Abstract:
An insertion instrument for inserting an orthopedic implant into a bone and guiding an implant attachment element into the bone comprising: a body having a first end and a second end and a bore extending along a central axis; a fixed arm and a deflectable arm coupled to the body second end, the fixed arm spaced from the deflectable arm forming an attachment element receiving passageway therebetween extending along the central axis, the fixed arm having an implant engaging free end spaced a fixed distance from the central axis; and an actuator mounted on the first end of the body for moving the deflectable arm away from the fixed arm while allowing the attachment element to traverse the passageway.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    In the field of total joint replacements it is often necessary to mount plates or bearing elements mounted on plates on resected or prepared joint surfaces for receiving or contacting other elements of the joint replacement. Although these plate-like implants may include tissue ingrowth surfaces, some form of initial attachment to bone is required. This initial attachment is often achieved by utilizing threaded elements such as bone screws to attach the plates to bone. For example tibial or glenoid implants may have plate like structures attached using screws. 
         [0002]    It is sometimes necessary to hold an implant with one instrument and then insert the bone screw through the plate with a second instrument. In addition, when using bone screws it is sometimes desired to drill a pilot hole in the bone prior to inserting the screws so that insertion forces within the bone by the bone screw are lessened. Obviously once the plate has been implanted it is necessary to remove any instrumentation from the plate. 
         [0003]    There has been a need for instrumentation which firmly grips an implant plate so that it may be located and held in position on the bone and can be used to simultaneously guide the insertion of a bone screw through a bore in the plate and into bone. This is particularly advantageous in shoulder operations where access to the glenoid area of the shoulder is somewhat limited. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    Therefore it is one aspect of this invention to provide an implant insertion system which provides positive attachment to a plate-like implant while permitting the insertion of a second implant, such as bone screw, through the instrument and a bore in the bone plate for attaching it to bone. 
         [0005]    It is a further aspect of the invention to provide such an instrument for use in a glenoid application particularly for use in a reverse shoulder where a convex bearing element is coupled to the bone of the glenoid. An insertion instrument for inserting an orthopedic implant onto a bone and guiding an implant attachment element into the bone useful for plate implantation has a body having a first end and a second end and a bore extending along a central axis. The body has fixed arms and a deflectable arm coupled to the body second end. The fixed arm is spaced is from the deflectable arm forming an attachment element passageway, for example a bone screw receiving passageway therebetween extending along the central axis. The fixed arm has an implant engaging free end spaced a fixed distance from the central axis. An actuator is mounted on the first end of the body for moving the deflectable arm away from the fixed arm while allowing the attachment element or bone screw to traverse the passageway. 
         [0006]    The bore in the body is at least partially threaded and the actuator has an outer threaded portion mating with the threaded bore in the body. The actuator includes a shaft having an internal bore co-axial with the central axis of the bore in the body. The bore allows the bone screw to pass through the actuator while the instrument is locked on the plate. The actuator shaft has a drive portion and/or handle portion extending outwardly of the first end of the body. The drive portion may be a lobed handle fixed to the shaft for rotation therewith which may be driven by hand. The fixed arm and the deflectable arm are integral with the body second end wherein the first end of the instrument body is a handle portion. The fixed arm may have a first width and the deflectable arm has a second width less than the first width. The fixed arm may have a width generally equal to a thickness of the handle. The deflectable arm is preferably positioned intermediate a pair of non-deflectable arms which are spaced a fixed distance from the fixed arm. Each of the pair of non-deflectable arms surrounding the deflectable arm have ends coupled to an end of the fixed arm. 
         [0007]    The invention can also be achieved by a system for implanting an orthopedic implant having a plate for attachment to a bone comprising a through bore and first and second coupling elements on a non-bone contacting surface of the plate. An attachment element, for example a bone screw, can be inserted into the plate bore using an insertion instrument comprising a body having a first and second end and a bore extending along a central axis. A fixed arm and a deflectable arm coupled to the body second end. The fixed arm is spaced from the deflectable arm forming an attachment element or bone screw receiving passageway therebetween extending along the central axis. The fixed arm has an end spaced a fixed distance from the central axis, and a coupling element for engaging the plate first coupling element. The deflectable arm has an end with a coupling element for engaging the plate second coupling element. An actuator is mounted on the body first end for moving the deflectable arm away from the fixed arm. The actuator has an internal bore allowing the attachment element or bone screw to traverse the passageway between the fixed and deflectable arms into the plate through bore. 
