Abstract:
An orthopedic implant including a body defining at least one landmark and a probe comprising a sensor spaced apart from the at least one landmark a set distance. The probe and sensor being releasably fixed to the body of the implant to limit movement of the sensor relative to the at least one landmark.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the full benefit of U.S. Provisional Application Ser. No. 61/351,142, filed Jun. 3, 2010, and titled “Orthopaedic Implants,” the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to identification of landmarks on orthopaedic implants. 
     BACKGROUND 
     Orthopaedic implants, such as the interlocking nail, have significantly widened the scope for intramedullary (IM) fixation of bone fractures. Anchoring an IM nail to a bone makes the construct more stable longitudinally and stops rotation of the nail within the bone. A typical IM nail fixation surgery involves a combination of jigs, x-ray imaging, and manual “eye-balling” to locate and drill the distal screw holes and to install the screws in the screw holes. 
     In IM nail fixation surgery, an IM nail is inserted into the canal of a fractured long bone in order to fixate the fractured ends together. Typically, the proximal locking is performed first and is usually carried out with a jig. Nail deformation during intramedullary insertion and manufacturing capabilities, however, may make a jig inaccurate for the distal screws. In fact, the positioning of the distal locking screws and alignment of the drill for the drilling of the distal screw holes is the most time consuming and challenging step of the implantation procedure. The two main reasons for failure in distal locking are (1) incorrect entry point on the bone and (2) wrong orientation/trajectory of the drill. If either of these problems occurs, then the drill will not go through the nail hole. 
     An inaccurate entry point also compounds the problem as the rounded end of the drill bit often slips, damaging healthy bone rendering it difficult to place another drill hole next to the inaccurate hole. Inaccurate distal locking may lead to premature failure with breakage of the nail through the nail hole, breakage of the screw, or the breaking of the drill bit within the bone. 
     In order to overcome the problems associated with distal locking, instrumented IM nails have been designed for distal locking. The instrumented IM nails include a probe having one or more sensors connected to one or more processors. Calibration of the IM nail is carried out to insure that the spatial relationship between the one or more magnetic sensors and one or more landmarks, such as screw holes on the IM nail, are known and accurate. Once calibrated, the IM nail is packaged for use, and the sensor(s) must maintain their position and orientation relative to the landmarks in order for the IM nail to be properly secured within the body of a patient. Limiting or preventing movement of the probe and the associated sensor(s) relative to the IM nail and/or the landmark(s) following calibration and packaging, and prior to use, has been a challenge. 
     Using adhesives to glue the probe and associated sensor(s) to the IM nail, and in particular, to a groove formed in the IM nail, have been an accepted technique for preventing movement of the probe and sensor(s) relative to the IM nail and landmark(s). Use of adhesives, however, have made it very difficult, and in most cases, impossible, to remove the probe, associated sensor(s), and adhesive following surgery. This has led to increased inventory and parts costs and has prohibited reuse of costly materials. 
     There remains a need for a solution that provides features or structures to the IM nail, and in particular, a groove formed in the IM nail, that sufficiently capture the probe and associated sensor(s) following calibration of the IM nail. Further, a need exists for insuring that the position and orientation of the sensor(s) relative to the landmark(s) on the IM nail remain set for targeting and locking of the IM nail within the body, and for providing for easy removal of the probe and associated sensor(s) after targeting and/or locking of the IM nail so that the probe and sensor(s) may be cleaned and reused again. Moreover, a need exists for an implant that includes a probe and associated sensor captured in a manner that permits targeting and locking of a driving end of the implant prior to fixation of the non-driving end. 
     SUMMARY 
     In a general aspect, an orthopaedic implant includes a body defining at least one landmark and a probe including a sensor spaced apart from the at least one landmark a set distance. The probe and sensor being releasably fixed to the body of the implant to limit movement of the sensor relative to the at least one landmark. 
     Implementations may include one or more of the following features. For example, the implant includes a longitudinal groove defined along an outer surface of the body, the longitudinal groove including a driving end portion and a non-driving end portion. The sensor is located in the non-driving end portion of the longitudinal groove. The longitudinal groove includes at least two side walls and a floor connecting the two side walls. The longitudinal groove includes at least a portion along a length of the longitudinal groove wherein the two side walls each form an acute angle with the floor. The longitudinal groove includes at least a second portion along the length of the longitudinal groove wherein the two side walls each form an angle of 90 degrees or greater with the floor. A length of the portion wherein the two side walls each form an acute angle with the floor is between about 0.025 inches to about 0.5 inches. The longitudinal groove receives the probe and sensor in one of a releasable interference fit, press fit, friction fit, or snap fit. The longitudinal groove receives the probe and sensor in a clearance fit and the probe is coupled to the driving end of the groove. The probe is prevented from rotation and translation within the groove. The implant further includes a cover over at least a portion of the groove. The cover is laser-welded to at least a portion of one of the groove and the implant. 
