Abstract:
A flexible segment system including: a first link; a first flexible hinge integral to the first link; and a second link integral to and continuing from the first flexible hinge.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to sheaths for the remote steering, guidance, navigation and manipulation of flexible instruments, such as endoscopes. 
     Endoscopic procedures typically employ endoscopic instruments that are maneuvered within or towards a target organ or tissue from a position outside the body. Examples of endoscopic procedures include sigmoidoscopy, colonoscopy, esophagogastroduodenoscopy, and bronchoscopy. Typically flexible endoscopes, which have flexible insertion tubes, are used for such procedures. The insertion tube of the endoscope is advanced by pushing it forward, and retracted by pulling it back. The tip of the tube may be directed by twisting and general up/down and left/right movements. Oftentimes, this limited range of motion makes it difficult to negotiate acute angles, creating patient discomfort and increasing the risk of trauma to surrounding tissues. 
     Endoscopes can also be employed in laparoscopic procedures. Such procedures typically involve introducing a trocar into a person&#39;s body and then inserting an endoscope tube through the trocar to the desired location. Rigid endoscopes, i.e., endoscopes having a less flexible, more rigid insertion tube (also sometimes referred to as laparascopes) are more typically used in laparoscopic procedures, as the need to advance such endoscopes through constricted anatomical structures is less pronounced. Maneuverability of the endoscope deployed in this fashion is limited, with little ability to navigate the endoscope independent of moving the insertion trocar. 
     There have been many attempts to design endoscopes as well as catheters, with improved steerability, however, the range of motion is generally limited. For example, U.S. Pat. No. 3,557,780 to Sato; U.S. Pat. No. 5,271,381 to Ailinger et al.; U.S. Pat. No. 5,916,146 to Alotta et al.; and U.S. Pat. No. 6,270,453 to Sakai describe endoscopic instruments with one or more flexible portions that may be bent by actuation of a single set of wires. The wires are actuated from the proximal end of the instrument by rotating pinions (Sato), manipulating knobs (Ailinger et al.), a steerable arm (Alotta et al.), or by a pulley mechanism (Sato). U.S. Pat. No. 5,916,147 to Boury et al. discloses a steerable catheter having four wires that run within the catheter wall. Each wire terminates at a different part of the catheter. The proximal end of the wires extend loosely from the catheter so that the physician may pull them. The physician is able to shape and thereby steer the catheter by selectively placing the wires under tension. 
     Steerable endoscopes have improved range of motion as compared to non-steerable flexible endoscopes or rigid endoscopes, but their range of motion is still generally limited. Further, these devices can be laborious to use, pulling each wires separately as in Boury et al., and may require a significant amount of training to become proficient in maneuvering the device through the patient&#39;s anatomy, as in the case of knob and pulley mechanisms. In addition, steerable endoscopes are expensive to maintain. Consequently, it would be advantageous to provide an easier to use, more cost-effective system to improve steering, navigation, guidance and manipulation of conventional flexible endoscopes. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides for a sheath that can receive a flexible instrument, e.g., flexible endoscopes, suction tubes, irrigation tubes, and tools with flexible shafts, such as, endoscopic tools (i.e., tools adapted for delivery through the working channel of an endoscope), lasers and energy sources, and that can route the instrument through the sheath such that a portion of the instrument can extend to or past the distal end of the sheath. The sheath can be manually manipulated from its proximal end to remotely steer, guide, manipulate and/or navigate the insertion tube at the distal end of the sheath. 
     In one variation of the invention, a sheath is provided having an elongate shaft and proximal and distal sections having multiple pairs of links, with one member of a pair located on the proximal section and the other of the pair located on the distal section. The sheath further includes a lumen that extends at least partially through the shaft and which opens through the distal section of the shaft. An inlet port in communication with the lumen is located between the proximal and distal sections of the sheath. The inlet port and shaft lumen allows for the insertion tube of an endoscope to extend through the sheath to the distal end of the sheath. The sheath further includes one or more sets of cables connecting the links of at least one discrete pair to one another, such that movement of one link of the connected pair causes corresponding relative movement of the other link of the pair. In further variations, multiple sets of cables are included, with each set connecting the links of a discrete pair. Movement of the proximal section results in corresponding movement of the distal section. 
