WO1995022934A1

WO1995022934A1 - Surgical chisel tool and method

Info

Publication number: WO1995022934A1
Application number: PCT/US1995/002353
Authority: WO
Inventors: Henry H. Fletcher; Andy Oushakoff
Original assignee: Synvasive Technology, Inc.
Priority date: 1994-02-23
Filing date: 1995-02-23
Publication date: 1995-08-31

Abstract

A surgical chisel tool is provided which includes a housing (10) having a cylinder (32) with a piston (34) which is propelled by compressed gas. A chisel bit assembly (18) is mounted to the tool for sliding movement so that depressing the tool against the work urges the chisel bit assembly (18) to project into the cylinder (32) a distance for striking by the piston (34). The piston (34) is propelled by the introduction of compressed gas and is decelerated as it approaches the chisel assembly (18) to strike it with a force dependent upon the distance the bit assembly (18) projects into the cylinder (32). A selector valve assembly (16) is also provided to enable the tool to be operated in a single shot or reciprocating fashion. Chisel bits (22) are provided and are configured to act to limit their penetration during use.

Description

SURGICAL CHISEL TOOL AND METHOD

BACKGROUND

In surgical procedures it is sometimes necessary to use chisels to cut away unwanted material from a rigid structure such as bones. As but one example, persons having implants such as hip prothesis may, after time, require revision of the joint, i.e., replacement of the implant. Joint revision requires removal of the femoral component of the implant which has been cemented into the shaft canal of the femur. Upon removal of the femoral component, the cement in the canal must be removed to prepare the canal to receive the replacement implant component and the cement used to hold the new component in place.

Heretofore it has been known, in addition to power drills and burs, to use hand held chisels to remove the cement which stubbornly adheres to the walls and bottom of the femoral shaft canal. Removal of the cement requires that the cement be aggressively attacked. However care must be taken not to damage the femur and related soft tissue. Accordingly, removal of the cement requires precision as to the amount and application of force necessary to remove the cement without damaging surrounding structures.

Pneumatically powered chisels are known and are useful to reduce the time necessary for the surgical procedure. These chisels mount one of a selection of chisels substantially rigidly to the tool. A trigger ports compressed air to pneumatically drive a piston in a reciprocating fashion to repeatedly strike the chisel and drive the chisel for cutting. To control chisel cutting force, the chisel trigger operates a proportion valve which controls air pressure provided to the piston and in turn the force imparted by the piston on the chisel.

A drawback with prior power chisels is that the reciprocating or rapid fire chisel does not provide an effective means to apply a single chisel impact which, during removal of cement under certain conditions, can be highly desirable. Occasions arise wherein the surgeon needs to precisely control chisel impact to one blow as opposed to a burst of rapid fire blows. The proportion valve and structures of the prior power chisels are ineffective in this regard. Still another drawback is that the proportion valve of prior tools is often inadequate to control the magnitude of the force imposed on the chisel, particularly while the piston is reciprocating and vibrating the tool. That force imparted to the chisel is dependent upon trigger position which may be difficult to gauge with any precision. Force control is advantageous to remove the cement without damaging the surrounding structure such as the femur.

There is, therefore a need for a surgical chisel which can overcome the problems and drawbacks noted above.

SUMMARY

A surgical chisel is provided that satisfies the need for chisel force control as well as providing for selection between (i) a single shot or chisel strike and (ii) reciprocating or repeating operation. This surgical chisel comprises (i) a chisel assembly, the chisel assembly includes a bit, one end of which defines the cutting tip for the chisel and (ii) a housing to receive the chisel assembly. Within the housing is a mount having an opening to pass the chisel assembly. A guide is disposed on the housing for slidable movement relative to the mount, the guide cooperating with the mount to retain the chisel assembly to the housing. Upon application of force to the bit as by pressing down on the tool, the chisel assembly is urged to project through the opening and from the mount a distance into the housing to a position for striking. A driver is provided in the housing to strike the chisel assembly when it projects from the mount. The driver is configured to impose a greater force on the chisel assembly the greater the distance the assembly projects from the mount.

Where the driver is a pneumatic or gas driven piston, the distance dependent driving force can be provided by driving the piston in a closed cylinder toward the mount. Gas trapped in the cylinder between the piston and mount during at least a portion of the piston stroke is compressed to decelerate the piston and strike the chisel assembly with a greater force the more the assembly projects into the cylinder. Additionally a bias such as a spring can act to decelerate the piston.

