Patent Description:
A powered surgical instrument, a surgical tool, used with some frequency is the powered surgical saw. This type of instrument is used to remove tissue, including bone and cartilage. Attached to the saw is a saw blade. A drive assembly internal to the saw reciprocates the blade in a back and forth motion. Often the saw includes a moving head. The head is the component of the saw to which the blade is mounted. Some blades are constructed to pivot back and forth, oscillate, in the plane in which the blade is oriented. This type of blade is referred to as a sagittal saw blade. A sagittal saw blade is provided with teeth that extend forward from the distal end of the blade body.

Many sagittal saws and their complementary blades are designed so that the blade extends distally forward of the blade head. One such assembly is disclosed in the Applicant's <CIT>Pub. This type of saw and blade are used to remove a section of bone. This is perhaps the most common type of sagittal saw.

A surgical saw includes an assembly for removably holding the blade to the saw. This is because the blade is often the single use component of the combined saw and blade assembly. One reason the blade is used once is that upon use of the blade, the teeth are immediately dulled. Owing to the economics, it is often more cost effective to use a new blade with each patient than go to the expense of sterilizing and resharpening a previously used blade.

A surgical sagittal saw is typically formed so that the head has a slot. The slot is the void space dimensioned to receive the proximal end of the blade. Often, the proximal end of the blade is provided with one or more openings. Each opening is dimensioned to receive a pin that is moveably mounted to the saw head. The seating of the pin in the blade opening releasably holds the blade to the head.

It is common practice to collectively dimension the saw head and blade so the slot facilitates the close slip fitting of the blade in the slot. This dimensioning facilitates the relatively easy insertion of the blade into the saw head and removal of the blade from the saw head. A result of this component dimensioning is that within the slot, there is small clearance between the blade and the interior surfaces of the saw head that define the slot. This means that within the slot the blade has space to move.

Owing to this tendency of the blade to move, the back-and-forth movement of the blade is not always in phase with the back-and-forth movement of the saw head. This out of phase movement occurs because when the saw head reverses direction, owing to the blade having a momentum in the opposite direction, the blade continues to move in the first direction. Thus, there may be times in the movement of the saw head and blade where these two components move in the opposed directions. This can result in the blade striking an adjacent surface of the saw head. This action is sometimes referred to as blade slap. A result of blades continually slapping against the saw head is that the material forming the head can fatigue. This component fatigue can result in the fracturing of the saw head. Once such a fracture occurs, at a minimum, it is necessary to replace the saw head.

The failure of the blade to move completely in unison with the saw head can even result in problems even when the blade does not strike the saw head. The lagging movement of the blade relative to the saw head is sometimes referred to as backlash. As a result of this movement each tooth of the blade may not, in a single phase of a single oscillatory cycle, move in an arc of sufficient length. More particularly, for a blade to efficiently function, during a single phase of movement, a tooth of the blade should move at least as far as the starting position of the adjacent tooth at the start of the phase. For example, when a blade sweeps right, a tooth should move to the right a sufficient distance so that, at the end of the sweep, the tooth will have moved to at least the location at which the adjacent tooth to the right of the blade was located at the start of the sweep. When a tooth engages in this degree of arcuate movement, there is high likelihood that, in the single sweep the tooth will have sheared away the bone located between that tooth and the adjacent right located tooth. This removal of all the bone between the teeth is what facilitates the efficient formation of the cut.

The problem arises because, owing to the backlash, the saw blade and by extension the teeth of the saw, in a single phase of movement, engages in an arcuate movement that is less than the arcuate movement of the saw head. In some situations that means that in the single phase of movement, a blade will not sweep to the location at which the adjacent tooth was located at the start of the sweep. When this event occurs, not all the bone between the teeth are sheared, cut away. This can reduce the efficiency of the cutting process.

In addition to the blade moving side to side relative to the saw head, a blade may be able to move up and down relative the head slot in which the blade is seated. This movement is sometimes referred to as the out of plane oscillation of the blade. Alternatively, this movement is sometimes referred to as blade whip. This out of plane movement of the blade relative to the saw can adversely affect the precision of the cut formed by the blade. This movement can also stress both the saw head and the proximal end of the blade, the portion of the blade seated in the saw head slot. The stressing of the saw head can result in the fracturing of the saw head. The stressing of the proximal end of the blade can result in the deformation of the blade. This deformation can also reduce the precision of the cut made by the blade.

Another disadvantage of this movement of the blade relative to the saw head is that it can result in the blade moving to a less than optimal position for the procedure being performed. When a sagittal saw is used to remove a large section of the bone such as a portion of the knee, the blade is often placed in a resection guide. This instrument is a block that is affixed to the bone adjacent where the cut is to be formed. The block is formed with one or more slots. The slots serve as guide paths through which the saw blade is inserted. By cutting the bone along the guide paths defined by the slots, the bone left after the cut will have the desired shape. This precision shaping of the bone ensures the proper fitting of an orthopedic implant to the bone. Owing to the flexure of the blade when fitted in one of these slots, the blade can gall, wear the material that defines the slots. This can result in the shape of the slot deforming from the shape needed to ensure that a cut formed based on the shape of the slot has the desired shape. Once this deformation of the resection guide occurs, the guide is no longer useful.

There is therefore a desire to provide a surgical sagittal saw and complementary blade that are constructed so that, when the saw and blade are actuated, the saw head and blade move as a single rigid structure. One means to ensure the saw head and blade move as a single rigid body is to provide a clamping assembly that, when set, applies an appreciable amount of force to the blade to hold the blade to the saw head. This typically means that the individual charged with blade insertion and blade removal needs to apply a significant amount of force in order to reset and release the clamping assembly. Requiring the individual responsible to perform these tasks to apply these forces can complicate the process of inserting and removing the blade. Requiring the individual to apply these forces can also slow the processes associated with both inserting and removing the blade. This is especially true if the individual has limited arm and hand strength. Further, if these forces are not properly applied, especially the force required to set the clamping assembly, the blade may not be fully locked to the saw head. When the saw is actuated this could result in a clearly undesirable event, the blade working free from the saw.

Document <CIT> describes a micro-saw blade for bonecutting surgical saws. The cutting blade includes a distal end comprising a plurality of cutting teeth and a shank portion adjacent the distal end. It also includes a proximal end adjacent the shank portion. The proximal end is shaped to attach to the surgical saw and includes an upper substantially planar surface and a lower substantially planar surface and a side edge extending between the upper and lower planar surfaces. The side edge at least in part defines an outer perimeter extending about the proximal end. The outer perimeter includes a plurality of indentations forming openings configured to receive and interface with protrusions extending from a surgical saw the blade is to be used with in a manner that the protrusions cooperatively impart motion to drive the blade.

This invention is related to a new and useful surgical saw and complementary blade for use with the saw. The saw and complementary blade of this invention are designed to ensure that, when the blade is removably attached to the head integral with the saw, the blade and saw head move as a single unit. A surgical saw is defined in claim <NUM>.

