US20080091144A1

US20080091144A1 - Canula sealing apparatus

Info

Publication number: US20080091144A1
Application number: US11/844,430
Authority: US
Inventors: Stuart Moran; Michael White; David Maine
Original assignee: Surgical Innovations Ltd
Current assignee: Surgical Innovations Ltd
Priority date: 2006-08-25
Filing date: 2007-08-24
Publication date: 2008-04-17
Also published as: EP2059180A1; JP2010501313A; ZA200901971B; AU2007287381B2; ATE455508T1; DK2059180T3; GB0705216D0; DE602007004505D1; ES2340219T3; EP2059180B1; US20100022959A1; AU2007287381A1; BRPI0715945A2; US8231579B2; GB0616816D0; GB2441113A; JP5162590B2; WO2008023200A1

Abstract

Cannula sealing apparatus includes a housing having a central axially facing aperture. A surgical instrument of 10.5 mm may seal with that aperture. Alternatively, a sealing member having an aperture that will seal with a 12 mm surgical instrument can be swung up to be aligned with the aperture. If a 10.5 mm instrument is required then a seal member can be swung up to have its seal aperture located over the central aperture. Each seal member is pivotal about a common axis. Each seal member has a surface that faces a housing such that both parts can seal at their facing surfaces when either of the seal members are swung up into the position where the opening is over the central opening.

Description

TECHNICAL FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to cannula sealing apparatus and methods of using cannula sealing apparatus. The present invention is particularly suited to such apparatus where surgical instruments of different sizes are required to be sealed with the same cannula sealing apparatus.
U.S. Pat. No. 5,512,053 describes a surgical cannula with a slidable reducer assembly to sealingly accommodate surgical instruments. The reducer assembly consists of multiple apertures having varying diameters such that the assembly can slide to selectively accommodate the exterior of surgical instruments having a variety of outer diameters.
U.S. Pat. No. 5,843,040 discloses a surgical sleeve that includes a housing having an opening through which surgical instruments are introduced into the surgical sleeve. A sleeve portion extends from the housing and has an inner diameter coaxial with the opening in the housing. A reducer assembly is removably secured to the housing and includes a rigid seal for rotation in a plane transverse to the sleeve portion. A resilient, laminar seal layer is generally coextensive with the seal disc and is disposed between the disc and the housing to sealingly engage a portion of the housing. A plurality of apertures are formed in the seal disc and seal layer and have varying diameters to define seals that are selectively movable, by rotation of the seal disc, over the opening in the housing to seal against exteriors of instruments disposed in the sleeve.
U.S. Pat. No. 5,201,714 provides a cannula for laparoscopic surgery wherein the cannula comprises a housing and an elongated tube with a passageway formed within the housing so that laparoscopic instruments may be passed through the housing and the elongated hollow tube into the abdominal cavity of a patient. A pair of rollers are mounted within the housing, the rollers being spring-urged together to close the passageway through the housing when an instrument is withdrawn. A slidable plate having apertures of different sizes are mounted in the housing with the apertures provided with slitted seals therein to close the passageway through the housing. The varying sized apertures in the slidable plate permit laparoscopic instruments of varying diameters to be used and to maintain an effective seal around the instrument.
WO 94 178 444 discloses a seal for use with a surgical instrument to provide a gas tight seal with the instrument having a diameter within a wide range of diameters. The seal comprises a seal body, an instrument seal, and a laterally compliant seal mounting. The seal body includes a bore through which the instrument is passed. The instrument seal extends radially outwards from an instrument port formed in the instrument seal through which the instrument is passed, and also extends axially from the instrument port in the direction opposite to that in which the instrument is passed through the instrument port. The laterally compliant seal mounting mounts the instrument seal to the seal body, forms a gas tight seal between the instrument seal and the seal body, and allows the instrument seal to move freely laterally in response to lateral movement of the instrument.
U.S. Pat. No. 5,607,397 and U.S. Pat. No. 5,569,206 disclose adaptors that can be attached around the cannula handle. The adaptors include a smaller seal that projects to one side of the handle and which can be pivoted over the handle about an axis perpendicular to the elongate axis of the cannula and to one side of that axis.

