Patent Publication Number: US-2010121380-A1

Title: Expandable Spinal Rods and Methods of Use

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/343,595 filed on Jan. 31, 2006, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Spinal rods are often used in the surgical treatment of spinal disorders such as degenerative disc disease, disc herniations, scoliosis or other curvature abnormalities, and fractures. Different types of surgical treatments are used. In some cases, spinal fusion is indicated to inhibit relative motion between vertebral bodies. In other cases, dynamic implants are used to preserve motion between attached to the exterior of two or more vertebrae, whether it is at a posterior, anterior, or lateral side of the vertebrae. In other embodiments, spinal rods are attached to the vertebrae without the use of dynamic implants or spinal fusion. 
     Spinal rods may provide a stable, rigid column that encourages bones to fuse after spinal-fusion surgery. Further, the rods may redirect stresses over a wider area away from a damaged or defective region. Also, a rigid rod may restore the spine to its proper alignment. In some cases, a flexible rod may be appropriate. Flexible rods may provide some advantages over rigid rods, such as increasing loading on interbody constructs, decreasing stress transfer to adjacent vertebral elements while bone-graft healing takes place, and generally balancing strength with flexibility. One disadvantage with conventional rods is that their rigidity and length, which may span several vertebrae, may require large surgical incisions to implant the rod. Therefore, surgical procedures requiring the installation of an elongated rod have often required invasive open procedures that are more costly to perform, and potentially more dangerous and more painful for the patient. 
     SUMMARY 
     Illustrative embodiments disclosed herein are directed to a spinal rod having an elongated tubular member that is inflatable with a substance from a first insertion profile to a second enlarged profile. In one embodiment, an expandable tubular reinforcement sleeve may be concentrically positioned relative to a balloon. The reinforcement sleeve may be inside of or outside of the balloon. The reinforcement sleeve may be bonded to the balloon. The substance and an adhesive used to bond the sleeve to the balloon may comprise a preactivated adhesive. The spinal rod may have two or more longitudinal reinforcing members and a joining member joining two or more of the longitudinal reinforcing members at a discrete point along each. The spinal rod may also include end members with the balloon secured at both end members. The balloon may be less wide than the end members when deflated and wider than the end members when inflated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of first and second assemblies comprising spinal rods attached to vertebral members according to one embodiment; 
         FIG. 2  is perspective view of a spinal rod according to one embodiment; 
         FIG. 3  is a lateral view of a spinal rod according to one embodiment; 
         FIG. 4  is a side cross section view of a spinal rod according to one embodiment; 
         FIG. 5  is an axial cross section view of a spinal rod according to one embodiment; 
         FIGS. 6-10  illustrate one exemplary percutaneous installation technique for installing a spinal rod according to one embodiment; 
         FIG. 11  illustrates one exemplary percutaneous installation technique for installing a spinal rod according to one embodiment; 
         FIG. 12  is perspective view of a spinal rod according to one embodiment; and 
         FIG. 13  is an end view of a spinal rod according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The various embodiments disclosed herein are directed to spinal rods that are characterized by at least one expandable portion. The expandable portion may be compressed or left unfilled during installation of the rod and may be filled with an injectable substance once the rod is positioned within the body. Similar devices and methods are disclosed in U.S. Pat. No. 6,899,713 to Shaolian et al., the relevant portions of which are incorporated by reference herein. Various embodiments of a spinal rod may be implemented in a spinal rod assembly of the type indicated generally by the numeral  20  in  FIG. 1 .  FIG. 1  shows a perspective view of first and second spinal rod assemblies  20  in which spinal rods  10  are attached to vertebral members V 1  and V 2 . In the example assembly  20  shown, the rod&#39;s  10  are positioned at a posterior side of the spine, on opposite sides of the spinous processes SP. Spinal rods  10  may be attached to a spine at other locations, including lateral and anterior locations. Spinal rods  10  may also be attached at various sections of the spine, including the base of the skull and to vertebrae in the cervical, thoracic, lumbar, and sacral regions. In one embodiment, a single rod  10  is attached to the spine. Thus, the illustration in  FIG. 1  is provided merely as a representative example of one application of a spinal rod  10 . 
