Abstract:
A surgical instrument including a cutting instrument for shaping a bone as well as an impaction/extraction device for use with the cutting instrument is disclosed.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to surgical instruments, and, more particularly, to surgical instruments for preparing the proximal end of a tibia for receiving a tibial prosthesis. 
     2. Description of the Related Art 
     Orthopaedic prostheses are commonly utilized to repair and/or replace damaged bone and tissue in the human body. For example, a knee prosthesis used in total knee arthroplasty may include a tibial base plate that is affixed to a resected or natural proximal tibia, a femoral component attached to a resected or natural distal femur, and a tibial bearing component coupled with the tibial base plate and disposed between the base plate and femoral component. Prostheses frequently seek to provide articulation similar to a natural, anatomic articulation of a knee joint, including providing a wide range flexion. 
     To prepare the relevant bones of the human body to receive prosthetic components, a variety of cutting instruments are sometimes utilized. In the case of the proximal tibia, a bone saw may be utilized to prepare a planar osteotomy of the proximal tibia which is then followed by drilling of the intramedullary canal of the tibia to accommodate a stem extending from the base plate of a tibial prosthesis. Many tibial prostheses include a keel extending from opposing sides of the stem of the tibial prosthesis. To further shape the tibia to receive the tibial keel, a broach is impacted into the proximal surface of the tibia to create a cavity sized to receive the keel of the tibial prosthesis. After impacting the broach, it must be extracted from the tibia while maintaining the shape of the cavity formed thereby. 
     When preparing the proximal tibia to receive a tibial prosthesis, instrumentation including a sizing plate may be utilized to facilitate forming a cavity in the tibia sized and shaped to accommodate the stem and keel of a tibial prosthesis that is properly positioned and oriented. The size of the sizing plate corresponds to the size of a prosthesis which is to be mated to the bone. The sizing plate is positioned atop the proximal tibia after the initial, planar osteotomy is performed. Positioning of the sizing plate provides an indication of the location and orientation of the final prosthesis and guides the location of the subsequent bone shaping steps, i.e., drilling and broaching, which are utilized to prepare the bone to receive the tibial prosthesis. 
     SUMMARY 
     The present disclosure provides a surgical instrument including a cutting instrument for shaping a bone as well as an impaction/extraction device for use with the cutting instrument. The impaction/extraction device includes a housing having an internal wall defining a longitudinal cannula and a central shaft positioned in the longitudinal cannula of the housing. The central shaft is moveable longitudinally within the longitudinal cannula of the housing. The central shaft is secured or releasably securable to the cutting instrument so that reciprocation of the central shaft within the housing can cause the cutting instrument to, alternatively, be impacted into or extracted from a bone. An extraction lever is pivotally connected to the housing and presents a proximally facing impaction surface adjacent to an impaction surface formed on a proximal end of the central shaft. The impaction surface formed on the proximal end of the central shaft is also proximally facing. With this configuration, impaction of the impaction surface of the central shaft as well as impaction of the impaction surface of the extraction lever can be done by impacting or striking these surfaces with a mallet in a proximal to distal motion. The extraction lever includes an extraction arm opposite the extraction lever and impaction surface, with the extraction arm positionable into contact with a distal facing extraction surface formed on the central shaft. In this configuration, impaction of the extraction lever impaction surface positions the extraction arm in contact with the extraction surface of the central shaft and applies a distal to proximal force to the central shaft to effect extraction of a tibial broach which has previously been impacted into the tibia. 
     The extraction lever impaction surface may be curved to facilitate impaction of the same with a mallet moving in a proximal to distal direction relative to the instrument. Specifically, as the extraction lever articulates to effect extraction of the broach from the tibia, the curved surface ensures that no matter the rotational position of the extraction lever, the extraction lever impaction surface presents a proximally facing surface transverse to the longitudinal axis of the central shaft. Specifically, the extraction lever impaction surface of this form of the present invention defines a curve in a plane containing the longitudinal axis of the central shaft and is substantially linear in a direction perpendicular to that plane. For the purposes of this description, substantially linear is meant to encompass deviations from linear within manufacturing tolerances. With respect to the surgical instrument of the present disclosure, “proximal” and “distal” are used with reference to a user of the instrument. Specifically, “proximal” denotes a position of the instrument closest to a user of the instrument, while “distal” refers to a portion of the instrument furthest from the user during use of the instrument. 
