Abstract:
A rod insertion system and at least two bone anchors including: a rod guide configured to accommodate a spinal stabilization rod therein; a holding device including a clamping portion configured to hold a portion of the rod guide; and an adapter configured to moveably support the holding device. The holding device is configured to move and pivot along an adapter such that the rod guide is positioned proximal to a rod channel of one of the at least two bone anchors. In a first state, the rod guide is fixed to the holding device by the clamping portion, and, in a second state in which the holding device supports the portion of the rod guide, the clamping portion is released from the portion of the rod guide to permit the orientation of the rod guide relative to the holding device to be polyaxially adjusted.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present disclosure claims the benefit of U.S. Provisional Patent Application Ser. No. 61/919,559, filed on Dec. 20, 2013, the contents of which are hereby incorporated by reference in their entirety, and claims priority to European Patent Application EP 13199223.2, filed on Dec. 20, 2013, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a rod insertion device for inserting a spinal stabilization rod into at least two bone anchors. The device includes a tubular rod guide that allows the spinal stabilization rod to move therethrough, a holding device configured to hold the rod guide, and an adapter configured to be connected to an extension which may be fixed to a receiving part of one of the bone anchors. 
         [0004]    2. Description of the Related Art 
         [0005]    It is known in the art to treat fractures of the spinal column, arthrodesis, scoliosis, etc. by stabilizing the spinal column using bone anchors implanted in two or more vertebrae and connecting the same by rigid or dynamically flexible stabilization rods to, for example, define a predetermined relative position and movement tolerance for each of the vertebrae involved. In operation, bone anchors are selectively provided to vertebrae and a stabilization rod is then used (e.g., inserted) to connect each of the bone anchors. Several methods and instruments have been developed to insert a rod into respective rod channels provided in receiving parts of the bone anchors. 
         [0006]    U.S. 2013/0096637 A1 discloses an instrument having a main body holding a tubular, curved rod holder which receives a rod. The rod can be advanced through slots of respective spinal implants. An extension at the main body functions as an adapter to connect to a post which is mounted to the receiving part of a spinal implant (e.g., a bone anchor). Keyways provided at the post and extension ensure that the main body attains a predetermined position with respect to the spinal implant. In operation, a handle is used to advance the rod holder with the rod mounted therein through the soft-tissue until a predetermined position proximal to a slot in the spinal implant is reached. Thereby, a set of bearings are provided in the main body which guide the rod holder. 
         [0007]    U.S. 2002/0161368 A1 discloses an installation instrument for a connecting element (e.g., a rod) including support arms that respectively connect to anchor extensions mounted to yokes of two adjacent bone anchors. An inserter for the rod is provided as a pivot arm which may pivot in a circular manner about an axis relative to the support arms. As a consequence, the rod is inserted into respective passage ways of the adjacent anchors by the pivoting movement of the inserter. 
         [0008]    U.S. Pat. No. 8,105,362 B2 discloses a rod insertion system. Extenders mounted at respective pedicle screw heads are provided with extender heads which are aligned with respect to each other using rod-like alignment members. The alignment members are slidably engaged with a pair of arms which securely connect to an arcuate guide tube. The arcuate guide tube holds an insertion member by which a spinal rod may be advanced through respective passageways of the pedicle screws using a rod insertion probe. 
         [0009]    U.S. Pat. No. 7,918,878 B2 discloses a minimally invasive surgical (MIS) system, wherein an inserter formed as a straight rod is held by a guide. The inserter is provided with a connecting member at its tip. The guide is connected to a manipulator assembly extending from a bone anchor, and the guide has an aperture through which the inserter is led such as to deposit the connecting member in an accurate position in passageways of two adjacent bone anchors. The aperture may be opened to release the inserter. 
       SUMMARY 
       [0010]    It is an object of the invention to improve systems and methods of inserting a rod into rod channels of at least two bone anchors in minimally invasive surgery (MIS). More specifically, it is an object to simplify the process of inserting a rod and to thereby increase the flexibility for an operator. 
         [0011]    According to embodiments of the invention, a rod insertion device is provided including a tubular rod guide, a holding device configured to hold (e.g., support) the rod guide, and an adapter configured to be connected to an extension which may be mounted to a receiving part of a bone anchor. The adapter is configured to movably support the holding device. Consequently, the adapter allows the holding device and the rod guide to move and pivot along a predetermined path such that a front portion of the rod guide reaches a desired position proximal to a rod channel of the first receiving part of a first bone anchor to which the extension may be mounted. 
