Patent Publication Number: US-9421028-B2

Title: Ultrasonic osteotome

Description:
CROSS-REFERENCE TOP RELATED APPLICATION 
     This application is a division of application Ser. No. 13/268,057 filed Oct. 7, 2011, now U.S. Pat. No. 8,894,673. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention also pertains to an ultrasonic surgical blade utilizable for incising bone. 
     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. 
     Over the past 30 years, several ultrasonic tools have been invented which can be used to ablate or cut tissue in surgery. Wuchinich et al. in U.S. Pat. No. 4,223,676 and Idemoto et al in U.S. Pat. No. 5,188,102 disclose such devices. 
     Ultrasonic surgical devices generally fall into two categories. One is a blunt tip hollow probe that vibrates at frequencies between 20 kc and 100 kc, with amplitudes up to 300 microns or more. Such devices ablate tissue by either producing cavitation bubbles which implode and disrupt cells, tissue compression and relaxation stresses (sometimes called the jackhammer effect) or by other forces such as microstreaming of bubbles in the tissue matrix. The effect is that the tissue becomes liquefied and separated. It then becomes emulsified with the irrigant solution. The resulting emulsion is then aspirated from the site. Bulk excision of tissue is possible by applying the energy around and under unwanted tumors to separate it from the surrounding structure. The surgeon can then lift the tissue out using common tools such as forceps. 
     A second kind of ultrasonic device uses a flat blade instead of a blunt hollow probe. Here a cutting action takes place. Such a flat ultrasonic blade is the subject of U.S. Pat. Nos. 6,379,371 and 6,443,969. As disclosed therein, the blade shape is semicircular at the distal portion with two straight sides parallel to the longitudinal axis and extending back to the shoulder that contacts the vibrating probe. Male threads are shown which mate with the female threaded socket of the probe (or transducer) to allow tight intimate contact of the probe and blade tip shoulder. When the two are torqued together, they form a single resonant body that will vibrate in sympathy with the transducer and generator combination. The distal end of the blade will vibrate with an amplitude set by the mechanical gain of the probe/tip geometry and the input amplitude provided by the transducer generator combination. This motion provided the cutting action for the tissue in question. 
     The blade of U.S. Pat. Nos. 6,379,371 and 6,443,969 was intended for the cutting or excising of bone or similarly hard tissue in surgical applications. In tests conducted in vitro and in vivo, it was noted that the blade, when sharp, cut both hard and soft tissue with similar ease. In delicate operations, such as sinus lift surgery or craniotomies where the goal is to cut an aperture in the front of the skull to expose sinus tissue or brain but not cut the membrane directly beneath the bony structure, this is very important. It is also important in spinal and brain surgery where bone tissue must be cut with a minimum of damage to underlying soft tissues such as the dura mater. It was noted in early in vitro testing that the blade, as it plunged through the cortex of the bone punctured the membrane or ripped it. After some experience, competent surgeons were able to master the technique, but the learning curve was steep. 
     In certain applications, such as sinus cavity lifts and maxillofacial surgery such as third molar extraction, a tool would be useful which could cut the harder bony material with less trauma while sparing the soft tissues underneath. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide an improved ultrasonic osteotome. 
     More particularly, it is an object of the present invention to provide an ultrasonic osteotome that facilitates bone-cutting procedures. 
     Another even more particular object of the present invention is to provide such an ultrasonic osteotome that reduces the likelihood of damage to soft tissues. 
     A further object of the present invention is to provide such an ultrasonic osteotome that exhibits increased stability, particularly in view of the magnitudes of force that are necessary. 
     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 
     An ultrasonic osteotome in accordance with the present invention comprises a shaft having a distal end portion with a lateral outer surface and further comprises a cutting blade connected to the distal end portion of the shaft at least in part at the lateral outer surface. The lateral outer surface extends so far on opposite sides of the blade as to block or stop penetration of the shaft into an incision formed in bone tissue by the blade. 
