Abstract:
An active cannula or sleeve which does more than merely maintain a channel or passage is usable to create and/or enlarge a channel or passage, to position a scope or instrument, to move or locate tissue, etc. The cannula can vary in size or shape as needed, intraoperatively. Because a cannula of the present invention is expandable, the surgeon can make a small relatively small incision, stretch the tissue with the expandable cannula, contract the cannula and remove it, allowing the skin to come back to its unstretched condition. Thus, a smaller incision can be made to fit the same size instrument. This results in less trauma and scarring and an easier operation. The cannulas are or can assume such a non-circular shape, to fit into a natural skin opening and cause less trauma. The devices can be used to seal off a space; to expand an existing space or a potential space for working or visualization; to move tissue (for example, to stretch an incision) or to protect it.

Description:
RELATED APPLICATIONS 
     This is a divisional of U.S. application Ser. No. 08/195,337, filed on Feb. 14, 1994 now U.S. Pat. No. 5,514,153. Application Ser. No. 08/195,337 is a continuation-in-part of U.S. application Ser. No. 07/792,730, filed on Nov. 15, 1991 now U.S. Pat. No. 5,295,994, and a continuation-in-part of U.S. application Ser. No. 08/054,416, filed on Apr. 28, 1993 now abandoned. Application Ser. No. 08/054,416, in turn, is a divisional of U.S. application Ser. No. 07/487,645, filed on Mar. 2, 1990 now U.S. Pat. No. 5,331,975. The benefit of the earlier filing dates of the aforementioned applications is hereby claimed. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to medical devices, and particularly to expandable medical devices such as cannulas, catheters, retractors, and similar devices. 
     Existing cannulas and/or retractors as used in endoscopic surgery today are passive devices which are fixed in length and width. They can not be varied intraoperatively in length and width to accommodate larger devices or varying size devices through the skin. 
     Skin and subcutaneous (subsurface) tissues are viscoelastic: they will gradually stretch without tearing. Once the tissue is slowly stretched it maintains its expanded condition for a period of time. Alternatively, the tissue can be stretched further, for example to progressively stretch out an incision. Then, after relaxation, the tissue will regain its original unstretched condition without having been damaged. 
     Current methods used for retracting tissue and improving visualization are mechanical separation using metal retractors during open surgery, or the direct pressure of an unconfined flow of fluid such as water or CO 2  during fiberoptic surgery. A typical mechanical external fixator has pins driven through the bones and mechanically distracts the elements of the joint. Problems with the water method include fluid extravasation including into and through the tissue itself. Increased pressure and swelling result in the area, resulting in edematous or swollen tissue. Excess pressure from mechanical retractors may cause necrosis or tissue death. With these methods, it is impossible to monitor the pressure being applied to the body tissues, and tissue damage or necrosis can result. 
     While operating from within the body, i.e., fiber optic assisted surgery as opposed to open surgery, there is no known way to selectively move or retract tissue, either hard tissue such as bone or soft tissue, out of the way to improve visualization. No device in use adequately allows a surgeon to create an actual space or expand a potential space in the body, by separating adjacent layers of tissue. The prior art does not disclose a retractor which is powerful enough and made of a material which is strong and resilient enough to, for example, separate tissue planes from within. Such a device, especially in the field of fiber optic surgery, would allow a surgeon to visualize and operate without using the conventional bulky and awkward mechanical retractors which require large open incisions. Such a device would also permit working within the body without damaging a great deal of tissue in the path between the skin opening and the working area, by minimizing the external orifice or skin incision. 
     SUMMARY OF THE INVENTION 
     The present invention is a system of retractors and/or cannulas with which a surgeon can use to take potential spaces within the body and turn them into existing spaces safely and easily and controllably in order to safely visualize appropriate tissue and operate. The cannula and/or retractor selectively moves appropriate tissue out of the way to enable a surgeon to see and work better within the body, and selectively moves body parts such as joint parts or soft tissue planes in order to create a space between the tissues for visualization and for working. 
     A cannula and/or retractor of the present invention may have a fluid-operated portion such as a balloon or bladder to retract tissue, not merely to work in or dilate an existing opening as for example an angioscope does. The fluid-filled portion is flexible, and thus there are no sharp edges which might injure tissue being moved by the retractor. The soft material of the fluid-filled portion, to an extent desired, conforms to the tissue confines, and the exact pressure can be monitored so as not to damage tissue. The expanding portion is less bulky and more compact, and the pressure it applies at the tissue edges can stop bleeding of cut tissue. These are all features not possessed by a conventional mechanical retractor. 
     With a typical mechanical retractor, the opening in the skin and thence inwardly must be larger than the surgical area being worked upon, in order to be able to get the mechanical retractor into position. The surgeon must damage a large amount of tissue which may be healthy, in order to expose the tissue to be worked on. The cannula and/or retractor of the present invention minimizes damage to tissue in the way of the tissue the surgeon needs to expose, which was previously cut in a large open exposure. With the cannula and/or retractor of the present invention, the opening at the skin is smaller at the skin where the device is inserted, and wider at the location inside the body where the cannula and/or retractor is expanded. The cannula and/or retractor is first placed into the body in an unexpanded condition, and then, as it is expanded, pushes tissue out of the way in deeper layers of the body one can see and safely operate on affected tissue. Thus, less undesired tissue damage occurs. 
     The bladder is pressurized with air or with water or another fluid. The fluid used in the bladder must be safe if it accidentally escapes into the body. Thus, besides air, such other fluids as dextrose water, normal saline, CO 21  and N 2  are safe. The pressure in the bladder is monitored and regulated to keep the force exerted by the retractor at a safe level for tissue to prevent tissue necrosis. The retractor can exert a pressure on the tissues of as high as the mean diastolic pressure of 100 mm of mercury, or higher for shorter periods of time, while still being safely controlled. Typical inflatable devices such as angioscopes do not have anywhere near the strength, or the ability to hold enough fluid pressure, or shapes to retract tissue as described herein. As compared to prior art devices, the retractor of the present invention operates with greater pressure within the bladder, since it is made of stronger materials such as Kevlar or Mylar which may be reinforced with stainless steel, nylon, or other fiber to prevent puncturing and to provide structural shape and support as desired. Such materials are strong enough to hold the necessary fluid pressure of about several pounds or up to about 500 mg Hg or more and exert the needed force on the tissue to be moved. The choice of material is well within the ability of one familiar with such materials and accordingly will not be gone into in further detail herein. The present retractor is thus able to exert substantially more force on adjoining tissues than a prior art device. The shapes of the retractors are specific for each application, and may include separate variable chambers which are sequentially controllable, to control the direction of tissue retraction. 
     Surgeons operate along tissue planes. Once a surgeon finds a tissue plane, he dissects along it, starting the separation process with the knife. The cannula and/or retractor holds the tissue layers apart and helps and eases in defining and further separating the tissue layers as the surgeon operates along the tissue planes, helping to spread and define the planes. The cannula and/or retractor helps to separate the tissue layers, increasing the space for operating, and improving the surgeon&#39;s ability to separate and visualize, leading to better and safer surgical technique. 
     A preferred use for the present retractor is in the field of fiber optic surgery, including endoscopy, arthroscopy, laparoscopy, etc. which require looking into and operating within a limited space with a fiber optic light and camera. The bladder expands into an area of soft tissue—for example the bursa—and pushes it out of the way. The bladder can be left in place during the operation, or it can be deflated and removed, and the arthroscope and other instruments can be put into the space created. 
     The bladder may be a bellows type device in which the material does not stretch but which expands when pressurized from within and which is collapsed by the use of suction. In this case, it would preferably be made of a polymer of the class including Kevlar or Mylar fabric for strength and structural integrity. The bladder may generally also be made from any very thin walled polymer. 
     The bladder may also be made from a biocompatible and/or biodegradable material, so that if it can not be removed from the body for some reason, or if the surgeon desires to keep the bladder in place in the body for a period of time, it will not damage the tissue and may eventually be reabsorbed into the body. Such a biodegradable bladder may be left under the skin postoperatively to stop postoperative bleeding or to keep tissue expanded. Alternatively, the bladder may be made of a stretchable material which stretches when pressurized from within, and then collapses partially of its own accord when depressurized or also with the help of suction. The retractor may be transparent for better visibility, but it need not be for some applications. Also, the retractor can be disposable. The material choice is within the skill of the art. One surface of the bladder may be made of or have thereon a reflective surface to reflect light to see around a corner. 
     A most typical construction for the cannula and/or retractor of the present invention is an inflatable bladder situated on the end of a shaft, which may be flexible or rigid, which is pushed through an extra opening in a scope or cannula or through a separate portal, and which expands at the end of the shaft. 
     The retractor can be located on a scope, either on the end thereof or movable axially through a channel along the length of the scope. The retractor can alternatively be mounted on a cannula. The retractor can be mounted on a separate shaft passing through an existing channel in a cannula; it can be inserted through a separate hole in the cannula or the scope; or it can be inserted through a separate opening in the body. The shaft with a retractor on the end can be pushed or slid through the cannula, side by side with a scope. Alternatively, the bladder can expand out of, then recess back into, a groove on a cannula or scope. The retractor can be used to create a space right by the scope, or possibly at a location spaced from the end of the scope. 
     The bladder itself can be round, eccentric, oval, conical, wedge-shaped, U-shaped, curved, angled, or it may be in any shape desirable to optimize the particular application. The bladder may be irregularly shaped when inflated, that is, it may expand to a greater radius in the area where it is desired to look (where greater exposure space is needed). 
     Vacuum can be used to deflate the bladder. The bladder may then be removed by sliding it out the portal directly. 
     The present invention is described herein as relating to cannulas and/or retractors. A cannula is a device for insertion into or through body tissue to provide a working passage for surgical instruments, scopes, etc., as in endoscopic or arthroscopic surgery. A catheter, on the other hand, is an artificial fluid passage primarily used for insertion through an existing body opening. The two types of devices have very different structures and structural requirements. For example, a catheter is usually flexible, very small in diameter, and not suitable for maintaining a working passage through normally closed body tissues, while a cannula is more rigid, larger in size, and designed specifically to provide a working passage for surgical instruments and scopes through normally closed body tissues. It should be understood, however, that many of the features of the present invention can with suitable modifications be applied to the catheter art. Accordingly, the present invention is not limited to cannulas per se, but may be applicable to catheters or other devices also. 
     The present invention defines an active cannula or sleeve which does more than merely maintain a channel or passage. It is an active device usable to enlarge a channel or passage, to position a scope or instrument, to move or locate tissue, etc. The cannula can vary in size or shape as needed, intraoperatively. Typically, with a passive (non-expandable) cannula, a surgeon must make an incision in the skin and muscle large enough to receive the largest instrument to be passed through the incision to the surgical area. Because a cannula of the present invention is expandable, the surgeon can make a small relatively small incision, stretch the tissue with the expandable cannula, contract the cannula and remove it, allowing the skin to come back to its unstretched condition. Thus, a smaller incision can be made to fit the same size instrument. This results in less trauma and scarring and an easier operation. 
