Abstract:
Interspinous distractor for percutaneous implantation comprising a central body ( 10 ) and two couples of stabilizears ( 14   a   , 14   b   ; 14   c   , 14   d ), hinged at the end of the body ( 10 ) in order to rotate from a closed position, which assists the percutaneous implantation of the distractor, to a spread apart position, which limits its movement stabilizing it in the interspinous gap. Means are provided for causing the rotation of the stabilizears that can be operated percutaneously, in particular, by means of cam shaped elements sliding axially and adapted to engage a cam-shaped surface, or by a system of tie members, and special tools. With respect to the known distractors it can implanted end extracted percutaneously and in a much easier way.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is the US national stage of International Application PCT/IB2008/001344 filed on May 28, 2008 which, in turn, claims priority to Italian Application PI2008A000010, filed on Feb. 7, 2008. 
     FIELD 
     The present invention relates to an interspinous vertebral distractor adapted to percutaneous implantation from a right or left direction with respect to the interspinous gap. 
     BACKGROUND 
     Intervertebral distractors are devices adapted to space two adjacent vertebrae. In particular, the distractors according to the present invention are prostheses for steady implantation in the space set between the spinous processes of two adjacent vertebrae, in order to maintain an intervertebral distraction adapted to limit the loads transmitted between the vertebrae in case of degenerative diseases of the intervertebral disc, thus limiting the associated painful effects. 
     With respect to other vertebral prostheses, interspinous distractors can be easily implanted, in view of the relative simplicity according to which the spinous processes of two adjacent vertebrae can be slightly spread apart. For the same reasons, such distractors do not jeopardize the local mobility of the spine when bending, and reduce hyperextension. Notwithstanding such advantages, known stabilization problems exist. In other words, an interspinous distractor has to be kept in position, in particular it has to be constrained with respect to movements, thus affecting its functionality or causing it to exit from the interspinous gap, with movements in a plane orthogonal to the spine. 
     In particular, WO2006102269 describes interspinous distractors for keeping the implant within the interspinous gap, comprising a central portion adapted to be contained in the interspinous gap providing an interspinous support adapted to maintain a desired distraction, and stop members consisting of two ends portions, one of which is fixed while the other is moveable, the latter comprising elements movable according to two extreme positions. The fixed end has a profile and a size such that it can be approached laterally against the spinous processes of the two adjacent vertebrae. Adjusting means are provided for the moveable end, on which the surgeon acts once the device is implanted, thus forming a bilateral limitation to sliding for the distractor according to its own longitudinal axis. The interspinous and the supraspinous ligament assist settling of the implant between the spinous processes, in particular with respect to movements in a plane orthogonal to the spine, thus ensuring a local mobility of the spine. 
     However, such device cannot be implanted percutaneously, in view of an excessive size of the fixed portion of the stop members, which influences the overall size of the distractor, and also because the means for adjusting the movable part of the stop members cannot be operated percutaneously. 
     A further device is also known, called Synthes®, comprising a central body with a substantially cylindrical shape and two couples of movable and reversible stop members that project from the central body, such that the radial size of the device, in a closed position, does not exceed the substantially cylindrical body. Once the body has been endoscopically placed between the spinous processes, the surgeon acts always percutaneously on position adjusting elements of such mobile stop members, causing them to partially exit from the body through suitable slits, the stop members being conformed to hook the spinous processes. Even in this case, the interspinous ligament assists placement of the prosthesis between the spinous processes. The mobile stop members, however, being housed in the cylindrical body, have to rotate in order to protrude from the respective slit. This entails a high internal mechanical complexity. Furthermore, the stop members have a portion remaining in the cylindrical body that is large enough to support the part protruding from the body, in order to assure enough blocking force to the distractor. The presence of the stop members and of the relative mechanisms in the cylindrical body does not allow having distractors under a certain size. 
     Examples of interspinous distractors, particularly devised for cervical vertebrae, are disclosed in US20060271049A1, US2007010813A1 and in US US2008108990A1. These distractors have a body from which a wing extends, which wing can move from a closed position, not exceeding the height of the body, to a spread apart position protruding laterally with respect to the body, and can then keep the body settled between two spinous processes, in order to carry out distraction and at the same time blocking an accidental movement of the body. 
     SUMMARY 
     It is therefore a feature of the present invention to provide an intervertebral interspinous distractor that comprises effective stop members of the body within the interspinous gap and at the same time allows a percutaneous implantation. 
