Abstract:
A device for the back-injection of an implant including a holder to allow a user to hold the device, an injection needle, a retainer for retaining the implant before the injection needle, a plunger having a distal part for injecting the implant during withdrawal of the needle, a protective sleeve, capable of adopting an injection position leaving the needle uncovered and a safety position covering the needle again after use of the device, and a spring designed to move the protective sleeve into their safety position, the movement of the spring being controllable by the user.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority of French patent application No. 0760289 filed on Dec. 21, 2007, the content of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This invention relates to the technical field of injecting one or more implants into the body of a subject. More specifically, but not exclusively, the invention concerns the intramuscular or sub-cutaneous injection of one (or several) solid or semi solid pharmaceutical components which are designated “implant” in what follows. The subject can be a mammal, particularly a human being. This will be designated as “subject” or “patient” in what follows. This implant is injected periodically, for example each month, into the subject&#39;s body about 10 mm (millimeters) below the surface of the subject&#39;s skin, this implant then dissolving into the subject&#39;s body during the month. In accordance with another possible application, the implant is an electronic chip used to identify a living being. 
     BACKGROUND OF THE INVENTION 
     This invention relates to the technical field of injecting one or more implants into the body of a subject. More specifically, but not exclusively, the invention concerns the intramuscular or sub-cutaneous injection of one (or several) solid or semi solid pharmaceutical components which are designated “implant” in what follows. The subject can be a mammal, particularly a human being. This will be designated as “subject” or “patient” in what follows. This implant is injected periodically, for example each month, into the subject&#39;s body about 10 mm (millimeters) below the surface of the subject&#39;s skin, this implant then dissolving into the subject&#39;s body during the month. In accordance with another possible application, the implant is an electronic chip used to identify a living being. 
     Patent EP 1 323 450 already known in the art teaches a device for injecting tablets of a drug, comprising a hollow needle fixed to a cylinder housing the tablets. The tablets are held in the cylinder before being introduced into the needle and then into the body of the subject. The tablets are maintained in position in the cylinder by flexible fingers which hold the tablets until the operator presses on the device&#39;s plunger rod and which then relax to allow the tablets to be introduced into the needle by deflection of the flexible fingers. 
     A disadvantage of such a device resides in the fact that the deflection of the flexible fingers puts the tablets under stress. The tablets are compressed both by the plunger pressed by the user and by the flexible fingers which exert a certain amount of resistance before giving way. For some implants, exerting stress upon them may be dissatisfactory. Indeed, certain implants are particularly fragile or easy to deform, due to the fact that they contain substances intended to dissolve within the subject&#39;s body. The pressure exerted on these implants may therefore damage them. In addition, for a deformable implant, the pressure exerted from above may increase its diameter to such an extent that the implant remains stuck inside the device. 
     SUMMARY OF THE INVENTION 
     This invention aims in particular to provide a device which guarantees that implants injected into the subject&#39;s body are intact. 
     This invention therefore concerns a device for injecting an implant comprising:
         a housing for receiving an implant located before an injection needle,   means for retaining the implant in the receiver housing,   means for deactivating the retaining means,   the retaining means being configured so as not to exert any stress on the implant.       

     A device is thus provided which guarantees that the implant will not be damaged or deformed by a stress. The device comprises deactivating means adapted to prevent the retaining means from damaging the implant when it is introduced into the needle. 
     It will be understood that “so as not to exert any stress on the implant” consists in not subjecting it to a force which could damage it. The device described above may therefore exert light pressure on the implant but without risk of damaging it. For example, for a PLA or PLGA implant, which are derivatives of lactic and glycolic acids, light pressure of, for example, up to 1 N (Newton) for a very fragile or deformable implant or up to 20 N (Newton) for a more resistant or less deformable implant, can be exerted on the implant without damaging it. 
     Among the advantages of the invention, it will be noted that the retaining means enable the implant to be held in the receiver housing when the needle has not been introduced into the subject&#39;s body and while no pressure has been exerted on the plunger rod. Therefore the device guarantees the user that there is no risk of the implant accidentally falling out of the device before the needle has been inserted into the subject&#39;s body. It is particularly important to ensure that the implant is indeed present in the device before injection due to the consequences of an implant not being injected, which can be considerable in medical terms if the user mistakenly believes that the injection has been performed. In addition, it is advantageous for the implant to be retained in the means designed for it before the needle and not in the needle so that the user of the device can ensure when the needle is inserted into the subject&#39;s body and preferably even when it is fully inserted that the implant is still in the device. If the implant had been held inside the needle instead of before the needle, once the needle is inserted into the subject&#39;s body the user would not be able to verify that the implant is still present in the device since it would no longer be possible to see the needle. This is a significant advantage since an implant that is held insecurely in the device could easily fall out of the device just before injection when the needle is lowered. 
