Patent Publication Number: US-2021169540-A1

Title: Minimally invasive spinal fusion system and method

Description:
PRIORITY CLAIM 
     This application claims the benefit under at least 35 U.S.C. § 120 as a continuation application of U.S. patent application Ser. No. 15/934,634 filed on Mar. 23, 2018, which is in turn a continuation of U.S. patent application Ser. No. 15/299,277 filed on Oct. 20, 2016 and now issued as U.S. Pat. No. 9,924,989, which is in turn a continuation of U.S. patent application Ser. No. 14/789,805 filed on Jul. 1, 2015 and now issued as U.S. Pat. No. 9,498,348, which is in turn a continuation of U.S. patent application Ser. No. 14/559,071 filed on Dec. 3, 2014 and now issued as U.S. Pat. No. 9,101,408, which in turn claims the benefit under 35 U.S.C. § 119(e) as a nonprovisional application of U.S. Prov. App. No. 62/039,863 filed on Aug. 20, 2014. Each of the foregoing priority applications are hereby incorporated by reference in their entireties. All applications for which a foreign or domestic priority is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. 
    
    
     BACKGROUND 
     Most spinal fusions are performed for patients with back pain with or without radicular symptoms (radiating pain) or neurogenic claudication (pain with walking) caused by degenerative disc disease (spondylosis). Roughly 90% of all spine surgeries involve fusion. Over 465,000 spinal fusions were performed in 2011 in the US at a cost of nearly 13 billion dollars. 
     Not to be limited by theory, pain from such pathology is believed to be caused by abnormal motion (instability). Fusion is performed to reduce or eliminate the motion of the degenerated disc segment by immobilizing the adjacent vertebral bodies. The majority of spinal fusions are performed with a posterolateral approach with bone graft material placed across the facets, lamina and transverse processes. A combination of transpedicular screws and connecting rods or plates provide immobilization of the vertebra until the bone graft material can form a solid bony fusion mass. A growing number of fusions are performed with an anterior approach with the bone graft placed in the disc space to allow bony fusion of the vertebral bodies across the disc space. Anterior fusions are typically performed in conjunction with posterolateral fusion rods to provide the immobilization needed for the bony fusion across the disc to occur. Bony fusion may take 6-12 months and fusion failure rates of 10-40% are reported in the literature. 
     SUMMARY 
     Disclosed herein are minimally invasive systems and methods for stabilizing a spine. In some embodiments, a method for stabilizing the spine includes one or more of the following steps: creating a pedicular access channel in a pedicle to access the interior of a first vertebral body; inserting an introducer cannula into the pedicle; inserting a hollow needle through a central lumen of the introducer cannula into the interior of the first vertebral body, through an intervertebral disc, and into the interior of a second vertebral body adjacent the first vertebral body; inserting an anchor through a central lumen of the hollow needle such that a distal end of the anchor is within the interior of the second vertebral body, a proximal end of the anchor is within the interior of the first vertebral body, and a central portion of the anchor spans the intervertebral disc; expanding the distal end of the anchor within the interior of the second vertebral body; expanding the proximal end of the anchor within the interior of the first vertebral body; flowing a first volume of bone cement media into the distal end of the anchor within the interior of the second vertebral body; flowing a second volume of bone cement media into the proximal end of the anchor within the interior of the first vertebral body; inserting a flexible rod through the central lumen of the hollow needle, such that a distal portion of the flexible rod is positioned within the interior of the second vertebral body and in contact with the first volume of bone cement media, the proximal portion of the flexible rod is positioned within the interior of the first vertebral body, and a central portion of the rod spans the intervertebral disc, wherein the flexible rod resides at least partially within an interior of the anchor. In some embodiments, substantially no bone cement media flows within the intervertebral disc. In some embodiments, the method does not involve a discectomy procedure. The bone cement media can include PMMA, for example, such as between about 1 cc and 5 cc, or about 2 cc and about 3 cc. The flexible rod can comprise a carbon fiber material, such as PEEK. Expanding the distal end of the anchor within the interior of the second vertebral body and expanding the proximal end of the anchor within the interior of the first vertebral body can comprise expanding a balloon. In some embodiments, inserting the anchor step comprises inserting the anchor carried proximate the distal end of a balloon catheter. In some embodiments, a central portion of the anchor is not expanded, and the distal and proximal expanded portions of the anchor have a maximal expanded diameter that is at least 1.5×, 2×, 3×, or more of the unexpanded diameter of the central portion of the anchor. The anchor can comprise a shape memory material, such as Nitinol. The anchor can be inserted in a compressed, substantially tubular configuration. The introducer cannula can have a diameter of, for example, between about 8 Gauge to about 12 Gauge. Following insertion of the flexible rod the first and second volumes of bone cement media harden, fixing the anchor and flexible rod in place. In some embodiments, flowing the second volume occurs after the inserting a flexible rod step, such that the proximal end of the flexible rod is in contact with the second volume of bone cement media after the flowing the second volume step. 
