Patent Publication Number: US-2015088137-A1

Title: Ultrasonic surgical instrument with dual end effector

Description:
FIELD OF THE INVENTION 
     This invention relates to an ultrasonic surgical instrument. More particularly, this invention relates to an ultrasonic surgical instrument with dual end effectors. Where the instrument particularly takes the form of an instrument to cut tissue such as cartilage and bone, the dual end effectors are parallel cutting blades. 
     BACKGROUND OF THE INVENTION 
     In the field of orthopedics, the cutting of living bone is a prerequisite for many procedures. Such procedures include the reconstruction of damaged tissue structures due to accidents, the grafting of healthy bone into areas damaged by disease, or the correction of congenital facial abnormalities like a receding chin line. Over several centuries, these tasks were performed through the utilization of devices called bone saws. 
     Traditional bone saws are categorized into several basic categories. Hand powered saws or drills are just that, hand held devices which require the operator to move the device in a fashion similar to that used for carpentry tools. Powered devices, whether electric or pneumatic, are of either the reciprocating or rotary type. The reciprocating devices use a flat, sword like blade where the back and forth motion is provided by a motor instead of the hand. The rotary devices use a rotating motor to spin a drill bit or a blade which has teeth arranged around its circumference similar to a table saw blade. All of these traditional bone saws are used today in medical procedures around the world. 
     While traditional saws are functional, they have many disadvantages. With either the band or reciprocating saws, for instance, it is not easy to initiate and direct a cut. A cut must start from an edge or, alternatively, a starting hole must be used. To create a starting hole, a drill or similar instrument is operated to bore into the bone. Subsequently, a cutting blade is inserted into the bored hole. The user can then proceed to cut. Alternatively, a rotary type blade may be used. However, when a rotary blade is used, the cut must follow a relatively straight path to prevent the blade from binding in the cut. With all blades the ability to create a curved or compound angle cut is extremely limited by the blade chosen. The relatively thick blades have a wide kerf; so that a significant thickness of the viable bone is lost in the cutting procedure. Physicians would like this width to be as thin as possible in most procedures where reconstruction is necessary. 
     Above all, the relatively slow linear or tangential speeds of conventional bone saw blades coupled with the teeth necessary for cutting result in high frictional losses, which becomes manifested as heat. Heat will cause necrosis of the tissue if the bone temperatures reach 47EC for more than a few seconds. When tissue necroses, the bone recedes after the surgery as the necrotic bone is overgrown. During such natural post-surgical tissue developments, the thickness of the cuts in the bone actually increases. The bone rescission process must be complete before healing can begin. To prevent the shortening of the length of the bone, metal plates and screws are used to fix the bone fragments in proper position. All of these factors obviously lead to increased operative time, and more importantly, to dramatically increased healing time, since the bone must knit across a greater span. Some studies have shown the strength of the bone to be effected negatively as well 
     To limit the tissue temperature rise in an attempt to reduce necrosis, some traditional surgical saws provide cooling liquid to the surgical site. Several researchers have proposed the use of ultrasonic tools for bone separation. The use of ultrasonic surgical instruments for cutting through various tissues is well known. While these devices are superior to the traditional saws in several aspects such as reduced kerf size, reduced noise, and superior ability for making complex geometric cuts, the temperature rise in bone due to frictional heating at the blade/tissue interface is still a significant problem. The problem is exacerbated with the use of ultrasonics due to the rapid motion involved as compared to that of traditional reciprocating saws. 
     U.S. Pat. No. 6,379,371 and U.S. Pat. No. 6,443,969 disclose an ultrasonic bone cutting blade with structure permitting adequate cooling when cutting bone. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide an ultrasonic bone cutting instrument with improved bone cutting capabilities. 
     A more particular object of the present invention to provide such an ultrasonic bone cutting instrument that cuts bone more quickly, with greater facility. 
     A further object of the present invention is to provide such improvements that may also be used for other types of ultrasonic surgical instruments. 
     These and other objects of the present invention will be apparent from the descriptions and drawings herein. Although every object of the invention is attainable by at least one embodiment of the invention, there is not necessarily any single embodiment that achieves all of the objects of the invention. 
     SUMMARY OF THE INVENTION 
     The present invention recognizes the need which exists for a more efficient ultrasonic bone cutting instrument that expedites bone cutting. The invention is directed in part to an ultrasonic cutting instrument which does not require predrilled holes for cutting, allows complex geometric cuts, has one or more continuous cutting surfaces, and provides for liquid irrigation at the blade/tissue interface. More specifically, the present invention pertains in part to an ultrasonically vibrated cutting instrument with a provision for delivery of a cooling medium for reducing and limiting thermal damage to living tissue. The present invention specifically targets the application of cutting viable bones in surgery, although the device is not exclusive to this application. 