     When used in combination with a support structure such as a tibial sizing plate, the surgical instrument of the present invention may incorporate at least one magnet positioned to attract the support structure to the housing of the surgical instrument as the support structure is indexed to the surgical instrument. Embodiments of the surgical instrument of the present invention may further include a ball detent or spring clip operable to hold the central shaft in a retracted position relative to the housing. The ball detent of this form of the present invention is useful in retracting the cutting instrument from the distal extent of the housing so that the surgical instrument can be secured to a support structure without interference from the cutting instrument. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a surgical instrument in accordance with the present invention; 
         FIG. 2  is a radial elevational view of impaction/extraction instrument in accordance with the present invention; 
         FIG. 3  is a cross-sectional view of the instrument illustrated in  FIGS. 1 and 2  taken along lines  3 - 3  of  FIG. 1 ; 
         FIG. 4  is a partial view of the impaction/extraction instrument illustrated in  FIGS. 1-3 , illustrating use of the same to impact a cutting instrument; 
         FIG. 5  is a partial view of the impaction/extraction instrument illustrated in  FIGS. 1-3 , illustrating use of the same to extract a cutting instrument; 
         FIG. 6  is a perspective view of a tibial sizing plate useable to guide the impaction/extraction instrument of the present invention; and 
         FIG. 7  is a sectional view illustrating a magnetic securement mechanism in accordance with the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein describe and illustrate exemplary embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-3 , impaction/extraction instrument  10  includes housing  12  and central shaft  14 . Referring to  FIG. 3 , housing  12  includes internal wall  16  defining a longitudinal cannula spanning proximal end  18  and distal end  20  of housing  12 . As illustrated in  FIG. 3 , central shaft  14  is positioned within the cannula formed by internal wall  16 . Internal wall  16  of housing  12  and the exterior of central shaft  14  have complementary geometries, e.g., circular geometries, which allow for axial reciprocation of central shaft  14  along its longitudinal axis L relative to housing  12 . Tibial broach  24  is secured to a distal end of central shaft  14 . 
     Referring to  FIGS. 2 and 3 , central shaft  14  includes internal wall  22  defining a T-shaped recess at a distal end of central shaft  14 . As illustrated in  FIG. 3 , internal wall  22  of central shaft  14  extends perpendicular to longitudinal axis L of central shaft  14  such that the T-shaped recess formed by internal wall  22  of central shaft  14  is perpendicular to the longitudinal axis L of central shaft  14 . Referring to  FIG. 2 , tibial broach  24  includes T-shaped protrusion  26  at a proximal end thereon. T-shaped protrusion  26  has a complimentary geometry to the geometry of the T-shaped recess formed by internal wall  22  of central shaft  14 . Specifically, T-shaped recess  26  is substantially congruent to the T-shaped recess formed by internal wall  22  of central shaft  14  and is sized such that a close fit can be formed therebetween. Referring to  FIG. 3 , central shaft  14  includes longitudinal bore  28  which is intersected by transverse bore  30 . Longitudinal bore  28  is sized to receive locating pin  32  as well as spring  34 . As illustrated in  FIG. 3 , longitudinal bore  28  is exemplified as a stepped bore having a smaller diameter portion receiving spring  34  and a larger diameter portion receiving locating pin  32 . Locating pin  32  includes proximal protrusion  36  which terminates distally at shoulder  38 . Proximal protrusion  36  is sized to be received within the interior of spring  34 . Shoulder  38  has a radial expanse greater than the radial expanse of spring  34  so that spring  34  rests against shoulder  38 . Locating pin  32  includes transverse bore  40  into which button  42  is positioned. Button  42  is secured to locating pin  32  so that movement of button  42  effects movement of locating pin  32 . As illustrated in  FIG. 3 , spring  34  biases locating pin  32  distally such that button  42  abuts the distal portion of the wall forming transverse bore  30 . 