In another aspect of the invention, the tool driver is a piston in a cylinder. A valve selectively ports compressed gas to the cylinder to drive the piston for a single stroke or reciprocating strokes to drive the chisel assembly. By selecting the mode, the surgeon can thereby select between a single shot or reciprocating mode. In another aspect of the present invention chisel bits are set forth for the tool. Each bit has a tip configured to remove unwanted material such as bone cement and is configured to limit insertion of the tip into the cement. Opposite the tip each bit has a drive end configured to register with the tool upon insertion and cooperate with the tool upon registry to prevent rotation of the bit relative to the tool. The drive end is also configured for releasable coupling to the tool.

DRAWINGS These and other features and advantages of the present invention will become apparent upon reference to the specification claims and drawings wherein:

Fig. 1 is a side sectional view of a partially exploded surgical chisel tool according to the present invention;

Figs. 2A-2C are further views of a portion of the tool of Fig. 1 showing passageways for the compressed gas operation of the tool;

Figs. 3A and 3B are, respectively, a top partial section view and an end view of a chisel bit for use with the tool of Fig. 1 ;

Fig. 3C are partial top views of the chisel having tips different from that of Figs. 3A-3B.

Fig. 4 is an end view of a rear valve body for a selector valve assembly of the chisel tool of Fig. 1 ;

Fig. 5 is an end view of a front valve body for the selector valve mechanism of the chisel tool of Fig. 1 ;

Fig. 6 is a partial sectional view of the tool of Fig. 1 in a selected single shot mode; and

Fig. 7 is a partial sectional view of the tool of Fig. 1 in a selected reciprocating mode. Turning to Fig. 1 , a chisel tool according to the present invention is shown. The tool has a housing as 10 including a portion of which is fashioned into a grip 12 suitable for holding the tool is one's hands, for example a pistol grip. Mounted to the housing in the manner described below is a nose assembly 14 as well as a selector valve assembly 16.

The tool is adapted to drive a chisel assembly 18 which includes an anvil 20 as well as a selected chisel bit 22. As shown in Figs. 1 , 3a and 3b, the bit 22 is generally cylindrical necking down to define a cutting tip 24 opposed by a drive end 26 which, when the bit is received by the tool will abut the anvil 20. The drive end 26 is generally cylindrical having fashioned thereon opposite flats 28 as well as opposing cylindrical circumferential notches 30 arranged substantially transverse to and intersecting the flats 28 the purposes of which will hereinafter become evident. A larger diameter pilot 29 is disposed proximate the notches 30. It is to be understood that while one embodiment of a chisel bit is illustrated for purposes of description, that chisel bits having various cutting tips and configurations are adapted to be interchangeably used with the tool.

The tip 24 of the bit 22 of Fig. 3A is shaped in substantially a V shape. Accordingly as the bit 22 is driven more of the tip 24 is caused to penetrate the material against the resistance offered thereby due to presentations of more of the cutting edge of the tip 24 and the configuration of the bit 22 necking down to fashion the tip 24. Accordingly chisel bit insertion can, to a degree, be limited due to the configuration of the bit 22 necking down to define tip 24. As more of the bit 22 and tip 24 is inserted more resistance is offered to limit progression of the tip 24 into the material.

With reference to Fig. 3C other tips 24a and 24b are shown for the bit 22. Tip

24a is forked to define tines 25. Again, as the bit 22 is driven the tines 25 penetrate however once the full profile of the tip 24a begins to penetrate, penetration is resisted and, to a degree, limited.

With reference to tip 26b, it presents an angled cutting surface. As more of tip

24b is inserted the contour of the tip 24b, in combination with the necking of cylindrical bit 22 acts to limit penetration.

Defined within the housing 10 and defining a longitudinal axis 31 for the tool as best shown in Fig. 1 is a cylinder 32 receiving a piston 34. At one end of the cylinder 32 there is rigidly fixed to the housing an anvil mount 36 and at the other end a resilient bumper 38. The cylinder 32 is generally closed to provide for the driving of the piston 34 between the bumper 38 and the mount 36 with pressurized gas such as air in a manner hereinafter described.

