Patent Publication Number: US-11376016-B2

Title: Surgical blade cartridge with a guide bar

Description:
FIELD OF THE INVENTION 
     This invention relates to a surgical blade cartridge that has a static guide bar and a blade that is pivotally mounted to the bar. More particularly, this invention is related to a surgical blade cartridge with a static guide bar that includes structural members useful for controlling the depth of the cut formed by the cartridge. 
     BACKGROUND OF THE INVENTION 
     A surgical saw blade is used to cut the tissue against which the blade is applied. Many surgical saw blades are configured to cut hard tissue, bone. A sagittal surgical saw blade is a surgical saw blade with a head that pivots around an axis that is perpendicular to the plane of the blade. Some surgical saw blades are known as reciprocating saw blades. This type of blade is designed to so the body of the blade moves back and forth along the longitudinal axis that extends along, though, the body of the blade. Both types of saw blade include features that facilitate the releasable attachment of the blade to the saw used to actuate the blade. The saw includes a motor. When the saw motor is actuated, the saw moves the blade in a back and forth pattern. As implied by the name, a reciprocating blade is, when actuated, considered to reciprocate back and forth. A sagittal saw blade, when actuated, is often considered to oscillate back and forth around a pivot point. 
     PCT Pub. No. WO 2006/017066A2/U.S. Pat. No. 7,497,860 and PCT Pub. No. WO 2007/030793/U.S. Pat. No. 7,704,254, the contents of both of which are incorporated herein by reference, each disclose a sagittal saw blade cartridge. A sagittal saw blade cartridge includes a static guide bar and a blade. The guide bar is an elongated assembly that is releasably attached to the handpiece, the saw, that actuates the cartridge. The blade is pivotally mounted to the guide bar. The blade has teeth that extend forward of the guide bar. Also part of the cartridge and internal to the guide bar are one or more drive links. Each drive link extends from the blade towards the proximal end of the guide bar. The drive links are reciprocated back and forth by a drive assembly internal to the saw. The reciprocation of the drive links causes the blade to pivot, to oscillate, back and forth. The pivoting of the blade is what enables the teeth to cut the tissue against which the blade is pressed. Sometimes, this type of cartridge is referred to as an oscillating tip saw blade cartridge. 
     An advantage of the sagittal surgical blade cartridge is that the only portion of the cartridge that pivots is the distally located blade. In contrast, a conventional sagittal saw blade pivots from its point of attachment to the saw to which the blade is attached. As a consequence the saw to which a cartridge is attached vibrates less than the saw to which a conventional sagittal saw blade is attached. Thus, the saw to which a sagittal surgical blade cartridge is attached can be easier to control than a saw to which a conventional surgical sagittal saw blade is attached. Also, it is common practice to use a cutting guide to properly position a sagittal saw blade relative to the tissue the blade is intended to cut. When a conventional blade is actuated, the oscillating movement of the blade wears against the surfaces of the cutting guide defining the slot in which the blade is seated. The guide bar of a surgical sagittal blade cartridge only minimally moves in this slot. Thus, by using a cartridge, instead of a conventional blade, less of the material forming the cutting guide is rubbed off the guide. This reduces the extent to which the surgeon has to flush worn off cutting guide material from the surgical site. Further, use of the oscillating tip blade reduces the extent to which the material forming the guide becomes so worn that the guide itself is rendered useless. 
     A surgical sagittal blade cartridge has another benefit over a conventional sagittal saw blade. Since the guide bar remains static when the blade is actuated, the practitioner can press one or more fingers against the guide bar. This facilitates the holding of the cartridge in the desired position as the cartridge is advanced against the tissue that is to be cut. 
     PCT Pub. No. WO 2006/017066A2/U.S. Pat. No. 7,497,860 also discloses a reciprocating blade cartridge. This cartridge has a blade that extends laterally, from a side of the bar portion of the cartridge. A drive rod internal to the bar reciprocates the blade back and forth along an axis that is parallel to the proximal-to-distal longitudinal axis through the bar. The Applicant&#39;s U.S. Prov. Pat. App. No. 62/268,536, the contents of which are explicitly incorporated by reference and contained in US Pat. Pub. No. 2020/0261100A1/PCT Pub. No. WO 2017/106533A2 also discloses a reciprocating blade cartridge. 
     Surgical blade cartridges work well for the purposes for which they are designed. Nevertheless, a surgical blade cartridge shares a limitation with a conventional surgical saw blade. It can be difficult for the surgeon pressing the blade cartridge against bone to control the depth of the cut of the cut of formed by the cartridge. Essentially a surgeon has to rely on the feel of the saw and cartridge to determine if the blade has formed the desired cut and the surgeon should stop applying a forward force to the cartridge. It is desirable to so stop plunging the blade forward because it is typically undesirable to allow the cartridge to cut the soft tissue inwardly of the bone. To ensure that blade cartridge does not advance beyond the desired depth, the surgeon is required to control the force applied to the saw. Specifically the force needs to be sufficient to overcome the resistive force of the bone against which the blade is applied. The force, however, cannot be so great that, when the blade breaks through the bone, the momentum of the saw, results in the appreciable advancement of the blade through the underlying soft tissue. Simultaneously with having to so regulate the force applied to the saw and cartridge, the surgeon needs to tactilely sense the change in the resistive force to which the cartridge is exposed. The sensing of the sudden drop off of this force functions as the cue that the cartridge has cut through the bone being cut and that it is necessary to stop applying a forward force to the saw and the blade. 
     Having to simultaneously perform these control and sensing steps can add to the physical and mental stress associated with applying either a sagittal saw blade or a sagittal saw blade cartridge to the bone in which the cut is to be formed. 
     Further, there are a number procedures for which the most appropriate blade to form the cut bone is the reciprocating blade. This is true for procedures that involve forming cuts in the jaw. This is also true in many situations when it is necessary to form a cut in the sternum, the bone that covers the heart and lungs. When performing this type of procedure, the motion and shape of the sagittal blade typically does not make it possible to use this type of blade to form the desired cut. The incorporated by reference PCT Pub. No. WO 2006/017066A2/U.S. Pat. No. 7,497,860 discloses a sagittal saw blade cartridge with a blade that projects laterally, from the side of the guide bar. Even this type of sagittal blade cartridge has not proven to be a suitable replacement for a reciprocating saw blade. There are some reciprocating saws specifically designed to use a reciprocating blade especially designed to cut through the sternum. This means that a facility that performs both orthopedic surgery and surgery on the chest must have two types of saws available. A first saw needs to be provided to drive the sagittal blades used by an orthopedic surgeon. A second saw needs to be provided to drive the reciprocating blade a chest surgeon uses to access organs and tissue below the sternum. 
     SUMMARY OF THE INVENTION 
     This invention relates to a new and useful surgical blade cartridge. The blade cartridge of this invention includes a bar and a blade that is mounted to the bar for oscillatory motion. Here oscillatory motion is understood to be repetitive back and forth motion. The surgical blade cartridge of this invention includes features that are useful for regulating the positon of the cartridge relative to the bone against which the cartridge is applied. These features are associated with the guide bar of the cartridge. 
     It is still a further feature of this invention to provide a reciprocating blade cartridge that can be used like a conventional reciprocating blade and is further constructed so the locus of movement of the blade is spaced from the saw used to actuate the blade. A further feature of this cartridge is that it can be attached to a saw designed to actuate the blade of a sagittal blade cartridge. 
     In many versions of the invention, the feature of the cartridge of this invention useful for limiting plunge is a structural member of the static guide bar that is located adjacent the space in which the teeth of the blade move back and forth. Typically this structural member is located adjacent one end of the space in which the teeth move. In some embodiments of this invention this structural member extends at least partially forward of the proximal end of the space in which the teeth move. In still other versions of the invention, this structural member extends forward of the space in which the teeth move. In some versions of the invention, the cartridge has plural extensions. Separate extensions are located on opposed sides the blade. 
     In some versions of this invention, this extension is an arm. The arm is constructed so the distal end of the arm is located laterally away from the teeth of the blade. When the cartridge is pressed against bone, the distal end of the arm rests against an uncut section of the bone. The uncut section of bone thus becomes a fulcrum point around which the arm pivots as the blade is rotated into tissue. 
     In some embodiments of this version of this version of the invention the bar is formed with two arms. Also in some versions of this invention, the arm is located so, longitudinally along the cartridge, the arm is located distal to the proximal most sweep position of the blade and proximal to the distal end of the blade. 
     In still other versions of the invention, the structural member of the guide bar includes a surface located forward of the blade. In these versions of the invention, the surface functions as a stop that limits the proximal movement of the cartridge away from the bone against which the cartridge is applied. The surface allows the blade to be used as a sternum saw. 
     In some embodiments of this version of the invention the blade is formed so the teeth are arranged linearly. Often in these embodiments of the invention, the cartridge is further formed so the blade reciprocates back and forth along an axis that intersects the longitudinal axis of the cartridge. In some of these embodiments of the invention, the blade is mounted to the cartridge so the head moves along a line that is not perpendicular to the longitudinal axis of the blade cartridge. It should also be understood that a cartridge of this invention may be configured so that cartridge blade undergoes a loop motion. This motion includes a longitudinal component in which a point on the blade engages in at least some repetitive proximal-to-distal motion. The same motion has a lateral component. The point engages in some repetitive side-to-side motion. Since the blade engages in some longitudinal motion the blade for the purposes of this invention is considered to engage in reciprocal motion. 