The blade for use therewith is provided with one or more lock teeth. The lock teeth are formed from material that, in comparison to the material from which the blade body and cutting teeth are formed, is relatively soft.

The saw includes a head. The head includes an anvil and a press. The press is located adjacent the exposed surface of the anvil and is moveable towards and away from the anvil. At least one of the anvil or the press is formed to define one or more slots. Each slot is dimensioned to receive a separate one of the blade lock teeth. The press or the anvil is formed with press surfaces. The press surfaces are in registration with the slots formed in the other of the anvil or the press.

To removably mount a blade to the saw, the press is first moved away from the anvil. The blade is placed between the anvil and the press so the one or more lock teeth seat in the complementary slots formed in the anvil or the press. The press is moved against the blade. More specifically, the press is displaced so that blade is compressed between the anvil and the press. As a result of this compression of the blade, the press surfaces push the lock teeth into the slots formed in the anvil or the press.

As a result of the lock teeth being pushed into the adjacent slots and the lock teeth being relatively soft, ductile, the lock teeth are deformed. Each lock tooth is deformed, becomes coined, around the surfaces of the anvil and the press that define the slots and the press surfaces. As a result of this deformation of the blade lock teeth, there is essentially no clearance between the lock teeth and the anvil and the press. The saw head and blade essentially become a single piece component. There is essentially no movement of the blade relative to the saw head.

In some versions, the blade lock teeth are further formed to have opposed faces. At least one tapered surface extends between the opposed faces. The tapered surfaces are the surfaces of the lock teeth that are disposed against the corners, the edges, of the saw head that define the slots and press surfaces. The portions of the lock teeth that define the tapered surfaces, during the process of locking the blade to the saw head, are the portions of the lock teeth that are coined.

In some versions of the invention, the press is a cap that is disposed over the anvil.

In some versions, the blade has plural sections. The sections of the blade that defines the one or more lock teeth are relatively soft. The remaining section of the blade, the section that defines the cutting teeth, is relatively hard. In some processes used to make this version of the invention, the stock from which the blade is formed is manufactured out of relatively hard material. The blade is selectively treated so as to result in the lock teeth being softer, more ductile, than the rest of the blade. In some processes used to make this version of the invention, the stock from which the blade is formed is relatively soft. More specifically, the stock is sufficiently ductile so that when pressure is applied to the lock teeth, the lock teeth will deform.

In some versions wherein the blade is formed out of materials of different hardnesses, the section of the blade defining the lock teeth is formed from a first material that is relatively soft. The majority, if not all of the rest of the blade is made out a material of sufficient hardness that it can cut the bone the blade is intended to cut.

In some versions, the proximal end of the blade is provided with a circularly shaped void. In some versions of this invention, at least one lock tooth extends inwardly from the perimeter of this void. In many versions of the invention, plural lock teeth extend inwardly into this void.

The saw and blade of this application may be designed as sagittal saws, oscillating saws or reciprocating saws. Also, for the purposes of this invention, a rasp is considered a type of saw blade.

The invention is pointed out with particularity in the claims. The above and further features and advantages of this invention are understood from the following Detailed Description taken in conjunction with the accompanying drawings in which:.

<FIG> and <FIG> depict a surgical saw assembly <NUM> constructed in accordance with this invention. Saw assembly <NUM> consists of a saw unit <NUM> and a blade <NUM>. The depicted saw assembly <NUM> is what is referred to as a micro sagittal saw. This saw is used to perform procedures on small bones. Examples of bones on which a micro surgical saw is used to perform surgery on include: the skull; the spine; the hand; and the foot. Internal to the saw <NUM> is a motor <NUM> represented by a phantom cylinder. Motor <NUM> includes a rotating shaft <NUM> represented by a smaller diameter phantom cylinder. The actuation of the motor <NUM> results in the back and forth oscillations of the blade <NUM>. More specifically, the blade <NUM> pivots back and forth around an axis that extends through the plane of the blade.

Saw unit <NUM> includes a body or shell <NUM>, seen best in <FIG> and <FIG>, that houses or holds the other components of the saw unit. Body <NUM> has a generally cylindrical main section <NUM>. Body main section <NUM> is dimensioned to be held in the hand. Typically, the saw body <NUM> is held between the thumb and forefinger or between the thumb and middle finger. Extending distally forward of the main section, the saw body <NUM> has a neck <NUM>. ("Distally" is understood to mean away from the surgeon; towards the site on the patient to which the blade <NUM> is applied. "Proximally" is understood to be towards the surgeon holding the saw unit <NUM>; away from the site on the patient to which the blade <NUM> is applied. ) The saw body <NUM> is dimensioned so that the neck <NUM> is, in planes perpendicular to the proximal-to distal longitudinal axis along the body, generally semicircular in cross section. Saw body <NUM> is further dimensioned so that the outer surface of the neck <NUM> is located radially inward from the outer surface of the body main section <NUM>. Forward of and integral with the neck <NUM>, the saw body <NUM> has a head <NUM>. In the depicted version of the invention, head <NUM> has a shape of a slice section of a sphere. More particularly, saw head <NUM> has a shape in which a first surface is along a plane that extends slightly above the mid-plane of the sphere. A second surface that is parallel to the first surface is located closer to what would be one of the poles of the sphere defined by the head <NUM>. Saw body <NUM> is further shaped so that the head <NUM>, relative to the longitudinal axis through the body <NUM>, extends outwardly of the neck <NUM>.

The saw body <NUM> is further formed so there is void space <NUM> internal to the body main section <NUM> as seen in <FIG>. The distal end of the body main section <NUM>, has an opening, opening not identified. Saw body <NUM> is further formed so there is a recess <NUM> in the neck <NUM>. Owing to the opening in the distal end of the body main section <NUM>, body void space <NUM> and recess <NUM> are contiguous. Saw body <NUM> is further formed so that saw head <NUM> has a bore <NUM> that extends through the head. The saw body <NUM> is formed so that bore <NUM> extends along an axis perpendicular to the longitudinal axis through the body. The distal end of recess <NUM> opens into bore <NUM>.

Returning to <FIG> it can be seen that motor <NUM> is disposed in void space <NUM> internal to the body main section <NUM>. Motor <NUM> is often electrically driven. A cable <NUM> extends proximally from the proximal end of the body <NUM>. Cable <NUM> is connected to a control console not illustrated and not part of the present invention. The control console supplies energization signals over cable <NUM> to the motor <NUM> that actuate the motor. Not shown are the connections between the individual conductors internal to the cable <NUM> to the motor <NUM>.

