Abstract:
A trocar assembly including a low-profile retractable shield deployable adjacent to a cutting element with a cross-sectional area which is small relative to the total cross-section of the assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional application of U.S. patent application Ser. No. 09/936,741, filed Sep. 13, 2001, now U.S. Pat. No. 6,837,874 which was a U.S. National Phase Patent Application under 35 U.S.C. 371 of PCT International Application No. PCT/IB00/00408, which has an international filing date of Mar. 14, 2000, and which claims priority from Israel Patent Application No. 128,989, filed Mar. 15, 1999, all incorporated herein by reference in their entirety. 

   FIELD OF THE INVENTION 
   The present invention relates to medical equipment, in particular to trocar and similar devices used in surgical procedures and intended for their improvement. 
   BACKGROUND OF THE PRIOR ART 
   Trocars are used in medicine for making orifices and trocar port placement in body cavity walls used further for diagnostic or surgical instrument insertion into body cavity. Trocar insertion into body cavity can be accompanied with internal organ injury. To prevent such a complication, the trocars are equipped with various protectors of piercing-cutting means. However, all known solutions do not eliminate the problem of internal organ injuries. 
   The safety trocar penetrating instrument is known from the U.S. Pat. No. 5,591,190, comprising port unit and trocar unit with obturator having piercing-cutting means. The device is equipped with protector for piercing-cutting means made as a tubular shield situated between obturator and tubular cannula of port unit and movable relative to obturator from the extended position when it encloses piercing-cutting means and prevents it from any contact, to the retracted one, when piercing-cutting means is open and can perforate the body cavity wall. Such a protector advances to the extended position when the resistance of body cavity wall drops after the exposed piercing, cutting means has already entered the body cavity, i.e. after internal organs could have ready been injured. 
   Another trocar and cannula assembly are known from the U.S. Pat. No. 5,246,425, wherein a tip protector comprises a plurality of projections which, by the authors&#39; idea should be displaced into an extended position before the piercing apex has been fully inserted into the body cavity. However, such mechanism leads to inevitable injury of body cavity wall, increased resistance to the device advance, the device advance in jerks, and high probability of protector jamming. Moreover, when these members pass through fibrous anatomical structures: aponeuroses, fascias, muscles, the structure fibers enter either the projections, or between the projections and tip. Further device advance is possible solely by rupturing these fibers which, in its turn, results in increased tissue injury and in the device hindered advance. 
   The tissue fibers incorporated between projections and tip can jam protector in the retracted position. In this case the jeopardy of internal body injury is even higher than by the performance of a trocar non-equipped with protector, since a surgeon, being sure of the device safety, operates with less caution. 
   A trocar with a shield is disclosed by U.S. Pat. No. 5,797,943. The geometry of the descried shield should, by the authors&#39; opinion, ensure successive protection of various zones in piercing-cutting means practically simultaneously with their penetration to the body cavity. 
   However, shield members have such sizes, shape, arrangement and contact zone with body cavity wall that they generate considerable resistance between the shield and the body cavity wall tissues, and the latter holds the shield in totally retracted position, up to the shield complete removal beyond the bounds of body cavity wall, which means that no successive protection of piercing-cutting members takes place as they enter the body cavity. 
   Similar demerit is found in U.S. Pat. Nos. 5,690,663, 5,709,671. A trocar, having improved tip configuration is disclosed by U.S. Pat. No. 5,709,671, where distal edge of tubular cannula is made sloping, to facilitate the device passing through body cavity wall. In fact, the surgeon has less difficulties in trocar passing through tissues since sloping edge of cannula operates as a wedge giving the benefit of force, which facilitates tissue rupture by trocar passing. But tissue injury during the trocar performance remains considerable. 
   SUMMARY OF THE INVENTION 
   The invention objective is the decrease of internal organ injury risk upon trocar performance. 
   Another invention objective is increased reliability of protector operation by preventing jamming and engagement of body cavity wall tissues between the members of trocar distal edge. 
   Another invention objective is decreased tissue injury of body cavity wall. 
   Another invention objective is facilitated trocar passing through body cavity wall. 
   Another invention objective is decreased material consumption for the device, design simplification and device low-cost manufacturing. 
   Another invention objective is independent of each other operation start and finish of cutting members dependable on tissue local biomechanical properties. 
   Another invention objective is accurate adaptation of orifice sizes in body cavity wall to the cannula diameter. 