     Also disclosed herein is a system for stabilizing the spine. The system can include, for example: an anchor having a proximal end, a distal end, and a central portion, the anchor having a compressed tubular configuration and an expanded configuration wherein the proximal end and the distal end of the anchor are expanded while the central portion of the anchor is not expanded, wherein the proximal end and the distal end of the anchor have maximal expanded diameters at their widest portions of at least about 2× the diameter of the central portion of the anchor, wherein the anchor is sized and configured such that the proximal end of the anchor can reside within the interior of a first vertebrae, the distal end of the anchor can reside within the interior of a second vertebrae adjacent the first vertebrae, and the central portion of the anchor spans an intervertebral disc between the first vertebrae and the second vertebrae, wherein the anchor is defined by a shape memory frame and interstices within the frame; and a flexible carbon fiber rod dimensioned to fit within an interior of the anchor, such that when implanted the flexible rod is configured to reside substantially within the anchor, wherein the distal end of the flexible rod is configured to reside within the distal end of the anchor within the interior of the second vertebrae, the proximal end of the flexible rod is configured to reside within the proximal end of the anchor within the interior of the first vertebrae and the central portion of the anchor is configured to span an intervertebral disc between the first vertebrae and the second vertebrae. The flexible carbon fiber rod comprises PEEK in some cases. When implanted, the flexible carbon fiber rod is configured to allow for at least 15 degrees, 30 degrees, or more of flexion of a patient&#39;s spine. In some embodiments, the system also includes a balloon catheter comprising a balloon configured to expand the proximal end and the distal end of the anchor. The anchor can be carried on a distal end of the balloon catheter. The system can also include a volume of bone cement media, such as PMMA. The system can also include an introducer cannula comprising a central lumen and a stylet configured to reside at least partially within the central lumen of the introducer cannula. The system can also include a curvable hollow needle comprising a central lumen configured to reside at least partially within the central lumen of the introducer cannula. The system can also include an injector needle in some embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates an access cannula that can be part of a spinal stabilization system, in some embodiments. 
         FIG. 1B  illustrates a hollow curvable needle that can be part of a spinal stabilization system, in some embodiments. 
         FIG. 1C  illustrates an anchor carried by a balloon catheter that can be part of a spinal stabilization system, in some embodiments. 
         FIG. 1D  illustrates a balloon catheter that can be part of a spinal stabilization system, in some embodiments. 
         FIG. 1E  illustrates a curvable media injector that can be part of a spinal stabilization system, in some embodiments. 
         FIG. 1F  illustrates a flexible carbon fiber rod that can be part of a spinal stabilization system, in some embodiments. 
         FIGS. 2A-2I  illustrate various steps of a method of stabilizing a spine, according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Because of the high morbidity and high cost of the current methods of spinal fusion, an effective, less invasive spinal fusion at lower cost would be a significant improvement. The proposed method of spinal fusion could be done percutaneously as an outpatient rather than as an open surgical procedure which typically requires a several day inpatient stay. 
     Systems and methods disclosed herein can, in some embodiments, involve currently available materials approved by the FDA for human use, as well as materials that could be approved at a later date. The implanted material can include, for example, one, two, or more sources of media, including bone cement material such as PMMA (polymethylmethacrylate), a shape memory material such as the superelastic memory alloy nitinol (nickel titanium), and a polymer, including carbon reinforced PEEK (polyether ether ketone), and/or organic thermoplastic polymer. PMMA is extremely resistant to compressive stress. PMMA bone cement can be made from methylmethacrylate, polymethylmethacrylate, esters of methacrylic acid, or copolymers containing polymethylmethacrylate and polystyrene. Carbon fiber reinforced polymers such as PEEK are extremely resistant to bending stress. Nitinol (nickel titanium alloy) is a shape memory alloy resistant to repetitive bending stress. 
     Candidates for conventional spinal fusion can benefit from the systems and methods disclosed herein. The fusion can involve cervical, thoracic, lumbar, and/or sacral vertebrae in some embodiments. In some embodiments, a subgroup of patients who may especially benefit are older patients with osteoporosis who are poor surgical candidates and have few options for treatment. 
