Patent Publication Number: US-6217555-B1

Title: Multiport trocar

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. Patent application Ser. No. 08/275,620, filed on Jul. 14, 1994, and issued as U.S. Pat. No. 5,569,205 on Oct. 29, 1996. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to surgical access devices, such as trocars, which are adapted to provide access across a body wall and into a body conduit or cavity. 
     2. Discussion of the Prior Art 
     Trocars of the past have typically included a cannula and a valve housing which together define an access or working channel for various surgical instruments. The cannula has been formed in the configuration of an elongate rigid cylinder which has been inserted, with the help of an obturator, into a body cavity, such as the abdominal cavity to provide access across a body wall, such as the abdominal wall. 
     In a typical abdominal laparoscopic surgery, the abdomen is insufflated to pressurize and thereby enlarge the cavity within which a surgical procedure is to be performed. Various instruments used in the procedure have been inserted, previously one at a time, through the working channel of the trocar to perform the surgery. In order to maintain the insufflation pressure when the instrument is inserted through the trocar, a valve has been provided in the housing to form a seal around the instrument. These instrument valves have typically been provided in the form of septum valves. When the instrument is removed, a zero closure valve has typically been provided to seal the trocar in order to maintain the insufflation pressure. 
     A septum valve similar to that disclosed and claimed by applicant in copending application Ser. No. 08/051,609 filed Apr. 23, 1993 and entitled Seal Assembly for Access Device is typical of the instrument valves. A typical zero closure valve might be in the form of a double duck bill valve such as that disclosed in the same application which is incorporated herein by reference. 
     Instruments vary in size and diameter. While the zero closure valves of the past can accommodate a relatively wide range of diameters, the septum valves are generally capable of stretching only a nominal amount to accommodate larger diameters. Accordingly, these valve sets are generally limited as to the size of instrument which they can accommodate. Attempts have been made to increase the range of septum valves by providing levers which prestretch the valve in order to reduce some of the friction forces. These universal septum valves, such as those disclosed and claimed by applicant in U.S. Pat. No. 5,209,737, are relatively complex in structure but nevertheless are able to accommodate a wide range of instruments. 
     In trocars of the past, the septum valves and zero closure valves have been formed as a valve set. This set has typically been configured along a common axis which extends through the opening of the septum valve, the zero closure valve, and the cannula. 
     In the past, only a single valve set was provided in the trocar. This necessitated that instruments used with the trocar be inserted only one at a time. Thus a first instrument would be inserted through the septum valve and the zero closure valve to gain access to the abdominal cavity. With the instrument in place, the septum valve would maintain the insufflation pressure. Once the first instrument was removed, this insufflation pressure was maintained by the zero closure valve. Only upon removal of the first instrument could a second instrument be inserted through the same septum valve and the same zero closure valve. 
     When an instrument was required that had a diameter outside the range of a particular valve set, the entire trocar had to be replaced with one which could accommodate a different range of diameters. In some cases alternative septum valves were provided each of which functioned with the same zero closure valve but accommodated a different range of instrument diameters. Even where the trocars of the past provided for alternative valve sets, only a single instrument could be inserted at a time. 
     SUMMARY OF THE INVENTION 
     These deficiencies of the prior art have been overcome with the present invention which provides for the insertion of two or more instruments into the same trocar at the same time. This trocar which provides for a seal assembly having multiple valve sets in a single valve housing, is significantly simplified so that manufacturing costs are greatly reduced. 
     Each of the valve sets in a preferred embodiment accommodates a different range of instrument sizes so that only a single trocar and seal assembly is required in order to accommodate all possible instrument sizes. Thus, a single simplified trocar can accommodate not only a full range of instrument sizes, but can even accommodate multiple instruments simultaneously. Not only is the single trocar less expensive to manufacture, but the number of assemblies and trocars required for a given surgical operation is also reduced. This will be greatly appreciated in a cost sensitive marketplace where as many as one million laparoscopic surgeries are performed annually in the United States, each requiring as many as four to six trocars per surgery. 
     Each of the valve sets is provided with characteristics for forming an instrument seal as well as a zero closure seal. These characteristics can be provided for the smallest range of instruments, by a single septum valve which additionally has zero closure characteristics. For larger valve sets, a septum valve is combined with a zero closure valve in each of the sets. In an embodiment wherein the cannula has a first axis, the septum valve a second axis, and the zero closure valve a third axis, at least one of the second and third axes is offset from the first axis. It may also be desirable to offset the second axis of the second septum valve from the third axis of the zero closure valve in order to accommodate more valve sets in the single valve housing. In these embodiments, the zero closure valves can be formed in any manner associated with the prior art, but the double duck bill valve configuration is preferred. 
     In one aspect of the invention, a trocar is adapted to extend across a body wall into a body cavity, and to form a seal around an instrument inserted through the trocar into the body cavity. The trocar comprises a cannula forming an elongate passage and a valve housing disposed at a proximal end of the trocar. A valve assembly is disposed relative to the housing and includes a first valve set forming a first working channel with the passage of the cannula and a second valve set forming a second working channel with the passage of the cannula. The first valve set includes a first septum valve and a first zero closure valve each disposed along the first working channel. The second valve set includes a second septum valve and second zero closure valve each disposed along the second working channel. The trocar further comprises means for further supporting at least one of the first septum valve and the second septum valve relative to the housing in a “floating” relationship with the cannula. 
