Abstract:
A torsional dissection tip and method of use comprising a longitudinal-torsional resonator having a cutting surface at a distal end with cutting teeth of a pitch optimized to the torsional or longitudinal displacement of the distal tip. The present art apparatus and method of use utilizes uniquely designed cutting surface geometries with the aforesaid pitch attributes for surgical applications. Utilization of the present art torsional dissection tip allows a surgeon to easily remove hard tissues such as bone without moving the present art instrument to any site except that which is to be dissected.

Description:
This application claims priority of U.S. Provisional Patent Application No. 60/584,978, filed Jul. 2, 2004 entitled Torsional Pineapple Dissection Tip. 
    
    
     BACKGROUND OF THE INVENTION 
     The art of the present invention relates to torsional dissection tips in general and more particularly to a tip for a linear or longitudinal ultrasonic generator which provides uniquely patterned and formed teeth which are able to uniquely provide torsional and linear dissection of hard or dense biological tissues including intracranial bone. The present art embodiments utilize a unique substantially pineapple shaped head. The art of the present invention is especially suited for dissection of bone and calcified neoplasm during neurosurgery, spinal surgery, orthopedic surgery, plastic/reconstructive surgery, and ear, nose, and throat surgery without the deleterious effects to nearby tissues presented with high speed drilling. 
     The prior art describes a longitudinal-torsional ultrasonic tissue dissection apparatus in U.S. application No. 09/833,109 filed Apr. 11, 2001 by Wuchinich, entitled Longitudinal-Torsional Ultrasonic Tissue Dissection published Nov. 29, 2001 with U.S. publication number 2001/0047166 A1. The aforesaid prior art describes an apparatus for providing torsional movement from a longitudinal ultrasonic generator but fails to provide optimum cutting teeth or head design for hard or dense biological tissues. The prior art utilizes a series of pyramidal shaped teeth spaced apart many times the torsional and/or linear cutting displacement. The aforesaid art is only marginally effective for the intended application. The present art provides a plurality of optimally spaced teeth with a pitch corresponding to a torsional and/or longitudinal stroke of the torsional ultrasonic generator. The present art embodiments provide the aforesaid with an expanded head with pyramidal projections located circumferentially around the distal shaft orifice. 
     During many surgical procedures, it is necessary to remove all or a portion of a bony structure in order to provide access to other tissue or organs. In other instances it becomes necessary to shape bone to facilitate approximation of implants, autologous materials, wound closure, etc. Often the shaping or removal of the bony material is done in close proximity to fragile and/or eloquent tissues. In these instances it is desirable that the instrument used for bone removal act in a manner that is predictable and precise. Specific requirements would include, but not be limited to minimization of torque at start up to prevent displacement of the instrument from intended tissue contact, minimized, precise, and discrete tissue impact to restrict alternate site injury potentially caused by the transmitted effect of the instrument, and an overall action that allows the surgeon to focus upon the area of interest rather than having to be concerned with complications secondary to the use of the instrument. 
     Much of the current state of the art as it relates to these applications is found in the employment of high-speed air motors or drills. Reaching rotational speeds of up to 95,000 rpm, burrs attached to the air motor affect removal of tissue at varied rates, dependent upon the surface of the burr. Hardened steel cutting tools remove bone rapidly and diamond coated tools affect removal at a much slower rate, but do so with a greater deal of forgiveness, as there is some degree of discrimination in the diamond means of tissue destruction. The spinning burr is directed against the bone to be removed and the cutting surface cuts or grinds it away. A disadvantage of the high-speed burr is a tendency to “skip” from the bone upon initial contact or displacement of the handpiece in the direction of rotation as it contacts the surface to be removed. Due to the constant rotation of the burr, surrounding tissue and/or materials, e.g. sutures, surgical patties, etc., can be inadvertently captured by the rotating shaft of the instrument, thus pulling the tissue and/or materials around the shaft in a “spooling” action. In the case of diamond coated burrs, clearance of chips from the operative site is minimized, thereby trapping the associated heat generated by contact between the tool and the bone. As such, excessive heat generation is a genuine concern, with temperatures in excess of 180 degrees Fahrenheit having been clinically documented. As the generally accepted heat threshold for the inducement of neuronal injury is approximately 109 degrees Fahrenheit, the heat generated by a diamond tool on a high-speed air motor constitutes a genuine clinical concern. 