The mount 36 has an opening 40 therethrough to slideably pass and guide the anvil 20. As can be seen, the anvil 20 has a shank 42 with a larger diameter head 44. The opening 40 reduces in diameter proximate to the cylinder 32 to closely pass and guide the anvil shank 42. An O-ring 46 seals the shank 42 and the mount 36 to prevent gas from escaping from the cylinder 32. The narrowing of the opening 40 proximate the cylinder 32 in cooperation with the larger diameter head 44 also limits the travel of the anvil 20 and, as described below, the projection of the anvil shank 42 into the cylinder 32. Opposite the cylinder 32 the mount 36 includes a pair of pins 48 which are generally parallel and tangentially intrude into the opening 40. The pins 48 act to limit the travel of the anvil 20 in a direction away from the cylinder 32 and accommodate insertion of the chisel bit 22 into the tool. A spring 49 disposed in the opening 40 acts to bias the anvil 20 to a withdrawn position within the opening 40 as shown in Fig. 1 .

Proximate the anvil 36 the nose assembly 14 includes a front locking ring 50 which in turn mounts a locking sleeve 52 to the tool such that the locking sleeve 52 can rotate relative to the front locking ring 50 between a first or open position to a second or locking position. For this purpose the front locking ring 50 has a rim portion 54 including an arcuate track (not shown) adapted to receive a ball 56 urged to maintain contact with the track by a spring 58 during rotation of the sleeve. The track at its ends has spherical seats (not shown) to nest the ball 56 when the locking sleeve is at each of the open and locked positions. The front locking ring 50 also includes a threaded portion 60 threaded to the housing 10 to rigidly fix the front locking ring 50 thereto.

The locking sleeve 52, which is secured to the front locking ring 50 for rotation between an open and locking position, is generally conical; however it can have any suitable shape. A bore 62 is fashioned in the locking sleeve 52 to pass chisel bit 22 in the manner hereinafter described for releasably mounting the bit 22 to the tool. The bore 62 is counter sunk to define an annular stop 64 for purposes of which will hereinafter become evident. The locking sleeve 52 also includes a cylindrical collar 66 which extends to be received between the anvil mount 36 and the front locking ring 50. The collar 66 is fashioned to have diametrically opposed channels 68 to extend toward the mount 36. To cooperate with the chisel assembly 18 to provide for control over force applied to the chisel bit 22 for cutting and to releasably secure the chisel bit 22 to the tool, the nose assembly 14 further includes a guide 70 disposed for sliding movement relative to the mount 36. As shown in Fig. 1 , the guide 70 is generally a hollow cylinder and is shaped so as to be slideably received by the counter sink of the bore 62. A smaller diameter, cylindrical neck 72 for the guide 70 is received in the bore 62. As can be appreciated with reference to Fig. 1 , the sliding movement of the guide 70 in a direction away from the anvil mount 36 is limited by the annular stop 64 fashioned in the locking sleeve 52. Resilient O-rings 74 cushion the engagement between the guide 70 and the stop 64. The rearward movement of the guide 70 is limited by contact with the mount 36. A spring 76 normally urges the guide 70 in a direction away from the mount 36 and against the O-rings 74 as shown in Fig. 1 .

To key the guide 70 to the locking sleeve 52, diametrically arranged balls 78 on the guide 70 are each trapped in a channel 68 of the locking sleeve collar 66. Accordingly, the locking sleeve 52 and the guide 70 are keyed for mutual rotation between the open and locking positions while permitting the guide 70 to slide toward and away from the mount 36.

To provide for the releasable mounting of the chisel bit 22 to the tool and for interchange thereof, the guide 70 further includes a pair of parallel arranged pins 80 which define opposed shoulders in the guide 70. As can be appreciated in Fig. 1 , the pins 80 are spaced apart from one another approximately the same distance as are the pins 48 for the mount 36.

To mount the chisel bit 22 to the tool, the pin pairs 80 and 48 cooperate to require registry with the chisel bit flats 28 for insertion of the bit 22 to a position to abut the anvil 20. Attempted insertion of the chisel bit 22 in an orientation such that the flats 28 are out of registry with the pins 80, 49 will prevent full insertion of the bit 22. Upon proper insertion of the chisel bit as registered by the pins 80 and 48 to a position where the drive end

26 abuts the anvil 20, locking sleeve 52 and the guide 70 keyed thereto are rotated from the open to the locking position whereupon the pins 80 rotate through 90 degrees to nest the shoulders defined thereby in the notches 30 to lock the chisel bit 22 to the guide 50 in an abutting relationship with the anvil 20. In the locking position, the spring 76 and 49 urge the bit 22 to a position whereat the anvil shank 42 is fully withdrawn into the mount 36. Pressing on the tool against the tip 24 of the bit 22 urges the chisel assembly 18 to retract into the tool and the anvil shank 42 to be projected from the mount 36 into the cylinder 32 for striking by the piston 34 in a manner described below. Greater pressure on the tip 24 urges the shank 42 to extend a greater distance into the cylinder 32. Release of the bit 22 retracts the chisel assembly 18 and more particularly anvil shank 42 from the cylinder 32 by virtue of the bias of the springs 76 and 49. The pilot 29 cooperates with bore 62 to stabilize and support the bit 22.

