thestructural member130 is affixed to (e.g., is of unitary construction with) the rod118 (which is positioned off-axis or off-center with respect to the structural member130), and takes the form of a plate having multiple features permitting thestructural member130 to function in the manner of an end cap or spring cap with respect to the inner and outerresilient elements132,134 (FIG. 2). Thestructural member130 includes aninterior end158, anexterior end160 opposite theinterior end158, apost162 axially positioned on theinterior end158, anannular channel164 formed in theinterior end158 around thepost162, a helically-shapedgroove166 formed in theinterior end158 around theannular channel164, anaperture168 passing through thestructural member130 between the interior and exterior ends158,160 thereof at anend170 of the helically-shapedgroove166, ashort groove172 formed in theexterior end160 adjacent theaperture168, and anotch174 formed in theexterior end160 at anend176 of theshort groove172. The structure and function of thestructural member130 will be described in greater detail hereinafter.
• Referring now toFIG. 10, the outerresilient element134 consists ofcoils178 sharing a common diameter and arranged sequentially about a common axis between acoil termination180 at anend182 of the outerresilient element134 and acoil termination184 at anotherend186 thereof opposite theend182. Extending from thecoil termination180, and substantially continuous therewith, is abend region188 of the outerresilient element134. Extending from thecoil termination184, and substantially continuous therewith, is abend region190 of the outerresilient element134.
• Thebend regions188,190 of the outerresilient element134 extend peripherally from therespective coil terminations180,184 along respective paths which, when viewed axially (see, e.g.,FIG. 13) from eitherend182,186 of the outerresilient element134, are defined by respective single radii that extend from the common axis of thecoils178 of the outerresilient element134 and that have extents approximately half that of the common diameter of thecoils178. As a result, thebend regions188,190 of the outerresilient element134 remain within the same peripheral outline defined by thecoils178 of the outerresilient element134. When viewed from the side, however, as inFIG. 10, thebend regions188,190 of the outerresilient element134 are seen to depart from the helical path defined by thecoils178.
• More particularly, thebend region188, when viewed from the side as inFIG. 10, is seen to include a curve or bend in the path of extension of thebend region188, according to which the material of the outer resilient element134: (1) initially curves away from theadjacent coil178 at thecoil termination180; (2) reaches an apex192 representing a point of maximum departure from theadjacent coil178; (3) curves therefrom back toward theadjacent coil178; and (4) terminates at abend region termination194 without fully returning to the helical path defined by thecoils178. Also, thebend region190, when viewed from the side as inFIG. 10, is seen to include a curve or bend in the path of extension of thebend region190, according to which the material of the outer resilient element134: (1) initially curves away from theadjacent coil178 at thecoil termination184; (2) reaches an apex196 representing a point of maximum departure from theadjacent coil178; (3) curves therefrom back toward theadjacent coil178; and (4) terminates at abend region termination198 without fully returning to the helical path defined by thecoils178. The structure and function of the outerresilient element134 will be described in greater detail hereinafter.
• In the assembled state of thedynamic stabilization element126 shown inFIG. 11, the inner resilient element132 (obscured, seeFIG. 2) is positioned within the outerresilient element134, between the respective posts143 (FIG. 4),162 (FIG. 7), and within the respective annular channels146 (FIG. 4),164 (FIG. 7) of thestructural elements128,130. Thebend region190 and thecoil178 at the end186 (FIG. 10) of the outerresilient element134 are threaded into the interior end140 (FIG. 6) of thestructural element128 until thebend region190 has substantially passed into or through theaperture148 of thestructural element128 and thebend region termination198 has been caused to drop or snap into place within the notch154 (FIG. 5) formed in theexterior end142 of thestructural element128. Thebend region188 and thecoil178 at the end182 (FIG. 10) of the outerresilient element134 are threaded into the interior end158 (FIG. 9) of thestructural element130 until thebend region188 has substantially passed into or through theaperture168 of thestructural element130 and the bend region termination194 (obscured, seeFIG. 10) has been caused to drop or snap into place within the notch174 (FIG. 8) formed in theexterior end160 of thestructural element130.
• Referring now toFIG. 12, the interface or spring junction between the outerresilient element134 and thestructural element130 is shown in greater detail. As indicated above, thebend region188 largely or completely extends into or through theaperture168 formed in thestructural element130, and thebend region termination194 is lodged within thenotch174 formed in theexterior end160 of thestructural element130. More particularly, aportion200 of thebend region188 of the outerresilient element134 near thecoil termination180 is lodged within the short groove172 (FIG. 9) formed in theexterior end160 of thestructural element130, aportion202 of thebend region188 associated with the apex192 thereof is lodged within theshort groove172 and in longitudinal contact with theexterior end160 of thestructural element130, and aportion204 of thebend region188 associated with thebend region termination194 is lodged within theshort groove172 to an extent of thenotch174. The outerresilient element134 is welded to theexterior end160 of thestructural element130 in the vicinity of thenotch174, e.g., via electronic-beam welding along an extent of theportion204 of thebend region188 that is lodged within thenotch174. The outerresilient element134 can be placed in a state of full compression in advance of such welding so as to ensure that after such welding, theportion202 of thebend region188 associated with the apex192 thereof is biased in favor of continuous longitudinal contact with theexterior end160 of thestructural element130 during normal in situ use of, and/or during representative mechanical testing of, thedynamic stabilization element126.
