Patent Publication Number: US-2021186577-A1

Title: Device for placing a receiving part onto a head of a bone anchoring element

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent Ser. No. 16/289,331, filed Feb. 28, 2019, which is a continuation of U.S. patent application Ser. No. 14/645,319, filed Mar. 11, 2015, now U.S. Pat. No. 10,258,390, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/953,510, filed on Mar. 14, 2014, the contents of which are hereby incorporated by reference in their entirety, and claims priority to European Patent Application EP 14160126.0, filed on Mar. 14, 2014, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention relates to a device or tool for placing a receiving part of a bone anchoring device onto a head of a bone anchoring element. The present invention further relates to such a receiving part of a bone anchoring device. The device or tool includes a holding portion, a collet for engaging the receiving part, and a corresponding engagement feature. 
     Fractures of the spinal column, arthrodesis, scoliosis, etc. are often treated by stabilizing the spinal column using bone anchors applied to two or more vertebrae and connecting the same via rigid or dynamically flexible stabilization rods, such as to define a predetermined relative position and movement tolerance for each of the vertebrae involved. In operation, vertebrae are first selectively supplied with bone anchors and a stabilization rod is then attached to connect each of the bone anchors. The connection of each of the bone anchors is established by a receiving part, which connects to a head of the bone anchoring element and receives a spinal rod in a rod receiving channel thereof. 
     In recent years, there has been a tendency to assemble such bone anchoring devices in situ. Methods of in situ assembling of the bone anchoring devices advantageously allow for easier or better visual inspection of several structures in place, such as particular neurological structures, etc., which may be critical or important for certain procedures, since the receiving parts are attached to the bone anchors in a subsequent step. New clinical methods and surgical steps may also become possible and/or easier to perform. Moreover, particular advantages arise in that preparation of very small MIS (minimally invasive surgery) accesses is made possible. 
     For example, a bone anchoring element is anchored in a vertebra first, where after a receiving part is placed onto a head of the bone anchoring element. However, such construction necessitates that the receiving part allows the head to be loaded therein from a bottom side of the receiving part. As a consequence, a bottom opening of the receiving part has an increased diameter, and the head has to be received by a portion of a pressure element or an inner cap provided within the receiving part which encompasses the head and locks the head against a seat formed adjacent the bottom opening. One early example is described in U.S. Pat. No. 6,471,705 B1 and EP 1 105 057 A1. 
     In view of the above, a need has arisen to also provide a device or tool that is suitable for placing a receiving part onto a head of a bone anchoring element. 
     Description of Related Art 
     U.S. 2011/0166606 A1 discloses a reduction tool designed to engage a body portion having a rod receiving channel and to insert a spinal rod therein. The tool includes an outer tube having engagement features at the distal end thereof, two opposite slots through which the rod is inserted, and an inner tube which advances a locking cap and the rod. The proximal end of the outer tube also has two opposite slots such that a pivot point is formed in a middle portion thereof and compression of the proximal end of the outer tube results in expansion of the distal end. As a consequence of such manipulation, engagement of a receiving part by the protruding engagement features provided at the distal end of the outer tube can be facilitated. Upon engagement, those protrusions are led into corresponding recesses formed in an outer circumferential surface of the receiving part. 
     However, the above described reduction tool is configured to engage a receiving part in a state in which the receiving part is preassembled with the bone anchoring element, and further, due to the pivoting expansion to engage and disengage the receiving part at its circumferential surface, a relatively large space is need in a patient&#39;s body rendering the tool less suitable for minimal invasive surgery and in situ operation. 
     U.S. 2012/0296171 A1 discloses an inserter including a driver and a receiver member wherein a head of a bone anchor to be inserted is securely connected to the inserter by virtue of the receiver member which is used in a collet-like fashion. The receiver member thereby receives the head and a cylindrical body is slid over a conical portion of the receiver member to compress deflectable flanges onto the head. A driving operation may then be performed with regard to the bone anchor. In this device, however, the receiver member is part of the inserter and cannot be released and used to receive a rod. 
     SUMMARY 
     It is thus an object of the invention to provide a device or tool for placing a receiving part onto a head of a bone anchoring element which improves known methods and devices. 
