Dynamic stabilization medical implant assemblies and methods
Bone screw assemblies include longitudinal connecting members that provide for dynamic stabilization, some including non-uniform portions that are configured to flex, contract or expand. Composite longitudinal connecting members include longitudinal segments made from different materials having different flexibilities. Polyaxial bone screw assemblies include change-out receivers for cooperating with replacement longitudinal connecting members having a different flexibility. Bone screw shanks for cooperating with one or more open receivers include treatment or coating to provide biologically active interface with bone.
This application claims the benefit of U.S. Provisional Application No. 60/722,300 filed Sep. 30, 2005. This application is also a continuation-in-part of U.S. patent application Ser. No. 10/958,743 filed Oct. 5, 2004, which is a continuation-in-part of U.S. patent application, Ser. No. 10/409,935 filed Apr. 9, 2003, now U.S. Pat. No. 6,964,666. This application is also a continuation-in-part of U.S. patent application Ser. No. 10/818,555, filed Apr. 5, 2004, which is a continuation of U.S. patent application Ser. No. 10/464,633 filed Jun. 18, 2003, now U.S. Pat. No. 6,716,214. This application is also a continuation-in-part of U.S. patent application Ser. No. 10/996,349 filed Nov. 23, 2004.
BACKGROUND OF THE INVENTIONThe present invention relates to apparatuses and methods for use in performing spinal surgery and, in particular, to structural members for use in spinal surgery including dynamic stabilization longitudinal connecting members and cooperating polyaxial bone screw assemblies providing protected motion in a non-fusion procedure. Certain flexible elongate connecting members or rods used in methods according to the invention have a substantially uniform shape, while other longitudinal connecting members according to the invention have flexible non-uniform portions with varied cross-section that preserve spinal motion, providing for flexure and/or compression and extension, in a dynamic stabilization method and structure. Bone screws according to the invention have a receiver for capturing and clamping a longitudinal connecting member that can swivel about a shank of the bone screw, allowing the receiver to be positioned in any of a number of angular configurations relative to the shank. Receivers according to the invention also include a change out feature, allowing for removal of a flexible longitudinal connecting member and cooperating receiver without removing the threaded shank that has been implanted into bone, and then replacing the receiver with a second receiver for accommodating a more rigid longitudinal connecting member of a different size.
Many spinal surgery procedures require securing various implants to bone and especially to vertebrae along the spine. For example, elongate longitudinal connecting members are often required that extend along a portion of the spine to provide support to vertebrae that have been damaged or weakened due to injury, disease or the like. Such longitudinal connecting members must be supported by certain vertebra and support other vertebra. The most common mechanism for providing such structure is to implant bone screws into certain bones which then in turn support the longitudinal connecting member or are supported by the longitudinal connecting member. Bone screws typically have a shank that is threaded and adapted to be implanted into a vertebral body of a vertebrae. Such bone screws also include a receiver designed to extend beyond the vertebrae and include a channel for receiving a longitudinal connecting member or other elongate member. The receiver may be open, swiveling with respect to the shank, providing ease in placement of the longitudinal connecting member within the receiver channel prior to clamping of the longitudinal connecting member within the channel and locking the longitudinal connecting member with respect to the receiver and the shank in a particular desired angle with respect to the shank, utilizing a closure member that also is inserted in the receiver channel.
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 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 of a size to provide substantially rigid support.
Fusion, however, has some undesirable side effects. One apparent side effect is the immobilization of a portion of the spine. Furthermore, although fusion may result in a strengthened portion of the spine, it also has been linked to more rapid degeneration and even hyper mobility of spinal motion segments that are adjacent to the portion of the spine being fused, reducing or eliminating the ability of such spinal joints to move in a more normal relation to one another. In certain instances, fusion has also failed to provide pain relief.
An alternative to fusion and the use of rigid longitudinal connecting members or other rigid structure has been a “soft” stabilization approach in which a flexible C- or U-shaped member or coil is utilized as a spring member fixed between a pair of pedicle screws in an attempt to create, as much as possible, a normal loading pattern between the vertebrae, both in flexion and extension. Such devices allow for some natural movement or flex. However, such devices may be undesirable as they extend upwardly and outwardly from the bone screw or anchor, creating an implant with a profile much larger than those using a traditional cylindrical longitudinal connecting member. Larger profile implants are almost always undesirable for placement in a human body and may limit the working space afforded to the surgeon during an implant procedure.
