Abstract:
A device and method for a minimally invasive surgical implantation to reduce radicular symptoms by inserting an expandable cervical distraction implant in the facet joint and distracting the adjacent cervical vertebrae to increase the foraminal dimension. The implant, when positioned in the cervical facet joint, expands to via delivery of an inflation medium to increase the space between the vertebrae, thereby increasing the foraminal area or dimension, and reducing pressure on the nerves and blood vessels of the cervical spine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 11/618,619 filed on Dec. 29, 2006, incorporated herein by reference in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0003]    Not Applicable 
       NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION 
       [0004]    A portion of the material in this patent document is subject to copyright protection under the copyright laws of the United States and of other countries. The owner of the copyright rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office publicly available file or records, but otherwise reserves all copyright rights whatsoever. The copyright owner does not hereby waive any of its rights to have this patent document maintained in secrecy, including without limitation its rights pursuant to 37 C.F.R. § 1.14. 
       BACKGROUND OF THE INVENTION 
       [0005]    1. Field of the Invention 
         [0006]    This invention pertains generally to an implantable distraction device, and more particularly to a cervical distraction device. 
         [0007]    2. Description of Related Art 
         [0008]    Chronic back problems cause pain and disability for a large segment of the population. Adverse spinal conditions are characteristic of age. With aging, generally comes an increase in spinal stenosis (including, but not limited to, central canal and lateral stenosis), and facet arthropathy. Spinal stenosis results in a reduction of foraminal area (i.e., the available space for the passage of nerves and blood vessels) which compresses the cervical nerve roots and causes radicular pain. Extension and ipsilateral rotation of the neck further reduces the foraminal area and contributes to pain, nerve root compression, and neural injury. However, neck flexion generally increases the foraminal area. 
         [0009]    Cervical disc herniations predominantly present with upper extremity radicular symptoms. The vast majority of these herniations do not have an associated neurologic deficit and present with pain only. A well-described treatment for cervical disc herniations is closed traction. There are a number of marketed devices that alleviate pain by pulling on the head to increase foraminal height. 
         [0010]    Cervical disc herniations have been treated with anterior and posterior surgery. The vast majority of these surgeries are performed through an anterior approach, which requires a spinal fusion. These surgeries are expensive and beget additional surgeries due to change in biomechanics of the neck. There is a 3% incidence of re-operation after cervical spine surgery. 
         [0011]    Therefore, an object of the present invention is to provide a minimally invasive device and surgery to increase foraminal height reduce radicular symptoms for patients with disc herniations. 
         [0012]    At least some of these objectives will be met in the following disclosure. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    A device and technique are disclosed for a minimally invasive surgical implantation to reduce radicular symptoms by inserting an expandable cervical distraction implant in the facet joint at an affected level to preserve the physiology of the spine. In particular, embodiments of the present invention provide for distracting the cervical spine to increase the foraminal dimension in extension and neutral positions. The implant of the present invention, when positioned in the cervical facet joint, expands to distract, or increase the space between, the vertebrae to increase the foraminal area or dimension, and reduce pressure on the nerves and blood vessels of the cervical spine. 
         [0014]    The procedure may be performed under conscious sedation in order to obtain intra-operative patient symptom feedback. 
         [0015]    When the distraction implant is optimally positioned in the facet joint, it is injected with a bio-inert hydrogel using a catheter inflation syringe with pressure/volume monitor. The injection of the hydrogel causes the implant to expand in order to achieve cervical distraction. At this point in the procedure, patient feedback regarding symptom improvement could be obtained. 
         [0016]    After achieving the desired distraction, the catheter is detached from the distraction implant and be removed. The patient is left with the distraction implant expanded in the facet joint with permanent increased foraminal height. 
         [0017]    Aspect of the invention is an apparatus for distracting first and second adjacent vertebrae. The apparatus has an expandable implant configured to be inserted in a collapsed configuration within a facet joint bounded by the first and second vertebrae, and expand within the facet joint to increase a foraminal dimension, e.g. foraminal height associated with the first and second adjacent vertebrae. 
         [0018]    Preferably, the expandable implant is configured to be installed in a facet joint located between at least one cervical vertebra. However, other locations are contemplated. 
         [0019]    In one embodiment, the expandable implant is configured to engage the articulating surfaces of the facet joint to increase the distance between the articulating surfaces, the distance correlating to the foraminal dimension. 