     Further, known cannulas are generally round, while skin expands (from an incision) in an elliptical fashion, between tissue planes. Thus, the present invention provides cannulas which are or can assume such a noncircular shape, to fit into the natural opening and cause less trauma. 
     The devices of the present invention are usable in endoscopic procedures generally. The devices can be used to seal off a space; to expand an existing space or a potential space for working or visualization; to move tissue (for example, to stretch an incision) or to protect it. Other uses within the skill of the art but not enumerated herein are within the scope of the invention. 
     The cannulas of the present invention allow for the progressive stretching of an incision in skin or subsurface tissue in order to allow improved exposure, while minimizing damage to the tissue by making the actual incision as small as possible. 
     In the arthroscopic model, a fixed cannula is placed through the skin to the subsurface tissues into a joint. Different size working devices (shavers, burrs, scissors, punches, scope, etc.) are placed through the cannula to visualize or to work in the subsurface area at the distal end of the cannula. The cannula can be progressively expanded or stretched radially outwardly, to stretch or expand the skin and subsurface tissues. The cannula typically expands along its entire length, although it may in some cases be expandable at selected portions along its length. 
     The expansion can be in a circular pattern, or it can be in an oval or elliptical or other pattern to accommodate (a) the tissue planes or (b) the instruments being inserted through the cannula. 
     The cannula can expand inwardly to act like a valve or a seal. Or it can expand both inward and outward. 
     The cannula is preferably flexible—that is, it is bendable about an axis extending perpendicular to the longitudinal extent of the cannula. In other words, the cannula as a long straight object is not rigid but can bend so that it is not straight. This allows the cannula to conform to the body tissues to the extent desired. 
     All cannula bodies can be multi-lumen for passages through which extend structure for control of bladders, tools, scope, etc. 
     In a first embodiment, a cannula may be of a stretchable material (such as a polymer) which is introduced into the body with a trocar. The trocar is then removed. Progressively larger dilating devices are placed inside the stretchable cannula, as needed, to progressively stretch out the skin and tissue to a larger size in order to introduce larger instruments through the cannula. Each time the cannula is enlarged, the stretched tissue remains in its stretched condition for a period of time because of its viscoelastic properties. 
     One way of stretching the cannula is by placing inside the stretchable cannula a bladder (round or elongated in the shape of a sausage, for example) which can be inflated to uniformly stretch the cannula and tissue. The bladder can be deflated and removed, leaving the enlarged opening. 
     In a second embodiment, the cannula is itself inflatable for expansion. The cannula is basically an inflatable cylinder with expansions in both the inner diameter and the outer diameter. As inflated, the device expands to a preformed shape with the inner diameter following the outer diameter and expanding outward to create a progressively larger opening. Filaments or cords can be placed between the inner and outer walls to limit their separation from each other. The inner wall can be more rigid. 
     In a third embodiment, the cannula includes one or more stretchable (inflatable or expandable) parts and one or more non-stretchable parts. The non-stretchable parts can be metal or plastic pieces such as curved plates, joined by the stretchable elements which extend longitudinally between them. These stretchable elements can be bladders. As larger devices are passed through the cannula, the stretchable portions expand and the plates move outwardly to stretch an appropriate opening. 
     In any of these cases, one can monitor and control the amount of pressure being applied to the tissue upon expansion of the cannula, so as to not exceed a certain critical pressure and damage tissue. This can be done by monitoring the actual size of expansion, the amount of air or fluid introduced to inflate the device, the fluid pressure within the device, etc. 
     There are numerous possibilities of a cannula-with-bladder or (catheter-with-bladder) construct. 
     One specific example is an arthritis irrigation system. This is a multi-lumen tube which has one lumen/portal for inflow of irrigation fluid and a second portal for suction (return). The tube is flexible and has its distal end placed in a joint to be irrigated. The tube is fixed in place by an expanding device as discussed 
     There can be one or more bladders at any given location or on any given instrument. Multiple bladders can be controlled as independent structures or as one unit. Specific structure and control is based on the particular application. 
     The surface of the material can be pebbled or roughened or ridged, or have serrated edges, to better grip tissue and hold the retractor in position. Of course, the surface must still remain smooth enough so that the retractor is easily removable without damage to the tissue it contacts. 
     The bladders can expand by well in excess of 200%. 
     The bladder is preferably made of an elastomeric material which is strong enough to move tissue as desired. A suitable material for the expandable bladder is Silastic® elastomer, which is available from Dow Corning in medical grades. Other suitable materials are silicone, or latex, or PVC. 
     The bladder may be made of a non-elastomeric material which is strong enough to move tissue as desired. A suitable material is Mylar® fabric. A non-elastomeric material may have a more controllable shape because it will not stretch. A non-elastomeric material will collapse inward automatically due to the pressure of the tissue around it, whenever it is not inflated. Many of the illustrated embodiments which are discussed as being made below. Fluid flowing through the joint flushes out debris in the joint. The device can include third or additional lumens for a scope or tools to pass through. Since the tube is both flexible and fixed in place, it can remain in the patient even when the patient is ambulatory. It thus provides a permanent passage for the surgeon to access the joint. 
     There can be multiple bladders at a location on the cannula, independently controlled, to position the cannula. At least one bladder is preferably at the tip of the device to expand or stretch tissue or to stabilize the device. 
     In any of the illustrated embodiments, the bladder can be made of a different material from the cannula, as opposed to, for example, a Fogarty catheter which is made of all one material. This will allow for variations in construction, with the bladder being made of one material to better perform its functions and the cannula or other supporting member being made of another material to better perform its functions. 
     The expanding (inflatable) bladders of the present invention are constructed in various manners as set forth below. The bladder can stretch cannula walls. The bladder can move tissue and allow selective manipulation of tissue, even arthroscopically. The bladder also has a tamponade effect, lessening bleeding in the surrounding tissues. 
     The bladder also distributes the retractive force, reducing stress on delicate tissues such as nerve tissue. of an elastomeric material can also be made of a none-lastomeric material. 
     The expandable bladder can be made of a biodegradable material. In such a case, the biodegradable portion can be made detachable from the remainder of the retractor, so that it can be detached and left in the body after surgery. This is useful, for example, to prevent adjacent tissue planes from scarring together after surgery. The biodegradable mass will in time disappear, allowing the tissues to adjoin after they are healed. 
     The bladder can be made of a composite material—that is, a particle or fiber-reinforced material. Many suitable materials are in use in industry. Composite materials can be made stronger while still retaining flexibility and fluid-sealing capabilities. Composite materials also provide the capability to have a bladder assume a specific shape upon expansion. 
     The bladder can be made of a composite biodegradable material. 
     The bladder(s) can be made of two different materials bonded together, such as a stretchable (low-modulus) and a non-stretchable (high-modulus) material. Mylar® and Silastic® are suitable materials, or metal for a stiff material. As the inflation fluid (typically air) is introduced, it takes the path of least resistance and the non-stretchable material fills out to its expanded shape first. Then the stretchable material expands, in a manner constrained by the already-expanded non-stretchable material. 
     The bladder can be made of a transparent material to provide a better view of the operating area and improved visualization. 
     The bladder may have a dual durometer layered construction, with a thin layer for fluid retention overlying a thicker layer for shaping. Other laminated constructions are possible, also. 
     The external shape of the retractor when expanded, and the amount of expansion, are designed for the specific application on which that retractor is to be used. For example, if the surgeon is working against bone, he can select a retractor which is configured so that it stays flat against the bone, and expands away in the opposite direction, to push tissue away from the bone and create a working and visualization space next to the surface of the bone. 
     There are several ways to control shape of expansion-thick and thin areas (gaps, ridges, stiffened areas, etc.), fiber reinforcing, dual durometer construction, different materials affixed together, tethering cords, and pre-shaping. 
     Upon application of a given amount of force, a thinner material will stretch more than a thicker material. Thus, all other factors being equal, an inflatable device will stretch more where it is thinner, and will stretch less where it is thicker. This occurrence can be used to control the shape into which a bladder expands when it is inflated by fluid under pressure. 
     As a simple example, it can readily be seen that if a bladder has one half made of a very thick material and one half made of the same material but much thinner, then upon the introduction of fluid under pressure, the thin material will stretch more quickly (easily), and the bladder will expand unevenly. The thin half of the bladder will deform more under the same pressure until the force needed to stretch it further is equal to the force needed to stretch the thicker material. The half made of the thicker material will then begin to stretch, also. Thus, the thickest point on the wall will be at the crown area (farthest out). 
     The areas of variation in cross section can be of various shapes and directions to control the expansion rates. For example, the circumference of a bladder can be configured as an incomplete hoop. Thus, most of the circumference is of a thicker material, while selected areas are thinner. Upon the introduction of fluid under pressure, the thinner areas will expand first, with each thicker area moving outwardly as a whole. 
     There can be ribs around the circumference. Areas of thickness or thinness can extend longitudinally, circumferentially, radially, or in broken segments. 
     A second way to control the shape of expansion is the use of a fiber reinforced (composite) material. The direction of the fibers, along with their number, spacing, layering, and length, controls the rate of expansion of the matrix material. Also, areas devoid of fibers will expand faster or further than areas with more or stiffer fibers. 
     Specifically, the fibers resist stretching along their length. Thus, the bladder will stretch more in a direction across the fibers, or where the fibers are not present, than in a direction along the fibers. Fibers can be placed at the edge of the bladder to maintain the shape of the bladder when inflated. Fibers can be layered, with one layer in one direction and another layer in another direction to control expansion in the other direction. Fibers can be placed in overlapping layers, to allow expansion in one plane only. 
     Adding fibers makes the bladder more puncture and tear resistant. Note that the bladder can, for this purpose, also be made of or include a self-sealing material. 
     A third way of controlling expansion shape is to pre-shape the bladder to assume a certain form when expanded. This is done in the molding process. The bladder is typically formed on a mandrel which is of a particular shape and which is sized about half way between the unexpanded and the expanded size of the bladder. 
     The pre-determined shape of the unexpanded bladder is basically a combination of varying wall thickness and ribbing, made on a three part mold. 
     In certain experimental models constructed to date, the bladder is bonded onto a nylon stalk of 7 mm O.D. The bladder is stretched from about 3 mm to about 7 mm at its smallest dimension. This pre-stretched area puts the material under tension. Any larger diameter portions are relaxed. As the bladder is expanded, the smaller diameter portion, which is already partially expanded, stretches at a limited rate. The larger diameter portion (under no load) expands at a faster rate. They balance out at a point where all the material is under basically the same load in tension. This is the point at which the shape is attained. 