     A further feature of the present invention provides an intervertebral interspinous distractor that can be blocked in a steady position from both body ends without introducing locking elements fixed from the outside. 
     A further feature of the present invention provides an intervertebral interspinous distractor, adapted to be percutaneously implanted, which is of much easier construction than prior art distractors, in particular with reference to the stop members. 
     Yet another feature of the present invention provides an intervertebral interspinous distractor, adapted to be percutaneously implanted, in particular for vertebrae of the lumbar-sacral zone of the spine. 
     A further feature of the present invention provides an intervertebral interspinous distractor, adapted to be percutaneously implanted, which has a small size, particularly adapted to introduction in interspinous spaces different from the lumbar region and to treat patients of low size, typically children. 
     It is also a feature of the present invention to provide an interspinous distractor, adapted to be percutaneously implanted and extracted, with relevant advantages for patients where the distractor is temporarily mounted in case of disc compressions awaiting permanent treatment. 
     A further feature of the present invention provides an intervertebral interspinous distractor, in particular for introduction between spinous processes of lumbar vertebrae, where the loads necessary for distraction are the highest. 
     Still another feature of the present invention provides an interspinous distractor which allows, without substantial structural changes, an implantation both in young patients and in elder patients, and for different degrees of disc degeneration. 
     Still another feature of the present invention provides an interspinous distractor adapted to be implanted in patients suffering from scoliosis or other deformations of the spine. 
     These and other features are achieved by an interspinous implant comprising: 
     an elongated body with a first and a second end and a predetermined transversal dimension, adapted to provide an interspinous support between two adjacent spinous processes, the body having a longitudinal axis; 
     a first and a second couple of mobile stabilizers, respectively connected to the first and second ends of the elongated body, the stabilizers being adapted to rotate from a closed position, in which they form a pointed extension of the elongated body, assisting a percutaneous implantation of the distractor, and a spread apart position, wherein the stabilizers in use limit the movement of the distractor, providing a barrier adapted to contain between them the spinous processes; 
     means that can be operated percutaneously movable along the axis and associated with the elongated body and the stabilizers, for bringing the stabilizers from the closed position to the spread apart position or vice versa, 
     the stabilizers being connected to the ends at pivot points distant from the axis, the stabilizers having with respect to the body a distal end and a proximal end, such that the means that can be operated percutaneously moving along the axis acts on the stabilizers for causing both the first and the second couple of stabilizers to rotate about the pivot points so that the distal end moves from the closed position to the spread apart position and the proximal end is kept closed to the axis. 
     The ability of adjusting percutaneously the position of the two stabilizers, from a closed introduction position to a spread apart stabilization position, allows at the same time to implant easily the device and to settle it in the interspinous gap, by mini-invasive implantation steps. 
     In particular, the position of the stabilizers can be changed with continuity, avoiding lateral backlash of the distractor without forcing too much the stabilizers against the spinous processes. Furthermore, it is possible to ensure that the stabilizers achieve a blocking position, since the stabilizers can be blocked in any desired position. 
     Advantageously, the means that can be operated percutaneously cause a non-simultaneous opening movement of the stabilizers with respect to the spinous processes in the approaching direction, with advantages for operators as they need not use imaging systems, for example with sonographic probes, for checking the relative position of the implant with respect to the spinous processes. In particular, it is possible to first open the distal stabilizers with respect to the hands of the surgeon, then causing them to touch the spinous processes in such spread apart position with a backward movement, and then opening the proximal stabilizers. Furthermore, this opening sequence allows to easily carry out distraction in presence of angular deformity, scoliosis, ossified tissues on the spinous processes that normally hamper introduction with known systems. 
     In a particular advantageous exemplary embodiment, at least one couple of the stabilizers can rotate about the pivot point beyond the spread apart position continuing further for angles larger than 90°, in particular, between 120° and 180°. In this way, a percutaneous extraction is permitted, preventing the ends of the stabilizers from blocking the extraction. In particular, the two stabilizers that can rotate about the pivot point beyond the spread apart position continuing further for angles larger than 90° have a curved shape with a concavity oriented opposite the axis of the body during introduction, and towards the axis of the body during extraction. 
     Advantageously, the elongated body has substantially elliptical transversal sections wherein, in use, a longer axis lies in a plane substantially orthogonal to the spine. 
     Furthermore, the elongated body can have a conical shape, preferably with a cone angle of 4-5°, which can be advantageously used in treating scoliosis. In this case, the larger diameter of the frustoconical is arranged on the side of the concavity of the deformity of the spine. 
