Patent Publication Number: US-2021186523-A1

Title: Interoperative aiming arm

Description:
TECHNICAL FIELD 
     The present disclosure relates to systems, assemblies, and methods for the insertion and fixation of an intramedullary nail into a medullary canal of a bone. 
     BACKGROUND 
     Intramedullary nails have long been used to treat fractures in long bones of the body such as fractures in femurs, tibias, and humeri. To treat such fractures, the intramedullary nail is inserted into a medullary canal of the long bone such that the nail spans across one or more fractures or fragments in the long bone. Bone anchors, such as bone screws, are then inserted through the bone and into the intramedullary nail at opposing sides of a fracture thereby fixing the intramedullary nail to the bone. The intramedullary nail can remain in the medullary canal at least until the fracture is fused. 
     SUMMARY 
     In one example, a method comprises aligning an axis of a cutting instrument with a bone-anchor fixation hole of an intramedullary nail, where the bone-anchor fixation hole extends through an outer surface of the intramedullary nail and the outer surface extends between a trailing end of the intramedullary nail and an insertion end of the intramedullary nail. The method further comprises inserting the cutting instrument through the bone-anchor fixation hole such that the cutting instrument is in contact with a guide body of a targeting guide, where the targeting guide is supported relative to the intramedullary nail such that the guide body is spaced outwardly from the outer surface of the intramedullary nail along a radial direction. The method yet further comprises driving the cutting instrument through the guide body so as to form an alignment aperture in the targeting guide, the alignment aperture having a central axis that is aligned with the bone-anchor fixation hole. 
     In another example embodiment, an intramedullary nail insertion system comprises a targeting guide and a spacer. The targeting guide has a guide body that has at least one solid portion. The spacer is configured to couple the targeting guide to an intramedullary nail that defines a bone-anchor fixation hole that extends along a central axis. The spacer and targeting guide are configured such that, when the spacer couples the targeting guide to the intramedullary nail, the guide body of the targeting guide is spaced radially outward from the intramedullary nail and a surface of the at least one solid portion is intersected by the central axis of the bone-anchor fixation hole of the intramedullary nail. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following description of the illustrative embodiments may be better understood when read in conjunction with the appended drawings. It is understood that potential embodiments of the disclosed systems and methods are not limited to those depicted. 
         FIG. 1  shows a perspective view of an intramedullary nail insertion system according to one embodiment; 
         FIG. 2  shows an exploded perspective view of the intramedullary nail insertion system of  FIG. 1 ; 
         FIG. 3  shows a cross-sectional view of the intramedullary nail insertion system of  FIG. 1 ; 
         FIG. 4  shows a perspective view of the intramedullary nail insertion system of  FIG. 1  with a cutting instrument extending into the targeting guide; 
         FIG. 5  shows a perspective view of the intramedullary nail insertion system of  FIG. 1  with an alignment aperture formed in the targeting guide; 
         FIG. 6  shows a first perspective view of an intramedullary nail of the intramedullary nail system of  FIG. 1  according to one embodiment; 
         FIG. 7  shows a second perspective view of the intramedullary nail of  FIG. 6 ; and 
         FIG. 8  shows a simplified flow diagram of a method of using an intramedullary nail insertion system according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Commonly, an intramedullary nail is implanted by driving the nail into a medullary canal of a long bone such as a tibia, fibula, humerus, or femur. To secure the intramedullary nail to the bone, the intramedullary nail can define at least one bone-anchor fixation hole that extends at least partially through the intramedullary nail. For example, the intramedullary nail can include at least one trailing bone-anchor fixation hole at a trailing portion of the intramedullary nail and at least one leading bone-anchor fixation hole at a leading portion of the intramedullary nail. The intramedullary nail can be secured to the bone by (1) drilling, for each bone-anchor fixation hole, a hole in the bone that aligns with the bone-anchor fixation hole, and (2) inserting, for each bone-anchor fixation hole, a bone anchor through the bone and into the bone-anchor fixation hole such that the bone anchor engages the bone on at least one side, such as opposed sides, of the intramedullary nail. 
     When the intramedullary nail is implanted in the bone, the bone obstructs the surgeon&#39;s view of the trailing and leading bone-anchor fixation holes of the intramedullary nail. Therefore, a targeting system or systems can be employed to determine the location of each bone-anchor fixation hole, and/or align a cutting instrument such as a drill bit with each bone-anchor fixation hole. Once the location of a bone-anchor fixation hole is determined and/or the cutting instrument is aligned with the bone-anchor fixation hole, a hole can be drilled into the bone to the bone-anchor fixation hole. A bone anchor can subsequently be inserted through the bone and into the bone-anchor fixation hole. 
     One method of targeting the at least one bone-anchor fixation hole includes using fluoroscopy to obtain moving X-ray images of the position of the drill bit relative to the bone-anchor fixation hole in real-time. However, the use of fluoroscopy can over expose the patient, and particularly the surgeon who performs numerous such procedures, to harmful X-rays. As an alternative to fluoroscopy, a guide can be affixed to the intramedullary nail, and the guide can be used to target at least one of the bone-anchor fixation holes with a cutting instrument such as a drill bit. Generally, the guide can include an alignment aperture that aligns with at least one bone-anchor fixation hole when the guide is affixed to the intramedullary nail. The cutting instrument can then be guided into the alignment aperture and through the bone to the bone-anchor fixation hole. 