         [0012]    The coordinated movement of the holding device and the rod guide is ensured by a clamping device which is configured to clamp a portion of the rod guide. An advantage arises in that the clamping device is also configured to selectively release the rod guide in the above described state, that is, when the front portion of the rod guide has entered the soft tissue under MIS conditions and is positioned proximal to the rod channel of the receiving part. Such release is provided in such a way that an orientation of the rod guide may be adjusted (e.g., corrected) in a polyaxial manner. In other words, the rod guide may be rotated as well as pivoted in this state. 
         [0013]    According to one specific embodiment, two distinct release states of the rod guide from the holding device may be realized. Therein, a full release is achieved by arranging the clamping portion such that the rod guide can be removed from the clamping portion. In this state, the rod guide is separated from the holding device but substantially maintains its position and orientation with the front portion positioned proximal to the receiving part since it will already be within the soft tissue when this release occurs. This may be achieved, for example, by arranging the clamping section in multiple distinct parts connected via a first locking arrangement which allows separation of respective parts and, thus, their removal. 
         [0014]    The other state of release is realized by a second locking arrangement provided at the clamping portion. Herein, a partial release is achieved, which means that a portion of the rod guide is still held by the clamping portion, but a re-orientation of the rod guide becomes possible in a polyaxial manner One specific example may be the provision of a ball-joint or swivel head mechanism for the connection between the portion of the rod guide to be clamped and the clamping portion, but other mechanisms achieving the polyaxial re-orientation may be possible as well. 
         [0015]    In this state, the rod guide is still securely held (e.g., supported) but small corrections to the orientation thereof are possible. 
         [0016]    Nevertheless, embodiments of the invention are possible in which only one of the two release states as described above is achievable. 
         [0017]    Another specific embodiment of the invention relates to the provision of a dedicated support structure for the adapter by which the holding device is moved such that the front portion of the rod guide attains its position proximal to the rod channel of the receiving part. The support structure provides for an initial translational (e.g., substantially linear) movement of the rod guide followed by a smooth transition towards a pivoting movement, allowing, for example, the curved rod guide to be introduced closer to the bone anchor which further reduces the harm for the patient. Such a support structure may be realized, for example, by a cam-like structure such as pins which slide in grooves, but other mechanisms using rods connected via hinges, joints, and rotation axes may be possible as well. 
     
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0018]    The invention will now be described with respect to embodiments taken in conjunction with the accompanying drawings. In the drawings: 
           [0019]      FIG. 1 : shows an overview of a rod insertion device according to a first embodiment in a state in which the rod insertion device is attached to an adapter which is attached to an extension mounted to a receiving part of a bone anchor; 
           [0020]      FIG. 2 : shows an exploded perspective view of the adapter shown in  FIG. 1 ; 
           [0021]      FIG. 3 : shows a top view of the adapter of  FIG. 2 ; 
           [0022]      FIG. 4 : shows a cross-sectional view along a plane A-A of the adapter in  FIG. 3 ; 
           [0023]      FIG. 5 : shows a cross-sectional view along a plane B-B of the adapter in  FIG. 4 ; 
           [0024]      FIG. 6 : shows a top view of a securing plate for the adapter shown in  FIG. 2 ; 
           [0025]      FIG. 7 : shows a cross-sectional view along a plane C-C of the securing plate in  FIG. 6 ; 
           [0026]      FIG. 8 : shows a perspective view of the holding device and the rod guide with a handle of the rod insertion device shown in  FIG. 1 ; 
           [0027]      FIG. 9 : shows an exploded view of the parts shown in  FIG. 8 ; 
           [0028]      FIG. 10 : shows an illustrative top view of the parts shown in  FIG. 8 ; 
           [0029]      FIG. 11 : shows a cross-sectional view of details of a second locking arrangement along a plane D-D shown in  FIG. 10 ; 
           [0030]      FIG. 12 : shows a cross-sectional view of details of a first locking arrangement along a plane E-E shown in  FIG. 10 ; 
           [0031]      FIG. 13 : shows a perspective view of a left side bracket shown in  FIGS. 8 and 9 ; 