         [0020]    The expandable implant may comprises an inflatable balloon configured to be filled with an inflation medium, e.g. hydrogel or the like, to distribute a compressive load on the articulating surfaces. 
         [0021]    Generally, the facet joint has a joint capsule that extends beyond the margin of the articulating surfaces. In a preferred embodiment, the expandable implant is configured to be delivered into the facet joint through an access hole created in the joint capsule. The expandable implant is ideally configured such that, in its expanded configuration, is larger than the access hole so that the expandable implant is retained in the facet joint once expanded. The expandable implant may also be configured to plug the access hole once expanded. Typically, the expandable implant is configured to occupy a substantial portion of the depth of the facet joint once expanded. 
         [0022]    In another preferred embodiment, the expandable implant is configured to dynamically stabilize the facet joint. Generally, the expandable implant increases and maintains a minimum distance between the articulating surfaces, while allowing motion of the first vertebrae with respect to the second vertebrae. 
         [0023]    For delivery, the expandable implant preferably attaches to a distal tip of a catheter to facilitate installation into the facet joint. The catheter transports the inflation medium into the expandable implant. The expandable implant is configured to detach from the catheter once the implant is expanded in the facet joint. 
         [0024]    Another aspect is a method of minimally invasively distracting first and second adjacent vertebrae. The method includes the steps of inserting an expandable implant, in a collapsed state, into a facet joint bounded by the first and second vertebrae, and expanding the expandable implant within the facet joint to increase a foraminal dimension associated with the first and second vertebrae. 
         [0025]    In a preferred embodiment, the expandable implant is installed in a facet joint located between at least one cervical vertebra. The expandable implant engages the articulating surfaces of the facet joint to increase the distance between the articulating surfaces. 
         [0026]    In many embodiments, inserting an expandable implant is achieved by creating an access hole through the joint capsule, and inserting the expandable implant in a collapsed configuration through the access hole and into the facet joint. Typically, the access hole is created with an introducer needle used to deliver the expandable member. 
         [0027]    In a preferred embodiment, an inflatable balloon is filled with an inflation medium causing the balloon to engage the articulating surfaces the expandable implant. A compressive load is imparted on the articulating surfaces to distract the first vertebra from the second vertebra. 
         [0028]    To inflate the expandable implant, a catheter is fed through the access hole and into the facet joint with the expandable implant attached to a distal tip of a catheter. An inflation medium is then delivered into the expandable implant via the catheter to inflate expandable implant with the inflation medium. Once inflated, the expandable implant detaches from the catheter once the implant is expanded in the facet joint. 
         [0029]    Dynamic stabilization of the facet joint is affected as a result of the expanded implant being disposed between the articulating surfaces of the facet joint. The distance between the articulating surfaces is maintained while allowing motion of the first vertebrae with respect to the second vertebrae. 
         [0030]    In one embodiment, the extent of inflation of the expandable member is determined via patient feedback while the expandable member is being inflated. 
         [0031]    Another aspect is a system for distracting a first vertebra from a second adjacent vertebra. The system includes a catheter and an expandable implant configured to be detachably installed in a collapsed configuration on the distal tip of the catheter. The expandable implant and catheter are configured to be inserted in into a facet joint bounded by the first and second vertebrae to expand the expandable implant within the facet joint to increase a neural foraminal height associated with the first and second vertebrae. 
         [0032]    Further aspects of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0033]    The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only: 
           [0034]      FIG. 1  is a lateral view of two cervical vertebral members in a stenosed condition. 
           [0035]      FIG. 2  is a view of an introducer needle being inserted into the facet joint of the vertebral members in accordance with the present invention. 
           [0036]      FIG. 3  illustrates an implant of the present invention being inserted into the facet joint. 
           [0037]      FIG. 4 . illustrates the implant of  FIG. 3  in an expanded configuration. 
           [0038]      FIG. 5  illustrates the implant of  FIG. 4  with the catheter detached from the implant and removed from the treatment site. 
           [0039]      FIG. 6  is another view of the placement of the implant in the facet joint in accordance with the present invention. 
           [0040]      FIG. 7  is an expanded view of the implant installed in a collapsed configuration on a catheter. 
           [0041]      FIG. 8  illustrates the implant of  FIG. 7  in an expanded configuration. 
           [0042]      FIG. 9  illustrates an implant of the present invention having a circular cross-section. 
           [0043]      FIG. 10  illustrates an implant of the present invention having an oval cross-section. 