SUMMARY OF THE INVENTION

It is an object of the present invention to attempt to overcome at least one of the problems associated with the above publications or other problems.
The present invention is defined in the claims appended hereto and elsewhere in the specification.
The opening in the housing may comprise a seal member.
The seal members may be provided on a first part of the apparatus that is detachable from a second part of the apparatus. A valve may be arranged to inhibit a flow of gas in at least one direction when no surgical instrument is being sealed by a seal member. At least one seal member may be arranged to be movable by the instrument of a surgeon.
The resilient seal or seals may include a circular hole for sealing against the instruments.
The pivotable member may include a resilient seal.
According to one embodiment of the invention, engagement of the friction member when the pivotable member moves between the positions, causes the friction member to deform.
According to another embodiment of the invention, when the pivotable member moves from the inoperative position to the operative position, during at least part of that movement, the friction member has no effect.
According to yet another embodiment of the invention, the pivotable member includes a channel spaced from a recess whereby, when moving the pivotable member from the inoperative to the operative position the relative movement causes the pivotable member to first be located in the channel, then frictionally engaging the space between the channel and the recess and then to engage with the recess.
According to yet another embodiment of the invention, the friction member locates in the recess when the pivotable seal is in the useable position.
According to yet another embodiment of the invention, the channel comprises an end section that is ramped so as to initiate deformation of the friction member.
According to yet another embodiment of the invention, the friction member comprises at least one resilient nipple.
According to yet another embodiment of the invention, at least one seal is resilient.
According to yet another embodiment of the invention, at least one resilient seal includes the friction members.
According to yet another embodiment of the invention, the resilient seal includes a circular opening that is supported by an adjacent non-resilient circular support of greater diameter than that of the resilient seal.
According to yet another embodiment of the invention, the circular position is raised.
According to yet another embodiment of the invention, the resilient seal is biased towards the circular support.
According to yet another embodiment of the invention, the distance between the opening of two resilient seals and the opening of their supports is the same.
According to yet another embodiment of the invention, the part that the seal is mounted on includes at least one clip and the removable seal includes at least one corresponding opening that is expandable over the clip, to retain the removable seal on the housing.
According to yet another embodiment of the invention, the housing includes a resilient seal.
According to yet another embodiment of the invention, seal members are used in a cannula instrument.
According to another embodiment of the invention, the cannula sealing apparatus includes a plurality of seal members each having a different sized aperture with which, in use, surgical instruments of different sizes may be inserted in a first direction to seal with a selected seal member. At least one seal member is pivotable from an operative position in which a surgical instrument may, in use, be inserted in the first direction to seal with that member and an inoperative position. The pivot axis of the pivotal movement of the sealing member is in a second direction, transverse to the first direction wherein the pivotal axis of the seal member is arranged, in use, to pass through an inserted surgical instrument.
According to another embodiment of the present invention, a housing of the apparatus includes an opening through which, in use, a surgical instrument may be inserted in the first direction with the seal affected by the seal members being arranged to be in the region of that opening. The pivotal axis of the seal member is spaced from the opening in the housing in a direction extending in the first direction.
According to yet another embodiment of the present invention, at least one seal is resilient and includes a circular opening that is supported by an adjacent non-resilient circular support of greater diameter than that of the resilient seal. The resilient seal is biased towards the circular support.
According to yet another embodiment of the invention, when each pivotable seal member is in the operable position, said pivotable seal member is restricted by a friction member. The frictional member restricts movement of the seal member away from the operable position.
A method of using a cannula sealing apparatus according to the present invention comprises the steps of providing a plurality of seal members each having a different sized aperture with which, in use, a surgical instrument of a different size can be inserted in a first direction to seal with a selected seal member. At least one seal member is pivoted from an operative position in which, a surgical instrument may, in use, be inserted in the first direction to an inoperative position. The seal member is pivoted about an axis extending in a second direction, transverse to the first direction to move between the operative and inoperative positions.
According to another embodiment of the present invention, a second surgical instrument of a different size to the first instrument is moved in the first direction to seal with the seal member of a different size. The seal member is pivoted about an axis extending in a second direction transverse to the first direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be carried into practice in various ways but one embodiment will now be described with reference to the accompanying drawings, in which:—
FIGS. 1, 2 and 3 are perspective views of a cannula sealing apparatus 10 arranged to receive instruments of different sizes;
FIG. 4 is a sectional view through the apparatus, and
FIG. 5 is an exploded view of FIG. 1.
FIG. 6 is a perspective view of the cannula being operated by the instrument.
FIGS. 7 a and 7 b are cross-sectional views of a cannula sealing apparatus 10 according to a second embodiment showing the pivot members in different positions.
FIG. 8 is a perspective view of a housing 28.
FIG. 9 is a top view of a seal for use with the housing shown in FIG. 8.
FIG. 10 is a perspective view of a pivot member for use with the housing shown in FIG. 8.
FIG. 11 is a rear perspective view of a pivot member for use with the housing shown in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS AND BEST MODE

