Patent Publication Number: US-9408644-B2

Title: Telescoping IM nail and actuating mechanism

Description:
BACKGROUND 
     1. Technical Field 
     This disclosure relates to a limb lengthening intramedullary (IM) nail that includes a telescoping structure and a magnetic actuating mechanism. More specifically, an IM nail is disclosed that includes a telescoping structure with an internal magnet and an external actuating mechanism that includes rotating magnets for non-invasive lengthening (distraction) or shortening (contraction) of the IM nail as needed. 
     2. Description of the Related Art 
     A variety of treatments for limb length discrepancies are known. Limb length discrepancies may arise from birth defects, improper bone growth, disease, or trauma. Treatments of leg length discrepancies include the use of shoe lifts and special boots to raise the foot in the equinus position. The field of orthopedics includes other techniques, such as stimulating epiphyseal growth, surgical shortening of the longer limb, and surgical lengthening of the short limb. 
     Current limb lengthening techniques generally apply Ilizarov&#39;s principle of tension-stress, wherein living tissue subjected to slow, steady tension becomes metabolically activated. Hence, upon the creation of a bone gap and a subsequent distraction of the gap, new bone may be formed to generate an increase in length. 
     In current limb lengthening techniques, bone of the limb is cut, called an osteotomy or corticotomy. The bone begins development of a callus at this location. The two bone portions are then pulled apart by a mechanical device that is surgically attached to the bone. This procedure is called distraction, in which the callus is stretched, thereby lengthening the bone. 
     The current mechanical devices used for limb lengthening include external fixators in the form of rings, connected by adjustable struts and that are transcutaneously connected to the bone using wires, pins, or screws. 
     Various length-adjustable IM nails include: shape memory alloys to lengthen a telescopic IM nail; implanted electric motors to provide a distraction force; hydraulic or pneumatic mechanisms or pumps; ratchet mechanisms; magnetically driven gear mechanisms; and some designs exploit movement by the patient to generate the distraction force. 
     SUMMARY OF THE DISCLOSURE 
     A length-adjustable IM nail and an actuator for distracting or contracting the disclosed IM nail are disclosed. 
     One disclosed IM nail comprises a proximal outer body that includes a proximal end and a distal end. The distal end of the outer body receives a portion of a distal body. The proximal outer body also accommodates an inner magnet. The inner magnet is coupled to a proximal end of a threaded shaft. The threaded shaft also includes a distal end that is rotatably coupled to the distal body. Further, the threaded shaft passes through a threaded block that is coupled to the proximal outer body. 
     As a result, rotation of the inner magnet and threaded shaft causes axial movement of the proximal outer body with respect to the distal body. In one embodiment, the distal end of the threaded shaft, while rotatably connected to the distal body, is connected to the distal body at a fixed position. That is, the shaft can rotate at the fixed position, but does not move with respect to the distal body. 
     An actuator is also disclosed that includes at least one outer magnet. The outer magnet is rotatably accommodated in its own housing, equipped with a drive mechanism for rotating the outer magnet about an axis that is parallel to the axis of the inner magnet of an IM nail. Imparting rotation to the outer magnet imparts rotation to the inner magnet disposed within the proximal outer body of the IM nail. Rotation of the inner magnet results in rotation of the threaded shaft, which imparts axial movement of the threaded block. The axial movement of the threaded block causes axial movement of the proximal outer body with respect to the distal body. 
     An actuator is also disclosed for increasing the torque applied to the inner magnet. Instead of a single magnet, the actuator includes first and second outer magnets. Each outer magnet is rotatably accommodated in its own housing and at an axis that is parallel to the axis of the inner magnet and IM nail. The housing of the first and second outer magnets are coupled together to maintain the first and second outer magnets in a spaced-apart angular relationship that permits the IM nail (and the patient&#39;s limb) to be positioned between the first and second outer magnets. A linkage couples the first and second outer magnets together and is capable of imparting rotation to the first and second outer magnets in the same direction which imparts rotation to the inner magnet and threaded shaft. 