     The guides and intermedullary nails are manufactured such that the alignment apertures of the guides are aligned with the respective bone-anchor fixation holes of the intramedullary nails. To ensure that the alignment apertures of the guides and bone-anchor fixation holes of the nails are properly aligned, tolerances between the guides and the intramedullary nails are tightly controlled during manufacturing. Moreover, the guides are commonly made from a material, such as carbon fiber, that is radiolucent and strong enough to ensure that the guides stay calibrated to the intramedullary nails. As a result, the guides can be relatively expensive, making them too costly for some areas of the world. 
     As an alternative to forming guide the guides with high cost materials and exacting tolerances, each guide can be custom constructed for a particular intramedullary nail as will be discussed herein. As a result, manufacturing tolerances between the guides and intramedullary nails need not be as tightly controlled, thereby reducing manufacturing costs. In addition, or alternatively, the guides can be constructed from a low-cost material, such as a thermoplastic, thereby reducing costs of the guides and allowing the guides to be discarded after a single use with a single intramedullary nail. 
     To custom construct a guide to a particular intramedullary nail, the intramedullary nail can be used as a guide to form at least one alignment aperture in the guide. For example, a cutting instrument, such as a drill bit or reamer, can be guided through the at least one bone-anchor fixation hole of the intramedullary nail and into the guide so as to cut the at least one alignment aperture into the guide. The alignment apertures of the guide can be custom formed after delivery to a medical facility, such as on a back table of an operating facility. As a result, tolerances between the guide and intramedullary nail need not be precisely controlled during transport of the guide. Alternatively, the alignment apertures of the guide can be custom formed prior to delivery, such as at a manufacturing or other facility, in which case, care should be taken during transport to ensure that the guide and/or intramedullary nail are not damaged to deformed in such a manner that causes tolerances between the guide and intramedullary nail to be lost. 
     Referring to  FIGS. 1 and 2 , an intramedullary nail insertion system is shown according to one embodiment. The system comprises a targeting guide  200  and a spacer  100 . The spacer can be, for example, an insertion handle that can be used to insert an intramedullary nail  400  into the bone, although embodiments of the disclosure are not so limited. In some embodiments, the system can additionally comprise the intramedullary nail  400 . It will be understood, however, that the targeting guide  200 , the spacer  100 , and the intramedullary nail  400  can be distributed separately from one another or can be distributed in groups of two or more of the targeting guide  200 , the spacer  100 , and the intramedullary nail  400 . Therefore, embodiments of the present disclosure can include as few as one of the targeting guide  200 , the spacer  100 , and the intramedullary nail  400 , or more than one, up to all, of the targeting guide  200 , the spacer  100 , and the intramedullary nail  400 . 
     In general, the targeting guide  200  has a guide body  204  that has at least one solid portion  205 . The spacer  100  is configured to couple the targeting guide  200  to the intramedullary nail  400  such that a surface of the at least one solid portion  205  is spaced radially outward from the intramedullary nail  400  and is intersected by a central axis C A  of at least one bone-anchor fixation hole  422  of the intramedullary nail  400 . The targeting guide  200 , and in particular, at least one alignment aperture (e.g.,  218  in  FIG. 5 ) of the targeting guide  200 , can be custom formed for the particular intramedullary nail  400  with which the targeting guide  200  is to be used. Thus, the targeting guide  200  can have a pre-customized configuration as shown in  FIGS. 1-3 , wherein at least one alignment aperture (e.g.,  218 ) is not formed in the targeting guide  200 , and a customized configuration as shown in  FIG. 5 , wherein at least one alignment aperture (e.g.,  218 ) is formed in the targeting guide  200 . 
     The targeting guide  200  may be customized by aligning an axis of a cutting instrument, such as a drill bit or reamer (e.g.,  600  in  FIG. 4 ), with a bone-anchor fixation hole  422  of the intramedullary nail  400 . The cutting instrument may then be inserted through the bone-anchor fixation hole  422  such that the cutting instrument is in contact with a surface of the at least one solid portion  205  of the targeting guide  200 . In so doing, the cutting instrument may be inserted on a side of the intramedullary nail  400  that is opposite the surface of the at least one solid portion  205  of the targeting guide  200 , and directed through the intramedullary nail  400  to the surface of the at least one solid portion  205  of the targeting guide  200 . The cutting instrument (e.g.,  600  in  FIG. 4 ) may then be driven through the guide body  204  at the surface of the at least one solid portion  205  so as to form an alignment aperture  218  (labeled in  FIG. 5 ) in the targeting guide  200 , the alignment aperture  218  having a central axis C A  that is aligned with the bone fixation hole  422  of the intramedullary nail  400 . Thus, the intramedullary nail  400 , and in particular, the bone-anchor fixation hole  422  can be used as a guide to form at least one alignment aperture  218  in the targeting guide  200  such that each of the at least one alignment aperture  218  aligns with a corresponding bone-anchor fixation hole  422 . 