     The present invention contemplates ultrasonic surgical instruments with multiple tools extending parallel to one another. The tools have respective operating heads and extend parallel to one another, generally side by side. However, one tool could be located concentrically within another tool. In the latter case the tools would have differently configured heads. Where the tools are laterally disposed, the heads might be mirror symmetric. 
     As discussed in detail hereinafter, an ultrasonic instrument in accordance with the present invention may take the form of a bone cutter, with planar blade bodies disposed adjacent one another, for out-of phase movement in parallel planes. 
     An ultrasonic surgical instrument in accordance with the present invention comprises at least two tools each including a respective operating head with an operative surface or edge. At least one source of ultrasonic mechanical vibratory energy is provided which produces at least two vibration modes out of phase with one another. The tools are each connected to the source of ultrasonic mechanical vibratory energy for enabling transmission of a respective one of the vibration modes into the respective tool so that the tools are driven out of phase with one another. 
     The tools typically extend parallel to one another in coextensive relationship. Thus the operative surfaces or edges of the tools are juxtaposed to one another. 
     The operating heads may be identical to one another. However, in some instruments, the operating heads may be mirror symmetric of concentric. In that latter case, one tool shaft may extend coaxially through the other tool shaft, so that one of the operating heads is surround by the other operating head. 
     Where the instrument is particularly adapted for bone cutting, the heads of the two tools may take the form of planar cutting blade bodies. Accordingly, an ultrasonic surgical instrument of the bone-cutting variety comprises, in accordance with the present invention, at least two cutting blades each comprising a substantially flat or planar blade body having a cutting edge extending parallel to the cutting edge of the blade body of the other of the at least two cutting blades. The instrument includes at least one source of ultrasonic mechanical vibratory energy having at least two vibration modes out of phase with one another. The at least two cutting blades are each connected to the source of ultrasonic mechanical vibratory energy for enabling transmission of a respective one of the vibration modes into the respective blade body so that the at least two cutting blades are driven out of phase with one another. 
     The two vibration modes typically have a common ultrasonic frequency. In addition, the two vibration modes are typically 180° out of phase with one another. Alternative phase relationships are possible. For instance, the vibration modes may be out of phase by 90° or a quarter wave. Alternatively, the phase difference may vary as when the activation frequencies differ slightly from one another (e.g., by 1000 Hz). 
     Pursuant to one embodiment of the present invention, the source of ultrasonic vibratory energy includes a single transducer assembly and a half wave connector horn, one and only one of the shanks of the at least two cutting blades being connected to the transducer assembly via the half wave horn, the other shank being connected directly to the transducer assembly. 
     Pursuant to another embodiment of the present invention, the source of ultrasonic vibratory energy includes two distinct transducer assemblies each producing one of the vibration modes and connected to a respective one of the at least two cutting blades. The two vibration modes may have one ultrasonic frequency in common and the vibration modes may be 180° out of phase with one another. 
     The cutting edge of each of the cutting blades preferably includes a smooth continuous cutting edge. The cutting edge is preferably disposed in a single plane and has an arcuate section at the distal end, with a pair of straight sections continuous with the arcuate section at opposite ends thereof. Each shank may be provided with an axially extending bore for the conveyance of cooling fluid to the respective cutting edge, the respective blade body being provided with an axially extending through-slot communicating at one end with the bore. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall view of a surgical system having a dual ultrasonic cutting blade in accordance with the present invention. 
         FIG. 2  is a schematic partial side elevational view of an ultrasonic cutting instrument having two blades, in accordance with the present invention. 
         FIG. 3  is a schematic perspective view of one of the blades of  FIG. 2   
         FIG. 4  is partially a block diagram and partially a side elevational view of an alternative embodiment of an ultrasonic cutting instrument having two blades, in accordance with the present invention. 