     Generally, that portion of the lateral outer surface of the shaft that comes into contact with the target tissue of the patient at a surgical site has a total effective width, measured perpendicularly to the blade, which is at least two times the thickness of the blade. More preferably, the tissue-contacting portion of the lateral outer surface has a width that is about three times the thickness of the blade. It is contemplated that the blade is a thin flat plate, with a thickness on the order of 0.020 inch. Consequently, the tissue-contacting portion of the lateral outer surface has a width that is at least about 0.040 to 0.060 inch wide. 
     Where the shaft is cylindrical at its distal end, the width of the tissue-contacting portion of the lateral outer surface is a fraction of the shaft diameter, typically between one-third and two-thirds. As described below, the shaft may have a rounded rectangular cross-section, so that the width of the tissue-contacting portion of the lateral outer surface is a larger fraction of the entire shaft width, as measured transversely to the blade. 
     In one embodiment of the present invention, the blade has an edge formed on at least one side (distal, proximal, or both) with a cutting notch adjacent to the lateral outer surface and a protruding bulge on a side of the notch opposite the lateral outer surface. Preferably, the edge is continuous over or along the notch and the bulge and has an arcuate form. At least along portions of the bulge, the edge must be smooth, that is, free of discontinuities, sharp notches, sharp teeth, or other sharp points that would tend to cut, lacerate, or otherwise damage soft tissue that is disposed adjacent to bone tissue that is being cut with the blade. 
     That portion of the blade&#39;s edge along the notch and the bulge may have an S-shaped configuration. 
     The notch may be beveled, serrated or toothed. In addition, the protruding portion or bulge may be formed with serrations or teeth (see  FIGS. 9-12 ). However, the serrations or teeth along at least an outer aspect of the bulge must be smoothly configured, without discontinuities or sharp points that would cut, lacerate, or otherwise damage soft tissue. 
     In this first embodiment of the invention, the blade is disposed on only one side of the distal end portion of the shaft, the shaft extending in a distal direction beyond the blade. Where the blade is formed with only one notch, either on the distal side or the proximal side, the other side of the blade is gently sloped at an acute angle towards the lateral surface of the shaft, so that the blade has the appearance of a sailboat keel. 
     In another embodiment of the present invention, the blade extends distally beyond a distal tip of the shaft. This embodiment of the osteotome has a blade width, i.e., that dimension of the blade measured between the cutting edge and the outer surface of the shaft, which varies so as to provide the user with multiple choices as to cutting depth. 
     In variations of this embodiment, the blade includes a distal end portion that is attached to the shaft at the blunt distal tip. Thus, the blade is attached to the shaft along the lateral outer surface thereof, as well as at the blunt distal tip. The blade has a pair of opposed major faces and a maximum thickness measured in a given direction perpendicular to the major faces, the blunt distal tip having a width or breadth measured substantially parallel to the given direction, the width or breadth of the shaft tip being sufficiently greater than the thickness of the blade so as to block or stop penetration of the shaft into an incision formed in bone tissue by the distal end portion of the blade. 
     Preferably, in this embodiment of the invention, the blade has a proximal blade portion with a proximally facing edge sloped at an acute angle relative to the lateral outer shaft surface at the distal end portion of the shaft. The distal end portion of the blade has a distally facing convex edge. The convex edge and the proximally facing edge are smoothly continuous with one another in a gently or smoothly arcuate curve. This curve may have the profile of a liquid drop, optionally skewed to one side. 
     Pursuant to another feature of the present invention, where the blade extends distally of the shaft tip, the blade has a first maximum width dimension as measured in a longitudinal direction between the convex blade edge and the blunt distal tip of the shaft. Also, the blade has a second maximum width dimension as measured in a transverse direction between a lateral edge of the blade and the lateral outer surface of the shaft. The first maximum width dimension and the second maximum width dimension may be substantially different from one another for enabling of facilitating variation in a depth of incision made via use of the osteotome. 
     In a specific embodiment of the invention, the blade may extend from one side of the shaft, over the distal shaft tip, to the opposite side of the shaft. In that case, the blade has a third maximum width dimension as measure in a transverse direction between another lateral edge of the blade and the lateral outer surface of the shaft on a side of the shaft opposite the second maximum width dimension. The third maximum width dimension may be different from both the first maximum width dimension and the second maximum width dimension. 
