Abstract:
A surgical access apparatus includes a housing, an access member extending from the housing and having a longitudinal passageway for passage of an object and defining trailing and leading ends and an elongated seal mechanism mounted relative to the housing. The elongated seal mechanism includes a trailing hub and a leading hub longitudinally spaced from the trailing hub, and being adapted for relative rotational movement about the longitudinal axis, a plurality of spokes extending between and connected to the trailing hub and the leading hub, and an elongated seal member disposed within the spokes and adapted to establish a sealing relation about the object. The spokes define a first minimum internal dimension in a first condition thereof in the absence of an object and defining a second minimum internal dimension in a second condition thereof upon insertion of the object and relative rotation of the trailing hub and the leading hub. The second minimum internal dimension is greater than the first minimum internal dimension. The at least two of the spokes are generally obliquely arranged at a first angle relative to the longitudinal axis when in the first condition thereof and are adapted to be generally arranged at a second angle relative to the longitudinal axis when in the second condition thereof, the second angle being less than the first angle.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of and priority to U.S. Provisional Application Ser. No. 60/931,935 filed on May 24, 2007, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a surgical access apparatus for permitting the introduction of a surgical instrument into a body cavity. In particular, the disclosure relates to a seal assembly for the access apparatus and being adapted to form a seal about a surgical instrument while centering the surgical instrument within the apparatus. 
     2. Background of Related Art 
     There are many different types of minimally invasive surgical procedures whereby a surgeon gains access to an internal surgical site through a small opening in the body. For example, a laparoscopic procedure involves the insertion of instruments through a small opening in a patient&#39;s abdomen. Also, an arthroscopic procedure allows a surgeon to examine the interior of a patient&#39;s joint through a small incision in the skin. A comprehensive term, used throughout the present disclosure to refer to this type of procedure, is endoscopic surgery. 
     Typically in an endoscopic surgery, a small incision is made in the skin and a cannula is inserted through the fascia into a body opening. A cannula is a narrow tube, typically 5 to 13 mm in diameter, which serves generally to hold the incision open and provide a conduit to the body cavity through which a surgeon may introduce and withdraw the various surgical instruments required by the desired procedures. An insufflation gas (most commonly carbon dioxide) may be introduced through the cannula into the body opening establishing a slight pressure. This practice inflates the body opening and provides a viewing space wherein a surgeon may insert a camera lens to monitor the procedure. The surgeon may then use the insufflated space to maneuver a variety of other instruments into position to manipulate the targeted tissue without contacting and damaging the surrounding tissue. 
     Of primary concern in these procedures is establishing a fluid tight seal across the cannula to maintain the integrity of the insufflated body cavity. To maintain the insufflation pressure and the corresponding working space, many types of seals have been introduced. One common difficulty with conventional seals is the inability of the seal to accommodate the entire range of instruments necessary to complete a surgical procedure. A single surgical procedure will often require many instruments having dissimilar diameters. To ensure that a fluid-tight connection with each of these instruments is achieved, a surgeon might need to select an instrument seal having an aperture sized slightly smaller than the smallest diameter instrument to be used. Because the instrument seal is elastomeric, it is possible the aperture will be able to expand sufficiently to accept the largest diameter instrument, but there will be some associated difficulty. There is a friction force associated with moving the instrument while it is in contact with the aperture of the instrument seal. This friction force is sometimes called an insertion or glide force, and it must be kept low enough such that manipulating the instrument is not awkward for the surgeon. Inserting a large diameter instrument into a small diameter aperture will likely cause insertion and glide forces which are too large to be appropriate for the endoscopic procedures which often involve delicate movements. 
     One simple solution to this problem is to provide an instrument seal which is removable during surgery. In this way, a surgeon could select the instrument seal sized most appropriately for each instrument and install the seal just before use. Although effective, this process can be time consuming and unnecessarily prolong the surgery. Some devices have been introduced to hasten this process such as a smaller diameter instrument seal that can be flipped into and out of position with a simple movement positioned proximally in relation to a conventional stationary large diameter instrument seal. This type of system is most effective for use with a limited number of instruments having diameters very close to one of the two instrument seal apertures, but, a surgeon may still encounter difficulty with insertion forces or maintaining a seal with intermediately sized instruments. 