     According to embodiments of the invention, the device includes a holding device and a collet held by the holding device. The collet has a distal end portion which is configured to be flexibly expanded and/or compressed, which allows engaging and/or disengaging of a corresponding receiving part. An engagement feature is provided at an outer contour, or outer surface, of the distal end portion of the collet. The engagement feature may engage a portion of an inner wall of a rod receiving channel or a bore of a receiving part. 
     More specifically, the engagement feature is not provided at an inner surface of a tube or shaft as proposed in some prior art, but instead on an outer surface, to engage an inner wall of the receiving part. The inner wall may be that of an inner bore extending, for example, from a top end to a bottom end of the receiving part or may be that of a rod receiving channel which is typically formed extending from the top end of the receiving part. Engagement with other inner walls is possible as well, as long as the engagement takes place within a perimeter of the receiving part and the release operation does not occur in a space beyond such perimeter, in particular by expansion. In embodiments described herein, the device may be compressed at its distal end when releasing the receiving part, for example, after implantation. 
     Consequently, it is not necessary to engage the receiving part on any of its circumferential outer surfaces. This, in turn, allows narrower channels through the tissue of the human body to be used to approach a target bone. Hence, aspects and embodiments of the invention are particularly applicable in minimally invasive surgery (MIS) and in situ assembly. 
     Engagement and disengagement of the device or tool from the receiving part is facilitated by radial expansion and compression of the distal end portion of the collet, respectively. It is not necessary to use an inner thread, which is generally available at inner walls of receiving parts to facilitate locking of a rod by a locking screw, to engage the device. Instead, quick locking and releasing of the receiving part with improved tactile response is possible when placing the receiving part onto the head. 
     With regard to the receiving part described herein, only minor structural changes have to be applied, if any, to generally available receiving parts. For example, engagement features may be provided at the inner walls of the rod receiving channels. The engagement features may be protrusions, spring-like projections, noses, recesses, and/or similar features which allow a latching connection with corresponding features of the device or tool. Such engagement features may even be provided within a region of an inner thread—if present. According to specific embodiments, even an inner thread might be considered to provide corresponding latching features into which the engagement features of the device or tool is configured to expand during engagement. 
     In one embodiment, a device or tool is provided for application to a bone anchoring device, wherein an inner cap is provided within a receiving part of the bone anchoring device, where the inner cap clamps the head of the bone anchoring element, thereby allowing frictionally limited movement of the clamped bone anchoring element when the device has not yet been finally locked. In this situation, the device or tool allows for a more efficient method for placing the receiving part onto the head. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       Advantageous features and aspects of the present invention will become more apparent from a detailed description of specific embodiments taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  shows a perspective view of the device or tool according to an embodiment of the invention with a collet in a locked position; 
         FIG. 2  shows the device shown in  FIG. 1  in use just prior to placement of a receiving part onto a head of a bone anchoring device and with an operation portion of the device having been removed; 
         FIG. 3  shows the device shown in  FIG. 1  in a disassembled state; 
         FIG. 4A  shows top and cross-sectional views of the holding portion of the device shown in  FIGS. 1 to 3 ; 
         FIG. 4B  shows a top perspective view of the holding portion shown in  FIGS. 4A and 4B ; 
         FIG. 4C  shows a bottom perspective view of the holding portion shown in  FIGS. 4A to 4C ; 
         FIG. 5A  shows a cross-sectional view of a tubular portion of a collet of the device shown in  FIGS. 1 to 3 ; 
         FIG. 5B  shows an enlarged view of a proximal end of the tube of the collet shown in  FIG. 5A ; 
         FIG. 5C  shows an enlarged view of a distal end portion of the collet shown in  FIG. 5A ; 
         FIG. 6A  shows a top perspective view of a separate proximal end portion of the collet according to the embodiment shown in  FIGS. 1 to 3 ; 