     It is contemplated that the blade is centrally disposed relative to the shaft, so that the blade lies in a common plane with the axis of the distal end portion of the shaft. In that event, the blade is disposed in a plane oriented substantially perpendicularly to the lateral outer surface even when the shaft is cylindrical. However, it is possible for the blade to be eccentrically disposed in a plane that is not coaxial with the distal end portion of the shaft, but extends parallel with the axis. In the latter case, the blunt distal tip extends eccentrically on laterally or transversely opposite sides of the distal end portion of the blade. 
     Pursuant to another feature of the present invention, the shaft and its lateral outer surface are curved to match a curvature of an outer bone surface. Thus, the lateral outer surface of the shaft has an arcuate profile in a longitudinal plane including an axis of the shaft. 
     As indicated above, the shaft may be cylindrical or have a cross-section that is of another shape, such as rectangular with rounded corners. In the latter instance, the lateral outer surface of the shaft includes a portion at the blade that is at least substantially planar. 
     An ultrasonic osteotome in accordance with the present invention facilitates bone cutting by preventing the blade from extending through a target bone tissue mass at a surgical site and substantially into soft tissue underlying the target bone. Thus, the ultrasonic osteotome described herein protects soft tissue while enabling a smooth clean incision through overlying bone. 
     Certain embodiments of the invention provide an adjustability in cutting depth by varying the angle at which the bone cutting blade enters the target tissue. The angle of the distal end portion of the shaft relative to a surface of a target tissue mass is readily observable and is associated with respective incision depths. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front elevational view of a first embodiment of an ultrasonic osteotome in accordance with the present invention. 
         FIG. 2  is a side elevational view of the ultrasonic osteotome of  FIG. 1 . 
         FIG. 3  is a front elevational view of a second embodiment of an ultrasonic osteotome in accordance with the present invention. 
         FIG. 4  is a side elevational view of the ultrasonic osteotome of  FIG. 3 . 
         FIG. 5  is a front elevational view of a third embodiment of an ultrasonic osteotome in accordance with the present invention. 
         FIG. 6  is a side elevational view of the ultrasonic osteotome of  FIG. 5 . 
         FIG. 7  is a front elevational view of a fourth embodiment of an ultrasonic osteotome in accordance with the present invention. 
         FIG. 8  is a side elevational view of the ultrasonic osteotome of  FIG. 7 . 
         FIG. 9  is a front elevational view of a fourth embodiment of an ultrasonic osteotome in accordance with the present invention. 
         FIG. 10  is a side elevational view of the ultrasonic osteotome of  FIG. 9 . 
         FIG. 11  is a top, front and side isometric view of the ultrasonic osteotome of  FIGS. 9 and 10 . 
         FIG. 12  is a top plan view of the ultrasonic osteotome of  FIGS. 9-11 . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 7 and 8  depict an ultrasonic osteotome  10  comprising a shaft  12  having a distal end portion (not separately designated) with a lateral outer surface  14  and a blunt or rounded distal tip  16 . A planar cutting blade  18 , with a shape vaguely similar to that of a sailboat keel, is connected to the distal end portion of shaft  12  along lateral outer surface  14 . 
     Lateral outer surface  14  and concomitantly shaft  12  extend so far on opposite sides of blade  18  as to constitute a block or stop to penetration of the shaft into an incision formed in bone tissue by the blade. More specifically, blade  18  has a pair of opposed major faces  18   a  and  18   b  and a maximum thickness t 1  measured in a given direction perpendicular to major faces  18   a  and  18   b , while shaft  12  has an effective width or breadth w 1  measured substantially parallel to the given measurement direction. Width or breadth w 1  of shaft  12  is sufficiently greater than thickness t 1  of blade  18  so as to block or stop penetration of shaft  12  into an incision formed in bone tissue by a distal end portion of the blade. In the case of osteotome  10 , the effective width or breadth w 1  of lateral outer surface  14  and shaft  12  is approximately equal to the entire width of the lateral outer surface  14  on the side of shaft  12  carrying blade  18 . Where the shaft has a cross-sectional shape that is a circle rather than an oblong with rounded corners, the effective width or breadth of the lateral outer surface and of the shaft may be less than the diameter of the shaft. 
