Abstract:
A trocar having a cutting shaft with a cutting surface at a distal end. The cutting shaft moves longitudinally with respect to an obturator such that in one position the cutting surface is in an exposed position suitable for application of a piercing force. Upon interruption of the piercing force to the cutting surface, the cutting surface moves longitudinally with respect to the obturator such that the cutting surface is in a retracted position within the obturator. The trocar may include a first spring urging the cutting surface to an exposed position and a second spring urging the cutting surface to a retracted position. The second spring has a slightly stronger biasing force than the first spring to bias the cutting surface to the retracted position.

Description:
The present invention relates to a trocar and in particular to a trocar that has a retractable cutting surface such as a retractable cutting blade. 
   Trocars are surgical instruments that are used to puncture tissue to gain access to body cavities. Generally, a cannula surrounds at least a portion of the trocar so that after the tissue is punctured, the cannula can provide access to the body cavity for endoscopic instruments and the like. Common to many trocars is that sharp tip used to puncture the tissue is withdrawn or covered after the tissue is punctured and the trocar is removed from the site of the puncture. 
   One such example is shown in U.S. Pat. No. 5,474,539 where an obturator having an attached piercing tip is movable from a protected position within the cannula to an advanced or operative position distally of the cannula. After piercing the tissue, the obturator and attached tip are automatically withdrawn to a retracted position within the cannula. A disadvantage to this type of system is that there must be an operative connection between the obturator and the cannula, which complicates the system and increases its cost. 
   Another proposed solution provides a safety shield that covers the blade. The problem with this solution is that the incision must be sufficiently large so that the shield can cover the blade. In addition, the friction between the shield and the tissue must be reduced or eliminated; otherwise, the movement of the shield to cover the blade may be too slow. 
   Therefore, it would be beneficial to provide a trocar that does not rely on an operative connection with the cannula and does not need a cannula within which to withdraw the cutting surface in order to position the cutting surface in a safety position. The trocar according to the present invention solves that problem. 
   SUMMARY 
   According to the present invention a trocar is provided with a cutting surface, blade, or tip that is retractable within the obturator. Advantageously, the cutting surface will automatically retract into the obturator after the cutting surface penetrates through the tissue and the corresponding presence of pressure against the cutting surface is reduced or removed. The cutting surface quickly retracts so that contact or damage any internal organs is reduced or avoided 
   In accordance with one embodiment of the present invention, a trocar is provided that comprises an outer housing, an inner housing, an obturator, a cutting shaft with a cutting surface at a distal end, and a spring that biases the cutting surface to an exposed position. The obturator is hollow with an open distal end and defines a longitudinal axis. The obturator surrounds the cutting shaft and cutting surface. The inner housing cooperates with the cutting shaft such that in a first position the cutting surface is retracted within the obturator and upon rotation of the inner housing from the first position, the cutting surface moves longitudinally with respect to the obturator to a second position wherein the cutting surface is exposed with the cutting surface located beyond the distal end of the obturator. 
   The cutting surface may have any known or suitable shape as is well known in the art or can be contemplated. In one embodiment, the cutting surface is removable from the cutting shaft. As a result, the cutting surface can be varied in its length, shape, or other features. Moreover, if the cutting surface is removable from the cutting shaft, a sharp surface can be provided as desired or needed. 
   Advantageously, the obturator is reusable, simple in construction, easy to clean, sterilize and maintain. Moreover, a cannula is not necessary for operation of the trocar so that the cannula is used to provide access for instrument insertion after penetration of the tissue. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of one embodiment of the trocar of the present invention. 
       FIG. 2  is an exploded view of one embodiment of the trocar of the present invention with a portion of the outer housing exposed to show internal features of the outer housing. 
       FIG. 3  is a partial cut-away view of the inner housing and with the second spring shown in exploded view with a portion of the spring being cut away to show one end of the spring. 
       FIG. 4  is an end view of the proximal end of the trocar with the outer housing removed to better illustrate features of the present invention. 
       FIG. 5  is a partial cross sectional view of the trocar with the cutting surface in a retracted position within the obturator. Elements have been removed to better show the operation of the cutting mechanism within the obturator and the pin within the cam slot of the inner housing. 