     Besides the accommodation of instruments of varying diameter, another characteristic desirable in an instrument seal is the ability of the seal to provide radial support to an instrument. Adequate radial support will aid in stabilizing the instrument so a surgeon will not need to divert attention from the surgical procedure to hold the instrument steady. Radial support is often provided by the very same features in a seal which assist in centering the instrument since providing a robust radial support at all points around the diameter of an instrument will naturally tend to keep the instrument centered. A need exists for an instrument seal capable of centering an elongated object and having an aperture that is truly flexible and modifiable in use. The seal should be able to accommodate an entire range of variously sized instruments without requiring any awkward manipulations to be performed by a surgeon. 
     SUMMARY 
     Accordingly, the present disclosure is directed to a surgical access apparatus. The surgical apparatus includes a housing, an access member extending from the housing and having a longitudinal passageway for passage of an object and defining trailing and leading ends and an elongated seal mechanism mounted relative to the housing. The elongated seal mechanism includes a trailing hub and a leading hub longitudinally spaced from the trailing hub, and being adapted for relative rotational movement about the longitudinal axis, a plurality of spokes extending between and connected to the trailing hub and the leading hub, and an elongated seal member disposed within the spokes and adapted to establish a sealing relation about the object. The spokes define a first minimum internal dimension in a first condition thereof in the absence of an object and defining a second minimum internal dimension in a second condition thereof upon insertion of the object and relative rotation of the trailing hub and the leading hub. The second minimum internal dimension is greater than the first minimum internal dimension. The at least two of the spokes are generally obliquely arranged at a first angle relative to the longitudinal axis when in the first condition thereof and are adapted to be generally arranged at a second angle relative to the longitudinal axis when in the second condition thereof, the second angle being less than the first angle. 
     The trailing hub and the leading hub are adapted for relative longitudinal movement when transitioning of the spokes between the first and second conditions. The spokes are normally biased toward the first condition thereof. The seal member may be arranged to normally bias the spokes toward the first condition thereof. The seal member includes trailing and leading flanges. The trailing and leading flanges are adapted to engage the trailing and leading hubs, respectively, to normally bias the trailing and leading hubs in a longitudinal direction toward each other corresponding to the first condition of the spokes. 
     The elongated seal mechanism includes an outer liner circumferentially disposed about the spokes and fixed from rotational movement relative to the longitudinal axis. The outer liner is engageable with one hub of the trailing and leading hubs during insertion and withdrawal of the object to prevent rotational movement of the one hub whereby the other hub is free to rotate to permit transitioning of the spokes between the first and second condition thereof. The outer liner is dimensioned to be engaged by the trailing hub during insertion of the object and cooperates to fix the trailing hub from rotation whereby the leading hub rotates and longitudinally moves relative to the trailing hub to permit the spokes to assume the second condition. The outer liner may be dimensioned to be engaged by the leading hub during withdrawal of the object and cooperates to fix the leading hub from rotation whereby the trailing hub rotates and longitudinally moves relative to the leading hub to facilitate withdrawal of the object. The outer liner may be dimensioned to engage and fix each of the trailing and leading hubs from rotational movement when in the first condition thereof. 
     The leading hub is adapted to longitudinally move in a leading direction during insertion of the object to disengage the outer liner to thereby rotate relative to the trailing hub and permit the spokes to transition from the first condition to the second condition. The trailing hub is adapted to longitudinally move in a trailing direction during withdrawal of the object to disengage the outer liner to thereby rotate relative to the leading hub and facilitate removal of the object. 
     Each of the spokes may be connected to the leading and trailing hubs by a living hinge. The spokes may be adapted to normally bias the object in general alignment with the longitudinal axis. 
     The apparatus incorporates the structure of an ancient toggle-action winepress to accomplish the movements described above and accommodate instruments of varying diameter without the need to replace seal parts. In its simplest form a toggle-action linkage includes two rigid members hinged at an angle in the center and supported on the ends with sliders allowing motion with one degree of freedom. Appropriately applying a force to the hinge will have a tendency to straighten out the linkage to provide a mechanical advantage at the two ends which will travel a shorter distance than the hinge, but with greater force. Combining this straightening-out principal with a mechanism for rotary motion will yield a device much like the ancient winepress described in H ARRY  W ALTON , T HE  H OW AND  W HY OF  M ECHANICAL  M OVEMENTS ; E XACTLY  H OW  M ACHINES  W ORK : E NGINES , T URBINES , T RANSMISSIONS , B RAKES , C LUTCHES , R OCKETS , A TOMIC  G ENERATORS , G YROSCOPES , G UIDANCE  S YSTEMS , pp. 25-27, E.P. Dutton &amp; Co., NY 1968. The structure includes a large capstan capable of rotating relative to the top brace to which it is attached on the underside. The top brace is rigidly connected to a base plate by a pair of round vertical bars which also provide a bearing surface for a sliding platen disposed between the base plate and the top brace. The top surface of the sliding platen is equipped with a circular array of sockets corresponding with a similar array on the lower face of the capstan. Two spokes are disposed obliquely between the capstan and the sliding platen, each with an upper end within a socket on the capstan and a lower end in a socket on the sliding platen. The capstan is equipped with a long handle which allows a pressman to turn the capstan, thereby straightening out the spokes and forcing the sliding platen downward toward the base plate where grapes are awaiting pressing. 