The pins 48 in cooperation with the bit flats 28 also prevent rotation of the bit 22 relative to the guide 70 and the tool and maintain proper registry.

To remove the bit 22, the locking sleeve 52 is rotated from the locking to the open position whereupon the shoulders defined by pins 80 disengage the notches 30 on the bit 22 releasing the bit 22 for removal from the tool.

As can be appreciated, the guide 70 provides for the locking of the selected bit 22 to the tool and also provides for the projection of the chisel assembly 18 into the cylinder 32 when the tool is pressed down on the bit 22.

To drive the piston 34 a supply of compressed gas is provided to the tool through a coupling 82. In a well known fashion the coupling 82 includes a vent line 84 surrounding an axially disposed compressed gas supply line 86. The compressed gas used to drive the piston 34 is vented in a manner described below to coupling vent 84 where it is vented away from the surgical site.

To selectively drive the piston 34 the tool includes a trigger assembly 88 having a trigger actuator 90. The actuator 90 operates the stem 92 of an actuator valve 94. The actuator valve 94 is disposed in a valve body 96 which defines a seat 98 to seat the actuator valve 94. The valve body 96 includes an annular chamber 100 which communicates with an annulus 102 the purpose of which will hereinafter become evident. Depressing on the trigger actuator 90 displaces the actuator valve 94 from the seat 98 to conduct compressed gas from the supply 86 through supply passageway 103 fashioned in the grip 12 into the chamber 100 and therefrom to the annulus 102. Release of trigger assembly 88 seats the actuator valve 94 on the seat 98 stopping the supply of compressed gas.

With reference to Figs. 2A-2C additional passageways will now be described for the ducting and venting and compressed gas for the operation of the tool. With reference to Fig. 2A the supply passageway 103 is shown to provide communication between the supply line 86 and the actuator valve 94. With reference to Fig. 2B a second passageway 104 is shown which provides communication between the annulus 102 and the selector valve assembly 16 in the manner hereinafter described. Actuation of the actuator valve 94 conducts air from the supply line 86 through the trigger assembly 88 to second passageway and to the selector valve assembly 16.

With reference to Fig. 2C, a vent line 106 is shown which provides communication with the cylinder 32 and a second annulus 108 at trigger assembly valve body 96. The second annulus 108 in turn communicates with a second vent passageway 110 which in turn communicates with the vent 84. The first vent line 106 communicates with the cylinder 32 substantially midway between the mount 36 and the bumper 38. A return passageway 1 12 functional while the tool is in a single shot mode is also provided in the housing 10 to provide communication between the cylinder 32 proximate the mount 36 and the selector valve assembly 16.

With reference to Figs. 1 , 4-7 the selector valve assembly 16 will now be described.

The selector valve assembly 16 includes a front valve body 114 which is positioned in an abutting relationship with bumper 38. The front valve body 114 has an axial port 116 which registers with an opening (not shown) in the bumper 38 to communicate compressed gas in the fashion hereinafter described into the cylinder 32 to propel the piston 34 toward the mount 36 and chisel assembly 18. An annular recess 118 spaced from and circumscribed about the port is provided and defines a cylindrical seat 119.

To cooperate with the front valve body 114 is a rear valve body 120 generally cylindrical in shape and as shown in Figs. 6 and 7 disposed in an abutting relationship with rear valve body 120. The rear valve body 120 has a center bore 121 to receive a cylindrical valve sleeve 122. The center bore 121 for the rear valve assembly 120 has a coaxial counter sink proximate the front valve body 114 to receive a valve disk 124 which is normally urged by a spring 126 nested in annular recess 118 in a direction away from the front valve body 114 and seat 119 to uncover the port 116. In addition to the centerbore 121 , the rear valve body 120 also includes as best shown in Fig. 5 first and second slots 128, 130 defined in the periphery of the rear valve body 120 proximate the rear valve body 114. The first slot 128 is positioned to register with the second passageway 104 and the front valve body recess 118. The second slot 130 is positioned to register with the return 112. A radial bore 132 extends between the second slot 130 and the centerbore 121 for purposes which will hereinafter become evident.