     In some embodiments, a plurality of bone-anchor fixation holes  422  can be used as guides to form a plurality of alignment apertures  218  in the targeting guide  200  such that each alignment aperture  218  aligns with a corresponding bone-anchor fixation hole  422 . Thus, the aforementioned process can be repeated by inserting the cutting instrument through one or more other bone-anchor fixation holes  422  to form one or more other alignment apertures  218 , each corresponding to one of the other bone-anchor fixation holes  422 . The intramedullary nail  400  can be subsequently implanted into the bone, and the at least one alignment aperture of the targeting guide  200  can be used to target the at least one bone-anchor fixation hole  422  with a cutting instrument, such as a drill bit or reamer. The cutting instrument can be guided into the at least one alignment aperture and through the bone to the at least one bone-anchor fixation hole  422 . 
     Referring now more specifically to the details of the system of  FIGS. 1-3 , the spacer  100  is configured to support the targeting guide  200  relative to the intramedullary nail  400  such that a surface of the at least one solid portion  205  of the guide body  204  of the targeting guide  200  is spaced radially outward from the intramedullary nail  400 . The spacer  100  has a first transverse end  102  and a second transverse end  104  that are offset from one another along a select transverse direction T. The select transverse direction T can be a radial direction that extends radially out relative to an axis of the intramedullary nail  400  when the spacer  100  is coupled to the intramedullary nail  400 . The spacer  100  can have a trailing end  103 , and a leading end  105  that is offset from the trailing end  103  along an insertion direction I. 
     The first transverse end  102  of the spacer  100  comprises a coupler  106  that is configured to couple to the intramedullary nail  400 . The coupler  106  can be configured to couple to the intramedullary nail  400  so as to fix a rotational orientation of the coupler  106  relative to the intramedullary nail  400  about a central axis A L . In some embodiments, the coupler  106  have a cylindrical shape that extends along the insertion direction I. The central axis A L  can be a central axis of at least one of the coupler  106  and a trailing end  404  of the intramedullary nail  400 . The coupler  106  can define at least one mating feature, such as at least one of a protrusion  107  and a recess  109 , that is configured to engage a corresponding at least one mating feature of the intramedullary nail  400 , such as at least one of a recess  416  and a protrusion  414  (shown in  FIG. 6  and discussed below), so as to fix a rotation orientation of the coupler  106  relative to the intramedullary nail  400 . The coupler  106 , and hence the at least one mating feature, can be disposed at the leading end  105  of the spacer  100 . In some embodiments, the coupler  106  can include a plurality of protrusions  107  (labeled in the enlarged view of  FIG. 2 ), each configured to engage a corresponding recess  416  of the intramedullary nail  400 . In such embodiments, each adjacent ones of the protrusions  107  can be separated a recess  109 . 
     When the spacer  100  is coupled to the intramedullary nail  400 , the at least one mating feature of the spacer  100  engages the at least one mating feature of the intramedullary nail  400  so as to prevent the intramedullary nail  400  from rotating relative to the spacer  100 . Moreover, in some embodiments, the at least one mating feature of the coupler  106  can be configured such that the spacer  100  can be coupled to the intramedullary nail  400  in only one select rotational orientation. Thus, the at least one mating feature can be configured so as to prevent the spacer  100  from being coupled to the intramedullary nail  400  in any other rotational orientation other than the select rotational orientation. This can ensure that the central axis C A  of each of the at least one bone-anchor fixation hole  422  properly aligns with (i) the same point on the surface of the at least one solid portion  205  of the guide body  204  of the targeting guide  200  in the event that the targeting guide  200  and intramedullary nail  400  are decoupled from, and then recoupled, to one another before formation of the at least one alignment aperture  218 , or (ii) a respective one of the at least one alignment aperture  218 , in the event that the targeting guide  200  is decoupled from, and then recoupled to, the intramedullary nail  400  after formation of the at least one alignment aperture  218 . 
     The spacer  100  can define a cannulation  116  (labeled in  FIG. 3 ) that extends through the first transverse end  102 , such as through the coupler  106 , along the insertion direction I. The spacer  100  can be configured (e.g., sized and shaped) such that the cannulation  116  aligns with a cannulation  426  of the intramedullary nail  400  when the spacer  100  is coupled to the intramedullary nail  400 . The cannulation  116  can be configured (e.g., sized and shaped) so as to receive a rod, such as a guide rod or reaming rod, therethrough. In some embodiments, the spacer  100  can be implemented as an insertion handle, and the handle can be used to guide the intramedullary nail  400  along the guide rod or reaming rod into the medullary canal of the bone during insertion of the intramedullary nail  400 . The cannulation  116  can extend through the coupler  106 . 