     It should be understood that this particular example and its dimensions are not limiting, and that any diameter can be used. This is an example of a specific sized cannula for a specific application. 
     With a typical material (silicone), the more you stretch the material, the more force is needed to stretch it further. 
     The prestretching of the bladder is done so that the bladder lies flat on the cannula body. The bonding areas are such that as the expansion takes place the material expands radially outwardly as well as axially. 
     It can alternately be doubled up at a certain area, such as the tip of a stalk or cannula. This will allow maximum expansion at the tip. 
     Tethering cords can be fixed to bladder portions and extend between them to control and/or limit the expansion of the bladder. This can be done with bladders made of a composite material or including plates or other thicker areas. In a cannula construct, the tethering cords can run between the cannula body to the crown of the bladder to control and/or limit its expansion. 
     Plates can be added in which will limit the shape of the bladder or create an edge. For example, if a flat plate is added, the bladder can expand in a circular fashion but the flat plate will remain flat and provide a flat area on the outside of the bladder. Or the plate can be circular, or at an angle to create an edge. There can be multiple such plates added to create specific shapes. Tethering cords can be used to extend to the plate. This can be useful in the cannula construct. 
     The bladder can also have a bellows-type construction for increased expansion control and structural rigidity. 
     Suction can be used to collapse any of the devices to facilitate removal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features of the present invention will become apparent to one skilled in the art upon a consideration of the following description of the invention with reference to the accompanying drawings, wherein: 
     FIG. 1 is a side elevational view of a joint irrigation apparatus; 
     FIG. 2 is a longitudinal sectional view through the apparatus of FIG. 1; 
     FIG. 3 is a view taken along line  3 — 3  of FIG. 1; 
     FIG. 4 is a view of an alternate embodiment of the apparatus of FIG. 1; 
     FIG. 5 is a transverse sectional view through an expanding cannula; 
     FIG. 6 is a view of the cannula of FIG. 5 in an expanded condition; 
     FIGS. 7A and 7B illustrates a cannula having an outwardly expanding bladder formed within the wall of the cannula; 
     FIGS. 8A and 8B illustrates a cannula having an inwardly expandable bladder formed in the wall of the cannula; 
     FIGS. 9A and 9B illustrates a cannula having an inwardly and outwardly expanding bladder formed within the wall of the cannula; 
     FIGS.  10 A- 10 C illustrate the expansion of a cannula having viscoelastic walls by means of an inserted inflatable member; 
     FIGS.  11 - 13  illustrate a cannula comprising a cylinder expandable along its entire length; 
     FIG. 14 illustrates an elliptical or an oval-shaped cannula having tethering cords; 
     FIG. 15 illustrates a square-shaped cannula having tethering cords; 
     FIG. 16 is a schematic view of a retractor shown in the unexpanded or contracted and expanded or extended conditions; 
     FIG. 17 is a schematic view of a retractor extending through a cannula and mounted on the end of a separate shaft; 
     FIG. 18 is a schematic view similar to FIG. 17 illustrating the use of a fiber optic scope with the retractor; 
     FIG. 19 is a schematic view showing a retractor inserted through a separate side opening in a cannula; 
     FIGS.  20 A-E are schematic views of a few of the many and various shapes in which the inflatable portion of the retractor may be formed; 
     FIG. 21 is a schematic view of a retractor shown mounted on the end of a cannula and having an opening therein for a scope to pass through; 
     FIG. 22 is a diagram of a fluid supply system for operating a retractor; 
     FIG. 23 is a view illustrating the use of a retractor to position the end of a scope; 
     FIG. 24 is a view similar to FIG. 23 further illustrating the use of a retractor to position the end of a scope; 
     FIG. 25 illustrates a cannula having a tethering cord connecting a balloon portion to the cannula wall; 
     FIG. 26 is a sectional view illustrating a continuous mass of body tissue which is free of an opening; 
     FIG. 27 is a schematic illustration depicting the manner in which the cannula of FIG. 25 is inserted into the mass of body tissue of FIG.  26  and expanded to form an open space in the mass of body tissue at a location adjacent to and axially outward from a distal end of the cannula; 
     FIG. 28 is an enlarged view of the cannula of FIG.  27  and illustrating the manner in which a fiberoptic scope and a tool are inserted through the cannula into the space formed in the body tissue at a location axially outward from the distal end of the cannula by expanding the cannula; 
     FIG. 29 is an enlarged fragmentary sectional view of a cannula having a flexible wall and tethers, the flexible wall being shown in a retracted condition; 
     FIG. 30 is a fragmentary sectional view, generally similar to FIG. 29, illustrating the flexible wall in an extended condition with a tether limiting outward movement of a portion of the flexible wall; 
     FIG. 31 is a fragmentary sectional distal end view, taken generally along the line  31 — 31  of FIG. 30, illustrating the manner in which a plurality of tethers extend outwardly from a main section of the cannula toward the flexible wall; 
     FIG. 32 is a fragmentary schematic plan view of a portion of a side wall of the flexible wall of the cannula of FIGS.  29 - 31  and schematically illustrating the relationship between reinforcing fibers in a proximal portion of the side wall; 
     FIG. 33 is a fragmentary plan view of another portion of the side wall of the flexible wall of the cannula of FIGS.  29 - 31  and schematically illustrating the relationship between reinforcing fibers in a distal portion of the flexible wall; 
     FIG. 34 is a plan view of a portion of an end wall of the flexible wall of FIGS.  29 - 31  and schematically illustrating the relationship between reinforcing fibers in the end wall; 
     FIG. 35 illustrates a cannula which is selectively expandable at one or more selected longitudinal locations; 
     FIGS. 36 and 37 illustrate a cannula having a plurality of circumferentially spaced expandable segments; 
     FIGS.  38 - 43  illustrate longitudinally extending radially expansible cannula segments; 
     FIGS. 44 and 45 illustrate expandable devices having textured surfaces; 
     FIGS.  46 - 49  illustrate a cannula having an expandable bladder portion with a varying wall thickness; 
     FIGS.  50 - 52  illustrate flexible bladder portions having relatively rigid members molded therein; 
     FIGS. 53 and 54 illustrate rigid members molded into the elastomeric material of an inflatable bladder circumscribing a cannula or other medical device; 
     FIGS. 55 and 56 illustrate a cannula having a bladder with a doubled-over bladder portion; 
     FIG. 57 is a schematic illustration of a cannula having the same general construction as the cannula of FIGS. 55 and 56, the cannula of FIG. 57 having tethers and being shown in a retracted condition; 
     FIG. 58 is a schematic illustration of the cannula of FIG. 57 in an extended condition with the tethers restraining movement of a flexible wall portion of the cannula; 
     FIG. 59 is a schematic illustration of a cannula having the same general construction as the cannula of FIG. 58, the cannula of FIG. 59 having a plurality of tethers disposed within a chamber formed by the expanded flexible wall of the cannula; 
     FIG. 60 is an end view, taken generally along the line  60 — 60  of FIG. 59, illustrating the manner in which a plurality of tethers are connected with the flexible wall of the cannula; 
     FIG. 61 is a sectional view, taken generally along the line  61 — 61  of FIG. 59, illustrating the manner in which a plurality of tethers extend outwardly from a main section of the cannula toward an inner side surface of the flexible wall of the cannula; 
     FIG. 62 is a sectional view, taken generally along the line  62 — 62  of FIG. 59, illustrating the manner in which a plurality of tethers extend outwardly from a main section of the cannula towards the inner side surface of the flexible wall; 
     FIG. 63 illustrates an expanded bladder having adjoining portions with different material characteristics; 
     FIG. 64 illustrates an expanding device having an expanding bladder made of a plurality of materials laminated together; 
     FIGS.  65 A- 65 C illustrate triangular-shaped expanding portions; 
     FIGS.  66 A- 66 C illustrate trapezoidal-shaped expanding portions; 
     FIGS.  67 A- 67 C illustrate the use of overlapping and/or incomplete fibers for expansion control; 
     FIGS.  68 - 76  illustrate a variety of bladder devices including reinforcing fibers and/or tethering cords; and 
     FIGS.  77 - 79  illustrate a structural unit comprising a series of expandable bladders laminated together. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS.  1 - 3  illustrate an arthritis irrigation apparatus  10 . The irrigation system  10  includes a cannula  12  having a disc portion  14  and a longitudinally extending cannula body  16 . A central wall  18  divides the cannula body  16  into two longitudinally extending lumens  20  and  22 . 
     An expandable bladder  30  is connected to or formed integrally with the cannula  12  at the distal end  32  and proximal end  34  of the cannula body  16 . The expandable bladder  30  includes a longitudinally extending wall portion  36  and a transversely extending wall portion  38 . The expandable bladder  30  is supplied with fluid under pressure through a fluid supply port  40  closed by a rubber diaphragm seal  42 . The lumens  20  and  22  are closed by similar diaphragm seals  44  and  46 , respectively. The cannula body  16  has a recessed portion  48  in which the bladder  36  fits when unexpanded. 
     The system  10  is inserted into a pre-made opening until the disc portion  14  engages the skin. Upon the introduction of fluid under pressure into the expandable bladder  30 , the bladder  30  expands from the unexpanded condition illustrated in FIG. 1 to the expanded condition illustrated in FIG.  2 . The bladder wall  36  moves radially outwardly, and skin or other tissue is trapped between the bladder wall  38  and the distal surface  49  of the disc portion  14  of the cannula  12 . 
     The system  10  is thus locked in place, with the distal end  32  in position in a joint. Appropriate instruments may then be inserted through the diaphragm seals  44  and  46  into the lumens  20  and  22 , respectively. For example, flushing fluid may be supplied to the joint through the lumen  20 , while it is removed from the joint by suction through the lumen  22 . When the joint is not being flushed, the diaphragm seals  42 ,  44  and  46  seal the openings in the system  10 , and the expanded bladder  30  retains the system  10  in place in the body. 
     It should be understood that any number of lumens, other than two, can be included in the cannula body  16 . The number of lumens is limited only by the size of the instruments to be inserted through the cannula body  16 . In a preferred embodiment, the disc portion  14  of the cannula body  12  is about the size of a nickel, with the cannula body  16  being correspondingly smaller. Of course, the dimensions and arrangement of the various portions of the system  10  could be modified to enable the placement of other instruments through the cannula body  16 . 
     Each of the lumens may have a controllable inflow-outflow portal. These can be substituted for the diaphragm seals. These portals may be a simple tube with an on-off valve attached, as is known in the art, or can be another suitable structure. 
