referring more specifically to the drawings , for illustrative purposes the present invention is embodied in the apparatus generally shown in fig2 through fig1 . 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 . fig1 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 . 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 . 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 . 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 . 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 . it should also be noted that fig1 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 . 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 fig1 ). 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 . fig2 - 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 . referring to fig2 , 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 . referring now to fig3 , 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 . 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 . fig4 illustrates the implant 60 in an expanded configuration within the facet joint . as shown in fig4 , 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 . 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 . 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 fig5 , 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 . 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 . fig6 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 fig6 . 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 . 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 . fig7 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 . fig8 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 . 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 . the cross section of the implant may comprise a variety of different shapes , as shown in fig9 - 12 . in fig9 , 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 . 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 fig1 . 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 . in an alternative embodiment shown in fig1 , the balloon 110 may comprise a bladder having upper wall 114 and lower wall 115 that are heat sealed at the sides 112 . as illustrated in fig1 , 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 . 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 . 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 fig9 , the width will roughly equal the height . however , as shown in fig1 - 12 , the width may be increased for the desired stabilizing effect . 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 . 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 .”
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 .