       FIG. 6  is a partial cross sectional view of the trocar with the cutting surface in a deployed or operative position and piercing the tissue but where the obturator has not yet entered the tissue opening. Elements have been removed to better show the operation of the cutting mechanism within the obturator and the pin within the cam slot of the inner housing. 
       FIG. 7  is a partial cross sectional view of the trocar with the cutting surface in a deployed or operative position and piercing the tissue and where the obturator has entered the tissue opening. Elements have been removed to better show the operation of the cutting mechanism within the obturator and the pin within the cam slot of the inner housing. 
       FIG. 8  is a partial cross sectional view of the trocar with the cutting surface blade after penetration through the tissue and in a partially retracted position within the obturator. There is no force applied to the cutting surface and the obturator is shown as partially entering the tissue opening. Elements have been removed to better show the operation of the cutting mechanism within the obturator and the pin within the cam slot of the inner housing. 
       FIG. 9  is an exploded view of another embodiment of the trocar of the present invention. 
       FIG. 10  is an exploded view of a portion of the trocar of  FIG. 9  and, in particular the proximal end of the trocar to show the relationship of the proximal end of the cutting shaft, the inner housing, the return spring and the actuation ring. 
       FIG. 11  is a perspective view of a portion of the inner housing of one embodiment with a portion cutaway to better show features of the present invention. In particular, the inner housing is shown with the actuation ring and return spring in position. 
       FIG. 12  is a side view of the outer housing of one embodiment to show the actuation ring and the outer housing indicator. 
       FIG. 13  is a side view of one embodiment of an inner housing and an intermediate member. 
   

   DESCRIPTION 
   Turning now to  FIGS. 1 and 2 , a trocar  10  of the present invention is shown. The trocar  10  includes an outer housing  20 , an inner housing  40 , a cutting shaft  120  that carries a cutting surface  130 , an obturator  140  that surrounds the cutting shaft  120  and from which the cutting surface  130  extends, a first spring  160 , and a second spring  170 . The trocar  10  may be described as being aligned along a longitudinal axis  12  and having a proximal end  14  and a distal end  16 . The proximal end  14  is the end of the trocar  10  defined by the outer housing  20  and the distal end  16  is the end of the trocar  10  from which the cutting surface  130  extends from the obturator  140 . 
   The outer housing  20  has an outer surface  22  and an inner surface  28 . The outer surface  22  may have any shape suitable for grasping. Accordingly, the outer housing  20  as shown in  FIG. 1  has a convex top portion  24  with a tapered sidewall  26 . The outer housing  20  can be made of any material suitable for a sterile environment. The inner surface of the outer housing  20  is cylindrical and has a diameter slightly larger than at least a portion of the outer surface  42  of the inner housing so that the outer housing  20  can surround the inner housing  40 . 
   A flange  34  extends from an inner portion of the outer housing  20  and contains threads  36  on its periphery that will threadably engage threads  154  provided on the inner portion of the proximal end  146  of the obturator. As will become clear from the discussion below, the flange  34  also receives one end  162  of a spring  160 . 
   As best seen in  FIG. 2 , the inner housing  40  is desirably cylindrically shaped and has an outer surface  42 , an inner surface  58 , a first (or proximal) end  46 , and a second (distal) end  50 . The inner housing  50  may be formed of two pieces, an inner piece  48  and an outer piece  52 . When formed of two pieces, each piece may be formed of a single material or of differing materials. In addition, when formed of two pieces the pieces are securely joined or attached such that movement of the outer piece  52  results in movement of the inner piece  48  and vice versa. Alternatively, the inner housing  50  may be formed of a single piece. 
   In one embodiment, at least a portion of the outer surface  42  adjacent the second end  50  defines a flange  56 . The distal end  32  of the outer housing  20  may abut the flange  56 . The outer surface of the second end  50  of the inner housing desirably has a gripping surface  54  so that the inner housing  40  can be grasped and rotated. The gripping surface  54  can have any suitable form or material. For example, the gripping surface  54  may be in the form of scalloping. 
