Abstract:
A method for the removal of an intervertebral disc or parts thereof to be treated that includes: inserting a first longitudinal bone anchor into a pedicle of a first vertebra; inserting a second longitudinal bone anchor into a pedicle of a second vertebra; bridging the first and second anchors using a bridging element including a first and second clamp; attaching adjustable extension arms to each of the two clamps; introducing a longitudinal guiding element into the intervertebral disc or the subchondral bone of one of the vertebral bodies adjacent of intervertebral disc; fixing a retractororthogonally on the longitudinal guiding element; connecting the free ends extension arms to the retractor; immobilizing the extension arms to obtain a rigid assembly; and using the retractor as an anatomically positioned platform for performing the removal of the intervertebral disc to be treated or parts thereof, and a kit and apparatus for performing the method.

Description:
BACKGROUND OF INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates to a method for the removal of intervertebral discs, to a kit for the removal of intervertebral discs and to an apparatus for the removal of intervertebral discs. 
         [0003]    2. Description of the Related Art 
         [0004]    A method for performing an intervertebral disc replacement and for anatomically establishing a reference point for an intervertebral disc to be replaced is known from Petit et al., Pub. No. US 2012/0116517 A1. In a first step bone anchors are anchored in the same vertebra, then in a second step, a linking bar is positioned between the two bone anchors and in a third step a platform is mounted on the linking bar. After adjusting and locking the position of a viewing element arranged on the platform an implantation instrument can be rotatably coupled to a rod affixed on the viewing element. This implantation instrument permits to implant a disc prosthesis or an osteosynthesis cage through a posterior, a postero-lateral or a lateral approach. One problem associated with the above described method is that the posterior or postero-lateral approach to the intervertebral disc space is achieved by means of a curved tubular implantation instrument which is pivotably coupled to the viewing element and which permits only a small operation field defined by the inner diameter of the tubular instrument. Furthermore, due to the curvature of the implantation instrument flexible instruments must be used. A further problem associated with the above described method is that the complete apparatus comprising the linking bar, the platform and the viewing element is attached to the actual vertebra by means of two pin like bone anchors. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    It is therefore an object of the invention to provide a method for the removal of intervertebral discs which permits a linear lateral or postero-lateral approach to the intervertebral disc space for inserting an artificial disk, prosthesis or cage therein. It is a further object of the invention to provide an apparatus for the removal of intervertebral discs which permits to adjust the operation field to a desired size. 
         [0006]    The invention solves the posed problem with a method for the removal of intervertebral discs as disclosed and claimed herein, with a kit for the removal of intervertebral discs as disclosed and claimed herein and with an apparatus for the removal of intervertebral discs as disclosed and claimed herein. 
         [0007]    The advantages of the method and apparatus according to the invention are essentially to be seen therein that:
       the retractor permits a linear lateral or postero-lateral approach to the intervertebral disc space so that no flexible instruments are required;   due to the adjustable extension arms and the longitudinal guiding element the retractor can be exactly positioned with a desired angle with respect to the sagittal plane of the patient;   the movable sliders of the retractor permit to reduce or enlarge the size of the operation field. The maximum size of the operation field is defined by the diameter of the through hole in the frame of the retractor; and   a stable fixation of the longitudinal bone anchors in the pedicles can be achieved.       
 
         [0012]    This is particularly important in the case of elderly patients where the pedicles provide regions with optimal bone quality. 
         [0013]    Further advantageous embodiments of the invention can be commented as follows: 
         [0014]    In a special embodiment the longitudinal guiding element is a Kirschner-wire or a bone pin. 
         [0015]    In a further embodiment the longitudinal guiding element comprises a navigational tool. 
         [0016]    Preferably, four or more longitudinal bone anchors are inserted into the pedicles of the first and second vertebrae. 
         [0017]    In another embodiment the longitudinal bone anchors are inserted into the transition zone of the superior facet joint of the vertebra. 
         [0018]    In again another embodiment the longitudinal bone anchors are inserted into the neck of the facet joint. 
         [0019]    In a further embodiment the longitudinal bone anchors and the longitudinal guiding element are inserted subcutaneously. 
         [0020]    In a further embodiment the method comprises a further step: using the retractor as an anatomically positioned platform for implanting an artificial disc or an osteosynthetic cage into the intervertebral space of the removed intervertebral disc. 