         [0008]    The bore in the body is at least partially threaded. The actuator has a shaft with an outer threaded portion mating with the threaded bore in the body and the actuator shaft internal bore is co-axial with the central axis of the bore in the body when mounted thereon. The actuator shaft has a rotatable drive portion extending outwardly of the first end of the instrument body. The drive portion is a handle, preferably a handle having multiple lobes for easy gripping with one&#39;s hand. The fixed arm and the deflectable arm are integral with the body second end. The first end of the instrument may be in form of a handle. The fixed arm has a first width and the second arm has a second width less than the first width. The deflectable arm is housed intermediate a pair of non-deflectable arms spaced from the fixed arm in a direction perpendicular to the axis by a crossmember at the end of the instrument. The crossmember is connected to the fixed arm and each non-deflectable arm and defines an opening for the bone screw intermediate the arms. Each of the pair of non-deflectable arms have ends fixed by the connector to an end of the fixed arm. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an isometric view of a base plate insertion tool viewed from the front; 
           [0010]      FIG. 1A  is an isometric view of the base plate insertion tool of  FIG. 1  when viewed from the side; 
           [0011]      FIG. 2  is an enlarged view of the leading end of the insertion tool of  FIGS. 1 and 2  having coupling elements adapted to engage an implant base plate; 
           [0012]      FIG. 2A  is a view looking towards the middle of the instrument along lines  2 A- 2 A of  FIG. 2  with the gripping arms in a relaxed non-engaged position; 
           [0013]      FIG. 2B  shows the view of  FIG. 2A  with the arms expanded against the base plate in an engaged position; 
           [0014]      FIG. 3  is a front view of the base plate insertion tool of  FIGS. 1 and 1A ; 
           [0015]      FIG. 4  is a side view of the base plate insertion tool of  FIG. 3 ; 
           [0016]      FIG. 5  is a cross-sectional view of the base plate insertion tool of  FIG. 4  along lines  5 - 5   
           [0017]      FIG. 6  is an isometric view of the axially movable actuator shown in the previous figures; 
           [0018]      FIG. 7  shows the base plate insertion tool of the present invention connected to a base plate after a second implant, such as a bone screw, has been located and inserted through the base plate. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Referring to  FIGS. 1 to 6  there is shown an isometric view of an insertion tool of the present invention generally denoted as  10 . Tool  10  has a first end including an axially movable actuator  22  including an opening  30 , a handle portion  12  fixedly coupled to a shaft portion  14  including a second or leading end  16  which includes a pair of coupling elements  18  and  20 . Coupling element  18  is mounted on a fixed crossmember  19 . Element  20  is mounted on a resiliently deflectable arm member  21  received within crossmember  19  and element  18  is located on non-deflectable (fixed) arm  38  which is part of crossmember  19 . Arm member  21  is coupled to leg  32  and member  38  is coupled to leg  33 . Handle portion  12 , shaft portion  14  and leading end  16  extend along a central longitudinal axis  17 . The insertion tool  10  is cannulated along axis  17  and has an axially moveable actuator  22  extending within an opening through handle portion  12  and through a bore in shaft  14 . Actuator  22  shown in  FIG. 6  is also cannulated by a bore  30   a  so that the entire assembly can receive a bone screw or other bone attachment implant through opening  30  which leads to bore  59  and implant a base plate onto bone. The axis of the bore  59  in actuator  22  is coaxial with axis  12  of insertion tool  10 . 
         [0020]    Referring to  FIGS. 1A and 6  it can be seen that handle  12  is comprised of two side plates  21  and  23  spaced to form a recess  24  allowing viewing of the outer surface of a shaft  58   a  of actuator  22 . Actuator  22  includes a handle  28  so that it may be rotated and axially moved as will be discussed below. Bore  59  of actuator  22  also allows for the insertion of a screwdriver through tool  10  to drive a bone screw into bone. End  16  of tool  10  also includes a pair of openings  44  and  46  to allow passage of the bone screw and screw driver. Opening  44  is at the end of shaft portion  14  and opening  46  is in crossmember  19 . Shown as fine lines in both  FIGS. 1 and 1A , are slits  31  which extend through the leading end  16  of the insertion tool which allows arm member  21  and leg portion  32  of the leading end to deflect outwardly with respect to shaft portion  14  and handle  12 . Crossmember  19  and the other leg  33  is fixed with respect to handle  12 . As will be discussed below, these slits may be created by electrical discharge machining (EDM). 
         [0021]    Referring to  FIGS. 2 ,  2 A,  2 B and  3  there is shown an enlarged view of the leading end  16  of the insertion instrument  10  which includes fixed coupling element  18  mounted on an end surface of a fixed arm  38  and element  20  mounted on an end surface of deflectable arm  21 . Elements  18  and  20  are peg-like extensions having recesses  40  and  42  respectively. Recesses  40  and  42  are adapted to receive mating coupling elements  36  and  37  on a base plate  39 . As shown in  FIG. 7  a bore  139  is provided in baseplate  39  for a bone screw. 