     The invention may in addition comprise one or more of the following characteristics. 
     The means for deactivating the retaining means are activated automatically once the needle is at least partially in the insertion position, i.e. inserted into the subject&#39;s body. Consequently, the user of the device does not need to perform any specific actions to initiate release of the implant held in the device which facilitates handling the device during injection. In particular, the user does not need to change hands to perform the transfer of the implant into the needle, to inject the implant into the subject&#39;s body or to withdraw the needle, and any abrupt movements which could be painful for a patient are therefore avoided. 
     The deactivating means act directly on the retaining means. In other words, the deactivating means do not act on the retaining means via the implant, thus avoiding any risk of damaging the implant. 
     The device comprises a plunger and the deactivating means are activated by this plunger, more specifically by the plunger moving into a predetermined position. The retaining means are automatically deactivated when, for example, the user presses the plunger to inject the implant, without any other action being required than to press the plunger. 
     The retaining means comprise a stop to retain the implant which can be in an activated retaining position before the needle is in the insertion position, i.e. before the needle starts to be inserted into the subject&#39;s body, as well as in a deactivated position once the needle is in the insertion position, i.e. once the needle has been at least partially inserted into the subject&#39;s body. Preferably, this retaining stop acts in reaction to the weight of the implant to prevent the implant from passing into the needle under the effect of gravity when the device is in the vertical position. This retaining stop can take the form of a stop extending in a transverse direction of the device below the implant, in particular between the implant and the proximal end of the needle. 
     The retaining stop is supported by a rubber tab. 
     The retaining means are supported by a retaining element and deactivation comprises firstly interaction between the retaining element and the implant receiver housing and secondly interaction between the retaining element and the plunger. 
     The deactivation means are adapted to shift the retaining means radially. The retaining stop can move into its deactivated position after a radial shift, generated for instance by a detent built into the implant receiver housing, the detent interacting with the retaining means when the device plunger is displaced. 
     The device comprises verification means configured so that the implant is visible to the user when it is held by the retaining means, in particular when the needle is in a position not visible to the user, for instance when completely inserted into the subject&#39;s body. 
     This invention also proposes a device for back-injection of an implant. Back-injection consists in injecting the implant while the needle is being withdrawn. The inventors aim to provide a device designed in such a manner that the device user can manually control the withdrawal of the needle from the patient&#39;s body. It is desired to avoid automatic withdrawal of the needle, carried out purely under the action of a spring, since automatic withdrawal can be painful to the patient for two reasons in particular: the user injecting the implant may not be used to using a back-injection device and in addition the needles of back-injection devices may be very long. 
     The invention therefore concerns a device for back-injection of an implant comprising:
         means for a user to hold the device,   an injection needle,   needle protection means, with an injection position which leaves the needle uncovered and a safety position covering the needle after use of the device,   return means for ensuring that the protection means return to their safety position from their injection position,   the movement of the return means being controllable by the user.       

     A device is therefore proposed wherein the protective means, usually a protective sleeve, can adopt their safety position to prevent the needle from remaining uncovered after it has been introduced into the patient&#39;s body. Preferably this safety position is adopted automatically, for instance by the release of the return means when the device&#39;s plunger arrives at the end of its travel, these return means causing a relative movement between the sleeve and needle so that the sleeve can protect the needle. It is proposed that an automatically initiated relative movement takes place between the sleeve and needle without, however, withdrawal of the needle from the patient&#39;s body being driven by the return means alone, without the user being able to control the movement of the device. Using this device therefore, the user can control the movement of the return means by at least partially opposing their release, preferably using the holding means so that the user can stop the return means from moving if he wishes or slow down or accelerate them. The holding means generally comprise a grip pressed by the user&#39;s fingers, preferably by the user&#39;s index and middle finger, fitted at the proximal end of the device. Once the needle has been inserted into the patient&#39;s body, withdrawal of the needle can be done at least partially by a backwards movement of the user&#39;s fingers so that the distance between the patient&#39;s skin and the holding means increases as the needle is withdrawn. 
