WO1994008518A1

WO1994008518A1 - Cavitation-generating tip for disintegrating tissue

Info

Publication number: WO1994008518A1
Application number: PCT/US1993/009693
Authority: WO
Inventors: Charles D. Kelman; Martin Fox
Original assignee: Kelman Charles D
Priority date: 1992-10-08
Filing date: 1993-10-08
Publication date: 1994-04-28

Abstract

An improved cutting tip (18) for use with a device (10) for disintegrating tissue located in a predominantly liquid environment. The device (10) includes an oscillation generator (14) which provides an oscillation movement along an axis (B) at an ultrasonic frequency. A cutting tip (18) is attached to the oscillation generator and is drawn and advanced in oscillating movement along the axis (B). The cutting tip is positioned in proximity to the tissue wherein the oscillations of the cutting tip cause the tissue to disintegrate, at least in part, through cavitation effects. The cutting tip (18) has a specific shape and leading frontal area (42) which provides means for creating and subsequently collapsing cavitation bubbles within the liquid during the oscillation movement. The tip also has a beveled exposed forward-facing edge (46), surrounding an aspiration opening, whose angled bevel prevents continuous 'vacuum bonding', due to vacuum aspiration, between the tip and the tissue being disintegrated.

Description

CAVITATION-GENERATING TIP FOR DISINTEGRATING TISSUE

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a device for use in the medical field for assisting in the disintegration and removal of tissue, and more particularly to an improved tip element of such a device which is specifically designed for extracting the cataracted natural lens from the eye of either a human or an animal.

A now common medical procedure in eye surgery in¬ volves the complete removal of a cataracted lens from a human eye to be later replaced with an intraocular lens. The known procedure includes making an incision in the cornea. To minimize patient trauma and unnecessary tissue damage, this incision is kept very small. The entire operation of disintegrating and removing the damaged natural lens tissue is performed using instruments placed within the small incision. A special vibratory instrument is used to assist in the lens tissue disintegration. The instrument functions effectively as a miniature jack hammer and includes detachable cutting tips which are analogous to jack hammer chisels. The cutting tip is generally tubular and is oscillated by the instrument along its axis at a very high frequency. The cutting tip is inserted into the incision and maneuvered by the surgeon throughout the capsular bag containing the natural lens literally being moved through the cataracted lens. The movement of the vibrating cutting tip causes the lens tissue to disintegrate. As the lens breaks apart, the resulting loose lens particles are carried from the posterior capsule by an aspiration fluid which flows into the posterior capsule by way of a first conduit and drawn under vacuum from the posterior capsule by way of the tubular cutting tip of the vibrating instrument.

U.S. Pat. 3,589,363 to Banko and Kelman discloses such a hand held instrument for breaking apart and removing tissue from a body site, such as cataracted lens tissue from a human eye. The content of U.S. Pat. 3,589,363 is hereby incorporated by reference.

There are several problems encountered by surgeons using the above procedure. A first problem is that the ideal location for the above-described incision restricts the acces- sibility of the surgeon's operating instruments within the posterior cavity. In other words, the typically straight cutting tips of the vibratory instrument cannot easily be maneuvered within the posterior cavity to effectively reach all parts of the lens to be removed. To overcome this accessibility problem with the known cutting tips, cutting tips have now been made with a 90 arc- degree bend so that the cutting tip may be maneuvered■to reach every part of the posterior cavity while operating through the small incision. This bent cutting tip feature is disclosed in my copending application serial no. 07/668,341, filed March 8, 1992, entitled: TISSUE SCRAPER DEVICE FOR MEDICAL USE, the content of which is hereby incorporated by reference.

