Abstract:
A trocar having a safety shield control mechanism that prevents the inner cannula from rotating and from moving axially when in the locked position. The safety shield control mechanism applies consistent pressure on the safety shield and has an open architecture for ease of sterilization. The trocar provides holding levels for different sizes of hands.

Description:
BACKGROUND OF THE INVENTION 
     1. FIELD OF THE INVENTION 
     The present invention relates to surgical instruments, and, more particularly, to trocars which are used to pierce or puncture an anatomical cavity to provide communication with the inside of the cavity during a surgical procedure. 
     2. DESCRIPTION OF THE PRIOR ART 
     Endoscopic surgery, and in particular laparoscopic surgery, constitutes a significant method for performing surgeries and has become the surgical procedure of choice, because of its patient care advantages over “open surgery.” In particular, a significant advantage of laparoscopic surgery over open surgery is the decreased post-operative recovery time. In most instances, a patient is able to leave the hospital within hours after laparoscopic surgery has been performed, as compared to the multi-day hospitalization necessary to recover from open surgical procedures. Further, laparoscopic surgery provides decreased incidents of post-operative abdominal adhesions and decreased post-operative pain. Cosmetic results are also enhanced with laparoscopic surgery. 
     A trocar is an essential medical instrument for use in laparoscopic surgery, because it is used to puncture the wall of an anatomical cavity. A trocar includes a tube or cannula and a sharp, generally pointed cutting element called an obturator. The obturator fits within the cannula and has a sharp piercing tip at its end. 
     Conventionally, a laparoscopic trocar insertion procedure is preceded by the insufflation of the abdominal cavity with carbon dioxide. The introduction of this gas into the abdominal cavity lifts the abdominal wall away from the internal viscera. The abdominal wall is then penetrated with the trocar, and after insertion of the trocar through the abdominal wall, the obturator is removed by the surgeon, leaving the cannula or tube protruding through the body wall. Laparoscopic instruments can then be inserted through the cannula to view internal organs or to perform surgical procedures. 
     Penetrating the wall of the abdominal cavity with the trocar is done relatively quickly, and while the obturator encounters a fair amount of resistance from the skin muscle and tissue membranes of the abdominal wall, the resistance to the trocar drops quickly once the cutting element passes through the abdominal wall. Within the abdominal cavity, the sharp point of the cutting element may easily injure or cut an internal organ upon the slightest of contacts. Accordingly, many trocars include a safety shield that snaps forward to cover the sharp point of the obturator, once the trocar has penetrated the abdominal wall. Preferably, the safety shield is locked into place once the abdominal wall has been penetrated, and cannot be unlocked absent positive intervention by the surgeon. 
     While locking safety shields for trocars have been available, the locking mechanisms employed in these trocars has suffered from the disability that consistent pressure is not placed on the safety shield. Further, the architecture of locking mechanisms in the prior art trocars has not been open, which has made those trocars difficult to sterilize. 
     Despite the fact that trocars are hand-held instruments, prior art trocars have been less than ergonomically friendly to the user. Rather, prior art trocars have suffered from the disability of being difficult to control, since they are not designed to provide for a plurality of hand positions or for different holding levels that allow for different size hands to manipulate the trocar. 
     The foregoing and other shortcomings of prior art trocars have been overcome by the trocar of the present invention. 
     SUMMARY OF THE INVENTION 
     A trocar in accordance with the present invention comprises a body assembly and a cannula assembly. The cannula assembly includes an outer cannula attached to the body assembly to define a bore therethrough and an inner cannula inserted in said bore; wherein the inner cannula has a length longer than the length of the outer cannula. 
     The trocar body includes a safety shield control mechanism having locked position and an unlocked position which is activated during surgical insertion of the trocar. This control mechanism includes a mounting mechanism which is attached to the trocar inside the body assembly to prevent not only rotation of the inner cannula, but also axial movement of the inner cannula in the locked position. The safety shield control mechanism also includes a trigger mechanism for placing the safety shield control mechanism in the unlocked position to allow limited axial movement of the inner cannula. 
     A trocar in accordance with the present invention also includes an obturator assembly in the bore of the trocar. The obturator has a sharp end which is shielded by the inner cannula when the safety shield control mechanism is in the locked position. The sharp end of the obturator becomes exposed during surgical insertion of the trocar when the safety shield control mechanism is in the unlocked position. 
     The mounting mechanism in the safety shield control mechanism includes a mounting bracket having vertical ribs and the inner cannula has axial slots for engagement with said vertical ribs to prevent rotation of the inner cannula. The mounting mechanism also has a locking arm assembly comprising two spring-loaded locking arms for engaging the proximal end of the inner cannula to prevent axial movement of the inner cannula in the locked position. 