   The inner surface  58  of the inner housing  40  has a groove  60  that circumscribes the inner surface  58  of the inner housing  40 . The groove  60  is located adjacent the proximal end  46  of the inner housing. The groove  60  receives a spring  170 , desirably a torsion spring such as a radial torsion spring. Therefore, the groove  60  has a width  62  that is about the same size as the width of the torsion spring. In addition, an aperture  64  is provided and it receives one end  172  of the spring. 
   The inner housing  40  cooperates with the cutting shaft  120  such that when the inner housing  40  is in a first position, the cutting surface  130  is retracted and when the inner housing  40  rotates to a second position, the cutting shaft  120  and the cutting surface  130  move laterally such that the cutting surface  130  is exposed. Referring back to  FIG. 2 , the cutting shaft  120  has a proximal end  122  and a distal end  128 . The distal end  128  carries a cutting surface  130 . The cutting surface  130  may have any known or suitable shape as is well known in the art or can be contemplated. In one embodiment, the cutting surface  130  is removable from the cutting shaft  120 . As a result, the cutting surface  130  can be varied in its length, shape, or other features. The proximal end  122  has a flange  124  that surrounds the outer surface of the cutting shaft. Desirably, the flange includes a pin  126  that is received within a cam slot  80  provided on the inner housing  40  as described below. 
   The cam slot  80  is located adjacent the distal end  50  of the inner housing  40 . The cam slot  80  is provided on the inner surface  58  of the inner housing  40 . Although the cam slot  80  can extend from the inner surface  58  to the outer surface  42 , it is desired that the cam slot  80  does not extend through to the outer surface because it will reduce the amount of surface that can become dirty or contaminated or caught by the operator. 
   The cam slot  80  has at least two portions  82 ,  92  defining two positions, e.g., a first position where the cutting surface  130  is retracted, i.e., not exposed and a second position where the cutting surface  130  is exposed. In one embodiment, the cam slot  80  has three portions  82 ,  92 ,  98  defining three positions. The first  82  and second portions  92  are the same as described above. The third portion  98  defines a position when pressure is exerted in a proximal direction against the cutting surface  130 . 
   As better seen in  FIGS. 5-7 , in one embodiment of the trocar  10  of the present invention, the cam slot  80  has a first portion  82 , a second portion  92 , and a third portion  98 . The first portion  82  has a first end  84 , a second end  86 , a proximal surface  88 , a distal surface  90 , and is angled from the longitudinal axis  12  such that when the pin  126  is at the first end  84  of the first portion  82 , the cutting shaft  120  is in the furthest proximal position. In this, the first position, the cutting surface  130  is retracted into the obturator  140  as shown in  FIG. 5 . The first portion  82  may have any suitable angle from the longitudinal axis depending on the force desired to return the cutting surface to the first position. 
   The second portion  92  has a first end (a proximal position)  94 , a second end (a distal position)  96 . The second end  96  is open at the distal end  50  of the inner housing  40  so that the pin  126  can engage the cam slot  80 . In other words, in order to assemble the trocar  10 , the second end  96  of the second portion  92  is open so that the pin  126  can slide into the cam slot  80 . In use, despite the fact that the second or distal end  96  of the second portion  92  is open, the cutting shaft  120  is stopped from distal movement when the flange  124  on the cutting shaft  120  contacts an inner flange  156  on the obturator  140 . When the pin  126  is in the distal end  96  of the second portion, the cutting surface  130  is exposed, i.e., the cutting surface  130  extends from the distal end  142  of the obturator  140  as best seen in  FIG. 6 , which is referred to as the second position. 
   The third portion  98  of the cam slot  80  connects the first portion  82  with the second portion  92  and is aligned normal to the longitudinal axis  12 . The third portion  98  has a stop  100  that is adjacent the distal end  86  of the proximal surface  88  of the first portion  82 . When the pin  126  is in the second position, the cutting surface  130  is exposed and pressure has been applied to the cutting surface  130  in a proximal direction such as by, for example, tissue or tissue body that the cutting surface  130  is penetrating. As a result, the pin  126  has traveled from the second portion  92  to the third portion  98  and is held by the stop  100  so that the cutting surface  130  can penetrate or cut the tissue or other material, as best seen in  FIG. 7 , which is referred to as the third position. 
