Abstract:
A spine implant includes an insert positioned between facets of a zygapophyseal joint. In various embodiments, the insert is configured to exert a distraction force on one or more facets of the zygapophyseal joint. The insert may comprise one or more members having one or more opposing facet interfacing portions. A securing member is configured to interface with the insert to secure the facets.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of application Ser. No. 13/346,435, filed Jan. 9, 2012 and entitled “Facet Device and Method,” which is a continuation of application Ser. No. 12/169,370, filed Jul. 8, 2008 and entitled “Facet Device and Method,” now U.S. Pat. No. 8,114,158, which is a continuation-in-part of application Ser. No. 11/197,566, filed Aug. 3, 2005 and entitled “Facet Device and Method,” now abandoned, which claims the benefit of U.S. Provisional Application No. 60/598,882, filed Aug. 3, 2004 and entitled “Spine Treatment Devices and Methods,” all of which are incorporated by reference herein in their entireties for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to devices to treat the spine, in particular in association with a facet joint, including but not limited to spinal stabilization devices, spinal distraction devices, spinal prostheses, devices to treat pain associated with the spine, and other spinal treatment devices. 
     DESCRIPTION OF THE RELATED ART 
     Certain spine conditions, defects, deformities (e.g., scoliosis) as well as injuries may lead to structural instabilities, nerve or spinal cord damage, pain or other manifestations. Back pain (e.g., pain associated with the spinal column or mechanical back pain) may be caused by structural defects, by injuries or over the course of time from the aging process. For example, back pain is frequently caused by repetitive and/or high stress loads on or increased motion around certain boney or soft tissue structures. The natural course of aging leads to degeneration of the disc, loss of disc height, and instability of the spine among other structural manifestations at or around the spine. With disc degeneration, the posterior elements of the spine bear increased loads with disc height loss, and subsequently attempt to compensate with the formation of osteophytes and thickening of various stabilizing spinal ligaments. The facet joints may develop pain due to arthritic changes caused by increased loads. Furthermore, osteophytes in the neural foramina and thickening of spinal ligaments can lead to spinal stenosis, or impingement of nerve roots in the spinal canal or neural foramina. Scoliosis also creates disproportionate loading on various elements of the spine and may require correction, stabilization or fusion. 
     Pain caused by abnormal motion of the spine has long been treated by fixation of the motion segment. Spinal fusion is one way of stabilizing the spine to reduce pain. In general, it is believed that anterior interbody or posterior fusion prevents movement between one or more joints where pain is occurring from irritating motion. Fusion typically involves removal of the native disc, packing bone graft material into the resulting intervertebral space, and anterior stabilization, e.g., with intervertebral fusion cages or posterior stabilization, e.g., supporting the spinal column with internal fixation devices such as rods and screws. Internal fixation is typically an adjunct to attain intervertebral fusion. Many types of spine implants are available for performing spinal fixation, including the Harrington hook and rod, pedicle screws and rods, interbody fusion cages, and sublaminar wires. 
     Alternatives have been proposed and tested to replace the need for spinal fusion to treat patients with back pain. These implants include artificial discs and artificial nucleus technologies that preserve motion. However, these implants do not directly address the forces borne by the facet joints. 
     The facet joints provide a means for load transmission, support and motion of the posterior spinal column. Disc height loss from degenerative disc disease and aging leads to increased load on the facet joints, which can lead to arthritic, painful, degenerative changes. 
     Often over the course of degenerative disc disease there is a narrowing of the neural foramen through which the nerves exit the spine. In addition to the degeneration of discs causing the narrowing of the foramen, there is also calcification around the foramen causing further narrowing or stenosis resulting in pain to the patient. Currently, these conditions may be treated by removing some or all of the lamina (laminectomy) or posterior bone adjacent or around the stenotic neural foramen 
     Given that the facet joint and its environs is a source of pain for some patients, some procedures have been developed or proposed to relieve pain associated with the facet joint. Partial or complete removal of the pathological facets, and replacement with a mechanical joint that preserves motion similar to a facet has been proposed. Additionally, individual degenerative facet articulations have been replaced with caps. 
     It would be desirable to provide improved devices and methods for relieving pain associated with the facet joints. 
     Spinal stenosis pain or from impingement of nerve roots in the neural foramina has been treated by laminectomy and foraminotomy, and sometimes reinforced with rod and screw fixation of the posterior spine. 