         FIG. 5  is a diagram of another dual ultrasonic cutting instrument in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIGS. 1 and 2 , an ultrasonic surgical system includes a handpiece  10  carrying a pair of laterally juxtaposed tools in the form of bone cutting blades  12  and  12 ′ disposed in parallel to one another. Handpiece  10  is attached to blades  12  and  12 ′ via respective probes  14  and  14 ′ and further includes a housing  16  which encases two piezoelectric crystal assemblies  17  and  17 ′ each of the kind disclosed in U.S. Pat. No. 5,371,429 to Manna. In response to two sinusoidal oscillating signals transmitted over a cable  18  from an ultrasonic generator  20 , the crystal assemblies  17  and  17 ′ in the handpiece produce longitudinal ultrasonic pressure waves transmitted through probes  14  and  14 ′ to blades  12  and  12 ′. Signal generator  20  is activated via a footswitch  22 . Handpiece  10  is also connected to an irrigation pump  24  via a tube  26 . Pump  24  moves an irrigant liquid from a reservoir or IV type hanging bag  28  through tube  26  to handpiece  10  in response to a signal carried over a cable  30  from signal generator  20  under the control of footswitch  22 . 
     The mechanical vibrations produced by the piezoelectric crystal assemblies  17  and  17 ′ in handpiece  10  are amplified mechanically via the transducers&#39; shapes and still further by the shapes of probes  14  and  14 ′ and blades  12  and  12 ′, using techniques known to those skilled in the art of ultrasonics. Probes  14  and  14 ′ are attached to handpiece  10  via externally threaded connections  31  and  31 ′, shown in  FIG. 2 . Probes  14  and  14  ‘ are thus replaceable by the user to facilitate the use of disposable sterile blades  12  and  12 ’ from one procedure to the next. Handpiece  10  may be sterilized by autoclaving as well as by other conventional methods. While probes  14  and  14 ′ can be sterilized, maintaining a good cutting edge and cleanliness is such a key issue that a disposable tip or a disposable tool/tip assembly is envisioned. The primary purpose of probes  14  and  14 ′ is to mechanically amplify the vibrations from the piezoelectric transducer assemblies  17  and  17 ′ and transmit those vibrations through to cutting blades  12  and  12 . 
     Blades  12  and  12 ′ are mirror symmetric and include planar operating heads or blade bodies  40  and  40 ′ with facing surfaces  102  and  102 ′ that are planar and closely disposed in parallel with one another. Generally, surfaces  102  and  102 ′ are spaced from one another by a gap (not designated) that is so narrow as to facilitate the production of a single cut while being conducive to the flow of liquid coolant between blades  12  and  12 ′. 
       FIG. 3  depicts cutting blade  12 , while cutting blade  12 ′ is essentially a mirror image thereof. As shown in  FIGS. 2 and 3 , blades  12 ,  12 ′ each include an integral shank portion  32 ,  32 ′ having an external screw thread  34  for replaceably mounting the blade to the respective probe  14 ,  14 ′. Alternatively, blades  12  and  12 ′ may be permanently attached to probes  14  and  14 ′. In the former case, blades  12 ,  12 ′ are tightened by a wrench (not shown) applied to wrench flats  36  on shank portions  32 ,  32 ′. Blades  12  and  12 ′ are shaped to amplify the longitudinal vibratory motions. More specifically, blades  12 ,  12 ′ include a shaft  37 ,  37 ′, intermediate shank  32 ,  32 ′ and planar body portion  40 ,  40 ′ comprising serial tapered or wedge-shaped sections  38 ,  38 ′ and  39 ,  39 ′ for focusing or concentrating ultrasonic vibratory energy and transmitting the energy to planar bodies  40 ,  40 ′ of blades  12 ,  12 ′. Each whole transducer half, horn and tip assembly is designed to resonate in a longitudinal or back and forth type of motion. This motion provides the cutting action at the tips of blades  12 ,  12 ′. 
     Planar blade body portions  40 ,  40 ′ are provided at ends opposite tapered portions  38 ,  38 ′ and  39 ,  39 ′ and shanks  32 ,  32 ′ with smooth continuous blade edges  42 ,  42 ′ including a central circularly arcuate section  44  ( FIG. 3  only) and a pair of linear end sections  46  and  48 , all in a single plane for each blade. Blade or cutting edge  44  is sharpened along a full radius of arcuate section  44 , as well as along straight sections  46  and  48 , with a knife type edge that can smoothly be drawn back and forth in a brushing type motion. This cutting edge structure allows the user to maintain a constant motion at the tip, which has been shown to be important to prevent overheating of the tissue at the surgical site. More particularly, blade edges  42  and  42 ′ are each beveled along a laterally outward side  104  and  104 ′ ( FIG. 2 ), facing away from the other blade  12 ′ and  12 , so that the peripheries are closely aligned for facilitating the production of a smooth narrow cut. 