A coupling assembly (<NUM>, <NUM>, <NUM>, <NUM>) is moveably mounted to the saw head (<NUM>) to releasably hold the saw blade, and comprises a drive link (<NUM>), a cap (<NUM>), a screw (<NUM>) and a knob (<NUM>). The drive link <NUM>, seen best in <FIG>, <FIG> and <FIG>, is pivotally mounted to the saw body head <NUM>. The drive link <NUM> includes a cylindrical stem <NUM>. Forward of stem <NUM>, the drive link <NUM> has an anvil in the form of a head <NUM> that is approximately disk like in shape. More specifically, drive link head <NUM> has two opposed surfaces <NUM> that are planar and parallel. In <FIG>, one surface <NUM> is fully illustrated and the edge of the opposed surface <NUM> is called out. The perimeters of surfaces <NUM> are generally circular in shape. The outer diameter of the head <NUM> is generally equal to the outer diameter of the widest portion of body head <NUM>. In the depicted version of the invention, the distal end of body head <NUM> is truncated. Thus, the most distally directed surface of trunk head <NUM> is a flat <NUM>. Flat <NUM> is present for manufacturing reasons and is otherwise not relevant to this invention.

The drive link <NUM> is further formed to have a hole <NUM> that extends between the link major surfaces <NUM>. Hole <NUM> is circular in shape and is concentric with the axis of the link head <NUM> that extends between the major surfaces <NUM>. The drive link <NUM> is further formed to have four arcuately islands <NUM>, two islands identified, that extend upwardly from the head major surface <NUM> that is directed away from saw body head <NUM>. The islands <NUM> are located adjacent the outer perimeter of hole <NUM> and are arcuately shaped. Each island <NUM> is arcuately spaced from the adjacent islands <NUM>. Thus, between each pair of islands <NUM> there is a void, a channel <NUM>, (two channels identified).

A pivot pin <NUM> and a bearing assembly <NUM> rotatably hold the drive link <NUM> to the body head <NUM>. The pivot pin <NUM>, as seen in <FIG>, has an elongated cylindrical stem <NUM>. Stem <NUM> is dimensioned so that the top of the stem, as seen in <FIG>, can be press fit or otherwise secured in the hole <NUM> formed in the drive link head <NUM>. The components forming the saw unit <NUM> are further dimensioned so that the pin stem <NUM> has a diameter less than the diameter of the saw body head bore <NUM>. Pin <NUM> is further formed so that at the end of the stem <NUM> opposite the end fitted to the drive link <NUM> there is head <NUM>. Pin head <NUM> extends radially outwardly from the stem <NUM>. The pivot pin <NUM> is formed with an axially extending through bore, bore <NUM>. Bore <NUM> extends from the top of the pin stem <NUM>, the portion of the pin fitted to the drive link <NUM> to and through the pin head <NUM>. While not seen it should be understood that the cylindrical inner wall of pivot pin <NUM> that defines bore <NUM> is threaded.

Bearing assembly <NUM>, seen best in <FIG>, includes sleeve shaped inner and outer races <NUM> and <NUM>, respectively. Inner race <NUM> is dimensioned to have a tight slip fit over pin stem <NUM>. Outer race <NUM> is dimensioned to have a press fit against the inner cylindrical wall of the body head <NUM> that defines bore <NUM>. It is further noted that races are dimensioned so that the inner race <NUM> extends above and below the outer race <NUM>. Two rings of ball bearings <NUM> provide the rotating interface between the races <NUM> and <NUM>. Not identified are the grooves in the surfaces of the races <NUM> and <NUM> in which the ball bearings <NUM> are seated.

When saw unit <NUM> is assembled, bearing assembly <NUM> rotatably holds pin <NUM> and, by extension, drive link <NUM> to the saw body head <NUM>. The components are dimensioned so that inner race <NUM> protrudes both above and below saw body head <NUM>. The drive link major surface <NUM> directed towards saw body head <NUM> is disposed against the section of the inner race <NUM> that projects above the head <NUM>. Pin head <NUM> is disposed against the section of the inner race <NUM> that projects below the saw body head <NUM>.

A linkage assembly, represented by a bar <NUM> in <FIG>, extends from the motor shaft <NUM> to the drive link stem <NUM>. This linkage assembly transfers the rotational motion of the motor shaft <NUM> into motion that causes the drive link <NUM> to oscillate back and forth. More specifically, when motor <NUM> is actuated, the linkage assembly causes the drive link <NUM> to oscillate back and forth around the top to bottom longitudinal axis through pin <NUM>. The structure of the linkage assembly is not part of the present invention.

A press in the form of cap <NUM>, seen best in <FIG>, is moveably mounted to the saw body <NUM> above the exposed major surface of drive link <NUM>. Cap <NUM> is generally circular in shape. The cap <NUM> is formed with a through hole <NUM> that extends top to bottom through the cap. Hole <NUM> is concentric with the top-to-bottom axis through the cap. The top of the cap <NUM> is further formed to have a tapered opening <NUM> that leads into hole <NUM>.

The bottom of the cap <NUM> is formed with a planar undersurface <NUM>. Three sets of arcuately shaped feet extend downwardly from undersurface <NUM>. These feet include the press feet <NUM> and stop feet <NUM> that are interleaved in a common circle. Feet <NUM> and <NUM> are arcuately spaced apart from each other. The saw unit <NUM> is constructed so the each press foot <NUM> is located over a separate one of the channels <NUM> of the underlying drive link <NUM>. The components are constructed so that each press foot <NUM> subtends an arc that is less than the arc of the underlying drive link channel <NUM>. Each stop foot <NUM> subtends an arc greater than the arc subtended by a single press foot <NUM>. The components forming the saw unit <NUM> are further constructed so that the arc separating adjacent stop feet <NUM> is greater than the arc of the drive link channel <NUM> located between and below the adjacent stop feet. Internal to this arc between adjacent stop feet <NUM> is one of the press feet <NUM> located between each pair of adjacent stop feet <NUM> Stated another way, each stop foot <NUM> is located above an underlying drive link island <NUM>. Each stop foot <NUM> subtends an arc less than the arc subtended by the underlying island <NUM>. Given that the arcuately adjacent feet <NUM> and <NUM> are spaced from each other, there is a gap <NUM> between the adjacent feet. Owing to the dimensioning of the drive link islands <NUM> and cap feet <NUM> and <NUM>, each gap <NUM> is partially located above an underlying end section of one of the drive link channels <NUM>. The remainder of each gap <NUM> is located above one of the drive link islands <NUM> that defines the perimeter of the channel.

The third set of feet cap <NUM> is formed to have are the arcuately shaped compress feet <NUM>. Compress feet <NUM> also extend downwardly from the cap undersurface <NUM>. The compress feet <NUM> are spaced radially outwardly and apart from the circle of press and stop feet <NUM> and <NUM>, respectively. In terms of arcuate slice sections of the cap <NUM>, each compress foot <NUM> is in registration with a separate one of the press feet <NUM> or one of the stop feet <NUM>. Each compress foot <NUM> subtends the same arc as the foot <NUM> or <NUM> with which the foot <NUM> is in registration. Each compress foot <NUM> is arcuately spaced apart from the adjacent compress feet <NUM>. Feet <NUM>, <NUM> and <NUM> all extend down the same distance from cap undersurface <NUM>.