Returning to Figs. 6 and 7, the valve sleeve 122 and the rear valve body 120 are coupled whereupon rotation of the valve sleeve 122 about its axis urges sleeve 122 axially forward and away from the front valve body 114. For this purpose, the rear valve body 120 may have a pair of opposing tabs 134 which engage a spiral grove 136 fashioned in sleeve 122. Accordingly rotation of the sleeve 122 causes the tabs 134 in cooperation with grove 136 to move the sleeve 122 toward and away from the front valve body 114.

To hold the front and rear valve bodies 114, 120 to the housing 10, the tool further includes a rear locking ring 138 threadedly coupled to the housing 10. The rear locking ring 138 retains the aforementioned valve bodies in abutting position. A pin 139 disposed between the housing 10 and the rear valve body 12 secures the rear valve body 120 against rotation within the housing 10.

The selector valve assembly has a knob 140 rotatable relative to the rear locking ring 138 to one of three positions. To accommodate the rotation of the knob 140, the rear locking ring 138 has an arcuate track 14 which receives a ball 142 urged by a spring 144 on the knob 140 to maintain ball 142 in contact with the track. Spherical recesses (not shown) at each of the three positions of single shot, reciprocating and safe are provided to retain the knob 140 in any one of the selected positions. Forcible rotation of knob 40 urges the ball 142 against bias of spring 144 from the spherical seat to permit the knob 140 to be repositioned.

The knob 140 is coupled to a knob insert 146 by suitable means such as screws or pins for mutual rotation. The knob insert 146 is generally cylindrical having a pair of opposing and axially extending ways 148 (Fig. 7) each adapted to receive a ball 150 which is mounted to sleeve 122 to key the sleeve 122 to the knob insert 146 and the knob 140 for mutual rotation. Accordingly rotation of the knob 140 and the knob insert 146 likewise rotates the sleeve 122 which, by virtue of the tabs 134 and the groove 136 acts to position the sleeve 122 within the rear valve body 120. With the foregoing structure in mind, the operation of the tool will now be described.

In a safe mode the knob 140 and the knob insert 146 are positioned such that the sleeve 122 is urged to depress disk 124 against its spring 126 to contact and cover the port 116. Depressing the trigger actuator 90 to direct compressed air through the second passageway 104 is thereby ineffective to admit compressed into the cylinder 32 to propel the piston 34. Accordingly inadvertent operation of the tool is prevented while the knob 140 is in the safe position.

Rotation of the knob 140 to a single shot position withdraws sleeve 122 from front valve body 1 14 to free the disk 124 under the urging of the spring 126, to uncover the port 1 16 as shown in Fig. 6. Depressing the trigger actuator 90 unseats the actuator valve 94 from the seat 98 directing compressed air through the trigger assembly chamber 100, the annulus 102 and to the second passageway 104. The compressed air is received at the rear valve body first slot 128 is communicated to the front valve body recess 118 and to the port 116. The compressed air in turn urges the piston 34 to be propelled toward mount 36.

At all times cylinder 32 is in communication with the vent by reason of the vent 106, the second annulus 108 and the second vent passageway 1 10. At initiation of the propulsion of the piston 34, the chamber 32 ahead of piston 34 is therefor at a vent pressure which can be atmospheric or substantially atmospheric. As the piston 34 travels in the cylinder 32, it reaches a point whereat the vent 106 is covered by the piston 34 and accordingly during the remainder of the stroke, gas trapped between the piston 34 and the mount 36 begins to be compressed as the piston 34 is driven to mount 36. The compression of gas ahead of the piston 34 during this portion of the piston stroke acts to decelerate the piston 34 as it approaches the mount 36. Passing the vent 106 the compressed air heretofore directed through the selector valve assembly 16 is directed to the vent 106 and is vented in the manner described above. Holding the trigger actuator 90 in an open or fire position causes the compressed gas fed through the selector valve assembly 16 to the cylinder 32 and to the vent 106 to hold the piston 34 against or substantially against the mount 36. Releasing the trigger actuator 90 and closing the actuator valve 94 on the seat 98 stops the flow of compressed gas whereupon gas is vented through the vent 106 freeing the piston 34 to return to the bumper 38. A return spring 152 urges the return of the piston 34 to the bumper 38.