           [0044]      FIG. 11  illustrates an implant of the present invention having a rectangular cross-section. 
           [0045]      FIG. 12  illustrates an implant of the present invention having 2-piece design. 
           [0046]      FIG. 13  illustrates an implant of the present invention having a taper along its length. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0047]    Referring more specifically to the drawings, for illustrative purposes the present invention is embodied in the apparatus generally shown in  FIG. 2  through  FIG. 13 . It will be appreciated that the apparatus may vary as to configuration and as to details of the parts, and that the method may vary as to the specific steps and sequence, without departing from the basic concepts as disclosed herein. 
         [0048]      FIG. 1  illustrates a simplified lateral view of a portion of the cervical spine  10 . The basic biomechanical unit or motion segment of the spine consists of two adjacent vertebrae  12  and  14  and the three joint articular complex through which they move and are constrained in relation to one another. The spine articulations generally consist of an intervertebral disc  26  located between the vertebral bodies  26  of adjacent vertebrae  12 ,  14 , and two facet joints  16  symmetrically located laterally from the sagittal plane at the posterior end of the vertebral bodies  26 . 
         [0049]    The facet joints  16  allow constrained spinal motion, while protecting the contained neural structures. From a kinematic viewpoint, the intervertebral facet joints  16  are highly constrained sliding planar articulations, lubricated by synovial fluid contained within the facet joint capsule  30 . In the cervical spine, the geometry of the cervical vertebral bodies provides a high degree of protection for the neural elements by limiting normal motion of the spine to within physiologic limits. The upward inclination of the superior articular surfaces of the facet joints allows for considerable flexion and extension, as well as for lateral mobility. 
         [0050]    Minimally invasive surgical access to the facet joint is well documented. Each vertebral segment comprises a spinous process  34  located at the posterior end of the vertebrae, with the vertebral body located anteriorly. Each vertebra comprises an inferior articular (or transverse) process  35  and the superior articular process  37  that form four posterior articulating, e.g. opposing subchondral, surfaces: two superior facets  18  and two inferior facets  16 . The inferior facet  18  from the inferior articular process  35  of the upper vertebra  12  and the superior facet from the superior articular process  37  of the lower vertebra  14  form the facet joint  16  on each lateral side of the spine. 
         [0051]    Located medial to the articular processes  37  and vertebral bodies  26  is an aperture, or intervertebral foramina  38 , that serves as a nerve root canal for the spinal nerves and vessels that transmit signals from the spinal chord to respective locations in the body. 
         [0052]    Each facet joint  16  is covered by a dense, elastic articular capsule  28 , which is attached just beyond the margins of the articular facets  18 ,  22 . The inside of the capsule is lined by a synovial membrane (not shown) which secretes synovial fluid for lubricating the facet joint. The exterior of the joint capsule is surrounded by a capsular ligament (not shown), which may be temporarily repositioned to give access for insertion of the extendable implant of the present invention, described in further detail below. Thus, from a posterior-lateral approach, access to the facet joint  16  is relatively straightforward and well prescribed, as compared to other regions of the spine which present a higher likelihood of trauma and risk of permanent damage. 
         [0053]    It should also be noted that  FIG. 1  depicts cervical foraminal stenosis, e.g. loss of height between the adjacent vertebrae  12 ,  14 . As a result of disc  36  herniation and corresponding height loss, the nerve root canal  38 , or intervertebral foraminal height, having a value H s , is narrowed relative to that of healthy anatomy. This narrowing of the foraminal height H s  often leads to compression of the spinal cord and nerve roots (not shown), causing radicular symptoms. 
         [0054]    As a result of the stenosed foraminal height H s , the height of the facet joint  16 , or distance between subchondral articulating surfaces  18  and  22 , is also narrowed, (shown as value D s  in  FIG. 1 ). This may pose complications in the facet joint  16  as well. However, more importantly, because the height of the disc will be relatively fixed, an increase in the facet joint height will also have a corresponding increase in foraminal height, as described in greater detail below. 
         [0055]      FIGS. 2-6  show the methods and system  50  of the present invention for performing a minimally invasive procedure configured to distract one or more of the facet joints  16  of vertebrae  12 ,  14 , thereby increasing the dimension of the neural foramen while retaining facet joint mobility. One of the major advantages of minimally invasive surgery is the ability to perform the procedure with minimal tissue trauma. Television image intensifier fluoroscopy may be used to provide guidance for surgeon placement of instrumentation and implants precisely to the desired anatomic target in the facet joint  16 . The radiographic landmarks are well taught and the relative procedural difficulty of this technique is low. 
