Abstract:
Seal assemblies are provided, comprising a seal holder including a cylindrical wall portion having a tapered distal portion, wherein the cylindrical wall portion defines a central passage. The seal assembly comprises a ball seal supported in the central passage of the seal holder. The ball seal includes a distal aperture and a proximal aperture, wherein the distal and/or proximal aperture is dimensioned for substantial sealed reception with a surgical instrument. The ball seal is adapted for angular movement relative to a central longitudinal axis of the seal holder upon angulation of the surgical instrument, whereby the ball seal substantially maintains the seal with the surgical instrument. The seal assembly comprises a seal cover defining an aperture formed in a transverse wall thereof. The seal cover is configured for connection with the seal holder for maintaining the ball seal within the central passage of the seal holder.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to seal assemblies adapted to permit the introduction of surgical instrumentation into a patient&#39;s body and, more particularly, to seal assemblies for use with an introducer which is intended for insertion into a patient&#39;s body, and for receiving an instrument in sealing engagement therewith. 
     2. Description of Related Art 
     Minimally invasive and laparoscopic procedures generally require that any instrumentation inserted into the body be sealed, e.g., provisions are made to ensure that gases and/or fluids do not enter or exit the body through an endoscopic incision, such as, for example in surgical procedures where the surgical region is insufflated. For such procedures, the introduction of a tube into anatomical cavities, such as the peritoneal cavity, is usually accomplished by use of a system incorporating a trocar and cannula assembly. Since the cannula is in direct communication with the interior of the peritoneal cavity, insertion of the cannula into an opening in the patient&#39;s body to reach the inner abdominal cavity may be adapted to maintain a fluid tight interface between the abdominal cavity and the outside atmosphere. In view of the desire to maintain the atmospheric integrity of the inner area of the cavity, a seal assembly for a cannula, which permits introduction of a wide range of surgical instrumentation and maintains the atmospheric integrity of the inner area of the cavity is desirable. In this regard, there have been a number of attempts in the prior art to achieve such sealing requirements. A difficulty encountered with conventional seal assemblies, however, is the inability of accommodating the wide range of sizes of instrumentation. In addition, angulation and/or manipulation of instrumentation within the cannula often present difficulties with respect to maintaining seal integrity. 
     SUMMARY 
     Accordingly, the present disclosure provides a surgical seal assembly for use with a surgical access device. The seal assembly comprises a seal holder including a cylindrical wall portion having a tapered distal portion, wherein the cylindrical wall portion defines a central passage dimensioned to permit passage of a surgical instrument through the seal holder. The seal assembly further comprises a ball seal supported in the central passage of the seal holder. The ball seal includes a distal aperture and a proximal aperture, wherein at least one of the distal and proximal aperture is dimensioned for substantial sealed reception of the surgical instrument. The ball seal is adapted for angular movement relative to a central longitudinal axis of the seal holder upon angulation of the surgical instrument, whereby the ball seal substantially maintains the seal with the surgical instrument. The seal assembly further comprises a seal cover defining an aperture formed in a transverse wall thereof. The seal cover is configured for connection with the seal holder for maintaining the ball seal within the central passage of the seal holder, wherein the proximal aperture of the ball seal is in registration with the aperture of the seal cover. 
     The ball seal may be fabricated from at least one of a substantially elastomeric and substantially resilient material. The ball seal may create a seal against a surface of the seal holder during passage of the surgical instrument through the seal holder in a first direction. The ball seal may create a seal against a surface of the seal cover during passage of the surgical instrument through the seal holder in a second direction. 
     The proximal aperture of the ball seal may be larger than the distal aperture of the ball seal. The seal cover may include a cylindrical wall extending from the transverse wall and being configured for positioning in the proximal aperture of the ball seal. The seal cover may further include a sloped portion between the transverse wall and the cylindrical wall. 
     The distal aperture of the ball seal may be larger than the proximal aperture of the ball seal. The seal holder may include a cylindrical inner wall portion extending proximally from a distal edge of the tapered portion and may be configured for positioning in the distal aperture of the ball seal. 