Another concern that arises when more flexible structure is utilized in a spinal medical implant is that of adequate fatigue strength or endurance limit. The concept of strength may be defined as the highest stress a material can withstand before it completely fails to perform structurally. Typically, the concept of strength takes into account the influence of a force upon a cross-sectional area of a material that ultimately causes a material to fail. Specifically, fatigue strength has been defined as the repeated loading and unloading of a specific stress on a material structure until it fails. Fatigue strength can be tensile, compression, shear, bending, or a combination of these. The dynamic conditions associated with spinal movement therefore provide quite a challenge for the design of elongate structural members that exhibit an adequate fatigue strength to provide stabilization and protected motion of the spine, without fusion, and allow for some natural movement of the portion of the spine being reinforced by the elongate structural member.
SUMMARY OF THE INVENTIONDynamic medical implant assemblies and methods according to the invention include various longitudinal connecting members. One such member has first, second and third integral and substantially coaxial portions. The first and second portions are substantially uniform and are sized and shaped to be receivable in an open receiver of a bone attachment structure. The third portion is non-uniform and is disposed between the first and second portions. In one embodiment, the third portion includes first and second substantially parallel axially spaced sides and a plurality of curved strips, each curved strip being integral with both the first side and the second side at either end thereof. The third, non-uniform portion therefore being both compressible and expandable in an axial direction. The third portion is hollow and appears substantially spheroidal when in an extended orientation.
Another longitudinal connecting member of the invention includes first, second and third integral portions, the first portion being substantially uniform and having a first diameter, the second portion being substantially uniform and having a second diameter and the third portion being solid and disposed between the first and second portions. The first and second portions are illustrated herein as being cylindrical in form with equal diameters. The third portion has a first width defined by a first longitudinal cross-section and a second width defined by a second cross-section disposed perpendicular to the first longitudinal cross-section. In the illustrated embodiments, the first width of the non-uniform portion is larger than the diameters of the first and second portions and the second width is smaller than the diameters of the first and second portions.
A further longitudinal connecting member according to the invention has a substantially uniform cross section, but is divided longitudinally into at least first and second segments wherein the first segment is substantially more flexible in comparison to the second section. Each section may be sized and shaped to be received by at least a pair of bone anchors, allowing for dynamic stabilization along one portion of the spine and rigid stabilization along a second portion of the spine by a single longitudinal connecting member. Such longitudinal connecting members may have at least a portion of the first segment being constructed of material different from the second segment. Such longitudinal connecting members may include first and second segments that are both made from a solid material.
Dynamic medical implant assemblies according to the invention that provide dynamic, protected motion of the spine further include bone anchors, such as polyaxial bone screw assemblies, that may include bone screw shanks that are treated to provide for a roughened or textured surface, such as by plasma cleaning or coating. Furthermore, such treatment may include coating with a material such as hydroxyapatite. Such treatments and coatings provide for bone bonding and in certain cases a bioactive interface between the bone attachment structure and the vertebra.
Further apparatus and methods according to the invention include providing a first assembly for use with a flexible longitudinal connecting member or a longitudinal connecting member with flexible portions, and also providing replacement receivers for receiving longitudinal connecting members of different diameters, for example, for implanting at a later time when a more rigid assembly may be required. Specifically, polyaxial bone screw assemblies are described herein that include a first receiver for cooperating with a first longitudinal connecting member, such as flexible, dynamic stabilization connecting member and also a second receiver for cooperating with a second longitudinal connecting member having a different diameter and flexibility. Both the first and second receivers are attachable and detachable to a bone screw shank, both prior to implantation and after the shank is implanted in a vertebra. Such allows for a fusionless initial attachment of the bone screw shank, first receiver and dynamic stabilization connecting member to the spine. Thereafter, if needed, during a procedure in which the bone screw shank remains implanted, the first receiver may be replaced with the second receiver and the dynamic stabilization connecting member replaced with another longitudinal connecting member having a different flexibility and a different diameter, for example, a solid rod having a smaller diameter, but greater rigidity. In some instances, it may be desirable to replace a first longitudinal connecting member with a second, more flexible connecting member having a greater or lesser diameter than the first longitudinal member. In all such dynamic stabilization procedures that do not include fusion, one aspect of the invention is to provide bone screw shanks that have had surface treatment or coating to provide a biologically active interface with the bone or at least some component of bone bonding on or bone ingrowth into the bone screw shank.
