Patent Publication Number: US-11638592-B2

Title: Disc nucleus removal devices and methods

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/872,679, filed on Oct. 1, 2015, and entitled “Disc Nucleus Removal Devices and Methods.” U.S. patent application Ser. No. 14/872,679 is a continuation of U.S. application Ser. No. 13/360,178, filed on Jan. 27, 2012, entitled “Disc Nucleus Removal Devices And Methods,” and now issued as U.S. Pat. No. 9,173,673. U.S. patent application Ser. No. 13/360,178 is a divisional of U.S. application Ser. No. 11/427,848, filed on Jun. 30, 2006, entitled “Disc Nucleus Removal Devices and Methods,” and now issued as U.S. Pat. No. 8,109,957. Each of these applications is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to medical devices and methods for removing tissue, and in particular, to medical devices and methods for removing nucleus tissue from an intervertebral disc. 
     BACKGROUND OF THE INVENTION 
     The intervertebral discs that reside between each vertebra of the spine act as shock absorbers between the vertebrae. The disc itself consists of a tough outer layer called the annulus, and soft inner material, called the nucleus. The soft nucleus absorbs the majority of the shock as the body moves, keeping the spine supple and supported. As one ages, both the annulus and the nucleus lose some of their cushioning ability, and a greater portion of the pressure is borne by the outside of the disc, the annulus. 
     An artificial disc (also called a disc replacement, disc prosthesis or spine arthroplasty device) is a device that is implanted into the spine to imitate the functions of a normal disc (i.e., carry load and allow motion). There are many artificial disc designs classified into two general types: total disc replacement and disc nucleus replacement. As the names imply, with a total disc replacement, all or most of the disc tissue is removed and a replacement device is implanted into the space between the vertebra. With a disc nucleus replacement, only the center of the disc (the nucleus) is removed and replaced with an implant. The outer part of the disc (the annulus) is not removed. Disc nucleus replacement surgery offers certain benefits compared to total disc replacement. Since a disc nucleus replacement device is designed to replace only the nucleus of the disc, the procedure is less time consuming and possesses less risk to surrounding structures. Another benefit of disc nucleus replacement surgery is that it results in the retention of a greater amount of tissue, which gives the disc a greater regenerative capacity. 
     An important aspect of disc nucleus replacement surgery is to remove all of the nucleus material before installing the nucleus replacement device. In addition, care must be taken to avoid creating too large a defect in the annular wall. Incomplete or inadequate clearance of the disc nucleus, or formation of too large an annular defect, can cause the nucleus replacement to be expelled from or to extrude from the disc space. 
     Accordingly, there remains a need for improved devices and methods for removing nucleus tissue from an intervertebral disc, and in particular, devices and methods for removing nucleus tissue that minimize the required annular defect. 
     SUMMARY OF THE INVENTION 
     The present invention provides devices and methods for removing tissue. In one aspect, a device for removing tissue is provided that includes a hollow elongate member having an outer wall and a lumen, a selectively deployable tissue-cutting element extending from the hollow elongate member, and an actuation member extending through the lumen and communicating with the hollow elongate member at a location that is distal to the tissue-cutting element. Movement of the actuation member can cause the tissue-cutting element to move from the insertion configuration where the tissue-cutting element is not deployed to a tissue-cutting configuration where the tissue-cutting element is deployed such that it is radially extended relative to the insertion configuration. In use, the actuation member effects deployment of the tissue-cutting element by compression of the elongate member, and the compression is effected by rotation of a portion of the elongate member distal to the tissue-cutting element. In one embodiment, the actuation member and the elongate member are adapted to move independently of one another, and/or the tissue-cutting element is adapted to move independently of the elongate member. 