The screw <NUM> and knob <NUM>, seen best in <FIG>, control the relative height of the cap <NUM> to the drive link <NUM>. Screw <NUM> has a head <NUM> dimensioned to seat in the tapered opening <NUM> of cap <NUM>. A shaft <NUM> extends downwardly from the head <NUM>. Shaft <NUM> is formed with threading (not illustrated). Shaft <NUM> is dimensioned to extend through the hole <NUM> internal to cap <NUM> and the bore <NUM> formed in pivot pin <NUM>. The screw shaft threading is engaged with the threading around the pivot pin bore <NUM>. A short cylindrical foot <NUM> projects from the end of the shaft <NUM> opposite screw head <NUM>. Foot <NUM> has a diameter less than that of the screw shaft <NUM>. When saw unit <NUM> is assembled, foot <NUM> projects a short distance below the pivot pin <NUM>.

Knob <NUM>, seen only in <FIG> and <FIG>, is attached to screw foot <NUM>. The knob <NUM> is thus located below the head <NUM> of the saw body <NUM>. Knob <NUM> rotates screw <NUM>. The component to which the screw <NUM> is attached, the pivot pin <NUM>, is held static to the drive link <NUM>. Therefore, the rotation of the screw by the knob <NUM> results in the raising and lowering of the screw head <NUM> relative to the drive link <NUM>.

The blade <NUM> of saw assembly <NUM> of this invention, as seen in <FIG>, is a single piece assembly. Blade <NUM> is shaped to have a body <NUM> that is generally planar in shape. At the proximal end of the body the blade has a foot <NUM>. Foot <NUM> is rounded in shape and has a diameter that is greater than the width of the more distal portions of the blade body <NUM>. The outer diameter of the foot <NUM> is substantially equal to the common diameter of the drive link head <NUM> and cap <NUM>. A slot <NUM> extends forward from the proximal end of foot <NUM>. Slot <NUM> has a width that allows the slot to receive screw shaft <NUM>. The blade <NUM> is further formed so that slot <NUM> opens up into a hole <NUM> that extends through the opposed planar faces of the blade foot <NUM>. Hole <NUM> is circular in shape and has a diameter greater than the width across slot <NUM>.

Blade <NUM> is further formed to have lock teeth <NUM> that extend inwardly from the portion of the foot that defines the outer perimeter of hole <NUM>. Each lock tooth <NUM> has a body <NUM> that is approximately in the shape of a truncated isosceles triangle. The bodies <NUM> of the lock teeth have the same top to bottom thickness as the top to bottom thickness of the blade body <NUM>. The thickness across each the body <NUM> of each tooth <NUM> generally decreases as the tooth extends inwardly toward the center of the hole. The portions of the teeth <NUM> closest to the center of hole <NUM> are rounded to define a circle that is concentric with the hole. A wing <NUM> projects arcuately outwardly from the each of the opposed side surfaces of the tooth body <NUM>. Each wing <NUM> is formed from two opposed tapered surfaces. Thus, the thickness across opposed faces of the body <NUM> of a lock tooth <NUM> is generally constant along the tooth body <NUM>. The thickness of each tooth wing <NUM> decreases along lines perpendicular to the line along which the tooth body <NUM> extends inwardly towards the center of hole <NUM>. In the illustrated version of the invention, the radially outermost portion of each tooth wing <NUM> is spaced inwardly from the perimeter edge of the foot that defines the outer perimeter of hole <NUM>. Given that each wing <NUM> is spaced from the adjacent perimeter of foot <NUM>, it should be appreciated there is void space between the foot and the wing, void space not identified. The components forming the saw assembly <NUM> of this invention are further dimensioned so that the parallel faces of the teeth body <NUM> have a side-to-side width that is both less than the width across a channel <NUM> formed in the drive link and greater than the width across a press foot <NUM> integral with the cap <NUM>.

The blade <NUM> is further formed so that cutting teeth <NUM> extend forward from the distal end of the blade body <NUM>. Cutting teeth <NUM> are designed to, when the blade <NUM> is oscillated, remove the tissue against which the teeth <NUM> are applied. The geometry of the cutting teeth <NUM> is not part of the present invention.

While blade <NUM> is a single piece assembly, there are differences in the characteristics of the features of the blade. More specifically, the lock teeth <NUM> are formed from material that is relatively soft, relatively ductile. This material typically, but not always, has a maximum hardness in the Rockwell B Range. The blade body <NUM>, including cutting teeth <NUM>, are formed from material harder than the material from which the lock teeth <NUM> are formed. Typically, the blade body and teeth are typically, but not always, formed from material that has a hardness in the Rockwell C Range.

One means of so fabricating the blade is to form the whole of the blade, the foot <NUM>, the body <NUM>, the lock teeth <NUM> and the cutting teeth <NUM> out of a single piece of hard metal. After the blade is so shaped, the lock teeth <NUM> are subjected to a further processing to soften the teeth <NUM>, increase their ductility. In one such process, the blade is formed from stainless steel. Once the blade <NUM> is formed, the lock teeth <NUM> are subjected to a localized annealing process. For example, the lock teeth <NUM> can be so annealed by directed a laser beam to the surface of the teeth. The photonic energy of the laser beam heats the teeth <NUM> to their annealing temperature. Once the lock teeth <NUM> are heated to the annealing temperature, the lock teeth are allowed to cool at a relatively slow rate. Often the cooling is at a controlled rate. Given that the relatively low thermal conductivity of the stainless steel, the heat generated by this remains localized. The heat does not therefore result in the undesired softening of the remainder of the blade <NUM>. As a result of this annealing process, the metal forming the lock teeth <NUM> becomes softer, more ductile, than the material forming the rest of the blade <NUM>.

A second means to so form the blade is described with reference to <FIG>. The blade 140a, is formed with a body, in <FIG>, body 148a, including the foot 142a and cutting teeth (not seen) out of the relatively hard material. Foot 142a is formed with a through hole <NUM>. A washer like member <NUM> formed from more ductile material is welded or otherwise secured to the through hole formed in the foot <NUM>. This washer like member <NUM> is formed to have the blade lock teeth 150a.

A saw assembly <NUM> of this invention is readied for use by coupling the blade <NUM> to the saw unit <NUM>. To prepare for this operation, knob <NUM> is rotated to cause screw head <NUM> to move to the position where the screw head is spaced from the drive link <NUM>. This allows cap <NUM> to be likewise be moved upwardly away from the drive link <NUM>. When the saw unit <NUM> is in this state, the saw unit is in the load or unlocked state.

Once the saw unit <NUM> is in the unlocked state, the cap <NUM> is moved away from the drive link <NUM> a sufficient distance, blade foot <NUM> is seated between the drive link head <NUM> and the underside of the cap <NUM>. The presence of slot <NUM> in the blade foot <NUM> facilitates the insertion of the blade around screw <NUM>. The saw unit and blade are placed in registration with each other as seen in <FIG>. The blade lock teeth <NUM> are seated over the channels <NUM> formed on the drive link head <NUM> so that each the wings <NUM> of each tooth <NUM> rest on the edges of the adjacent and spaced apart islands <NUM>. Thus, the portion of the tooth <NUM> between the wings <NUM> is thus disposed in the channel <NUM> between the islands <NUM>. The cap <NUM> is positioned so that each press foot <NUM> is disposed over the face of the tooth body <NUM> opposite the face that is disposed in the underlying drive link channel <NUM>.

