Abstract:
A straight cutting tip for a full large bore subcutaneous implantation instrument is provided. An incising shaft body defines an axial bore extending continuously throughout the incising shaft body&#39;s length. The axial bore is open on both distal and proximal ends of the incising shaft body and has a non-circular cross section of at least five millimeters. A beveled surface is transversely formed beginning on a top surface and ending on a bottom surface of the incising shaft body. A cutting tip with a pair of longitudinal straight cutting edges is formed on each side and is progressively defined outwardly from the cutting tip to the sides of the beveled surface at the bottom surface of the incising shaft body. An attachment point is formed on the proximal end of the incising shaft body.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application is a continuation application of U.S. patent application Ser. No. 11/484,084, filed Jul. 10, 2006, pending; which is a continuation-in-part of U.S. patent application Ser. No. 11/345,617, filed Feb. 1, 2006, pending; which is a continuation of U.S. patent application Ser. No. 11/025,770, filed Dec. 20, 2004, abandoned; which is a continuation of U.S. patent application Ser. No. 10/222,719, filed Aug. 15, 2002, abandoned; which is a continuation of U.S. Pat. No. 6,436,068, issued Aug. 20, 2002, the priority dates of which are claimed and the disclosures of which are incorporated by reference. 
     
    
     FIELD 
       [0002]    The present invention relates in general to subcutaneous implantation instruments and methods and, in particular, to a straight cutting tip for a full large bore subcutaneous implantation instrument. 
       BACKGROUND 
       [0003]    Health care assessment includes the review and analysis of physiometry collected and recorded by electronic data sensors. The type and quality of physiometry can depend upon the type and location of sensor used. External sensors, such as thermometers, blood pressure cuffs, heart rate monitors, and the like, are limited in the kinds of information, which they are able to collect, and can encumber the patient. Implantable in situ sensors can provide a direct stream of recorded physiometry, but are invasive and require surgical implantation. 
         [0004]    Recent advances in microchip technology have created a new generation of highly integrated, implantable sensors and medical devices, such as implantable cardioverter defibrillators, pacemakers, and insertable loop recorders. For instance, PCT Publication Nos. WO/2000/004945, to Habib et al., published Feb. 3, 2000, and WO/2000/004946, to Habib et al., published Feb. 3, 2000, respectively describe an implantable sensor chip and treatment regiment, the disclosures of which are incorporated by reference. Each sensor chip can collect and transmit physiometric data by wireless telemetry to a receiver external to a body. Similarly, the emerging Bluetooth wireless communication standard, described at http://www.bluetooth.com/developer/specification/specification.asp, proposes a low cost, small form factor solution for short range data communications, potentially suitable for use in implantable sensor technology. 
         [0005]    Nevertheless, microchip sensors must still be implanted via some form of surgical procedure. Minimally invasive implantation using large bore needles or flat-edged blades is impracticable because sensors, particularly when embodied using microchip technology, favor a prismatic shape with substantially rectangular cross sections that are incompatible with circular bores. As well, large bore needles can core out flesh, skin, or hide, when used in animals, as the instruments are inserted subcutaneously, which creates a risk of infection. Moreover, wider-tipped instruments, such as a hollow point chisel, can potentially cause tearing, gouging, or similar injury due to the width of the cutting edge. 
         [0006]    In addition, although current surgical implantation approaches attempt to minimize the size of incision and degree of invasiveness, implantation is, at best, costly, time-consuming, traumatic, requires multiple instruments and maneuvers, and potentially risky to the patient. For example, anesthetizing is conventionally performed using a topical or local anesthetic agent on the implantation site. 
         [0007]    Subcutaneous implantable sensors offer the best compromise between in situ sensors and external sensors and are potentially insertable with a simple injection, rather than surgical procedure. These sensors are typically implanted below the dermis in the layer of subcutaneous fat. Several approaches to the subcutaneous implantation of solid materials have been described. 
         [0008]    An insertion and tunneling tool for a subcutaneous wire patch electrode is described in U.S. Pat. No. 5,300,106, to Dahl et al., issued Apr. 5, 1994. The tunneling tool includes a stylet and a peel-away sheath. The tunneling tool is inserted into an incision and the stylet is withdrawn once the tunneling tool reaches a desired position. An electrode segment is inserted into the subcutaneous tunnel and the peel-away sheath is removed. Although providing a tool for subcutaneous implantation, the Dahl device requires an incision into the subcutaneous fat layer and forms an implantation site larger than the minimum sized required by the electrode segment. Further more, the cylindrical bore precludes the injection of non-conforming solid sensors or materials. 
         [0009]    An implant system for animal identification that includes a device for implanting an identification pellet in a fat layer beneath the hide or skin of an animal is described in U.S. Pat. No. 4,909,250, to Smith, issued Mar. 20, 1990. The device includes a curved needle-like tube that terminates at a tapered, sharpened point. An elongated, flexible plunger is slidably received within the needle-like tube. The pointed tip is inserted through the hide or skin and the plunger is actuated to drive the identification pellet from the tip into the fat layer. However, the Smith device uses an oversized open bore which can cause coring of the hide or flesh. 