     The tissue-cutting element can have a variety of configurations. In one embodiment, the tissue-cutting element can be formed on at least a portion of the hollow elongate member. In another embodiment, the tissue-cutting element can be an arm that is formed by the portion of the elongate member that is between adjacent slits. The at least two adjacent slits can be formed in the outer wall of the elongate member and located proximal to a distal end of the elongate member. The slits can extend proximally over a distance that is less than a length of the elongate member. In other embodiments, the tissue-cutting element can include at least two radially-extendable arms that are formed between a plurality of slits. In alternate embodiments, the tissue-cutting element can be helically shaped and/or include a sharpened edge. The actuation member can also have a variety of configurations, however in one embodiment, the actuation member comprises at least one tether. 
     The device can also include a variety of other features to facilitate the removal of tissue. In one embodiment, the lumen of the elongate member can be adapted accommodate an irrigation fluid and/or suction. By way of non-limiting example, a fluid input conduit and a suction conduit can be disposed in the lumen. In another embodiment, the outer wall of the elongate member can be adapted to be positioned within a cannula. For example, the distal portion of the elongate member that includes the tissue-cutting element can include a ledge that abuts a shoulder of the cannula, such that the tissue-cutting element protrudes from the cannula. 
     The device can also include a locking mechanism that is adapted to hold the actuation member in the actuated position. Additionally or alternatively, the device can include a steering element that is adapted to control directional movement of the elongate member. The steering element can have a variety of configurations, and in one embodiment, the steering element is a joint formed between proximal and distal ends of the elongate member. In another embodiment, the steering element can be a tether that extends through the lumen of the elongate member and is coupled to the elongate member, which is flexible, at a location that is distal to the tissue-cutting element. 
     Methods for the removing tissue are also disclosed herein. In one aspect, a method for removing tissue includes positioning a tissue removal device at a site within a disc space, the tissue removal device having an elongate member with at least one selectively deployable tissue-cutting element and an actuation member. The method further includes applying a force to the actuation member to cause the tissue-cutting element to move from a non-deployed insertion configuration to a deployed, tissue-cutting configuration in which the tissue-cutting element is radially extended relative to the insertion configuration, and manipulating the tissue removal device within the disc space to cut and remove selected disc tissue. In one embodiment, the hollow elongate member is adapted move independently from the actuation member, and/or the tissue-cutting element is adapted to move independently of the elongate member. 
     The method can also include a variety of other steps to facilitate tissue removal. In one embodiment, the method can further include delivering fluid to the tissue site through the lumen. Alternatively or additionally, the method can include applying suction to the tissue site through the lumen and/or positioning at least a portion of the elongate member within a cannula for delivery to the disc space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG.  1 A  is a perspective view of one embodiment of a tissue removal device disclosed herein in an insertion configuration; 
         FIG.  1 B  is a perspective view of the distal end of the device of  FIG.  1 A  in the insertion configuration; 
         FIG.  1 C  is a perspective view of the distal end of the device of  FIG.  1 B  in the tissue-cutting configuration; 
         FIG.  1 D  is a perspective view of the distal end of the device of  FIG.  1 C  following activation of a steering mechanism; 
         FIG.  2    is a perspective view of another embodiment of a tissue removal device in a tissue-cutting configuration; 
         FIG.  3 A  is a perspective view of yet another embodiment of a tissue removal device in an insertion configuration; 
         FIG.  3 B  is a perspective view of the device of  FIG.  3 A  positioned within a disc nucleus and in the tissue-cutting configuration; 
         FIG.  4    is a perspective view of another embodiment of a tissue removal device in a tissue-cutting configuration; 
         FIG.  5    is a perspective view of another embodiment of a tissue removal device in an insertion configuration; 
         FIG.  6 A  is a perspective view of another embodiment of a tissue removal device in an insertion configuration; 
         FIG.  6 B  is a perspective view of the device of  FIG.  6 A  in the tissue-cutting configuration; 
         FIG.  7    is a perspective view of another embodiment of a tissue removal device in an insertion configuration; and 
         FIG.  8    is a perspective view of yet another embodiment of a tissue removal device in an insertion configuration. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those of ordinary skill in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention. 