     In an additional aspect of the invention, a trocar assembly includes a cannula having an axis extending between a proximal end and a distal end. A housing disposed at the distal end of the cannula includes a rigid housing portion fixed to the cannula and an axially compressible elastomeric housing portion disposed proximally of the rigid housing portion. Together the rigid and elastomeric housing portions form a working channel with the cannula of the trocar. This channel is sized and configured to receive an obturator having a shaft with an axis extending to a sharp distal tip. When the obturator is operatively disposed, this distal tip extends beyond the distal end of the cannula. The trocar assembly includes means associated with the shaft of the obturator and at least one of the cannula and the rigid housing portion for preventing insertion of the obturator into the cannula beyond the operative position of the obturator in order to avoid substantial axial compression of the elastomeric housing portion. 
     In a further aspect of the invention, a trocar assembly includes a cannula having a first axis and a valve housing forming a working channel with the cannula. A first septum valve is disposed relative to the housing and includes portions defining a first opening having a second axis. A second septum valve is disposed relative to the housing and has portions defining a second opening having a third axis. At least one of the second axis of the first septum valve and the third axis of the second septum valve is offset from the first axis of the cannula. 
     In still a further aspect of the invention, a trocar includes a cannula having a first axis and a septum valve disposed along the working channel of the trocar and forming an opening having a second axis. The septum valve is formed of an elastomeric material stretchable between a first natural position wherein the opening of the septum valve is disposed with the second axis offset from the first axis of the cannula, and a second stretched position wherein the second axis of the septum valve is generally aligned with the first axis of the cannula. Means is provided for supporting the septum valve relative to the cannula to permit movement of the septum valve from the first natural position to the second stretched position without substantial deformation of the opening of the septum valve. 
     Other aspects of the invention provide structural accommodation for various embodiments of a valve assembly including more than one valve set. In one case, the valve assembly includes an elastomeric sidewall that connects proximal portions of the valve assembly with distal portions of the valve assembly. The distal portions are sandwiched between the cannula and valve housing to form a seal with these elements. The valve housing extends to a proximal wall where the proximal portions of the valve assembly engage an end cap which is movable transverse of the trocar axis in contact with the proximal surface of the valve housing. The sidewall of the valve assembly is held in elastomeric tension to bias the end cap against the valve housing. 
     Transverse movement of the end cap is limited by a projection which extends from either the valve housing or the end cap to provide an interference fit between the projection and the other of the valve housing and end cap. 
     A rigid partition is provided within the valve housing and extends along the axial length of the valve sets. This rigid partition is movable with the end cap and the valve assembly to inhibit contact between the sidewalls of the housing and the axial walls of the valves which would otherwise undesirably deform the valves and permit leakage of the insufflation gas. 
    
    
     These and other features and advantages of the invention will become more apparent with the description of preferred embodiments and reference to the associated drawings. 
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a preferred embodiment of the trocar of the present invention; 
     FIG. 2 is an axial cross-section view taken along lines  2 — 2  of FIG. 1, and illustrating a preferred embodiment of a valve housing and associated valve assembly; 
     FIG. 3 is a top plan view taken along lines  3 — 3  of FIG. 2; 
     FIG. 4 is a radial cross-section view taken along lines  4 — 4  of FIG. 2; 
     FIG. 5 is an axial cross-section view similar to FIG.  2  and illustrating an additional embodiment of a valve housing; 
     FIG. 6 is a cross-section view similar to FIG.  2  and illustrating a small sized instrument and a medium sized instrument simultaneously operatively disposed through first and second valve sets of the trocar; 
     FIG. 7 is a radial cross-section view similar to FIG.  6  and illustrating a large instrument in the form of an obturator operatively disposed in the trocar; 
     FIG. 8 is a side view partially in section of the trocar illustrating a flapper valve having zero closure characteristics in a further embodiment of the invention; 
     FIG. 9 is a top plan view taken along lines  9 — 9  of FIG. 8; 
     FIG. 10 is a perspective view illustrating an instrument inserted into a trocar comprising a further embodiment of the invention; 
     FIG. 11 is an exploded axial cross-section view of the trocar embodiment of FIG. 10 illustrating components including (from top to bottom) an end cap, a valve assembly, a partition structure, a valve housing, and a cannula; 
     FIG. 12 is an axial cross-section assembled view of the trocar illustrated in FIG. 11; 
     FIG. 13 is an axial cross-section view of the partition structure illustrated in FIG. 11; 
     FIG. 14 is a top plan view of the partition structure of FIG. 11; 
     FIG. 15 is an enlarged side elevation view of the partition structure of FIG.  11 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A multiport trocar is illustrated in FIG.  1  and designated generally by the reference numeral  10 . The trocar  10  is representative of any access device including a cannula  12  which is in the form of a hollow elongate cylinder having a distal end  14  and a proximal end  16 . It is this cannula  12  which is sized and configured to extend across a body wall, such as an abdominal wall  15 , into a body conduit or cavity, such as a blood vessel or an abdominal cavity  17 . The cannula  12  is preferably rigid, or semi-rigid and in preferred embodiments is formed of plastics or surgically compatible metals such as stainless steel. A passage  18  formed by the walls of the cannula  12  extends along a central axis  21 . 