         [0056]    Referring to  FIG. 2 , a standard discography introducer needle  44  (e.g. approximately 21 gauge needle) is be inserted into the outer facet capsule  28  to create a perforation or access hole  32  into the facet joint cavity  30 . Dye may then be injected through the introducer needle  44  to fluoroscopically confirm that the introducer needle  44  is in the facet joint cavity  30 . 
         [0057]    Referring now to  FIG. 3 , a catheter  52  having an expandable implant  60  coupled to the distal end  54  of the catheter  52 , may then be guided over into the facet joint cavity  30  through needle  44  such that the distal tip  42  of the implant is located in the proper position in cavity  30 . 
         [0058]    Once the implant  60  is placed at the correct location of the facet joint  16 , the implant is injected with a bio-inert hydrogel to inflate the catheter. Inflation may be achieved with a catheter inflation syringe  56 , and the pressure and/or volume may be observed via monitor  58 . Further visualization may be achieved by including a contrast dye within the hydrogel. The hydrogel and expandable balloon may be similar to the materials found in the HyperGlide Occlusion Balloon Catheter by Micro Therapeutics, Inc., used for vascular occlusions. 
         [0059]      FIG. 4  illustrates the implant  60  in an expanded configuration within the facet joint. As shown in  FIG. 4 , the hydrogel-inflated expandable implant  60  generates an outward compressive force F on the subchondral surfaces  18  and  22  to increase the distance between them to a desired treatment or nominal value D T . This correspondingly increases the height of the intervertebral foramin to a treatment or nominal value H T . The value of D T , and resulting increase in H T  may be predetermined by the surgeon prior to the surgery based on pre-op analysis of the patient&#39;s condition and anatomy, and/or may also be iteratively devised by patient feedback of symptom improvement during the procedure. 
         [0060]    The size of implant  60  is configured to distract the joint and reverse narrowing of the nerve root canal  38  and alleviate symptoms of cervical stenosis. However, it is also within the scope of the present invention to size the implant according to other spinal conditions, for example to correct for cervical kyphosis or loss of cervical lordosis. 
         [0061]    Once the desired inflation/distraction is achieved, the catheter  52  is detached from the implant  60 , and fed out of the patient&#39;s body. Referring now to  FIG. 5 , the expanded implant  60  will occupy the joint cavity  30  such that it will occlude the opening  32  in the facet capsule  28 . Because the inflated implant  60  is larger than the opening  32  caused by the violation of the joint by the introducer needle  44 , the implant  60  acts as a plug to close off the joint cavity  30 . In addition, because the implant is confined within the boundaries of the joint cavity  30 , including the facet surfaces  18 ,  22  and capsule  28 , it will remain in its installed position without further anchoring to hold the device in place. Due to the properties of synovial joints and the configuration of the implant  60 , it is unlikely that the implant  60  will extrude from the joint once it has been implanted. If further constraint is desired, the external walls of the balloon may be fabricated to have a surface roughness or texture configured to inhibit motion with respect to the walls  18 ,  22  of the facet joint. 
         [0062]    If symmetrical distraction is desired between the adjacent vertebrae, the procedure may be repeated for the second facet joint located between the target vertebrae. However, it is contemplated that only one implant may be necessary to alleviate radicular symptoms. 
         [0063]      FIG. 6  illustrates a preferred placement of the implant  60  within the facet joint  16 . The average width of the cervical facet is approximately 9 mm. The average depth of the cervical facet is also approximately 9 mm. The preferred location of the capsule is generally the center third of the facet joint cavity  30 , as its approximate size will be about 3-4 mm in width, as shown in  FIG. 6 . The length of the implant  60  will be approximately 8-9 mm, or roughly the depth of the facet joint cavity  30 , and therefore may preferably occupy all or nearly all of the joint depth. Preferably, the implant  60  will be configured to expand to up to a height of approximately 3 mm or more. It is appreciated that the above sizing of the implant may vary accordingly to accommodate patient anatomy, condition, or desired foraminal height increase or other preferences defined by the surgeon. 