         FIG. 6B  shows a bottom perspective view of the proximal end portion of the collet shown in  FIG. 6A ; 
         FIG. 6C  shows a cross-sectional view of the proximal end portion of the collet shown in  FIGS. 6A and 6B ; 
         FIG. 7A  shows a perspective view of a plunger of the device shown in  FIGS. 1 to 3 ; 
         FIG. 7B  shows an enlarged view of a tip portion of the plunger shown in  FIG. 7A ; 
         FIG. 8  shows a fixation device formed as a follower pin of the device shown in  FIGS. 1 to 3 ; 
         FIG. 9  shows an operation portion of the device shown in  FIGS. 1 to 3 ; 
         FIG. 10A  shows top and cross-sectional views of a receiving part of a bone anchoring device according to an embodiment of the invention; 
         FIG. 10B  shows a perspective view of the receiving part shown in  FIG. 10A ; 
         FIG. 11A  shows top and cross-sectional views of an inner cap of the bone anchoring device according to an embodiment of the invention; 
         FIG. 11B  shows a perspective view of the inner cap shown in  FIG. 11A ; 
         FIG. 12  shows a cross-sectional view of a first step of a method of using the device or tool shown in  FIGS. 1 to 3 ; 
         FIG. 13A  shows an enlarged perspective view of the distal end portion of the collet of the device or tool and the receiving part in the same state shown in  FIG. 12 ; 
         FIG. 13B  shows a second step of advancing the distal end portion of the collet into the receiving part; 
         FIG. 13C  shows a third step in which the distal end portion of the collet is engaged with inner walls of the receiving part; 
         FIG. 14  shows a cross-sectional view of the device in the same state as shown in  FIG. 13C , with the distal end portion of the collet being locked by a plunger of the device or tool; 
         FIG. 15A  shows a partial cross-sectional view of a fourth step of the method of using the device in which the device and receiving part are guided to a head of a bone anchoring element when in the state shown in  FIG. 14 ; 
         FIG. 15B  shows a fifth step in which the head is introduced and snapped into an inner cap in the receiving part; 
         FIG. 15C  shows a sixth step in which the device is drawn or pulled in a direction away from the receiving part; 
         FIG. 16A  shows a seventh step in which the distal end portion of the device or tool is unlocked; 
         FIG. 16B  is a cross-sectional view showing a proximal portion of the device or tool with the tensioned resilient member; and 
         FIG. 16C  shows a subsequent step of the method of using the device or tool in which the unlocked distal end portion of the collet of the device is released from the receiving part. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of a device or tool for assembling a bone anchoring device is described with respect to  FIGS. 1-9 , a corresponding embodiment of a receiving part and an inner cap of a bone anchoring device is described with reference to  FIGS. 10A-11B , and an illustrative example of a method of using the device or tool with the bone anchoring device is described with reference to  FIGS. 12-16C . 
     An overview of the device  1  for placing a receiving part onto a head of a bone anchoring element is shown in  FIGS. 1-3 . The device  1  according to this embodiment includes a holding portion  2 , a collet  3 , an operation portion  4 , a plunger  5 , and a resilient member  6  (e.g., a spring). A fixation device  21  provided as a follower pin can be applied to the holding portion  2  to establish a connection with plunger  5 , and a cap-like proximal end portion  35  can be provided to the collet  3  to allow attaching the operation portion  4  to a proximal end of the collet  3  and to provide a proximal abutment face  353  for the resilient member  6  as will be further described below. 
       FIG. 1  shows the device  1  in a state in which the operation portion  4  is not pressed, and as a consequence, the collet  3 , or a distal end portion  31  thereof, is in a locked state since a tip portion  52  of plunger  5  extends into the distal end portion  31  of the collet  3 , as will be explained in further detail below. 
     Similarly, the device  1  as shown during use in  FIG. 2  is also in the locked state, however, the operation portion  4  has been removed from the device  1 . In the locked state, a receiving part  7  is securely attached to (e.g., connected to) the distal end portion  31  of the collet  3 , and may thus be safely guided through an incision channel cut into tissue of a patient (not shown) towards a head  91  of a bone anchoring element  9 , which has already been anchored in a pedicle of a vertebra as shown in  FIG. 2 . The state shown in  FIG. 2  substantially corresponds to that shown in  FIG. 14  illustrating a method of use, which will be discussed in further detail below. 
       FIGS. 4A to 9  illustrate the separate parts of the device or tool  1 . 