• Though not shown inFIG. 12, a portion (not separately shown) of the bend region190 (FIG. 10) near the coil termination184 (FIG. 10) is similarly lodged within the short groove152 (FIG. 5) formed in the exterior end142 (FIG. 6) of thestructural element128, a portion (not separately shown) of the bend region190 (FIG. 10) associated with the apex196 (FIG. 10) thereof is lodged within theshort groove152 and in longitudinal contact with theexterior end142 of thestructural element128, and a portion (not separately shown) of thebend region190 associated with thebend region termination198 is lodged within theshort groove152 to an extent of the notch154. The outerresilient element134 is welded to theexterior end142 of thestructural element128 in the vicinity of the notch154, e.g., via electronic-beam welding along an extent of the portion (not separately shown) of thebend region190 that is lodged within the notch154 (FIG. 5). The outerresilient element134 can be placed in a state of full compression in advance of such welding for the same reasons and to achieve a similar biasing effect in thebend region190 as is described above with reference to thebend region188.
• A cooling/supercooling step may be advantageously undertaken in advance of welding such as is described immediately hereinabove. In accordance with such a step, the outerresilient element134 and thestructural members128,130 are immersed in a bath of liquid nitrogen, and are withdrawn therefrom shortly before theresilient element134 is welded to thestructural elements128,130. Cooling/supercooling of the outerresilient element134 and thestructural members128,130 functions to reduce the likelihood that high levels of heat will be experienced at a distance from the respective weld regions associated therewith. Accordingly, a given heat-affected zone associated with the migration of heat generated by electronic beam welding can be shrunken and/or reduced in extent, as can any soft or weak spot in such heat-affected zone associated with sharply reduced Rockwell hardness. This cooling/supercooling step was observed to increase resilient element durability during representative mechanical testing.
• Referring toFIGS. 13 and 14, the above-described welding process produces aweld region206 incorporating portions of theexterior end160 of thestructural element130 at theend176 of theshort groove172 in the vicinity of thenotch174, as well as portions of thebend termination194 of thebend region188 of the outerresilient element134. Theportion204 of thebend region188 is long enough, and the corresponding portion of theshort groove172 is long enough, such thatweld region206 terminates at apoint208 along the extent of thebend region188 well short of the apex192 thereof Accordingly, theweld region206 also terminates well short of acorresponding apex210 of theshort groove172 against which theportion202 of thebend region188 is biased. To the extent theportion204 of thebend region188 includes a heat-affectedzone212 associated with the process used to affix the outerresilient element134 to thestructural element130,such region212 also terminates at apoint214 along the extent of thebend region188 well short of the apex192 thereof, as well as well short of the apex210 of theshort groove172. Theportion202 of thebend region188 and theexterior end160 of thestructural member130 are in intimate and continuous longitudinal contact along theshort groove172 at least from the apex210 thereof and for anextent216 extending toward theaperture168. Beyond theextent216, theshort groove172 tends to depart from intimate contact from theportion200 of thebend region188 for anextent218 extending fully to theaperture168. The significance and functional benefits of such structure and/or such assembly arrangement between thebend region188 of the outerresilient element134 and theexterior end160 of thestructural element130 will be explained more fully hereinafter.
• Turning now toFIGS. 15 and 16, in operation, thedynamic stabilization element126 of the spinal stabilization system100 (FIG. 2) permits relative rotational motion, as well as relative translational motion, as between therod118 and theattachment member102, and/or as between therod118 and the ball/spherical element110, while providing enhanced spinal support for the patient, e.g., in the “neutral zone” described more fully in the ‘270 Application. More particularly, thedynamic stabilization element126 as a unit, and/or the outerresilient element134 by itself, supports either and/or both of spinal extension and spinal flexion. Referring toFIG. 15, thedynamic stabilization element126 is shown as it would appear while supporting spinal extension, wherein anextent220 of, for example, less than 5° of relative rotation as between therod118 and the ball/spherical element110 is produced. Such spinal extension can also produce approximately one millimeter of travel in theresilient element134 relative to the initial position thereof (i.e., wherein theresilient element134 is preloaded in tension so as to be slightly extended), such that theresilient element134 may now actually assume a fully compressed state. Referring toFIG. 16, thedynamic stabilization element126 is shown as it would appear while supporting spinal flexion, wherein anextent222 of, for example, greater than 10° of relative rotation as between therod118 and the ball/spherical element110 is produced. Such spinal flexion can produce approximately one and one-half millimeters of travel (i.e., additional extension) in theresilient element134 relative to the initial position thereof.
• Referring again toFIG. 14, the outerresilient element134 is shown in a state of full compression against theinterior end158 of thestructural element130. As discussed above, when the outerresilient element134 is in this condition, thebend region188 of the outerresilient element134 is biased toward contact with theexterior end160 of thestructural element130. To the extent the outerresilient element134 is caused to expand from its fully compressed state, this bias is not relaxed. Rather, this bias is only reinforced by such torsional and/or bending forces as may tend to urge theportion200 of thebend region188 further through theaperture168 in the direction of theinterior end158. (For example, depending on the particular axial and/or lateral forces imposed upon the outerresilient element134, theportion200 of thebend region188 can tend to bend and/or twist close to/closer to the angled exterior surface associated with theextent218 of the short groove172). At the same time, theportion202 of thebend region188 remains lodged in theshort groove172, where it remains in intimate contact with theexterior end160 ofstructural element130, and as such is not