         [0010]    A trocar for inserting implants is described in PCT Publication No. WO/1999/053991, to Peery, published Oct. 28, 1999. An implant retention trocar includes a cannula for puncturing the skin of an animal and an obturator for delivering the implant. A spring element received within the cannula prevents an implant from falling out during the implant process. The cannula has a distal tip design which causes a minimum of trauma and tearing of tissue during implant insertion. However, the distal tip design is specifically directed to cannulas having a substantially circular bore and thereby limits the size and shape of implant which can be inserted through the Clarke trocar. 
         [0011]    An instrument for injecting implants through animal hide is described in U.S. Pat. No. 5,304,119, to Balaban et al., issued Apr. 19, 1994. The instrument includes an injector having a tubular body divided into two adjacent segments with a hollow interior bore. A pair of laterally adjacent tines extend longitudinally from the first segment to the distal end of the tubular body. A plunger rod has an exterior diameter just slightly larger than the interior diameter of the tubular body. With the second segment inserted beneath the animal hide, the push rod is advanced longitudinally through the tubular body, thereby pushing the implant through the bore. As the implant and rod pass through the second segment, the tines are forced radially away from each other, thereby dilating or expanding the incision, and facilitating implant. The instrument is removed from the incision following implantation. Though avoiding the coring of animal hide or flesh, the instrument forms an implantation site larger than the minimum sized required by the implant and causes potentially damaging compaction of the implant against the laterally adjacent times during implant delivery. 
         [0012]    Therefore, there is need for a non-surgical instrument and method for subcutaneous implantation of sensors and solid materials that preferably does not require an incision preparatory to instrument insertion. 
         [0013]    There is a further need for a subcutaneous implantation instrument and method capable of implanting sensors and other solid materials that are not readily disposed to implantation through a substantially circular bore. 
         [0014]    Moreover, there is a further need for a subcutaneous implantation instrument and method which is minimally invasive, preferably creating the smallest needed implantation site, and capable of implantation without exposing the implant to longitudinal stresses. 
         [0015]    There is a still further need for an implantation instrument that provides a progressive widening of an implantation site. Such progressive widening would facilitate the use of wider-tipped instruments that provide sufficient girth to admit implantable sensors and medical devices with lowered patient trauma. Preferably, such an instrument would include provision for application of an anesthetic agent. 
       SUMMARY 
       [0016]    An implantation instrument and method of use for implanting sensors and other solid materials in a subcutaneous or other site is provided. As used herein, “subcutaneous” refers generally to those implantation sites located within a body below the skin. The implantation instrument consists of an incising shaft attached to a syringe body. The syringe body and incising shaft both define a substantially non-circular hollow bore for accommodating the sensor or solid material. The subcutaneous site is formed by a cutting edge on the distal end of the incising shaft. The subcutaneous site can be cleared using a clearing trocar slidably received within the hollow bore. The sensor or solid material is advanced through the hollow bore and delivered into the subcutaneous site. The depth of the subcutaneous site can be limited using a penetration limiting mechanism. 
         [0017]    One embodiment provides a straight cutting tip for a full large bore subcutaneous implantation instrument. An incising shaft body defines an axial bore extending continuously throughout the incising shaft body&#39;s length. The axial bore is open on both distal and proximal ends of the incising shaft body and has a non-circular cross section of at least five millimeters. A beveled surface is transversely formed beginning on a top surface and ending on a bottom surface of the incising shaft body. A cutting tip with a pair of longitudinal straight cutting edges is formed on each side and is progressively defined outwardly from the cutting tip to the sides of the beveled surface at the bottom surface of the incising shaft body. An attachment point is formed on the proximal end of the incising shaft body. 
         [0018]    A further embodiment provides a curved cutting tip for a full large bore subcutaneous implantation instrument. An incising shaft body defines an axial bore extending continuously throughout the incising shaft body&#39;s length. The axial bore is open on both distal and proximal ends of the incising shaft body and has a non-circular cross section of at least five millimeters. A beveled surface is transversely formed beginning on a top surface and ending on a bottom surface of the incising shaft body. A cutting tip with a pair of longitudinal curved cutting edges is formed on each side and is progressively defined concave outwardly from the cutting tip to the sides of the beveled surface at the bottom surface of the incising shaft body. An attachment point is formed on the proximal end of the incising shaft body. 