     A valve housing  23  also forms a significant part of the trocar  10 . In the illustrated embodiment, the valve housing  23  includes a rigid housing portion  25  and an elastomeric housing portion  27  which together define a housing cavity  30 . 
     The rigid housing portion  25  is preferably formed of plastic and disposed at the proximal end  16  in a fixed relationship with the cannula  12 . In the illustrated embodiment, a pair of finger tabs  32  are formed as an integral part of the rigid housing portion  25  and provide means for engaging the trocar  10  and manipulating the cannula  12  into a preferred operative position. A collar  34  is disposed distally of the tabs  32  where it is sized and configured to receive the proximal end  16  of the cannula  12 , as best illustrated in FIG.  2 . 
     The elastomeric housing portion  27  is preferably formed of natural rubber and includes a cylindrical side wall  36  and an end wall  38  which are integral in a preferred embodiment. The side wall  36  is preferably centered on the axis  21  of the cannula  12  while the end wall  38  is transverse, for example perpendicular, to the axis  21 . In a preferred embodiment, the side wall  36  of the elastomeric housing portion  27  is joined to and forms a seal with the rigid housing portion  25  at a circumferential joint  40 . 
     The cavity  30  formed by the valve housing  23  is in fluid communication with the passage  18  of the cannula  12 . Together this cavity  30  and passage  18  form a working channel  41  of the trocar  10 . In the illustrated embodiment, this channel  41  extends from regions exterior of the trocar  10 , through the end wall  38 , into the housing cavity  30 , and through the passage  18  and the distal end  14  of the cannula  12 . Thus the trocar  10  functions as an access device so that instruments can be inserted through the seal housing  23  and the cannula  12  into the abdominal cavity  17 . 
     In a typical laparoscopic surgery, the trocar  10  is disposed with the cannula  12  extending across the abdominal wall  15  and into the abdominal cavity  17 . In order to increase the working space at the surgical site, the abdominal cavity  17  is typically pressurized or insufflated. In the trocar  10  illustrated in FIG. 3, this insufflation of the abdominal cavity  17  is implemented by use of an insufflation tube  45  which is in fluid communication with the housing cavity  30  as well as the passage  18  of the cannula  12 . 
     After the abdominal cavity  17  is appropriately insufflated, various instruments, such as catheters, guide wires, graspers, staplers, can be inserted through the working channel  41  of the trocar  10  to perform various functions within the abdominal cavity  17 . It is important in such an operation, that the insufflation pressure be maintained both when the instruments are disposed within the working channel  41  of the trocar  10 , as well as when the instruments are removed from the working channel  41 . Such is the function of a valve assembly  46  which is typically disposed within the housing cavity  30  or formed as part of the valve housing  23 . 
     The valve assembly  46  of the present invention is sized and configured to accommodate a surgical instrument having substantially any diameter regardless of the size limitations of a single valve. Such instruments are represented by a catheter  48 , a retractor  49  and a obturator  50  best illustrated in FIGS. 6 and 7. In the following discussion, the catheter  48 , retractor  49  and obturator  50  are sometimes referred to respectively as the small, medium and large instruments  48 ,  49 ,  50 , and collectively as the instruments  48 ,  49  and  50 . 
     As noted, these instruments  48 - 50  will vary widely in diameter. For example, the small size instrument  48  might include a guidewire or catheter up to two millimeters in diameter. The medium size instrument  49  might include graspers or refractors between two and five millimeters in diameter. The large size instrument  50  might include an obturator or laparoscope having diameters as small as five millimeters and as large as eleven or twelve millimeters. 
     This entire range of diameters, for example from zero to eleven or twelve millimeters, can be accommodated with the single multiport trocar  10  of the present invention. In this concept, the valve assembly  46  includes at least two and preferably three or four valve sets each adapted to receive a different range of instrument sizes, and collectively to accommodate the entire range of instrument sizes. In the illustrated embodiment the valve a assembly  46  includes a small valve set  52 , a medium valve set  54  and a large valve set  56 . These valve sets  52 ,  54  and  56  form, with the passage is of the cannula  12 , three respective working channels  41   a ,  41   b , and  41   c.    
     Each of the valve sets  52 - 56  must have characteristics for forming a seal around the associated instrument  48 - 50  when it is operably disposed in the working channel  41 , as well as characteristics for forming a seal across the working channel  41  when the associated instrument  48 - 50  is removed. For the small valve set  52 , both of these characteristics can be provided by a single septum valve  58  which has an opening  59  small enough to close upon itself in the absence of the instrument  48 , but large enough to accommodate instruments of up to about two millimeters in diameter. 