     FIG. 4 illustrates an alternate embodiment of the system  10  in which a system  50  includes a round or doughnut-shaped bladder  52  extending between the distal end  32  and the proximal end  34  of the cannula wall  16 . This doughnut-shaped bladder can be easier or less expensive to manufacture, and also can provide more cushioning effect to the tissues which it engages. Again, tissue is trapped between the bladder  52  and the disc portion  14  of the cannula  12 , to retain the system  50  in place in the body. 
     FIGS. 5 and 6 illustrate a variable size cannula in which inflatable bladders push apart two relatively rigid portions to move tissue. FIGS. 5 and 6 are transverse cross sections through a longitudinally extending cannula  60 , which can be any desired length. The cannula  60  expands radially outwardly along its length. 
     The cannula  60  includes a first C-shaped portion  62  having ends  64  and  66  and a second C-shaped portion  68  having ends  70  and  72 . An inflatable bladder  74  has one end portion  76  fixed to the end portion  64  of the portion  62 . The opposite end portion  78  of the bladder  74  is fixed to the end portion  70  of the portion  68 . Similarly, a bladder  80  has one end portion  82  fixed to the end portion  66  of the portion  62 , and its second end portion  84  fixed to the end portion  72  of the portion  68 . 
     The portion  62  has an outwardly facing surface  86  and the portion  68  has an outwardly facing surface  88 . The cannula  60  has a central opening  90  which is enlarged in size upon expansion of the bladders  74  and  80  to provide a larger working space while reducing tissue damage. Upon the introduction of fluid under pressure into the bladders  74  and  80 , the portions  62  and  68  are moved away from each other to engage tissue with their surfaces  86  and  88 , respectively. The relatively rigid portions  62  and  68  provide increased pushing strength of the cannula  60  as compared to a soft inflatable bladder. Further, the cannula  60  also holds its structural shape better and is able to maintain the opening better. Thus, with the cannula  60 , a limited incision can be made in the tissue, which incision is then enlarged by the cannula itself rather than with a cutting device. The application of suction to the bladders  74  and  80  causes them to deflate to return the cannula  60  to its unexpanded condition. The tissue is viscoelastic and thus will stretch out during its expansion by the expander  60 , and then return to its original unexpanded shape, i.e., the original size of the incision after removal of the cannula. Thus, less tissue damage results. 
     Cannulas in accordance with the present invention may have one or more bladders as part of the cannula wall. These may create inward or outward expansion. For example, FIGS. 7A and 7B illustrate a longitudinal portion of a cannula  92  having a wall portion  94  defining a central opening  96  through which surgical instruments or the like can be passed. The wall portion  94  includes a portion  98  partially defining a fluid chamber  100  which may be supplied with fluid under pressure through a fluid supply line  102  extending through the cannula wall  94 . On the introduction of fluid under pressure into the volume  140 , the wall portion  98  of the cannula  92  expands radially outwardly, from the unexpanded condition of FIG. 7B to the expanded condition of FIG. 7A, as a seal or retainer against tissue. 
     Similarly, the cannula  104  illustrated in FIGS. 8A and 8B includes a wall  106  having an inner portion  108  defining a fluid volume  110 . Upon the introduction of fluid under pressure through a supply passage  112  in the wall  106 , the wall portion  108  expands radially inwardly to close at least partially the central opening  113  in the cannula  104 . The expanding portion  114  of the cannula  104  thus acts as a valve or seal for the central opening  110  of the cannula. This can be very useful if it is desired to close the central opening  110  while leaving the cannula  104  in place in the body tissue. The central passage  113  can also be closed completely. Alternatively, the wall portion  108  can lamp onto an instrument or scope extending through the passage  113  to lock it in place. 
     In addition to the cannula inner seals or valves formed by the radially inwardly expanding bladder walls, the present invention contemplates cannula inner seals formed by other structures. For example, a simple mechanical seal can be used such as a diaphragm seal like the seals  44  and  46  (FIGS.  1 - 3 ). Other forms of mechanical seals can be used, such as a membrane (iris) valve, screw lock, twist lock, or luer lock. It is intended that these alternatives be included within the scope of the invention. 
     FIGS. 9A and 9B illustrate a cannula  116  having an expanding portion  118  in its wall  120 . Upon the introduction of fluid under pressure through a fluid supply passage  122  in the wall  120 , a portion  124  of the cannula wall  120  expands radially outwardly while a longitudinally co-extensive portion  126  of the wall  120  expands radially inwardly to partially or completely close a central longitudinally extending passage  128 . Thus, the cannula  116  has a portion  118  which expands both inwardly and outwardly. The cannulas of FIGS.  7 - 9  thus illustrate the principle of expanding either inward or outward or both at selected axial locations along the longitudinal extent of a cannula. 
     FIGS.  10 A- 10 C illustrate the expansion of a stretchable cannula by an expandable member inserted therein. A cannula  130  has a wall  132  defining a central longitudinally extending passage  134 . The cannula  130  is made of a stretchable material having viscoelastic properties whereby the wall  130  when stretched outwardly will retain its stretched condition for a period of time. An expander  136  includes a stalk  138  on the end of which is mounted an expanding portion  140 . Upon insertion of the expander  136  into the cannula  130  as illustrated in FIG. 10B, the expanding portion  140  may be expanded radially outwardly by the introduction of fluid under pressure through the stalk  138 , to stretch a wall portion  142  of the cannula wall  132  radially outwardly. Upon subsequent deflation of the expanding portion  140  of the expander  136 , and removal of the expander  136  from the cannula  130 , the cannula wall portion  142  remains in its stretched condition for at least a period of time. The cannula  130  is thereby retained in place in the surrounding tissues while instruments or a scope can be passed through it. 
     The present invention contemplates monitoring the pressure applied to tissue by the expanding cannula. This can be done, for example, with any known pressure sensor or strain gauge. Such is indicated schematically at  144  in FIG. 10C as being on the wall of the device  136  used to stretch the cannula  130 . Alternatively, it is indicated schematically at  146  in FIG. 10C as being on the wall of the cannula  130 . 
     FIGS.  11 - 13  illustrate a cannula  150  which comprises a cylinder expandable along its entire length. The cannula  150  has a central longitudinally extending working passage  152  defined by an inner wall  154 . An inflation space  156  separates the inner wall  154  from an outer wall  158  of the cannula  150 . A series of tethering cords  160  extend between the inner wall  154  and the outer wall  158 . 
     The inner and outer walls  154  and  158 , respectively, of the cannula  150  are constructed so that, upon the introduction of fluid under pressure into the inflation space  156 , both walls expand radially outwardly to a larger diameter. Fluid is introduced through a fluid inflow means (not shown) which may be a simple tube or valve in fluid communication with the inflation space  156 . The cannula  150  expands from the condition shown in FIG. 12 to a further expanded condition as illustrated in FIG.  13 . The tethering cords  160  limit movement of the outer wall  158  of the cannula  150  from the inner wall  154  of the cannula  150 . In a preferred embodiment, the tethering cords  160  comprise fibers (either solid or stranded) having their ends fixed to the inner wall  154  and the outer wall  158  and extending therebetween. The tethering cords  160  may be unextensible, or they may be somewhat extensible upon the application of a relatively large amount of force. Use of the tethering cords  160  is advantageous in that it allows for controlled expansion of spaced portions of an inflatable device. 
     The cannula  150  is circular in cross sectional shape. It should be understood that the present invention is not limited to circular cannulas, but specifically contemplates the provision of cannulas of any type described herein of other cross sectional shapes. The cross sectional shape of a particular cannula may be selected in accordance with a particular application for that cannula. For example, an elliptical or oval-shaped cannula  162  (FIG. 14) may be more suitable for insertion between adjacent tissue planes, as it conforms more to the opening between the tissue points. The oval-shaped cannula  162  includes an outer wall  164 , an inflation space  166 , an inner wall  168 , and a working passage  170  extending axially therethrough. Optionally a plurality of tethering cords  172  extend between the inner wall  168  and the outer wall  164 , and limit movement of the outer wall  164  from the inner wall  168 . 
     FIG. 15 illustrates, as exemplary of the other shapes of cannulas which may be provided, a rectangular (in this case square) shaped cannula  174  optionally having a plurality of tethering cords  176  extending between the outer cannula wall  178  and an inner cannula wall  180 . The inner wall  180  defines a working passage  182  extending longitudinally through the cannula  174 . 
     FIG. 16 illustrates schematically a retractor  510  in accordance with the present invention. The retractor  510  includes a fluid supply structure  512  and an expandable balloon or bladder  514  having a flexible wall located at or near the end of the structure  512 . The bladder is expandable, under the force of fluid under pressure, from an unexpanded or retracted condition as indicated in full lines at  514  to an expanded or extended condition as shown in broken lines at  516 . In the expanded condition, the transverse dimension  518  of the bladder  514  is significantly greater than its transverse dimension before expansion, that is, the dimension  520 . Also, in the expanded condition, the transverse dimension  518  of the bladder  514  is significantly greater than its longitudinal dimension  520 . 
     When the bladder of the retractor is expanded inside the body, it retracts tissue. As seen in FIG. 17, a bladder  522  is mounted on the end of a separate shaft  524  within a cannula or scope  526 . The cannula or scope  526  has been inserted into the body through an opening  528  in the skin (either pre-existing or made in situ) which has a transverse dimension  530 . The bladder  522  when in its unexpanded condition as shown in broken line is smaller than the dimension  530  of the body opening, but when expanded, it expands to a dimension  532  which is significantly greater than the dimension  530 . An actual space or working space  534  is formed which was not present before the expansion of the bladder. 
     The newly-formed working space may be used, for example, for better use of a fiber optic scope as illustrated in FIG.  3 . In FIG. 18, a retractor  510  is passed through an opening  536  in a cannula  538 . A fiber optic scope shown schematically at  540  is also passed through the cannula  538 . The cannula  538  is inserted into the body through an opening in the body tissues  542  which is only as large as the outer diameter of the cannula  538 . The retractor  510  is then inflated, with air or another fluid being supplied through a rigid or flexible shaft  544  to an expandable bladder  546 . The bladder  546  expands transversely, retracting the tissues  542  transversely and creating a working space  534 . By axial manipulation of the shaft  544 , the bladder  546  is movable either toward the end of the scope  540  in the direction as indicated by the arrow  548 , or away from the end of the scope  540  as indicated by the arrow  550 , as desired. Such manipulation of the retractor can selectively move and place the adjoining body tissues where the surgeon wants them to enable better use of the scope  540  by the surgeon. 