     In a refinement, an angle defined by the inner magnet (as the apex) and the first and second outer magnets can range from about 120 to about 180°. Angles of less than 120° may result in the two outer magnets generating some opposing forces instead of cooperating forces. 
     In a refinement, the distal body comprises an elongated slot. The threaded block comprises a radial extension that extends through the slot of the distal body and that is coupled to the proximal outer body for causing axial movement of the proximal outer body with respect to the distal body when the threaded block moves axially as a result of rotation of the threaded shaft. 
     In another refinement, the distal end of the threaded shaft is rotatably received in a distal block that is coupled to the distal body for coupling the distal end of the threaded shaft to the distal body. In a further refinement of this concept, the threaded shaft passes through the distal block and is coupled to an end cap. The threaded shaft is free to rotate within the distal block but the end cap serves to maintain the position of the distal end of the threaded shaft in a fixed position within the distal body because at least one of the distal block or the end cap is fixed to the distal body. 
     In other refinement, the first outer magnet is coupled to a drive mechanism. Further, the linkage that couples the first and second outer magnets together translates rotation imparted to the first outer magnet by the drive mechanism to rotation of the second outer magnet. In a further refinement of this concept, the linkage is a linkage assembly that comprises a first linkage that couples the first outer magnet to an arcuate linkage that couples the first linkage to a second linkage that couples the arcuate linkage to the second outer magnet. In still a further refinement of this concept, the drive mechanism is activated by a switch disposed on the housing of the first outer magnet. 
     In other refinement, the first and second outer magnets rotate about parallel axes and in the same direction to increase the torque imposed on the inner magnet disposed within the outer body of the IM nail. 
     In another refinement, the arcuate linkage is accommodated in an arcuate housing that couples the housings of the first and second outer magnets together to maintain the first and second outer magnets in an angular relationship of about 120 to about 180° with respect to each other, with the axis of the inner magnet being the apex and the rotational axes of all three magnets being parallel or as close to parallel as feasible, given the operation conditions. 
     In a refinement, the distal body of the IM nail includes at least one transverse hole for receiving a fixation element to couple the distal body to a patient&#39;s bone. 
     In another refinement, the actuator comprises a user interface that displays the magnitude of the axial distraction or axial compaction of the IM nail. 
     In a refinement, the inner magnet is disposed within a carrier or casing that is coupled to the proximal end of a threaded shaft. 
     One, two and three magnet actuators are disclosed. 
     A method for adjusting the length of an IM nail is also disclosed which includes providing an IM nail as disclosed above, providing an actuator as disclosed above and placing the actuator so an outer magnet is disposed relative to the IM nail, and rotating the outer magnet to impart rotation to the inner magnet and threaded shaft which imparts axial movement of the threaded block and proximal outer body with respect to the distal body. 
     A rotation axis of the outer magnet may be parallel to, perpendicular to, or non-parallel to an axis of the intramedullary nail. 
     According to some aspects of the present invention there may be provided a length adjustable intramedullary nail system, including: an intramedullary (IM) nail comprising a proximal outer body comprising a proximal end and a distal end, the distal end of the proximal outer body receiving a portion of a distal body, the proximal outer body accommodating an inner magnet, the inner magnet being coupled to a proximal end of a threaded shaft, the threaded shaft comprising a distal end rotatably coupled to the distal body, the threaded shaft passing through a threaded block, the threaded block being coupled to the proximal outer body; and an actuator comprising at least one outer magnet rotatably accommodated in its own housing, the housing of the outer magnet rotatably holding the outer magnet along an axis that is substantially parallel to an axis of the inner magnet, the actuator further comprising a drive mechanism that imparts rotation to the inner magnet and threaded shaft which imparts axial movement of the threaded block and proximal outer body with respect to the distal body. 
     According to some embodiments, the distal body has an elongated slot, the threaded block has a radial extension that extends through the slot and that is coupled to the proximal outer body. 