     The ball seal may be substantially spherical. 
     According to another aspect of the present disclosure, a surgical access device is provided. The surgical access device includes a cannula assembly having a sleeve defining a lumen and supporting a closure valve at a proximal end thereof; and a seal assembly supported at a proximal end of the cannula assembly. 
     The seal assembly comprises a seal holder including a cylindrical wall portion having a tapered distal portion, wherein the cylindrical wall portion defines a central passage dimensioned to permit passage of a surgical instrument through the seal holder and into the lumen of the cannula assembly. The seal assembly further comprises a ball seal supported in the central passage of the seal holder. The ball seal includes a distal aperture and a proximal aperture, wherein at least one of the distal and proximal aperture is dimensioned for substantial sealed reception of the surgical instrument. The ball seal is adapted for angular movement relative to a central longitudinal axis of the seal holder upon angulation of the surgical instrument, whereby the ball seal substantially maintains the seal with the surgical instrument. The seal assembly further comprises a seal cover defining an aperture formed in a transverse wall thereof. The seal cover is configured for connection with the seal holder for maintaining the ball seal within the central passage of the seal holder, wherein the proximal aperture of the ball seal is in registration with the aperture of the seal cover. 
     The cannula assembly may include a cannula housing supported on a proximal end of the sleeve. The cannula housing may be configured to support the closure valve therein and is configured to selectively engage the seal assembly. 
     The cannula housing may include a port opening formed therein and is configured for operative receipt of a luer fitting therein. 
     According to another aspect of the present disclosure, a surgical seal assembly for use with a surgical access device is provided. The seal assembly may include a cannula assembly including a cannula sleeve defining a central passage dimensioned to permit passage of a surgical instrument through the cannula sleeve; and a substantially spherical seal member defining a proximal opening and a distal opening and a non-cylindrical bore providing communication therethrough between the proximal and distal openings. The substantially spherical seal member may have an outer diameter, and the distal and proximal openings may be smaller than the outer diameter. At least one of the distal and proximal opening may be dimensioned for substantial sealed reception of the surgical instrument. The seal member may be adapted for angular movement relative to a central longitudinal axis of the cannula sleeve upon angulation of the surgical instrument, whereby the seal member substantially maintains the seal with the surgical instrument. 
     According to another aspect of the present disclosure, a surgical seal assembly for use with a surgical access device is provided. The seal assembly may include a cannula assembly including a cannula sleeve defining a central passage dimensioned to permit passage of a surgical instrument through the cannula sleeve; and a substantially spherical seal member having an outer diameter and defining a proximal opening and a distal opening, wherein the distal and proximal openings are smaller than the outer diameter. The seal member may define a non-cylindrical bore providing communication therethrough between the proximal and distal openings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing features of the present disclosure will become more readily apparent and will be better understood by referring to the following detailed description of preferred embodiments, which are described hereinbelow with reference to the drawings wherein: 
         FIGS. 1 and 2  are perspective views of a cannula assembly and a seal assembly in accordance with the principles of the present disclosure; 
         FIG. 3  is a perspective view, with parts separated, of the cannula and seal assemblies of  FIGS. 1 and 2 ; 
         FIG. 4  is a longitudinal, cross-sectional view of the cannula and seal assemblies of  FIGS. 1 and 2 , as taken through  4 - 4  of  FIG. 2 ; 
         FIG. 4A  is a longitudinal, cross-sectional view of the cannula and seal assemblies of  FIGS. 1 and 2 , as taken through  4 - 4  of  FIG. 2  with an instrument being inserted therein and with a ball seal of the seal assembly being shown in a distal position; 