     A wide variety of link systems can be used to form the proximal and distal sections of the sheath. In one variation of the invention, a link system is provided where the links form flexible segments. The flexible segments comprise a unit of at least one link and at least one flexible hinge, with adjacent flexible segments joined by flexible hinges. Pairs of flexible segments form the proximal and distal sections. Cables connecting the flexible segments of at least one discrete pair to one another, such that movement of one flexible segment of the connected pair causes corresponding relative movement of the other flexible segment of the pair 
     The invention further provides methods of introducing, e.g., a flexible endoscope into a patient&#39;s body by inserting the sheath at a desired location and advancing the endoscope through the inlet port and into the sheath. In certain variations, introduction of the sheath can be aided through the use of a trocar. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a sheath according to one embodiment of the invention, in an articulated position, with a flexible endoscope passing through the sheath; 
         FIG. 2  is a side view of the sheath of  FIG. 1 ; 
         FIGS. 2A and 2B  are enlarged views of the distal end and proximal end sections of the sheath of  FIG. 2  designated  2 A and  2 B, respectively; 
         FIGS. 3A-3C  show perspective, side, and end views, respectively, of a flexible segment that forms a portion of the distal section of  FIG. 2A . 
         FIG. 4  shows a top view of the sheath and endoscope of  FIG. 1 , with parts broken away and with the sheath in an unarticulated position; 
         FIG. 5  shows a top view of the sheath and endoscope of  FIG. 1 , with parts broken away and with the sheath in an articulated position; 
         FIG. 6  is a top view of the sheath of  FIG. 2 ; 
         FIG. 7  is a cross-sectional view of the sheath of  FIG. 6  taken along the plane designated by line  7 - 7 ; 
         FIG. 8  is an enlarged cross-sectional view of the portion of the sheath of  FIG. 7  designated  8 , showing part of the distal section of the sheath in greater detail; 
         FIG. 9  is an enlarged cross-sectional view of the portion of the sheath of  FIG. 7  designated  9 , showing part of the handle portion of the sheath in greater detail; 
         FIG. 10  is an exploded perspective view of the handle portion of the sheath of  FIG. 2 ; and 
         FIGS. 11A and 11B  show side and perspective views, respectively, of the cable guide disposed in the handle portion of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     As previously described, sheaths according to the invention are configured to receive and pass a flexible instrument through the sheath such that the tip of the instrument can emerge from the distal end of the sheath. The proximal and distal sections of the sheath are adapted such that movement or articulation of the proximal section produces corresponding movement or articulation of the distal section. For purposes of illustration only, such a sheath will now be described with respect to its use with a flexible endoscope, but it will be understood that use with a variety of flexible instruments is contemplated. Typically for use with a flexible endoscope, the sheath can be inserted to a desired location of a patient&#39;s body and the flexible endoscope is introduced into the sheath. Alternatively the endoscope can first be introduced into the sheath and the combination advanced together. Movement of the distal section of the sheath, which is controlled by the proximal section, moves the tip end of the endoscope insertion tube, thus moving the tip of the endoscope. Thus the endoscope can be easily steered, maneuvered, and guided by simple manipulation of the proximal section of the sheath, greatly simplifying navigation of a standard flexible endoscope, and allowing for easy and enhanced maneuverability of the endoscope when deployed, e.g., in a patient&#39;s body, whether in conventional endoscopic or laproscopic use. 