           [0032]      FIG. 14 : shows the left side bracket of  FIG. 13  but from another viewpoint; 
           [0033]      FIG. 15 : shows the left side bracket of  FIG. 13  but from yet another viewpoint; 
           [0034]      FIG. 16 : shows a cross-sectional view, a top view, and a perspective view of a pin of the second locking arrangement shown in  FIG. 9 ; 
           [0035]      FIG. 17 : shows an enlarged portion of a clamped portion of the rod guide of  FIG. 1 ; 
           [0036]      FIG. 18 : shows a side view of a cutting piece received by the rod guide shown in  FIG. 1 ; 
           [0037]      FIG. 19 : shows an enlarged portion of a tip of the cutting piece of  FIG. 18 ; 
           [0038]      FIG. 20 : shows a side view of the rod guide with the handle shown in  FIG. 1 ; 
           [0039]      FIG. 21 : shows a top view of the rod guide with the handle of  FIG. 20 ; 
           [0040]      FIG. 22 : shows a cross-sectional side view of the rod guide of  FIGS. 20 and 21 ; 
           [0041]      FIG. 23 : shows a first step of a method of using the rod insertion device according to the first embodiment; 
           [0042]      FIG. 24 : shows a second step of the method of using the rod insertion device according to the first embodiment; 
           [0043]      FIG. 25 : shows a third step of the method of using the rod insertion device according to the first embodiment; 
           [0044]      FIG. 26 : shows a fourth step of the method of using the rod insertion device according to the first embodiment; 
           [0045]      FIG. 27 : shows a fifth step of the method of using the rod insertion device according to the first embodiment; 
           [0046]      FIG. 28 : shows a sixth step of the method of using the rod insertion device according to the first embodiment; 
           [0047]      FIG. 29 : shows a seventh step of the method of using the rod insertion device according to the first embodiment; 
           [0048]      FIG. 30 : shows an eighth step of the method of using the rod insertion device according to the first embodiment; 
           [0049]      FIG. 31 : shows a ninth step of the method of using the rod insertion device according to the first embodiment; 
           [0050]      FIG. 32 : shows a tenth step of the method of using the rod insertion device according to the first embodiment; 
           [0051]      FIG. 33 : shows an eleventh step of the method of using the rod insertion device according to the first embodiment; 
           [0052]      FIG. 34 : shows a twelfth step of the method of using the rod insertion device according to the first embodiment; 
           [0053]      FIG. 35 : shows an overview of a rod insertion device according to a second embodiment of the invention in a perspective view, and the rod insertion device is shown attached to an extension mounted on a receiving part of the bone anchor; 
           [0054]      FIG. 36 : shows an exploded view of the rod insertion device of  FIG. 35  without the adapter and the inner cutting piece. 
       
    
    
     DETAILED DESCRIPTION 
       [0055]    A first embodiment of a rod insertion device according to the invention will be described with respect to  FIGS. 1 through 22 , and a corresponding method of using the rod insertion device according to the first embodiment will be described with respect to  FIGS. 23 through 34 . 
         [0056]    An overview of the rod insertion device  1  according to the first embodiment is shown in  FIG. 1 . The main parts of the rod insertion device  1  are an adapter  2 , a holding device  3  including a base portion  4  and a clamping portion  5 , a rod guide  6  with handle  7 , and a removable inner cutting piece  8 . The rod insertion device  1  of this embodiment is applied to a series of extensions  9 ,  9 ′,  9 ″ with each extension mounted to a respective receiving part  90  of a bone anchor  901  (a shank of the bone anchor is not visible in the embodiments as it is fully immersed in the bony material of a respective pedicle of vertebrae  100 ). 
         [0057]    It is noted that the extension  9  in this embodiment is not considered a part of the rod insertion device  1 . However, according to other embodiments, the extension  9  may be part of the rod insertion device. Extension devices, such as the extension  9 , primarily serve to assemble parts to a bone anchor and facilitate final fixation but may herein additionally be used to define the position of the bone anchor to which it is mounted relative to the adapter and, thus, to the rod insertion device  1 . 
         [0058]    In the following, the above-described ingredient parts of the rod insertion device will be described in detail in  FIGS. 2 through 22  and reference of their function will be taken with respect to the method steps illustrated in  FIGS. 23 through 34 . 
