Patent Publication Number: US-9883895-B2

Title: One way sliding device for intramedullary intertrochanteric fixation implants

Description:
PRIORITY CLAIM 
     The present application is a Continuation Application of U.S. patent application Ser. No. 13/122,887 filed on Apr. 6, 2011, now U.S. Pat. No. 9,084,643; which is a 371 application of PCT Patent Application Serial No. PCT/US2009/058019 filed on Sep. 23, 2009, which claims priority to U.S. Provisional Application Ser. No. 61/111,825 filed on Nov. 6, 2008. The entire disclosures of these patents/applications are expressly incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to devices for treating fractures of long bones and, in particular, to internal fixation devices. 
     BACKGROUND 
     Fractures commonly occur in the femur, for example in the femoral neck, intertrochanteric and peritrochanteric regions. Such fractures may be fixed with an intramedullary device and an implant. As is understood by those skilled in the art, the intramedullary device (e.g., an intramedullary nail) is positioned in the medullary canal of a long bone such as the femur. An implant, which may be formed as a helical blade or a lag screw, may then be inserted laterally through bone to pass through an opening of the intramedullary device until a free end of the Implant enters the head of the bone. For example, where the bone is a femur, the implant passes through the shaft of the femur, through the intramedullary device and into the femoral head via the neck of the femur to secure the femoral head to a remaining portion of the femur. After implantation, such an implant may move laterally relative to the intramedullary nail along the path over which it was inserted. Some lateral movement of the implant is expected. However, in some cases, the implant may migrate medially through the intramedullary device, resulting in a protrusion through the femoral head and into the acetebulum causing complications. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a device for treating fractures, comprising an intramedullary member sized and shaped for insertion along a longitudinal axis of a bone within a medullary canal thereof, the intramedullary member including an opening extending obliquely therethrough, the opening, when the intramedullary member is in a desired position within a bone, aligning with a desired axis along which an implant is to be inserted into the bone, the intramedullary member including a channel formed therewithin and opening to the opening and a locking mechanism mounted in the channel, the locking mechanism including a locking abutting structure extending into the opening in combination with an implant sized to be slidably received through the opening and inserted along the desired axis, the implant including a plurality of implant abutting structures aligned to engage the locking abutting structure preventing medial movement of the implant relative to the intramedullary member. 
     The present invention is further directed to a method comprising inserting an intramedullary member into a medullary canal of a bone and inserting an implant into a bone via an opening in the intramedullary member, a shaft of the implant including a plurality of abutting structures distributed along a portion of a length of the shaft, each of the abutting structures including an angled lateral surface and a medially-facing abutting surface in combination with moving a locking mechanism to a locked configuration in which a pawl of the locking mechanism extends into the opening to engage the abutting surface of one of the abutting structures corresponding to a desired medial-most position of the implant, the angled lateral surfaces of the abutting structures permitting lateral movement of the implant relative to the pawl. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side view of a device according to a first exemplary embodiment of the invention; 
         FIG. 2  shows a side view of a distal facing surface of an implant of the device of  FIG. 1 ; 
         FIG. 3 a    shows a perspective view of a locking mechanism of the device of  FIG. 1 ; 
         FIG. 3 b    shows a perspective view of a locking mechanism and an intramedullary device according to an alternate embodiment of the present invention; 
         FIG. 3 c    shows a perspective view of the locking mechanism of  FIG. 3   b;    
         FIG. 4  shows a side view of an intramedullary nail and the locking mechanism the device of  FIG. 1 , in a first configuration; 
         FIG. 5  shows a perspective view of the intramedullary nail and the locking mechanism of  FIG. 4 ; 
         FIG. 6  shows a side view of the intramedullary nail and the locking mechanism of the device of  FIG. 1 , in a second configuration; 
         FIG. 7  shows a perspective view of the intramedullary nail and the locking mechanism of  FIG. 6 ; 
         FIG. 8  shows a perspective view of the device of  FIG. 1 ; 
         FIG. 9  shows a side view of the device of  FIG. 1 ; 
         FIG. 10  shows an opposite side view of  FIG. 9 ; 
         FIG. 11  shows a lateral cross-section of the device of  FIG. 1 ; 
         FIG. 12  shows a side view of a device according to a second exemplary embodiment of the present invention; 
         FIG. 13  shows a cross-sectional view of an implant of the device of  FIG. 12 ; 
         FIG. 14  shows a perspective view of a locking mechanism of the device of  FIG. 12 ; 
         FIG. 15  shows a perspective view an intramedullary nail and the locking mechanism of the device of  FIG. 12 , in a first configuration; 
         FIG. 16  shows another perspective view of the intramedullary nail and the locking mechanism of  FIG. 15 ; 
         FIG. 17  shows a side view of the intramedullary nail and the locking mechanism of the device of  FIG. 12 , in a second configuration; 
         FIG. 18  shows a perspective view of the intramedullary nail and the locking mechanism of  FIG. 17 ; 
         FIG. 19  shows a perspective view of a device according to a third exemplary embodiment of the present invention; 
         FIG. 20  shows another perspective view of the device of  FIG. 19 ; 
         FIG. 21  shows a perspective view of a locking mechanism of the device of  FIG. 19 ; 