     A back-injection device of this type offers the user similar functionality to a liquid injection device with a syringe and automatically released protective sleeve while still providing the technical features required by a device for back-injection of solid or semi-solid implants, notably necessary means for injecting the implant as the needle is withdrawn. It will be noted that implant back-injection has the advantage of not exerting any stress on the implant at the moment it leaves the needle to remain in the patient&#39;s body, unlike a standard injection where the product (a liquid drug for instance) is pushed through the patient&#39;s skin. In a standard injection, if the implant is fragile it will be broken when it is pushed through the skin. With back-injection, however, the implant does not move through the skin, it fills a cavity left by the needle as it is withdrawn: the implant is transported to the proximal end of the needle while being subjected to as little stress as possible, the needle is then withdrawn from the patient&#39;s body leaving the implant in the patient&#39;s body at the same depth as when it was at the distal end of the needle. When the needle is withdrawn automatically, under the action of a spring, the user cannot control needle withdrawal manually because of the internal back-injection mechanism which is not accessible from outside the device, which can be disturbing if he is used to using liquid injection devices. If the user is not used to using a back-injection device, his use of the device could be clumsy and therefore painful to the patient. Thanks to the invention, the user can control withdrawal of the needle from the patient&#39;s body manually, as with certain liquid drug injection devices. The back-injection device therefore operates in a way familiar to the user. It will be noted that the back-injection device according to the invention preferably ensures automatic back-injection, i.e. that the implant is transferred automatically from the needle into the patient in a single action when then needle is retracted, but that also back-injection can be, at least partially, manual. When the implant is positioned at the distal end of the needle, it can be planned that needle withdrawal, at least at the beginning, is performed manually by the user moving back his fingers. This initial withdrawal of the needle creates a space in the patient&#39;s body into which the implant can be introduced without exerting any force upon it, by pressing on the plunger. Then, continuing pressure on the plunger can automatically release the needle protective means and the remainder of the retraction of the needle from the patient&#39;s body. The operations of transferring the implant into the patient&#39;s body and protecting the needle can therefore be performed simultaneously (automatic back-injection) or successively (manual back-injection). 
     In addition, the device comprises means for retaining the implant before the injection needle. As explained above, it is particularly advantageous for the implant to be held before the needle and not in the needle so that the user of the device can check, at the moment when the needle is inserted into the subject&#39;s body and, preferably, even when it is fully inserted, that the implant is still in the device. Moreover, the implant may be easier to hold before the needle than in the needle. In addition, since the travel range of the implant before leaving the needle is longer when it is held before the needle, there is less risk of the implant leaving the device at the moment when the user is going to insert the needle into the patient&#39;s body. 
     Retention before the needle can be performed as described above using deactivation means or by exerting light pressure on the implant, so as to hold it by friction, for instance with flexible fingers. 
     The back-injection device may also comprise one or more of the following characteristics. 
     The device includes a plunger comprised of two separable parts, a distal part and a proximal part, the distal part being intended to position the implant flush with the distal end of the needle. 
     The device comprises retractable means for connecting the protective means to the holding means. When the device is in the injection position, the protective means are connected to the holding means and when the device is in the safety position, the protective means are disconnected from the holding means. For instance, the retractable connecting means comprise latching means located respectively on the proximal end of the protective means and on a part joined to the holding means. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood from the following description, given solely by way of example and by referring to the drawings wherein: 
         FIG. 1   a  is a partial longitudinal sectional view of part of a device according to a first embodiment the invention, showing the retaining means in the activated position; 
         FIG. 1   b  is a similar view to  FIG. 1   a , illustrating the retaining means during deactivation; 
         FIG. 1   c  is a similar view to  FIG. 1   a , illustrating the retaining means in the deactivated position; 
         FIG. 2   a  is a top view of the retaining means in a device according to a second embodiment of the invention; 
         FIG. 2   b  is a partial longitudinal sectional view of part of the retaining means of  FIG. 2   a;    
         FIG. 2   c  is a partial longitudinal sectional view of part of the retaining means of  FIG. 2   a , the sectional view being perpendicular to the sectional view of  FIG. 2   b.    
         FIG. 3   a  is a side view of an injection device according to a third embodiment of the invention, the device being represented in the injection position; 
         FIG. 3   b  is a longitudinal sectional view along arrow  3   b  in  FIG. 3   a;    
         FIG. 3   c  is a longitudinal sectional view along arrow  3   c  in  FIG. 3   a;    
         FIGS. 3   d ,  3   e  and  3   f  are respectively similar views to views  3   a ,  3   b  and  3   c , the device being in its safety position; 
         FIGS. 4   a  to  4   f  are respectively similar views to  FIGS. 3   a  to  3   f  of an injection device according to a fourth embodiment of the invention; 
         FIG. 5  is a view of a device according to a fifth embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As can be seen in  FIGS. 1   a  to  1   c , an injection device  10  comprises a housing  12  for receiving an implant, this housing  12  comprising a distal end  14  to which is fixed, permanently in this example, an injection needle  16  intended to be inserted into the body of a subject. The injection device also comprises a plunger  18 , plunger  18  comprising a rod whose proximal end is fitted with a pusher (not shown) and with the distal end fitted with a thrust surface  20 . Plunger  18  can be made of several sections as in the third and fourth embodiments. 
