Abstract:
A spinal implant for treating lumbar spinal stenosis or as an adjunct to spinal fusion. The implant includes a body portion having an interior cavity. A plurality of locking wings are adapted and configured to move between a stowed position retracted within the interior cavity of the body portion and a deployed position extended from the interior cavity of the body portion. In the deployed position, the wings fix the implant in a selected interspinous space. A cable and wheel arrangement moves the plurality of locking wings from the stowed position to the deployed position and a ratchet/pawl assembly prevents backward movement of the wings.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to the following applications: U.S. patent application Ser. No. 11/743,086, filed May 1, 2007; U.S. Provisional Patent Application No. 60/959,799, filed Jul. 16, 2007; U.S. Provisional Patent Application No. 60/961,780, filed Jul. 24, 2007; U.S. Provisional Patent Application No. 61/000,831, filed Oct. 29, 2007; and U.S. Provisional Patent Application No. 61/001,430, filed Nov. 1, 2007, each of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject invention is directed to spinal implants, and more particularly, to an interspinous implant with deployable wings for treating lumbar spinal stenosis, methods for the percutaneous implantation of the interspinous implant, and techniques for determining an appropriate size of the interspinous implant. 
     2. Description of Related Art 
     The spine consists of a column of twenty-four vertebrae that extend from the skull to the hips. Discs of soft tissue are disposed between adjacent vertebrae. The vertebrae provide support for the head and body, while the discs act as cushions. In addition, the spine encloses and protects the spinal cord, which is surrounded by a bony channel called the spinal canal. There is normally a space between the spinal cord and the borders of the spinal canal so that the spinal cord and the nerves associated therewith are not pinched. 
     Over time, the ligaments and bone that surround the spinal canal can thicken and harden, resulting in a narrowing of the spinal canal and compression of the spinal cord. This condition is called spinal stenosis, which results in pain and numbness in the back and legs, weakness and/or a loss of balance. These symptoms often increase after walking or standing for a period of time. 
     There are number of non-surgical treatments of stenosis. These include non-steroidal anti-inflammatory drugs to reduce the swelling and pain, and corticosteroid injections to reduce swelling and treat acute pain. While some patients may experience relief from symptoms of spinal stenosis with such treatments, many do not, and thus turn to surgical treatment. The most common surgical procedure for treating spinal stenosis is decompressive laminectomy, which involves removal of parts of the vertebrae. The goal of the procedure is to relieve pressure on the spinal cord and nerves by increasing the area of the spinal canal. 
     Interspinous process decompression (IPD) is a less invasive surgical procedure for treating spinal stenosis. With IPD surgery, there is no removal of bone or soft tissue. Instead, an implant or spacer device is positioned behind the spinal cord between the spinous process that protrudes from the vertebrae in the lower back. A well-known implant used for performing IPD surgery is the X-STOP® device, which was first introduced by St. Francis Medical Technologies, Inc. of Alameda Calif. However, implantation of the X-STOP® device still requires an incision to access the spinal column to deploy the X-STOP® device. 
     It would be advantageous to provide an implant for performing IPD procedures that could be percutanously inserted into the interspinous space and effectively treat lumbar spinal stenosis. 
     SUMMARY OF THE INVENTION 
     The subject invention is directed to a spinal implant used primarily for interspinous process decompression procedures that can be percutaneously introduced into the interspinous space. In its most basic configuration, the device includes a body portion having an interior cavity, a plurality of locking wings adapted and configured to move between a stowed position retracted within the interior cavity of the body portion and a deployed position extended from the interior cavity of the body portion, and means for moving the plurality of locking wings from the stowed position to the deployed position. 
     The subject invention is also directed to a method of percutaneously placing a spinal implant during an interspinous process decompression procedure, which includes, among others, the steps of providing a spinal implant having a body portion containing a plurality of deployable locking wings that are dimensioned and configured to engage the spinous processes of adjacent vertebrae at symptomatic disc levels, advancing a curved stylet through the skin from one side of the spine down into the spinous processes between the symptomatic disc levels, guiding the spinal implant along the path defined by the curved stylet into the spinous processes from a unilateral approach, and subsequently deploying the locking wings to engage the spinous processes of adjacent vertebrae. 
     The subject invention is further directed to a method of percutaneously placing a spinal implant that includes the steps of providing a spinal implant having a body portion containing a plurality of deployable locking wings dimensioned and configured to engage the spinous processes of adjacent vertebrae at symptomatic disc levels, advancing a curved stylet through the skin from one side of the spine, down into the spinous process between the symptomatic disc levels and out through the skin on the opposite side of the spine, so as to enable a bilateral approach to the spinous process. The method further includes the steps of guiding the spinal implant along the path defined by the curved stylet into the spinous processes from either side of the spine and subsequently deploying the locking wings to engage the spinous processes of adjacent vertebrae. 
     The implant may be advantageously used for various treatments including as an adjunct to a fusion, for treatment of back pain and as a treatment to alleviate symptoms of a protruding lumbar disc. 
     The subject invention is further directed to a tool kit for facilitating the percutaneous implantation of the device. The kit includes one or more of the following components: a stylet assembly having a graduated positioning stylet, a curved stylet and an adjustable bridging portion with curved guide sleeve for the curved stylet. The kit may further include a set of curved tubular dilators of varying diameter and a plurality of implants of varying size. 
     The subject invention is also directed to an apparatus for measuring the optimum size of an interspinous implant for treating lumbar spinal stenosis. The apparatus includes distracting means dimensioned and configured for percutaneous insertion into the interspinous space between adjacent spinous processes, wherein the distracting means is movable between a closed insertion position and an open distracting position. The apparatus further includes deployment means for moving the distracting means between the closed insertion position and the open detracting position, wherein an amount of movement of the deployment means corresponds to an optimum size of interspinous implant for placement in the interspinous space between the adjacent spinous processes. 