     The second transverse end  104  of the spacer  100  can comprise a coupler  120  that is configured to couple the spacer  100  to the targeting guide  200 , although, in alternative embodiments, the spacer  100  and targeting guide can be monolithic with one another. The coupler  120  can be configured to couple the spacer  100  to the targeting guide  200  so that the spacer  100  and targeting guide  200  are positionally fixed relative to one another. Thus, when coupled to the targeting guide  200 , the spacer  100  can be fixed (e.g., translationally and rotationally) to the targeting guide  200 . 
     In some embodiments, the spacer  100  can be an insertion handle. For example, the spacer  100  can have an outer surface  114  between the first end  102  and the second end  104 . The outer surface  114  can define a grip that is configured to be grasped by a hand of a medical professional during insertion of the intramedullary nail  400 . Thus, the spacer  100  can be grasped by a medical professional to guide the intramedullary nail  400  into the medullary canal. It will be understood, however, that the spacer  100  need not be an insertion handle, and that a separate insertion handle can be coupled to the intramedullary nail  400  to implant the intramedullary nail  400  before targeting the at least one bone-anchor fixation hole  422  with the targeting guide  200 . In other embodiments, the spacer  100  may be larger than may be effectively gripped by a user. The spacer  100  may be straight between the first transverse end  102  and second transverse end  104 , or may have one or more curves or bends (not shown) between the first transverse end  102  and second transverse end  104 . The spacer  100  may be formed of a single unitary piece of material or may be formed from multiple components that are coupled to one another. 
     In one embodiment, the system can comprise a fastener  300  (shown in  FIGS. 2 and 3 ) that is configured to fasten the spacer  100  to the intramedullary nail  400  so as to positionally fix the spacer  100  and intramedullary nail  400  to one another. The fastener  300  can be configured as any suitable fastener, and various such fasteners are known in the art.  FIG. 2  shows one example fastener  300  that has a first coupler end  302 , and a second end  304  offset from the first coupler end  302  along the insertion direction I. The second coupler end  304  can include threading  308  that is configured to engage threading  410  (see  FIG. 6 ) of the intramedullary nail  400  so as to secure the fastener  300  to the intramedullary nail  400 , although it will be understood that the second coupler end  304  can include a quick connect/disconnect or other suitable feature other than threading. In one embodiment, the threading  308  can be male threading that is configured to engage female threading of the intramedullary nail  400 . 
     The first coupler end  302  can include an engagement surface  306  that is configured to be engaged by an instrument or a medical professional so as to rotate the fastener  300  to engage the threading  308  of the fastener  300  with the threading  410  of the intramedullary nail  400 . In one embodiment, the engagement surface  306  can be an internal surface that defines a non-circular cross-section, such as a hexagon, polygon, or other shape, that can be engaged by a driving instrument such that rotation of the driving instrument causes a corresponding rotation of the fastener  300 . In other embodiments, the engagement surface  306  can be a handgrip that can be gripped by a user&#39;s hand to secure the fastener  300  to the intramedullary nail  400 . 
     The fastener  300  can include a stop or a shoulder  310  that is configured to abut the spacer  100  when the fastener  300  is secured to the intramedullary nail  400  so as to prevent the spacer  100  from moving in a rearward direction R, opposite the insertion direction I, relative to the intramedullary nail  400 . The stop or shoulder  310  has a cross-sectional dimension in a plane that is perpendicular to the insertion direction I. The cross-sectional dimension can be measured from a first point on the stop or shoulder to a second point on the stop or shoulder, the first and second points being on opposed sides of the axis A L . Further, the cross-sectional dimension of the stop or shoulder  310  can be greater than a cross-sectional dimension of the cannulation  116  such that the spacer  100  limits an insertion depth of the stop or shoulder  310  into the cannulation  116  along the insertion direction I. Thus, when the spacer  100  is coupled to the intramedullary nail  400 , the spacer  100  can be trapped between the intramedullary nail  400  and the stop or shoulder  310  of the fastener  300 . 
     With continued reference to  FIGS. 1-3 , the targeting guide  200  has a first guide end  201 , and a second guide end  203  opposite the first guide end  201  along the insertion direction I. The targeting guide  200  has a guide body  204  that extends between the first guide end  201  and the second guide end  203 . The targeting guide  200  can comprise a coupler  202  that is configured to couple the targeting guide  200  to the spacer  100  at an attachment location, although, in alternative embodiments, the spacer  100  and targeting guide  200  can be monolithic with one another at the attachment location. The coupler  202  can be attached to the guide body  204 . For example, the guide body  204  can extend from the coupler  202 , such as along the insertion direction I. The coupler  202  can be configured to couple the targeting guide  200  to the spacer  100  so that the spacer  100  and targeting guide  200  are positionally fixed relative to one another. Thus, when coupled to the spacer  100 , the targeting guide  200  can be fixed to the spacer  100  with respect to translation and rotation. 