     According to some embodiments, the distal end of the threaded shaft is rotatably received in a distal block that is coupled to the distal body for coupling the distal end of the threaded shaft to the distal body. 
     According to some embodiments, the distal end of the threaded shaft passes through a distal block and is coupled to an end cap, the threaded shaft is free to rotate within the distal block, at least one of the distal block or end cap fixing the threaded shaft to the distal body. 
     According to some embodiments, the actuator further comprises a first outer magnet is coupled to a drive mechanism and a linkage that couples the first outer magnet to a second outer magnet wherein rotation imparted to the first outer magnet by the drive mechanism also results in rotation to the second outer magnet. 
     According to some embodiments, the linkage is a linkage assembly that comprises a first linkage that couples the first outer magnet to an arcuate linkage that couples the first linkage to a second linkage that couples the arcuate linkage to the second outer magnet. 
     According to some embodiments, the drive mechanism is activated by a switch disposed on the housing of the first outer magnet. 
     According to some embodiments, the first and second outer magnets rotate about parallel axes and in a same direction. 
     According to some embodiments, the arcuate linkage is accommodated in an arcuate housing that couples the housings of the first and second outer magnets together to maintain the first and second outer magnets in angular relationship with respect to each other, wherein an angle defined by an axis of the first outer magnet, an axis of the inner magnet and an axis of the second outer magnet, with the axis of the first outer magnet as the apex, ranges from about 120 to about 180°. 
     According to some embodiments, the distal body of the IM nail includes at least one transverse hole for receiving a fixation element to couple the distal body to bone. 
     According to some embodiments, the actuator comprises a user interface that displays an axial distraction or an axial compaction of the IM nail. 
     According to some aspects, an actuator includes at least one magnet having an axis oriented to be non-parallel to an axis of an intramedullary nail, and the magnet is configured for rotation about the magnet axis. A user interface displays the magnitude of axial distraction or axial compaction of an intramedullary nail caused by rotation of the magnet. 
     According to some embodiments, the actuator includes at least a second magnet coupled to the first magnet and having an axis oriented to be non-parallel to the intramedullary nail axis. The second magnet is configured for rotation about the second magnet axis. Alternatively, the second magnet has an axis oriented parallel to the intramedullary nail axis. 
     According to some aspects of the present invention there may be provided length-adjustable intramedullary (IM) nail, including: a proximal outer body comprising a proximal end and a distal end; the distal end of the proximal outer body receiving a portion of a distal body; the proximal outer body accommodating an inner magnet, the inner magnet being coupled a proximal end of a threaded shaft; the threaded shaft comprising a distal end rotatably coupled to the distal body at a fixed position, the threaded shaft passing through a threaded block, the threaded block being coupled to the proximal outer body; and wherein rotation of the inner magnet imparts rotation to the threaded shaft which imparts axial movement of the threaded block and proximal outer body with respect to the distal body. 
     According to some embodiments, the distal body includes an elongated slot, the threaded block includes a radial extension that extends through the slot and that is coupled to the proximal outer body. 
     According to some embodiments, the distal end of the threaded shaft is rotatably received in a distal block that is coupled to the distal body for coupling the distal end of the threaded shaft to the distal body. 
     According to some embodiments, the distal end of the threaded shaft passes through a distal block and is coupled to an end cap, the threaded shaft is free to rotate within the distal block, at least one of the distal block or end cap fixing the threaded shaft to the distal body. 
     According to some embodiments, the distal body of the IM nail includes at least one transverse hole for receiving a fixation element to couple the distal body to bone. 
     According to some aspects of the present invention there may be provided a method of adjusting the length of an intramedullary (IM) nail, the method including: providing an intramedullary (IM) nail comprising a proximal outer body comprising a proximal end and a distal end, the distal end of the proximal outer body receiving a portion of a distal body, the proximal outer body accommodating an inner magnet, the inner magnet being coupled a proximal end of a threaded shaft, the threaded shaft comprising a distal end rotatably coupled to the distal body, the threaded shaft passing through a threaded block, the threaded block being coupled to the proximal outer body; placing an actuator comprising first and second outer magnets around the IM nail so the first and second outer magnets are disposed on either side of the inner magnet; and rotating the first and second outer magnets to impart rotation to the inner magnet and threaded shaft which imparts axial movement of the threaded block and proximal outer body with respect to the distal body. 