     As shown in FIG. 19, the retractor  510  may be inserted into a cannula  552  through a separate opening  554  therein. The opening  554  is shown on the side of the cannula  552 , although, of course, it may be on the end of the cannula as is typical. Alternatively, the retractor  510  may be inserted into the body through an opening in the body tissues separate from the opening through which the fiber optic scope is inserted. Either of these options allows for greater flexibility in the insertion and positioning of the retractor  510  relative to the other instruments being used such as the arthroscope. 
     Also as indicated in FIG. 19, the bladder  558  may be eccentric or eccentrically located relative to the opening  560  at the junction between the bladder  558  and the shaft  562 . This is accomplished by using known techniques to form the bladder  558  of a material, construction, and shape such that it expands into the eccentric shape as illustrated in FIG. 19 when inflated by fluid under pressure through the shaft  562 . In this manner, an improved visualization and working space  534  is created which is eccentrically located relative to the other instruments being used. This may be preferable when the surgeon is using an angled scope. 
     FIG. 19 is illustrative of the fact that the bladder of the retractor of the present invention may be formed so as to expand into any particular shape as desired for the particular application. This feature is also shown schematically in FIGS. 20A through 20E which illustrate, respectively, retractor bladders which assume in their expanded states in round, oval, eccentric, oblong, and conical shapes. Such shapes may generally be called “nonuniform” shapes for purposes of the present invention, and retractors with such a shape will expand in a “non-uniform” manner. Such shapes may include, for example, wedge- or U-shaped filaments which collapse at the skin, then expand at deep tissue planes for visualization and working space. The bladder may also cup and protect vital tissues such as nerves and arteries while working on other tissues such as muscle. 
     Another typical form of construction is illustrated in FIG. 21, which shows a bladder  564  which in its expanded condition assumes a toroidal shape. Again, the width  566  of the bladder  564  is significantly greater than its length  568 . The bladder  568  is expanded by fluid under pressure received through a fluid channel  570  formed between a cannula or scope outer wall  572  and inner wall  573 . By virtue of the toroidal shape of the bladder  568 , the leading end  574  of the scope  576  may be passed axially completely through the retractor into the working space  534  which has been created in the tissues  578 . Such a bladder  564  may also be mounted on a separate shaft inserted through the scope of the cannula. 
     In all cases, the fluid pressure within the bladder of the retractor is monitored and controlled to keep the force exerted by the retractor at a safe level for tissue to prevent tissue necrosis. As indicated schematically in FIG. 22, a retractor  510  is supplied with fluid under pressure from a fluid pressure source  580  via a fluid supply line  582 . A regulator  584  controls the supply of fluid to the retractor  510 . A pressure sensor  586  is located within the retractor  510  and senses the pressure of the fluid within the retractor  510 . The pressure sensor  586  sends a signal which is representative of the fluid pressure within the retractor  510 , via wiring  588 , to a monitor  590 . The monitor  590  is connected via control wiring  592  to the pressure regulator  584 . The pressure of the fluid within the retractor  510  may thus be monitored and controlled either manually or automatically, by means which are well known in the art and so need not be described further herein. The source  580  of fluid supply may be, for example, the air pressure supply which is commonly found in hospital operating rooms. 
     By virtue of this ability to monitor the pressure within the retractor  510 , the retractor  510  can also be a useful diagnostic tool. The strength or pressure or resistance of tissue to movement can be measured by the pressure required to move it. 
     FIGS. 23 and 24 illustrate the use of a retractor of the present invention to stabilize a fiber optic scope. The retractor  510  (FIG. 23) includes a bladder  594  which retracts the body tissues  596  away from the scope  598 . Since the bladder  594  engages and pushes radially outwardly on body tissues  596  all around the scope  598 , the retractor becomes fixed in position when it is so expanded. If the bladder  594  is fixed to the end of the scope  598 , the retractor  510  thereby fixes the end of the scope  598  in position relative to the body tissues  596 . When a camera is being used with the scope  598 , the picture normally moves or jumps around because of the movability of the end of the scope  598 . This is prevented by so using the retractor  510  to stabilize the scope  598 , leaving the surgeon with both hands free to work and a steady view of the work area. 
     FIGS. 23 and 24 also illustrate how the retractor of the present invention can be used to control the placement of the tip of a fiber optic scope. The retractor  510  is formed with an eccentric bladder  594  which retracts the body tissues  596  away from the scope  598  to a greater distance in one direction than in another. Thus, by rotating the retractor  510 , the surgeon can place the tip of the scope  596  closer to the body tissue  599  (FIG. 23) on one side of the working space  534 , or to the body tissue  597  (FIG. 24) on the other side of the working space  534 . Such variable placement can, of course, also be attained via use of a retractor  510  which includes a bladder which can be expanded to varying shapes. 
     The retractor of the present invention has many uses in the surgical field. The retractor  510  can be used to retract soft tissue from bone, for example within a joint. The retractor  510  is inserted between the bone and the soft tissue  112 . The bladder  594  is then expanded. The soft tissue is forced away from the bone. The surgeon may then use a fiber optic scope or other instrument to work within the working space created by the retractor  510 . The retractor of the present invention can provide the force needed to move the soft tissue away from the bone may vary between about 100 and 1000 mm Hg, and thus, it is important to maintain the proper pressure between the two. The retractor  510  can do this since it operates on high fluid pressures of about 10 to 1000 mm Hg and it utilizes a high strength material such as Kevlar, Mylar, or another durable polymer such as Polylite®, a product of Reichhold Chemicals, Inc. This simple retraction of soft tissue from bone would otherwise be impossible. 
     FIG. 25 illustrates the use of a tethering cord to position a bladder portion relative to a cannula wall. A cannula  190  has a main section with an outer wall  192  and an inner wall  194  spaced therefrom. The wall  194  divides the interior of the cannula  190  into a working passage  196  and an inflation fluid passage  198 . The passage  198  opens into a bladder or flexible wall  200  fixed at the distal end  202  of the cannula  190 . Tethering cords  204  extend between the cannula wall  192  and a junction or crown  206  of the bladder or flexible wall  200 . The tethering cords  204  limit movement of the crown portion  206  of the bladder or flexible wall  200  from the cannula wall  192 . 
     The cannula  190  of FIG. 25 is only illustrative of the many ways in which bladder portions can be positioned relative to cannula portions by tethering cords such as the tethering cord  204 . The number and positioning and length of the tethering cords determines the relative movement of the various bladder portions to which they are attached, thus aiding in controlling the expanded shape of the bladder relative to the cannula. 
     The cannula  190  can be used to create an open space in a continuous mass of body tissue. Thus, a continuous mass  207  (FIG. 26) of body tissue is free of naturally occurring openings. The mass  207  of body tissue is enclosed by skin  208 . The skin  208 , like the mass  207  of body tissue, is free of naturally occurring openings. 
     A small slit or incision  209  (FIG. 27) is formed by a surgeon in the skin  208 . The cannula  190  is then inserted through the slit  209  in the skin  208 . At this time, the bladder  200  in a retracted condition in which it is tightly disposed against the outer wall or main section  192  of the cannula. 
     Once the cannula  190  has been inserted through the slit  209  and moved into the mass  207  of body tissue, the bladder or flexible wall  200  is moved from the retracted condition to an extended condition. This is accomplished by a conducting fluid pressure through the passage  198  into the flexible wall  200 . The fluid pressure expands the flexible wall  200  from a contracted condition to an extended condition. 
     As the flexible wall  200  is extended, a portion  211  of the mass  207  of body tissue is moved outward away from the outer wall  192  of the main section of the cannula  190 . Thus, as the flexible wall  200  is inflated, an outer side surface of the flexible wall presses against the portion  211  of the mass  207  of body tissue, in the manner indicated schematically by arrows in FIG.  27 . This pressure moves at least part of the portion  211  of the mass  207  of body tissue toward the left (as viewed in FIG.  27 ). As this occurs, force is transmitted from the portion  211  of the mass of body tissue to a portion  213  (FIG. 27) of the mass  207  of body tissue. 
     The force transmitted through the mass  207  of body tissue to the portion  213  of the body tissue moves the portion  213  of the body tissue away from the distal or axially outer end  202  of the cannula  190 . As this occurs, an open space  215  is formed at a location in the mass  207  of body tissue where there was no space prior to insertion of the cannula  190  and expansion of the flexible wall  200 . 
     The portion  213  of the mass  207  of body tissue is moved away from the distal end  202  of the cannula  190  under the influence of force which is transmitted through the mass of body tissue from the portion  211  of the body tissue to the portion  213  of the mass of body tissue. Thus, the outer side surface of the flexible wall  200  is effective to apply force, in the manner indicated by arrows in FIG. 27, against only the portion  211  of the mass  207  of body tissue. Force is transmitted by body tissue from the portion  211  of the mass of body tissue to the portion  213  of the mass  207  of body tissue. The force transmitted through the body tissue moves the portion  213  of the mass  207  of body tissue away from the distal end  202  of the cannula  190  and thereby create the open space  215  in the mass  207  of body tissue. 
     Creation of the open space  215  in the mass of body tissue provides a viewing area adjacent to the distal end  202  of the cannula  190  for a surgeon to operate. Thus, a endoscope  217  and an operating tool  219  can be inserted through the passage  196  in the cannula  190 . The outer or distal ends of the endoscope  217  and operating tool  219  project beyond the distal end  202  of the cannula  190  into the open space  215 . This enables a surgeon to view the distal end of the operating tool  219  through the endoscope  217  and to view the portion of the mass  207  of body tissue which is to be operated on with the tool  219 . Of course, since the surgeon can view the operations being performed by the tool  219 , the work of the surgeon on the body tissue  207  is greatly facilitated. 
     The flexible wall or bladder  200  of the cannula  190  (FIG. 28) includes a side wall  191  and an end wall  193  which are formed of an elastomeric material. When the cannula  190  is inserted through the incision  209 , the natural resilience of the elastic end wall  193  and elastic side wall  191  causes the bladder or flexible wall  200  to tightly enclose the outer wall  192  of the cannula  190 . This results in the tethers  204  being enclosed by the bladder or flexible wall  200  and being pressed against the outer wall  192  of the cannula  190 . 
     After the cannula  190  has been inserted through the incision  209  and moved into the continuous mass  207  of body tissue, the bladder  200  is inflated to cause the elastic side wall  191  and end wall  193  of the bladder  200  to move outward to the extended condition shown in FIG. 28. A radially and axially inner end  195  of the side wall  191  of the bladder  200  is bonded to the outer side surface of the outer wall  192  of the cannula  190 . A radially inner end of the end wall  193  is bonded at  197  to the outer side surface of the outer wall  192  of the cannula  190 . An opening for the fluid passage  198  extends through the outer wall  192  at a location between the connection  195  of the side wall  191  with the outer wall  192  of the cannula  190  and the connection  197  of the end wall  193  with the outer wall  192  of the cannula. 