     The guide body  204  has an inner guide surface  210 , and an outer guide surface  212  that is opposite the inner surface  210 . The inner guide surface  210  can be positioned closer to the intramedullary nail  400  than the outer guide surface  212  when the targeting guide  200  is coupled to the intramedullary nail  400 . The guide body  204  has at least one solid portion  205  that is devoid of any through-holes. The at least one solid portion  205  can include at least a portion of the inner guide surface  210 . The at least one solid portion  205  can extend between the inner guide surface  210  and the outer guide surface  212 , such as from the inner guide surface  210  to the outer guide surface  212 . The at least one solid portion  205  is preferably solid from the inner guide surface  210  to the outer guide surface  212 . However, in alternative embodiments, the guide body  204  can have a cavity (not shown) between the inner surface  210  and the outer surface  212  at the at least one solid portion  205 . The at least one solid portion  205  can include at least a portion, up to an entirety, of the inner guide surface  210 . At least a portion of the guide body  204 , such as a portion or portions that include the at least one solid portion  205 , can be formed from a material, such as a polymer, that is radiolucent and that can be easily drilled. At least a portion of the guide body  204 , such as a portion or portions that include the at least one solid portion  205 , can be molded, such as injection molded. The targeting guide  200  is preferably formed from a material or materials that are sufficiently rigid so as to prevent the targeting guide  200  from deflecting when the at least one alignment aperture  218  is formed therein. 
     At least one solid portion  205  of the guide body  204  (e.g., at  214 ) can be aligned along the insertion direction I with an attachment location of the targeting guide  200  that attaches to the spacer  100 . For example, in embodiments where the spacer  100  and targeting guide  200  are separate components, as opposed to being monolithic with one another, at least one solid portion  205  can be aligned with the coupler  202  along the insertion direction I. In addition, or alternatively, at least a portion of the guide body  204  can extend circumferentially about the intramedullary nail  100  when the targeting guide  200  is coupled to the intramedullary nail  100 . Note that the targeting guide  200  can have any suitable shape so as to align the at least one solid portion  205  of the inner surface  210  with a central axis A c  of at least one of the bone-anchor fixation holes  422 . 
     The coupler  202  of the targeting guide  200  can define at least one mating feature that is configured to mate with at least one mating feature of the coupler  120  of the spacer  100 . For example, the at least one mating feature of the targeting guide  200  can include at least one of a protrusion and a recess, and the at least one mating feature of the spacer  100  can include another one of the at least one of the protrusion and recess. The at least one of the protrusion and recess of the targeting guide  200  can be configured to mate with the at least one of the protrusion and a recess of the spacer  100 . In one example, the targeting guide  200  can include at least two mating features, such as a pair of protrusions  202   a  and  202   b,  that are configured to mate with at least two mating features of the spacer  100 , such as a pair of recesses  108   a  and  108   b.  The at least two mating features of each of the targeting guide  200  and the spacer  100  can be offset from one another. The mating features of the targeting guide  200  and spacer  100  can be configured such that, when mated, the mating features limit rotation of the targeting guide relative to the spacer  100  about an axis C F  (see  FIG. 2 ) that extends along the transverse direction T. 
     The intramedullary nail insertion system can include a fastener  500  that that is configured to secure the targeting guide  200  to the spacer  100 , although the fastener  500  can be omitted in embodiments where the targeting guide  200  and spacer  100  are integral to one another. The fastener  500  can be configured to secure the targeting guide  200  to the spacer  100  so as to limit or prevent translation of the targeting guide  200  relative to the spacer along the transverse direction T. 
     In one example, the fastener  500  can include a shaft  502  having a first end  504  and a second end  506 . The first end  504  can be configured to attach to at least one of the spacer  100  and the targeting guide  200 . For example, the first end  504  can include threading that is configured to engage threading of at least one of the spacer  100  and the targeting guide  200 , although fastening mechanisms other than threading are contemplated. The second end  506  of the fastener  500  can include a drive surface  508  that is configured to be engaged by a user or instrument to turn the fastener  500 . In one example, the drive surface  508  can define a handle, although the drive surface  508  could alternatively include a socket that is configured to receive a drive surface of a driving instrument such as a screw driver. The fastener  500  can include an inner surface  510  that has a cross-sectional dimension that is greater than a cross-sectional dimension of the shaft  502 . The inner surface  510  can be part of the handle, although embodiments of the disclosure are not so limited. 
     The coupler  120  of the spacer  100  can have an opening  122 , and the coupler  202  of the targeting guide  200  can have an opening  208  that is configured to be aligned with the opening  122  along an axis AF when the spacer  100  and targeting guide  200  are coupled to one another. The shaft  502  of the fastener  500  can be configured to be received through the opening of one of the spacer  100  and the targeting guide  200  into the opening of another one of the spacer  100  and the targeting guide  200 . At least one of the opening  122  and opening  208  can define threading that is configured to receive the threading of the fastener  500  (in embodiments that employ threading). When the second end  506  of the shaft  502  is fastened to one of the spacer  100  and the targeting guide  200 , the other of the spacer  100  and the targeting guide  200  can be trapped between the inner surface  510  of the fastener  500  and the one of the spacer  100  and the targeting guide  200  so to prevent translation of the spacer  100  and targeting guide  200  relative to one another along the transverse direction T. 