     The holding portion  2  is shown in  FIGS. 4A-4C  in top, cross-sectional, top perspective, and bottom perspective views, respectively. The holding portion  2  of this embodiment has a substantially tubular shape with a textured profile at its outer surface to allow safe gripping by operating staff. In use, the holding portion  2  is held with one hand, and a thumb may for example be used to press the operation portion  4 . The holding portion  2  has an inner bore extending from a proximal end  27  towards a distal end  28  thereof. A first bore portion  22  having a comparatively large diameter extends from the proximal end  27 , and a second bore portion  23  extends from the distal end  28  towards one another. The second bore portion  23  has a smaller diameter as compared with the first bore portion  22 . At the transition between the first bore portion  22  and the second bore portion  23 , which both extend along a common longitudinal axis, a shoulder  24  serving as a distal abutment face for one end of the resilient member  6  further described below is formed. 
     A threaded bore  25  transversely extends through a wall of the holding portion  2 , and a further bore  26  having a smaller diameter extends through the wall of the holding portion  2  on an opposite side of the holding portion  2  along the same axis as threaded bore  25 . Bores  25 ,  26  are configured to receive the fixation device  21  shown in  FIG. 8 . More specifically, the fixation device  21  has a threaded section  211  configured to be threaded into the threaded bore  25 , a narrower unthreaded pin portion  213  configured to fit into the bore  26  of the holding portion  2 , and a cylindrical middle portion  212  configured to slidably fit through an oblong aperture or hole  38  of the collet  3  further described below. The fixation device  21  functions as a follower pin and fixes the plunger  5  to the holding portion  2 , such that both the holding portion  2  and the plunger  5  together form a first unit of the device  1 . 
     The collet  3  is depicted in  FIGS. 5A to 5C , and can include a separate proximal end portion  35  formed as a cap-like member as depicted in  FIGS. 6A-6C . The collet  3  has a substantially tubular shape (tube  37 ) and its outer diameter is selected such as to slidably fit into the narrower second bore portion  23  of the holding portion  2 . When assembled, a longitudinal axis Z of the collet  3  is coaxial with central axes of the first and second bore portions  22 ,  23  of the holding portion  2 . 
     The collet  3  has a distal end portion  31  which is defined by two tongues  311 ,  312  which, in turn, are formed by two opposite slots  32  extending from a tip portion  33  of the collet  3  along the longitudinal axis Z up to a predetermined distance from the tip portion  33 . The tip portion  33  of the distal end portion  31  is recessed from the overall cylindrical shape of the collet  3  and shaped such as to fit into a rod receiving channel and an inner bore of the receiving part  7 . Upon engagement of the receiving part  7  by the distal end portion  31 , an abutment face  331  of the collet  3  abuts a top face of the receiving part  7 . Moreover, two rounded projections are formed as engagement features  34  on each of the tongues  311 ,  312  at the tip portion  33  of the collet  3 . These projections extend in a lateral or radial direction from the collet  3 . 
     The length of the slots  32  and the thickness of the walls of the collet  3  are dimensioned and the material or materials are selected such that both tongues  311 ,  312  are provided with resiliency such as to be expanded or compressed, depending on forces exerted during operation of the device  1 . 
     For example, in this embodiment, the plunger  5  as shown in  FIGS. 7A and 7B  is used to prevent compression of, and may even expand, the tongues  311  and  312  of the collet  3 . The plunger  5  is substantially rod-shaped and has a cylindrical portion  51  having a diameter configured to slidably fit into an inner bore  301  of the collet  3 . The plunger  5  further has a partially cylindrical tip portion  52  having a smaller diameter as compared with the cylindrical portion  51  and a conical portion  54  at a transition between the cylindrical portion  51  and the tip portion  52 . The diameter of the cylindrical part of the tip portion  52  of the plunger  5  is substantially the same as a diameter of a narrow diameter bore  314  (e.g., a bore hole) which is provided at a distal region of the collet  3  and extends from a shoulder  313  forming an end of the inner bore  301  of the collet  3  to a distal end of the tip portion  33 . 