capable of being deflected any further in the direction of theinterior end158 by such axial and/or lateral forces. Accordingly, such axial and/or lateral forces are prevented from directly acting upon either of theweld region206 or the heat-affectedzone212 of the outerresilient element134. More particularly, the consistent, continuous longitudinal contact between theportion202 of thebend region188 and theexterior end160 of thestructural element130 along theshort groove172 thereof acts as a permanent ‘fulcrum’, beyond which the torsional and/or bending forces arising in theportion200 of thebend region188 are not necessarily transmitted as such to theweld region206 or the heat-affectedzone212, at least not in a form capable of producing fatigue-inducing stress in such region/zone. In other words, the active region of the outerresilient element134 extends no further toward theweld region206 or the heat-affectedzone212 than the apex192 of thebend region188. Since such regions are physically separated from the apex192 via corresponding structural features of the outerresilient element134 and thestructural member130, and/or via the manner in which the same are affixed to each other, such forces as are applied to theweld region206 and the heat-affectedzone212 during in situ use or representative mechanical testing will have been channeled into a cantilevered arrangement. In accordance with such cantilevered arrangement, a fulcrum (e.g., theextent216 within the short groove172) provides theweld region206 with significant mechanical advantage by which to resist such forces without experiencing undue internal stress.
• Thedynamic stabilization element126 associated with thespinal stabilization system100 described hereinabove with regard toFIGS. 2-14 provides numerous advantages in comparison to other spinal stabilization systems associated therewith. Referring again toFIGS. 11 and 14, and while not necessarily intending to be bound by theory, improved reliability and durability is achieved with the disclosed dynamic stabilization element based at least in part on the fact that the heat-affected zone associated with the process of joining the outerresilient element134 to thestructural elements128,130 via welding is physically separated from the active region of the outerresilient element134, and is therefore isolated from the cyclical stress associated with repeated extension/contraction and/or bending during normal use and/or representative mechanical testing. More particularly, theportion202 of thebend region188 of the outerresilient element134 fully separates theportion202 of the outerresilient element134 from theportion204 thereof at which the outerresilient element134 is welded to thestructural member130. In like measure, and in a similar fashion, the welded and threaded connection between the outerresilient element134 and thestructural member128 provides similar advantages. Typically, due to the particular structures and assembly methods described above, the heat-affected zone in exemplary embodiments of the present disclosure is observed to extend axially approximately 005″-0.030″ from the weld region along the material of the outerresilient element134, and the active region of the outerresilient element134 extends no farther in the direction of the welded interfaces than therespective apexes192,196 of thebend regions188,190. Since thebend regions188,190 are each approximately 0.150 inches in length, the increased reliability/durability found in the dynamic stabilization element of the present disclosure has been shown to be at least partially due to the fact that the active region of the outerresilient element134 is substantially completely shielded from any material degradation that may result from the assembly step, e.g., via electronic-beam welding. In other words, to the extent the use of E-beam welding reduces the Rockwell hardness of a portion or portions of the outerresilient element134, such portion or portions are substantially completely shielded from fatigue-producing levels of cyclic stress.
• Thedynamic stabilization element126 associated with thespinal stabilization system100 described hereinabove with regard toFIGS. 2-14 can be the subject of numerous modifications and variations while still exhibiting the above-discussed advantages over other dynamic junctions for spinal stabilization systems. For example, therod118 can be repositioned to an axial position with respect to thestructural member130. Thebend region termination194 can be affixed to thestructural member130 by other welding processes than E-beam welding, and/or by one or more non-welding means of attachment, such as by clamping or the use of mechanical fasteners appropriate for use in conjunction with small gage springs, by an adhesive-based process, or via the use of a single mold to form the two components together as a single piece. To the extent such attachment schemes result in respective attachment regions along which thebend region termination194 is affixed to the structural member, such attachment regions are similarly disposed physically separately relative to the respective active region of the outer resilient element134s(whether or not heat-affected zones are present), and are thereby similarly shielded from the types and levels of cyclical stress known to produce fatigue failure. The outerresilient element134 need not necessarily be configured in the manner of a coil spring, but may instead take the form of one or more other types of resilient elements, such as a leaf spring, a torsion spring or bar, etc. Additionally, the outerresilient element134 may be employed in a dynamic junction that does not also include the innerresilient element132. Many other variations and/or modifications are possible.
• Although the present disclosure has been disclosed with reference to exemplary embodiments and implementations thereof, those skilled in the art will appreciate that the present disclosure is susceptible to various modifications, refinements and/or implementations without departing from the spirit or scope of the present invention. In fact, it is contemplated the disclosed connection structure may be employed in a variety of environments and clinical settings without departing from the spirit or scope of the present invention. Accordingly, while exemplary embodiments of the present disclosure have been shown and described, it will be understood that there is no intent to limit the invention by such disclosure, but rather, the present invention is intended to cover and encompass all modifications and alternate constructions falling within the spirit and scope hereof.