     At least a portion of the longitudinal groove includes one of a dovetail, polygonal, oval, keyhole, or circular cross-sectional shape. The longitudinal groove is configured to receive the probe such that an outer surface of the probe is positioned at or below an outer surface of the body of the implant. The groove includes an opening to the outer surface of the implant and the opening has a width which is less than a diameter of the probe. The landmark is selected from the group consisting of a structure, a hole filler, a polymer screw hole window such as PEEK, a void, a boss, a channel, a detent, a flange, a groove, a member, a partition a step, an aperture, a bore, a cavity, a dimple, a duct, a gap, a notch, an orifice, a passage, a slit, a hole, or a slot. 
     The implant further includes an element having a body with an outwardly extending formation, and wherein the longitudinal groove further includes a recess or through-hole defined in the groove configured to receive the outwardly extending formation. The outwardly extending formation is received in the recess or through-hole via a snap-fit connection or screw-in connection. The probe includes one of an elongated polymer tape or a printed circuit board in contact with the body of the element such that the probe can be separated from at least a portion of the element following implantation of the implant. A portion of the body of the element that is attached to the probe is perforated to permit separation of the probe from the element. 
     The implant further includes a film shrink-wrapped around the probe and the body of the implant to releasably secure the probe and sensor to the implant. The film includes a set of perforations to permit separation of the probe and the sensor from the implant following implantation of the implant into a body. The probe includes an outwardly extending formation that is configured to pierce the shrink-wrapped film when brought into contact with the film. The film is made from a biodegradable or biocompatible material. The tear strength of the film is lowest along the line parallel to the long axis of the probe 
     In another general aspect, a method includes releasably fixing a probe including a sensor to an orthopaedic implant such that the sensor is spaced apart from at least one landmark defined in the orthopaedic implant a set distance, and calibrating the sensor such that a spatial relationship is known between the sensor and the at least one landmark. 
     Implementations may include one or more of the following features. For example, fixing the probe includes placing the probe in a clearance fit in a longitudinal groove on the surface of the implant and coupling a driving end of the probe to the implant such that the probe is prohibited from rotating and translating within the groove. The method further includes placing a cover over at least a portion or preferably the entire length of the groove. Placing the cover includes laser-welding the cover to one of the implant and the groove. The method further includes removing the probe and the sensor from the orthopaedic implant following implantation of the implant into a body. Releasably fixing the probe and the sensor to the implant includes placing at least a portion of the probe into at least one longitudinal section of a longitudinal groove formed in the implant, the at least one longitudinal section of the longitudinal groove configured to receive the probe in one of a interference fit, press fit, friction fit, or snap fit. The probe includes one of an elongated polymer tape or a printed circuit board, and releasably fixing the probe and sensor to the implant includes securing an element having a body with an outwardly extending formation into a recess defined in a longitudinal groove formed in the implant via a snap-fit connection, and coupling the probe and sensor to the body of the element such that the probe and sensor can be separated from at least a portion of the element. Releasably fixing the probe and sensor to the implant includes shrink-wrapping a film around the probe and the body of the implant to releasably secure the probe and sensor to the implant. 
     In another general aspect, an intramedullary nail includes a body defining at least one screw hole, a longitudinal groove with a driving end portion and a non-driving end portion formed along an outer surface of the body, and a probe including a sensor. The probe is releasably secured within the longitudinal groove such that the sensor is spaced apart from the at least one screw hole a set distance. 
     Implementations may include one or more of the following features. For example, the longitudinal groove includes at least two side walls and a floor connecting the two side walls. The longitudinal groove includes a first portion along a length of the longitudinal groove wherein the two side walls each form an acute angle with the floor and a second portion along the length of the longitudinal groove wherein the two side walls each form an angle of approximately 90 degrees or greater with the floor. The longitudinal groove retains the probe at or below the outer surface of the implant. The groove includes an opening to the outer surface of the implant and the opening has a width which is less than a diameter of the probe. The groove further includes a cover. The cover is laser-welded to at least one of the implant and the groove. The probe is prevented from rotating and translating within the groove. 