   An obturator  140  surrounds the cutting shaft  120  and, when the cutting shaft  120  is in the first position, the cutting surface  130  is completely withdrawn inside the obturator  140 . The obturator  140  has a distal end  142 , from which the cutting surface  130  extends, and a proximal end  146 , which cooperates with the proximal end  122  of the cutting shaft  120  and the inner housing  40 . At least one longitudinal slot  148  is provided at the proximal end  146  of the obturator  140 . Desirably, a first longitudinal slot  148  and a second longitudinal slot  150  are provided at the proximal end  146  of the obturator  140 . The second slot  150  may be provided at any suitable location relative to the first slot  148 . In some embodiments, the second slot  150  is opposite the first slot  148 . 
   The first slot  148  receives the pin  126  provided on the cutting shaft  120  and the pin extends outwardly from the obturator  140 . The first longitudinal slot  148  extends from the proximal end  146  of the obturator  140  toward the distal end  142  of the obturator  140 . The first longitudinal slot  148  extends a distance such that when the pin  126  abuts the distal end of the slot  148 , the cutting surface  130  is exposed a desired distance from the distal end  142  of the obturator  140 . 
   The second longitudinal slot  150  receives one end  174  of the second spring  170 . The second longitudinal slot  150  extends from the proximal end  146  of the obturator  140  toward the distal end  142  of the obturator. 
   A flange  152  is provided adjacent the proximal end  146  of the obturator  140 . The flange  152  may act as a stop for the inner housing  40  and to limit the distance the inner housing  40  can slide in a distal direction. 
   As noted above, a first spring  160  is provided and it is desirably a coil spring having a first end  162  and a second end  164 . The first end  162  is received within the flange  34  provided on the inner surface  28  of the outer housing  20  opposite the top of the outer housing  24 . The second end  164  abuts the flange  124  provided on the cutting shaft  120  to bias the cutting shaft  120  in a distal direction, i.e., in a direction such that the cutting surface  130  will be in an exposed position. If desired, the second end  164  may be fixed to the flange  124  on the cutting shaft  120 . 
   The trocar  10  also has a second spring  170 , desirably in the form of a torsion spring, such as a radial torsion spring. The second spring  170  has a first end  172  that extends outward from the spring  170  and is received in an aperture  64  provided in the groove  60  of the inner surface  58  of the inner housing  40 . The second end  174  extends inward from the spring  170  and is received in the at least one of the longitudinal slots  148 ,  150  of the obturator  140 . Desirably, the second end  174  extends into the second longitudinal slot  150 . 
   It will be understood by one of skill in the art that because the first  172  and second  174  ends of the second spring  170  are retained in a position relative to each other that the inner housing  40  will be biased to a first position. In addition, rotation of the inner housing  40  will act against the spring tension or force of the second spring  170 . The second spring can be manufactured to provide a suitable force or torque. In one embodiment, the spring provides a torque at 90° in the range from about 20 to about 40 N·mm, suitably in the range from about 24 to about 31 N·mm. 
   Operation of the trocar  10  will now be described.  FIG. 5  shows the safety position of the trocar  10  with the cutting surface  130  disposed within the obturator  140 . In this position, the cutting shaft  120  is retracted to its most proximal position and the pin  126  is at the first end  84  of the first portion  82  of the cam slot  80 . In a desired embodiment, the tension or spring force of the second spring  170  is greater than the spring force of the first spring  160 . Because the force of second spring  170  overcomes the force of the first spring  160 , which biases the cutting surface  130  to an exposed position, the inner housing  40  is biased to the position shown in  FIG. 5 . In addition, because the inner housing  40  is biased to the position shown in  FIG. 5 , the pin  126  is at the first end  84  of the first portion  82  of the cam slot  80  and thus, the cutting shaft  120  is at its most proximal position. 