         FIG. 22  shows a side of the locking mechanism of  FIG. 21 ; 
         FIG. 23  shows a perspective view of a first element of the locking mechanism of  FIG. 21 ; 
         FIG. 24  shows another perspective view of the first element of  FIG. 23 ; 
         FIG. 25  shows a perspective view of a second element of the locking mechanism of  FIG. 21 ; 
         FIG. 26  shows another perspective view of the second element of  FIG. 25 ; 
         FIG. 27  shows a lateral cross-section of an intramedullary nail and locking mechanism of the device of  FIG. 19 ; 
         FIG. 28  shows a side view of a device according to a fourth exemplary embodiment of the present invention; 
         FIG. 29  shows a side view of an intramedullary nail, locking mechanism and pawl of the device of  FIG. 28 , in a first configuration; 
         FIG. 30  shows a perspective view of the intramedullary nail, locking mechanism and the pawl of  FIG. 29 ; 
         FIG. 31  shows a side view of the intramedullary nail, locking mechanism and the pawl of the device of  FIG. 28 , in a second configuration; 
         FIG. 32  shows a perspective view of the intramedullary nail, locking mechanism and the pawl of  FIG. 31 ; 
         FIG. 33  shows a front view of the locking mechanism of the device of  FIG. 28 ; 
         FIG. 34  shows a perspective view of a pawl of the device of  FIG. 28 ; 
         FIG. 35  shows a side view of a device according to a fifth exemplary embodiment of the present invention; 
         FIG. 36  shows a side view of an implant of the device of  FIG. 35 ; 
         FIG. 37  shows a side view of a locking mechanism of the device of  FIG. 35 ; 
         FIG. 38  shows a cross-sectional side view of the locking mechanism of  FIG. 37 ; 
         FIG. 39  shows a perspective view of the device of  FIG. 35 , in an initial implanted position; 
         FIG. 40  shows a perspective view of the device of  FIG. 35 , in a final implanted position; and 
         FIG. 41  shows a perspective view of a canted plate of the locking mechanism of  FIG. 37 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The present invention relates to devices for treating fractures of long bones and, in particular, to internal fixation devices. It is noted that although exemplary embodiments of the present invention are described below with respect to the treatment of fractures of the femur, the invention is not intended to limit the application of the invention to such fractures, as the invention may also be employed in the treatment of other fractures such as, for example, the humerus, tibia, etc. It should also be noted that the terms distal and proximal, used herein, refer to a direction toward (proximal) and away from (distal) a user of the device. As indicated above, fractures of long bones, particularly fractures in which a break is formed between a trochanteric head and a shaft of the bone, may be treated by implanting an intramedullary device along an axis of the shaft of the bone (i.e., in the medullary canal). An implant may then be inserted laterally through the bone to pass through the intramedullary device into the trochanteric head. Devices according to the present invention are designed to permit a desired degree of migration of the implant back toward the point through which it was inserted into the bone (i.e., lateral migration) while minimizing migration of the implant further into the trochanteric head toward the acetebulum (i.e., medial migration). 
     As shown in  FIGS. 1-11 , a device  100  according to an exemplary embodiment of the present invention comprises an implant  102  and an intramedullary nail  104  including a locking mechanism  106  (e.g., a ratchet mechanism) permitting limited migration of the implant  102  through the nail  104  laterally while preventing medial migration. As shown in  FIG. 1 , an oblique opening  108  extending through the nail  104  in a plane substantially perpendicular to a longitudinal axis of the nail  104 . The opening  108  is sized to receive the implant  102  therethrough. A channel  110  extending through a portion of the nail  104  along the longitudinal axis opens to the opening  108  houses the locking mechanism  106 . In the embodiment shown, the channel  110  and the locking mechanism  106  extend distally of the opening  108  so that the locking mechanism  106  engages a distal side of the implant  102  when the implant  102  is inserted through the oblique opening  108 . Those skilled in the art will understand that the channel  110  and the locking mechanism  106  may alternatively be located on the proximal side of the implant  102 . The locking mechanism  106  includes a biasing member  140  (e.g., a spring) engaging a pawl member  105  to urge the pawl member  105  into contact with the implant  102 . 
     As shown in  FIG. 2 , a distal facing surface of a locking engaging portion of the implant  102  which, when assembled in a desired configuration, overlaps with the channel  110  includes features for engaging corresponding structures of the pawl member  105 . Specifically, the implant  102  comprises a shaft  112  extending from a proximal end  114  to a distal end (not shown) coupled to the proximal end of a blade or other bone engaging structure (not shown). As would be understood by those skilled in the art, the bone engaging structure may be formed as a helical blade extending distally from the distal end of the shaft  112 . It will be understood by those of skill in the art however, that the bone engaging structure may be any other fixation means such as, for example, a lag screw. 
     The locking engaging portion of the shaft  112  includes a plurality of abutting structures  116  spaced from one another along a portion of a length of the shaft  112 . Each of the abutting structures  116  includes a ramped surface  117  extending from a position adjacent to a radially inner end of the abutting structure  116  immediately distal thereto and angling gradually outward to an abutting surface  119 . As would be understood by those of skill in the art, the abutting surfaces  119  of the abutting structures  116  may extend substantially perpendicular to a longitudinal axis of the implant  102 . 