     The subject invention is also directed to a method for measuring the optimum size of an interspinous implant for treating lumbar spinal stenosis. The method includes the step of percutaneously inserting distracting means into the interspinous space between adjacent spinous processes, wherein the distracting means is movable between a closed insertion position and an open distracting position. The method further includes the step of moving the distracting means between the closed insertion position and the open detracting position, and then correlating movement of the distracting means to an optimum size of interspinous implant for placement in the interspinous space between adjacent spinous processes. 
     In one embodiment, the subject technology is directed to an interspinous implant for placement between spinous processes of symptomatic disc levels including a shell having upper and lower shell portions defining four interior grooves that terminate in openings in the shell, the shell having a pawl adjacent each opening. Four deployable ratcheting locking wings slidably couple in a respective groove between: i) a stowed position in which the wings are within the grooves; and ii) a deployed position in which the wings extend outward from the shell. Each wing has a set of ratchet teeth for engaging and locking the respective pawl in the deployed position. A pair of coaxial locking wheels rotatably mount in the shell to selectively exert a force against each locking wing to move the locking wings from the stowed to the deployed position and a deployment cable couples to the wheels to actuate rotation of the wheels. 
     The implant may further have a guide on the shell for accommodating a stylet during a percutaneous placement procedure. Additionally, two wings may be located on first parallel, spaced apart geometric planes that extend on a first side of a centerline of the shell, with the other two wings are located on second parallel, spaced apart geometric planes that extend on a second side of the centerline of the shell. The interspinous implant may also include a placement tool for introducing the shell into the spinous process. The placement tool may include an elongated tubular stem having a straightened distal portion and a curved proximal portion that form a central lumen for accommodating the deployment cable and a coupling sleeve on the straightened distal portion for selectively engaging the shell. In another embodiment, the placement tool may be an elongated tubular stem that is curved. 
     The interspinous implant may also include a stylet assembly for percutaneous insertion of the interspinous implant. The stylet assembly includes an elongated graduated positioning stylet for setting a position of the stylet assembly over a central axis of a spine, a curved stylet for gaining lateral access to an interspinous space and an adjustable guide bridge having a central portion extending between the positioning stylet and the curved stylet for guiding the positioning stylet, the bridge also having a curved guide sleeve for guiding the curved stylet. The curved stylet may be sized and configured for a unilateral or bilateral insertion. 
     The interspinous implant may also include an actuating mechanism including an elongated, arcuate, hollow cable attachment device having a tapered distal end with radially inwardly extending flexible prongs that form a distal opening, a deployment cable having a distal end attached to the interspinous implant and a proximal end having a ball captured by the flexible prongs and a second tube for insertion into the cable attachment device to deflect the flexible prongs and, in turn, release the ball therefrom after deployment of the interspinous implant. 
     In another embodiment, the subject technology is directed to a method of placing a spinal implant comprising the steps of: providing a spinal implant having a body portion containing a plurality of deployable locking wings dimensioned and configured to engage the spinous processes of adjacent vertebrae at symptomatic disc levels; advancing a curved stylet through the skin from one side of the spine down into the spinous processes between the symptomatic disc levels; guiding the spinal implant along a path defined by the curved stylet into the spinous processes from a unilateral approach; and deploying the locking wings to engage the spinous processes of adjacent vertebrae. 
     In still one more embodiment, the subject technology is directed to a device for measuring percutaneously an optimum size of an interspinous implant. The measuring device includes a proximal deployment portion including a plunger tube carrying a rod, a distal measuring assembly including four connected arms pivotally connected at four coupling joints, a central shaft connected to the rod of the plunger tube a proximal end and connected to the coupling joint on a distal end and two opposed concave cradles adjacent opposed coupling joints adapted to engage a spine when the rod and, in turn, the central shaft is pulled in a proximal direction while the plunger tube remains stationary, so that the connected arms expand from a closed to a measuring position. The measuring device may also include a strain gauge operatively associated with the plunger tube and rod for determining a force to be applied by an interspinous implant. 
     In another embodiment, the measuring device includes an elongated body portion having a pair of jaw members at a distal end thereof for positioning in the interspinous space, a cradle on each jaw member, the cradles being adapted and configured to cup an adjacent spinous process, a plunger tube and a rod partially housed within the plunger tube and attached to the jaw members for selectively moving the jaw members from a closed position to an open position in which the cradles engage the spinous process, wherein a travel distance of the rod within the plunger tube correlates to a length to which an interspinous space was distracted. 
     The subject technology also includes a method for measuring the optimum size of an interspinous implant for treating lumbar spinal stenosis including the steps of percutaneously inserting distracting means into the interspinous space between adjacent spinous processes, wherein the distracting means is movable between a closed insertion position and an open distracting position, moving the distracting means between the closed insertion position and the open detracting position and correlating movement of the distracting means to an optimum size of interspinous implant for placement in the interspinous space between adjacent spinous processes. 
