Patent Publication Number: US-2012035667-A1

Title: Locking mechanisms for pivoting bone anchors

Description:
BACKGROUND 
     The present invention relates to a spinal implant and a manner of using the same, and more particularly, but not exclusively, relates an orthopedic device for treatment of spinal deformities. 
     The use of spinal implants to address orthopedic injuries and ailments has become commonplace in spinal surgery. In this arena, it is often desired to decrease the invasiveness of the procedures, improve implant integrity, reduce the potential for revision surgery, and provide more positive patient outcomes. Some of these implants utilize bone anchors that depend on interconnection between various components of the bone anchor to assemble the implant and implant systems associate therewith. In certain situations, it may be desirable for the bone anchor to include multi-axial capabilities so that a proximal portion of the bone anchor can pivot relative to the bone engaging portion of the bone anchor to facilitate assembly of the implant and alignment of the vertebrae to which the implant is attached. However, certain types of bone anchors lack a locking capability to prevent pivoting of the bone anchor after the construct is finally assembled and positioned in the patient. Thus, there is a need for additional contributions in this area of technology 
     SUMMARY 
     According to one aspect, a unique bone anchor is provided to engage an elongate connecting element that extends along the spinal column to aid in the assembly of a spinal fixation system. The bone anchor includes multi-axial capabilities during implantation of the connecting element, and is lockable to a fixed orientation during assembly of the fixation system. Other aspects include unique methods, systems, devices, instrumentation, and apparatus involving a bone anchor with multi-axial capabilities that is lockable to a fixed or substantially fixed orientation. 
     The bone anchors include a distal shaft for engaging bony structure of a vertebral body and a proximal post pivotably mounted at or near the proximal end of the shaft. The bone anchors include a locking member that is engageable to the post and to the shaft to lock the post in a selected angular orientation relative to the shaft. 
     According to one embodiment, the shaft includes a head about which the distal end of the post is pivotably mounted. The locking member includes a stem portion positioned in a central lumen of the post and a securing portion engageable to the proximal end of the post to contact the proximal end of the stem in the lumen and force the distal end of the stem into contact with the proximal end of the head of the shaft to lock the post in position relative to the shaft. In another embodiment, the post includes a distal end received in and pivotally mounted to a proximal end of the shaft. The locking member includes an elongated stem received in a lumen of the post that opens at a distal end of the post in the shaft and at an opposite proximal end of the post. A proximal securing portion of the locking member engages the post to force the distal end of the stem in contact with a proximally facing surface of the shaft. In yet another embodiment, the proximal end of the shaft forms a receptacle that pivotably houses a ball-shaped member at a distal end of the post. The locking member includes an elongated stem received in a lumen of the post. The lumen opens at a distal end of the ball-shaped member in the receptacle and at an opposite proximal end of the post. A proximal securing portion of the locking member engages the post to force the distal end of the stem in contact with an inner surface of the receptacle. In a further refinement of this embodiment, the ball-shaped member is slotted so that the stem of the locking member expands the ball-shaped member to frictionally engage the inner surface of the receptacle. In a further refinement of any embodiment, an insert is provided in the lumen of the post that is deformed by the stem of the locking member into contact with the shaft to lock the post in position relative to the shaft. 
     Related features, aspects, embodiments, objects and advantages of the present invention will be apparent from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a posterior view of a spinal fixation system engaged to the spinal column of a patient. 
         FIG. 2  is an elevation view of a bone anchor of the spinal fixation system of  FIG. 1 . 
         FIG. 3  is an end elevation view of the bone anchor of  FIG. 2 . 
         FIG. 4  is an enlarged detailed view of a portion of the bone anchor of  FIG. 2 . 
         FIG. 5  a perspective view of a locking member of the bone anchor of  FIG. 2 . 
         FIG. 6  is a longitudinal cross-section of a portion of the bone anchor of  FIG. 2 . 
         FIG. 7  is a perspective view of another embodiment bone anchor. 
         FIG. 8  is an elevation view in partial longitudinal cross-section of the bone anchor embodiment of  FIG. 7 . 
         FIG. 9  is a perspective view of another embodiment bone anchor. 
         FIG. 10  is a cross-section view along line  10 - 10  of  FIG. 9 . 