     The trigger mechanism of the safety shield control mechanism includes apparatus for moving the locking arm assembly to an unlocked position to allow limited axial movement of the inner cannula toward the rear of the trocar. In a preferred embodiment the trigger mechanism comprises a plunger-like button shaft which extends from the outside of the trocar body to the inside of the trocar body. The portion of the button shaft which is outside the trocar body has an end for threaded engagement with a spring-loaded cap. The portion of the button shaft on the inside of the trocar body has a tapered end which is slidably engaged in a hole in the locking arm assembly to move the locking arm assembly to the unlocked position when the spring-loaded cap is depressed. 
     A trocar in accordance with the present invention also includes a spring-loaded flapper valve assembly which is located inside the trocar body assembly at the rear of the trocar body assembly. This flapper valve assembly closes to seal the bore of the trocar when the obturator assembly is removed from this trocar. 
     A trocar in accordance with the present invention is fabricated to provide two holding levels to accommodate different size hands. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a perspective drawing of a trocar in accordance with the present invention. 
     FIG. 2 is an exploded drawing of a trocar in accordance with the present invention. 
     FIG. 3 is a perspective drawing of a portion of the proximal end of the inner cannula depicted in FIGS. 1 and 2. 
     FIG. 4 is a top view lower trocar body shown in FIG. 2 which illustrates the safety shield control mechanism in a trocar in accordance with the present invention. 
     FIGS. 5-7 are perspective drawings of various aspects of the safety shield mechanism of FIG.  4 . 
     FIGS. 8 and 9 are perspective drawings of the flapper valve assembly of a trocar in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It will be appreciated that the present invention can take many forms and embodiments. Some embodiments of the invention are described so as to give an understanding of the invention. The embodiments described herein are intended to be illustrative, and not limiting, of the present invention. 
     With reference first to FIG. 1, a perspective view of a trocar assembly  10  in accordance with the present invention is illustrated. Trocar assembly  10  includes a cannula subassembly  20  comprising outer cannula  30  and inner cannula  40 , each of which is a tubular member. Trocar assembly  10  further includes trocar body subassembly  50  which is described in more detail below and obturator subassembly  60 . In FIG. 1, inner cannula  40  is in its extended position which results in the pointed or sharp end  61  of obturator subassembly  60  being shielded by the distal end of inner cannula  40 . 
     With reference to FIG. 2, the proximal end of outer cannula  30  is attached to lower trocar body  51 , and a variety of different methods exist that are well known to those skilled in the art for effecting such attachment. Preferably, however, lower trocar body  51  has a threaded bore  53  for receiving the threaded proximal end  31  of outer cannula  30  so that outer cannula  30  is removable from lower trocar body  51 . Stop flange  32  limits the extent of threaded engagement between inner cannula  30  and lower trocar body  51 . The outer cannula  30  and lower trocar body  51  align to have a central axial bore for receiving the inner cannula  40  and the obturator subassembly  60 . The central bore is larger in the lower trocar body  51  than in the outer cannula. 
     The inner cannula  40  is a tube adapted to be slidably inserted through the bore in lower trocar body  51  and into outer cannula  30 . Cylinder  41  is press fit on the inner cannula  40  near its proximal end and the diameter of cylinder  41  is larger than the diameter of the bore of lower trocar body  51 , which prevents inner cannula  40  from sliding completely through lower trocar body  51 . 
     With reference to both FIGS. 2 and 3, a portion  42  of the surface area of cylinder  41  is flattened, and a guide pin  43  is installed in the flattened portion  42  perpendicular to the flattened portion  42 . Also, two axial slots  44  and  45  are formed in cylinder  41 . The two axial slots  44  and  45  in cylinder  41  are circumferentially spaced the same distance from flattened portion  42 . The guide pin  43  and the two axial slots  44  and  45  engage and cooperate with the safety shield control mechanism as described below. 
     An annular space  47  is defined between cylinder  41  and the proximal end of outer cannula  40 , and one end of spring  46  slips over the proximal end of outer cannula  40  and into this annular space. The other end of spring  46  engages spring retaining washer  49 , which also has a bore therethrough and which fits into upper trocar body  52  of trocar body subassembly  50 . Upper trocar body  52  is attached to lower trocar body  51  by threaded engagement, thereby permitting upper trocar body  52  to be removed from lower trocar body  51 . Gasket  54  is interposed between upper and lower trocar bodies. 
     The obturator subassembly  60  includes a pyramidal-shaped knife  61 , and a elongated stem or shaft  62 , and an arcuate-shaped cap  63 . The obturator subassembly  60  is adapted to extend and move longitudinally through upper trocar body  52  and inner cannula  30 . As noted above, inner cannula  40  serves as a safety shield for the knife  61  when the inner cannula is in the extended position as shown in FIG.  1 . The obturator subassembly  60  may be easily removed from the trocar assembly. 