     At its distal end, locating pin  32  includes spherical distal end  44 . As illustrated in FIG.  3 , spherical distal end  44  projects into the T-shaped recess defined by internal wall  22  of central shaft  14  in the normally biased position of locating pin  32 . Spherical end  44  of locating pin  32  may be withdrawn from the T-shaped recess formed by internal wall  22  of central shaft  14  by actuating button  42  proximally so that locating pin  32  is moved against the spring biasing force of spring  34 . 
     To operably secure tibial broach  24  to impaction/extraction instrument  10 , button  42  is actuated proximally against the spring biasing force of spring  34  to withdraw spherical distal end  44  of locating pin  32  from the T-shaped recess defined by internal wall  22  of central shaft  14 . With spherical distal end  44  of locating pin  32  withdrawn from the T-shaped recess, T-shaped protrusion  26  of tibial broach  24  can be positioned within the T-shaped recess formed by internal wall  22  of central shaft  14 . In this position, actuation of button  42  may cease so that spring  34  biases locating pin  32  downwardly and spherical distal end  44  of locating pin  32  is positioned within divot  46  formed in a proximal end of tibial broach  24 . 
     With tibial broach  24  secured to impaction/extraction instrument  10 , the central shaft  14  can be pulled proximally relative to housing  12  to move tibial broach  24  proximally relative to housing  12  such that distal end  48  of tibial broach  24  does not extend distally from distal end  20  of housing  12 . In this way, the distal most extent of tibial broach  24  will not extend beyond the distal most extent of housing  12  and, therefore, securement of impaction/extraction instrument  10  to a support structure, as will be further described hereinbelow, will not be interfered with by tibial broach  24 . To hold tibial broach  24  in this retracted position, central shaft  14  includes divot  50  sized to receive ball  52  of a ball detent mechanism. As illustrated in  FIG. 3 , divot  50  can take the form of an annular groove extending about the circumference of central shaft  14 . With tibial broach  24  in the withdrawn position, ball  52  engages divot  50  to hold tibial broach in a position such that it does not extend beyond distal end  20  of housing  12 . Divot  50  may, in alternative embodiments, comprise a spherical divot sized to receive ball  52 . To move tibial broach  24  from this position, impaction surface  54  may be impacted by mallet  56  ( FIG. 1 ). 
     The ball detent mechanism utilized to hold tibial broach  24  in its withdrawn position includes transverse bore  58  intersecting internal wall  16  at opening  60 . Opening  60  can be a circular opening having a diameter less than the diameter of ball  52 . Positioned within transverse bore  58  is spring  62  and set screw  64 . In an alternative embodiment, set screw  64  may be replaced with a cap which is welded in place within transverse boar  58 . In the finally seated position of set screw  64  illustrated in  FIG. 3 , spring  62  is compressed against ball  52  such that ball  52  extends beyond opening  60  and into the longitudinal cannula defined by internal wall  16  of housing  12 . As central shaft  14  is moved proximally, ramp  66  formed on central shaft  14  engages ball  52  so that ball  52  is moved against the biasing force of spring  62  and withdrawn from the cannula defined by internal wall  16  of housing  12 . As central shaft  14  is moved further proximally such that ball  52  is aligned with divot  50 , biasing force of spring  62  positions ball  52  in divot  50  as described hereinabove. The retracted position of tibial broach  24  is illustrated in  FIG. 1 . 
     A position of tibial broach  24  corresponding to its maximum extension distally from distal end  20  of housing  12  is illustrated in  FIGS. 2 and 3 . In this position, extraction lever  68  can be utilized to apply a distal to proximal force to central shaft  14  and move central shaft  14  and tibial broach  24  proximally. Extraction lever  68  is pivotally connected to housing  12  by cylindrical pivot pin  70 . Cylindrical pivot pin  70  is pivotally received in a pivot aperture sized to allow rotation but not radial translation of cylindrical pivot pin  70  relative to the pivot aperture. In the embodiment illustrated in  FIG. 3 , extraction lever  68  includes cylindrical aperture  72  into which cylindrical pivot pin  70  is positioned. In this embodiment, cylindrical aperture  72  is sized to receive cylindrical pivot pin  70  to pivotally connect extraction lever  68  to housing  12 , with cylindrical aperture  72  sized to allow rotation of extraction lever  68  relative to housing  12  but not to allow translation of extraction lever  68  in a direction oriented radially from cylindrical pivot pin  70 . In alternative embodiments, cylindrical pivot pin  70  may be fixedly secured to extraction lever  68  but may be pivotally connected within a cylindrical aperture formed in yolk  84  ( FIG. 1 ) in a similar fashion to the pivotal connection between cylindrical pivot pin  70  and cylindrical aperture  72  described above. 