     Referring now to  FIGS. 6 and 7 , an intramedullary nail  400  is shown according to one embodiment. It will be understood that intramedullary nail  400  is but one example, and that other intramedullary nails can be used with the system described herein. The intramedullary nail  400  has an insertion or leading end  402 , and a trailing end  404  offset from the leading end  402  along the rearward direction R, opposite the insertion direction I. The leading and trailing ends  402  and  404  can be spaced from one another along a central nail axis AN that can be straight or bent. Further, the intramedullary nail  400  has an outer surface  420  that extends between the leading and trailing ends  402  and  404 , such as from the leading end  402  to the trailing end  404 . In some embodiments, the intramedullary nail  400  can define a cannulation  426  that extends therein between the leading and trailing ends  402  and  404 . The trailing end  404  can include a fastener  406  that is configured to receive the fastener  300 . For example, the fastener  406  can define a recess or opening  408  that is configured to receive the fastener end  304 . The fastener  406  can include female threading  410  that engages male threading of the fastener  300 , although other fastening mechanisms are contemplated. 
     The trailing end  404  can also include a fastener  412  that is configured to engage the coupler  106  of the spacer  100  so as to rotatably fix the spacer  100  and intramedullary nail  400  relative to one another with respect to rotation about the central nail axis AN. In one embodiment, the fastener  412  can comprise at least one of a protrusion  414  and a recess  416  that is configured to engage a corresponding one of a recess and a protrusion of the spacer  100 . For example, the fastener  412  can comprise at least one protrusion  414 , such a plurality of protrusions or teeth. Each protrusion  414  can be configured to engage at least one corresponding recess in the spacer  100 . Each of the at least one protrusion  414  can extend from a trailing end surface  405  of the intramedullary nail  400  towards the leading end  402  of the nail  400 . The fastener  414  can define at least one recess  416 , such as a plurality of recesses, that extends into the trailing end surface  405  towards the leading end  402 . Each of the at least one recess  416  can be configured to receive a corresponding protrusion  107  of the spacer  100 . Further, in embodiments having a plurality of protrusions  414 , each of the at least one recess  416  can extend between adjacent ones of the protrusions  414 . Thus, in such embodiments, the protrusions  414  and recesses  416  can alternate around the opening  408 . 
     The intramedullary nail further defines a set of one or more trailing bone-anchor fixation holes  422  that extend through the outer surface  420  at the trailing end  404 , and a set of one or more leading bone-anchor fixation holes  424  that extend through the outer surface  420  at the leading end  402 . The set of one or more trailing holes  422  are configured to be disposed on a first side of a fracture in a bone that defines the medullary canal, and the set of one or more leading holes  424  are configured to be disposed on a second side of the fracture in the bone. Thus, the nail  400  can be configured such that the fracture is to be disposed between the set of one or more trailing holes  422  and the set of one or more leading holes  424 . Each trailing aperture  422  and each leading aperture  424  is configured to receive a bone anchor such that the bone anchor fixedly attaches the intramedullary nail  400  to the bone. Each bone-anchor fixation hole  422  and  424  can be either locking aperture having threads that are configured to be engaged by threads of bone screws, or can be non-locking apertures. 
     Turning now to  FIG. 8 , a method of using the intramedullary insertion system will be described. The method comprises a step  701  of coupling the targeting guide  200  to the intramedullary nail  400 . In one example, where the spacer  100  and targeting guide  200  are separable components, the coupling step  701  can comprise a step of coupling the targeting guide  200  to the spacer  100  and a step of coupling the spacer  100  to the intramedullary nail  400 . The targeting guide  200  can be coupled to the spacer  100  before or after the spacer  100  is coupled to the intramedullary nail  400 . In another example, where the spacer  100  and targeting guide  200  are monolithic with one another, the coupling step  701  can comprise a step of coupling the spacer  100  to the intramedullary nail  400 , without separately coupling the spacer  100  to the targeting guide  200 . Note that, in some embodiments, the targeting guide  200  can be pre-coupled to the spacer  100  such that the step of coupling the targeting guide  200  to the spacer  100  can be omitted. Additionally, or alternatively, the spacer  100  can be pre-coupled to the intramedullary nail  400  such that the step of coupling the spacer  100  to the intramedullary nail  400  can be omitted. When the targeting guide  200  is coupled to the intramedullary nail  400 , the central axis C A  of at least one bone-anchor fixation hole  422  intersects a surface of at least one solid portion  205  of the targeting guide  200 . 
     The method can comprise a step  702  of aligning an axis of a cutting instrument  600 , such as a drill bit or reamer, with a bone-anchor fixation hole  422  of the intramedullary nail  400 . The cutting instrument  600  can be aligned on a side of the intramedullary nail  400  that is opposite the at least one solid portion  205  of the inner surface  210  of the targeting guide  200 . 
     The method can comprise a step  703  of inserting the cutting instrument  600  through the bone-anchor fixation hole  422  such that the cutting instrument  600  is in contact with the inner surface  210  of the targeting guide  200 , where the targeting guide  200  is supported relative to the intramedullary nail  400  such that the inner surface  210  is spaced outwardly from the outer surface  420  of the intramedullary nail  400  along a radial direction. 