     The present invention provides devices and methods for tissue removal. The tissue removal devices disclosed herein generally include an elongate member that has a tissue-cutting element formed on a distal end thereof. An actuation member can extend through the elongate member and couple to the tissue-cutting element to control or influence the configuration and/or orientation thereof. Upon actuation of the member, the sections of the elongate member that contain the tissue-cutting elements bow or deflect to expose cutting surfaces. The device can then be manipulated within a target site to cut tissue so that it can be removed by suction or other means. One skilled in the art will appreciate that the device can be used to remove a variety of types of tissue, however in an exemplary embodiment the device can be used in spinal surgery to remove disc nucleus tissue. 
       FIGS.  1 A- 1 D  illustrate one embodiment of a tissue removal device  10  that includes a hollow elongate member  12  having an outer wall  11  and a lumen  13 , and one or more selectively deployable tissue-cutting elements  19  formed on at least a portion of the hollow elongate member  12 . The device  10  can also include an actuation member  14  that extends through the lumen  13  to selectively activate the cutting elements  19 . In one embodiment, the actuation member  14  is coupled to the hollow elongate member  12  at a location that is distal to the tissue-cutting element  19 . 
     The elongate member  12  can have virtually any configuration that allows it to be inserted to a surgical site. In one aspect, the member  12  is configured for delivery to the surgical site in a minimally invasive manner, such as via a cannula. As shown, the member  12  is substantially cylindrical and sufficiently strong to be inserted into tissue. The elongate member  12  can also include features to facilitate minimally invasive delivery, and as shown in  FIGS.  7  and  8   , which will be discussed in more detail below, the distal-most portion of the elongate member  612 ,  712  can be pointed or rounded. A lumen  13  can extend through at least a portion of the elongate member  12 , and can be adapted to house an actuation member  14 , discussed above. Further, the lumen  13  can accommodate an irrigation fluid and/or suction delivery to the tissue site, as will be discussed below. For example, as shown in  FIGS.  3 B and  5   , which will also be discussed in more detail below, a fluid input conduit  260 ,  460  and a suction conduit  262 ,  462  can be disposed within the lumen  213 ,  413  to accommodate fluid delivery, and/or removal of tissue, such as by suction. 
     The elongate member  12  can have a variety of sizes, depending upon the intended use of the device  10 . However, in one embodiment where the device  10  is used for disc nucleus removal, the elongate member  12  can have an outer diameter of about 5 mm (or less) when it is in the insertion configuration. The elongate member  12  can also be formed from a variety of materials, such as biocompatible metals, medical grade plastics, and/or combinations thereof. Exemplary biocompatible metals can include stainless steel, titanium, titanium alloys, cobalt chromium alloys, nitinol, and combinations thereof. Exemplary medical grade plastics can include nylon, polyolefins, ABS, PEEK, polysulfones, polyacetal, and combinations thereof. 
     At least one tissue-cutting element  19  can be formed on the distal end  12   b  of the member  12  that is able to be exposed (e.g., by extending radially) when subjected to a force.  FIG.  1 B  illustrates the device  10  in which the tissue-cutting element  19  is in the insertion configuration where the tissue-cutting element  19  is not deployed to a tissue-cutting configuration, and  FIG.  1 C  illustrates the device  10  where the tissue-cutting element  19  is deployed such that it is radially extended relative to the insertion configuration. The tissue-cutting element can be radially extended to a variety of diameters. For example, when the device is used to remove disc nucleus material, the device can have an outer diameter in the range of about 6 mm to 16 mm when in the tissue-cutting configuration. 
