Abstract:
Apparatus for treating a fracture of a bone of a subject including an intramedullary (IM) nail insertable into a medullary canal of the bone of the subject. The IM nail has a proximal head that defines at least one hole therethrough. A sleeve, which includes a locking mechanism, is engaged with the hole when the sleeve is inserted in the hole. This engagement prevents rotational movement between the sleeve and the nail and inward and outward longitudinal movement of the sleeve relative to the nail.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Continuation Application of U.S. application Ser. No. 10/616,218 filed Jul. 8, 2003 now U.S. Pat. No. 7,455,673, the entire contents of which are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to apparatus for treating femoral fractures, and specifically to apparatus for coupling bone portions across a fracture. 
     BACKGROUND OF THE INVENTION 
     Intramedullary (IM) nails are implantable devices used to stabilize fractures and allow for bone healing. IM nails are inserted into the medullary canal of the long bones of the extremities, e.g., the femur or tibia. Currently-used IM nails have a head region that generally includes at least one hole, transverse to the longitudinal axis of the nail, for receiving anchoring means, such as a screw, to secure the nail within the medullary canal of the bone. Some such anchoring means include at least one sleeve, which passes through the transverse hole, and through which a screw assembly typically passes freely. A proximal end of the head region protrudes from the proximal end of the bone, to facilitate post-implantation access to the IM nail, if desired. The proximal end of the head region, which protrudes from the bone, is a continuous extension of the head region, not structurally or visually distinct from the more distal portion of the head region that includes the holes. 
     U.S. Pat. No. 4,827,917 to Brumfield, which is incorporated herein by reference, describes an IM system including a screw and an intramedullary rod. The screw has a threaded portion and a smooth portion, and the rod has a head, stem and a longitudinal bore. There is at least one pair of coaxial holes through the stem, transverse to the longitudinal axis of the rod, for receiving first anchoring means, such as a nail, screw or bolt, to secure the rod within the marrow canal of the femur. There are at least a proximal pair of coaxial holes and a distal pair of coaxial holes in the head of the rod in an angled direction toward the femoral head relative to the longitudinal axis of the rod. The distal pair of head holes is adapted to slidingly receive the screw so as to permit the threaded portion of the screw, in use, to engage the femoral head and to allow sliding compression of a femoral neck or intertrochanteric fracture. 
     U.S. Pat. No. 5,032,125 to Durham et al., which is incorporated herein by reference, describes an IM hip screw that includes an IM rod, a lag screw and a sleeve for slidably receiving the lag screw. The sleeve is received in a passage in the IM rod having an axis positioned at an angle relative to the longitudinal axis of the IM rod such that the axis of the sleeve is directed toward the head of the femur. The IM hip screw is described as permitting sliding compression of selected fractures, particularly intertrochanteric fractures and fractures of the femoral neck. 
     U.S. Pat. No. 6,235,031 to Hodgeman et al., which is incorporated herein by reference, describes an IM system that includes an IM rod, a lag screw, and a lag screw collar. The rod has a proximal end with a transverse bore extending therethrough. The lag screw has a distal end with coarse bone engaging thread elements and a proximal end with screw threads. When in use, the lag screw is substantially axially aligned with the transverse bore of the rod. The lag screw collar has an outer diameter sized to rotatably fit within the transverse bore of the rod. The collar also has an inner diameter and internal screw threads adapted to cooperate with the screw threads of the proximal end of the lag screw. The lag screw collar may have an increased outer diameter at one end thereof which is at least slightly larger than a diameter of the transverse bore of the rod. 
     U.S. Pat. No. 6,443,954 to Bramlet et al., which is incorporated herein by reference, describes an IM system that includes a lag screw assembly extending through a radial bore in an IM nail. The lag screw is inserted into one portion of a bone and deployed to fix the leading end. The IM nail is placed in the IM canal of a portion of the bone and the trailing end of the lag screw assembly is adjustably fixed in the radial bore to provide compression between the lag screw assembly and the IM nail. The IM nail has a cap screw in the proximal end holding the lag screw assembly and a tang in the distal end. The tang has legs extending through the nail to fix the distal end in the IM canal. 
     U.S. Pat. No. 6,648,889 to Bramlet et al., which is incorporated herein by reference, describes an IM system that includes an IM nail for insertion in the femur. The nail has an axial bore and an intersecting transverse bore. A lag screw is inserted through the transverse bore and turned into the head of the femur. A slotted sleeve is inserted over the lag screw and through the transverse bore with the slots aligned with the axial bore. A sleeve lock is inserted into the axial bore, and has a locking tab which engages the slots in the sleeve preventing rotational movement between the sleeve and the nail and longitudinal movement of the sleeve relative to the nail. A compression screw is turned into the trailing end of the lag screw and engages the encircling sleeve to provide longitudinal translation between the lag screw and sleeve to apply compressive force across a fracture. 
     U.S. Pat. No. 6,926,719 to Sohngen et al., which is incorporated herein by reference, describes an IM nail having a modular configuration, including a nail member having a chamber formed on the proximal end thereof. An insert having at least one opening therein for receiving a bone screw or fastener is disposed within the chamber and is secured therein by a locking ring. Various inserts are described for use to achieve selected bone screw or fastener configurations. 