     According to some embodiments, the distal body includes an elongated slot, the threaded block comprising a radial extension that extends through the slot and that is coupled to the proximal outer body, axial movement of the proximal outer body with respect to the distal body results in movement of the radial extension along the slot. 
     According to some embodiments, the method further includes the step of fixing the distal end of the threaded shaft to the distal body so the threaded shaft may rotate within the distal body but has a fixed axial position with respect to the distal body. 
     According to some embodiments, the method further includes the step of coupling the first outer magnet to a drive mechanism and a linkage assembly that couples the first and second outer magnets together wherein rotation imparted to the first outer magnet by the drive mechanism also imparts rotation to the second outer magnet. 
     Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the disclosed methods and apparatuses, reference should be made to the embodiments illustrated in greater detail in the accompanying drawings, wherein: 
         FIG. 1  is a plan view of an IM nail made in accordance with this disclosure; 
         FIG. 2  is a plan view of the IM nail disclosed in  FIG. 1  illustrating the IM nail in a distracted or extended position; 
         FIG. 3  is an end view of a disclosed actuator mechanism in position and surrounding a disclosed IM nail (the patient&#39;s limb is not shown); 
         FIG. 4  is a side view of the actuator and IM nail disclosed in  FIG. 3 ; 
         FIG. 5  is a top plan view of the actuator and IM nail disclosed in  FIGS. 3-4 ; 
         FIG. 6  is a perspective view of a disclosed actuator and IM nail; 
         FIG. 7  is an end view of another disclosed single-magnet actuator mechanism in position and surrounding a disclosed IM nail (the patient&#39;s limb is not shown); 
         FIG. 8  is an end view of another disclosed two-magnet actuator mechanism in position and surrounding a disclosed IM nail (the patient&#39;s limb is not shown); 
         FIG. 9  is an end view of a disclosed three-magnet actuator mechanism in position and surrounding a disclosed IM nail (the patient&#39;s limb is not shown); 
         FIG. 10  is an end view of another disclosed three-magnet actuator mechanism in position and surrounding a disclosed IM nail (the patient&#39;s limb is not shown); 
         FIG. 11  is an end view of a circular track actuator mechanism in position and surrounding a disclosed IM nail; 
         FIG. 12  is an end view of another circular track actuator mechanism in position and surrounding a disclosed IM nail; and 
         FIG. 13  is an end view of another disclosed single-magnet actuator mechanism in position and surrounding a disclosed IM nail. 
     
    
    
     It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein. 
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
       FIG. 1  is a plan view of a disclosed telescoping IM nail  10 . The IM nail  10  includes a proximal outer body  12  having a proximal end  14  and a distal end  16 . The distal end  16  of the proximal outer body  12  accommodates at least a portion of a distal body  18 . The distal body  18  also includes a proximal end  20  and a distal end  22 . The proximal outer body  12 , in addition to accommodating at least a portion of the distal body  18 , also accommodates an inner magnet  24 . The inner magnet  24  may be accommodated in a casing or carrier to facilitate the coupling of the inner magnet  24  to the threaded rod  28 . The inner magnet  24  may be rotated about the axis  25  of the IM nail  10  by the actuator  26  illustrated in  FIGS. 3-6  and discussed below. 
     Returning to  FIG. 1 , the inner magnet  24  is coupled to a threaded rod  28  which can be seen extending through the elongated slot  30  of the distal body  18 . The threaded rod  28  passes through the proximal end  20  of the distal body  18  and a bearing  32  before being coupled to the inner magnet  24 . The bearing  32  engages the inner wall  34  of the proximal outer body  12 . Similarly, a proximal bearing  36  is coupled to the inner magnet  24  to facilitate rotation of the inner magnet  24  within the proximal outer body  12 . 