         [0019]    A further embodiment provides a straight cutting tip for a partial large bore subcutaneous implantation instrument. An incising shaft body defines an axial bore extending part way through the incising shaft body&#39;s length and a plunger bore communicatively connected to the axial bore. The axial bore is open on only a distal end of the incising shaft body and has a non-circular cross section of at least five millimeters. The plunger bore is open on only a proximal end of the incising shaft body. A beveled surface is transversely formed beginning on a top surface and ending on a bottom surface of the incising shaft body. A cutting tip with a pair of longitudinal straight cutting edges is formed on each side and is progressively defined outwardly from the cutting tip to the sides of the beveled surface at the bottom surface of the incising shaft body. An attachment point is formed on the proximal end of the incising shaft body. 
         [0020]    A further embodiment provides a curved cutting tip for a partial large bore subcutaneous implantation instrument. An incising shaft body defines an axial bore extending part way through the incising shaft body&#39;s length and a plunger bore communicatively connected to the axial bore. The axial bore is open on only a distal end of the incising shaft body and has a non-circular cross section of at least five millimeters. The plunger bore is open on only a proximal end of the incising shaft body. A beveled surface is transversely formed beginning on a top surface and ending on a bottom surface of the incising shaft body. A cutting tip with a pair of longitudinal curved cutting edges is formed on each side and is progressively defined concave outwardly from the cutting tip to the sides of the beveled surface at the bottom surface of the incising shaft body. An attachment point is formed on the proximal end of the incising shaft body. 
         [0021]    A further embodiment provides an upwardly curved cutting tip for a full large bore subcutaneous implantation instrument. An incising shaft body concavely curved on a top surface in an arc of approximately 20° defines an axial bore extending continuously throughout the incising shaft body&#39;s length. The axial bore is open on both distal and proximal ends of the incising shaft body and has a non-circular cross section of at least five millimeters. A beveled surface is transversely formed beginning on the top surface and ending on a bottom surface of the incising shaft body. A cutting tip with a pair of longitudinal straight cutting edges is formed on each side and progressively defined outwardly from the cutting tip to the sides of the beveled surface at the bottom surface of the incising shaft body. An attachment point is formed on the proximal end of the incising shaft body. 
         [0022]    A further embodiment provides A cutting tip for a large full bore subcutaneous implantation instrument with penetration limiting mechanism. An incising shaft body defines an axial bore extending continuously throughout the incising shaft body&#39;s length. The axial bore is open on both distal and proximal ends of the incising shaft body and has a non-circular cross section of at least five millimeters. A stopping flange is mounted on a bottom surface of the incising shaft body at an angle of between approximately 30° and 60° bent in a proximal direction. A beveled surface is transversely formed beginning on a top surface and ending on the bottom surface of the incising shaft body. A cutting tip with a pair of longitudinal straight cutting edges is formed on each side and is progressively defined outwardly from the cutting tip to the sides of the beveled surface at the bottom surface of the incising shaft body. An attachment point is formed on the proximal end of the incising shaft body. 
         [0023]    A further embodiment provides a cutting tip for a polygonal large bore subcutaneous implantation instrument. An incising shaft body defines an axial bore extending continuously throughout the incising shaft body&#39;s length. The axial bore is open on both distal and proximal ends of the incising shaft body and has a cross section in the shape of a simple closed polygon with a height of at least five millimeters. A beveled surface is transversely formed beginning on a top surface and ending on a bottom surface of the incising shaft body. A cutting tip with a pair of longitudinal straight cutting edges is formed on each side and is progressively defined outwardly from the cutting tip to the sides of the beveled surface at the bottom surface of the incising shaft body. An attachment point is formed on the proximal end of the incising shaft body. 
         [0024]    One principal value of such a subcutaneous implantation instrument and method would be to enable the subcutaneous insertion of implantable objects and devices, such as sensors, without an operating room or special procedures room. In essence, the subcutaneous implantation instrument and method reduce insertion of implantable objects and devices having non-conforming shapes to be the functional equivalent of an injection. 