Once the components of saw assembly <NUM> are so aligned, knob <NUM> is rotated to place the saw unit <NUM> in the run or locked state. Specifically, the knob <NUM> is rotated to lower screw <NUM> and, by extension, cap <NUM>. As the cap <NUM> is lowered, the press feet <NUM> press against underlying blade lock teeth <NUM>. Since the drive link <NUM> is static, the drive link head <NUM>, including islands <NUM> function as a static anvil. Cap <NUM>, having press feet <NUM>, functions as a press. Owing to the ductile nature of the lock teeth <NUM>, the movement of the press feet towards the drive link results in the teeth deforming between the drive link and the cap. As seen by reference to <FIG> and <FIG>, the overlying press foot <NUM> presses against the tooth main body to push the tooth into the underlying channel <NUM> in the drive link. In <FIG>, the perimeters of feet <NUM>, <NUM> and <NUM> are depicted as dashed lines. Cap <NUM> thus functions as the press and the faces of the press feet <NUM> are thus the press surfaces of the cap <NUM>. The movement of the press feet <NUM> causes the tooth wings <NUM>, which are thinner than the adjacent tooth main body <NUM>, to bend around the edges around the perimeter of the islands <NUM>. Once the locking teeth <NUM> seat against the underlying portion of the link main surface that defines the bases of the channels <NUM>, the continued motion of the press feet causes the portions of the teeth main body adjacent the edges of the press feet to bend around these edges. Thus, as seen in <FIG>, the wing portions <NUM> of each tooth as well as a small sections of the tooth base <NUM> adjacent the wings moves are bent into the gaps <NUM> between the press feet <NUM> and the adjacent stop feet <NUM>.

Cap <NUM> is lowered against the drive link until the stop feet <NUM> abut the underlying islands <NUM> integral with the drive link <NUM>. In <FIG>, to minimize confusion, the islands <NUM> against which feet <NUM> abut are not shown. Once the cap <NUM> is so positioned, the saw unit can be considered in the run or locked state.

A further effect of the lowering of cap <NUM> is that, as seen in <FIG>, the compress feet <NUM> bear against the blade foot <NUM>. As a consequence of the press feet <NUM> pushing the locking teeth <NUM> into the channels <NUM> and the compress feet <NUM> pushing against the blade foot <NUM>, the blade foot is pushed against circular section of the drive link major surface <NUM> located radially outwardly of islands <NUM>. The blade foot <NUM> is thus compressed by the drive link major surface <NUM> and the opposed cap compress feet <NUM>.

As a result of the locking of the blade <NUM> to the saw unit <NUM>, the blade foot <NUM> is more than compressed between the drive link <NUM> and cap <NUM>. The deformation of the blade lock teeth <NUM> around the adjacent components of the drive link and cap essentially make the drive link, the cap and the blade a single piece assembly. There is no clearance between the drive link <NUM> and the saw blade <NUM>. When the drive link <NUM> is oscillated, blade <NUM> oscillates as one with the drive link <NUM>. There is essentially negligible, if any, movement of the blade <NUM> relative to the drive link and cap. The undesirable effects associated with saw unit components <NUM> and <NUM> and the blade <NUM> moving relative to each other are essentially eliminated.

These undesirable effects include the movement of the blade relative to the saw that can adversely affect the precision of the cuts made be the blade. Still another undesirable effect that is essentially eliminated is the wear on the saw unit that results from the blade slap. A further undesirable effect this invention reduces if not eliminates is the frictionally induced heating that can occur as a result of the movement of the blade relative to the saw unit. Furthermore, since the blade <NUM> for all intents and purposes moves in unison with the saw coupling assembly, during each phase of an oscillatory cycle, the blade undergoes essentially the same arcuate sweep as the coupling assembly. This ensures that, in each sweep a tooth of the blade will sweep to at least the location of the adjacent tooth at the start of the sweep. The sweeping of the tooth along this arc increases the likelihood that, in the sweep all the bone between the teeth was, in the sweep sheared away. The removal of all this bone in a single sweep can enhance the efficiency of the cutting process.

A further advantage is due to the fact that, because the blade <NUM> is firmly attached to the coupling assembly, there is little, if any, whip, oscillation of the blade outside of the plane of the cut. This means that when the blade is initially applied against bone, the blade can be used to form an initial cut that is thinner than the cut that is sometimes formed when the blade engages in whip motion. Since this initial cut is thinner, the surgeon can use a blade that is thicker than the blade the surgeon may otherwise use to form the cut. A benefit of using this thicker blade is that this blade will inherently be stiffer than a thinner blade. This is beneficial because as the blade is advanced deeper into the bone the stiffness of the blade reduces the extent to which any blade flexure adversely affects the precision of the cut.

Another feature of this invention is that blade is not only compressed between the drive link and the press feet <NUM>. The blade is also compressed between the drive link major surface <NUM> and the cap compress feet <NUM>. This substantially reduces the likelihood that, if the press feet and drive link fail to collectively hold the blade lock teeth <NUM> to the saw unit <NUM>, the blade will rapidly work free of the saw unit.

A further benefit of this invention, is that blades of different thicknesses can be clamped between the drive link <NUM> and cap <NUM>. The primary design criteria in providing a saw unit of this invention able to accept these different blades is that the screw should allow the cap to move above the blade a sufficient height so a blade having the largest thickness for use with the saw unit can be inserted between the drive link and the cap.

<FIG> is directed to an alternative saw unit 40a of this invention. The majority of the components of saw unit 40a are identical to the components of first described saw unit <NUM>. These components are not redescribed. Instead of being provided with a knob to raise and lower screw <NUM>, saw unit 40a has an arm <NUM>. Arm <NUM> is pivotally attached to the foot <NUM> integral with the screw <NUM>.

This construction of the invention has a further benefit by selective forming the pitch of the threading integral with pivot pin <NUM> and screw <NUM>. Specifically, the saw unit 40a can be constructed so that the orientation of the arm relative to the saw unit body <NUM> serves as an indicia regarding whether or not the saw unit is in the fully locked/run state. For example, in some versions of the invention, the components can be arranged so that when the saw unit 40a is so locked arm <NUM> is parallel with the longitudinal axis of the saw unit body <NUM>.

In more preferred versions of this construction of the invention, the orientation of the arm <NUM> serves as both an indication of the run or load state of the saw unit 40a and the type of blade <NUM> mounted to the saw unit. For example in some versions of the invention, when a blade that has a relatively large top face to bottom face thickness is fully locked to saw unit 40a the arm <NUM> is both parallel to the longitudinal axis of the saw body <NUM> and is pointed distally forward. When a blade with a relatively thin top face to bottom face thickness is fitted to the saw unit 40a, an extra half turn or one and half turns of the screw may be needed to lock the blade. When such a blade is so mounted, the arm <NUM> will be aligned with the longitudinal axis of the saw body <NUM> and point proximally rearward.