         [0059]    The adapter  2  and its detail parts are illustrated in  FIGS. 2 through 7 . The adapter  2  includes a cuboid body  21  with substantially flat sidewalls  22  and rounded edges. The cuboid body  21  has an inner bore  281  which is dimensioned to slidingly receive an upper part of one of the extensions  9 ,  9 ′, or  9 ″ shown in  FIG. 1 . Within the bore  281 , a flat portion  283  is formed which serves to guide respective flat portions  92 ,  92 ′,  92 ″ of the extensions. Due to the flat portion  283 , rotation of the adapter  2 , when attached to the extension  9 , is prevented and the orientation of the rod insertion device  1  when assembled together is predefined with respect to the bone anchor  901 . 
         [0060]    At an upper end of the bore  281 , an opening  24  towards the top face of the adapter  2  is formed which allows access to the bore. A small shoulder  282  (see  FIG. 4 ) serves as an abutment for the adapter  2  with respect to an upper end of the extension  9 . 
         [0061]    As illustratively shown in  FIGS. 23 and 24 , in a method of using the rod insertion device  1 , the first two steps of attaching the adapter  2  to the extension  9  are illustrated. 
         [0062]    Thereby, in  FIG. 23 , the adapter  2  is slid (see numeral  1023 ) onto a distal end of the extension  9 . In  FIG. 24 , a step of securing the adapter  2  on top of the extension  9  using a securing plate  25  is illustrated as numeral  1024 . The securing plate  25  is shown in more detail in  FIGS. 6 and 7 . The securing plate  25  includes a plate portion  255  that is dimensioned to be slid into a slot  29  of the adapter  2 . A plate-shaped operating portion  251  allows the securing plate to be pushed into the slot  29  against a biasing force of a spring  26  which is attached to a nose  253  (see  FIG. 6 ), and the operating portion  251  abuts a face  284  within an opening  28  (see  FIG. 5 ). 
         [0063]    An inner, almost circular opening  254  formed within the plate portion  255  allows the top portion of the extension  9  to be introduced therethrough when it is slid upwards within the bore  281  of the adapter  2 . For this purpose, the securing plate  25  may be retained in position by introducing a pin  27  into hole  270  formed in the top face of the adapter  2 . Thereby, a tip of the pin  27  enters into engagement with an opening  252  formed in the plate portion  255  of the securing plate  25  (see  FIG. 6 ). Once the top portion of the extension  9  abuts the shoulder  282  at the upper end of the bore  281 , a partially circular recess  91  formed in the upper portion of extension  9  faces the securing plate  25 , such that, by virtue of the spring  26 , the securing plate  25  is urged into and against the recess  91  of the extension  9 , i.e., the securing plate  25  latches into recess  91 , thereby fixing and securing the adapter  2  on the extension  9 . 
         [0064]    As shown in  FIG. 2 , the adapter  2  has grooves  23   a,    23   a ′,  23   b,    23   b ′ in opposing sidewalls  22  (e.g., sides) thereof. As will be described below, each of these grooves form part of a support structure for supporting the base portion  4  of the holding device  3  shown in  FIG. 1 . In the installed state of the adapter  2 , the flat side surfaces  22  (e.g., sidewalls) in which these grooves are formed are oriented in a direction transverse to a line defined by the arrangement or row of the bone anchors  901  and the extensions  9 ,  9 ′,  9 ″. 
         [0065]    As shown in  FIGS. 8-10 , which detail the holding device  3  and the rod guide  6  with the handle  7 , the holding device  3  includes the base portion  4  which includes a main wall  40  and two sidewalls  41 ,  42  forming a U-shape which, upon attachment to the adapter  2 , embrace the same at sidewalls  22 . The sidewall  41 , shown on the left side in the figures, includes two pins  43   a,    43   b  at its distal end, and the right sidewall  42  includes two pins  43   a ′,  43   b ′ at its distal end. These pins are designed and shaped to respectively fit into grooves  23   a,    23   b,    23   a ′, and  23   b ′ of the adapter  2 . 
         [0066]    As can be seen in  FIG. 25 , showing a third step of using the rod insertion device  1 , the base portion  4  may be attached to the adapter  2  (see numeral  1025 ) by inserting the pins  43   a,    43   b,    43   a ′, and  43   b ′ into upper ends of the grooves  23   a,    23   b,    23   a ′, and  23   b ′, respectively, from a top side of the adapter  2 . 
