Abstract:
Automatic dilator devices for generating minimally invasive access apertures for surgical procedures or endoscopic surveillance. The automatic dilators comprise a number of spreader tubes nested one inside the other. The devices deploy automatically by means of coupled mechanical mechanisms which insert one spreader after the other distally into the patient&#39;s tissue. Each spreader moves distally into the tissue by means of a screwing action, by which rotation is converted into linear motion of the neighboring spreader, immediately external to it, by means of interaction between a helical thread form on a surface of a spreader being engaged by a section of thread, or by one or more protrusions on the opposing face of the next spreader external to the rotating spreader. Such a combination of helical thread and follower enables a rotatory mechanism to be used to deploy one nested spreader tube after the other, by continuous rotary motion.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of dilators, especially sets of nested spreaders adapted for automatic insertion by means of mechanical motion conversion mechanisms. 
       BACKGROUND OF THE INVENTION 
       [0002]    Sets of dilators are used in surgery in order to create an opening into a patient&#39;s body in order to gain access for such tasks as surgical or endoscopic procedures. They are particularly useful for minimally invasive surgical procedures, since the opening need be no larger than is required for the desired access. A dilator set comprises a series of dilator tubes of increasing diameter, each having a sharpened chamfered end so that they can be inserted with minimal tissue trauma, with the smallest diameter dilator tube inserted first, and the dilator tubes of increasing diameter inserted sequentially thereafter in order to enlarge the opening generated. Once the final and largest dilator tube has been inserted, the smaller inner ones can be removed, leaving a clear aperture for performing the desired surgical or endoscopic procedure. 
         [0003]    Current sets of dilators are inserted manually one after the other by the surgeon, which is a time consuming procedure whose quality can be variable depending on the way the procedure is conducted. Some prior art dilator sets and the methods of using them are described in U.S. Pat. No. 4,772,266 to L. E. Groshong et al, for “Catheter Dilator/Sheath Assembly and Method” and in U.S. Pat. No. 5,792,044 to K. T. Foley et al, for “Devices and Methods for Percutaneous Surgery” and in U.S. Pat. No. 7,811,303 to T. W. Fallin et al., for “Bodily Tissue Dilation Systems and Methods” and in US Paten Application Publication No. 2013/0041398 to J. Goddard et al, for “Dilator”. 
         [0004]    A power driven dilator insertion system, such as using a power drive or a drill, or a robot could greatly speed up the insertion process. Additionally, the use of robotic procedures in computer aided surgery has raised the need for a dilator set, which can be inserted automatically into the patient&#39;s body, preferably without human intervention, other than perhaps initial alignment of the insertion position and direction. 
         [0005]    There therefore exists a need for an automatically inserted dilator set which overcomes at least some of the disadvantages of prior art manual dilator sets. 
         [0006]    The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety. 
       SUMMARY 
       [0007]    The present disclosure describes new exemplary automatic dilator devices for generating minimally invasive access apertures for performing surgical procedures or endoscopic surveillance. The automatic dilators have a common feature in that they comprise a plurality of spreader tubes nested one inside the other, which are deployed automatically by means of mechanical screw-based mechanisms which couple adjacent spreaders and ensure insertion of one spreader after the other distally into the patient&#39;s tissue. These coupled screw-based mechanisms are either (i) the mutual interaction of a rotating thread engaging element, such as one or more teeth, or a tab or tabs, or a section of thread form on the external surface of a first spreader element, with a helical thread formed on the inside surface of a second spreader element disposed external to the first spreader element which is constrained to move longitudinally as the thread engaging element rotates, or conversely, (ii) the mutual interaction of a rotating helical thread formed on the external surface of a first spreader element with a thread engaging element, such as one or more teeth, or a tab or tabs, or a section of opposing thread form, on the internal surface of a second spreader element disposed external to the first spreader element and constrained to move longitudinally as the helical driving thread rotates. A common feature is that the devices have a transfer mechanism that ensures sequential deployment of the spreaders, from the innermost to the outermost, by switching the thread engagement once the previous spreader has reached its required position, from one spreader to that immediately external to it. 
         [0008]    According to a first exemplary implementation, each spreader interacts with the neighboring spreader, immediately external to it, by means of a short section of external threading or teeth or a tab or tabs on the external wall of the inner spreader meshed with an internal thread on the outer spreader. Rotation of the inner spreader while the outer spreader is prevented from rotating causes the outer spreader to move linearly relative to the rotating inner spreader, in much the same way as a nut, held so that it cannot rotate, rides down (or up) a screw as the screw is rotated. This combination of external and internal threading is applied to the nested spreader tubes of the device, and a rotatory mechanism is used to deploy one spreader tube after the other, by means of a continuous rotary motion. The dilator devices incorporate mechanisms which automatically transfer the longitudinal motion from an inner spreader to that immediately external to it, once the inner spreader has reached its intended depth of insertion. For an orthopedic access dilator, this mechanism can be the abutment of the spreader on the target bone, such that the prevention of further longitudinal motion of that spreader causes it to rotate together with the spreader immediately inwards of it, and thus to generate longitudinal motion in the spreader immediately external to it. In this way the automatic dilator device can be inserted into the patient by means of a continuous rotary motion in one direction, such as could be supplied by a surgical drill, or a robotic rotary drive. 
         [0009]    According to a second implementation, each of the spreader tubes is individually rotated by means of a splined shaft running through either the spreader tube itself (in the case of the innermost spreader tube) or through a cover on the spreader tube, and engaging with internal spline grooves formed in that spreader tube or cover. A short proximal section of this splined shaft is formed without any splining, and the longitudinal position of the spreaders relative to this unsplined section is arranged such that all of the spreaders proximal to the spreader being deployed have their internal splined cover located at the unsplined section of the splined shaft, such that they do not rotate. When the spreader being deployed has reached its fully deployed position, its internal splined cover disengages from the distal end of the splined drive shaft, such that it no longer rotates, and the spline shaft with the drive assembly can be moved proximally so that the next outwardly disposed spreader tube is now engaged by the splined shaft and commences to turn and to move distally down the dilator device. In addition, a rotation blocking assembly is used to prevent rotation of all of the outer spreaders except that one which is driving the next spreader external to it, and this rotation blocker is moved proximally with the drive assembly to free that next spreader to enable it to rotate. This implementation also includes specific mechanical mechanisms, which will be fully expounded the Detailed Description section below, for defining which of the spreaders should be locked into position, and which should be enabled to rotate by the rotation of the splined tube. The operation regarding which spreaders should be locked into position and which be allowed to engage with the splined drive shaft has been described in the Detailed Description section below, by means of a hand held element such as a hand-grip, but it is to be understood that the operation of the device can equally well be performed using a clutch assembly in the case of a fully automatic insertion mechanism, such that an automatic sequential insertion of the spreader tubes is achieved, starting with the narrowest—the innermost one—and ending with the outermost one. 
         [0010]    A third implementation, like the above-mentioned second implementation, has a series of concentric spreader tubes, each having an internal thread formed on its inside surface, but whose distal motion is generated by means of a set of spring-loaded hinged pawl elements mounted on the innermost element, each pawl element having an externally protruding tooth which meshes with the internal threads of the spreader tubes external to it, driving each of the spreader tubes distally into the tissue as the innermost element is rotated. As soon as a spreader tube reaches its distal deployed location, the external toothed protrusions on the hinged pawl elements slip off the end of the internal thread of that spreader, and being spring-loaded in an outward direction, now mesh with the internal thread on the next outwardly positioned spreader tube element at its distal end, and rotation of the inner element now begins to move that next outwardly positioned spreader tube longitudinally into the tissue. This implementation thus has the advantage over the second implementation that the successive insertion of the spreader tubes takes place automatically on continuous rotation of the innermost element, without the need for any intermediate operations to switch between successive spreaders. 
         [0011]    There is thus provided in accordance with an exemplary implementation of the devices described in this disclosure, a an automatic dilator device, comprising: 
         [0000]    (i) a plurality of concentric spreader tubes nested one inside the other, ranging from the innermost spreader tube to the outermost spreader tube, at least some of the spreader tubes comprising at least one protrusion on their outer wall and at least some of the spreader tubes having a helical thread formed on their inner wall, the at least one protrusion being adapted to engage the helical thread formed on the inner wall of the spreader tube disposed immediately external to it,
 