         [0021]    In again a further embodiment the method comprises after insertion of the first and second longitudinal bone anchors into the pedicles of the first and second vertebrae the further step of: spreading the first and second bone anchors to therewith move the two adjoining vertebrae further apart by using a spreader to enlarge the intervertebral space, particularly for facilitating insertion of an intervertebral disc replacement implant or of an intervertebral implant. 
         [0022]    In another embodiment the hinge of the bridging element is loosenably locked. 
         [0023]    In another embodiment the method further comprises, before a retractor is fixed orthogonally on a longitudinal guiding element, the step of fitting a first tubular dilatator onto the longitudinal guiding element. 
         [0024]    Preferably, the method additionally comprises the step of subsequently and telescopically pushing one or more further tubular dilatators over the first dilatator. Therewith, the advantage can be achieved that the tubular dilatators permit to open the operation field to a desired extent. 
         [0025]    In a further embodiment the method further comprises, after using the retractor as an anatomically positioned platform for performing the removal of the intervertebral disc to be treated or parts thereof, the step of pulling or pushing sliders which are slideably arranged on the retractor towards or away from the guiding element until a desired opening as an operation field is achieved. 
         [0026]    In a further embodiment the method comprises the additional step of inserting extension blades in blades attached to the sliders of the retractor. 
         [0027]    In again a further embodiment the method comprises the additional step of inserting a pin in each extraction blade to affix the same in position relative to the retractor. 
         [0028]    According to a further aspect of the invention, there is provided a kit for the removal of intervertebral discs or parts thereof and for the implantation of disc prosthesis or osteosynthesis cages, the kit comprising: a) two or more longitudinal bone anchors; b) one or more bridging elements comprising a first and second clamp connected by a hinge; c) two or more adjustable extension arms attachable to the clamps; d) one or more longitudinal guiding elements; and e) one or more retractors. 
         [0029]    In a special embodiment the kit further comprises one or more dilatators which are slideable over the guiding element, respectively over the previous dilatator. 
         [0030]    In another embodiment the kit further comprises two or more pins for fixation of extension blades of the retractor to bone. 
         [0031]    In accordance with again a further aspect, an apparatus for the removal of intervertebral discs is provided which comprises:
       at least two longitudinal bone anchors affixable to a pedicle each;   a bridging element comprising a first and a second clamp, wherein each clamp of the bridging element is loosenably affixed to one bone anchor;   at least a first and a second adjustable extension arm, wherein each one end of the extension arms is loosenably affixed to one of the first and second clamps;   a retractor which is loosenably affixed to the other ends of the extension arms, wherein the retractor comprises:   a frame which defines a plane and a central axis orthogonal to the plane and which includes a lower side directed towards a vertebra, an upper side and a through hole coaxially to the central axis; and   at least two sliders which are slideably arranged at the frame on opposite sides and parallel to the plane defined by the frame so as to be moved towards and away from the central axis and which are loosenably fixable relative to the frame in a desired position.       
 
         [0038]    In another embodiment each extension arm comprises at least one articulation which is reversibly lockable. 
         [0039]    In another embodiment a blade is attached to each slider so that each blade protrudes from the lower side of the frame essentially parallel to the central axis. 
         [0040]    In again another embodiment the at least one bridging element comprises a hinge connecting the first and second clamp. 
         [0041]    In a further embodiment the hinge of the at least one bridging element is reversibly lockable. 
         [0042]    In another embodiment the apparatus further comprises extension blades whereof each one is loosenably affixable to one of the blades of the retractor. 
         [0043]    Preferably, each slider comprises teeth arranged along a longitudinal side of the slider, wherein the longitudinal side extends from an inner end of the slider directed towards the central axis to an opposite outer end of the slider; and wherein the frame comprises a guidance each for the sliders which is provided with a pawl resiliently biased into engagement with the teeth of the respective slider. 
         [0044]    In another embodiment the apparatus additionally comprises one or more cross beams each comprising a first and a second clamp connected by a hinge, wherein each clamp of the one or more cross beams is loosenably affixable to one bone anchor. 