     On a distal side, blade  18  has an edge  20  with a cutting notch  22  adjacent to lateral outer surface  14 . Edge  20  also has a protruding portion or bulge  24  on a side of notch  22  opposite lateral outer surface  14 . Edge  20  is continuous over or along notch  22  and bulge  24  and has an arcuate S-shaped form. In other words, blade edge  20  has no discontinuities, sudden gaps, sharp notches, sharp teeth, or other pointy features that would tend to cut, lacerate, or otherwise damage soft tissue that is disposed adjacent to bone tissue that is being cut with blade  18 . 
     Notch  22  may be beveled, serrated or toothed. Protruding portion or bulge  24  may be beveled, serrated or toothed, but any serrations or teeth particularly along a laterally or radially outer periphery of blade  18  must be smoothly configured, without discontinuities or sharp points that would cut, lacerate, or otherwise damage soft tissue. Generally, notch  22  comes into contact only with bone tissue, while protruding portion or bulge  24 , particular a most lateral part thereof, may come into contact with soft tissue underlying a target bone structure. 
     Blade  18  is disposed on only one side of the distal end portion of shaft  12 . Shaft  12  extends in a distal direction beyond blade  18 . Blade  18  is formed on a proximal side with a generally linear edge section  26  gently sloped at an acute angle relative to lateral outer surface  14 . It is to be noted that blade  18  may be modified to provide notch  22  and bulge  24  on a proximal side and linear edge section  26  on a distal side. Alternatively, both the distal side and the proximal side may be formed with notch and bulge, in which case there is no linear edge section  26 . 
     Shaft  12  is depicted as having a rounded oblong configuration, with a rectangular cross-section having rounded corners. However, other shaft geometries, such as cylindrical or triangular are possible. 
       FIGS. 1 and 2  depict another ultrasonic osteotome  30  comprising a shaft  32  having a distal end portion (not separately enumerated) with a cylindrical lateral outer surface  34  and a blunt distal tip  36 . A cutting blade  38  is connected to the distal end portion of shaft  32  both along cylindrical lateral outer surface  34  and blunt distal tip  36 . 
     Blade  38  has a proximal blade portion  40  with a proximally facing approximately linear edge  42  sloped at an acute angle relative to lateral outer shaft surface  34 . Blade  38  has a distal end portion  44  with a distally facing convex edge  46 . Convex edge  46  and linear edge  42  are continuous with one another in a gently or smoothly arcuate curve having the profile of a liquid drop, skewed to one side. Blade edges  42  and  46  may be beveled or serrated, but any serrations must be smooth, without points or jagged features, to avoid soft tissue damage. 
     Lateral outer surface  34  extends so far on opposite sides of proximal blade portion  40  as to block or stop penetration of shaft  32  into an incision formed in bone tissue by the proximal portion of blade  38 . Similarly, blunt distal tip  36  extends so far on opposite sides of distal blade portion  44  as to block or stop penetration of shaft  32  into an incision formed in bone tissue by the distal portion of blade  38 . For instance, where blade  38  has a pair of opposed major faces  38   a  and  38   b  and a maximum thickness t 2  measured in a given direction perpendicular to major faces  38   a  and  38   b , blunt distal tip  36  has a width or breadth w 2 , measured substantially parallel to the given measurement direction, that is sufficiently greater than thickness t 2  of blade  38  so as to block or stop penetration of blunt distal tip  36  into an incision formed in bone tissue by distal end portion  44  of blade  38 . 
     Blade  38  has a width, i.e., that dimension of the blade measured between the cutting edge  42 ,  46  and outer surface  34 ,  36  of shaft  32 , which varies so as to provide the user with multiple choices as to cutting depth. Thus, depending on the angle of tilt of shaft  32  relative to the surface of a target bone structure during an application of the ultrasonically vibrating osteotome  30  to the bone, blade  38  generates an incision of adjustable depth. 
     More specifically, proximal portion  40  of blade  38  has a maximum width d 1  measured between a most laterally displaced point  48  of the blade edge and lateral outer surface  34 , while distal end portion  44  of blade  38  has a maximum width d 2  measured between a most distal point  49  of blade edge  46  and blunt distal tip  36 . Typically, width measurements d 1  and d 2  are significantly different from one another and convex edge  46  provides a continuous change in blade width between point  48  and  49 , thereby enabling the user to fine tune the depth of cut by controlling the angle at which shaft  32  meets the bone surface at the surgical site. 