     It is to be understood that each feature of the disclosed implants and methods may be interchanged and coupled freely with the various other features to utilize any combination thereof. These and other features of the interspinous implant and percutaneous placement method of the subject invention will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiment taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the interspinous implant of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail hereinbelow with reference to certain figures, wherein: 
         FIG. 1  is a perspective view of an interspinous implant in accordance with the subject invention, which includes a main shell portion having a plurality of locking wings and an insertion tool to facilitate percutaneous introduction of the implant into the spine; 
         FIG. 2  is a top plan view of the interspinous implant of  FIG. 1 , illustrating the locking wings in a deployed position; 
         FIG. 3  is a side elevational view of the interspinous implant of  FIG. 1 ; 
         FIG. 4  is a cross-sectional view taken along line  4 - 4  of  FIG. 3  illustrating a locking wheel disposed within the main shell of the interspinous implant for deploying a pair of opposed lock wings; 
         FIG. 5A  is a detailed perspective view of the lower portion of the main shell of the interspinous implant of  FIG. 1 ; 
         FIG. 5B  is a plan view of the inside of the lower portion of the main shell of  FIG. 5A ; 
         FIG. 5C  is a side view of the inside of the lower portion of the main shell of  FIG. 5A ; 
         FIG. 5D  is a proximal end view of the lower portion of the main shell of  FIG. 5A ; 
         FIG. 6A  is a detailed perspective view of the upper portion of the main shell of the interspinous implant of  FIG. 1 ; 
         FIG. 6B  is a plan view of the inside of the upper portion of the main shell of  FIG. 6A ; 
         FIG. 6C  is a side view of the inside of the upper portion of the main shell of  FIG. 6A ; 
         FIG. 6D  is another side view of the inside of the upper portion of the main shell of  FIG. 6A  with the inside shown in phantom lines; 
         FIG. 6E  is a proximal end view of the upper portion of the main shell of  FIG. 6A ; 
         FIG. 6F  is a distal end view of the upper portion of the main shell of  FIG. 6A ; 
         FIG. 7A  is a detailed perspective view of a locking wing of the interspinous implant of  FIG. 1 ; 
         FIG. 7B  is a side view of the locking wing of  FIG. 7A ; 
         FIG. 7C  is a top view of the locking wing of  FIG. 7A ; 
         FIG. 7D  is a bottom view of the locking wing of  FIG. 7A ; 
         FIG. 7E  is an end view of the locking wing of  FIG. 7A ; 
         FIG. 8A  is a detailed perspective view of a locking wheel of the interspinous implant of  FIG. 1 ; 
         FIG. 8B  is a top view of the locking wheel of  FIG. 8A ; 
         FIG. 8C  is a side view of the locking wheel of  FIG. 8A ; 
         FIG. 8D  is an end view of the locking wheel of  FIG. 8A ; 
         FIG. 8E  is a detailed top view of another locking wheel and a portion of the actuating mechanism for use in the interspinous implant of  FIG. 1 ; 
         FIG. 9A  is a detailed perspective view of a placement tool for use with the interspinous implant of  FIG. 1 ; 
         FIG. 9B  is a side view of the placement tool of  FIG. 9A ; 
         FIG. 9C  is a top view of the placement tool of  FIG. 9A ; 
         FIG. 9D  is a distal end view of the placement tool of  FIG. 9A ; 
         FIG. 10A  is a perspective view of the interspinous implant of the subject invention, in cross-section to illustrate the four locking wings and two locking wheels in a stowed position; 
         FIG. 10B  is a perspective view of the interspinous implant of the subject invention, in cross-section to illustrate the four locking wings and two locking wheels in a deployed position; 
         FIG. 11  is a perspective view of the interspinous implant of the subject invention, with the four locking wings fully retracted and stowed within the shell of the device; 
         FIG. 12  is an elevational view of the stylet assembly used to percutaneously deploy the interspinous implant of the subject invention; 
         FIGS. 13 through 16  illustrate the percutaneous introduction of the interspinous implant of the subject invention by way of a unilateral approach from one side of the spine; 
         FIGS. 17 through 21  illustrate the percutaneous introduction of the interspinous implant of the subject invention by way of a bilateral approach from either side of the spine; 
         FIG. 22  is a perspective view of a placement or cable attachment device utilized in conjunction with the interspinous implant of the subject invention; 
         FIG. 23  is a distal end view of the attachment device of  FIG. 22 ; 
         FIG. 24  is an illustration of an apparatus for measuring the optimum size of an interspinous implant, which is shown in an initial measuring position; 
         FIG. 25  is an illustration of the apparatus shown in  FIG. 24  in an open or distracting position; 
         FIG. 26  is an illustration of another apparatus for measuring the optimum size of an interspinous implant, which is shown in an insertion or closed position; 
         FIG. 27  is an illustration of the apparatus shown in  FIG. 26  in an open or distracting position; and 
         FIG. 28  is a top plan view of a tool kit for facilitating the percutaneous placement of a spinal implant. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention overcomes many of the prior art problems associated with implants to relieve spinal stenosis. The advantages, and other features of the system disclosed herein, will become more readily apparent to those having ordinary skill in the art from the following detailed description of certain preferred embodiments taken in conjunction with the drawings which set forth representative embodiments of the present invention and wherein like reference numerals identify similar structural elements. All relative descriptions herein such as horizontal, vertical, left, right, upper, and lower are with reference to the Figures, and not meant in a limiting sense. For reference, proximal is generally the area or portion adjacent or near the surgeon whereas distal refers to the portion remote or away from the surgeon. 
     Spinal Implant 
     Referring now  FIG. 1 , there is illustrated an interspinous implant constructed in accordance with a preferred embodiment of the subject invention and designated generally by reference numeral  10 . Implant  10  is particularly well adapted for use in performing minimally invasive surgical procedures for treating spinal stenosis, including, for example, interspinous process decompression (IPD). 
     It is envisioned however, that the implant  10  of the subject invention can be used in other spinal procedures as well, including, but not limited to as an adjunct to spinal fusion procedures. Those skilled in the art will readily appreciate from the following description that the interspinous implant of the subject invention is well adapted for percutaneous insertion, and thus overcomes many of the deficiencies of prior art devices presently used in IPD procedures. That is, the implant  10  is dimensioned and configured for introduction and placement through a small stab skin incision. 
