Patent Publication Number: US-6654999-B2

Title: Method of manufacturing an ultrasonic tool

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application is a divisional application of application Ser. No. 09/298,125, filed Apr. 23, 1999, now U.S. Pat. No. 6,256,859 B1 to Stoddard et al., which claims priority to provisional application Ser. No. 60/101,703, filed on Sep. 25, 1998. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to ultrasonic surgical apparatus for fragmenting and aspirating tissue. More specifically, the present disclosure relates to aspirating tools suitable for use in an ultrasonic surgical apparatus for aspirating tissue and to a method of manufacturing such aspirating tools. 
     2. Background of Related Art 
     Devices which effectively utilize ultrasonic energy for a variety of applications are well-known in a number of diverse arts. The application of ultrasonically vibrating surgical devices used to fragment and aspirate unwanted tissue with significant precision and safety has led to the development of a number of valuable surgical procedures. Accordingly, the use of ultrasonic aspirators for the fragmentation and surgical removal of tissue from a body has become known. Initially, the technique of surgical aspiration was applied for the fragmentation and removal of cataract tissue. Later, such techniques were applied with significant success to neurosurgery and other surgical specialties where the application of ultrasonic technology through a handheld device for selectively removing tissue on a layer-by-layer basis with precise control has proven feasible. 
     Typically, ultrasonic surgical devices for fragmenting and aspirating tissue include an ultrasonic transducer supported within a handpiece, an ultrasonically vibrating tool, an extender connecting the tool to the ultrasonic transducer and a sleeve or flue positioned about the tool. The tool includes a longitudinally extending central bore having one end located adjacent a distal tip and a second end located adjacent the proximal end of the tool. The proximal end of the tool is adapted to engage a vacuum source to facilitate aspiration of fluid. The flue is positioned about the tool to define an annular passage. Irrigation fluid is supplied through the annular passage around the tip to the surgical site where it mixes with blood and tissue particles and is aspirated through the bore in the tool. By mixing the irrigation fluid with the blood and tissue particles, coagulation of the blood is slowed down and aspiration thereof is aided. U.S. Pat. Nos. 5,015,227 and 4,988,334 disclose such ultrasonic surgical devices and are hereby incorporated by reference. 
     In any surgical procedure, it is necessary that a surgeon be afforded good visibility of the surgical site. Thus, it is important that the ultrasonic tool and flue be configured and dimensioned not to obscure visibility at the surgical site. One problem associated with manufacturing small diameter tools for the above-described ultrasonic surgical devices is machining an even smaller throughbore in the tool. Presently, tools with throughbores having diameters as small as 0.062 inches are known. Efforts to consistently manufacture ultrasonic tools having smaller diameter throughbores have not proven feasible. 
     Ultrasonic tools having large diameter throughbores are also advantageous during certain surgical procedures. For example, where highly compliant tissue mixed with blood is aspirated, there is increased likelihood of occlusion of the aspiration conduit due to the coagulation of the blood. To make matters worse, ultrasonic vibration of the tool acts to increase the rate of coagulation of the blood within the tool. 
     One problem associated with manufacturing ultrasonic tools having large diameter throughbores is that the threaded connector on the tool must be dimensioned to be attached to the same handpiece to which the small diameter tools are to be attached. Therefore, in large diameter tools, there is less material between the base of the threads on the threaded connector at the proximal end of the tool and the throughbore. As a result, the fracture rate of the large diameter ultrasonic tools is substantially higher than that of small diameter ultrasonic tools in the area of the threads. 
     Accordingly, a need exists for improved ultrasonic tools for use with apparatus for ultrasonically fragmenting and aspirating tissue and improved methods of manufacturing such ultrasonic tools which are more resistant to stress fracture and which have smaller diameter throughbores. 
     SUMMARY 
     In accordance with the present disclosure, an ultrasonic surgical apparatus is disclosed for fragmenting and aspirating tissue. The apparatus includes a handpiece which encloses a transducer having a magnetostrictive or piezoelectric stack. An aspirating tool having a throughbore is connected to the transducer by a connector body. A manifold having an irrigation port is positioned about the aspirating tool. During a surgical procedure, irrigation fluid is supplied through the irrigation port into manifold to the distal end of the aspirating tool, where the irrigation fluid mixes with fragmented tissue and blood from the surgical site. The blood and tissue are removed from the surgical site via the throughbore in the aspirating tool. 