(ii) a rotation mechanism coupled to at least one of the spreader tube, such that when the rotation mechanism rotates a first spreader tube, a linear motion of a second spreader tube disposed immediately external to the first spreader tube is generated, and
 
(iii) a mechanical arrangement associated with at least the second spreader tube, such that when the second spreader tube reaches a predetermined deployed position, the mechanical arrangement transfers rotary motion of the rotation mechanism to the second spreader tube.
 
         [0012]    In such an automatic dilator device, the rotational mechanism may comprise a splined drive shaft, disposed axially through the innermost spreader tube, and adapted to mesh separately with an internally splined section associated with each of the spreader tubes, such that rotation of the splined shaft causes a spreader tube with which it is meshed to rotate. 
         [0013]    Furthermore, the mechanical arrangement may comprise an axial motion mechanism that moves axially to selectively prevent or allow rotary motion of any of the spreader tubes. 
         [0014]    In the above described splined shaft implementation, the splined shaft may have an unsplined section at its proximal end, and the plurality of concentric spreader tubes may be initially positioned and of such lengths that the unsplined section does not mesh with the internally splined section associated with those the spreader tubes which it is not desired to rotate. In such a case, the mechanical arrangement should comprise an axial motion mechanism which moves the splined shaft in a proximal direction such that its splined section meshes with the internally splined section associated with that spreader tube which it is desired to be rotated, which previously was disposed opposite the unsplined section. 
         [0015]    According to a further implementation, the axial motion mechanism may comprise at least one axially moveable pin disposed off-axis to the spreader tubes, such that the axial motion inserts the at least one pin into an off-axis aperture in an end element of the spreader tube to selectively prevent or allow rotation of the spreader tube. 
         [0016]    Additionally, in a splined shaft implementation of these automatic dilator devices, the splined drive shaft may have a length such that when a spreader tube reaches its predetermined deployed position, the internal splined section associated with the spreader tube slips of the end of the splined shaft and out of engagement with the splines, such that it is no longer rotated by the splined shaft. 
         [0017]    In any of the above described implementations, the rotation mechanism may be adapted to deploy the plurality of concentric spreader tubes sequentially by rotation in one direction. Such rotation may be robotically generated. 
         [0018]    Yet other implementations may involve a dilator device, comprising: 
         [0000]    (i) a plurality of spreader tubes nested one inside the other, each of the inner ones of the spreader tubes comprising a section of external threading on its outer wall which is adapted to mesh with an internal thread on the inner wall of the spreader tube disposed immediately external to it and in close juxtaposition to it, such that rotation of a spreader tubes causes it to screw longitudinally into the spreader tube disposed immediately external to it,
 
(ii) a partially splined drive shaft disposed axially through the innermost spreader tube, and meshing with an internal splined section associated with each of the spreader tubes, and
 
(iii) a mechanism for axially moving the splined drive shaft relative to the spreader tubes, with its splined sections positioned to mesh sequentially with successively outwardly disposed spreader tubes, such that rotation of the partially splined drive shaft is adapted to cause the plurality of spreader tubes to deploy sequentially into a tissue of a patient.
 
