Surgical cutting instrument

Abstract

A surgical tool for cutting bones, casts and the like including a housing having a cutting knife extending from its forward end. The cutting knife is pivoted to a plunger which is movably disposed within one end of the housing while a piston is normally positioned at the other end. The piston is accelerated under air pressure to impact the plunger thereby causing the knife to move through a cutting stroke. Suitable valve means are provided to control the entry and venting of compressed air to and from the housing.

Description

BACKGROUND OF THE INVENTION

This invention relates to surgical instruments and, more particularly, to a tool for cutting bones and the like during surgical operations.

During surgery, especially in the chest cavity region, it is often necessary for the physician to obtain access to areas which are obstructed by bone structure. One example is in open heart surgery where unobstructed access to the hear is a necessity. In this case, the sternum or breastbone covers the chest cavity and prevents the required access. Therefore, the sternum must be cut to enable the surgeon to work.

Various types of apparatus have been used to cut through bones during surgery. For example, a hand-held chisel-type instrument has been employed wherein the knife end of the chisel is held against the bone while the surgeon taps the other end with a mallet. This type of device is not entirely satisfactory since it is difficult to control the direction of the chisel and, additionally, the surgeon must make a conscious effort to avoid hitting the patient with the mallet. Another bone cutting instrument in current use is a compact saber-saw type device sometimes referred to as a "Sarnes" saw. However, the depth of cut of such an instrument is not always precisely controllable and its use may result in inadvertently cutting into an organ. Further, this device is actuated by a foot pedal which has been found to be rather cumbersome. Still another instrument used in surgical applications of the type described is a circular-type saw whose blade traverses an arcuate cutting stroke, commonly known as a "Stryker" saw. This instrument is rather slow in operation and its depth of cut is rather limited due to the configuration of its gearbox. Further, it is possible that the saw may inadvertently damage underlying tissue during the cutting operation.

OBJECTS OF THE INVENTION

Accordingly, an object of this invention is to provide a new and improved surgical cutting instrument.

Another object is the provision of a new and improved surgical cutting instrument for bones and the like having a configuration especially suitable for cutting the sternum or breastbone.

Still another object is to provide a new and improved surgical cutting instrument whose cutting rate and direction is precisely controllable and is capable of being operated using only one hand.

A further object is to provide a surgical cutting instrument wherein the cutting knife has an arcuate cutting stroke whose action is away from the thoracic contents.

A still further object is to equip the cutting knife with safety features so that the danger of mishaps during surgery is lessened.

A still further object of this invention is to provide a new and improved valve system for controlling the entry and venting of compressed air to and from the instrument.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of this invention, these and other objects are attained by providing a surgical instrument in which a knife having an end yoked to a plunger is located within a housing. A piston is provided rearwardly of the plunger and is accelerated by an air drive to move forwardly and impact the plunger thereby moving the knife through a cutting stroke. The knife forms an angle with the housing and has a cutting edge which moves tranversely during a cutting stroke. A valve system forms a part of the air drive and operates in a manner such that the depression of a trigger causes the knife to move through a single cutting stroke. To repeat another stroke, the trigger must be released and then depressed again.

DESCRIPTION OF THE DRAWINGS

A more complete description of the invention and its advantages will be readily appreciated by reference to the following detailed description when considered in connection with the accompanying drawings in which:

FIG. 1 is a side view of the surgical cutting instrument of the present invention illustrating a typical application;

FIG. 2 is a side view in partial section of the instrument illustrating the movement of the knife;

FIG. 3 is a view of the knife in section taken along line 3--3 of FIG. 2;

FIG. 4 is a view of the knife in section taken along line 4--4 of FIG. 2;

FIG. 5 is a top view partially broken away showing the valve structure of the instrument;

FIG. 6 is a view in section taken along line 6--6 of FIG. 2;

FIG. 7 is a view in section taken along line 7--7 of FIG. 2;

FIG. 8 is an enlarged detail view in section of the valve showing the compressed air entry passage and venting passage closed; and