It should be understood that if the arm points forward when the saw is initially placed in the lock state, the blade may extend below the blade. This could require the pivoting of the arm proximally rearward to ensure the full insertion of the blade.

<FIG> depicts a portion of an alternative blade 140b of this invention. Blade 140b contains many of the same features of blade <NUM>. To avoid redundancy these features are neither redescribed nor again illustrated. The difference between blades <NUM> and 140b concerns the shape of the locking tooth. Blade 140b has lock teeth <NUM>, one of which is seen in cross section in <FIG>. In cross section, a lock tooth <NUM> can be considered trapezoidal in shape. The tooth <NUM> has opposed parallel lower and upper faces <NUM> and <NUM>, respectively. Lower face <NUM> is longer in length than upper face <NUM>. Tapered side surfaces <NUM> extend upwardly from the opposed ends of the lower face. Side surfaces <NUM> extend to the ends of the adjacent upper face <NUM>. The teeth <NUM> are formed so the opposed side surfaces of each tooth are symmetric. Side surfaces <NUM> and outer sections of upper face <NUM> opposed to the side surfaces thus form the outer surfaces of the wings of lock tooth <NUM>.

A benefit of blade 140b over blade <NUM> is that it may be more economical to provide a blade with teeth <NUM> than with teeth <NUM>. When blade 140b is provided, care must be taken to ensure that the blade is orientated so that the teeth bottom surfaces seat in the channels <NUM> between drive link islands <NUM>.

The foregoing is directed to specific versions of the invention. The invention may have features different from what has been described.

For example, the features of the different versions of the invention may be incorporated together.

Further, while the described saw of this invention is a sagittal saw, this invention is not limited to sagittal saws. This invention may be employed as part of reciprocating surgical saw. A reciprocating surgical saw consists of a saw unit and complementary blade that are arranged so that when the saw unit is actuated, the blade moves back and forth along a path of travel identical or close to being parallel to the longitudinal axis of the blade. The saw assembly of this invention may also be constructed as an oscillating saw. An oscillating saw is a saw designed to pivot a blade around an axis that extends along the axis of the saw unit. For the purposes of this invention, since each of the blades repetitively move back and forth, the saw that so cycles the blade is considered to reciprocate the blade back and forth. Another version of the saw unit of this invention is an acetabular cup remover. An acetabular cup remover, as implied by its name, is a specialized saw used to remove a previously implanted artificial acetabular cup. For the purposes of this invention, since each of the blades is repeatedly cycled back and forth, the saw that so cycles the blade is considered to reciprocate the blade back and forth.

Just as this invention is not limited to a particular type of saw, the saw unit is not limited to saw units having electrically powered motors. In alternative versions of the invention, the motor may be a hydraulically or pneumatically driven motor or actuator. If the saw unit includes an electrically driven motor or actuator, it may be possible to attach a battery to the saw unit in order to provide the current needed to actuate the motor.

The described saw unit <NUM> of this invention is a micro sagittal saw. This saw assembly of this invention may be part of what is referred to as a heavy duty surgical saw. A heavy duty surgical saw is designed to remove large sections of tissue such as the bone of the leg. This is the type of saw disclosed in the previously mentioned <CIT>Pub. Often a heavy duty surgical saw unit looks different than the elongated saw unit of <FIG>. More specifically, a heavy duty surgical saw is often pistol shaped. The saw has a handgrip and barrel that typically extend forward from the handgrip. The motor is disposed in the handgrip or the barrel. The saw head extends forward from the distal end of the barrel.

The various assemblies of this invention may vary from what has been described. For example, the clamping assembly that urges the press feet the anvil may not always include a threaded screw. In some versions of this invention, a rod able to move relative to the head of the saw unit performs this function. The rod is moved between the run and load positions by a manual actuating camming system. The Applicant's <CIT>Pub. No. <CIT> disclose how a rod may be so mounted to a saw head. In some versions of the invention, the assembly that moves the press against the anvil may not have a moving component that extends through the blade. Thus, in some versions of the invention, the press may be a plate located over the face of the blade opposite the face directed to the anvil. One or more linkage members located around the outer surface of the blade connect the press plate to the rest of the saw unit. These linkage members are actuated to urge the plate against the blade (into the run position) or away from the blade (into the load position).

In some versions of the invention the components forming the anvil and press are formed with complementary features to facilitate the registration of these components when the saw head is moved between the locked and load states. For example, one of the cap or the drive link may be provided with a pin. The other of the drive link or cap is provided with a bore for receiving the pin. The seating of the pin in the bore ensures the registration of the cap feet to the underlying anvil of the drive link.

Further, there is no requirement that, relative to gravity reference, the press feet, when moving towards the blade and the anvil move downwardly in the plane of gravity. In some versions of the invention, when the press feet are moved towards the blade and anvil, the member that includes the press fit may move in any direction relative to gravity reference plane. Thus while in the primary version of this invention the press feet carrying press is a cap, it is understood that this press may not always be located above the anvil. In alternative constructions of the invention, this press, relative the gravity reference plane be located to the side or below the anvil.

It should likewise be understood that the anvil and press of this invention may have alternative constructions. For example, there is no requirement that in all versions of the invention, the press be provided with compress feet that function as the backup features to hold the blade to the saw unit. In some versions of the invention either one of the anvil or press is provided with protruding features. The complementary blade is provided with both the lock teeth and through openings. When the blade is mounted to the saw unit, the blade is positioned so that the protruding features associated with the saw unit seat in the openings formed in the blade. The seating of the protruding features in the blade functions as the backup assembly that substantially eliminates the likelihood that the blade can work free of the saw unit. In some versions of the invention, the saw unit and blade do not have any features that provide a redundant lock of the blade to the saw unit.

It is similarly within the scope of this invention that the saw unit have components analogous to the compress feet but no components similar to the stop feet. In some versions of the invention, components functionally equivalent to both the stop feet and the compress feet may be omitted. In some versions of the invention, a press foot and a compress foot may be different sections of a single component. In some versions of the invention, a stop foot and a compress foot may be different sections of a single component.

Some saw units and blades of this assembly may be provided so that when the saw unit press feet coin the blade lock teeth, the press feet partially or fully penetrate a portion of the lock teeth. It is further contemplated that in most versions of the invention the blade will have plural deformable lock teeth and the saw unit has one or more features able to deform these teeth. However, it is also within the scope of this invention that the blade have a single deformable lock tooth and the saw unit has a single press foot for deforming the lock tooth. Likewise, while often preferable, there is no requirement that in all versions of the invention, that the press deforms the lock teeth so that the teeth, when deformed, abut the underlying base surface of the anvil. In <FIG> these are the portions of major surface <NUM> that defines the bases of channels <NUM>.

