Abstract:
A method of performing vertebral facet fusion by lateral approach and related devices. The lateral approach to facet fusion involves identifying the lateral mass and introducing any of the fixation methods known or described herein laterally at one or more facets through the use of a Kirschner wire guide, a cannulated bone drill and cooperatively cannulated staple guide. A surgical bone staple have a perforated bridge is used across the lateral facet joint where fixation is required. Where fusion is desired, a bone screw have lateral perforations of the shank is inserted through the cannulated staple guide and bridge perforation at the joint to promote fusion. A staple cap and graft container for overlay grafting may be utilized for additional fusion. The method involves less surgical time, reduced blood loss and discomfort for the patient as compared to the posterior approach.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 12/283,438 for a “Method Of Lateral Facet Approach, Decompression And Fusion Using Screws And Staples As Well As Arthroplasty” filed Sep. 11, 2008 now U.S. Pat. No. 8,894,651 from which priority is derived and which is incorporated herein by reference. U.S. patent application Ser. No. 12/283,438 derives priority from provisional application 60/993,233 filed on Sep. 11, 2007 which is further incorporated herein by reference 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of approach to the lateral cervical facet for the purposes of spondylosyndesis or arthoplasty techniques as well as related devices. 
     2. Description of the Background 
     Human spinal degeneration is a natural result of aging and may lead to a medical condition known as spinal stenosis in which the spinal canal narrows and compresses the spinal cord and neural structures. Spinal stenosis is often accompanied or even caused by a herniated intervertebral disk. Patients suffering from the condition often experience significant pain and limited range of motion and mobility. Laminectomy is a surgical procedure for treating spinal stenosis in which one or both lamina are removed, often along with the spinous process, in order to relieve the pressure on the spinal cord and the related pain. Unfortunately, this procedure suffers from one major drawback, namely that it can compromise the stability of the spine, particularly when performed in the cervical region of the spine but also in the lumbar and thoracic regions as well. 
     Cervical facet fusion is a procedure in which the facet joints between two or more vertebra are joined together to stabilize the spine and eliminate motion which may contribute to spondylosis, or continued degeneration, and prevent progressive deformity. Cervical facet fusion is commonly performed in conjunction with laminectomy. The standard approach for decompressive laminectomy and/or facet fusion is the posterior approach which may be performed through variety of methods. The classic method involves passing wires through drill holes in the articular processes and binding two longitudinal struts of bone to the posterior columns of the articular processes. Another technique uses lateral mass screws that are connected via a metal rod. However, regardless of the method used, the posterior approach for posterolateral cervical facet fusion is time-consuming, results in resection of important connective tissue and musculature, involves moderate blood loss and often results in the patient suffering from shoulder pain for a significant period after surgery. Posterior approach patients also usually require inpatient hospital care for 2 to 3 days, require drains and experience high incidence of surgical site infection. 
     A variety of devices from different manufacturers have been developed for utilization in spinal surgeries such as facet fusion. Many of these devices are intended for fusion or fixation of the vertebra in the cervical region and elsewhere. These devices commonly consists of one or more plates and screws, pegs, or rods with fixating connectors that may be joined to the bone in order to stabilize the spine. Other devices take the form of a staple. Considerable effort has been expended on preventing the counter-rotation and withdrawal of screws as well as the ability of the devices to secure adjacent vertebra. Considerably less effort has been expended on making such devices less intrusive and quicker to implant (while still maintaining efficacy). 
     Although the noted spinal fixation devices as well as others have furthered technological development, none are done through lateral cervical approach and none provide a small profile of fixation or arthroplasty. It would thus be advantageous to provide a cervical staple, screw fusion fixation or arthroplasty for lateral cervical facet joint that: (1) allows for a more precise and a much smaller profile of fixation than prior art devices, (2) imposes less blood loss, (3) minimizes surgical time (4) avoids traction on the esophagus and trachea as in the anterior approach, (5) is minimally invasive, (6) is lightweight, and (7) is inexpensive to manufacture and sell to provide for widespread use. It would further be advantageous to provide the tools necessary to perform such a procedure such as a staple delivery guide device that is accurate, precise, and quick to load and deploy. 