     The threaded rod  28  includes a proximal end  38  coupled to the inner magnet  24  and a distal end  40  that is accommodated within a distal block  42  and connected to an end cap  44 . The threaded rod  28  also passes through a threaded block  46 . The threaded block  46  is coupled to the proximal outer body  12 . Hence, rotation of the inner magnet  24  (or carrier) results in rotation of the threaded rod  28  and rotation of the threaded rod  28  within the threaded block  46 . Because the threaded block  46  is coupled to the proximal outer body  12 , rotation of the inner magnet  24  and threaded rod  28  results in axial movement of the proximal outer body  12  in either direction along the axis  25  of the IM nail  10 . At least one of the distal block  42  or end cap  44  is fixed to the distal body  18  so the position of the distal end  40  of the threaded rod  28  is fixed in the position shown in both  FIGS. 1 and 2  with respect to the distal body  18 . The distal body  18  also includes a plurality of openings  50  for coupling the distal body  18  to the patient&#39;s bone. 
     Turning to  FIG. 2 , the inner magnet  24  has been rotated resulting in rotation of the threaded rod  28  and movement of the threaded block  46  and outer body to the left as shown in  FIG. 2  which results in a distraction or lengthening of the IM nail  10 . 
     The rotation of the inner magnet  24  is caused by the actuator  26  illustrated in  FIGS. 4-6 . In comparing  FIGS. 1 and 2 , the reader will note that the positions of the distal block  42 , end cap  44  and distal end  40  of the threaded rod  28  with respect to the distal body  18  remain unchanged. The elongated slot  30  disposed within the distal body  18  provides for a convenient means for sliding the threaded block  46  in either direction along the axis  25  of the IM nail  10 . 
     Turning to  FIG. 3 , one disclosed actuator  26  is shown in a position where it surrounds the IM nail  10 . The inner magnet is shown at  24  and the north-south coordinates for the inner magnet  24  as well as the first and second magnets  52 ,  54  are also illustrated. The first and second outer magnets  52 ,  54  are each accommodated within housings  56 ,  58 . The first and second magnets  52 ,  54  are rotatable about axes  60 ,  62  that are generally parallel with the axis  25  of the IM nail  10 . Rotation of the first and second outer magnets  52 ,  54  about the axes  60 ,  62  in the same direction or in the direction of the arrows  64 ,  66  imparts rotation to the inner magnet  24  and threaded rod  28  ( FIGS. 1-2 ). 
     Rotation of the first and second outer magnets  52 ,  54  may be initiated by an actuator button  68 . The actuator button  68  may be used to activate a drive mechanism shown schematically at  70  which rotates the first outer magnet  52  in the direction of the arrow  64 . The first outer magnet  52  may be coupled to a linkage  72  which, in turn, is coupled to an arcuate linkage  74  which, in turn, is coupled to a linkage  76  which imparts rotation to the second outer magnet  54  in the direction of the arrow  66 . The arcuate linkage  74  may be accommodated in an arcuate housing  78  which may also be used to support a user interface  80  for indicating to the surgeon or physician the amount of distraction or compaction imposed on the IM nail  10  as the result of operating the actuator  26 . Preferably, the interface  80  is supported on the arcuate housing  78  so that a display panel  82  is readily visible to the physician or surgeon. As illustrated in  FIGS. 4 and 5 . An additional perspective view of an actuator  26   a  is illustrated in  FIG. 6 . 
     The linkages  70 ,  72 ,  74 ,  76 ,  274  ( FIG. 8 ) may include any one or more of a flexible drive mechanism, gearing combinations, belt drives, worm gears, hydraulic drives, pneumatic drives, hydrostatic drives, chain drives, and bar linkage drives. The actuator  68  and linkage  70  may be a motor, such as a stepper motor with a shaft (not shown) coupled to the outer magnet  52 . The magnet  52  may also be driven by a motor (not shown) with drive belts, gear, worm gears, chain drive, etc., linking the magnet  52  to the other magnet(s)  54 ,  352 ,  452  ( FIGS. 9-10 ). Each magnet may also be equipped with its own motor with the motors controlled by a microprocessor (not shown). In short, one skilled in the art will appreciate that an abundance of options exist for imparting rotational motion to the magnet(s)  52 ,  54 ,  352 ,  452 . 