Claims (13)

1. A spinal stabilization element, comprising:

(a) a spring cap;

(b) an attachment member that is structurally associated with the spring cap, said attachment member being substantially transversely oriented relative to the spring cap and adapted to be mounted with respect to a first pedicle screw; and

(c) a resilient element that includes a bend termination at an end thereof,

wherein said bend termination of said resilient element and said spring cap are integrally formed.

2. The spinal stabilization element according toclaim 1, wherein said resilient element defines a central axis and wherein said attachment member is offset from said central axis.

3. The spinal stabilization element according toclaim 1, wherein said spring cap defines an interior end and an exterior end, and wherein said resilient element is flush relative to the exterior end of the spring cap.

4. The spinal stabilization element according toclaim 1, wherein said resilient element is selected from the group consisting of a coil spring, a leaf spring, a torsion spring and a torsion bar.

5. The spinal stabilization element according toclaim 1, wherein said resilient element defines a second end opposite said bend termination and a central axis, and wherein said bend termination and said second end of said resilient element are spaced from one another along said axis.

6. The spinal stabilization element according toclaim 5, wherein said resilient element is compressible and extendable along said axis.

7. In combination:

(a) a first element including:

(i) a first spring cap;

(ii) an attachment member that is structurally associated with the first spring cap, said attachment member being substantially transversely oriented relative to the first spring cap and adapted to be mounted with respect to a pedicle screw; and

(iii) a resilient element that includes a bend termination at an end thereof, wherein said bend termination of said resilient element and said first spring cap are integrally formed; and

(b) a second element including a second spring cap in spaced relation relative to the bend termination of said resilient element and configured to be mounted with respect to a second pedicle screw.

8. The combination according toclaim 7, wherein said resilient element defines a central axis and wherein said attachment member of said first spring cap is offset from said central axis.

9. The combination according toclaim 7, wherein said resilient element defines a second end and said second end of said resilient element is operatively coupled to said second spring cap.

10. The combination according toclaim 7, wherein said resilient element defines an axis, said first and second ends of said resilient element are spaced from one another along said axis, and said resilient element is compressible and extendable along said axis.

11. The combination according toclaim 7, wherein said resilient element is selected from the group consisting of a coil spring, a leaf spring, a torsion spring and a torsion bar.

12. A spinal stabilization system comprising:

(a) first and second pedicle screw;

(b) a first element including:

(i) a first spring cap;

(ii) an attachment member that is structurally associated with the first spring cap, said attachment member being substantially transversely oriented relative to the first spring cap and adapted to be mounted with respect to a pedicle screw; and

(iii) a resilient element that includes a bend termination at an end thereof, wherein said bend termination of said resilient element and said first spring cap are integrally formed; and

(c) a second element including a second spring cap in spaced relation relative to the bend termination of said resilient element and configured to be mounted with respect to a second pedicle screw.

13. The spinal stabilization system according toclaim 12, wherein said resilient element is selected from the group consisting of a coil spring, a leaf spring, a torsion spring and a torsion bar.

Images