   To actuate and expose the cutting surface  130  from the distal end  142  of the obturator  140 , the inner housing  40  is rotated to the position shown in  FIG. 6 . As a result, the pin  126  travels downwardly in the first portion  82  of the cam slot  80 , across the third portion  98  and into the second portion  92  of the cam slot  80 . Although the second spring  170  acts to bias the inner housing  40  to the position shown in  FIG. 5 , the wall of the second portion  92  of the slot  80  prevents the inner housing  40  from rotating. In this position, the first spring force  160  biases the cutting surface  130  to an exposed position with the cutting surface  130  extending beyond the distal end  142  of the obturator  140 . The cutting surface  130  will distally extend a distance dictated by either the length of the first spring  160 , the flange  152  provided on the obturator  140 , or a combination of both. 
   The cutting surface  130  is now ready to be used. When the cutting surface  130  contacts, for example, the tissue body of the abdominal wall, pressure is exerted in a proximal direction against the cutting surface  130 . The spring force of the first spring  160  is such that it is less than the pressure required to penetrate the tissue body and is such that the pin  126  moves to the proximal position  94  of the second portion  92  of the cam slot  80 . In this position, the inner housing  40  is not constrained from rotational movement by the pin  126  in the third portion  98  of the cam slot  80  and therefore, the inner housing  40  rotates in a direction such that the pin  126  moves toward the first portion  82  of the cam slot  80 . The pin  126  moves along the third portion  98  of the cam slot  80  until it contacts the stop  100 . The pin  126 , cutting shaft  120 , and cutting surface  130  remain in this position until the pressure against the cutting surface  130  is reduced to a degree or by an amount such that it is less than the distally biasing force of the first spring  160  or is removed. 
   As noted above, the angle of the first portion  82  of the cam slot  80  will determine the amount of force that the second spring  170  must provide to overcome the biasing force of the first spring  160  and move the cutting shaft  120  and pin  126  to the proximal end  84  of the cam slot  80 . In other words, the greater the angle of the first portion  82 , the greater the force that the second spring  170  must provide. Likewise, the smaller the angle of the first portion  82 , the lower the force that the second spring  170  must provide. 
   When the pressure against the cutting surface  130  is reduced to a degree or by an amount such that it is less than the distally biasing force of the first spring  160  or is removed (e.g. when the cutting surface  130  completely penetrates the tissue), the first spring  160  biases the cutting shaft  120  (and thus the pin  126 ) in a distal direction. As a result, the pin  126  is moved from the stop  100  and, because the force of the second spring  170  is greater than the force of the first spring  160 , the inner housing  40  rotates such that the pin  126  travels in a proximal direction along the first portion  82  of the cam slot  80  as best seen in  FIG. 8  until the pin  126  reaches the proximal position  84  of the first portion  82  of the cam slot  80 , as best seen in  FIG. 5 . The cutting surface  130  is then in its fully retracted position (the safety position). Thus, the cutting surface quickly retracts so that the cutting surface does not contact or damage any internal organs, blood vessels, or unintended areas. 
   It will be appreciated that during operation of the trocar  10  that the inner housing  40  rotates but does not move laterally and that the cutting shaft  120  moves laterally but does not rotate. In addition, the trocar  10  of the present invention provides a cutting surface  130  that immediately and automatically retracts after the cutting surface  130  has penetrated the tissue body. In other words, after the manual actuation of the cutting surface  130  to expose the cutting surface  130  to a use position (the second position), the retraction of the cutting surface  130  to a retracted or safety position is immediate and automatic. 
   Turning now to  FIG. 9  another embodiment of the present invention is illustrated. In describing this embodiment like reference numerals will be used to identify like parts. As with the previously described embodiment, the trocar  10  is provided with an outer housing  220 , an inner housing  240 , a cutting shaft  120  that carries a cutting surface  130 , an obturator  140  that surrounds the cutting shaft  120 . In addition, the trocar includes an actuation ring  200  and a return spring  210 . As with the previously described embodiment, the cutting shaft  120 , the obturator  140 , the first spring  160  and the second spring  170  in this embodiment function in the same manner as the previously described embodiment. In this embodiment, the outer housing  220  has a top portion  222  and a sidewall  224  extending from the top portion. The top portion  222  and sidewall  224  may be separate pieces or may be a single unitary piece. The sidewall  224  is provided with a slot  226  that is preferably substantially laterally oriented (best seen in  FIG. 12 ). Adjacent the slot  226 , icons  228  may be located to provide a visual indication of the state of the cutting surface  130 . In other words, the icons  228  may indicate whether the cutting surface  130  is in an extended or a retracted position. 