     As shown in  FIG. 3 a   , the pawl member  105  includes an implant engaging surface  130  angled to substantially align with an angle of the opening  108 . A pawl  126  including a proximally facing abutting surface  127  extends out from the surface  130  so that, when in an operational position, the abutting surface  127  of the pawl  126  engages an abutting surface  119  of one of the abutting structures  116  of the Implant  102 . Thus, engagement between the pawl  126  and the abutting structure  116  of the shaft  112  prevents movement of the implant  102  medially relative to the nail  104 . However, the implant  102  may slide laterally as the angled distal surface of the pawl  126  and the angled surfaces  117  of the abutting structures  116  allow the shaft  112  to slide laterally over the pawl member  105 . A protrusion  128  including a ramped surface  134  extends outward from the implant engaging surface  130  by a distance greater than the pawl  126  so that, during insertion of the implant  102  through the opening  108 , contact between the shaft  112  and the protrusion  128  moves the locking engaging portion of the shaft  112  out of contact with the pawl  126  until the implant  102  has been advanced to a desired position in the bone. When in the desired position, the implant  102  is rotated about its longitudinal axis to a locking orientation in which the protrusion  128  aligns with and enters a groove  118  formed in the shaft  112 . At this point, the abutting structures  116  of the shaft  112  and the pawl  126  are aligned with one another so that, as the implant  102  moves toward the pawl member  105  due to the insertion of the protrusion  128  into the groove  118 , the pawl  126  engages one of the abutting structures  116  corresponding to the desired medial-most position of the implant  102 . As described above, engagement between the abutting surface  127  of the pawl  126  and the abutting surface  119  of the abutting structure  116  prevents further medial migration of the implant  102 . This contact between the pawl member  126  and the corresponding abutting structure  116  is maintained by the biasing member  140  which urges the pawl member  105  toward the shaft  112  at all times. 
     To ensure that the locking mechanism  106  does not move beyond the first and the second configuration, the locking mechanism  106  may also include an elongated hole  124  extending laterally through the locking mechanism  106 , distally of the shoulder  122 , for receiving a pin (not shown) which fixes the locking mechanism  106  to the intramedullary nail  104 . Thus, the intramedullary nail  104  also includes a hole  136  extending laterally therethrough, distally of the oblique opening  108  such that the position of the hole  136  corresponds to a position of the elongated hole  124 . The hole  136  may be substantially circular such that the intramedullary nail  104  remains stationary while the locking mechanism  106  moves relative to the intramedullary nail  104  along the longitudinal axis. It will be understood by those of skill in the art that the pin inserted through the holes  124 ,  136  fixes the locking mechanism  106  to the intramedullary nail  104  such that the locking mechanism  106  and the intramedullary nail  104  may not rotate relative to one another, but may move between the first configuration and the second configuration along the longitudinal axis of the intramedullary nail  104 . 
     In an alternative embodiment, as shown in  FIGS. 3 b -3 c   , a locking mechanism  106 ′ may include a pawl member  105 ′ formed with a recess  124 ′ rather than an elongate hole for fixing the locking mechanism  106 ′ within an intramedullary nail  104 ′. The recess  124 ′ may be fixed within the intramedullary nail  104 ′ via a pin  137 ′ that is inserted into the intramedullary nail  104 ′ and the recess  124 ′. The locking mechanism  106 ′ is substantially similar to the locking mechanism  106  and may be used in the device  100  in substantially the same manner. The recess  124 ′ may be formed on an outer surface  125 ′ of the pawl member  105 ′ and may include a first portion  142 ′, a second portion  144 ′ and a third portion  146 ′. The first portion  142 ′ extends longitudinally along a portion of the outer surface  125 ′ from an edge  156 ′ of the pawl member  105 ′ to a proximal end  148 ′ of the first portion  142 ′. The second portion  144 ′ extends substantially horizontally along a portion of the outer surface  125 ′ from the proximal end  148 ′ of the first portion  142 ′ to an opposite end  150 ′. The third portion  146 ′ extends from the end  150 ′ longitudinally along the outer surface  140 ′ in a distal direction. The first portion  142 ′, the second portion  144 ′ and the  146 ′ are connected such that they form a single continuous recess  124 ′. 
     The intramedullary nail  104 ′ includes a hole  136 ′ extending laterally through one side of the intramedullary nail  104 ′, distally of an oblique opening  108 ′ such that a positioning of the hole  136 ′ corresponds to position of the recess  124 ′. The hole  136 ′ is adapted and configured to receive the pin  137 ′ therethrough. A length of the pin  137 ′ may be slightly longer than a thickness of the intramedullary nail  104 ′. The thickness is determined by a distance from an outer surface  109 ′ of the intramedullary nail  104 ′ to a channel  110 ′ of the intramedullary nail  104 ′, which extends longitudinally therethrough. Thus, when the pin  137 ′ is inserted through the hole  136 ′ such that a proximal end  152 ′ of the pin  137 ′ is flush with the outer surface  109 ′, a distal end  154 ′ of the pin  137 ′ extends into the channel  110 ′ for engaging the recess  124 ′. The hole  136 ′ may be substantially circular such that the intramedullary nail  104  remains substantially stationary while the locking mechanism  106 ′ moves relative to the intramedullary mail  104 ′ along the longitudinal axis. 
     To fix the locking mechanism  106 ′ within the intramedullary nail  104 ′, a biasing member  140 ′ of the locking mechanism  106 ′ may be inserted into the channel  110 ′ along with the pawl member  105 ′ such that the biasing member  140 ′ urges the pawl member  105 ′ into a position of contact with an implant (not shown) that is inserted into the opening  108 ′. The pawl member  105 ′ is inserted distally into the channel  110 ′ until the distal end  154 ′ of the pin  137 ′ that is inserted into the hole  136 ′ engages the first portion  142 ′ of the recess  124 ′ via the edge  156 ′ of the first portion  142 ′. The pawl member  105 ′ is pressed further distally against the urging of the biasing member  140 ′ such that the first portion  142 ′ slides along the pin  137 ′ until the proximal end  148 ′ of the first portion  142 ′ is in contact with the pin  137 . The pawl member  105 ′ may then be rotated about a longitudinal axis thereof such that the second portion  144 ′ slides along the pin  137 ′ until the pin  137 ′ is contacting the opposite end  150 ′ of the second portion  144 ′. Upon reaching the opposite end  150 ′, the pawl member  105 ′ may be released, the biasing member  140 ′ urging the pawl member  105 ′ in a proximal direction such that the third portion  146 ′ slides along the pin  137 ′ until the pin  137 ′ engages a distal end  158 ′ of the third portion  146 ′. Thus, it will be understood by those of skill in the art that once the locking mechanism  106 ′ is fixed within the intramedullary nail  104 ′, the locking mechanism  106 ′ is movable along the longitudinal axis to engage the implant, as described in regard to the device  100 . Longitudinal movement of the locking mechanism  106 ′ results in sliding of the third portion  146 ′ longitudinally along the distal end  154 ′ of the pin  137 ′. 