     The nail further includes an element having a body with an outwardly extending formation, and wherein the longitudinal groove further includes a recess defined in the longitudinal groove and configured to receive the outwardly extending formation via a snap-fit connection. The probe includes one of an elongated polymer tape or a printed circuit board being in contact with the body of the element such that the probe can be separated from at least a portion of the element following implantation of the intramedullary nail. A portion of the body of the element that is attached to the probe is perforated to permit separation of the probe from the element. 
     The nail further includes a film shrink-wrapped around the probe and the body of the nail to releasably secure the probe and sensor to the nail. The film includes a set of perforations to permit separation of the probe and the sensor from the nail following implantation of the nail into a body. The probe includes an outwardly extending formation that is configured to pierce the shrink-wrapped film when brought into contact with the film. The film is made from a biodegradable or biocompatible material. The tear strength of the film is lowest along a line parallel to a long axis of the probe 
     The disclosed apparatuses and methods include several advancements. For example, the disclosed apparatuses and methods provide features and structures that sufficiently capture a probe and associated sensor(s) in a calibrated position and orientation to permit the instrumented IM nail to perform its designed targeting function, yet allow for easy removal of the probe and sensor(s) after targeting. This permits reuse of the probe and sensor(s) with other IM nails, lowers inventory costs, and reduces the number of parts and materials required to be left behind in the body of a patient. Moreover, the disclosed apparatuses and methods provide features that permit locking of the nail at the driving end of the implant prior to locking or fixing the non-driving end of the implant. In addition, the disclosed apparatuses and methods assist in limiting or preventing tissue from dislodging or causing the probe and associated sensor to translate or rotate in the groove during, for example, insertion of the IM nail into the body of the patient. Further, the disclosed apparatuses and methods provide features and structures that limit or eliminate bone-in growth in the groove and thus, allow the implant to be removed easily later during revision surgery or when a new implant is required. 
     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 
         FIG. 1  illustrates a system for identifying a landmark. 
         FIG. 1A  illustrates an alternative implementation of a landmark identifier for use in the system of  FIG. 1 . 
         FIG. 2  is a detailed prospective view of the orthopaedic implant of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the orthopaedic implant taken along one of the portions  62  of the orthopaedic implant of  FIG. 2 . 
         FIG. 3A  is a cross-sectional view of the orthopaedic implant taken along one of the portions  62  of the orthopaedic implant of  FIG. 2 . 
         FIG. 4  is a cross-section view of the orthopedic implant taken along portion  4 - 4  of  FIG. 2 . 
         FIG. 4A  is a cross-section view of the orthopedic implant taken along one of the portions  64  of the orthopaedic implant of  FIG. 2 . 
         FIG. 5  is an enlarged view of one of the portions  62  of the orthopaedic implant of  FIG. 2 . 
         FIG. 6  is a cross-sectional view of an alternative implementation of the orthopaedic implant assembly  28 . 
         FIG. 7  is a cross-sectional view of an alternative implementation of the orthopaedic implant assembly  28 . 
         FIG. 7A  is a cross-sectional view of an alternative implementation of the orthpaedic implant assembly  28 . 
         FIG. 8  is an alternative implementation for limiting or preventing translation and rotation of the probe  50  within the groove  60 . 
         FIG. 9  is a top view of a bushing for use in an alternative implementation of the orthopaedic implant. 
         FIG. 10  is a side view of the bushing of  FIG. 6 . 
         FIG. 11  is a top view of the alternative implementation of the orthopaedic implant. 
         FIG. 12  is a cross-sectional view of the orthopaedic implant of  FIG. 8  taken along a longitudinal axis of the implant. 
         FIG. 13  illustrates another implementation of a orthopaedic implant assembly. 
     
    
    
     It should be understood that the drawings are not necessarily to scale and that the disclosed implementations are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosure 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 implementations illustrated herein. 