OBJECTS AND ADVANTAGES OF THE INVENTIONTherefore, it is an object of the present invention to overcome one or more of the problems with polyaxial bone screw assemblies described above. An object of the invention is to provide dynamic medical implant stabilization assemblies and methods for spinal surgery that include bone screws having an affinity to bone and further include connecting members and/or receiver members that may be removed and replaced to provide for the implantation of flexible, semi-rigid or rigid connecting members. Another object of the invention is to provide dynamic medical implant stabilization assemblies having longitudinal connecting members with portions having various configurations for providing flexible, dynamic stabilization. Additionally, it is an object of the invention to provide a lightweight, reduced volume, low profile polyaxial bone screw and longitudinal connecting member assembly. Furthermore, 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 tools 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.
The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
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.
With reference to
With reference to
During use, rotation of the body 8 utilizes the thread 24 for gripping and advancement in the bone and is implanted into the vertebra 13 leading with the tip 28 and driven down into the vertebra 13 with an installation or driving tool 31, so as to be implanted in the vertebra 13 to near the neck 26, as shown in
The shank 4 has an elongate axis of rotation generally identified by the reference letter A. It is 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 assembly 1 in actual use.
The neck 26 extends axially outwardly and upwardly from the shank body 8 to a base 34 of the capture structure 10. The neck 26 generally has a reduced radius as compared to an adjacent top 36 of the shank body 8. Further extending axially and outwardly from the neck 26 is the capture structure 10 that provides a connective or capture apparatus disposed at a distance from the body top 36 and thus at a distance from the vertebra 13 when the shank body 8 is implanted in the vertebra 13.
The capture structure 10 is configured for connecting the shank 4 to the receiver 6 or 7 and then capturing the shank 4 in the receiver 6 or 7. The capture structure 10 has an outer partially spherically shaped surface 40 extending from the base 34 to a top portion 44. The illustrated base 34 has a smooth surface, but it is foreseen that the base 34 may have a high-friction or roughened surface, such as a scored or knurled surface. Formed on an upper part 46 of the surface 40 is a helical guide and advancement structure 48. The guide and advancement structure 48 retains the substantially spherical outer shape of the surface 40 at a crest thereof, but may be otherwise described as a substantially square thread form, sized and shaped to mate with a cooperating guide and advancement structure 50 disposed on an inner surface 52 of the receiver 6 disposed adjacent to and defining an opening 54 of a lower end or bottom 56 of the receiver 6. Preferably, the guide and advancement structure 48 is relatively thick and heavy to give strength to the thread and prevent the thread from being easily bent or deformed when axial pressure is applied to the shank 4 to maintain the capture structure 10 in the receiver 6, as described further below. The second or replacement receiver 7 also includes an inner guide and advancement structure (not shown), substantially identical to the guide and advancement structure 50 for mating with the guide and advancement structure 48.
The guide and advancement structure 48 winds about the upper portion 46 in a generally helical pattern or configuration that is typical of threads and can have various pitches, be clockwise or counterclockwise advanced, or vary in most of the ways that conventional square threads vary. The guide and advancement structure 48 has a leading surface or flank 58 and a trailing surface or flank 59. As used herein, the terms leading and trailing refer to the direction of advancement of the capture structure 10 into the guide and advancement structure 50 of the receiver 6 aligning the axis A of the shank 4 with an elongate axis of rotation B of the receiver 6 and directing the capture structure 10 toward the receiver 6, as shown by the straight arrow C illustrated in
The leading surface 58 has an inner edge 62 and an outer edge 63. The trailing surface 59 has an inner edge 66 and an outer edge 67. As is typical of square threads, a root surface 69 between the inner edges 62 and 66 is parallel to the axis of rotation A and has an axial length that remains substantially constant throughout the threadform. Likewise, an axial distance between the outer edges 63 and 67 remains substantially constant, while the size of a crest or connecting surface 70 between the edges 63 and 67 varies, due to the spherical form of the crest surface 70. As can be seen, for example, in
Although the substantially square threadform 48 is described herein, it is foreseen that other thread types, such as V-threads, inverted thread types, such as inverted buttress threads, other thread-like or non-thread-like guide and advancement structures, such as flange form helically wound advancement structures may be utilized according to the invention.