     Embodiments of both versions of this invention are often constructed so the blade projects outwardly beyond the sides of the proximal end of the guide bar. In these embodiments of the invention the cartridge is thus further formed so the guide bar can be said to have a proximally located foot and a distally located head. The foot is the portion of the bar mounted to the saw used to actuate the cartridge. The head, which is located forward of the foot, is the portion of the cartridge from which the blade and one or more arms extend. Owing to the relatively large width of the blade, in comparison to the bar foot, the bar head is also typically larger in side-to-side width than the bar foot. 
     Some blade cartridges of this invention are designed so the blade oscillates around an axis that extends through the plane of the blade. These versions of the invention are sometimes referred to as a surgical sagittal blade cartridges. 
     Other blade cartridges of this invention include a blade that oscillates back and forth along a line that is coplanar if not parallel to the longitudinal axis through the static guide bar. These versions of the invention are sometimes referred to as surgical reciprocating blade cartridges. These versions of the invention include the drive links and blades of the basic cartridge of this invention. These versions of the invention also include pivot link. The pivot link transfers to reciprocal motion of the drive links to the blade so as to cause the reciprocal movement of the blade. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is pointed out with particularity in the claims. The above and further features and benefits of the invention are understood from the following Detailed Description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of a first surgical blade cartridge of this invention attached to a saw used to actuate the cartridge; 
         FIG. 2  is a plan view of the cartridge of  FIG. 1 ; 
         FIG. 3  is an exploded view of the cartridge of  FIG. 1 ; 
         FIG. 4  is a perspective view of the blade internal to the cartridge of  FIG. 1 ; 
         FIG. 5  is a perspective view of the cartridge of  FIG. 1  with the top plate removed; 
         FIG. 6  is a side and partial cross sectional view depicting how a structural component of the guide bar of the cartridge of this invention both functions as a pivot arm; 
         FIG. 7  is a perspective view of a second surgical blade cartridge of this invention attached to the saw; 
         FIG. 8  is side plan view of the cartridge of  FIG. 7 ; 
         FIG. 9  is an exploded view of the cartridge of  FIG. 7 ; 
         FIG. 10  is an exploded view of the blade and interconnecting link internal to the cartridge of  FIG. 7 ; 
         FIG. 11  is a perspective view of the cartridge of  FIG. 7  with the top plate removed; 
         FIG. 11A  is a an enlarged plan view of a section of the blade of the cartridge of  FIG. 7 ; 
         FIG. 12  is a side and partial cross sectional view of how the cartridge of  FIG. 7  is used to both cut bone and function as a stop and guard for regulating the depth of the cut; 
         FIG. 13  is a perspective view of a third surgical blade cartridge of this invention; 
         FIG. 14  is an exploded view of the cartridge of  FIG. 13 ; 
         FIG. 15  is an exploded view of the drive link-and-blade sub-assembly of the cartridge of  FIG. 13 ; 
         FIG. 16  is a perspective view of the cartridge of  FIG. 13  with the top plate removed; 
         FIG. 17  is a perspective view of a fourth surgical blade cartridge of this invention; 
         FIG. 18  is an exploded view of the cartridge of  FIG. 17 ; 
         FIG. 19  is a perspective view of the drive link-and-blade sub-assembly of the cartridge of  FIG. 17 ; 
         FIG. 20  is a perspective view of the cartridge of  FIG. 17  with the top plate removed; 
         FIG. 21  is a perspective view of the cartridge of  FIG. 17  with the top plate removed and an alternative blade seated in the guide bar; and 
         FIG. 22  is a perspective view of the blade of  FIG. 21 . 
     
    
    
     DETAILED DESCRIPTION 
     I. First Cartridge 
       FIG. 1  illustrates a saw  30  to which a surgical sagittal blade cartridge  60  of this invention is removably attached. Saw  30  includes a body or housing  32 . In the depicted version of the invention, housing  32  is pistol shaped. A head  34  extends distally forward from the distal end of the housing  32  and is the most distal component of the saw  30 , (Here, “distal” is understood to means away from the surgeon holding the saw  30 ; towards the site to which the cartridge  60  is applied. “Proximal” is understood to mean towards the surgeon holding the saw  30 ; away from the site to which the cartridge  60  is applied.) The head  34  is shaped to receive the proximal end of cartridge  60 . A coupling rod  36 , the head of which is seen, is slidably mounted to the saw head  34 . When coupling rod  36  is in the run position, a portion of the rod presses against the cartridge  60  to hold the cartridge to the head  34 . When the coupling rod  36  is in the load position, the coupling rod  36  does not press against cartridge  60 . This allows the cartridge  60  to be removed from the head and a new cartridge releasably attached to the head. A wing nut  38 , partially seen, attached to the head  34  moves the coupling rod  36  between the run and load positions. 
     A motor  42 , represented by a phantom cylinder, is disposed inside the barrel of housing  32 . Motor  42  is connected to a pair of drive pins  44 , one pin identified, that are mounted to the head  34  to project above the surface on which the cartridge  60  is seated. Drive pins  44  are mounted to the head  34  to engage in opposed oscillatory motion. A trigger  46 , located below the saw head  34 , is the manually actuated member that is depressed to control the actuation of the saw. A battery  48  is seen attached to the butt end of the grip portion of the housing  32 . In the depicted version of the invention, motor  42  is an electric motor. Battery  48  provides the current required to energize the motor  42 . 
     The cartridge  60 , as seen in  FIGS. 2 and 3 , includes a guide bar  62  to which a blade  150  is pivotally mounted. Drive links  130 , one link identified, extend proximally from opposed sides of the blade  150 . The drive links  130  terminate at a location forward of the proximal end of the guide bar  62 . 
     Guide bar  62  is a laminate structure that includes a bottom plate  88  and an inner plate  104  disposed over the bottom plate  88 . A top plate  124 , also part of the guide bar  62 , is secured over the exposed face of the inner plate  88 . Collectively, plates,  88 ,  104  and  124  are formed so the guide bar  62 , at the proximal end, has a foot  64 . Foot  64  is shaped so that, extending from the proximal end of the foot, which is the proximal end of the guide bar  62 , the sides of the foot taper slightly outwardly. Forward of the foot  64 , plates  88 ,  104  and  124  are shaped so the guide bar has a trunk  66 . From where the trunk  66  extends forward from the foot  64 , the sides of the guide bar  62  taper inwardly. 
     At the distal end of the trunk  66 , guide bar  62  is shaped to have a head  68 . Head  68  is the most distal portion of the guide bar. The guide bar head  68  is shaped to have two opposed outwardly extending back faces  70 , the edges of which are identified in  FIG. 2 . Each face  70  extends laterally outwardly from the distal end of the adjacent side of the trunk  66 . In the illustrated version of the invention, the guide bar  62  is formed so that as each face  70  extends laterally outwardly, the face extends a short distance distally forward. The bottom plate  88  and top plate  124  are formed to, forward of the back faces  70  provide the guide bar with a distally directed, curved front face  72 , the edge of which is identified in  FIG. 2 . Guide bar  62  is shaped so that the front face  72  subtends an angle between 110 and 180°. As discussed below, the guide bar is formed so that the inner plate  104  does not extend the same length as the bottom plate  88  and top plate  124 . Accordingly, there is elongated slot  74  in the bar front face  72  between the inner and bottom and top plates  88  and  124 , respectively. Slot  74  is identified in  FIG. 5 . 
     The guide bar  62  is further formed so that between each end of the back face  70  and the adjacent end of front face  72  an arm  78  (arms identified in  FIG. 1 ) projects laterally outwardly from the head  68 . Each arm  78  includes a base  80 , one base identified in  FIG. 2 . The base  80  is the portion of the arm that projects laterally away from the head  68 . A forearm  82 , also part of the arm  78 , one forearm identified in  FIG. 2 , extends longitudinally forward from the free end of the base. The free end of each forearm  82  is rounded. Fingers  84  protrude outwardly from the outer side surface of each forearm  82 . Each finger  84  is triangular shape so as to have a pointed tip, (finger tips not identified). Owing to the free end of each forearm  82  being rounded, the fingers  84 , appear to be arranged in a circular pattern around the forearm from which they extend. 
     Immediately forward of the proximal end of the plate, bottom plate  88  is formed to have two laterally spaced apart openings  90  (one identified). Top plate  124  is formed to have two openings  126  (one identified) that are each positioned to be in registration with a separate one of the bottom plate openings  90 . Openings  90  and  126  are identical in shape. The bottom plate  88  is further formed to define two openings  94  (one opening identified). Openings  94  are located in the portion of the plate  88  that forms the proximal portion of the head portion of the plate. Each opening  94  is longitudinally aligned with a separate one of the openings  90 . Top plate  124  is formed to have two openings  128 . Each opening  128  is positioned to be in registration with a separate one of the bone plate openings  94 . Openings  94  and  128  are identical in shape. 