     In a first configuration, shown in  FIGS. 4-5 , when no implant  102  is present in the opening  108 , the implant engaging surface  130  substantially aligns with a wall of the oblique opening  108  while the pawl  126  and the protrusion  128  extend into the oblique opening  108 . Then, as an implant  102  is inserted into the opening  108 , contact between the implant  102  and the ramped surface  134  forces the pawl member  105  into the channel  110  to a second configuration in which the protrusion  128  is moved into the channel  110  to a second configuration shown in  FIGS. 6 and 7  to allow the implant  102  to be advanced medially through the opening  108 . The pawl member  105  is constrained so that it does not move further into the opening  108  than desired (i.e., beyond a desired first configuration), by a pin  135  passing through an opening  136  in the intramedullary nail  104 , and through an elongated opening  124  in the pawl member  105 . As described above, when the implant  102  has been inserted to a desired position in the bone, the implant  102  is rotated about its axis until the groove  118  aligns with the protrusion  128 . At this point the biasing member  140  moves the pawl member  105  back to the first configuration with the protrusion  128  received within the slot  118  and the pawl  126  engaging one of the abutting structures  116  of the implant  102  corresponding to the desired maximum insertion of the implant  102  into the bone. Thereafter, as forces are applied to the implant  102  (e.g., as weight is placed on the bone), the implant  102  may move laterally as ramped surfaces  117  slide over the pawl  126 . The abutting surface  119  engages the pawl  126  preventing any further movement medially. In addition, as each abutting surface  119  moves laterally past the pawl  126 , a new medial-most position of the implant  102  is defined. 
     The intramedullary nail  104  may further include a shoulder  138  within the channel  110  positioned below the oblique opening  108 . A reduced diameter shaft  120  extends from an end of the pawl member  105  to a shoulder  122  at an end of an upper portion of the pawl member  105 . The biasing member  140  is received between the shoulder  122  and the shoulder  138  of the channel  110  to urge the pawl member  105  toward the opening  108 . A diameter of a portion of the channel  110  closer to the opening  108  than the shoulder  138  is larger than a diameter of the portion of the channel  110  extending past the shoulder  138  away from the opening  108 . It will be understood by those of skill in the art that the diameters of these portions the channel  110  correspond to the diameters of the proximal end  118  of the pawl member  105  and the shaft  120 , respectively. 
     In use, the intramedullary nail  104  is inserted into an intramedullary canal (e.g., of a femur) with a central axis of the oblique opening  108  substantially aligned with a central axis of the femoral neck. It will be understood by those of skill in the art that the intramedullary nail  104  may be inserted into the bone using any accepted insertion method. For example, a guidewire may be inserted into the medullary canal of the longitudinal shaft and the intramedullary nail  104  slid therealong. Thus, it will also be understood by those of skill in the art that the intramedullary nail  104  and the locking mechanism  106  housed therewithin may also include a guide wire lumen along the longitudinal axis thereof. Once the intramedullary nail  104  has been appropriately positioned, the implant  102  is inserted through the bone into the oblique opening  108  to a desired position and the implant  102  is rotated to return the locking mechanism  106  to the first configuration preventing further medial movement as described above. 
     If it becomes necessary to remove the implant  102  for any reason, however, the implant  102  may be rotated about the central axis of the oblique opening  108 , as shown in  FIG. 11  to move the protrusion  128  out of the groove  118  and force the pawl member  105  back to the first configuration. At this point the locking mechanism  106  is disengaged from the abutting structures  116  of the implant  102  and the implant  102  may be slid entirely out of the opening  108  even after the protrusion  128  is located distally beyond the distal end of the groove  118 . If the bone engaging structure of the implant  102  is formed as a helical blade, those skilled in the art will understand that this structure may be rotatably coupled to the shaft  112  of the implant  102  so that the engagement between the locking mechanism  106  and the abutting structures  116  of the implant  102  is maintained. Thus, any rotation of the helical blade during insertion would not require a corresponding rotation of the shaft  112 . However, it will be understood by those of skill in the art that the bone engaging structure of the implant  102  may be any known capable of securing the femoral head and neck to the shaft through engagement of an intramedullary nail  104 . 
     As shown in  FIGS. 12-18 , a device  200 , according to another embodiment of the present invention comprises an implant  202  and an intramedullary nail  204  with a locking mechanism  206  housed therewithin. The device  200 , as shown in  FIG. 12 , is substantially similar to the device  100  described above including a biasing member  240  (e.g., a spring) moving the locking mechanism  206  within a channel  210  of the nail  204  along a longitudinal axis of the nail  204 . The locking mechanism  206  also moves between first and second configurations in which a pawl  226  is brought into and out of the opening  208  to engage and disengage abutting structures  216  of the implant  202 . 