     European Patent Application Publication EP 0 521 600 to Lawes, which is incorporated herein by reference, describes an IM system that includes an IM rod having an angulated opening to receive a femoral neck screw having a threaded portion at its distal end, and locking means acting between the neck screw and the wall of the angulated opening to prevent relative rotation between the screw and the rod. 
     PCT Publication WO 02/083015 to Ferrante et al., which is incorporated herein by reference, describes an orthopedic screw having a screw head, a screw body with a distal tip, a shank with an enlarged diameter at the trailing end and a thread extending radially outward from the shank, and an internal capture surface. The screw is used with an orthopedic implant system, which includes an orthopedic implant and a driver capable of engaging the internal capture of the screw. 
     SUMMARY OF THE INVENTION 
     In some embodiments of the present invention, an intramedullary (IM) system for implantation in a medullary canal of a femur of a subject, comprises an IM nail having a head and a stem. The head of the IM nail defines at least one hole, which is oriented in an angled direction toward the femoral head relative to the longitudinal axis of the IM nail. The head hole is adapted to receive a sleeve, which is adapted to slidably receive a screw, so as to permit a threaded portion of the screw to engage a femoral head of the subject and to allow sliding compression of a femoral neck or intertrochanteric fracture. The sleeve comprises a locking mechanism, which engages the head hole, preventing rotational and longitudinal movement between the sleeve and the head hole. The locking mechanism typically comprises a depressible male coupling element, such as a tab, configured so that when the sleeve is inserted into the head hole and properly aligned, the tab engages a female coupling element, such as a notch, located on the inner surface of the head hole, thereby locking the sleeve to the head hole. 
     In some embodiments of the present invention, an IM system comprises an IM nail having a head and a stem. The head of the IM nail comprises a distal portion, which typically includes at least one head hole, and a proximal portion, having a diameter less than a diameter of the distal portion. For some applications, the diameter of the proximal portion is less than about 50% of the diameter of the distal portion. Such a narrower proximal portion typically allows greater regrowth and healing of the neck of the femur towards the area of the greater trochanter, than generally occurs upon implantation of conventional IM nail heads. At the same time, because a proximal end of the narrower proximal portion generally remains easily locatable on the external surface of the femur in the area of the tip of the greater trochanter or the piriformis, a surgeon typically can readily locate the IM nail if post-operative access to the implant becomes necessary. For some applications, the IM system further comprises the sleeve locking mechanism described hereinabove. 
     In some embodiments of the present invention, an IM locating tool is provided for locating an IM nail, a proximal portion of which does not extend to the surface of the femur. Without the use of this IM locating tool, it is sometimes difficult for a surgeon to locate such an IM nail if post-operative access to the implant becomes necessary. To use the locating tool, the surgeon temporarily couples one or more connecting elements of the locating tool to respective head holes of the IM nail. As a result, a proximal end of the locating tool is positioned directly over the site on the surface of the femur at which the surgeon should drill. 
     It is noted that use of the term “head” with respect to the IM nail is intended to distinguish at least a portion of the proximal end of the nail from the stem of the nail. In some embodiments, the head is separated by a neck region from the stem, while in other embodiments, the head and stem are generally continuous. 
     There is therefore provided, in accordance with an embodiment of the present invention, apparatus for treating a fracture of a bone of a subject, including: 
     an intramedullary (IM) nail, adapted to be inserted in a medullary canal of the bone of the subject, and including a proximal head that defines at least one hole therethrough; and 
     a sleeve, including a locking mechanism, which locking mechanism is adapted to engage the hole when the sleeve is inserted in the hole, such engagement preventing rotational and longitudinal movement between the sleeve and the hole. 
     In an embodiment, the apparatus includes a screw, and the sleeve is adapted to slidably receive the screw. 
     In an embodiment, the proximal head is shaped so as to define a female coupling element located on a surface of the hole, and the locking mechanism includes a depressible male coupling element, configured to engage the female coupling element so as to prevent the rotational and longitudinal movement. For some applications, the female coupling element is shaped to define a notch. For some applications, the male coupling element includes a tab. For some applications, the depressible male coupling element is adapted to engage the female coupling element when the sleeve is inserted in the hole to a fixed depth and then rotated until the depressible male coupling element engages the female coupling element. 
     There is also provided, in accordance with an embodiment of the present invention, apparatus for treating a fracture of a bone of a subject, including an intramedullary (IM) nail, adapted to be inserted in a medullary canal of the bone of the subject, the IM nail including a proximal head having a distal portion and a proximal portion, the distal portion having a distal diameter, and the proximal portion having a proximal diameter less than or equal to about 80% of the distal diameter. 
     For some applications, the proximal diameter is less than or equal to about 50% of the distal diameter. For some applications, the proximal diameter is equal to between about 5 mm and about 10 mm and the distal diameter is equal to between about 11 mm and about 17 mm. For some applications, a length of the proximal portion is equal to between about 10% and about 50% of a length of the distal portion. 
     In an embodiment, the distal portion defines at least one hole therethrough, and including a sleeve, which includes a locking mechanism, which locking mechanism is adapted to engage the hole when the sleeve is inserted in the hole, such engagement preventing rotational and longitudinal movement between the sleeve and the hole. 