   The above noted objectives are accomplished by a safety trocar assembly having a port unit with elongated obturator removably inserted through the cannula and having a handle on its proximal end and a penetrating end on its distal end. The penetrating end is exposed through the cannula open distal end and has a cutting means, a penetrating apex, and a sloping side wall immovable relative to obturator. The obturator is provided with a protector means having a bias means and a movable penetrating apex shield that in its retracted position opens the penetrating apex and in its extended position closes the penetrating apex preventing it from any contact with patient&#39;s organs. In the projection onto transverse plane, the obturator sloping side wall surrounds the penetrating apex shield. It means that the penetrating and, consequently, also the penetrating apex shield have little cross section dimensions in comparison with the obturator. This allows reduction of the resistance of body tissue during penetrating apex shield displacement to its extended position and provides fast acting protection of the penetrating apex immediately after the penetration of penetrating apex distal end into the body cavity, however, before the penetrating end has been fully inserted. Further dilation of the orifice in the body wall is carried out by cutting means located on the sloping side wall. The penetrating apex shield is made tubular of circular or flattened cross section, totally closed or having a slot on one side. The distal edge of this shield forms a fence precluding the introduction, jamming; and engagement of tissue fibers of the body cavity wall between the penetrating apex shield and the penetrating apex as well as between the penetrating apex shield segments. As a result, the injury of body cavity wall is decreased and trocar passing through body cavity wall is facilitated. 
   According to the present invention, the shield, particularly made plate-shaped and the perimeter of its cross section insignificantly exceeds the perimeter of tissue incision made by the cutting means. Moreover, the height of this plate-shaped shield (the plate thickness) amounts 0.4 to 2 mm for obturator with outer diameter 10 to 12.5 mm and 0.4 to 1.2 mm for obturator with outer diameter 5 to 6.5 mm. This shield is a fast acting protector entering the tissue incision without substantial resistance of tissue incision edges and enabling the shield entry the body cavity immediately after entry there the cutting means. As a result, the risk of patient internal organ injury is significantly decreased. 
   In version embodiment, a safety trocar assembly comprises a penetrating means with at least two penetrating zones and a protector means with independent protector members, made as shields, for independent protection of each of said penetrating zones, and a resilient bias means for each of the protector members. This protects the penetrating zone (knife) which enters the body cavity independently of other penetrating zones (knives) which have not yet entered the body cavity and continue to cut the tissue. In version embodiment, there are distal and proximal penetrating zones provided with a distal and a proximal independent shield, respectively. The distal penetrating zone is the first one that enters the body cavity and is a main cause of internal organ injury, so its independent and fast protection eliminates trocar procedure complications. 
   In version embodiment, the displacement of the proximal shield from the extended position to the retracted position demands greater force than identical displacement of the distal shield. That can be achieved by larger rigidity of the bias means (in the form of a spring) of the proximal shield than one of the distal shield. As a result, the proximal penetrating zone forms such final dimensions of orifice that is accurately adapted to the cannula outer diameter. Described penetrating and protector means have so simple a design (for example, making protector and biasing members as a one detail) so as to permit their arrangement in the limits of obturator distal part. Such implementation increases trocar reliability and reduces its manufacturing cost. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various embodiments of the safety trocar assembly of the subject application will be described below with reference to the following drawings wherein: 
       FIG. 1  is a perspective view of trocar assembly with tubular penetrating apex shield. 
       FIG. 2  is a longitudinal section of trocar assembly of the  FIG. 1 . 
       FIG. 3  is a perspective view of trocar assembly with spring penetrating apex shield. 
       FIG. 4  is a perspective view of distal part of trocar assembly of the  FIG. 3 . 
       FIG. 5  is a longitudinal section of trocar assembly of the  FIG. 4  and demonstrates penetrated apex shield in extended position. 
       FIG. 6  is a longitudinal section of trocar assembly of the  FIG. 4  and demonstrates penetrated apex shield in retracted position. 
       FIG. 7  is a perspective view of trocar assembly with groove penetrating apex shield. 
       FIG. 8  is a longitudinal section of distal part of trocar assembly of the  FIG. 7  with groove shield in extended position. 
       FIGS. 9-11  are sections of trocar assembly of the  FIG. 8  on the levels  9 - 9 ,  10 - 10 ,  11 - 11 , respectively. 
       FIG. 12  is a longitudinal section of distal part of trocar assembly and groove shield of the  FIG. 8 . 
       FIG. 13  is a longitudinal section of distal part of trocar assembly of the  FIG. 7  with groove shield in retracted position. 
       FIG. 14  is a longitudinal section of distal part of trocar assembly and groove shield of the  FIG. 13 . 
       FIG. 15  is a perspective view of trocar assembly with two independent tubular shields. 
       FIG. 16  is a left-hand view of device of the  FIG. 15 . 
       FIG. 17  is a longitudinal section of device of the  FIG. 15 . 
       FIG. 18  is a longitudinal view of trocar unit of device of the  FIG. 17 . 
       FIG. 19  is a perspective view of the trocar unit of the  FIG. 18 . 
       FIGS. 20-25  demonstrate successive changes in mutual positions of the shields at the stages of trocar penetrating end passing though body cavity wall. 
       FIG. 26  is a perspective view of trocar assembly with low profile protector. 
       FIG. 27  is a knife-side view of distal part of trocar assembly of the  FIG. 26 . 
       FIG. 28  is a left-hand view of the trocar assembly of  FIG. 26 . 
       FIG. 29  is a protector-side view of distal part of trocar assembly of the  FIG. 26 . 