     A novel lateral approach is herein proposed for facet fixation and fusion or arthroplasty that avoids many of the drawbacks of the known approaches. The lateral approach is done through a minimally invasive method, offers direct access to the facet joint, provides secure stabilization, and permits early mobilization of the patient. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the invention to provide a surgical screw including holes or perforations along the threaded body and central shaft of the screw to allow bone growth there through and facilitate fusion of a facet joint. 
     Another object is to provide a quick solid fixation staple and method to add stability to the spine in patients who have not had prior surgical stabilization of the spine or for patients who have previously undergone surgical fusion anteriorly. It is a further object to secure overlay graft material on the vertebral surface to promote long term fixation. 
     An additional object is to provide a cervical staple and a surgical screw that are inexpensive to manufacture and sell to provide for widespread use. 
     Yet another object is to provide a method of lateral cervical facet fusion, which is a minimally invasive surgical method and that reduces attending staff requirements and operative time. 
     Yet another object of the present invention is to provide a staple placement guide and method of use that retains, places and releases a vertebral staple with certainty and precision. 
     These and other objects are accomplished by a lateral approach to facet fusion which involves less surgical time, reduced blood loss and discomfort for the patient as compared to the posterior approach. The lateral approach to facet fusion involves identifying the lateral mass and then introducing any of the fixation methods known or described herein laterally at one or more facets through the use of Kirschner wire (K-wire) and a hollow staple guide delivery device to deliver a surgical bone staple across the lateral facet joint where fixation is required. Where fusion is desired, a bone screw having lateral perforations of the shank is inserted at the joint to promote fusion. The staple and screw may be used in conjunction with one another or individually. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment and certain modifications thereof, in which: 
         FIG. 1  is a perspective view of a patient indicating the dermal incision for lateral approach. 
         FIG. 2  is a diagram of the steps for lateral facet approach and fusion using screws and staples according to the present invention. 
         FIG. 3  is a front perspective view of the screw. 
         FIG. 4  is a side perspective view of the screw in conjunction with the staple. 
         FIG. 5  is a bottom perspective view of the screw in conjunction with the staple. 
         FIG. 6A  is a partial perspective view of the distal end of the staple guide. 
         FIG. 6B  is a partial perspective view of the distal end of the staple guide relative to the staple of the present invention. 
         FIG. 6C  is a partial perspective view the staple of the present invention being loaded onto the distal end of the staple guide before rotation. 
         FIG. 6D  is a partial perspective view the staple of the present invention fully loaded onto the distal end of the staple guide. 
         FIG. 7  is a partial perspective view of the loaded staple guide advanced over the cannulated drill bit and K-wire. 
         FIG. 8  is a perspective view of the staple with the screw installed and the cap exploded. 
         FIG. 9  is a perspective view of the staple with the screw installed and the cap in position. 
         FIG. 10  is a perspective view of the screw and staple installed in the C5-C6 facet joint before the cap is in place. 
         FIG. 11  is an abstracted section of the C5 and C6 vertebra showing the location of the screw and staple. 
         FIG. 12A  is a front view of a staple guide loaded with a staple according to the present invention. 
         FIG. 12B  is a side view of a staple guide loaded with a staple according to the present invention. 
         FIG. 12C  is section view of a staple guide loaded with a staple according to the present invention along A-A of  FIG. 12B . 
         FIG. 12D  is partial section view of a staple guide loaded with a staple according to the present invention at Detail B of  FIG. 12C . 
         FIG. 12E  partial perspective view of a distal end of a staple guide according to the present invention. 
         FIG. 12F  is bottom view a staple guide according to the present invention. 