         FIG. 11  is an elevation view in partial longitudinal cross-section along line  11 - 11  of the bone anchor embodiment of  FIG. 9 . 
         FIG. 12  is an elevation view of a post of the bone anchor of  FIG. 9 . 
         FIG. 13  is a longitudinal cross-section of the post of  FIG. 12 . 
         FIG. 14  is a perspective view of another embodiment bone anchor. 
         FIG. 15  is an elevation view in partial longitudinal cross-section along line  15 - 15  of the bone anchor embodiment of  FIG. 14 . 
         FIG. 16  is a perspective view of another embodiment bone anchor. 
         FIG. 17  is a longitudinal section view of the bone anchor of  FIG. 16 . 
         FIG. 18  is an elevation view of the bone anchor of  FIG. 16 . 
         FIG. 19  is an elevation view of the bone anchor of  FIG. 16  rotated 90 degrees about its central longitudinal axis from the orientation of  FIG. 18 . 
     
    
    
     DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any such alterations and further modifications in the illustrated devices, and such further applications of the principles of the invention as illustrated herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
       FIG. 1  illustrates a posterior spinal stabilization system  20  implanted at a desired skeletal location of a patient. More specifically, as depicted in  FIG. 1 , system  20  is affixed to one or more of bones B of the spinal column segment SC from a posterior approach. Bones B include one or more vertebrae V and sacrum S of spinal column segment SC. Spinal fixation system  20  may be employed in spinal column segments SC including sacrum S and one or more vertebrae V, or in spinal column segments that comprise two or more vertebrae V. System  20  includes several bone attachment devices  22  and at least two elongate spinal connecting elements  23  structured to selectively interconnect with bone attachment devices  22 . In system  20 , bone attachment devices  22  are affixed to various locations of the spinal column segment SC and interconnected with connecting elements  23 , which are positioned on opposite sides of the medial or sagittal plane of the spinal column and extend in the cephalad-caudal direction to provide bi-lateral stabilization. Connecting elements  23  may also be interconnected by one or more crosslink devices  24  that extend medially-laterally across the sagittal plane to provide additional stabilization for treating spinal disorders. 
     Posterior stabilization system  20  may be used for, but is not limited to, treatment of degenerative spondylolisthesis, fracture, dislocation, scoliosis, kyphosis, spinal tumor, and/or a failed previous fusion associated with spinal column segment SC. Furthermore, spinal column segment SC may comprise any one or combination of the cervical, thoracic, lumbar and sacral regions of the spinal column. In certain procedures, spinal stabilization system  20  is secured to a spinal column segment SC with bone attachment devices  22  that include a distal bone engaging portion and a shaft portion that extends proximally from the bone engaging portion. The connecting elements  23  are offset to a side of respective ones of the bone attachment devices  22  and mounted to the proximal shaft portion with a coupling assembly. In one specific embodiment, the coupling assembly is like that found in Medtronic Sofamor Danek&#39;s TSRH® 3D spinal system. Of course, any suitable coupling assembly may be used to secure connecting elements  23  to one or more of the bone attachment devices. Furthermore, the bone attachment devices may be employed in surgical procedures and fixation systems like those described in the 2009 Medtronic Sofamor Danek USA, Inc. publication entitled “TSRH-3D PLUS MPA™ SPINAL INSTRUMENTATION DEFORMITY AND DEGENERATIVE SURGICAL TECHNIQUE”, which is incorporated herein by reference. 
     Connecting elements  23  can be in the form of an elongated spinal rod. The spinal rod may be solid or hollow along some or all of its length and/or may be of homogenous or heterogeneous composition. The spinal rod may also be of uniform cross-section along its entire length, or have a variable cross-section along its length. The spinal rod may include one or more interconnected spinal rod portions that lengthen or adjust in length to accommodate growth of spinal column segment SC over time in the cephalad-caudal directions. The spinal rod can be rigid, flexible, or include one or more flexible portions to permit at least limited spinal motion. Other embodiments of connecting element  23  contemplate any suitable spinal stabilization element positionable along the spinal column, including plates, bars, tethers, wires, cables, cords, inflatable devices, expandable devices, and formed in place devices, for example. 