       FIG. 30  is a longitudinal section of distal part trocar assembly of the  FIG. 29 . 
       FIG. 31  is a longitudinal section of the distal part of trocar assembly of the  FIG. 29  with protector displaced to retracted position. 
       FIG. 32  is a perspective view of trocar assembly with low profile inverted shield. 
       FIG. 33  is left-hand view of device of the  FIG. 32 . 
       FIG. 34  is a top view of distal part of device of the  FIG. 32 . 
       FIG. 35  is a knife-side view of distal part of device of the  FIG. 32 . 
       FIG. 36  is a shield-side view of distal part of device of the  FIG. 32 . 
       FIG. 37  is a longitudinal view of device of the  FIG. 32 . 
       FIG. 38  is a view of trocar unit of device of the  FIG. 32 . 
       FIG. 39  is a longitudinal section of distal part of device of the  FIG. 32  with shield in extended position. 
       FIG. 40  is a longitudinal section of distal part of device of the  FIG. 32  with shield between extended and retracted positions. 
       FIG. 41  is a longitudinal section of distal part of device of the  FIG. 32  with shield in retracted position. 
       FIG. 42  is a perspective view of trocar assembly with two independent low profile inverted shields. 
       FIG. 43  is a left-hand view of device of the  FIG. 42 . 
       FIG. 44  is an enlarged distal part of device of the  FIG. 42 . 
       FIG. 45  is a longitudinal section of distal part of device of the  FIG. 42 . 
       FIG. 46  is a distal part of device of the  FIG. 42  with shields between extended and retracted positions. 
       FIG. 47  is a longitudinal section of device of the  FIG. 46 . 
       FIG. 48  is a distal part of the device of the  FIG. 42  with shield in retracted position. 
       FIG. 49  is a longitudinal section of device of the  FIG. 48 . 
       FIG. 50  is a perspective view of safety trocar with three independent shields. 
       FIGS. 51 ,  52  are views of distal part of device of the  FIG. 50  from knife- and shield-side, respectively. 
       FIG. 53  is a longitudinal section view of distal part device of the  FIG. 50 . 
       FIG. 54  is a longitudinal section view of distal part device of the  FIG. 50  with plated shield in retracted position. 
       FIGS. 55-63  demonstrates positions of shields at various penetration stages of the distal part of  FIG. 50  device through body cavity wall. 
       FIG. 64  is a perspective view of trocar assembly, wherein proximal bias members of lateral shields are made more rigid than distal ones. 
       FIG. 65  is a knife-side view of distal part of device of the  FIG. 64 . 
       FIG. 66  is a shield-side view of distal part device of the  FIG. 64 . 
       FIG. 67  is a longitudinal section view of device of the  FIG. 66 . 
       FIG. 68  is a longitudinal section view of device of the  FIG. 66  with plated shield in retracted position. 
       FIG. 69  is a perspective view of trocar assembly with low profile inverted stepwise shield. 
       FIGS. 70-72  demonstrate the displacement stages of shield of device of the  FIG. 69  from extended to retracted position. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Safety trocar assembly is intended for making orifices in body cavity wall and generation of conditions for subsequent introduction of instruments into a body cavity. 
   Before addressing specific implementations of the present invention in detail, it should be noted that the invention will be presented with reference to numerous examples, each of which illustrates one or more preferred feature of the invention. These various preferred features may each be used individually to advantage with an otherwise conventional trocar. In most preferred implementations, however, multiple preferred features are combined to provide a trocar with greatly enhanced levels of safety to the patient and/or professional staff, and/or to provide numerous other advantages as will become clear from the following description. 
   Turning now to the Figures,  FIGS. 1 and 2  illustrate a first embodiment of a trocar assembly  1  in which a retractable shield  14  is deployed to selectively shield only the distal portion of a penetrating end  10 . As a result, the shield extends itself as soon as the distal portion clears the tissue wall, well before fill penetration of end  10  occurs. 
   More specifically,  FIG. 1  shows trocar assembly  1 , comprising trocar unit  2  and port unit  3 .  FIG. 2  shows a longitudinal section of trocar assembly  1  in enlarged scale. Port unit  3  has tubular cannula  4 , port housing  5  and inner seals  6 ,  7  located in port housing  5  and aimed to maintain insulation of the body cavity. Tubular cannula  4  has an open distal end  8 . Trocar unit  2  has elongated obturator  9  adapted to be removably inserted through cannula  4  and having a penetrating end  10  exposed through cannula  4  open distal end  8 . Penetrating end  10  has penetrating apex  11  and a sloping side wall  12 . Longitudinal opening  17  of obturator  9  houses protector means  13  comprising tubular penetrating apex shield  14  adapted to actuate between a retracted position and an extended position (shown in  FIG. 2 ), when shield  14  surrounds penetrating apse  11 , and sloping side wall  12  surrounds shield  14  from the outside. Distal edge  15  of shield  14  forms uninterrupted hedge. Protector means  13  comprises bias means made as a compression spring  16 . In the embodiment shown in  FIGS. 1 ,  2  penetrating apex  11  formed by pointed distal edge of cylindrical piece  18 , having circular ledge  19  which is abutted by circular ledge  20  of penetrating apex shield  14 , when shield  14  reaches its extended position. Stopper bushing  21  abutted by spring  16  is tightly placed on proximal end of cylindrical piece  18 . 