     Referring to  FIGS. 1 through 4 , the interspinous implant  10  of the subject invention includes a main shell or body portion  12  having upper and lower shell portions  12   a ,  12   b . The shell portions  12   a ,  12   b  may have an interference fit or be held together by a fastener (not shown) inserted in a threaded hole  44 . The shell portions  12   a ,  12   b  are preferably formed from a biocompatible polymeric material that has a modulus of elasticity that is substantially similar to that of bone, for example, polyetheretherketon thermoplastic (PEEK) or a similar material. The main shell  12  may also be made of a biocompatible metal such as a titanium alloy or like material. The main shell  12  is dimensioned and configured for placement between the spinous processes of symptomatic disc levels. (See also  FIGS. 5A and 5B ). Placement of the implant in this manner limits extension at the symptomatic levels, while preserving mobility and alignment. While the shell  12  has a generally bullet or frusto-conical shape, it is envisioned that the curved end section could be truncated or presented in a flattened orientation, whereby the shell would assume a barrel-shaped configuration among many other variations. The shell  12  has opposing depressions  13  that serve to match the profile of the adjacent bone when deployed. 
     The lower shell portion  12   b  includes an optional guide  15  for accommodating a stylet during a percutaneous placement procedure, as best seen in  FIGS. 5A-5D  and described in further detail below. The guide  15  has a bore  17  that can slide over a stylet. The main shell  12  houses four deployable ratcheting locking wings  14   a - 14   d  adapted and configured to engage adjacent vertebral portions of the spinous process. The shell  12  has four openings  46   a - 46   d  that allow the locking wings  14   a - 14   d  to extend outward from the shell  12 . The locking wings  14   a - 14   d  are preferably formed from a lightweight, high-strength biocompatible material, such as, for example, titanium or a similar material. 
     During deployment of the implant  10 , the locking wings  14   a - 14   d  are stowed within the shell  12  of the implant  10 , as best seen in  FIGS. 10A and 11 , forming a streamlined structure. As best seen in  FIGS. 4 ,  5 A,  5 B,  6 A,  6 B,  10 A and  10 B, two curved guide tracks  19  formed within the shell portions  12   a ,  12   b  accommodate the wings  14   a - 14   d  in the stowed position. 
     Each locking wing  14   a - 14   d  includes a set of ratchet teeth  16 , as best seen in  FIGS. 7A-7C . The ratchet teeth  16  on each wing  14   a - 14   d  are dimensioned and configured to engage a corresponding pawl structure  18  formed adjacent the openings  46   a - 46   d  on the shell  12  during deployment, so as to lock the wings  14   a - 14   d  in the desired position. The locking wings  14   a - 14   d  fixate the adjacent spinous processes. While the implant  10  is used primarily as a spacer between spinous processes, the selectively deployable wings  14   a - 14   d  enable the implant  10  to be used to distract the spinous process as well. Advantageously, once the wings  14   a - 14   d  are deployed to fixate the spinous processes, migration of the implant  10  is prevented. 
     As best seen in  FIG. 3 , the two wings  14   c  and  14   b  on the side of the implant  10  are located on parallel, spaced apart geometric planes that extend on the side of the horizontal centerline of the implant shell  12 . In other words, in a deployed position, locking wing  14   b  resides in a deployment plane that is parallel to the deployment plane of locking wing  14   c . Similarly, locking wing  14   a  resides in a plane that is parallel to the deployment plane of locking wing  14   d . It follows that, locking wings  14   a  and  14   c  reside in a common deployment plane, and locking wings  14   b  and  14   d  reside in a common deployment plane. This orientation helps to prevent migration of the device and maintain stability within the spinous process. 
     The movement or deployment of the locking wings  14   a - 14   d  is controlled or otherwise effectuated by a pair of coaxial locking wheels  20   a  and  20   b , shown in FIGS.  4  and  8 A- 8 D. The locking wheels  20   a  and  20   b  have a central opening  25   a  and  25   b , respectively, for mounting on a central hub  21  in the shell  12 . Locking wheel  20   a  nestles in upper shell portion  12   a  to control the movement of wings  14   a  and  14   c , while locking wheel  20   b  nestles in lower shell portion  12   b  to control the movement of wings  14   b  and  14   d . More particularly, each of the opposed ends  23   a ,  23   b  of locking wheels  20   a ,  20   b  are adapted and configured to exert a force against a bearing surface  22  formed at the end of each locking wing  14   a - 14   d , which is best seen in  FIGS. 10A and 10B . 
     In accordance with a preferred embodiment of the subject invention, the locking wheels  20   a ,  20   b  and thus the locking wings  14   a - 14   d  are controlled by a deployment cable  27 , shown in  FIG. 10B . One or more cables may be employed. The deployment cable  27  attaches to a key-shaped opening  41  formed in the locking wheels  20   a ,  20   b  to facilitate remote actuation of the locking wheels  20   a ,  20   b  and corresponding movement of the ratcheting locking wings  14   a ,  14   b . The cable  27  splits on the distal end and terminates in two balls (not shown). Each ball can pass through the respective key-shaped opening  41  and be selectively captured therein. The cable  27  passes out of the shell  12  via a passage  90  for use by the surgeon. Once deployed, the cable  27  may be disengaged from the key-shaped opening  41  or cut as described below. 
     Alternatively, the key-shaped opening  41  may be located further from the pivot point of the locking wheels  20   a ,  20   b  to provide a greater mechanical advantage. The cable  27  may also form a loop by attaching to the two key-shaped openings  41 . The loop may be a simple loop at the distal end of the cable  27  or a long loop that passes out of the shell via passage  90 . Additionally, a similar second loop of cable (not shown) might attach to two other key-shaped openings on the opposite ends of the locking wheels  20   a ,  20   b  to further increase the mechanical force during deployment. The second loop of cable would also pass out of the implant  10  through a passage similar to passage  90  but formed in the distal end of the implant  10 . Once deployed, the cable loop may either be cut or left as part of the implant  10 . 