     Advantageously, the interspinous distractor has a first and a second lateral stabilizers that are arranged, in use, below the median horizontal plane of the body of the distractor, and that are shorter than corresponding third and fourth stabilizers arranged, in use, above the median plane. In this way, interferences with the vertebra just below the two distracted vertebrae are prevented, for example in presence of scoliosis or other vertebral degenerations. 
     Furthermore, advantageously, each lateral stabilizer is asymmetrical in a vertical plane. In this way, a possible interference with the lateral processes of the adjacent vertebrae of the spine is avoided. 
     Advantageously, the stabilizers are enclosed laterally between fixed protection shells. In this way, a “torpedo-like” profile of the distractor is obtained, which is of assistance during a percutaneous implantation and extraction. 
     The means that can be operated percutaneously, in a first exemplary embodiment, comprises a rod slidingly arranged in a longitudinal recess of the elongated body, the rod having at one end a cam-shaped portion adapted to be put in a space comprised within the stabilizers of the first couple, such stabilizers each having a cam-shaped surface at the proximal end with respect to the body, adapted to engage with a cam-shaped portion of the rod so that a translation of the rod causes a rotation of the lateral stabilizers. 
     In particular, the proximal end has a convex shape, and the cam-shaped portion of the rod has a corresponding concave shape, whereby the convex shape and concave shape form two conjugate profiles. 
     Alternatively, the conjugate profiles of the proximal end and of the cam-shaped portion of the rod are convex, and have on the surface gear-like portions. 
     Advantageously, the rod has a gripping end opposite to the cam-shaped portion, and this gripping end is adapted to be maneuvered percutaneously with a first tool. 
     Preferably, the gripping end is adapted to engage with a spanner-like portion of the tool, this gripping end being selected from the group comprised of a female end for a respective male spanner-like portion, and a male end for a respective female spanner-like portion. 
     Advantageously, the means that can be operated percutaneously comprises a cam-shaped element adapted to be housed in a space comprised within the stabilizers of the second couple and to be maneuvered with a second tool, and the cam-shaped element is engageable and lockable on a portion of the rod opposite to the cam-shaped portion, in order to cause a rotation of the stabilizers of the second couple from the closed position to the spread apart position. 
     In particular, the portion of the rod opposite to the cam-shaped portion has a threaded portion and the cam-shaped element is a cam-shaped nut adapted to be screwed on the threaded portion to cause a rotation of the stabilizers of the second couple from the closed position to the spread apart position or vice-versa. 
     Preferably, the second tool has a spanner-like portion adapted to engage with the cam-shaped nut. 
     Advantageously, the intervertebral distractor comprises means for guiding the cam-shaped element and the tool towards the distraction body arranged in an intervertebral interspinous gap. 
     In particular, the means for guiding can comprise a wire, and the rod has an axial hole from which the wire extends, whereby the cam-shaped element and the tool are guided along the axis of the rod by the wire. 
     Preferably, the axial hole of the rod is a through hole and the wire is adapted to guide the prosthesis towards the interspinous gap. In particular, it is possible to use a K wire, known also as Kirschner wire, which, as well known, is sufficiently stiff for such use. 
     Advantageously, a tubular guide is provided having at the end means for releasably engaging the intervertebral distractor, the tool being in use guided towards the gripping end of the rod and towards the nut through the tubular guide. 
     Preferably, the engagement means between distractor and tubular guide comprises a couple of teeth arranged at one end of the tubular guide, adapted to engage with corresponding holes provided in the distractor. 
     Advantageously, in order to percutanously extract the intervertebral distractor, a tool is provided; the tool is adapted to engage with the head of the screw for rotating it. The tool is further associated with a device adapted to keep the nut still. In particular, the device adapted to keep the nut still has a plurality of arms telescopically protruding from the tool adapted to engage with the head of the screw, the plurality of arms being suitable to form a gripper that grips the head of the screw. 
     In a second exemplary embodiment of the invention, the means that can be operated percutaneously comprises: a flexible tie member fixed to the stabilizers of at least one of the couples of stabilizers, so that such stabilizers are brought from the closed position to the spread apart position by pulling the tie member, and means for blocking the flexible tie member when the stabilizers have achieved the spread apart position. 
     Advantageously, the means for blocking the flexible tie member are reversible, in order to be released for bringing the stabilizers from the actual spread apart position to the closed position for extracting the implant. 