       FIGS. 3 and 4  depict a further ultrasonic osteotome  50  comprising a shaft  52  having a distal end portion (not separately designated) with a cylindrical lateral outer surface  54  and a blunt distal tip  56 . A cutting blade  58  is connected to blunt distal tip  36  and to lateral outer surface  54  on opposite sides of shaft  52 . 
     Blade  58  has a first proximal blade portion  60  with a proximally facing approximately linear edge  62  sloped at an acute angle relative to lateral outer shaft surface  54  on one side of shaft  52 . Blade  58  has a second proximal blade portion  60 ′ with a proximally facing approximately linear edge  62  sloped at an acute angle relative to lateral outer shaft surface  54  on an opposite side of shaft  52 . Blade  88  has a distal end portion  64  with a distally facing convex edge  66 . Convex edge  66  and linear edges  62  and  62 ′ are continuous with one another in a gently or smoothly arcuate curve having the profile of an asymmetric liquid drop. Blade edges  62 ,  62 ′ and  66  may be beveled or serrated, but any serrations must be smooth, without points or jagged features, to avoid soft tissue damage. 
     Lateral outer surface  54  extends so far on opposite sides of proximal blade portion  60  or  60 ′ as to block or stop penetration of shaft  52  into an incision formed in bone tissue by that proximal portion of blade  58 . Similarly, blunt distal tip  56  extends so far on opposite sides of distal blade portion  64  as to block or stop penetration of shaft  52  into an incision formed in bone tissue by the distal portion of blade  58 . For instance, where blade  58  has a pair of opposed major faces  58   a  and  58   b  and a maximum thickness t 3  measured in a given direction perpendicular to major faces  58   a  and  58   b , blunt distal tip  56  has a width or breadth w 3 , measured substantially parallel to the given measurement direction, that is sufficiently greater than thickness t 3  of blade  58  so as to block or stop penetration of blunt distal tip  56  into an incision formed in bone tissue by distal end portion  64  of blade  58 . 
     Blade  58  has a width dimension, measured between the continuous cutting edge  62 ,  66 ,  62 ′ and the outer surface  54 ,  56  of shaft  52 , which varies so as to provide the user with multiple choices as to cutting depth. Accordingly, blade  58  is utilizable to generate +an incision of a depth that depends on the angle of tilt of shaft  52  relative to the surface of a target bone structure during an application of the ultrasonically vibrating osteotome  50  to the bone. 
     First proximal portion  60  of blade  58  has a maximum width d 1 ′ measured between (i) a most laterally displaced point  68  of the blade edge on one side of shaft  52  and (ii) lateral outer surface  54 . Second proximal blade portion  60 ′ has a maximum width d 3 ′ measured between (i) a most laterally displaced point  68 ′ of the blade edge on another side of shaft  52  and (ii) lateral outer surface  54 . Distal end portion  64  of blade  58  has a maximum width d 2 ′ measured between a most distal point  69  of convex blade edge  66  and blunt distal tip  56 . Typically, width measurements d 1 ′, d 2 ′, d 3 ′ are significantly different from one another and convex edge  66  provides a continuous change in blade width between points  68 ,  68 ′ on the one hand and point  69  on the other hand, thereby enabling the user to fine tune the depth of cut by controlling the angle at which shaft  52  meets the bone surface at the surgical site. 
       FIGS. 5 and 6  depict yet another ultrasonic osteotome  70  comprising a shaft  72  having a distal end portion (not separately enumerated) with a cylindrical lateral outer surface  74  and a blunt distal tip  76 . A cutting blade  78  is connected to the distal end portion of shaft  72  only along cylindrical lateral outer surface  74 . Blade  78  is disposed in greatest part only along one side of shaft  72 . Lateral outer surface  74  and blunt distal tip  76  extend so far on opposite sides of blade  78  as to block or stop penetration of shaft  72  into an incision formed in bone tissue by the blade. 