         [0019]    Another example implementation can involve a dilator device, comprising: 
         [0000]    (i) a plurality of concentrically nested spreader tubes, each having a section of internal threading on its inner wall, and
 
(ii) a spiked rod with a rotator element, disposed within the innermost spreader tube, the rotator element comprising at its distal end at least one outwardly biased tooth element which meshes with the inner thread of the spreader tube immediately external to it, wherein rotation of the rotator element is adapted to cause the at least one outwardly biased tooth element to move the innermost spreader tube longitudinally in a distal direction, until the outwardly biased tooth element springs outwardly off the proximal end of the internal threading on the innermost spreader tube, and onto the internal threading on the next outwardly positioned spreader tube.
 
         [0020]    In such a dilator device, the outwardly biased tooth element may be a hinged pawl element incorporated into the rotator element, spring loaded such that it has an outwardly directed force acting on its end remote from the hinge, and may have an externally protruding tooth which meshes with the inner thread of the spreader tube immediately external to it. 
         [0021]    Other implementations may further involve a dilator device, comprising: 
         [0000]    (i) a plurality of concentrically nested spreader tubes, juxtaposed spreader tubes being mechanically linked by means of a helical thread form on one wall of one of the juxtaposed spreader tubes and at least one protrusion element engaging with the helical thread form on the facing wall of the second one of the juxtaposed spreader tubes,
 
(ii) a rotation mechanism coupled to the inner one of the juxtaposed spreader tubes, such that when the rotation mechanism rotates the inner one of the juxtaposed spreader tube, a linear motion of the second one of the juxtaposed spreader tubes is generated in a direction parallel to the axis of the spreader tubes, and
 
(iii) a motion transferring mechanism associated with at least the second one of the juxtaposed spreader tubes, such that when the second one of the juxtaposed spreader tubes reaches a predetermined deployed position, the motion transferring mechanism transfers the rotationary motion of the rotation mechanism to the second one of the juxtaposed spreader tubes.
 
         [0022]    In such a dilator device, the helical thread may be disposed on an inner wall of an outer one of the juxtaposed spreader tubes, and the at least one protrusion element disposed on an outer wall of the inner one of the juxtaposed spreader tubes. Alternatively, the helical thread may be disposed on an outer wall of an inner one of the juxtaposed spreader tubes, and the at least one protrusion element disposed on an inner wall of the outer one of the juxtaposed spreader tubes. In either of these situations, the at least one protrusion element may be any one of a section of thread form, a set of one or more teeth or a set of one or more tabs. 
         [0023]    Yet other implementations perform a method of automatically inserting a dilator device into a subject, comprising: 
         [0000]    (i) providing a plurality of concentric spreader tubes nested one inside the other, ranging from the innermost spreader tube to the outermost spreader tube, at least some of the spreader tubes comprising at least one protrusion on their outer wall and at least some of the spreader tubes having a helical thread formed on their inner wall, the at least one protrusion being engaging the helical thread formed on the inner wall of the spreader tube disposed immediately external to it,
 
(ii) rotating at least one of the spreader tubes, such that a linear motion of a second spreader tube disposed adjacently outwards of the first spreader tube is generated, and
 
(iii) providing a mechanical arrangement associated with the spreader tubes, such that when the at least one spreader tube reaches a predetermined deployed position, the mechanical arrangement transfers rotary motion to the second spreader tube disposed adjacently outwards of the first spreader tube. Such a method may comprise the step of providing further rotation until all of the plurality of concentric spreader tubes are deployed within the tissues of the subject.
 
