Abstract:
A cannulated retrograde reamer that is adjustable to create tunnels of multiple different diameters. The cannulated retrograde reamer substantially reduces the risk of tunnel malposition and/or misalignment, and can be adjusted to create a range of tunnel diameters, thereby allowing inventory levels to be reduced for a surgical case.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of the priority of U.S. Provisional Patent Application No. 61/733,479 filed Dec. 5, 2012 entitled SURGICAL INSTRUMENT, and U.S. Provisional Patent Application No. 61/757,843 filed Jan. 29, 2013 entitled SURGICAL INSTRUMENT. 
     
    
     TECHNICAL FIELD 
       [0002]    The present application relates generally to surgical instruments, and more specifically to surgical instruments having at least one cutting member, such as a rotatable blade for use in retrograde cutting of bone. 
       BACKGROUND 
       [0003]    Some surgeons have performed anterior cruciate ligament (ACL) surgery using a retrograde approach to create the femoral ACL tunnels (i.e., “All-Inside ACL Reconstruction”). As illustrated in  FIG. 1 , this approach typically requires a surgical instrument  100  that can drill a tunnel  102  in a retrograde fashion, as the surgeon pulls-back (see directional arrow  108 ) on the retrograde reamer  104  from a bone joint space  106  towards the lateral femoral cortex. However, such a surgical instrument tends to create a tunnel that is not truly circular, or worse, the tunnel can be created along a pathway that diverges from the intended trajectory, and thus may not be anatomic and/or may cause injury to neurovascular structures, etc. In addition, such a surgical instrument is generally specific for creating tunnels of a certain fixed diameter, which requires having access to a large inventory of instruments for one surgical case. 
         [0004]    Moreover, surgeons who conduct ACL reconstruction generally prefer to mimic the natural anatomy to achieve optimal results. The placement of a tendon graft in the original footprint of the ACL is generally referred to as “anatomic ACL reconstruction”. One feature of anatomic ACL reconstruction is the proper placement of the tunnels for the tendon graft. The tunnel exit in the space of the bone joint should be accurate to ensure the functionality of the graft. Further, the tunnel exit on the lateral side of the femur (thigh) should be appropriately placed to ensure adequate tunnel length. It would be desirable to have improved surgical instruments that can assist the surgeon in the proper placement of the femoral tunnel. 
       SUMMARY 
       [0005]    In accordance with the present application, a retrograde reamer is disclosed that is adjustable to create tunnels of multiple different diameters. In one aspect, the disclosed retrograde reamer is cannulated. In another aspect, the disclosed retrograde reamer is configured to create tunnels having distinct stepped diameters. In still another aspect, the disclosed retrograde reamer includes at least one cutting member, and a mechanism operative to gradually move the cutting member from a deployed position to a stored, closed, or collapsed position to create a tapered tunnel. The mechanism can be linked to rotations of the cutting member so that, for predetermined numbers of rotations, the cutting member moves specified distances toward the stored, closed, or collapsed position. 
         [0006]    In a further aspect, the disclosed retrograde reamer includes a first tubular shaft having a sidewall, which includes at least one opening therethrough. The retrograde reamer further includes a second shaft movably disposed within the first tubular shaft, and at least one cutting member movably disposed in the first tubular shaft. The cutting member is operative, in response to the second shaft moving from a first position to a second position within the first tubular shaft, to move through the opening to an outside position that is at least partially outside the first tubular shaft, thereby defining a cutting diameter. 
         [0007]    The disclosed cannulated retrograde reamer can be configured to accommodate a guide wire. Further, the cannulated retrograde reamer substantially reduces the risk of tunnel malposition and/or misalignment, and can be adjusted to create a range of tunnel diameters, thereby allowing inventory levels to be reduced for a surgical case. 