     DETAILED DESCRIPTION 
     Referring to the accompanying drawings in which like reference numbers indicate like elements,  FIG. 1  illustrates one disclosed system  10  for identifying a landmark. The system  10  includes a processor  12 , a magnetic field generator  16 , a landmark identifier  18 , and an orthopaedic implant assembly  28 . The system  10  also includes a monitor  14  electrically connected to the processor  12  and an insertion handle  40  removably attached to an orthopaedic implant  30  of the orthopaedic implant assembly  28 , and in a particular example, to a driving end  30   a  opposite a non-driving end  30   b  of the orthopaedic implant  30 . The processor  12  is depicted as a desktop computer in  FIG. 1  but other types of computing devices may be used. As examples, the processor  12  may be a desktop computer, a laptop computer, a personal data assistant (PDA), a mobile handheld device, or a dedicated device. The magnetic field generator  16  is a device available from Ascension Technology Corporation of 107 Catamount Drive, Milton Vt., U.S.A.; Northern Digital Inc. of 103 Randall Drive, Waterloo, Ontario, Canada; or Polhemus of 40 Hercules Drive, Colchester Vt., U.S.A. Of course, other generators may be used. As examples, the field generator  16  may provide a pulsed direct current electromagnetic field or an alternating current electromagnetic field. The system  10  may also include a control unit (not shown) connected to the magnetic field generator  16 . The control unit controls the field generator  16 , receives signals from small mobile inductive sensors, and communicates with the processor  12 , either by wire or wirelessly. The control unit may be incorporated into the processor  12  either through hardware or software. 
     The system  10  may be referred to as a magnetic position tracking system. For illustrative purposes, the system  10  may include a magnetic field generator  16  comprised of suitably arranged electromagnetic inductive coils that serve as the spatial magnetic reference frame (i.e., X, Y, Z). The system  10  may also include small mobile inductive sensors, which are attached to the object being tracked. It should be understood that other variants could be easily accommodated. The position and angular orientation of the small mobile inductive sensors are determined from its magnetic coupling to the source field produced by magnetic field generator  16 . 
     It is noted that the magnetic field generator  16  generates a sequence, or set, of six, different spatial magnetic field shapes, or distributions, each of which is sensed by the small mobile inductive sensors. Each sequence enables a sequence of signals to be produced by the small mobile inductive sensors. Processing of the sequence of signals enables determination of position and/or orientation of the small mobile inductive sensors, and hence the position of the object to which the small mobile inductive sensor is mounted relative the magnetic coordinate reference frame which is in fixed relationship to the magnetic field generator  16 . The processor  12  or the control unit may use the reference coordinate system and the sensed data to create a transformation matrix comprising position and orientation information. 
     The landmark identifier  18  is used to target a landmark, such as a landmark on the orthopaedic implant assembly  28 . The landmark identifier  18  may include one or more small mobile inductive sensors or may include the field generator. The landmark identifier  18  has a second sensor  20 . The landmark identifier  18  may be any number of devices. As examples, the landmark identifier may be a device that includes a structure that provides a user with an understanding of the location and orientation of a hidden landmark. For example, the landmark identifier can include a drill guide, a drill sleeve, a drill, a drill nose, a drill barrel, a drill chuck, or a fixation element. In some implementations, the structure can be a housing having an opening, or other structure that indicates the location and orientation of a landmark. In  FIG. 1 , the landmark identifier  18  is a drill sleeve and includes a sensor  20 . The landmark identifier  18  may include one or more of a serrated tip  22 , a tube  24 , and a handle  26 . The tube  24  also may be referred to as a bushing, cylinder, guide, or drilling/screw placement guide. The second sensor  20  is oriented relative to an axis of the tube  24 . The tube  24  may receive a drill. This offset of the sensor  20  from the tube  24  allows the position and orientation of the tube to be located in space in six dimensions (three translational and three angular) relative to the magnetic field generator  16  and/or another sensor in the system. The processor  12  may need to be calibrated to adjust for the offset distance of the second sensor  20 . The landmark identifier  18  and the field generator  16  may be combined into a single component. For example, the field generator  16  may be incorporated within the handle  26 . 