     Bottom plate  88  is further formed to have a keyhole shaped opening  92 . Opening  92  is longitudinally centered over the longitudinal axis of the plate  88 . Opening  92  is located in the portion of the plate  88  that forms the proximal portion of the trunk section of the plate. The inner plate  104  is formed to have an identically shaped opening  112 . The top plate  124  has an opening  127 . When the plates  88 ,  104  and  124  are assembled together, bottom plate opening  92  and inner plate opening  112  are in registration. Top plate opening  127  is disposed over openings  92  and  112 . Openings  92 ,  112  and  127  are collectively dimensioned to receive the head of saw coupling rod  36 . A more complete understanding of this arrangement is disclosed in the now explicitly incorporated by reference U.S. Prov. Pat. No. 62/160,234 the contents of which are contained in PCT Pub. No. WO 2016/182981A2/US Pat. Pub. No. 2018/0064448A1 
     A triangular plate  98  is welded or otherwise secured to the inner face of the bottom plate  88 . Plate  98  is located over the portion of the bottom plate  88  that forms a portion of the head  68  of the guide bar  62 . 
     At the proximal end, inner plate  104  is formed to have a base  106 . Two spaced apart outer tines  108  extend distally forward from the opposed ends of base  106 . An inner tine  110  extends forward from the center of the base  106 . The inner plate  104  is formed so that the outer tines  108  are laterally spaced away from the inner tine  110 . The inner tine  110  is the portion of the inner plate in which opening  112  is formed. It is further observed that the inner tine  110  is formed to have a distal end head  114  that is rounded in shape. 
     The inner plate  104  is further formed so a beam  118  extends laterally outwardly from the distal end of each outer tine  108 . Beams  118  are portions of the inner plate  104  that are the structural components of the plate  104  that form part of the guide bar head  68 . The L-shaped outer end of each inner beam  118  is the section of the beam that is the structural component of the inner plate  104  that form part of the arm  78  and fingers  84  on the side of the bar with which the beam is associated. 
     Top plate  124  is essentially identical in shape to the bottom plate  88 . One difference between the two plates  88  and  124  is that there is no supplemental plate welded or otherwise secured to the inner surface of the top plate  124 . 
     The blade  150 , as seen in  FIG. 4 , is formed to have a proximal web  158 . The blade  150  is formed so that web  158  has a thickness that is no greater than the thickness of inner plate  104 . Web  158  is generally trapezoidal in shape. The proximal end of the web  158  is the widest portion of the web. When blade  150  is in the centered position within the guide bar  62  the major axis of the web  158  is collinear with the major axis of the guide bar. Extending proximally from web  158  and away from the longitudinal axis of the web, blade  150  is shaped to have two feet  152 . Feet  152  have the same thickness of web  158 . Each foot  152  extends between one of the outer tines  108  and the inner tine  110  of the adjacent inner plate  104 . An opening  154 , (one opening identified) extends top to bottom through each foot  152 . Between the feet  152  blade  150  is formed to have a curved, proximally directed face  156 , the edge of which is identified. The blade  150  is shaped so that blade face  156  can seat against and pivot around the head  114  integral with the inner tine  110 . 
     A distal web  160  extends outwardly away from the distal end of the proximal web  158 . Distal web  160  has the same thickness of the proximal web  158 . Webs  158  and  160  can collectively considered the base of blade  150 . Distal web  160  can thus oscillate in the space within the guide bar head  68  between the bottom and top plates  88  and  124 , respectively. The distal web  160  extends laterally outwardly beyond the proximal web  158 . The front face of distal web  160  is curved. More particularly, the components forming cartridge  60  are constructed so the curved distal face of the distal web will essentially be flush with the distal face of the head  68  of the guide bar. It should be understood that the arc subtended by distal web  160  is approximately 20 to 50° less than arc of the front face  72  of the cartridge bar head  68 . 
     The blade  150  is further formed so as to have an opening  162  that extends side-to-side through the distal web  160 . 
     Collectively, feet  152 , proximal web  158  and distal web  160  are sometimes collectively referred to as the base of the blade  150 . 
     An arcuately shaped head  166  extends outwardly around the outer distally directed edge of the distal web  160 . Teeth  168  protrude outwardly from the head  166 . Teeth  168  have a geometry that facilitate the cutting of the tissue, typically bone, the cartridge  60  is intended to cut. The geometry of the teeth  168  are not part of the present invention. The head  166  and, more particularly the teeth  168 , have a side to side width that is greater than that of the base of the blade  160 . Specifically, the width is large enough so the kerf the teeth form in the bone against which the cartridge  60  is applied is able to receive the guide bar  62 . At a minimum, this typically means the teeth  168  have a width at least as great as the width between the opposed outer faces of the bottom and top plates  88  and  124 , respectively. 
     A drive link  130  is disposed in each of the elongated spaces on either side of the inner tine  110  of the inner plate  104  as seen in  FIGS. 3 and 5 . Each drive link  130  is in the form of an elongated flat strip of metal. The drive links  130  are formed so that, at the proximal end of each link, there is a foot  132 , one foot identified. Each foot  132  is formed to have a center located through hole  134 , one hole identified. Through holes  134  are dimensioned so that the associated drive link foot  132  can seat around the adjacent saw head drive pins  44 . Each drive link  130  is shaped so that foot  132  has a thickness that is greater than the thickness of the metal strip forming the main body of the link. The thickness of feet  132  is typically no greater than the thickness of the guide bar  62 . 
     Two fingers  138 , one identified in each of  FIGS. 2 and 3 , extend distally forward from the distal end of the main body of each drive link  130 , one finger identified. Fingers  138  overlap and are spaced apart from each other. More particularly, fingers  138  are spaced apart from each a sufficient distance so that a blade foot  152  can seat between each pair of fingers. Each finger  138  is formed with a hole  140 , one hole  140  identified in  FIG. 3 . The holes  140  of each pair of fingers  138  are in registration with each other. 
     As part of the process of assembling cartridge  60  of this invention, the blade  150  is positioned so that each blade foot  152  is disposed between a pair of drive link fingers  138 . A pin  142 , one pin identified, that extends through the finger holes  140  and the blade foot opening  154  located between the finger holes  140 . The pin  142  pivotally holds the foot  152  to the associated drive link  130 . 
     During the assembly of the cartridge  60 , the inner plate  110  is initially welded or otherwise secured to the bottom plate  88  or to the top plate  124 . After this operation is completed, the drive links-and-blade assembly is positioned so that the drive links  130  are seated in the elongated spaces on either side of the inner tine  110 . The curved proximally directed face  156  of blade  150  is seated against the curved distally directed face of head  114  integral with the inner tine  110 . The top plate  124  or bottom plate  88  is then welded or otherwise secured to the exposed face of the inner plate  110 . At the completion of the process of assembling the cartridge  60 , the drive link feet  132  seat in plate openings  90  and  128 . The drive link fingers  138  seat in openings  94  and  128  formed, respectively in the guide bar bottom plate  88  and top plate  124 . 
     When the cartridge  60  is assembled, plate  98  extends from the inner face of bottom plate  88 , through the opening  162  to the inner face of the top plate  124 . Plate  98  provides structural support for the guide bar so as to prevent the bar plates  88  and  124  from collapsing inwardly against the blade  150 . 
     Saw  30  and cartridge  60  are prepared for use by fitting the cartridge  60  is fitted to the saw head  34 . As a result of this attachment, each drive pin  44  is seated in a separate one of the holes  134  formed in a drive link foot  132 . Coupling rod  36  extends through the overlapping openings  92 ,  112  and  127  of the cartridge  60 . The coupling rod  36  is lowered over the guide bar  62  so the head of the coupling rod (not identified) presses against the surface of inner plate  104  exposed through top plate opening  127 . This press action holds the cartridge  60  to the saw head  34 . When the cartridge  60  is secured to the drive head, the drive pins  44  and drive links  130  cooperate to urge the blade  150  proximally. The proximally directed face  156  of the blade  150  is urged against the curved face of head  114  internal to the cartridge  60 . 
     Saw  30  is actuated by depressing trigger  46 . This results in the actuation of the motor  42 . The actuation of the motor  42  results in the back and forth oscillation of the drive pins  44 . The drive pins  44  to cause the drive links  130  to engage in opposed back and forth reciprocation of the drive links. The opposed back and forth motion of the drive links  130  causes the blade to pivot back and forth around the head  114  internal to the cartridge. The pivoting action of the blade teeth  168  causes the teeth to cut the tissue against which the cartridge is pressed. 
     To cut tissue, typically bone  180 , the saw  30  and cartridge  60  are positioned so the teeth  168  of the blade  150  are directed towards the bone as seen in  FIG. 6 . As part of this process, one of the arms  78  is positioned so the fingers  84  integral with the arm press against an uncut section of the bone. The bone against which the fingers  84  rests functions as the static location around which the arm  78  pivots. Fingers  84  are located to one side of the zone in which the teeth  168  of the blade  150  travels. A portion of the weight of the saw  30  and cartridge  60  is thus transferred through the arm and fingers to the section of the bone against which the fingers are pressed. This reduces weight of the saw and cartridge the surgeon has to overcome in order to control the rate of the plunge of blade  150  into the bone. 