     The large valve set  56  is representative of the other valve sets in the valve assembly  46 . This large valve set  56  includes a large septum valve  61  as well as a large zero closure valve  63 . These valves  61  and  63  can be of the type disclosed in applicant&#39;s copending application Ser. No. 08/051,609 filed on Apr. 23, 1993 and entitled Seal Assembly for Access Device. 
     In order to accommodate a large instrument, such as the obturator  50 , the large septum valve  61  is provided with a hole  65  which in its natural state has a diameter, such as about five millimeters. Forcing the instrument  50  with a diameter larger than about five millimeters through this hole  65  causes the valve  61  to expand so that it forms a tight seal with the outer surface of the instrument  50 . However, when the instrument  50  is removed, the septum valve returns to its natural state leaving the hole  65  in an open state. Under these circumstances, the zero closure valve  63  is of particular importance as it fully closes in the absence of the instrument  50 . This insures that the working channel  41   c  through the large valve set  56  is fully closed when the instrument  50  is removed. 
     The medium valve set  54  is similar to the large valve set  56  in its function, however, it is generally smaller in size. Thus the medium valve set  54  includes a medium septum valve  67  and a medium zero closure valve  70 . As was the case with the large septum valve  61 , the medium septum valve  67  has a hole  71  which is sufficiently large to accommodate medium size instruments between about two millimeters and five millimeters, for example. This medium septum valve  67  does not fully close as did the small septum valve  58 , so the zero closure valve  70  is required to seal the working channel  41   b  through the medium valve set  54  when the instrument  49  is removed. 
     In order to accommodated the multiple valve sets  52 - 56  within a single valve housing  23 , the lateral orientation of the respective septum valves  58 ,  67  and  61  in the end wall  38  can be of particular importance. With reference to FIG. 3, it will be noted that the three septum valves  58 ,  67  and  61  are each centered on an associated longitudinal axis  72 ,  74  and  76 . Similarly, the zero closure valves  70  and  63  are centered on respective longitudinal axes  78  and  81 . 
     Each of the axes  72 - 76 , associated with the respective septum valves  58 ,  67  and  61 , is separated or off set from the axis  21  of the trocar  10  by a different distance. In the illustrated embodiment the axis  76  associated with the large septum  61  is disposed closest to the axis  21 . This orientation is preferred since a larger instrument, such as the obturator  50 , requires a more vertical orientation with the trocar  10  due to the fact that its diameter more closely approaches that of the cannula  12 . Thus, by locating the axis  76  relatively close to the axis  21 , the septum valve  61  is required to move only a small distance in order to achieve the more vertical orientation required by the large instrument  50 . 
     As illustrated in FIG. 6, the medium sized instruments, such as the retractor  49 , can pass through the cannula  12  at an angle so that the medium size instrument  49  does not require as vertical an orientation as the large instrument  50 . Thus the medium septum valve  67  need not move as close to the axis  21  of the cannula  12  for operative disposition of the instrument  49 . For this reason, the axis  74  of the medium septum valve  67  can be offset from the axis  21  of the cannula  12  a distance greater than that separating the axis  76  of the large septum valve  61  from the axis  21  of the cannula  12 . With respect to the small septum  58 , its axis  72  can be located at an even greater distance from the axis  21 . Not only do small instruments, such as guidewires and the catheter  48 , require very little vertical orientation, but they are often flexible so that no movement of the septum  58  is required for operative disposition of these small instruments. 
     For the reasons just discussed, it is important that the septum valves  61  and  67  be located so that they can move from their natural position, in the absence of the instruments  49 ,  50  to a more centered position, in the presence of the instruments  49 ,  50 . This movement must occur without substantial deformation of the septum valve  67  and  61  so that the valve portions forming the respective holes  71  and  65  can form a suitable seal with the outer surface of the instruments  49 ,  50 . 
     In a preferred embodiment, this movement without deformation is accommodated by two characteristics of the trocar  10 . First, the end wall  38  is formed of an elastomeric material thereby permitting the septum valves  58 ,  67  and  61  to move laterally within the end wall  38 . Perhaps more importantly, the side wall  36  of the housing portion  27  is also formed of an elastomeric material and is easily deflected laterally. This movement of the side wall  36  carries the entire end wall  38  to a desired position without deformation of the associated septum valve  58 ,  67  and  61 . Thus the septum valves  58 ,  67  and  61  have a floating relationship with the cannula  12  which permits them to move laterally while still maintaining their properties for forming a seal with the outer surface of the associated instrument  48 - 50 . This lateral deflection of the side wall  36  is illustrated in both FIGS. 6 and 7 for the respective instruments  49  and  50 . 
     In the foregoing embodiment, the septum valves  58 ,  67  and  61  are formed in the end wall  38  of the elastomeric housing portion  27 . It will be apparent, however, that these valve  58 ,  67  and  61  can be formed generally in any wall which is transverse to the axis  21  of the cannula  12 . The resulting valve wall can be included within the housing cavity  30  or can form part of the valve housing  23 . Nevertheless, it is generally preferred that the septum valves  58 ,  67 , and  61  be formed in the proximal-most wall, such as the end wall  38 , of the valve housing  23 . 