     The sheath will typically include an elongate shaft separating the proximal and distal sections. The shaft can be relatively stiff or rigid for laparoscopic use or it may be more flexible for endoscopic use. The proximal and distal sections will typically have multiple pairs of links, with one member of a pair located on the proximal section and the other of the pair located on the distal section. The terms “link” as used herein refer to a discrete portion or defined area at one end of the sheath that corresponds to another discrete portion or defined area at the opposite end of the sheath. The links are generally, but need not be cylindrical, and are generally axially aligned relative to one another, in an unarticulated condition. In any event, the sheath will include a plurality of links or segments that are members of discrete pairs, with one link of each pair being situated at the proximal section, and the other link or segment at the distal section. Sets of connecting cables connect the links of a discrete pair to one another so that movement of one link of a pair causes a corresponding movement of the other link or segment in the pair. A variety of link systems and connecting cables are compatible for forming the proximal and distal sections of the sheath, including but not limited to those described in pending and commonly owned U.S. application Ser. No. 10/444,769, filed on May 23, 2003, U.S. application Ser. No. 10/928,479, filed on Aug. 26, 2004, and U.S. application Ser. No. 10/948,911, filed on Sep. 24, 2004, and U.S. application Ser. No. 10/997,372 entitled “Articulating Mechanisms and Link Systems With Torque Transmission In Remote Manipulation of Instruments and Tools”, filed Nov. 23, 2004, incorporated herein by reference in their entirety. As used herein, the term “active link” or “active link pair” refers to links that are directly connected to one another by a cable set. The term “spacer link” or “spacer link pair” refers to links that are not directly connected by a cable set. Spacer links can nevertheless be disposed between active links and provide for the passage of cable sets that connect active links. The ability to independently manipulate individual links allows for the proximal and distal sections to readily form complex three-dimensional configurations and geometries, in order to easily guide and navigate the endoscope insertion tube. 
     In certain variations of the invention, the proximal and distal sections of the sheath will include multiple pairs of flexible segments, such as those described in commonly owned and pending U.S. application Ser. No. 10/948,911, filed on Sep. 24, 2004. Such flexible segments usually include one or more adjacent links connected by flexible hinges that bend or flex. A flexible segment capable of movement in two dimensions with a single degree of freedom can have a single flexible hinge that connects two links. Alternatively, two or more flexible hinges can connect two links where the hinges are aligned in parallel. A flexible segment capable of movement in three dimensions with two degrees of freedom can have two flexible hinges oriented at an acute angle to one another connecting to three links. For a maximum three-dimensional range of motion, the angle will be orthogonal. A flexible segment pair refers to a flexible segment at one end section of the sheath that corresponds to a flexible segment at the other end section of the sheath. In order to achieve the greatest freedom of motion in three dimensions, at least one flexible hinge of the sheath is oriented orthogonal to at least one other hinge of the mechanism. However, the invention also contemplates configurations where flexible hinges are oriented parallel or are offset at any acute angle. As used herein, the term “active flexible segment” or “active flexible segment pair” refers to flexible segments that are directly connected to one another by a cable set. The term “spacer flexible segment” or “spacer flexible segment pair” refers to flexible segments that are not directly connected by a cable set. Spacer flexible segments can nevertheless be disposed between active flexible segments and provide for the passage of cable sets that connect active flexible segments. 
       FIG. 1  depicts an embodiment of a sheath according to the present invention with an endoscope deployed through the sheath. Sheath  100  includes elongate shaft  150 , handle  170 , proximal section  125  and distal section  126 . Endoscope  10  includes camera/video coupler  16 , port  14  for accessing the working channel of the endoscope, and insertion tube  12  extending from body  15  of the endoscope. Inlet port  172  extends from handle  170  and receives insertion tube  12  of endoscope  10 . The insertion tube passes through the inlet port  172  and through shaft  150 , with the tip of insertion tube  12  exiting from distal section  126  of the sheath. As depicted in  FIG. 1 , sheath  100  is shown in an articulated position, with the distal section in an articulated position that corresponds to that o the proximal section.  FIG. 2  shows the sheath in the straight, unarticulated configuration. 