     The operation of the winepress exhibits a complex motion in the spokes. The upper ends of the spokes rotate with respect to a vertical axis about which the capstan turns while remaining at the same vertical elevation. On the other hand, the lower ends of the spokes translate downward while remaining at the same radial position. This motion straightens out the rigid spokes with respect to the vertical axis providing the mechanical advantage of a toggle-action mechanism. As the spokes are straightened out, the relative spacing of the top ends of the spokes remains constant as does the relative spacing at the lower ends. The relative spacing between the midpoints of the two spokes, however, will increase. It is this dispersal of the midpoints that makes the winepress motion particularly useful in designing an adjustable seal to accommodate larger and larger instruments. Additionally, if the winepress capstan were turned in an opposite direction, the spokes would lean over causing the sliding platen to rise while the relative spacing between the midpoints decreased. This radial congregation of the midpoints is useful for a seal accommodating smaller diameter instruments. 
     Increasing the number of rigid spokes arranged obliquely in a circular array around a central longitudinal axis can produce a conceptually useful geometry. The surface formed by the spokes as the number of spokes approaches infinity resembles a hyperboloid of one sheet. This surface has an hourglass profile with a narrow throat diameter in the center, which can be modified by the motion of the spokes. Straightening out the spokes elongates the hourglass, opening the throat until the spokes are completely vertical and the surface resembles a cylinder. Leaning the spokes compresses the hourglass, thereby closing the throat. In any configuration, the narrowest throat diameter would always be defined by the midpoints of the spokes. 
     Generally stated, the present disclosure relates to a winepress seal for a cannula assembly which may exhibit components mimicking the movements of the winepress spokes and components having an adjustable hourglass profile. The winepress seal employs these features to selectively create a fluid-tight connection with variously sized surgical instruments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the detailed description of the embodiments given below, serve to explain the principles of the disclosure. 
         FIG. 1  is an exploded perspective view of a cannula assembly incorporating a dual seal system constructed in accordance with the present disclosure; 
         FIG. 2  is an exploded perspective view of the winepress seal assembly of  FIG. 1 ; 
         FIG. 3A  is an enlarged side view with portions cut-away of the winepress seal assembly in a first condition in the absence of an instrument; 
         FIG. 3B  is a cross-sectional view of the dual seal system illustrating the winepress seal assembly in the first condition; 
         FIG. 4A  is a view similar to  FIG. 3A  illustrating the winepress seal assembly in a second expanded condition to accommodate an instrument; 
         FIG. 4B  a view similar to  FIG. 3B  illustrating the winepress seal assembly in the second condition; 
         FIG. 5A  is a front view of an unrolled spoke tube of the winepress seal assembly; 
         FIG. 5B  is a side plan view of an individual spoke of the spoke tube of  FIG. 5A ; 
         FIG. 6A  is front plan view of a bladed spoke; and 
         FIG. 6B  is a side plan view of the bladed spoke of  FIG. 6A . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present disclosure contemplates the introduction into a person&#39;s body of all types of surgical instruments including clip appliers, graspers, dissectors, retractors, staplers, laser fibers, photographic devices, endoscopes and laparoscopes, tubes, and the like. All such objects are referred to herein generally as “instruments.” In the drawings and in the description which follows, the term “proximal,” as is traditional, will refer to the direction toward the operator or a relative position on the surgical device or instrument which is closer to the operator, while the term “distal” will refer to the direction away from the operator or a relative position on the instrument which is further from the operator. 