         FIG. 4B  is a longitudinal, cross-sectional view of the cannula and seal assemblies of  FIGS. 1 and 2 , as taken through  4 - 4  of  FIG. 2  with the instrument being withdrawn therefrom and the ball seal of the seal assembly being shown in a proximal position; 
         FIG. 5  is a longitudinal, cross-sectional view of the cannula and seal assemblies of  FIGS. 1 and 2 , as taken through  5 - 5  of  FIG. 2 ; 
         FIG. 5A  is a longitudinal, cross-sectional view of the cannula and seal assemblies of  FIGS. 1 and 2 , as taken through  5 - 5  of  FIG. 2  with the instrument being inserted therein and with the ball seal of the seal assembly being shown in the distal position; 
         FIG. 5B  is a longitudinal, cross-sectional view of the cannula and seal assemblies of  FIGS. 1 and 2 , as taken through  5 - 5  of  FIG. 2  with the instrument being withdrawn therefrom and the ball seal of the seal assembly being shown in the proximal position; 
         FIG. 6  is a perspective view, with parts separated, of a cannula assembly and a seal assembly according to an alternate embodiment of the present disclosure; 
         FIG. 7  is a longitudinal, cross-sectional view of the cannula and seal assemblies of  FIG. 6 , as taken through  7 - 7  of  FIG. 6 ; 
         FIG. 7A  is a longitudinal, cross-sectional view of the cannula and seal assemblies of  FIG. 6 , as taken through  7 - 7  of  FIG. 6  with an instrument being inserted therein and with a ball seal of the seal assembly being shown in a distal position; 
         FIG. 7B  is a longitudinal, cross-sectional view of the cannula and seal assemblies of  FIG. 6 , as taken through  7 - 7  of  FIG. 6  with the instrument being withdrawn therefrom and the ball seal of the seal assembly being shown in a proximal position; 
         FIG. 8  is a longitudinal, cross-sectional view of the cannula and seal assemblies of  FIG. 6 , as taken through  8 - 8  of  FIG. 6 ; 
         FIG. 8A  is a longitudinal, cross-sectional view of the cannula and seal assemblies of  FIG. 6 , as taken through  8 - 8  of  FIG. 6  with the instrument being inserted therein and with the ball seal of the seal assembly being shown in the distal position; 
         FIG. 8B  is a longitudinal, cross-sectional view of the cannula and seal assemblies of  FIG. 6 , as taken through  8 - 8  of  FIG. 6  with the instrument being withdrawn therefrom and the ball seal of the seal assembly being shown in the proximal position; 
         FIG. 9  is a schematic, longitudinal, cross-sectional view of a cannula assembly and a seal assembly according to another embodiment of the present disclosure; and 
         FIG. 10  is a longitudinal, cross-sectional view of a ball seal in accordance with another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The seal assembly of the present disclosure, either alone or in combination with a seal system internal to a cannula assembly, provides a substantial seal between a body cavity of a patient and the outside atmosphere before, during and after insertion of an instrument through the cannula assembly. Moreover, the seal assembly of the present invention is capable of accommodating instruments of varying diameters, e.g., from about 5 mm to about 15 mm, by providing a gas tight seal with each instrument when inserted. The flexibility of the present seal assembly greatly facilitates endoscopic surgery where a variety of instruments having differing diameters are often needed during a single surgical procedure. 
     The seal assembly contemplates the introduction and manipulation of various types of instrumentation adapted for insertion through a trocar and/or cannula assembly while maintaining a fluid tight interface about the instrumentation to preserve the atmospheric integrity of a surgical procedure from gas and/or fluid leakage. Specifically, the seal assembly accommodates angular manipulation of the surgical instrument relative to the seal housing axis. This feature of the present disclosure desirably minimizes the entry and exit of gases and/or fluids to/from the body cavity. Examples of instrumentation include clip appliers, graspers, dissectors, retractors, staplers, laser probes, photographic devices, endoscopes and laparoscopes, tubes, and the like. Such instruments will be collectively referred to herein as “instruments or instrumentation”. 