     When the bladder or flexible wall  200  (FIG. 28) is to be inflated from the retracted condition to the extended condition shown in FIG. 28, fluid pressure is conducted through the passage  198  into the bladder  200 . As the fluid pressure flows into the bladder  200 , an annular chamber  199  is established around the outer wall  192  of the cannula  190 . As this occurs, the side wall  191  of the bladder  200  presses body tissue radially outward and axially away from the distal end  202  of the cannula  190  in the manner indicated by the arrows in FIG.  27 . As this is occurring, the body tissue extends axially outward from the junction  206  between the side wall  191  and end wall  193  of the bladder or flexible wall  200 . The body tissue which extends outward from the junction or crown  206  of the bladder  200  is tensioned and tends to continue outward from the junction. Due to the fact that the end wall  193  extends radially outward from the cylindrical outer wall  192  of the cannula  190 , an opening is formed immediately axially outward from the end wall  193  as the bladder  200  is inflated. 
     As the bladder  200  is inflated, the tether cords  204  are extended from a nonlinear configuration toward the linear configuration illustrated in FIG.  28 . When the bladder or flexible wall  200  reaches the fully inflated condition shown in FIG. 28, an inflated structure is formed. The tether cords  204  restrain the junction between the side wall  191  and  193  from moving further radially outward. This results in the elastic side wall  191  having a configuration corresponding to the configuration of a portion of a cone and the elastic end wall  193  having a configuration corresponding to the configuration of a flat annular disk. The side wall  191  and end wall  193  are initially formed to this configuration while they are in a stretched condition over a forming tool. The tethering cords  204  cooperate with the side wall  191  and end wall  193  to ensure that the inflated structure formed by the bladder  200  has the configuration illustrated in FIG.  28 . 
     The body tissue  207  which is pressed radially outwardly and axially away from the distal end  202  of the cannula  190  by movement of the bladder  200  from the retracted condition to the expanded condition shown in FIG. 28 causes the body tissue to move away from the end wall  193  as the bladder is inflated. This results in the formation of the open space  215  axially outwardly from the end wall  193 . Thus, the portion  211  of the body tissue disposed to the left (as viewed in FIG. 28) of the inflated bladder or flexible wall  200  pulls or tensions the portion of the body tissue which extends across the circular crown portion or junction  206 . The forces transmitted through the body tissue itself tends to pull the body tissue away from the end wall  193  to form the open space  215  in the manner illustrated in FIG.  28 . 
     A cannula  600  (FIGS. 29 and 30) has the same general construction as the cannula  190  of FIGS.  25 - 28 . The cannula  600  includes a tubular main section  601  having a cylindrical outer wall  602  which extends from a proximal end portion (not shown) of the cannula  600  to a distal end portion  604  of the cannula. A flexible wall or bladder  606  is connected with the wall  602  of the main section  601 . The flexible wall  606  has a proximal end portion  607  which is bonded to an annular shoulder  608  formed in the wall  602 . A cylindrical clamp ring  609  also secures the proximal end portion  607  to the wall  602  of the main section  601  of the cannula  600 . 
     A distal end portion  610  of the flexible wall  606  is connected to the distal end of the main section  601  of the cannula  600 . In the illustrated embodiment of the invention, the distal end portion  610  of the flexible wall is bonded to the distal end of the main section  601  of the cannula  600 . However, the distal end portion  610  of the flexible wall  606  could be connected to the distal end of the main section  601  in other ways, such as by the use of a mechanical retainer. When the flexible wall  606  is in the initial or retracted condition shown in FIG. 29, the flexible wall tightly adheres to the main section  601  of the cannula  600  to provide a smooth outer surface which has a minimum of interference with body tissue as the cannula  600  is inserted into a continuous mass of body tissue. 
     An inner wall  612  cooperates with the wall  602  to form a passage  614  for fluid. The passage  614  has a proximal end (not shown) at which fluid under pressure is conducted into the passage. The passage  614  has a plurality of circular distal openings  616  through which fluid can flow from the passage  614  to a space enclosed by the flexible wall  606 . 
     When the flexible wall  606  is to be inflated, fluid pressure flows through the passage  614  and opening  616  and is applied against an inner side surface  617  (FIG. 29) of the flexible wall. The fluid pressure applied against the inner side surface  617  of the flexible wall  606  causes the flexible wall to move from the retracted condition shown in FIG. 29 toward the fully extended condition shown in FIG.  30 . As this occurs, a plurality of tether cords  618  are pulled from a nonlinear or coiled configuration toward the linear configuration shown in FIGS. 30 and 31. 
     When the flexible wall  606  is in the retracted condition shown in FIG. 29, the flexible wall covers the tethers  618  and presses them firmly against the tubular wall  602  of the main section  601  of the cannula  600 . Since the tethers  618  are enclosed by the flexible wall  606 , they do not interfere with insertion of the cannula  600  into a continuous mass of body tissue  207  where an opening does not naturally occur. The relatively high pressure fluid conducted from the passage  614  through the openings  616  move the flexible wall  606  outwardly away from the main section  601  of the cannula  600  to initiate the formation of an inflation fluid chamber  620 . As this occurs, the flexible wall  606  forms an inflated structure  622 . 
     The inflated structure  622  has a side wall  624  and an end wall  626 . The side wall  624  and end wall  626  are connected at a circular junction  628 . The side wall  624  has a configuration corresponding to the configuration of a portion of a cone while the end wall  626  has a configuration corresponding to the configuration of a flat annular disk when the flexible wall  606  is in the fully extended position of FIG.  30 . The tethering cords  618  limit outward movement of the junction  628  between the side wall  624  and the end wall  626  to impart the desired configuration to the inflated structure  622 . 
     Each of the tethering cords  618  has an outer end portion which is secured to the inner side surface  617  of the flexible wall  606  at the junction  628 . In the illustrated embodiment of the invention, the tethering cords  618  are bonded to the elastomeric material forming the flexible wall  606 . However, it is contemplated that the tethering cords  618  could be connected with the flexible wall  606  in many different ways. The inner end portions of the tethers  618  are bonded to the main section  601  of the cannula  600 . The inner end portions of the tethers  618  could be secured to the main section  601  of the cannula  600  in many different ways other than bonding. 
     The tethering cords  618  limit radially outward movement of the junction  628  between the end wall  626  and side wall  624 . By limiting outward radial movement of the end wall  626  and the side wall  624 , the tethering cords  618  restrain the elastic material of the flexible wall  606 . This results in the inflated structure  622  having a configuration which corresponds to the configuration of a portion of a cone. 
     Once the flexible wall  606  has been moved to the extended condition of FIG. 30, instruments, such as an endoscope and/or operating tools, can be inserted through a cylindrical central opening  630  (FIG. 31) formed in the main section  601  (FIGS. 29 and 30) of the cannula  600 . In addition to the tethers  618 , reinforcing fibers  632  (FIGS. 32,  33  and  34 ) are utilized to impart the desired configuration to the inflated structure  622 . 
     A portion of the reinforcing fibers  632  is disposed in the side wall  624  (FIGS. 32 and 33) of the inflated structure  622 . Another portion of the reinforcing fibers  632  is disposed in the end wall  626  of the inflated structure  622 . The reinforcing fibers  632  cooperate with the elastomeric material, which may be silicone, or latex, to restrain the elastomeric material of the flexible wall  606  against excessive stretching under the influence of fluid pressure applied against the inner side surface  617  (FIGS. 30 and 31) of the flexible wall  606 . 
     In the illustrated embodiment of the invention, the inflated structure  622  has a configuration corresponding to the configuration of a portion of a cone. Therefore, a proximal portion  607  of the side wall  604  has a smaller diameter than a distal end portion  633  of the side wall  624 . The density of reinforcing fibers  632  in the proximal end portion  607  (FIG. 32) of the side wall  624  is greater than the density of reinforcing fibers  632  in the distal portion  633  of the side wall  624 . By having the reinforcing fibers in the proximal end portion  607  (FIG. 32) of the side wall  624  closer together, the reinforcing fibers are effective to limit outward radial expansion of the proximal portion  607  of the side wall  624 . The relatively widely spaced reinforcing fibers  632  (FIG. 23) in the distal end portion  633  of the side wall  624  allow the distal end portion  633  of the side wall  624  to expand radially outwardly to a greater extent than the proximal end portion  607  of the side wall  624 . 
     The reinforcing fibers  632  in the proximal end portion  607  of the side wall  624  (FIG. 32) include fibers  634  having longitudinal axes which extend generally parallel to a longitudinal central axis of the main section  601  of the cannula  600 . In addition, reinforcing fibers  635  extend circumferentially around the distal portion  607  of the side wall  624 . The reinforcing fibers  635  have longitudinal axes which extend generally perpendicular to the longitudinal axis of the reinforcing fibers  634 . The longitudinal extending fibers  634  and the circumferentially extending fibers  635  reinforce the proximal portion  607  of the side wall  624  to limit the extent to which the fluid pressure applied against the inner side surface  617  of the side wall is effective to stretch the elastomeric material of the flexible wall  606 . 
     Similarly, the distal end portion  633  (FIG. 33) of the side wall  624  has longitudinally extending fibers  636  having longitudinal axes which extend parallel to the longitudinal central axis of the main section  601  of the cannula  600 . The reinforcing fibers  632  in the distal end portion  633  of the side wall  624  also include circumferentially extending fibers  637  which are perpendicular to the longitudinally extending fibers  636 . The reinforcing fibers  632  in the distal portion of the side wall  624  are far more widely spaced than the reinforcing fibers in the proximal end portion  607  of the side wall  624 . This enables the elastomeric material of the distal end portion  633  to stretch under the influence of fluid pressure applied against the inner side surface  617  (FIG. 30) of the side wall  624 . Therefore, the distal portion  633  of the side wall  624  stretches to have a substantially greater diameter than the proximal portion  607  of the side wall  624 . 
     The reinforcing fibers  632  in the end wall  626  (FIG. 34) include fibers  638  which extend radially outwardly from the cylindrical passage  630  through the main section  601  of the cannula. Circumferentially extending fibers  639  cooperate with the radially extending fibers  638  to limit the expansion of the end wall  626  under the influence of fluid pressure applied against the inner side surface  617  of the flexible wall  606 . During formation of the flexible wall  606 , the elastomeric material of the flexible wall is configured to have a configuration corresponding to the desired, generally conical, configuration of the inflated structure  622  (FIG.  30 ). 
     The cannula  600  is inserted into a continuous mass of body tissue, corresponding to the continuous mass  207  (FIG. 26) of body tissue, with the flexible wall  606  of the cannula  600  in the retracted condition illustrated in FIG.  29 . This enables the cannula  600  to be inserted through a relatively small incision formed in the skin enclosing the continuous mass of tissue. Prior to insertion of the cannula  600  into the continuous mass of tissue, the continuous mass of tissue is free of any openings. As the cannula  600  is inserted into the continuous mass of body tissue with the flexible wall  606  in the retracted condition of FIG. 29, the relatively smooth outer side surface of the cannula is effective to press aside the body tissue with a minimum of damage to the tissue. 