   The inner housing  240  has a first or proximal end  242  and a second or distal end  244 . The distal end  244  of the inner housing is contiguous with the flange  152  of the obturator  140 . As with the inner housing of the other embodiments, the inner surface  246  of the inner housing  240  has a groove (not shown) that circumscribes the inner surface  246  of the inner housing  240  to receive the second spring  170  in the same manner as with the inner housing  40 . 
   The inner housing  240  is provided with a cam slot  80  located adjacent the distal end  244  of the inner housing  240 . The cam slot  80  is provided on the inner surface of the inner housing  40 . Although the cam slot  80  can extend through the entire wall of the inner housing, it is not necessary that the cam slot  80  does so. Accordingly, the cam slot  80  may be provided only on the inner surface  246  of the inner housing, which will reduce the amount of surface that can become dirty or contaminated or caught by the operator. Alternatively, the actuation ring  200  can be located so that the actuation ring  200  covers the cam slot  80 . 
   The cam slot  80  has at least two portions  82 ,  92  defining two positions, e.g., a first position where the cutting surface  130  is retracted, i.e., not exposed and a second position where the cutting surface  130  is exposed. In one embodiment, the cam slot  80  has three portions  82 ,  92 ,  98  defining three positions. The first  82  and third portions  98  are the same as described above. The second portion  92  in the inner housing  240  is angled. Desirably, the angle is in a direction opposite that of the travel of the pin  126  as the pin travels from the cutting surface extended position to the cutting surface retracted position. 
   The inner housing  240  is also provided with a first radially extending pin  250  and a second radially extending pin  252  spaced from the first radially extending pin. The first radially extending pin engages a slot  202  provided in the inner surface  202  of the actuation ring  200  to drivingly connect the actuation ring  200  to the inner housing  240 . The slot  204  extends around a portion of the inner surface  202  of the actuation ring  200 , the purpose of which will become clear from the following text. Alternatively, the pin may be dispensed with and the actuation ring  200  may be drivingly connected to the inner housing in another conventional manner. Or, the actuation ring and the inner ring may be formed as a single piece. 
   The second radially extending pin  252  extends through the slot  226  of the side wall  224  of the outer housing  220 . The second radially extending pin  252  can therefore provide a visual indication whether the cutting surface  130  is in an extended or a retracted position. It will be understood by those of skill in the art, that the second radially extending pin  252  in conjunction with the icons  228  can provide an enhanced visual indication. 
   As noted above, a return spring  210  is provided. The return spring is provided with a first end  212  and a second end  214 . The first end  212  engages a cavity  206  formed on the bottom  208  of the actuation ring  200 . The second end  214  engages a cavity  158  formed on the flange  152  of the obturator  140 . When the first end  212  and the second end  214  are received in their respective cavities, the actuation ring  200  will be biased toward a rest position. In practice, the actuation ring  200  is drivingly connected to the inner housing  240  by the engagement of the pin  250  in the slot  204  so that the shaft  120  and thus the cutting surface  130  will be in the retracted position (indicated with the icon  228  “safe” in  FIG. 12 ). 
   To actuate and expose the cutting surface  130  from the distal end  142  of the obturator  140 , the actuation ring  200  is rotated to drivingly rotate the inner housing  240  such that the pin is in the second portion  92  of the cam slot  80 . In other words, as the actuation ring  200  is rotated, one end wall (not shown) of the slot  204  contacts the first radially extending pin  250  to drivingly rotate the inner housing  240 . The second radially extending pin moves from one end of the slot  226  (indicated with the icon  228  “safe” in  FIG. 12 ) to the other end of the slot (indicated with the icon  228  “armed” in  FIG. 12 ). The cutting surface  130  is then exposed. When the force rotating the actuation ring  200  is released, the actuation ring  200  is biasingly moved to its rest position, while the inner housing  240  remains in position because the slot  204  rides over the pin  250  without moving the inner housing  240 . 