         FIG. 13A  is a front view of a staple guide loaded with a staple and screw according to the present invention. 
         FIG. 13B  is a side view of a staple guide loaded with a staple and screw according to the present invention. 
         FIG. 13C  is section view of a staple guide loaded with a staple and screw according to the present invention along A-A of  FIG. 13B . 
         FIG. 13D  is partial section view of a staple guide loaded with a staple according to the present invention at Detail B of  FIG. 13C . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides for a minimally invasive surgical implantation method and apparatus for cervical spine implants that preserves the structure and to a limited degree the function of the spine. In addition to stabilization by instrumentation, embodiments of the invention provide for introduction of graft material at or near the facet joint for promotion of joint fusion. 
     Two facet joints are formed between each pair of adjacent vertebrae of the human spine. Each vertebra has two superior articulating facets and two inferior articulating facets, with each superior facet of a lower vertebra meeting and aligning with an inferior facet of an upper vertebra to form one facet joint on each side of the spine. In the cervical spine, the upward inclination of the superior articular surfaces of the facet joints allows for considerable flexion and extension, as well as for lateral mobility. Each facet joint is covered by a dense, elastic articular capsule that is lined by a synovial membrane that secretes synovial fluid to lubricate the facet joint. The exterior of the joint capsule is surrounded by a capsular ligament that must be cut or displaced as part of some embodiments of the presently disclosed method for fusing the facet joints. 
       FIG. 1  depicts the neck region of a patient  100  indicating the position of the dermal incision  101  for lateral approach. With reference to  FIGS. 2 and 7 , after initial incision a Kirschner wire or K-wire  57  is inserted past the medial or posterior scalenes or trapezius muscle, depending on the particular cervical vertebra to be fused, to reach the intended facet joint. The K-wire  57  is inserted into the facet joint within medial plane of the joint in which the articular cartilage typically resides. The orientation of the medial plane of the joint will vary depending on the vertebral position in along the spine. The K-wire  57  may be smooth walled or, preferably threaded as depicted in  FIG. 7  to provide greater holding power within the join. A trocar end is also preferred. The K-wire is used to facilitate alignment of instruments at the facet without impingement on the surrounding structures. The spinal accessary nerve is the only critical structure in the area that should be avoided. Injury to the nerve will cause paralysis of the scapula muscles. Particular care should be taken where threaded K-wire is utilized in order to avoid damage to the nerve. The location of the K-wire in relation to the facet joint is monitored and verified by medical imaging techniques such as X-ray imaging. Most desirably surgical direct semiconductor detection is used to provide real time monitoring. 
     Once the K-wire  57  is in position a cannulated drill bit  52  with drill guide and stop is inserted over the wire and advanced to the bone surface. In a preferred embodiment the cannulated drill bit  52  includes an integral tap portion to simultaneously tap the interior surface of the pilot hole as the drill is advanced. In an alternate embodiment a separate cannulated tap may be advanced over the K-wire to tap the pilot hole after removal of the cannulated drill bit. A surgical drill is used to drive the bit while the drill guide and stop limits the depth of the pilot hole to slightly less than the ultimate length of the screw (from the bottom of the head) (as described below) and in any event less than the opposing faces of the facet joint so as not to penetrate entirely through the joint. The bit diameter is preferably 1 mm smaller than the minor diameter of the bone screw  7  ( FIG. 3 ) such that where, for example, 4.5 mm and 5.5 mm diameter bone screws are contemplated for use at varying points along the spinal column, 3.5 mm and 4.5 mm bit diameters would be utilized, respectively. 