     By virtue of its features, the seal assembly further defines a substantially reduced profile when assembled together and mounted to a cannula assembly. This reduced profile advantageously increases the working length of instruments introduced into the body cavity through the cannula assembly. In addition, the reduced profile permits enhanced angulation of a surgical instrument relative to the seal housing axis. 
     In the following description, as is traditional the term “proximal” refers to the portion of the instrument closest to the operator while the term “distal” refers to the portion of the instrument remote from the operator. 
     Referring now to the drawings, in which like reference numerals identify identical or substantially similar parts throughout the several views,  FIGS. 1-5  illustrate the seal assembly  100  of the present disclosure mounted to cannula assembly  200 . Cannula assembly  200  may be any conventional cannula suitable for the intended purpose of accessing a body cavity and permit introduction of instruments therethrough. Cannula assembly  200  is particularly adapted for use in laparoscopic surgery where the peritoneal cavity is insufflated with a suitable gas, e.g., CO 2 , to raise the cavity wall from the internal organs therein. Cannula assembly  200  is typically used with an obturator assembly (not shown) which is a sharp pointed instrument positionable within the passageway of the cannula assembly  200 . The obturator assembly is utilized to penetrate the abdominal wall and then subsequently removed from the cannula assembly  200  to permit introduction of the surgical instrumentation utilized to perform the procedure. 
     With reference to  FIGS. 1-5B , cannula assembly  200  includes cannula sleeve  202  and cannula housing  204  mounted to an end of the sleeve  202 . Any suitable means, known in the art, for mounting cannula sleeve  202  to cannula housing  204  are envisioned including threaded arrangements, bayonet coupling, snap-fit arrangements, adhesives, etc. Cannula sleeve  202  and cannula housing  204  may be integrally formed. Cannula sleeve  202  defines a longitudinal “X 1 ” axis extending along the length of sleeve  202 . Sleeve  202  further defines an internal longitudinal lumen passage  206  dimensioned to permit passage of surgical instrumentation therethrough. 
     Adjacent a distal end of cannula sleeve  202  is formed an aperture  212  which extends through the wall of sleeve  202  and is in fluid communication with lumen  206  of sleeve  202 . Aperture  212  permits passage of insufflation gases through cannula sleeve  202  during the surgical procedure. 
     Sleeve  202  may be formed of stainless steel or other rigid materials such as a polymeric material or the like. Sleeve  202  may be clear or opaque. The diameter of sleeve  202  may vary, but, typically ranges from about 10 mm to about 15 mm for use with the seal assembly  100  of the present disclosure. 
     Cannula housing  204  includes port opening  214  ( FIG. 3 ) and luer fitting  216  positioned within the port opening  214 . Luer fitting  216  is adapted for connection to a supply of insufflation gaseous is conventional in the art and incorporates valve  218  to selectively open and close the passage of the luer fitting  216 . 
     Cannula housing  204  may include and supports a housing insert  210  therewithin. Housing insert  210  defines a stem  210   a  extending therefrom and configured for insertion or placement within port opening  214  of cannula housing  204 . 
     Cannula housing  204  further includes and supports duckbill or zero closure valve  220  configured for positioning within housing insert  210 . Closure valve  220  tapers distally and inwardly to a sealed configuration. Closure valve  220  defines a slit  222  which opens to permit passage of the surgical instrumentation and closes in the absence of the instrumentation. Closure valve  220  is preferably adapted to close upon exposure to the forces exerted by the insufflation gases in the internal cavity. Other zero closure valves are also contemplated including single or multiple slit valve arrangements, trumpet valves, flapper valves, etc. Closure valve  220  rests upon an internal shelf  210   b  of housing insert  210  when assembled. 
     With continued reference to  FIGS. 1-5B , seal assembly  100  will be discussed in detail. Seal assembly  100  may be a separate component from cannula assembly  200  and, accordingly, adapted for releasable connection to the cannula assembly  200 . Alternatively, seal assembly  100  may be incorporated as part of cannula assembly  200 . 