         [0067]    As can be seen in  FIG. 26 , which shows a fourth step of using the rod insertion device  1 , the pins of the base portion smoothly slide within the grooves in the sidewalls  22  of the adapter  2 . Upper portions  231   a  and  231   b  of respective grooves  23   a  and  23   b  (see  FIG. 2 ) have a slightly curved but almost linear shape, such that an almost translational, vertical movement (see numeral  1026 ) of the holding device  3  and the rod guide  6  occurs. Thereby, the arrangement of the holding device  3  and the rod guide  6  held by the clamping portion  5  is such that a front portion  64  of the rod guide  6  (see  FIG. 1 ) is oriented substantially parallel to the extension  9  and perpendicular to a skin surface (not shown) of the patient to allow an effective cut by a tip  81  of the cutting piece  8  (shown in  FIGS. 18 and 19 ) protruding from the front portion  64  of the rod guide  6 , to be further described below. Moreover, the translational movement  1026  allows an incision into the soft tissue that is close to the position of the bone anchor  901  and the extension  9 . 
         [0068]    As shown in  FIG. 27 , which shows a fifth step of the method in which a cutting edge  811  of the tip  81  has entered the soft tissue (not shown), the pins  43   a,    43   b,    43   a ′,  43   b ′ have entered a bottom section  232   a,    232   b  (e.g., an end portion) of the grooves  23   a  and  23   b  (see  FIG. 2 ) which are elliptically curved such that the holding device  3  and the rod guide  6  perform a pivoting movement  1027 . The curvature of the pivoting movement almost corresponds to the curvature of the tubular rod guide  6 . As a consequence, the rod guide  6  is introduced at a small incision point in the skin surface and soft-tissue ensuring the well-known advantages of minimally invasive surgery (MIS). 
         [0069]    As shown in  FIG. 28  showing a sixth step of the method, the front portion  64  of the rod guide  6  has attained or reached a position proximal to the receiving part  90  and the rod channel (not shown) formed therein. At this stage, the pins  43   a,    43   b,  etc. of the base portion  4  have also reached ends of their respective tracks in the grooves  23   a,    23   b,  etc., where stops may be arranged to indicate and give a tactile response to the operator that an end position has been reached. At this stage, the cutting piece  8 , which is more detailed in  FIGS. 18 and 19 , may be removed using handle  84 . The inner cutting piece  8  is formed of a curved rod having the tip  81  with the cutting edge  811  and an intermediate stop  83  (e.g., abutment) which ensures that only the tip  81  protrudes from the front portion  64  of rod guide  6  in the inserted state. The curvature of the cutting piece  8  corresponds to that of a curved tube portion  60  of the rod guide  6 . 
         [0070]    Next, the clamping portion  5  of the holding device  3  will be explained with regard to  FIGS. 8 through 16 . The clamping portion includes two brackets  51 ,  52  which are pivotably connected to a hinge  45  provided at an intermediate wall portion  44  (e.g., a main wall) of the base portion  4 . In this specific embodiment, the hinge is formed of upper and lower eyelets  46 ,  47  (e.g., holes) formed in respective protrusions from the main wall  44  and a bolt  48  which can be inserted into these holes. The brackets  51 ,  52  include eyelets  56 ,  57  at their ends, respectively, which may be brought into alignment with eyelets  46 ,  47  of the main wall  44 . The brackets  51 ,  52  may be pivoted about the hinge  45  towards and away from each other. 
         [0071]    The left-side bracket  51  includes a partial semi-spherical recess  58 , and the right-side bracket  52  also includes a partial semi-spherical recess  59  which are aligned with each other and have substantially the same size and radius, such that, when flat end faces  511 ,  521  of the brackets  51 ,  52  abut each other , the semi-spherical recesses  58 ,  59  form a substantially spherical, inner space leaving small openings at the upper and lower ends thereof to allow the rod guide  6  to extend therethrough, as will be further explained below. As becomes apparent from  FIGS. 8 and 9  in conjunction with  FIG. 1 , this spherical, inner space is configured to receive a spherical, ball-shaped portion  61  of the rod guide  6 . Thereby, the dimensions of the spherical, ball-shaped portion  61  may be, for example, slightly larger than those of the semi-spherical recesses  58 ,  59 , such that a clamping function may be achieved when a first locking arrangement  53  (e.g., a first locking device) is tightened. Nevertheless, the dimensions of the spherical, inner space and the ball-shaped portion  61  may be identical. Details of the first locking arrangement can be seen in  FIG. 12 . 