Advancement of the capture structure 10 into the receiver 6 is accomplished by rotating the shank 4 in a counterclockwise direction about the axes A and B and into the receiver 6 as illustrated in
In the embodiment shown, the shank 4 further includes a longitudinal connecting member and tool engagement structure 74 projecting upwardly from the top portion 44 of the capture structure 10. The tool engagement structure 74 has a hexagonally shaped head 76 with a substantially domed top 78. The structure 74 is coaxial with both the threaded shank body 8 and the capture structure 10. The head 76 is sized and shaped for engagement with the driving tool 31 shown in
In the embodiment shown, to provide further mechanical advantage during installation of the shank 4 into the vertebra 13, the capture structure 10 includes a counter-sunk portion 80 formed in the top 44, the portion 80 adjacent to and surrounding the head 76. The portion 80 includes a planar seating surface 82 disposed perpendicular to the axis A and spaced from the top portion 44. Contiguous to both the surface 82 and the top 44 are faces 84 that are disposed parallel to the axis A and thus are substantially perpendicular to the surface 82. The faces 84 form a hex-shaped outer periphery of the counter-sunk portion 80. The tool 31 includes an outer surface portion 90 sized and shaped to mate with the bottom and both side walls of the counter-sunk portion 80, such that a bottom 91 of the tool 31 seats on the surface 82 and the outer surface portion 90 is adjacent to and engaging the faces 84 when the tool 31 is disposed about and engaging with the hexagonally shaped head 76.
The domed top end surface 78 of the shank 4 is preferably convex, curved or dome-shaped as shown in the drawings, for positive engagement with the longitudinal connecting member 19 when the bone screw assembly 1 is assembled, as shown in
The shank 4 shown in the drawings is cannulated, having a small central bore 92 extending an entire length of the shank 4 along the axis A. The bore 92 is defined by an inner substantially cylindrical wall 95 of the shank 4 and has a first circular opening 96 at the shank tip 28 and a second circular opening 98 at the top domed surface 78. The bore 92 is coaxial with the threaded body 8 and the capture structure 10. The bore 92 provides a passage through the shank 4 interior for a guide pin or length of wire 103 inserted into a small pre-drilled bore 105 in the vertebra 13 prior to the insertion of the shank body 8, the pin 103 providing a guide for insertion of the shank body 8 into the vertebra 13.
The receiver 6 is partially cylindrical in external profile and includes a base portion 110 extending from the end 56 to a V-shaped surface 111 disposed at a periphery of a longitudinal connecting member seating surface 112 and extending radially outwardly and downwardly therefrom. The base 110 is integral with a pair of upstanding and spaced arms 114. The surface 112 and the arms 114 forming a U-shaped channel 116 between the arms 114 and having an upper opening 119. The lower surface 110 defining the channel 116 preferably has substantially the same radius as the longitudinal connecting member 19. In operation, the longitudinal connecting member 19 preferably is located just above the channel lower surface 112, as shown in
Each of the arms 114 has an interior surface 122 that defines an inner cylindrical profile and includes a discontinuous helically wound guide and advancement structure 124 beginning at a top 125 of the receiver 6 and extending downwardly therefrom. The guide and advancement structure 124 is a partial helically wound flange-form configured to mate under rotation about the axis B with a similar structure disposed on the closure structure 16, as described more fully below. However, it is foreseen that the guide and advancement structure 124 could alternatively be a V-shaped thread, a buttress thread, a square thread, a reverse angle thread or other thread-like or non-thread-like helically wound guide and advancement structure for operably guiding under rotation and advancing the closure structure 16 between the arms 114, as well as eventual torquing when the closure structure 16 abuts against the longitudinal connecting member 19.
The receiver 6 includes external apertures or grip bores 128 disposed on each of the arms 114 for positive engagement by holding tools to facilitate secure gripping of the receiver 6 during assembly of the receiver 6 with the shank 4. Furthermore, the grip bores 128 may be utilized to hold the receiver 6 during the implantation of the shank body 8 into the vertebra 13. The bores 128 are centrally located on the respective arms 114 and communicate with upwardly projecting hidden recesses 129 to further aid in securely holding the receiver 6, for example, to an end guide or holding tool 130 or an intermediate guide or holding tool 131 illustrated in
Communicating with the U-shaped channel 116 of the receiver 6 is a chamber or cavity 136 substantially defined by a partially spherical inner surface 138 that is disposed primarily in the base portion 110 of the head beneath the interior cylindrical surface 122 of the arms 112 and 114 and extending into the inner surface 52 that is further defined by the guide and advancement structure 50. The cavity 136 communicates with both the U-shaped channel 116 and a bore 140 that also is defined by the guide and advancement structure 50, that in turn communicates with the opening 54 at the bottom 56 of the receiver 6.
The guide and advancement structure 50 includes a leading surface 152 and a trailing surface 156. Similar to what is described herein with respect to the guide and advancement structure 48 of the capture structure 10, the guide and advancement structure 50 is preferably of a square thread type as such structure provides strength and stability to the assembly 1, with the leading surface 152 and the trailing surface 156 being substantially parallel. A crest surface 157 spanning between the leading surface 152 and the trailing surface 156 is curvate, having a radius the same or substantially similar to a radius of the cavity spherical wall 138. As with the guide and advancement structure 48, it is foreseen that other types of threaded and non-threaded helical structures may be utilized in accordance with the present invention for the receiver 6.