         [0008]    Other features, functions, and aspects of the invention will be evident from the Detailed Description that follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments described herein and, together with the Detailed Description, explain these embodiments. In the drawings: 
           [0010]      FIG. 1  is a diagram of a conventional surgical instrument configured to drill tunnels through bone in a retrograde fashion; 
           [0011]      FIG. 2  is an illustration of an exemplary surgical instrument (also referred to herein as the “retrograde reamer”) configured to drill tunnels through bone in a retrograde fashion, in accordance with the present application; 
           [0012]      FIGS. 3   a - 3   c  depict diagrams of a first illustrative example of use of the retrograde reamer of  FIG. 2 ; 
           [0013]      FIG. 4  depicts diagrams of a second illustrative example of use of the retrograde reamer of  FIG. 2 ; 
           [0014]      FIG. 5  depicts diagrams of a third illustrative example of use of the retrograde reamer of  FIG. 2 ; 
           [0015]      FIG. 6  illustrates a plurality of alternative embodiments of the retrograde reamer of  FIG. 2 ; 
           [0016]      FIGS. 7   a  and  7   b  illustrate a first alternative embodiment of the retrograde reamer of  FIG. 2 ; 
           [0017]      FIGS. 8   a  and  8   b  illustrate a second alternative embodiment of the retrograde reamer of  FIG. 2 ; 
           [0018]      FIGS. 9   a  and  9   b  illustrate a third alternative embodiment of the retrograde reamer of  FIG. 2 ; 
           [0019]      FIGS. 10   a  and  10   b  illustrate a fourth alternative embodiment of the retrograde reamer of  FIG. 2 ; 
           [0020]      FIGS. 11   a  and  11   b  illustrate a fifth alternative embodiment of the retrograde reamer of  FIG. 2 ; 
           [0021]      FIGS. 12   a  and  12   b  illustrate a sixth alternative embodiment of the retrograde reamer of  FIG. 2 ; 
           [0022]      FIGS. 13   a  and  13   b  illustrate a seventh alternative embodiment of the retrograde reamer of  FIG. 2 ; 
           [0023]      FIG. 14  illustrates an eighth alternative embodiment of the retrograde reamer of  FIG. 2 ; and 
           [0024]      FIGS. 15   a - 15   c  illustrate a ninth alternative embodiment of the retrograde reamer of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The disclosures of U.S. Provisional Patent Application No. 61/733,479 filed Dec. 5, 2012 entitled SURGICAL INSTRUMENT, and U.S. Provisional Patent Application No. 61/757,843 filed Jan. 29, 2013 entitled SURGICAL INSTRUMENT, are hereby incorporated herein by reference in their entirety. 
         [0026]    With reference to  FIG. 2 , an illustrative embodiment of components of an exemplary surgical instrument  200  (also referred to herein as the “retrograde reamer”) is disclosed, in accordance with the present application. As shown in  FIG. 2 , the components of the retrograde reamer  200  include an elongated inner shaft  206 , an elongated outer tubular shaft  205 , and a plurality of cutting members  204  movably coupled to the elongated outer tubular shaft  205 . The outer tubular shaft  205  includes internal threads at a distal end  207  thereof. The plurality of cutting members  204  (e.g., two (2) cutting members) are located near the distal end  207  of the outer tubular shaft  205 . The inner shaft  206  includes an externally threaded distal tip  202 . 
         [0027]    When the retrograde reamer  200  is assembled, the inner shaft  206  is rotationally mounted within the elongated outer tubular shaft  205  such that the threaded distal tip  202  is engaged with the internal threads at the distal end  207  of the outer tubular shaft  205 . To deploy and actuate the cutting members  204 , the inner shaft  206  is rotated repeatedly (i.e., multiple revolutions), thereby causing the distal end  207  of the outer tubular shaft  205  to move toward a proximal end of the outer tubular shaft  205 . As the inner shaft  206  turns and the distal end  207  of the outer tubular shaft  205  moves proximally, the two (2) cutting members  204  near the distal end  207  of the outer tubular shaft  205  flex and expand outwardly, creating a progressively increasing cutting diameter. Once the cutting members  204  have reached a desired position, the relative positions of the inner shaft  206  and the outer tubular shaft  205  can be locked. The retrograde reamer  200  can then be rotated (such as by a drill) to create a retrograde tunnel having a desired diameter. 
         [0028]    To remove the retrograde reamer  200  from a bone joint after tunnel creation, the inner shaft  206  is rotated in the opposite direction, thereby causing the distal end  207  of the outer tubular shaft  205  to move distally, and the cutting members  204  to flex back, and close or collapse to their pre-deployment (i.e., flat) configuration. Once the cutting members  204  have returned to their pre-deployment configuration, the retrograde reamer  200  can be removed from the surgical site. 
         [0029]    It is noted that two or more cutting members like the cutting members  204  may be provided. For example, three, four, five, six, or any other suitable number of cutting members may be incorporated in the retrograde reamer  200 . Further, the cutting members  204  may be hinged, and/or may have sharpened edges. The sharpened edges may be coated with a metal or metal alloy, or diamond-like carbon to enhance strength and cutting performance. 
         [0030]    It is further noted that the inner shaft  206  can be cannulated to accommodate a guide wire. The retrograde reamer  200  may also be connected to suction means so that cut tissue can be aspirated from the surgical site through the cannulated inner shaft  206 . The inner shaft  206  could also include a handle with a counter that could indicate the current tunnel diameter as a function of the number of shaft revolutions. The mechanical force generated during retraction/closure of the cutting members  204  after tunnel creation can be made to overcome the resistance of any residual tissue caught in the cutting members  204 . The presence of such residual tissue is a frequent nuisance of conventional retrograde reamers. 