         [0025]    Still other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein is described embodiments of the invention by way of illustrating the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various obvious respects, all without departing from the spirit and the scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a perspective view of an instrument for implanting sensors or solid materials in a subcutaneous or other tissue location in accordance with the present invention; 
           [0027]      FIG. 2A  is a longitudinal cross-sectional view of the implantation instrument with a straight incising shaft; 
           [0028]      FIG. 2B  is a longitudinal cross-sectional view of the implantation instrument with a curved incising shaft; 
           [0029]      FIG. 3  is a diagrammatic view illustrating the implantation of an object into a subcutaneous site; 
           [0030]      FIG. 4A  is a diagrammatic view illustrating the clearing of a subcutaneous site using the implantation instrument fitted with a clearing trocar in accordance with a further embodiment; 
           [0031]      FIG. 4B  is a diagrammatic view illustrating the subcutaneous implantation of an object using the implantation instrument fitted with a pushing stylet in accordance with a further embodiment; 
           [0032]      FIGS. 5A-D  are transverse cross-sectional views of the implantation instrument illustrating, by way of example, various bore configurations; 
           [0033]      FIG. 6  is a segmented side view of a clearing trocar; 
           [0034]      FIG. 7  is a segmented side view of a pushing stylet; and 
           [0035]      FIGS. 8A-8B  are section views illustrating penetration limiting mechanisms for use with the implantation instrument; 
           [0036]      FIG. 9  is a perspective view of an instrument for implanting objects in a subcutaneous or other tissue location in accordance with a further embodiment of the present invention; 
           [0037]      FIGS. 10A-10C  are perspective views of cutting edges formed on distal edges of incising shafts, in accordance with further embodiments; 
           [0038]      FIG. 11  is a longitudinal cross-sectional view of a subcutaneous implantation instrument in accordance with a further embodiment; 
           [0039]      FIG. 12  is a top plan view of the subcutaneous implantation instrument of  FIG. 11 ; 
           [0040]      FIGS. 13-15  are transverse cross-sectional views of the dissecting tool assembly of  FIG. 11 ; 
           [0041]      FIG. 16  is a longitudinal cross-sectional view of a subcutaneous implantation instrument in accordance with a still further embodiment; 
           [0042]      FIG. 17  is a top plan view of a subcutaneous implantation instrument in accordance with an even further embodiment; and 
           [0043]      FIGS. 18-20  are perspective diagrams showing a method of use for the subcutaneous implantation instrument in accordance with one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0044]      FIG. 1  is a perspective view of an instrument  10  for implanting objects in a subcutaneous or other tissue location in accordance with the present invention. The implantation instrument  10  consists of two principal groups of components, an incising body consisting of an incising shaft  11  and a syringe body  15 , and a delivery assembly consisting of a plunger assembly  20 . The instrument  10  can be used to non-surgically implant an object, such as a sensor or monitor, medical therapeutic device, or other solid or semi-solid object. The delivery assembly is received into the syringe body bore by sliding the plunger assembly  20  through proximal bore opening  19 . An implantable object is received into the syringe body bore. During an implant procedure, the implantable object is deployed into the incising shaft and thence inserted subcutaneously into an implantation site by progressive distal urging of the plunger assembly  20 , as further described below beginning with reference to  FIG. 18 . 
         [0045]    The incising shaft  11  is a hollow point chisel that is formed with a beveled and rounded tip  12  that tapers into a surgically sharp cutting edge  13  formed on a distal edge. The beveled tip  12  includes a distal bore opening  14  through which the implantable object is delivered into the implantation site. 
         [0046]    The implantable object includes medical monitoring and diagnostic devices, such as an implantable physiometry sensor, and non-medical monitoring devices, such as an environmental or activity monitor. Such sensors generally record data for subsequent retrieval and can be autonomously triggered or triggered manually by the implant recipient. One implantable sensor microchip suitable for use in the present invention is described in PCT Publication No. WO/2000/004945, to Habib et al., published Feb. 3, 2000, the disclosure of which is incorporated by reference. Such a sensor could be used for monitoring and collecting physiological or chemical measures. A further implantable monitoring device suitable for use is the Reveal insertable loop recorder, manufactured by Medtronic, Inc., Minneapolis, Minn., which is an implantable heart monitor for diagnosing the causes of syncope and other transient heart symptoms involving rhythm-related disorders, as described in U.S. Pat. No. 5,331,966, issued Jul. 26, 1994 to Bennett et al; U.S. Pat. No. 6,230,059, issued May 8, 2001 to Duffin; and U.S. Pat. No. 6,317,626, issued Nov. 13, 2001 to Warman, the disclosures of which are incorporated by reference. Other medical monitoring and diagnostic devices are possible. 
         [0047]    The implantable object also includes non-sensor-type implantable medical devices, including implantable medical devices for therapeutic uses, such as administering cardiac pacing or rhythm therapy; providing neural, muscle, or organ stimulation; cancer treatment; and delivering or dosing medication. As well, the present invention has equal applicability to implantation of other types of non-medical sensors, including location and identification sensors, such as radio frequency identification (RFID) tags. Such sensors could include data transmitters with which to exchange recorded data and instructional signals. 
         [0048]    Finally, the implantable object can include solid or semi-solid materials, such as a gelatinous drug bolus. In one embodiment, the implantable object has approximate dimensions of 5 mm by 10 mm by 20 mm, although other dimensions can be equally suitable. The critical dimension is the cross-sectional profile, that is, the height and width, of the implant, which must conform to passage through the syringe body and incising shaft bores. Other non-linear, prismatic shapes are equally usable provided the implantable object can fit within the confines of the syringe body and incising shaft bores. The implant could also be folded or compacted to minimize the cross-sectional profile with the implant unfolding or expanding upon implantation. As well, the implant is preferably protected against damage by encasement within, for example, a mannitol pellet in the case of a solid drug delivery system or epoxy in the case of an implantable sensor or medical device. Other sizes, shapes, and types of non-liquid implantable objects are possible. 