     Blade  78  has a proximal blade portion  80  with a proximally facing approximately linear edge  82  sloped at an acute angle relative to lateral outer shaft surface  74 . Blade  78  has a distal end portion  84  with a distally facing convex edge  86 . Distal end portion  84  is disposed distally of, and nearly entirely laterally of, blunt distal tip  76 . Convex edge  86  and linear edge  82  are continuous with one another in a gently or smoothly arcuate curve having the profile of a liquid drop, skewed to one side. Blade edges  82  and  86  may be beveled or serrated, but any serrations must be smooth, without points or jagged features, to avoid soft tissue damage. 
     Lateral outer surface  74  extends so far on opposite sides of proximal blade portion  80  as to block or stop penetration of shaft  72  into an incision formed in bone tissue by the proximal portion of blade  78 . Similarly, blunt distal tip  76  extends so far on opposite sides of distal blade portion  84  as to block or stop penetration of shaft  72  into an incision formed in bone tissue by the distal portion of blade  78 . For instance, where blade  78  has a pair of opposed major faces  78   a  and  78   b  and a maximum thickness t 4  measured in a given direction perpendicular to major faces  78   a  and  78   b , blunt distal tip  76  has a width or breadth w 4 , measured substantially parallel to the given measurement direction, that is sufficiently greater than thickness t 4  of blade  78  so as to block or stop penetration of blunt distal tip  76  into an incision formed in bone tissue by distal end portion  84  of blade  78 . 
     Blade  78  has a width, i.e., that dimension of the blade measured between the cutting edge  82 ,  86  and outer surface  74 ,  76  of shaft  72 , which varies so as to provide the user with multiple choices as to cutting depth. Thus, depending on the angle of tilt of shaft  72  relative to the surface of a target bone structure during an application of the ultrasonically vibrating osteotome  70  to the bone, blade  78  generates an incision of adjustable depth. 
     More specifically, proximal portion  80  of blade  78  has a maximum width d 1 ″ measured between a most laterally displaced point  88  of the blade edge and lateral outer surface  74 , while distal end portion  84  of blade  78  has a maximum width d 2 ″ measured between a most distal point  89  of blade edge  86  and blunt distal tip  76 . Typically, width measurements d 1 ″ and d 2 ″ are significantly different from one another and convex edge  86  provides a continuous change in blade width between point  88  and  89 , thereby enabling the user to fine tune the depth of cut by controlling the angle at which shaft  72  meets the bone surface at the surgical site. 
     Blades  18 ,  38 ,  58 , and  78  are centrally disposed relative to the respective shafts  12 ,  32 ,  52 , and  72 , so that the blades each lie in a common plane with an axis of symmetry of the distal end portion of the respective shaft. Thus, blades  18 ,  38 ,  58 , and  78  are disposed in planes oriented substantially perpendicularly to lateral outer surfaces  14 ,  34 ,  54 , and  74 . Alternatively, it is possible for blades  18 ,  38 ,  58 , and  78  to be eccentrically disposed, i.e., disposed in planes that are not coaxial with the distal end portions of the respective shafts  12 ,  32 ,  52 , and  72 , but extend parallel with the respective axis of symmetry. In this alternative configuration, blunt distal tips  36 ,  56 , and  76  extend eccentrically on laterally or transversely opposite sides of distal end portions  44 ,  64 , and  84  of blades  32 ,  52 , and  72 , respectively. 
     Shafts  12 ,  32 ,  52 , and  72  and the respective lateral outer surfaces  14 ,  34 ,  54 , and  74  may be curved to match curvatures of outer bone surfaces, as indicated at  90 ,  92 ,  94 , and  96 . In that case, lateral outer surfaces  14 ,  34 ,  54 , and  74  each have an arcuate profile in a longitudinal plane including an axis of the respective shaft  12 ,  32 ,  52 , and  72 . 
     An ultrasonic osteotome in accordance with the present invention facilitates bone cutting by preventing the blade from extending through a target bone tissue mass at a surgical site and substantially into soft tissue underlying the target bone. Thus, the ultrasonic osteotome described herein protects soft tissue while enabling a smooth clean incision through overlying bone. 