         [0072]    More specifically, the first locking arrangement  53  includes a hinged support  531  (e.g., a hinge) provided at the right-side bracket  52  which is formed as a single piece with a threaded shaft  532 . The threaded shaft  532  may engage an internal thread  533  formed in a nut  534 . Upon clamping the ball-shaped portion  61  of the rod guide  6 , parts  531 - 534 , which together form a tensioning screw, are pivoted about the hinge  531  to insert the shaft  532  into a recess  535  formed at an end of the left-side bracket  51 , after which the nut  534  may be tensioned (e.g., tightened) into a form-fit groove  536  to obtain a secure connection, as shown, in particular, in  FIG. 12 . 
         [0073]    As can be seen in  FIG. 31 , further described below, the first locking arrangement  53  allows the brackets  51 ,  52  to be completely removed from around the ball-shaped, spherical portion  61  by pivoting the brackets away from each other. 
         [0074]    The clamping portion  5  (e.g., a clamping device) of this embodiment includes a second locking arrangement  54  (e.g., a second locking device), which is shown in more detail in  FIGS. 9 ,  11 , and  16 . 
         [0075]    As can be best seen in  FIG. 11 , the second locking arrangement  54  may serve to fix the position and orientation of the ball-shaped, spherical portion  61  of the rod guide  6  within the inner, spherical space defined by the semi-spherical recesses  58 ,  59  of the brackets  51 ,  52 , respectively. For this purpose, the second locking arrangement includes a nut  544 , into which a latching pin  541  is attached (e.g., press-fit or threaded), and which is shown in more detail in  FIG. 16 . The latching pin  541  has a generally cylindrical shape except for a shoulder  547  and a nose  548  formed at its distal end. A coil spring  543  may be fitted over the cylindrical portion of the latching pin  541  to abut the shoulder  547  on the one side and an inner, annular shoulder  546  formed by undercut bore  514  which is provided in the left-side bracket  51 . As a consequence, as can be seen in  FIG. 11 , the latching pin  541  is urged by the coil spring  543  towards the semi-spherical recess  58  and—if the spherical ball-shaped portion  61  of the rod guide  6  is inserted—into a bore  62  formed therein. 
         [0076]    Thereby, the nose  548  provided at the distal end of the latching pin  541  is designed to fit into a respective recess  621  formed in the bore  62  when the latching pin attains a specific orientation. 
         [0077]    As can be seen in  FIGS. 9 ,  11 , and  16 , a pin  542 , fitted into a respective hole  545  of the latching pin  541  and protruding from both ends of the hole  545 , may latch either into a recess  512  positioned remote from the semi-spherical recess  58  or into a recess  513  which is closer to the semi-spherical recess  58  (see  FIGS. 14 and 15 ). The recesses  512 ,  513  define two different indexing positions for the latching pin  541  such that, when the pin  542  is latched into the recess  512 , the distal end of the latching pin  541  (the nose  548 ) does not protrude into the semi-spherical recess  58 , and when the pin  542  latched into the recess  513 , the distal end of the latching pin  541  protrudes into the semi-spherical recess  58  or into the bore hole  62  of the spherical ball-shaped portion  61  of the rod guide  6  to fix the same. Because the latching pin  541  is urged towards the inner spherical space defined by the recesses  58 ,  59 , the operator has to pull the nut  544  outwards (e.g., away from the recesses  58 ,  59 ) in order to switch between the locked state and a released state with respect to the spherical, ball-shaped portion  61 . 
         [0078]    An overview of the rod guide  6  with the handle  7  is given in  FIGS. 20-22 . The handle  7  of this embodiment can be removed from the rod guide by a button  71 . The rod guide  6  includes the curved tube portion  60  having an inner bore  67  whose diameter may correspond to that of a stabilization rod  95 , and the front portion  64  defining an exit from the tube. The spherical, ball-shaped portion  61  is provided at an upper part of rod guide  6 , and the curved tube portion  60  extends therefrom. The curved tube portion is fitted into an annular extension  63  provided at a lower portion of the spherical, ball-shaped portion  61 . The inner bore  67  extends through the spherical, ball-shaped portion  61  up to an opening  65  (e.g., an entry hole) formed in a rear part  66  of the rod guide and defining an entry for the stabilization rod into the inner bore  67 . The rear part  66  of the rod guide  6  provides for a connection to handle  7 . 