Variations in the blade of this invention are also possible. For example, it should be understood that this invention is not limited to the disclosed feature of where the blade lock teeth are arranged around a circle. <FIG> illustrates an alternative blade <NUM> of this invention. Blade <NUM> is a reciprocating saw blade. Blade <NUM> has a body <NUM> with opposed proximal and distal sections <NUM> and <NUM>, respectively. The blade <NUM> is formed with cutting teeth <NUM> that extend outwardly from a side surface of the blade distal section <NUM>.

Plural lock teeth <NUM>, <NUM> and <NUM> extend from the opposed sides of the blade proximal section <NUM>. Lock teeth <NUM>, <NUM> and <NUM> thus extend outwardly from the perimeter edges of the blade body. In the illustrated version of the invention the lock teeth <NUM>, <NUM> and <NUM> are symmetrically arranged around the proximal to distal longitudinal axis along the blade body <NUM>. Lock teeth <NUM>, <NUM> and <NUM> are more ductile, more prone to deformation, when a force is applied then the blade body <NUM>, especially the portion of the body that defines the cutting teeth <NUM>.

Each lock tooth <NUM>, <NUM> and <NUM> has a main body <NUM>, only two identified. At least one tapered wing extends outwardly from the main body of each lock tooth <NUM>, <NUM> and <NUM>. In the illustrated version of the invention, a single tapered wing <NUM> extends distally forward from the body of each lock tooth <NUM>. Two tapered wings <NUM> extend outwardly from the opposed sides of each lock tooth <NUM>. A single tapered wing <NUM> extends proximally from the side of each lock tooth <NUM>. It should be understood that <FIG> illustrates another feature of this invention, there is no requirement that each lock tooth have two opposed tapered wings. Blade <NUM> further illustrates another aspect of this invention. Specifically, blade <NUM> is further designed so that the outer edges of the tapered wings of the lock teeth are parallel to the outer edges of the bodies of the lock teeth from which the wings extend. In some versions of the invention, the lock teeth may be shaped so that extending away from the section of the perimeter of the blade from which the teeth extend, the edges of the tapered wings extend outwardly from the adjacent tooth body.

Likewise, it should be appreciated that there is no requirement that in all versions of the blade the lock teeth project outwardly from the more proximal sections of the blade body. Similarly, in versions of the invention where the blade has a foot with inwardly projecting lock teeth, the foot may have a width less than the width of the more distal sections of the blade body. Likewise, the lock teeth may be arranged to project proximally into space adjacent the proximal end of the blade.

Further, it should be understood that in some versions of the invention, one or more of the lock teeth may not have tapered sections. In some versions of the invention the wing portions of the teeth may simply be thinner in cross sectional thickness than the portion of the teeth body from which the wings extend. In some versions of the invention, the lock teeth may be of constant cross sectional thickness along the whole of the teeth. Likewise, in some versions of the invention, the top to bottom thickness of the blade lock teeth may not equal the top to bottom thickness of the blade body. In many versions of the invention, the blade locking teeth may be thinner than the blade body. There can be versions of the invention wherein the thickness of the blade locking teeth is greater than that of the blade body.

Saw blade <NUM> is further designed so that lock teeth wings <NUM>, <NUM> and <NUM> are spaced away from the perimeter edge of the portion of the blade body <NUM> from which the bodies of teeth <NUM>, <NUM> and <NUM> extend. Thus there is a void, a gap, between each wing and the adjacent perimeter of the blade body. It should be understood that spacing of the wings away from the perimeter of the blade body minimizes the force needed to deform, coin, the wings when the anvil and press are brought together. It is within the scope of this invention that in some versions of the blade the reduced cross sectional thickness portions of the lock teeth extend from the perimeter portions of the associated blade bodies. In some embodiments of these versions of the invention, the one or more lock teeth do not have section of constant thickness. Thus in some versions of the invention, there is no break, no separation, between one or more of the lock teeth and the adjacent perimeter portion of the blade body from which the teeth extend.

Likewise, it is within the scope of this invention that blade will have lock teeth having different shapes and or dimensions. For example, there is no requirement that in all versions of the invention the lock tooth (or teeth) project outwardly of the adjacent edge of the blade body. <FIG> illustrates another sagittal saw blade <NUM> of this invention. Blade <NUM> includes a body <NUM>. The body has a proximal section <NUM> and a distal section <NUM> located forward of the proximal section. Body distal section <NUM> has a side-to-side width greater than that of the distal section <NUM>. Cutting teeth <NUM> extend forward from the body distal section <NUM>.

Blade <NUM> has a single lock tooth <NUM>. Lock tooth <NUM> is generally U-shaped. The lock tooth <NUM> is formed so as to have a base section <NUM> integral with and located immediately proximal to the proximal end of the body proximal section. The base section <NUM> of the lock tooth <NUM> thus forms the proximal end of the blade <NUM>. Two arms <NUM>, also part of lock tooth <NUM>, extend distally forward from the opposed ends of the base section <NUM>. The perimeter of each arm <NUM> integral with the lock tooth <NUM> is flush with perimeter of the portion of the base proximal section <NUM> immediately forward of the arm.

In this versions of the invention, the lock tooth is shaped to have an outer perimeter section <NUM>. The outer perimeter section <NUM> of the tooth <NUM> has a thickness less than that of the section <NUM> of the tooth located inward of the perimeter section. In some versions of the invention, this perimeter section <NUM> is tapered relative to the rest of the tooth <NUM>. In other versions of invention, the perimeter section <NUM> is stepped inwardly relative to the rest of the tooth <NUM>.

Thus it should be understood that a blade of this invention may be constructed so the perimeter of the lock tooth is flush with the perimeter of the adjacent section of the blade with which the tooth is associated. In still other versions of the invention, the blade is shaped so the perimeter of the lock tooth is located inwardly of the perimeter of the section of the blade with which the tooth is associated.

Alternative versions may be employed to form a blade of this invention out of single metal workpiece. For example, it is within the scope of this invention, that the whole of the blade, the lock tooth (or teeth) the blade body and the cutting teeth are formed out of material that is relatively soft. Then portions of the blade other than the lock teeth are selectively hardened.

One means of so manufacturing the blade is described by reference to the flow chart of <FIG>. Initially, the blade or, more often plural blades, are cut from a relatively soft metal, step <NUM>. One such metal is a <NUM> Series Stainless Steel such as a <NUM> Stainless Steel. This sheet has a thickness of approximately <NUM>. The blades are laser cut. In this cutting process, the basic perimeters of the cutting teeth and the blade body and formed. As part of this process, the lock teeth are partially shaped. More specifically the stock from which the blade is formed is shaped so as to define the outer perimeters of the lock teeth.

An optional part of step <NUM> is the machine grinding of the partially formed blade so as to sharpen the edges of the cutting teeth.

In a step <NUM> the whole of the blade is hardened. In one version of this method of the invention, the blade is hardened by diffusing a hardening agent into the blade. This agent is diffused into the blade below the surface of the blade. One hardening agent that can be diffused into the blade is carbon. For example, in one diffusion process, the blade is heated to a temperature between <NUM> and <NUM>. Carbon is diffused into the whole of the blade to a depth of between <NUM> and <NUM>. One such process is the process of Kolsterising that is performed Bodycote plc of Macclesfield, Cheshire, United Kingdom. As a result of this diffusion of material into the blade, the blade has a hardened outer layer. This hardened outer layer extends to and is part of the lock teeth.