     As aforesaid, recently a means of accomplishing the aforesaid objectives has become commercially available as described in the Wuchinich application. This instrument consists of an ultrasonic motor or generator connected to a shaped tip. The motor is designed to vibrate longitudinally (along its axis), at a fixed frequency with variable amplitude. The tip is designed to convert the longitudinal vibration to a combination of longitudinal and torsional vibration. The aforesaid art teaches how to make an instrument that incorporates longitudinal-torsional motion and how this tip might then be applied to tissue. It does not describe potential tip geometry or configuration that may or may not be advantageous. 
     Commercially available embodiments of the aforesaid art utilize a working surface having a plurality of teeth or grooves spaced substantially greater than the torsional and/or linear cutting displacement rather than distinct substantially pyramid shaped teeth which are spaced two times or less than the aforesaid displacement. The present art utilizes a plurality of pyramid or tetrahedral shaped teeth arrayed on the working surface which are spaced in all embodiments at least two times or less than the maximum aforesaid displacement. 
     Accordingly, it is an object of the present invention to provide a torsional dissection tip having a plurality of optimally spaced teeth with a pitch corresponding to a torsional and/or longitudinal stroke of the torsional ultrasonic generator. 
     Another object of the present invention is to provide a torsional dissection tip having a plurality of optimally spaced teeth, at least two times or less than the longitudinal or torsional tool surface displacement, which may take many different forms, including but not limited to pyramid or tetrahedral shapes, yet function optimally. 
     SUMMARY OF THE INVENTION 
     To accomplish the foregoing and other objects of this invention there is provided a torsional dissection tip for use with an ultrasonic motor. The apparatus is especially suited for use with and during orthopedic surgery. As aforesaid, the present art utilizes a plurality of pyramid, tetrahedral, or other shaped teeth arrayed on the working or cutting surface which are spaced in all embodiments at least two times or less than the maximum aforesaid displacement. (i.e. amplitude) 
     For the preferred embodiment, tooth pitch, i.e. distance between successive teeth, is 0.3 or 1 mm, but may comprise any length provided the aforesaid criteria are met. Alternative embodiments of the present art may utilize any type of teeth with a pitch which is substantially optimum for the torsional or longitudinal displacement. For the present and prior art, torsional vibration displacement is typically 300 microns (0.3 mm), with the ratio of longitudinal to torsional displacement regulated by the construction of the tip. While commercially available embodiments of the prior art, such as available from Miwatec of Kawasaki Japan, are capable of accomplishing the clinical objective of bone removal, said prior art requires constant motion of the instrument tip to avoid excessive heat generation, tissue necrosis, and neuronal injury. It is theorized that this excessive heat generation is caused by bone rubbing the sides of the grooves as opposed to the tips of the grooves. That is, the instrument tip typically has both longitudinal and torsional movement and said longitudinal movement is substantially parallel with the prior art grooves. This longitudinal movement when utilized with the prior art does not remove tissue but simply heats said tissue. This excessive heat generation is avoided in the present art via utilization of said plurality of pyramid shaped teeth with the aforesaid optimum spacing. 
     The present art invention comprises a longitudinal-torsional resonator (L-T resonator) having a cutting surface tip comprising a plurality of teeth arranged with a pitch, i.e. distance between successive teeth in a plane of motion, substantially equal to the torsional displacement of said tip. Said L-T resonator has a first or proximal end having a preferably female threaded portion which connects with an ultrasonic generator or electromechanical transducer and a second or distal end having said cutting surface plane. A central axis of said L-T resonator is centrally located and extends from said first end to said second end. In a preferred embodiment, a tubular aspiration and/or irrigation path extends from said threaded portion through said second end with an approximate 0.059 inch diameter and forms an orifice at said second or distal end. Alternative embodiments may utilize a plurality of irrigation path diameters. Also in a preferred form, from said first end to said second end said L-T resonator tapers in step form with preferably three steps. Alternative embodiments may utilize any number of steps or simply taper said L-T resonator and further use numerous first end connecting methods recognized within the art including but not limited to screw threads, pins, press fits, welding, brazing or the connection may be metallurgically continuous with the ultrasonic generator. Said ultrasonic generator or electro-mechanical transducer is described in the prior art and is only referenced herein as it interfaces with the present invention. 
     As described within the prior art, within the body of said L-T resonator is a cross sectional mass which is inhomogeneous. Said inhomogeneous section may take the form of twisting a flat bar or grooving a round one, i.e. spiraling grooves around the circumference, or varying the density or elasticity of the bar in a helical manner. This inhomogeneity should preferentially be made in the portion of the bar subjected to maximum stress. When the aforesaid inhomogeneity is introduced, longitudinal motion of the ultrasonic generator is at least partially converted into torsional motion at the working surface or distal tip. In the preferred embodiment, said inhomogeneity comprises a plurality of helical grooves within the second step of the L-T resonator. 
