Abstract:
A flexible auger design for low-torque transmitting drive shafts, which allows effective tissue material transport through curved, flexible tubes and channels. A hollow auger has a hollow center, so that the helical member hugs the inner wall of the tube and material is transported along the center axis and the inner wall of the tube. The hollow flexible auger allows for transportation of material from an operative location in the patient (material removal) as well as to operative location in the patient (material delivery).

Description:
CONTINUING DATA 
       [0001]    This application claims priority from co-pending U.S. provisional patent application U.S. Ser. No. 62/032,754, filed Aug. 4, 2014, entitled “Flexible Transport Auger”, (Thommen et al.), the specification of which is incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The natural intervertebral disc contains a jelly-like nucleus pulposus surrounded by a fibrous annulus fibrosus. Under an axial load, the nucleus pulposus compresses and radially transfers that load to the annulus fibrosus. The laminated nature of the annulus fibrosus provides it with a high tensile strength and so allows it to expand radially in response to this transferred load. 
         [0003]    In a healthy intervertebral disc, cells within the nucleus pulposus produce an extracellular matrix (ECM) containing a high percentage of proteoglycans. These proteoglycans contain sulfated functional groups that retain water, thereby providing the nucleus pulposus within its cushioning qualities. These nucleus pulposus cells may also secrete small amounts of cytokines such as interleukin-1β and TNF-α as well as matrix metalloproteinases (“MMPs”). These cytokines and MMPs help regulate the metabolism of the nucleus pulposus cells. 
         [0004]    In some instances of disc degeneration disease (DDD), gradual degeneration of the intervetebral disc is caused by mechanical instabilities in other portions of the spine. In these instances, increased loads and pressures on the nucleus pulposus cause the cells within the disc (or invading macrophages) to emit larger than normal amounts of the above-mentioned cytokines. In other instances of DDD, genetic factors or apoptosis can also cause the cells within the nucleus pulposus to emit toxic amounts of these cytokines and MMPs. In some instances, the pumping action of the disc may malfunction (due to, for example, a decrease in the proteoglycan concentration within the nucleus pulposus), thereby retarding the flow of nutrients into the disc as well as the flow of waste products out of the disc. This reduced capacity to eliminate waste may result in the accumulation of high levels of toxins that may cause nerve irritation and pain. 
         [0005]    As DDD progresses, toxic levels of the cytokines and MMPs present in the nucleus pulposus begin to degrade the extracellular matrix, in particular, the MMPs (as mediated by the cytokines) begin cleaving the water-retaining portions of the proteoglycans, thereby reducing its water-retaining capabilities. This degradation leads to a less flexible nucleus pulposus, and so changes the loading pattern within the disc, thereby possibly causing delamination of the annulus fibrosus. These changes cause more mechanical instability, thereby causing the cells to emit even more cytokines, thereby upregulating MMPs. As this destructive cascade continues and DDD further progresses, the disc begins to bulge (“a herniated disc”), and then ultimately ruptures, causing the nucleus pulposus to contact the spinal cord and produce pain. 
         [0006]    Two of the more common treatments of the herniated disc are the discectomy, total disc replacement and the fusion. In a discectomy, the surgeon removes the bulging disc material. In a fusion, the surgeon clears out a portion of the disc, inserts an intervertebral implant into the disc space. In each case, removal of disc material is an important step. 
         [0007]    Automatic transportation of cut disc material has shown to be a significant challenge for automated disc removal tools, especially with small diameter tools designed for minimally invasive surgery. Auger designs have been shown to be very effective in terms of transportation. However, as flexibility and steerability are desirable in disc removal tools, transport augers should also be flexible. 
         [0008]    U.S. Pat. No. 7,591,790 (“Pflueger”) discloses an apparatus for removing tissue and/or other material from a patient. The apparatus generally includes a handpiece and a tissue removal mechanism connected thereto. The tissue removal mechanism includes a cannula having an open distal tip and an outer diameter of less than about 5 mm, or less than about 2 mm. The mechanism further includes a rotatable element having a distal portion with helical threading. The distal portion of the rotatable element extends beyond the open distal tip of the cannula in order to allow tissue to prolapse between turns of the helical threading. The apparatus is designed to draw soft tissue into the cannula upon rotation of the rotatable element and without the need for supplemental sources of aspiration. The auger of the &#39;790 patent design has a center axis that is solid, which means that the removed material is transported against the auger itself. 