     The tissue-cutting element  19  can have any configuration that allows it to be configured to cut tissue (e.g., radially extend) upon the application of a force (e.g., compression) thereto. In one embodiment, the tissue-cutting element  19  can include at least one arm (arms  20   a - 20   j  are shown in  FIGS.  1 A- 1 D ) that is formed as a result of adjacent slits (slits  18   a - 18   e  are shown in  FIGS.  1 A- 1 D ) in the outer surface  11  of the elongate member  12 . The slits can have a variety of shapes, and the shape of the slits can determine the shape of the resulting tissue-cutting arm. As shown in  FIGS.  1 A- 1 D , the slits  18   a - 18   e  can be substantially elongate, which can result in substantially elongate arms  20   a - 20   j . In other embodiments, such as shown in  FIG.  5   , the slits can be formed in a spiral pattern which can result in substantially helical arms  420   a ,  420   b . Alternatively, as shown in  FIGS.  6 A- 8   , the slits (slits  518   a ,  618   a ,  718   a  are shown) can be substantially ovular or triangular to form arms  520   a - b ,  620   a - b ,  720   a - b  having a complementary shape. The slits can also have a variety of sizes, depending upon the number of arms desired and the diameter of the elongate member, however when the device is used to remove nucleus disc material, the slits can have a width in the range of about 0.1 mm to 3 mm. 
     The arms can also have a variety of sizes depending upon the intended application of the device, however the arms can generally extend proximally from a position adjacent to the distal end of the device over a distance that is less than a length of the elongate member. By way of non-limiting example, when the device is used to remove disc nucleus material, the arms can be separated by a distance in the range of about 0.1 mm to 3 mm and extend a distance in the range of 5 mm to 50 mm along the elongate member. One skilled in the art will appreciate that a variety of techniques can be used to form the slits, and hence the arms, however in an exemplary embodiment, the slits can be formed by a laser cutting technique or an EDM technique. 
     While  FIGS.  1 A- 1 D  illustrates a device that has about 10 arms  20   a - 20   j  that are radially disposed around the circumference of the elongate member  12 , one skilled in the art will appreciate that the device can have any number of arms arranged in any configuration about the elongate member. The arms can also include a variety of features to facilitate cutting of tissue. For example, in one embodiment each arm can include at least one sharpened edge, at a leading edge of the device, that can act as a blade for cutting tissue. It is understood that the cutting elements need not include a sharpened edge, as the device can be configured for use with energy-assisting cutting such as, for example, by connection to a RF generator or an ultrasound transducer. One skilled in the art will appreciate that the shape and geometry of the cutting blades can be modified depending upon the type of cutting motion desired, that is forward, reverse, back and forth (i.e., wanding), side to side, or rotary cutting. For example, the angle of the cutting edge relative to the elongate member can vary whether a forward, reverse, back and forth (i.e., wanding), side to side, or rotary cut is desired. 
     A variety of techniques can be used to apply a force to the tissue-cutting elements to cause them to radially extend into a tissue-cutting configuration. In one embodiment, the device can include an actuation member that can extend through the elongate member and couple to the distal most portion of the tissue-cutting element. While the actuation member can have a variety of configurations, as shown in  FIGS.  1 A- 1 D , the actuation member can be two tethers  14 ,  16  or other cable-like element. A variety of techniques can be used to couple the actuation members to the tissue-cutting element. In one embodiment, as shown in  FIGS.  1 A- 1 D , the actuation members  14 ,  16  can be coupled to an end cap  22  that is positioned on the distal most end of the elongate member  12 . The actuation members  14 ,  16  can be coupled to the center of the end cap  22  to prevent biasing of the device  10 . While the end cap  22  can have a variety of configurations, as shown, it should be of a shape to facilitate ease of insertion. For example, it can be rounded or bullet-shaped. The end cap  22  can be formed of a single piece or it can be formed of a washer  26  and a nut  24 . In use, a force, such as tension, can be applied to both of the actuation members  14 ,  16 , which causes the end cap  22  to move towards the proximal end of the device  12   a  and compress the tissue-cutting element  19 , thereby causing it to radially expand. The elongate member  12  can then be moved independently of the actuation members  14 ,  16  to cut tissue. Additionally, the tissue-cutting elements  20   a - 20   j  can also be moved independently of the elongate member  12  to cut tissue. While  FIGS.  1 A- 1 D  illustrate a device  10  that has two actuation members  14 ,  16 , in other embodiments such as  FIG.  4   , the device  310  can have one actuation member  314  that is disposed within the lumen  313  of the device  310  to effect actuation. 