     In an prior art embodiment, said cutting surface plane is positioned substantially tangential and away from the outside diameter of the L-T resonator at said second end. That is, said surface is preferably positioned on a short arm at said second end away from the outer diameter or circumference of said L-T resonator. Preferably said cutting surface is planar or has a radius which substantially conforms to the radius from the central axis of the L-T resonator to the cutting surface. A preferred embodiment of the present art cutting surface is preferably positioned substantially tangential and parallel in at least a 180 degree arc and away from the outside diameter of the L-T resonator at said second end. That is, said surface is preferably positioned on a short substantially circular arm or projection at said second end away from the outer diameter or circumference of said L-T resonator. Preferably said preferred embodiment cutting surface has a tapered radius or tapered surface relative to the central axis of the L-T resonator whereby said cutting surface forms a partial conical surface with the smallest radius of said conical surface at the second or distal end. As shown in the figures, the present art uniquely incorporates a plurality of cutting teeth on said cutting surface which, unlike the prior art, are capable of cutting hard tissue both longitudinally and torsionally. In the form described, each of said teeth substantially come to a point maximally away from said central axis. In a preferred form, said teeth are pyramidal or tetrahedral in shape and uniformly positioned onto said cutting surface. Said teeth may take substantially one dimensional triangular or rectangular, cubical, or other tetrahedral, pentahedral, or pyramidal forms with any number of surfaces in alternative embodiments without departing from the scope of the present art. 
     The present art invention allows the efficient removal of bone with torsional or longitudinal motion of the instrument tip. The device may be applied to ultrasonic motors that vibrate longitudinally, in torsion, or a combination of both longitudinal and torsional motion. That is, unlike grooves of the prior art, the present art plurality of teeth will remove dense tissues when motion is applied in any two dimensional direction along the plane of the plurality of teeth. 
     The vibration amplitude or displacement at the working surface is typically approximately 300 microns (0.3 mm) and the tooth pitch is, in a preferred embodiment, substantially equal to said vibration amplitude. The shape of the teeth and array pattern may take many forms provided the working surface provides a plurality of teeth. For alternative embodiments, the tooth pitch should be no greater than two times the vibration amplitude and as aforesaid, in a preferred form, be equal to or less than the vibration amplitude. This allows the path swept by the vibrating teeth to coincide or overlap with the path of the adjacent tooth. In this manner bone is removed along the entire working surface of the tip, disallowing the entrapment of the heat by the intimate contact of the sides of the teeth with the bone. As such, heat generation is minimized, bone removal is maximized, and deleterious secondary effects are eliminated. 
     The art of the present invention may be manufactured from a plurality of materials having the elastic and hardness properties desired, including but not limited to titanium alloys, commercially pure titanium, and super-elastic alloys such as nitinol. The present art may further utilize anti-reflective surface treatments, coatings, or processes to optimize operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Numerous other objects, features and advantages of the invention should now become apparent upon a reading of the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a left side perspective view of a prior art embodiment of the torsional dissection tip which is substantially symmetric with a right side perspective view. 
         FIG. 2  is a left side plan view thereof which is substantially symmetric with a right side plan view. 
         FIG. 3  is a left side perspective view of a preferred embodiment of the torsional pineapple dissection tip which is substantially symmetric with a right side perspective view. 
         FIG. 4  is a top side plan view of a preferred embodiment of the torsional dissection tip. 
         FIG. 5  is a right side plan view thereof which is substantially symmetric with a left side plan view. 
         FIG. 6  is a bottom plan view thereof. 
         FIG. 7  is a plan front view thereof. 
         FIG. 8  is a rear plan view thereof. 
         FIG. 9  is a cross sectional view thereof taken along lines  9 - 9  of  FIG. 7 . 
         FIG. 10  is an exploded top plan view of the distal end of a preferred embodiment tip. 
         FIG. 11  is an exploded right plan view thereof of the distal end of the tip which is symmetric with a left plan view. 
         FIG. 12  is an exploded front plan view thereof of the distal end of the tip. 
         FIG. 13  is an exploded bottom plan view thereof of the distal end of the tip. 
         FIG. 14  another exploded top plan view of the distal end of the preferred embodiment tip with preferred dimensions. 
         FIG. 15  is a exploded perspective view thereof of the distal end of the tip. 
         FIG. 16  is another exploded right side plan view thereof of the distal end of the tip which is symmetric with a left plan view. 