     As best seen in  FIGS. 1-3 ,  9 A- 9 D and  11 , the interspinous implant  10  is associated with a placement tool  24  adapted and configured to facilitate the percutaneous introduction of the implant  10 . Placement tool  24  includes an elongated tubular stem  26  having a straightened distal portion  26   a  and a curved proximal portion  26   b . In another embodiment, the tubular stem  26  may be curved without a straightened portion. The tubular stem  26  has a central lumen  29  for accommodating the proximal portion of the deployment cable  27 . At a distal end, the placement tool  24  has a coupling sleeve  28  for selectively engaging a locking cuff  49  on a tail  10   b  of the shell  12 . The sleeve  28  has a slot  92  and the cuff  49  has one or more protrusions  94  that engage to form a twist lock to selectively couple the placement tool  24  to the shell  12 . The sleeve  28  may also form a cutting surface  51 , as best seen in  FIGS. 10A and 10B , against which the cable  27  may be routed for cutting. As the sleeve  28  rotates, a protrusion  59  lifts the cable  27  so that the cutting surface  51  can sever the cable  27  after the locking wings  14   a - 14   d  have been deployed by the locking wheels  20   a ,  20   b . When the cable  27  is a long loop, one end is simply released while the other end of the cable  27  is pulled to remove the cable  27 . It is also envisioned that each locking wheel  20   a ,  20   b  may have a loop or respective cable  27 . In still another embodiment, the cable  27  is relatively short and remains attached to the locking wheels  20   a ,  20   b  after deployment. To actuate the locking wheels  20   a ,  20   b , there is a secondary longer cable (not shown) that passes from the proximal to the distal end of the placement tool  24  and loops around the cable  27 . The secondary cable then passes back out of the proximal end of the placement tool  24 . The ends of the secondary cable are pulled in order to pull cable  27  and, in turn, actuate the locking wheels  20   a ,  20   b . Then, one end of the secondary cable is simply released, while the other end is pulled to remove the secondary cable. 
     Referring to  FIG. 8E , another embodiment of a locking wheel  20 ′ is shown. The locking wheel  20 ′ has spaced grooves located on the central hub  21 ′ adapted and configured to engage complementary spaced teeth on an actuating mechanism  27 ′. The central hub  21 ′ is relatively thicker near the central opening  25 ′ so that the teeth on the conical head of the actuating mechanism  27 ′ effectively interdigitate with the grooves to form a gear drive mechanism. Various other shapes could also form an effective gear drive mechanism. The actuating mechanism  27 ′ is preferably a rod that extends along the long axis of the implant  10 . The conical head of the actuating device  27 ′ may be between the two locking wheels  20 ′ or each locking wheel may have a respective actuating mechanism  27 ′. On the other end (not shown), the actuating mechanism  27 ′ terminates near the end of the shell  12  and forms a slot. A screwdriver type of device (not shown) would insert down the placement tool  24  and couple to the rod slot. By turning the screwdriver type device, the actuating mechanism  27 ′ would turn and, thereby, one or both of the locking wheels  20 ′ would turn in opposite direction to accomplish deployment of the locking wings  14   a ,  14   b  of the implant  10 . 
     Stylet Assembly 
     Referring now to  FIG. 12 , there is shown a stylet assembly  30  adapted and configured to facilitate the percutaneous insertion of the interspinous implant  10 . The stylet assembly  30  includes an elongated graduated positioning stylet  32  for setting the position of the assembly  30  over the central axis of the patient&#39;s spine. On a distal end, the graduated positioning stylet  32  has a pointed tip  31  adapted and configured to be inserted in the patient. On a proximal end, the graduated positioning stylet  32  has a knob  37  to allow a surgeon to more easily control the stylet  32 . The stylet assembly  30  further includes a curved stylet  34  for gaining lateral access to the interspinous space and an adjustable guide bridge  36  having a curved guide sleeve  36   a  for the curved stylet  34 . The adjustable guide bridge  36  also has a central portion  36   b  to act as an insertion guide for the graduated positioning stylet  32 . The curved stylet  34  has a distal end  33  adapted and configured to be inserted in the patient and a proximal end with a handle/travel stop  34   a . The relationship between the handle/travel stop  34   a  and curved guide sleeve  36   a  sets a maximum insertion depth of the curved stylet  34 . 
     Unilateral Placement of the Implant 
     Referring to  FIG. 13 , in use the graduated stylet  32  is advanced through a small percutaneous incision in the patient&#39;s back, under fluoroscopy, so that the pointed tip  31  reaches to the interspinous space. The distance (D) from the skin to the interspinous space is then noted, based on graduations on the stylet  32 . Alternatively, the same distance can be measured from a pre-operative CT scan. In each event, the center guide sleeve  36   b  of the adjustable guide bridge  36  is positioned over stylet  32 , and the distance (D) is marked off in a direction perpendicular to the length of the spine. This distance (D) corresponds to the adjusted length of the adjustable guide bridge  36  of stylet assembly  30 . Thereafter, the curved stylet  34  is advanced down to the interspinous space through the curved guide sleeve  36   a  of the adjustable guide bridge  36 . The curved stylet  34  has a radius of curvature equal to D so that upon insertion, the distal end  33  moves adjacent the pointed tip  31  of the graduated stylet  32  at the interspinous space. At this point of advancement of the curved stylet  34 , the travel stop  34   a  at the end of the stylet  34  abuts the guide sleeve  36   a  to prevent further extension. Thereupon, the travel stop  34   a  is threadably or otherwise removed from the end of the curved stylet  34 , and the remainder of the stylet assembly  30  including the graduated stylet  32  are removed as well. However, the curved stylet  34  remains in place as shown in  FIG. 14 . 