         [0022]    Leading end  16  of instrument  10  includes bores  44  and  46  through which a bone implant such as a bone screw can traverse. End  16  includes deflectable leg  32  and deflectable arm  21  and fixed leg  33  and fixed arm  38 . Coupling element  20  is integral with arm  21  and moves with the deflection of legs  32  and arm  21 . Leg  32  is separated from a pair of non-movable legs  52  by slits  31 . Non-deflectable legs  52  are on either side of deflectable leg  32  and are each connected to fixed leg  33  by crossmember  19 . Crossmember  19  includes bore  46  which may intersect slits  31  to allow leg  32  and arm  21  to deflect. Preferably deflectable leg  32  formed by slits  31  extends from adjacent a plate  54  at the base of handle portion  12  all the way to end surface of arm  21 . Referring to  FIGS. 2A and 2B , there is shown enlarged leading ends  16  of shaft portion  14  coupled to a base plate  39 . Base plate  39  may be attached to a glenoid and includes a central bore  139  for receiving a bone screw. In  FIG. 2A  the legs  32  and  33  are in a relaxed position whereas in  FIG. 2B  they are in an expanded engaged position. As can be seen in the expanded position, leg  32  and arm  21  shift outwardly thereby expanding holes  44  and  46  about 0.3 inches so that recess  42  of legs  18  and  20  engage coupling elements  36  and  37  on base plate  39 . As will be discussed below, rotation of handle  22  forces deflectable leg  32  and arm outwardly thereby moving coupling element  20  into tight engagement with the coupling element  37  on base plate  39 . Slits  31  extend inwardly between legs  52  and leg  32  to the cannulated central bore of the instrument  10  from adjacent plate  54  so that the actuator  22  can cause the deflection of leg  32 . Slits  31  end in small through bores  56  which provide additional flexibility and which make using EDM easier by providing a starting location. 
         [0023]    Referring to  FIGS. 3-5  there is shown various views of the insertion instrument of the present invention. As can be seen in  FIG. 4 , slits  31  extend from bores  56  adjacent plate  54  to the end surface of arm  21  of leading end  16  of instrument  10 . Referring to  FIGS. 5 and 6 , there is shown actuator  22  which includes a cylindrical cannulated shaft or tube portion  58  inserted in and surrounding bore  59 . The outer surface of shaft  58  includes threaded portions  60  and  62  which threadably engage helical threaded portions  63 . Shaft portion  14  of insertion tool  10  includes a bore  45  ending in opening  44 . Shaft  58  has a tapered free end  64  best shown in  FIG. 6 . End  64  is preferably a section of a cone tapering inwardly towards axis  17 . The diameter of bores  45  and  59  are sufficiently large to accommodate the head of the bone screw or other attachment element which attaches the base plate to the glenoid. 
         [0024]    During manufacturing, the bore  59  is machined with the leg  33  deflected outwardly 0.3 inches so that a ramp  67  is formed when the deflected leg  33  springs inwardly. The ramp  67  is about halfway down the bore  59 . As a result of this manufacturing method the leg will deflect 0.3 inches at the distal end when the center tube is fully inserted and there is no baseplate attached to the instrument. When the baseplate  39  is attached to the instrument  10  the spring deflection is only allowed to be about 0.125 inches before the baseplate is fully engaged by the instrument. To fully engage the baseplate requires about  1  full turn of the center tub  58  based on the pitch and location of the thread at the top of the center tube. 
         [0025]    The slits  31  are about 0.010 inches wide, which width is obtained using the thinnest wire available for the wire EDM. Having thinner slits means that there is less rotational “slop” in the design. The spring arm is about 4.75 inches long, and the part is about 0.050 inches thick where the spring arm attaches to the rest of the instrument. The spring arm thickness is not a constant 0.050 inches, and for example is about 0.080 inches thick just below a ramp  67  formed on an inner surface of the spring arm  33 . These dimensions are for stainless steel, and using other metals may require modifications to either the spring element dimensions, the force required to screw in the center tube, and/or the thread pitch at the top of the center tube. 
         [0026]    As can be seen in  FIG. 5  as handle  22  is rotated clockwise screw portions  60  and  62  engage threads  63  and cause the tapered outer surface  66  of end  64  to advance and engage ramp  67  formed on the inner facing surface of arm  33  in the area at the end of an enlarged bore portion  68  of cannulated bore  45 . As shaft  58  advances axially upon rotation toward end  16  arm  32  coupling element  20  is deflected outwardly of axis  17 . Portion  68  is sized to accommodate an outer diameter of tubular shaft  58  while still allowing bore  59  to be large enough to allow the screw head to pass through bore  59  and bore  45  of the instrument  10 . 
         [0027]    Referring to  FIG. 7  there is shown instrument  10  coupled to base plate  39  with a bone screw  110  partially inserted through a bore  111  in base plate  39 . Actuator  22  has been axially advanced towards end  16  of instrument causing leg  32  and arm  21  to deflect outwardly and lock the instrument to the baseplate  39  by the engagement of pins  18  and  20  and elements  36  and  39 . Screw  110  has been previously passed through cannulated bores  45  and  59  along with a drive tool (not shown), such as a screwdriver, and driven into the glenoid area  112  of scapula  114 . When screw  110  is fully seated on base plate  39  by use of the screwdriver (not shown) handle  22  is rotated counterclockwise thus allowing arm  21  and leg  32  to spring back into its original position in alignment with arms  52  so that coupling element  20  is disengaged from the coupling element  37  on the base plate  39 . At this point there is sufficient clearance between the coupling elements  18  and  20  on the insertion tool and the coupling elements  36 ,  37  on base plate  39  to allow removal of the tool from the glenoid site. 
         [0028]    While the insertion tool has been described for use in connection with a glenoid base plate, it could also be used for example with a tibial base plate or any implant requiring a bone screw to be inserted while the implant, such as a bone plate, is held in position on the bone by tool  10 . 
         [0029]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.