     After drilling of the pilot hole the drill guide and stop are removed and a Calcar type bone planer is advanced over the cannulated drill bit  52  which preferably remains in place to stabilize the joint and maintain a centered position in the pilot hole. In an alternate embodiment the bit may be removed and the planer advanced over the K-wire only or advanced over the K-Wire prior to utilization of the bit to prepare the pilot hole. The planer is advanced to the bone surface and used to prepare a flat area in the cortical layer for seating of the staple as described below. The diameter of the plane should be approximately equal to or slightly greater than the length of the staple bridge  5  (see  FIG. 4 ), also as described below. The planer is removed. If not already completed simultaneous with the drilling step, a cannulated tap may be advanced over the K-wire to tap the hole (after removing the cannulated drill bit) and thereafter remain in place on the K-wire as a centered guide. 
     A bone staple  1 , as depicted in  FIGS. 4 and 5 , is inserted over the facet joint via a staple guide  40  ( FIG. 6 ). The bone staple  1  includes at least first and second legs  4  joined by and extending from the lower surface of a bridge  5  that joins them at or near their proximal end. The legs each terminate at their distal end in a bevel or point  6  that is able to penetrate cortical bone. In the depicted embodiment the legs  4  extend through and above the upper surface of the bridge  5  to form pins  11  terminating in annularly enlarged heads  8 . It should be noted that while legs  4  are depicted as contiguous members extending both above and below the bridge  5  (from tip to head), the legs need not be so limited. That is to say, the pins  11  extending from the upper surface of the bridge may be offset from the legs  4  extending downward from the lower surface of the bridge. Further, the pins  11  may be entirely separate members positioned on the upper surface of the bridge without regard to the position of the legs on the lower surface. 
     A hole or aperture  3  is provided from the upper surface of the bridge  5  to the lower surface. The relative position of the aperture with respect to the pins  11  or edges of the bridge  5  (depending on the embodiment) is critical to proper loading and deployment of the staple in and by the staple guide  40  as described below. The position of the legs  4  with respect to the aperture is less critical and, in as much as the staple is intended to span the facet joint, it is sufficient that at least one leg be provided on either side of the aperture so as to penetrate both adjacent vertebra. Preferably, as seen in  FIG. 4 , both legs are defined by a plurality of annular or outwardly oriented notches  2  formed with beveled walls defining a serrated outer surface that resist withdrawal from the bone once inserted. Legs  4  are preferably from 4 mm to 8 mm in length, more preferably 5 mm 7 mm, and from 2 mm to 4 mm in diameter, more preferably 2 mm. 
     Pins  11  extend to and terminate in enlarged heads  8  which are preferably flat. The heads  8  may be provided with a slightly conical upper surface or, preferably, a small protrusion (as depicted) to serve as a standoff from the surface of the staple guide and detent when loaded therein as described below. Alternately, the heads  8  may be with a ball, dome or other form for cooperative engagement with the staple guide  40 . 
     The bridge  5  is a planar member that has its maximum length along a major axis that is greater than or equal to its length along a perpendicular minor axis. In a preferred embodiment pins  11  are symmetrically positioned along the major axis on either side of an aperture  3  that is also centered on the major axis. The aperture  3  extends from the upper surface of the bridge  5  to its lower surface and may be provided at its perimeter with a recess for countersinking the head  14  of the bone screw  7  (described below) into the bridge  5  for greater resistance to lateral movement of the staple  1 . Alternately, the upper surface of the bridge  5  may be flat to engage the underside of the head  14  as depicted. 
     In the preferred embodiment the legs  4 , like the pins  11 , are symmetrically positioned along the major axis on either side of the aperture  3  but, as noted, it is not critical that this be so. The bridge  5  is preferably rectilinear in form having side edges parallel to the major axis and joined by rounded or arcuate ends, as depicted in  FIG. 8 . The bridge  5  may alternately be elliptical in shape (as depicted in  FIG. 5 ), having length along its major axis equal to or greater than that along the minor axis, or any other planar form. The bridge  5  is preferably from 10 mm to 16 mm in length and pins  11  are preferably approximately 7 mm to 12 mm on-center and more preferably 9 mm on center. Legs  4 , pins  11  and bridge  5  are preferably constructed of durable, surgically, implantable material such as titanium or stainless steel. Bridge  5  may alternately be constructed of PEEK and may be integrally formed or connected via known manufacturing techniques including welding, compression and mechanical integration. 