     Referring initially to  FIG. 1 , the dual seal system of cannula assembly  1  in accordance with the principals of the present disclosure is illustrated. The dual seal system includes winepress seal assembly  100  which is adapted to form a seal about a surgical object. Cannula assembly  1  includes a bottom housing  10  which is configured to mount or accept a cannula  12  on its distal side. The cannula  12  is intended to be partially inserted into a body cavity through a small incision in the skin to provide access to the body cavity. Bottom housing  10  includes diametrically opposed extensions  11  which provide a surface for an operator to grip the cannula assembly  1  with two fingers. An interior ledge within bottom housing  10  supports flange  21  on duckbill valve  20 . Duckbill valve  20  is an elastomeric member with a pair of distally extending substantially flat lips  23  which are normally biased together to create a substantial fluid-tight seal through the cannula in the absence of an instrument. Lips  23  may be easily separated upon the insertion of an instrument from the proximal side. 
     Winepress support  30  includes central opening  33  extending from its distal end to its proximal end, and tab  31  configured for attachment to bottom housing  10 . Ridge  37  is disposed about central opening  33  such that when winepress support  30  is connected to bottom housing  10 , ridge  37  abuts the proximal face of flange  21  of duckbill valve  20  creating a substantially fluid-tight interface. Support column  39  is hollow and encircles central opening  33  on the proximal side of the winepress support  30 . Central opening  33  is configured to slidingly accept winepress assembly  100  up to a distal face of support ring  131  of liner  130 . 
     Upper housing  40  includes central bore  41  configured to encompass winepress seal assembly  100  when top housing  40  is connected to bottom housing  10  by any conventional means. Central passageway  51  of cap  50  is configured to slidingly engage the winepress assembly  100  down to a proximal face of support ring  131  of liner  130  of the winepress seal assembly  100 . An interior rim  53  disposed within central passageway  51  abuts the proximal face of support ring  131  of winepress assembly  130 . Although certain parts of winepress assembly  100  are capable of relative motions as described in greater detail below, liner  130  is held securely in position because its support ring  131  is disposed between the support column  39  of winepress support  30  and the interior rim  53  of cap  50 . Cap  50  may be securely attached to the top housing  40  by any conventional means and may be configured to make a snap fit connection. Central passageway  51  extends to the proximal side of cap  50  and permits entry of an elongated object into the winepress assembly  100 . The cannula assembly  1  contains a central corridor which is only closed by lips  23  on duckbill valve  20 . 
     Referring now to  FIG. 2 , in conjunction with  FIG. 1 , the winepress assembly  100  of the present disclosure will be described in greater detail. Winepress assembly  100  includes an elastomeric seal  110 , a lower or leading end cap  120 , a liner  130 , a spoke tube  140 , and an upper or trailing end cap  150 . Each component of winepress assembly  100  is in general alignment with the central longitudinal axis “k” of cannula  1  and includes a central shaft which allows an elongated object to pass through. 
     Elastomeric seal  110  includes throat  111  which extends the entire length of elastomeric seal  110  to accept an elongated object inserted there through. Elastomeric seal  110  is bowed inward near its midpoint to give it an hourglass shape such that a minimum interior throat diameter near the center may sealingly engage the elongated object. As discussed below, the flexibility of elastomeric seal  110  allows the minimum interior throat diameter to be modified to be used with variously sized objects. Also included on elastomeric seal  110  are lower and upper collars  113 ,  117  protruding radially from the throat  111  at the distal or leading and proximal or trailing ends, respectively. Lower and upper collars  113 ,  117  include lower and upper beads  115 ,  119  protruding from their exterior surfaces. The beads define a maximum outer dimension of the elastomeric seal  110  and are each adapted to create a seal around the periphery of their respective collar  113 , 117 . Lower bead  115  is adapted to sealingly and slidingly engage an interior surface of central opening  33  in winepress support  30  such that longitudinal translation of lower collar  113  will not compromise the seal within the winepress assembly  100 . Upper bead  119  is adapted to similarly engage an interior surface of the central passageway  51  through cap  50 . 
     The throat  111  of elastomeric seal  110  is intended to be the innermost component radially of winepress seal  100 . Radially surrounding the throat  111  and between the collars  113 ,  117  is spoke tube  140 . Spoke tube  140  includes an array of spokes  145 , connected by hinges  143  to leading hub  141  and trailing hub  147 . A proximal face on trailing hub  147  abuts a shelf  155  on upper end cap  150 , while a distal face of leading hub  141  abuts a similar shelf (not visible) on lower end cap  120 . The end caps  120 ,  150  may be rigidly attached to the hubs  141 ,  147  by any conventional means including an appropriate adhesive. In one embodiment, end caps  120 , 150  are respectively secured to the hubs  141 , 147  in a manner which may prevent rotational movement of the secured components. Lower end cap  120  includes a flat face  121  on its distal side and an array of teeth  123  on the opposite side. Similarly, upper end cap  150  includes a flat face  151  on its proximal end and an array of teeth  153  on its distal end. End caps  120 ,  150  may be identical parts disposed with opposite orientations. Radially surrounding the spoke tube  140  and disposed longitudinally between the end caps  120 ,  150  is liner  130 . Liner  130  includes support ring  131  and an array of notches  133  along the proximal and distal faces. Support ring  131  is sandwiched between cap  50  and support column  39  of winepress support  30  to hold the liner  130  firmly in position. 