       FIG. 1A  illustrates an alternative implementation that combines the functionalities of the landmark identifier  18  and the field generator  16  with a removable component, such as a drill sleeve  2022 , into a handheld landmark identifier  2016  that may be used in the system  10 . The handheld landmark identifier  2016  houses an electromagnetic field generator (not shown) that may include one or more induction coils or other elements to create a suitable electromagnetic field or fields. The electromagnetic field generator is mounted in or on an autoclavable material and encapsulated in an autoclavable housing body  2018  that may be easily sterilized. The housing body  2018  includes a coupling member  2018   c  that passes through the internal body and the housing  2018  and removably engages one or more attachable components, such as drill sleeve  2022  having a serrated tip  2024 , or other suitable tools, such as a screw driver sleeve or other drill sleeves as selected by a surgeon. The housing body  2018  includes a first covering  2018   a  formed from an autoclavable material, such as an overmolding of silicone material, and may include a second covering  2018   b  that provides an additional layer of protection or insulation, or aesthetics at an outer edge of the housing  2018 . The second covering  2018   b  may be formed from an autoclavable material similar or different than the first covering  2018   a.    
     Unlike the landmark identifier  18  illustrated in  FIG. 1 , the handheld landmark identifier  2016  does not require the sensor  20  because the origin of the global space (the area in which the electromagnetic field is generated) can be defined within the landmark identifier  2016 . For example, one axis of the global space coordinate system can be the longitudinal axis of the drill sleeve or other component  2022 . In that situation, the other two axes of the global space coordinate system can be defined by planes orthogonal to that longitudinal axis and to each other. An advantage of incorporating the field generator into the landmark identifier  2016  includes a smaller size field generator because it can be brought into the local working space (area which may include the landmarks such as implant holes that are to be targeted for screw placement), therefore requiring a smaller electromagnetic field. In addition, use of the landmark identifier  2016  eliminates the necessity of X-ray devices for targeting of transfixion elements, such as radiation-emitting, fluoroscopic “c-arms,” which have been used during tibial and femoral nail cases to achieve proper distal screw placement. 
     The orthopaedic implant assembly  28  may include the implant  30  and one or more small mobile inductive sensors. In the implementation shown in  FIGS. 1 and 2 , the orthopaedic implant assembly  28  includes a probe  50  disposed within a longitudinal groove  60  formed in the implant  30 . The probe  50  includes a tape body  51  and a first sensor  32  disposed within or on the tape body  51 . The probe  50  is disposed within the groove  60 . The tape body  51  of the probe  50  may have a rectangular, circular, oval, or square geometry to assist in orienting the tape body  51  as it is placed into the implant  30 , and the geometry may be constant or varying along a length of the probe  50 . In some implementations, the tape body  51  may be a hollow metal tube. The probe  50  may include a lead or wire (not shown) coupled to the first sensor  32  to transmit, for example, a signal from the first sensor  32  to the processor  12 . The lead may be made from biocompatible wire. As an example, the lead may be made of DFT wire available from Fort Wayne Metals Research Products Corp., 9609 Indianapolis Road, Fort Wayne, Ind. 46809. DFT is a registered trademark of Fort Wayne Metals Research Products Corp. Alternatively, the first sensor  32  may be coupled to the processor  12  via a wireless connection. 
     In  FIGS. 1 and 2 , the implant  30  is in the form of IM nail but other types of implants may be used. As examples, the implant may be an IM nail, a bone plate, a shoulder prosthetic, a hip prosthetic, or a knee prosthetic. The implant  30  may be made from any suitable biocompatible material, such as, titanium, cobalt chrome, stainless steel, biodegradable polymer, or other biocompatible material. The implant  30  may include a cannulation  33 . 
     The first sensor  32  is oriented and in a predetermined position relative to one or more landmarks on the implant  30 . As examples, the landmark may be a structure, a void, a boss, a channel, a detent, a flange, a groove, a member, a partition, a step, an aperture, a bore, a cavity, a dimple, a duct, a gap, a notch, an orifice, a passage, a slit, a hole, or a slot. In addition, the landmark may be a hole filler, a polymer screw hole window such as PEEK, or other identifier formed in or on the implant  30  that identifies or indicates the location on the implant  30  through which a surgeon may form a through hole or other aperture during implantation for receiving a fixation member, such as a screw. In  FIGS. 1 and 2 , the landmarks are transfixion holes  31 . The offset of the first sensor  32  from the landmark allows the position of the landmark to be located in space in six dimensions (three translational and three angular) relative to the magnetic field generator  16  or another sensor in the system, such as the second sensor  20 . The processor may need to be calibrated to adjust for the offset distance of the first sensor  32 . 
