Abstract:
A cannula for use in implanting a solid object into living tissue, the cannula retaining the solid object in its interior prior to the execution of the implantation process by means of a structural impediment. The execution of the implantation process circumvents the structural impediment and allows the implant object to move from the cannula into the living tissue.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to hypodermic syringes and more particularly to hypodermic syringes for implanting solid objects beneath the skin of fish, birds, animals, and humans. 
         [0002]    The art or science of restoring or preserving health has always included the injection or withdrawal of fluids from the bodies of living things. With the development of miniaturized mechanical and electrical devices that serve therapeutic purposes and more prosaic purposes such as tracking and identification, the implantation of solid things within a body has become a reality. The implantation processes first utilized surgical procedures but as miniaturization techniques became more and more effective, the surgical approach has given way to the use of devices modeled on the hypodermic syringe for injecting fluids. 
         [0003]    The hypodermic syringe has long been used to aspirate or inject fluids for diagnostic or therapeutic purposes. It consists of a barrel which constitutes a fluid reservoir, a cannula for insertion into the body, the cannula being connected in a leak-proof way to the barrel, and a plunger that slides within the barrel and either pushes the fluid in the barrel through the canula and into the body or pulls fluid from the body into the barrel by means of an induced vacuum in the barrel. 
         [0004]    The adaptation of the conventional hypodermic syringe for the implantation of solid objects in living bodies has taken a rather predictable path. The adaptation has focused on objects that are elongated and usually cylindrical that will slide within a more-or-less conventional cannula. A pusher rod that slides within the cannula and pushes on the object during the implantation process is attached to the plunger and the sliding seal between the plunger and the barrel is removed, thereby permitting air trapped in the barrel by the plunger to escape around the plunger. 
         [0005]    A typical hypodermic syringe for the implantation of solid objects in living bodies is shown in  FIG. 1 . It consists of barrel  1 , plunger  3 , gasket  5 , hub  7 , and cannula  9 . The pointed distal end of the cannula is provided by a bevel obtained by means of a bevel grinder. A cylindrical object  11  is shown in place in the cannula ready to be implanted into a body. 
         [0006]    Plastic plunger  3  freely slides within barrel  1 . The presence of synthetic rubber gasket  5  provides a user with the feel of a conventional fluid-injecting hypodermic syringe. The purpose of the gasket is to provide a frictional force that resists the movement of the plunger, just like the fluid-tight seal in a fluid-injecting syringe. Since there is no need for a leak-proof seal for a solid-object-implanting syringe, the gasket can be made of a porous material or air channels can be incorporated in the gasket to allow air to pass freely through the gasket, thereby avoiding air pressure build-up in the barrel that might force air through the cannula and the incision in the body during the implantation procedure. 
         [0007]    If the gasket  5  is made of a material that provides a gas-tight seal, the air-escape channel  13  beneath the gasket allows air trapped in region  15  of the barrel  1  to escape to region  17  and the outside environment. The push-rod portion  19  of the plunger  3  freely slides within the cannula  9 . 
         [0008]    The metal hub  7  attaches to the barrel  1  by means of a standard Luerlock connector. The cannula  9  is held securely within the hub as a result of crimping the hub. 
         [0009]    The barrel  1  is a conventional 3-cm 3  plastic hypodermic syringe barrel like those used in fluid-injecting hypodermic syringes and is commercially available from a number of sources. 
         [0010]    An enlarged sectional view of the plunger  3  taken on the plane  2 - 2  of  FIG. 1  is shown in  FIG. 2 . The four fins  21  in freely-sliding contact with the inside surface of the barrel  1  serve to guide the plunger along a straight-line path. The region  17  of the barrel  1  through which the air trapped in the barrel behind the gasket  5  escapes to the outside environment is shown in the context of the plunger. 
         [0011]    An enlarged side view of the portion of the plunger containing the gasket channel  23  but without the gasket  5  is shown in  FIG. 3 . The air-escape channel  13  is shown extending through the walls  25  and  27  of the gasket channel  23 . 