         [0024]    Throughout this disclosure, the terms distal and proximal have their accepted meaning, distal referring to the direction into the patient&#39;s body, while proximal refers to the direction out of the patient&#39;s body and towards the applicator of the device. In the drawings of the present disclosure, since the device is shown entering a subject&#39;s body at the bottom section of the drawings, the proximal direction is shown upwards, and the distal direction, downwards. 
         [0025]    Furthermore, although the mechanisms for switching between successive spreaders has been generally described in this disclosure using manually operated procedures, this is not meant to limit the invention, and it is to be understood that any of these mechanisms can equally well be performed using automated assemblies such as clutches and linear or rotary electromechanical actuators. 
         [0026]    Additionally, although the dilator devices work equally well whether the continuous helical thread is on the inner or the outer surface of the spreaders, with the thread engaging elements incorporated accordingly to face the helical thread—with the exception of course of the innermost and outermost spreaders which need not have both thread and thread engaging elements—all of the examples described in this disclosure use a continuous helical thread form on the internal surfaces of the spreaders, and the thread engaging elements on the facing outer surfaces. It is to be understood, however, that this is not intended to limit the invention, and that either configuration is equally operable. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: 
           [0028]      FIGS. 1 to 8  illustrate schematically a first exemplary auto dilator having a nest of spreaders with internal helical threads and opposing external protrusions on the spreaders external thereto to engage with the internal helical threads, rotation of the spreader with the internal helical thread causing the spreader with the external protrusions to move linearly, the series of figures showing the way in which the auto dilator is inserted into the patient&#39;s body tissue, step-by-step; 
           [0029]      FIG. 9  is a schematic assembly drawing of a second exemplary implementation of the automatic dilators described in this disclosure, also having internal helical threads engaging with external protrusions on the spreaders adapted to engage with the internal threads on the spreader immediately outwards of the protrusions, but differing from the dilator of  FIGS. 1-8  in that the rotation and deployment of successive spreaders is controlled by a mechanical mechanism incorporating a splined shaft directing which spreader is operative in rotating to provide linear motion to that immediately outward of it; 
           [0030]      FIGS. 10 to 23  illustrate schematically how, step-by-step, the automatic dilator shown in  FIG. 9 , can be deployed into a patient&#39;s body tissue; 
           [0031]      FIG. 24  is a schematic assembly drawing of a third exemplary implementation of the automatic dilators described in this disclosure, using a series of spring loaded external pawls to switch the linear motion from one spreader to the next; and 
           [0032]      FIGS. 25 to 27  illustrate schematically how, step-by-step, the automatic dilator shown in  FIG. 25 , can be deployed into a patient&#39;s body tissue 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    Reference is now made to  FIGS. 1 to 8 , which is a series of schematic illustrations of a first exemplary implementation of the automatic dilators described in this disclosure, showing the sequential stages of insertion of the dilator. The device comprises a number of hollow dilator tubes having incrementally increasing diameters, such that the dilator tubes fit sequentially within each other to form a nest of dilator tubes of increasing diameter, starting with the innermost and finishing with the outermost. The outer diameter of any one of the set is a sliding fit within the inner diameter of the next largest dilator tube, such that the set covers a complete range of diameters from the inner diameter of the innermost dilator to the outer diameter of the outermost dilator. Each of the dilator tubes has an internal screw thread over the whole length of its inner wall, and each of the dilator tubes, except the outermost one, has a section of screw thread formed on its outer wall at its proximal end. This section can be a short section covering typically only one or a few turns. Although the short screw thread section is used as the example for this implementation, it is to be understood that the devices are not intended to be so limited, but that the section of screw thread can be replaced by one or more teeth or tabs, or any other elements protruding from the outer wall, that can mate with the internal thread of the inner spreader. As a result of this combination, when a particular dilator tube is rotated, the short external screw thread section at its proximal end riding within the internal screw thread of the dilator tube immediately external to it, causes the dilator tube external to the rotated tube to move longitudinally relative to the position of the dilator tube being rotated, the relative direction of motion depending on the handedness of the threads generating the motion. Since it is conventional practice to positively activate rotary mechanical mechanisms by means of clockwise rotation of the actuating handle, and since the function of the auto-dilator is to drive the dilator tubes distally into the patient&#39;s tissues, the screw threads should be left-handed so that clockwise rotation of the actuating handle of the auto-dilator results in the desired distal motion of each successive outer tube. 
         [0034]    In  FIGS. 1 to 8 , there is shown an exemplary auto dilator using the above described arrangement of internal and external threads, for use in orthopedic applications, though it is to be understood that this is merely one exemplary implementation, and that dilators for use in other applications can also be constructed in the same manner. The exemplary device shown in  FIGS. 1 to 8  comprises five separate dilator tubes or spreaders,  12 ,  16 ,  17 ,  18 ,  19 , though a different number can also be used. 
         [0035]    Reference is now made to  FIG. 1 , which shows the device after the first stage of insertion has been performed. The auto dilator is first positioned on the patient&#39;s skin  13 , and, using the drive handle  14  at the proximal end of the device, the innermost element, a spiked rod  10 , is driven into the subcutaneous tissue down to the bone surface  11 , to which the auto dilator is intended to prepare an access passageway. A guide wire (not shown in the drawings) can be optionally used in order to define the position of insertion of the innermost element. The distal end of the spiked rod is adapted to make firm or penetrating contact with the bone surface  11 . It may be fitted with a freely rotatable point, such that the rod can rotate freely even whilst its spiked point is firmly embedded in the bone, though this feature is not essential, since the spiked point may also be adapted to rotate within the bone surface without being dislodged from its intended position. The spiked rod has a number of external threads or protrusions  15  at its proximal end, so that as the rod is turned in a clockwise direction, the teeth of its external screw thread or the protrusions running within the groove of the internal thread of the spreader immediately external to it, causes that first spreader  12  to move distally down through the patient&#39;s skin  13 , spreading the tissue as it proceeds. The chamfered distal end of the innermost spreader, with its leading edge sliding along the outer surface of the spiked rod, assists in enabling it to penetrate the patient&#39;s tissue with minimal damage to the tissue. 
         [0036]    Once the innermost spreader  12  reaches its destination position against the bone surface  11 , it can no longer move longitudinally into the patient&#39;s tissue, and since the spiked rod is continuing to turn, the innermost spreader  12  locks itself to the rotating spiked rod, and rotates itself in unison with the spiked rod. Once this action takes place, the commencement of the rotation of the few external threads  15  or the protrusions at the proximal end of the innermost spreader  12 , which are meshed with the internal thread of the next spreader  16  (next in the sense of the radially outward direction from the innermost spreader), cause that next spreader  16  to move distally down the innermost spreader  12  by means of the screw action of the two meshing thread forms. This action continues until, as shown in  FIG. 2 , the next spreader  16  also reaches its destination at the surface of the bone  11 , and its downward motion is stopped. At that point, it too begins to rotate in unison with the innermost spreader  12  and the spiked rod  10 , and by the same action as it has itself previously undergone, using the few external threads or the protrusions at the proximal end, it begins to pull the next outermost spreader, the third spreader  17 , downwards into the patient&#39;s tissue. This process continues until the third spreader  17  reaches its most distal point, as shown in  FIG. 3 , when the fourth spreader  18  begins its distal motion, and so on in  FIGS. 4 and 5 , in which the fourth spreader  18 , and the fifth spreader  19  are shown to have been respectively completely inserted. The chamfered leading edge of each spreader is the leading edge, which is that which slides along the outer surface of the previously deployed spreader, thus providing a spreading effect to the tissue it is passing through, rather than a cutting effect. 
         [0037]      FIG. 5  now shows all five of the spreaders fully inserted, having spread the patient&#39;s tissue to the required diameter for the access aperture desired. As seen in  FIG. 5 , the outermost spreader  19 —the fifth spreader in this example device—is longer than the previous, more internally disposed spreaders, and it is this outer spreader which constitutes the dilator tube, which will be used for providing access to the surgical site on the patient&#39;s bone. However, the dilator is not yet usable since its entire internal volume is taken up with the previous spreaders and the spiked rod. In order to utilize the dilator, it is necessary to remove all of the internal spreader tubes  12 ,  16 ,  17 ,  18 , and the spiked rod  10 , with their drive mechanism, leaving only the outermost spreader  19 . 