     Then, as shown in  FIGS. 14 and 15 , successive dilators  40 ,  42  are placed over the curved stylet  34 , while observing the interspinous space under fluoroscopy. The dilators  40 ,  42  also may have radii of curvature equal to D. The dilators  40 ,  42  serve to distract the interspinous space. Although two dilators  40 ,  42  are shown, more or less could be utilized to accomplish the desired distraction of the interspinous space. Once the adequate distraction of the interspinous space is observed, the implant  10  is percutaneously inserted through a lumen  43  formed in the last dilator  42 . Preferably, the dilators  40 ,  42  distract the spinous processed and the implant  10  only maintains the distraction although the implant  10  may also perform distraction. Alternatively, the deployment of the implant  10  may be done by threading the implant  10  over the curved stylet  34  as a guide into the interspinous space by way of the guide bore  15  on the lower shell portion  12   b.    
     The implant  10  is maneuvered down to the interspinous space. As shown in  FIG. 16 , the implant  10  has a knob  39  selectively attached to the placement tool  24  to help the physician maneuver the implant  10 . The knob  39  may include an extension that inserts into the central lumen  29  in order to make the stem  26  more rigid. Once the implant  10  is in position, the dilator  42  may be removed, while maintaining the position of the implant  10  for subsequent deployment of the locking wings  14   a - 14   b.    
     Actuating the Locking Wings after Unilateral Insertion 
     Once the shell  12  is nestled between the spinous processes so that contact is made with the bone at the depressions  13 , the locking wings  14   a - 14   d  are deployed. The surgeon utilizes the cable  27  to deploy the locking wings  14   a - 14   d  and, thereby, fix the position of the implant  10 . The distal end  27   a ,  27   b  of the cable  27  is attached to the coaxial locking wheels  20   a ,  20   b , respectively, so that as the cable  27  is pulled proximally, the locking wheels  20   a ,  20   b  rotate about the central hub  21  in the shell  12 . 
     The opposing ends  23   a ,  23   b  of the locking wheels  20   a ,  20   b  push against the bearing surfaces  22  of the respective locking wings  14   a - 14   d  so that the locking wings  14   a - 14   d  are urged outward in the guide tracks  19  of the shell  12 . As the ratchet teeth  16  of the locking wings  14   a - 14   d  move outward past the pawl structure  18  of the shell  12 , the pawl  18  engages the corresponding ratchet tooth  16  to prevent the locking wings  14   a - 14   d  from moving inward back into the shell  12 . As a result of the outward movement, the locking wings  14   a - 14   d  engage the spinous processes until the surgeon feels adequate resistance, e.g., deployment. Once the locking wings  14   a - 14   d  are deployed, the cable  27  is released or cut. The implant  10  then remains deployed between the spinous processes. In one embodiment, a biasing element or elements such as a spring extends between the locking wheels  20   a ,  20   b  so that movement thereof does not occur before or after deployment. 
     In one embodiment, to release the cable  27 , a second cable (not shown) extends down the placement tool  24 . The second cable loops around the cable  27  and returns through the central lumen  29  of the placement tool  24 . The surgeon can pull on the second cable to effect a pull on cable  27 . Once the locking wings are deployed, the surgeon releases one end of the second cable loop, and then pulls this second cable out of the placement tool  24 , thus leaving cable  27  with the implant in the patient. 
     Bilateral Placement of the Implant 
     Referring to  FIGS. 17-21 , there are illustrated the operative steps used in the bilateral placement of the interspinous implant  10  of the subject invention. First, as shown in  FIG. 17 , the central portion  36   b  of the adjustable guide bridge  36  is positioned over the graduated stylet  32 , and the graduated stylet  32  is inserted to the depth of the patient&#39;s spine. The measured distance (D) is used to size the adjustable guide bridge  36 . A second curved stylet  34 ′, similar to curved stylet  34  but longer, is then advanced through the skin down to the interspinous space through the curved guide sleeve  36   a  of the adjustable guide bridge  36 . The curved stylet  34 ′ is also extendable, and the advancement of the curved stylet  34 ′ continues until the distal end  33  of the curved stylet  34 ′ punctures the skin on the opposite side of the spine. 
     As shown in  FIGS. 18 and 19 , the adjustable guide bridge  36  and graduated stylet  32  are removed. Successive tubular dilators  50 ,  52  are placed over the curved stylet  34 ′ while observing the interspinous space under fluoroscopy. These dilators  50 ,  52 , with successively larger diameters, are along the same route as the curved stylet  34 ′ through the interspinous space until distal ends  53 ,  55  respectively, pass out of the patient&#39;s body. 
     Once adequate distraction of the interspinous space is observed, the interspinous implant  10 , with a profile slightly less than the diameter of the larger dilator  52 , is percutaneously inserted through the lumen  57  of the last dilator  55 . The surgeon guides the implant  10  down to the interspinous space, approaching from either or both sides of the spine, as shown in  FIG. 20 . Alternatively, once the interspinous space has been adequately distracted by the dilators  50 ,  52 , a stylet guide (not shown) could again be inserted after removal of the last dilator  52 . The implant  10  could then be inserted over the stylet guide into the interspinous space. 
     Actuating the Locking Wings after Bilateral Insertion 
     As best seen in  FIG. 20 , to actuate the locking wings  14   a - 14   d , the implant is inserted through the final dilator  52  using the placement tool  24   a  attached to the proximal tail  10   b  of the implant  10 . By passing a second placement tool  24   b  into the dilator  52  in an opposing direction, the second placement tool  24   b  attaches to a distal nose  10   a  of the implant  10 . Each placement tool  24   a ,  24   b  has a corresponding knob  39   a ,  39   a  on the proximal end. The final dilator  52  is fully or partially removed while maintaining the position of the implant  10  with the placement tool  24   a  or tools  24   a ,  24   b , as the case may be. 