         [0045]    The foregoing and other features of the invention are hereinafter more fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the present invention may be employed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0046]    Several embodiments of the invention will be described in the following by way of example and with reference to the accompanying drawings in which: 
           [0047]      FIG. 1  illustrates a perspective view from lateral of an embodiment of the apparatus according to the invention from lateral; 
           [0048]      FIG. 2  illustrates a perspective view from dorsal-lateral of a portion of the spinal column with pedicle pins inserted according to a first step of an embodiment of the method according to the invention; 
           [0049]      FIG. 3  illustrates a perspective view from dorsal-lateral of a portion of the spinal column with a clamp fitted to a part of the pedicle pins according to a second step of the embodiment of the method according to the invention; 
           [0050]      FIG. 4  illustrates a perspective view from dorsal of a portion of the spinal column with two cross beams according to the embodiment of the method according to the invention; 
           [0051]      FIG. 5  illustrates a perspective view from dorsal-lateral of a portion of the spinal column with adjustable extension arms attached to the clamps according to a third step of the embodiment of the method according to the invention; 
           [0052]      FIG. 6  illustrates a perspective view from lateral of a portion of the spinal column with a Kirschner-wire specifying the operating field according to a fourth step of the embodiment of the method according to the invention; 
           [0053]      FIG. 7  illustrates a perspective view from lateral of a portion of the spinal column with a first dilatator fitted on the Kirschner-wire according to a fifth step of the embodiment of the method according to the invention; 
           [0054]      FIG. 8  illustrates a perspective view from lateral of a portion of the spinal column with a second dilatator fitted on the first dilatator according to a sixth step of the embodiment of the method according to the invention; 
           [0055]      FIG. 9  illustrates a perspective view from lateral of a portion of the spinal column with a the retractor fitted on the last dilatator according to a seventh step of the embodiment of the method according to the invention; 
           [0056]      FIG. 10  illustrates a perspective view from lateral of the retractor of the embodiment of the apparatus according to the invention of  FIG. 1  when being opened with a separating tool; 
           [0057]      FIG. 11  illustrates a perspective view from lateral of the retractor of the embodiment of the apparatus according to the invention of  FIG. 1  when being fully opened; 
           [0058]      FIG. 12  illustrates a lateral view of the extension blades according to the embodiment of the apparatus according to the invention of  FIG. 1 , where the extension blades are attached to a special screwdriver; 
           [0059]      FIG. 13  illustrates a perspective view from lateral of the extension blades inserted in the blades of the retractor according to an eighth step of the embodiment of the method according to the invention; 
           [0060]      FIG. 14  illustrates a side view of the retractor during insertion of the extension blades in the blades of the retractor according to the eighth step of the embodiment of the method according to the invention; 
           [0061]      FIG. 15  illustrates a perspective view from dorsal-lateral of a portion of the spinal column with a light adapter attached to the retractor according to a ninth step of the embodiment of the method according to the invention; 
           [0062]      FIG. 16  illustrates a lateral view of the retractor when being closed according to a tenth step of the embodiment of the method according to the invention; 
           [0063]      FIG. 17  illustrates a perspective view from dorsal-lateral of the retractor with four Hohmann-adpaters attached thereto according to another embodiment of the method according to the invention; 
           [0064]      FIG. 18  illustrates a perspective view from dorsal of the retractor with four Hohmann-levers attached to the Hohmann-adapters during preparation of the operation field according to the embodiment of the method according to the invention of  FIG. 17 ; 
           [0065]      FIG. 19  illustrates a perspective view from dorsal-lateral of the retractor with four Hohmann-levers fixed to a Hohmann-adapter each according to the embodiment of the method according to the invention of  FIG. 17 ; 
           [0066]      FIG. 20  illustrates a perspective view from lateral of the retractor during fixation of the extension blades according to the embodiment of the method according to the invention of  FIG. 17 ; 
           [0067]      FIG. 21  illustrates a perspective view from lateral of the retractor during fixation of the extension blades with pins according to the embodiment of the method according to the invention of  FIG. 17 ; 
           [0068]      FIG. 22  illustrates a cross section of an extension blade of according to the embodiment of the apparatus according to the invention of  FIG. 1 , where a pin is inserted in the extension blade; and 
           [0069]      FIG. 23  illustrates a top view of the retractor which the Hohmann-levers removed according to the embodiment of the method according to the invention of  FIG. 17 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0070]    The terms “comprises”, “comprising”, “includes”, “including”, “having” and their conjugates mean “including but not limited to”. This term encompasses the terms “consisting of” and “consisting essentially” of. 
         [0071]    The phrase “consisting essentially of” means that the method may include additional steps, but only if the additional steps do not materially alter the basic and novel characteristics of the claimed method. 
         [0072]    As used herein, the singular form “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a compound” or “at least one compound” may include a plurality of compounds, including mixtures thereof. 
         [0073]    Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range. 