     The first sensor  32  and the second sensor  20  are coupled to the processor  12 . Again, this may be accomplished by wire or wirelessly. The first sensor  32  and the second sensor  20  may be a six degree of freedom sensor configured to describe the location of each sensor in three translational axes, generally called X, Y and Z and three angular orientations, generally called pitch, yaw and roll. By locating the sensor in these reference frames, and knowing the location and orientation of each sensor, the landmark identifier  18  may be located relative to the landmark on the implant  30 . In one particular implementation, the information from the sensors allows for a surgeon to plan the surgical path for fixation and properly align a drill with a blind fixation hole  31 . Exemplary sensors  32 ,  20  are six degrees of freedom sensor from Ascension Technology Corporation of 107 Catamount Drive, Milton Vt., U.S.A.; Northern Digital Inc. of 103 Randall Drive, Waterloo, Ontario, Canada; or Polhemus of 40 Hercules Drive, Colchester Vt., U.S.A. Of course, other sensors may be used. 
     As shown in  FIGS. 1 and 2 , the probe  50 , which includes the tape body  51  and the first sensor  32  disposed within or on the tape body  51 , are disposed within the longitudinal groove  60  formed in an outer surface of the implant  30 . The groove  60  extends from a driving end  30   a  of the implant  30  to a non-driving end  30   b  of the implant  30  so that the first sensor  32  may be placed in a desired proximity to the landmarks  31  to be targeted. Of course, the groove  60  may be located anywhere along the length of the implant  30  in order to position the first sensor  32  within the desired proximity to the landmarks  31 . Further, although the first sensor  32  is shown positioned near the landmarks  31  formed in the non-driving end  30   b  of the implant  30 , the first sensor  32  may be positioned near the landmarks  31  formed in the driving end  30   a  of the implant  30 . In this manner, having the probe  50  within groove  60 , instead of within the central cannula  33 , permits locking of the implant  30  using the landmarks  31  at the driving end  30   a  of the implant  30  prior to affixing the implant  30  at the non-driving end  30   b.    
     The groove  60  may include one or more portions  62  formed at intermittent locations along the length of the groove  60  to receive the probe  50 , and more particularly, the tape body  51 , in order to rigidly and mechanically capture the probe  50  and the first sensor  32  in a fixed position relative to the implant  30 . For example, as shown in  FIGS. 3 and 5 , the portions  62  include two side walls  62   a  and a floor  62   b  intersecting the two side walls  62   a . The walls  62   a  form an acute angle θ with the floor  62   b  such that a cross section of the portion  62  forms a dovetail when viewed from an end of the groove  60  ( FIG. 3 ). These dovetail-shaped side walls  62   a  and floors  62   b  provide an interference, press, friction, or snap fit between the probe  50  and the groove  60  by pressing the sections of the probe  50  received in the portions  62  against the floor  62   b.    
     The force to capture the probe  50  in a position and orientation relative to the implant  30 , and the force required to remove the probe  50  from the groove  60 , for example, upon completion of targeting the landmarks  31 , depends on a number of factors. These factors include the length (l) of each dovetail portion  62 , the opening width (t), height (h), and floor width (b) of each dovetail side wall portion  62  ( FIG. 5 ), and the location and number of dovetail portions  62  along the length of the groove  60 . As an example, the optimization of the length (l) of each dovetail portion  62  provides a balance between the force required to snap or press the probe  50  into each of the portions  62  and the force to remove the probe  50  following targeting. In an exemplary implementation, the length (l) is about 0.025 inch to about 0.5 inch, or alternatively, about 0.075 inch to about 0.15 inch, the height (h) of each portion  62  is about 0.055 inch, the opening width (t) is about 0.078 inch, and the floor width (b) is about 0.083 inch. The ratios of the height (h), the opening width (t), and the floor width (b) to, for example, the diameter of the probe  50 , in some implementations, are in the range of about 65% to about 73%, about 92% to about 96%, and at least 100% respectively. 
     The groove  60  may have as many as five to six dovetail portions  62  along its length, and in some implementations, a portion  62  is positioned to correspond to the location on the probe  50  where there is a change in a radial angle along the probe axis to insure that the probe  50  remains secured within the groove  60  within the transition portion of the implant  30 . For example, as shown in  FIG. 2 , implant  30  includes at least one transition section  30   c  that forms an angle between the driving end  30   a  and the non-driving end  30   b  of the implant  30 . At least one dovetail portion  62  is positioned within transition section  30   c  to ensure that the probe  50  is secured within the transition section  30   c . In other implementations, a minimum of one to two dovetail portions  62  may be sufficient to fix the probe  50  and the first sensor  32  in place relative to the implant  30 . In implementations where only one dovetail portion  62  is provided in the groove  60 , the dovetail portion  62  may be positioned near the driving end  30   a  of the implant  30  to secure the probe  50  within the groove  60 . 