Once the blade is hardened, in a step <NUM>, sections of the hardened layer that are parts of the lock teeth are removed. For example, when the blade of <FIG> is fabricated, material is removed to define the wings 154b. The blade 140b of <FIG> is understood to be a variation of blade <NUM> of <FIG>. The removal of this material removes the sections of the hardened layer that would have been above the wings 154b. The removal of material in step <NUM> may be accomplished by electro-discharge machining or grinding.

It should be understood that in this method of manufacture the bodies 152b of the lock teeth 150b retain their hardened outer layers. In <FIG>, the hardened outer layer is represented by the stippling that extends of the blade body 148b as well as the bodies 152b of the lock teeth 150b. The absence of the stippling of the wings 154a of the lock teeth 150b represents that these sections of the lock teeth do not include the hardened outer layers. Thus, in these versions of the invention, while sections of the lock teeth 150b are relatively ductile, other sections of the lock teeth may be as hard the cutting teeth.

Once the blade is fully shaped, the blade is cleaned, sterilized and packaged, step <NUM>. Upon the complete of step <NUM>, the blade is ready for shipment and eventual use.

It should be understood that the method of <FIG> may be used to fabricate of a blade of this invention wherein the lock teeth have a constant thickness. In order to manufacture this version of the blade, a version of step <NUM> is executed so as to remove the hardened layers over the whole of each lock tooth.

In variations of the method of manufacture of <FIG>, the hardened layer may be removed by laser etching, grinding or the selective application of an abrasive material against the lock teeth.

In a variation of this method of manufacture, the whole of the blade is formed. A mask is deposited over the sections of the lock teeth that are to remain relatively ductile. Once the mask is formed, the hardening agent is diffused into the blade. The sections of the blade into which the hardening agent is diffused thus develop a hardened outer layer. The mask prevents the hardening agent from diffusing into the mask section (or sections) of the lock teeth. After the mask is removed, these sections of the lock teeth are thus more ductile than at least the cutting teeth of the blade.

In some versions of this method of manufacture of this invention, the removal of the portions of the lock teeth to form the wings or other reduced thickness sections of the lock teeth is performed before the hardening agent is diffused in the blade so as to form the hardened outer layer. In other versions of this method of manufacture, after the hardening process is completed, the blade is subjected to the final shaping to form the reduced thickness sections of the lock teeth.

Other processes may be employed to harden at least the cutting teeth of the blade while leaving the lock teeth relatively soft and ductile. In an alternative process, the sections of the blade to be hardened are hardened by bombarding these sections of the blade with nitrogen ions. Alternatively, once the blade is formed a coating may be applied to at least the cutting teeth to harden these teeth relative to the lock teeth. One coating that can be applied is titanium nitride coating. An alternatively hardening coating that can be applied is a diamond like carbon coating.

In a variation of this process, the hardened coating is applied to the whole of the blade. The coating is then removed from the sections of the lock teeth that should be more ductile than the cutting teeth. The same process, electro-discharge machining, laser etching, grinding or abrasive application used to remove the hardened diffused layer may be employed to selectively remove the hardened coating.

Alternatively, when a coating is applied to harden at least the cutting teeth of the blade, a mask is applied to the sections of the blade that is not be provided with the coating. Once the coating process is completed, the mask is removed.

Another means to selectively harden at least the cutting teeth of the blade so they are harder than the lock tooth (or teeth) is a selective heating process. In a selectively hardening process, a laser is typically applied to the blade to only heat the portions of the blade to be hardened. The photonic energy of the laser is used to heat the portions of the blade to be hardened to a temperature that is higher than the annealing temperature of the material. The heated portion (or portions) of the blade are cooled. This cooling is performed at a rate that is typically faster than the rate of cooling for an annealing process. As a result of this rapid cooling, the heated portion (or portions) of the blade is (are) locked into a state in which it (they) are harder than prior to the heating.

From the above it should be clear that in some versions of the invention, the blade is fabricated so that the lock tooth (or teeth) and body are of the same hardness and only the cutting teeth is harder than the lock tooth (or teeth). Likewise in some versions of the invention, the blade may be formed so sections of the blade body close to the cutting teeth are relatively hard and sections the blade body close to the lock tooth (or teeth) are softer.

For the purposes of this invention it is understood that a rasp is considered a species of a saw blade. A rasp is a file like cutting attachment. A rasp is typically, but not always, reciprocated back and forth along a line collinear with the longitudinal axis of the body of the rasp. A rasp 202a is generally seen in <FIG>. The rasp 202a is an alternative version of the reciprocating saw blade <NUM> of <FIG>. The rasp 202a is formed so the teeth <NUM> extend outwardly from the major surfaces of the body <NUM>. This is different from a conventional saw wherein the teeth project out from the edge surfaces of the blade body. When this invention is implemented as a rasp, the deformable lock tooth or lock teeth <NUM>, <NUM>, <NUM> extend outwardly from the body of the rasp in the vicinity of the proximal end of the body. The cutting teeth project outwardly from the major surfaces body of the rasp at the distal end of the rasp.

It should likewise be appreciated that the shapes of the saw unit anvil and press track the arrangement of lock held in place by the anvil and press. If the lock teeth are arranged linearly, than so are the features of the anvil and press that coin the lock teeth.

Claim 1:
A surgical saw (<NUM>), said saw including:
a body (<NUM>);
a coupling assembly (<NUM>, <NUM>, <NUM>, <NUM>) moveably mounted to the body adapted to releasably hold a saw blade (<NUM>, 140a, 140b, 140b, 140c, <NUM>, 202a, <NUM>, <NUM>) to the coupling assembly, the coupling assembly including: an anvil (<NUM>) and a press (<NUM>), said press capable of movement towards and away from the anvil, wherein said anvil or said press is formed with at least one channel (<NUM>) and the other of said press or anvil includes at least one press foot (<NUM>) capable of being received in the channel; and an assembly for selectively bringing the press towards and away from the anvil; and
a motor (<NUM>) internal to the body (<NUM>) that is connected to the coupling assembly so as to cause the reciprocating movement of the coupling assembly and the like reciprocating movement of the saw blade to be held by the coupling assembly,
characterized in that:
said anvil (<NUM>) or said press (<NUM>) is formed with plural channels; and the other of said press or anvil includes plural said press feet (<NUM>), said press feet being positioned to seat in separate channels; and
the assembly for selectively bringing the press towards and away from the anvil is adapted to selectively bring the press towards and away from the anvil so that, when the press is brought towards the anvil, a press foot presses a lock tooth (<NUM>, 150a, <NUM>, <NUM>, <NUM>, <NUM>) associated with the blade into a channel (<NUM>) associated with the press foot so that the at least one of the press or anvil coins the lock tooth.