   Device  1  is operated as follows: 
   Surgeon holds device  1  by housing  5  and push member  22  situated on obturator  9  proximal end. Device  1  is oriented approximately perpendicular to body cavity wall and is pressed to it, applying pushing effort to push member  22 . The resistance force of pierced tissues applied to shield distal edge  15 , displaces shield  14  towards retracted position so that penetrating apex  11  strips bare and pierces body cavity wall tissues. In this process, shield uninterrupted distal edge  15  forms a hedge precluding the introduction and engagement of tissue fibers of body cavity wall between shield  14  and penetrating apex  11 , thus ensuring smooth motion of device  1  through the tissues. When penetrating apex  11  and shield distal edge  15  have entered a patient&#39;s body cavity, however, before penetrating end  10  has been fully inserted the force applied to shield distal edge  15  is removed, and spring  16  returns shield  14  to extended protected position, and further movement of penetrating end  10  to body cavity occurs with protected penetrating apex  11 , which precludes the injury of inner organs. Penetrating apex  11  can have diversified shapes, for instance, conical or pyramidal one, with cutting edges (not shown in the Fig.). 
   Turning now to  FIGS. 3-6 , these illustrate a variant of the embodiment of  FIGS. 1 and 2  in which the shield is implemented as a helical coil of resilient wire formed with a closed portion  114  acting as the shield and a spring portion  116  which provides forward biasing. In other respects (preferred dimensions etc.), this implementation is similar to the previous embodiment. More specifically,  FIG. 3  shows safety trocar assembly  101 , comprising trocar unit  102  and port unit  103 . 
     FIG. 4  shows distal part  123  of device  101  in enlarged scale, and  FIG. 5  shows a longitudinal section of distal part  123 . Penetrating end  110 , protruding through cannula  104  open distal end  108 , has penetrating apex  111  made integral with obturator  109 , penetrating apex shield  114 , and bias means made as a compression spring  116 . In this, shield  114  and spring  116  are made as a single piece from coiled springy rod fixed in obturator  109  circular groove  124 . Penetrating end  110  also has sloping side wall  112 , whereon outer cutting means  125 ,  126  made as outer cutting members are located, and which can be made of the same material as obturator  109 . 
     FIGS. 4 ,  5  show shield  114  in extended protected position. 
     FIG. 6  shows shield  114  in retracted position 
   Trocar assembly  101  operates similarly to trocar assembly  1 . 
   Turning now to  FIGS. 7-14 , these illustrate a similar concept as applied to a penetrating end formed as a flat knife. Specifically in relation to configurations employing cutting edges provided by flat blades, it is preferred that the shield element(s) are formed as low-profile shields in a manner that they experience very low resistance to returning to their distal protective positions almost immediately that the cutting edge clears the tissue wall. 
   In order to better define the preferred geometrical features which ensure this rapid return of the shield to its operative position, reference will be made in the description and claims to various terminology which is defined as follows: 
   the “proximal protected position” of the shield is the extreme proximal position of the shield which offers complete protection of the cutting edge. 
   Turning now to the structural details of this embodiment,  FIG. 7  shows a safety trocar assembly  201 , comprising trocar unit  202  and port unit  203 . 
     FIG. 8  shows longitudinal section of obturator  209  distal part  227  in enlarged scale. Obturator distal part  227  comprises penetrating apex  211  with penetrating apex cutting means looking like distal knife  228  and outer cutting member looking like proximal knife  225 . Both knives— 228 ,  225 —are made on the plate-shaped base  229 , which has two springy arms  230 ,  231  with ledges  232 ,  233  in its proximal section, said ledges ensuring engagement of plated base  229  and obturator  209 . Penetrating apex shield  214  is made as two-sided low profile shield and has longitudinal slot  234  plate base  229  passes through. Bias means is made as a compression spring  216 , which abuts shield  214  with its distal face  235 , whereas its proximal one abuts plate-shaped base  229 . In  FIGS. 7 ,  8 ,  12  shield  214  is in extended position so that its further distal displacement is limited by ledge  219  on plate-shaped base  229 , which is abutted by shield  214  ledge  220 . In  FIGS. 13 ,  14  shield  214  is in acted position. 
   Device  201  operates similarly to device  1 . 
   Turning now to  FIGS. 15-25 ; these illustrate a particularly preferred embodiment which combines a distal-portion shield of the type illustrated in  FIGS. 1 and 2  with a locking mechanism. 