A second problem encountered by surgeons during the above procedure involves the quick and clean removal of large (e.g. quarter sections) pieces of lens tissue remaining in the eye after an initial "cracking" of the lens. As the surgeon disintegrates these large pieces they may clog the tubular cutting tip, being drawn and held against the tip by the vacuum of the aspirating fluid existing therethrough. The prior art has attempted to solve this problem by angling the front end of the cutting tip so that the "vacuum effect" which holds an oversized piece of lens tissue may be easily overcome by the force of the tip being drawn away from the tissue during the receding stroke of its reciprocating movement. Such an angled tip is shown in the above-identified U.S. 3,589,363. However, the intended purpose of the angled tip disclosed in U.S. 3,589,363 patent is to provide a tip having greater maneuver¬ ability and to create a cutting edge to more effectively break through tissue. Therefore, an ideal tip angle which maximizes effective fluid aspiration, yet still prevents tip-clogging, had not been realized.

It has been determined by the applicant that the disintegration of tissue in the immediate vicinity of the cutting tip is enhanced by the cavitation effect resulting from the ultrasonic oscillation of the cutting tip within the liquid filled environment of the posterior capsule.

Whenever any object having a distinct frontal surface area, with respect to the direction of movement, moves rela¬ tively quickly within a fluid, a low pressure region (i.e., negative pressure with respect to the surrounding fluid) is developed just behind, or adjacent to, such frontal surface. If the magnitude of negative pressure developed within the low pressure region exceeds (becomes more negative than) the negative pressure required to vaporize the particular fluid, the fluid will vaporize, creating bubbles called cavitation bubbles.

Thus, when the cutting tip of the above-described vibratory instrument moves in a direction away from the surface of the tissue to be disintegrated, a sudden low pressure region is developed within the adjacent fluid resulting in the forma¬ tion of cavitation bubbles. It is believed that during each oscillation, as the cutting tip continues to move away from the tissue surface the pressure in the expanding newly formed cavitation bubbles decreases. It is further believed that when the point is reached, during each cycle, where the fluid pressure outside the bubble exceeds the pressure in the expand¬ ing cavitation bubbles, there results a collapse of the cavita¬ tion bubbles and they are quickly re-absorbed into the fluid. The pressure waves in the fluid resulting from the substantial- ly simultaneous collapsing of thousands of such tiny bubbles, operate on the tissue to help disintegrate it. The rate of "collapse" of the cavitation bubbles determines the degree of assistance to disintegrating the nearby tissue. The greater the number of cavitation bubbles formed and the quicker the rate of collapse of the bubbles, the greater will be the desired damage to the nearby tissue.

It is therefore an object of the present invention to utilize the destructive effects of cavitation bubbles to disintegrate unwanted tissue. It is another object of the invention to provide a cutting tip for use with a vibratory instrument which is both curved to provide accessibility and angled to prevent tissue clogging so that the generation of cavitation bubbles may be more effective in disintegrating the large pieces of tissue to be removed from the human eye.

It is a further object of the invention to provide a cutting tip which will produce a maximum number of cavitation bubbles in the region between the tip and the tissue to be disintegrated.

SUMMARY OF THE INVENTION

An improved tip for use with a device for disinte¬ grating tissue located in a predominantly liquid environment. The device includes an oscillation generator which provides an oscillation movement along an axis at an ultrasonic frequency. The tip is connected with the oscillation generator and is moved to and for in oscillating movement along the axis. The tip is positioned in proximity to the tissue such that the oscillations of the tip cause the tissue to disintegrate. The tip has a specific shape and leading frontal area which pro- vides means for selectively creating and destroying cavitation bubbles within the liquid during the draw stroke of oscillation movement of the tip. The destruction of the cavitation bubbles in this manner substantially accomplishes the disintegration of the adjacent tissue. The shape of the cutting tip is such that substantially more frontal area is available for producing and concentrating cavitation bubbles than with prior tips. The tip includes an internal conduit extending along the length there¬ of. This aspiration and/or irrigation conduit is curved near the distal end of the tip and terminates at a frontal opening of the tip. The tip is both curved to provide greater maneu¬ verability within the posterior cavity and includes a forward facing opening which is disposed at a slight angle. The angled tip is such that a particular piece of tissue being disinte- grated is intermittently forced into contact with the tip and then separated immediately thereafter. The curved conduit portion forms a throat behind the frontal opening. The forward facing, peripheral edge surrounding the frontal opening and the forward facing outer surface of the curved tip each provide frontal surface area. The throat includes a curved internal surface which provides additional frontal surface area to the tip as it is drawn away from a tissue surface. This combined frontal surface area helps create low pressure in the fluid adjacent the tissue surface. As stated above, the low pressure fluid causes cavitation bubbles to form.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an overall cross-sectional side view of a vibratory instrument showing a tip in accordance with the present invention attached thereto;. Fig. 2 is a partial cross-sectional side view of an eye showing the vibratory instrument including the cutting tip in an operational position in accordance with the invention;