     The location of the zero closure valve  70  and  63  can also be critical in a particular embodiment. It is not required that the axes  78  and  81  associated with the zero closure valves  70  and  63  respectively, be aligned with the axes  74  and  76  of the associated septum valves  67  and  61 . This alignment of valves within a valve set, which is characteristic of the prior art, is not required by the present invention. Rather the location of the zero closure valves  70  and  63  is generally dependent on two different considerations. 
     First, the zero closure valve  70  must be positioned such that the instrument  49  passing through the associated septum valve  67  also passes through zero closure valve  70 . Similarly, the zero closure valve  63  must be positioned so that the instrument  50 , passing through the associated septum valve  61  also passes through the zero closure valve  63 . As can be seen from FIG. 3, this requirement is not particularly stringent so that the septum valves  67  and  61  can be located relatively close to the central axis  21  while the associated zero closure valve  70  and  63  are located relatively far from the central axis  21 . 
     The second consideration for location of the zero closure valves  70  and  63 , is based on their proximity to each other. It is important that when the medium instrument  49  is positioned within the medium valve set  54 , that it not interfere with the ability of the large zero closure valve  63  seal the working channel  41   c . This generally requires that the medium zero closure valve  70  be separated from the large zero closure valve  63  a distance sufficient to prevent deformation of the large zero closure valve  63 . 
     In the illustrated embodiment, this interference with a non-associated zero closure valve  63  is of perhaps greatest concern with respect to the medium valve set  54 . In this valve set  54 , the medium instrument  49  will typically have a more angled disposition within the housing cavity  30  than the large instrument  50 . Furthermore, the large zero closure valve  63  will typically extend further into the housing cavity  30 , as illustrated in FIG. 2, making it more susceptible to interference from the medium instrument  49 . 
     The double duck bill valve configuration illustrated for the zero closure valves  63  and  70  is particularly beneficial in avoiding this interference. Each of these zero closure valves  70  and  63  includes respectively, a cylindrical side wall  82  and  83 , and a closure structure defined by walls  85  and  87 . These walls  85 ,  87  define lateral recesses  89 ,  92  as they converge to lines  94 ,  96 , respectively, which form the cross seal associated with this type of zero closure valve. These lines  94  and  96  are best illustrated in FIG.  4 . The configuration of the walls  85 ,  87  and the associated recesses  89 ,  92  and lines  94 ,  96  are described in greater detail in applicant&#39;s copending application Ser. No. 08/051,609. 
     In general, this configuration of the zero closure valves  70  and  63  facilitates a structure wherein one of the valves, such as the valve  70 , can be provided with a side wall, such as the side wall  82 , which is shorter than the side wall, for example the side  83 , associated with the other zero closure valve, such as the valve  70 . Then, a recess or indentation  98 , can be formed in the other side wall, such as the side wall  83 . It will be apparent that this solution will be equally appropriate with a longer side wall  82  in the medium zero closure valve  70 , and an appropriate indentation, such as the indentation  98 , in that sidewall  82 . 
     Another way of accommodating the close proximity of the zero closure valves  70  and  63  is to orient the associated seal lines  94  and  96  so that neither is disposed along a line interconnecting the axes  78  and  81  of the respective valve  70  and  63 . Since these seal lines  94  and  96  extend to the greatest diameter of the associated walls  85  and  87  they are most susceptible to interference by an instrument  78 ,  80  extending through the opposite valve set  54 ,  56 . By orienting these lines  94  and  96 , as illustrated in FIG. 4, the natural recesses  89  and  92  formed between lines  94 ,  96  are automatically faced toward the opposing axis  78 ,  81 . 
     As one contemplates an appropriate length for either of the side walls  83 ,  85 , it must be appreciated that additional length will ultimately demand a longer valve housing  23 . For comparison, it will be noted that in the embodiment of FIG. 2, the zero closure valve  63  extends beyond the joint  40  between the rigid housing portion  25  and the elastomeric housing portion  27 . In an embodiment wherein the length of the seal housing  23  is to be minimized, it may be desirable to shorten the side walls  85  associated with the zero closure valve  63 . This could produce an embodiment wherein neither of the zero closure valves  63  or  70  extends beyond the joint  40  between the housing portions  25  and  27 . 
     When an instrument, such as the instruments  49  and  50 , is removed from the trocar  10 , it is desirable that the elastomeric housing portion  27  return to its natural state wherein its side wall  36  is coaxial with the central axis  21 . This return to the natural state is facilitated in a preferred embodiment wherein the housing portion  27  is provided with a plurality of ribs  101  which extend radially and longitudinally of the side wall  36  within the housing cavity  30 . 
     In a preferred embodiment, the entire elastomeric housing portion  27  (including the ribs  101 ) and the entire valve assembly  46  (including the septum valves  58 ,  67 ,  61  and the zero closure valves  70 ,  63 ) are formed as an integral structure from an elastomeric material such as latex. 