     In one embodiment as illustrated in  FIG. 1 , the spinal rods  10  are secured to vertebral members V 1 , V 2  by pedicle assemblies  12  comprising a pedicle screw  14  and a setscrew  16 . In other embodiments, the spinal rod assemblies  20  may be secured to more than two vertebral members, including for example vertebral member V 3 . The outer surface of spinal rod  10  is grasped, clamped, or otherwise secured between the pedicle screw  14  and setscrew  16 . Other mechanisms for securing spinal rods  10  to vertebral members V 1 , V 2  include other types of pedicle screws, hooks, cables, and other such devices. Examples of other types of retaining hardware include threaded caps, screws, and pins. Spinal rods  10  are also attached to plates in other configurations. Thus, the exemplary pedicle assemblies  12  shown in  FIG. 1  are merely representative of one type of attachment mechanism. 
     The spinal rod assemblies  20  comprise an inflatable spinal rod  10  such as the embodiment illustrated in  FIG. 2 .  FIG. 2  shows an elevated perspective view of an inflatable spinal rod  10  in an uninflated state. The spinal rod  10  comprises a first end  22 , a second end  24  and a compliant, inflatable balloon  26  between the first end  22  and the second end  24 . The balloon  26  may be constructed in a variety of ways, including techniques utilized for balloon angioplasty applications. The first end  22  comprises a self-sealing valve  28 , which allows an injectable substance to flow into, but not out of, the balloon  26 . The injectable substance that is inserted into the spinal rod  10  may include certain hardenable media, such as epoxy, PMMA, polyurethane, and silicone. Further, the substance may have a lesser or greater viscosity in a cured form as compared to its precured form. 
     The second end  24  of the spinal rod  10  comprises a tip  30  that is constructed of a biocompatible material. The balloon  26  comprises a suitable complaint biocompatible material, such as a polymer that may include nylon, polyethylene, polyurethane, silicone, polyethylene, polypropylene, polyimide, polyamide, and polyehteretherketone (PEEK). The balloon  26  may be formed from materials that are used in other conventionally known biomedical applications, such as balloon angioplasty. The spinal rod  10  may be reinforced with concentric layers of similar or dissimilar materials and/or fabrics. 
     Generally, the balloon  26  is an impermeable structure that can be collapsed diametrically for delivery and expanded in situ during implantation. Further, the exemplary balloon  26  comprises thin, reinforcing rails  32  running longitudinally along the balloon  26 . Generally, the rails  32  are flexible, but maintain their substantially elongated shape to help the uninflated balloon  26  maintain an elongated shape during insertion (as will be described below). The rails  32  may be constructed of metals such as titanium or nitinol or non-metals such as PEEK, UHMWPE, and carbon-fiber reinforced polymers and resins. The rails  32  may be constructed of other suitable materials as will be understood by those with skill in the art with reference to this disclosure. In one embodiment, the rails  32  extend over substantially the entire proximal to distal length of the balloon  26 . In one embodiment, the rails  32  extend over less than the entire proximal length of the balloon  26 . The rails  32  may comprise such elements as rods, wires, and cables. 