     There is further provided, in accordance with an embodiment of the present invention, apparatus for treating a fracture of a bone of a subject, including an intramedullary (IM) nail, adapted to be implanted in the bone, such that no portion of the IM nail extends to an external surface of the bone. 
     In an embodiment, the IM nail includes a proximal head that defines one or more proximal head holes therethrough, and including a locating device, which includes: 
     one or more connecting elements, fixed to a distal end of the locating device, the connecting elements adapted to be temporarily coupled to respective ones of the proximal head holes; and 
     a location indicating element, fixed to a proximal end of the locating device, the location indicating element adapted to indicate, when the connecting elements are coupled to the holes, a location on the external surface of the bone substantially directly over a location of a proximal end of the proximal head. 
     For some applications, the one or more connecting elements include exactly one connecting element. 
     For some applications, each of the one or more connecting elements includes a locking mechanism, adapted to engage one of the proximal head holes when the connecting element is inserted in the proximal head hole, such engagement preventing rotational and longitudinal movement between the connecting element and the proximal head hole. 
     In an embodiment, the apparatus includes one or more sleeves, adapted to be coupled to respective ones of the proximal head holes, and the one or more connecting elements are adapted to be coupled to the respective ones of the proximal head holes by being coupled to respective ones of the sleeves when the one or more sleeves are coupled to the respective ones of the proximal head holes. For some applications, each of the one or more sleeves includes a locking mechanism, adapted to engage one of the holes when the sleeve is inserted in the hole, such engagement preventing rotational and longitudinal movement between the sleeve and the hole. 
     In an embodiment, the IM nail includes a proximal head having a proximal end, the proximal head defining at least one hole therethrough, and defining a longitudinal channel, open to the hole and to the proximal end, and the apparatus includes a bendable, resilient elongated element, which includes a sharp tip, the element adapted to be inserted (a) into the hole, (b) through at least a portion of the channel, (c) through the proximal end of the proximal portion, and (d) through the bone, so as to indicate a location on the external surface of the bone substantially directly over the proximal end of the proximal head. For some applications, the tip includes a screw thread. Alternatively, the tip includes a drill bit. 
     There is yet further provided, in accordance with an embodiment of the present invention, apparatus for locating an intramedullary (IM) nail implanted in a bone of subject, the IM nail having a proximal head that defines one or more holes therethrough, the apparatus including: 
     one or more connecting elements, adapted to be disposed at a distal end of the apparatus, the connecting elements adapted to be temporarily coupled to respective ones of the holes; and 
     a location indicating element, fixed to a proximal end of the apparatus, the location indicating element adapted to indicate, when the connecting elements are coupled to the holes, a location on an external surface of the bone substantially directly over a location of a proximal end of the proximal head, when no portion of the IM nail extends to the external surface of the bone. 
     For some applications, the one or more connecting elements include exactly one connecting element. 
     In an embodiment, each of the one or more connecting elements includes a locking mechanism, adapted to engage one of the holes when the locking mechanism is inserted in the hole, such engagement preventing rotational and longitudinal movement between the connecting element and the hole. 
     In an embodiment, the apparatus includes one or more sleeves, adapted to be coupled to respective ones of the holes, and the one or more connecting elements are adapted to be coupled to the respective ones of the holes by being coupled to respective ones of the sleeves when the one or more sleeves are coupled to the respective ones of the holes. For some applications, each of the one or more sleeves includes a locking mechanism, adapted to engage one of the holes when the sleeve is inserted in the hole, such engagement preventing rotational and longitudinal movement between the sleeve and the hole. 
     There is still further provided, in accordance with an embodiment of the present invention, apparatus for treating a fracture of a bone of a subject, including an intramedullary (IM) nail, adapted to be inserted in a medullary canal of the bone of the subject, the IM nail including a proximal head having a distal portion and a proximal portion, the proximal portion visually discrete from the distal portion, the proximal portion adapted to aid in locating the IM nail, and the distal portion adapted to be coupled to at least one element. 
     For some applications, the distal portion is adapted to be coupled to the at least one element, the at least one element being selected from the list consisting of: a nail, a screw, a pin, and a sleeve. 
     In an embodiment, the distal portion defines at least one hole therethrough, and including a sleeve, which includes a locking mechanism, which locking mechanism is adapted to engage the hole when the sleeve is inserted in the hole, such engagement preventing rotational and longitudinal movement between the sleeve and the hole. 
     There is additionally provided, in accordance with an embodiment of the present invention, a method for treating a fracture of a bone of a subject, including: 
     inserting, in a medullary canal of the bone of the subject, an intramedullary (IM) nail having a proximal head that defines at least one hole therethrough; 
     inserting a sleeve in the hole; and 
     locking the sleeve to the hole by moving the sleeve within the hole, so as to prevent rotational and longitudinal movement between the sleeve and the hole. 
     There yet additionally provided, in accordance with an embodiment of the present invention, a method for treating a fracture of a bone of a subject, including inserting, in a medullary canal of the bone of the subject, an intramedullary (IM) nail having a proximal head having a distal portion and a proximal portion, the distal portion having a distal diameter, and the proximal portion having a proximal diameter less than or equal to about 80% of the distal diameter. 