     Once the cannula  600  has been inserted into the continuous mass of body tissue, fluid under pressure is conducted through the passage  614  (FIG. 29) to initiate inflation of the flexible wall  606 . As this occurs, the flexible wall  606  begins to move away from the main section  601  of the cannula  600 . This results in an outer side surface  640  of the flexible wall  606  pressing against the body tissue to move the body tissue away from the main section  601  of the cannula  600 . 
     As the inflation of the flexible wall  606  continues, the outer side surface  640  of the flexible wall disposed on the conical side wall  624  presses the tissue both radially outwardly and axially away from the distal end of the main section  601  of the cannula  600 . As this occurs, force is transmitted through the body tissue itself to pull the body tissue away from the end wall  626  and the distal or axially outer end of the cannula  600  to initiate the formation of an open space immediately axially outwardly of the end wall  626 . 
     As the flexible wall  606  continues to move away from the retracted condition of FIG. 29 toward the fully extended condition of FIG. 30, the tethers  618  are straightened. When the flexible wall  606  reaches the fully extended condition of FIG. 30, the tethers  618  limit outward movement of the junction  628  between the end wall  626  and side wall  624 . Thus, force is transmitted through the tethers  618  from the junction  628  to the main section  601  of the cannula  600  to limit outward movement of the junction  628 . The reinforcing fibers  632  (FIGS. 32,  33  and  34 ), cooperate with the tethers  618  to give the side wall  624  the conical configuration shown in FIG.  30  and the end wall  626  a flat annular disk-shaped configuration. 
     FIG. 35 illustrates a cannula  210  which is selectively expandable at one or more selected longitudinal locations. The cannula  210  includes a series of expandable wall segments defining a longitudinally extending central working passage  212 . The expandable segments illustrated include a segment  214 , a segment  216 , a segment  218 , and a segment  220 . As an example, the segment  218  is expandable, upon the introduction of fluid under pressure, to an expanded condition as illustrated at  222  in FIG.  35 . Thus, in accordance with the principles illustrated in FIG. 35, a cannula or other inflatable medical device can be expanded for positioning or sealing at one or more selected longitudinal locations. 
     FIG. 36 similarly illustrates a cannula  224  having a plurality of expandable segments  226  through  234  spaced circumferentially around the distal end portion  236  of the cannula  224 . Each of the segments  226 - 234  is selectively expandable, as illustrated in FIG. 37 showing the segment  234  expanded radially outwardly. Accordingly, it is seen that the present invention also contemplates a cannula or bladder, or other inflatable medical device, having a plurality of circumferentially disposed segments expandable radially outwardly upon the selective control of the user of the device. Such selective expansion is useful in selectively positioning the cannula within the tissue in which it is located, in avoiding damage to certain tissue such as nerve tissue, or in protecting or moving certain tissue selectively. 
     FIGS.  38 - 43  illustrate such longitudinally extending radially expansible segments of a cannula or bladder or other inflatable medical device in accordance with the present invention. Each segment shown is one of a series of similar segments (not shown) spaced circumferentially around or formed as part of the wall of a cannula or other device  250 . The expansible segment  240  illustrated in FIGS.  38 - 43  is formed as a bellows or accordion and is expandable to a larger extent at its distal end  244  than at its proximal end  242 . If the distal end  244  of the expansible segment  240  is located adjacent a distal end of a cannula, the cannula will thus be expandable directly at its tip. The bellows-like construction of the segment  240  provides significant structural rigidity and can transmit in a controlled manner a significant amount of force between its radially outer surface  246  and its radially inner surface  248  adjacent the wall of the cannula  250 . The segment  240  is inflated by introduction of fluid under pressure in a known manner into the inflation space  252  (FIG.  41 ). 
     The expandable segment  254  illustrated in FIGS. 42 and 43 has a smooth outer skin  256  supported by a plurality of expandable bellows-shaped hoops  258  spaced longitudinally along the length of the segment  254 . The skin  256  presents a smooth surface to adjoining tissues upon expansion of the segment  254 . The hoops  258  provide structural rigidity to the segment  254 , and control the shape of expansion of the skin  256 . It should be understood that other configurations of the hoops  258 , which support the skin  256  of the segment  254 , are contemplated. 
     FIGS. 44 and 45 illustrate expandable devices having textured surfaces for grip and location control. The retractor  260  illustrated in FIG. 44 includes a stalk portion  262  and a bladder portion  264  attached thereto. The bladder portion  264  has a pebbled surface  266 . The retractor  268  (FIG. 45) has a stalk portion  270  and a bladder portion  272 . The bladder  272  has a ribbed surface  274 . Other types of texturing or finishing may be provided for an expandable device in accordance with the present invention. Any suitable surface configuration may be used to increase the grip provided between the outer surface of the expandable device and the tissue which it contacts. It should be noted that the surface texturing may also increase the structural rigidity of the expanded device. 
     FIGS.  46 - 49  illustrate an expanding device  280  which is preshaped and has a varying wall thickness in its expanding bladder portion. The expanding device  280  includes a support member  282  which may be a solid stalk or a hollow cannula or other member. The support member  282  has a widened proximal portion  286 , a narrower diameter central portion  288 , and a widened distal portion  290 . 
     Bonded to the support member  282  is an expanding bladder  292 . The expanding bladder  292  includes a proximal portion  294  bonded to the proximal portion  286  of the support member  282 . The expanding bladder  292  also includes a distal portion  296  bonded to the distal end portion  290  of the support member  282 . Extending distally from the portion  294  is a first expanding portion  298  having a thinner wall section at its proximal end  300  and a thicker wall section at its distal end  302 . Extending distally from the expanding portion  298  to the thin wall portion  296  is a second expanding portion  304 . The second expanding portion  304  is thicker at its proximal end  306  than at its distal end  308 , having a tapering cross section between the first expanding portion  298  and the distal end portion  296 . 
     When in the unexpanded condition, the first and second expanding portions  298  and  304 , respectively, of the expandable bladder  292  generally lie flat within the recess formed by the narrow portion  288  of the support member  282 . Upon the introduction of fluid under pressure into the interior of the bladder  292  through a port (not shown) in the support member  282 , the bladder  292  expands from the condition illustrated in FIG. 46 to the condition illustrated in FIG.  47 . The expanding portions  298  and  304  expand radially outwardly as illustrated. Because the material of the bladder  292  is thinner at its axially outer end portions  300  and  308 , that material stretches more and so the thicker portions  302  and  306  move radially outwardly the greatest amount. The proximal and distal end portions  294  and  296 , respectively, are prestretched, that is, stretched to a diameter greater than their relaxed condition, for insertion over the support member  282 . 
     Thus, it is seen that the wall thickness of a bladder can be varied at selected locations to control the rates and distances of expansion of the bladder portions. Further, portions of the bladder can be prestretched so that they reach their maximum elongation at an earlier amount of expansion. These factors can be used to control the expanded shape of the bladder. 
     In addition, there may be provided ribs such as the longitudinally extending ribs  310  illustrated in FIGS. 48 and 49 which are of an increased wall thickness to provide structural support and expansion control of the elastomeric material of the bladder. The ribs  310  are illustrative of any region of increased wall thickness used to control the shape of expansion. Such regions may run longitudinally as illustrated in the device  280 , or may run transversely or circumferentially or in other directions. Taken in combination, all of these factors are usable to control the shape of expansion of an inflatable medical device. 
     In accordance with a further embodiment of the invention, relatively rigid members such as plates may be molded into relatively flexible bladder portions to define edges and surfaces, as illustrated in FIGS.  50 - 52 . A medical device  312  (FIG. 50) includes a support member  314  such as a cannula to which is attached an expanding (elastomeric) bladder  316 . The attachment between the bladder  316  and the support member  314  is not shown in these particular cross-sectional views, but may be in any manner known or as described herein. The bladder  316  has an elastomeric curved portion  318  and an elastomeric portion  319 . A plate  320  is molded into the bladder  316  and has an edge  322 . A second plate  324  molded into the bladder  316  has an edge  326 . Upon the introduction of fluid under pressure into the volume between the support member  314  and the bladder  316 , the bladder expands radially outwardly from the condition shown in FIG. 50 to the condition shown in FIG.  51 . Although the elastomeric portion  318  of the bladder  316  changes dimensions, the plates  320  and  324  do not. Thus, the expanding device  316  includes flat surfaces and edge surfaces which move radially outwardly and maintain their rigid condition upon expansion of the device  312 . The plates  320  and  324  thus control and partially define the expanded shape of the device  312 . 
     Alternatively or additionally, as illustrated in FIG. 52, tethering cords  328  may be employed between the support member  314  and the plates  320  and  324 . The tethering cords  328  also serve to control and/or limit expansion of the device  312 . Additionally, it can be seen that the device of FIG. 52 includes elastomeric bladder portions  330  extending directly between the plates  320  and  324  and the support member  314 . Again, this is an alternative form of the construction. Expanding bladders constructed in accordance with the present invention can use any one or more of these various means of controlling or limiting the expansion of the inflatable medical device, in order to achieve the optimum structure for the particular application. 
     FIGS. 53 and 54 further illustrate the use of rigid plates or members molded into elastomeric material of an inflatable medical device. An expanding bladder  332  is fixed circumferentially by means not shown around a cannula  334 . The cannula  334  includes a cannula wall  336  defining a longitudinally extending central opening  338 . The expanding bladder  332  includes an elastomeric material  340  within which are molded a series of relatively rigid plates  342 . Between the expanding bladder  332  and the cannula wall  336  is a fluid inflation space  344 . Upon the introduction of fluid under pressure into the inflation volume  344 , the expanding bladder  332  expands radially outwardly from the condition shown in FIG. 53 to the condition shown in FIG.  54 . The elastomeric material  340  stretches and elongates circumferentially. The areas of the elastomeric material  340  which are devoid of plates  342  stretch further, thus allowing the plates  342  to separate. The plates  342 , which were previously in overlapping position, are separated as illustrated in FIG.  54 . The plates  342  impart structural rigidity and strength to the elastomeric material  340 . The invention is not limited to the particular configuration of rigid plates and elastomeric material illustrated, but contemplates any such configuration of relatively rigid members or portions in a relatively stretchable matrix material. 