     However, the pawl member  205  of the locking mechanism  206  does not include a protrusion similar to the protrusion  128  for engaging the implant  202  and moving the pawl member  205 . The implant  202  may be substantially similar to the implant  102  except that no groove similar to the groove  118  is provided. Rather, a shaft  212  of the implant  202  may include a plurality of notches  218  extending longitudinally along a portion of a length thereof and separated from one another around the circumference of the shaft  212  by a distance corresponding to a separation of a pair of notch engaging wings  228  extending from an implant engaging surface  230  of the pawl member  205 . Thus a first one of the wings  228  is received within a corresponding one of the notches  218 . When the wings  228  are received in the notches  218 , the abutting structures  216  of the implant  202  are aligned with the pawl  226  of the pawl member  205 . Engagement between the wings  228  and the notches  218  prevents the shaft  212  from rotating within the opening  208 . As shown in  FIG. 14 , the locking mechanism  206  may be substantially similar to the locking mechanism  106  with the pawl  226  extending from the implant engaging surface  230  and engaging the abutting structures  216  to prevent medial movement of the implant  202  beyond a defined medial-most position. 
     The locking mechanism  206  includes a laterally facing hole  246  which is aligned with a corresponding opening  250  adjacent to the lateral end of the opening  208  so that a tool may be inserted therethrough to engage the pawl member  205  and move it manually between from the first configuration, shown in  FIGS. 15-16 , to the second configuration, shown in  FIGS. 17-18 . The hole  246  may include a ramped surface  248  so that when a pin  252  is inserted into the hole  246  via the hole  250 , the pin  252  slidingly engages the ramped surface  248  pushing the pawl member  205  further into the channel  210  disengaging the locking mechanism  206  from the abutting structures  216  to permit insertion and/or withdrawal of the implant  202  from the opening  208  to the second configuration. It will be understood by those of skill in the art that the ramped surface  248  enables the size of the hole  246  to be minimized so that the hole  248  does not need to extend into an elongated hole  224  of the locking mechanism  206  which engages a pin (not shown) in the same manner as the pin  135  of the device  100  to prevent the pawl member  205  from moving into the opening  208  beyond the first configuration. 
     The device  200  may be employed in substantially the same manner as the device  100  as described above. However, when inserting the implant  202  through the nail  204 , the pin  252  is inserted into the hole  246  of the locking mechanism  206  via the hole  250  to move the locking mechanism  206  to the second configuration. The implant  202  is then inserted to the desired position in substantially the same manner described above and the pin  252  is removed to allow the pawl member  205  to return to the first configuration through the bias of the biasing member  240  to lock the locking mechanism  206  to the abutting structures  216  and prevent further medial movement of the implant  202 . As with the device  100 , the shape of the abutting structures  216  allows the implant  202  to move laterally over the pawl  226 . 
     As shown in  FIGS. 19-27 , a device  300  according to another embodiment of the invention comprises an implant  302  and an intramedullary nail  304  with a locking mechanism  306  housed therewithin. The device  300 , as shown in  FIGS. 19-20  is substantially similar to the devices  100 ,  200  described above except as specifically indicated below. The implant  302  is also substantially similar to the implant  102 , including a shaft  312  with a plurality of abutting structures  316  and a longitudinal groove  318 . Similarly to the intramedullary nail  104 , the intramedullary nail  304  includes an oblique opening  308  for receiving the implant  302 . However, a channel  310  of the intramedullary nail  304  in which the locking mechanism  306  is housed extends proximally from the oblique opening  308  toward a proximal end of the intramedullary nail  304 . 
     As shown in  FIGS. 21-22  a pawl member  305  of the locking mechanism  306  is further comprised of a first element  318  and a second element  320 . The first element  318  may be coupled to the second element  320  such that the first element  318  and the second element  320  are movable relative to one another both along and about a longitudinal axis. As shown in  FIGS. 23-24 , the first element  318  includes a head portion  360 , a shaft  362  and a ball  372  at a distal end  366  of the shaft  362  configured to engage a correspondingly shaped recess in the second element  320 . A diameter of the ball  372  may be larger than a diameter of the shaft portion  362 . 
     The head portion  360  extends proximally from a proximal end  364  of the shaft  362  and includes threading  368  around an outer surface thereof. The head portion  360  further includes a driving structure  376  at a proximal end  370  thereof configured to receive a driving tool. For example, the driving structure  376  may be a hexagonal recess configured to receive a hexagonally shaped bit of a driving tool. It will be understood by those of skill in the art, however, that the driving structure  376  may take any of a variety of shapes and sizes so long it is configured to receive a tool capable of rotating the first element  318  relative to the second element  320  and the intramedullary nail  304 . An annular groove  322  formed in a distally facing surface at a distal end  374  of the head portion  360  receives a proximal end  344  of a biasing member  340  (e.g., a spring). The biasing member  340  may extend around the shaft  362  of the first element  318 . The first element  318  may also include a lumen  378  extending longitudinally therethrough, to accommodate instruments such as reaming rods or guidewires, etc. 
     As shown in  FIGS. 25-26 , the second element  320  extends from a proximal end  380  to a distal end  382  and includes a space  346  in a central portion thereof sized and shaped to accommodate the ball  372  of the first element  318  to form a ball and socket joint. The proximal end  380  includes a hole  384  that extends into the space  346  to accommodate the shaft portion  362  when the ball  372  is received within the space  346 . The second element  320  may further include an opening  348  along a portion of an outer surface  386  of the second element  320  such that the ball  372  may be snapped into the space  346  via the opening  348 . The opening  348  should be smaller than a diameter of the ball  372  so that the second element  320  must be slightly deformed to snap the ball  372  thereinto and the ball  372  may not become easily disengaged therefrom. 