     Seal assembly  100  includes a seal housing or holder  110 , a ball seal  120 , and a seal cover  130 . Seal assembly  100  defines central seal axis “X 2 ” which is preferably parallel to the axis “X 1 ” of cannula sleeve  202  and, more specifically, coincident with the axis “X 1 ” of the cannula sleeve  202 . 
     Seal housing or holder  110  includes a cylindrical wall portion  112  having a tapered distal portion  114  and a transverse annular wall or flange  116  extending from a proximal end thereof. Seal holder  110  defines central passage  118  which is dimensioned to receive a surgical instrument and laterally confine ball seal  120 . 
     As best shown in  FIGS. 4 and 5 , tapered distal portion  114  is obliquely arranged relative to seal holder axis “X 2 ” and extends radially inwardly relative thereto in a distal direction. Tapered distal portion  114  assists in creating a seal in combination with ball seal  120 , when the instrument is introduced into cannula assembly  200 , as will be discussed in greater detail below. 
     Ball seal  120  has a substantially spherical profile and includes a distal aperture  122  and a proximal aperture  124 . Distal aperture  122  has a diameter which is relatively smaller than proximal aperture  124 . Ball seal  120  has a diameter substantially equal or smaller than a diameter of cylindrical wall portion  112  of seal holder  110  such that ball seal  120  may be seated within central passage  118  of seal holder  110 . Distal aperture  122  and proximal aperture  124  may share a common central axis. 
     Ball seal  120  may be fabricated from a suitable resilient and/or elastomeric material, such as, for example, natural rubber, polyisoprene. 
     Seal cover  130  includes a transverse wall  132 , a cylindrical wall  134  depending in a distal direction from transverse wall  132  and defining a central lumen or passage  136 . Seal cover  130  defines a sloped or angled portion  138  between transverse wall  132  and cylindrical wall  134 . Cylindrical wall  134  is dimensioned for receipt within proximal aperture  124  of ball seal  120 . Cylindrical wall  134  is further dimensioned such that a distal edge thereof terminates at a location proximal of a distal edge of seal holder  110 . 
     Sloped portion  138  is obliquely arranged relative to seal housing axis “X 2 ” and extends radially inwardly relative to the seal holder axis “X 2 ” in the distal direction. Sloped portion  138  assists in guiding the inserted instrument into lumen  206  of cannula assembly  200 , particularly, when the instrument is non-aligned or off-axis relative to the seal holder axis “X 2 ”, or introduced at an angle relative to the seal holder axis “X 2 ”. Sloped portion  138  provides more flexibility to the surgeon by removing the necessity that the instrument be substantially aligned with the seal holder axis “X 2 ” upon insertion. 
     Seal cover  130  may include an outer wall  139  configured for selective engagement with cannula housing  204  in order to secure seal assembly  100  to cannula assembly  200 . 
     When seal assembly  100  is assembled, ball seal  120  of seal assembly  100  is interposed between seal holder  110  and seal cover  130 . In particular, ball seal  120  is slidably and rotatably interposed between seal holder  110  and seal cover  130  so as to translate in an axial direction and rotate about longitudinal axis “X 1 , X 2 ”. In particular, ball seal  120  may translate distally to a distal position in response to insertion of an instrument “I” through the seal assembly  100  such that ball seal  120  contacts seal holder  110  and forms two annular seals therewith. As best shown in  FIGS. 4A and 5A , ball seal  120  engages the tapered distal portion  114  of seal holder  110  at annular contact point CP 1  and engages cylindrical wall portion  112  at annular contact point CP 2 . Annular contact points CP 1  and CP 2  are merely illustrative of the specific points of the annular seals that ball seal  120  engages in the respective cross-sectional views shown by  FIGS. 4A and 5A . Nonetheless, ball seal  120  engages the seal holder  110  such that ball seal  120  is in circumferential contact with the seal holder  110  at a plurality of annular contact points that form the annular seals described above. 