     Referring to  FIGS. 2 and 4 , in addition to the one or more dovetail portions  62 , the groove  60  may include one or more portions  64  formed adjacent to the dovetail portions  62  and at intermittent locations along a length of the groove  60 . Like the portions  62 , the portions  64  may include two side walls  64   a  and a floor  64   b  intersecting the two side walls  64   a . The side walls  64   a  may form right angles with the floor  64   b  such that a cross section of the portion  62  is substantially square or rectangular when viewed from an end of the groove  60  ( FIG. 4 ). Other implementations where the side walls form angles greater than 90 degrees with the floor are also within the scope of the invention. As shown in  FIG. 4 , unlike portions  62 , the probe  50  does not interact with the side walls  64   a  of the portions  64 . However, in other implementations, the dimensions of the side walls  64   a  and the floor  64   b  may be sized such that the side walls  64   a  and the floor  64   b  interact with the probe  50  to provide, for example, an additional interference fit between the side walls  64   a  and/or the floor  64   b.    
     An alternative implementation of groove  60 , and specifically, portions  62 , is shown in  FIG. 3A . In the implementation of  FIG. 3A , portions  162  are formed with a substantially circular cross-sectional shape (when viewed from an end of the groove  60 ) that receives the probe  50 . The portions  162  include an opening  163  formed between two walls  163   a ,  163   b  for receiving the probe  50  within the circular cross-sectional area of the portions  162 . The opening  163  has a width which is less than a diameter of the probe  50 . End portions of the walls  163   a ,  163   b  provide an interference, press, friction, or snap fit between the probe  50  and the groove  60  to maintain the probe  50  in position within the portions  162  and to limit movement of the probe  50  caused, for example, by tissue grabbing or dislodging the probe during, for example, insertion of the implant  30  in a bone. 
     Referring to  FIGS. 3A and 4A , in addition to the one or more circular portions  162 , the groove  60  may include one or more circular portions  164  formed adjacent to the portions  162  and at intermittent locations along a length of the groove  60 . Like the portions  162 , the portions  164  are formed with a substantially circular cross-sectional shape (when viewed from an end of the groove  60 ) that receives the probe  50 . As shown in  FIG. 4A , unlike portions  162 , the probe  50  is free to move within the portions  164 . However, in other implementations, the dimensions of the circular portion  164  may be sized such that the probe  50  interacts with portions of the opening  164   a  formed by end portions  164   b ,  164   c  of the implant  30  to provide, for example, an additional interference fit between the probe  50  and the portions  164 . As illustrated in  FIGS. 3A and 4A , when received within the portions  162 ,  164 , the outer surface of the probe  50  is positioned at or below the outer surface of the body of the implant  30 , which assists in preventing or limiting tissue from dislodging or causing the probe  50  to translate or rotate during, for example, insertion of the implant  30  in a bone. In certain implementations, however, it may also be positioned above the outer surface of the implant  30 , if necessary. 
     In use, the probe  50 , including the first sensor  32 , is secured within the groove  60  of the implant  30 , by pressing or snapping the probe  50  into the one or more dovetail portions  62  formed in the longitudinal groove  60 . The implant  30  may then be calibrated. Calibration is analogous to registration in computer assisted surgery. Calibration may be needed for different reasons. For example, sensor calibration may be needed to correct for manufacturing tolerances. The system may be designed based upon a computer-aided-design model, and calibration is used to accurately place the sensors relative to one another or to the one or more landmarks  31 . For example, calibration may be necessary to determine the spatial relationship between the first sensor  32  and one or more of the landmarks  31 . The processor or the control unit may include software to generate X, Y, Z, pitch, yaw, and roll offset values to locate the sensors in a global coordinate system or simply placement relative to one another. The system may be manufactured and calibrated during manufacturing and assigned a unique identifier, such as a serial number, color code, bar code, or RFID tag. If the system needs to be re-calibrated, the unique identifier may be used to retrieve the offset values, either locally or over a network. Further, the unique identifier may be used to retrieve other data, such as the size of the IM nail or the length of the IM nail and/or the probe. 