         [0049]    The incising shaft  11  is fixably attached to the syringe body  15  through frictional, adhesive, or preformed constructive means, as is known in the art. Both the incising shaft  11  and syringe body  15  define a substantially non-circular hollow bore extending continuously along a shared longitudinal axis, as further described below with reference to  FIGS. 5A-D . 
         [0050]    The plunger assembly includes a plunger  16 , an interconnecting plunger shaft  17  and a plunger end piece  18 . The plunger  16  is conformably shaped to fit within the syringe body bore. The plunger end piece  18  facilitates deployment of the plunger assembly through the syringe body bore and is preferably shaped to fit a thumb or palm impression. In a further embodiment, the non-circular hollow bore opens to the distal end of the incising shaft  11  and extends only partly through to thereby form a cavity, rather than a tube, but with provision for the sliding of the plunger shaft  17 . 
         [0051]    In the described embodiment, the implantation instrument  10  is designed for inexpensive and disposable use utilizing low-cost, sanitizable materials. The implantation instrument  10  can be used for out-patient or non-surgical subcutaneous implant and insertion of an implantable object, as further described below beginning with reference to  FIG. 18 . The incising shaft  11  can be fashioned from surgical grade stainless steel and has the approximate dimensions of approximately 10 mm by 5 mm in cross section. The incising shaft  11  is approximately 50 mm long and the length can be varied to accommodate different implantation depths. The plunger  16  is formed from plastic and rubber and preferably forms a watertight seal within the syringe body bore and has the approximate dimensions of approximately 8 mm by 3 mm in cross section. The plunger shaft  17  and plunger end piece  18  are formed from plastic or similar material. Other materials, as would be recognized by one skilled in the art, could be substituted. 
         [0052]    In a further embodiment, the syringe body  15  and plunger assembly can be replaced by an automated injection system, such as used with immunization injection guns or similar devices. These devices typically employ compressed air or other inert gases to administer medication in lieu of manual plungers. Other automated variations include spring-loaded and similar mechanical injection systems. The incising shaft  11  is fixably attached to the automated injection system which functions as a delivery mechanism in place of the syringe body  15  and plunger assembly. Thus, the implant would be pushed through the incising shaft bore using the compressed air or gas, or mechanical equivalent. 
         [0053]      FIG. 2A  is a longitudinal cross-sectional view of the implantation instrument  10  with a straight incising shaft  11 . The hollow bore defined by both the incising shaft  11  and the syringe body  15  runs along a common shared axis. The incising shaft bore  22  is sized to allow the implant to advance smoothly into the implantation site under the forward lateral urging of the plunger assembly  20 . The syringe body bore  23  must be at least as large as the incising shaft bore  22 , but can be slightly larger to accommodate lubricants, anesthetizing agents, or similar coatings, such as mannitol, applied over the implantable object. 
         [0054]    The syringe body  15  preferably includes a circular collar  21 , pair of winglets, ears, or eyelets, or similar structure, optionally formed on a proximal end of the syringe body  15  to assist a user in depressing the plunger assembly  20 . 
         [0055]      FIG. 2B  is a longitudinal cross-sectional view of the implantation instrument with a curved incising shaft  24 . The curved incising shaft  24 , as well as the syringe body  15  and related components, are shaped into a substantially continuous curve along the ventral side. The curvature helps regulate the penetration depth of the incising shaft and, in the described embodiment, has an arc of approximately 20 degrees. 
         [0056]      FIG. 3  is a diagrammatic view illustrating the implantation of an implantable object  28 , including a sensor, implantable medical device, such as an implantable cardioverter defibrillator, pacemaker, or insertable loop recorder, or other solid material into a subcutaneous site. Other implantable objects are possible. During implantation, the incising shaft  11  is inserted through the dermis  25  and guided into the layer of subcutaneous fat  26 , above the layer of muscle  27 , to a subcutaneous implantation site. The implantable object  28  is fed through the proximal bore opening  19  or received through the distal bore opening of the syringe body  15 . The implantable object  28  is then further advanced through the syringe body bore  23  and the incising shaft bore  22  by the plunger  16  into the subcutaneous site. Note that although the foregoing view illustrates an implant into the subcutaneous fat layer, one skilled in the art would appreciate that subcutaneous implantation locations are not strictly limited to the subcutaneous fat layer and are generally termed as those implantation locations situated subdurally within a body under the skin. Accordingly, subcutaneous implantation sites further include locations that are intramuscular and submuscular, or within a body cavity, including intrathoracic. 
         [0057]      FIG. 4A  is a diagrammatic view illustrating the clearing of a subcutaneous site using the implantation instrument  10  fitted with a clearing trocar  29  in accordance with a further embodiment. The clearing trocar  29 , as further described below with reference to  FIG. 6 , is mounted to its own handle or plunger assembly and has a sharp cutting tip  30  for optionally clearing a subcutaneous site prior to delivery of the implant. 