FIG. 9 is an enlarged detail view in section of the valve system showing the venting passage closed and the compressed air entry passage open.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein like reference characters designate identical or corresponding parts throughout the several views, FIG. 1 illustrates the instrument 10 of the present invention used to cut through the sternum, or breastbone, of a patient. This is one typical use of the instrument. The instrument 10 includes a generally cylindrical housing 12 and a knife 14 operably connected to the housing's forward end. Generally, one end of a flexible tube 16 is coupled to a fitting extending from the rear of housing 12 while the other end (not shown) is coupled to a source of compressed air or other suitable gas for driving the knife. The lower end, or protective shoe, 18 of the knife 14 is inserted within the clavicular notch in the sternum 22 of a patient 24 situated at the top of the sternum at the base of the neck. As seen, the instrument is held so that the top surface of guide 18 engages the lower surface of the sternum, resulting in the knife being accurately positioned. Upon depressing a trigger 28 (FIG. 5), knife 14 travels through a cutting stroke transverse to the knife edge in the direction of arrow 26. Upon releasing trigger 28, knife 14 returns to its original retracted position. In this manner, a surgeon may guide the instrument 10 in a desired path at a precisely controlled rate.

As shown in FIG. 2, housing 12 is formed by a generally cylindrical barrel 30 connected to a threaded cap member 32. A piston 34 is normally held by a spring 36 against the edge of a bumper 38 which is integrally formed with an end plug 40, which plug is threaded into the rear end of housing 12 to make an air-tight seal at that end. The rear surface 42 of piston 34 and the forward surface 44 of bumper 38 define a chamber 45 into which compressed air is admitted through a valve (described below) at the initiation of a cutting stoke. A pair of O-rings 46 are fastened around the outer surface of piston 34 to prevent compressed air from leaking around the piston into the portion of housing 12 forward of piston 34.

Cap 32 is formed having an interior slot 58 which extends from the threaded lip 48 terminating slightly before the cap's front end. A cylindrical recess 54 is formed in the inner wall 47 of the cap coaxial with the housing longitudinal axis 52. Finally, an elongated reduced diameter cylindrical recess 50 is formed tangentially to recess 54 and extends from the end of recess 54 beyond the end of slot 58 and terminates just before opening to the exterior. Referring to FIG. 2, it is seen that one end of spring 36 bears against a shoulder contiguous with wall 47 formed between recess 54 and the threaded lip 48 of the cap.

A plunger 62 is slidably mounted within cap 32. The plunger 62 has a cylindrical body 64 integrally formed with a reduced diameter cylindrical boss 66. The boss 66 is eccentrically formed relative to the cylindrical body 64 so that the cylindrical surfaces are tangential along an imaginary line 56 (FIG. 7). The plunger has appropriate dimensions so that the cylindrical body is slidably received within cylindrical recess 54 while the cylindrical boss is received within the elongate recess 50 as seen in FIG. 2. A slot 68 is formed laterally through boss 66 which is aligned with the slot 58 in cap 32. Finally, an extended aperture 69 is provided in the side wall of cap member 32 which communicates with the bore 50 and is in alignment with the slot 58.

The knife 14 includes a blade 70 at its lower end and a shank portion 74 at its upper end. The blade 70 has a cutting edge 72 which slopes downwardly and inwardly in a generally straight line terminating in an arcuate portion adjacent the base of the blade. This shape is important for reasons discussed below. As seen in FIGS. 3 and 4, the blade 70 has a sharp cutting edge 72 while the shank edge 76 is blunt. The lower end 18 of the knife is provided with a guide, or shoe, 77 having a substantially planar surface with a rounded, upturned leading lip 78.