Accordingly, depression on the trigger actuator 90 causes the tool to provide a single shot to the chisel assembly for the desired cutting. Furthermore, the compression of the gas ahead of the piston 34 as it moves toward the mount 36 as well as the bias imposed by the return spring 152 acts to decelerate the piston 34 during the end portion of its stroke, causing the piston 34 to strike the chisel assembly 18 and more particularly the anvil shank 42 with a greater force the more the shank 42 extends into the cylinder 32. This enables the user of the tool to control the force applied to the chisel assembly 18 by simply pressing on tool and more particularly the bit tip 24 which projects the chisel assembly 18 into cylinder 32. The harder the user presses on the bit 24 the more the shank 42 is projected into the cylinder and, accordingly, the more force that is applied by the piston 34 to the chisel assembly 18 and to the cutting tip 24. Advantageously, therefore, force control of the tool is related to the more force the user pushes on the tool against the work.

In the repeat fire mode as shown in Fig. 7 the knob 140 is positioned such that a bore 154 of the sleeve 122 is brought into registry with the radial bore 132 of the rear valve body 120. The bore 154 of the sleeve 122 provides communication to an axial bore 156 in the sleeve 122. Accordingly, axial bore 156 of sleeve 122, by virtue of the rear valve body second slot 130 and the radial bore 132 is brought in communication with the return line 112 for purposes which will hereinafter become evident.

In the multi shot reciprocating or repeat position, the trigger actuator 90 is depressed conducting compressed gas through the second passageway 104, the first slot 128 to the annular recess 118 under the disk 124 and to the port 116 to propel the piston 134 in the manner described above. As the piston 134 is driven by the compressed gas toward the mount 136, the gas compressed ahead of the piston 134 as described above is also compressed in the return 112 which, by virtue of the second slot 130, the radial bore 132 and the bores 154 and 156 of the sleeve 122, urge the disk 124 to momentarily close the port 116. When closed, the compressed gas is thereby directed above the closed disk 124 back through return line 112 to act, in cooperation with the return spring 152 to return the piston 134 at the end of its stroke back to bumper 36. During the return stroke as the piston 34 covers the vent 106, the valve disk 124 under the urging of the spring 126 again uncovers the port 116 to direct compressed air to propel the piston 34 in the manner described above. Accordingly, it can be appreciated that while the trigger actuator 90 is depressed to direct compressed air to the selector valve assembly 16, the piston 34 will reciprocate within the cylinder 32 to drive the chisel assembly 18 in the manner described above, i.e., with a force applied dependent upon the distance the chisel assembly 18 and more particularly anvil shank 42 projects into cylinder 32 due to the deceleration of the piston 34.

To accommodate the multiple operation of the tool between a single shot and repeated shot operation, the trigger assembly 88 is adapted so as not to act as a proportional valve. That is, upon depressing of the trigger actuator 90 substantially full pressure is ducted to the selector valve assembly 16. Force control is provided by the user simply pressing on the tool against the work as described above providing greater feel and control during the operation of the tool.

As can be appreciated, the cylinder 32 and piston 34 as well as shank 42 can be configured to, for a given gas pressure impose a greater or lesser maximum force on the chisel assembly 18.

It is to be understood that the tool described above is adapted to be used interchangeably with various chisel bits as selected from a set thereof. These bits may have different contoured cutting tips depending on the application.

Although the present inventor has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. For example.the chisel assembly including the bit and anvil described above could simply be embodied as a single bit presented through mount 36 for striking by piston 34. Therefore, the spirit and scope of the appended claims should not be limited to the descriptions of the preferred embodiment or the preferred versions contained therein.

Claims

What is claimed is:

1 . A powered chisel tool comprising:

(a) a housing having a longitudinal axis;

(b) a chisel assembly having a chisel bit; (c) a guide disposed for slidable movement relative to the housing, the guide mounting the chisel bit, application of force to the chisel bit sliding the guide relative to the housing to position the chisel assembly axially within the housing; and

(d) a driver in the housing to strike the chisel assembly as within the housing to drive the bit for cutting with a force dependent upon the axial position of the assembly within the housing.

2. The tool of Claim 1 including a bias to act upon the guide application of force to the chisel bit sliding the mount against the bias to position the chisel drive assembly within the housing.

3. The tool of Claim 1 wherein the guide has at least one shoulder and the chisel bit has at least one notch, rotation of the guide bringing each shoulder into engagement with a corresponding notch defined on the chisel bit to secure the bit to the guide, rotation of the guide disengaging each shoulder from its corresponding notch releasing the chisel bit for removal from the guide and tool.