         [0031]    In addition, the inner shaft  206  can be replaced with a shaft that is connected to the distal end  207  of the outer tubular shaft  205  to enable control of cutter deployment by a ratchet-locking system, or any other suitable locking mechanism. The locking mechanism can be located at a proximal end of the retrograde reamer  200 . The ratchet-locking system can be configured to adjust the cutting diameter of the cutting members  204  by ratcheting in either direction. The axial position of the inner shaft  206  can be locked (e.g., by teeth) at the desired cutting diameter. When engaged, such teeth can prevent the inner shaft  206  from moving. When disengaged, the inner shaft  206  is movable. Movement of the inner shaft  206  in a proximal direction activates the cutting members  204  and increases the cutting diameter. Movement of the inner shaft  206  in a distal direction decreases the cutting diameter and effectively deactivates the cutting members  204 . In some embodiments, the locking mechanism may be configured to be similar to a cable tie. 
         [0032]    The disclosed surgical instrument will be further understood with reference to the following illustrative examples. In a first illustrative example, as described with reference to steps  1 - 7  of  FIG. 3   a , a retrograde reamer, such as a 2.4 mm retrograde reamer  316 , is employed in conjunction with a 4.5 mm reamer. As depicted in step  1  (see  FIG. 3   a ), a 2.4 mm guide wire  302  is drilled into a bone joint  304  using a suitable drill  306 , bullet  308 , and guide  310 . As depicted in step  2 , the bullet  308 , the guide  310 , and the drill  306  are removed. As depicted in step  3 , a 4.5 mm reamer  312  is drilled over the guide wire  302  using a suitable drill  314 . As depicted in step  4 , the drill  314  and the 2.4 mm guide wire  302  are removed. As depicted in step  5 , the 2.4 mm retrograde reamer  316  is inserted into the 4.5 mm reamer  312 . For example, the 2.4 mm retrograde reamer  316  can extend out of a distal end of the 4.5 mm reamer  312 , or extend through windows in the 4.5 mm reamer  312 . As depicted in step  6 , a cutting member  318  of the 2.4 mm retrograde reamer  316  is deployed. As depicted in step  7 , after the 2.4 mm retrograde reamer  316  is used to retro-ream a tunnel  320  through the bone joint  304 , the cutting member  318  is closed or collapsed, and the surgical instrument system is removed.  FIG. 3   b  depicts an alternative to step  4  of  FIG. 3   a , in which only the 2.4 mm guide wire  302  is removed, and the 2.4 mm retrograde reamer  316  is inserted through the back end of the drill  314 . 
         [0033]    With further regard to the first illustrative example,  FIG. 3   c  depicts how the tunnel  320  can be measured using a measurement gauge  322  inside the bone joint  304 . As shown in  FIG. 3   c , the measurement gauge  322  can be held against the bone joint  304  during the retro-reaming operation. Further tunnel measurement options include (1) using the measurement gauge  322  on the outside of the bone joint  304  to visualize the reamer markings, (2) leaving only the bullet  308  in place while measuring the tunnel  320 , (3) leaving both the bullet  308  and the guide  310  in place while measuring the tunnel  320 , and (4) using, on the outside of the 4.5 mm reamer  312 , a measurement sleeve  324  (see  FIG. 3   c ) that is manually held against the bone joint  304 . 
         [0034]    In a second illustrative example, as described with reference to steps  1 - 4  of  FIG. 4 , a 4.5 mm reamer  402  is employed as a retro-reaming instrument. As depicted in step  1  (see  FIG. 4 ), a 2.4 mm guide wire  404  is drilled into a bone joint  406  using a suitable drill  408 , bullets  410 ,  412 , and guide  414 . As depicted in step  2 , the internal 2.4 mm bullet  410  is removed. As depicted in step  3 , the 4.5 mm reamer  402  is operated, using the drill  408 , to drill a tunnel, from the outside in, over the guide wire  404  through the larger bullet  412  with the guide  414  in place. As depicted in step  4 , the 4.5 mm retro-reaming instrument  402  is used to retro-ream a tunnel  416  through the bone joint  406 . With reference to this second illustrative example, the 4.5 mm retro-reaming instrument  402  can be self-actuating. Alternatively, a 2.4 mm actuator rod can be employed to actuate the 4.5 mm retro-reaming instrument  402  to retro-ream the tunnel  416  through the bone joint  406 . 