A compression spring 80 has one end seated within recess 50 while the other normally bears against the end of the boss 66 of the plunger. The shank portion 74 of knife 14 is inserted through the aligned openings of aperture 69, and cooperating slots 68, 58. Referring to FIG. 2 in conjunction with FIG. 6, stepped bore 82 is formed through an upper portion of cap 32. A bore 84 is provided within the knife shank portion 74 which aligns with bore 82 when the knife is positioned. A bolt 86 is threaded within aligned bores 82, 84 to provide a pivot for the knife. Further, a slot 90 is formed in that portion of the knife shank which is positioned within the confines of the slot 68 in boss 66. Another bore 92 (FIG. 6) is formed in boss 66 and is aligned with slot 90. A stub shaft 94 is then inserted through an access bore 95 to cooperate with the aligned slot and bore, the shaft being held in place by a set screw 96. The piston 34 is positioned within barrel 30, and spring 36 normally urges the piston to the rear of the barrel.

FIGS. 5, 8 and 9 show the valve system. The housing barrel 30 is formed with a pair of handgrips 97 having fluted edges to facilitate holding by the operating physician. In the preferred embodiment of the invention, one of these handgrips provides a housing for the valve system. As the actuating trigger protrudes from the front edge of the handgrip containing the valve system, it is apparent that a right-handed physician would prefer the valve apparatus to be provided in the upper handgrip (as seen in FIG. 5) so as to be able to depress the trigger with his right forefinger, while a left-handed physician would prefer such apparatus to be provided in the lower handgrip. Of course, bot embodiments come within the scope of the present invention.

A bore 98 terminating in an enlarged diameter length 100 is formed in the handgrip parallel to the longitudinal axis of the housing. An actuating rod 102 having an enlarged rearward end 104 has its forward end fixed to trigger 28 and is slidably mounted within bore 98. A spring 106 is provided around rod 102 and received within a counterbore 107 immediately behind trigger 28, the cross section of the trigger and counterbore preferably being identical and non-circular so as to prevent rotation of the former in the latter. The force of spring 106 normally maintains the trigger and actuating rod in the position shown in FIG. 5 which is the forward or neutral position.

Still referring to FIGS. 5, 8 and 9, a ferrule 108 is fit into the enlarged diameter length of bore 98 adjacent to a shoulder 110 defined by the intersection of the enlarged and reduced diameter lengths of bore 98. Ferrule 108 has an inwardly turned lip 109 formed at its rearward end defining a venting port 112 (FIGS. 8 and 9) and has a second venting port 114 formed in its side wall. This second venting port 114 communicates with an air passage 116 which opens to the external atmosphere at the rear edge of the handgrip 97. A fitting 118 which includes a fluid connector 120 on one end on which the flexible tube 16 may be attached and an inwardly turned lip 126 on the other end is threaded to the end of the enlarged diameter length 100 of bore 98. Prior to threading fitting 118 into the bore, a ball 124 and a spring 122 are inserted and a snap ring 125 is provided within an internal groove to retain them therewithin so that the ball is urged against an inlet port 128 formed by lip 126. This inlet port is normally closed by ball 124 which is urged over the opening action of spring 122. As best seen in FIG. 8, an elongate bolt 130 is threaded into the enlarged end 104 of actuating rod 102. A ball 132 is slidably mounted on the bolt's shank via a bore formed through the ball. A spring 136 is positioned over the bolt shank and normally urges the ball against the bolt head 134. Finally, an air passage 138 is provided having one end extending into the chamber 45 within the housing (FIG. 5) and the other end opening into the length of bore 98 between venting port 112 and inlet port 128.

An understanding of the cooperation of the valve elements can best be understood through a description of the operation of the device. FIG. 5 shows the instrument in its neutral state, i.e., the knife 14 is in its retracted position (see solid lines in FIG. 2), the piston 34 is biased against bumper 38 under the force of spring 36, and the trigger 28 is in its forwardmost position. As seen in FIG. 5, with the trigger in its neutral (forward) position, the ball 132 is in a position within ferrule 108 such that venting ports 112, 114 are open. When a source of compressed air (or any other gas under pressure) is attached to the end (not shown) of flexible tube 16, the combination of forces due to air pressure and spring 122 maintains ball 124 against inlet port 128 thereby closing it. As the operating physician depresses trigger 28, the actuating rod 102 moves bolt 130 rearwardly together with ball 132. As shown in FIG. 8, after a certain amount of movement, ball 132 is positioned over venting port 112 thereby closing it. As the trigger is further depressed, the bolt 130 continues to travel rearwardly through the bore formed in ball 132 while spring 136 maintains the ball against venting port 112. In the last stages of trigger depression, the bolt head 134 advances through the aligned port 128 and contacts ball 124 moving it against the force of the compressed air and spring 122 thereby opening inlet port 128. This allows compressed air to enter through the inlet port and into the chamber behind piston 34 through air passage 138. The forces exerted on the piston by he compressed air move the piston at great velocity until it impacts plunger 62 driving it forward. The moving plunger causes the cutting tool 70 to move through a cutting arc to its final position shown in phantom lines in FIG. 2.