       FIGS. 2A and 2B  depict proximal and distal sections  125  and  126  in greater detail. Proximal and distal sections  125  and  126  are formed of a plurality of flexible segments. Flexible segments  111  and  112 ,  113  and  114 ,  115  and  116 ,  117  and  118 ,  119  and  120 , and  121  and  122 , respectively, are each members of a discrete pair, with one flexible segment of a pair ( 111 ,  113 ,  115 ,  117 ,  119  or  121 ) at proximal section  125  with the other ( 112 ,  114 ,  116 ,  118 ,  120  or  122 ) at distal section  126 . As depicted, flexible segment  111  at proximal section  121  is formed of links  101 ,  103  and  105  connected by flexible hinges  107  and  109  oriented orthogonal to each other. Cable channels are located and pass through the periphery of each link for accepting passage and connection of cable sets. The distal section flexible segments also include a central channel  128  running through the longitudinal axis of the flexible segments of the distal section to accommodate passage of the endoscope, as further detailed herein. Flexible segment  112  is depicted in greater detail in  FIGS. 3A-3C , and more clearly depict central channel  128  and cable channels  129  of the flexible segments. Paired flexible segment  112  at distal section  126  similarly is formed of links  102 ,  104  and  106  connected by flexible hinges  108  and  110  oriented orthogonal to one another and likewise include similar cable channels and can also include a central channel. The remaining flexible segments of both the proximal section ( 113 ,  115 ,  117 ,  119 , and  121 ) and distal section ( 114 ,  116 ,  118 ,  120 , and  122 ) have the same configuration with the last link of one segment also functioning as the first link of the next segment. And as shown, each flexible hinge is oriented orthogonal to adjacent hinges. As previously noted flexible segments of such configuration move in two degrees of freedom and are moveable in three dimensions. The proximal flexible segments ( 111 ,  117 ,  119  and  121 ) are connected to the distal flexible segments ( 112 ,  118 ,  120  and  122 ) by sets of cables  131 ,  137 ,  139  and  141 , respectively. These flexible segment pairs are thus active flexible segments. Flexible segments  113  and  114 , and  115  and  116  are not directly connected by a cable set and thus function as spacer segments. The depicted configuration of active and spacer segments is for illustration only, and it is to be understood that arrangements and combinations can vary, depending on the application. 
     Each active flexible segment at the proximal section of the sheath is connected to its corresponding active flexible segment at the distal section by at least one and preferably two or more cables. Each cable set may be made up of at least one and preferably two or more cables. As noted, movement of one active flexible segment pair is controlled by its corresponding cable set and is independent of any other flexible segment pair. In certain variations, for example, a cable set will include three cables spaced 120 degrees apart. By using a set of three cables to connect an active flexible segment having at least one flexible hinge oriented orthogonal to at least one other flexible hinge, each active flexible segment pair can be manipulated or moved in three degrees of freedom, independently of any other active pairs. These three degrees of freedom include up/down motion, left/right motion, and rotational or “rolling” motion (whether or not the flexible segment is in a straight or bent configuration). By combining a plurality of active flexible segments, multiple degrees of freedom are achieved, allowing the proximal and distal sections of the sheath to be shaped into various complex configurations. 
     The use of flexible segments in proximal and distal sections  125  and  126  has certain advantages. One is simply the flexibility provided by the flexible segments. For even greater flexibility, flexible segments combining two flexible hinges between links, such as those described in pending and commonly owned U.S. application Ser. No. 10/948,911, filed on Sep. 24, 2004, incorporated herein by reference in its entirety, may be used. Another advantage is ease of manufacture and assembly, as the proximal and distal sections can be manufactured as continuous pieces having multiple links connected by the flexible hinges. A further advantage is an increased ability to transmit torque along the sheath. However, there are other link systems that can be used in the sheaths of the present invention that also transmit torque, including but not limited to the link systems described in pending and commonly owned U.S. application Ser. No. 10/997,372, entitled “Articulating Mechanisms and Link Systems With Torque Transmission In Remote Manipulation of Instruments and Tools”, filed Nov. 23, 2004, incorporated herein in its entirety. 