     The distal end  382  includes a first protrusion  326  for engaging the abutting structures  316  and a second protrusion  328  for engaging the longitudinal groove  318 . An angled surface  325  of the first protrusion  326  may be formed substantially parallel to the angle of ramped surfaces  317  of each of the abutting structures  316  to minimize resistance to the proximal sliding of the abutting structures  316  over the protrusion  326 . As with the prior embodiments, contact between an abutting surface  327  of the protrusion  326  and an abutting surface  319  of any of the abutting structures  316  prevents the implant  302  from moving medially beyond an initially set medial-most position. The second protrusion  328  is sized and shaped to be received within the longitudinal groove  318  such that the longitudinal groove  318  may slide therealong. The first and the second protrusions  326 ,  328  may be positioned on opposite sides of one another relative to the longitudinal axis of the implant  302  such that engagement of the first protrusion  326  with the plurality of notches  316  and engagement of the second protrusion  328  with the longitudinal groove  318  prevents rotation of the shaft  312  of the implant  302  about a longitudinal axis of the opening  308 . The proximal end  380  of the second element  320  may also include a groove  338  surrounding the opening  384  for receiving a distal end  342  of the biasing member  340  so that the biasing member  340  urges the second element  320  into contact with the implant  302 . 
     The second element  320  further includes a longitudinal element  388  extending from the outer surface  386  along at least a portion of a length of the second element  320 . As shown in  FIG. 27 , the longitudinal element  388  may be configured to be slidable within a longitudinal slot  390  within the channel  310  of the intramedullary nail  304  such that the second element  320  and the intramedullary nail  304  are movable relative to one another along the longitudinal axis, but incapable of rotating relative to one another about the longitudinal axis. 
     The implant  302  may be inserted into the oblique opening  308  of the intramedullary nail  304  until the implant  302  is in a desired position relative to the nail  304  and the bone. Once a desired position had been reached, the assembled locking mechanism  306  may be inserted into the channel  310  of the intramedullary nail  304  by aligning the longitudinal element  388  with the longitudinal slot  390  such that the locking mechanism  306  may be slid longitudinally through the nail  304 . The driving tool may then be inserted into the driving means  376  to drive the locking mechanism  306  a desired distance into the channel  310  by rotating the first element  318  relative to the second element  320  as would be understood by those skilled in the art. Thus, the channel  310  may include a threading (not shown) corresponding to the threading  366  of the first element  318  such that the first element  318  and the channel  310  may engage one another. As the first element  318  rotates about the longitudinal axis, the first element  318  pushes the second element  320  further into the channel  310 . The locking mechanism  306  may be driven into the channel  310  until the distal end  382  of the second element  320  contacts the shaft  312  of the implant  302 . 
     The implant  302  should be positioned such that upon contact of the locking mechanism  306  with the shaft  312 , the first protrusion  326  engages one of the abutting structures  316  corresponding to the desired medial-most position of the implant  302  and the second protrusion  328  engages the longitudinal groove  318 . As with the previously described embodiments, after the implant  302  has been engaged by the locking mechanism  306 , the implant  302  may move laterally relative to the opening  308  but is prevented from moving medially by contact between the abutting surface  327  of the protrusion  326  and the abutting surface  319  of the corresponding abutting structure  316  of the implant with the biasing member  340  operating to maintain the required contact between the protrusion  326  and the corresponding abutting structure  316 . 
     As shown in  FIGS. 28-34 , a device  400  according to a further embodiment of the invention may be substantially similar to the device  300 , but in addition to being comprised of an implant  402  and intramedullary nail  404 , a ratchet mechanism thereof comprises first and second portions  406  and  492 , respectively, on opposite sides of the implant  402  from one another. As shown in  FIG. 28 , the implant  402  includes a shaft  412  including a plurality of abutting structures  416  distributed along a portion of a length of the shaft  412 . Similarly to the implants  102 ,  202  and  302 , each of the abutting structures  416  is angled toward a proximal end  414  of the shaft  412  with a distal facing abutting surface  419  which, in a first configuration, engages a pawl of the second portion  492  of the locking mechanism to prevent movement of the implant  402  medially after an initial position of the implant  402  is set (e.g., upon implantation) while allowing lateral migration of the implant  402 . 
     The intramedullary nail  404  may be substantially similar to the intramedullary nail  304 , except that a channel  410  extends across the oblique opening  408  from a proximal end  494  proximal of the opening  408  to a distal end  496  distal of the oblique opening  408 . The first portion  406  of the locking mechanism is housed in the portion of the channel  410  extending proximal of the oblique opening  408  while the second portion  492  is housed in the portion of the channel  410  distal of the oblique opening  408 . 
     Similarly to the locking mechanism  306 , the first portion  406  includes a first element  418  couplable to a second element  420  with a biasing member  440  held therebetween in a groove  422  of the first element  418  and a groove  438  of the second element. The first element  418  and the second element  420  may be coupled to one another via ball  472  of the first element  418  which is insertable into a space  446  of the second element  420 , as shown in  FIG. 33 . The second element  420 , however, includes an elongated protrusion  428  extending from a distal end  482  of an outer surface  486  of the second element  420  radially outside a circumference of the opening  408 . The elongated protrusion  428  is longer than a diameter of the oblique opening  408  such that, when the locking mechanism  306  is moved longitudinally through the channel  410  from a first configuration to a second configuration, the elongated protrusion  428  crosses the opening  408  to operate the second portion  492  of the locking mechanism causing the second portion  492  to pivot. Specifically, the distal end  482  remains proximal to the opening  408  at all times while the protrusion  428  extends along and outside the opening  408  to reach the second portion  492 . In the first configuration, as shown in  FIGS. 29-30 , the first portion  406  of the locking mechanism is positioned within the channel  410  with the elongated protrusion  428  separated from the second portion  492 . As shown in  FIGS. 31 and 32 , when moved into the second configuration, the first portion  406  of the locking mechanism moves distally though the channel  410  moving the elongated protrusion  428  distally past the oblique opening  408  to pivot the second portion  492  so that a pawl  426  protruding from an implant facing surface  430  of the second portion  492  engages the abutting structure  416  corresponding to the desired medial-most position of the implant  402 . 