         FIG. 17  another exploded front plan view thereof of the distal end of the tip. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, there is shown in  FIGS. 1-2  a prior art embodiment and in  FIGS. 3-17  a preferred embodiment of a torsional dissection tip  10  having a longitudinal-torsional resonator  12  (L-T resonator) having a cutting surface tip  14  comprising a plurality of teeth  29  arranged with a pitch, i.e. distance between successive teeth  29  in a plane of motion, substantially equal to the torsional displacement of said tip  10 . Said L-T resonator  12  has a first or proximal end  18  having a preferably female threaded portion  19  which connects with an ultrasonic generator or electro-mechanical transducer and a second or distal end  20  having said cutting surface plane  22 . A central axis  24  of said L-T resonator  12  is centrally located and extends from said first end  18  to said second end  20 . In a preferred embodiment, a tubular irrigation path  26  extends from said threaded portion  19  through said second end  20 . Also in a preferred form, from said first end  18  to said second end  20  said L-T resonator  12  tapers  28  in step form  30  with preferably three steps  30 . Alternative embodiments may utilize any number of steps  30  or simply taper said L-T resonator  12  and further use numerous first end  18  connecting methods recognized within the art including but not limited to screw threads, pins, press fits, welding, brazing or the connection may be metallurgically continuous with the ultrasonic generator. Said ultrasonic generator or electro-mechanical transducer is described in the prior art and is only referenced herein as it interfaces with the present invention  10 . 
     As described within the prior art, within the body of said L-T resonator  12  is a cross sectional mass which is inhomogeneous  32 . Said inhomogeneous section  32  may take the form of twisting a flat bar or grooving a round one, i.e. spiraling grooves  34  around the circumference, or varying the density or elasticity of the bar in a helical manner. This inhomogeneity  32  should preferentially be made in the portion of the bar subjected to maximum stress. When the aforesaid inhomogeneity  32  is introduced, longitudinal motion of the ultrasonic generator is at least partially converted into torsional motion at the working surface or distal tip  20 . In the preferred embodiment, said inhomogeneity  32  comprises a plurality of helical grooves  34  within the second step  30  of the L-T resonator  12 . 
     In a prior art embodiment, said cutting surface  22  plane is preferably positioned substantially tangential and away from the outside diameter of the L-T resonator  12  at said second end  20 . That is, said surface  22  is preferably positioned on a short arm  23  at said second end  20  away from the outer diameter or circumference of said L-T resonator  12 . Preferably said cutting surface  22  is planar  25  or has a radius  27  which substantially conforms to the radius from the central axis  24  of the L-T resonator  12  to the cutting surface  22 . In said prior art embodiment said planar cutting surface  22  has substantially rectangular dimensions of 0.079 by 0.048 inch but may be of any desirable size or area. As shown in the figures, the present art uniquely incorporates a plurality of cutting teeth  29  on said cutting surface  22  which are capable of cutting hard tissue both longitudinally and torsionally. In the form described, each of said teeth  29  substantially come to a point  31  maximally away from said central axis  24 . In a preferred form, said teeth  29  are pyramidal or tetrahedral in shape and uniformly positioned onto said cutting surface  22 . Said teeth  29  may take substantially one dimensional triangular or rectangular, cubical, or other tetrahedral, pentahedral, or pyramidal forms with any number of surfaces in alternative embodiments. 
     In a preferred embodiment said cutting surface  22  is substantially partially conical  36  with a portion of the conical surface  36  removed  38  and replaced with a flat surface  40 . Further alternative embodiments may utilize a full conical surface as aforedescribed without utilization of said flat  40 . Said flat  40  surface represents a safe area which will not cut during operation. 
     In the preferred embodiment, said cutting surface  22  specifically comprises a partial conical surface  36  initially having a 0.080 inch radius relative to the central axis and tapering  42  at a 30 degree angle to a smaller radius at said distal end. Other radii and angles may be utilized in further alternative embodiments. Said surface  22  preferably consists of an expanded head  44  with pyramidal projections located circumferentially around the distal  20  shaft tubular irrigation path  26  orifice. Preferably the length of said surface as measured along the central axis  24  of the L-T resonator is approximately 0.048 inch with an actual surface length of approximately 0.055 inch but may comprise a plurality of other lengths in alternative embodiments. In the preferred embodiment, said flat  40  replacing a portion of said partially conical surface  36  is positioned 0.040 inch relative to or from said central axis  24  and represents a smooth non-cutting surface along the conical surface  36 . In a preferred embodiment, said flat surface  40  is planarly parallel with said central axis  24 . Also in the preferred embodiment, said surface  36  comprises four adjacent rows of teeth  29  circumferentially arranged around the surface of said partially conical surface  36 , each tooth  29  at a substantially 21 degree angle relative to an adjacent row tooth  29 . The pointed portion or projection of each tooth  29  of each row are preferably positioned adjacent to a trough or indented portion of the successive row teeth. Further alternative embodiments may vary this pattern and number provided the substantially conical form is retained. In the preferred alternative embodiment, the L-T resonator shaft which connects with said cutting surface  36  is approximately 0.079 inch diameter and tapers with an approximate 0.039 inch radius to said initial 0.080 inch radius of the cutting surface  36 . Utilizing the aforesaid geometric form provides at least 260 degrees of cutting surface in a preferred embodiment. 