     When initially assembled, winepress assembly  100  may be configured to assume a normal configuration as depicted in  FIGS. 3A and 3B . Elastomeric seal  110  is designed to have a relaxed length such that collars  113 ,  117  press end caps  120 ,  150  into engagement with the liner  130 . In this initial configuration, the spokes  145  are biased to the inclined arrangement shown and the elastomeric seal assumes its most narrow throat diameter. Spokes  145  remain linear or straight, pivoting only at the hinges on each end. 
     Upon insertion of an elongated object, certain components of winepress seal assembly  100  may be caused to move relative to one another to accommodate the object. In operation, an elongated object such as instrument  99  depicted in  FIGS. 4A and 4B , is inserted from the proximal end to engage the minimum diameter section of the throat  111  of elastomeric seal  110 . The engagement of teeth  153  on upper end cap  150  with the notches  133  on the stationary liner  130  initially prevents any rotational movement of the end cap  150  and the trailing hub  147 . Upon further passage of the instrument  99 , the throat  111  widens to accept the instrument  99  with the elastomeric seal  110  pushing radially outwardly against spokes  145 . This in turn causes the leading hub  141  to simultaneously translate distally to cause distal displacement of the end cap  120  until a gap is formed between the teeth  123  on the lower end of the end cap  120  and the notches  133  on the distal end of the liner  130 . Thus, the leading hub  141  (and lower cap  120 ) is free to rotate thereby enabling the spokes  145  to move toward a generally linear arrangement to increase the effective internal diameter of the spokes  145 . The elastomeric seal  110  no longer constrained by the locked spokes  145  is free to be stretched radially outwardly to stretch the throat  111 . It is noted that during insertion of the instrument  99 , the teeth  153  of the upper end cap  150  may remain engaged with the notches  133  of the liner  130  due to the distal force placed on the elongated seal  110 , and the resulting distal force placed on the upper end cap  150 . When the throat  111  has opened sufficiently to accommodate the instrument  99 , the natural tendency of the elastomeric seal or seal  110  to return to its initial minimum throat configuration provides the radial pressure required to maintain a seal about the instrument  99 . Furthermore, the spokes  145  (again shown in combination in  FIG. 4B ) may push radially inwardly on the outer surface of the throat  111  of the elongated seal  110  from several directions simultaneously such that the instrument  99  is biased into a general alignment with the central longitudinal axis “k”. During manipulation of instrument  99 , the elastomeric seal  110 , spoke tube  140  and end caps  120 ,  150  may all translate proximally together with the instrument  99  until a gap is formed on both the proximal and distal sides of stationary liner  130  as seen in  FIGS. 4A and 4B . This open throat configuration supports a limited amount of longitudinal translation in either direction until one of the end caps  120 ,  150  engages the liner  130 . 
     When instrument  99  is withdrawn, the process works in reverse. The withdrawal of the instrument  99  causes the elongated seal  110  to move in a proximal direct due to engagement with the throat  111  of the elongated seal  110 . This withdrawal closes the gap between the liner  130  and the lower end cap  120  with the teeth  123 , 133  of the respective components interlocking. The gap between upper end cap  150  and the liner  130  may be increased. Once the instrument moves past the minimum throat diameter region and disengages from the elastomeric seal  110 , the resiliency of the components will cause the trailing hub  147  to rotate under the biasing influence of elastomeric seal  110  and translate distally until winepress  100  returns to the initial minimum throat diameter configuration of  FIG. 3A . As the spoke tube  140  transitions from the configuration of  FIG. 4A to 3A , the spoke centers will again congregate about the central longitudinal axis “k” pushing inwardly on the minimum diameter region of the elastomeric seal  110 . The length of elastomeric seal is again reduced to the relaxed length driving the movement of the other components to make the transition. 