         [0064]    The size, configuration, and placement of implant  60  are configured to provide distraction of the facet joint, while also preserving the mobility between the adjacent vertebrae  12 ,  14 . For example, translation of the articular surfaces  18 ,  22  with respect to each other (e.g. along the plane of the surfaces) is not restrained, while the undesired translation normal to the articular surfaces  18 ,  22 , (e.g. collapsing), is inhibited. Additionally, the adjacent vertebrae  12 ,  14  are allowed to rotate about the long axis of the implant  60  with respect to each other, as well as rotate about the spinal column axis. Thus, the implant  60  of the present invention allows for dynamic stabilization and distraction of the facet joint to increase and maintain foraminal height. 
         [0065]      FIG. 7  illustrates an expandable balloon implant  60  in a collapsed configuration and attached to distal end  54  of catheter  52 . The walls  72  of the balloon may be folded over along the length L of the balloon to minimize the profile of the balloon  60 . 
         [0066]      FIG. 8  illustrates expandable balloon implant  60  in its expanded configuration. Balloon implant  60  is generally comprised of one or more exterior walls that are configured to hold and retain the inflatable medium, e.g. hydrogel. In some embodiments, the implant  60  may have a central lumen (not shown), emanating at proximal end  76 , and terminating at distal end  74  through the length L of the balloon. The central lumen allows the implant  60  to be fed over a guide wire, or like device, to the target location in the facet joint  16 . 
         [0067]    The proximal end  76  will also have a port  70  allowing flow of the inflation medium into the bladder of the balloon. This port  70  may be self-sealing, wherein the port automatically seals upon detaching catheter  52 , or may incorporate a plug (not shown) or other sealing mechanism that may be fed over guide wire  40  to close and seal up port  70  once the catheter  52  is removed. 
         [0068]    The cross section of the implant may comprise a variety of different shapes, as shown in  FIGS. 9-12 . In  FIG. 9 , balloon implant  80  comprises an outer wall  82  having a generally circular shape, thus creating a cylindrical structure across the length of the balloon. The thickness T of the external wall  82  is configured to withstand the compressive loads associated with the facet joint in the cervical spine, and may be varied accordingly. With the cylinder shape implant  80 , the outer wall will generally contact and engage the facet surfaces  18 ,  22  in a line down the depth of the facet cavity  30 . The diameter D of the outer wall  82  will be sized for the desired increase of the foraminal height, e.g. ranging from approximately 1 mm to over 3 mm. 
         [0069]    As illustrated in  10 , balloon implant  90  may comprise a elliptical or oval cross section, having a height H sized for desired increase of the foraminal height, and width W. A rectangular cross section may also be used, as shown with implant  100  of  FIG. 11 . 
         [0070]    The implants  80 ,  90  and  100  may be fabricated by a number of methods currently available in the art. For example, the implant may be formed as a single piece structure over a mandrel (not shown) having varying cross section for the central lumen (if needed) and outer walls  82 ,  92 ,  102 . 
         [0071]    In an alternative embodiment shown in  FIG. 12 , the balloon  110  may comprise a bladder having upper wall  114  and lower wall  115  that are heat sealed at the sides  112 . 
         [0072]    As illustrated in  FIG. 13 , the balloon may also be tapered along its length to accommodate the anatomy of the facet joint  16 , as seen with balloon  120 , wherein the leading or distal end  124  has a smaller profile than the trailing or distal end  126 . 
         [0073]    The extendable implants above may comprise an elastic material, e.g. biocompatible polymer, which allows the implant to expand to a varying range in sizes. Alternatively, the implant may comprise an inelastic material that has a maximum inflation capacity, and wherein a number of predetermined sizes may be available to the surgeon according to the desired size determined by the surgeon. 
         [0074]    The implant  60  will generally be sized to accommodate the geometry of the patient anatomy and target foraminal height. For cervical herniations, the implant  60  will typically be installed from the C4/C5 joint down to C7/T1 (95% of all cervical herniations occur at C5/6 &amp; C6/7). The height of the implant  60  may range from approximately 1 mm to over 3 mm, depending on the patient anatomy. For the cylindrical-shaped balloon  80  of  FIG. 9 , the width will roughly equal the height. However, as shown in  FIGS. 10-12 , the width may be increased for the desired stabilizing effect. 
         [0075]    Although the embodiments disclosed above are directed primarily to installation in the cervical facet joint, it is contemplated that the devices and methods may also be used to increase foraminal dimension in other regions of the spine, e.g. thoracic, lumbar, etc. 
         [0076]    Although the description above contains many details, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.”