     Referring back to  FIGS.  1 A- 1 D , the device  10  can also include a steering mechanism to facilitate directional motion. While the steering mechanism can have a variety of configurations, as shown the steering mechanism can be one of the tethers  14 ,  16  that extend through the elongate member  12  and are coupled to the distal end  12   b  or end cap  22  of the device  10 . In other embodiments, the tether can be extend through the lumen of the device and be eccentrically coupled to the end cap to bias the device in one direction. In use, tension can be applied to one of the tethers  14 , 16  to cause the distal end  12   b  of the elongate member  12  to bend towards the direction of the tether being activated  14 ,  16 , as shown in  FIG.  1 D . 
       FIG.  2    illustrates another embodiment of a tissue removal device  110 . The device  110  is similar to the device  10  of  FIGS.  1 A- 1 D , and includes a hollow elongate member  112  having an outer wall  111  and a lumen (not shown) extending therethrough, a selectively deployable tissue-cutting element  119  formed on at least a portion of the hollow elongate member  112 , and an actuation member (not shown) extending through the lumen and coupled to an end cap  122  located distal to the tissue-cutting element  119 . The device  110  also includes a steering mechanism  128  to facilitate directional movement of the tissue-cutting element  119 , and a handle  138 . However, unlike the steering mechanism  19  described above with respect to  FIGS.  1 A- 1 D , which relies on bending the member  12  using tethers  14 , 16 , the steering mechanism  128  includes a joint. As shown, the joint  128  is formed on the elongate member  112 , at a position that is proximal to the tissue-cutting element  119 . A variety of joints can be used, such as the U-joint  128  shown in  FIG.  2   . In use, tension can be applied to the joint  128  to bias the tissue-cutting element  119  to one side. 
     A variety of techniques can be used to facilitate motion of the joint  128 . By way of non-limiting example, two pull wires  130 ,  132  can extend through at least a portion of the elongate member  112  and couple to elongate member  112  at a location that is distal to the joint  128 . Control elements  134 ,  136  can be formed on the proximal end of the wires  130 ,  132  and can be used to grip and apply tension to one of the wires  130 ,  132  to effect directional movement of the tissue-cutting element  119 . While  FIG.  2    shows control elements  134 ,  136  formed on the wires  130 ,  132 , in other embodiments, the wires can extend through a handle formed on the proximal end of the elongate member, and can be coupled to a lever, knob, or dial that can be activated to cause tension to be applied thereto. 
     As noted above, the elongate member  112  can also include a handle  138  that is located on the proximal end  112   a  thereof to facilitate manipulation and handling of the device  110 . While the handle  138  can have any configuration that allows a user to conveniently hold and operate the device  110 , in one embodiment the handle  138  has a substantially elongate shape. The handle  138  can include features to facilitate actuation of the actuation member. For example, the handle  138  can include a sliding actuator lever  131  that can be coupled to the actuation member and that allows tension to be selectively applied thereto. In alternate embodiments, rotatable knobs or dials can be used to selectively apply tension to the actuation member. A locking mechanism (not shown) can also be associated with the sliding actuator lever to hold the actuation member in a desired position once tension is applied. 
     The handle  138  can also include a driving mechanism to facilitate movement of the tissue-cutting element  119  to effect cutting of tissue when it is in the tissue-cutting configuration. For example, as shown, the handle  138  can include a rotatable knob  140  to effect rotational movement of the tissue-cutting element  119 . Additionally, the handle can include features to facilitate the removal of tissue, such as a port for delivering suction and/or irrigation to the elongate member, or it can be adapted to couple to an external suction and/or irritation port. One skilled in the art will appreciate the variety of features that can be formed on the handle. 