     On opposing sides of cylindrical pivot pin  70 , extraction lever  68  includes extraction lever impaction surface  74  and extraction arm  76 . Extraction lever impaction surface  74  faces proximally, away from distal end  20  of housing  12 . Because extraction lever impaction surface  74  faces proximally, it can be impacted by mallet  56  ( FIG. 1 ) along a trajectory parallel to the impaction required to seat tibial broach  24 , as will be further described hereinbelow. 
     Extraction arm  76  resides within slot  78  formed in central shaft  14 . As illustrated in  FIG. 3 , slot  78  terminates proximally in extraction surface  80 . Extraction surface  80  faces distally, away from impaction surface  54  which forms the proximal end of impaction/extraction instrument  10 . With this arrangement, impaction of extraction lever impaction surface  74  with mallet  56  positions extraction arm  76  to contact extraction surface  80  and apply a distal to proximal force to central shaft  14  which will tend to pull tibial broach  24  proximally from the position illustrated in  FIG. 3  toward the withdrawn position illustrated in  FIG. 1 . Movement of extraction arm  76  relative to housing  12  is accommodated by slot  82  formed in housing  12 . 
     Referring to  FIG. 3 , extraction lever impaction surface  74  has a radially outward most extent relative to longitudinal axis L of central shaft  14  illustrated as distance D. Distance D measures no more than 10 cm. With extraction lever impaction surface  74  spaced no more than 10 cm from longitudinal axis L of central shaft  14 , the torque imparted to impaction/extraction instrument  10  when mallet  56  strikes extraction lever impaction surface is minimized and therefore toggling of tibial broach  24  within the broached bone will be minimized. Furthermore, the center of impaction surface  74  is spaced approximately 25 mm from the center of cylindrical pivot pin  70 . With an expected impaction force on the extraction head of approximately 7 kN, this would result in a torque about the center of cylindrical pivot pin  70  of about (7,000 N)×(0.025 m)=175 Nm. The inventors of the present invention have concluded that a torque of less than 300 Nm is desired to prevent toggling of tibial broach  24  during extraction thereof. In certain embodiments of the present invention, distance D can be as little as 5 cm. In alternative embodiments of the present invention, distance D can be any value between 5 and 10 cm in 0.5 cm increments, i.e., 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5 or 10.0 cm. 
     In an exemplary embodiment of the present invention, the lever ratio of the extraction lever is approximately 1.6:1. What this means is that the length of the arm extending from the center of cylindrical pivot pin  70  to a terminal end of extraction lever  68  adjacent to extraction lever impaction surface  74  is approximately 1.6 times the length of extraction arm  76  from the center of cylindrical pivot pin  70  to a second terminal end of extraction lever  68  on extraction arm  76 . The inventors of the present application have determined that a lever ratio of extraction lever  68  anywhere between 3:1 to 1:1 strikes an appropriate balance between decreasing toggling of tibial broach  24  during extraction while also providing an instrument actuateable with a comfortable amount of force applied by the user. 
     Extraction lever impaction surface  74  defines a curve in a plane containing the longitudinal axis of central shaft  14 . The section plane along which  FIG. 3  is taken is such a plane. As illustrated in  FIG. 3 , extraction lever impaction surface  74  is curved in a plane containing longitudinal axis L of central shaft  14 . While extraction lever impaction surface  74  is curved in a plane containing longitudinal axis L of central shaft  14 , it is substantially linear in a direction perpendicular to such plane. “Substantially linear” is meant to encompass linear configurations and those configurations within manufacturing tolerances of being linear. What this means is that in planes parallel to the plane along which the cross-sectional view of  FIG. 3  is taken, the profile of extraction lever impaction surface  74  remains unchanged. Curving of extraction lever impaction surface  74  facilitates articulation of extraction lever  68  by impacting extraction lever impaction surface  74  with mallet  56 . Specifically, the curvature of extraction lever impaction surface  74  means that mallet  56  can be actuated in a proximal to distal direction d as illustrated in  FIG. 5  while maintaining good contact with extraction lever impaction surface  74  throughout a full range of motion of extraction lever  68 . 