         [0009]    US 2013-0103067 (“Fabro”) discloses tissue removal devices, wherein the tissue removal device may comprise a handheld housing, a motor, and a tissue removal mechanism coupled to the handheld housing. The tissue removal mechanism may comprise a tubular member, a rotatable elongated member disposed within a lumen of the tubular member, a first impeller distal to the rotatable elongated member, and a second impeller adjacent the first impeller. Fabro discloses a discectomy device comprising a wire wrapped around a core. 
         [0010]    U.S. Pat. No. 6,033,105 (“Barker”) discloses an integrated bone cement mixing and delivery system using an auger mechanism as the means for advancing the bone cement through the delivery chamber. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention relates to a flexible hollow auger for low-torque transmitting drive shafts, which allows for effective tissue material transport through curved, flexible tubes and channels. 
         [0012]    In one embodiment, the present invention describes a hollow flexible auger. An hollow auger has a hollow center, so that the helical member hugs the inner wall of an outer tube. In use, material is transported along both the center axis and the inner wall of the tube. The hollow flexible auger allows for transportation of material from an operative location in the patient (material removal) as well as to an operative location in the patient (material delivery). 
         [0013]    When the hollow flexible auger allows for transportation of tissue material from an operative location in the patient (tissue removal), the target tissue may be soft tissue (such as intervertebral disc tissue) or hard tissue (such as the cancellous bone of a vertebral body). 
         [0014]    This design has the potential of providing very low manufacturing costs, which could present an economic advantage in single-use applications. The present invention is especially designed for use in transporting excised material from an intervertebral disc, but could find application in other medical areas in which transportation of solid or liquid material along a curved or flexible tube or channel is desired. 
         [0015]    In one embodiment, the flexible auger is made from a standard helical spring and a shrunken heat-shrink tube disposed over and contacting the spring. When the heat-shrink tube is shrunk through application of heat, the final assembly takes on a thread-like appearance. 
         [0016]    Therefore, in accordance with the present invention, there is provided a biomedical material transfer device comprising:
       a) a transfer element having a proximal end portion, a distal end portion, and an intermediate portion comprising a flexible, hollow auger, and   b) a drive element adapted to rotate the transfer element, the drive element having a distal end portion,   wherein the distal end portion of the drive element is connected to the proximal end portion of the transfer element.       
 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0020]      FIGS. 1A and 1B  disclose a biomedical material transfer device of the present invention. 
           [0021]      FIG. 2A  discloses a second device of the present invention. 
           [0022]      FIG. 2B  discloses a second device of the present invention. 
           [0023]      FIGS. 2C-2D  disclose longitudinal cross-sections of the transfer element component of the present invention. 
           [0024]      FIGS. 3A-B  disclose the device of the present invention further comprising a flexible inner shaft disposed within the hollow auger. 
           [0025]      FIGS. 4A and 4B  disclose various geometries of the opening at the distal end portion of the transfer element. 
           [0026]      FIGS. 5A-C  disclose the device of the present invention further comprising a flexible inner tube disposed within the hollow auger. 
           [0027]      FIG. 6  discloses a pulling mechanism. 
           [0028]      FIG. 7  discloses a necked flexible auger of the present invention. 
           [0029]      FIG. 8  disclose the device of the present invention having an inlet for fluid passage. 
           [0030]      FIG. 9  discloses a cross-section of the outer cannula that surrounds the flexible auger, wherein a plurality of lumens are disposed in the cannula wall. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    Now referring to  FIGS. 1A and 1B , there is provided a biomedical material transfer device  1  comprising:
       a) a transfer element  3  having a proximal end portion  5 , a distal end portion  6 , and an intermediate portion  7  comprising a flexible, hollow auger  7 , and   b) a drive element  9  adapted to rotate the transfer element, the drive element having a distal end portion  11 ,   wherein the distal end portion of the drive element is connected to the proximal end portion of the transfer element.       
 
         [0035]    Now referring to FIG.  2 AD, in one embodiment, the flexible auger is made out of a coiled mono filament such as a standard (metallic) helical spring  13  and a heat shrinkable (or dip coating) polymeric (such as PTFE) tube  15  disposed over it. The spring may be made from various materials, including metallic, polymeric-based or ceramic-based materials. Preferably, however, the spring is metallic. The helical spring has an outer diameter D 1 , and the shrink tube has an inner diameter substantially equivalent to the outer diameter of the helical spring, so that the outer surface  17  of the helical spring contacts the inner surface  19  of the tube. If sufficient heat is applied to the tube, the non-contact portions  21  of the tube begin to shrink to a minimum diameter D 2 , while the contact portions of the tube keep their original diameter D 1  wherever they touch the helical spring. In this manner, the heat-shrunk tube forms “valleys and summits” and provides a thread-like appearance. The thread produced by this design is able to transport material within the auger upon rotation. 