Fig. 3 is a front view of the eye of Fig. 2; Fig. 4 is a partial, sectional side view of a cutting tip assembly in accordance with a preferred embodiment of the invention; and

Fig. 5 is a front view of the cutting tip in Fig. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Fig. 1, a vibratory instrument 10 which may be used to remove a cataracted eye lens is shown. The instrument 10 includes a housing 12, an internal ultrasonic oscillation generator 14, a protective sleeve tip 16 and a tubular cutting tip 18. The protective sleeve tip 16 is tubular and is attached to the housing 12. The protective sleeve 16 is stationary with respect to the housing 12 and, once inserted in the eye, with respect to the patient (not shown) .. The cutting tip 18 is positioned within the tubular protective sleeve 16 and is attached to a forward end of the oscillation generator 14. The oscillation generator 14 recip¬ rocates the cutting tip 18 along an axis A at a predetermined ultrasonic oscillation rate. The instrument 10 also includes an irrigation fluid inlet line 20 which is in fluid communica- tion with the tubular protective sleeve 16 and an aspirating fluid outlet line 22 which communicates with an internal passage in the tubular cutting tip 18.

As described above, a small incision 24 is made in the cornea 26 and an opening is made in the anterior wall 28 using a scalpel or similar cutting instrument. Together, these two openings provide access to the interior of the capsular bag 30 through which the vibratory instrument 10 is inserted by a surgeon, as shown in Figs. 2 and 3. The protective sleeve 16 contacts the tissue of the cornea 26 adjacent the small inci- sion 24. The purpose of the protective sleeve 16 is to protect the healthy tissue (i.e., the tissue lying adjacent the inci¬ sion 24) from the oscillating cutting tip 18 positioned there¬ in. The protective sleeve 16 also provides one-way isolated fluid communication directly with the posterior capsule 30 for providing irrigation fluid to the surgical site.

The cutting tip 18 is also positioned through inci¬ sion 24 but operates within the protective sleeve 16. Only a forwardmost portion 32 of the cutting tip 18 extends past the protective sleeve 16 into contact with the cataracted natural lens 34. As the oscillation generator 14 oscillates the cutting tip 18 back and forth along the axis A, the surgeon maneuvers the forwardmost portion 32 of the cutting tip 18 throughout the posterior cavity, to disintegrate and aspirate the separated particles of the cataracted lens 34.

The rate of oscillation of the oscillation generatox is preferably in the range between 10 khz and 25 khz. The exact frequency used depends on several factors including the precise shape of the cutting tip, the type of tissue being disintegrated and the degree of disintegration desired.

Referring to Figs. 4 and 5, a cutting tip 18 in accordance with the invention is shown having a tip shaft or tube 36 positioned along an axis B, a connection end 38, a securing flange 40 and a tip end 42. The tip end 42 is most important in controlling the localized densities of cavitation and bubble collapse. The tip end 42 is bent with respect to the longitudinal axis B, and is positioned along a bent-portion axis C. The preferred angle G between axis B and axis C is between 30 and 45 arc degrees. The tip end 42 includes a tip opening 44, which is actually one end of the tube 36. The tip opening 44 has a peripheral front tip surface 46. The front tip surface 46 lies in a plane D which intersects the longitu¬ dinal axis B at a predetermined acute angle F of about 75 arc degrees (15 arc degrees from a normal line extended from axis B) . As described in greater detail below, this beveled front tip surface 46 accelerates fragment disintegration by intermit¬ tently "vacuum- bonding" with large tissue fragments. As the cutting tip 18 oscillates along the longitudinal axis B, the opening 44 moves along an axis E which is generally parallel to but displaced from axis B.