         [0035]    In a third illustrative example, as described with reference to steps  1 - 2  of  FIG. 5 , a 4.5 mm reamer  502  is employed as the bullet for a guide wire  504 . As depicted in step  1  (see  FIG. 5 ), using a suitable drill  506  and guide  508 , the guide wire  504  is inserted in a bone joint  510  through the combined bullet/4.5 mm reamer  502 . As depicted in step  2 , the drill  506  is engaged with the combined bullet/4.5 mm reamer  502 , and a 4.5 mm tunnel  512  is reamed through the bone joint  510 . In effect, the bullet becomes the 4.5 mm reamer  502 . Allowing the 4.5 mm reamer  502  to serve as the bullet reduces the need to remove the bullet after drilling the guide wire  504 . It is noted that a holder for the bullet may be configured to allow lateral removal of the guide  508 . 
         [0036]      FIG. 6  depicts a plurality of alternative embodiments  700 ,  800 ,  900 ,  1000 ,  1100 ,  1200 ,  1300 ,  1400  of the disclosed retrograde reamer. As shown in  FIGS. 7   a  and  7   b , the retrograde reamer  700  includes one or more blades  702 , one or more wedge members  704 , and one or more flex members  706 . During use, the guide wire is typically removed from the surgical site, and the blades  702  connected to the respective flex members  706  are inserted into a tubular shaft  701  of, for example, a 4.5 mm reamer, thereby causing the blades  702  to impinge against the respective wedge members  704  and move in a radial fashion out of the shaft  701  through corresponding slots  708  in the shaft  701 . In some embodiments, the shaft  701  can have a stepped internal diameter. Further, in some embodiments, the flex members  706  can be implemented as hinges. The blades  702  connected to the respective flex members  706  can be advanced through the tubular shaft  701  to deploy the blades  702 , and subsequently retracted into the shaft  701  to close or collapse the blades  702 . The diameters of tunnels created using the retrograde reamer  700  are adjustable based on how far the wedge members  704  drive the blades  702  through the respective slots  708  in the shaft  701 . Alternatively, the diameters of tunnels created using the alternative configuration  700  can be fixed. It is noted that the retrograde reamer  700  can be keyed to fenestrations of the 4.5 mm reamer. 
         [0037]      FIGS. 8   a  and  8   b  depict detailed views of the alternative configuration  800  of the retrograde reamer. As shown in  FIGS. 8   a  and  8   b , the retrograde reamer  800  includes a shaft  803 , and one or more blades  802  connected by a pivot  805  to a distal end of the shaft  803 . In some embodiments, the shaft  803  can have a reamer tooth  810  at its distal end. During use, the guide wire is typically removed from the surgical site, and the shaft  803  and blades  802  are inserted into a tubular shaft  801  of, for example, a 4.5 mm reamer. In this case, the blades  802  can be keyed to support slots  808  in the shaft  801 . To deploy the blades  802 , the pivot  805  is advanced past a distal end of the shaft  801  (see directional arrow  812 ), a toggling mechanism pivotably places the blades  802  in a cutting position (see directional arrow  814 ), and the shaft  803  is rotated, for example, by a quarter turn (see directional arrow  818 ), and then retracted into the shaft  801  to place the blades  802  into the corresponding support slots  808  (see directional arrow  816 ). To close or collapse the blades  802 , the pivot  805  is advanced past the distal end of the tubular shaft  801  (see directional arrow  812 ) to pivotally place the blades  802  along the longitudinal axis of the shaft  803 , and the shaft  803  is rotated by a quarter turn (see directional arrow  818 ) and then retracted back into the shaft  801  (see directional arrow  816 ). In some embodiments, the retrograde reamer  800  can include a single-sided blade (L-shaped blade configuration), or double-sided blades (T-shaped blade configuration). The diameters of tunnels created using the L-shaped or T-shaped blade configuration are typically fixed. It is noted that the L-shaped blade configuration generally requires less penetration into a bone joint space for deployment. It is further noted that the toggle mechanism for deploying the blades  802  can be implemented using torsion springs, pull wires, a push rod, a spring plunger, or any other suitable toggle mechanism. 
         [0038]      FIGS. 9   a  and  9   b  depict detailed views of the alternative configuration  900  of the retrograde reamer. As shown in  FIGS. 9   a  and  9   b , the retrograde reamer  900  includes an internal shaft  903 , a tubular external shaft  905 , and one or more blades  902 . In some embodiments, the distal end of the external shaft  905  can have a pointed or sharpened tip. During use, the external shaft  905  can function as a guide wire. To deploy the blades  902 , the internal shaft  903  is retracted into the tubular shaft  905  (see directional arrow  912 ), causing the blades  902  to deploy through corresponding slots  909  in the shafts  903 ,  905 , as well as through corresponding slots  908  in a tubular shaft  901  of, for example, a 4.5 mm reamer. To collapse the blades  902 , the internal shaft  903  is advanced into the tubular shaft  905 . In some embodiments, the retrograde reamer  900  includes a single blade. The diameters of tunnels created using the blades  902  are typically fixed. It is noted that the mechanism for deploying the blades  902  can be implemented using torsion springs, pull wires, a push rod, a spring plunger, or any other suitable mechanism. It is further noted that the retrograde reamer  900  can be keyed to fenestrations of the 4.5 mm reamer. 