A reusable cannula 14 has an upwardly facing opening 16 in which a valve 18 is located with an outwardly projecting lip 20 on the valve sitting on an upwardly facing annular rim 22. A gas input/output line 24 is connected to the cannula just below the valve 18 and an on/off valve 26 is provided on the line 24.
A single use seal housing 28 is detachably connected to the reusable cannula 14 with a bayonet connection comprising circumferentially spaced projections (not shown) 30 on the housing 28 cooperating with outwardly facing circumferentially spaced recesses 31 on the cannula such that the housing 28 can first be pushed down on the cannula 14 with the projections moving along axially extending recesses and then with the housing 28 being rotated relative to the cannula 14. The projections then move along circumferentially extending recesses until end stops are reached. This locks the housing 28 on the cannula 14. This also traps and seals the lip 20 on the rim 22 with an axially facing annular surface 33 of the housing 28 compressing the resilient lip slightly.
The housing 28 includes a central axially facing aperture 32. Two arcuate seal members 34 and 36 are pivotally mounted on the housing 28 by pivot members 38 at each side. End stops 35 limit pivotal movement in one direction. The pivot members 38 extend perpendicularly to the axis of the cannula 14 and radially to that axis and, from the outside towards the axis they extend first through an arm 42 of the seal member 36 and then through an arm 40 of the seal member 34 and then through the housing 28.
In use, the housing 28 is connected to the cannula 14. A tip 44 of trocar instrument (only the bottom part of which is shown) in FIG. 5 is pushed first through the opening 32 in a first direction then through the valve 18 and then along and through an elongate tube 46 of the instrument to the position shown in FIG. 5. The instrument is then inserted through an opening 32 in the abdominal wall with the trocar instrument expanding that opening 32 and with the exterior of the tube 46 sealing with the abdominal wall opening 32. The periphery of the trocar seals with a sealing element 37 mounted in the opening 32 of the housing 28. Alternatively the trocar can be inserted through the opening 32 when the tube 46 already extends through the abdominal wall.
The on/off valve 26 is opened and gas is supplied through the inlet. This gas flows between the trocar on the tube 46 to inflate the abdominal cavity. Endoscopic operations with any endoscopic instrument including a camera instrument can then be carried out in a well known manner.
When the trocar is withdrawn back through the opening 32 the valve 18 effects a seal such that gas from the abdominal cavity is unable to escape.
The opening 32 also comprises a seal member 37 in addition to the pivoting seal members 34 and 36. Each seal member includes a membrane (not shown) that extends inwardly and that is resilient such that the trocar is able to seal with that opening 32. Whilst the description so far has been in relation to trocar instruments it will be appreciated that any instrument used in endoscopic surgery may be used with the cannula sealing apparatus.
The diameter of the opening 32 is such that instruments of nominal 12 mm diameter can seal with that opening 32 as shown in FIG. 2. In some instances though instruments of different diameter may be required to seal with an opening 32 in the region of the opening 32.
When a nominal 5 mm diameter instrument is to be used the seal member 34 is moved upwardly about the pivot members 38 until the centre of the nominal 5 mm diameter aperture 48 is coincident with the elongate axis of the tube 46 as shown in FIG. 1. A nominal 5 mm instrument can then be used with that instrument sealing with the seal member 34. Similarly a nominal 10 mm diameter instrument can seal with the seal member 36 by pivoting the member 34 back to the position shown in FIG. 2 and moving the seal member 36 up over the opening 32 as shown in FIG. 3. The movement of each seal member may be initiated either by hand or by the end of the surgeon's instrument. In the latter case, as shown in FIG. 6, the tip 45 of the instrument abuts a side face of the respective seal member 34 and relative movement between the instrument and housing 28 affects the rotation of the seal member 34, 36.
The selection of a tailored seal for each trocar diameter means the feel to the surgeon pushing the instrument in or withdrawing the instrument from a seal member 34, 36 is the same, regardless of the diameter of that member.
The facing surfaces of the housing 28 and the seal members 34 and 36 must seal when the openings of the members are concentric with the openings 32 of the housing.