         [0058]    Prior to implantation, the clearing trocar  29  is slidably received into the syringe body  15  and is advanced until the cutting tip  30  is even with the proximal bore opening  19  of the incising shaft  11 . During operation, the incising shaft  11  and clearing trocar  29  are inserted through the dermis  25  and guided into the layer of subcutaneous fat  26 , above the layer of muscle  27 . 
         [0059]    The cutting edge  13  of the beveled tip  12  makes an entry incision through the dermis  25  and is laterally pushed into the subcutaneous fat  26  until the cutting edge  13  is adjacent to the subcutaneous site. The clearing trocar  29  is then urged through the subcutaneous fat  26  by advancement of its handle or plunger assembly to prepare the implantation site for delivery of the implantable object  28 , including an implantable sensor, medical device, or other solid material. The clearing trocar  29  is then withdrawn from the subcutaneous site and out of the implantation instrument  10 . 
         [0060]      FIG. 4B  is a diagrammatic view illustrating the subcutaneous implantation of an implantable object  28  using the implantation instrument  10  fitted with a pushing stylet  31  in accordance with a further embodiment. The pushing stylet  31 , as further described below with reference to  FIG. 7 , has a blunt tip  32  for advancing the implantable object  28  through the syringe body bore  23  and incising shaft bore  22  and into the subcutaneous site. The cross section of the pushing stylet  31  closely conforms to the incising shaft bore  22  while the plunger  16  closely conforms to the syringe body bore  23 . The pushing stylet  31  thus extends the reach of the plunger assembly  20  and allows the syringe body bore  23  to have a different cross-section than the incising shaft bore  22 . 
         [0061]    The pushing stylet  31  is used while the incising shaft  11  is in situ in the subcutaneous layer  26 . Prior to delivery, the implantable object  28  is fed through the proximal bore opening  19  of the syringe body  15  and further advanced within the syringe body bore  23  by contact with the plunger  16 . The pushing stylet  31  is slidably received into the syringe body  15  and is advanced until the blunt tip  32  contacts the implantable object  28 . During operation, the implantable object  28  is urged through the incising shaft bore  22  by the pushing stylet  31  and into the subcutaneous site by advancement of the plunger assembly. Upon delivery of the implantable object  28  into the subcutaneous site, the incising shaft  11  and pushing stylet  31  are withdrawn. 
         [0062]    Although operation of the implantation instrument  10  is described with reference to the implantation of sensors or solid materials into a subcutaneous site situated within the layer of subcutaneous fat  26 , implantations could also be effected in other subcutaneous, intramuscular, intraperitoneal, intrathoracic, intracranial, intra joint, as well as other organ or non-subcutaneous sites, as would be recognized by one skilled in the art. In addition, the foregoing procedure could be modified to forego the use of the clearing trocar  29  for small implantable objects  28 . The clearing effect of the clearing trocar  29  can be approximated by use of the incising shaft  11  alone whereby the incising shaft  11  is inserted into the subcutaneous site and then withdrawn by reverse deployment, thereby forming a slightly overwide implantation site. 
         [0063]    The operations of subcutaneous implantation can be carried out over a plurality of sites and with the same or different implantable objects  28 . Similarly, several implantable object  28  could be implanted at the same subcutaneous site during a single implantation operation. 
         [0064]      FIGS. 5A-D  are transverse cross-sectional views of the implantation instrument  10  illustrating, by way of example, various bore configurations.  FIG. 5A  illustrates an incising shaft  35  with a substantially rectangular bore  36 .  FIG. 5B  illustrates an incising shaft  37  with a substantially square bore  38 .  FIG. 5C  illustrates an incising shaft  39  with a substantially oval bore  40 . And  FIG. 5D  illustrates an incising shaft  41  with a substantially hexagonal bore  42 . Note the circumferential shape of the incising shaft need not follow the internal shape of the incising shaft bore. Other bore configurations, including variations on oval, rectangular, square, pentagonal, hexagonal, heptagonal, octagonal, and similar equilateral or non-equilateral shapes, are feasible. 
         [0065]    In the described embodiment, the rectangular bore  36  has the dimensions of approximately 10 mm by 5 mm. The syringe body bore  23  has a length of approximately 5 cm. 
         [0066]      FIG. 6  is a segmented side view of a clearing trocar  45 . The clearing trocar  45  consists of a beveled tip  47  on the distal end of the clearing trocar  45  and a clearing trocar shaft  46  affixed, either fixably or removably, to the distal end of a plunger  16 . 
         [0067]    During a clearing operation, the clearing trocar  45  is fully extended from the distal bore opening  14  of the incising shaft  11 . The clearing trocar shaft  46  is only long enough to clear out the subcutaneous site. The plunger  16  acts as a stop that limits the extent of penetration of the clearing trocar  45 , thereby preventing the clearing trocar  29  from incising too deeply into the subcutaneous fat  29 . In addition, the clearing trocar  29  is sized to approximate the girth of the incising shaft bore  22  and will clear a subcutaneous site only as wide as minimally necessary to facilitate implantation of the implantable object. In the described embodiment, the clearing trocar  45  has a length of approximately 2 cm beyond the tip of the syringe body  15 . 