       FIGS.  3 A- 8    illustrate other embodiments of a tissue removal device  210 ,  310 ,  410 ,  510 ,  610 ,  710 . The device  210  of  FIGS.  3 A- 3 B  is similar to the device  10  of  FIGS.  1 A- 1 D , and includes a hollow elongate member  212  having an outer wall  211  and a lumen  213 , and a selectively deployable tissue-cutting element  219  formed on at least a portion of the hollow elongate member  212 . The device  210  also includes an actuation member  214  that extends through the lumen  213  and is coupled to an end cap  222  located distal to the tissue-cutting element  219 . However, the device  210  shown in  FIGS.  3 A- 3 B , unlike the device  10  of  FIGS.  1 A- 1 D , has a single cutting arm  220   a  that is formed as a result of the formation of two slits (slit  118   a  is shown) in the elongate member  212 . Such a single cutting arm  220   a  can be used for directional cutting. As shown in  FIG.  3 B , when a force (e.g., tension or a rotational force applied to threaded members) is applied to move the device  210  from the insertion configuration to the tissue-cutting configuration, the tissue-cutting element  119  is radially extended in only one direction, and used to cut tissue in a certain area, for example by a back and forth motion or a rotary motion. Once cut, the tissue can be removed from the tissue site by the application of fluid and/or suction through fluid input conduit  260  and/or suction conduit  262  that are disposed within the lumen  213 , as noted above. 
       FIG.  4    illustrates another embodiment of a tissue removal device  310 . The device  310  is also similar to the device  10  of  FIGS.  1 A- 1 D , and includes a hollow elongate member  312  having an outer wall  311  and a lumen  313 , and a selectively deployable tissue-cutting element  319  formed on at least a portion of the hollow elongate member  312 . The device  310  also includes an actuation member  314  that extends through the lumen  313  and is coupled to an end cap  322  located distal to the tissue-cutting element  319 . However, unlike the device  10  in  FIGS.  1 A- 1 D , the device  310  can have two opposed tissue-cutting elements  320   a ,  320   b  that are formed as a result of two slits (slit  318   a  is shown). The device  310  can also have an actuation member  314  that is threadably mated to end cap  322 . As the actuation member is rotated, a compressive force will be applied to end cap  322 , causing the arms  320   a ,  320   b  to bow out. This results in the device  310  having a bulb-shaped configuration when in the tissue-cutting configuration. Although the actuation of the embodiment shown in  FIG.  4    is described with respect to rotation of a threaded member, one skilled in the art will understand that tension can alternatively be applied to the actuation member. 
       FIG.  5    illustrates yet another embodiment of a tissue removal device  410 . The device  410  is similar to the device  10  of  FIGS.  1 A- 1 D , and includes a hollow elongate member  412  having an outer wall  411  and a lumen  413 , and a selectively deployable tissue-cutting element  419  formed on at least a portion of the hollow elongate member  412 . The device  410  also includes an actuation member  414  that extends through the lumen  413  and is coupled to an end cap  422  located distal to the tissue-cutting element  419 . However, unlike the device  10  in  FIGS.  1 A- 1 D , the device  410  includes helically shaped cutting elements  420   a ,  420   b  that are formed as result of spirally cut slits. The cutting member can be formed as a result of a single helix, or numerous helices formed in or extend from the elongate member. In use, force (e.g., tension or a rotational force applied to threaded members) is applied to compress the outer walls of the helix, thereby causing expansion thereof. When in the tissue-cutting configuration, the device  410  can be substantially tubular in shape, having a substantially constant diameter. Additionally, and when moved to cut tissue (e.g., by rotation of the helical cutting elements  420 ,  420   b ), the helically-shaped cutting elements  420   a ,  420   b  can help initiate tissue movement into the device  410 . 