     There is still additionally provided, in accordance with an embodiment of the present invention, a method for treating a fracture of a bone of a subject, including implanting an intramedullary (IM) nail in the bone, such that no portion of the IM nail extends to an external surface of the bone. 
     There is also provided, in accordance with an embodiment of the present invention, a method for locating an intramedullary (IM) nail implanted in a bone of subject, the IM nail having a proximal head that defines one or more holes therethrough, the method including temporarily coupling one or more connecting elements to respective ones of the holes, in a manner that brings a location indicating element to a position from which the location indicating element indicates a location on an external surface of the bone substantially directly over a location of a proximal end of the proximal head, when no portion of the IM nail extends to the external surface of the bone. 
     For some applications, the method includes coupling the connecting elements to the location indicating element. 
     There is further provided, in accordance with an embodiment of the present invention, a method for locating an intramedullary (IM) nail implanted in a bone of a subject, the IM nail having a proximal head that has a proximal end, the proximal head defining at least one hole therethrough, the method including inserting a bendable, resilient elongated element, having a sharp tip, 
     (a) into the hole, 
     (b) through at least a portion of a longitudinal channel defined by the proximal head, the channel open to the hole and to the proximal end, 
     (c) through the proximal end of the proximal portion, and 
     (d) through the bone, 
     so as to indicate a location on an external surface of the bone substantially directly over the proximal end of the proximal head, when no portion of the IM nail extends to the external surface of the bone. 
     There is yet further provided, in accordance with an embodiment of the present invention, a method for treating a fracture of a bone of a subject, including: 
     inserting, in a medullary canal of the bone of the subject, an intramedullary (IM) nail having a proximal head having a distal portion and a proximal portion, the proximal portion visually discrete from the distal portion; 
     positioning the proximal portion to aid in locating the IM nail; and 
     coupling at least one element to the distal portion. 
     There is still further provided, in accordance with an embodiment of the present invention, apparatus for use with an intramedullary (IM) nail implanted in a bone of subject, the IM nail having a proximal portion and a distal portion that defines one or more holes therethrough, the apparatus including: 
     a support, adapted to be coupled to the proximal portion; 
     a pin, adapted to be inserted through, at any given time, one of the holes and into the bone in a vicinity of a fracture of the bone; and 
     a multi-axial control element, adapted to be coupled to the support and to the pin, and to move the pin translationally and rotationally, so as to reduce and align the fracture, respectively. 
     Typically, the multi-axial control element includes a biaxial control element, which is adapted to move the pin in a cephalad direction and rotationally, so as to reduce and align the fracture, respectively. 
     In an embodiment, the biaxial control element includes a first member and a second member, both coupled to the support, the first and second members including a first set screw and a second set screw, respectively, the first and second set screws adapted to: 
     move the pin in the cephalad direction when both of the first and second set screws are rotated substantially simultaneously, and 
     move the pin rotationally when exactly one of the first and second set screws is rotated. 
     For some applications, the biaxial control element includes a shaped element coupled to at least one of the set screws, such that rotation of the at least one of the set screws in a first direction induces movement of the pin in the cephalad direction, and such that rotation of the at least one of the set screws in a second direction, opposite to the first direction, induces movement of the pin in the caudal direction. 
     The holes are typically elongated in parallel with a longitudinal axis of the IM nail. 
     There is also provided, in accordance with an embodiment of the present invention, apparatus for treating a fracture of a bone of a subject, including: 
     an intramedullary (IM) nail, adapted to be implanted in an intramedullary canal of the bone, the IM nail including a proximal portion and a distal portion that defines one or more holes therethrough; and 
     an introducer, including: 
     a support, adapted to be coupled to the proximal portion; 
     a pin, adapted to be inserted through, at any given time, one of the holes and into the bone in a vicinity of the fracture; and 
     a multi-axial control element, adapted to be coupled to the support and to the pin, and to move the pin translationally and rotationally, so as to reduce and align the fracture, respectively. 
     There is additionally provided, in accordance with an embodiment of the present invention, apparatus for use with an intramedullary (IM) nail implanted in a bone of subject, the IM nail having a proximal portion and a distal portion that defines one or more holes therethrough, the apparatus including: 
     a support, includes means for coupling the support to the proximal portion; 
     a pin, adapted to be inserted through, at any given time, one of the holes and into the bone in a vicinity of a fracture of the bone; and 
     means for moving the pin translationally and rotationally, so as to reduce and align the fracture, respectively. 
     In an embodiment, the means for moving the pin include means for moving the pin in a cephalad direction and rotationally, so as to reduce and align the fracture, respectively. 