         [0036]    Preferably, the hollow auger comprises a tube  15  and a substantially helical element  13  housed within the tube. More preferably, the tube has an inner surface  19  and the substantially helical element extends inwardly from the inner surface. 
         [0037]    In some embodiments, a helical coil is integrated into the tubing. 
         [0038]    In some embodiments, the transfer element comprises a substantially helical element and a membrane wrapped around the substantially helical element. Preferably, the membrane is a heat-shrunk membrane, the substantially helical element has a first diameter D 1 , the tube has a first diameter D 2 , and, and the first diameter D 1  is greater than the second diameter D 2 . Preferably, this tube has a thread-like topology. 
         [0039]    Now referring to  FIG. 2   a , optionally, the proximal end portion of the transfer element comprises a second tube  21  having a threaded outer surface  23 . This second tube of the transfer element may be integral with the substantially helical element housed within the first tube. However, this second tube of the transfer element may also be discrete from (i.e., not be integral with) the substantially helical element housed within the first tube. 
         [0040]    In some embodiments, the second tube of the transfer element rotates with the substantially helical element housed within the first tube, while in others the substantially helical element housed within the first tube rotates independently of the second tube of the transfer element. 
         [0041]    In some embodiments, the substantially helical element housed within the first tube has a cross-sectional thickness, and the tube has an outer diameter, and the cross-sectional thickness of the helical element is between 3% and 30% of the diameter. 
         [0042]    Preferably, the intermediate portion of the transfer element is flexible. 
         [0043]    Preferably, the distal end portion of the transfer element is adapted to cut intervertebral disc tissue and to fit between opposing vertebrae. 
         [0044]    Still referring to  FIG. 2   a , in some embodiments, the distal end of the transfer element comprises a cutting tip  25 , wherein the cutting tip has a proximal end portion  27  adapted to mate with the substantially helical element. Preferably, the distal end of the transfer element comprises a distal end opening (not shown).
       Typically, the drive element  9  comprises either a drive handle or a motor.       
 
         [0046]    In some embodiments, the device further comprises a tubular shaft surrounding the transfer element and connected to the housing that surrounds the drive element, this housing having a relative rotational or translational movement to the drive element. The tubular shaft is optionally transparent. 
         [0047]    Now referring to  FIGS. 3A and 3B , in some embodiments, the device further comprises a flexible inner shaft  31  disposed within the hollow auger. Preferably, the flexible inner shaft is hollow. Preferably, the flexible inner shaft comprises a narrow-wound spring. 
         [0048]    In some embodiments, the device further comprises an outer cannula, wherein the hollow auger is disposed within the outer cannula. In some embodiments, the outer cannula comprises a wall and an inner bore, wherein the wall has at least one lumen therein. 
         [0049]    In some embodiments, the device further comprises a wire running longitudinally in the lumen. Preferably, the outer cannula comprises a wall and an inner bore, wherein the wall has at least one stationary wire running longitudinally therein. 
         [0050]    In some embodiments, the hollow auger has one or more steering mechanisms attached thereto. These steering mechanisms may include at least one pulling mechanism, or at least one pushing mechanism, or a combination thereof. 
         [0051]    In some embodiments, the proximal end portion of the transfer element is more rigid than the hollow auger. 
         [0052]    In some embodiments, the proximal end portion of the transfer element comprises an inlet adapted to provide fluid transfer (for purposes such as irrigation, heating or cooling) to a space between the flexible auger and the flexible inner shaft. 
         [0053]    In some embodiments, the proximal end portion of the transfer element comprises an inlet adapted to provide fluid transfer (for purposes such as irrigation, heating or cooling) to a space between the flexible auger and the outer cannula. 
         [0054]    In some embodiments, the hollow auger has a length having a variable bending stiffness. 