         [0068]      FIG. 7  is a segmented side view of a pushing stylet  50 . The pushing stylet  50  consists of a blunt tip  52  on the distal end of the pushing stylet  50  and a pushing stylet shaft  51  affixed, either fixably or removably, to the distal end of a plunger  16 . 
         [0069]    During a delivery operation, the pushing stylet  50  is extended from the distal bore opening  14  of the incising shaft  11 . The pushing stylet shaft  51  is only long enough to clear the distal bore opening  14 . The plunger  16  acts as a stop that limits the lateral travel of the pushing stylet  50 . In the described embodiment, the pushing stylet  50  has an additional length of approximately 2 cm beyond the tip of the syringe body  15 . 
         [0070]      FIGS. 8A-8B  are section views illustrating penetration limiting mechanisms for use with the implantation instrument  10 . The penetration limiting mechanisms limit the depth of penetration of the incising shaft  11  and help prevent excessive penetration.  FIG. 8A  shows a fixed penetration limiting mechanism consisting of a stopping flange  55  attached to the incising shaft  11 . The position of the stopping flange  55  along the incising shaft  11  can be adjusted by loosening a hold-down screw  58  and sliding the stopping flange  55  into the desired location. The lower edge of the stopping flange  55  has a bend  57  with an angle τ, preferably between approximately 30° and 60°, thereby forming an elbow  56  which stops lateral travel upon contact with the skin. 
         [0071]      FIG. 8B  shows an adjustable penetration limiting mechanism consisting of a stopping flange  60  attached a frictional collar  64 . The stopping flange  60  and frictional collar  64  are slidably attached to the incising shaft  11 . An adjustable collar  64 , preferably in threaded communication  65  with the frictional collar  64 , manually stops deployment of the penetration limiting mechanism by tightening the frictional collar  64  against the incising shaft  11 . The lower edge of the stopping flange  60  has a bend  62  with an angle υ, preferably between approximately 30° and 60°, thereby forming an elbow  61  which stops lateral travel upon contact with the skin. 
         [0072]      FIG. 9  is a perspective view of an instrument for implanting objects in a subcutaneous or other tissue location in accordance with a further embodiment of the present invention. The instrument is equipped with the stopping flange  55  shown in  FIG. 8A . Other forms of penetration limiting mechanisms, both fixed and adjustable, could be used, as would be readily apparent to one skilled in the art. 
         [0073]    In addition to being flat and chisel-like, the cutting edge of the incising shaft can be shaped as a progressive cutting or clearing blade, or a dissecting tool suitable for use in facilitating subcutaneous insertion.  FIGS. 10A-10C  are perspective views of progressive cutting edges  71 ,  81 ,  91  formed on distal edges of incising shafts  70 ,  80 ,  90  in accordance with further embodiments. The cutting edge can be shaped to facilitate subcutaneous insertion, such as when necessary to penetrate areas of thick epidermis, for instance, on the hands or feet, or animal hide. For instance, the cutting edge  71  can be shaped into a point or semi-point, which can initially pierce and progressively enlarge an implantation site. Similarly, the cutting edge  81  can be shaped into a rounded or curved edge, which can also progressively enlarge an implantation site, but without initial piercing. In addition, the cutting edge  91  upwardly curved or angled, which can help shape the implantation site to more closely follow the contours of the object to be implanted. Other cutting edge shapes are possible. Moreover, dissecting tools could be used in addition to or in lieu of the progressive cutting edges, such as a flat or shaped dissecting tool. 
         [0074]      FIG. 11  is a longitudinal cross-sectional view of a subcutaneous implantation instrument  100  in accordance with a further embodiment. A dissecting tool assembly  101  is removably affixed to the distal end of the incising shaft  11  with a coupling sheath  103 , which can be constructed as an over sleeve frictionally fit over the incising shaft  11 , a snap-off assembly that detaches from the incising shaft  11  by twisting or distal movement, or some other type of coupling that is non-integral to the incising shaft  11 . The dissecting tool assembly  101  includes a needle tip  102  that defines a lumen that internally interfaces to the bore opening  14  of the incising shaft  11  and which can be used to inject a local anesthetic agent or other liquid or semi-liquid substance into the implantation site. The needle tip  102  also progressively defines a pair of cutting blades along each outward facing edge. 
         [0075]      FIG. 12  is a top plan view of the subcutaneous implantation instrument  100  of  FIG. 11 . The cutting blades are oriented longitudinally and planar to the cutting edge  13  of the incising shaft  11 . The cutting blades provide cutting edges  105 , which gradually increase the width of the incision made when the implantation instrument  100  is inserted subcutaneously. The cutting edges  105  can be straight, concave, convex, or a combination thereof. 