To break up the cataracted lens, the surgeon first uses the vibrating cutting tip 18 to make a shallow and short groove near the center of the lens. The cutting tip 18 is then repositioned and another somewhat longer groove is made perpen¬ dicular to the first one, forming a small cross shape. During the procedure the surgeon elongates and deepens the grooves until they extend completely across the lens and almost com- pletely therethrough. The grooves are made deeper by removing small amounts of cataracted tissue along the groove-lines until eventually, the relatively brittle lens cracks. The grooves control the breakup of the lens by encouraging two intersecting cracks to separate the large lens into four relatively equal and more manageable-sized quarter sections.

In carving out each groove, the lens has now become somewhat smaller in volume. However, the complete removal of the lens now requires that each of the four quarter sections be disintegrated. To disintegrate a quarter section in a con- trolled manner, the surgeon first positions the cutting tip 18 against a selected quarter section. The surgeon uses the cavitation effects of the oscillating tip, described in greater detail below, together with the strong suction of the aspira¬ tion fluid moving through the tube 36 to effectively and quickly disintegrate the quarter section.

As the tip moves away from the tissue of the quarter section during one half of each reciprocation cycle, a negative pressure is generated in the fluid between the tip and the tissue surface. This negative pressure (if great enough) creates cavitation bubbles to form both on and adjacent the surface of the tissue and within the cells making up the tissue. Eventually, as the tip either continues to move further away from the tissue surface or reverses direction and advances towards the tissue, the negative pressure decreases in magnitude. As the pressure increases, the cavitation bubbles collapse as they are absorbed back into the surrounding fluid. It is believed that this collapse of cavitation bubbles causes cell walls to burst apart and tissue to disintegrate.

As this cavitation-assisted disintegration of tissue of each quarter section at the cell level occurs, the vacuum from the aspiration of fluid continuously pulls adjacent quarter section tissue into contact with the tip, but only for an instant. During each reciprocating stroke of the cutting tip, the tip "escapes" the strong vacuum bond formed by the sucking action of the aspiration fluid. It is important for the vacuum bonding to occur so that the tissue to be destroyed will remain in the proximity of the tip and not have the tendency to float out of position so that there result is quicker disintegration of the tissue. However, it is also important for the tip to separate from the tissue surface so that a negative pressure may develop to form the beneficial destructive cavitation bubbles. It is the combination of these two operations which most effectively break up and remove the remaining quarter sections. The angle F formed between the plane D and the longitudinal axis B, preferably about 75 arc degrees, influences the amount of time the tissue will remain under the vacuum bond with the tip (for a given oscillation rate and vacuum magnitude) , therefore controlling the amount of direct tissue adherence. Thus, the angle F of the peripheral front tip surface 46 allows the tip to more easily pull itself from the tissue surface by creating a "weak point" from which the "vacuum bond" may break. If, for example, the front beveled angle is 90 arc degrees or perpendicular to the longi¬ tudinal axis B, i.e. the axis of oscillation, it is likely that the required vacuum magnitude used to irrigate the eye during the operation will generate too strong a vacuum bond which will prevent the tip from separating, cavitation bubbles from forming and the cavitation effects from assisting in the disintegration of tissue. Cavitation bubbles are both created and destroyed at a rate which is dependent on the type and density of the fluid in the surrounding area, the size of the frontal area as the tip recedes, and the rate of tip oscillations. The frontal area of the cutting tip 18 as viewed from the connection end 38 (rear end) controls the magnitude of the negative pressure developed as the cutting tip 18 recedes (moves away from the tissue) . In this embodiment, as viewed in Fig. 4 has a frontal area which includes an upper outer wall surface 48, a lower outer wall surface 52, a lower inner wall surface 50 and a upper inner wall surface 54. All wall surfaces are curved following the contours of the tubular tip 18. As the cutting tip 18 moves away from the tissue (recedes) , the upper inner wall surface 54, the outer lower wall surface 52 and the frontal surface 46 together create a local low pressure region in the area in front of the tip end 42.