     The handpiece is adapted to receive a plurality of different size aspirating tools. One such aspirating tool includes a throughbore having a diameter of about 0.045 inches. In order to form such a small diameter throughbore, a two-step drilling process is used. During the first step a proximal portion of the throughbore is drilled using a drill bit having a diameter of 1.25-2.5 times the desired bore diameter. During the second step, a distal portion of the bore is drilled to the desired diameter. The transition between the proximal and distal portions of the throughbore is positioned at a node. 
     Another aspirating tool adapted for use with the handpiece includes a throughbore having a diameter of preferably about 0.104 inches. During manufacturing, the aspirating tool is machined, the throughbore is drilled, and the proximal end of the tool is threaded. Next, the threads are masked and the aspirating tool is titanium nitride coated. By masking the threads prior to titanium nitride coating, stress concentrations formed in the threads are eliminated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various preferred embodiments are described herein with reference to the drawings, wherein: 
     FIG. 1 is a perspective view of an ultrasonic surgical apparatus constructed in accordance with the present disclosure; 
     FIG. 2 is another perspective view of the ultrasonic surgical apparatus of FIG. 1 in accordance with the present disclosure; 
     FIG. 3 is a side cross-sectional view of the surgical apparatus of FIG. 1; 
     FIG. 4 is a top cross-sectional view of the surgical apparatus of FIG. 1; 
     FIG. 5 is a perspective view of one embodiment of an aspirating tool suitable for use with the ultrasonic surgical apparatus shown in FIG. 1; 
     FIG. 6 is a side cross-sectional view of the aspirating tool shown in FIG. 5; 
     FIG. 7 is a perspective view of the aspirating tool shown in FIG. 5 with a titanium nitride coating covering all but the threads of the tool; 
     FIG. 8 is a perspective view of another embodiment of an aspirating tool suitable for use with the ultrasonic surgical apparatus shown in FIG. 1; 
     FIG. 9 is a side cross-sectional view of the aspirating tool shown in FIG. 8; 
     FIG. 10 is a perspective view of the aspirating tool shown in FIG. 8 after the tool has been bent; and 
     FIG. 11 is a side cross-sectional view of the aspirating tool shown in FIG.  10 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of the presently disclosed apparatus for ultrasonically fragmenting and aspirating tissue will be described in detail with reference to the drawings, in which like reference numerals designate identical or corresponding elements in each of the several views. 
     Referring now to FIGS. 1 and 2, one embodiment of the presently disclosed apparatus for ultrasonically fragmenting and aspirating tissue is shown generally as  10 . Apparatus  10  is embodied in a handpiece  12 . Handpiece  12  includes a housing  14  which may be formed of a sterilizable plastic or metal, but is preferably plastic. Housing  14  connects to an irrigation manifold  16  at a distal end portion. Manifold  16  includes an irrigation port and tube  18  therein communicating with an opening  20  at a distal end thereof. A tip  22  is shown at a distal end of handpiece  12 . Tip  22  is vibrated to fragment tissue during surgery as will be described in further detail hereinbelow. 
     An aspiration line  24  is mounted externally of housing  14 . Aspiration line  24  includes release tabs  26  for dismounting a distal end portion of aspiration line  24 . Further, a clip  28  is included on a proximal end portion of aspiration line  24  for holding irrigation tube  18 . Tab  26  permits detachment of aspiration line  24  from housing  14  when depressed. Clip  28  permits detachment from housing  14 . 
     Referring to FIGS. 3 and 4, housing  14  encloses a transducer housing (coilform)  40  having a magnetostrictive stack  41 . An aspirating tool  44  is connected to a connecting body  42 . Stack  41 , connecting body  42  and tool  44  form a resonant vibrator  30  which vibrates in the ultrasonic frequency range. 
     Aspirating tool  44  includes a tip  22  and a throughbore  34 . Tip  22  vibrates in the ultrasonic frequency range with a longitudinal amplitude in excess of about 5 mils (0.005 inch). During operation of apparatus  10 , irrigation fluid is supplied through irrigation port  18  (FIG. 2) into flue  16 . Flue  16  and tool  44  define an annular cavity  36  therebetween. Irrigation fluid is supplied from flue  16  through cavity  36  to the distal end of tip  22 . The irrigation fluid is drawn from preaspiration holes ( 32 ) and the surgical site into inlet  31  of throughbore  34  along with fragmented tissue, blood, etc., and is removed from the surgical site via throughbore  34  and aspiration line  24 . A transverse bore (preaspiration holes)  32  which communicates with throughbore  34  is formed in the distal end of tip  22 . Bore  32  provides an alternate route for fluid to enter throughbore  34  when inlet  31  of aspirating tool  44  becomes clogged. 