     There is still additionally provided, in accordance with an embodiment of the present invention, a method for treating a fracture of a bone of a subject, the method including: 
     inserting an intramedullary (IM) nail in an intramedullary canal of the bone, the IM nail having a proximal portion and a distal portion that defines one or more holes therethrough; 
     inserting a pin through one of the holes and into the bone in a vicinity of the fracture; 
     temporarily coupling, via at least one intermediary element, a portion of the pin external to a body of the subject to the proximal portion of the IM nail; and 
     moving the pin translationally and rotationally, so as to reduce and align the fracture, respectively. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more fully understood from the following detailed description of embodiments thereof, taken together with the drawings, in which: 
         FIG. 1  is a schematic illustration of an intramedullary (IM) system in place in a femur, in accordance with an embodiment of the present invention; 
         FIG. 2A  is a schematic illustration of a head of the IM nail of  FIG. 1 , and  FIG. 2B  is a cross-sectional illustration of the head through the line  2 B- 2 B of  FIG. 2A , in accordance with an embodiment of the present invention; 
         FIG. 3  is a schematic illustration of a sleeve for use with the IM system of  FIG. 1 , in accordance with an embodiment of the present invention; 
         FIGS. 4A and 4B  are cross-sectional illustrations of a head with one of the holes of  FIG. 2A  through the line  4 A- 4 A of  FIG. 2A , in accordance with embodiments of the present invention; 
         FIGS. 5A and 5B  are schematic illustrations of a head of an IM nail, in accordance with embodiments of the present invention; 
         FIG. 6  is a schematic illustration of an IM locating tool, in accordance with an embodiment of the present invention; 
         FIG. 7  is a schematic illustration of another IM locating tool, in accordance with an embodiment of the present invention; 
         FIG. 8  is a schematic illustration of an introducer applied to a femur, in accordance with an embodiment of the present invention; 
         FIG. 8A  is an enlarged view of the circled portion in  FIG. 8 ; and 
         FIGS. 9A and 9B  are schematic illustrations of motion of a pin of the introducer of  FIG. 8 , in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  is a schematic illustration of an intramedullary (IM) system  10  in place in a femur  20 , in accordance with an embodiment of the present invention. The IM system comprises an IM nail  30 , having a proximal head  32  and a stem  34 ; at least one screw  40  for securing the IM nail at the head within a femoral head  23  of femur  20 ; and at least one sleeve  50 . Alternatively, another anchoring element, such as a nail or bolt is used, instead of screw  40 . IM system  10  typically further comprises at least one distal anchoring element  60 , such as a screw, nail, or bolt, to secure IM nail  30  at stem  34  within a canal  22  of femur  20 . For some applications, head  32  and/or stem  34  define a longitudinal bore (not shown). 
       FIG. 2A  is a schematic illustration of head  32  of IM nail  30 , and  FIG. 2B  is a cross-sectional illustration of head  32  through the line  2 B- 2 B of  FIG. 2A , in accordance with an embodiment of the present invention. Head  32  defines at least one hole  36 , typically two holes, as shown in the figures. Holes  36  are typically oriented in an angled direction toward a femoral head  23  ( FIG. 1 ) relative to a longitudinal axis of IM nail  30 . 
     Reference is again made to  FIG. 1 . In an embodiment of the present invention, head holes  36  are adapted to receive respective sleeves  50 , which in turn are adapted to slidably receive screws  40 , so as to permit a threaded portion of the screws to engage femoral head  23  and to allow sliding compression of a femoral neck  24 , an intertrochanteric fracture  25 , and/or a subtrochanteric fracture  26 . 
       FIG. 3  is a schematic illustration of sleeve  50 , in accordance with an embodiment of the present invention. Sleeve  50  comprises a locking mechanism  51 , which engages head hole  36 , preventing rotational and longitudinal movement between sleeve  50  and head hole  36 . The locking mechanism typically comprises a male coupling element, such as a tab  52  fixed to the outer surface of a depressible tongue  54 , which is adapted to flex inwards toward the center of the sleeve when pressure is applied thereto. When the pressure is removed, tab  52  engages female coupling element, such as a notch  72  of hole  36 , as described hereinbelow with reference to  FIG. 4A . It is noted that in embodiments of the present invention, prevention of rotational and longitudinal movement between sleeve  50  and head hole  36  is not obtained by simply pressure-fitting the sleeve in the hole, or by simply screwing the sleeve in the hole, either of which generally would result in gradual loosening of the sleeve over time. In addition, sleeve  50  typically is shaped to define at least one cutout  56  to receive a screwdriver used by the surgeon to align the tab with the notch, as described hereinbelow with reference to  FIGS. 4A and 4B . 
       FIGS. 4A and 4B  are cross-sectional illustrations of one of holes  36  of head  32  through the line  4 A- 4 A of  FIG. 2A , in accordance with an embodiment of the present invention. An inner grooved surface  70  of hole  36  is shaped to define a notch  72 , which tab  52  engages when sleeve  50  is inserted into hole  36  and properly aligned, thereby locking sleeve  50  to hole  36 . In the embodiment shown in  FIG. 4A , the radius R 1  of grooved inner surface  70  adjacent to notch  72  is less than the maximum radius R 2  of inner surface  70  in a region further away from notch  72 . To insert sleeve  50  into hole  36  and engage locking mechanism  51 , the surgeon typically first rotationally orients the sleeve so that tab  52  is aligned with a region of hole  36  having maximum radius R 2 , for example at the upper portion of hole  36 . The surgeon then inserts the sleeve in the hole until tab  52  of sleeve  50  meets the upper portion of hole  36 , which blocks further insertion of the sleeve. The surgeon then rotates the sleeve so that tab  52  approaches notch  72 . As tab  52  approaches notch  72 , tab  52  (and tongue  54 ) is gradually depressed by inner surface  70 , until the tab reaches the notch and the tongue springs back into its original position, forcing the tab into the notch, and locking it therein. Such a locking mechanism is generally impervious to loosening under cyclical loading, even over the course of many years. By contrast, two pieces which are attached without a locking mechanism (e.g., by being screwed together or wedged together) are susceptible to gradual loosening over time. 