A juncture of the interior surface 122 and the cavity inner surface 138 forms an opening or neck 158 that has a radius extending from the Axis B that is smaller than a radius extending from the Axis B to the inner surface 138. Also, a radius from the lower opening 54 to the Axis B is smaller than the radius extending from the Axis B to the inner surface 138 and the inner surface portion 52 defining the guide and advancement structure 50. Thus, the cavity or chamber 136 is substantially spherical, widening and opening outwardly and then inwardly in a direction toward the lower opening 54. However, it is foreseen that other shapes, such as a cone or conical shape, may be utilized for a head inner cavity according to the invention. Also, a cylindrical head inner cavity with a retainer ring located approximate the lower opening 54 could be utilized according to the invention.
After the guide and advancement structure 48 of the capture structure 10 is mated and rotated to a position within the cavity 136 and further upwardly and axially into non-engagement beyond the trailing surface 156 of the guide and advancement structure 50, the capture structure 10 is rotatable or swingable within the cavity 136 until later frictionally locked in place, and cannot be removed from the receiver 6 through the upper neck 158 or through the lower bore 140 without reversing the assembly process with the components in axial alignment. As shown in
The illustrated second or replacement receiver 7 is substantially identical to the receiver 6 in form and function, constructed for engagement with the capture structure 10 as previously described herein with respect to the receiver 6, therefore the disclosure herein with respect to the receiver 6 is incorporated by reference with respect to the receiver 7. The receiver 7 differs from the receiver 6 in that the receiver 7 is sized to snugly receive the longitudinal connecting member or longitudinal member 20 that is of a different size diameter or width than the longitudinal connecting member 19. In the embodiment illustrated in
The elongate longitudinal connecting members or longitudinal members, such as the longitudinal connecting members 19 and 20 that are utilized with the assembly 1 can be any of a variety of implants utilized in reconstructive spinal surgery, but are typically elongate structures with substantially uniform cylindrical portions for placement within the receivers 6 and 7 respectively. The illustrated longitudinal connecting member 19 has a smaller diameter than a diameter of the illustrated longitudinal connecting member 20, providing an initial flexible structural connection between bone screw assemblies 1, that may then be replaced with a more rigid connection, if necessary, utilizing the replacement receiver 7 and the longitudinal connecting member 20, as will be described in greater detail below. As will also be described in greater detail below with respect to
The longitudinal connecting member portions that are received by the receiver 6 or 7 include cylindrical surfaces 162 or 163, respectively. The illustrated surfaces 162 and 163 are smooth but they could be textured. The longitudinal connecting members 19 and 20 are also preferably sized and shaped to snugly seat near the bottom of the U-shaped channels 116 and 160 of respective receivers 6 and 7, and, during normal operation, are positioned slightly above the bottom of the channels 116 and 160, respectively, near, but spaced from, respective lower surfaces 112 and 161. The longitudinal connecting member cylindrical surfaces 162 or 163 normally directly or abutingly engage the shank top surface 78, as shown in
With reference to
The illustrated closure top 16 has a generally cylindrically shaped body 170, with a helically wound guide and advancement structure 172 that is sized, shaped and positioned so as to engage the guide and advancement structure 124 on the receiver arms 114 to provide for rotating advancement of the closure structure 16 into the receiver 6 when rotated clockwise and, in particular, to cover the top or upwardly open portion of the U-shaped channel 116 to capture the longitudinal connecting member 19, preferably without splaying of the arms 114. The body 170 further includes a base or bottom 174 having a pointed longitudinal connecting member engaging projection or point 175 extending or projecting axially beyond a lower rim 176. However, it is foreseen that the bottom could be flat and smooth and/or flat and knurled. The closure structure 16, with the projection 175 frictionally engaging and abrading the longitudinal connecting member surface 162, thereby applies pressure to the longitudinal connecting member 19 under torquing, so that the longitudinal connecting member 19 is urged downwardly against the shank domed surface 78 that extends into the channel 116. Downward biasing of the shank surface 78 operably produces a frictional engagement between the longitudinal connecting member 19 and the surface 78 and also urges the capture structure 10 toward the base 110 of the receiver 6, as will be described more fully below, so as to frictionally seat the capture structure buttress thread 48 and/or lower portion 72 against the threaded inner surface 52 of the receiver 6, also fixing the shank 4 and capture structure 10 in a selected, rigid position relative to the receiver 6.