     Turning to  FIG. 7 , another disclosed actuator  126  is shown with a single outer magnet  152 . The arcuate housing  178  surrounds the IM nail  10 . The inner magnet is shown at  24  and the north-south coordinates for the inner magnet  24  as well as the single magnet  152  are also illustrated. The outer magnet  152  is accommodated within a housing  56  and is rotatable about the axis  60  that are generally parallel with the axis  25  of the IM nail  10 . The actuator  126  of  FIG. 6  will generally impose less torque on the inner magnet  24  than the actuator  26  of  FIG. 3 . 
     Turning to  FIG. 8 , another two-magnet actuator  226  is shown in a position where it surrounds the IM nail  10 . The first and second outer magnets  52 ,  54  are each accommodated within housings  56 ,  58  but the arcuate housing  278  and linkage  227  has been modified to support the magnets  52 ,  54  so their respective axes  60 ,  262  at an angle θ of about 120° with respect to each other, using the nail axis  25  as the apex. Rotation of the first and second outer magnets  52 ,  54  about the axes  60 ,  262  in the same direction or in the direction of the arrows  64 ,  266  imparts rotation to the inner magnet  24  and threaded rod  28  ( FIGS. 1-2 ). The angle θ may range from about 120 to about 180°. Further, the single magnet actuator  126  may also be used, but some operators may choose a magnet  152  ( FIG. 7 ) that is stronger than the magnet  52  ( FIGS. 3 and 8 ). 
       FIGS. 9 and 10  illustrate three-magnet actuators  326 ,  426 . Middle magnet  352 ,  452  are disposed between the first and second magnets  52 ,  54 . Additional linkages  372 ,  472 ,  474 ,  574  are shown. The three magnet actuators  326 ,  426  are ideal for incorporating a wireless communications interface  380  as discussed above. 
       FIGS. 11 and 12  illustrate a circular track actuator  700  that houses one or more magnets  702  that are driven to run along inner and outer tracks  704 ,  706  of the actuator  700 . In  FIG. 11 , two permanent magnets are shown, though any number of permanent magnets appropriately oriented can be driven to run along the tracks, such that the magnets drive the inner magnet of the nail  10  in axial rotation. In  FIG. 12 , two electromagnets are pulsed and synced, such that the magnets drive the inner magnet of the nail  10  in axial rotation. One or more than one electromagnet can be used to accomplish this. When multiple magnets  702  are used in the tracks of  FIGS. 11 and 12 , the magnets are linked together to maintain their relative angular orientation. The magnet(s) can be driven mechanically, for example, using a handle, or by a motor or mechanisms described above. 
     Turning to  FIG. 13 , another disclosed actuator  526  is shown with a single outer magnet  552 . The arcuate housing  578  surrounds the IM nail  10 . The inner magnet is shown at  24  and the north-south coordinates for the inner magnet  24  as well as the single magnet  552  are also illustrated. The outer magnet  552  is accommodated within a housing  556  and is rotatable about the axis  60 . In this embodiment, rather than being parallel to IM nail axis  25 , axis  60  is rotated tangentially relative to arcuate housing  578  to form an angle that is between greater than zero and up to +/−90 degrees, with a 90 degree angle being illustrated. The non-parallelism of the rotation axes, for example, the illustrated perpendicular arrangement, allows for a greater actuation distance (i.e., the shortest distance between the magnets), for example, about 50% greater, as compared to the arrangement in which the axes are parallel. For magnet  24  and  552  of the same size, a 90 degree angle provides the greatest actuation distance. The greater actuation distance accommodates patient&#39;s with larger legs. 