       FIGS.  6 A- 6 B  illustrate yet another embodiment of a tissue removal device  510 . The device  510  is similar to the device  10  of  FIGS.  1 A- 1 D , and includes a hollow elongate member  512  having an outer wall  511  and a lumen  513 , and a selectively deployable tissue-cutting element  519  formed on at least a portion of the hollow elongate member  512 . The device  510  also includes an actuation member  514  that extends through the lumen  513  and is coupled to an end cap  522  located distal to the tissue-cutting element  519 . However, unlike the device  10  in  FIGS.  1 A- 1 D , the device  510  includes two substantially ovular slits (slit  518   a  is shown) that form arms  520   a ,  520   b . In use, a force is applied to compress the arms  520   a ,  520   b  and the device  510  moves from the insertion configuration ( FIG.  6 A ) to the tissue-cutting configuration ( FIG.  6 B ), and the arms  520   a ,  520   b  extend radially to cut tissue. 
     The device  510  can also include features that facilitate insertion within a cannula  550 . While a variety of features can be used, as shown each elongate member  512  can include opposed ledges  582 ,  584  that are formed thereon at a location that is proximal to the tissue-cutting element  519 . The ledges  582 ,  584  are adapted to abut corresponding shoulders  572 ,  574  that are formed on a cannula  550 . One skilled in the art will appreciate that the ledges and shoulders can have a variety of sizes, depending upon the intended use of the device. In use, and as a force (i.e., tension) is applied to the actuation member  514 , the ledge  582 ,  584  is pressed against the shoulder  572 ,  574  to facilitate the radial expansion of the tissue-cutting element  519 . 
       FIG.  7    illustrates yet another embodiment of a tissue removal device  610 . The device  610  is similar to the device  10  of  FIGS.  1 A- 1 D , and includes a hollow elongate member  612  having an outer wall  611  and a lumen  613 , and a selectively deployable tissue-cutting element  619  formed on at least a portion of the hollow elongate member  612 . The device  610  also includes an actuation member  614  that extends through the lumen  613  and is coupled to an end cap  622  located distal to the tissue-cutting element  619 . However, unlike the device  10  in  FIGS.  1 A- 1 D , the device  610  includes two substantially triangular slits (slit  618   a  is shown) that form arms  620   a ,  620   b . The device  610  can also include features that facilitate insertion within a cannula  650 . As noted above, the elongate member  612  of the device  610  can include a substantially rounded distal end. Additionally, and similar to the device  510  of  FIGS.  6 A- 6 B , each elongate member  612  can include opposed ledges  682 ,  684  that are formed thereon at a location that is proximal to the tissue-cutting element  619 . The ledges  682 ,  684  are adapted to abut corresponding shoulders  672 ,  674  that are formed on a cannula  650 . In use, and as a force (e.g., tension) is applied to the actuation member  614 , the ledge  682 ,  684  is pressed against the shoulder  672 ,  674  to facilitate the radial expansion of the tissue-cutting element  619 . 
       FIG.  8    illustrates yet another embodiment of a tissue removal device  710 . The device  710  is similar to the device  10  of  FIGS.  1 A- 1 D , and includes a hollow elongate member  712  having an outer wall  711  and a lumen  713 , and a selectively deployable tissue-cutting element  719  formed on at least a portion of the hollow elongate member  712 . The device  710  also includes an actuation member  714  that extends through the lumen  713  and is coupled to an end cap  722  located distal to the tissue-cutting element  719 . However, unlike the device  10  in  FIGS.  1 A- 1 D , the device  710  includes two substantially triangular slits (slit  718   a  is shown) that form arms  720   a ,  720   b . The device  710  can also include features that facilitate insertion within a cannula  750 . As noted above, the elongate member  712  of the device  710  can include a substantially pointed distal end. Additionally, and similar to the device  510  of  FIGS.  6 A- 6 B , each elongate member  712  can include opposed ledges  782 ,  784  that are formed thereon at a location that is proximal to the tissue-cutting element  719 . The ledges  782 ,  784  are adapted to abut corresponding shoulders  772 ,  774  that are formed on a cannula  750 . In use, and as a force (i.e., tension) is applied to the actuation member  714 , the ledge  782 ,  784  is pressed against the shoulder  772 ,  774  to facilitate the radial expansion of the tissue-cutting element  719 . 