     Referring to  FIGS. 2-3 , there is shown one embodiment of a bone attachment device in the form of bone anchor  30 . Bone anchor  30  includes a distal shaft  32  extending on a central longitudinal axis  34  from a distal end  36  to a proximal housing or head  38 . Shaft  32  is shown smooth, but may include threads, grooves, flutes, adhesives, wings, gulls, or any other suitable bone engaging structure. Distal end  36  includes a pointed configuration to facilitate entry into bone. A post  40  is pivotally mounted to head  38 . Post  40  includes an elongated body extending along a central longitudinal axis  42  from a distal end  44  to an opposite proximal end  46 . 
     Referring further to  FIGS. 4 and 6 , head  38  includes a pair of arms  48 ,  50  extending along opposite sides of a receptacle  52  to form a U-shaped clevis or yoke. Distal end  44  of post  40  is positioned in receptacle  52 . Each of the arms  48 ,  50  includes a bore  54 ,  56 , respectively, that receive respective ones of mounting pins  58 ,  60 . Mounting pins  58 ,  60  extend from bores  54 ,  56  and into receptacle  52  for receipt in a respective one of recesses  62 ,  64  formed in the sides of post  40  adjacent to distal end  44 . Pins  58 ,  60  can be captured by staking a circumferential edge of each in the respective bore  54 ,  56  of head  38 . Post  40  is pivotable about a pivot axis  43  extending through the centers of pins  58 ,  60 . Pivot axis  43  is orthogonal to central longitudinal axes  34 ,  42  so that central longitudinal axis  42  is positionable at any angle within a single plane that is defined by axes  42 ,  34 . The selected angle of axis  42  relative to axis  34  can range from +80 degrees from central longitudinal axis  34 , as shown by the positioning of central longitudinal axis  42 ′, to −80 degrees from longitudinal axis  34 , as shown by the positioning of central longitudinal axis  42 ″. In a non-pivoted orientation, post  40  is positioned so its central longitudinal axis  42  forms a 180 degree angle with central longitudinal axis  34  so that axes  34 ,  42  are co-linear with one another. Post  40  is positionable at any angle relative to longitudinal axis  34  between these orientations, as indicated by the positioning of central longitudinal axis  42 ′″. 
     Post  40  includes a central lumen  66  that extends on central longitudinal axis  42  and opens at distal end  44  and at proximal end  46 . Central lumen  66  extends between recesses  62 ,  64  but is isolated from recesses  62 ,  64  by the body of post  40  in the illustrated embodiment to avoid interference with pins  58 ,  60 . When it is desired to secure post  40  in a desired angular orientation relative to shaft  32 , a locking member  70  is positionable through lumen  66  and engaged to post  40  and shaft  32 . As further shown in  FIG. 5 , locking member  70  includes an elongated stem  72  extending from a distal end  74  to a proximal head  76 . Locking member  70  also includes a securing portion  78  between head  76  and stem  72  that engages post  40 . In the illustrated embodiment, securing portion  78  includes a cylindrical shape with external threads that threadingly engage internal threads at the proximal end opening of lumen  66  ( FIG. 8 ). When it is desired to lock post  40  in a selected angular orientation relative to shaft  32 , locking member  70  is threadingly engaged to post  40  and into lumen  66  until distal end  74  contacts shaft  32  in receptacle  52 . Receptacle  52  is defined by a bottom surface  53  that extends along and between the inner sides of arms  48 ,  50 . Distal end  74  of locking member  70  creates a point force on shaft  32  that locks post  40  and prevents pivoting movement of post  40  relative to shaft  32 . 
     As shown further below with respect to  FIG. 8 , head  76  includes an internal driving recess  80  to receive a driving tool to facilitate application of the desired force to locking member  70  in order to lock post  40  in position relative to shaft  32 . In the illustrated embodiment, driving recess  80  forms an internal hex-shaped recess. Other embodiments contemplate other configurations for the driving recess, including star-shaped, Allen-shaped, T-shaped, slot-shaped, or other suitable configuration. In still other embodiments, head  76  includes an external configuration to receive a driving tool thereover, including hex shapes, box-shapes, or other suitable external configuration. Head  76  can also be provided with both internal and external configurations to receive driving tools. In yet a further embodiment, the material thickness joining securing portion  78  to head  76  can be sized so that head  76  is severed or removed from the remaining portion of locking member  70  upon application of a threshold torque. This provides a reduced profile or no profile configuration for locking member  70  extending from the proximal end of post  40  when post  40  is locked in position relative to shaft  32 . 