To this end, whilst the arms 40 and 42 are at different axial extents relative to the axis of pivotal movement, the arcuate surfaces of the seal members 34, 36 that can face the opening 32, have the same part cylindrical or part spherical surface as a part cylindrical or part spherical surface of the housing 28 in the region shown by the line 50. A soft sealing surface that may be slightly resilient is applied to the surfaces of the seal members that seal with the housing 28. This gives a constant feel to the switching of one opening member or another.
Whilst two pivoting seal members have been described there may be more or less than two seal members 34, 36 with, for instance, when there are three pivotable seal members each of which may be located over the fixed central aperture 32, two of those members may be located to a common side of that aperture 32. At that side, when the member furthest from the aperture 32 is required to be used, the one nearest to the aperture 32 may first be moved over and past that aperture 32 with movement of the previously furthest member then being moved over the central aperture 32.
Whilst apertures of nominal 5, 10 and 12 mm diameter have been described it will be appreciated that apertures of any diameter may be provided such as 5, 7, 10, 12 and 16 mm. The larger diameter openings 32 are particularly suited to operations effected on obese patients. Furthermore the seals maybe colour coded, so that the surgeon may easily select the correct seal size by visual reference to the colour.
FIGS. 7 to 10 show a second embodiment of a cannula 14. The cannula 14 is substantially in accordance with the first embodiment herein described wherein a single use housing 28 is detachably connected to a reusable cannula 14. However, rather than the arcuate seal members 34, 36 being pivotally mounted to the housing, the seal members 34, 36 are mounted to rockers 54, 56. A part cylindrical surface 50 of the housing 28 includes resilient nipples 60 that engage the rockers 54, 56 to provide a frictional resistance against movement of the rockers 54, 56 towards or away from an operable position in which the arcuate seal members 34, 36 are concentric with the axis of the cannula 14. For instance, during use, rocker 54 can be freely pivoted to the position shown in FIG. 7 a in which the nipple 60 begins to engage the rocker 54. In order to rotate the rocker 54 further towards the concentric position, the nipple 60 must deform. The deformed nipple 60 presses on the underside of the rocker 54 creating friction resisting movement of the rocker 54. When the rocker 54 reaches a concentric position, as shown in FIG. 7 b, the nipple 60 is aligned with a circular recess 90 in the rocker 54 which allows the nipple 60 to return to its original shape. In order to misalign the rocker 54 from this position, it is necessary to deform the nipple 60. It has been found that this arrangement provides sufficient friction resistance against the movement of the rockers 54 away from the operable position, such that the cannula 14 will move within the patient before the rocker 14 moves in relation to the housing 28.
FIG. 8 shows the cannula housing 28 in more detail. A semi-annular protrusion 62 extends from either side of the housing 28. A central axially facing aperture 32 is defined in the housing 28 by a tubular section having an outside wall 64. Two clips 66, 68 are formed on the top of the housing 28. The clips 66, 68 create overhanging ledges 69. The semi-annular protrusion 62, tubular section, and clips 66, 68 are formed integrally to the housing 28.
FIG. 9 shows a seal 37 that clips onto the housing 28. This seal 27 is made from a resilient material. The seal 37 includes a central hole 70 and two openings 71, 72 located on either side of the central hole 70. The openings 71, 72 correspond to the clips 66, 68 of the housing 28. Accordingly, the seal 37 can be assembled on to the housing 28 by stretching the openings 71, 72 over the clips 66, 68 and locating an area of the seal adjacent to the flat edge 73, 74 of the openings 71, 72 under the ledges 69. The seal 27 is sized so as to be stretched or alternatively or additionally slightly compressed when fitted under the ledges 69. This ensures that the seal 37 is held firmly to the housing 28 thereby creating a seal. The central hole 70 is also sized so as to fit tightly about the outside wall 64 of the tubular section 64. The central hole 70 comprises a stepped bore wherein a thin section of the seal 37 extends over the top of the tubular section and restricts the aperture 32. When assembled to the housing 28 the edge of the central hole 70 thereby creates a lip seal against suitably sized surgical instruments that are inserted through the housing 28.
The seal 37 prevents fluid from escaping the housing 28 through the central axially facing aperture 32 by forming a seal against the top of the tubular section, the outside wall 64 and the top of the housing 28. This creates a large surface area against which to seal. Furthermore the top of the tubular section acts as a support for the seal 37 and the seal 37 may be resiliently biased against the top of the tubular section.