         [0079]    Returning to the description of the method of using the rod insertion device  1 ,  FIG. 29  shows a seventh step and a state in which—after having removed the inner cutting piece  8 ,—the arc-shaped or curved spinal stabilization rod  95  is inserted into the entry hole  65  formed in the rear part  66  of the tubular rod guide  6  (see numeral  1029 ) and advanced into the inner bore  67 . Details of the tubular rod guide  6  are shown in  FIGS. 20 through 22 . The spinal stabilization rod  95  is advanced until its tip exits from the inner bore  67  of the curved rod portion  60  at the front portion  64  of the rod guide  6  in this step. 
         [0080]    This state is depicted in  FIG. 30 , which shows an eighth step of the method of using the rod insertion device  1 . While upon further advancing (numeral  1029 ) the spinal stabilization rod  95  into and through the rod channel of the receiving part  90 , an operator may choose to adapt (e.g., change) the orientation of the spinal stabilization rod  95  and the rod guide  6 . Therefore, the nut  544  of the second locking arrangement  54  is pulled and rotated (see numeral  1030   b ) in order to retract the latching pin  541  from the bore  62  of the spherical, ball-shaped portion  61  of the rod guide  6 . Because the spherical, ball-shaped portion  61  may still be clamped by the tensioning screw of the first locking arrangement  53 , the nut  534  of the tensioning screw is slightly rotated to reduce the tensioning force (see numeral  1030   a ). As a consequence, the fixation of the rod guide due to the second locking arrangement  54  and the clamping due to the first locking arrangement  53  is lifted, while the spherical ball-shaped portion  61  is still supported by (e.g., contained within) the spherical, inner space formed by the recesses  58  and  59 . As a result, the spherical, ball-shaped portion  61  functions like a ball joint, allowing polyaxial pivoting movements (see numeral  1030   c ) and corrections of the 3D-orientation of the rod guide  6  within the spherical, inner space. 
         [0081]    The annular extension  63  at one side of the spherical, ball-shaped portion  61  as well as the rear part  66  at the other side of the spherical, ball-shaped portion  61  allow for a sufficient degree of pivoting as can best be seen in  FIG. 11 . 
         [0082]      FIG. 31  shows a ninth step of the method of using the rod insertion device  1 . The advancement (numeral  1029 ) of the spinal stabilization rod  95  continues with its tip entering a rod channel of the second receiving part  90 ′ of the second bone anchor  901 . 
         [0083]    Occasionally, the operator may want to apply a greater degree of re-orientation and gain a greater degree of control over further advancement of the spinal stabilization rod  95 . For this purpose, the operator unscrews the tensioning screw (parts  531 - 534  shown in  FIG. 9 ) and releases the tensioning screw from the recess  535  and the groove  536 . As a consequence, the brackets  51  and  52  may be pivoted (see numeral  1031 ) and move away from each other to fully release the rod guide  6  from the spherical, inner space formed by the recesses  58 ,  59 . 
         [0084]    As the holding device  3  is no longer needed, the base portion  4  with the clamping portion  5  may be pushed upward with the pins  43   a,    43   b,    43   a ′,  43   b ′ sliding through the respective grooves  23   a,    23   b,    23   a ′,  23   b ′ to be removed from the adapter  2 . The state is depicted in  FIG. 32 , which shows a tenth step of the method of using the rod insertion device  1 . The operator may control further alignment  1029  by just exerting forces via handle  7  onto the rod guide  6 . As an example, the spinal stabilization rod  95  is further advanced through the third receiving part  90 ″ which may not be in-line with the first and second receiving parts  90 ,  90 ′ in this specific embodiment. 
         [0085]    As shown in  FIG. 33 , which shows an eleventh step of the method, the handle  7  with the rod guide  6  may be removed from the end of the rod  95  after the same has been fully brought into place. After performing a further step (not shown) of providing set screws, etc. through the inner bores of the extensions  9 ,  9 ′,  9 ″ towards the receiving part in order to fixate the spinal stabilization rod  95  within the rod channels, an unused end portion  95   a  may be removed by separating (see numerals  1034   a ) the same from the inserted rod  95  at a predetermined breaking point  96  (see also  FIG. 34  which illustrates a twelfth step of the method). The unused rod end  95   a  may be drawn out (see numeral  1034   b ) of the soft tissue. At this stage, the adapter  2  is also removed from the first extension  9 . 