     Variations of the sheath can also include proximal section links or segments that may include a channel for receiving a locking rod that can secure and retain the proximal end of the sheath in a fixed position. Instead of a rod, a locking sleeve may be fitted over the proximal end of the sheath to secure and retain the proximal end in a fixed position. This may be advantageous in situations where it is desirous to maintain the endoscope in a fixed location, once it has been steered to that location through use of the sheath. Other mechanisms for locking the sheath in a fixed, articulated position include but are not limited to those described in U.S. application Ser. No. 10/928,479, filed on Aug. 26, 2004, incorporated herein in its entirety. 
       FIGS. 4 and 5  further show sheath  100  in greater detail with the proximal and distal ends in a straight, unarticulated configuration ( FIG. 4 ) or in a curved, articulated configuration ( FIG. 5 ). As can be seen, distal section exhibits corresponding, inverse movement relative to the proximal end. Furthermore, the degree of bending or flex of the distal section is proportionally greater than that of the proximal section. This proportional scaling of movement is accomplished by increasing or decreasing the cable channel pattern radius in the links or flexible segments, at either the proximal or distal end, as is further described in pending and commonly owned U.S. application Ser. No. 10/948,911 incorporated herein by reference in its entirety. As can be seen in  FIGS. 4 and 5 , the radial distance of the cables from central axis of the segments of the proximal section is greater than that in the distal section. The result is that small, controlled movements outside of the body allow for a greater degree of movement at the distal section, which may be advantageous when guiding and navigating a retained endoscope inside the body. 
     In the proximal and distal sections of sheath  100 , there is a one to one, or symmetrical, correspondence of flexible segments. This is not always necessary and there may be applications where it is desirable for a sheath to have asymmetrical arrangements of links or flexible segments at the proximal and distal sections. For example, additional spacer links or flexible segments can be added to the proximal or the distal section, which can be desirable for providing additional length to the proximal or distal sections. In addition the inclusion of additional (or a greater relative number of) of spacer links or flexible segments at either the proximal or distal section allows for the proportional scaling of movement or motion of the corresponding other section. For example, the inclusion of additional spacer links or flexible segments (or a greater relative number of spacer links or flexible segments) at the proximal section would require a more exaggerated movement by the user at the proximal section to achieve the desired motion at the distal section. This could be advantageous in situations where fine, delicate controlled movements were desired, such as, for example, situations where there is a risk that a user may not possess the necessary dexterity to perform the desired procedure absent such proportional scaling of the distal section movement or motion. Alternatively, additional spacer links or flexible segments (or a greater relative number of spacer links or flexible segments) could be provided on the distal section, in which case the degree of distal section movements would be proportionally greater than those of the proximal end, which may also be desirable for particular applications. Spacer links or flexible segments are typically unconstrained, that is, when the distal section of the sheath, contains the individual spacer links or spacer flexible segments the distal section can not resist movement due to laterally applied forces (as opposed to active links or flexible segments which can be constrained to resist movement due to a laterally applied force). Thus, the provision of spacer links or flexible segments decreases the rigidity of the proximal or distal section in those areas that contain such spacer links or flexible segments, which can be desirable when navigation of the sheath through or around sensitive or fragile anatomical structures. 
     As seen in  FIGS. 4 and 5 , the resulting directional movement of the distal section  126  is inverted relative to proximal section  125 . In other variations, mirrored movement can be achieved by twisting or rotating the cable sets 180 degrees as they pass through the sheath. Other variations on movement can be achieved by twisting or rotating the cables any amount between 0 to 360 degrees. 