     As shown in  FIG. 34 , the second portion  492  is sized and shaped to fit within the portion of the channel  410  extending distally of the opening  408 . A proximal surface  430  thereof may be angled to substantially align with a surface of the oblique opening  408  when in the first configuration. The second portion  492  is rotatably mounted in the channel  410  including, for example, a hole  424  for receiving a pin (not shown) inserted via a corresponding hole  436  in the intramedullary nail  404 . The second portion  492  rotates about the pin when contacted by the protrusion  428  so that the pawl  426  pivots into the opening  408  to engage the abutting structures of the implant  402 . To bias the second portion  492  toward the first configuration in which the pawl  426  remains outside the oblique opening  408 , the device  400  further comprises a biasing member lumen  498  within the intramedullary nail  405  and a biasing member  500 . The biasing member  500  may be housed within the lumen  498  such that a proximal end  502  of the biasing member  500  abuts the distal end  431  of the second portion  492  while a distal end  504  of the biasing member  500  abuts a distal end  506  of the lumen  498 . Thus, the second portion  492  is biased toward the first configuration at all times except when the elongated protrusion  428  presses the implant facing surface  430  of the second portion  492  to the second configuration. 
     The device  400  may be used in substantially the same manner as the devices  100 ,  200  and  300 . Upon positioning of the intramedullary nail  404  within the femoral shaft, the implant  402  may be inserted through the oblique opening  408  of the intramedullary nail while the first and second portions  406 ,  492 , respectively, of the locking mechanism are in the first configuration—i.e., with neither the elongated protrusion  428  nor the pawl  426  extending into the opening  408 . After the implant  402  has been inserted through the opening  408  to a desired position in the bone, the first portion  406  is moved into the second configuration in the same manner described above for the device  300  to move the elongated protrusion  428  distally until it presses against the implant facing surface  430  of the second portion  492 , pivoting the second portion  492  and moving the pawl  426  into the oblique opening  408  to engage the abutting structure  416  corresponding to the desired position of the implant  402  and defining a medial-most position for the implant  402 . As described above, the geometry of the abutting structures  416  is selected to permit lateral migration of the implant  402  through the opening  408 . 
     As shown in  FIGS. 35-41 , a device  600  according to yet another embodiment of the invention may be substantially similar to the device  300  except as specifically described below. As shown in  FIG. 35 , the device  600  comprises an implant  602 , an intramedullary nail  604  and a locking mechanism  606 . As shown in  FIG. 36 , the implant  602  includes a shaft  612  with a single recessed and tapered surface  616  as opposed to the plurality of abutting surfaces as described above in regard to implant  302 . The tapered surface  616  extends from a proximal end  614  to a distal end  615  with a taper of the surface  618  increasing from the proximal end  614  to the distal end  615  so that a length of a wall  614 ′ at the proximal end  614  is less than a length of a wall  615 ′ at the distal end  615 . The tapered surface  616  is adapted and configured to receive a portion of the lock mechanism  606 . The intramedullary nail  604  may be substantially similar to the intramedullary nail  304 , including an oblique opening  608  for receiving the implant  602  and a channel  310  for housing the locking mechanism  606  therein, proximally of the oblique opening  608  toward a proximal end of the intramedullary nail  604 . 
     As shown in  FIGS. 37-38 , the locking mechanism  606  may be substantially similar to the locking mechanism  306  of the device  300 . Similarly, the lock mechanism  606  includes a first element  618  couplable to a second element  620  with a biasing member  640  (e.g., a spring) held therebetween. In addition to the biasing member  640 , the lock mechanism  606  further includes a canted plate  692  held between a distal end  642  of the of the biasing member  640  and a proximal end  680  of the second element  620  selectively preventing movement of the second element  620  toward the first element  618 . Specifically, the canted plate  692  includes an opening  698  therethrough closely matching in size and shape an outer surface of a shaft  662  of the first element  618  so that, when the canted plate  692  is angled away from a plane substantially perpendicular to a longitudinal axis of the shaft  662 , frictional engagement between a perimeter of the opening  698  and the outer surface of the shaft  6662  prevents relative movement between the first element  618  and the second element  620 . The first element  618  is substantially similar to the first element  318 , including a head portion  660  at a proximal end of the shaft  662  and a coupling element  672  at a distal end  666  thereof configured to engage a correspondingly shaped recess in the second element  620 . A threading of the head portion  660  may engage an inner surface of the intramedullary nail  604  in the same manner described above. 