     The exemplary spinal rod  10  further comprises a plurality of straps  34  that are secured to the rails  32  at discrete points  36 . In one embodiment, the straps  34  are substantially rigid and maintain a substantially circular shape. In one embodiment, the straps  34  maintain a shape of the balloon  26 . In one embodiment, the straps  34  are flexible members that allow the rails  32  to expand and contract relative to one another depending on whether the balloon  26  is in a compressed or inflated state. In either case, the straps  34  may maintain a desired spacing between the rails  32 . The straps  34  may also prevent the rails  32  from grouping together towards one side of the rod  10  as the injectable substance is inserted into the balloon  26 . Also, as shown in  FIG. 2 , the straps  34  may be disposed at various points along the rails  32 , including at or towards the first end  22 , at or towards the second end  24 , and at intermediate points therebetween. Further, the straps  34  may be used to secure substantially all rails  32  that are disposed in the spinal rod  10 . In this case, the straps  34  may be circumferentially disposed within the balloon  26 . Alternatively, the straps  34   a  may be used to secure fewer than all rails  32 . In this case, the straps  34  may be radially disposed within the balloon  26 . Also, the straps  34 ,  34   a  may be oriented normal to, transverse to, or oblique to a longitudinal axis A of the rod  10 . 
     In one embodiment illustrated in  FIG. 3 , the spinal rod  10   a  comprises two layers. A detailed cross section of this embodiment of spinal rod  10   a  is shown in  FIG. 4 .  FIG. 4  also illustrates a self-sealing valve  28  in the form of a duck-bill valve. Other types of one-way valves, including check valves and reed valves, may be used. The self-sealing valve  28  may permit an injectable substance  35  to enter and remain in the balloon  26 . The exemplary spinal rod  10   a  includes a reinforcing structure  38  such as a woven or braided mesh contained within the balloon  26 . The reinforcing structure  38  may be constructed of a wide variety of woven or nonwoven fibers, fabrics, metal mesh such as woven or braided wires, polymeric fibers, ceramic fibers, and carbon fibers. Biocompatible fabrics or sheet material such as ePTFE and Dacron®, Spectra®, and Kevlar® may also be used. The use of a braided sleeve may produce higher structural resistance to sheer stress as a result of torsional loads. The braided reinforcing structure  38  may also help distribute the rails  32  in a homogenous manner. The reinforcing structure  38  may have radiographic markers, such as metallic wires, including materials such as gold, platinum or tantalum, disposed therein for visibility of the spinal rod  10  via radiographs or fluoroscopy. Alternatively, a radiopaque material, such as barium sulfate or tantalum powder, may be dispersed among the materials forming the reinforcing structure  38 . The expandability and constraining effects provided by the reinforcing structure  38  may also be controlled with the weaving or braiding pattern of the sleeve. 
     The reinforcing structure  38  may resist kinking of the balloon  26  as the balloon  26  is advanced around corners such as during advancement through an aperture (e.g., portal or eyelet) on a bone anchor  14 . As shown, the reinforcing structure  38  may be positioned within the balloon  26 . The reinforcing structure  38  may alternatively be embedded within the wall of the balloon  26 , or carried on the outside of the balloon  26  much like a conventional stent. 
     The reinforcing structure  38  may comprise braided fibers that are disposed within the range of from about 15 to about 45 degrees relative to a longitudinal axis A. The braids may be in the form of a plain weave. This braided reinforcing structure  38  may conform dimensionally to the inside diameter of the balloon. In one embodiment, the reinforcing structure  38  has a diameter of about 6 mm. 
     In the illustrated embodiment, the plurality of longitudinally extending rails  32  is disposed between the balloon  26  and the reinforcing structure  38 . In one embodiment, the rails  32  are bonded to the reinforcing structure  38 . In one embodiment, the rails  32  are bonded to the balloon  26 . In other embodiments, the balloon  26  is disposed interior to the reinforcing structure  38 , with the rails  32  disposed therebetween. Some examples of suitable adhesives that may be used to bond the rails  32 , balloon  26 , straps  34 , and reinforcing structure  38  include light curing acrylics and cyanoacrylates, silicones, polyurethanes, and epoxies available from Loctite® of Rocky Hill, Conn., USA. Certain varieties of these materials may also be used as the injectable substance  35 . These include light curing adhesives and preactivated epoxies. Preactivated epoxies are one example of an adhesive that will begin to cure once exposed to a certain wavelength of light (e.g., UV, IR), but will not set for some number of minutes thereafter. Thus, in one embodiment, a preactivated epoxy may be used as an injectable substance  35  in the rod  10 . The curing process for the preactivated epoxy may be initiated before the rod  10  is inserted into a subject, with a full set occurring after the rod  10  is implanted. That is, the injectable substance may remain fluid or pliable during the installation procedure. For example, the injectable substance (or adhesive) may have a first stiffness at the time when the surgeon begins to insert the rod  10  into the subject. Then, as the substance cures further, the substance may have a second stiffness at the time when the surgeon secures the rod  10  to vertebrae within the subject. 