     In this specific embodiment, the tip portion  52  further includes a conical tip portion  55  having a slightly increasing diameter that is larger than that of the cylindrical part of the tip portion  52 , and a conical transition portion  53  between the conical tip portion  55  and the cylindrical part of the tip portion  52 . In addition, the plunger  5  has at its opposite end a bore  56  through which the fixation device  21  may be inserted, as described above, to form a first unit of the device  1  between the holding portion  2  and the plunger  5 . 
     Since the plunger  5  is configured to slide within the inner bore  301  of the collet  3 , the tip portion  52  of the plunger  5  is allowed to enter the narrow diameter bore  314  of the collet  3  wherein by virtue of the conical tip portion  55  having a larger diameter than the narrow diameter bore  314 , the tongues  311 ,  312  are radially expanded (e.g., are spread apart or urged radially outwardly) in this embodiment. The length of the tip portion  52  including the conical tip portion  55  substantially corresponds to the length of the narrow diameter bore  314 . From the above, it becomes clear that once the tip portion  52  has entered the bore  314  of the collet  3 , compression of the tongues  311 ,  312  is impeded, and even a slight expansion (e.g., spreading) of the tongues  311 ,  312  may be facilitated. 
     As explained above, the holding portion  2  and the plunger  5  form a common unit in this embodiment where the parts are fixed relative to one another. On the other hand, the collet  3  is allowed to move with respect to those parts of the device along the longitudinal axis Z. The extent of such movement is defined by the length of the oblong hole  38  through which the fixation device  21  extends as a follower pin in an assembled state.  FIGS. 12 and 14  show two different states of the device  1  in cross-sectional illustrations. More specifically,  FIG. 12  shows a state in which the operation portion  4  and the collet  3  are moved distally relative to holding portion  2  and plunger  5 , which yields a state in which the tip portion  52  and the conical tip portion  55  of the plunger  5  are retracted from the narrow diameter hole  314  and the shoulders  313 . In this state, the tongues  311 ,  312  can be compressed or expanded, thereby representing an unlocked position or a release position of the device  1 . In this unlocked or release position, the fixation device  21  is at a proximal end of the oblong hole  38  of the collet  3 . The unlocked or release position allows easy attachment or removal of the tongues  311 ,  312  to the receiving part  7 . 
     Meanwhile,  FIG. 14  shows a second state in which the collet  3  has been retracted in a proximal direction relative to the holding portion  2  and the plunger  5 . In this state, the tip portion  52  enters the narrow diameter bore  314  of the collet  3 , thereby preventing compression of the tongues  311 ,  312 . This state corresponds to a lock position of the plunger  5  with respect to the collet  3 . The lock position may be advantageously achieved, for example, when the projections or engagement features  34  are engaged into respective features provided at the receiving part  7 . Hence, a safe and secure engagement of the receiving part  7  to the device or tool  1  can be achieved. As can be seen in  FIG. 14 , in the lock position, the fixation device  21  is positioned at an opposite distal end of oblong hole  38 . The oblong hole  38  limits the movement of the collet  3  with respect to the plunger  5 , and the ends of the oblong hole  38  toward the proximal direction and distal direction define, for example, the release position and the lock position, respectively. 
     Returning to the description of the collet  3 , the proximal end portion  35  may be formed as a separate cap-like member, as shown in  FIGS. 6A through 6C . The proximal end portion  35  includes a cylindrical tubular portion  352  having an inner thread  351  that can be threaded on an outer thread  36  provided at a proximal end of the tubular portion of the collet  3  as shown in  FIG. 5B . The proximal end portion  35  further has an inner bore  354  sized to receive therein a pin-like projection  42  of the operation portion  4  shown in  FIG. 9 . The cylindrical portion  352  has the same outer diameter as that of the cylindrical tube portion  37  of the collet  3 . Further, a cap-like annular projection  355  is provided on the proximal end portion  35  whose diameter corresponds to that of the first bore portion  22  of the holding portion  2 . As a consequence, a surface at a bottom side of the annular projection  355  serves as an abutment face  353  for a proximal end of the resilient member  6 . 