     Once the saw and cartridge are so positioned, the surgeon pivots the assembly downwardly, into the bone in order to make the desired cut. Once one section of the bone  180  is cut, the cartridge is withdrawn from the cut. The cartridge is repositioned to cut a new section of bone. In  FIG. 6  this is seen by the different depiction of the bone to the left and right of the blade  150 . To the left of the blade  150 , the bone is shown with surface shading. This is represent that this section of the bone has been cut. The right of the blade  150  the bone is depicted as cross hatched. This is to indicate that the bone is not cut and that the right side arm is disposed on top of the bone. 
     Arm  82  and fingers  84  are thus understood to limit the movement of bar  212 , the movement of the whole of cartridge  60  towards the tissue, the bone against which the blade  150  is directed. 
     II. Second Cartridge 
       FIG. 7  illustrates a second cartridge  210  of this invention releasably mounted to the saw  32 . Cartridge  210 , as seen in  FIGS. 8 and 9 , includes a guide bar  212  to which a blade  292  is moveably mounted. The previously described drive links  130  are moveably mounted in the guide bar  212 . The fingers  138  integral with links  130  are connected to a common pivot link  276 . The pivot link  276  is connected to the blade  292 . Collectively, the pivot link  276  and the blade  292  are connected together so the oscillation of the pivot link around a point results in the back and forth reciprocation of the blade along a line coincident with the longitudinal axis of the blade. Given that the blade of this version of the invention moves along a linear path of travel, this version of the invention is sometimes referred to as a surgical reciprocating saw blade cartridge. 
     Guide bar  212  is a laminate structure consisting of a bottom plate  240 , an inner plate  252  and a top plate  268 . Plates  240 ,  252  and  268  are formed so the guide bar  212  has a foot  214  is essentially identical to the previously described foot  64 . Forward of foot  214 , the guide bar has a trunk  216 . Trunk  216  is essentially identical in shape to trunk  66 . 
     The guide bar  212  has a head  217  that extends forward from the trunk  216 . The head is formed so as to extend laterally outwardly from the sides of the trunk  216 . Head  217  is shaped to have a first side  218 , the edge of which is identified, that extends along a line that is parallel to the proximal-to-distal longitudinal axis through cartridge  210 . At the distal end of the first side  218  the head has a front face  220 , the edge of which is identified. The head  217  is shaped so that the front face extends perpendicularly from the first side  218  towards the longitudinal axis of the cartridge. The front face  220  does not extend the whole length of the head. Instead that front face terminates at a location near the longitudinal center axis of the cartridge  210 . The head  217  is further formed so that a recessed face  222 , the edge of which is identified, extends proximally inward from the free end of the front face. As the recessed face  222  extends inward from the front face, the recessed face extends towards the first side  218 . 
     Opposite the first side  218 , the head  217  is formed to have a second side  224 . From the proximal end of the head  217 , as the second side  224  extends distally, the second side  224  extends inwardly, towards the longitudinal axis of the cartridge. The second side  224  does not extend to the longitudinal axis of the cartridge. Instead, the second side terminates at a curved tab  234 . 
     Tab  234  is spaced away from the opposed recessed face  222  of the head. Thus between face  222  and tab  234  the head is formed to have a notch  230 . The head  217  is formed so that the major axis through notch  230  is along a line that is angled relative to the longitudinal axis of the cartridge  210 . The head  217  is further formed so that notch  230  opens into a slot  232  that extends through the head, from the outer face of the bottom plate  240 , the inner plate  252  and to the outer face of the top plate  268 . Slot  232  has a major axis that is parallel to the major axis of notch  230 . Slot  232  is longer in length than the notch  230 . Thus, slot  232  separates the proximal end of recessed surface  222  from the rest of the head  217 . Slot  232  also separates tab  234  from the portion of the head  217  immediately proximal to the tab. 
     The bottom plate  240  is formed to have the openings  90 , the opening  92  and the openings  94  previously described with respect to plate  88 . Bottom plate  240  also has an opening  242 . Opening  242  is oval shaped. The opening  242  is located between the openings  94  and the portion of the bottom plate  240  that defines slot  232 . The bottom plate  240  is shaped so the major axis of the opening  242  is parallel to the major axis of slot  232 . 
     Inner plate  252 , seen in  FIGS. 9 and 11 , is formed to have the base  106  and inner tine  110  of the previously described inner plate  104 . At one end of the base  106  a first outer tine  254  extend distally forward. A second outer tine  258  extends distally forward from the opposed ends of base  106 . Outer tines  254  and  258  are understood to be parallel to and spaced apart from the inner tine  110 . 
     A first peninsula  256  extends forward the free end of the first outer tine  254 . First peninsula  256  is the section of inner plate  252  that forms one side of the inner portion of head  217  of the guide bar  212 . A second peninsula  260  extends forward from the free end of the second outer tine  258 . Second peninsula is the section of the inner plate  252  that forms the second side of the inner portion of the head  217  of the guide bar. At their distal ends peninsulas  256  and  260  are spaced apart from each other so as to form the center slice section of notch  230 . As a result of peninsulas  256  and  260  being spaced apart from each other, the peninsulas  256  and  260  also form the center portion of the center slice section of slot  232 . Peninsula  256  is shaped to form an end portion  262  of the center slice section of slot  232 , identified in  FIG. 11 . The end portion  262  of slot  232  extends beyond the ends of the slot defined by the bottom plate  240  and the top plate  268 . Peninsula  260  is shaped to form the opposed second end portion  264  of the center slice section of slot  232 . This end portion of slot  232  also extends beyond the end portion of the slot defined by plates  240  and  268 . These slot end portions  262  and  264  are thus located between the opposed and spaced apart inner face of the bottom plate  240  and the top plate  268 . 
     Top plate  268  has an outer shape that is essentially identical to that of the bottom plate  240 . The top plate  268  is formed to have the openings  126 , the opening  127  and the openings  128  previously described with respect to plate  124 . Top plate  268  has an opening  270 . Opening  270  is identical in shape to bottom plate opening  242 . When cartridge  210  is assembled, opening  270  is in registration with opening  242   
     The blade  292  as seen in  FIG. 10 , includes an elongated, rectangularly shaped base  296 . Base  296  is dimensioned to seat in slot  232  internal to the guide bar  212 . The base  296  has a length that, while less than that of the length of the slot  232  is sufficiently long so that regardless of the position of the base in slot  232 , the opposed ends of the base are seated in the opposed end portions  262  and  264  of the slot. Thus the base is able to reciprocate along the longitudinal axis of the axis of slot  232  while the bottom and top plates  240  and  268 , respectively, hold the base to the guide bar  212 . 
     Blade  292  is further formed so an elongated slot  298  extends through the opposed faces of the base  296 . Slot  298  does not extend to either end of the base  295 . As part of the process of assembling of assembling cartridge  210 , pins  308  are mounted to the guide bar  212  to extend between the bottom and top plates  240  and  268 , respectively. One pin  308  identified in each of  FIGS. 9  and  11 . Each pin  308  is mounted to the guide bar extend through the slot  298  internal to the blade  292 . Not identified are the holes in plates  240  and  268  in which the pins  308  are mounted. The pins  308  stabilize the reciprocal movement of the blade  292  in the slot  232 . 
     A socket  294  extends proximally from the proximally directed end of the base  296 . Socket  294  is positioned so that when cartridge  210  is assembled, the socket is located in the void between the opposed peninsulas  256  and  260  of the inner plate  252 . The socket  294  is formed to have a circular opening  295 . Opening  295  extends inwardly from the proximal end of the socket  294 . The blade socket  294  and base  296  are understood to have a common side to side thickness essentially equal to the side to side thickness of the inner plate  252 . 
     The blade  292  also has a head  302 . The head  302  extends distally forward from the distally directed end of the base  296 . Head  302  to have the teeth  304  suitable for cutting the tissue against which the blade  292  is applied. The head  302  and, more particularly, teeth  304  have a side to side thickness greater than that of the blade base  296 . More specifically, the teeth  304  have a thickness such that the kerf cut by the teeth will be sufficient to accommodate at least the head  217  of the guide bar  212 . 
     When cartridge  210  is assembled, the teeth  304  are located in the portion of the slot  232  immediately adjacent notch  230 . Teeth  304  are thus located inwardly of the recessed face  222  and tab  234  of the guide bar  212 . As seen in  FIG. 11A , each tooth  304  has a rake surface  305  and a clearance surface  307  that extends the from the rake surface  305 , (one of each of the rake and clearance surfaces identified.) In the illustrated version of the invention, each rake surface  305  extends along a plane that is perpendicular to the longitudinal axis through the blade  292 . Cartridge  210  is constructed so the rake surfaces  305  face recessed face  222  of the guide bar  212 . Each clearance surface  307  angles away from the rake surface  305  with which the clearance surface is associated. More particularly, each clearance surface  307  extend both proximally and towards tab  234 . The edge where the complementary rake surface  305  and a clearance surface  307  of a tooth  304  meet is the cutting edge  306  of the tooth. 