   In a further preferred feature, which may be used either alone or in combination with the locking mechanism, the distal-portion shield is combined with a conventional large-diameter shield, in this case formed as concentric cylinders, to provide two-stage protection. The distal-portion shield provides immediate protection as soon as the distal portion of the penetrating end clears the tissue wall ( FIG. 23 ), while the large-diameter shield provides additional protection once the penetrating end is fully inserted ( FIG. 25 ). In the most preferred implementation shown here, the locking mechanism is operative to lock both shields when the obturator is removed. More specifically,  FIG. 15  shows safety trocar assembly  401  with mutually independent shields  414 ,  436 . Device  401  comprises trocar unit  402  and port unit  403 . Port unit has tubular cannula  404  and port housing  405 . 
     FIG. 16  shows a left-hand view of device  401 . 
     FIG. 17  shows a longitudinal section view of device  401 . 
   Trocar unit  402  has obturator  409  comprising distal part  427  and proximal part  438 . Penetrating end  410  comprising penetrating apex  411 , sloping side wall  412  and outer cutting members  425 ,  426450  with cutting edges  451  protruding above the sloping side wall  412  level. There are two tubular shields: penetrating apex shield  414  and outer shield  436 . There are two independent, separate for both shields  414  and  436  bias means made as compression springs  416 ,  451 . There is common for both shields  416 ,  436  lock means  435  comprising obturator-situated controlling member  440 , partially protruding laterally of obturator distal part  427 , and adapted to the interaction with inner surface  441  of tubular cannula  404 . Controlling member is made integral with abutting member  442 , having outer abutting surface  443  and inner abutting surface  452 . Abutting member  442  by springy legs  444 ,  445  is spring-loaded to obturator  409 . 
     FIG. 18  shows a longitudinal section of trocar unit  402  of device  401 . 
     FIG. 19  shows top view of trocar unit  402 . 
   In  FIGS. 18 ,  19  lock means  435  is in lock position and locks shields  414  and  436  in protected position. Shield  436  wall has through elongated slot  446  with two different-width sections—distal section  447  is narrower than proximal section  448 . Controlling member  440  has width less than that of slot  447  distal section, whereas abutting member  442  is wider than distal section  447  but narrower than slot  448  proximal section. 
   When trocar unit  402  is outside port unit  403  ( FIGS. 18 ,  19 ), legs  444 ,  445  shift abutting member  442  to the lock position, when abutting member  442  partially enters slot  446  proximal section  448 , and outer abutting surface  443  is set opposite of ledge  449  on outer shield  436 , precluding shield  436  distal displacement, and inner abutting surface  452  is set opposite of proximal face  453  of penetrating apex shield  414 , also precluding shield  414  proximal displacement. Unlocking of both shields  414 ,  436  occurs with trocar unit  402  entering port unit  403 , which takes place when controlling member  440  interacts with cannula  404 , and thus forces abutting member  442  out of interaction zone with shields  414 ,  436 . 
     FIGS. 20-25  show operating shields on successive stages of penetrating end  410  passing through body cavity wall  454 . 
     FIG. 20  shows staring moment of trocar assembly  401  interaction with body cavity walk when outer shield  436  is between its extended and retracted positions, penetrating apex shield  414  is in retracted position, and penetrating apex  411  has incorporated into body cavity wall  454 . 
     FIG. 21  shows the moment when both shields  414 ,  436  are forced out by body cavity wall tissue to retracted position. 
     FIG. 22  shows the moment when both shields  414 ,  436  are in retracted position, and penetrating apex  411  has penetrated into body cavity. 
     FIG. 23  shows the moment immediately after the displacement of penetrating apex shield  414  to extended protected position. In this process, outer cutting members  426 ,  426 ,  450  continue cutting tissue. 
     FIG. 24  shows the moment before shield  436  operation. 
     FIG. 25  shows both shields  414 ,  436  in extended position. 
   As can be seen, independent performance of shields  414  and  436  greatly ensures trocar safe operation. 
   Turning now to  FIGS. 26-31 , these show a further embodiment of the present invention as applied to an obturator  509  with a distal knife  528 . In this case, a one-sided low profile shield  514  is used. Since the cross-sectional area of the shield adds relatively little to the cross-sectional area of the knife itself, the shield advances through the incision to its distal position to provide protection almost immediately on penetration of the tissue wall. Preferably, according to the terminology defined above, the shield local comparative height along the proximal screen area for a one-sided shield is below 0.8. 
     FIG. 26  shows safety trocar assembly  501  with one-sided low profile shield  514 . Device  501  has trocar unit  502  and port unit  503 . Port unit  503  has cannula  504  and port housing  505 . 
     FIG. 27  shows the view of device distal part  523  from the side of penetrating apex cutting means made as distal knife  528 . 
     FIG. 28  shows left-hand view of device  501 . 
     FIG. 29  shows device distal part  523  from the side of shield  514 . 
     FIG. 30  shows longitudinal section of device distal part  523  when shield  514  is in extended position. 
   Trocar unit  502  has obturator  509  with penetrating end  510  with sloping side wall  512  and outer cutting members  525 ,  526  so that outer cutting members  525 ,  526  are made integral with obturator  509 . Indented distal knife  528  is made on plate-shaped base  529 , and has one-sided low profile shield  514  with bias means made as compression spring  516 . 