The illustrated closure structure 16 further includes a substantially planar top surface 178 that has a centrally located, hexalobular internal driving feature 180 formed therein (sold under the trademark TORX),which is characterized by an aperture with a 6-point star-shaped pattern. It is foreseen that paired off-axis apertures, on-axis multi-lobular and other driving features or apertures, such as slotted, hex, tri-wing, spanner, and the like may also be utilized according to the invention. With reference to
It is foreseen that a closure structure according to the invention may be equipped with a break-off feature or head, the closure structure sized and shaped to include a break-way region that breaks at a preselected torque that is designed to properly seat the closure structure in the receiver 6. Such a closure structure would include removal tool engagement structure, such as a pair of spaced apart apertures or bores, a countersunk hex-shaped aperture, a left hand threaded bore, or the like, fully accessible after the break-off head feature breaks away from a base of the closure structure.
In use, prior to the polyaxial bone screw assembly 1 being implanted in a vertebra according to the invention, the shank capture structure 10 is typically pre-loaded by insertion or bottom-loading into the receiver 6 through the opening 54 at the bottom end 56 of the receiver 6. The capture structure 10 is aligned with the receiver 6, with the axes A and B aligned so that the guide and advancement structure 48 of the capture structure 10 is inserted into and rotatingly mated with the guide and advancement structure 50 on the receiver 6. The shank 4 is rotated in a counter-clockwise direction to fully mate the structures 48 and 50, as shown in
In the position shown in
With reference to
It is foreseen that in an alternative method according to the invention, the shank 4 is first implanted into the vertebra 13 by rotation of the shank 8 into the vertebra 13 using the driving tool 31 that operably drives and rotates the shank 8 by engagement thereof with the hexagonally shaped extension head 76 of the shank 4. As already described herein, when the driving tool 31 engages the head 76 during rotation of the driving tool 31, the outer portion 90 also engages the faces 84 and a bottom of the tool 31 is fully seated upon and frictionally engages with the planar surface 82 disposed in the counter-sunk portion 80 of the capture structure 10. It may be desirable to only partially implant the shank 8 into the vertebra 13, with the capture structure 10 extending proud to provide space for the attachment of the receiver 6 to the shank 4. The receiver 6 is then attached to the shank 4 by inserting the receiver 6 onto the capture structure with the axes A and B aligned and mating the thread 48 with the thread 50 by rotating the receiver 6 in a clockwise direction. The head is then rotated until the thread 48 disengages with the thread 50 and the capture structure 10 is freely rotatably disposed in the head cavity 136. Then, the shank body the shank 4 can be further driven into the vertebra 13, if necessary, utilizing the driving tool 31 as already described herein. The remainder of the implant assembly includes elements that have been previously described.
With particular reference to
With reference to
With reference to
According to a method of the invention, the bone screw assembly 1 and the longitudinal connecting member 19 are implanted as shown in
If desired, selected vertebrae are abraded or otherwise prepared in a manner known in the art, including tissue removal, the addition of bone chip or other bone material, and/or bone growth promoting material, to result in fusion of the portion or portions of the spine being more rigidly fixed in place by the replacement receivers 7 and the longitudinal connecting member 20. Each replacement receiver 7 is then mounted on a capture structure 10, and rotated in a clockwise fashion, mating a guide and advancement structure on the inner surface of the receiver 7 (not shown) with the guide and advancement structure 48, the receiver 7 being rotated to fully mate the guide and advancement structures until the guide and advancement structure 48 is disengaged and the capture structure 10 is disposed in the receiver 7, the receiver 7 being freely rotatable with respect to the capture structure 10. The same procedure is followed along the spine to replace each receiver 6 with a receiver 7.
With reference to
With reference to
It is foreseen that other types of capture connections may also be used in bone screws according to the invention, including, but not limited to, conical, spherical, threaded, and frictional connections and retaining rings.
With reference to
As illustrated in
The longitudinal connecting member 219 is implanted into an assembly 201 having the first receiver 206 in a manner similar or identical to the implantation procedure previously described herein with respect to the longitudinal connecting member 19 and the assembly 1 having the receiver 6. It is foreseen that the shank 204 may or may not be cannulated and that the assembly 201 may further include a closure structure similar to the closure top 16 or other types of closure structure, for example, as described in U.S. Pat. No. 6,716,214, for advancement into the receiver 206 and biasing against the flexible longitudinal connecting member 219.