         [0038]    Reference is now made to  FIG. 6  which illustrates how this is achieved. In  FIG. 6 , the actuating handle  14  is being rotated anticlockwise, and this action causes the nest of internal spreaders  12 ,  16 ,  17 ,  18 , to rotate anticlockwise also, such that the outer screw thread on the fourth, penultimate spreader  18  meshing with the internal screw thread of the outermost spreader  19 , causes the entire internal nest of spreaders to move proximally upwards through the outermost spreader  19 , until they can be removed from the outermost spreader  19 . The spiked rod  10  can then also be removed proximally, as shown in  FIG. 7 , followed by the activation handle and its mechanism  14 , leaving just the outermost spreader tube  19 , as shown in  FIG. 8 , which can then be utilized as the dilator tube for the surgical procedure to be undertaken. 
         [0039]    Reference is now made to  FIG. 9 , which is a schematic assembly drawing of a second exemplary implementation of the automatic dilators described in this disclosure.  FIG. 9  also includes a drawing of the assembled automatic dilator. This auto-dilator differs from that shown in  FIGS. 1 to 8 , in that it incorporates positive mechanical mechanisms for ensuring that each successive spreader reaches its destined position and is locked into place, and to ensure that the spreader deployment is performed in the correct sequential manner. In addition this implementation, more readily enables the auto dilator to be used in soft tissue without a bone structure to position its destination point accurately. As in the previous implementation, this auto dilator operates on the principle of a nested series of spreaders, each, except the innermost one, having an external thread form which engages with an internal thread section on the spreader immediately outward of it. However, unlike the previous implementation, in this model, each spreader is inserted longitudinally by a conventional screw action, in that as a particular spreader is rotated, it descends distally through the neighboring spreader immediately outward of it and into the patient&#39;s tissues, by conventional screw action of its external thread screwing into the internal thread of that outer spreader. In  FIG. 9 , there is shown an auto dilator with four nested spreaders, marked  91 ,  92 ,  93  and  94  in descending order of size. Spreader  91  has a cover  116 , spreader  92  has a cover  96 , and spreader  93  has a cover  95  all of which are fixed onto the proximal ends of the spreaders. The cover of innermost spreader  94  is already attached to the top end of spreader  94 . A hollow splined rod  111  runs through all of these covers to the distal end of the spreaders, as shown in more detail in the blown-up drawing of the hollow splined rod running through cover  95 . The proximal end of the hollow splined rod  111  is attached to a rotating handle  112 , such that when handle  112  is rotated, the splined rod  111  rotates with it. A short section  100  of the proximal end of the splined rod has a reduced diameter, without splines. Inside of the hollow splined rod  111 , there is a rod  98  having a spiked end, similar to that shown in the embodiment of  FIGS. 1 to 8 . At the distal end of the spiked rod  98 , there is a pointed tip  120 , to enable insertion of the spiked rod with minimal tissue damage, and which defines the position to which the auto dilator is to be inserted. In addition, there is a mechanism  89 ,  99 ,  110 , at the distal end for locking the innermost spreader  94  to the spiked rod  98 . The spiked rod  98  extends proximally to an operating handle  119  used for its insertion into the patient&#39;s tissue. Between the rotating handle  112  and the cover  116  of the outermost spreader  91 , there is a collar-shaped cylindrical enclosure  114 , with a raised shoulder at its proximal end, and the rotating handle  112  fits over this raised shoulder and is attached to the cylindrical enclosure  114  by means of locking screws  113  which fit under the shoulder after the rotating handle has been mounted over the shoulder, but which do not clamp the cylindrical enclosure, such that they allow the handle  112  to rotate freely relative to the cylindrical enclosure  114 . The cylindrical enclosure  114  can be held stationary while the rotating handle  112  is rotated by means of a static handle  125  attached to the cylindrical enclosure. The cylindrical enclosure  114  has two spiral grooves  101  diametrically formed in its outer surface. A pair of positioning screws  117 , one passing through each of the spiral grooves, is screwed into the top cover  116 , and the position of the positioning screws  117  in the spiral grooves defines the longitudinal position of the cover  116  inside the collar shaped cylindrical enclosure  114 . Three predefined positions are formed in the spiral grooves  101 , defining three different heights of the cover  116  within the collar shaped enclosure  114 , and hence also the longitudinal distance of the rotating handle  112  from the top of the spreader assembly, as defined by the cover  116  of the outermost spreader  91 . Although in  FIG. 9 , the longitudinal height of the cover  116  inside the collar-shaped enclosure is shown as being determined by the position of two positioning screws  117  moving in two spiral slots  101 , it is to be understood that this is only one method by which the height of the cover  116  can be adjusted and set, and that any other mechanism which achieves this object can equally well be used. Attached to the distal side of the rotating handle  112 , there is a slip ring bearing  115 , having two rotation prevention pins  118  extending in a distal direction into the covers of the spreaders. Further details of the component parts will now be expounded in the following explanation showing how the auto dilator operates. 
         [0040]    Reference is now made to  FIGS. 10 to 24  in conjunction with  FIG. 9 , to illustrate how this exemplary auto-dilator operates, and to explain the sequential stages of insertion of the spreaders. Each of  FIGS. 10 to 24  illustrates a particular stage of insertion of the auto-dilator, generally in two views—a side elevation view and a cross sectional view showing the disposition of the internal parts. 
         [0041]    In  FIG. 10 , the auto dilator is shown ready for insertion. In this drawing, it is observed that the length of the spreaders are linearly staggered, such that the outermost spreader  91  is the longest and the succeeding spreaders  92 ,  93 ,  94  are successively shorter, each difference in length being equal to the incremental change in height of the cover  116  between each preset position of the positioning screws  117 . The differences in height are manifested at the top ends of the spreaders, such that the rotation prevention pins  118  protrude different lengths into the successive spreaders. Additionally, the unsplined top section  100  of the splined rod  111  is of such a length that in the initial undeployed situation of  FIG. 10 , the splines only mesh with the innermost spreader  94 , which is the spreader with the most distally positioned proximal end. 
         [0042]    In  FIG. 11 , there is shown insertion of the spiked rod  98  into the patient&#39;s tissue by means of pressure on, and also optionally rotation of the handle  119 . The other details are as numbered in  FIG. 10 , and are not repeated in this drawing or the following ones, if not necessary to explain operation of the auto-dilator. 
         [0043]    In  FIG. 12 , insertion of the innermost spreader  94  is commenced by the rotation of the handle  112 , such that the splined rod  111  rotates with it. Because of the dense detail of the assembled dilator drawings in  FIGS. 12 to 24 , reference should also be made to the assembly drawing of  FIG. 9  to see clearly how the insertion procedure is executed. In  FIG. 12 , as the splined rod rotates, its splines, being meshed with the inner splines in the cap of the innermost spreader  94 , also cause the innermost spreader  94  to rotate. The meshing of the outer thread of the innermost spreader  94  with the internal thread of spreader  93 , its immediately neighboring outwardly positioned spreader, causes spreader  94  to screw downwards into the patient&#39;s tissue. Because of the clear unsplined top section  100  of the splined rod  111 , rotation of the splined rod does not have any effect on the other spreaders, which are not rotated by rotation of the splined rod. The cylindrical enclosure  114  and all of the remaining components attached thereto are kept from rotating by means of the handle  125 . Furthermore, the rotation prevention pins  118  attached to the rotating handle  112 , project into covers  95  and  96  of spreaders  93  and  92  respectively, holding them static. When spreader  94  reaches its bottommost position, as shown in  FIG. 13 , its distal end pushes an annular locking ring  99  (see  FIG. 9 ) in a distal direction, thereby releasing the locking fingers  89  of the locking spring  110 , shaped like an omega, which can then expand in an output direction into an internal groove  126  formed on the end of innermost spreader  94 . This action locks innermost spreader  94  to the spiked rod  98 , which, since it is held in a static position within the patient&#39;s tissue by means of handle  119 , also clamps innermost spreader  94  into position at its most distal position, with its end at the target position to which the auto-dilator is to be deployed in the patient&#39;s tissue. Furthermore, the innermost spreader  94  is also prevented from rotating further by means of this clamping mechanism. At this point, the innermost spreader  94  has thus been deployed into its correct within the patient&#39;s tissue. The length of the splines on the shaft  111  are such that when the spreader  94  reaches its completely deployed position, its cap  99  has just slipped off the end of the splines on shaft  111 , which can therefore no longer continue to rotate spreader  94 . 
         [0044]    Reference is now made to  FIG. 14 , which illustrates the following step, in which the next spreader  93 , in an outward direction, must now be deployed. In order to do so, two actions must be performed: 
         [0000]    (i) Firstly, the splined drive shaft  111  must be released from engagement with innermost spreader  94 , and must be engaged with the next outer spreader  93 .
 