     The device  10  is intended to receive a solid or semi-solid implant  22 . In this example, implant  22  is a single block but it could be made of several distinct tablets stacked on top of each other. 
     According to the example described, the needle  16  is hollow with a diameter of 2 mm and a length of about 40 mm. It is intended to deposit implant  22  at a depth of about 10 mm below the surface of the subject&#39;s skin. Implant  22  is particularly fragile or easy to deform and is intended to dissolve in the subject&#39;s body, for instance over the course of a month following its injection. It is produced by an extrusion or injection process and comprises a support material made of PLA or PLGA mixed with a drug. 
     As can be seen, the receiver housing  12  is located just before the injection needle  16 . Moreover device  10  comprises visualizing means  17  enabling the presence of implant  22  in the device to be checked. These means  17  are for example a window built into the receiver housing  12 , designed so that implant  22  can be seen when it is in the device in a way similar to that shown in  FIG. 1   a.    
     In this application, the direction “before” is designated with reference to the direction in which implant  22  is injected. Therefore housing  12  is located before needle  16 , i.e. it is located between needle  16  and the proximal end (the end opposite the needle) of device  10 . 
     Device  10  also comprises means  26  for retaining implant  22  in receiver housing  12 , the means being able to adopt an activated position shown in  FIG. 1   a  and a deactivated position shown in  FIG. 1   c . In this example, the retaining means are a perforated retaining element  26  of generally tubular shape. Element  26  is mounted so that it slides within receiver housing  12 . Element  26  comprises a tubular housing  28  intended to receive implant  22 . This housing  28  is designed so as not to substantially exert any stress on implant  22  when it is situated within element  26 , whether the retaining means are in the activated or deactivated position. The retaining means have a proximal end  30  and a distal end  32 . 
     The distal end  32  has a distal retaining stop  34  for securing the implant which can adopt an active retaining position as shown in  FIG. 1   a  and a deactivated retaining position as shown in  FIG. 1   c . As can be seen on the figures, the retaining stop  34  extends in the transverse direction Y of device  10 , this direction Y being perpendicular to the longitudinal direction X of device  10 . When in the activated position retaining stop  34  is designed to act against the weight of implant  22  when the device  10  is in the vertical position with needle  16  downwards, as shown on the figures, to prevent implant  22  from entering the needle  16  under the force of gravity when the device is in the position shown in  FIG. 1   a . As can be seen, this stop  34  is located below implant  22 , more specifically between implant  22  and the proximal end  36  of the needle. In its activated position, stop  34  therefore retains implant  22  in the housing  28  before the needle  16 . The distal end  32  of retaining means  26  can move between an activated position shown in  FIG. 1   a  and a deactivated position shown in  FIG. 1   c , by means for example of at least one rubber tab seated on this end  32 , this tab supporting stop  34 . 
     Device  10  also comprises means for deactivating the distal retaining means  34 . These deactivation means comprise an engagement tooth  38  built into the distal end of retaining element  26 , joined onto stop  34 , this engagement tooth being intended to interact with a detent  40  formed on the inner distal end of receiver housing  12  so that when the retaining element  26  is in the activated position shown in  FIG. 1   a , the movement of this element  26  in the direction X generates an interaction between tooth  38  and detent  40  so that the distal retaining stop  34  moves into its deactivated position as shown in  FIG. 1   c.    
     The proximal end  30  of the retaining element also comprises a proximal retaining stop  42  to keep the implant in the housing  28  when device  10  is in the vertical position, the needle  16  being uppermost, i.e. in the opposite direction to that depicted in  FIG. 1   a . As can be seen in  FIG. 1   a , stop  42  extends in the transverse direction Y of device  10 . This stop  42  is supported by one or more rubber tabs supported by the proximal end  30  of retaining element  26 . End  30  is also intended to be crossed by plunger  18  and comprises a surface  44  forming a detent intended to interact with a beveled surface  46  at the distal end of plunger  18 . The surface  44  forming the detent is primarily intended to form a stop for the distal end of plunger  18  as can be seen in  FIG. 1   b  and then to move radially out of the way by elastic deformation when element  26  is at the end of its travel in the receiver housing  12 . The surface  44  and the beveled surface  46  are the means for deactivating retaining stop  42 . 
     Note that retaining means  26  are designed not to exert any stress on implant  22 . In particular, if these means  26  exert any pressure on implant  22 , this pressure does not exceed a certain force depending on the implant&#39;s fragility or strain capability. Depending on the implant, this force does not exceed 1 Newton, or does not exceed 20 Newtons so that the pressure cannot damage or expand the implant  22 . 