         [0086]    The first and second locking arrangements  53  and  54  of the clamping portion  5  according to the first embodiment advantageously facilitate two different states of releasing the rod guide  6  from the clamping portion  5 . The operator can selectively control the advancement of the spinal stabilization rod through the rod channels by selecting between a predetermined insertion path when the rod guide is clamped and fixed, in which state partial release and polyaxial re-orientation of the rod guide is possible, and full release from the holding device depending on the situation. Polyaxial corrections are thus applied with less effort, and the method of inserting a rod is simplified. On the other hand, a secure insertion is improved since the operator may have full control over the insertion process. 
         [0087]    A second embodiment of the invention will be described with reference to  FIGS. 35 and 36 . Like numerals denote the same parts as in the first embodiment and will not be described repeatedly. A main difference of the rod insertion device  1 ′ of the second embodiment with respect to the first embodiment is seen in the clamping portion  5 ′. Herein, first and second brackets  51 ′ and  52 ′ are not provided as pivoting parts but as being translationally movable or slidable towards and away from each other. 
         [0088]    Therefore, protruding pins  537  of the first bracket  51 ′ are provided to be inserted into respective holes in the second bracket  52 ′. By virtue of undercuts  538 , the connection between the brackets  51 ′,  52 ′ is locked by inserting a locking plate  536  of a first locking arrangement  53 ′, which corresponds in function to the first locking arrangement  53  of the first embodiment, into a slot  536   a,  such that, when the locking plate  536  is lifted, a recessed portion  539  of the locking plate  536  engages with the undercuts  538 . 
         [0089]    The function of a second locking arrangement  54 ′ is similar to that of the second locking arrangement  54  of the first embodiment. 
         [0090]    In use, the locking position of the locking plate  536  is ensured by the annular abutment  83  of the inner cutting piece  8  (see  FIG. 18 ). This is because the locking plate  536  has an upper flange which latches onto the annular abutment  83 . Having cut a path through the soft tissue using the cutting edge  811  at the tip  81 , the cutting piece  8  may be lifted by the handle  7  to remove the same. As a consequence, the abutment  83  is removed and the locking piece  536  may be slid further into slot  536   a  such that the protruding pins  537  are released from the second bracket  52 ′ (i.e., the recessed portion  539  disengages from the undercuts  538 ). Further advancement of the rod guide  6  and the spinal stabilization rod  95  into the soft tissue may now be performed manually as the path has been predefined. 
         [0091]    The materials employed for each of the parts in the embodiments described above may be selected from metals, such as stainless steel, titanium, nickel, and/or titanium alloys, etc., or from plastic materials as long as certain durability and rigidity conditions are met and bio compatibility is guaranteed. 
         [0092]    The stabilization rod  95  may also be made from biocompatible metals or plastics. In one embodiment, the rod has a curvature which corresponds to that of the rod guide. 
         [0093]    The invention also provides for an embodiment including the rod inserter as described above wherein two or more rod guides are provided which differ from each other by the radius of curvature of their respective curved tube portions  60 . Corresponding rods having appropriate curvatures may then also be selected according to the application. 
         [0094]    Several modifications of the above embodiments may be made without departing from the scope of the invention as defined in the appended claims. 
         [0095]    For example, fixation means other than the above-described tensioning screw or indexing pin may be used to clamp, lock, and fixate the rod guide in the clamping portion. 
         [0096]    Moreover, instead of the support structure defined as pairs of grooves and pins sliding therein, a hinge mechanism may be provided and/or a single rotation axis may be employed to facilitate the pivoting movement of the holding device and the rod guide. 
         [0097]    Further, parts such as the handle  7  or the inner cutting piece  8  may be omitted. 
         [0098]    Still further, the bone anchors and extensions to which the present rod insertion device is applied may be of various types, for example, the bone anchors may be embodied as polyaxial bone anchors or monolithic bone anchors and the shape and design of the rod channels may be selected from a variety of categories known in the art.