(ii) Secondly, the rotation prevention pins  118  must be retracted from spreader  93  to enable it to be turned freely by the splined driver shaft  111 .
 
Both of these results are achieved by the single action of freeing the positioning screws  117  in the cylindrical enclosure  114 , and by moving the enclosure  114  together with its attached rotary handle  112  in a proximal direction until the next screw position is reached, and by retightening the positioning screws  117  in that position, as can be observed by comparison of the position of the screws  117  in the elevation drawings of  FIG. 13  (positioning screws  117  in top position) and  FIG. 14  (positioning screws  117  in middle position).
 
         [0045]    Reference to the sectional drawing of  FIG. 14  now shows the operative result of this action. Both the splined drive shaft  111  and the pin assembly  115  are attached to the rotary handle  112 . Therefore, the motion of the rotary handle  112  in the proximal direction, away from the nest of spreader tubes partially inserted into the patient&#39;s tissue, results in the motion proximally of the splined drive shaft  111  and the pin assembly  115  with its rotation prevention pins  118  away from the spreader tube assembly, as can be readily seen by the enlarged space  127  between the cover  116  of the outermost spreader tube  91  and the roof of the cylindrical enclosure  114  to which the rotary handle  112  is attached. This action essentially enables the two desired results mentioned above: 
         [0000]    (i) The splined drive shaft moves proximally by an amount which releases its distal end from engagement with the internal spline grooves of the innermost spreader tube  94 , and at the same time, the proximal end of the splines moves up and now engages the cover  95  of the second spreader tube  93 , where previously, in  FIG. 13 , that cover was positioned longitudinally in the unsplined top section of the splined shaft, so that it did not rotate with rotation of the splines.
 
(ii) The rotation prevention pins  118  move proximally by an amount which frees their insertion into the cover  95  of spreader  93 , such that spreader  93  is no longer prevented from rotating, and can now be turned freely by the splined driver shaft  111 .
 