     Systems and methods for spinal fusion or stabilization are described herein. Various non-limiting embodiments of elements that can be used within systems and methods herein are illustrated in  FIGS. 1A-1F . The system can include, in some embodiments, an access cannula  10  having a proximal end  16 , a handle  14 , and a distal end  18  with a central lumen  12  (shown in  FIG. 1A ) with at least one input port and exit port. The central lumen  12  of the access cannula  10  can house an inner stylet (not shown) therethrough. The system can also include a curvable needle  20  having a distal end  24 , with a central lumen  22  (shown in  FIG. 1B ) configured to fit within the central lumen  12  of the access cannula  10 , and a perforated anchor  30  having a central lumen, a first end, a second end, and an elongate section between the first and the second end. The access cannula  10  and/or the curvable needle  12  can have indicia along its length which can be radiopaque markers in some embodiments. 
     The anchor  30  is shown in  FIG. 1C  in a radially compressed, generally tubular configuration, and can be sized and configured to be placed within the central lumen  12  of the access cannula  10  for delivery into the spine, and mounted over the distal end of a high-pressure balloon catheter  41  or other expandable member in some embodiments. The anchor  30  can include perforations or cells sized and configured to allow for the passage of liquid bone cement therethrough, while allowing preventing passage of bone cement after hardening (e.g., solid cement) which remains confined within the anchor  30 . The perforations or cells can be laser cut or otherwise created within the anchor  30 . The first end  32  and the second end  34  of the anchor  30  can each include one or more discrete radially and/or axially expandable sections, such as a self-expandable or balloon-expandable section. In some embodiments, the expandable first end  32  and second end  34  can be expanded in diameter to about or at least about 1.25×, 1.5×, 1.75×, 2×, 3×, 4×, 5×, 6×, 7×, 8×, 9×, 10×, or more relative to the unexpanded diameter of the anchor  30 . In some embodiments, the central elongate section  36  of the anchor is non-expandable or expandable/expanded to a lesser degree than the end sections  32 ,  34 . The anchor  30  can be made of, for example, a metal or metallic alloy, such as a shape memory material such as nitinol or Elgiloy for example, stainless steel, and/or a polymer (including biodegradable polymers) or other materials in other embodiments. The anchor  30  can be sized and configured such that the first end  32  is contained within the cancellous bone of a first vertebrae, the second end  34  is contained within the cancellous bone of a second vertebrae adjacent the first vertebrae (either in a cephalad or caudal direction), and the elongate section  36  spans an intervertebral disc between the first and second vertebrae. 
     As illustrated in  FIG. 1D , the system can also include one, two, or more expandable members such as a balloon  40  on or proximate the distal end of balloon catheter  41  and configured to radially expand the anchor. In some embodiments the expandable member has sufficient strength to create a cavity within the cancellous bone as well. In some embodiments, the balloon  40  can be inflated to an inflation pressure of about or at least about 15 atm, 20 atm, 25 atm, 30 atm, or more. 
     The system can also include a cement injection needle  50  which can have a distal steerable and/or curvable portion in some embodiments as illustrated in  FIG. 1E . The injection needle  50  (as well as curvable needle  20 ) can have a bent or curved unstressed state (e.g., made of a shape memory material) that is substantially straight while housed within a tube/sheath having sufficient column strength, but assumes its unstressed state upon advancing out of, or withdrawal of the tube/sheath. In some embodiments, the needle  50  is steerable and curvable by, for example, the use of one, two, or more pullwires operably connected to the distal end of the needle  50  and operably connected proximally to an adjustment control, such as a wheel, dial, or other element that can be adjusted by the physician to adjust the tension on the pullwire(s) and thus adjust the degree of curvature of the distal end of the needle  50 , such as through a working range. The needle  50  can include one, two, or more distally facing and/or laterally facing exit ports for delivery of the cement or other media to a location within the cancellous bone. 
     As illustrated in  FIG. 1F , the system can also include one, two, or more flexible rods  60  with first end  62  and second end  64 , such as carbon fiber rods configured to be at least partially or completely housed within the central lumen of the anchor. In some embodiments the rods  60  are sufficiently flexible to not substantially hinder flexion or extension of the spine when implanted into a patient. As noted above, the rods may be made of PEEK, carbon fiber PEEK, polyetherketoneketone (PEKK), polysulfone, polyetherimide, polyimide, ultra-high molecular weight polyethylene (UHMWPE), cross-linked UHMWPE, nano-material reinforced polymers, another medical grade polymer material, or a hybrid metal-polymer rod in some embodiments. In some embodiments, the rods are sized and configured to span no more than a single intervertebral disc (although the rods could be sized and configured to span multiple discs in other embodiments), and can be from about 1 mm to about 3 mm in diameter in some cases, such as about 2 mm in diameter. 