     The method can comprise a step  704  of driving the cutting instrument  600  through the guide body  204  of the targeting guide  200  so as to form an alignment aperture  218  in the targeting guide  200 . The alignment aperture  218  should have a central axis C A  that is aligned with the bone-anchor fixation hole  422 . Note that, in performing steps  703  and  704 , a guide sleeve (not shown) can be coupled to the bone-anchor fixation hole  422  such that the guide sleeve extends from the intramedullary nail  400  towards the inner surface  210  of the targeting guide  200 . The guide sleeve can then provide additional guidance as the cutting instrument  600  is inserted through the guide sleeve and into the targeting guide  200  to form the alignment aperture  218 . Steps  702  and  703  can be repeated one or more times to form one or more additional alignment apertures  218 . Steps  702  and  703  (and optionally step  701 ) can be performed within a surgical facility such as at a back table of the surgical facility. Alternatively, steps  701  to  703  can be performed prior to shipping the intramedullary nail insertion system to the surgical facility, such as in a manufacturing facility. In some embodiments, the method can comprise a step of enlarging the alignment aperture  218  using a larger cutting instrument, such as a larger drill bit or reamer. 
     The method can comprise a step  704  of inserting the intramedullary nail  400  into the medullary canal of the bone. In one example, the inserting step  704  can comprise de-coupling the targeting guide  200  from the intramedullary nail  400 , inserting the intramedullary nail  400  into the medullary canal, and then re-coupling the targeting guide to the intramedullary nail  400  such that the central axis C A  of each of the at least one alignment apertures  218  is aligned with a corresponding bone-anchor fixation hole  422 . In another example, the inserting step  704  can comprise inserting the intramedullary nail  400  into the medullary canal, while the targeting guide  200  remains coupled to the intramedullary nail  400 . The intramedullary nail  400  is inserted into the medullary canal of a patient along the insertion direction I by applying a force to the nail  400  along the insertion direction. This may be achieved by, for example, using a hammer to drive the intramedullary nail  400  into the canal. 
     The method can comprise a step  705  of forming at least one hole in the bone that is aligned with the at least one bone-anchor fixation hole  422  of the intramedullary nail  400 . The forming step  705  can comprise a step of aligning a central axis of a cutting instrument, such as a drill bit or reamer, with the at least one alignment aperture  218  of the targeting guide  200 , a step of inserting the cutting instrument through the at least one alignment aperture  218  such that the cutting instrument is in contact with the bone, and a step of driving the cutting instrument through the bone to the at least one bone-anchor fixation hole  422  of the intramedullary nail  400 . In one example, step  705  can comprise attaching at least one sleeve to the at least one alignment aperture  218  of the targeting guide  200  such that the at least one sleeve extends from the at least one alignment aperture  218  towards the bone. The cutting instrument can be inserted through the at least one sleeve such that the sleeve protects the surrounding soft tissue as the cutting instrument cuts into the bone. 
     The method can comprise a step  706  of inserting at least one bone anchor through the bone and into the at least one bone-anchor fixation hole  422 . The step  706  can comprise inserting the at least one bone anchor through the at least one alignment aperture  218 . In one example, the at least one bone anchor can be inserted through the at least one sleeve such that the sleeve protects the surrounding soft tissue as the bone anchor is passed therethrough. In one such example, the at least one sleeve can comprise a first sleeve, and a second sleeve disposed within the first sleeve. The second sleeve can be sized to receive the cutting instrument, and the first sleeve can be sized to receive the at least one bone anchor after the first sleeve has been removed after cutting the hole in the bone. Steps  705  and  706  can be repeated for each additional bone anchor to be inserted into a bone-anchor fixation hole  422  of the intramedullary nail  400 . 
     In step  704 , the intramedullary nail  400  can be implanted by driving the nail  400  into a medullary canal of a long bone such as a tibia, fibula, humerus, or femur. Prior to insertion of the assembly  400 , a medical professional can enlarge the medullary canal to make room for the nail  400 . For example, the medullary canal can be enlarged by inserting a reaming rod (not shown) down the medullary canal, and guiding a reamer head (not shown) with at least one cutting edge down the reaming rod such that the at least one cutting edge bores out the medullary canal. The reaming rod can be flexible so as to bend with the contour of the medullary canal. In some examples, the distal end of the reaming rod can have an enlarged distal tip, such as a ball-shaped tip, that can prevent the reamer head from traveling past the distal end of the reaming rod. After enlarging the medullary canal, the intramedullary nail  400  is driven down into the enlarged medullary canal. In some cases, the reamer head can be removed, leaving the reaming rod in place, and the intramedullary nail assembly  100  can then be guided down the reaming rod into the medullary canal. As such, the reaming rod can be received in the cannulation  426  of the intramedullary nail  400  as the nail  400  is driven down the reaming rod into the medullary canal. 