     The expanding device illustrated in FIGS. 55 and 56 includes a doubled-over bladder portion to allow maximum expansion at the distal end portion of the device. The device includes a cannula or stalk or other support member  350 . An expanding bladder  352  is bonded at  354  to a proximal portion  356  of the support member  350 , and at  358  to a distal end portion  360  of the support member  350 . The material of the expanding bladder  352  is doubled-over at  362  adjacent the distal end portion  360 . Upon the introduction of fluid under pressure into the volume defined by the bladder  352 , through a fluid supply port  364 , the bladder  352  expands from the condition shown in FIG. 55 to the condition shown in FIG.  56 . Because of the doubled-over portion  362  of the bladder  352 , maximum expansion is gained at the distal end of the device rather than at the center or the proximal end of the expanding bladder  352 . Again, such a device may include bladder portions having varying wall thicknesses as discussed above, tethering cords, etc., all to control the expanded shape of the device. 
     The expanding device illustrated in FIGS. 57 through 62 includes a doubled-over bladder portion to allow maximum expansion at the distal end portion of the device in the manner previously described in connection with FIGS. 55 and 56. The device includes a cannula having a main section or stalk  850 . An expanding bladder or flexible wall  852  is bonded at  854  to a proximal end portion  856  of the support member  850  and at  858  to a distal end portion  860  of the main section  850  (FIGS.  57  and  58 ). The material of the expanding bladder  852  is doubled-over at  862  adjacent to the distal end portion  860 . 
     Upon introduction of fluid under pressure into the volume defined by the bladder  852 , through a fluid supply port  864  (FIG.  57 ), the bladder or flexible wall  852  expands from the condition shown in FIG. 57 to the condition shown in FIG.  58 . Because of the doubled-over portion  862  of the bladder  852 , maximum expansion is gained at the distal end of the device rather than at the center or proximal end of the expanding bladder  852 . Again, such a device may include bladder portions having varying wall thicknesses as discussed above or reinforcing fibers to control the expanded shape of the device. 
     In the embodiment illustrated in FIGS. 57 and 58, tethering cords  870  extend from the main section  850  of the cannula to a junction  872  between a side wall  874  and an end wall  876  (FIG. 58) of the flexible wall or bladder  852 . The tethering cords  870  limit the extent of outward movement of the junction  872  when the flexible wall or bladder  852  is inflated from the retracted condition of FIG. 57 to the extended condition of FIG.  58 . The side wall  874  of the inflated flexible wall has a configuration corresponding to the configuration of a portion of a cone. The end wall  876  has a configuration corresponding to the configuration of an annular disk. However, it should be understood that the end wall  876  slopes radially and axially outwardly from a location where the side wall  876  is connected with the main section  850  of the cannula to the-junction  872  between the end wall and the side wall  874 . 
     In accordance with a feature of this embodiment of the invention, tethering cords  870  extend outwardly from the distal end portion of the main section  850  to the junction  872  between the side wall  874  and end wall  876 . The tethering cords  870  limit outward movement of the flexible wall or bladder  852  to assist in imparting the desired configuration to the bladder when it is in the expanded condition of FIG.  58 . Although only a pair of tethering cords  870  are shown in FIGS. 57 and 58, it should be understood that there is a circular outer array  880  of tethering cords which extend from the main section  850  of the cannula outwardly to the junction  872 . Although any desired number of tethering cords could be used, in the illustrated embodiment of the invention, there are nine tethering cords in the circular array  880  of tethering cords. 
     In the embodiment of the invention illustrated in FIGS.  59 - 62 , the cannula has the same general construction as the cannula of FIGS. 57 and 58. However, in the embodiment of the invention illustrated in FIGS.  59 - 62 , tethering cords are provided between an inner side surface of the side wall  874  of the bladder or flexible wall and the main section  850  of the cannula. Since the embodiment of the invention illustrated in FIGS.  59 - 62  is generally similar to the embodiment of the invention illustrated in FIGS. 57 and 58, similar numerals have been utilized to designate similar components. 
     In accordance with a feature of the embodiment illustrated in FIGS.  59 - 62 , an intermediate array  882  of tethering cords  870  extends between the main section  850  of the cannula and the inner side surface of the flexible wall or bladder  852 . In addition, an axially inner array  884  of tethering cords  870  extends between the inner side surface of the bladder or flexible wall and the main section  850  of the cannula. 
     The three arrays  880 ,  882 , and  884  of tethering cords  870  used to restrain outward movement of the flexible wall or bladder  852  in the embodiment of the invention illustrated in FIGS.  59 - 62  are effective to cause the extended flexible wall  852  to form an inflated structure having a generally conical configuration. 
     FIG. 63 illustrates an expanding bladder  370  having adjoining portions with different material characteristics. The device is shown in end view as disposed circumferentially around a cannula  372 . Alternate portions  374  of the device are made of a first material having a first set of material characteristics, while the interfitted portions  376  are made of a second material having a second set of material characteristics. For example, one material may have a lower modulus of elasticity and the other a higher modulus of elasticity. One may be thicker and the other thinner. One may be elastomeric and the other not. Other combinations are possible. The portions may be bonded together with adhesive, may be heat-sealed together, or may be solvent sealed. One portion can be made of metal. PVC is also a suitable material. 
     Upon the introduction of fluid under pressure into the expanding device  370 , the portions  374  and  376  expand or move at different rates or into different shapes. The adjoining of different materials can be used to control the expanded shape of the device  370 . 
     FIG. 64 illustrates an expanding device  380  having an expanding bladder  382  made of a plurality of materials laminated together. The expanding portion  382  is mounted on a stalk or cannula  384 . The bladder  382  includes an outer layer  386  of a first material laminated to an inner layer  388  of a second material. Again, the layers may have differing material characteristics—perhaps polymers with specific properties bonded together. For example, the layer  386  may be of a different durometer from the material of the layer  388 . One of the layers may provide structural support while the other provides fluid sealing capabilities. One layer may provide puncture resistance while the other provides expansion shape control. These are some of the many properties available with such laminated structures. 
     It should also be noted that the expandable bladder  382  has an expanded dimension many times greater than its unexpanded dimension as illustrated in dashed lines in FIG.  64 . This is illustrative of the large degree of expansion which the expandable bladders of the present invention are able to generate. For example, expandable bladders in accordance with the present invention have been built having expansion rates of approximately 700% as compared to the unexpanded diameter. 
     FIG. 65A illustrates a triangular shaped expanding element  400  fixed to a supporting device indicated at  402 . The expanding element  400  has relatively thin walled portions  404  and a relatively thick wall portion  406 . Upon the introduction of fluid under pressure into the volume  408  defined by the bladder  400 , the relatively thin walled portions  404  are stretched to a greater extent than the relatively thick walled portion  406 . In the similar expanding segment  410  (FIG.  65 B), a fiber  412  is embedded in the elastomeric material of the expanding segment to control and limit its expansion. Again, in the similar expanding segment  414  illustrated in FIG. 65C, a fiber mesh  416  is embedded in the elastomeric material of the expanding segment to strengthen it and to control its expansion. 
     The expanding segments illustrated in FIGS. 66A,  66 B, and  66 C are similar to FIGS.  65 A- 65 C in structural composition but are trapezoidal shaped rather than triangular shaped. FIG. 66A illustrates an expanding segment  418  connected with a support member  420 . The segment  418  includes relatively thin walled portions  422  and a relatively thick walled portion  424 . Upon the introduction of fluid under pressure into the volume defined by the expanding portion  418 , the relatively thin walled portions  422  stretch to a greater extent than the relatively thick walled portion  4246  whereby the relatively thick walled portion  424  moves radially outwardly to a greater extent. The expanding segment  426  (FIG. 66B) includes an embedded reinforcing fiber  428  for expansion control purposes. The expanding segment  430  (FIG. 66C) includes an embedded fiber mesh  432  for structural support and expansion control purposes. The structural compositions and uses of embedded fibers and fiber meshes illustrated in FIGS. 65 and 66 are merely illustrative of the various ways in which fibers embedded in the elastomeric material of an expanding medical device can be used to control the expansion thereof. 
     FIGS.  67 A- 67 C illustrate the use of overlapping and/or incomplete reinforcing fibers for expansion control. A stretchable elastomeric material  434  (FIG. 67A) has a plurality of fibers or other reinforcing elements  436  embedded therein. As the stretchable material  434  is elongated, the elastomeric material in the stretch zones  438  (FIG. 67C) between the fiber portions  436  stretches to a greater extent than the material immediately around the fibers  436 . Further, the embedded fibers resist transverse expansion of the elastomeric material while encouraging longitudinal expansion as shown. These drawings are merely illustrative of the use of the concept of overlapping fibers with stretch zones to control expansion rates of an elastomeric material used in an expanding medical device such as a cannula or catheter. The present invention contemplates other such arrangements of fibers or reinforcing elements in the elastomeric materials. 
     For example, FIGS.  68 - 70  illustrates a bladder retractor  440  fixed to a cannula  442 . A plurality of circumferentially extending reinforcing fibers  444  are embedded in an elastomeric matrix material  446 . In addition, a plurality of tethering cords  448  extend radially between the cannula  442  and the elastomeric material  446  to limit the radially outwardly expansion. As can be seen in FIG. 70, the reinforcing fibers  444  are not complete but rather are broken fibers extending circumferentially within the matrix material  446  to define stretch zones between them. Alternatively, the reinforcing fibers may be complete, as illustrated in FIGS. 71 and 72. In the retractor  450  illustrated in FIGS. 71 and 72, a plurality of complete circumferentially extending reinforcing fibers  452  are embedded in the matrix material  454 . The retractor  456  illustrated in FIGS. 73 and 74 includes a plurality of longitudinally extending incomplete reinforcing fibers  458  embedded in the matrix material  460 . The retractor  462  illustrated in FIGS. 75 and 76 includes a plurality of longitudinally extending complete reinforcing fibers  464  embedded in an elastomeric matrix material  466 . Again, the invention contemplates other such configurations of reinforcing fibers embedded in matrix materials, and is not limited to those shown. 
     FIGS.  77 - 79  illustrate a series of expandable bladders laminated together to define a structural unit  470 . A series of upper longitudinally extendable bladders  472  have their ends fixed between an upper member  474  and a central member  476 . A series of lower longitudinally extending bladders  478  have their ends fixed between the central member  476  and a lower member  480 . A covering or retainer  482  (FIG. 79) may enclose all of the units. Upon the introduction of fluid under pressure, the bladders  472  and  478  expand longitudinally from the condition illustrated in FIG. 77 to the condition illustrated in FIG.  78 . When the bladders  472  and  478  are fully inflated as illustrated in FIG. 54, they define, together with the members  474 ,  476  and  480  and the retainer  482 , a rigid structural unit. This type of laminated bladder construction will find many suitable uses. It should be understood that other configurations of bladders laminated together are contemplated and are within the scope of the invention. 
     From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications in the invention. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.