     Generally, that portion of lateral outer surface  14 ,  34 ,  54 ,  74  or of blunt distal tip  36 ,  56 ,  76  that comes into contact with the target tissue of the patient at a surgical site has a total effective width, measured perpendicularly to the respective blade  18 ,  38 ,  58 ,  78 , which is at least two times the thickness of the blade. More preferably, the tissue-contacting portion of the lateral outer surface  14 ,  34 ,  54 ,  74  or of blunt distal tip  36 ,  56 ,  76  has a width that is about three times the thickness of the respective blade  18 ,  38 ,  58 ,  78 . It is contemplated that blades  18 ,  38 ,  58 ,  78  are thin flat plates, with thicknesses on the order of 0.0020 inch. Consequently, the tissue-contacting portion of the lateral outer surface  14 ,  34 ,  54 ,  74  or of blunt distal tip  36 ,  56 ,  76  has a width that is at least about 0.0040 to 0.0060 inch wide. 
     In the case of shafts  32 ,  52 , and  72  which are cylindrical at their distal ends, the widths of the tissue-contacting portion of the lateral outer surface  14 ,  34 ,  54 ,  74  is a fraction of the shaft diameter, typically between one-third and two-thirds. 
     Blades  18 ,  38 ,  58 , and  78  provide incision depths generally between 4 and 10 mm. 
       FIGS. 9-12  depict an ultrasonic osteotome  110  comprising a shaft  112  having a distal end portion (not separately designated) with a lateral outer surface  114  and a blunt or rounded distal tip  116 . A serrated planar cutting blade  118 , with a shape vaguely similar to that of a fish fin, is connected to the distal end portion of shaft  112  along lateral outer surface  114 . 
     Lateral outer surface  114  and concomitantly shaft  112  extend so far on opposite sides of blade  118  as to constitute a block or stop to penetration of the shaft into an incision formed in bone tissue by the blade. More specifically, blade  118  has a pair of opposed major faces  118   a  and  118   b  and a maximum thickness t 1 ′ measured in a given direction perpendicular to major faces  118   a  and  118   b , while shaft  112  has an effective width or breadth w 1 ′ measured substantially parallel to the given measurement direction. Width or breadth w 1 ′ of shaft  112  is sufficiently greater than thickness t 1 ′ of blade  118  so as to block or stop penetration of shaft  112  into an incision formed in bone tissue by the blade. In the case of osteotome  110 , the effective width or breadth w 1 ′ of lateral outer surface  114  and shaft  12  is generally between one-third and one-half the radius of shaft  112  (which is cylindrical except for distal tip  116 ). Thus, lateral surface  114  is a portion of the entire cylindrical outer surface of shaft  112 , that portion being located on the side of shaft  112  carrying blade  118 . 
     Blade  118  has a cutting edge  120  with an inner or notch section  122  adjacent and inclined with respect to lateral outer surface  114 . Edge  120  also has a protruding portion or bulge  124  on the distal or forward facing side. Blade  118  is disposed on only one side of the distal end portion of shaft  112 . Shaft  112  extends in a distal direction beyond blade  18 : distal tip  116  is located distally of bulge  124 . Blade  118  is formed on a proximal and outer side with a generally linear edge section  126  gently sloped at an acute angle relative to lateral outer surface  114 . 
     Inner edge or notch section  122 , edge bulge  124  and outer edge section  126  are formed with serrations or teeth  128 . Serrations or teeth  128 ′ along an outer aspect of bulge  124  (at least) are smoothly configured, without discontinuities or sharp points that would cut, lacerate, or otherwise damage soft tissue. 
     Shafts  112  and lateral outer surface  114  may be curved to match curvatures of outer bone surfaces, as discussed above with reference to bone curves  90 ,  92 ,  94 , and  96 . 
     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 example, while the blades shown in the drawings are primarily designed for cutting bone tissue under a distally applied (pushing) force, it is possible to rearrange the orientation of the blades on the shafts so that cutting occurs mainly under a proximally applied (pulling) force. Pursuant to such a modification, in the embodiment of  FIGS. 7 and 8 , notch  22  and bulge  24  would face in the proximal direction rather than the depicted distal direction. Similarly, in the embodiment of  FIGS. 9-12 , blade  118  could be reversed 180° in its orientation. 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.