Similar to the procedure previously described herein with respect to the receiver 6 and the longitudinal connecting member 19, if, after time, further damage or weakness of the spine occurs, a method according to the invention allows for replacement of the flexible longitudinal connecting member 219 with the more rigid longitudinal connecting member 220, without removal of the bone screw shank 208 from the vertebra 213. In such a procedure, partial disassembly is accomplished by using a driving tool to remove the closure structures (not shown) from receivers 206, followed by removal of the longitudinal connecting member 219, preferably in a percutaneous fashion. The receiver 206 is then removed from the bone screw shank 204 by aligning the retaining structure/bone shank combination coaxially with the receiver 206 and then placing downward pressure on the retaining structure 211, causing the spline capture structure 210 to move upwardly toward the U-shaped channel of the receiver 206, disengaging the retaining structure 211 from the capture structure 210. The retaining structure 211 is then rotated about a central axis of the shank 204 about 60 degrees, aligning the splines of the capture structure 210 with axially aligned through-channels in the retaining structure 211, followed by upward movement of the receiver 206, with splines of the capture structure 210 entering the axial through-channels, allowing the receiver 206 and the retaining structure 211 to be disengaged and removed from the bone screw shank 204.
If desired, selected vertebrae are abraded or otherwise prepared in a manner known in the art, including but not limited to tissue removal, the addition of bone chip or other bone material, and/or bone growth promoting material to result in fusion of the portion or portions of the spine being more rigidly fixed in place by the replacement receivers 207 and the cooperating longitudinal connecting member 220. Each replacement receiver 207 with cooperating retaining structure 211 therein is then mounted on a capture structure 210 by placing the receiver 207 and aligned retaining structure 211 downwardly on the shank 204 until the capture structure 210 extends beyond the retaining structure 211. Then, the capture structure 210 is mated with the retaining structure 211 by rotating the retaining structure 211 about a central axis thereof about 60 degrees, followed by downward movement of the retaining structure, with splines of the capture structure 210 entering recesses in the retaining structure 211 as described in U.S. Pat. No. 6,716,214. The same procedure is followed along the spine to replace each receiver 206 with a receiver 207.
With reference to
With reference to
The longitudinal connecting member 250 also may be made of different materials (metal and non-metal) along the length thereof. For example, with respect to
As previously discussed herein, a concern that arises in non-fusion dynamic stabilization procedures is the fatigue strength and thus the longevity of longitudinal connecting members and other structural members used in such procedures. In the apparatus and methods described thus far herein, the more flexible longitudinal connecting members 19, 219 and 250 may be changed out, when need arises, and replaced with identical replacement longitudinal connecting members 19, 219 or 250, respectively; with a more rigid longitudinal connecting member 20 or 220; or with a composite connecting member made from two or more different materials along a length thereof. Further embodiments according to the invention are shown in
With reference to
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With further reference to
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With reference to
Although the longitudinal connecting member 416 is shown with the fixed bone screw 417, it is noted that the connector 416 and all other longitudinal connecting members 19, 20, 250, 260, 280, 300, 320, 340, 360, 380, 400 and 420 described in this application may be received in a variety of open bone screws, including, but not limited to, polyaxial, hinged and fixed bone screws as well as hooks and other types of bone anchors. It is further noted that all of the longitudinal connecting members described in this application may be made from metal or non-metallic materials as well as composites of such materials.
With reference to
It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.
Claims
1. In a medical implant assembly including at least two bone attachment structures, the improvement comprising:
- a longitudinal connecting member having an axis and further having first, second and third integral portions extending along the axis, the third portion being disposed between the first and second portions, the first and second portions being substantially uniform and each receivable in an open receiver of a bone attachment structure, the third portion having first and second substantially parallel axially spaced sides and a plurality of curved strips, each curved strip integral with both the first side and the second side at either end thereof, the third portion being both compressible and expandable along the axis.
2. The improvement of claim 1 wherein each bone attachment structure has an open receiver for receiving the longitudinal connecting member and a shank, the shank having a surface altered by at least one of
- i) a surface roughening treatment; and
- ii) a coating
- to provide a bioactive interface between the bone attachment structure and a vertebra.
3. The improvement of claim 2 wherein the shank surface is plasma coated.
4. The improvement of claim 2 wherein the shank surface is coated with hydroxyapatite.
5. The improvement of claim 1 wherein at least one of the first and second portions includes at least one elongate segment, the segment being made from a different material than a remainder of the first and second portions resulting in the elongate segment having a flexibility different than a flexibility of the remainder of the first and second portions.
6. The improvement of claim 1 wherein at least a length of the first portion measured along the axis is made from a different material than the second portion.
7. In a medical implant assembly including at least two bone attachment structures, the improvement comprising:
- a) a longitudinal connecting member having first, second and third integral and substantially coaxial portions, the third portion disposed between the first and second portions, the first and second portions being substantially uniform and receivable in an open receiver of a bone attachment structure, the third portion being hollow and substantially ellipsoid when under tension.