     As can be seen from  FIGS. 12 and 14 , the resilient member  6  is held within the first bore portion  22  of the holding portion  2  and urges the proximal end portion  35  of the collet  3  away from the abutment face  24  of the holding portion  2  in a proximal direction. Thus, in a state where no external forces are exerted onto the operation portion  4 , as shown in  FIG. 14 , the operation portion  4  and the collet  3 , together with its proximal end portion  35 , are retracted in the proximal direction relative to the holding portion  2  and the plunger  5 . 
     Next, an embodiment of a receiving part  7  of the bone anchoring device that is suitable for interaction with the device or tool  1  is described with reference to  FIGS. 10A and 10B . The receiving part  7  has a bore  700  extending from a first end  72  (e.g., a top end) towards a second end  73  (e.g., a bottom end), wherein an opening  701  is formed at the bottom end  73 . Adjacent to the opening  701 , a seat  75  is formed which defines an accommodation space for accommodating a head receiving portion  82  of an inner cap  8 , which in turn is configured to clamp a head  91  of a bone anchoring element  9  such as that shown in  FIG. 2 . The bore  700  includes an inner wall  71  and, at an upper portion of the inner wall  71 , an inner thread is formed for receiving a locking device (not shown), such as a setscrew. An abutment feature  76 , such as a recess, is formed in a middle portion of the inner wall  71  and is configured to receive corresponding abutment features  813 ,  814  (e.g., projections) of the inner cap  8  shown in  FIGS. 11A and 11B . 
     The receiving part  7  also includes a rod receiving channel  74  which extends from the first end  72  and has a substantially U-shape. The rod receiving channel  74  thus forms two legs and two inner walls  79  having the U-shape. As can be seen particularly in  FIG. 10B , two recesses or engagement features  77  having rounded edges are formed in an upper portion of each of the inner walls  79 . These engagement features  77  are configured and shaped to receive the engagement features  34  provided at the distal end portion  31  of the collet  3  of the device  1 . The recesses  77  each extend in a lateral direction, perpendicular to a longitudinal axis of the bore  700 , which will also be coaxial with the longitudinal axis Z of the collet  3  when the receiving part  7  is assembled with the device or tool  1 . Accordingly, the lateral or radial expansion and compression of the distal end portion  31  (e.g., of the tongues  311 ,  312 ), respectively, facilitates engagement and disengagement of the receiving part  7  with the device  1 . 
     It may be noted that the receiving part  7  shown in  FIGS. 10A and 10B  further includes another engagement feature  78  provided at a circumferential surface  702  of the receiving part  7 . The engagement feature  78  can allow for engaging of the receiving part  7  externally with other instruments as known in the art. 
     An example of an inner cap  8  for use with the receiving part  7  in one embodiment of the bone anchoring device is illustrated in  FIGS. 11A and 11B . The inner cap  8  includes a substantially cylindrical portion  81  and a substantially semi-spherical head receiving portion  82 . The head receiving portion  82  has resilient flanges  84  separated by slots  85 , where the flanges  84  are together configured to receive and clamp the head  91  of the bone anchoring element  9  in a snap-on fashion. In the clamped state, a resilient force can be exerted onto the head  91 , to provide some friction against free pivoting movement of the bone anchoring element  9 . Such a feature provides an advantageous degree of pre-locking for the bone anchoring device. 
     The cylindrical portion  81  has a diameter substantially corresponding to the diameter of the bore  700  and, as explained above, the abutment features  813 ,  814  provided at tips of legs  811 ,  812  may abut against edges of the recess  76  to prevent the inner cap  8  from falling out of the bore  700 . Moreover, the recess  76  is provided at a distance from the opening  701  of the receiving part  7  such that, upon introduction of the head  91  through the opening  701 , the inner cap  8  may move upward allowing the flanges  84  to expand and to snap on the head  91 . Upon final locking of the head  91 , the inner cap  8  is urged down toward the seat  75  to compress the flanges  84  onto the spherical head  91  of the bone anchoring element  9 . 
     Next, operation of the device or tool  1  with the receiving part  7 , or a method of use, is explained with reference to  FIGS. 12 through 16C .  FIGS. 12 through 14  illustrate steps of engaging the receiving part  7  with the device  1 , while  FIGS. 15A through 16C  reveal steps of placing and releasing the receiving part  7  on and from the head  91  of the bone anchoring element  9 , respectively. 