         [0055]    The stated pitch of the auger communicates the number of turns of the helix over a given distance. The pitch determines the ratio between speed and force during tissue removal. A steeply-pitched auger (i.e., a few turns per millimeter) is able to remove material more quickly than a shallow-pitched auger. However, a shallow pitched auger enables better force transmission than the steeper pitch. Hence, there is a tradeoff in pitch with respect to the desirable speed and force qualities. In preferred embodiments, the pitch of the flexible auger is between 3.5 and 7.0 mm. 
         [0056]    It is believed that the variable pitch embodiments of the present invention may be advantageous in applications involving material delivery. 
         [0057]    The geometry of the opening at the distal end portion of the transfer element determines how tissue enters the auger. As shown in  FIG. 4A , a straight tip  47  (i.e. an edge perpendicular to the longitudinal axis) only allows material to enter from directly in front of the auger, whereas an angled tip  49  (as shown in  FIG. 4B ) allows material to enter from one side of the auger. One angled tip embodiment comprises a distal opening cut at 30° relative to the straight tip. Preferably, the outer diameter of the opening of the distal end portion of the transfer element is less than 10 mm. In some embodiments, the distal end portion of the transfer element is a tube having a length of about 60 mm and an articulation radius of 15-21 mm (as measured at the inside of the bend). 
         [0058]    In some embodiments, the overall length of the material transfer element is between about 10 mm and 1000 mm, and preferably approximately 220 mm. 
         [0059]    In some embodiments, the distal end portion of the transfer element has an outer diameter of no more than 30 mm. 
         [0060]    In some embodiments, the distal end portion of the transfer element comprises a cutting tip adapted to cut intervertebral disc tissue, so that the overall device is a tissue removal device. Typically, a robust, inexpensive coupling method is carried out to connect the distal cutting tip to the intermediate auger. This coupling method should provide strength to the overall device and allow (e.g., not impede) tissue transport. In one coupling embodiment, the proximal end portion  27  of the cutting tip  25  is provided with a helical channel  28  to mate with the distal end portion of the helix of the hollow auger. In other embodiments, the distal end portion of the helix may be spot welded to the proximal end portion of the cutting tip. 
         [0061]    In one embodiment, the tissue removal device comprises a flexible central shaft and a helically-shaped shrink tube (i.e., without a helical coil). The first step in the manufacture of this embodiment involves making the transfer device described above, inserting a flexible shaft down its center bore, and then removing the helical coil by screwing it out of the assembly, thereby leaving behind the helically-shaped shrink tube disposed over the flexible central shaft. 
         [0062]    Therefore, in accordance with the present invention, there is provided a material transfer device comprising:
       a) a transfer element having a proximal end portion, a distal end portion, and an intermediate portion consisting of a flexible membrane having a threadform shape and a flexible central shaft housed longitudinally within the membrane,   b) a drive element adapted to rotate the transfer element, the drive element having a distal end portion,   wherein the distal end portion of the drive element is connected to the proximal end portion of the transfer element.       
 
         [0066]    In one embodiment, the material transfer device consists of a flexible central shaft surrounded by a helical coil (i.e., without the shrink tube). If the particles-to-be-transported have an adequate size and sufficient viscosity, a flexible central shaft surrounded by a “floating” helical coil can be sufficient to transport that material. This coil can be moved axially relative to the central shaft to effect particle transport, or rotated relative to the central shaft, or both. Axial movement of the coil can include both advancement and retraction. 
         [0067]    Therefore, in accordance with the present invention, there is provided a material transfer device comprising:
       a) a transfer element having a proximal end portion, a distal end portion, and an intermediate portion consisting of a flexible helix and a flexible shaft housed within the helix,   b) a drive element adapted to rotate the transfer element, the drive element having a distal end portion,
 
wherein the distal end portion of the drive element is connected to the proximal end portion of the transfer element.
       
 
         [0070]    In one embodiment, the transfer element comprises a flexible central shaft surrounded by a flexible helical coil, which is surrounded by a flexible heat-shrink tube. 
         [0071]    In one embodiment, this flexible central shaft could be formed from a narrow-wound helical spring. 
         [0072]    In some embodiments, and now referring to  FIGS. 5A-C  the device comprises a cannulated torque-transmitting inner flexible shaft disposed in a flexible hollow auger, which in turn is disposed in an outer cannula. In such an embodiment, there may be three working lumens:
       a) a cylindrical lumen  61  within the cannulated torque transmitting shaft  63  (this lumen can be used for placement of a flexible guide wire);   b) a first helical lumen  64  between the auger membrane wall  65  and the torque transmitting shaft (this lumen can be used for irrigation); and   c) a second helical lumen  67  between the auger membrane and the outer cannula  69  (this lumen can be used for material transport).       