     More recently, as an alternative to laminectomies and related procedures, implants have been proposed that distract the spine from a posterior approach. In particular, a wedge-like implant inserted between two adjacent spinous processes has been proposed to relieve pressure on spinal nerves and nerve roots. A kyphosis is induced, which opens the space of the spinal canal and neural foramen, thereby reducing the effect of spinal stenosis. However, this type of distraction of adjacent spinous processes is suboptimal for several reasons: The resulting kyphosis is non-physiologic, leading to increased load on the anterior portion of the disc and the vertebral bodies. This can increase the risk of disc degeneration and vertebral compression fracture. The implant tends to bend the spine forward. The spinous processes may fracture due to the distraction forces of the wedge implant. Bone may collapse around the spinous process. The implant may weaken, tear, or stretch stabilizing ligaments of the spine, such as the supraspinous ligament, interspinous ligament, ligamentum flavum, posterior longitudinal ligament, or capsule of the zygapophyseal joint. The amount of distraction is not adjustable to the specific amount of stenosis, and cannot be easily readjusted months to years after the device has been implanted. 
     It would accordingly be desirable to provide a distraction device that reduces or avoids some or all of these issues. 
     Pain due to instability of the spine has also been treated with dynamic stabilization of the posterior spine, using elastic bands that connect pedicles of adjacent vertebrae. 
     The typical techniques for fusion, decompression, and dynamic stabilization require open surgical procedures with removal of stabilizing muscles from the spinal column, leading to pain, blood loss, and prolonged recovery periods after surgery due in part to the disruption of associated body structures or tissue during the procedures. 
     Accordingly, it would be desirable to provide less invasive devices and methods for treating pain or discomfort associated with the spinal column. It would also be desirable to provide such devices and methods that are less damaging to associated tissue. 
     Spine surgeons commonly use metallic or polymeric implants to effect or augment the biomechanics of the spine. The implants frequently are attached or anchored to bone of the spine. Sites typically considered appropriate for boney attachment have high density or surface area, such as, for example, the pedicle bone, the vertebral body or the cortical bone of the lamina. The spinous process contains thin walls of cortical bone, and thus, has been considered as not ideal for anchoring spinal implants as they may not support the implants under physiologic loads, or the intermittent high loads seen in traumatic situations. Fixation has been attempted from spinous process to spinous process with poor results. 
     A translaminar facet screw as used by some surgeons goes through the base of spinous process to access the cancellous bone of the lamina. A disadvantage of this device is that it is not suitable for attaching to a pedicle screw and the depth and angle during deployment can be very difficult to track or visualize, thus increasing the possibility that the screw would extend into the spinal canal. A facet screw is screwed between opposing facets of a zygapophyseal joint. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is directed to providing a device and method for alleviating discomfort and or deformity associated with the spinal column. Another aspect of the present invention is directed to providing a minimally invasive implant and method for alleviating discomfort associated with the spinal column. Another aspect of the present invention provides an anchoring device and method that requires less surrounding tissue damage or disruption. Other aspects of the invention may supplement or bear load for degenerated or painful joints, e.g., the facet joint. 
     One aspect of the invention provides for repair or reconstruction of a dysfunctional facet joint. For example, by entering the capsule of the facet joint, creating a space between articulating facets by removing synovium, cartilage, and some bone from within the zygapophysial joint, and, then, inserting a motion preserving prosthesis. Motion preserving prostheses may include a smooth and/or curved surface, a sphere, an egg shaped/oval implant, or a self contained “ball and socket” joint. Magnetic plates with like poles facing each other may be attached to interfacing articulating portions of the facets. Attachment of the motion preserving prosthesis may involve extensions from the prosthesis that partially or completely penetrate each of the facets. 
     Another aspect of the invention provides for repairing the encapsulating ligaments with suture, adhesive, a patch, or other materials after a capsule of the zygapophysial joint has been invaded for tissue removal and insertion of a prosthesis. One aspect of the invention includes an elastic encapsulating wrap used to stabilize the facet joints. 
     According to an embodiment of the invention, a facet distraction implant is provided for maintaining a space that is formed between the facet articulations of adjacent vertebrae when the joints are distracted. The facets may be distracted using a known distraction method or technique and an implant may be placed between the facets. A securing device according to the invention may be positioned to anchor each of the facet articulations of a facet joint to each other in distraction to maintain the opening of the corresponding neural foramen. The prosthesis may include a distraction element that exerts a distracting force on the joint. 
     Various aspects of the invention are set forth in the description and/or claims herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of a facet implant in accordance with the invention. 