     One skilled in the art will appreciate that each of the various designs provides for disc removal with cutting surfaces. The cutting surfaces can be located along the leading edge(s) of the blade(s) and can be tapered to a relatively sharp cutting tip or plane. The helically shaped cutting elements allow for cutting via rotary motions prompting the collection of the loose disc tissue in the central portion of the device and for aspiration with the central cannula. The multiple blades of the helical shaped cutting element provide for the exposure of additional cutting surfaces for each rotation when compared to the dual blade device shown in  FIG.  4   . This added exposure reduces the number of rotations required to remove tissue. In addition, the multi-blade helical device allows for one blade to pull/tension the tissue and the second to cut under tension, this can also enhance the ability to remove tissue. 
     The devices disclosed herein can be used to remove tissue from, for example, the nucleus of a disk. While the method is described in connection with device of  FIGS.  3 A- 3 B , a person skilled in the art will appreciate that various other devices can be used. In one embodiment, and following preparation of the patient and surgical site as is known in the art, the device can be inserted to the target tissue, e.g., the nucleus of the disc, via a hole in the annular wall. As shown in  FIG.  3 B , the device  210  can be inserted through a cannula  250  to position the device  210  within the disc nucleus  254 . The device  210  is preferably inserted in the insertion configuration, as shown in  FIG.  3 A . Such an insertion configuration is particularly advantageous in that it minimizes the size of the annular defect and enables the use of minimally invasive surgical techniques. Once inserted into the disc nucleus material, and if the device includes a steering mechanism, the steering mechanism can be activated to further position the device within the disc at the site of the tissue to be removed. 
     Once the device  210  is positioned within the nucleus  254 , a force can be applied to the actuation member  214 . For embodiments where the actuation member is a tether  214 , the tether  214  can be pulled in the proximal direction to cause the tissue-cutting element to radially expand to the tissue-cutting configuration. Depending upon the configuration of the device, the tension can be applied to the tether directly, or by movement of a lever, dial, or knob formed on a handle of the device. As a result, the device  210  moves from the insertion configuration to the tissue-cutting configuration, where the tissue-cutting arm  220   a  is radially expanded relative to the elongate member  212 , as shown in  FIG.  3 B . The actuation member can then optionally be locked in position using a locking mechanism to maintain the radial expansion of the tissue-cutting element. 
     Once the device is in the tissue-cutting configuration, the device can be moved to cut tissue, and it can be steered, as appropriate, to reach areas of the nucleus that require removal of tissue. Depending upon the type of tissue cut desired, the device can be rotated, moved forward, or moved in reverse. One skilled in the art will appreciate that movement of the device can be effected by directly moving the elongate member, by moving a lever, dial, or knob on the handle of the device, and/or by activating an energy source to deliver energy to the tissue-cutting element. As the tissue is being cut, or alternatively, once all of the tissue is cut, the tissue fragments can be removed from the disc. While a variety of removal techniques can be used, in one embodiment and still referring to  FIG.  3 B , suction and/or irrigation can be applied through a fluid input conduit  260  and a suction conduit  262  that are disposed within the lumen  213 . In other embodiments, the elongate member can be removed and a separate tissue removal device can be inserted into the nucleus space to clear the tissue. 
     Following the removal of the tissue, the locking mechanism can optionally be unlocked and the force that is applied to the actuation member released. This causes the tissue-cutting element to radially retract back to the insertion configuration. The device can then be removed from the tissue, leaving behind a substantially tissue-free nucleus space and minimizing the size of the annular defect. 
     One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.