     The second element  620  may be substantially similar to the second element  320 , extending from a proximal end  680  to a distal end  682  and including a space  646  in a central portion thereof for slidably accommodating the coupling element  672  of the first element  618  to permit relative movement therebetween along a longitudinal axis of the intramedullary nail  604 . In place of the first and second protrusions of the previous embodiments, the second element  620  includes a single elongate protrusion  626  engaging the tapered surface  616  of the implant  602 . The elongate protrusion  626  extends from the distal end  682  of an outer surface  686  of the second element  620  and tapers to a reduced thickness toward a distal tip  626  thereof. A taper of the elongate protrusion  626  may be selected so that the thin distal tip  626  may be received within the thinner distal end  615  of the tapered surface  616  with the increasing depth of the tapered surface  616  permitting the progressively thicker more proximal portions of the protrusion  626  to enter into engagement with the tapered surface  616  as the implant  602  is advanced distally through the nail  604 . The tapered surface  616  may be formed so that, when the implant  602  has been advanced a desired distance through the nail  604 , the protrusion  626  is fully received against the tapered surface  616  adjacent to the proximal end  614  thereof locking the implant  602  in a distal-most permitted position. Specifically, as the biasing member  640  moves the second element  620  distally urging the protrusion  626  further into engagement with the tapered surface  616 , the canted plate  692  acts as a locking preventing the second element  620  from being moved proximally back toward the first element  618 . This maintains the thicker proximal portion of the protrusion  626  in engagement with the tapered surface  616  preventing distal movement of the implant  602  relative to the nail  604  as the thickness of the proximal portion of the protrusion  626  exceeds a depth of the more distal portion of the tapered surface  616 . A length of the elongate protrusion  626  is substantially equal to or greater than a diameter of the oblique opening  608  such that an entire width of the tapered surface  616  of the implant  602  may be engaged by a contacting surface  625  of the elongate protrusion  626 . 
     The implant  602  may be inserted through the opening  608  into a desired position within the bone. During insertion of the implant  602 , the locking mechanism  606  is in a first position within the intramedullary nail  604  in which the elongate protrusion  626  does not extend into the opening  608 . Once the implant  602  has been inserted through the opening  608  to the desired position, the locking mechanism  606  is driven distally through the channel  610  to a second position in which the elongate protrusion  626  contacts the implant  602  and the contacting surface  625  abuts the recessed and tapered portion  616 . Thus, it will be understood by those of skill in the art that, when implanted to the desired depth within the bone, the tapered surface  616  of the implant  602  extends across the opening  608  of the intramedullary nail  604 . 
     Specifically, with the locking mechanism  606  in the second position, the device  600  is in an initial implanted position, as shown in  FIG. 39  with a distal portion of the contacting surface  625  abutting the tapered surface  616 . Due to the increasing taper of the tapered surface  616  distally along the shaft  612  and the biasing member  640  which biases the second element  620  of the locking mechanism  606  to move away from the first element  618  along a longitudinal axis of the intramedullary nail  604 , the implant  602  is permitted to migrate proximally through the opening  608  while maintaining contact between the contacting surface  625  and the tapered surface  616  toward a final proximal-most position, as shown in  FIG. 40 . The final position is reached after the implant  602  has moved laterally through the opening  608  until a width of the distal end  615  of the tapered surface  616  is contacted by the contacting surface  625 . As the implant  602  moves laterally through the opening  608 , the biasing member  640  pushes the second portion  620  of the locking mechanism distally such that the elongate protrusion  626  maintains constant contact with the tapered surface  616 . 
     At all times until and after the implant  602  reaches the final implanted position, the implant  602  is prevented from moving medially through the opening  608  via the canted plate  692  which locks the locking mechanism  606  preventing the second portion  620  from moving proximally within the channel  610  toward the first element  618  which is fixed within the intramedullary nail  604 . As shown in  FIG. 41 , the canted plate  692  includes a first portion  694  and a second portion  696  angled relative to one another, substantially perpendicularly of one another. As described above, the second portion  696  includes an opening  698  extending therethrough with a proximal surface of the canted plate  692  engaging a distal end  642  of the biasing member  640  while a distal end  700  of the first portion  694  engages a proximal surface  680  of the second element  620  with the shaft  662  of the first element  618  received through the opening  696 , a surface of the second portion  696  abutting the distal end  642  of the biasing member  640 , while an edge  700  of the first portion  694  abuts the proximal end  680  of the second portion  620 . The opening  698  is only slightly larger than a perimeter of the shaft  662  such when the implant  602  attempts to move medially through the oblique opening  608 , the implant  602  pushes the second portion  620  in a direction P, angling the second portion  696  relative to the shaft  662  and bringing an Inner surface  702  of the opening  698  into contact with an outer surface  704  of the shaft  662  preventing the shaft  662  from sliding therethrough and preventing the second portion  620  from moving in the direction P. 
     The device  600  may be used in substantially the same manner as described above in regard to the device  300 . Once the intramedullary nail  604  has been positioned in an intramedullary canal of a bone, the implant  602  may be inserted medially through the oblique opening  608  until the implant  602  is in the desired position in the bone. As the implant  602  is being inserted through the opening  608 , the locking mechanism  606  is maintained in the first position with the elongate protrusion  626  held proximally above the opening  608 , leaving a clear path for the insertion of the implant  602  therethrough. After the implant  602  has reached a desired distal-most position in the bone with the tapered surface  616  extending across the opening  608  of the intramedullary nail  604 , the locking mechanism  606  is driven distally into the intramedullary nail  604  until the elongate protrusion  626  extends into the opening  608  with the contacting surface  625  in engagement with the tapered surface  616  of the implant  602  in the second position. Even after the implant  602  is within the opening  608  in the initial implanted position, the implant  602  move proximally through the opening  608  while distal movement relative to the nail  604  is substantially prevented. However, once the implant  602  has reached the final implanted position, the implant  602  is prevented from further movement proximally and distally relative to the nail  604  as described above. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the structure and the methodology of the present invention, without departing from the spirit or scope of the invention. Thus, it is intended that present invention cover the modifications and variations of this invention provided that they come within the scope of the appended claims and their equivalents.