     The lateral flexibility desired for the elastomeric housing portion  27  also produces an axial flexibility which may not be desired when the trocar  10  is used with obturators of the prior art. As illustrated in FIG. 7, the obturator  50  of the present invention is typical of those of the past in that it includes a handle  102  and a shaft  103  having a sharp distal tip  104 . This obturator  50  is designed for axial insertion through the valve housing  23  and into the cannula  12  as illustrated by the dotted line position in FIG.  7 . Further axial movement into the cannula  12  brings the obturator  50  to an operative position where the sharp distal tip  104  of the obturator  50  extends beyond the distal end  14  of the cannula  12 . This operative position is shown by the solid line position of the obturator  50  in FIG.  7 . Once the obturator  50  is disposed in its operative position within the cannula  12 , further axial pressure on the handle  102  is intended to force the sharp distal tip  104  through the abdominal wall  15  to position the distal end  14  of the cannula  12  within the abdominal cavity  14 . 
     With obturators of the past, this axial pressure was directed through the handle and applied against the proximal end of the valve housing. In the present invention, however, this additional pressure on the proximal end of the housing  23  would only seek to compress the elastomeric housing portion  27 . This would not only make it difficult to insure the operative disposition of the sharp tip  96  beyond the cannula  12 , but also could damage the elastomeric housing portion  27 . 
     In a preferred embodiment, illustrated in FIG. 7, the obturator  50  is provided with an enlargement or projection  105  which is fixed to the outer surface of the shaft  95 . In the illustrated embodiment, the projection  105  takes the form of an annular flange which extends radially outwardly from the outer surface of the shaft  95 . When the obturator  50  is inserted from its dotted line position in FIG. 7 to its solid line operative position, this projection  105  moves through the housing cavity  30  into engagement with the proximal end  16  of the cannula  12  which functions as a stop for the projection  105 . Since the projection  105  is larger than the inside diameter of the cannula  12  in this embodiment, further axial movement of the obturator  50  is prevented. In this operative position of the obturator  50 , the distal tip  104  of the shaft  103  extends beyond the distal end  14  of the cannula  12 , but the handle  102  does not axially compress the elastomeric housing portion  27 . In general, the projection  105  can be positioned along the shaft  102  at any location where it can engage part of the rigid housing portion  25 , such as the collar  34 , or the proximal end  16  of the cannula  12 . 
     A further embodiment of the invention is illustrated in the perspective view of FIG.  10 . In this embodiment, structures similar to those previously discussed will be designated with the same reference numeral followed by the lower case letter “a”. Thus in FIG. 10, the trocar  10   a  includes a cannula  12   a , having a distal end  14   a  and a proximal end  16   a , and a valve housing  23   a  which partially defines a housing cavity  30   a . The trocar  10   a  also includes the insufflation tube  45   a  and is illustrated in combination with a retractor  49   a  which is representative of various surgical instruments. Both the cannula  12   a  and the valve housing  23   a  are aligned along the axis  21   a  of the trocar  10   a.    
     In the embodiment of FIG. 10, the housing cavity  30   a  is also partially defined by an end cap  121  which is movable transverse to the axis  21   a  at the proximal end  16   a . The end cap  121  includes access ports  123 - 127  which provide access for small, medium and large diameter instruments, respectively, into a working channel  41   a  of the trocar  10   a.    
     Reference to the exploded view of FIG. 11 will show that the trocar  10   a  also includes a valve assembly  46   a  and a partition structure  130 . Another feature associated with this embodiment is the modularity of construction which provides for a quick disconnect between the cannula  12   a  and the remainder of the trocar including the valve housing  23  and the valve assembly  46   a . This quick disconnect in the illustrated embodiment takes the form of a bayonet connection including tabs  132  and associated slots  134 . 
     The concept of modularity offers several advantages to this embodiment of the invention. For example, if a different seal assembly  46   a  is desired for a particular trocar, that assembly with its housing  23  can be replaced without removing the cannula  12   a  from its operative site. This same feature permits the replacement of a valve assembly  46   a  which has been torn or is otherwise inoperative. The quick release separation between the housing  23  and cannula  12   a  also facilitates rapid and complete desufflation of the abdominal cavity. 
     The cannula  12   a  of this embodiment extends from the distal end  14   a  to an enlarged proximal portion  136  having a proximal facing end surface  138 . The valve housing  23   a  has a lower skirt  141  which is sized to receive the proximal portions  136  of the cannula  12   a . It is this skirt  141  which defines the slots  134  of the bayonet connection. Extending in the opposite direction from the skirt  141  is a sidewall  143  which extends proximally to an end surface  145 . It is the side wall  143  together with the end cap  121  which define the housing cavity  30   a.    
     Between the skirt  141  and the sidewall  143 , an annular flange  147  extends inwardly providing a proximal facing surface  152  and a distal facing surface  154 . An annular projection  156 , which extends from the flange  147  toward the skirt  141 , will be discussed in greater detail below. 