     In particular, the means for blocking the flexible tie member comprises a couple of counter-rotating friction wheels or circular sectors arranged about respective axes substantially perpendicular to a direction defined by the stretched flexible tie member, such wheels or circular sectors being such that they keep an interference position due to the mutual friction exerted and with the flexible tie member arranged between them. 
     As apparent from the above, and as much clearer from the description of the preferred exemplary embodiments, the stop members have limited mechanical complexity and are easy to manufacture, improving the distractors of the prior art. 
     The distractor according to the invention may have a nominal size selected from the group comprised of: 8, 10, 12, 14 mm, thus being adapted to a percutaneous implantation. 
     Preferably, the elongated body and the stabilizers are made of a metal material, in particular titanium or titanium alloy. Advantageously, the elongated body and the stabilizers have an outer coating surface of a material based on a thermoplastic polymer, which is chosen according to the disc degeneration degree of the vertebra supported by the distractor. In particular, for a slight degeneration degree, in particular for second or third disc degeneration degrees according to the Pfirman classification, soft materials are more suitable, with reference to the spinous apophysis characteristics, whereas if the degeneration is much more serious (fourth or fifth disc degeneration degrees) a harder material is indicated, i.e. having a modulus of elasticity close to that of the bones concerned with the implant. In particular, the material with modulus of elasticity close to that of the bones can be selected among polyaryletherketones, known for their good biocompatibility characteristics. In particular, the polymer can be polyetheretherketone, also known commercially as PEEK®. 
     By way of example, softer materials, adapted to treat less serious degenerations, can be instead selected among polyurethane foams. Such coating material also assists the introduction of the distractor between the spinous processes and limits the even unlikely possibility of mechanical local overloads on the spinous processes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be made clearer with the following description of an exemplary but not limitative embodiment thereof, with reference to the attached drawings wherein: 
         FIG. 1A  is a perspective view of a first interspinous distractor according to the invention, where the stabilizers of both couples of stabilizers are in closed position; 
         FIG. 1B  is a perspective view of an elongated body comprised in the distractor of  FIG. 1A ; 
         FIG. 1C  is a perspective view of a second embodiment of an interspinous distractor according to the invention, where the stabilizers of both couples of stabilizers are in open position; 
         FIG. 2A  is an elevational partially cross-sectional side view of an interspinous distractor according to the invention, where the position of the stabilizers is changed by means of cam-shaped elements adapted to be housed in a space between the stabilizers; 
         FIG. 2B  shows a rod present in the distractor of  FIG. 2A ; 
         FIG. 2C  shows the distractor of  FIG. 2A  after variation of the position of the stabilizers of the first couple by means of a tool; 
         FIG. 2D  shows means operated percutaneously for adjusting the position of the stabilizers of the second couple, comprising a cam-shaped nut adapted to be screwed on a screw threaded portion of the rod and one tool adapted to engage this nut, as well as guiding means to wire and for tool; 
         FIG. 2E  shows the distractor of  FIG. 2A  after variation of the position of the stabilizers of the second couple by means of the nut and the tool; 
         FIG. 2F  shows the median cross sectional view F-F of the elongated body of the distractor shown in  FIG. 2E ; 
         FIG. 2G  is a view of a cam-shaped nut; 
         FIG. 3A  shows a portion of lumbar vertebrae, where the distractor can be inserted according to the invention; 
         FIGS. 3B-3D  show the steps of introducing the distractor according to the invention; 
         FIG. 4A  shows a tubular guide and an embracing portion thereof on the body of the distractor; — 
         FIGS. 4B-4C  show two steps of interaction of the tubular guide with the rod, in the exemplary embodiment of  FIGS. 2A-2G ; 
         FIG. 5A  is an elevational side view of an intervertebral distractor of interspinous type according to the invention, where the position of the stabilizers is changed by means of flexible tie members connected to them; 
         FIG. 5B  shows the distractor of  FIG. 5A  after variation of the position of the stabilizers of the first couple by means of traction of a first flexible tie member; 
         FIG. 5C  shows a wire pulling member, consisting of a couple of friction wheels; 
         FIG. 5D  shows the distractor of  FIG. 5B  after opening also of the stabilizers of the second couple by means of traction of a second flexible tie member, the two flexible tie members being pulled by the member of  FIG. 5C ; 