         [0039]      FIGS. 10   a  and  10   b  depict detailed views of the alternative configuration  1000  of the retrograde reamer. As shown in  FIGS. 10   a  and  10   b , the retrograde reamer  1000  includes a shaft  1005  having a pivotable distal end  1007  with a pointed or sharpened tip. During use, the guide wire is typically removed from the surgical site, and the shaft  1005  is inserted into a tubular shaft  1001  of, for example, a 4.5 mm reamer. To deploy the pointed or sharpened tip of the pivotable distal end  1007 , the distal end  1007  of the shaft  1005  is advanced past a distal end of the 4.5 mm reamer (see directional arrow  1012 ), the distal end  1007  is rotated up to 180° at a pivotable joint to a cutting position (see directional arrow  1014 ), and the shaft  1005  is retracted to place the distal end  1007  into a support slot  1009  in the shaft  1001  (see directional arrow  1016 ). To close or collapse the pointed or sharpened tip of the pivotable distal end  1007 , the shaft  1005  is advanced past the distal end of the 4.5 mm reamer (see directional arrow  1012 ), the distal end  1007  is rotated to pivotally place the distal end  1007  along the longitudinal axis of the shaft  1005 , and the shaft  1005  is retracted back into the tubular shaft  1001  (see directional arrow  1016 ). The diameters of tunnels created using the pivotable distal end  1007  are typically fixed. It is noted that the mechanism for deploying the pivotable distal end  1007  can be implemented using a torsion coil  1004 , a laser cut hypotube, a micro-universal joint, or any other suitable mechanism. In some embodiments, the shaft  1005  can function as the guide wire. In addition, in some embodiments, the pivotable joint of the pivotable distal end  1007  can have more than one seating position. 
         [0040]      FIGS. 11   a  and  11   b  depict detailed views of the alternative configuration  1100  of the retrograde reamer. As shown in  FIGS. 11   a  and  11   b , the retrograde reamer  1100  includes a shaft  1105  having a distal end with a pointed or sharpened tip, and one or more blades  1106  attached to one or more flex members  1104 . For example, the flex members  1104  can be made from a Nitinol alloy, or any other suitable material. During use, the shaft  1105  and blades  1106  are inserted into a tubular shaft  1101  of, for example, a 4.5 mm reamer. To deploy the blades  1106 , the shaft  1105  is rotated to position the blades  1106  in registration with slots  1109  in the shaft  1101  (see directional arrow  1112 ), and then advanced to move the blades  1106  attached by the flex member  1104  through the slots  1109  (see directional arrows  1114 ). To close or collapse the blades  1106 , the shaft  1105  is retracted, closing or collapsing the blades  1106  within the shaft  1101 , and then rotated to move the blades  1106  away from the slots  1109 . In some embodiments, the Nitinol alloy can be employed as the cutting member. The diameters of tunnels created using the alternative configuration  1100  are adjustable based on how far the blades  1106  are deployed through the slots  1109 . Alternatively, the diameters of tunnels created using the alternative configuration  1100  can be fixed. 
         [0041]      FIGS. 12   a  and  12   b  depict detailed views of the alternative configuration  1200  of the retrograde reamer. As shown in  FIGS. 12   a  and  12   b , the retrograde reamer  1200  includes a shaft  1205  having a distal end with a pointed or sharpened tip, and one or more blades  1206  attached to a sidewall of a tubular shaft  1201  (e.g., a 4.5 mm reamer) by one or more flex members  1209 . During use, the shaft  1205  is inserted into the tubular shaft  1201  of the 4.5 mm reamer. To deploy the blades  1206 , the shaft  1205  is retracted through the tubular shaft  1201 , and a deployment member such as a wire  1207  (e.g., a flat wire or rod) connected to the blade  1206  is pulled to deploy the blade  1206  through a slot  1211  in the shaft  1201  (see directional arrow  1212 ). To close or collapse the blades  1206 , the shaft  1205  is advanced into the tubular shaft  1201 , impinging against the blade  1206  and closing or collapsing the blade  1206  within the shaft  1201 . The diameters of tunnels created using the retrograde reamer  1200  can be adjustable based on how far the wire  1207  deploys the blade  1206  through the slot  1211  in the shaft  1201 . Alternatively, the diameters of tunnels created using the retrograde reamer  1200  can be fixed. It is noted that the retrograde reamer  1200  of the retrograde reamer can be keyed to fenestrations of the 4.5 mm reamer. 