     While holding the implant  10  in position with the placement tools  24   a ,  24   b , the deployment cable (not shown) is pulled to actuate the locking wings  14   a - 14   d  of implant  10 . A distal end of the cable is attached to the coaxial locking wheels  20   a ,  20   b  so that as the cable is pulled, the locking wheels  20   a ,  20   b  rotate about the central hub  21  in the shell  12 . The opposing ends  23   a ,  23   b  of the locking wheels  20   a ,  20   b  push against the bearing surfaces  22  of the respective locking wings  14   a - 14   d  so that the locking wings  14   a - 14   d  slide outward in the guide tracks  19  of the shell  12 . As the ratchet teeth  16  of the locking wings  14   a - 14   d  move outward past the pawl structure  18  of the shell, the pawl  18  engages the corresponding ratchet tooth  16  to prevent the locking wings  14   a - 14   d  from moving inward back into the shell  12 . As a result of the outward movement, the locking wings  14   a - 14   d  engage the spinous processes until the surgeon feels adequate resistance, e.g., deployment as shown in  FIG. 21 . 
     Once the locking wings  14   a - 14   d  are deployed, the cable is released and the placement tools  24   a ,  24   b  are detached from the nose  10   a  and tail  10   b  of the implant  10 . The implant  10  then remains deployed between the spinous processes, as shown in  FIG. 21 . Before fully detaching the placement tool  24   a  from the implant  10 , the deployment cable is cut. To cut the cable, the placement tool  24   a  rotates the cutting surface  51  and, in turn, the cable is severed by being routed against the cutting surface  51 . 
     It is envisioned that the placement tools  24   a ,  24   b  each attach to the interspinous implant  10  through a selective twist lock as noted above. Alternatively, the placement tools  24   a ,  24   b  could be designed to also have tapered ends with prongs that attach to a bulbous portion of the nose  10   a  and tail  10   b  of the interspinous implant  10 . Similarly, an unlocking rod could be inserted into the placement tools  24   a ,  24   b  or dilator  52  to disengage them from the shell  12 . 
     Alternative Control Device 
     Referring now to  FIGS. 22 and 23 , a control device  60  is shown. The control device  60  may be used to actuate the cable(s)  27  or to place the implant  10 . Accordingly, the size and shape may vary significantly from that shown because the principle of operation is widely applicable. The control device  60  has an arcuate tube  61 . Preferably, the arcuate tube  61  has a radius of curvature of D. 
     The control device  60  may be used to actuate the cable  27  so that cutting is not required by detaching from the cable  27  after deployment. For example, the arcuate tube  61  has a tapered distal end  62 . The tapered end  62  has radially inwardly extending flexible prongs  64  with longitudinal slots  66  in between. The prongs  64  form a distal opening  68 . It is envisioned that the proximal end of the deployment cable  27  would be attached to a small ball (not shown) on the proximal end of the cable  27 . The ball would have a diameter slightly greater than the opening  68  so that the ball is captured in the tapered distal end  62 . In particular, the flexible prongs  64  of the cable attachment device  60  capture the cable ball. By capturing the cable ball, the control device  60  can be used to pull the cable  27  by pulling the device  60 . 
     Once the cable  27  has been pulled, with the deployment of the locking wings  14   a - 14   d  of the implant  10 , the ball of the cable  27  is released from the tapered distal end  62  of the arcuate tube  61 . Release of the ball from the control device  60  is accomplished by inserting a second tube  67  into the arcuate tube  61 , as shown in  FIG. 22 . The second tube  67  would have a slightly smaller diameter than the arcuate tube  61 . The tube  67  provides adequate force to deflect the prongs  64  resulting in an increase in diameter of the opening  68  and, in turn, release of the ball on the end of the deployment cable  27 . Thus, a predetermined, short amount of cable  27  may be left implanted. 
     It is also envisioned that the implant  10  could be designed so that deployment of the wings  14   a - 14   d  is accomplished from the nose  10   a  and tail  10   b  of the shell  12 , bilaterally, whereby two separate cables could be used to deploy the wings  14   a - 14   d , doubling the mechanical advantage provided during a unilateral approach using a single deployment cable  27 . The control device  60  may be used with one or both such cables. 
     In another embodiment, the control device  60  is used to place the implant  10 . The flexible prongs  64  would attach to indentations on the implant  10 . Two control devices  60  could be used with one attaching to each end of the implant  10 . Thus, the arcuate tubes  61  could be used to position the implant  10 . Upon deployment of the locking wings  14   a - 14   d , second tubes  67  would be used to release the control devices  60  from the implant  10 . 
     Using the Locking Wings to Distract 
     In an alternative approach, the locking wings  14   a - 14   d  are used to distract the spinous process. Rather than inserting increasing diameter dilators, the implant  10  is put in position. Then, the cable  27  is used to not only deploy the locking wings  14   a - 14   d  but the locking wings  14   a - 14   d  are also sized and configured to engage and distract the spinous process. For example, each locking wing  14   a - 14   d  may have a hook shaped protrusion positioned to distract the spine as the wings  14   a - 14   d  are deployed. 
     Implant in Deployed Position 
     Once deployed, the interspinous implant  10  of the subject invention is attached to the adjacent spinous processes. The implant  10  provides restriction of movement of the spine in both extension as well as flexion. With slight modification of the locking wings  14   a - 14   d , however, the locking wings  14   a - 14   d  could alternatively be designed to simply abut the spinous processes, and thereby the implant  10  could allow flexion of the spine. 
     It is also envisioned that the implant  10  can permanently engage the spinous processes. For example, the tips of the locking wings  14   a - 14   d  can be sharp to create penetration of the spinous processes. The tips of the locking wings  14   a - 14   d  could be modified so that the edge that forms a point on opposing claws so that the opposing wings could penetrate deeper or through the spinous process bones. Further, the direction of the points on the opposing claws could be reversed. Additionally, the tips of the wings  14   a - 14   d  could have one or more barbs to prevent disengagement. Still further, the tips of the wings  14   a - 14   d  could have perforations that allow for bony in-growth from the spinous processes. In addition to being offset, preferably, the curves of the locking wings  14   a - 14   d  are slightly different to allow the opposing claims not to meet so that each can penetrate deeper through the bone. 