     With continued reference to  FIG. 4A , in use and during insertion into cannula assembly  200  of an instrument having a diameter greater than the diameter of distal aperture  122  of ball seal  120 , as the instrument “I” is inserted into and through central lumen  136  of seal cover  130 , the instrument “I” passes through distal aperture  122  of ball seal  120 . The frictional force or resistance of ball seal  120  along the outer surface of the instrument “I”, as the instrument “I” is advanced into lumen  206  of cannula assembly  200 , causes ball seal  120  to translate distally and contact or seal against a surface of seal holder  110 , e.g., against an inner surface of tapered distal portion  114  of seal holder  110 , as seen in  FIGS. 4A and 5A  and as discussed above. 
     Further and during withdrawal of the instrument “I” from cannula assembly  200 , the frictional force or resistance of ball seal  120  along the outer surface of the instrument “I” as the instrument “I” is withdrawn from lumen  206  of cannula assembly  200  causes ball seal  120  to translate proximally to a proximal position where ball seal  120  contacts or seals against a surface of seal cover  130 , e.g., against an inner surface of transverse wall  132  and/or against a distal edge of cylindrical wall  134 , and/or against a surface of seal holder  110 , e.g., against cylindrical wall portion  112  of seal holder  110 . In this manner, ball seal  120  forms an annular seal with seal cover  130  and an annular seal with seal holder  110 . As best shown in  FIGS. 4B and 5B , ball seal  120  engages the inner surface of transverse wall  132  and/or against a distal edge of cylindrical wall  134  at annular contact point CP 3  and engages cylindrical wall portion  112  of seal holder  110  at annular contact point CP 4 . Annular contact points CP 3  and CP 4  are merely illustrative of the specific points of the annular seals that ball seal  120  engages in the respective cross-sectional views shown by  FIGS. 4B and 5B . Nonetheless, ball seal  120  engages seal cover  130  and seal holder  110  such that ball seal  120  is in circumferential contact with seal cover  130  and seal holder  110 . In this respect, ball seal  120  is in circumferential contact at a plurality of annular contact points that form the annular seals described above. 
     Turning now to  FIGS. 6-8B , a seal assembly, according to an alternate embodiment of the present disclosure, for use with cannula assembly  200  is generally designated as  300 . Seal assembly  300  is substantially similar to seal assembly  100  and thus will only be discussed in detail herein to the extent necessary to identify differences in construction and operation thereof. 
     Seal assembly  300  includes a seal housing or holder  310 , a ball seal  320 , and a seal cover  330 . 
     Seal housing or holder  310  includes a cylindrical outer wall portion  312   a  having a tapered distal portion  314 , a cylindrical inner wall portion  312   b  extending proximally from a distal end of tapered distal portion  314 , and a transverse annular wall or flange  316  extending from a proximal end thereof. Seal holder  310  defines central passage  318  which is dimensioned to receive a surgical instrument and laterally confine ball seal  320 . Cylindrical inner wall portion  312   b  terminates in a free proximal end or edge. 
     As best shown in  FIGS. 7 and 8 , tapered distal portion  314  is obliquely arranged relative to seal holder axis “X 2 ” and extends radially inwardly relative thereto in a distal direction. Tapered distal portion  314  assists in creating a seal in combination with ball seal  320 , when the instrument is introduced into cannula assembly  200 , as will be discussed in greater detail below. 
     Ball seal  320  has a substantially spherical profile and includes a distal aperture  322  and a proximal aperture  324 . Distal aperture  322  has a diameter which is relatively larger than proximal aperture  324 . Distal aperture  322  is dimensioned so as to receive cylindrical inner wall portion  318   a  of seal holder  310  therewithin. 
     Ball seal  320  has a diameter substantially equal to or smaller than a diameter of cylindrical outer wall portion  312   a  of seal holder  310  such that ball seal  320  may be seated within a space defined between cylindrical outer wall portion  312   a  and cylindrical inner wall portion  312   b  of seal holder  310 . Distal aperture  322  and proximal aperture  324  of ball seal  320  may share a common central axis. 