     The actuator  526  can include more than one outer magnet, such as illustrated in  FIGS. 8-10 , but with the additional outer magnets oriented non-parallel to the IM nail axis. In addition or alternatively, additional outer magnets can be oriented parallel to the IM nail axis. 
     INDUSTRIAL APPLICABILITY 
     The disclosed IM nail  10  utilizes a telescoping structure in the form of a proximal outer body  12  coupled to a distal body  18  by a threaded rod  28  and threaded block  46 . Both distraction and compaction of the proximal and distal bodies  18  with respect to each other is possible. Typically, a patient&#39;s bone is severed via an osteotomy for purposes of lengthening the bone over time. The IM nail  10  may employ neodymium magnets for the inner and outer magnets  24 ,  52 ,  54 ,  152 ,  352 ,  452  to actuate rotation of the threaded rod  28 . Rotation of the threaded rod  28 , in turn, results in axial movement the proximal outer body  12  with respect to the distal body  18 . When both the proximal outer body  12  and distal body  18  are affixed to portions of the segmented bone, the segmented portions of the bone may be distracted or contracted as necessary by rotation of the threaded rod  28 /inner magnet  24 . In the embodiments shown, the threaded rod  28  is under tension during axial loading conditions such as standing/ambulating or distraction and contraction of the IM nail  10 . 
     The external actuating mechanisms  26 ,  26   a ,  126 ,  226 ,  326 ,  426  are designed to provide sufficient torque to rotate the inner magnet  24  despite the distance between the inner magnet  24  and outer magnets  52 ,  54 ,  152 ,  352 ,  452 . Rotation of the inner magnet  24  must also overcome any compressive load imparted by associated soft tissue of the patient. Accordingly, the position of the outer magnets  52 ,  54 ,  152 ,  352 ,  452  may be used maximize torque to the inner magnet  24  and threaded rod  28  assembly. A preferred orientation is illustrated in  FIG. 8 , where the axes  25 ,  60 ,  262  of the inner and outer magnets  24 ,  52 ,  54  form an angle of about 120°. 
     Accordingly, radially magnetized inner and outer magnets  24 ,  52 ,  54 ,  152 ,  352 ,  452 , a small diameter threaded rod  28  and the proximal outer body  12  and distal body  18  of the telescoping IM nail  10  can be used to illicit both distraction and contraction of several portions of a diaphyseal bone. 
     In one embodiment, the threaded rod  28  is affixed to the inner magnet  24 , eliminating any degrees of freedom other than axial rotation of the inner magnet  24  and axial rotation of the threaded rod  28 . The bearings  32 ,  36  enable the inner magnet  24  to rotate freely within the proximal outer body  12 . The distal body  18  is dimensioned so that the proximal outer body  12  is free to move either axial direction with respect to the distal body  18 . The telescoping ability of the IM nail  10  allows the IM nail  10 , when affixed to bone via the proximal outer body  12  and distal body  18 , to both distract and contract adjacent pieces of bone. The proximal end  20  of the distal body  18  includes a through hole through which the threaded rod  28  can freely pass. The threaded rod  28  is then threadably connected to the threaded block  46  via matching threads. The distal body  18  includes an elongated slot  30  or other structure to permit the threaded block  46  to slide freely in either axial direction. Various means can be used to affix or couple the threaded block  46  to the proximal outer body  12 . The distal block  42  is preferably coupled or affixed to the distal body  18  and the threaded rod  28  and end cap  44  can rotate freely without an alteration of the position of the distal end  40  of the threaded rod  28  with respect to the distal body  18 . 
     The larger proximal outer body  12  moves axially with the threaded block  46  during distraction, contraction and loading. As a result, the threaded rod  28  is maintained in a constant tension. Because the threaded rod  28  is not compressed, the strength of the IM nail  10  structure is increased and binding between the threads of the threaded rod  28  and threaded block  46  are minimized. More specifically, during distraction, the points of contact between the threaded rod  28 /inner magnet  24  are at the threaded rod  28 , threaded block  46  interface and at the junction between the inner magnet  24  and the proximal end  20  of the distal body  18  as illustrated in  FIG. 2 . During contraction, the points of contact between the threaded rod  28 /inner magnet  24  are disposed at the threaded rod  28 /threaded block  46  interface and at the junction between the inner magnet  24  (or magnet carrier) and the proximal end of the distal body  18  as illustrated in  FIG. 1 . As a result, the loading forces in either axial direction during contraction or distraction are located at essentially the same interfaces. 