     Pivot link  276  is planar in shape. The link  276  has the same thickness as the base  296  of the blade  202  so the link can move in the void between the bottom and top plates  240  and  268 , respectively, of the guide bar  212 . The pivot link has a base  284 . The base is dimensioned to move within the space between the two peninsulas  256  and  260 . Two spaced apart feet  278  extend proximally from the base  284 . Feet  278  are analogous in shape and function to feet  152  of blade  150 . The pivot link  276  has a proximally directed face  280  between the feet  278 . Face  280  is analogues in shape and function to face  156  of blade  150 . Previously described pins  142  pivotally hold each foot  278  to the adjacent drive link  130 . Not identified are the openings in the feet  278  through which the pins  142  extend. 
     Also part of the pivot link is a head  286 . The head  286  extend forward from the base  284 . Head  286  is circular in shape. More particularly, the head  286  is dimensioned to closely fit in and rotate in the control space  295  internal to the socket  294  integral with the blade  292 . 
     A plate  288  is welded or otherwise secure over each exposed face of the socket  294 . Each plate  288  is oval in shape. When cartridge  210  is assembled, the components are arranged so the head  286  integral with the pivot link  276  and the surrounding socket  294  integral with the blade are disposed between the openings  242  and  270  in the guide bar  212 . Each plate  288  seats in a separate one of the openings. The components are constructed so that each plate  288  can reciprocate longitudinally in the opening in which the plate is seated. Plates  288  retain the head  286  integral with the pivot link  276  in the socket  294  integral with the blade. 
     Cartridge  210  is readied for use the same basic steps used to ready cartridge  60  for use. Cartridge  210  is attached to the saw  50  so the reciprocation of the drive pins  44  results in the like reciprocation of the drive links  130 . 
     Cartridge  210  is used to cut bone when the bone is especially desirable to ensure the blade does not cut any tissue below the bone. One such procedure in which cartridge  210  is used is a procedure in which it is necessary to cut the sternum. The sternum is the plate like bone in the chest. The sternum covers the heart and lungs. The sternum is cut open in order to access these organs and organs in the chest. To avoid damage to the sternum it is imperative that that blade, when making this cut, not cut below the bone. 
     Cartridge  210  is positioned so the teeth of the blade  292  face the edge of the bone to be cut. As seen in  FIG. 12 , the cartridge  210  is preferably positioned so that the longitudinal axis through the blade  292  is angled such that section of the blade adjacent guide bar tab  234  leads the section of the blade adjacent recessed surface  222 . The cartridge is further positioned so the recessed surface is disposed immediately below the section of bone being cut. 
     Trigger  46  is depressed to actuate the blade  292 . More particularly, the actuation of pins results in the back and forth reciprocation of the drive links  130 . The reciprocation of the drive links  130  oscillates the pivot link  276  around head  114  of tine  110 . The arcuate oscillation of the pivot link  276  reciprocates the blade  292  back and forth in slot  232 . 
     The reciprocating blade  292  is pressed against the sternum to form the desired cut. The surgeon holding the saw  30  and cartridge exerts a slight upwardly force of the saw so as to hold recessed face  222  against the inner surface of the sternum immediately forward of the moving blade  292 . Further, during one-half of a single reciprocating cycle of the blade  292 , the blade moves towards the recessed face  222 . During this phase of blade motion, the rake surfaces  305  of the teeth grab into the face of the bone being cut. This action, along with the movement of the blade towards the recessed surface  222 , results in the blade applying a force against the bone that serves to pull the recessed surface  222  against the inner surface of the sternum. Thus, the cutting action of the cartridge adds to the force the surgeon applies in order to hold recessed surface  222  against the sternum. In  FIG. 12  the formation of the cut is depicted by the fact that to the left of the blade head  302 , the uncut tissue is depicted in cross section. To the right of the side  218  of the guide bar  212  surface shading shows the face of the cut bone. 
     This holding of recessed surface  222  of the cartridge  210  against the inner surface of the sternum reduces the likelihood that soft tissue will become trapped between the sternum and the recessed surface. Reducing the incidence of this tissue being so trapped results in a like reduction in the incidence of this tissue being inadvertently cut. Further it should be understood that the portion of the bar  212  that defines surface  222  and that abuts the bone prevents the bar and thus the whole of cartridge  210  from being drawn away from the bone. This ensures that the blade  292  forms a cut that extends between the opposed proximal and distal facing surfaces of the bone. 
     During the second phase of a reciprocating cycle of the blade  292 , the blade moves from the recessed surface  222  towards tab  234 . In this phase of the cycle, the clearance surfaces  307  of the teeth move past the tissue. Owing to the geometry of the teeth, the clearance surfaces  307  only rub against tissue. Thus, this motion of the blade does not drive the guide bar so the section of guide bar  21  that defines end portion  262  of slot  232  is driven into the soft tissue that underlies the sternum. 
     Thus cartridge  210  of this invention is designed to substantially eliminate the possibility that the moving blade  292  will press against tissue and organs below the sternum not intended to be cut. 
     This invention eliminates the need to some instances have a sternum saw ready for use. As implied by its name, a sternum saw is a saw with features to ensure that, when the blade of the saw is applied to the sternum, the blade cuts through the sternum and is not applied against the issue and organs below this bone. Eliminating the need to provide this custom saw can reduces the expenses associated with performing a procedure on a patient when a part of the procedure involves cutting the sternum. 
     A further feature of this version of the invention is that the section of the head  217  of guide bar  210  that follows the blade  292  into the sternum is relatively long, often greater than 1 cm in length. Owing to this section of the guide bar having a relatively long length, when this section of the guide bar enters the cut, this section of the guide bar essentially block the guide bar from moving outside of the plane of the cut being formed by the cartridge  210 . This ensures that cut formed by the guide bar is relatively straight. 
     III. Third Cartridge 
       FIGS. 13 and 14  illustrate an alternative sagittal blade cartridge  340  of this invention. Cartridge  340  includes a guide bar  342  to which a blade  410  is pivotally mounted. Cartridge  340 , is shaped to be releasably attached to saw  32 . 
     Guide bar  342  includes a bottom plate  344 , an inner plate  356  and a top plate  374 . Collectively, the plates  344 ,  380  and  374  forming the guide bar  342  are shaped so the bar has the foot  64  and trunk  66  of cartridge  60 . Bottom plate  344  is thus formed with openings  90  and  92 . The top plate  374  is formed with openings  126  and  127 . The bottom and top plates  344  and  374 , respectively, of guide bar  342  are formed to define head  346  of the guide bar. Head  346  is similar in shape to head  68  of cartridge  60 . A difference between the two cartridges is that bottom and top plates  344  and  374 , respectively, are formed to defining, respectively two openings  348  and  376 , one of each opening identified. The bottom plate openings  348  are analogues to openings  94  integral with cartridge  60 . The top plate openings  376  are analogues to openings  128  integral with cartridge  60 . 
     Guide bar  342  is formed to have the shoulders  80 , forearms  82  and fingers  84  integral with cartridge  60 . 
     Inner plate  356 , the features of which are best seen in  FIGS. 14 and 16 , has the base  106  common to the above-described cartridges  60  and  210  of this invention. Two outer tines  358  and an inner tine  376  extend distally forward from the base  106 . Each outer tine  358  has a proximal section similar in shape to the proximal section of the tines  108 . At the distal end of the proximal section of the tine  358 , each tine is shaped to form a land  360 . Each land  360  is formed so as to have a distally directed face  362 , (one face identified), that is arcuate in shape. The distal faces  362  of the two tines  358  are located on a single arc. Collectively, the components forming the guide bar  342  are constructed so that the distal faces  362  of inner plate  356  are spaced inwardly of the adjacent distally directed faces of bottom plate  344  and top plate  374 . Consequently, when the plates are assembled to form the guide bar, a slot  430  extends inwardly from and between the distal ends of bottom plate  344  and the top plate  374 . The opening into slot  430  is identified in  FIG. 13 . 
     Each outer tine  358  is further forward to have an inwardly directed face  364  (one face identifies). The inwardly directed faces  364  of the two tines  358  are directed towards each other. Lands  360  are further formed so that as each face  362  extends proximally from the distal end of the land, the face angles inwardly toward the longitudinal center axis through the plate  356 . Thus, between the lands  360  there is a gap, (gap not identified). Extending proximally from the distal ends of the lands  360 , the width across this gap decreases. 
     Each land  360  is further formed to define a slot  366 . Each slot  366  extends inwardly from the inner face  364  of the land  360  in which the slot is formed. Each slot  366  is arcuate in shape. More specifically, as each slot  366  extends away the longitudinal axis of the inner plate  356 , the slot curves towards the proximal end of the plate. Each land  360  is further formed to define plural ribs  368 , two ribs identified. Inner plate  356  is formed so that the ribs  368  extend inwardly from the opposed faces of each land  360  that define each slot  366 . The inner plate  356  is also formed so that the ribs  368  extend outwardly from the distally directed face  362  of each land. 
     The section of each tine  358  that is part of the shoulder  80 -forearm  82 -finger  84  section of the tine  358  extends outwardly from the side edge of the land  360 . 
     Inner tine  376  of the inner plate  356  is similar in shape to the previously described inner tine  110 . Inner tine  376  is formed to have the previously described openings  112  and head  114 . The most significant difference between the inner tines is that inner tine  376  is longer than inner tine  110 . More specifically, the inner plate  356  is shaped so the tine head  114  is located in the proximal portion of the gap between the opposed tapered inwardly directed faces  362  of lands  360 . 