     Although a cylindrical configuration for balloon  26  is illustrated herein, any of a variety of alternative cross sectional configurations may be utilized. The overall length, diameter and wall thickness of the spinal rod  10  may be varied, depending on the particular treatment and access site. In one embodiment, the spinal rod  10  has an inflated length between about 20 and 120 mm, and often between about 50 mm and about 80 mm for adjacent vertebrae V 1 , V 2  fixation. Longer lengths may be appropriate where more than two vertebrae V 1 , V 2 , V 3  are joined to the spinal rod  10 . Further, the spinal rod  10  may have an inflated diameter of generally between about 5 mm and 20 mm. The spinal rod  10  may have a deflated diameter of between about 4 mm and 7 mm, which permits installation into conventional rod securing anchors such as pedicle screws  14 . Generally, the expandability and constraint of the device may be partially controlled with the balloon  26  diameter and thickness. 
     The construction of an alternative embodiment of a composite spinal rod  10   b  is illustrated in the cross section view shown in  FIG. 5 . In this embodiment, an inflatable balloon  26  is provided, as has been discussed. A first reinforcing structure  40  such as a stent, or a braided or woven structure as discussed above is concentrically positioned exterior to the balloon  26 . A second reinforcing structure  42  is concentrically disposed within the balloon  26  in the embodiment. In one embodiment the first reinforcing structure  42  comprises a diameter of about 5 mm. 
     The second reinforcing structure  42  is spaced radially inwardly from the first reinforcing structure  40  and the balloon  26 . For example, in one embodiment, the second reinforcing structure  42  comprises a diameter of about 4 mm. A plurality of rails  32  is axially oriented within the annular space between the balloon  26  and second reinforcing structure  42 . A plurality of rails  32  may also be disposed between the balloon  26  and the first reinforcing structure  40 .  FIG. 5  also shows a strap  34  joining the rails  32 . A variety of alternate constructions can be readily utilized in accordance with the teachings herein. For example, three or more reinforcing structures may be utilized. The layering sequence of the various components may be changed, and other features added or deleted depending upon the desired performance of the finished spinal rod  10 . In addition, although the balloon  26  in one embodiment comprises a single layer balloon, other materials may be utilized. In addition, multiple layer balloons may be utilized, with or without reinforcing structures  40 ,  42  such as stents, wires, or woven tubular support structures disposed therebetween. Further, two or more of the components  26 ,  32 ,  40 ,  42  shown in  FIG. 5  may be bonded to one another prior to insertion into a subject patient. The bonds may be formed using biocompatible adhesives, such as those described above. 
     The embodiments of a spinal rod  10  disclosed herein may be inserted into a patient using a variety of surgical implantation techniques. Certainly, open and mini-open surgical procedures are possible. Percutaneous procedures are also possible. For instance,  FIGS. 6-10  illustrate one exemplary percutaneous installation technique. In  FIG. 6 , a hollow needle  44 , such as a 16 gauge or 18 gauge needle, is inserted percutaneously into the subject S at location P 1  and advanced to the one of the bone screws  14 . While the hollow needle  44  is shown engaging the superior bone screw  14  in vertebrae V 2 , the hollow needle  44  can initially engage the bone screw  14  in the inferior vertebrae V 1 . 