         [0012]    Several different techniques have been used to hold the implant object  11  securely within stainless-steel cannula  9 . One technique is to place a compressible plastic cap over the distal end of the implant object. When the implant object is inserted into the distal end of the cannula  9 , the cap becomes wedged between the implant object and the cannula thereby holding the implant object within the cannula by frictional forces. There is a short throw in injecting the implant object thereby providing better control of the implant process. However, the plastic cap accompanies the implant object into the animal. This technique also requires the implant object to be loaded into the cannula from the distal end which tends to be more difficult. Also, the inside diameter of the cannula has to be significantly larger than the implant object diameter to enable the entry of the plastic cap into the interior of the cannula. 
         [0013]    Another technique is to hold the implant object mechanically (by means of a washer-type device) within the barrel near the point of connection of the cannula to the barrel. With this approach the plunger must be pushed much further to inject the implant object into the animal with the accompanying problem of achieving precise control of the implant process. Also, the passage of the implant object from barrel to cannula may make the injection process difficult at times. This technique is attractive however, in spite of these difficulties during the injection process, in that there is little risk in damaging the cannula point when the implant object is loaded into the barrel prior to the attachment of the cannula to the barrel. 
         [0014]    Still another technique for holding an implant object in a cannula is by crimped regions that exist at four locations spaced at 90-degree intervals around the circumference of the cannula. This technique is best described with the aid of the two orthogonal views of cannula  9  shown in  FIG. 4 . The cannula is designed to handle cylindrical implant objects having outside diameters falling within a range defined by a minimum outside diameter (minOD) and a maximum outside diameter (maxOD). The minimum inside diameter (minlD) that a cannula is permitted to have is made just enough larger than the maxOD as to allow an implant object having a maxOD outside diameter to move back and forth without binding in a cannula having a minlD inside diameter. Slot  29  has a length approximately equal to two-thirds of the nominal length of the implant object. The width of the slot is equal to no more than one-half and no less than one-third the nominal diameter of the implant object. Crimps  31  are placed in the middle portion of the cannula. 
         [0015]    The four crimp regions  31  of  FIG. 4  (the one on the underside does not show) extend from the closed end of the slot  29  for a distance equal to about one-quarter of the nominal diameter of the implant object. The crimp regions taper inward so that the distance between opposing crimp regions is greater than the maxOD of the implant object at the slot end and is less than the minOD at the terminal ends of the crimp regions. With this dimensional arrangement, any implant object satisfying the minOD and maxOD requirements can be pushed into the cannula and be held securely by the crimp regions at some position within the crimp regions. 
         [0016]    An alternative embodiment of the cannula omits the crimp regions  31  and utilizes the existence of slot  29  as a means for holding the implant object in the cannula. The maxID of the cannula is chosen to be slightly less than the minOD of the implant object. Then, as an implant object satisfying the minOD and maxOD requirements is pushed into the open end of the cannula, the edges of the slot spring apart and hold the implant object in the cannula until it is implanted into a body. 
         [0017]    This technique also requires the implant object to be inserted into the cannula from the distal end thereby risking damage to the tip of the cannula and its cutting edges. Also, in the crimp-region version of the technique, the length of the cannula must be greater to provide room for the crimp regions. 
         [0018]    None of the current cannula designs are completely satisfactory insofar as retaining the implant object within the cannula prior to executing the implantation process. 
       BRIEF SUMMARY OF THE INVENTION 
       [0019]    The invention is a cannula with a structural impediment which prevents an implant object from falling out of the cannula at the distal end as a result of changes in cannula orientation prior to the execution the implantation process. 
         [0020]    The cannula is adapted to receive an implant object into its interior at the proximal end, the cannula being attachable to an implantation device having a push-rod which enters the cannula at its proximal end. An operator utilizes the implantation device to make an incision in a body with the cutting edge of a bevel at the distal end of the cannula. The operator completes the implantation process by pushing on the push-bar thereby causing a force to be applied to the implant object which results in the implant object moving from a position within the cannula out through the distal end and into the body. 
         [0021]    The structural impediment which prevents the implant object from falling out of the cannula at the distal end as a result of changes in cannula orientation prior to the execution of the implantation process is automatically circumvented during the execution of the implantation process. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0022]      FIG. 1  is a side view of a prior-art hypodermic syringe for implanting solid objects. 