         [0042]      FIGS. 13   a  and  13   b  depict detailed views of the alternative configuration  1300  of the retrograde reamer. As shown in  FIGS. 13   a  and  13   b , the retrograde reamer  1300  includes a shaft  1305  having a distal end with a pointed or sharpened tip, and one or more blades  1306  rotatably attached to a tubular inner shaft  1303  of, for example, a 4.5 mm reamer. During use, the shaft  1305  is initially inserted into the inner shaft  1303 , which is disposed within a tubular outer shaft  1301  of the 4.5 mm reamer. To deploy the blades  1306 , the shaft  1305  is retracted through the inner shaft  1303 , the outer shaft  1301  is rotated to disengage the blades  1306  from the shaft  1301  (see directional arrow  1312 ), and the outer shaft  1301  is advanced to rotatably position the blades  1306  substantially perpendicular to the respective shafts  1301 ,  1303  (see directional arrow  1314 ). To close or collapse the blades  1306 , the outer shaft  1301  is retracted to allow the blades  1306  to rotate back against the inner shaft  1303 , and the shaft  1305  is advanced into the tubular inner shaft  1303  to maintain the blades  1306  against the shaft  1303 . The diameters of tunnels created using the retrograde reamer  1300  can be fixed. 
         [0043]      FIG. 14  depicts a detailed view of the alternative configuration  1400  of the retrograde reamer. As shown in  FIG. 14 , the retrograde reamer  1400  includes a shaft  1407  having a distal end with a pointed or sharpened tip, and one or more helical blades  1406  (e.g., single or double helix, or interlocking helix members) attached to a tubular outer shaft  1401  of, for example, a 4.5 mm reamer, which also has a tubular inner shaft  1405 . During use, the shaft  1407  is inserted into the tubular inner shaft  1405 . To deploy the helical blades  1406 , the tubular outer shaft  1401  is rotated (see directional arrow  1414 ) and advanced (see directional arrow  1412 ) to unwind the helical blades  1406  away from the inner shaft  1405 , thereby forming an adjustable cutting diameter. To close or collapse the helical blades  1406 , the outer shaft  1401  is rotated in the opposite direction and retracted to wind the helical blades  1406  back against the inner shaft  1405 . The diameters of tunnels created using the retrograde reamer  1400  are adjustable based on how far the helical blades  1406  are deployed to form the cutting diameter. Alternatively, the diameters of tunnels created using the retrograde reamer  1400  can be fixed. 
         [0044]      FIGS. 15   a - 15   c  depict a further alternative embodiment  1500  of the disclosed retrograde reamer. The retrograde reamer  1500  is an expandable reamer that can be used to perform an anterior cruciate ligament (ACL) repair or reconstruction using the outside in technique. Further, the retrograde reamer  1500  can interface with a suitable aimer to assist the surgeon in the proper placement of the femoral tunnel. 
         [0045]    In some embodiments, the retrograde reamer  1500  is cannulated to allow the surgeon to use a standard 2.4 mm guide wire to place the tunnel. As shown in  FIGS. 15   a - 15   c , the retrograde reamer  1500  includes a main shaft  1504 , an outer sleeve  1502 , and a plurality of cutting members  1506  (e.g., two (2) cutting members). The cutting members  1506  are contained within the main shaft  1504 , and swing outward upon activation of the outer sleeve  1502 . The outer sleeve  1502  has windows that allow the respective cutting members  1506  to pass therethrough. The cutting members  1506  move via a rotation about a guide pin  1508 . The cutting members  1506  have a cam profile to ensure that, while the outer sleeve  1502  applies axial force, the cutting members  1506  swing outward.  FIGS. 15   a  and  15   b  depict the retrograde reamer  1500  in a closed or collapsed configuration and an open configuration, respectively. 
         [0046]      FIG. 15   c  depicts the open configuration of the retrograde reamer  1500  in greater detail. The retrograde reamer  1500  allows the use of a standard 2.4 mm guide pin. Further, the outer sleeve  1502  is configured to deploy and retract the cutting members  1506 . Moreover, the retrograde reamer  1500  can be cannulated to allow deployment and drilling over a guide wire. The cutting members  1506  can also be changed to accommodate all desired sizes (e.g., 6 mm to 13 mm). Advantages of the retrograde reamer  1500  include its capability to have a cannulated configuration, the integral configuration of the cutting members  1506 , its capability to be powered via a suitable drill, and its capability to be configured with the dual cutting members  1506 , which may allow more accurate tunnel formation. 