     With reference to  FIGS. 6A-D  and  12 A-F, the staple guide  40  is a cannulated rod preferably approximately 100 mm in length characterized by a central longitudinal void  41  extending though its length to a distal end  42 , the void  41  being preferably but not necessarily centered within the cross section of the guide. The distal tip  42  of the guide  40  is provided with a structure to selectively capture and release the heads  8  of the staple  1  by relative rotation of the staple and guide. In a preferred embodiment an annular channel  43  is provided in the distal end  42  of the guide  40  encircling a point of rotation. It is preferred that the point of rotation be the center of the guide  40  cross section and it is further preferred that the point of rotation be concentric with the longitudinal void  41 . Those skilled in the art may observe that where the annular channel is not concentric about the longitudinal void, it will be sufficient that the aperture  3  be aligned with the longitudinal void when captured in the staple guide  40 . 
     The inner and outer walls of the channel  43  are each provided with an annular protrusion  44  such that the channel  43  cross section has a necked form that will capture the enlarged heads  8  of the pins  11  of the staple  1 . The size and spacing of heads  8  are chosen for cooperative engagement within the channel  43 , as depicted in  FIG. 6D  or  12 D. In order to be able to start the heads  8  into the channel  43  lateral openings  48  are provided by removing a segment of the channel  43  on opposing side of guide  40  and thereby creating flat sides  49  on the guide  40 . The cord length of the opposing circular segments removed from the staple guide cross section are chosen to tangentially intersect the inner wall of the channel  43 . To load the staple  1  into the guide  40  the major axis of the staple is oriented perpendicular to the flat sides  49  of the guide  40  (as in  FIG. 6C ) and the flat sides advanced and positioned between the heads  8  of staple. The staple can then be rotate 90 degrees (as in  FIG. 6D  so that the pins  11  and heads  8  enter the channel  43  via the lateral openings  48 , the enlarged heads being engaged by the annular protrusions  44  to retain the staple in place until the rotation is reversed to release the pins and staple after implantation. A dimple  47  may be provided within the channel  43  to receive the small protrusion provided the top of head  8  to act as a detent securing the staple  1  in the guide. In this loaded position the aperture  3  of the staple is necessarily concentrically aligned with void  41  of the guide  40 . 
     With reference to  FIG. 7 , the void  41  of the guide  40  is sized slide over the cannulated drill bit  52  which, as stated, remains in the pilot hole during portions of the procedure as a centering guide. In an alternate embodiment in which the bit has been removed and a separate tap has been used to prepare the inner surface of the pilot hole, the guide would be sized to slide over the tap which would remain in place to serve as a guide in lieu of the bit. The loaded staple guide  40  is positioned over the K-wire  57  and cannulated bit  52  and advanced to the bone surface such that the distal tips  6  of the legs  4  engage the surfaces of the vertebrae, one on either side of the facet joint. In this way the aperture  3  of the bridge  5  is necessarily aligned with the pilot hole in the joint which remains supported and aligned by the drill bit. The legs  4  of the staple  1  are then driven into the bones by force. Force may be applied by manually by the surgeon or by surgical bone hammer, slide hammer integral to the staple guide  40 , or other known surgical technique. With the staple secured across the facet joint the K-wire and cannulated drill bit are removed from the pilot hole via the central void  41  of the staple guide  40  which remains in place and engaged to the staple  1 . A bone screw  7  is delivered via the now vacant central void  41  of the staple guide  40 , as depicted in FIGS.  7  and  13 A-D, and rotationally driven through the aperture  3  of the staple bridge  5  into the pilot hole in the bone by a cooperative driving tool engaging screw head  14 . The driving tool (not pictured) is advanced through the void  41  of the guide  40 . After the staple  1  is secured in place by the screw  7  the staple guide  40  is rotated about is longitudinal axis to release the heads  8  of the pins  11  from the channel  43  via lateral openings  48 , thus permitting the staple guide  40  to be removed. 