         FIG. 5E  shows the median cross sectional view E-E of the elongated body of the distractor shown in  FIG. 5D ; 
         FIG. 6A  shows the exemplary embodiment of the distractor of  FIG. 5A , where the stabilizers that are arranged in use below to a median horizontal plane of the body of the prosthesis are shorter than the stabilizers arranged, in use, above the plane; 
         FIG. 6B  shows the distractor of  FIG. 6A  after variation of the position of the stabilizers of the first couple by means of traction of a first flexible tie member; 
         FIG. 6C  shows a wire pulling member, consisting of a couple of friction wheels; — FIG. 6D  shows the distractor of  FIG. 6B  after opening also of the stabilizers of the second couple by means of traction of a second flexible tie member, the two flexible tie members being pulled by the device shown in additional detail in  FIG. 6C ; 
         FIG. 6E  shows the median cross sectional view E-E of a distractor according to the exemplary embodiment of the distractor of  FIG. 6A , where the stabilizers are also asymmetrical, and arranged asymmetrically with respect to the diametrical vertical plane of the body of the distractor; 
         FIG. 6F  shows the median cross sectional view E-E of a distractor according to the exemplary embodiment of the distractor of  FIG. 6A , wherein the stabilizers are also symmetrical with respect to a longitudinal median plane, and are arranged asymmetrically with respect to the diametrical vertical plane of the body of the distractor; 
         FIG. 7  shows the device of  FIG. 6A-F  arranged between the spinous apophysis of two adjacent vertebrae  67  and  68 ; 
         FIG. 8A  is a cross sectional view of an interspinous distractor according to the invention, where the position of the stabilizers is changed by means of cam-shaped elements adapted to be housed in a space between the stabilizers; — FIG. 5B  shows a rod comprised in the distractor of  FIG. 8A ; 
         FIG. 8C  shows the distractor of  FIG. 8A  after variation of the position of the stabilizers of the first couple by means of a tool similar to that shown in  FIG. 2B ; 
         FIG. 8D  shows a cam-shaped nut for adjusting the position of the stabilizers of the second couple, the nut being adapted to be screwed on a screw threaded portion of the rod shown in  FIG. 2B  and to be maneuvered by a tool shown in  FIG. 2D  and in  FIG. 10 ; 
         FIG. 8E  shows the distractor of  FIG. 2A  after variation of the position of the stabilizers of the second couple by means of the nut and the tool; 
         FIG. 8F  shows a median cross sectional view F-F of the elongated body of the distractor shown in  FIG. 8E ; 
         FIG. 8G  shows the distractor of  FIG. 8  A-C-E where the position of the stabilizers of the second couple has been changed in a backward position to assist percutaneous extraction; 
         FIG. 9  shows the distractor of  FIG. 8  A-G and one tool for bringing the stabilizers of the second couple from the spread apart position of  FIG. 8E  to the backward position of  FIG. 8G ; 
         FIG. 10  shows a tool that engages the nut of  FIG. 8D  of the tool of  FIGS. 8A-G  for moving the stabilizers of the second couple from the closed position to a spread apart anatomic position, the position being chosen to give the stabilizers a desired opening angle; 
         FIG. 11  shows a detail of an alternative conjugate profile adapted to provide the rotation of two stabilizers of the distractor of  FIGS. 8A-G ; and 
         FIG. 12  is a cross sectional view of a distractor having a different shape of the central body, and stabilizers that can be operated with mechanisms similar to the distractor of  FIGS. 8A-G ; 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1A and 1B , a first interspinous vertebral distractor  100  is described, comprising an elongated body  10  and two ends  11  and  12  at which two couples of stabilizers  14   a - b  and  14   c - d  are connected by two supports  33  and two couples of hinges  13 . Each stabilizer  14   a - d  has internally a slot that houses a portion of the corresponding support  33 , shaped such that it allows a rotation about the corresponding hinge  13 . In particular, the hinges  13  are distant from the longitudinal axis  1  and each stabilizer  14   a - d  has with respect to body  10 , a distal end and a proximal end. In this way, it is possible to insert the implant percutaneously, in the way hereinafter described in the various exemplary embodiments, with a movement along the axis  1 , acting on the proximal end for causing stabilizers  14   a - b  and  14   c - d  to rotate about the pivot points  13 . 
     In  FIG. 1A , distractor  100  is shown with both couples of stabilizers  14   a - b  and  14   c - d  in closed position, in which configuration distractor  100  is ready for a percutaneous implantation within the spinous processes of two adjacent vertebrae.  FIG. 1B  shows instead the elongated body  10  of the distractor alone. 