4. The tool of Claim 1 wherein the driver includes (a) a pneumatic cylinder having at one end a mount, the guide slidable relative to the mount to project the chisel assembly into the cylinder, (b) a piston disposed in the cylinder, (c) a source of pressurized gas, (d) a valve to selectively direct pressurized gas into the cylinder to drive the piston to strike the chisel assembly projected from the mount.

5. The tool of Claim 4 wherein the tool further includes means for deceleration the piston as it approaches the mount to strike the chisel assembly with a force dependent upon the distance the chisel assembly projects into the cylinder.

6. The tool of Claim 5 wherein the decelerating means includes a spring to bias against the piston.

7. The tool of Claim 5 wherein the cylinder is closed, the piston compressing gas ahead of it as it approaches the mount to decelerate the piston.

8. The tool of Claim 7 further including a spring disposed in the cylinder to act against the piston to decelerate the piston as it approaches the mount.

9. A chisel tool for removing cement from bone comprising: (a) a housing;

(b) a mount secured to the housing, the mount having an opening therethrough;

(c) a sleeve attached to the housing for rotation between an open position and a locked position;

(d) a chisel assembly including a bit, the chisel assembly disposed to extend into the opening of the mount;

(e) a guide keyed to the sleeve for rotation therewith between the open and locked position and slidable toward and away from the mount, rotation of the sleeve to the lock position coupling the chisel assembly to the sleeve, sliding of the sleeve a distance toward the mount projecting the chisel assembly a like distance from the mount; and (f) a driver to strike the chisel assembly as projected from the mount opening to drive the bit for cutting with a force dependent upon the distance of the projection of the assembly from the mount.

10. The tool of Claim 9 wherein the chisel assembly includes an anvil slideably disposed in the mount opening and a removable bit adapted to be inserted into the guide to abut the anvil when the sleeve and guide are in the open position, rotation of the sleeve and guide to the locked position coupling the bit to the guide to slide therewith to project the anvil from the mount for striking by the piston.

1 1 . The tool of Claim 10 further including a bias disposed to urge the guide in a direction away from the mount, application of force on the chisel assembly bit sliding the chisel assembly against the bias to project the anvil from the mount.

12. The tool of Claim 1 1 wherein the guide includes at least one shoulder and the bit has at least one notch, rotation of the guide to the locked position locating each shoulder in a corresponding notch to couple the bit to the guide, rotation of the guide to the open position disengaging each shoulder from its notch to release the bit for removal.

13. The tool of Claim 12 wherein the guide has a bore to receive the bit and at least one pin tranverseley intersecting the bore to define the shoulder.

14. The tool of Claim 13 having a pair of parallel pins disposed to intersect the bore to define the shoulders, the bit including a pair of notches each adapted to receive a shoulder when the guide is in the lock position to couple the bit to the guide.

1 5. The tool of Claim 13 wherein the bit has flats cooperating with the pins to register the receipt of the bit into the guide bore and restrain the bit against rotation relative to the guide.

1 6. The tool of Claim 10 wherein the driver includes (a) a pneumatic cylinder having at one end the mount, (b) a piston disposed in the cylinder, (c) a source of pressurized gas, (d) a valve to selectively direct pressurized gas into the cylinder to drive the piston to strike the chisel assembly projected from the mount.

17. The tool of Claim 1 6 further including means for decelerating the piston as it approaches the mount to strike the chisel assembly with a greater force the greater the distance it projects from the mount.

18. A surgical chisel operated by compressed gas comprising:

(a) a housing;

(b) a chisel assembly having a cutting tip and an opposed anvil; (c) a cylinder defined in the housing having at one end a mount with an opening to receive the anvil for projection of the anvil into the cylinder;

(d) a piston disposed in the cylinder;

(e) a selector valve assembly adapted to be selectively positioned at a first or second operational mode, the first mode directing compressed gas to drive the piston for a single stroke to strike the anvil with a single blow and the second mode directing compressed gas to drive the piston to reciprocate within the cylinder to repeatedly strike the anvil; and

(f) an actuator to control the supply of compressed gas to the selector valve assembly.

19. The chisel of claim 18 further including a guide adapted to mount the chisel assembly for sliding movement to project the anvil a selected distance into the cylinder.

20. The chisel of Claim 19 wherein the cylinder is closed, gas compressed in the cylinder as the piston approaches the mount to decelerating the piston to strike the anvil with a force dependent upon the distance the anvil projects into the cylinder.