     Moreover, element  26  is kept in the position shown in  FIG. 1   a  by means for holding element  26  in the receiver housing  12 . Element  26  is held in position for example by light friction between it and receiver housing  12 , this friction being overcome when the user of device  10  presses on plunger  18  as can be seen in  FIG. 1   b , so that element  26  is capable of moving in direction X when plunger  18  is pressed. 
     The operation of injection device  10  will now be described. 
     Before inserting the needle  16  into the subject&#39;s body, as can be seen in  FIG. 1   a , the retaining means  26  are in the activated position with the retaining stops  34 ,  42  holding the implant inside housing  28 . As can be seen, implant  22  is held before injection needle  16  and its presence can be checked using the means  17  for verifying the presence of the implant. Moreover, element  26  is held by friction within housing  12  according to the position illustrated in  FIG. 1   a  by the holding means described above. 
     In  FIG. 1   a , the needle  16  is positioned in such a way as to be at least partially inserted into the subject&#39;s body. In this example, needle  16  in  FIG. 1   a  is considered to be completely inserted into the subject&#39;s body, i.e. that it is at the depth with respect to the surface of the subject&#39;s skin where it is desired to place the implant  22 , for instance the distal extremity of needle  16  is 10 mm from the subject&#39;s skin. Note that even if needle  16  is entirely inserted into the skin, the presence of implant  22  can nevertheless be verified using means  17 . 
     Implant  22  is then released by being first introduced into the needle  16  (as can be seen in  FIG. 1   c ) and then into the subject&#39;s skin. To perform this injection, the user of the implant device  10  presses on the pusher of plunger  18  which moves it in the longitudinal direction X downwards. When the user presses on plunger  18 , the thrust surface  46  of the plunger presses on the thrust surface  44  which moves the retaining element  26  in the X direction, as can be seen in  FIG. 1   b . The friction exerted by the means for holding element  26  in housing  12  is less than the thrust exerted by the plunger  18  on the thrust surface  44  so that element  26  moves in the X direction when plunger  18  is pressed. 
     Under the pressure of plunger  18 , when element  26  reaches the end of its travel within receiver housing  12  (shown in  FIG. 1   b ), the engagement tooth  38  and detent  40  interlock, radially moving the rubber tabs on the distal end  32  and in particular the retaining stop  34 . Since this retaining stop  34  is moved away from the central axis of the injection device  10 , it is in the deactivated position so that it no longer retains implant  22  in housing  28 . Moreover, since retaining element  26  has reached the end of its travel in the receiver housing  12 , further pressure on the plunger  18  by the user causes the proximal end  30  of retaining element  26  to deform. More specifically, the surface  46  of the plunger acts on the detent  44  which deforms, allowing plunger  18  to cross through retaining element  26 . The plunger  18  can then push implant  22  into needle  16  as can be seen in  FIG. 1   c . In this position, implant  22  is in the needle and can then be injected into the subject&#39;s body. 
     As can be seen, the various deactivation means, firstly the tooth  38  and detent  40  and secondly the detent  44  and thrust surface  46  are initiated automatically once the needle  16  has been inserted into the subject&#39;s body. These deactivation means are operated by plunger  18 , more precisely by the movement of the plunger from an initial position shown in  FIG. 1   a  to a final position shown in  FIG. 1   c.    
     Moreover, the deactivation means  38 ,  40 ;  44 ,  46  act directly on the retaining means  26 , more specifically by interaction between on one hand the receiver housing  12  and the retaining element  26  and on the other between plunger  18  and retaining element  26 . Consequently, these deactivation means do not act directly on implant  22  so that no stress is exerted on the implant to deactivate the retaining means. 
     Note that the invention is not limited to the previously described embodiments. 
     In the embodiment in  FIGS. 1   a  to  1   c , element  26  is maintained in receiver housing  12  by friction between element  26  and housing  12 . Another advantageous way of keeping element  26  in housing  12  is shown in  FIGS. 2   a  to  2   c . As can be seen in  FIG. 2   a , the retaining means  26  in this embodiment comprise four rubber tabs on its proximal end  30 . Two of these diametrically opposed rubber tabs, referenced  47 , have lugs  48  on their outer surface, these lugs being intended to engage with a slot  49  made in the receiver housing  12 , as can be seen in  FIG. 2   b . These means  48 ,  49  constitute an upper stop for positioning element  26  intended to ensure it is maintained in an initial position similar to that in  FIG. 1   a  with a light engagement. This engagement is released when plunger  18  moves down so that element  26  is moved in accordance with  FIG. 1   b . Moreover, two other diametrically opposed tabs  51  are located on the proximal end of element  26 . These tabs  51  have interior lugs  52  intended to form detents similar to detent  44  as can be seen in  FIG. 2   c . This embodiment ensures extremely reliable positioning of element  26  in its initial position shown in  FIG. 1   a.    