   Referring to  FIG. 13 , another embodiment of a portion of the trocar of the present invention is shown. In  FIG. 13 , a portion of the inner housing  240  is shown with an intermediate member  300  surrounding the inner housing  240 . The intermediate member  300  may be integrally formed as or with the actuation ring (not shown) or it may be separate from the actuation ring. When the intermediate member  300  is separate from the actuation ring, the actuation ring may be fixed to the intermediate member in any suitable manner such as by press fitting or the like. 
   As with the inner housing  240  of the other embodiments, the inner surface of the inner housing has a groove (not shown) that circumscribes the inner surface of the inner housing to receive the second spring  170  in the same manner as with the other inner housings. In addition, the inner housing is provided with a cam slot (not shown) as described in connection with the other inner housings. 
   The intermediate member  300  surrounds the inner housing and in general surrounds the distal portion of the inner housing. The intermediate member  300  has a radially extending pin  310  that rides in the slot  204  of the actuation ring  200 . The intermediate member radially extending pin  310  is also attached to the inner housing  240  in any suitable manner so that movement of the intermediate member  300  causes corresponding movement of the inner housing  240 . 
   The intermediate member  300  is provided with a peripheral groove  330  about a portion of the outer periphery  320 . In addition, the bottom  302  of the intermediate member  300  is provided with a slot  304  that extends about a portion of the circumference of the bottom  302  of the intermediate member  300 . The slot has a first end  306  and a second end  308 . A traveling pin  340  has a first end  342  extending in the groove and a second end  344  that extends through the slot  304  and engages the cavity  158  formed on the flange  152  of the obturator  140 . 
   The traveling pin  340  is biased to a position adjacent the first end  306  of the slot  304  by a biasing member  360 . The biasing member  360  can have one end  362  attached to the traveling pin  340  and a second end  364  attached to a portion of the intermediate member  300 . As shown in  FIG. 13 , a stationary pin  370  is provided to secure a second end  364  of the biasing member  360 . The biasing member  360  can have any suitable form and is shown as a coil spring in  FIG. 13 . 
   The first end  342  of the traveling pin  340  may be provided with a first  346  and a second shoulder  348  that will aid in the travel of the traveling pin  340  in the groove  330 . In this regard, the first shoulder  346  may be adjacent one wall  332  of the groove and the second shoulder  348  may be adjacent the opposite wall  334  of the groove. Where a first  346  and second  348  shoulder is provided, one end  362  of the biasing member  360  may be attached to the traveling pin  340  in the area between the first  346  and second  348  shoulder. 
   When the second end  344  of the traveling pin  340  is received in the cavity  158 , the actuation ring  200  will be biased toward a rest position. In practice, the actuation ring  200  is drivingly connected to the inner housing  240  by the engagement of the intermediate member radially extending pin  310  with the inner housing  240  and with the slot  204  of the actuation ring  200  so that the shaft  120  and thus the cutting surface  130  will be in the retracted position (indicated with the icon  228  “safe” in  FIG. 12 ). 
   To actuate and expose the cutting surface  130  from the distal end  142  of the obturator  140 , the actuation ring  200  is rotated to drivingly rotate the inner housing  240  such that the pin  126  is in the second portion  92  of the cam slot  80 . In other words, as the actuation ring  200  is rotated, one end wall (not shown) of the slot  204  contacts the intermediate member radially extending pin  310  to drivingly rotate the inner housing  240 . When the force rotating the actuation ring  200  is released, the actuation ring  200  is biasingly moved to its rest position by the biasing member  360 , while the inner housing  240  remains in position because the slot  204  rides over the intermediate member radially extending pin  310  without moving the inner housing  240 . 
   It is to be understood that, while the invention has been described above in conjunction with the specific embodiments, the description is intended to illustrate and to limit the scope of the present invention, which is defined by the scope of the claims. For example, while several or the parts have been described as being formed as separate parts, it is possible to form them as a single piece. Advantageously, one of skill in the art will understand that the trocar  10  of the present invention will operate independently of a cannula, although the use of a cannula with the trocar  10  is contemplated. The cannula may surround the proximal end of obturator and, after penetration of the tissue body (e.g., the abdominal wall), the cutting surface will retract into the obturator (but not into the cannula), the cannula can be placed, and the trocar can be withdrawn from the cannula to provide an access port, as is known in the art.