 
         [0076]    In some embodiments, and now referring to  FIG. 6 , the device has one or more pulling mechanisms  71  attached to the hollow auger that can simultaneously manipulate both the helical coil pitch and diameter. 
         [0077]    Within narrow curves, and now referring to  FIG. 7 , the outer diameter of the flexible auger could be made permanently slightly smaller in order to prevent contact/friction with the outer cannula. This embodiment provides a clearance between the helix and the cannula. The manufacture of this neck  73  can also be achieved in a very cost effective manner with helical springs. 
         [0078]    In another embodiment, the bending stiffness along the flexible auger could be varied by producing the heat-shrink tube via an intermittent extrusion process, as described in U.S. Pat. No. 4,888,146, the specification of which is incorporated by reference in its entirety. This process can provide a soft tip or a combination of flexibility and stiffness for insertion. In many cases, such extrusions are used to replace manually assembled composite shaft constructions (i.e. hand layups).” 
         [0079]    In some embodiments, the proximal portion of the transfer element is designed to be rigid in order to stabilize turning movement and bearing in case of torque transmission. In some embodiments thereof, the end of the shrink tube itself might be the bearing surface. 
         [0080]    In some embodiments, and now referring to  FIG. 8 , the proximal portion of the transfer element comprises a sealable inlet  75  that provides irrigation into the space between the hollow auger and the inner shaft. Alternatively, the proximal portion of the transfer element comprises a sealable inlet that provides irrigation into the space between the hollow auger and the outer cannula. The inlet may also allow the provision of a) fluids that provide heating or cooling, or b) material delivery as well. The inlet is one possible design feature that allows providing cooling fluid/irrigation/material transport from outside to the lumen between the flexible inner shaft and shrink tube of the embodiments described in  FIGS. 5A-C . 
         [0081]    In some embodiments, and now referring to  FIG. 9 , there is at least one lumen  77  disposed in the wall  79  of the outer cannula that surrounds the flexible auger. This lumen can be used to perform various functions. For example, a surgeon could perform device steering by pulling or pushing strings that run through such a lumen in the outer cannula wall. Another lumen in the outer cannula wall could provide irrigation. Yet another lumen  81  in the outer cannula wall could allow visualization by providing imaging means (such as optical fibres) that run through the lumen. Therefore, in some embodiments, the cannula that surrounds the flexible auger comprises a wall and an inner bore, wherein the wall has at least one longitudinal lumen therein. In some embodiments, the outer cannula can have two or more lumens of similar size and shape, or of varying sizes and shapes. One common two lumen configuration, sometimes referred to as a double-D, may be used for a peripherally-inserted central cannula (or PICC lines). PICC lines may also have three lumens with a cross-sectional view that represents a ‘peace sign.’ Two- and three-lumen configurations in which the lumens are dissimilar in size and shape are frequently used for percutaneuous transluminal coronary angioplasty (PTCA) catheters. More simple cannulae, such as those used for drainage, may require only one lumen. Other applications, such as drug atomizing devices, may require tubing with more than a dozen lumens. 
         [0082]    In some embodiments, reinforced wire technology could be adopted to achieve steering capabilities of the outer cannula that surrounds the flexible auger. These wires  83  are housed in the above-described lumen and should be able to be moved axially in order to provide a push/pull steering capability. 
         [0083]    In other embodiments, the cannula comprises a wall and an inner bore, wherein the wall has at least one stationary wire running longitudinally therein. Longitudinal wires or fibers incorporated into an extrusion cross-section provide specific benefits, such as structural support or electrical data transmission. Wires can also provide excellent stretch resistance but limits flexibility depending on the number and location of reinforcing members. It is also possible to combine braided or spiral reinforcing with linear reinforcing elements to produce a hybrid design. Reinforcement material, tensile strength, size, and placement of the elements are critical aspects with linear reinforcing. High-tensile stainless steel round wire is commonly used for wire reinforcing. In thin wall sections, flat wire provides an excellent alternative. Other materials, such as aramid fiber or polymer monofilaments, can also be used for specialty linear reinforcement applications. 
         [0084]    In some embodiments, the outer cannula could comprise an elastomer bulk with an internal metal wire pattern for reinforcement. The arrangement of the wire pattern can determine the outer cannula&#39;s ability to flex in certain directions, while being stiffer in other directions. 