         FIG. 2  is a schematic side view of a facet implant in accordance with the invention. 
         FIG. 3  is a schematic posterior lateral perspective view of a facet implant in accordance with the invention. 
         FIG. 4  is a side partial cross section of a facet implant in accordance with the invention. 
         FIG. 5  is a side partial cross section of a facet implant in accordance with the invention. 
         FIG. 6  is a schematic posterior lateral perspective view of a stenotic neural foramen of a posterior spine. 
         FIG. 7  is a schematic posterior lateral view of a facet implant in accordance with the invention. 
         FIG. 8  is a side schematic view of a facet implant in accordance with the invention. 
         FIG. 9  is a side schematic view of a facet implant in accordance with the invention. 
         FIG. 10  is a side schematic view of a facet implant in accordance with the invention. 
         FIG. 11  is a side schematic view of a facet implant in accordance with the invention. 
         FIG. 12  is a side schematic view of a facet implant in accordance with the invention. 
         FIG. 13  is a side schematic view of a facet implant in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIGS. 1-5  illustrate facet repair prostheses in accordance with an embodiment of the invention. Prosthesis  410  comprises a ball bearing  411  implanted between the caudal and the cephalic facets  412 ,  413  of the zygapopyhseal joint. ( FIG. 1 ) The joint is prepared by removing soft tissue between the joints and creating a concavity on adjacent facet plates for receiving the ball bearing. 
     In  FIG. 2 , magnets  415 ,  416  including smooth interacting bearing surfaces are respectively screwed into the cephalic and caudal facets  417 ,  418  of the zygapopyhseal joint  419 . The magnets  415 ,  416  are oriented so that like poles face each other (e.g. North-North or South-South) to provide a distraction force at the joint. The magnets may have a center hole through which a rod is inserted to resist the tendency of one magnet to move relative to the other. Each end of the rod may have a diameter larger than the center holes. This system may be used in other joints in the body to maintain separation between the joints. 
     Referring to  FIG. 3 , a joint prosthesis  420  is positioned between the cephalic and caudal facets  426 ,  427 . The prosthesis comprises a ball  421  providing a bearing surface for the motion of the facets  426 ,  427 , and opposing posts  422 ,  423  screwed in or otherwise implanted in the facets  426 ,  427 , respectively for securing the ball  421  within the joint. The ball  421  may include openings for receiving the posts, e.g., in a tapered interference type fitting, to secure the posts  422 ,  423  to the ball  421  and to secure the ball  421  within the joint. 
     This facet repair may be performed percutaneously or via minimally invasive surgical techniques, for example using percutaneously positioned distracting instruments to distract the joint, for example, an expanding balloon or forceps like distractors. Using a hollow needle percutaneously positioned into the joint, an expandable or self-expanding facet distraction implant may be placed in position through the hollow lumen of the needle into the joint. A polymer material may be injected into the joint through a percutaneously inserted needle. 
       FIG. 4  illustrates a material  440  such as a polymer injected between the cephalic and caudal facets  426 ,  427 . The material  440  forms a flexible member  441  that allows some movement of the joint due to the flexible properties and/or the shape that permit articulation of the joint. A securing member  442  extends through the facets  426 ,  427  and the material  440  to further hold the member  441  in place in the joint capsule and/or to prevent implant extrusion. The securing member  442  includes anchors  443 ,  444  that anchor to the outside or within the facets  426 ,  427  to hold the securing member  442  in place while permitting some motion for example through spacing at or in the joint. The securing member  442  may for example, comprise a screw, or may be constructed of a flexible material such as a flexible polymer. The securing member may also comprise a band constructed of fibers strands such as Kevlar™, polypropylene or polyethylene, or constructed of a fiber reinforced polymer. The anchors  443 ,  444  may be of a material such as titanium, or PEAK that may be screwed or crimped on to the securing member  442 . The polymer may be injected into the joint capsule into opening  443   a  in the anchor  443 , through a lumen  442   a  in the securing member  442  and through holes  442   b  or pores in the securing member  442 . This may be done when the joint is distracted or otherwise positioned as desired. 