It should be noted that the articulated linkage assembly comprising plunger 62, shaft 94, slot 90, knife 14, bolt 86 and cap 32 actually forms a Scotch or slotted yoke-type drive. Such a linkage controls the force and direction of the knife during the cutting stroke. Specifically, upon impact of the piston into the plunger, sufficient force is transmitted through the linkage to cut through most bone structure. The linkage also results in the knife moving in the particular lateral direction as described above which facilitates the bone-cutting operation. Of course, as the piston 34 moves forward, the air in front of it within the housing must be vented. To accomplish this, a bore 140 (FIG. 2) is provided in plunger 62 through which the air travels, finally exiting from the device through the elongate aperture 69.

It should be noted that in the preferred embodiment, the knife edge 72 moves in a generally transverse direction relative to itself and, broadly speaking, the direction of travel is substantially parallel to the longitudinal axis of the cutting tool. This direction makes the device suitable for cutting bone structure (and especially the sternum) while resulting is less bone dust being generated during the operation (relative to a "sawing" type of action).

The instant device includes various safety features. After inserting the knife 14 into the incision against the bone (FIG. 1) and prior to commencing the cutting operation, the operating physician urges the instrument upwardly to engage the planar shoe or guide 77 with the lower surface of the sternum. This assures the physician that the knife will not be inadvertently thrust too far into the chest cavity. Further, referring to FIG. 2, it is seen that the arc described by shoe 77 during a cutting stroke is in a slightly upward direction due to the particular placement of elements of the articulated linkage. This is inteded to assure that the knife will not move downwardly and cut those internal organs below the bone being cut. Another benefit of this upward direction derives from the fact that after heart surgery, it is not uncommon for the heart to actually adhere to the bottom surface of the sternum. At reoperation, the cutting stroke allows the rounded shoe lip 78 to insert itself between the heart and the sternum thereby separating them. The shape of the cutting edge 72 also provides a safety feature. As pointed out above, the cutting edge slopes downwardly and inwardly in a generally straight line terminating in an arcuate portion adjacent the base of the blade. As the knife moves in the cutting direction, should the shoe not be flush against the bottom surface of the sternum, the generally straight edge portion acts as a wedge against the bone causing the knife to move upwardly relative to the bone until the shoe engages the bottom surface. At this point the arcuate portion of the cutting edge begins its action. Thus, the shape of the blade itself provides an important safety feature.

After the piston has impacted against the plunger, it is ready to return to its original position under the force of spring 36 upon release of the trigger. Residual high pressure air exits from the cylinder through a high pressure vent 133 which extends from the interior of the cylinder to the exterior through the handgrip which does not house the trigger apparatus. The vent is directed forwardly through bore 146 of the instrument so as not to direct a high pressure stream of air towards the patient or the physician. Without this venting, the piston would tend to jam and the cutting action would be weaker since spring 36 would have to be heavy enough to overcome the residual high pressure air in the cylinder.

Upon release of the trigger, head 134 of bolt 130 retracts permitting ball 124 to close the inlet port 128 cutting off the supply of compressed air to the housing and, upon further retraction, removes ball 132 from its closed position thereby opening venting port 112. Piston 34 begins to move rearwardly under the force of spring 36 causing the air contained within the housing behind piston 34 to be vented through the air passage 138 through venting ports 112, 114 and out through air passage 116. The ball valves may be provided with packings as shown. The knife returns to the initial neutral position under the force of spring 80 which also causes the plunger 62 to return to its initial cocked position.