       FIGS. 12 and 13A  show a first step of the process, before engagement of the device or tool  1  with the receiving part  7 . As can be seen in  FIG. 12 , the operation portion  4  is already actuated (arrow Op) against the urging force of the coil spring of resilient member  6 . Consequently, the operation portion  4  and the collet  3  with the proximal end portion  35  are advanced distally relative to the holding portion  2  and the plunger  5 , or put another way, the holding portion  2  and the plunger  5  are retracted proximally relative to the collet  3 . As a result, the tip portion  52  including the conical tip portion  55  of the plunger  5  is retracted from the narrow diameter hole  314  inside the distal end portion  31  of the collet  3 . The tongues  311 ,  312  can then be resiliently compressed. 
     A second step of the process is shown in  FIG. 13B . The tip portion  33  of the distal end portion  31  is introduced into an inner space of the receiving part  7  formed by the bore  700  and the rod receiving channel  74 . The distal end portion  31  is introduced into the receiving part  7  along the longitudinal axis Z of the collet  3 . Because the cross-sectional profile of the tip portion  33  of the collet  3  corresponds to the cross section of the inner space of the receiving part  7 , the tip portion  33  may initially fit snugly into the inner space. However, the engagement features  34  protrude laterally outward from other parts of the tip portion  33  and eventually abut the top edges of the rod receiving channel  74 . Due to the rounded surfaces of the engagement features  34 , the tongues  311 ,  312  deflect radially inward along a direction R perpendicular to the longitudinal axis Z, i.e., the tongues  311 ,  312  are compressed towards each other (see arrows C). 
     As shown in  FIG. 13C , the engagement features  34  then latch into respective recesses of the engagement features  77 , thereby allowing the tongues  311 ,  312  to expand again (see arrows E).  FIG. 14  shows the same third step of the process shown in  FIG. 13C , and it becomes apparent that releasing the operation portion  4  leads to a retraction of the collet  3  relative to the plunger  5  (see arrow A), or put another way, an advancement of the holding portion  2  and the plunger  5  distally relative to the collet  3 , due to the urging force of the resilient member  6 . Thereby, the conical tip portion  55  and the tip portion  52  of the plunger  5  enter the narrow diameter hole  314  of the collet  3 , locking the engagement between the collet  3  and the receiving part  7  (i.e., in the “lock position”). More specifically, the tip portion  52  prevents any further compression of the tongues  311 ,  312 , such that engagement features  34  cannot be easily released from engagement features  77 . Moreover, further tightening or attachment of the receiving part  7  to the collet  3  is achieved by the conical tip portion  55 , which expands or urges the tip portion  33  and the engagement features  34  further into the engagement features  77  of the receiving part  7 . 
     In this arrangement, as shown in  FIG. 14 , the operation portion  4  may be removed from the device  1  as indicated by arrow Rem. Removal of the operation portion  4  prevents unintended release of the receiving part  7 , for example, during intermediate steps of the method. Meanwhile, due to the structure of the device  1  and the receiving part  7 , release of the receiving part  7  from the collet  3  after placement or implantation of the receiving part  7  can be accomplished via a simple withdrawal movement of the device  1 , as will be further explained below. 
       FIG. 15A  shows a fourth step of the method. The receiving part  7  is guided by the device  1  through an incision (not shown) in the tissue of the patient towards the head  91  of the bone anchoring element  9 , whose shank  92  has already been driven into bone material of a vertebra  100  (see arrow G). 
       FIG. 15B  shows a fifth step of the method in which the head  91  is introduced through the bottom opening  701  into the accommodation space of the bore  700  and clicked into the head receiving portion  82  of the inner cap  8  (see arrow Cl). Thereby, prior to being clicked into the head receiving portion  82  and clamped in a pre-lock position, the inner cap  8  first moves upwards within the bore  700  until the projections  813  latch into the recesses  76  and abut against upper edges or surfaces of the recesses  76 . This abutment prevents the inner cap  8  from moving further upwards. Having reached this position, the flanges  84  of the head receiving portion  82  can be deflected outwards to receive the head  91  therein in a snap-on fashion. 