     The partition structure  130  includes a proximal end wall  161  having a proximal surface  163 . Extending downwardly in FIG. 11 from the end wall  161 , is a partition  165  which has a particular configuration discussed in greater detail below. The partition  165  extends to a bottom surface  167 . Extending upwardly from the surface  163  of the end wall  161  are a plurality of buttons  170  which facilitate a snap fit relationship between the partition structure  130  and the end cap  121 . 
     The valve assembly  46   a  is similar to that previously disclosed in its inclusion of multiple valve sets each having a septum valve which is defined in an end wall  172  having a proximal surface  174 . Extending downwardly in FIG. 11 from the end wall  172  is a sidewall  176  and an inwardly extending shoulder  178  having a distal facing surface  181 . A cylindrical annulus  183  extends axially from the shoulder  178  to a distally facing surface  187 . This surface  187  is extended radially outwardly by a flange  185 . 
     The end cap  121  has a generally planar configuration defined by a wall  190  having a distally facing surface  192 . Extending upwardly from the wall  190  are a plurality of cylinders  194  and  196  which aid in aligning the instruments and protecting the septum valve formed in the end wall  172  of the valve assembly  46   a . Extending downwardly in FIG. 11 from the end wall  190  is an annulus  198  which functions to prevent deformation of the zero closure valve. Also extending downwardly from the end wall  190  are a plurality of male components  197  which register with the female projections  170  in a snap fit relationship. 
     These various components of FIG. 11 are also illustrated in the assembled view of FIG.  12 . Of particular interest in this view are the relationships among the flange  185  of the valve assembly  46   a , the flange  147  of the housing  23   a , and the surface  138  of the cannula  12   a . In this construction, the flange  185  is sandwiched between the surface  138  of the cannula  12   a  and the surface  154  of the flange  147 . It is this combination which automatically forms a seal between the valve assembly  46   a , the housing  23   a  and the cannula  12   a . The seal is enhanced by the projection  156  on the flange  147  which increases the sealing relationship between the flange  147  and the elastomeric flange  185 . 
     The interrelationships of the various components of the trocar  10  can be best understood with reference to the assembled view of FIG.  12 . Initially a subassembly can be formed between the end cap  121 , the valve assembly  46   a  and the partition structure  130 . In the preferred method of assembly the partition structure  130  is inserted through the opening at the bottom of the valve assembly  46   a  where the partition  165  extends around the zero closure valves of the assembly. The proximal end wall  161  of the structure  130  is brought into contact with the end wall  172  of the valve assembly  46   a . With the projections  170  of the structure  130  extending through concentric holes in the end wall  172 . 
     With the partition structure  130  operatively positioned within the valve assembly  46   a , the end cap  121  can be moved into position over the top of the valve structure  46   a . In this step, the projections  197  of the end cap  121  extend into the buttons  170  associated with the partition structure  130  preferrably in a snap fit relationship. This snap fit completes the subassembly by maintaining the end wall  190  of the end cap  121 , the end wall  172  of the valve assembly  46   a , and the end wall  161  of the partition structure  130  in a generally fixed relationship. The resulting top view of the subassembly is best illustrated in FIG.  4 . In this view, the valve sets are not shown in detail, but nevertheless are represented by their reference numerals  52   a ,  54   a  and  56   a.    
     The subassembly including the end wall  121 , the valve assembly  46   a , and the partition structure  130  can then be mounted in the housing  23   a . This is accomplished in the preferred method by introducing the end of the subassembly including the structure  130  into the top of the housing  23   a  until the surface  192  of the end wall  190  on the end cap  121  is brought into contact with the proximal surface  145  of the side wall  143 . Since the end wall  190  is larger in diameter than the hole at the proximal end of the housing  23   a , the end cap  121  cannot pass further into the housing cavity  30   a.    
     A particularly advantageous feature of the present invention biases the end cap  121  in this sliding contact relationship with the surface  145  of the housing  23 . This bias is obtained by stretching or tensioning the side walls  176  of the valve assembly  46   a . With the end cap  121  fixed axially in the proximal direction, the stretched configuration of the sidewalls  176  can be maintained by fixing the distal end of the valve assembly  46   a  axially in the distal direction with the sidewall  176  stretched therebetween. In a preferred embodiment the distal end is fixed by fitting the outwardly extending annular flange  185  of the valve assembly  46   a  over the inwardly extending annular flange  147  associated with the housing  32   a . In this step, the distally facing surface  181  of the valve assembly  46   a  is also brought into contact with the proximal facing surface  152  of the housing  23   a . The interlocking relationship of the flange  147  and  185  is assisted by the projection  156  on the annular flange  147  and a similar projection on the flange  185 . 
     To further maintain the fixed relationship of the flanges  185  and  147 , the cannula  12   a  can be introduced distally into the channel defined by the skirt  141 . This brings the proximal surface  138  of the cannula  12   a  into abutting relationship with the distally facing surface  187  of the valve assembly  46   a . It also sandwiches the elastomeric flange  185  between the surface  154  of the flange  147  and the surface  138  of the cannula  12   a . This not only maintains the elastomeric flange  185  in a fixed relationship with the housing  23   a  and cannula  12   a , but also enhances formation of seals between these adjacent elements. As previously discussed, the cannula  12   a  can be held in its operative position by a quick disconnect structure such as the bayonet fitting formed between the tabs  132  and slots  134 . 