Thus, each time the trigger 28 is depressed, the knife undergoes a single cutting stroke and returns to the neutral position upon release of the trigger. This arrangement provides precise control of the cutting rate which is desirable in the surgical opertions in which the tool is to be utilized. Of course, the instrument may be employed in other applications within the scope of the present invention. For example, it is also suitable for cutting casts, i.e., removing casts from limbs after the bone has set.

The particular valve structure of the present invention provides numerous advantages independent of the cutting instrument with which it has been disclosed. The valve comprises a compound device in that it handles high pressure air input while venting residual air trapped between the piston and the cylinder head. This cycle is undergone by only a single depression of the trigger. The valve is adapted to admit high pressure air upon exertion of only a relatively small force on the trigger. Further, the valve is simple in construction and relatively easy to manufacture.

Obviously, numerous modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

What is claimed is:

1. A surgical cutting instrument comprising:

a housing;

a knife including a shank portion which extends into said housing and a knife edge portion, said shank being pivotally connected to said housing;

a movable piston slidably disposed within said housing;

a floating plunger slidably disposed within said housing in coaxial alignment with said piston; and

a movable linkage connected to said housing and permanently connecting said knife shank portion to said plunger for causing said knife edge portion to move in a cutting stroke substantially parallel to the longitudinal axis of the housing upon movement of said plunger.

2. A cutting instrument as recited in claim 1 wherein said blade as a knife edge which follows a generally straight line sloping downwardly and inwardly and has and arcuate shaped lower edge.

3. A cutting instrument as recited in calim 1 wherein said knife is connected with said housing so that it forms a substantially right angle to the longitudinal axis of said housing.

4. A cutting instrument as recited in claim 1 wherein said moving means includes pivot means for connecting said knife shank portion to said housing so that movement of said knife comprises a pivotal movement.

5. A cutting instrument as recited in claim 4 wherein said knife shank portion has a slot formed therein and said plunger includes a pin which is disposed within said slot so that when said plunger is driven forward upon being struck by the piston, said knife is pivoted.

6. A cutting instrument as recited in claim 1 further including a planar guide shoe provided on the free end of said knife edge portion, said shoe having a leading edge which is formed with a rounded lip.

7. A cutting instrument as recited in claim 1 wherein said means for moving said piston toward said plunger comprises pneumatic valve means, said valve means, upon actuation, causing said piston to strike said plunger a single time.

8. A cutting instrument as recited in claim 7 wherein said valve means comprise:

actuation means;

a first passage from the interior of said housing to the external atmosphere having a normally open first port;

a second passage from the interior of said housing to the external atmosphere having a normally closed second port; and

means for closing said first port and opening said second port upon operation of said actuation means.

9. A cutting instrument as recited in claim 8 wherein said valve means further include:

an elongated rod movably mounted in said housing wherein said actuation means includes means for moving said rod along its axis;

a first ball slidably mounted on said rod;

spring means yieldingly urging said ball to an extreme position on said rod so that upon actuating said rodmoving means said rod moves a first distance and said ball is moved against and closes said first port; and

a second ball normally yieldingly urged against and closing said second port in axial alignment with said elongate rod so that upon movement beyond said first distance, said rod end contacts said second ball moving it away from and opening said second port.

10. A surgical cutting instrument comprising:

an elongate housing having a forward end and a rearward end;

a knife movably connected to said forward end and extending from the housing at a substantially right angle to the longitudinal axis thereof;

yielding means for normally urging said knife toward said housing rearward end; and

means including a movable piston slidably disposed within said housing and normally biased toward said rearward end and a movable plunger normally spaced apart from said piston and permanently connected through a slotted linkage to the shank of said knife for moving said knife through a cutting stroke when said piston is driven against said plunger, the path of said stroke being substantially parallel to the longitudinal axis of said housing.