         [0046]    Reference is now made to  FIG. 15 , which illustrates the result of rotation of handle  112 , such that the splined rod  111  rotates with it and consequently also the second to innermost spreader  93 . Its external threads propel it down the internal thread system of the next outward spreader  92 , further spreading the patient&#39;s tissues, until it reaches its distal target position next to the innermost spreader, where the splines on the splined drive shaft  111  slip out of the internal splined grooves in its cover  95 , and thus no longer propel it distally downwards. 
         [0047]    At this point both of the innermost spreaders are deployed and reference is now made to  FIG. 16 , which illustrates how the device is adjusted again, so that the third from the innermost spreaders  92  can now be deployed. This is done in a similar manner to that shown in  FIG. 14 , but this time, the positioning screws  117  are shifted from the middle position in the cylindrical enclosure to the most distal position. The height of space  127  then increases even more from its height when pins  117  were in the intermediate position. Pins  118  now only prevent cover  116  of outer spreader  91  from rotating. 
         [0048]    In this position, the proximal motion of the splined drive shaft  111  and the rotation prevention pin assembly  115  and its pins  118  away from the spreader tube assembly causes the splined drive shaft to release from engagement with the internal spline grooves of the cover  95  of spreader tube  93 , and to engage with the spline grooves of cover  96  of spreader tube  92 , and in addition, causes the rotation prevention pins  118  to move proximally to free their insertion in the cover  96  of spreader  92 , such that spreader  92  is no longer prevented from rotating, and can now be turned freely by the splined driver shaft  111 . Rotation of handle  112  can then be used to deploy the third innermost spreader  92 , further spreading the patient&#39;s tissue until it reaches the target destination alongside the first two spreaders,  93 ,  94 . This position is shown in  FIG. 17 , where the presence is shown of the locking screws  113 , which lock the rotating handle  112  to the cylindrical enclosure body  114 . 
         [0049]    Reference is now made to  FIG. 18  to illustrate the deployment of the final and outermost spreader  91 . Since the outer spreader  91  cannot be inserted by screwing into any other element external to it, a somewhat different technique must be adopted. The locking screws  113  used to attach the rotating handle  112  to the cylindrical enclosure body  114  are removed, enabling the rotating handle  112  to be physically disconnected from the cylindrical enclosure body  114 . At this point, rotation of the cylindrical enclosure body  114  attached to the cover  116  of the outermost spreader  91 , enables the outermost spreader  91  to be screwed distally over the external threads of the penultimate spreader  92 , until it reaches its fully deployed position over the first three spreaders. A fine external thread on the outer surface of the outer spreader, and even on the outer surfaces of the other spreaders, may facilitate their insertion into the tissue of the subject, though such outer threads play no part in the dynamics of the insertion mechanism of the device. 
         [0050]    Reference is now made to  FIG. 19 , which shows the outer spreader  91  fully deployed, and the rotating handle  112  at the top end of the splined shaft  111  on the unsplined part  100 , while the cylindrical enclosure body  114  has been screwed down with the outermost spreader towards the entry point of the device on the patient&#39;s skin. All that remains now in order to leave the outermost spreader  91  lodged in the patient&#39;s tissues, is for the nest of the three innermost spreaders  92 ,  93 ,  94 , to be removed from inside the outermost spreader  91 , together with the drive spline shaft, the spiked rod, and the cylindrical enclosure body  114 . This procedure is now shown in  FIGS. 20 to 23 . 
         [0051]    Referring first to  FIG. 20 , the positioning screws  117  are removed from the spiral groove in the cylindrical enclosure  114 . Then in  FIG. 21 , there is shown that the cylindrical enclosure  114 , together with the top cover  116  of the outermost spreader  91  can be raised, leaving only the nest of spreaders and the splined drive shaft  111 , held in the patient&#39;s tissues. 
         [0052]    Reference is now made to  FIG. 22 , which shows how, by rotation of the splined drive shaft  111 , together with the spiked rod, in an anticlockwise direction, all of the spreaders  92 ,  93 ,  94 , and other components internal to or attached to the outermost spreader  91 , screw out of the outermost spreader  91 , leaving it alone penetrated through the patient&#39;s skin  113 , and fixed in the patient&#39;s tissue, as shown in  FIG. 23 . 
         [0053]    As previously mentioned, in this described implementation, all of the motion steps are described only as mechanical motion steps without reference to the manner in which these steps are performed. It is to be understood that the disclosure is intended only to explain the mechanical steps necessary in order to deploy the described auto dilator. In this respect, although manual operation may be the simplest way of using the device, it is to be understood that the disclosure is in no way intended to limit the device to such use. Thus, if the device is to be completely automated, such that it could be used on a robotic surgical system, rotary and linear actuators could be used for each rotary or linear motion step, with the sequence being controlled and monitored by means of a robotic controller, and sensors or encoders incorporated on the various mechanical parts. For instance, the use of manually adjusted positioning screws  117  in a spiral groove  101  in the cylindrical enclosure  114  could readily be replaced by any other method of controlling and locking the longitudinal motion required. Thus, for instance, a motorized linear motion drive could readily be used in fully robotic operation of the auto-dilator. The various rotary motions could also readily be replaced by at least some of servomotors with rotary encoders and position sensors. 
         [0054]    This second exemplary implementation of the automatic dilators described in this disclosure has a possible disadvantage or inconvenience in that the longitudinal position of the cylindrical enclosure  114  has to be shifted by means of the positioning screws  117 , or an alternative positioning mechanism, to enable deployment of successive spreaders. 
         [0055]    Reference is now made to  FIG. 24  which illustrates schematically a third exemplary implementation of an automatic dilator as described in this disclosure, in which the complete insertion procedure is performed by one continuous screwing motion.  FIGS. 25 to 27  illustrate how the dilator of  FIG. 24  operates through its various stages of insertion into the subject&#39;s tissue. The exemplary dilator shown in  FIGS. 24 to 27  has an internal dilation rod with only two spreaders external thereto, but it is to be understood that this is only one example, and that the device could have a larger number of spreaders to increase its expansion range. 
         [0056]    Like the previously described examples, this implantation also depends upon the rotation of the thread form of an inner element meshed with the thread form of the spreader tube element immediately external to it, such that as the inner thread form is rotated, if the outer spreader tube is prevented from rotating, it will move longitudinally and into the subject&#39;s tissue. This implementation differs from the previous ones in that the rotating inner thread takes the form of a set of radially positioned, spring-loaded, hinged pawl elements, each having a toothed protrusion which meshes with the inner thread of the spreader immediately external to it, driving it distally into the tissue as the toothed protrusions rotate. As soon as the immediately external spreader element reaches its distal deployed location, the toothed protrusions on the hinged pawl elements slip off the end of the internal thread on that first spreader element, and being spring-loaded in an outward direction, now mesh with the internal thread on the next outwardly positioned spreader element, and rotation of the innermost element now begins to move that next outwardly positioned spreader longitudinally into the tissue. 