           [0023]      FIG. 2  is a sectional view of that portion of the plunger that resides in the barrel. 
           [0024]      FIG. 3  is a side view orthogonal to the side view of  FIG. 1  showing the portion of the plunger containing the gasket recess. 
           [0025]      FIG. 4A  is a top view of the prior-art cannula. 
           [0026]      FIG. 4B  is a side view of the prior-art cannula. 
           [0027]      FIG. 5A  is a sectional view of a first preferred embodiment of the invention. 
           [0028]      FIG. 5B  is a side view of a first preferred embodiment of the invention. 
           [0029]      FIG. 6A  is a sectional view of a second preferred embodiment of the invention. 
           [0030]      FIG. 6B  is a side view of a second preferred embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    The invention is a cannula wherein the implant object is inserted into the cannula at the proximal end and is prevented from sliding out at the distal end by a structural impediment at the bevel site. The structural impediment can be achieved in a variety of ways. Changing the cross-sectional shape of the cannula from circular to oval at the bevel site is one possible way. A preferred embodiment of the cannula is shown in  FIG. 5 . 
         [0032]    The side view of the distal portion of cannula  33  with bevel  35  at the distal end is shown in  FIG. 5B . Cylindrical implant object  37  is shown at rest in the distal portion after having been inserted from the proximal end of the cannula. 
         [0033]    A cross-sectional view of cannula  33  from a point at the upper part of bevel  35  and looking toward the proximal end is shown in  FIG. 5A . Cannula  33  has a circular shape  39  from the proximal end to bevel  35  and there transitions to an elongated shape  41 . This transition prevents the implant object  37 , after being inserted into the circular proximal end of cannula  33 , from going any further than the elongated distal end (see  FIG. 5A  and the relative dimensions of the circular proximal end of cannula  39 , transplant object  37 , and the elongated distal end of cannula  41 ). 
         [0034]    The elongated distal end  41  of the cannula is an impediment to the movement of the implant object out of the cannula&#39;s distal end. Thus, implant object  37  cannot accidentally slide out of the distal end of cannula  33  as the cannula assumes a variety of orientations prior to the execution of the implantation process. With the initiation of the implantation process by pressing on the plunger the attached push-rod makes contact with and applies a force to the proximal end of implant object  37  which in turn applies forces to the sides of the cannula that have transitioned into an elongated shape. As a result of the bevel  35  there is a gap  55  in the wall of cannula  33 . As the force exerted by the push-rod increases, implant object  37  forces the sides of the elongated portion of cannula  33  apart, gap  55  increases, and the structural impediment to the passage of implant object  37  out of the distal end of cannula  33  is circumvented. 
         [0035]    Another way of preventing an implant object from sliding out of the distal end of a cannula prior to the execution of the implantation process is shown in  FIG. 6 . 
         [0036]    A side view of the distal portion of cannula  43  is shown in  FIG. 6B  The distal end of cannula  43  has a bevel  45 . Implant object  47  is inserted into cannula  43  from the proximal end. The structural impediment which prevents the unintended passage of the implant object out of the cannula through the distal end are dimples on opposite sides of the cannula in the bevel region. Dimple  49  is shown in  FIGS. 6A and 6B  and dimple  51  is shown in  FIG. 6A . The dimples are of sufficient size as to prevent the implant object  47  from sliding out through the distal end of the cannula, regardless of the orientation of the cannula. 
         [0037]    When the implantation process is initiated by pressing on the plunger the attached push-rod makes contact with implant object  47  and applies a force to the proximal end of implant object  47  which in turn applies outward forces to dimples  49  and  51  and the cannula walls in which they are formed. The gap  53  in the cannula wall resulting from bevel  45  increases as the forces on the dimples increase. The two sides of the cannula spread apart, and ultimately the spread is sufficient for the implant object to pass by the dimples and out of the distal end of the cannula. Thus, the structural impediment blocking the exit of the implant object from the distal end of the cannula is circumvented by the execution of the implantation process.