         [0076]      FIGS. 13-15  are transverse cross-sectional views of the dissecting tool assembly  101  of  FIG. 11 . On a distal end, the needle tip  102  internally defines a lumen of approximately 16 French, which tapers outwardly to a larger diameter bore and substantially non-circular bore of approximately 30 gauge on the proximal end. The cutting edges  105  become increasingly pronounced towards the proximal end of the needle tip  102 . Other lumen, bore sizes, and cutting edge arrangements are possible. 
         [0077]      FIG. 16  is a longitudinal cross-sectional view of a subcutaneous implantation instrument  110  in accordance with a still further embodiment. A curved dissecting tool assembly  111  bends in a gradual arc  112  upwardly towards the incising blade  11  to facilitate implantation. The curved dissecting tool assembly  111  can be used with either the straight incising shaft  11  or curved incising shaft  24 . The curvature enables the implantable object to be more easily oriented parallel to the surface of the skin, rather than at an angle. 
         [0078]      FIG. 17  is a top plan view of a subcutaneous implantation instrument  121  in accordance with an even further embodiment. A scissored dissecting tool assembly  122  is divided into two halves, which are each attached to a handle  123  that is pivotably mounted  124 , in the manner of a pair of scissors. The handles  123  can be operated outwardly to cause the distal end of the scissored dissecting tool assembly  122  to open and longitudinally cut into the surrounding tissues, thereby widening the implantation site. Once the implantation site has been suitably cleared, the scissored dissecting tool assembly  122  remains open and the plunger assembly  20  is progressive urged distally to insert the implantable object. The scissored dissecting tool assembly  122  can be straight or curved to facilitate implantation. Other forms of scissored dissecting tool assemblies are possible. 
         [0079]      FIGS. 18-20  are perspective diagrams showing a method of use for the subcutaneous implantation instrument  121  in accordance with one embodiment. Referring first to  FIG. 18 , the subcutaneous implantation instrument  130  can be used for out-patient or non-surgical subcutaneous insertion of an implantable object, such as an implantable sensor, medical device, or solid material. The implantation instrument  10  enables the subcutaneous insertion of implantable objects and devices, such as sensors, without an operating room or special procedures room. The implantation instrument  10  reduce insertion of implantable objects and devices having non-conforming shapes to be the functional equivalent of an injection. 
         [0080]    The subcutaneous implantation instrument  130  can be sold or marketed as part of a package that combines an implantable object  134  with the subcutaneous implantation instrument  130 , particularly where the subcutaneous implantation instrument  130  is provided as a single-use disposable unit. Thus, the subcutaneous implantation instrument  130  can be offered with an implantable  134  object already disposed within the syringe body  131 , with the entire package sealed ready for use inside sterile packaging (not shown). Alternatively, the subcutaneous implantation instrument  130  can be offered in combination with an implantable object  134  that is packaged separately. 
         [0081]    At the outset of the procedure, an implantation site  137  can be locally anesthetized using the subcutaneous implantation instrument  130  by fitting the incising shaft  132  with a dissecting tool assembly  136 , as provided in a further embodiment, described above with reference to  FIG. 11  et seq. The coupling sheath  103  of the dissecting tool assembly  136  removably fits over the distal end of the incising shaft  132 . The implantation site  137  is cleaned and sterilized and the needle tip  102  is inserted subcutaneously. The needle tip  102  and cutting blades on the dissecting tool assembly  136  form a progressively larger opening as the subcutaneous implantation instrument  130  is pressed downward through the skin. The plunger assembly  133  is then pressed distally to inject a local anesthetic agent into the subcutaneous implantation site. 
         [0082]    Referring next to  FIG. 19 , the dissecting tool assembly  136  is withdrawn from the implantation site  137  and removed from the incising shaft  132 , thereby exposing the cutting edge of the incising shaft  132 . The bare incising shaft  132  is inserted into the previously cleared implantation site  137  and pressed downward. Depending upon the configuration of the cutting edges  105  of the dissecting tool assembly  136 , the cutting edge of the incising shaft  132  may only need to enlarge the opening, rather than clearing a full width opening. 
         [0083]    Referring finally to  FIG. 20 , downward movement of the subcutaneous implantation instrument  130  is stopped when the appropriate depth for implantation has been reached and, if necessary, is urged slight back to clear the incising shaft  137  from the actual subcutaneous implantation site. The plunger assembly  133  is again pressed distally to deploy the implantable object  134  into the incising shaft  134  and thence to insert the implantable object  134  into the subcutaneous implantation site. The incising shaft  132  is withdrawn and the wound is appropriately dressed to complete the implantation procedure. Through use of the method, the subcutaneous sensor insertion of implantable objects and devices, such as sensors, having non-conforming shapes is thereby reduced to be the functional equivalent of an injection. 
         [0084]    While the invention has been particularly shown and described as referenced to the embodiments thereof, those skilled in the art will understand that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.