         [0085]    In some embodiments, the helical element in the flexible auger is a standard helical spring. Typically, this spring can be made out of biocompatible metals, such as titanium alloy, stainless steel and cobalt chrome. In some embodiments, the tube component of the flexible auger is a tube made out of heat shrink material. Typically, the heat shrink material is a polymeric, such as a PTFE. 
         [0086]    Also in accordance with the present invention, there is provided a method comprising the steps of:
       a) passing a helical spring into a tube comprising a heat-shrink material,   b) heating the tube to effect shrinking of the tube onto the helical spring to form an auger,   c) inserting the auger into an intervertebral disc,   d) rotating the auger to effect removal of intervertebral disc material.       
 
         [0091]    In addition to the above-described heat shrink method of making the auger of the present invention, there is further contemplated additional embodiments of creating a flexible auger that entail low manufacturing costs. 
         [0092]    In a first embodiment, the method comprises physically expanding a tube over a helical spring and then letting the tube contract. In this embodiment, the tube member in its initial state has an inner diameter ID that is smaller than the outer diameter OD of the spring. The tube can then be physically expanded in diameter by known methods (e.g., with high-pressure air, or with heat) until it reaches a dimension where its ID is larger than the OD of the spring. In this expanded condition, the tube is passed over the spring. When the force/energy upon the tube is removed, the tube in this assembly reverts to its original dimensions, except in the locations where it touches the helical spring member. The resulting product is an auger-like assembly with peaks and valleys. 
         [0093]    Therefore, in accordance with the present invention, there is provided a method comprising the steps of:
       a) applying a physical force upon a tube to expand the tube,   b) passing a helical spring into the expanded tube,   c) releasing the physical force upon the tube to effect shrinking of the tube onto the helical spring to form an auger,   d) inserting the auger into an intervertebral disc,   e) rotating the auger to effect removal of intervertebral disc material.       
 
         [0099]    In a second embodiment, the method comprises radially compressing the helical spring and then applying heat to the spring to allow its stressed areas to expand to a larger diameter. In this embodiment, the helical spring&#39;s outer diameter is reduced from its resting state (e.g., by winding the helical spring very tightly, or by pulling the helical member and thereby producing an elongated spring having a smaller outer diameter). In this reduced-diameter configuration, the radially compressed spring can be inserted into the tube member. Upon release of the mechanical force causing diameter reduction, the helical spring reverts to its original dimensions. Because the tube member possesses some flexibility, the elastic nature of the tube allows it to be deformed by the pressure of the expanding helical member upon the tube ID. Another auger-like assembly with valleys and summits is thereby produced. 
         [0100]    Therefore, in accordance with the present invention, there is provided a method comprising the steps of:
       a) applying a physical force upon a helical spring to radially compress the spring,   b) passing the compressed helical spring into a tube having an inner diameter,   c) heating the compressed spring to effect radial expansion of the helical spring so as to contact the inner diameter of the tube and form an auger,   d) inserting the auger into an intervertebral disc,   e) rotating the auger to effect removal of intervertebral disc material.       
 
         [0106]    In a third embodiment, the method comprises simultaneously applying heat and vacuum to an ordinary polymeric tube to obtain the same effect as a heat shrink. In this embodiment, the tube member is made of a material that is not heat-shrinkable, but rather is plastically deformable under heat and so over time arrives at an elastomeric state. In this embodiment, the tube member has an inner diameter ID in its initial state that is larger than the outer diameter OD of the helical spring, so that the helical member can be inserted into the tube member. Once the spring is inside the tube, a low pressure region/vacuum is created inside of the tube member, and the tube member is heated at the same time. These conditions create deformation in the wall of the tube member caused by the vacuum pulling towards the center of the tube. This reduces the diameter of the tube member, except for the locations where the helical member contacts the inside of the tube and so prevents deformation of the tube member in these areas. This results in another auger-like assembly with valleys and summits. 
         [0107]    Therefore, in accordance with the present invention, there is provided a method comprising the steps of:
       a) passing a helical spring into a tube having a bore and comprising a polymeric material,   b) simultaneously heating the tube and applying a vacuum to the bore of the tube to effect shrinking of the tube onto the helical spring to form an auger,   c) inserting the auger into an intervertebral disc,   d) rotating the auger to effect removal of intervertebral disc material.