     Once the trocar  10  has been assembled, the operative features of the concept become readily apparent. One of these features has to do with the floating relationship between the seal sets, such as the set  54   a  and  56   a  illustrated in FIG.  13 . This floating of the seal sets in order to accommodate the off-axis insertion of instruments was disclosed by Ritchart et al in U.S. Pat. No. 5,209,737. 
     In the embodiment of FIG. 13, floating of the seal sets  54   a  and  56   a  is facilitated by permitting the end cap  121  to move transverse to the axis  21   a  in sliding engagement with the side wall  143  of the housing  23   a . While this floating movement of the end cap  121  could be accomplished in enlarged recess, as taught by Ritchart et al, the size of the housing  23   a  can be reduced if the end cap  121  is permitted to define the largest diameter of the trocar  10  at its proximal end. In this case, the outside diameter of the side wall  143  of the housing  23   a  does not exceed the diameter of the end cap  121 . 
     While the end cap  121  is permitted to float laterally or radially of the housing  23   a , this float must be limited in order to protect the valve sets  54   a ,  56   a . In the illustrated embodiment, this protection is afforded by the annulus  98  which extends into the valve cavity  30   a . As the end cap  121  moves laterally, the annulus  198  approaches the sidewall  143  and eventually reaches a point of interference where the end cap  121  cannot be further laterally displaced. Thus the annulus  198  ensures that operation of the seals  54   a  and  56   a  is not inhibited by extensive lateral movement of the end wall  121 . 
     The medium seal set  54   a  (including the septum valve  67   a  and zero closure valve  70   a ) and the large seal set (including the septum valve  61   a  and zero closure valve  63   a  may also benefit from additional isolation. In a typical situation, an instrument will be inserted through one of the seal sets, such as the set  54   a , where the associated septum valve forms a seal with the instrument. In this particular valve set, the zero closure valve  70   a  will be open and non-sealing as long as the instrument is in place. The concern at this point is with the operation of the zero closure valve  63   a  associated with the other valve set. If the instrument is allowed to tilt or is otherwise brought into contact with the zero closure valve  63   a , associated with the other valve set  56   a , that valve  63   a  can be deformed resulting in leaking of the insufflation gas. 
     To prevent this leakage and deformation, it is desirable to isolate the zero closure valves  63   a  and  70   a  to some extent, from each other. This is the function of the partition  165  in the structure  130 . This partition  165  extends generally around each of the zero closure valves  63   a  and  70   a  associated with the valve sets  56   a  and  54   a , respectively. When these zero closure valves  63   a  and  70   a  are formed in close proximity to each other for example with their respective axes separated by less than the sum of their radii, the partition  165  may be slightly broken immediately between the zero closure valves  63   a  and  70   a . In this case, the partition  165  forms a continuous curtain around the valve sets  54   a  and  56   a  typically in the shape of a figure eight as best illustrated in FIG.  15 . 
     From the foregoing discussion it is apparent that the trocar  10  of this invention can accommodate all sizes of instruments from the smallest instrument, such as the catheter  48 , to the largest instrument, such as the obturator  50 , which can pass through the associated cannula  12 . Multiple septum valves  58 ,  67  and  61  can be formed in any transverse wall disposed interiorly of the valve housing  23  or at the end wall  38  of the elastomeric housing portion  27 . These septum valves  58 ,  67  and  61  can be formed at different distances from the central axis  21  in the manner previously discussed. For each of the larger valve sets, for example the medium valve set  54   a  and large valve set  56   a , a zero closure valve may be required. These valves, such as the zero closure valves  70   a  and  63   a , can be provided in any form associated with the prior art. Double duck bill valves such as those illustrated in FIGS. 1-7 are particularly appropriate for this concept. However, a separate flapper valve, such as those designated by the reference numerals 107 and 109 in FIGS. 8 and 9 can be provided for the respective valve sets  54  and  56 . 
     In a particularly desirable embodiment, the end cap  121  can be formed in sliding engagement with the housing  23   a . This embodiment is enhanced by the small size of the housing  23   a  which is not greater than the diameter of the end cap  121 . The valve assembly  46   a  can be stretched to maintain the end cap  121  in sliding engagement with the housing  23   a . The annulus  98  can be formed to uniformly limit the lateral displacement of the end cap  121  relative to the housing  23   a . The partition  165  further protects the zero closure valves  63   a  and  70   a  from interference due to operation of an adjacent valve set. The modular concept permits the cannula  12   a  to be separated from the housing  23   a  while at the same time providing a quick disconnect fitting which will function to enhance the seal between the valve assembly  46   a  and the housing  23   a.    
     Given these wide variations, which are all within the scope of this concept, one is cautioned not to restrict the invention to the embodiments which have been specifically disclosed and illustrated, but rather encouraged to determine the scope of the invention only with reference to the following claims.