     Another embodiment bone attachment device is shown in  FIGS. 7-8  in the form of bone anchor  130 . Bone anchor  130  is similar to bone anchor  30  and includes a distal shaft  132  extending on central longitudinal axis  134  from distal end  136  to a proximal housing or head  138 . Shaft  132  is shown with threads, but may include any other suitable bone engaging structure. Distal end  136  includes a pointed configuration to facilitate entry into bone. Bone anchor  130  further includes a proximal post  140  that is pivotably mounted head  138  of shaft  132  with post  140  extending on a central longitudinal axis  142 . Post  140  includes an elongated body extending from a distal ball-shaped member  144  to an opposite proximal end  146 . The mounting arrangement of post  140  to shaft  132  allows post  140  to pivot about a point  143  in the central of the ball-shaped member so that central longitudinal axis  134  and central longitudinal axis  142  define multiple planes within which post  140  can pivot relative to shaft  132 . 
     Head  138  extends outwardly from shaft  132  and defines a receptacle  152  that receives ball-shaped member  144  of post  140 . Head  138  defines a proximal end opening  148  and a retaining member  150  projecting into opening  148  to capture ball-shaped member  144  in receptacle  152  while allowing post  140  to pivot in any plane to an angular orientation relative to shaft  132 . In order to lock post  140  in a selected angular orientation relative to shaft  132 , locking member  70  can be positioned with stem  72  in longitudinal lumen  166  of post  140  and securing member  78  is threadingly engaged to internal threads  154  at the proximal end opening of lumen  166 . Locking member  70  is advanced until distal end  74  contacts an internal concave surface  156  of receptacle  152  to provide a point force sufficient to lock post  140  in position relative to shaft  132 . 
     In the illustrated embodiment of  FIGS. 7-8 , shaft  132  is threaded and includes a double-lead thread which is provided with a flat thread crest and angled leading and trailing thread faces. In the illustrated embodiment, one of the leads of the double-lead thread extends along the entire length of the threaded shaft, with the other lead extending along only a proximal portion of the threaded shaft. To provide this type of thread configuration, one of the double-leads is removed from the distal portion of the threaded shaft. In other embodiments, both of the interleaved threads of the double-lead thread extend along substantially the entire length of the threaded shaft. Each lead of the double-lead thread defines a constant and uniform thread pitch. In some embodiments, the threaded shaft defines a uniform major thread diameter which runs out onto a cylindrical portion  139  of the shaft that joins head  138 . In other embodiments, the proximal portion of the threaded shaft defines a uniform major thread diameter, but the distal portion of the threaded shaft defines a major thread diameter which inwardly tapers toward the distal tip  136 . In other embodiments, the major diameter of the threaded shaft portion is larger than the outer diameter of the cylindrical portion  139 . However, in other embodiments, the major diameter of the threaded shaft portion is smaller than the outer diameter of the cylindrical portion  139 . Furthermore, in some embodiments, the distal portion of the threaded shaft defines a uniform minor thread diameter extending proximally from the distal tip  136 , with a proximal portion of the threaded shaft defining a minor thread diameter which outwardly tapers in a proximal direction. In other embodiments, the distal portion of the threaded shaft defines a minor thread diameter that outwardly tapers from the distal tip  136  in a proximal direction at a first taper angle, with an intermediate portion of the threaded shaft defining a uniform minor thread diameter, and with a proximal portion of the threaded shaft defining a minor thread diameter which outwardly tapers in a proximal direction at a second taper angle which is less than the first taper angle. Additionally, in some embodiments, the distal end portion of the threaded shaft is provided with a pair of oppositely-disposed, semi-circular cutting flutes that intersect at least two full thread turns and which extend to the minor diameter of the thread to provide the threaded shaft with self-cutting and/or self-tapping capabilities. 