     A second embodiment of an interspinous distractor  800 , shown in  FIG. 1C , has still an elongated body  10  similar to the elongated body of distractor  100 , whereas each couple of stabilizers  84   a - b  and  84   c - d  is enclosed between two fixed shells  49 ; furthermore, stabilizers  84   a  and  84   b , in open position, have a convex face oriented opposite to body  10 ; in particular, stabilizers  84   b  and  84   d , that are arranged in use below a plane perpendicular to the spine, are shorter than stabilizers  84   a  and  84   d , as described hereinafter. 
       FIGS. 2A-2G  show an exemplary embodiment of the distractor indicated as  200 , in which a rod  20  is present, the rod being able to slide in a longitudinal recess  15  of elongated body  10 , having transversal sections substantially homothetic to the median cross section shown in  FIG. 2F . At one end of the rod  20 , shown in detail in  FIG. 2B , a cam-shaped portion  21  is visible, adapted to engage with the eccentric or cam-shaped surfaces  17   a - b  of stabilizers  14   a - b , causing a rotation thereof. The opposite end  22  is instead configured to be maneuvered with a tool  4 , for example with a hexagonal head  41 , or a screw driver end. During this translation, rod  20  engages also the recesses  16  and  18 , which are formed respectively between the two stabilizers  14   c - d  and  14   a - b.    
     By way of this maneuver, rod  20  can translate from the actual position shown in  FIG. 2A  to the position shown in  FIG. 2C , and stabilizers  14   a - b  rotate about portions  43  running from the closed position to the spread apart position, whereas stabilizers  14   c - d  remain still in closed position. This is advantageous in use since a surgeon can choose a second moment for blocking the distractor in position, while stabilizers  14   a - b  abut against the spine, seeking a better position for body  10 . 
     A portion  23  of rod  20  close to end  22  ( FIG. 2B ) has a threaded portion  23  on which a nut  25  ( FIG. 2G ) of the distractor can be screwed. This nut  25  has a through hole  27   a , and a cam-shaped surface  26 , adapted to engage with the cam surfaces  17   c - d  of stabilizers  14   c - d , causing a rotation thereof. 
     Nut  25  is maneuvered by a tool  5  that has an hexagonal female head  51  adapted to engage with cam-shaped nut  25  ( FIGS. 2D and 2E ). 
     By this maneuver, the nut  25  moves to the position shown in  FIG. 2E  and stabilizers  14   c - d  rotate running from the closed position of  FIG. 2C  to the spread apart position of  FIG. 2E . 
     In  FIG. 2D , a guiding wire  27  is visible, for example a Kirschner or K wire, passing in rod  20  through end  22  and recess  29  ( FIG. 2F ). When arranging the distractor in the interspinous gap, the wire  27  extends rigidly in the patient, thus allowing the introduction in a first phase of tool  4  and in a second phase of tool  5 . In this way, tools  4  and  5  can be guided towards distraction body  1  to the interspinous position. To allow the movement of the wire  27 , the tools  4  and  5  have recesses  42  and  52  ( FIGS. 2C and 2E ). Obviously, the introduction can be made also without guiding means  27 . 
     In the various exemplary embodiments of the distractor as described in the present application, stabilizers  14   a - d  are advantageously made of titanium and the central body  10  has a core  8  of titanium and a coating surface  3 , for example made of polyetheretherketone (PEEK®); this is shown in the median cross sectional view of  FIG. 2F , according to plane F-F whose shape is shown in  FIG. 2E ; in this cross-section, central recess  15  and rod  20  with recess  29  are also shown. Alternatively, the coating surface  3  can be made of a soft material, for example polyurethane foam, according to the disc degeneration degree of the patient. 
     In  FIGS. 3A-3C  it is shown in more detail how the device  200  as described can be guided towards the interspinous gap  69  set between the spinous apophysis  67  and  68  of two adjacent vertebrae, by means of a Kirschner wire  27 . To this end, as already said above, rod  20  ( FIG. 2B ) is open axially. Furthermore, in order to place the distractor in the interspinous gap, a tubular guide  8   a  can be provided, as shown in detail in  FIG. 4A . The guide has, at one end thereof, a couple of gripping teeth  81  adapted to engage with conjugate holes  82  arranged within the longitudinal recess  16  of stabilizers  14   c  and  14   d . The tubular guide has an inner recess such that it allows the movement of the tools  4  and  5  of  FIGS. 2C and 2E , as shown respectively in  FIGS. 4B and 4C , for opening the couples of stabilizers,  14   a - b  and  14   c - d  respectively. 