     Further alternative embodiments may vary the aforesaid specific geometric attributes. Specifically, said conical form  36  may be replaced with a radially conical form or pure radial form. Further alternative embodiments may vary the type, pitch, style, and location of teeth. Placement, orientation, and shape of the flat surface  40  may vary or be eliminated in alternative embodiments. 
     The present art invention allows the efficient removal of bone with torsional or longitudinal motion of the instrument tip  14 . The device may be applied to ultrasonic motors that vibrate longitudinally, in torsion, or a combination of both longitudinal and torsional motion. That is, unlike grooves of the prior art, the present art plurality of teeth  29  will remove dense tissues when motion is applied in any two dimensional direction along the plane of the plurality of teeth  29 . 
     As aforesaid, in the prior art embodiment, the plane of the working surface  22  is substantially parallel yet offset to the central axis of the distal tip  20  of the instrument, however the position of the working surface can be varied in a virtually limitless manner. For the preferred embodiment, the plane of the working surface is substantially partially conical  36  and offset to the central axis  24  of the distal tip  20  of the instrument, and also allows a varied positioning of the working surface in a virtually limitless manner. The plurality of pyramid shaped teeth  29  are arrayed on the working surface  22  with the pointed portions  31  farthest from said central axis. 
     The vibration amplitude or displacement at the working surface  22  is typically approximately 300 microns (0.3 mm) and the tooth  29  pitch is in a preferred embodiment substantially equal to said vibration amplitude. The shape of the teeth  29  and array pattern may take many forms provided the working surface provides a plurality of teeth  29 . For alternative embodiments, the tooth  29  pitch should be no greater than two times the vibration amplitude and as aforesaid, in a preferred form, be equal to or less than the vibration amplitude. This allows the path swept by the vibrating teeth  29  to coincide or overlap with the path of the adjacent tooth  29 . In this manner bone is removed along the entire working surface of the tip  14 , disallowing the entrapment of the heat by the intimate contact of the sides of the teeth  29  with the bone. As such, heat generation is minimized, bone removal is maximized, and deleterious secondary effects are eliminated. The term “amplitude” as used herein refers to the peak displacement in a single direction as in the definition of the amplitude of a sinusoid and the term “stroke” refers to the total displacement, i.e. twice the amplitude, as in the peak-to-peak value of a sinusoid. 
     During operation, the unique cutting surface or head  22 ,  44  allows surgeon orientation of the distal end or tip with a minimal of manipulation. With the preferred embodiment, the surgeon may obtain a 360 degree angle of attack onto the target tissue with less than or equal to a 90 degree hand rotation. This unique minimization of hand manipulation is not found in prior art torsional dissection tips. 
     The art of the present invention may be manufactured from a plurality of materials having the elastic and hardness properties desired, including but not limited to titanium alloys, commercially pure titanium, and super-elastic alloys such as nitinol. The present art may further utilize anti-reflective surface treatments, coatings, or processes to optimize operation. 
     Those skilled in the art will appreciate that a torsional dissection tip  10  has been shown and described. The present invention is contemplated as effective in the removal of bone, bony prominences, calcified neoplasm, cartilage, cartilaginous materials, intervertebral disc, and other pathologies when the cutting surface  22  contacts such. The device is especially useful during neurosurgery, especially inside-out bone dissection once the superficial cortex has been removed, spinal surgery, orthopedic surgery, plastic/reconstructive surgery, and ear, nose, throat surgery, and other surgeries whereby the aforesaid tissues are encountered. 
     Having described the invention in detail, those skilled in the art will appreciate that modifications may be made of the invention without departing from its spirit. Therefore, it is not intended that the scope of the invention be limited to the specific embodiments illustrated and described. Rather it is intended that the scope of this invention be determined by the appended claims and their equivalents.