       FIGS. 9-13  show another embodiment bone anchor  230  that is similar to bone anchor  130 . However, bone anchor  230  includes a post  240  with an expandable ball-shaped end member  244  that expands to lock it in position in head  238  of shaft  232 . Shaft  232  includes an elongated body extending on central longitudinal axis  234  from distal end  236  to proximal head  238 . Post  240  includes an elongated body extending on central longitudinal axis  242  from ball-shaped member  244  at its distal end to proximal end  246 . Ball shaped member  244  pivots about its center  243  in head  238  in any direction relative to central longitudinal axis  234 . Locking member  70  is positionable through lumen  266  of post  240  to expand ball-shaped member  244  into engagement with the inner wall surfaces  256  of receptacle  248  of head  238 . 
     As shown in  FIGS. 12-13 , post  240  includes a number of slots  245  that bifurcate ball-shaped member  244  into a number of segments  247 . Slots  245  open at the distal end of post  140 , and extend into ball-shaped member  244  to intersect lumen  266 . Slots  245  extend proximally through ball-shaped member  244  to cylindrical sleeve portion  249  of post  240 . Sleeve portion  249  extends from ball-shaped member  244  to proximal end  246 . Similar to posts  40  and  140 , sleeve portion  249  of post  240  includes internal threads  254  formed in an enlarged proximal portion  267  of lumen  266  adjacent to proximal end  246 . 
     In use, shaft  232  is engaged to the bony structure of the vertebra, and post  240  is manipulated to the desired angular orientation relative to shaft  232 . Locking member  70  is inserted into lumen  266  of post  240  and securing portion  78  is threadingly engaged to threads  254 . Stem  72  acts as a wedge to open ball member  244  by moving segments  247  radially outwardly to frictionally engage inner wall surface  256  of head  238  and provide an interference fit therewith. In addition, the distal end  74  of stem  72  can be advanced to penetrate or seat against the portion of inner wall surface  256  aligned with lumen  266 . 
     Referring to  FIGS. 14-15 , there is shown another embodiment bone anchor  330  that is identical to bone anchor  130  discussed above except that a material insert  370  is provided in lumen  166  of post  140 . Material insert  370  is pushed distally by distal end  74  of stem  72  as locking member  70  is threadingly engaged in post  140 . Material insert  370  can be made from a material that deforms more readily than the material of shaft  132  so that insert  370  deforms as it is compressed between stem  72  and inner surface  156  of head  138  of shaft  132  while reducing the potential for undesired deformation of shaft  132 . 
     Referring to  FIG. 16-19 , there is shown another embodiment of the bone attachment device in the form of bone anchor  430 . Bone anchor  430  includes a distal shaft  432  extending on a central longitudinal axis  434  from a distal end  436  to a proximal head  438 . Shaft  432  includes threads as shown, but may include any other suitable bone engaging structure. Distal end  436  includes a pointed configuration to facilitate entry into bone. A post  440  is pivotally mounted around head  338 . Post  440  includes an elongated body extending along a central longitudinal axis  442  from a distal end  444  to an opposite proximal end  446 . 
     Distal end  444  of post  440  includes a pair of arms  448 ,  450  extending along opposite sides of head  438  to form a U-shaped clevis or yoke. Head  438  of shaft  432  is positioned in a receptacle defined between arms  448 ,  450 . Each of the arms  448 ,  450  includes a bore  454 ,  456 , respectively, that receives mounting pin  458 . Mounting pin  458  extends from bore  462  that extends laterally through opposite sides of head  438  and into bores  454 ,  456  of arms  448 ,  450 . Pin  458  can be fixed in bore  462  so that pin  458  rotates in each bore  454 ,  456  of arms  448 ,  450 . Post  440  is pivotable about a pivot axis  443  defined by pin  458  that is orthogonal to central longitudinal axes  434 ,  442  so that central longitudinal axis  442  is positionable at any angle in a plane that is defined by axes  442 ,  434 . The selected angular orientation can range from +90 degrees from central longitudinal axis  434 , as shown in  FIG. 18  by the positioning of central longitudinal axis  442 ′, to −90 degrees from longitudinal axis  434 , as shown by the positioning of central longitudinal axis  442 ″. In a non-pivoted orientation, post  440  is positioned so its central longitudinal axis  442  forms a 180 degree angle with central longitudinal axis  434  so that axes  434 ,  442  are co-linear with one another. Post  440  is pivotable relative to shaft  432  so that central longitudinal axis  442  is oriented at any angle relative to longitudinal axis  434  between these orientations, as indicated by the positioning of central longitudinal axis  442 ′″. 