   When penetrating end  510  passes through body cavity wall, the tissue resistance force shifts shield  514  to retracted position ( FIG. 31 ), and stripped knife  528  makes an orifice in the tissue. Low profile protectors, both one-sided, and two-sided—are the protectors against instantaneous operation, i.e. they operate upon knife minimal penetration to body cavity. 
     FIGS. 32-41  show a further embodiment with shields for the lateral blades. Advantageously, the shield may be formed in such a manner as to provide protection for the distal portion of the blade while the proximal portion is still operative, thereby providing enhanced protection. 
     FIG. 32  shows safety trocar assembly  701  with one-sided low profile inverted shield  736 . Device  701  has trocar unit  702  and port unit  703 . Port unit  703  has cannula  704  and port housing  705 . Trocar unit has obturator  709  (FIG.  34 —top view of device  701  distal part  723 ) with penetrating end  710 . Penetrating end  710  comprises blunt apex  755 , sloping side wall  712 , two knives  725 ,  725  and inverted shield  736 . 
     FIG. 35  shows device distal part  723  from the side of knives  725 ,  726 , 
     FIG. 36  shows device distal part  723  from the side of shield  736 . 
     FIG. 37  shows longitudinal section of device  701 . 
     FIG. 38  shows longitudinal section of device  701  trocar unit  702 . Trocar assembly  701  has lock means  735  for shield  736 . Lock means  735  has obturator-situated controlling member  740 , partially protruding laterally of obturator  709  and adapted to the interaction with inner  740 ,  741  of cannula  704 . Controlling member  740  is made integral with abutting member  742 , having abutting surface  743 . Abutting member  742  is spring-loaded to obturator  709  by springy legs  744 ,  745 . Shield  736  has abutting bar  758 . When trocar unit  702  ( FIG. 38 ) is outside the port unit  703 , legs  744 ,  745  shift abutting surface  743  to the level of abutting bar  758 , and such mutual disposition of shield  736  and lock means  735  is the lock position which prevents shield  736  proximal displacements 
   Unlocking of shield  736  takes place when trocar unit  702  is introduced to port unit  703  but only after protected penetrated end  710  passes through distal inner seals  706 ,  707  so that controlling member  740 , being resisted by cannula  704  inner surface  741 , shifts abutting member  742  from the interaction zone with abutting bar  758 . 
     FIGS. 39 ,  40 ,  41  show longitudinal section of device  701  distal part  723  in enlarged scale at shield  736  various performance stages. 
     FIG. 39  shows shield  736  in extended position. Shield  736  is made plated and besides abutting bar  758  has protection edges  759 ,  760 , guiding slots  761 ,  762 , through which cotters  763 ,  764  are passing, window  765 , wherein bias compression spring  716  is mounted, whose distal end abuts shield  73 , whereas proximal end  766  is fixed to plate-shaped base  729  of knives  725 ,  726 . Shield  736  is an inverted shield which means that when it shifts from extended position to retracted position, the opening of knives  725 ,  725  starts from their proximal sections  767 ,  768 . This operation mechanism of shield  736  is achieved owing to the fact that relative to the device longitudinal axis the incidence angle of the line connecting distal point  769  and proximal point  770  on protection edge  759  is more acute than the incidence angle of the line connecting distal and proximal points  771 ,  772  on knife  725 . 
     FIG. 41  shows shield  736  in retracted position. Consequently, as penetrating end  710  enters body cavity, closing of knives  725 ,  726  starts from their distal sections which ensures low injury level. 
   The embodiment of  FIGS. 42-49  generally parallels the embodiment of  FIGS. 32-41 , but provides independently operative shields for the lateral blades. Thus,  FIG. 42  shows a safety trocar assembly  801  with two independent low profile inverted shields  836 ,  871 . Device  801  comprises trocar unit  802  and port unit  803 . Port unit  803  comprises cannula  804  and housing  805 . 
     FIG. 43  shows left-hand view of device  801  in enlarged scale. 
     FIG. 44  shows device  801  distal part  823  in enlarged scale. Trocar unit  802  comprises obturator  809  with pen ting end  810  which is formed by blunt apex  855 , sloping side wall  812 , with protection edges  859 ,  860  of shields  836 ,  871 , and knives  825 ,  826  protruding above it. Shields  836 ,  871  are made plated and equipped with independent bias compression springs  816 ,  851 . Knives  825 ,  826  ( FIG. 49 ) are made on plate-shaped bases  829 ,  872 . 
     FIGS. 45-59  show mutual arrangement of knives  825 ,  826  and shields  836 ,  871  at various operation stages of shields  836 ,  871 .  FIG. 45  shows both shields  836 ,  871  in extended-protected position.  FIGS. 46 ,  47  show shields  836 ,  871  in intermediate position between extended and retracted position, when only proximal sections  867 ,  868  of knives  825 ,  826  are open.  FIGS. 48 ,  49  show shields  836 ,  871  in retracted position, when both knives  825 ,  826  are open along their entire lengths. 