The cavitation phenomenon encourages cavitation bubbles to form in the region of negative pressure, such as, in this case, in and adjacent to the tissue of a cataracted lens 34 of an eye. The collapse of the cavitation bubbles causes the adjacent lens tissue to erode away. By controlling the size and shape of the frontal area of the tip, the amount and location of tissue erosion may be controlled.

In the above-described preferred embodiment of the invention the peripheral front tip surface 46 is uniform in radial thickness completely around the tip opening 44. The upper inner wall surface 54, the lower outer wall surface 52 and the peripheral front tip surface 46 cooperate to generate cavitation bubbles in a uniform manner. Preferably the outside diameter of the tip is about 0.9mm and the wall thickness is about 0.15mm. The bent portion is preferably about 3mm in length.

It will be appreciated that the foregoing specifica¬ tion and accompanying drawings are set forth by way of illus- tration and not limitation of the present invention, and that various modifications and changes may be made therein without departing from the spirit and scope of the present invention which is to be limited solely by the scope of the appended claims.

Claims

What is Claimed is: 1. A surgical tool tip for disintegrating tissue located in a predominantly liquid environment, said tip being attachable to a generator providing reciprocating movement to said tip along a first axis at an ultrasonic frequency, in use said tip being positioned in proximity to said tissue, said tip movement causing said tissue to disintegrate, said tip compris- ing: a hollow tube having a straight body with a longitudinal second axis, said body being connected to one end of a front segment having a third axis, said second and third axes meeting at a first angle, an end of said body away from said front segment being adapted to attach to said generator for reciprocating movement with said first and second axes parallel, the other end of said front segment having an end face lying generally in a plane that is transverse to said second axis, said end face having an opening centered about said third axis and an outer peripheral edge and an inner peripheral edge, said inner peripheral edge being defined by said centered opening, said outer peripheral edge being defined by the outer periphery of said hollow tube, said outer periph- eral edge of said end face being smooth and devoid of sharp edges.

2. A tip for disintegrating tissue as in claim l, wherein said end face has a generally uniform radial thickness with respect to said third axis.

3. A tip for disintegrating tissue as in claim 1, wherein said end face plane intersects said second axis at a second angle between approximately 50 and 89 degrees.

4. A tip for disintegrating tissue as in claim 1, wherein said outer peripheral edge is substantially rounded.

5. A tip for disintegrating tissue as in claim 1, wherein a region of said end face between said outer peripheral edge and said inner peripheral edge is substantially a quadrant in cross-section along said third axis.

6. A tip as in claim 1, wherein said second axis and said third axis intersect at a first angle between approxi- mately 30 and 45 degrees.

7. A tip as in claim 3, wherein said second angle is in the order of approximately 75 degrees.

8. A tip for disintegrating tissue as in claim 5, wherein said region of said end face is substantially smooth and continuous along the entire periphery of said tip.

9. A tip for disintegrating tissue as in claim 1, wherein a region of said end face between said outer peripheral edge and said inner peripheral edge is substantially semi- circular in cross-section on a plane which includes said third axis.

10. A tip for disintegrating tissue as in claim 5, wherein said quadrant cross-section has a radius of approxi- mately 0.15mm, the wall thickness of said hollow tube being approximately 0.15mm.

11. A tip for disintegrating tissue as in claim 9, wherein said semi-circular cross-section has a radius of approximately 0.075mm, the wall thickness of said hollow tube being approximately 0.15mm.

12. A tip for disintegrating tissue as in claim 9, wherein said region of said end face is substantially smooth and continuous along the entire periphery of said tip.