     Connector body  42  includes a threaded bore  48  configured and dimensioned to receive the threaded proximal end  54  of aspirating tool  44 . Although apparatus  10  is illustrated with an aspirating tool having a large diameter throughbore, different size aspirating tools, two of which will be disclosed in detail hereinbelow, can be substituted for the one presently shown. Each of the different size tools includes an identically sized threaded proximal end dimensioned to be received in threaded bore  48  of connector body  42 . Thus, a variety of aspirating tools can be releasably connected to a single handpiece. 
     FIGS. 5-7 illustrate one aspirating tool  144  suitable for use with the above-described apparatus for ultrasonically fragmenting and aspirating tissue. Aspirating tool  144  includes tip  122 , a large diameter throughbore  134 , a transverse bore  132  communicating with throughbore  134 , an elongated body  150 , a hexagon engagement portion  152  and a threaded proximal end  154 . Aspirating tool  144  is constructed from high-strength materials capable of handling the stress associated with ultrasonic vibration. Metals such as titanium and its alloys are preferred. Moreover, elongated body  150  is gausian to reduce the stresses to which the tool is subjected. 
     Referring to FIG. 6, because aspirating tool  144  includes a large diameter throughbore, which is preferably about 0.104 inches in diameter, and because threaded proximal end  154  of tool  144  has an outer diameter which is dimensioned to be received in threaded bore  48  of connector body  42  (FIG.  4 ), only a small amount of material, illustrated as “a” in FIG. 6, separates the base of the threads and throughbore  134 . This area of reduced thickness defines a weakened portion of the aspirating tool  144  where fractures generally occur during use. 
     Typically, during manufacturing of an aspirating tool, after the body has been machined, the throughbore has been drilled, and the proximal end has been threaded, the entire tool is coated with titanium nitride yo improve the wear resistance of the tool. Titanium nitride is brittle and has a tendency to crack. It has been discovered that when the titanium nitride cracks, stress concentrations build at the cracks. When these cracks occur on the threaded proximal end of tool  144 , the thin walled material at the thread line tends to fracture. Thus, an improved method of manufacturing a large diameter bore aspirating tool has been developed. After aspirating tool  144  has been machined, throughbore  134  has been drilled, and proximal end  154  has been threaded, the threads are asked using known masking techniques. The titanium nitride coating  160  is then applied to aspirating tool  144  such that threaded proximal end  154  is not coated (See FIG.  7 ). By masking threaded end  154  of aspirating tool  144 , illustrated as “b” in FIG. 7 during the step of titanium nitride coating, cracks resulting in stress concentrations are not formed in the threads and the aspirating tool  144  is more resistant to fracture. 
     FIGS. 8 and 9 illustrate a small diameter aspirating tool, shown generally as  244 , suitable for use with the above-described apparatus for fragmenting and aspirating tissue. Aspirating tool  244  includes an elongated body  250  having a tip  222  and a threaded proximal end  254 , a stepped throughbore  234 , a transverse bore  232 , and a hexagon engagement portion  252 . Stepped throughbore  234  includes a larger diameter proximal portion  234   a  and a smaller diameter distal portion  234   b . Smaller diameter portion  234   b  is preferably about 0.045 inches in diameter. 
     During manufacturing of aspirating tool  244 , tool body  250  is machined. Next, throughbore  234  is drilled out using a two step process. During the first step, the proximal portion  234   a  of throughbore  234  is drilled out using a drill bit having a diameter of about 1.25-2.5 times larger than the desired diameter of throughbore  234   b . During the second step, the distal portion  234   b  of throughbore  234  is drilled out to the desired diameter. The transition or shoulder  235  is positioned at a node. Preferably, distal portion  234  has a diameter of about 0.045 inches. After throughbore  234  has been drilled out, proximal end  254  of aspirating tool  244  can be tapped or threaded and tool  244  can be coated with a titanium nitride coating. 
     Referring to FIGS. 10 and 11, if an angled tool is desired, aspirating tool  244  can be bent after drilling throughbore  234  by inserting a metal rod (not shown) into throughbore  234  and mechanically bending aspirating tool  244  until the desired curvature is achieved. The metal rod prevents throughbore  234  from collapsing during the bending step. 
     It will be understood that various modifications may be made to the embodiments disclosed herein. For example, the order of the process steps for manufacturing the aspirating tools may be varied. Further, a variety of different size throughbores may be formed in the aspirating tools. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.