     In the alternate embodiment shown in  FIG. 4B , the radius R 3  of inner surface  70  adjacent to notch  72  is substantially equal to the maximum radius R 2  of inner surface  70 . Hole  36  in this alternate embodiment is typically flared, such that the tab is depressed during insertion of sleeve  50  into hole  36 . Insertion of sleeve  50  into hole  36  in this alternate embodiment does not necessarily include rotation of sleeve  50  (as is described with reference to  FIG. 4A ). 
       FIG. 5A  is a schematic illustration of a head  132  of IM nail  30 , in accordance with an embodiment of the present invention. In this embodiment, head  132  of IM nail  30  comprises a distal portion  180 , which includes one or more head holes  136 , and a proximal portion  182 . Proximal portion  182  is adapted to aid in locating IM nail  30 , while distal portion  180  is adapted to be coupled to at least one element, such as a nail, screw, or a sleeve. Proximal portion  182  is visually and structurally distinct from distal portion  180 . Alternatively or additionally, proximal portion  182  has a diameter D 1  that is less than a diameter D 2  of distal portion  180  adjacent to proximal portion  182 . For some applications, diameter D 1  is between 50% and about 80% of diameter D 2 , or is less than about 50% of diameter D 2 . For some applications, diameter D 1  is between about 25% and about 50% of diameter D 2 . Typically, for IM nails intended for use in adults, diameter D 1  is between about 5 mm and about 10 mm, and diameter D 2  is between about 11 mm and about 17 mm. A length L 1  of proximal portion  182  is typically equal to between about 10% and about 50% of a length L 2  of head  132 . For example, length L 1  may be between about 10 mm and about 35 mm, and length L 2  may be between about 40 mm and about 60 mm, in IM nails intended for use in adults. Although head  132  is shown in the figures as narrowing suddenly, for some applications the diameter of the head decreases gradually from D 2  to D 1 . For some applications, such as for use in conjunction with the techniques described hereinbelow with reference to  FIG. 6  or  7 , (a) proximal portion  182  is removable, in which case the surgeon typically removes the proximal portion after implanting IM nail  30 , or (b) head  132  does not comprise proximal portion  182 , so that head  132  does not extend to the surface of femur  20 . 
       FIG. 5B  is a schematic illustration of head  132  of IM nail  30 , in accordance with an embodiment of the present invention. In this embodiment, a longitudinal axis of proximal portion  182  is oriented at an angle β with respect to a longitudinal axis of distal portion  180 . Angle β is typically between about 4 and about 40 degrees, in this embodiment. Optionally, a proximal surface  190  of distal portion  180  is oriented at an angle α with respect to the longitudinal axis of distal portion  180 . Angle α is typically between about 4 and about 40. 
     During an implantation procedure, IM nail  30  is typically inserted into femur  20  so that a proximal end  184  of proximal portion  182  is generally flush with or slightly protrudes from a surface region  27  of femur  20  in a vicinity of the greater trochanter or the piriformis ( FIG. 1 ). As a result, a surgeon generally can readily locate the IM nail if post-operative access to the implant becomes necessary. In addition, such a narrower proximal portion typically allows greater regrowth and healing of the neck of the femur towards the area of the greater trochanter, than generally occurs upon implantation of conventional IM nail heads. 
     For some applications, IM nail  30  comprises both narrower proximal portion  182  and locking mechanism  51 , as described hereinabove. For other application, the IM nail comprises only one of these features, but is generally otherwise conventional. 
       FIG. 6  is a schematic illustration of an IM locating tool  200 , in accordance with an embodiment of the present invention. In this embodiment, proximal portion  32  of IM nail  30  does not extend to surface region  27  of femur  20 . Without the use of IM locating tool  200 , it is sometimes difficult for the surgeon to locate proximal portion  32  of IM nail  30  if post-operative access to the implant becomes necessary. A distal end  220  of the locating tool comprises or is removably coupled to one or more connecting elements  240 , which typically comprise a locking mechanism similar to locking mechanism  51 , for locking to IM nail  30 , as described hereinabove with reference to  FIG. 3 . Alternatively, connecting elements  240  comprise another locking mechanism, such as protrusions, clips, or pegs. 
     To use the locating tool, the surgeon temporarily couples connecting elements  240  to respective head holes  36  of IM nail  30 . For some applications, the surgeon performs this coupling by removing any sleeves or screws present in holes  36 , and inserting a sleeve (not shown), which may be similar to sleeve  50  described hereinabove with reference to  FIG. 3 , into each hole  36 . The surgeon then couples each connecting element  240  to one of the sleeves. Alternatively, connecting elements  240  are directly coupled to head holes  36 . In either case, after the connecting elements are in a fixed position with respect to IM nail  30 , tool  200  is typically placed or slid onto the connecting elements, so as to assume a known, rigid position with respect thereto. (In embodiments in which connecting elements  240  are an integral part of tool  200 , this step is not necessary.) The use of at least two connecting elements  240  provides for a known, fixed orientation of IM locating tool  200  with respect to IM nail  30 . For applications that use only a single connecting element  240 , means are provided for ensuring a fixed rotational angle between connecting element  240  and hole  36 , thereby providing a known, fixed orientation of IM locating tool  200  with respect to IM nail  30 . For example, such means may include a slot in hole  36 . 