     Two drive links  384 , best seen in  FIG. 15 , are disposed in the guide bar  342 . The drive links  384  are similar in shape to the previously described drive links  130 . The only difference between the drive links is that drive links  384  are longer in length than drive links  130 . Thus it should be understood that when cartridge  340  is assembled, the fingers  138  integral with drive links  384  seat in the openings  348  and  376  formed in the guide bar  342 . 
     A pivot link  392  is pivotally attached to the fingers integral with the drive links  384 . Pivot link  392  includes a base  396 . The feet  278  integral with the previously described pivot link  276  extend proximally from the base  396 . A curved distally directed face  394 , analogues to face  280  is located between the feet. Face  394  is the surface of the link that presses against the head  114  of tine  376 . 
     Pivot link  392  is further formed to have a head  398  that extends distally forward from the base  396 . Head  398  is circularly shaped. A neck  397 , connects the head  398  to the base. The pivot link is formed so neck  397  has a side-to-side width less than the diameter of head  398 . 
     Blade  410  is formed so as to have an arcuately shaped beam  414 . Beam  414  is shaped to seat in and oscillate in slot  430  internal to the guide bar  342 . Thus beam  414  subtends an arc less than the arc of guide bar slot  430 . The beam  414  is formed to have in the center a notch  416 . Notch  416  extends distally forward from the proximal end of the beam  414 . The notch is centered on the midline of the beam. The notch  416  is shaped to receive head  398  of the pivot link  392 . In many preferred versions of the invention notch  416  is U-shaped. 
     The blade  410  is formed so as to have two legs  412 . The legs extend outwardly and proximally from the beam on the opposed sides of notch  416 . Legs  412  and beam  414  can collectively be considered the base of blade  410 . Each leg  412  extends outwardly away from the proximal to distal longitudinally axis of the cartridge. As each leg  412  extends away from the longitudinal axis of the cartridge  340 , the leg curves proximally. More specifically the components of cartridge  340  are formed so that the opposed proximal and distally directed faces of the legs will seat against the crests of the ribs  368  that protrude in the slots  366 . When the blade  410  is so seated, the curved proximally directed faces of beam  414  rest against the crests of the ribs  368  that project forward of the front face of the lands  360 . Each leg  412  is further understood subtends an arc less than the arc subtended by the slot  366  in which the leg is seated. The seating of the legs  412  in the slots  366  internal to the guide bar  342  is what retains the blade  410  in the guide bar. The relative dimensioning of the components of cartridge  340  allows the legs  412  to oscillate in the slots  366 . 
     Blade  410  is further formed so as to have teeth  420  that project forward from the distally directed face of the beam  414 . In the illustrated version of the invention, the teeth are set. This means the teeth are angled so as to extend out of the plane of the blade  410 . In the illustrated version of the invention some teeth, one identified as tooth  420   a , are angled so as to extend into the planes of  FIGS. 15 and 16 . Other teeth, one identified as tooth  420   b , are angled so as to extend out of the plane of  FIGS. 15 and 16 . The set of the teeth  420   a ,  420   b  is such that the kerf cut by the teeth is of sufficient width that at least the head of the guide bar can be received in the kerf. 
     When the cartridge  340  is assembled, each drive link  384  is located in the elongated space between the inner tine  376  and one of the outer tines  358 . Pins  142 , one identified in  FIG. 15 , connect each drive link  384  to a foot of the pivot link  392 . Head  398  of the pivot link  392  seats in the proximally opening notch  416  of the blade  410 . 
     Cartridge  340  operates in the same general manner and is used in the same general way as cartridge  60  of this invention. The reciprocation of the drive links  138 , oscillates the pivot link  392  in an arc centered on the head  114  of the inner tine  376 . The oscillatory movement of the pivot link  392  is transferred through head  398  to the blade  410 . The blade  410  thus engages in a back and forth oscillation in an arc centered on the head  114  of the inner tine  376 . In many versions of the invention, cartridge  340  is constructed so in the blade  410  is able to pivot between 3 and 10° either side of the longitudinal axis through guide bar  362 . It should be understood that when cartridge  340  is actuated, there is some relative motion between the pivot link  392  and the blade  410 . 
     A difference between the two cartridges  60  and  340  is that for having an arcuate set of teeth with the same radius and that subtends the same arc, blade  410  of cartridge  340  has a smaller mass than the mass of blade  150  of cartridge  60 . A second difference between the two blades concerns the points around which the blades oscillate. Blade  150  pivots around the center of tine head  114 . Blade  410  rotates around center point of the arc on which slots  366  are centered. This point, while on tine  110 , is located proximal to the center of tine head  114 . A benefit of blade  410  having this reduced mass and proximally displaced center of oscillation is that vibratory forces produced by blade  410  are less than that produced when blade  150  is oscillated. This means that, when actuated, cartridge  340  vibrates less than cartridge  60 . 
     The reason blade  410  rotates around a center point proximal to the center of head  114  internal to blade bar  34  is due to how the blade  410  is connected to drive links  130 . The drive links  130  are not physically attached to the blade  410 . Instead, drive links  130  are through pivot link  392 , connected to blade  410 . Further, pivot link  392  are not simply connected together so that the pivot link is only able to rotate in notch  416  internal to the blade. Owing to the shape of the head  398  of the pivot link and notch  416 , the head is able to both pivot in the notch and engage in some minor longitudinal movement within the notch. The ability of the pivot link  392  and blade  410  to engage in this movement relative to each other is what results in the blade  410  moving around a pivot point that is spaced proximally from the center of the tine head  114 . 
     IV. Fourth Embodiment 
     An alternative cartridge, specifically a sternum cartridge  440  of this invention is initially described by reference to  FIGS. 17 and 18 . Cartridge  440  is referred to as a sternum cartridge because this cartridge is designed to cut the sternum while limiting the cutting of the tissue below the sternum. The cartridge  440  includes a guide bar  442 . A distal foot  488  is integrally attached to and located forward of the guide bar  442 . A blade  520 , also part of the cartridge  440  extends between guide bar  442  and distal foot  488 . The blade  520  is moveably mounted to the guide bar  442  and foot  488  so as to engage in reciprocal movement between the guide bar and the foot. 
     Guide bar  442  is a laminate structure that includes a bottom plate  450 , an inner plate  460  and a top plate  480 . Collectively, the plates  450 ,  460  and  480  are shaped so that guide bar  442  has the foot  64  and torso  66  of the previously described guide bars. To distinguish the foot  64  from the distal foot  488 , foot  64  will be referred to as the proximal foot  64  of the guide bar  442 . Plates  450 ,  460  and  480  are further formed so that guide bar  442  has a head  444 . The guide bar  442  is shaped so that on one side, the left side of the bar when viewed from the proximal end of the bar in  FIG. 17 , the head has a side face  446 , the edge of which is identified. Guide bar  442  is formed so that extending distally from the torso  66 , the side face  446  tapers outwardly from the longitudinal axis along the guide bar. On the opposed side of the head  444 , guide bar  442  has a side face  448 . The head is formed so that the side face is located outwardly from the adjacent narrow width portion of the torso  66 . The guide bar is further formed so that the side face  448  extends along a line that is parallel to the longitudinal axis of the longitudinal axis along the guide bar  442 . 
     The bottom plate  450  is formed to have the openings  90  and  92  common to the previously described bottom plates. The previously described openings  94  are formed in the section of the bottom plate  450  that defines the head  444  of the guide bar  442 . An additional opening  452  is also formed in bottom plate  450 . The bottom plate  450  is formed so that opening  452  is located between the opening  94  closest to the portion of the plate that forms the side face  448  and the side face  448 . The bottom plate is formed so opening  452  is arcuate and shape and centered along a curve that would be located outwardly of side face  446  of the guide bar  442 . Proximal to opening  452 , the bottom plate  450  is formed to have a through hole  454 . 
     Bottom plate  450  is further formed to have a nose  456 . Nose  456  extends distally forward from the portion of the bottom plate  450  that is slightly offset from the center of the guide bar  442 . More particularly, the nose  456  extends forward from a location that is slightly closer to side face  448  of the guide bar than side face  446 . 
     Inner plate  460 , as seen in  FIGS. 18 and 20 , has the base  106  common to the previously described inner plates. The previously described inner tine  110  extends forward from the center of the base  106  of plate  460 . An outer tine  462  extends forward from left end of base  106  of inner plate  460 . Tine  462  is essentially identical in shape to the corresponding outer tine  108  of inner plate  104 . The inner plate  460  is further formed so a proximal beam  464  and a distal beam  466  extend forward from tine  462 . Proximal beam  464  is the structural member of the inner plate that actually extends forward from the free end of the tine  462 . The inner plate  460  is formed so that as the proximal beam extends forward the beam  464  extends inwardly. More particularly, beam  464  extends to the space between the noses  456  and  484  of the bottom and top plates  450  and  480 , respectively. Distal beam  466  extends distally forward from the free end of the proximal beam  464 . The inner plate  460  is formed so the longitudinal axis of the distal beam  466  is laterally offset from and parallel to the longitudinal axis through the guide bar  452 . 