     Post  440  includes a central lumen  466  that extends on central longitudinal axis  442  and opens at distal end  444  and at proximal end  446 . When it is desired to secure post  440  in a desired orientation relative to shaft  432 , a locking member  470  is positionable into the proximal end opening of lumen  466  and engaged to post  440 . Locking member  470  includes a proximal head  476  and a distal securing portion that extends into lumen  466  to contact a proximal end  475  of an elongated stem  472  that is housed in lumen  466 . Stem  472  extends from a distal end  474  to a proximal end  475 . As locking member  470  is threadingly advanced into lumen  466 , securing portion  478  contacts proximal end  475  of stem  472  to push distal end  474  of stem  472  against a proximal end of head  438  when it is desired to lock post  440  in a selected angular orientation relative to shaft  432 . Distal end  474  creates a point force on head  438  that locks post  440  in the selected angular orientation and prevents pivoting movement of post  440  relative to shaft  432 . 
     Head  476  includes an external driving configuration to receive a driving tool to facilitate application of the desired force to lock post  440  relative to shaft  432 . In the illustrated embodiment, the driving configuration forms an external hex-shape. Other embodiments contemplate other configurations for driving locking member  470 , including external box shapes and other shapes, and/or internal recesses that are hex-shaped, star-shaped, Allen-shaped, T-shaped, slot-shaped, or other suitable configuration. In yet a further embodiment, the material thickness joining head  476  to securing portion  478  can be sized so that head  476  is severed or removed from securing portion  478  upon application of a threshold torque. This provides a reduced profile or no profile configuration for locking member  470  extending from the proximal end of post  440  when post  440  is located in position relative to shaft  432 . 
     The bone anchors discussed herein can be used in any suitable spinal stabilization system. Surgical instruments can also be mounted to the bone anchors for using in positioning components of the fixation system and in aligning vertebrae of the spinal column. For example, an elongated extension or other instrument can be removably engaged to the proximal end of the post of the bone anchors discussed herein during implantation. The extension can then be removed so that a locking member or portion of the locking member can be engaged to the post to lock the post in the selected angular orientation relative to the shaft. 
     The bone anchors discussed herein can be provided in a number of sizes and configurations, including varying lengths, diameters and bone screw thread arrangements. The post can include a smooth outer surface, and may also include a tool engaging configuration formed on its inner and/or outer surfaces. The bone anchors discuss herein can be formed of titanium, stainless steel, cobalt-chrome or any other suitable biocompatible metal or non-metal material. The bone anchors include a proximal post and a distal shaft that is threaded or otherwise configured for anchoring within vertebral bone. The proximal post is connected directly to the distal shaft portion, although embodiments where the post is indirectly connected to the shaft are also contemplated. In some embodiments, a housing or head is provided between the post and shaft to provide a location in which to pivotably mount the post to the shaft. In some embodiments, the head or housing is formed integrally with the shaft. Other embodiments contemplate that the head or housing is integrally formed with the post, or is a separate component that is separately attached the post and to the shaft. In any event, the head or housing provides a connection that allows the post to pivot relative to the shaft. Of course, it is understood that the relative size of the components can be modified for the particular vertebra(e) to be instrumented and for the particular location or structure of the vertebrae to which the bone anchor will be engaged. 
     Although various embodiments have been described as having particular features and/or combinations of components, other embodiments are possible having a combination of any features and/or components from any of embodiments as discussed above. As used in this specification, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, the term “a member” is intended to mean a single member or a combination of members, “a material” is intended to mean one or more materials, or a combination thereof. Furthermore, the terms “proximal” and “distal” refer to the direction closer to and away from, respectively, an operator (e.g., surgeon, physician, nurse, technician, etc.) who would insert the medical implant and/or instruments into the patient. For example, the portion of a medical instrument first inserted inside the patient&#39;s body would be the distal portion, while the opposite portion of the medical device (e.g., the portion of the medical device closest to the operator) would be the proximal portion. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that all changes and modifications that come within the spirit of the invention are desired to be protected.