     Seal cover  330  includes a transverse wall  332  defining a central opening  336 . Seal cover  330  may included an outer wall  339  configured for selective engagement with cannula housing  204  in order to secure seal assembly  300  to cannula assembly  200 . 
     When seal assembly  300  is assembled, ball seal  320  of seal assembly  300  is interposed between seal holder  310  and seal cover  330 . In particular, ball seal  320  is slidably and rotatably interposed between seal holder  310  and seal cover  330  so as to translate in an axial direction and rotate about longitudinal axis “X 1 , X 2 ”. In particular, ball seal  320  may translate distally to a distal position in response to insertion of an instrument “I” through the seal assembly  300  such that ball seal  320  contacts seal holder  310  and forms two annular seals therewith. As best shown in  FIGS. 7A and 8A , ball seal  320  engages the tapered distal portion  314  of seal holder  310  at annular contact point CP 1  and engages cylindrical wall portion  312  at annular contact point CP 2 . Annular contact points CP 1  and CP 2  are merely illustrative of the specific points of the annular seals that ball seal  320  engages in the respective cross-sectional views shown by  FIGS. 7A and 8A . Nonetheless, ball seal  320  engages the seal holder  310  such that ball seal  320  is in circumferential contact with the seal holder  310  at a plurality of annular contact points that form the annular seals described above. 
     With continued reference to  FIG. 7A , in use and during insertion into cannula assembly  200  of an instrument, having a diameter greater than the diameter of proximal aperture  324  of ball seal  320 , as the instrument “I” is inserted into and through central opening  336  of seal cover  330 , the instrument “I” passes through proximal aperture  324  of ball seal  320 . The frictional force or resistance of ball seal  320  along the outer surface of the instrument “I”, as the instrument “I” is advanced into lumen  206  of cannula assembly  200 , causes ball seal  320  to translate distally and contact or seal against at least one surface of seal holder  310 , e.g., against an inner surface of tapered distal portion  314  of seal holder  310  and/or against an inner surface of cylindrical outer wall portion  312   a , as seen in  FIGS. 7A and 8A  and as discussed above. 
     Further and during withdrawal of the instrument “I” from cannula assembly  200 , the frictional force or resistance of ball seal  320  along the outer surface of the instrument “I”, as the instrument “I” is withdrawn from lumen  206  of cannula assembly  200 , causes ball seal  320  to translate proximally to a proximal position where ball seal  320  contacts or seals against a surface of seal cover  330 , e.g., against an inner surface of transverse wall  332 , and/or against a surface of seal holder  310 , e.g., against cylindrical wall portion  312  of seal holder  310 . In this manner, ball seal  320  forms an annular seal with seal cover  330  and an annular seal with seal holder  310 . As best shown in  FIGS. 7B and 8B , ball seal  320  engages the inner surface of transverse wall  332  and/or against a distal edge of cylindrical wall  334  at annular contact point CP 3  and engages cylindrical wall portion  312  of seal holder  310  at annular contact point CP 4 . Annular contact points CP 3  and CP 4  are merely illustrative of the specific points of the annular seals that ball seal  320  engages in the respective cross-sectional views shown by  FIGS. 7B and 8B . Nonetheless, ball seal  320  engages seal cover  330  and seal holder  310  such that ball seal  320  is in circumferential contact with seal cover  330  and seal holder  310 . In this respect, ball seal  120  is in circumferential contact at a plurality of annular contact points that form the annular seals described above. 
     Turning now to  FIG. 9 , a seal assembly, according to an alternate embodiment of the present disclosure, for use with cannula assembly  200  is generally designated as  400 . Seal assembly  400  is substantially similar to seal assembly  100  and thus will only be discussed in detail herein to the extent necessary to identify differences in construction and operation thereof. 
     Seal assembly  400  includes a seal lower housing  410 , a ball seal  420 , and a seal upper housing  430 . Seal lower housing  410  includes a substantially hemispherical recess  411  formed therein. Seal lower housing  410  is configured for support on an end of sleeve  202  of cannula assembly  200 , at a location above or proximal of closure valve  220 . 