       FIG. 5  illustrates a material  450  such as a polymer injected between the cephalic and caudal facets  426 ,  427 . The material  450  forms an implant  451  that allows some movement of the joint due to the flexible properties and/or a shape that permits articulation of the joint. A securing member  452  extends through the facets  426 ,  427  and the material  450  to further hold the implant  451  in place in the joint capsule. The securing member  452  includes an anchor  453  that anchors the member to the outside or within the facet  426 , (or alternatively to the outside or within the facet  427 ) to hold the securing member  452  in place. The securing member  452  further includes a tapered end that allows the securing member  452  to be inserted through the joint capsule and anchored into facet  427 . The securing member may be a screw with a threaded tip  454  that screws into the bone. The securing member can further include a flexible portion that allows some movement of the securing member and joint. The anchor  453  may include an opening  453   a  into a lumen  452   a  in the securing member  452 , for injecting a polymer into a lumen  452   a  in the member and then through holes  452   b  into the joint capsule to form the implant  451 . 
     According to the invention, a facet joint device as described herein may be used in combination with an artificial disc or other spinal implants, e.g., to maintain the integrity of the facets. The facet joint distraction or replacement devices and procedures described herein may be used in conjunction with anteriorly placed implants, e.g., in a load sharing arrangement. The facet joint resurfacing, distraction or augmentation as well as the anterior implants may be used with a process to pedicle distraction or stabilizing device as described herein. Various spinal implants may also be used with facet resurfacing, facet distraction or augmentation procedures. 
     In accordance with one aspect of the invention, narrowing or stenosis of the neural foramen may be treated using a device configured to distract the facet joint. Accordingly, a distraction system is provided for distracting the facet joint. 
     Referring to  FIG. 6 , a portion of the spine is illustrated with adjoining vertebrae prior to distraction. The neural foramen  250  between a first vertebra  251  and a second vertebra  252  is stenotic. At the zygapophyseal joint capsule  253 , there is no gap between the cephalic and caudal facets  254 ,  255 . 
     Referring to  FIG. 7 , the portion of the spine of  FIG. 6  is illustrated with a facet distracter implant  256  in place between the cephalic facet  254  and the caudal facet  255 . The implant  256  comprises a distracting portion  257  and anchors  258 ,  259  comprising barbs or bone anchors. The distracting portion may include a distracting element as described with respect to  FIGS. 8-13  herein. The anchor  258  is positioned in bone above the cephalic facet  254  while the anchor  259  is positioned in the bone below the caudal facet  255 . The facet distracter implant  256  includes a sensor  256   a , the type of which may be selected to sense one of a number of different parameters. Pressure sensors, strain gauges, or other sensors may be used to sense load seen by the facet joint. This information may be used to monitor the condition of the facet joint or determine if fusion may be necessary. The other facet joint implants described herein may also include similar sensors. 
     The procedure for implanting the device generally includes opening the zygapophyseal joint capsule with a scalpel. Then the adjacent vertebrae are distracted by one of a number of known distraction methods or by distracting the joint mechanically using devices such as a wedge or expanding rod or balloon between adjacent spinous processes, or between other parts of adjacent vertebrae. The tissue between the facets  254 ,  255  is then debrided and/or denervated. The implant is then inserted between the facets  254 ,  255  after the joint is distracted. The anchors  258 ,  259  engage the interfacing portions of the bone of the facets  254 ,  255 . 
       FIG. 8  illustrates a distracter implant  260  positioned between facets  254 ,  255 . The distracter implant  260  comprises a block  261  wedged between the facets  254 ,  255 . In  FIG. 9  an alternative distracter  262  implant comprises a ball  263 . In  FIG. 10  an active distracter implant  265  comprise a coiled spring  266 . In  FIG. 11 , the distracter implant  265   a  comprises an expandable polymer  266   a , e.g., a hydrogel or expandable gel foam. In  FIG. 12  the distracter implant  267  comprise an expandable member  268  that may be expanded to distract the joint  253  by inflating with a curable polymer, a liquid, gas or other material. The distraction may occur after implantation to adjust the level of distraction. The expandable member may also be adjusted after implanting by increasing or removing the inflation medium, e.g. using a needle or accessing the member through a one-way valve.  FIG. 13  illustrates a shrink-wrap  269  placed partially around the joint  253 . The shrink-wrap or other material comprises, e.g., a Dacron material that holds the block  261  or other implant in place between facets  254 ,  255 . The material may encourage ingrowth of tissue. The material may be coated with a material that reduces tissue ingrowth to permit the joint to move or reduces adhesions to prevent pain. The material may include burrs or barbs that secure the material to the bone or it may be secured, e.g. with suture anchors. The implants may be constructed, for example, of a metal, polymer or ceramic, may be coated or imbedded with therapeutic agents (e.g. a steroid or lidocaine) or other material.