     As further illustrated in  FIGS. 2 and 3 , blades  12  and  12 ′ also incorporate structure providing a path for coolant from irrigation pump  24  ( FIG. 1 ) to reach blade edges  42  and  42 ′, as well as tissues being cut during a surgical procedure. For conducting irrigant to blade edges  42  and  42 ′ and the surgical site, probes  14  and  14 ′ are formed with axial passageways or bores  50  and  50 ′ which communicate with respective axial passageways or bores  52  and  52 ′ in blades  12  and  12 ′ and more particularly in shanks  32  and tapered blade portions  38  and  39 . The irrigation fluid is typically a sterile saline solution supplied in hanging bag  28  ( FIG. 1 ). Bag  28  is punctured with a vented IV spike supplied at the end of a sterile tube set  54 . The spike allows the fluid to flow into a silicone tube section  55  of tube  26  of set  54 . Silicone tube section  55  passes through pump  24  which takes the form of a peristaltic or roller type pump. Pump  24  pushes the fluid along tube  26  to a connection at the handpiece  10 . The fluid travels through an integral channel inside the handpiece  10 , as described in U.S. Pat. No. 5,371,429. From handpiece  10  the fluid travels through probes  14  and  14 ′ to blades  12  and  12 ′. 
     The disclosures of U.S. Pat. Nos. 6,379,371 and 6,443,969 are hereby incorporated by reference to explicate further the possible structures of blades  12  and  12 ′. For instance, each blade  12 ,  12 ′ may include a longitudinal or axially extending through-slot  56  in the respective planar body portion  40 ,  40 ′ facilitating fluid distribution not only along cutting edges  42 ,  42 ′ but also throughout the gap between blade bodies  40 ,  40 ′ (and tapered blade sections  39 ,  39 ′). 
     Probes  14  and  14 ′ extend side by side and parallel to one another. Probes  14  and  14 ′ have respective shafts, heads (blades  12  and  12 ′) and coupling shanks  32 . 
     Tools or blades  12  and  12 ′ and more particularly planar blade body portions  40  and  40 ′ thereof extend parallel to one another in coextensive relationship. Thus the operative surfaces or edges  42  and  42 ′ of the tools are juxtaposed to one another. Planar blade bodies  40  and  40 ′ are disposed adjacent one another, for out-of phase movement in parallel planes. Piezoelectric crystal assemblies  17  and  17 ′ are transducers that function as respective sources of ultrasonic mechanical vibratory energy producing respective vibration modes that are out of phase with one another. Ultrasonic signal generator  20  produces dual out-of-phase electrical waveforms that are separately fed to transducers or crystal assemblies  17 ,  17 ′. Shanks  31  and  31 ′ of tools or blades  12  and  12 ′ are respectively connected to piezoelectric crystal assemblies  17  and  17 ′ for enabling transmission the respective modes of mechanical vibratory energy into the respective tool shafts so that the tools or blades  12  and  12 ′ are driven out of phase with one another. 
     The two vibration modes of crystal assembly transducers  17 ,  17 ′ typically have a common ultrasonic frequency. In addition, the two vibration modes are typically 180° out of phase with one another. Alternative phase relationships are possible. For instance, the vibration modes may be out of phase by 90° or a quarter wave. Alternatively, the phase difference may vary continuously by having the activation frequencies differ slightly from one another (e.g., by 1000 Hz). The frequency difference is enough to enable phase shifting but not enough to appreciably affect the resonance or standing wave characteristics of the blades  12 ,  12 ′. 
     As depicted in  FIG. 4 , an ultrasonic surgical instrument  60  includes two cutting blades  62 ,  64  and a singular source  66  of ultrasonic vibratory energy in the form of a piezoelectric transducer assembly. One cutting blade  62  is connected directly to transducer assembly  66 . The other cutting blade  64  is connected indirectly to transducer assembly  66  via a half wave connector horn  68 . Half-wave horn  68  causes blade  64  to oscillate 180° out of phase with blade  62 . 
       FIG. 5  schematically depicts an ultrasonic surgical instrument  70  including two concentrically or co-axially disposed tools or probes  72  and  74  each operatively connected to a respective source  76 ,  78  of ultrasonic waveform energy such as a piezoelectric crystal array. Sources  76  and  78  produce ultrasonic standing waves in tools or probes  72 ,  74  that are out of phase with one another. Surgical instrument may serve as a bone drill, with a central suction channel  80 . 
     Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. For instance, it is possible for an ultrasonic instrument assembly to incorporate plural ultrasonic instrument tools with respective vibration modes that are out of phase with one another by a quarter wave (90°) or some other magnitude. Moreover, the phase shift might be varying, for instance, where the vibration modes are of different frequencies. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.