     Turning now to  FIGS. 6-9 , it can be seen that shaft  150  includes a passageway for routing a received endoscope. As  FIG. 9  shows in particular detail, handle  170  includes port  172  in communication with inner lumen  154  of shaft tube  152 . Shaft tube  152  extends from the inlet port into handle  170  and through shaft  150  until it terminates at the distal end of the shaft where it abuts and is secured to link  106  of flexible segment  122 , as shown more clearly in  FIG. 8 . Alternatively, link  106  could include a counterbore to accept shaft tube  152 . Connecting cables, including cables  131 , that connect flexible segments of proximal and distal sections  125  and  126  enter the handle from proximal section  125 , where they are routed around shaft tube  152 , through guide bracket  160 , and then through shaft  150  in lumen  151  created by the space between the inner wall of shaft  150  and outer wall of shaft tube  152 . Guide bracket  160  is positioned in handle  170  to both center and orient shaft tube  152  as it enters the shaft as well as to orient the cables as they are routed around the shaft tube and into lumen  151  of the shaft. At the distal section, link  106  is attached and secured against both shaft  150  and shaft tube  152 . Flexible tube  156  extends through the central channel of the flexible segments of distal section  126  and abuts against shaft tube  154 , such that lumen  158  of the flexible tube and lumen  154  of the shaft tube form a continuous lumen for passing the insertion tube of flexible endoscope that extends from inlet port  172  through handle  170  shaft  150 , and distal section  126 , and that opens at the distal end of distal section. Flexible tube  156  is secured to shaft tube  152  and/or link  106  and is otherwise dimensioned to slip fit within central channel  128  (see  FIG. 3C ) of the flexible segments of the distal section, such that when the distal section is bent, the links of the flexible segments that form the distal section can move relative to the flexible tube. 
     Shaft tube  152  can have variable flexibility or stiffness as it extends from the inlet port  172  and handle  170  through the shaft  150 . In certain variations, the portion of the shaft tube that extends from inlet port  172  through the handle will be relatively rigid to aid in guiding the endoscope insertion tube through an initial curved pathway as it travels from the port into the shaft. As the shaft tube extends through the shaft, its relative flexibility or stiffness may vary with that of the shaft. In some instances, it may be desirable for the shaft to be relatively stiff which would in essence supply rigidity to an otherwise flexible endoscope deployed through the sheath. This might be advantage for example in laproscopic procedures, where the use of the sheath with a rigid shaft would essentially transform a flexible endoscope into a rigid endoscope. In variations where the shaft is flexible, it may be further advantageous to provide individual lumens to transmit the cables through shaft as an alternative to passing the cables through common lumen  151 . Such a configuration can aid in resisting localized shifting and splaying of the cables that may result from flexing of the shaft. Flexible tube  156  on the other hand needs to retain adequate flexibility regardless of the flexibility of the shaft so as not to restrict movement and articulation of distal section  126 . Flexible tube  156  is not necessary in variations where the distal section uses a link system with a fully enclosed central channel. It will be appreciated that the shaft length itself can vary, depending on the application. In certain variations, the shaft itself can be formed of links or flexible segments. 
       FIG. 10  shows the handle assembly in greater detail. Handle  170  is formed of handle body  174  and handle plate  176  secured together by screws  175 . Handle body  174  includes opening  177  at its proximal end. Flexible segment  121  of proximal section  125  attaches at opening  177 . Opening  178  at distal end of handle body  174  is similarly configured for receipt and attachment of shaft  150  (see  FIG. 9 ). Handle body  170  further includes guide slots  186  and  184  (see  FIG. 9 ), and handle plate  176  includes guide slot  182 , that receive and secure arms of guide bracket  160 . Guide bracket  160  is shown in greater detail in  FIGS. 11A and 11B . Guide bracket  160  includes center ring  162  with horizontal and vertical arms  164  and  166 , respectively, extending from the center ring. Arm  164  and  166  are secured into guide slots  184 ,  182  and  186 . Shaft tube  152  is received through center ring  162  of guide bracket  160  to support the tube and orient it for passage into shaft  150 . With shaft tube  152  in place through the central ring of the bracket, grooves  168  together with the outer wall of tube  152  form individual guide channels to guide and orient the connecting cables as they are routed into lumen  151 . Alternatively, such guide channels could be integrally formed in face  179  of the distal end of the handle  170 . In such a case, a centering channel could also be provided in the face to orient the shaft tube  152 . 