     FIGS. 45-49  show symmetrical operation of shields  836 ,  871 , but inasmuch as shields  836 ,  871  are made independent and are equipped with independent bias springs  816 ,  851 , so the operation of shields  836 ,  871  can be independent, non-simultaneous (not shown on Figs.). The operation non-simultaneity stems from resistance non-simultaneity of tissue elements of body cavity wall. That is the concept of independent shields permits to take into account and to respond automatically to local properties of tissues. 
   However, for the surgeon the mode of device  801  operation does not differ from that of similar alternative devices. 
     FIGS. 50-63  illustrate an alternative type of shield for lateral blades, in this case combined with a distal knife and shield similar to those of  FIGS. 26-31 . The lateral shields are here implemented as resilient elements which react substantially independently to force applied near their distal and proximal ends. As a result, this configuration also provides protection for the distal portion of the blades while the proximal portion is still operative ( FIGS. 61 and 62 ).  FIG. 50  shows perspective view of safety trocar assembly  901  comprising trocar unit  902  and port unit  903 . Port unit  903  has cannula  904  and housing  905 . Trocar unit has obturator  909  with penetrating end  910 . Penetrating end is formed by sloping side wall  912 , penetrating means  973  for orifice formation in body cavity wall, and protector means  913  for said penetrating means  973 . Penetrating means  973  comprises penetrating zones formed by knives  928 ,  925 ,  967 ,  926 ,  968  made on common plate-sided base  929  ( FIG. 53 )  50  that knives  925  and  967 , as well as knives  926  and  968  have cutting edges confluent with one to another. Each penetrating zone has protector member, and each protector member has its own bias member. For penetrating zone  928  made as indented knife, protector member is made as plane-shaped shield  914 , whereas bias member as compression spring  916 . 
   Protector members  969  and  970  of knives  925 ,  967  have bias means  951 ,  979 , respectively, so that protector members  969 ,  970  are made as a common shield  936 . Common shield  936  and bias means  951 ,  979  are made as a single resilient part, having a slat  980 , which in extended position ( FIGS. 51 ,  52 ,  53 ) is situated parallel to cutting edge of knives  925 ,  967 , and bias means  951 ,  979  made as resilient elements, each of them being connected to slat  980  by one its end  981 ,  982 , whereas the other one  983 ,  984  is connected to the plate-shaped base  929 . Protector members  985  and  986  of knives  926  and  968  have bias means  987 ,  988 , respectively, so that protector members  985 ,  986  are made as a single resilient part, having a slat  990  which in extended position is situated parallel to cutting edges of knives  926 ,  968 , and 
   bias means  987 ,  988  are made as resilient elements, each of them being connected to slat  980  by one its end  991 ,  992 , whereas the other ones  993 ,  994  are connected to the plate-shaped base  929 . 
     FIGS. 55-63  show mutual arrangement of protector members at various stages of penetrating end  910  passing through body cavity wall  954 . 
     FIG. 55  shows shields  914 ,  936 ,  989  in extended position. 
     FIG. 56  shows shield  914  in retracted position, and open knife  928  creates an orifice in body tissue. 
     FIG. 57  shows protector members  969 ,  985  displaced to retracted position, and knives  925 ,  926  create orifice in body tissue., 
     FIG. 58  shows all shields  914 ,  936 ,  989  in retracted positions. 
     FIG. 59  shows knife  928  entry to body cavity. 
     FIG. 60  shows the point immediately after shield  914  displacement to extended protected position. 
     FIG. 61  shows knives  925  and  926  entry to body cavity, one of them  925  being shown protected by protector member  969 , which displays independent operation of symmetrical protector members  969  and  985 , thus ensuring maximal fast operation of protector members, and, consequently, minimal injury of internal organs. 
     FIG. 62  shows protector members  914 ,  969 ,  985  in extended-protected position. 
     FIG. 63  shows penetrating end  910  as totally entering the body cavity, with totally protected penetrating means. 
     FIGS. 64-68  show an embodiment generally similar to that of  FIGS. 50-53 , but wherein the resilient elements are formed with greater spring resistance at their rear proximal end than at their distal end, thereby also tending to preclude over-widening of the incision. 
     FIG. 64  shows a safety trocar assembly  2001  comprising trocar unit  2002  and port unit  2003 . Port unit  2003  has cannula  2004  and housing  2005 . Trocar unit has obturator  2009  with penetrating end  2010 . Penetrating end is formed by sloping side wall  2012 , penetrating means  2073  for orifice formation in body cavity wall, and protector means  2013  for said penetrating means  2073 . Penetrating means  2073  comprises penetrating zones formed by knives  2028 ,  2025 ,  2067 ,  2026 ,  2068  made on common plate-sided base  2029  ( FIGS. 65 ,  67 ) so that knives  2025  and  2067 , as well as knives  2026  and  2068  have cutting edges confluent into each other. Each penetrating zone has protector member, and each protector member has its own bias member. For penetrating zone  2028  made as indented knife, protector member is made as plate-shaped shield  2014 , and bias member is made as compression spring  2016 . 