     Moreover, the retaining element in these examples is an element  26  of generally tubular shape whose distal end  32  and proximal end  30  comprise rubber tabs. The retaining means can take numerous other shapes. According to another example, this retaining element  26  could have a generally tapered shape, the diameter of its distal end  32  being greater than the diameter of its proximal end  30  to ensure more reliable interaction between elements  38 ,  40 ,  44 ,  46 . Moreover, this element  26  is not necessarily a part separate from the other parts of the implant device. The retaining means could be made using one or more parts of the injection device  10  that have a function other than that of retaining implant  22 . 
     Moreover, the injection device described above can be a back-injection device as will be described below. 
     An injection device  60  according to a third, fourth and fifth embodiment of the invention will now be described, in reference to  FIGS. 3   a  to  5 . 
     As can be seen in  FIGS. 3   a  to  3   f , according to a third embodiment the device  60  comprises an injection needle  62  which before device  60  starts to be used is covered by a protective cap  64 . Device  60  also comprises an intermediate housing  66  and protective means  68  referred to in the remainder of the document as “protective sleeve  68 ”, intended to cover the needle again after using the device, as can be seen in  FIGS. 3   d  to  3   f . In this embodiment, the intermediate housing  66  is external and the sleeve  68  positioned within intermediate housing  66 , co-axially with the longitudinal X axis of the device. 
     In this embodiment, sleeve  68  is made of two parts, i.e. a distal part  67  which protects the needle when the device is in the safety position and a proximal part  69 , fastened to the distal part  67 , which holds the sleeve in the injection position and also holds the sleeve in the safety position. 
     The intermediate housing  66  includes means  70  for holding the device. The holding means  70  comprise a grip  72  for supporting the user&#39;s fingers, in particular the user&#39;s index and middle finger. In this example, the holding means  70  comprise a rotating flange projecting out from the intermediate housing  66  next to its proximal end  74 . The device  60  also comprises a plunger  76 . As can be seen in particular in  FIGS. 3   b  and  3   e , plunger  76  comprises a pusher  78 , to be pressed by the user&#39;s thumb, a proximal part  80  and a distal part  82  which can be separated from proximal part  80 . Plunger  76  also comprises means  84  for releasing the return means as described below, these means  84  comprising a funnel shape between the proximal part  80  and pusher  78  intended to form an impulse surface when the plunger is moved in the direction indicated by arrow  86 . 
     The device  60  also comprises return means  88 , situated between the intermediate housing  66  and the sleeve  68 , which are compressed when device  60  is in the injection position and which can adopt an extended or rest position when the device is in the safety position as shown in  FIGS. 3   d  to  3   f . Means  88  are a compression spring. 
     As shown in  FIG. 3   b , means  88  are maintained in a compressed state, in the injection position, by a distal stop  90  built into sleeve  68  and by a proximal stop  92  built into intermediate housing  66 . As shown in  FIG. 3   f , the distal stop  90  of the sleeve can move in translation into a safety position. In this embodiment, stop  90  also acts to keep sleeve  68  in the safety position by engaging with means such as rubber tabs  94  that can move radially, supported by intermediate housing  66 . 
     Sleeve  68  is held in the injection position by retractable lugs  96  built into its proximal part  69 , more specifically near the proximal end of this proximal part  69 . The proximal part  69  also comprises means  98  for releasing return means  88  intended to act in conjunction with means  84  of plunger  76 . 
     As shown in  FIGS. 3   a  to  3   c , sleeve  68  and intermediate housing  66  form together at their distal end a housing for receiving one or more implants  100 , located before needle  62 , intended to be injected into the body of a patient. Device  60  also comprises means  102  for retaining implant  100  in the receiver housing. In the example of  FIGS. 3   a  to  3   f , the retaining means  102  fulfill their retaining function by means of flexible fingers exerting light pressure on implant  100 . Nevertheless, these retaining means  102  can be replaced by retaining means such as those described above, for example by retaining means  26  which can be deactivated by deactivation means so as to exert virtually no stress upon implant  100 . 
     The intermediate housing  66  also comprises verification means  104 , in this example comprised of a window built into housing  66 , enabling the user to see whether implant  100  is held effectively by retaining means  102 . 
     The operation of the device shown on  FIGS. 3   a  to  3   f  will now be described. 