         [0074]    Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases “ranging/ranges between” a first indicate number and a second indicate number and “ranging/ranges from” a first indicate number “to” a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween. 
         [0075]    It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements. As used herein the term “method” refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the medical arts. 
         [0076]    The word “optionally” is used herein to mean “is provided in some embodiments and not provided in other embodiments”. Any particular embodiment of the invention may include a plurality of “optional” features unless such features conflict. 
         [0077]      FIGS. 1 to 16  illustrate an embodiment of the apparatus  30  according to the invention essentially including a retractor  19  which is loosenably affixed to each one end of two extension arms  16 ,  17 , a bridging element  20  to which the other ends of the extension arms  16 ,  17  are affixed and a plurality of bone anchors  11 ,  12 . Exemplarily, two longitudinal bone anchors  11 ,  12  are affixed to each a pedicle  2 ,  4  of a first and a second vertebra  6 ,  7  ( FIG. 2 ) on the same side of the sagittal plane  8  and two further longitudinal bone anchors  11 ′,  12 ′ are affixed to each a pedicle  3 ,  5  of the first and second vertebrae  6 ,  7  on the other side of the sagittal plane  8 . 
         [0078]    The bridging element  20  comprises a first and a second clamp  13 ,  14  and a hinge  15  arranged between the first and second clamps  13 ,  13 . Each clamp  13 ,  14  of the bridging element  20  is loosenably affixed to one bone anchor  11 ,  12 . Each one end of the extension arms  16 ,  17  is loosenably affixed to one of the first and second clamps  13 ,  14  of the bridging element  20 . 
         [0079]    The extension arms  16 ,  17  each comprise a centrally positioned articulation  9  which is reversibly lockable by means of a turning knob  41 . Furthermore, each end of the extension arms  16 ,  17  is provided with a ball-and-socket joint  38  and terminally arranged a snap-on mounting  42  that can be mounted to respective pegs  43  ( FIG. 3 ) which are terminally positioned at the clamps  13 ,  14  of the bridging element  20 . To avoid a relative rotation between the extension arms  16 ,  17  and the clamps  13 ,  14  of the bridging element  20  the pegs  43  and the complementary cavities (not shown) in the snap-on mountings  42  have a polygonal cross section. The snap-on mountings  42  can be detached from the pegs  43  by pushing a push-button  45  provided on the snap-on mounting  42 . 
         [0080]    Additionally, a first and a second cross beam  10 ,  10 ′ are attached to the bone anchors  11 ,  11 ′,  12 ,  12 ′. Each cross beam  10 ,  10 ′ comprises a first and a second clamp  39 ,  40  which are connected by a hinge  15 . Exemplarily, the first cross beam  10  is attached to the first bone anchor  11 ′ on the side of the sagittal plane  8  which is opposite to the bridging element  20  and to the second bone anchor  12  which is on the same side of the sagittal plane  8  as the bridging element  20 . The second cross beam  10 ′ is attached to the second pair of longitudinal bone anchors  11 ′,  12 ′ which is affixed to the pedicles  3 ,  5  of the first and second vertebrae  6 ,  7  on the side of the sagittal plane  8  which is opposite to the bridging element  20  ( FIGS. 2 to 4 ). 
         [0081]    The retractor  19  essentially comprises a frame  29  which defines a plane  33  and a central axis  34  orthogonal to the plane  33  and which includes a lower side  36  directed towards a vertebra, an upper side  37  and a through hole  35  coaxially to the central axis  34 . Further, the retractor  19  comprises exemplarily four sliders  32  which are slideably arranged at the frame  29  on opposite sides and parallel to the plane  33  defined by the frame  29 . The sliders  32  can be moved towards and away from the central axis  34  and are loosenably fixable relative to the frame  29  in a desired position. Each slider  32  is provided with teeth  44  ( FIG. 11 ) arranged along a longitudinal side of the slider  32 , extending from an inner end of the slider  32  directed towards the central axis  34  to an opposite outer end of the slider  32 . The frame  29  comprises a guidance each for the sliders  32  which is provided with a pawl (not shown) resiliently biased into engagement with the teeth  44  of the respective slider  32 . Furthermore, the frame  29  is provided with similar pegs  43  as the clamps  13 ,  14  of the bridging element  20  so that the snap-on mountings  42  on the other ends of the extension arms  16 ,  17  can be attached to the pegs  43  on the frame  29  of the retractor  19 . 