     The spinal stabilization system can also include one, two, or more volumes of media for injection into the cancellous bone. The media could include, for example, one, two, or more bone cement materials such as PMMA, for injecting into the first and second end of the anchor to stabilize the anchor within adjacent vertebrae. In some embodiments the media could be injected in a liquid or gel-like state that hardens or otherwise solidifies some time after injection into the vertebral cavity. The media could also include, for example, bone growth material, stem cells, and/or one, two, or more other therapeutic agents, such as a growth factor, anesthetic agent, steroid or other anti-inflammatory agent, narcotic or non-narcotic pain control agent, an antibiotic, an antibody, an anti-cancer chemotherapeutic agent, radiation-emitting materials, and the like. 
       FIGS. 2A-2I  illustrate a method of performing a minimally invasive (e.g., percutaneous) spinal fusion procedure, according to some embodiments of the invention. Access to the first vertebra V 1  can be with an unipedicular or bipedicular approach with an access cannula  10 , such as a straight cannula about 8, 9, 10, 11, 12, or other gauge in dimension, as illustrated in  FIG. 2A . The cannula  10  can be advanced to just beyond the pedicle P into the posterior vertebral body and the inner stylet is then removed. 
     Through the cannula  10 , a needle  20 , such as a shape memory nitinol needle with a curved unstressed state, such as about 12 gauge in dimension (or 1, 2, 3, 4, or more gauge smaller than the diameter of the central lumen  12  of the cannula  10  in some cases), would be advanced and the distal end curved in a cephalad direction as shown (or a caudal direction in other embodiments) to cross the intervertebral disc space D into the anterior inferior aspect of the adjacent vertebral body V 2 , as illustrated in  FIG. 2B . 
     The inner stylet of the nitinol needle  20  can be removed and a stent-like perforated anchor  30 , which can be a metal or metal alloy such as a nitinol anchor mounted on a high pressure balloon can be passed through the needle  20  to span the intervertebral disc space D, as illustrated in  FIG. 2C . The balloon catheter  41  can be deployed, and the distal end  32  of the anchor  30  in the superior vertebral body V 2  can be dilated with the balloon  40  (not shown for clarity) to open up the anchor&#39;s interstices (cells), as shown in  FIG. 2D . The balloon  40  can be withdrawn into the inferior vertebral body V 1  and the proximal portion  34  dilated, as shown in  FIG. 2F . 
     The balloon catheter  41  can be removed and a curvable and/or steerable hollow injection needle  50 , such as a nitinol needle having an about  14  gauge dimension in some embodiments can be advanced into the distal end  32  of the anchor  30 . In some embodiments, the balloon catheter  41  need not be withdrawn immediately after creating a cavity in either the superior vertebral body V 2  or the inferior vertebral body V 1  (but can be deflated in some embodiments), and the injection needle  50  can pass through a lumen of the balloon catheter  41 , or be integral with the balloon catheter  41  in some embodiments. An appropriate amount of media  90 , such as bone cement or other stabilizing material, such as between about 1-5 cc or 2-3 cc, or about 1 cc, 1.5 cc, 2 cc, 2.5 cc, 3 cc, 3.5 cc, 4 cc, 4.5 cc, or 5 cc of PMMA bone cement in some embodiments, can be injected into the distal  32  portion of the anchor  30  under imaging, such as constant fluoroscopic visualization as the cement flows through the interstices of the anchor  30  and into the normal bone marrow space and bony trabeculae, as shown in  FIG. 2E . This will stabilize the anchor  30  in place and maximize the surface area contact of cement  90  and bone as the media cures. In some embodiments, the bone cement  90  is injected into cavities within the vertebrae only, and no bone cement  90  or substantially no bone cement  90  resides or migrates into the intervertebral disc space D, either within or outside the central elongate portion  36  of the anchor  30  which is not radially expanded in some embodiments. This can be advantageous in some cases, such that hardened bone cement  90  or other material is not present in the intervertebral disc space D allowing for maintenance of some degree of spinal flexion, extension, and rotation postoperatively. In some embodiments, partial or complete discectomies are not required to be performed during the procedure, to better maintain the intervertebral disc D as mentioned above. However, in some embodiments, the stabilization procedure can be synergistically performed in conjunction with another operative procedure in the same operative session, or within a month, 2 weeks, 1 week, 5, 4, 3, 2, or 1 days, or the same day; either before or after the spinal stabilization procedure, which can be another minimally invasive spinal procedure in some embodiments. For example, one or more discectomies to remove a disc herniation can be performed. In some embodiments, the procedure can also be performed in conjunction with a laminectomy done to decompress the spinal canal (for patients with spinal stenosis), or in conjunction with posterior distraction of the spinous processes to decrease in-folding of the ligamentum flavum and to reduce the amount of neuroforaminal compromise (e.g., the X-STOP procedure from Medtronic, Inc., Minneapolis, Minn.). 