8. The improvement of claim 7 wherein each bone attachment structure has an open receiver for receiving the longitudinal connecting member and a shank, the shank having a surface altered by at least one of
- i) a surface roughening treatment; and
- ii) a coating
- to provide a bioactive interface between the bone attachment structure and a vertebra.
9. The improvement of claim 8 wherein the shank surface is plasma coated.
10. The improvement of claim 8 wherein the shank surface is coated with hydroxyapatite.
11. A polyaxial bone screw assembly comprising:
- a) at least first and second bone attachment structures, each structure having an open receiver and a shank, the shank treated with at least one of i) a surface texture; and ii) a coating
- to provide a bioactive interface between the bone attachment structure and a vertebra; and
- b) a longitudinal connecting member receivable in the open receivers of the first and second bone attachment structures, the longitudinal member having at least one flexible portion for providing protected motion of the spine.
12. The assembly of claim 11 wherein when assembled, the longitudinal connecting member directly frictionally engages an upper portion of the shank.
13. The assembly of claim 11 wherein the shank surface is plasma coated.
14. The assembly of claim 11 wherein the shank surface is coated with hydroxyapatite.
15. The assembly of claim 11 wherein the longitudinal connecting member has first, second and third integral and substantially coaxial portions, the third portion disposed between the first and second portions, the first and second portions being substantially uniform and receivable in the open receiver of the bone attachment structure, the third portion having first and second substantially parallel axially spaced sides and a plurality of curved strips, each curved strip integral with both the first side and the second side at either end thereof, the third portion being both compressible and expandable in an axial direction.
16. A medical implant kit comprising:
- a) a polyaxial bone screw shank;
- b) a first receiver having a first opening, the first receiver swivelably attachable to the shank and removable therefrom when the shank is implanted into a vertebra of a spine;
- c) a first longitudinal connecting member closely receivable in the first opening of the first receiver, the first connecting member sized and shaped to allow protected motion of the spine;
- d) a second receiver swivelably attachable to the shank when the shank is attached to the vertebra, the second receiver having a second opening of a different size than the first opening of the first receiver; and
- e) a second longitudinal connecting member sized and shaped to be closely receivable in the second opening of the second receiver, the second longitudinal member having a different amount of flexibility than the first longitudinal member.
17. The kit of claim 16 wherein the bone screw shank includes at least one of
- a) a surface roughening treatment; and
- b) a coating
- to provide a bioactive interface between the bone attachment structure and a vertebra.
18. The kit of claim 16 wherein the shank surface is plasma coated.
19. The kit of claim 16 wherein the shank surface is coated with hydroxyapatite.
20. A surgical method comprising:
- a) providing a polyaxial bone screw shank attachable to a first receiver;
- b) implanting the shank and attached first receiver into a vertebra of a spine;
- c) providing a first longitudinal connecting member sized and shaped to be closely receivable in the first receiver and to allow protected motion of the spine;
- d) securing the first longitudinal connecting member in the first receiver; and
- e) providing a second receiver attachable to the shank when the shank is implanted in the vertebra and sized and shaped to receive a second longitudinal connecting member, the second member having a different degree of flexibility than the first member.
21. The method of claim 20 comprising the subsequent steps of:
- f) removing the first longitudinal connecting member from the first receiver;
- h) replacing the first receiver with the second receiver without removing the bone screw shank from the vertebra; and
- i) securing the second longitudinal connecting member to the second receiver.
22. A longitudinal connecting member comprising at least first and second elongate segments wherein each of the segments is sized and shaped to be adapted to be received between a pair of bone anchors; the first segment being comparatively stiff and the second segment being comparatively flexible in comparison to the first segment.
23. The longitudinal connecting member of claim 22 wherein at least a portion of the first segment is made from a material different from the second segment.
24. A longitudinal connecting member of substantially uniform cross section and being longitudinally divided into at least first and second integral segments wherein the first segment is substantially more flexible in comparison to the second section.
25. The connecting member of claim 24 wherein at least a portion of the first segment is constructed of material different from the second segment.
26. The connecting member of claim 24 wherein the uniform cross-section is substantially circular in shape.
27. The connecting member of claim 24 wherein both the first and second segments are substantially solid.
Type: Application
Filed: Aug 24, 2006
Publication Date: Jan 18, 2007
Inventor: Roger Jackson (Prairie Village, KS)
Application Number: 11/509,386
International Classification: A61F 2/30 (20060101);