     Typically, the reamer head should be selected based on the size of the intramedullary nail  400 . However, medical professionals can have difficulty in selecting an appropriately sized reaming rod for a particular intramedullary nail and reamer head. On the one hand, if a reaming rod is selected in which the distal tip is too small, then the reaming head can translate past the distal tip, thereby cutting further into the bone than needed. On the other hand, if a reaming rod is selected in which the distal tip is larger than the cannulation  426  of the nail  400 , then the distal tip might not fit through the cannulation  426  of the intramedullary nail  400 . In such a case, it may be difficult, or impossible, to pull the distal tip through the cannulation  426  so as to remove the reaming rod from the intramedullary nail  400  after the nail  400  is implanted. 
     In one aspect of the disclosure, one or more, up to all, of the spacer  100 , the targeting guide  200 , the fastener  300 , and the intramedullary nail  400  can include a verification hole (not shown) that is configured to receive at least a portion of the reaming rod, such as the distal tip. The verification hole, which can also be referred to as a go/no-go hole, can have a cross-sectional dimension that is specific to the size of the specific intramedullary nail  400  that is being used. In particular, the verification hole can have a cross-sectional dimension that corresponds to a size of an appropriately-sized reaming rod, such as to a cross-sectional dimension of the distal tip. Before inserting the reaming rod into the medullary canal, the medical professional can insert the distal tip of the reaming rod into the verification hole to determine whether the reaming rod is an appropriate size. The medical professional can repeat this step until an appropriately-sized reaming rod is identified. The appropriately-sized reaming rod can then be used to implant the intramedullary nail  400 . 
     Referring briefly to  FIG. 5 , the targeting guide  200  of  FIGS. 1 to 3  is shown according to one embodiment with an alignment aperture  218  formed therein. Although not shown, the targeting guide  200  can have one or more additional alignment apertures  218  formed therein. The targeting guide  200  is manufactured in accordance with steps  702  to  704  (and optionally step  701 ). Each alignment aperture  218  has a central axis C A  that is aligned with a bone-anchor fixation hole  422  when the targeting guide  200  is coupled to the intramedullary nail  400 . The central axis C A  of each alignment aperture  218  can extend along the same direction as a central axis of a respective one of the bone-anchor fixation holes  422 . In at least some embodiments, the central axis C A  of each alignment aperture  218  can be in-line or co-linear with a central axis of a corresponding bone-anchor fixation hole  422 . 
     According to various embodiments, targeting guides of the disclosure may be formed from relatively inexpensive materials, such as polymers, including thermoplastics. The use of inexpensive materials may reduce manufacture costs compared to conventional alignment guides that are not custom constructed to a specific nail and that are formed from more expensive materials. Using less expensive materials may also make it more practical to dispose each targeting guide after a single use. This can also eliminate a need to sterilize the targeting guides between uses. 
     In addition, each pre-customized targeting guide of the disclosure can be used with a wider range of intramedullary nails than a comparable conventional alignment guide. A comparable conventional alignment guide is typically constructed to be usable only with an intramedullary nail having a specific size, shape, and bone-anchor fixation hole pattern. A pre-customized targeting guide of the present disclosure, on the other hand, can be usable with a variety of different intramedullary nails having different sizes, shapes, and bone-anchor fixation hole patterns. In particular, a pre-customized targeting guide of the present disclosure can be customized by forming at least one alignment aperture  218  to match the bone-anchor fixation hole pattern of any intramedullary nail in a variety of differently sized and shaped intramedullary nails. 
     Although there has been shown and described the certain embodiments of the present disclosure, it will be readily apparent to those skilled in the art that modifications may be made thereto which do not exceed the scope of the appended claims. The embodiments described in connection with the illustrated embodiments have been presented by way of illustration, and the present invention is therefore not intended to be limited to the disclosed embodiments. Furthermore, the structure and features of each the embodiments described above can be applied to the other embodiments described herein. Accordingly, those skilled in the art will realize that the invention is intended to encompass all modifications and alternative arrangements included within the spirit and scope of the invention, as set forth by the appended claims. 
     It should be noted that the illustrations and descriptions of the examples and embodiments shown in the figures are for exemplary purposes only, and should not be construed limiting the disclosure. One skilled in the art will appreciate that the present disclosure contemplates various embodiments. Additionally, it should be understood that the concepts described above with the above-described examples and embodiments may be employed alone or in combination with any of the other examples and embodiments described above. It should further be appreciated that the various alternative examples and embodiments described above with respect to one illustrated embodiment can apply to all examples and embodiments as described herein, unless otherwise indicated. 
     Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about,” “approximately,” or “substantially” preceded the value or range. The terms “about,” “approximately,” and “substantially” can be understood as describing a range that is within  15  percent of a specified value unless otherwise stated. 
     Conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and/or steps. Thus, such conditional language is not generally intended to imply that features, elements, and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular embodiment. The terms “comprising,” “including,” “having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. 
     While certain example embodiments have been described, these embodiments have been presented by way of example only and are not intended to limit the scope of the inventions disclosed herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions, and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions disclosed herein. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of certain of the inventions disclosed herein. 
     It should be understood that the steps of the exemplary methods set forth herein are not necessarily required to be performed in the order described, and the order of the steps of such methods should be understood to be merely exemplary. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments of the present invention. 
     Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.