     It will be appreciated that while the provision of handle  172  and inlet port  172  adds a level of convenience, it is not essential. Alternative variations of sheaths according to the invention can have the distal section connect directly to the shaft with the inlet port extending from the shaft itself. In other variations, the inlet port need not extend from the shaft but can simply be an opening to the lumen of the shaft tube that is flush with the shaft surface. 
     Consistent with the above considerations, the sheath may further be of any size and shape, as the purpose dictates. Links are generally, but need not be, cylindrical, and as previously mentioned include channels for passage of the cables that connect the flexible segment pairs as well as passage of the received endoscope. Depending on the applications, the links and shaft can be dimensioned to accommodate multiple tubes for receiving multiple instruments through the same sheath. The cable channel diameters are usually slightly larger than the cable diameters, creating a slip fit. For typical endoscopes, representative diameters of links may range from about 1 mm to about 3 mm for small endoscopes, about 4 mm to about 8 mm for mid-sized endoscopes, and about 9 mm to about 15 mm or more for large endoscopes. Overall length of the links will vary, usually depending on the bend radius desired between links. Cable diameters may also vary according to the application. For typical endoscopic applications, a representative diameter may range from about 0.1 mm to about 3 mm. 
     The sheath may be formed of a number of materials known in the art and that can vary according to the application. For ease of manufacture, injection moldable polymers can be used including, e.g., polyethylene or copolymers thereof, polyethylene terephthalate or copolymers thereof, nylon, silicone, polyurethanes, fluoropolymers, poly (vinylchloride); and combinations thereof, or other suitable materials known in the art. Also, for rigid tubes or shafts, stainless steel can be used. 
     For certain applications a lubricious coating may be placed on the sheath if desired to facilitate advancement of the sheath. The lubricious coating may include hydrophilic polymers such as polyvinylpyrrolidone, fluoropolymers such as tetrafluoroethylene, or silicones. A radioopaque marker may also be included on the distal section of the sheath to indicate the location of the sheath upon radiographic imaging. Usually, the marker will be detected by fluoroscopy. 
     Cable flexibility may be varied, for instance, by the type and weave of cable materials or by physical or chemical treatments. Usually, cable stiffness or flexibility will be modified according to that required by the intended application of the sheath. The cables may be individual or multi-stranded wires made from material, including but not limited to biocompatible materials such as nickel-titanium alloy, stainless steel or any of its alloys, superelastic alloys, carbon fibers, polymers, e.g., poly (vinylchloride), polyoxyethylene, polyethylene terephthalate and other polyesters, polyolefin, polypropylene, and copolymers thereof; nylon; silk; and combinations thereof, or other suitable materials known in the art. 
     The cables may be affixed to the links or flexible segments of an active pair according to ways known in the art, such as by using an adhesive or by brazing, soldering, welding, and the like, including methods described in pending and commonly owned U.S. application Ser. Nos. 10/444,769, 10/928,479, and 10/948,911 incorporated herein by reference in their entirety. 
     Although the many sheaths that have been illustrated in the accompanying figures have a certain number of flexible segments and flexible segment pairs, this is solely for the illustrative purposes. Any number of links and link pairs or flexible segments and flexible segment pairs may be employed, depending on such factors as the intended use and desired length of the sheath. 
     All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes to the same extent as if each individual publication, patent or patent application were specifically and individually indicated to be so incorporated by reference. Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit and scope of the appended claims.