         [0047]    In an exemplary mode of operation, the guide pin  1508  (e.g., a 2.4 mm guide pin) can be drilled using a suitable aimer. Using the retrograde reamer  1500  in the closed or collapsed configuration (see  FIG. 15   a ), a tunnel (e.g., a 4.5 mm tunnel) can then be drilled, from the outside in, through bone into the space of a bone joint. Next, the cutting members  1506  can be activated and deployed by moving the outer sleeve  1502  relative to the main shaft  1504 , thereby causing the cutting members  1506  to pass through the windows in the outer sleeve  1502 . A tunnel having a desired diameter and depth can then be drilled through the bone in a retrograde fashion, using the cutting members  1506  in their deployed positions. The outer sleeve  1502  and main shaft  1504  can then be advanced back into the space of the bone joint, allowing the cutting members  1506  to be retracted within the main shaft  1504 . Finally, the outer sleeve  1502 , the main shaft  1504 , as well as the cutting members  1506  in their retracted or collapsed positions, can be removed from the surgical site. 
         [0048]    Having described the above illustrative embodiments, further modifications to and/or variations of the disclosed surgical instrument may be made, as described below with reference to the following examples. Example 1 is a retrograde reamer for use in surgical procedures that includes a first tubular shaft, at least one second shaft movably disposable within the first tubular shaft, and at least one cutting member movably coupled to one of the first tubular shaft and the second shaft. In response to relative movement of the first tubular shaft and the second shaft, the cutting member is adapted to be displaced from a collapsed position to at least one deployed position, thereby defining at least one cutting diameter. 
         [0049]    In Example 2, the subject matter of Example 1 can optionally include features wherein the cutting member is movably coupled to the first tubular shaft. 
         [0050]    In Example 3, the subject matter of any one of Examples 1-2 can optionally include features wherein the cutting member is disposed adjacent a distal end of the first tubular shaft, and wherein, in response to relative rotational movement of the first tubular shaft and the second shaft, an externally threaded portion at a distal end of the second shaft is operative to threadingly engage an internally threaded portion at the distal end of the first tubular shaft, thereby causing the distal end of the first tubular shaft to axially move in a proximal direction, and the cutting member to be displaced from the collapsed position to the deployed position. 
         [0051]    In Example 4, the subject matter of any one of Examples 1-2 can optionally include features wherein the cutting member includes one or more helical blades, and wherein, in response to relative rotational and axial movement of the first tubular shaft and the second shaft, the helical blades are operative to unwind from the second shaft, thereby displacing the helical blades from the collapsed position to the deployed position. 
         [0052]    In Example 5, the subject matter of any one of Examples 1-2 can optionally include features wherein the first tubular shaft has a sidewall, the sidewall including at least one opening therethrough, and wherein the retrograde reamer further includes a flex member operative to movably couple the cutting member to the sidewall of the first tubular shaft substantially opposite the opening in the sidewall, and a deployment member coupled to the cutting member. The deployment member is operative, in response to being pulled distally, to displace the cutting member in a radial fashion from the collapsed position to the deployed position, such that the cutting member passes at least partially through the opening in the sidewall of the first tubular shaft while being displaced to the deployed position. 
         [0053]    In Example 6, the subject matter of Example 1 can optionally include features wherein the cutting member is movably coupled to the second shaft. 
         [0054]    In Example 7, the subject matter of any one of Examples 1 and 6 can optionally include features wherein, in response to relative axial movement of the first tubular shaft and the second shaft, the cutting member is operative to be displaced from the collapsed position to the deployed position. 
         [0055]    In Example 8, the subject matter of any one of Examples 1, 6, and 7 can optionally include at least one wedge member disposed within the first tubular shaft adjacent a distal end of the first tubular shaft, and at least one flex member adapted to movably couple the cutting member to the second shaft. In response to relative axial movement of the first tubular shaft and the second shaft, the cutting member is operative to impinge against the wedge member, thereby causing the flex member to be displaced from a first position substantially parallel to a longitudinal axis of the second shaft to a second off-axis position, and the cutting member to be displaced from the collapsed position to the deployed position. 
         [0056]    In Example 9, the subject matter of Example 8 can optionally include features wherein the first tubular shaft has a sidewall with at least one opening formed therethrough, and wherein, in response to the displacement of the flex member, the cutting member is operative to be displaced in a radial fashion from the collapsed position to the deployed position, the cutting member passing at least partially through the opening in the sidewall of the first tubular shaft while being displaced to the deployed position. 
         [0057]    In Example 10, the subject matter of any one of Examples 1 and 6 can optionally include features wherein the cutting member is movably coupled at a distal end of the second shaft by a pivot pin. 
         [0058]    In Example 11, the subject matter of Example 10 can optionally include features wherein, in response to axial movement of the second shaft in a distal direction, the cutting member is operative to move distally and to rotate about the pivot pin, thereby displacing the cutting member from the collapsed position to the deployed position. 