     A needle-tipped, semi-rigid guidewire  46  is introduced through the lumen of the hollow needle  44  and through the rod seat in the bone screw  14  in vertebrae V 2 . The guidewire  46  is directed and advanced towards the second bone screw  14  in vertebrae V 1 . Certain known techniques for advancing the guidewire  46  may be used. For instance, U.S. Pat. No. 6,899,713 disclosed above presents several techniques. The guidewire  46  is then extracted at a second percutaneous incision P 2  as shown in  FIG. 7 . Then, a flexible introducer sheath  48  is passed over the guidewire  46  along the entire guidewire tract entering incision P 1  and exiting incision P 2 . The guidewire  46  is removed after the introducer sheath  48  is placed. 
     Next, as shown in  FIG. 8 , an uninflated, inflatable spinal rod  10  is attached to a proximal pushing catheter  50  and advanced through the introducer sheath  48  until the inflatable spinal rod  10  advances between and beyond the two bone screws  14  in vertebrae V 1 , V 2 . Once the spinal rod  10  is positioned in or on the bone screws  14 , the sheath  48  is removed. At various points in the procedure, the placement of the components, including the spinal rod  10 , may be confirmed by fluoroscopy or other radiographic or imaging technique. 
     Then, as shown in  FIG. 9 , the balloon  26  of the inflatable spinal rod  10  is inflated with an injectable substance as disclosed above. The substance may comprise a rapid setting, liquid polymer, or its equivalent, and the polymer is allowed to set. A setscrew  16  (as shown in  FIG. 1 ) or other retaining hardware may be used to secure the spinal rod  10  to each bone screw  14 . In one embodiment, the liquid polymer is or includes polymethylmethacrylate or other hardenable media such as those discussed elsewhere herein. In one application, the inflated balloon  26  of the inflatable spinal rod  10  expands longitudinally and radially beyond the head of each bone screw  14 , which helps fix the bone screws  14  in relation to each other. 
     Finally, as shown in  FIG. 10 , the delivery or pushing catheter  50  is detached from the inflatable spinal rod  10  by pulling on the catheter  50 . The method can be repeated on the opposite side of the spinous processes of the subject&#39;s S spinal column, thereby repositioning or fixing the one or more unstable, seperated or displaced vertebrae or the one or more portions of one or more vertebrae bilaterally. The percutaneous incisions P 1 , P 2  are closed or sealed as necessary and routine postoperative care administered. 
     An alternative installation approach contemplates a minimally invasive percutaneous procedure as shown in  FIG. 11 . The procedure shown in  FIG. 11  incorporates an installation instrument  80 . One example of an instrument suitable for this type of installation is the Sextant Rod Insertion System available from Medtronic Sofamor Danek in Memphis, Tenn., USA. The installation instrument includes support arms  78  that are coupled to pedicle screw extensions  76 . The support arms  78  are pivotally connected to a rod holder  82  about pivot P. The first and second pedicle screws  14  and pedicle screw extensions  76  are engaged to the first and second vertebrae V 1 , V 2 , respectively, through first and second percutaneous punctures in the subject S. If desired, a surgeon can manipulate the pedicle screw extensions  76  to apply a load to compress or distract the vertebrae V 1 , V 2  prior to installing rod  10   c . As disclosed above, the uninflated spinal rod  10   c  may have various structural components, including rails  32  and reinforcing structure  38 . In one embodiment, these components  32 ,  38  may provide sufficient structure for insertion using this illustrated technique. Specifically, the rod  10   c  is installed through a third percutaneous puncture in the subject S using the installation instrument  20 . The rod  10   c  is brought into engagement with the pedicle screws  14  by rotating the rod holder  82  about pivot P. 