     While neodymium magnets are suggested, other magnets may be employed as will be apparent to those skilled in the art. The first and second outer magnets  52 ,  54  are preferably disposed at an angle θ ranging from about 120 to about 180° with respect to each other and the arcuate linkages  74 ,  274 ,  374 ,  474 ,  574  and arcuate housings  78 ,  178 ,  278 ,  378 ,  478  are preferably dimensioned to accommodate a patient&#39;s limb in which an IM nail  10  has been inserted. To accomplish these objectives, each outer magnet  52 ,  54 ,  152 ,  352 ,  452  may be mounted within its own housing  56 ,  58 ,  356 ,  456  and a singular actuating mechanism  68 ,  70 ,  72 ,  74 ,  274 ,  76 ,  372 ,  474 ,  478  either interior or exterior to the housings  56 ,  58  may be employed to spin both magnets in the same direction as illustrated in  FIGS. 3 and 8 . Upon actuation, the spinning of the first and second outer magnets  52 ,  54 , or single outer magnet  152  will provide additive torque to the inner magnet  24  housed within the IM nail  10 . 
     As will be apparent to those skilled in the art, different types of permanent magnets, electro magnets, different magnet shapes and different mounting types or locations of the magnets  24 ,  52 ,  54 ,  152  may be employed. The structure of the housings  56 ,  58 ,  78 ,  178 ,  278  may also vary in terms of shape, relative dimensions and construction. The linkage between the magnets  52 ,  54  (see  72 ,  74 ,  76  in  FIGS. 3 and 8 ) can be accomplished by a variety of means such as a flexible drive mechanism, gearing combinations, belt drives, worm gears, hydraulic drives, pneumatic drives, hydrostatic drives, chain drives, bar linkage drives, etc. The mechanical link between the magnets  52 ,  54 ,  152  and the housings  56 ,  58 ,  156  may also vary using flexible drive mechanisms, gearing combinations, belt drives, worm gears, hydraulic drives, pneumatic drives, hydrostatic drives, chain drives, bar linkage drives, etc. 
     Further, the magnets  52 ,  54 ,  24 ,  152  may be oriented in configurations or directions other than axially such as 360° circumferential rotation, e.g. spun around the axis of the limb rather than the axis of the inner magnet  24 ). The magnets  52 ,  54 ,  152  could also be driven in a linear direction in either a continual (constant force) or pulsing action. The location of the actuation mechanism  68 ,  70  could be disposed in either housing  56 ,  58 , within the arcuate housing  78 ,  178 ,  278 , on the user interface  80  or outside of the housings  56 ,  58 ,  78 ,  178 ,  278  altogether. 
     The actuator button  68  may be provided in the form of a helical push button, turn handle, linear gearing, worm gearing, spur gears, helical gears, rack and pinion gears, pawls, hydraulic actuation, pneumatic actuation, hydrostatic actuation, magnetic actuation, brush and brushless electrical motors, including stepper motors. The lengthening monitor or user interface  80  may be solid state or an electro-mechanical device. The interface  80  may also be a wireless device that would not appear on the housing. The information to be displayed would be shown on a monitor in the operating room. Hence, the interface  80  and display panel  82  are truly optional, given the wireless technology that is currently available. The interface  80  may measure pull changes of the inner magnet  24  or linear movement of the inner magnet  24 . The display  82  of the interface  80  may be analog or digital. The specific information displayed on the display  82  may vary depending upon need and may be programmable by the surgeon or physician. 
     The interface  80  may also employ alarms or alerts to warn the physician or user of distraction/contraction that deviates from the original prescription. 
     While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.