     Before using back-injection device  60 , implant  100  is present in the device, its presence being checked with means  104 . Injection starts by removing protective cap  64  to leave needle  62  uncovered so that the user of the device can insert it into the body of the patient into whom it is desired to inject implant  100 . The user holds device  60  between his index and middle finger, these two fingers pressing against holding means  72  with the user&#39;s thumb ready to push the pusher  78  in the direction of arrow  86 . Note that the needle is completely uncovered before being introduced into the patient&#39;s body so that the user can see exactly what he is doing and can manually control the insertion of the needle as with a liquid injection device. Once the needle has been completely introduced into the patient&#39;s body, whose skin is represented by the dotted line  106 , the user pushes plunger  76  by pressing on pusher  78 . The movement of pusher  78  causes proximal part  80  of the plunger&#39;s distal part  82  to move, causing implant  100  to move into needle  62 . Once implant  100  is positioned flush with the distal end of needle  62 , plunger  76  reaches a position in which means  84  can engage with means  98 . More specifically, impulse surface  84  of plunger  76  causes socket  98  in sleeve  68  to move radially aside, this movement causing tabs  96  to retract and return means  88  to be released. This retraction causes tabs  96  to pass beyond retaining projection  92  of the intermediate housing  66  in the direction of arrow  86  so that the retaining stop  90  of sleeve  68  moves in the direction of arrow  86  under the force of return means  88 . This displacement moves sleeve  68  in direction  86  which causes plunger part  82 , which has been previously fastened to sleeve  68  by friction or click tabs, to move into the needle to keep the implants in place and causes the sleeve  68  to adopt the safety position shown in  FIGS. 3   d  to  3   f  so that sleeve  68  can cover needle  62  again as it is withdrawn from the patient&#39;s body. Once the needle has been completely withdrawn, it is covered completely by sleeve  68  and stops  90  engage with means  94  in housing  66  to keep the device in the safety position. Since part  82  of the plunger pushes automatically on the implant to keep it in the patient&#39;s body as the sleeve is released, the term automatic back-injection is used. 
     Note that, as an alternative, back-injection can be performed manually. In this case, plunger  76  is in a single part which cannot be attached to sleeve  68  and implant injection takes place before tabs  96  are retracted. At the moment when implant  100  is at the distal end of needle  62 , the user can slightly withdraw device  60  which starts to remove the needle and leaves a space in the patient&#39;s body to introduce implant  100  without any stress. After this slight withdrawal, the user can press again on pusher  78 , which enables plunger  76  (not fastened to the sleeve) to push implant  100  into the patient&#39;s body. Then, further pressure on pusher  78  causes tabs  96  to retract, automatically releasing protective means  68 . 
     As can be seen from the figures, the distance between the holding means  70  and the patient&#39;s skin  106  has been increased from value D 1  when the device is in the injection position to value D 2  when the device is in the safety position. Device  60  therefore enables implant  100  to be back-injected, i.e. implant  100  is injected or more precisely remains in position in the patient&#39;s body at the moment when the needle  62  is withdrawn from the patient&#39;s body. In addition to back-injection, the invention proposes automatic protection of the needle by the sleeve  68  as it is withdrawn, the needle not being left uncovered while allowing the user to control needle withdrawal manually with means  70 . To withdraw needle  62  from the patient&#39;s skin  106 , the user&#39;s fingers move backwards. If the user does not control his fingers, they are moved by the movement of return means  88  which initiate release of sleeve  68  from within intermediary housing  66 . In this case, needle withdrawal occurs automatically without manual control by the user. Nevertheless, the user can control needle withdrawal manually by controlling the movement of means  88  with means  70 . The user can for instance slow down or stop the movement of means  88  by exerting a force on holding means  70  against the force exerted by return means  88 . 
     The back-injection device  60  illustrated in  FIGS. 4   a  to  4   f  has a different structure to the device of  FIGS. 3   a  to  3   f  but similar operation. 
     In this embodiment, the sleeve  68  is on the outside and the intermediate housing  66  moves inside sleeve  68  co-axially with respect to axis X. 
     In this embodiment, sleeve  68  has retractable means  110  at its proximal end, comprised in this example of two rubber tabs  110 , each with retractable lugs  112  intended to engage with intermediate housing  66 . The retractable lugs  110  also comprise detents  113  intended to engage with plunger  72 . Sleeve  68  also comprises means  114  for keeping the sleeve in the safety position, these means  114  being intended in the example to engage with intermediate housing  66 . 