         [0082]    Furthermore, a blade  24  ( FIGS. 1 ,  11  and  12  to  15 ) is attached to each slider  32  so that each blade  24  protrudes from the lower side  36  of the frame  29  essentially parallel to the central axis  34  of the frame  29  of the retractor  19 . The retractor  19  can additionally comprise extension blades  25  whereof each one is loosenably affixable to one of the blades  24  of the retractor  19 . The extension blades  25  can be fixed to the vertebrae by means of pins  31  ( FIG. 22 ) whereof each one pin  31  extends through a bore arranged in the extension blades  25 . 
         [0083]    The above described apparatus  30  can be assembled by using respective parts of a kit, wherein a preferred embodiment of the kit comprises: a) two or more longitudinal bone anchors  11 ,  12 ; b) one or more bridging elements  20 ; c) two or more adjustable extension arms  16 ,  17 ; d) one or more longitudinal guiding elements  18 ; and e) one or more retractors  19 . 
         [0084]    Additionally, the kit can comprise one or more dilatators  21 ,  22 ,  23  which are slideable over the guiding element  18 , respectively over the previously inserted dilatator  21 ,  22 . Further, the kit can comprise two or more pins  31  for fixation of extension blades  25  of the retractor  19  to bone. 
         [0085]      FIGS. 2 to 23  illustrate an embodiment of the method according to the invention. In a first step ( FIG. 2 ) at least a first pair of first and second longitudinal bone anchors  11 ,  12  is inserted into the pedicles  2 ,  4  of a first and a second vertebra  6 ,  7  on the same side of the sagittal plane  8  and on either side of the intervertebral disc  1  to be treated. Optionally, to increase the stability of the apparatus  30  ( FIG. 1 ) a second pair of first and second longitudinal bone anchors  11 ′,  12 ′ can be inserted into the pedicles  3 ,  5  of the first and the second vertebra  6 ,  7  on the other side of the sagittal plane  8  and on either side of the intervertebral disc  1  to be treated. 
         [0086]    As illustrated in  FIG. 3 , in a second step a bridging element  20  is affixed to the first pair of bone anchors  11 ,  12 . Thereto, a first clamp  13  arranged at one end of the bridging element  20  is fastened to the first bone anchor  11  and a second clamp  14  arranged at the other end of the bridging element  20  is fastened to the second bone anchor  12 . The bridging element  20  further comprises a hinge  15  positioned between the first and second clamp  13 ,  14 . At this stage, the level of the clamps  13 ,  14  does not matter because the level will be compensated at a later step of the method. 
         [0087]    Optionally, at this stage of the surgical procedure a spreader can be attached to a pair of first and second bone anchors  11 ,  12  so that the surgeon can spread the first and second bone anchors  11 ,  12  to therewith move the two adjoining vertebrae  6 ,  7  further apart so as to enlarge the intervertebral space, particularly for facilitating insertion of an intervertebral disc replacement implant or of an intervertebral implant. 
         [0088]    A cross beam  10  can be exemplarily attached to the first bone anchor  11 ′ of the second pair of a first and a second bone anchor  11 ′,  12 ′ and to the second bone anchor  12  of the first pair of a first and a second bone anchor  11 ,  12 . In this case the cross beam  10  is to be attached to the bone anchors  11 ′,  12  before the bridging element  20  is attached to the bone anchors  11 ,  12 . The cross beam  10  allows to increase the stabilization. It is possible to use only one cross beam  10 . However, when necessary a second cross beam  10 ′ ( FIG. 4 ) can be used, which is exemplarily attached to the second pair of longitudinal bone anchors  11 ′,  12 ′ which is affixed to the pedicles  3 ,  5  of the first and second vertebrae  6 ,  7  on the side of the sagittal plane  8  which is opposite to the bridging element  20 . 
         [0089]    In a third step as illustrated in  FIG. 5  each an adjustable extension arm  16 ,  17  is attached to one of the clamps  13 ,  14  of the bridging element  20 . Each extension arm  16 ,  17  comprises an articulation with a locking system. Further, there are marking letters (not shown) positioned on each clamp  13 ,  14  and on the snap-on mountings  42  of each extension arm  16 ,  17  which are to be matched. The extension arms  16 ,  17  are to be locked once attached to the bridging element  20 . 