13. A surgical tool tip, for use with a handpiece having an ultrasonic generator therein, for disintegrating and aspirating cataracted lens tissue, said tip comprising: a hollow tube having a straight shank portion and a tip portion connected at one of its ends to said shank portion and having an axis inclined with respect to axis of said shank portion, attachment means at the end of said shank portion remote from said tip portion for attaching said tip to the handpiece for vibration thereof at ultrasonic frequency, means connecting the interior of said tip with a vacuum source for providing aspiration therethrough of disintegrated tissue, said inclined tip portion having, at its free end, an end face lying generally in a plane that is transverse to the axis of said tip portion, said end face having an opening centered about said axis of said tip portion and the leading peripheral edge of said end face formed by said opening having a rounded smooth contour devoid of sharp edges, whereby the risk of injury by accidental contact during surgery, of said leading peripheral edge of said tip portion, with the tissue of the capsular bag which contains the cataracted lens, will be substantially reduced.

14. A device for disintegrating tissue located in a predomi- nantly liquid environment, said device including an oscillation generator providing an oscillation movement along an axis at an ultra-sonic frequency, a cutting tip operatively connected to said oscillation generator to be drawn and advanced in oscil- lating movement along said axis, said cutting tip being posi- tioned in proximity to said tissue wherein said oscillation of said cutting tip causes said tissue to disintegrate, said cutting tip comprising: a tube having a bent front section, a rear section, a straight body section connecting said front and rear section, and an exposed forward-facing opening in said front section, said exposed forward-facing opening being centered about and oscillated along a second axis of movement displaced from said straight body section and parallel to said first axis of movement, said bent front section of said tube defining a leading frontal area as it advances along said second axis of movement and a retreating frontal area as it is drawn back along said second axis of movement, whereby said frontal area creates cavitation bubbles within said liquid during said draw stroke of said front section of said cutting tip along said second axis of movement.

15. A device for disintegrating tissue in accordance with claim 1, wherein said leading frontal area includes the area of a peripheral edge around said forward-facing opening, said peripheral edge having a generally uniform radial thick- ness with respect to said second axis of movement.

16. A device for disintegrating tissue in accordance with claim 15, wherein said front section includes an outer convexly bent portion which lies external to said tube between said peripheral edge and said straight body section, said front section further includes an inner concavely bent portion which lies at the interior of said tube between said peripheral edge and said straight body section, said outer bent portion and said inner bent portion having a prescribed forwardly facing surface area for forming cavitation bubbles, said leading frontal area including also said surface area of said inner concave bent portion and said outer convex bent portion.

17. A device for disintegrating tissue located in a predominantly liquid environment, said device including an oscillation generator providing an oscillation movement along a first axis at an ultra-sonic frequency, a cutting tip opera- tively connected to said oscillation generator to be drawn and advanced in oscillating movement along said first axis, said cutting tip being positioned in proximity to said tissue wherein said oscillations of said cutting tip causes said tissue to disintegrate, said cutting tip comprising: a tube having a front section, a rear section, a straight body section, and an exposed forward-facing opening lying in a first plane, said exposed forward-facing opening being centered about and oscillated along a second axis of movement, said second axis of movement being displaced with respect to said straight body section said first plane inter- secting said first axis at an angle between 50 and 89 arc degrees to prevent continuous vacuum bonding between said forward facing opening and the tissue while facilitating intermittent vacuum bonding.

18. A device for disintegrating tissue located in a predominantly liquid environment, said device comprising: a tube having a front section, a rear section, a straight body section connecting said front and rear sections, and said front section having an exposed forward- facing opening, said straight body section lying along a first axis for and being moveable in an oscillatory manner at a predetermined frequency, said exposed forward-facing opening being centered about a second axis for movement along said second axis at said predetermined frequency when said straight section is oscillated, said second axis being parallel to and displaced from said straight body section said forward-facing opening lying in a first plane, said first plane intersecting said first axis at an acute angle within the range of 50 and 89 arc degrees, said tube having a conduit therein for fluid communication between said forward-facing opening and said rear section whereby the tissue to be disintegrated becomes inter- mittently vacuum bonded to said front section and immediately released therefrom in response to said tube being oscillated.