     In order for the spoke centers to congregate upon the relative translation and rotation of the trailing and leading hubs  141 ,  147  as described above, the hinges  143  will need to support a complex multi-dimensional pivot of the spokes  145  at each end. A ball-in-socket joint could support this motion allowing a spoke to lean radially inwardly as it also leans longitudinally toward the hub. Because a ball-in-socket joint can be costly to manufacture and maintain due to its complexity, alternatively a living hinge may be used. Generally, a living hinge is a thin and flexible region of the material of a part connecting two more rigid sections of the part allowing for relative motion of the more rigid sections. Because this type of hinge has no frictionally contacting surfaces, it can be designed to have excellent fatigue resistance when formed from a moldable plastic such as polypropylene. Of course any suitable material may be selected for a particular application. 
       FIGS. 5A and 5B  illustrates a spoke tube  240  providing living hinge joints. The living hinges  243  are simply sections of material having a reduced profile when compared to the body of the spoke  245  which connect the leading and trailing hubs  241 ,  247 . The spokes  245  may lean in any direction with respect to the hubs  241 ,  247  because the flexibility of the material will allow the hinges  243  to bend in any direction. Also evident in  FIGS. 5A and 5B  is that leading and trailing hubs may be substantially flat and rectangular when initially molded. The flexibility of the material selected will allow the structure to be rolled into a shape similar to the spoke tube  140  in  FIG. 2  and to create the necessary passageway through the hubs. A seam  149  will be created on both the trailing and leading hubs. The seam  149  may be joined by any conventional means including an appropriate adhesive which may also be used to join the hubs  141 ,  147  to the end caps  120 ,  150 . The adhesive or other means used for attachment of the end caps  120 ,  150  to the hubs  141 ,  147  should allow no relative motion between either end cap and its respective hub. Because each end cap will move exactly along with its respective hub when so attached, the end caps  120 ,  150  can be said to become part of the hubs  141 ,  147 . 
     One other consideration in forming the winepress  100  is the mechanism by which winepress  100  is biased to the normal initial minimum throat diameter. As discussed above, the elastomeric seal  110  is preferably designed with a relaxed length adapted to perform this function. However, other methods may be possible. For example, the spokes  145  may be initially molded obliquely with respect to the hubs  141 ,  147  such that their natural bias is to the leaned position depicted in  FIG. 4A  where the spokes  145  have an angle with respect to the central longitudinal axis which is greater than the angle of the spokes depicted in  FIG. 3A . 
     It may be advantageous to incorporate into the winepress assembly  100  a bladed spoke tube  340  having bladed spokes  345  like the one shown in  FIGS. 6A and 6B . The bladed spoke  345  is flattened in one direction and remains wide in an orthogonal direction giving each spoke  345  two parallel flat faces  349 . The wide direction allows the spoke  345  to maintain some rigidity and resist bending. If the spokes  345  are oriented appropriately, the flattened direction will allow for a closer spacing of the spokes  345  and therefore a greater total number of spokes to be attached to the hubs  341 ,  347 . One characteristic of the spoke tube  140  which limits the number of spokes  145  that may be attached is the minimum throat diameter configuration the spoke tube  140  assumes for the reception of small diameter instruments. To achieve this configuration, the spokes  145  will be in oblique relation to a great extent. Not only will the spoke centers congregate radially toward the central longitudinal axis as discussed above, each spoke center will become crowded by the centers of the neighboring spokes  145  as can be seen in  FIG. 3A . For a given minimum throat diameter to be achieved, the abutment of the spoke centers with the neighboring spoke centers limits the number of spokes  145  which may be used. If spokes  145  are too thick and inadequately spaced, the spoke centers will abut one another before both end caps  120 ,  150  encounters the liner  130  and a sufficiently narrow throat diameter can be achieved. It can be seen then how a bladed spoke  345  can provide a reduced thickness in the proper direction to allow more spokes  345  to be stacked without overcrowding. If oriented and spaced appropriately, the flat faces  349  of the bladed spokes  345  will abut one another when the spoke tube is configured to receive small diameter instruments. This arrangement will allow for a greater number of spokes  345  to be incorporated without requiring the spokes  345  to be too thin to maintain the necessary rigidity. A greater number of spokes  345  may be desirable to create a greater closing force about an instrument or to provide a greater radial support to an instrument. 
     Finally, the elastomeric seal  110  may be omitted from the winepress assembly  100  creating a centering device that does not sealingly engage an instrument. Without the elastomeric seal  110 , the minimum throat diameter is defined by the central portions of the spokes  145 . The operation of the spokes  145  would not change except that the elongated object would contact the spokes directly at their midpoints. 
     Although the foregoing disclosure has been described in some detail by way of illustration and example, for purposes of clarity or understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims.