Abstract:
A specially-shaped tube for gaining access to and removing mechanical fasteners such as pedicle screws. A small arthroscopic incision is made over the location of the fastener. A guide wire is then placed into the incision and attached to the fastener. A series of progressively enlarging dilator tubes are slipped into the incision to progressively enlarge its diameter. The present invention (a “screw extractor tube”), a hollow tube having a contoured upper extremity, is then placed into the incision over the largest dilator tube. The screw extractor tube is advanced until its lower extremity surrounds the head of the fastener. The dilator tubes are then removed. At this point, the screw extractor tube holds open the incision and provides access to the fastener through its hollow interior. A specially designed extractor tool is inserted into the screw extractor tube. An arthroscope is preferably also inserted through the screw extractor tube so that the surgeon can visualize the process. The screw extractor tube can be rotated in the incision so that its contoured upper extremity allows greater access. Jaws on the end of the extractor tool are clamped to the fastener&#39;s head. The extractor tool is then rotated to back out the fastener. Once the fastener is freed from its installed position, the extractor tool withdraws it through the screw extractor tube. Other conventional processes—such as debridement—may also be performed through the screw extractor tube.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]    This application pertains to subject matter also disclosed in my copending application for the invention entitled “CLAMPING SCREW EXTRACTOR,” filed on Oct. 7, 2002, and having application Ser. No. 10/266133. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable.  
         MICROFICHE APPENDIX  
         [0003]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0004]    1. Field of the Invention  
           [0005]    This invention relates to the field of orthopaedic surgery. More specifically, the invention comprises a specially-shaped tube which provides access for the removal of orthopaedic hardware using only a small incision.  
           [0006]    2. Description of the Related Art  
           [0007]    The field of orthopaedic medicine involves the application of plates and screws to stabilize compromised articulations in the human body. One typical application is stabilization of the lumbar vertebrae after collapse of one or more intervertebral disks. FIG. 1 is an illustration of two lumbar vertebrae  10 . Intervertebral disk  11  lies between the two. In this example, instability of the spine has necessitated the joining of the two vertebrae.  
           [0008]    It is well known in the art that vertebrae can be joined by bone grafting. However, it is generally necessary to stabilize the position of the two vertebrae for some period in order to allow the joining to occur. Accordingly, plate  12  is attached to the two vertebrae. Typically two plates  12  would be applied, with one lying on each side of the posterior spinous processes. Each plate  12  is pierced by a set of holes, through which pedicle screws  14  are inserted.  
           [0009]    In order to install pedicle screws  14 , holes must be drilled through the pedicle portions of the two vertebrae. Pedicle screws  14  are then threaded into these holes and tightened. If all goes well, the two vertebrae will eventually fuse together, thereby eliminating any articulation at the joint. The fusing will ideally render the patient asymptomatic, though obviously somewhat less flexible.  
           [0010]    The ideal result is not always achieved, however. Those skilled in the art will know that great variations exist in human anatomy. They will also know that the surgeon is unable to fully visualize the structures involved. These factors may lead to imperfect results.  
           [0011]    The reader will observe in FIG. 1 that nerve root  20  exits the foramen between the two vertebrae in a position which is close to the lower pedicle screw  14 . A portion of this pedicle screw  14  may protrude beyond the surface of the lower vertebra  10  (As the vertebra comprises a highly irregular shape, the hole drilled therethrough may intersect the outer surface at one or more points. A portion of the threaded pedicle screw shaft may thereby be exposed). This portion may rest against nerve root  20 , possibly even compressing nerve root  20 . In such an event, the patient may experience common neurological symptoms, such as pain or numbness.  
           [0012]    After the joint has stabilized, it may be desirable to remove pedicle screw  14  (as well as possibly plate  12 ). This operation has typically been performed under general anesthesia. A substantial incision is made through the skin  18 , and fascia  16 , to reveal the spinal column. The muscles and other structures attached to the posterior spinous processes must then be removed in order to expose pedicle screw  14 . A wrench is then used to back pedicle screw  14  out of the bone and remove it through the open incision. It is often difficult to determine whether a particular pedicle screw is the source of the neurological symptoms experienced by the patient. As the patient is asleep during the procedure, there is no way to determine if the removal of the screw altered the symptoms until much later.  
           [0013]    [0013]FIG. 2 shows another common factor in the placement of such hardware. The reader will observe that pedicle screw  14  is angularly displaced from the axial center of the hole through plate  12 . This angular displacement is sometimes necessary in order to accommodate the shape of the vertebra. On other occasions, it is simply a result of the imperfect drilling process. Whatever the cause, the angular displacement may necessitate a larger incision since the socket head of the removing device must be aligned with screw head  22 .  
         BRIEF SUMMARY OF THE PRESENT INVENTION  
         [0014]    The present invention comprises a specially-shaped tube for gaining access to and removing mechanical fasteners such as pedicle screws. A small arthroscopic incision is made over the location of the fastener. A guide wire is then placed into the incision and attached to the fastener. A series of progressively enlarging dilator tubes are slipped into the incision to progressively enlarge its diameter. The present invention (a “screw extractor tube”), a hollow tube having a contoured upper extremity, is then placed into the incision over the largest dilator tube. The screw extractor tube is advanced until its lower extremity surrounds the head of the fastener. The dilator tubes are then removed. At this point, the screw extractor tube holds open the incision and provides access to the fastener through its hollow interior.  
           [0015]    A specially designed extractor tool is inserted into the screw extractor tube. An arthroscope is preferably also inserted through the screw extractor tube so that the surgeon can visualize the process. The screw extractor tube can be rotated in the incision so that its contoured upper extremity allows greater access. Jaws on the end of the extractor tool are clamped to the fastener&#39;s head. The extractor tool is then rotated to back out the fastener. Once the fastener is freed from its installed position, the extractor tool withdraws it through the screw extractor tube. Other conventional processes—such as debridement—may also be performed through the screw extractor tube.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is an isometric view, showing a prior art plate and pair of pedicle screws.  
         [0017]    [0017]FIG. 2 is an isometric view, showing a pedicle screw.  
         [0018]    [0018]FIG. 3 is an isometric view, showing an initial incision.  
         [0019]    [0019]FIG. 4 is an isometric view, showing the installation of successive dilator tubes.  
         [0020]    [0020]FIG. 5 is an isometric view, showing a screw extractor tube.  
         [0021]    [0021]FIG. 6 is an isometric view, showing the installation of a screw extractor tube.  
         [0022]    [0022]FIG. 7 is an isometric view, showing the components of an extraction tool.  
         [0023]    [0023]FIG. 8 is an isometric view, showing the details of the collet.  
         [0024]    [0024]FIG. 9 is an isometric view, showing the details of the collet.  
         [0025]    [0025]FIG. 10 is an isometric view, showing the interaction of the components comprising the extraction tool.  
         [0026]    [0026]FIG. 11 is an isometric view, showing the insertion of an extraction tool.  
         [0027]    [0027]FIG. 12 is an isometric view, showing how the extraction tool attaches to a pedicle screw.  
         [0028]    [0028]FIG. 13 is an isometric view, showing how the extraction tool attaches to a pedicle screw.  
         [0029]    [0029]FIG. 14 is an isometric view, showing how the extraction tool unscrews a pedicle screw.  
         [0030]    [0030]FIG. 15 is an isometric view, showing how the extraction tool backs out the pedicle screw.  
         [0031]    [0031]FIG. 16 is an isometric view, showing a complete view of the extraction tool in position.  
         [0032]    [0032]FIG. 16B is an isometric view, showing details of the screw extractor tube in use.  
         [0033]    [0033]FIG. 16C is an isometric view, showing details of the screw extractor tube in use.  
         [0034]    [0034]FIG. 17 is an isometric view, showing the extraction of an angularly offset pedicle screw.  
         [0035]    [0035]FIG. 18 is an isometric view, showing the extraction of an angularly offset pedicle screw.  
         [0036]    [0036]FIG. 19 is an isometric view, showing the extraction of an angularly offset pedicle screw.  
         [0037]    [0037]FIG. 20 is an isometric view, showing the extraction of an angularly offset pedicle screw with a socket extractor.  
         [0038]    [0038]FIG. 21 is an isometric view, showing an alternate screw extractor tube.  
         [0039]    [0039]FIG. 22 is an isometric view, showing an alternate screw extractor tube.  
         [0040]    [0040]FIG. 23 is an isometric view, showing an alternate screw extractor tube. 
     
    
     REFERENCE NUMERALS IN THE DRAWINGS  
       [0041]    [0041]                                               10   vertebra   12   plate       14   pedicle screw   16   fascia       18   skin   20   nerve root       22   screw head   24   small incision       26   first dilator tube   28   second dilator tube       30   screw extractor tube   32   access cut       34   high wall curve   36   side wall curve       38   low wall curve   40   tenth dilator tube       42   handle   44   shaft       46   thread sleeve   48   collet       50   insertion cylinder   52   threaded bore       54   jaw   56   split       58   knurled surface   60   tapered journal       62   threaded journal   64   threaded journal       66   threaded bore   68   straight bore       70   tapered bore   72   extraction tool       74   arthroscope   76   hollow interior       78   undercut   80   screw head cavity       82   lumbar region   84   guide wire       86   socket extractor   88   large tube       90   first alternate tube   92   second alternate tube       94   third alternate tube   96   shear plane       98   filleted shear plane   100   notch                    
       DETAILED DESCRIPTION OF THE INVENTION  
       [0042]    Referring now to FIG. 1, the objective for which the invention was primarily designed is the removal of one or more pedicle screws  14 . Radiographic techniques are used to locate the suspicious pedicle screw. Turning now to FIG. 3, small incision  24  is made directly over the pedicle screw. A guide wire  84  is then placed on the screw head, with its free end extending out of the incision as shown.  
         [0043]    Turning now to FIG. 4, first dilator tube  26  is placed in the incision by slipping it along the guide wire. First dilator tube  26  is a hollow tube having an inner diameter greater than the guide wire. By inserting it into the incision along the guide wire, the incision is dilated slightly. Next, a succession of dilator tubes, each having a slightly larger diameter than its predecessor, is slipped into place within the incision. Second dilator tube  28  is shown in position, ready to be slipped over first dilator tube  26 . The incision is thereby incrementally expanded to a diameter of approximately 16 mm. The process of installing the dilator tubes, along with more detailed descriptions of the tubes themselves, is found in U.S. Pat. No. 5,472,426 to Bonati et.al., which is incorporated herein by reference. The succession of dilator tubes can be added without removing any prior dilator tubes. In the alternative, each preceding dilator tube can be removed once it has guided its successor into position (so that there are never more than two dilator tubes in the incision at any one time).  
         [0044]    The last dilator tube—which comprises the present invention—has a specialized design intended to facilitate the screw extraction process. FIG. 5 shows this specialized tube, denoted as screw extractor tube  30 . The upper view in FIG. 5 shows screw extractor tube  30  from the side. The reader will observe that a specialized shape is cut into the portion intended to provide access to the incision. High wall curve  34  extends across the leading portion. Relief curve  36  lies behind this. Finally, low wall curve  38  blends into the cylindrical body of the tube. These three curved portions are referred to collectively as access cut  32 .  
         [0045]    [0045]FIG. 6 shows the original incision with tenth dilator tube  40  in place (being the last in a succession often tubes of incrementally expanding diameters). Screw extractor tube  30  operates as an eleventh dilator tube. It is placed over tenth dilator tube  40  and down into the incision. Tenth dilator tube  40  is then removed. Once in position, screw extractor tube  30  provides access to the exposed head portion of the pedicle screw through its hollow interior  76 . The number of dilator tubes employed is not critical to the invention—so long as they provide a gradual dilation of the incision.  
         [0046]    Thus, using the devices and procedures described, a surgeon can gain access to the pedicle screw by making only a small incision. Such an incision can be made under local anaesthetic. This fact is significant, because it means that the patient remains conscious. The patient can be questioned as to perceived neurological symptoms while the operation is proceeding.  
         [0047]    Screw extractor tube  30  has a relatively small size—with an outside diameter of 18 to 19 mm and an inside diameter of 17 to 18 mm. An arthroscope is preferably placed through hollow interior  76  in order to visualize the pedicle screw head and surrounding region. A device intended to extract the pedicle screw must simultaneously be inserted through hollow interior  76 . Those skilled in the art will thereby be informed that the device intended to remove the pedicle screw mut be very compact. FIG. 11 shows screw extractor tube  30 , with a suitable extraction tool  72  and arthroscope  74  being inserted through its hollow interior.  
         [0048]    [0048]FIG. 7 shows extraction tool  72  in more detail, with its major components being separated to aid visualization. The major components are: handle  42 , shaft  44 , thread sleeve  46 , and collet  48 . As the assembly is a surgical instrument, it must be capable of undergoing sterilization treatments in an autoclave. Shaft  44 , thread sleeve  46 , and collet  48  are preferably made of stainless steel. Handle  42  is preferably molded in a temperature-resistant polymer such as BAKELITE.  
         [0049]    [0049]FIG. 8 shows collet  48  in greater detail. Its primary structure is mating cylinder  50 . Four jaws  54  extend from the top of this structure (with “top” referring to the orientation as shown in the view). The jaws are separated from one another by four corresponding splits  56  (The number of jaws employed is not a critical feature, though a minimum of two are necessary). The reader will observe that the exterior surfaces of the four jaws  54  expand outward to form tapered journal  60  (which assumes the form of a truncated cone). The four jaws form a hollow interior denoted as screw head cavity  80 . Undercuts  78  are formed just beneath each knurled surface  58 . These features allow the four jaws  54  to grip a screw head which is angularly offset from the axial center of collet  48  (the importance of which will be made apparent in the following).  
         [0050]    [0050]FIG. 9 depicts collet  48  from a different perspective. Insertion cylinder  50  is hollow. Threaded bore  52  extends into its interior—from the right hand side in the view as shown. It is not necessary to thread the full length of the hollow interior. The threaded portion indicated as threaded bore  52  may only extend for a portion of the available length. Those skilled in the art, having reviewed FIGS. 8 and 9, will realize that collet  48  generally assumes a form which is similar to an industrial collet as used in vertical milling machines (such as the Morse Taper or R-8 standards).  
         [0051]    [0051]FIG. 10 depicts a portion of extraction tool  72 , illustrating the interaction of the various components. Threaded journal  64  on shaft  44  threads into threaded bore  66  on thread sleeve  46 . Both these threads are left hand threads, meaning that shaft  44  screws into thread sleeve  46  in a counterclockwise direction. Shaft  44  is typically screwed in until it stops, meaning that shaft  44  and thread sleeve  46  rotate as a unit during operation. In fact, shaft  44  and thread sleeve  46  could be made as one integral unit, with the use of two separate units being merely a choice of machining convenience (owing primarily to the need to machine and thread threaded journal  62 ).  
         [0052]    Insertion cylinder  50  of collet  48  slides into straight bore  68  within thread sleeve  46 . The diameters of the two cylindrical portions are closely matched so that they may slide relative to one another without wobbling.  
         [0053]    Once shaft  44  is threaded into thread sleeve  46 , threaded journal  62  extends into the interior of straight bore  68 . When collet  48  is then pushed into straight bore  68 , threaded bore  52  will engage threaded journal  62 . Both these threads are left hand threads, meaning that if collet  48  is rotated in a counterclockwise direction, it will thread onto threaded journal  62 . Those skilled in the art will therefore know that if shaft  44  and thread sleeve  46  are rotated in a counterclockwise direction (when viewed from the direction of the handle toward the collet), while collet  48  is held stationary, collet  48  will be drawn further into tapered sleeve  46  (drawn from left to right in the view as shown). As this process continues, tapered journal  60  will come to bear against tapered bore  70 . As shaft  44  is rotated further, the jaws  54  of collet  48  will be squeezed together. This feature allows the device to grip a screw which is to be extracted.  
         [0054]    [0054]FIG. 10B shows extraction tool  72  assembled and ready for use. FIG. 11 shows screw extractor tube  30  in position within small incision  24 . Arthroscope  74  is fed down into screw extractor tube  30  to allow the surgeon to visualize the pedicle screw and surrounding structures. Extraction tool  72  is then inserted as shown.  
         [0055]    [0055]FIGS. 12 through 15 illustrate the operation of the extraction tool. The reader should understand that pedicle screw  14  is fixed in a vertebra. Likewise, plate  12  is attached to the exterior of the same vertebra. Many other features—such as the incision, the screw extractor tube, the muscle structure, and various other anatomical features—are omitted from these views for purposes of visual clarity.  
         [0056]    [0056]FIG. 12 shows extraction tool  72  descending toward screw head  22 . In FIG. 13, jaws  54  have come to rest against screw head  22 . At this point, the surgeon rotates shaft  44  in a counterclockwise direction (when viewed from the handle end). Thread sleeve  46 , which is attached to shaft  44 , also rotates in a counterclockwise direction. Knurled surfaces  58  on the inward facing sides of jaws  54  drag against screw head  22 , which causes collet  48  to rotate more slowly than tapered sleeve  46 . The result is that collet  48  is rotationally shifted with respect to thread sleeve  46  in a counterclockwise direction ( when viewed from the handle end). The interaction of threaded bore  52  and threaded journal  62  then pulls tapered journal  60  against tapered bore  70 , squeezing jaws  54  inward as shown. As jaws  54  are squeezed inward, knurled surfaces  58  grip the screw head more tightly. Those skilled in the art will realize that this is a mutually supporting process, meaning that as torque is applied to the device, it simultaneously applies torque to the screw head and squeezes the jaws more tightly into the screw head. Eventually, jaws  54  will be locked to the screw head.  
         [0057]    [0057]FIG. 14 shows the assembly just after jaws  54  have locked to the screw head. As the surgeon continues rotating shaft  44  in a counterclockwise direction, pedicle screw  14  begins rotating in a counterclockwise direction—thereby backing it out of the vertebra. FIG. 15 shows this process as it continues, with pedicle screw  14  backing out.  
         [0058]    [0058]FIG. 16 shows the application of screw extractor tube  30  and extraction tool  72  with more of the surrounding elements illustrated. The reader will observe that screw extractor tube  30  is in place within incision  24 . Both extraction tool  72  and arthroscope  74  are placed within the hollow interior of screw extractor tube  30 . The reader will observe that screw extractor tube  30  provides access from the patient&#39;s exterior to the head of pedicle screw  14 .  
         [0059]    [0059]FIG. 16B shows a closer view of screw extractor tube  30  in position within incision  24 . The complex cut in the upper extremity of screw extractor tube  30  allows more convenient insertion and manipulation of the tools involved. FIG. 16C is a still closer view. The upper extremity of screw extractor tube  30  is not cut in a direction which is perpendicular to its central axis. It is cut, instead, at an angle. This fact makes the insertion of the instruments easier. The surgeon would insert the instruments from the side facing the viewer into the tube&#39;s interior. A perpendicular cut across screw extractor tube  30 —such as found on its lower extremity—means that the instruments would have to be inserted through an area equal to the area of the tube&#39;s internal diameter. By using an angled cut, the instruments can be inserted through a substantially larger oval.  
         [0060]    Of course, the upper extremity of screw extractor tube  30  is preferably a more complex shape than a simple angled cut. Access cut  32  is bounded on its upper side by high wall curve  34  and on its lower side by low wall curve  38 . These curves are joined by a pair of side wall curves  36  to create a smooth shape. When inserting instruments, the surgeon will introduce them until they bear against the inward surface of high wall curve  34 . High wall curve  34  will then guide the instruments down into hollow interior  76 . The reader will observe that access cut  32  is composed of smoothly joined curves. This feature eliminates the snagging or abrasion of the instruments. It also prevents laceration of the incision should a portion of access cut  32  slip into the incision.  
         [0061]    The shape of access cut  32  also assists in the removal of orthopaedic hardware. Returning now to FIG. 16, the reader will observe that the particular pedicle screw  14  shown was not inserted perpendicularly with respect to plate  12 . Instead, it is angularly offset by approximately 15 degrees. This represents a realistic scenario, as it is often not possible to ideally place the orthopedic hardware—given variations in human anatomy.  
         [0062]    [0062]FIG. 17 shows a closer view of the same assembly, with hidden lines being shown as well. The reader will observe that pedicle screw  14  is angularly offset from extraction tool  72 . Jaws  54  are capable of engaging an angularly displaced screw head due to the presence of screw head cavity  80  and undercuts  78  on the jaws. Another feature is desirable to provide sufficient working room for the tool, however.  
         [0063]    As explained previously, the side wall of screw extractor tube  30  opens into access cut  32 . Once the surgeon has inserted screw extractor tube  30  into position, it is free to rotate. Thus, access cut  32  can be rotated to any desired angular position. The surgeon can visualize the position and angular offset of the pedicle screw by inspecting its head. For the scenario shown, extractor tube  30  has been rotated so that access cut  32  is facing the head of pedicle screw  14 . With this orientation, the surgeon is able to orient extraction tool  72  more closely to the axial orientation of the pedicle screw. The surgeon then rotates shaft  44  in a counterclockwise direction (viewed from the handle end) to clamp jaws  54  on the screw head and begin extracting pedicle screw  14 .  
         [0064]    [0064]FIG. 18 shows the extraction process midway through. As the surgeon continues rotating shaft  44  in a counterclockwise direction, pedicle screw  14  continues backing out of the vertebra Those skilled in the art will know that the angular offset between jaws  54  and the screw head continuously changes through each cycle of rotation, much in the fashion of a universal joint. Again, the shape of jaws  54 —including the undercuts  78 —means that the oscillation in the engagement angle between jaws  54  and the screw head is not a problem. The combination of torque and clamping force means that the engagement will remain secure.  
         [0065]    [0065]FIG. 19 shows pedicle screw  14  when it is nearly free of the vertebra. It may be necessary for the surgeon to displace screw extractor tube  30  to a small extent in order to complete the extraction. The pliable nature of the structures surrounding screw extractor tube  30  allows such limited motion.  
         [0066]    The reader will recall from the prior disclosure that the surgical procedures illustrated can be performed under a local anaesthetic. Thus, the patient is conscious and able to respond to questioning. If the pedicle screw illustrated was causing the compression of a nerve root in the installed position, one would expect the nerve to be decompressed once the position illustrated in FIG. 19 is reached. The surgeon can question the patient as to the neurological symptoms at this point. If the symptoms have resolved, then the surgeon can be confident that the pedicle screw was the source of the problem. If they have not resolved, then the pedicle screw is likely not the source of the problem. The surgeon can then elect to reinstall the screw and possibly move to another location to repeat the extraction cycle on another pedicle screw.  
         [0067]    Once the pedicle screw is removed, screw extractor tube  30  continues to provide access for other finishing procedures. In some instances, the removal of the pedicle screw may leave small bone fragments behind. It may therefore be desirable to administer irrigation and suction (“debridement”) to the area from which the pedicle screw was removed. The surgeon may elect to do so before removing screw extractor tube  30  and closing the incision. Screw extractor tube  30  can obviously be used in the performance of other procedures apart from extraction tool  72 . It can provide access for mechanical tissue removal, laser tissue destruction and removal, arthroscopic visualization of internal structures, and other prior art procedures.  
         [0068]    Those skilled in the art will appreciate that the use of extraction tool  72  and screw extractor tube  30  (incorporating access cut  32 ) allow these procedure to be performed through a very small incision. An open and much larger incision has been used traditionally. FIG. 20 provides some alternate tools. It does not represent a prior art technique, but it is helpful for purposes of comparison because the equipment illustrated in FIG. 20 represents what would be encountered if the presently disclosed techniques were practiced without the use of the specially shaped screw extractor tube  30  and extraction tool  72 .  
         [0069]    First, a socket extractor  86  is shown. This is a conventional wrench having a hexagonal female socket configured to engage the screw head. The shaft of such a tool must be angularly aligned with pedicle screw  14  (or very nearly so). Second, in the absence of an access cut, a much larger screw extractor tube must be used. This element is shown in FIG. 20 as large tube  88 .  
         [0070]    Having read the foregoing, those skilled in the art will realize that extraction tool  72  and screw extractor tube  30  are complementary to each other in the performance of the process disclosed. The shape shown for access cut  32  can be the subject of endless variations. The embodiment shown in FIG. 5 incorporates smooth and curved transitions which facilitate the use of the device and which minimize the risk of lacerating surrounding tissue. However, other simpler variations can also be used.  
         [0071]    [0071]FIG. 21 shows first alternate tube  90 . In this version, access cut  32  assumes the form of an angled shear plane  96 . FIG. 22 shows second alternate tube  92 , wherein access cut  32  assumes the form of filleted shear plane  98 . Filleted shear plane  98  incorporates a curved (or “filleted”) edge to eliminate a sharp corner which might snag a tool. Those skilled in the art will appreciate that the embodiment shown in FIG. 22 contains a high wall curve, two side wall curves, and a low wall curve Oust like the preferred embodiment in FIG. 5). The version shown in FIG. 22, however, does not have a low wall curve which is blended smoothly into the cylindrical side wall.  
         [0072]    [0072]FIG. 23 shows third alternate tube  94 . In this embodiment, access cut  32  takes the form of notch  100 , which is simply a relief cut into the side wall of the tube. All these embodiments of the screw extractor tube serve to illustrate the variations which are possible on the design of these elements. All these variations can be used to perform the present process. However, the embodiments shown in FIGS. 11 through 19 are preferred.  
         [0073]    The preceding descriptions contain significant detail regarding the novel aspects of the present invention. They should not be construed, however, as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. Thus, the scope of the invention should be fixed by the following claims, rather than by the examples given.