     Typically, coupling IM locating tool  200  to IM nail  30  automatically positions a proximal end  230  of the locating tool so as to indicate a site  228  of surface region  27  substantially directly over proximal portion  32  of the IM nail. The surgeon typically uses knowledge of the location of site  228  in order to determine an appropriate location at which to drill. For some applications, proximal end  230  comprises means for guiding a marking device  250  or drill, such as a hole through which the marking device or drill is inserted. 
       FIG. 7  is a schematic illustration of an IM locating tool  300 , in accordance with an embodiment of the present invention. An IM nail  302  comprises a proximal portion  304  which does not extend to a surface region  306  of a femur  308 . The proximal portion defines one or more head holes  310 , and a longitudinal channel  312  open to at least one of the head holes and to a proximal end  314  of proximal portion  304 . Without the use of IM locating tool  300 , it is sometimes difficult for the surgeon to locate proximal portion  304  of IM nail  302  if post-operative access to the implant becomes necessary. 
     IM locating tool  300  comprises an elongated element that is both bendable and resilient, i.e., is able to bend while maintaining longitudinal strength. A tip  316  of tool  300  is sufficiently sharp to pass through femur  308 . In order to locate a site  318  of surface region  306  substantially directly over proximal portion  304  of the IM nail, the surgeon inserts tool  300 , sharp end first, into one of head holes  310 . The surgeon guides the tool through channel  312 , so that the tool bends to conform with the channel. After pushing the tool so that tip  316  reaches the end of channel  312  at proximal end  314 , the surgeon continues to push with sufficient force so that tip  316  punches through femur  308  and emerges from surface region  306  at site  318 , thereby externally indicating the location of the site. Alternatively, tip  316  is threaded, and the surgeon rotates tool  300  so as to screw tip  316  through femur  308 . Further alternatively, tool  300  comprises a flexible drill bit, and the surgeon drills the tool through femur  308 . The surgeon typically uses knowledge of the location of site  318  attained through use of tool  300  in order to determine an appropriate location at which to drill during post-operative access to the IM nail. 
     Reference is now made to  FIGS. 8 and 8A , which are schematic illustrations of an introducer  400  applied to a femur  402 , in accordance with an embodiment of the present invention. Introducer  400  is adapted to actively reduce and align a fracture  404  of femur  402 , such as a subtrochanteric fracture, while generally minimizing the required size of an incision in the vicinity of the fracture. Introducer  400  comprises a support  406 , a coupling element  408 , and a multi-axial control element, such as a biaxial control element  410 . Coupling element  408  is adapted to couple introducer  400  to an IM nail  412 , which is inserted into a medullary canal  414  of femur  402 . For example, coupling element  408  may comprise a male element adapted to be inserted into a hole defined by a proximal end of a proximal head  416  of IM nail  412 . Other coupling mechanisms used by conventional introducers may also be used. One or more neck screws  420  secure the IM nail at the head within a femoral head  422  of femur  402 . Introducer  400  is typically shaped so as to define one or more holes (not shown) for guiding respective neck screws  420  during their insertion into femoral head  422 . 
     Introducer  400  is shaped to facilitate use with a pin  424 . During a procedure (which is generally performed using real-time imaging, such as fluoroscopy), pin  424  is inserted through femur  402  and through an elliptical or otherwise elongated hole  426 , defined by a distal region  428  of IM nail  412  in a vicinity of fracture  404 , such that the fracture is between the pin and coupling element  408 . For some applications, pin  424  is threaded in a vicinity of a bone-penetrating tip  430  thereof and/or in a vicinity of one or both regions  432  thereof that pass through femur  402 . Pin  424  typically has a diameter of between about 3 and about 6 mm, typically between about 4 and about 5 mm. 
     Reference is now made to  FIGS. 9A and 9B , which are schematic illustrations of motion of pin  424 , in accordance with an embodiment of the present invention. Biaxial control element  410  is adapted to move pin  424  along two axes, as follows:
         translationally, for example, in a cephalad (anterior) direction toward support  406  (i.e., in the direction generally indicated by arrow  434 ). In this manner, bone-penetrating tip  430  and a physician-manipulated end  436  of pin  424  generally move equal distances ( FIG. 9A ). Such cephalad movement serves to reduce fracture  404 ; and   rotationally, such that bone-penetrating tip  430  and physician-manipulated end  436  move in opposite directions, i.e., tip  430  moves closer to or further away from support  406  in one of the directions generally indicated by arrow  438 , while end  436  moves in the opposite direction ( FIG. 9B ). Such rotational movement serves to properly align fragments  440  and  442  of femur  402  with one another ( FIG. 8 ).