21 . The chisel of Claim 20 further including a bias to cooperate to decelerate the piston.

22. A surgical chisel operated by compressed gas comprising:

(a) a housing; (b) a chisel assembly having a cutting tip and opposing anvil;

(c) a cylinder defined in the housing, the cylinder having at one end a mount with an opening to receive the anvil for projection of the anvil into the cylinder;

(d) a piston disposed in the cylinder;

(e) a selector valve assembly having a port communicating with the cylinder and a valve disk, the selector valve assembly positionable in any one of (i) a safe position where the valve disk closes the port, (ii) a single shot position where the disk is displaced from the port to admit compressed gas into the cylinder to propel the piston to stroke the anvil with a single blow in the cylinder for a single stroke, and (iii) a reciprocating position where the disk cycles to open and close the port to propel the piston in a reciprocating fashion to strike the anvil with repeated blows; and

(f ) an actuator to selectively supply compressed gas to the selector valve assembly.

23. The chisel of Claim 22 further including means for movably mounting the chisel assembly to project the anvil a selected distance into the cylinder.

24. The chisel of Claim 23 further including means for decelerating the piston as it approaches the mount to strike the anvil with a force dependent upon the distance the anvil projects into the cylinder.

25. The chisel of Claim 20 wherein the deceleration means includes the cylinder being closed whereupon gas is compressed by the piston as it approaches the mount to decelerate the piston.

26. A surgical chisel operated by compressed gas comprising: (a) a housing;

(b) a chisel assembly having a cutting tip;

(c) a cylinder defined in the housing having at one end a mount with an opening to receive the chisel assembly for projection of the chisel assembly into the cylinder;

(d) a piston disposed in the cylinder; (e) a selector valve assembly adapted to be selectively positioned at a first or second operational mode, the first mode directing compressed gas to drive the piston for a single stroke to strike the chisel assembly with a single blow and the second mode directing compressed gas to drive the piston to reciprocate within the cylinder to repeatedly strike the chisel assembly;

(f ) a guide disposed for slidable movement relative to the mount, the guide mounting the chisel assembly in a position to project from the mount, application of force to the chisel assembly sliding the guide to project the chisel assembly a distance from the mount; and

(g) a driver to strike the chisel assembly as projected from the mount to drive the chisel assembly with a force dependent upon the distance the chisel assembly projects from the mount.

27. The chisel of claim 26 wherein the guide is rotatable relative to the chisel assembly and includes at least one shoulder, the chisel assembly having at least one notch, rotation of the guide positioning each shoulder in a notch to secure the chisel assembly to the guide.

28. A method for chiseling cement from bone comprising:

(a) selecting a chisel assembly having a desired cutting tip;

(b) removeably attaching the chisel assembly to a housing, the housing having a guide disposed for slidable movement relative to the housing, the guide removeably attaching the chisel assembly to the housing; (c) urging the cutting tip against the bone to slide the guide and position the chisel assembly relative to the housing; and

(d) driving the chisel assembly with a force dependent upon the position of the chisel assembly within the housing to chisel the cement from bone.

29. The method of claim 28 wherein the chisel assembly includes a removable bit having the desired cutting tip, the removable attaching step including inserting the bit into the guide and rotating the guide to a locked position to interlock the guide to the bit.

30. The method of claim 29 wherein the driving step includes propelling a piston in a cylinder to strike the chisel assembly, the method further including setting a selector valve to either of a single shot or reciprocating mode and depressing a trigger, depressing the trigger with the selector valve in the single shot mode propelling the piston for a single strike of the chisel assembly and depressing the trigger with the selector in the reciprocating mode reciprocatingly propelling the piston to repeatedly strike the chisel assembly.

31 . A removable chisel bit for a bone chisel tool comprising: a chisel bit having at one end narrowed to define a tip configured for cutting unwanted material from a bone and an opposite drive end adapted to receive impact for driving the bit when the bit is mounted to the tool, the opposite end having at least one flat for registering the positioning of the bit in the tool and at least one notch adapted to receive a shoulder on the tool to removeably couple the bit to the tool.

32. The bit of claim 31 having a pair of flats and a pair of notches, the notches arranged substantially transverse to the flats.

33. The bit of claim 31 wherein the tip has a V-shape.

34. The bit of Claim 31 wherein the tip has a forked configuration.

35. The bit of claim 31 wherein the tip has an angled cutting surface.