     In an alternate embodiment, the pins  11  and heads  8  of the staple  1  are omitted altogether as is the inner wall of the arcuate channel  43  at the distal end  42  of the guide  40 . In such an embodiment staple is loaded into the guide by inserting the bridge  5  between the outer walls of the arcuate channel and rotating as described above such that the arcuate ends of the bridge are captured between the outer walls of the arcuate channel which are provided with an annular protrusion as described above. 
     In yet another alternate embodiment, the lateral openings  48  are omitted by failing to remove the opposing segments of the channel  43  in favor of distal openings. Distal openings are formed by omitting a portion of the lateral protrusions at opposing positioned around the arcuate channel such that the heads  8  of the pins  11  can be advanced into the channel from a distal position before being rotated into the channel and captured. 
     Bone screw  7  may be any known bone screw but is preferably a screw having a cylindrical, externally shank  9  topped at one end by a head  14  adapted to be engaged by a fastener-driving tool as depicted in  FIGS. 3 ,  4  and  5 . The shank  9  of the screw  7  may be hollow along some or all of its length and is further preferably provided with one or more perforations  10  positioned along the linear axis of the shank  9  and extending through the shank  9  perpendicular to its linear axis are provided to allow bone growth through the screw in order to fuse the joint into which it is driven and secure the screw in place. The distal tip of the screw may be blunt or may be tapered to a sharp point  12 . 
     With reference to  FIGS. 8 and 9 , after the staple  1  is secured in place in the facet joint by screw  7  a cap  50  is placed over the visible portions of the staple. The cap  50  is cooperatively formed to envelope the exposed surface of the bridge  5  and screw  7 . The cap  50  is provided with resilient members on its inner surface which engage the heads  8  of the pins  11  by snap fit or friction fit so as to removeably secure the cap  50  in place over the staple  1 . A loop  58  on the outer surface of the cap  50  is provided to which bone graft material may be secured. In a preferred embodiment an envelope  59  containing bone graft material may be sutured to the loop  58  and positioned between the transverse processes of the affected vertebrae or directly on the surface of the inferior vertebral lamina depending on the location of the site along the spine. The envelope is preferably made of woven polyethylene or polyester fabric and may contain allograft, autograft or synthetic graft material, with or without human osteogenic growth factors, such as bone morphogenetic proteins, transforming growth factor, and platelet-derived growth factor. Fusion at the transverse process or lamina by only graft serves to further secure and support stability of the facet joint. After the graft material is secured in position the incision is closed. 
       FIG. 10  depicts the location of bone screw  7  and staple  1  after implantation to stabilize the right C5-C6 facet joint  101 . The cap  50  and bone envelope  59  are omitted for clarity.  FIG. 10  is an abstraction of the C5-C6 vertebra indicating the position of the screw  7  and staple  1  in the facet joint  102 . It should be noted that the C5-C6 facet joint here is referenced by way of illustration and the present method may be utilized at other cervical and non cervical joints. 
     The above-described lateral approach to facet fusion and related devices can be equally applied to other areas of the spine including the lumber and thoracic regions. Although the staple  1 , screw  7  and cap  50  have particular utility for the lateral approach to facet fusion, one skilled in the art will understand that the present invention can be equally applicable to other approaches to facet fusion and to fusion or fixation of other skeletal structures. 
     Having now fully set forth the preferred embodiments and certain modifications of the concept underlying the present invention, various other embodiments as well as certain variations and modifications of the embodiments herein shown and described will obviously occur to those skilled in the art upon becoming familiar with said underlying concept. It is to be understood, therefore, that the invention may be practiced otherwise than as specifically set forth in the appended claims.