When assembled to the housing 28 the seal 37 creates an outer profile substantially as herein described wherein the top of the housing 28 presented to the rockers 54 forms a part cylindrical surface. The seal 37 also includes nipples 60. Although four nipples 60 are shown, the function provided by the nipples 60 can be equally achieved with one or two nipples 60 or a plurality of nipples 60 in various arrangements. The part cylindrical profile is also interrupted by an annular ridge 76 that is formed around the central hole 70. The ridge 76 is raised from the top of the seal 37.
FIG. 10 shows the rocker 54. The rocker 56 is similar. The top of the rocker 54 is arranged to accept a seal 34, 36, wherein the seal 34, 36 is similar to seal 37 as described above. The rocker 54, 56 includes a central hole 78 and two clips 79, 80 on either side of the hole. Again the seal (not shown) is assembled to the rocker 54, 56 by stretching the openings 71, 72 over the clips 79 and locating an area of the seal 34, 36 under the ledges there formed. Again the seal 34, 36 extends over a tubular section defining a central hole with the same features as that of the seal for the housing 28.
Each rocker 54, 56 includes arms 82, 84. The arms include circular apertures 83, 85, which are sized to fit about the semi-annular protrusions 62 on the housing 28. Stop members 86, 87 project inwardly. When assembled to the housing 28 the stop members 86 abut the ends of the semi-annular protrusion 62 to restrict the movement of the rocker 54,56. The rockers 54, 56 are sized differently so that the arms of one rocker may fit inside the arms of the other rocker, when both are assembled to the housing 28.
FIG. 11 shows the underside of the rocker 54. The rocker 58 is similar. The circular recess 90 is formed so that, when the rocker 54 is in the concentric position, the circular recess 90 and corresponding nipple 60 is aligned. A guide channel 91 is formed extending from a leading edge 92 of the rocker 54. The guide channel 91 comprises a first section that is sized so as to accommodate the nipple 60, without deforming the nipple 60. A second section of the channel is ramped so as to initiate the compressing of the nipple 60. The end of the second section is spaced from the circular protrusion.
When the rocker 54 is assembled to the housing 28, the rocker 54 can pivot between the inoperable and operable positions by rotating about the semi-annular recesses. As mentioned, the movement is limited by abutment of the stop member. The rockers 54 and 56 may be moved between the inoperable position and the operable, concentric position, by rotating the rockers 54, 56. By way of example, rocker 54 may be rotated manually towards the concentric position. As the leading edge 92 moves over the annular ridge 76, it compresses the ridge thereby forming a seal between the ridge and underside of the rocker 54. When the leading edge reaches the nipple 60, the channel 91 first accommodates the nipple 60 in the first section, without deforming the nipple 60. As the rocker 54 is moved further, the nipple 60 engages the ramped section of the channel 91 and the nipple 60 is urged to compress. Maximum friction is created as the compressed nipple 60 moves between the channel 91 and circular recess 90. When aligned with the circular recess, the nipple 60 locates therein. This acts to provide a ‘click’ functionality to the rocker 54 such that the rocker 54 ‘clicks’ into the concentric position. The rocker 54 can be moved back to the stored position in a reverse of the above process.
Each of the three seals provided by the housing 28 or the rockers 54, 56 when in place, is effected by a seal whose inner opening for the instrument is very close to the inner edge of the tubular member that the seal 37 is biased towards. This ensures good support for each seal 37. The radial distance from the opening of the seal 37 to the inner edge of the supporting tubular housing 28 may be substantially the same for all three seals.
The frictional resistance provided by each seal 37 may be the same.
Either rocker 54, 56 may be moved manually or by an instrument of the surgeon that may subsequently extend through the cannula 14. Whilst two rockers 54, 56 have been described only one may be present.
Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A cannula sealing apparatus including a plurality of seal members each having a different sized aperture with which, in use, surgical instruments of different sizes may be inserted in a first direction to seal with a selected seal member, at least one seal member being pivotable from an operative position in which a surgical instrument may, in use, be inserted in the first direction to seal with that member and an inoperative position characterised in that the pivot axis of the pivotal movement of the sealing member is in a second direction, transverse to the first direction.