     With reference now to FIGS. 8 and 9, the rearmost position of upper trocar body  52  includes a flapper valve assembly  80 , having a valve door  81  and a valve handle assembly  82 . A slot  83  is milled in upper trocar body  52  for receiving the lower portion of valve handle assembly  82 , and the upper portion of valve handle assembly terminates outside of upper trocar body  52  and has a handle  84 . The flapper valve assembly  80  is spring-mounted using spring  85 . The portion of valve door  81  that faces to the rear of upper trocar body  52  has a dome-shaped central portion  86  which is surrounded at its base by circular-shaped gasket  87 . The valve door  81  may be opened by turning handle  84  counter-clockwise or by insertion of the obturator assembly  60  into the bore in upper trocar body  52 . When the obturator assembly  60  is removed from the trocar, spring  85  causes valve door  81  to close and gasket  87  functions as a seal to minimize the escape of gas that has been introduced into the patient&#39;s abdomen. 
     The axial position of the inner cannula  40  in the trocar assembly is controlled by a safety shield control or snap back mechanism which is located in the lower trocar body  51  and which is removably engaged with the inner cannula  40 . As described in more detail below, positive intervention by the surgeon is required to activate the safety shield control mechanism. When this mechanism is activated, inner cannula  40  is permitted to move axially inward toward the housing assembly to expose the sharp tip of obturator assembly  60 . This safety shield control mechanism provides visual and aural signals to the surgeon respecting engagement and disengagement of the inner cannula  40  as a safety shield for the pointed or sharp end. When the trocar cannula subassembly  20  and safety shield control mechanism  53  are properly coupled, operation of the inner cannula  40  as a safety shield can be verified without the obturator subassembly  60  being inserted in the trocar. 
     With reference to FIGS. 4-7, the safety shield control or snap back mechanism of a trocar in accordance with the present invention comprises a mounting bracket  301 , having two vertical ribs  302  and  303 . These vertical ribs  302  and  303  are engaged by the axial slots  44  and  45 , respectively, formed in cylinder  41  of inner cannula  40 . The safety shield control mechanism of FIGS. 4-7 also includes two locking arms  304  and  305  which are rotably mounted to mounting bracket  301  on shaft  306  and the position of locking arms  304 ,  305  is spring-biased toward the bore of the trocar. As shown in FIG. 7, locking arms  304  and  305  are machined such that an axial space  307  exists between them, and axial space  307  lines up with space  309  in mounting bracket  301 . Locking arms  304  and  305  are joined together at their tops by a dowel pin (not shown) in arm  304  which fits into a hole formed in arm  305 . The safety shield control mechanism is installed in and attached to the barrel of lower trocar body  51  as shown in FIG.  4  and this attachment is made using a bolt. 
     To install the inner cannula  40  in the trocar, axial slots  44  and  45  engage vertical ribs  302  and  303  and guide pin  43  moves in the space defined by slots  309  and  307 . The inner cannula  40  is then pushed forward until the lip  310  of locking arms  304  and  305  is on top of the proximal end of inner cannula  40 . Inner cannula  40  is prevented from rotating by the engagement of the vertical ribs  302  and  303  with axial slot  44  and  45  and is prevented from moving axially by locking arms  304  and  305 . 
     The safety shield mechanism also has a trigger mechanism comprising a button shaft having one portion  311  with a diameter d 1 , and a second portion  314  with a smaller diameter d 2 . The button shaft is held in lower trocar body  51  by a button bushing  315 . The button shaft has a tapered end  312  that engages the opening  313  in locking arm  305 . The second portion  314  of the button shaft has a threaded end to engage the corresponding threads in cap  317 . A spring  318  is interposed between cap  317  and button bushing  315 . 
     The safety shield mechanism is activated as follows. When the trocar is to be inserted into the patient, the distal end of inner cannula  40  is brought into contact with the patient&#39;s abdomen. The trigger mechanism is then activated by depressing cap  317 , which causes the button shaft to move to the right in FIG.  4 . As the tapered portion of the button shaft moves to the right in FIG. 4, arms  304  and  305  move away from the bore of the trocar, thereby releasing inner cannula  40  from its locked position. As the surgeon pushes on the trocar to insert it into the patient, the force on the inner cannula  40  from the patient&#39;s abdominal wall causes the inner cannula  40  to move rearward, thereby exposing the sharp end of the obturator assembly  60 . The extent of this rearward movement is controlled by guide pin  43  and slots  307  and  309 . When the sharp end of the obturator assembly  60  and the inner cannula  40  pass through the abdominal wall of the patient, the trocar encounters decreased resistance. At this time, the spring  46  causes inner cannula  40  to snap back to its extended position as shown in FIG. 1, and the inner cannula  40  thus shields the sharp end of the obturator assembly. 
     With reference again to FIG. 1, a trocar in accordance with the present invention provides two holding levels for different size hands. The trocar may be grasped by smaller sized hands where the cannula sub-assembly engages the trocar body subassembly. Alternatively, the trocar may be grasped by larger sized hands at grove  58 . 
     Lastly, a trocar in accordance with the present invention includes stop cock  59  which is threadably engaged in lower trocar body  51 . A source of carbon dioxide(not shown) is connected to stop cock  59  to maintain the level of insufflation of the abdominal cavity during the laparoscopic procedure.