   Protector members  2069  and  2070  of knives  2025 ,  2067  have bias means  2056 ,  2079 , respectively, so that protector members  2069 ,  2070  as made as a common shield  2036 . Common shield  2036  and bias means  2051 ,  2079  are made as a single resilient part, having a slat  2080 , which in extended position ( FIGS. 64 ,  65 ) is situated parallel to cutting edges of knives  2025 ,  2067 , and bias means  2051 ,  2079  are made as resilient elements, each of them being connected to slat  2080  by one its end  2081 ,  2082 , whereas the other one  2083 ,  2084  is connected to the plate-shaped base  2029 . Protector members  2085  and  2086  of knives  2026  and  2068  have bias means  2087 ,  2088 , respectively, so that protector members  2085 ,  2086  are made as a common shield  2089 . Common shield  2089  and bias means  2087 ,  2088  are made as a single resilient part, having a slat  2090 , which in extended position is situated parallel to cutting edges of knives  2026 ,  2068 , and bias means  2087 ,  2088  are made as resilient elements, each of them being connected to slat  2090  by one its end  2091 ,  2092 , whereas the other ones  2093 ,  2094  are connected to the plate-shaped base  2029 . In this, proximal bias means  2079  is made more rigid than distal bias means  2051 , consequently, the displacement of proximal protector member  2070  and knife  2067  opening, and further on, tissue cutting at this level of penetrating means occurs at higher tissue tension than by tissue cutting at the level of knife  2025 . 
   Shield  2089  operates in similar manner. 
   Such tissue cutting mechanism precludes generation of excessive diameter orifice in body cavity wall. 
     FIGS. 65-72  show an embodiment generally similar to that of  FIGS. 32-41 , in which the shield is formed with a stepped edge. The inclination of the steps to the longitudinal axis of the assembly varies from greatest at the distal part of the shield to least at the proximal part of the shield. This tends to ensure that less force is required to cause retraction of the shield at smaller diameters of hole than at large diameters, thereby limiting over-widening of the incision. Thus,  FIG. 82  shows safety trocar assembly  3001  with low profile inverted shield  3036 . Device  3001  has trocar assembly  3002  and port assembly  3003 . Port assembly  3003  has cannula  3004 , and housing  3005 . Trocar assembly has obturator  3009  with penetrating end  3010  formed by blunt apex  3055 , and sloping side wall  3012 , with protector edges  3059 ,  3060  of shield  3036  and knives  3025 ,  3026  protruding over it. 
   Trocar assembly  3001  has lock means  3035  for shield  3036 . Lock means  3035  has obturator-situated controlling member  3040 , partially protruding laterally of obturator  3009 , and adapted to the interaction with inner surface  3041  of cannula  3004 . Controlling member  3040  is made integral with cutting member  3042 , having abutting surface  3043 . Abutting member  3042  by springy legs  3044 ,  3045  is spring-loaded to obturator  3009 . Shield  3036  has abutting bar  3058 . When trocar unit  3002  is outside port unit  3003 , legs  3044 ,  3045  shift abutting surface  3043  to the level of abutting bar  3058 , and such mutual arrangement of shield  3036  and lock means  3035  is the lock position (not shown in the Fig.), wherefrom shield  3036  proximal displacement is impossible. 
     FIGS. 70 ,  71 ,  72  show longitudinal section of device  3001  distal part  3023  in enlarged scale at various stages of shield  3036  operation 
     FIG. 70  shows shield  3036  in extended position. Shield  3036  is made plated and has, in addition to abutting bar  3058  and protection edges  3059 ,  3060 , guiding slots  3061 ,  3062 , through which cotters  3063 ,  3064  are passing, window  3065 , wherein bias compression spring  3016  is mounted, abutting shield  3036  by its distal end, and fixed to plate-shaped base  3029  by its proximal end. 
     FIG. 70  shows shield  3036  in the position intermediate between extended and retracted ones. 
     FIG. 71  shows shield in retracted position. 
   Protector edges  3059 ,  3060  are made stepwise with varying slope of steps  3095  so that in distal-proximal direction the slope of steps  3095  relative to device  3001  longitudinal axis decreases, and, consequently, in the same direction decreases the force of steps  3095  engagement with the tissue, hence, larger tension is required for shield  3036  proximal displacement upon tissue interaction with proximal steps than it is for tissue interaction with distal steps, and hence, cutting of tissue at the level of distal sections  3025 ,  3026  occurs with smaller tissue tension than at the level of proximal sections of knives  3025 ,  3026 . Such tissue cutting mechanism precludes generation of excessive diameter orifice in body cavity wall. 
   Although the present invention has been shown and described in terms of preferred embodiments, it will be appreciated that various changes and other modifications are contemplated within the spirit and scope of the present invention as defined by the following.