     Predetermining a Size of the Implant 
     Referring now to  FIGS. 24 and 25 , there is shown an apparatus  100  and a method for measuring percutaneously the optimum size of an interspinous implant  10 , which can range from about 8 mm in diameter to about 14 mm in diameter, depending upon the anatomy of the patient and the location of the implant  10  in the spinous process. Those skilled in the art will readily appreciate that the interspinous measurement devices disclosed herein can also be used to measure or otherwise determine an optimum degree of force for interspinous distraction. 
     Referring to  FIG. 24 , the measurement apparatus  100  is shown in a closed position, as the measurement apparatus  100  is percutaneously introduced into the interspinous space. The apparatus  100  includes a proximal deployment portion  110  that includes a plunger tube  102  carrying a rod  104 . The rod  104  extends approximately flush with at the distal end  106  of the plunger tube  102 . 
     The apparatus  100  further includes a distal measuring assembly  112 , which consists of four connected arms  114   a - 114   d . The connected arms  114   a - 114   d  are pivotally connected at four coupling joints  115   a - 115   d . The rod  104  of the plunger tube  102  extends on the distal end to connect to the coupling joint  115   c . Adjacent the coupling joints  115   b ,  115   d , there are two opposed concave cradles  116   a ,  116   b  are adapted and configured to cup the adjacent spinous processes. 
     To measure percutaneously the optimum size of an interspinous implant  10 , the apparatus  100  is placed so that the opposed concave cradles  116   a ,  116   b  are between adjacent spinous processes. The rod  104  is held stationary while the plunger tube  102  is pushed in a distal direction. The connected arms  114   a - 114   d  are driven to expand into a trapezoidal shape as shown by movement arrows “a” in  FIG. 25 ). The expansion of the connected arms  114   a - 114   d  may cause the spinous processes to be distracted if not already done so by dilators. A measurement of the travel distance of rod  104  within in the tube  102  will correlate to the length to which the interspinous space was distracted, i.e., the size of the trapezoidal shape. Thus, the travel distance of the rod  104  can be used to determine the appropriate size of the interspinous implant  10 . To facilitate measuring the travel distance, the rod  104  may have graduations or markings that correspond to an actual measurement or otherwise identify the appropriate size selection of the implant  10 . 
     To measure the optimum degree of force for interspinous distraction, the plunger tube  102  and/or rod  104  are operatively associated with a strain gauge (not shown). Appropriate laboratory testing could be done to determine the optimal degree of distractive force so that the apparatus  100  is calibrated. The calibrated apparatus  100  could then be utilized to determine the appropriate implant  10  to apply that optimal force. To calibrate the apparatus  100 , a clinical study could be performed where the amount of distractive force is correlated with radiological studies showing the degree of distraction. Further, clinical studies could be performed looking at long term clinical results, as well as possible subsidence of the implant  10  into the spinous processes, with different degrees of force exerted. 
     Referring to  FIGS. 26 and 27 , there is illustrated another device  200  for measuring percutaneously the optimum size of interspinous implant  10  in the closed and open positions, respectively. The measuring device  200  includes an elongated body portion  210  having a pair of jaw members  212   a ,  212   b  at the distal end thereof for positioning in the interspinous space. The jaw members  212   a ,  212   b  have respective cradles  214   a ,  214   b  adapted and configured to cup the adjacent spinous processes. 
     Movement of the jaw members from the closed position of  FIG. 26  to the open or measuring position of  FIG. 27  is controlled in a conventional manner (e.g., by oppositely angled cam slots or the like) by way of a flexible rod  216  that extends through the body portion  210 , for example, similarly to plunger tube and rod as shown in  FIGS. 24 and 25 . Again, a measurement of the travel distance of the rod  216  within the body portion  210  may correlate to the length to which the interspinous space was distracted or even directly to the size of the appropriate implant  10 . Further, a strain gauge may be used, for example by coupling the strain gauge to the plunger tube  102  or rod  216 , to determine a preferable amount of force to apply. 
     It is also envisioned and within the scope of the subject disclosure that a temporary balloon can be inserted into the interspinous space to determine the appropriate size of implant  10  to be used. Additionally, an optimum force required for interspinous distraction could be correlated with the amount of pressure required to blow up the balloon. Thus, the size of the implant and the optimum force would be determined by how much the balloon was inflated to obtain that optimum pressure. 
     A Tool Kit for Percutaneous Placement the Implant 
     Referring to  FIG. 28 , a tool kit  400  for facilitating the percutaneous implantation of the implant  10  is shown. The tool kit  400  would preferably include an enclosure  410  containing, among other things, a stylet assembly  30 , which includes the elongated graduated positioning stylet  32 , the curved stylet  34  and the adjustable bridging portion  36  with curved guide sleeve  36   a . It is envisioned that the tool kit  400  would include either a curved stylet  34  configured for a unilateral approach to the spinous process (see  FIG. 13 ), or a curved stylet  34 ′ adapted and configured for a bilateral approach to the spinous process (see  FIG. 18 ), or it could include both types of curved stylets. 
     The tool kit  400  may also include one or more implants  10  of varying sizes. In addition, the tool kit  400  preferably includes a set of tubular dilators (e.g., dilators  42 ,  50 ,  52 ) of varying diameter that correspond to the varying implants  10 . The dilators may have two different lengths depending upon whether the dilators  42 ,  50 ,  52  are used in a bilateral approach procedure or a unilateral approach procedure. It is envisioned that the tubular dilators  42 ,  50 ,  52  could range from about 8 mm or less up to about 14 mm or greater. The dilators, curved stylet, and the placement tools would also have different radii of curvature to accommodate the body shape of different patients. Of course, the implants could be packaged separately for use with an insertion kit sized by the radius of curvature of the dilators, curved stylet, and the placement tools. 
     While the apparatus and methods of subject invention have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and cope of the subject invention.