         [0090]      FIG. 6  illustrates a fourth step where the operation field is defined by introducing a longitudinal guide element  18 , e.g. a Kirschner-wire into the intervertebral disc  1  to be treated at an angle between 80° and 90° with respect to the sagittal plane  8  of the patient ( FIG. 2 ) by using X-ray. Alternatively, the longitudinal guide element  18  can be introduced into the subchondral bone of one of the vertebral bodies adjacent of intervertebral disc  1  to be treated. Thereby, only the position of the tip of the guide element  18  is important, the angle of guide element  18  will be adjusted in a further step. 
         [0091]    In a fifth step a first dilatator  21  is fitted on the longitudinal guide wire  18  as illustrated in  FIG. 7 . Furthermore, in a sixth step a second dilatator  22  is fitted on the first dilatator  21 . Optionally, a third dilatator  23  can be fitted on the second dilatator  22  ( FIG. 8 ). 
         [0092]    Subsequently, in a seventh step as illustrated in  FIG. 9  the retractor  19  is fitted on the outermost, i.e. the third dilatator  23  in the present exemplary embodiment. The lower sections of the extension arms  16 ,  17  are locked to the retractor  19  with a locking system. Further, there are marking letters (not shown) positioned on the snap-on mountings  42  of the extension arms  16 ,  17  and on the retractor  19  which are to be matched. The lower sections of the extension arms  16 ,  17  are locked with a button on their locking devices. In this seventh step the retractor  19  can be adjusted in the proper position. After this adjustment is completed, the locking systems on each extension arm  16 ,  17  are tightened. The position of the retractor  19  for the operation is now fixed and should not be modified. Any further manipulation of the extension arms  16 ,  17  must be avoided. 
         [0093]    As shown in  FIG. 10  the retractor  19  can be opened with a special separating tool. The maximum opening range is the inner ring of the retractor  19 . As the retractor  19  is opened, each click indicates a potential locking position for the blades  24  ( FIG. 11 ) of the retractor  19 .  FIG. 11  illustrates the fully opened retractor  19 . 
         [0094]    Before insertion of the extension blades  25  a screwdriver is attached to the extension blades  25  as illustrated in  FIG. 12 . Then, in an eighth step as shown in  FIG. 13  the extension blades  25  are inserted in the blades  24  of the retractor  19 . It is possible to pre-fix the extension blades  25  on the blades  24  of the retractor  19  with a screwdriver as shown in  FIG. 14 . The screwdriver has to be removed when the extension blades  25  are in their position. If necessary the retractor  19  could be closed and reopened depending on the anatomical situation. 
         [0095]    In a ninth step as illustrated in  FIG. 15  a light adapter  26  can be attached to the retractor  19  on one of the free positions of the retractor locking system. The light adapter  26  can be used to fix a standard surgical lightning system. 
         [0096]    In an tenth step as illustrated in  FIG. 16  the retractor  19  is closed on the positions indicated by arrows A. It is possible to lock or unlock each individual blade  24 . If it is necessary to reopen the retractor  19 , it is possible to do that with a special separating tool (not shown). 
         [0097]    Subsequently, as illustrated in  FIG. 20  the extension blades  25  can be fixed in their final position by using a screwdriver. Thereafter, the extension blades  25  can be fixed in a sixteenth step ( FIGS. 21 and 22 ) with pins  31  after removing the screwdriver. 
         [0098]    In another embodiment of the method according to the invention—if desired by the surgeon—Hohmann-levers  28  can be used for the surgical procedure as illustrated in  FIGS. 18-21 . In this case the Hohmann-levers  28  are used to prepare the operation field before the extension blades  25  are fixed in their final position. As illustrated in  FIG. 17 , the Hohmann-adapters  27  can be attached to the frame  29  of the retractor  19 , exemplarily in four positions. Due to the close quarters of the frame  29 , two vis-a-vis positions are recommended. Subsequently, each a Hohmann-lever  28  can be used to prepare the operation field so that no tissue remains on the intervertebral disc  1  and the nerves are moved outside the operation field. Then, as illustrated in  FIG. 19  each Hohmann-lever  28  can be fixed to the respective Hohmann-adapter  27  after the Hohmann-levers  28  have been softly tapped in with a hammer. 
         [0099]    The extension blades  25  can then be fixed in their final position by using a screwdriver ( FIG. 20 ). Thereafter, the extension blades  25  can be fixed ( FIGS. 21 and 22 ) with pins  31  after removing the screwdriver. For the subsequent intervertebral disc operation the Hohmann-levers  28  must be removed ( FIG. 23 ). 
         [0100]    Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the broad scope of the appended claims.