     The injection needle  50  can be withdrawn and one, two, or more flexible rods  60 , such as an approximately 2 mm in diameter carbon reinforced PEEK curved rod would be placed through the anchor  30  with the distal end  62  of the rod  60  advanced into the cement  90  in the superior vertebral body V 2  before the cement has time to solidify, as shown in  FIG. 2G . The injection needle  50  could be reintroduced into the proximal dilated end  34  of the anchor  30  in the inferior vertebral body V 1  and another volume of media, e.g., about 2-3 cc of PMMA can be injected to imbed the proximal end  64  of the rod  60  in cement  90  and into the cavity, extending into the surrounding bony trabeculae, as shown in  FIG. 2H . In some embodiments, the procedure can also advantageously benefit patients who also have a vertebral body compression fracture by restoring or improving the vertebral height of the fractured vertebrae. 
     The one, two, or more generally flexible carbon fiber rods  60 , which can be generally positioned along the cranial-caudal axis, span the disc space D and can limit translational movement but allow some limited flexion and extension, in contrast to conventional spinal fusions wherein any relative movement of adjacent fused vertebrae may no longer be possible. In some embodiments, multiple rods  60  can be placed side-by-side if additional stabilization is required. The PMMA cement  90  immobilizes the proximal  64  and distal  62  ends of the one or more rods  60  in the adjacent vertebral bodies V 2 , V 1 , but the cement  90  can be absent in the central portion  36  of the anchor  30  (e.g., in the intervertebral disc space D; the cement  90  does not extend beyond the vertebral endplates into the disc space D in some embodiments), which advantageously preserves some degree of flexion and extension movement as noted above, such as about, at least about, or no more than about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more degrees of flexion and/or extension, such as between about 1 degree and about 5 degrees, or between about 2 degrees and about 5 degrees in some embodiments. The proximal  64  and/or distal ends  62  of the rods  60  can extend some distance beyond the expanded portions  32 ,  34  of the anchor  30  filled with bone cement  90  in some embodiments. The anchor  30  limits excessive extension and advantageously prevents loosening, displacement, or other migration of the rod(s)  60 . The rods  60  can advantageously further maintain the height of the intervertebral disc space D and prevent the vertebrae V 1 , V 2  from collapsing on each other. An embodiment of a system after implantation and removal of the curvable needle and cannula is illustrated in  FIG. 21 . In some embodiments, any number of the foregoing steps can be repeated in order to effect multi-level spinal fusions depending on the desired clinical result. 
     Various other modifications, adaptations, and alternative designs are of course possible in light of the above teachings. Therefore, it should be understood at this time that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein. It is contemplated that various combinations or subcombinations of the specific features and aspects of the embodiments disclosed above may be made and still fall within one or more of the inventions. Further, the disclosure herein of any particular feature, aspect, method, property, characteristic, quality, attribute, element, or the like in connection with an embodiment can be used in all other embodiments set forth herein. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above. Moreover, while the invention is susceptible to various modifications, and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the invention is not to be limited to the particular forms or methods disclosed, but to the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the various embodiments described and the appended claims. Any methods disclosed herein need not be performed in the order recited. The methods disclosed herein include certain actions taken by a practitioner; however, they can also include any third-party instruction of those actions, either expressly or by implication. For example, actions such as “accessing a vertebral body” includes “instructing the accessing of a vertebral body.” The ranges disclosed herein also encompass any and all overlap, sub-ranges, and combinations thereof. Language such as “up to,” “at least,” “greater than,” “less than,” “between,” and the like includes the number recited. Numbers preceded by a term such as “approximately”, “about”, and “substantially” as used herein include the recited numbers (e.g., about 10%=10%), and also represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, and “substantially” may refer to an amount that is within less than 10% of, within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of the stated amount.