     As shown in  FIG. 15C , the device or too  1  can then be pulled in a proximal direction away from the bone anchoring element  9  (see arrow W), and as a result, the inner cap  8  moves downward within the bore  700  (e.g., the receiving part moves up as illustrated) and is pressed against the seat  75  by the pulling force. As a consequence, the head  91  is clamped within the inner cap  8  and the receiving part  7  cannot move further up easily and also cannot be easily released from the clamped state. 
       FIGS. 16A and 16B  show a seventh step of the method in which, as shown in  FIG. 16B , further proximal pulling of the holding portion  2  leads to compression of the resilient member  6  because the holding portion  2  is effectively drawn upwards or proximally by the operating staff, while the collet  3  remains stationary relative to the receiving part  7 . Once the head  91  and the inner cap  8  are in the clamped state shown in  FIG. 15C , the collet  3  cannot be drawn further up easily, and the holding portion  2  can then be moved with respect to collet  3  under the increasing upward tensioning or biasing force exerted on the coil spring of the resilient member  6  when the holding portion  2  is still being pulled up (see arrow B). This, in turn, leads to retraction (see arrow F) of the plunger  5  and the conical tip portion  55  from the distal end portion  31  of collet  3 . Upon such tensioning, the position of the plunger  5  corresponds to the released or unlocked position with respect to the distal end portion  31 , and further withdrawing of the device  1  in the proximal direction allows compression of the tongues  311 ,  312  (see arrow C in  FIG. 16A ) and, therefore, release of the device or tool  1  from attachment with the receiving part  7 . As noted above, upon drawing up the holding portion  2 , the resilient member  6  is tensioned with an increasing force. Thereby, the resilient member  6  is configured or selected to be tensioned or compressed by an amount of force that is less than a clamping force exerted by the flexible head receiving portion  82  of the inner cap  8  on the head  91 . Hence, the receiving part  7  is released by the device or tool  1  before the head  91  can unclamp or be removed from the inner cap  8 , even when the head receiving portion  82  is not pressed against the seat  75 . 
     As shown in  FIG. 16C , the collet  3  can then disengage from the receiving part  7  (see arrow D) which has now been safely placed onto the head  91  of the bone anchoring element  9 . Meanwhile, since forces are no longer exerted onto the device  1  by the receiving part  7 , the collet  3  is then immediately retracted proximally relative to the holding portion  2 , again, under the urging force of the resilient member  6 , such that the device  1  returns into its initial locked state. 
     Meanwhile, the released receiving part  7  is pre-locked, which means that, by virtue of friction created between the head receiving portion  82  and the clamped head  91 , the receiving part  7  assumes and is held at a certain posture or angular position with respect to the bone anchoring element  9 , which can still be easily repositioned by hand or by an instrument. Further possible steps include supplying a spinal rod (not shown) to the receiving part  7 , wherein the spinal rod is inserted into the rod receiving channel  74 . Moreover, a locking screw (not shown) can then be screwed into the inner thread at the inner wall  79  of the receiving part  7  to lock the spinal rod in the receiving part  7 , where the spinal rod can then press onto a U-shaped or V-shaped groove at the cylindrical portion  81  of the inner cap  8 , to push or urge the inner cap  8  further downwards in the receiving part  7  in order to firmly and finally lock the receiving part  7  and head  91  together. 
     It may be noted that various modifications may be applied to the various aspects and embodiments of the invention which are within the scope of the appended claims and their equivalents. For example, in the above embodiments, metal materials, such as titanium, nickel titanium alloys, Nitinol, or other body-compatible metals, can be employed for each of the components. However other materials, such as plastic materials, PEEK, etc., can also be used. 
     Moreover, in the above embodiments, a receiving part employing an inner cap having a specific head clamping function is used. Nevertheless, other structures of receiving parts having, for example, pressure elements and/or other inner caps may also be used. 
     Meanwhile, in the above embodiments, tongues on the device or tool are expanded to engage engagement features provided at a receiving part. However, other engagement features may also be used. For example, it is also contemplated that movable engagement parts may be provided at a tip of a shaft which expand within an inner space of a receiving part upon engagement. 
     While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is instead intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.