         [0059]    In Example 12, the subject matter of any one of Examples 1, 6, 10, and 11 can optionally include features wherein the first tubular shaft has a sidewall with at least one slot formed therethrough, and wherein, in response to axial movement of the second shaft in a proximal direction, the cutting member is operative to move proximally, thereby causing the cutting member to be placed in the slot in the deployed position. 
         [0060]    In Example 13, the subject matter of any one of Examples 1 and 6 can optionally include features wherein the at least one second shaft includes a second tubular shaft, and an internal shaft disposed within the second tubular shaft. 
         [0061]    In Example 14, the subject matter of Example 13 can optionally include features wherein the first tubular shaft, the second tubular shaft, and the internal shaft each have a sidewall including at least one opening formed therethrough, and wherein, in response to relative axial movement of the second tubular shaft and the internal shaft, the cutting member is operative to be displaced from the collapsed position to the deployed position, the cutting member passing at least partially through respective sidewall openings of the first tubular shaft, the second tubular shaft, and the internal shaft while being displaced to the deployed position. 
         [0062]    In Example 15, the subject matter of any one of Examples 1 and 6 can optionally include features wherein the cutting member is adapted to correspond to a pivotable distal end of the second shaft. 
         [0063]    In Example 16, the subject matter of Example 15 can optionally include features wherein, in response to axial movement of the second shaft in a distal direction, the pivotable distal end of the second shaft is operative to rotate, at a pivotable joint, from the collapsed position to the deployed position. 
         [0064]    In Example 17, the subject matter of any one of Examples 15-16 can optionally include features wherein the first tubular shaft has a sidewall including at least one slot formed therethrough, and wherein, in response to axial movement of the second shaft in a proximal direction, the pivotable distal end of the second shaft is operative to move proximally, thereby causing the pivotable distal end to be placed in the slot in the deployed position. 
         [0065]    In Example 18, the subject matter of any one of Examples 1 and 6 can optionally include features wherein the cutting member has a first cutting member portion and a second cutting member portion, and a flex member interconnecting the first and second cutting member portions. 
         [0066]    In Example 19, the subject matter of Example 18 can optionally include features wherein the first tubular shaft has a sidewall including at least one opening formed therethrough, and wherein, in response to axial movement of the second shaft toward a distal end of the first tubular shaft, the flex member is operative to allow the first and second cutting member portions to be displaced from the collapsed position to the deployed position, the first and second cutting member portions passing at least partially through the sidewall opening of the first tubular shaft while being displaced to the deployed position. 
         [0067]    In Example 20, the subject matter of any one of Examples 1 and 6 can optionally include features wherein the cutting member is adapted, in the collapsed position, to be selectively engaged with and disengaged from the first tubular shaft, and wherein, in response to relative rotational movement of the first tubular shaft and the second shaft, the cutting member is operative to be disengaged from the first tubular shaft, and to be displaced from the collapsed position to the deployed position. 
         [0068]    Example 21 is a method of operating a retrograde reamer in a surgical procedure that includes providing a retrograde reamer, the retrograde reamer including a first tubular shaft, at least one second shaft movably disposable within the first tubular shaft, and at least one cutting member movably coupled to one of the first tubular shaft and the second shaft, performing relative movement of the first tubular shaft and the second shaft, and, in response to the relative movement of the first tubular shaft and the second shaft, displacing the cutting member from a collapsed position to at least one deployed position, thereby defining at least one cutting diameter. 
         [0069]    In Example 22, the subject matter of Example 21 can optionally include features wherein the performing of relative movement of the first tubular shaft and the second shaft includes performing relative rotational movement of the first tubular shaft and the second shaft. 
         [0070]    In Example 23, the subject matter of any one of Examples 21-22 can optionally include features wherein the performing of relative movement of the first tubular shaft and the second shaft includes performing relative axial movement of the first tubular shaft and the second shaft. 
         [0071]    In Example 24, the subject matter of any one of Examples 21-23 can optionally include features wherein the performing of relative movement of the first tubular shaft and the second shaft includes performing relative rotational and axial movement of the first tubular shaft and the second shaft. 
         [0072]    In Example 25, the subject matter of any one of Examples 21-24 can optionally include features wherein the retrograde reamer further includes a flex member movably coupling the cutting member to a sidewall of the first tubular shaft at a location substantially opposite an opening in the sidewall, and a deployment member coupled to the cutting member, and wherein the method further includes pulling the deployment member distally, and, in response to the deployment member being pulled distally, displacing the cutting member in a radial fashion from the collapsed position to the deployed position, the cutting member passing at least partially through the opening in the sidewall of the first tubular shaft while being displaced to the deployed position. 
         [0073]    It will be appreciated by those of ordinary skill in the art that still further modifications to and variations of the disclosed surgical instrument may be made without departing from the inventive concepts disclosed herein. Accordingly, the invention should not be viewed as limited except as by the scope and spirit of the appended claims.