 
Elongated hole  426  typically has a length of about 10 mm to about 12 mm. Pin  424  is typically inserted through elongated hole  426  near a distal end thereof, which allows substantial rotation and cephalad motion of the pin before the pin comes in contact with a proximal end of the hole, e.g., about 10 mm of motion. ( FIG. 8  shows the pin already at the proximal end of hole  426 .)
       

     Reference is again made to  FIGS. 8 and 8A . After fracture  404  has been reduced and aligned, a screw (not shown) is typically screwed through a hole  444 , defined by distal region  428  of IM nail  412 , into fragment  440 , in order to fix IM nail  412  to fragment  440 . Hole  444  is typically circular and positioned distally to elongated hole  426  (as shown), or proximal thereto (configuration not shown). Pin  424  is then removed from elongated hole  426 . Optionally, a second screw (not shown) is screwed through elongated hole  426  into fragment  440  to further fix the IM nail to the fragment. 
     In an embodiment of the present invention, distal region  428  of IM nail  412  defines a secondary elliptical or otherwise elongated hole  446 , in a distal vicinity of elongated hole  426 . In this embodiment, after removal of pin  424  from elongated hole  426 , the pin is inserted through secondary hole  446 . Biaxial control element  410  further moves pin  424  in the cephalad direction towards support  406 , in order to further reduce fracture  404 . Typically, about 10 mm of reduction is performed using elongated hole  426 , and up to about an additional 10 mm of reduction is performed using secondary elongated hole  446 , for a total reduction of up to about 20 mm. It has been the inventor&#39;s experience that fractures rarely require reduction of more than about 20 mm, after initial reduction with a fracture table. 
     In an embodiment of the present invention, biaxial control element  410  comprises a first member such as a first leg  448 , and a second member such as a second leg  450 , the first and second members comprising set screws  452  and  468 , respectively. The first and second legs each define one or more elliptical or otherwise elongated holes  464  and  458 , respectively. When inserted into elongated hole  426  of IM nail  412 , pin  424  passes through one of holes  464  and one of holes  458 . The pin is initially positioned near respective distal ends of the holes. Tightening set screw  452  pushes the pin towards a proximal end of the one of the holes  464 , while tightening set screw  454  pushes the pin towards a proximal end of the one of the holes  458 . Therefore:
         tightening both set screws to the same extent and substantially simultaneously moves pin  424  in the cephalad direction towards support  406 ;   tightening only set screw  452  rotates pin  424  clockwise, in order to align fragments  440  and  442 ; and   tightening only set screw  468  rotates pin  424  counterclockwise, in order to align fragments  440  and  442 .       

     Typically, a combination of such tightening motions is performed in order to reduce and align fracture  440 . It is noted that for some configurations (such as that shown in  FIG. 8 ), tightening one of the set screws also induces some net cephalad motion of the center of pin  424 . For some applications, one or both of legs  448  or  450  are removably coupled to support  406  by coupling elements  460  or  462 , respectively (e.g., comprising screws or clips). For example, leg  450  may be removably coupled to support  406 , in which case leg  448  and support  406  are used to insert IM nail  412  into intramedullary canal  414 . The absence of leg  450  during this insertion generally makes introducer  400  easier to manipulate. After insertion of the IM nail, leg  450  is coupled to support  406 . 
     In an embodiment, biaxial control element  410  comprises an optional shaped element, such as shaped element  454 , coupled within biaxial control element  410  so as to provide means for pulling pin  424  (or otherwise inducing motion of pin  424 ) in the caudal direction. Shaped element  454  is coupled via a joint  456  to the proximal tip of set screw  452 . (Alternatively or additionally, a shaped element is coupled to set screw  452 .) Pin  424  passes through a hole in shaped element  454 , such that joint  456  allows set screw  452  to rotate while shaped element  454  substantially does not rotate. In addition, joint  456  couples shaped element  454  and set screw  452  such that movement of either one along the proximal/distal axis induces movement of the other one in the same direction. In particular, distal (caudal) motion of set screw  452  causes corresponding caudal motion of pin  424 . (By contrast, in embodiments not having shaped element  454  or equivalents thereof, proximal motion of set screw  452  causes cephalad motion of pin  424 , while distal motion of set screw  452  does not induce any substantial motion of pin  424 .) It is noted that the configuration and shape of shaped element  454  shown in  FIG. 8  is by way of illustration and not limitation. A person of ordinary skill in the art of mechanical design, having read the disclosure of the present patent application, would be able to develop other substantially equivalent means for providing cephalad and caudal motion of pin  424 . 
     In an embodiment of the present invention, introducer  400  is used in conjunction with a surgical plate having one or more elliptical or otherwise elongated holes through which pin  424  is inserted (configuration not shown). The plate is secured to the outside of femur  402  in a position suitable for reducing fracture  404  and for aligning fragments  440  and  442 . For this embodiment, techniques described hereinabove with reference to  FIGS. 8 ,  9 A, and  9 B are adaptable for use with the surgical plate, in a manner which would be readily ascertainable by one skilled in the art to which this invention pertains. 
     It will be appreciated that although some embodiments of the present invention have been shown and described herein for use in a femur, these embodiments may be adapted for use in other long bones of the extremities, such as the tibia and humerus, in a manner which would be readily ascertainable by one skilled in the art to which this invention pertains. It will also be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description.