     In one embodiment, the rod holder  82  is cannulated to allow a surgeon to introduce an injectable substance through the rod holder  82  and into the rod  10   c . A needle or other injection instrument is used to inject the injectable substance into the port J in the rod holder  82 . Alternatively, a catheter may be inserted through the cannulated rod holder  82 . Once the rod  10   c  is positioned as desired (possibly verified by fluoroscopy), the rod  10   c  may be inflated as described above. Alternatively, the rod  10   c  may be wholly or partially inflated with an injectable substance prior to insertion. In one embodiment, the injectable 
       FIGS. 12 and 13  illustrate an alternative embodiment of an inflatable rod  10  comprising dissimilar end members  52 ,  54  on opposite sides of an inflatable portion  110 . The first and second rod ends  52 ,  54  include a clamping portion  56 . The clamping portions  56  may have similar widths and may further have a substantially similar cross section. Further, first rod end  52  includes a tapered portion  58  that decreases in width from the clamping portion  56  towards a distal end  60 . The tapered portion  58  may improve the ease with which the rod  10   d  is inserted, such as when inserted longitudinally using the percutaneous techniques disclosed herein. The clamping portion  56  may be sized to fit within conventional rod securing devices such as the bone screws  14  shown in  FIG. 1  and described above. For example, the clamping portion  56  may have a diameter within a range between about 4 and 7 mm. The rod ends  52 ,  54  may be constructed from a variety of surgical grade materials. These include metals such as stainless steels, cobalt-chrome, titanium, and shape memory alloys. Non-metallic rods, including polymer rods made from materials such as PEEK and UHMWPE, are also contemplated. The spinal rod  10  may have rigid or flexible rod ends  52 ,  54 . 
     The inflatable portion  110  may have a structure similar to one or more of the embodiments disclosed above. That is, the inflatable portion  110  may have a substantially impermeable balloon structure  126  that can be collapsed diametrically for delivery and expanded in situ during implantation. The inflatable portion  110  may have one or more layers of reinforcing structure  138  that may be embodied as a braided, mesh, or woven structure as described above. Further, the exemplary inflatable portion  110  may comprise thin, reinforcing rails  32  running longitudinally along the inflatable portion  126 , though none are specifically shown in  FIG. 12 . 
       FIG. 12  depicts an embodiment of the spinal rod  10   d  with the inflatable portion  110  in an inflated state. An injectable substance may be inserted into the inflatable portion  110  through a self-sealing valve  62  that is disposed within the visible, which suggests that the inflatable portion  110  may collapse to a size that is thinner than the overall width of the first and second end portions  52 ,  54 . In the expanded state, the inflatable portion  110  extends wider than the first and second end portions  52 ,  54 , which may provide some off-axis stability in compression. In one embodiment, the injectable substance contained within the inflatable portion  110  retains some flexibility after curing, which assists in a dampening effect of the rod  10   d . With this configuration, the spinal rod  10   d  may replicate some of the stability that is provided by a facet joint in a healthy subject. 
       FIG. 13  shows an end view of the spinal rod  10   d , looking into the proximal end of the second end member  54 . In the illustrated embodiment, the expandable members  126 ,  138  of the inflatable portion  110  are disposed between concentric columns  64 ,  66 ,  68 . Three columns  64 ,  66 ,  68  are shown, though more or fewer columns may be used. In the embodiment depicted, the balloon  126  is disposed between an inner column  64  and an intermediate column  66 . The reinforcing structure  138  is disposed between the intermediate column  66  and an outer column  68 . In other embodiments, the reinforcing structure  138  and the balloon  126  may be disposed between the same two column members  64 ,  66  or  66 ,  68 . In one embodiment, the inflatable portion  110  does not include reinforcing structure  138 . As suggested above, other embodiments may include a balloon  126  that has a reinforcing structure  138  embedded therein. 
     Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description. 
     As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. 
     The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. For instance, embodiments disclosed herein have contemplated one balloon structure  26 ,  126 , perhaps with one or more rails  32  or reinforcing structures  38 ,  138 . In other embodiments, multiple concentric layers of balloons  26 ,  126  may be used. Also, the illustrated embodiment provided in  FIGS. 12 and 13  include a single intermediate section between end portions  52 ,  54 . In an alternative embodiment, the rod may comprise multiple intermediate sections disposed between additional clamping portions  56 . The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.