     An L-shaped arm  468  extends laterally from one side of the distal beam  466  adjacent the distal end of the beam  466 . Arm  468  is directed towards side face  448  of the guide bar  442 . The inner plate is further formed so that the outer section of arm  468 , in addition to being parallel to and spaced away from beam  466 , extends proximally inward, towards the head  444  of the guide bar  442 . 
     Inner plate  460  is formed so a second outer tine, tine  470  extends distally forward from the end of base  106  opposite the end of the base from which outer tine  462  extends. The proximal section of outer tine  470  has a shape similar to that of the proximal section of tine  108 . Outer tine  470  is further formed so as to have distal section, section  472 , that is located laterally away from the proximal section. The outer tine  470  is formed so that the distal section  472  is located laterally outwardly the base  106  of inner plate  460 . In the illustrated version of the invention, the inner plate  460  is formed so distal section  472  extends outwardly from the rest of the tine  472  at a location forward of where the opening  112  is in the inner tine  110 . Both outer tines  462  and  470  are spaced away from the inner tine  110 . Not identified are the spaces between the tines. Owing to the outward spacing of the distal section  472  of outer tine  470 , the width of the space between the distal section  472  of the outer tine  470  and the inner tine  110  is greater than the width of the space between the proximal section of the outer tine  470  and the inner tine  110 . 
     The top plate  480  is formed to have the openings  126  and  127  common to the previously described top plates. The previously described openings  128  are formed in the section of the top plate  480  that is part of the head  444  of the guide bar  442 . Top plate  480  is also formed to have an opening  482 . Opening  482  is identical in shape to opening  452  of the bottom plate  450 . A hole  483  is also formed in the top plate  480 . Hole  483  is identical to bottom plate hole  454 . When the guide bar  442  is assembled, the top plate opening  482  is in registration with the bottom plate opening  452  and hole  483  is in registration with hole  454 . 
     Top plate  480  is further formed to have a nose  484  similar to nose  456  of the bottom plate  450 . It should thus be appreciated that when the guide bar  442  is assembled, noses  456  and  484  are in registration and the distal beam  466  extends forward from the space between the noses. 
     The distalmost section of distal beam  466  and the arm  468  integral with the beam  466  serve as the center component of distal foot  488 . An end plate  490  is disposed over each arm  468  and the adjacent portion of the distal beam  466 . Thus the distal foot  488  is a laminate sub-assembly that consists of the two end plates  490  and the sections of the distal beam  466  and arm  468  disposed between the end plates. The end plates  490  are shaped to extend over the whole of the arm  468  and the distal section of beam  466 . The distal foot  488  thus has a side-to-side thickness greater than that of the adjacent distal beam  466 . In some versions of the invention the components forming cartridge  440  are dimensioned so that side to side thickness of the distal foot  488  is greater than that of the guide bar  442 . Each end plate  490  is formed with a notch  492 , one seen in  FIG. 18 . Each end plate  490  is formed so the notch  492  extends distally from the proximal end of the plate and opens inwardly from the face of the plate that abuts the beam  466  and arm  468 . The notches  492  subtend the three-sided space defined by distal section of the distal beam  466  and arm  468 . 
     Each end plate  490  is formed with a hole  494 , one hole  494  identified, that extends between the major faces of the plate. Each hole  494  opens into the portion of the plate  490  that defines the base of the notch  492 . When cartridge  440  is assembled, the individual holes  494  are coaxial and the axis around which the holes are centered extends through the three-sided space defined by distal section of the distal beam  466  and arm  468 . 
     It is further observed that the components forming the distal foot  488  are shaped so the foot has a toe  489 . Toe  489  is the portion of the foot that projects forward of the below discussed teeth  526  of the blade  520 . 
     Drive links  130  are disposed in the guide bar  442  of cartridge  440 . One drive link  130  is located in the space between inner tine  110  and the outer tine  462 . The second drive link  130  is located in the space between the inner tine  110  and outer tine  470 . 
     The distal ends of the drive links  130  are connected to a pivot link  502  also disposed in the guide bar  442 . The pivot link  502 , as seen best in  FIG. 19 , includes a U-shaped beam  504 . Beam  504  has a width that allows the beam to seat within the fingers  138  of the drive links  130 . The center section of the beam  504  has a curved U-shaped, proximally directed face  506 . When cartridge  440  is assembled, face  506  is the surface of the beam that presses against and pivots around the head  114  of inner tine  110 . 
     Pins  142  pivotally connect the tine fingers  138  to the opposed ends of beam  504 . Not seen are the holes in the ends of the beam  504  in which pins  142  are seated. 
     The pivot link  502  also includes a pair of parallel, spaced apart overlapping fingers  508 , one seen. The fingers  508  extend from the end of the beam  504  that is directed towards side face  448  of the guide bar  442 . Fingers  508  are similar in shape to the fingers  138  integral with the drive links  130 . Not identified are holes that extend through the fingers  508 . The components forming the cartridge  440  are arranged so that when the cartridge is assembled, each finger  508  seats in a separate one of openings  452  and  482  formed, respectively in the bottom plate  450  and top plate  480 . 
     The saw blade  520  is an elongated, planar structure, as seen best in  FIG. 19 . The saw blade includes a base  522 . Base  522  is dimensioned so seat in the space defined by the opposed spaced apart inner faces of the bottom and top plates  450  and  480 , respectively, and on one side inner tine  110  and, on the opposed side, distal section  472  of outer tine  470 . Forward of the base  522 , the blade has a head  524 , alternatively identified herein as a body  524 . The blade is further formed so that teeth  526  extend forward from the elongated face of the body  524 . More particularly, the teeth  526  extend forward from the face of the body directed to the side face  448  of the guide bar  442 . Blade  520  is formed so that teeth have a width, the dimension along axes perpendicular to the longitudinal axis through the blade, that is sufficient so a kerf cut by the teeth is of sufficient width that at least the portion of beam  466  immediately adjacent blade  520  can be received in the kerf. 
     Saw blade  520  is formed to have two oval shaped openings  530  and  532  the major axes of which are parallel to the longitudinal axis of the blade. Opening  530  is located in base  522 . Opening  532  is located in the end of blade body  524  spaced from the base  522 . While not seen in the drawings, it should be understood that the blade is formed with a third oval opening. This opening is located in the base  522  so as to between opening  530  and the body of the blade. The major axis of this opening is perpendicular to the major axis of opening  530 . The below described pin  540  extends through this opening. 
     When cartridge  440  is assembled, the base  522  of the blade seats in the void space internal to the guide bar  442  defined by the opposed bottom plate  450  and top plate  480  and tine  110  and distal section  472  of tine  470 . The free end of blade body  524  seats in the space between the distal section of distal beam  466  and arm  468  and between plates  490 . The components are dimensioned so that when the blade  520  is so seated the face of the blade body  524  opposite the face from which teeth extend is in close proximity too if not abutting the adjacent side face of distal beam  466 . Also it should be understood that the blade  520  and more particularly, teeth  524  are configured so the kerf cut by the teeth will be of sufficient width to receive distal beam  466 . It is further understood that the components of the cartridge  440  are selected so the kerf cut by blade  520  is less than the side-to-side thickness across the adjacent distal foot  488 . 
     Two pins  538  and  542 , hold the blade  520  to the guide bar so the blade is able to engage in reciprocal motion. Pin  538  extends through openings  454  and  483  in, respectively, the bottom plate  450  and top plate  480  and opening  530  in the blade. Pin  542  is seated in the holes  494  formed in the end plates and extend through opening  532  in the blade body  524 . A pin  540  connects pivot link  502  to the blade  520 . The opposed ends of pin  540  are seated in fingers  506 . The pin extend through the oval opening in the blade base  522  adjacent the blade body  524 . 
     Cartridge  440  is attached to the saw  30  using the same general steps used to attach the previously described cartridges of this invention to the saw. 
     Saw is positioned adjacent the bone to be cut. This bone is typically the sternum. The saw is properly positioned when the toe  489  integral with the distal foot  488  of the cartridge is located immediately adjacent the underside of the bone to be cut. Once cartridge  440  is properly positioned, the saw motor  42  is actuated to reciprocate the blade  520 . More specifically the oscillation of the drive pins reciprocates the drive links  130 . The reciprocating motion of the drive links  130  oscillates the pivot link  502  around the head  114  of the inner tine  110 . The oscillation of the pivot link  502 , is through pin  540  transferred to the blade  522 . More specifically, the oscillations of the pivot link cause the blade to reciprocate back and forth along the longitudinal axis that extends through the blade. The blade teeth  526  therefore cut the bone against which the blade  520  is pressed. 
     As the cartridge cuts through the bone, the surgeon holds the saw so the distal foot  488  presses against the underside of the bone. As long as the surgeon holds the saw  32  and cartridge  440  in this position, the blade  520  will not bear against tissue below the bone. This prevents the unintended cutting of the tissue below the bone. 
     A difference between the cartridges  210  and  440  is that the distance between the cutting teeth  526  and the trailing end of beam  466  of cartridge  440  is less than the distance between teeth  304  and the trailing side  218  of cartridge  210 . This makes it easier to turn cartridge  440  in a kerf than to turn cartridge  210  in kerf of the same width. Thus, cartridge  440  is especially useful for form a cut in the bone that is not linear in direction. 