         [0057]    In  FIG. 24 , there is shown an assembled and an exploded isometric view of an exemplary design of this implementation of the complete auto dilator  150 , showing its component parts. The innermost element of the device is the spiked rod  157 , which has a sharpened spike  177  at its distal end. This is the embodiment shown in the assembled drawing on the right hand side of  FIG. 24 . According to an alternative implementation, in order to ease insertion of the spiked rod into the patient&#39;s tissue, a number of graded chamfers  166  can be provided to the spiked rod  157 , as shown in the exploded unassembled view on the left hand side of  FIG. 24 , to expand its diameter to the internal diameter of the first spreader tube  152 . In this case, the first spreader tube  152  should be allowed to extend only along the parallel section of the spiked rod, to avoid unnecessary trauma to the patient&#39;s tissue as it is inserted. A handle  151  is provided at the proximal end of the spiked rod. The spiked rod is incorporated within an actuating tube  158 , which has an internal bore adapted to take the spiked rod. In the example shown in  FIG. 24 , the actuating tube  158  sits on a shoulder  159  on the spiked rod, so that the enlarged outer diameter of the spiked rod is contiguous with the outer diameter of the actuating tube  158 . In the construction shown in  FIG. 24 , the spiked rod  157 , with its distal spiked spreader point needs to be dismountable in order for it to be inserted into the actuating tube  158 . The actuating tube  158  has its own rotation handle  153  at its proximal end. 
         [0058]    At its distal end, the actuating tube has a number of grooved longitudinal indentations  160 , four in number in the example shown in  FIG. 24 , though it is to be understood that any other practical number of such grooved indentations could be provided, even a single indentation. In each of these grooved indentations  160 , there is fitted a spring loaded pawl element  156 , hinged on a pin  54  such that the pawl element  156  is enabled to swing in an outwards direction. The pawl elements  156  are fitted with an internal spring (not shown) which biases them in the outward direction. The pawl elements  156  each have an externally protruding tooth  161  at the end opposite to that at which they are hinged. 
         [0059]    The entire inner assembly comprising the spiked rod  157  and the actuating tube  158  with its spring-loaded pawl elements  156 , is located within the inner bore of the first spreader element  152 , with its chamfered distal end. This spreader element has an internal thread  162  and the externally protruding teeth  161  of the spring-loaded pawl elements  156  fit into the internal thread  162 . The externally protruding teeth  161  should be in axially staggered positions such that they are positioned to all fit correctly into the internal thread  162 , even though they contact the internal thread at different circumferential orientations. 
         [0060]    External and concentrically to the first spreader element  152 , there is located a second spreader element  155 , also having an internal thread form  164 , and although no further spreader elements are shown in the device of  FIG. 24 , it is to be understood that more spreaders could be incorporated external to second spreader element  155 . 
         [0061]    Reference is now made to  FIGS. 25 to 27 , which include assembled and cut away sections of the assembled auto dilator of  FIG. 24 , to illustrate how the device operates in use. In  FIG. 25 , section A-A shows the assembled auto dilator  150 , with the operative structure of one of the spring-loaded pawl elements  156  shown in blown-up detail. Referring to this blown-up drawing, the spring-loaded pawl element  156  is shown with its protruding tooth  161  lodged in the internal thread  162  of the first spreader element  152 . In order to deploy the auto dilator, after the spiked rod  157  has been inserted into the tissue to the depth required, the rotation handle  153  of the first spreader element  152  is turned while the handle  151  of the spiked rod  157  is held stationary, in case the friction of the spiked rod  157  and its spike  177  stuck into the subject&#39;s tissue does not hold it stationary. As the first spreader element  152  rotates, the static protruding tooth  161  riding in its internal thread, causes the first spreader element  152  to move distally over the spiked rod and into the tissue, widening the opening in the tissue. Section B-B shows the device in axially directed cross section. 
         [0062]    Reference is now made to  FIG. 26 , which shows the first spreader element  152  almost fully deployed, with the protruding teeth  161  of the spring-loaded pawl elements  156  still riding in the internal thread  162  of the first spreader element  152 . The blown-up detailed drawing shows this clearly. 
         [0063]    Reference is now made to  FIG. 27 , which shows the situation when the first spreader element  152  has reached its most distal deployed position. The length of the spreader element  152  and hence of the internal thread  162  of the first spreader element, is adapted to be such that as the spreader element reaches its fully deployed position, the toothed protrusion  161  of the spring-loaded pawl  156  jumps out of the internal thread  162  in an outwards direction because of its spring loading, until it lodges within a groove at the distal end of the internal thread  164  of the second spreader element  155 , as shown in the blown-up detailed drawing. As the handle  153  continues to rotate, together with the toothed protrusion, the second spreader tube  155  now starts to move distally over the previously deployed first spreader element  152 , actuated by the protruding tooth  161  now riding in the internal thread  164  of the second spreader tube  155 . 
         [0064]    Once the second spreader tube is fully deployed, further spreader tubes can be sequentially installed, with the toothed protrusions of the spring-loaded pawls jumping from one internal thread to the next in outward going order as each spreader tube completes its insertion and releases the protruding tooth element  161  from its own thread to spring further out to engage the internal thread in the next outwardly positioned spreader tube. 
         [0065]    Although this third implementation has been described using a toothed projection on a hinged, spring loaded pawl as the element used for engaging the inner threads of the consecutive spreader tubes, it is to be understood that this is only one exemplary method by which to achieve engagement with the internal thread form. The invention is not intended to be limited thereto, but includes any alternative structure involving an externally protruding tooth, or teeth, which are rotated so as to cause the internal threaded element with which it or they engage to move distally. 
         [0066]    This implementation thus enables insertion of a sequence of spreader tubes by means of a continuous rotation action, without the need for any intermediate action in order to switch from one spreader tube to the next. This implementation is therefore suitable for a simple robotically actuated entry procedure. 
         [0067]    It is appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as variations and modifications thereto which would occur to a person of skill in the art upon reading the above description and which are not in the prior art.