     Referring to  FIG. 1 , impaction/extraction instrument  10  can be utilized to broach tibia T in the following manner. After initially osteotomizing proximal surface P of tibia T, tibial sizing plate  86  is chosen, oriented with respect to tibial T and secured thereto. Techniques for osteotomizing proximal surface P of tibia T can include securing a cut guide to tibia T which guides an oscillating saw to cut proximal tibia T. Examples of such techniques can be found in the Zimmer NexGen LPS Fixed Knee Surgical Technique bearing copyright dates of 2002, 2008, the entire disclosure of which is hereby explicitly incorporated by reference herein. Alternative techniques for osteotomizing the proximal tibia and utilizing a sizing plate can be found in the Zimmer NexGen CR Flex and LPS Flex Knees Surgical Technique with posterior referencing instrumentation bearing copyright dates of 2010, 2011 and the Zimmer NexGen MIS Tibial Component Cemented Surgical Technique bearing copyright dates of 2005, 2006, 2008, 2009 and 2010, the entire disclosures of which are hereby explicitly incorporated by reference herein. Additionally, preparation of a tibia to receive a tibial prosthesis is shown and described in U.S. Pat. No. 5,634,927, assigned to the assignee of the present disclosure, the entire disclosure of which is hereby explicitly incorporated by reference herein. 
     After pinning tibial sizing plate  86  to tibia T, impaction/extraction instrument  10  can be indexed to tibial sizing plate  86  so that impaction/extraction instrument  10  is supported and guided by tibial sizing plate  86 . Referring to  FIGS. 2 and 7 , impaction/extraction instrument  10  includes bosses  88  extending distally from distal ends  20  of housing  12 . Bosses  88  are sized, shaped and spaced to cooperate with apertures  90  ( FIG. 6 ) in tibial sizing plate  86  to index impaction/extraction instrument  10  to tibial sizing plate  86 . In a portion of housing  12  adjacent to each boss  88 , a chamber holds a magnet  92  as illustrated in  FIG. 7 . Magnets  92  are oriented relative to their respective bosses  88  such that when each boss  88  is positioned within an aperture  90  to index impaction/extraction instrument  10  to tibial sizing plate  86 , magnet  92  will be positioned over a proximal surface of tibial base plate  86 . When using a metallic base plate  86 , magnets  92  will draw tibial sizing plate  86  toward impaction/extraction instrument  10  and facilitate indexing of impaction/extraction instrument  10  to tibial sizing plate  86 . During this process of indexing impaction/extraction instrument  10  to tibial sizing plate  86 , tibial broach  24  can maintain the extracted position illustrated in  FIG. 1  so that it cannot interfere with the indexing process. 
     With impaction/extraction instrument  10  properly indexed to tibial sizing plate  86 , mallet  56  may be utilized to strike impaction surface  54  to seat tibial broach  24  in tibia T and create an aperture in tibia T sized to accommodate the keel of a tibial prosthesis. Specifically, while using one hand to grasp housing  12 , a surgeon may use his or her other hand to actuate mallet  56  so that its head collides with impaction surface  54  to impact the impaction surface and effect seating of tibial broach  24  in tibia T. Prior to broaching tibia T, aperture  94  may be formed in tibia T to accommodate distal end  48  of tibial broach  24 . As distal end  48  of tibial broach  24  enters aperture  94 , teeth  96  of tibial broach  24  contact the bone of tibia T and effect cutting of the same. Final seating of tibial broach  24  is signaled when undersurface  98  opposing impaction surface  54  contacts proximal end  18  of housing  12  as illustrated in  FIGS. 3 and 4 . In this position, mallet  56  may be utilized to provide an impaction force to extraction lever impaction surface  74  as illustrated in  FIG. 5 . Such impaction force creates a torque about the center of cylindrical pivot pin  70  ( FIG. 3 ) and generates an extraction force in a distal to proximal direction along longitudinal axis L of central shaft  14 . 
     While this invention has been described as having an exemplary design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.