     Ball seal  420  has a substantially spherical profile and includes a distal aperture  422  and a proximal aperture  424 . Distal aperture  422  has a diameter which is different than proximal aperture  424 . As seen in  FIG. 9 , distal aperture  422  of ball seal  420  may be relatively larger than proximal aperture  424  of ball seal  420 . Ball seal  420  defines a hollow cavity, chamber or the like  426 . 
     Seal upper housing  430  includes a transverse wall  432  defining a central opening  436  therein that extends into a substantially hemispherical recess  431 . Central opening  436  of seal upper housing  430  is in registration with proximal aperture  424  of ball seal  420 . Seal upper housing  430  is configured for connection with seal lower housing  410  such that hemispherical recess  431  thereof is in registration with hemispherical recess  411  of seal lower housing  410 . 
     When seal assembly  400  is assembled, ball seal  420  of seal assembly  400  is interposed between seal lower housing  410  and seal upper housing  430 . In particular, ball seal  420  is slidably and rotatably seated within hemispherical recesses  411  and  431  of seal lower housing  410  and seal upper housing  430  so as to translate in an axial direction and rotate about longitudinal axis. 
     In use and during insertion into cannula assembly  200  of an instrument having a diameter greater than the diameter of proximal aperture  424  of ball seal  420 , as the instrument is inserted into and through central aperture  436  of seal upper housing  430 , the instrument passes through proximal aperture  424  of ball seal  420 . The frictional force or resistance of ball seal  420  along the outer surface of the instrument, as the instrument is advanced into lumen  206  of cannula assembly  200 , causes ball seal  420  to contact or seal against at least one surface of seal lower housing  410 , e.g., against an inner surface of hemispherical recess  411  of seal lower housing  410 . 
     Further, during withdrawal of the instrument from cannula assembly  200 , the frictional force or resistance of ball seal  420  along the outer surface of the instrument, as the instrument is withdrawn from lumen  206  of cannula assembly  200 , causes ball seal  420  to contact or seal against a surface of seal upper housing  430 , e.g., against an inner surface of hemispherical recess  431  of seal upper housing  430 . 
     Turning now to  FIG. 10 , a ball seal, according to an alternate embodiment of the present disclosure, for use with cannula assembly  200  and with either seal assembly  100 ,  200 , is generally designated as  520 . 
     Ball seal  520  may have a substantially spherical profile and defines a bore  521  therein. Bore  521  defines a central longitudinal axis “X” and includes a first aperture  522 . Bore  521  terminates at an end wall  523  defining a second aperture  524  therein. First aperture  522  has a diameter “D 1 ” which is relatively larger than a diameter “D 2 ” of second aperture  524 . First aperture  522  and second aperture  524  may share a common central axis co-incident with the central longitudinal “X” axis. 
     Ball seal  520  is configured and dimensioned such that a maximum thickness “D 3 ” of ball seal  520 , which defines the dimensions of bore  521 , is relatively larger than a thickness “D 4 ” of end wall  523 . It is contemplated that diameter “D 1 ” of bore  521  is selected so as to receive cylindrical wall  134  of seal cover  130  (see  FIGS. 3-5 ) when ball seal  520  is in a first orientation, or to receive cylindrical inner wall portion  312   b  of seal holder  310  (see  FIGS. 6-8 ) when ball seal  520  is in a second orientation. It is further contemplated that diameter “D 2 ” of end wall  523  is selected to define an instrument seal. 
     Ball seal  520  may be fabricated from a suitable resilient and/or elastomeric material, such as, for example, natural rubber, polyisoprene. 
     While the invention has been particularly shown, and described with reference to the preferred embodiments, it will be understood by those skilled in the art that various modifications and changes in form and detail may be made therein without departing from the scope and spirit of the invention. Accordingly, modifications such as those suggested above, but not limited thereto, are to be considered within the scope of the invention.