     In addition, sleeve  68  comprises a stop  115  intended to press on return means  88 . The intermediate housing  66  comprises a body  116  for receiving the implant  100 , the implant being held in position by retaining means  102 . In addition, the intermediate housing  66  comprises a stop  118  intended to press on the proximal end of return means  88 . In this embodiment, the intermediate housing  66  is made of two parts, a proximal part  120  supporting holding means  70  fastened to a distal part  122 , comprising the body for receiving the implant  100 . The intermediate housing  66  is fitted with means  123  for keeping sleeve  68  in the safety position, in this case tabs  123  intended to engage with slots  114 . 
     In this embodiment, the pusher  78  of the plunger  72  incorporates means  124  for releasing securing means  112 , through the shape of the cap on pusher  78 . 
     The operation of device  60  shown on  FIGS. 4   a  to  4   f  is similar to that of the device shown on  FIGS. 3   a  to  3   f , the main steps being described below. 
     The user first removes the protective cap  64  and then inserts the needle  62  into the patient&#39;s body. The user then pushes on pusher  78  which moves rods  80  and  82  of plunger  72  and therefore the implant  100  which is introduced into the distal end of the needle  62 . When plunger  72  reaches the end of its travel, release means  124  engage with the rubber detent  113  moving the rubber tabs  110  radially out of the way and retracting lugs  112 . Once lugs  112  have retracted, the return means  88  are released and can extend in the direction indicated by arrow  126 . This release of return means  88  causes intermediate housing  66  to move in the direction of arrow  126  and thus to protect needle  62  by sleeve  68  as shown in  FIGS. 4   d  to  4   f . The device is then held in the safety position by the interaction of means  114  and  123 . 
     In the same way as for the third embodiment, it can be seen that the user can control withdrawal of the needle from the patient&#39;s skin  106  manually. 
     The embodiment of  FIG. 5  is relatively similar to that of  FIGS. 3   a  to  3   f . Nevertheless, in addition to holding means  70  at the proximal end of intermediate housing  66 , the device  60  comprises means  107  for guiding the distal holding of the device, distal holding being intended to facilitate insertion of the needle into the patient&#39;s body. These means  107  are fitted to housing  66  near its distal end. They can comprise a visual indicator, a protuberance (as shown in  FIG. 5 ) or a roughened surface. They are intended to indicate a distal zone that the user can use to perform the injection. 
     Obviously, such guide means  107  can be implemented on all the other embodiments. In the case of the embodiment of  FIG. 4 , means  107  could be installed on the sleeve  68 . 
     A few remarks on the operation of the device of  FIG. 5  which are equally applicable to the other embodiments will now be made. Before starting to inject the patient, device  60  is in the configuration of  FIG. 5 . To introduce the needle  62  into the skin, the user holds device  60  by its distal part, preferably by holding the guide area  107  between the fingers of his right hand if he is right-handed. It may be more practical for the user to introduce the needle while holding device  60  in this zone  107 , since device  60  may be relatively long, for example a length of 200 mm between the end of needle  62  and pusher  78 . More precisely, the user holds the proximal end  108  of the guide zone  107  with his right hand. With his other hand, the left hand, the user can pinch the patient&#39;s body to create a hard surface for introducing the needle. Once the needle has been completely inserted into the patient&#39;s body, the user can stop pinching the patient&#39;s body and with his freed left hand take hold of the distal end  109  of zone  107 , freeing his right hand which lets go of end  108  and can then grip the holding means  70  to activate plunger  76  and proceed onto the steps of injection and needle withdrawal. In the embodiment of  FIG. 5 , plunger  76  is made of a single part and back-injection is preferably manual. 
     Note that the embodiments of the back-injection device  60  can take forms other than those described. In particular, the embodiments can be combined with any of the other embodiments. 
     Note that the devices of the third, fourth and fifth embodiments ( FIGS. 3   a  to  5 ) are devices for back-injection of an implant, preferably automatic back-injection but also being able to perform manual back-injection as has been described. A device provided with automatically released protective means  68  is therefore proposed, avoiding contamination by the needle and ensuring manual or automatic back-injection, guaranteeing that the implant is injected without experiencing any stress. Whether back-injection is manual or automatic, the invention proposes to control manually the movement of protective means  68  using holding means  70 . For manual back-injection, the user carries out the implant injection himself, by withdrawing the needle from inside the patient&#39;s body and exerting pressure on the plunger before the automatic release of the protective means. For automatic back-injection, the operator does not have to worry about injecting the implant, this being performed during the release of the protective means, since the sleeve and distal part  82  of the plunger are fastened together beforehand, so that the release of the sleeve causes part  82  to act and transfer the implants towards the skin when the needle is withdrawn from the body. 
     Similar operation can be envisaged for an injection device other than a back-injection device.