2. A cannula sealing apparatus as claimed in claim 1 in which the second direction is perpendicular to the first direction.

3. A cannula sealing apparatus as claimed in claim 1 in which the pivotal axis of the seal member is arranged, in use, to pass through an inserted surgical instrument.

4. A cannula sealing apparatus as claimed in claim 1 in which at least one seal member includes spaced pivotal mountings on each side of the apparatus.

5. A cannula sealing apparatus as claimed in claim 1 including an opening in a housing of the apparatus through which, in use, a surgical instrument is arranged to be inserted in the first direction with the seal effected by the seal members being arranged to be in the region of that opening.

6. A cannula sealing apparatus as claimed in claim 5 in which pivotal axis of the seal member is spaced from the opening in the housing in a direction extending in the first direction.

7. A cannula sealing apparatus as claimed in claim 5 in which the pivotally movable seal member includes a surface that is arranged, in use, to surround and seal with the surface of the housing that surrounds the opening.

8. A cannula sealing apparatus as claimed in claim 7 in which the surfaces of the seal member and housing are part cylindrical.

9. A cannula sealing apparatus as claimed in claim 7 in which the surfaces of the seal member and the housing are part spherical.

10. A cannula sealing apparatus as claimed in claim 7 in which at least one surface includes a resilient material.

11. A cannula sealing apparatus as claimed in claim 1 including at least two pivotally movable seal members.

12. A cannula sealing apparatus as claimed in claim 11 in which, when both of the pivotally movable seal members are in the inoperative position, the seal of each seal member is located to a different side of the first direction.

13. A cannula sealing apparatus as claimed in claim 11 in which each seal member is pivotally movable about the same pivot axis.

14. A cannula sealing apparatus as claimed in claim 13 in which, in the region of the pivot axis, one seal member is axially inwards of the other seal member.

15. The cannula sealing apparatus as claimed in claim 1 wherein, when each pivotable seal member is in the operable position, said pivotable seal member is restricted by a friction member such that the frictional member restricts movement of the seal member away from the operable position.

16. The cannula sealing apparatus as claimed in claim 15, wherein the friction member is located on the housing.

17. The cannula sealing apparatus as claimed in claim 15 wherein the friction member engages with the pivotable members.

18. The cannula sealing apparatus as claimed in claim 15 wherein the friction member is resilient.

19. A method of using a cannula sealing apparatus comprising a plurality of seal members each having a different sized aperture comprising inserting a surgical instrument of first size in a first direction to seal with a seal member of a first size aperture and then removing that instrument and subsequently pivoting at least one seal member from an inoperative position to an operative position in which a second surgical instrument of a different size to the first instrument is moved in the first direction to seal with the seal member of a different size characterised in that the seal member of a different size is pivoted about an axis that passes through the surgical instrument when inserted.

20. A method of using a cannula comprising inserting a surgical instrument through the cannula along a first axis, and, before inserting the surgical instrument, selecting an appropriately sized seal member so that the selected seal member seals against the instrument, the method comprising selecting at least one pivotable seal member and pivoting said seal member about an axis transverse to the first axis and from an inoperable position to an operable position, in which the seal member is coincident with the first axis, the method including causing a frictional member to engage the seal member, when the seal member is in the operable position, such that the frictional member restricts the seal member from moving away from the operable position.