     It should also be understood that cartridge  440  is typically designed as a use once item. This means that each time the cartridge is used, the practitioner is assured that the beam  466  that connects the distal foot  488  to the guide bar is straight and in line with the blade  520 . 
     It should further be understood that while cartridge  440  includes a blade  520  that reciprocates, the cartridge can be attached to and actuated by a saw  30  designed to actuate a cartridge with a sagittal blade. This means that a medical facility using cartridge  440  of this invention does not have to provide a saw separate from the saw  30  used to actuate a blade that engages in sagittal motion in order to actuate a blade that engages in reciprocal motion. 
       FIG. 21  illustrates how an alternative saw blade  560  may be fitted to cartridge  440 . Saw blade  560 , as seen in  FIG. 22 , includes a base  562  similar to base  522  of blade  520 . A difference between the two blades  520  and  560  is that base  562  is shorter than base  522 . A blade body  564 , similar to blade body  524 , extends from base  562  of blade  560 . Previously described teeth  526  extends outwardly from the exposed elongated face of blade body  564 . 
     Blade  560  is further formed to have a circular opening  568  in the base  562 . Opening  568  is the opening in the blade that receives the previously described pin  540 . The blade  560  is further formed to have an elongated, oval shaped opening  570  in the end of the body  564  spaced from the base  562 . The blade  560  is formed so that the major axis of the opening  570  is angled relative to the longitudinal axis through the blade  560 . More particularly, extending from the end of opening  570  adjacent the free end of the blade body  564  towards the base  562 , the major axis of opening  570  angles away from the face of the body  564  from which the teeth  526  extend. 
     When a version of cartridge  440  in which blade  560  is installed is assembled, the base  562  seats in the head  444  of the guide bar  442 . The free end of body  564  seats in foot  488 . Pin  540  extends through opening  568 . Pin  542  is disposed in opening  570 . 
     When a cartridge  440  with blade  560  is actuated, the drive links  130  and pivot link  502  move as previously described. The oscillation of pivot link  502  is, through pin  540  transferred to the blade  560 . More particularly it should be understood that pin  540  engages in a movement along a loop. The movement of the pin  540  causes a like movement of the blade base  562 . The movement of the free end of blade body  564  is constrained by portion of the body that defines the opening  570  in which pin  542  is seated. As a result of the blade body  564  being so constrained, the blade, when actuated, engages in reciprocal movement along a curved path. The motion of the blade thus has a longitudinal component in which the blade  560  reciprocates between the guide bar  442  and the foot  488 . The motion of the blade also has a lateral component in which the blade moves towards and away from the distal beam  466 . Thus while this movement is non-linear, since at least a component of the movement is longitudinal, for the purposes of this invention, the movement is considered a reciprocal loop motion. 
     V. Alternative Embodiments 
     The above is directed to specific versions of the invention. Other versions of the invention may have features different from what has been described. It should also be understood that the various versions of the invention may be combined. Likewise not all versions of each described cartridges may include all the features described as being associated with that cartridge. 
     For example, when the guide bar is provided with a structural member to reduce the weight of the saw and cartridge in the hand of the surgeon, the guide bar may only be provided with a single member, a single arm. It may not be necessary to provide this arm with fingers or like features that penetrate the tissue against which the arm is pressed. In the illustrated version of the invention, the arm includes a shoulder so and a forearm  82  that is angled from the shoulder. In some versions of the invention, the extension, the arm that extends from the guide bar may have an alternative shape. For example, the extension may be linear in shape. Further in the illustrated version of the invention, the arm extends slightly forward of the most proximal space in which the teeth of the blade sweep. In an alternative version of the invention, this arm may not extend forward of the location of the blade teeth. Alternatively, depending on the construction of the cartridge, there may be a reason to construct this at least one extension so the distal end of the extension is located forward of the most distally located teeth integral with the blade  150 . 
     It should be understood from the description of cartridge  410  that there is no requirement that in all versions of the invention the structural member that limits movement of the bar always have a side-by-side width that is equal to or less than the width of the rest of the bar. Thus, some versions of the invention guide bar  62  and formed so that the forearms  82  and any teeth  84  are have a side to side thickness greater than the side to side thickness of the portion of the guide arm from which the adjacent blade  150  extends. More particularly the forearms and any teeth have a side-to-side thickness that is greater than the width of the kerf cut by the blade  150 . This feature makes it possible to, after the cut is formed, rest the forearm and any teeth on a sections of the bone that have been cut. More particularly, the forearm or teeth rest on the sections of the bone on the opposed sides of the cut. 
     The structural component that serves as a stop that limits the upward movement of the cartridge may be different than the described recessed surface  222 . For example in some versions of the invention, the cartridge may be provided with a tab that extends forward of the blade  292 . This tab is formed to have a planar surface adjacent the teeth of the blade. This plane is contained in a plane that intersects the plane in which the blade is oriented. It should be understood that in this version of the invention the kerf cut by the blade will not be so wide as to fully receive this stop. The kerf will be of sufficient width to receive the portion of the guide bar located immediately proximal to the teeth. 
     Likewise in versions of the invention in which the structural member of the guide bar is a stop there is no requirement that in all versions of the invention the cartridge be designed so the blade reciprocates on a linear path. In some versions of the invention, the blade may be mounted to the cartridge so as to oscillate in an arc, in other words engage in sagittal motion. Similarly, in versions of the invention in which the structural member is a pivot arm, the blade may be mounted to the guide bar so as to be able to reciprocate linearly. 
     There is no requirement in all versions of the invention that the blade have a length greater than the width of the portion of the guide bar mounted to the associated saw. In some versions of the invention the exposed portion of the blade, the teeth, may subtend a line that is smaller in width than the proximal portion of the guide bar. This is especially true for versions of the invention designed to perform small bone surgery. Small bone surgery is generally surgery on the hand, the foot, the skull or the spine. 
     Similarly, there is no requirement that in all versions of the invention the blade be constructed so that the head and teeth have a width greater than that of the base. Blade  520  and  560 , for example may be constructed so the heads and teeth of these blades have a width equal to their basis. The significant design requirement is that the kerf cut by the teeth of blades  520  and  560  be of sufficient depth to accommodate at least the portion of the beam  466  that immediately follows the blade into the bone. It should of course be recognized that in some versions of cartridge  440  it may be useful to provide a blade that is designed so as to have a head, or at least teeth, that have a thickness greater than the thickness of the base of the blade. 
     Likewise the invention is not limited to assemblies that include two drive links for pivoting the blade. Some cartridges of this invention may have a single drive link or three or more drive links. In versions of the invention with a single drive link the distal end of this link may be connected to a pivot link. The pivot link is connected to the blade to reciprocate the blade. More particularly it is anticipated that in these versions of the invention, one end of the pivot link may be pivotally mounted to the bar. For example, this end of the pivot link may be ring shaped. The link is pivotally attached to the bar by a pin that extends through the center of the ring. The opposed end of the pivot link is attached to the blade. In these versions of the invention the drive link is attached to a section of the pivot link located between the end of the link pivotally attached to the bar and the end of the link to which the blade is attached. 
     Further it is within the scope of this invention to provide a cartridge wherein the moving blade extends laterally away from a side surface of the guide bar. In these versions of the invention, the guide bar may be constructed so that a stop protrudes outwardly from the plane of the bar. Typically this stop is located slightly forward of the distal end terminus of the zone of travel of the teeth integral with blade. 
     It should be appreciated that in versions of the invention wherein a pivot link is employed to transfer motion to the blade head may also be employed in cartridges of this invention that do not include structural features that limit movement of the cartridge relative to the tissue against which the blade is pressed. 
     Thus some reciprocating cartridges of this invention may not have a structural feature that limit the movement of the bar. 
     Similarly some cartridges of this invention may include the pivot link and features for retaining the blade in the cartridge and not have a structural feature that limits the movement of the bar. Thus it may be desirable to provide this type of cartridge when it is desirable to provide a cartridge with moving components that are collectively designed to minimize vibration and for which it is not necessary to provide a feature that limits movement of the bar relative to the tissue against which the tissue is applied. This type of cartridge may include a blade that moves in a sagittal motion or a blade that engages in a reciprocal motion. 
     It should likewise be understood that in some versions of the invention wherein the bar is formed to retain the blade, the bar may only have a single internal void space for receiving a complementary portion of the blade. 
     Likewise the presence of one or more legs  412  spaced apart from the arcuate beam  414  of the blade may be present in a cartridge of this invention without requiring the blade to be connected to the one or more drive links  130  by a pivot link. This versions of the cartridge may be useful when it is desirable to for a given radius at the distal end of the blade reduce the mass of the blade without requiring the cartridge to be designed so that the point around which the blade pivots is proximal to the axis around which the blade is attached to the bar. 
     Similarly, alternative means may be provided to couple the pivot link to the blade so these two components are able to both pivot and move longitudinally relative to each other. At the simplest, this assembly may consist of forming the pivot link with a notch that extends proximally inwardly from a distally directed face of the link. The blade has a toe that is seated in this notch. Collectively the pivot link notch and blade toe are shaped to allow the pivot link and blade to both pivot and move longitudinally relative to each other. 
     Accordingly, it is an object of the appended claims to cover all such variations and modifications that come within the true spirit and scope of this invention.