       FIGS. 5A-D  show again the interspinous distractor  100  of  FIG. 1A , where the means which can be operated percutaneously for adjusting the position of stabilizers  14   a - b  and  14   c - d  comprises flexible tie members or wires  6  and  7 . In particular, flexible tie member  6  has two ends  61   a  and  61   b  fixed to stabilizers  14   a - b , in this case through two hinges  13 . A rod  19  is also provided, guiding two branches of flexible tie member  6  towards the two stabilizers  14   a - b . Flexible tie member  6  comes out from distractor  1  running through the longitudinal recess  15  of elongated body  10  and through recess  16  determined between the two stabilizers  14   c - d . An end  62  of flexible tie member  6 , opposite to ends  61   a - b , remains out of the body of the patient. 
     In the same way, a flexible tie member  7  has two ends  71   c - d  fixed to stabilizers  14   c - d  by two hinges  13  and a rod  19 . This flexible tie member comes out of distractor  1 , running also through the recess  16 . An end  72 , opposite to ends  71   c - d  remains out of the body of the patient. A traction on the flexible tie members  6  and  7 , effected from an endoscopic position, allows bringing respectively stabilizers  14   a - b  and  14   c - d  from the closed position shown in  FIG. 5A  to the spread apart position shown in  FIG. 5D . 
     Once the stabilizers of the two couples are brought to the respective spread apart positions, the two flexible tie members  6  and  7  act as guiding means for a device  30  for blocking the stabilizers in the spread apart position; this device has a couple of friction counter rotating wheels  31 , and a tool  9  is used, comprising a recess  91  and a head  92  adapted to arrange the device  30  to a contrast with support  33 . Traction on wires  6  and  7  forces the device  30  in this position, due to the friction exerted with and between friction wheels  31 . 
     Alternatively, or in addition to the friction wheels, circular sectors can be provided opposite to each other and in geared fashion, kept in blocked position with the locked wires within them. As a further alternative, or in addition, the wires can be locked with rings of a metal material, for example titanium, sliding along the wire and then locked on the wire with plastic deformation, in order to prevent a back sliding of the wire. 
     Also in this case, the central body and the stabilizers have a core of titanium, with a coating surface  3  of polyetheretherketone (PEEK®), as shown in  FIG. 5E , which is a cross sectional view of elongated body  10  according to plane E-E, whose shape is indicated in  FIG. 5D , where central recess  15  and flexible tie member  6  are also shown. 
     Similarly, the operation of distractor  600  shown in  FIGS. 6A-D  provides the same concepts. This distractor differs from distractor  100  of  FIGS. 5A-D , since stabilizers  14   b  and  14   d , which are arranged in use below the median horizontal plane of body  10  of the distractor, are shorter than the corresponding stabilizers  14   a  and  14   c , as shown, in particular, in  FIGS. 6A and 6B . This arrangement is used to avoid interference with the spinous processes or lateral processes of the vertebra just below the two distracted vertebrae, which can occur, in particular, when there are vertebral degenerations or in case of scoliosis. Furthermore, device  600  has stabilizers  64   a - d  that are asymmetrical with respect to a desired vertical plane; such stabilizers can be conceptually obtained cross-sectioning corresponding stabilizers of the type  14   a - d , symmetrical, with a vertical plane parallel to the axis of the distractor, and removing one of the two parts of each lateral stabilizer thus obtained, typically the part having smaller size. This is used in order to avoid an interference with the lateral processes, as shown in  FIG. 7 . 
     Alternatively to what shown in  FIG. 6D ,  FIG. 6E  represents a solution with stabilizers that are symmetrical with respect to their own longitudinal median plane, but arranged asymmetrically with respect to the vertical median plane of the body of the distractor. 
     The distractor  800  shown in  FIGS. 8A-E , as well as in  FIG. 1C , has the two couples of stabilizers  84   a - b  and  84   c - d  enclosed between fixed protection shells  49 . The opening/closing movement of the stabilizers is performed by translating a rod  70  ( FIG. 8B ) with a cam-shaped end  77 , and a nut  75  with a cam-shaped surface  76  ( FIG. 8D ), the translation being operated by a tool in a similar way as described for distractor  200  of  FIGS. 2A-G . 
     In this device, an anatomic solution is used that provides lower stabilizers  84   b  and  84   d  of length lower than the higher stabilizers  84   a  and  84   c . Like in the exemplary embodiments previously described, the concave part of the stabilizers of the couple  84   a - b  is oriented, in open position, opposite to the central body  10 , the stabilizers of this couple being adapted to rotate from the closed position of  FIG. 8A  to the spread apart position of  FIGS. 5C and 8D , and eventually to the closed position shown in  FIG. 8G . This is used to assist a percutaneous extraction of the distractor from the interspinous gap, the extraction occurring according to the direction  89  of the arrow shown in  FIG. 8G . 
     Concerning the stabilizers of the couple  84   c - d , their convex part is oriented, in the spread apart position, opposite to the central body. Furthermore, stabilizers  84   c - d  are capable of rotating about the pivot point  83  beyond the spread apart position continuing further for angles larger than 90°, in particular, between 120° and 180°, and in  FIG. 8G  of about 150°. As shown in  FIG. 8G , the two stabilizers  84   c - d  have a curved shape with concavity such that, during the introduction according to arrow  88  ( FIG. 8A ), it is oriented opposite to the axis  1  of the body and, during the extraction according to arrow  89  ( FIG. 8G ), it is oriented according to the same side of the axis  1  of the body. 
     The stabilizers of such couple  84   c - d  can then rotate from the closed position of  FIG. 8A  to the spread apart position of  FIGS. 5C and 5D , up to reaching the closed position shown in  FIG. 8G . In the latter closed position, stabilizers  84   c - d  have a rotation induced by the same extraction, once the cams  84   c  and  84   d  have abandoned the cam-shaped portion  76  of the cam-shaped nut  75 . In particular, the opposite concavity of stabilizers  84   c - d  is used to assist the percutaneous extraction of the distractor from the interspinous gap according to the direction  89 . With a numbering similar to that relative to distractor  200 , the other elements of the distractor  800  are described in  FIGS. 8A-8G . 
     As shown in  FIG. 9 , in order to adjust the opening angle of a distal couple of stabilizers  84   c - d  by rod  70 , a tool  90  can be used, having a couple of symmetrical tools  96  engageable with two horizontal pins  99  integral to a fixed portion of the distractor  800 , for example with protective shells  49 , such tools being adapted to block nut  75  in a determined position; tool  90  comprises, furthermore, a rotatable device  94  with an hexagonal female head adapted to engage with the male head of rod  70 ; with a rotation of the tool it is therefore possible to move rod  70 , causing a translation associated with the rotation, suitable for moving stabilizers  84   c - d  with micrometric precision and according to reproducible positions. 
     With reference to  FIG. 10 , the proximal end of stabilizers  84   c  and  84   d  have a convex shape, which can be a cam-like shape  87   c  and  87   d , whereas the cam-shaped portion  76  of the rod has a corresponding concave shape, whereby the convex and concave shapes form two conjugate profiles. This allows a micrometric adjustment of stabilizers  84   c  and  84   d.    
     An alternative exemplary embodiment that can be applied to any embodiments of the invention is shown in  FIG. 11 , providing conjugate profiles  130   c - d  of the proximal end and of the cam-shaped portion  120  of the rod that are convex, and may have gear-like portions on the surface (not shown). 
       FIG. 12  shows, according to another exemplary embodiment of the invention, a distractor  900  having central body  110  with the shape of a right circular frustum of cone, with the generatrix at an angle  113  of 5° with respect to the axis. Like the central body  10  of the device  800  of  FIGS. 8A-G , the central body  110  has a coating  108  of a material chosen according to the disc degeneration degree of the patient, and an inner core  103  of titanium. To provide the frustum-conic shape of the central body  110 , the core  108  has an end  104  having size larger than the end  105 , as well as stabilizers  114   a/b  larger than stabilizers  114   c/d . The distractor  900  can be used advantageously for patients suffering from scoliosis. In this case, the part of stabilizer corresponding to end  104  is placed according to the part of the spine that has a concavity. In analogy to distractor  800 , distractor  900  has its lower stabilizers  114   b  and  114   d  having a length lower than the higher stabilizers of a same couple, respectively  114   a  and  114   c , and this is an anatomic solution that makes the distractor  900  also suitable for treating patients suffering from scoliosis. The position of stabilizers  114   a - d  is adjusted acting on movable components of the distractor  900  similar to those of the distractor  800 , in particular, stabilizers  114   a  and  114   d  are brought from a closed position to a spread apart position and vice-versa by translating a rod  111  similar to rod  70  of  FIG. 8B , whereas stabilizers  114   b  and  114   c  are moved by nut  112  similar to nut  75  of  FIG. 8D , owing to the cam surfaces of the rod and of the nut adapted to engage, respectively, the couples of cam surfaces of stabilizers  114   a - d  and  114   c - d.    
     Obviously, the solution of  FIG. 12  can be applied to any desired type of interspinous distractor. 
     The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.