     Following calibration, the implant  30  may be packaged and shipped to an end user, such as a physician, who then performs an implantation procedure. During shipping and implantation of the implant  30 , the probe  50  and the first sensor  32  are secured within the groove  60  via an interference or snap fit between the dovetail portions  62  and the probe  50 , as described above. Once targeting of one or more of the landmarks  31  is complete, the probe  50  and the first sensor  32  may be removed from the implant  30  and sterilized for reuse with another implant  30 . 
       FIG. 6  illustrates an alternative implementation of the orthopaedic implant assembly  28  including the orthopaedic implant  30 . As shown in  FIG. 6 , the probe  50  and associated sensor, such as sensor  32 , are received in the longitudinal groove  60  formed in the implant  30 . Similar to the other implementations discussed above, the groove  60  may extend from the driving end  30   a  of the implant  30  to the non-driving end  30   b  of the implant. The groove  60  may include an additional cut-out portion  60   a  located near the outer portion of the implant  30  as shown in  FIG. 6 . A lid or cover  100  may be attached to the implant  30  within the groove  60 , and particularly within the cut-out portion  60   a  of the groove  60 . The lid or cover  100  may be attached within the cut-out portion  60   a  of the groove  60  by laser-weld, gluing, or other acceptable attachment means. In another implementation, the lid or cover  100  may be attached to the implant  30 , for example, to an outer surface of the implant  30 . The lid or cover  100  prevents bone in-growth in the groove  60  and thus, allows the implant to be removed easily later during, for example, revision surgeries or when a new implant is required. The lid or cover  100  also prevent tissue from touching the probe  50  during installation of the implant  30  into the body and therefore, may also assist in preventing rotation or translation of the probe  50 . 
       FIG. 7  shows an alternative to the cover or lid  100  of  FIG. 6  for preventing bone in-growth in the groove. As shown in  FIG. 7 , an outer sleeve  150  may be placed around the periphery or a portion of the periphery of the orthopaedic implant  30 . The outer sleeve  150  may be coupled to the implant  30  via press fit or other means known to one skilled in the art. The outer sleeve  150  covers over the groove  60 , and acts as the lid  100  of  FIG. 6  to prevent bone in-growth in the groove  60 , following, for example removal of the probe  50  from the groove  60  following implantation of the implant  30  into bone tissue. The outer sleeve  150  can include one or more longitudinal slits so long as it can grab on the implant  30  and cover the groove  60 . Although the outer sleeve  150  is shown as encircling the periphery of the implant  30 , the outer sleeve  150  may encircle only a portion of the periphery of the implant  30  as long as the outer sleeve  150  can attach to the implant  30  or groove  60  and cover the groove opening. Alternatively, a similar sleeve  155  ( FIG. 7A ) can be used in place of the outer sleeve  150  and adapted to be placed around the periphery or a portion of the periphery of the probe  50 . The sleeve  155  can include one or more longitudinal slits, and can cover only a portion of the periphery of the probe  50  so long as the sleeve  155  can cover the groove opening. In the implementation of  FIG. 7A , the probe  50  and the sleeve  155  are, for example, press-fitted in the groove  60 . The sleeve  155  acts in a similar manner to the lid  100  of  FIG. 6  to prevent bone in-growth in the groove  6  following, for example, removal of the probe  50  from the groove  60 . 
       FIG. 8  illustrates a coupling mechanism for coupling the probe  50  to the implant  30  for limiting or preventing translation and rotation of the probe  50  and associated sensor  32  within the groove  60  relative to the implant  30 . As shown in  FIG. 8 , a retention mechanism  200  includes a body portion  202  with an anti-rotation cross section such as a rectangular cross section as shown and two leg portions  204 ,  206  extending from the body portion  202 . In one implementation, the leg portions  204 ,  206  include generally V-shaped, deflectable portions  204   a ,  206   a  configured and shaped to mate with mating portions (such as corresponding grooves, voids or receptacles (not shown)) formed within the groove  60 . As shown in  FIG. 8 , the retention mechanism  200  defines a through hole  210  through which the probe and included sensor may pass and be retained via glue, crimping, friction fitting or any attachment means known to one skilled in the art. 
     In use, the retention mechanism  200  may be inserted, for example, into the longitudinal groove  60  at the driving end  30   a  of the implant  30  by compressing the leg portions  204 ,  206  towards each other. As the retention mechanism  200  is inserted into the longitudinal groove  60 , the leg portions  204 ,  206  ride along the inside surface of the longitudinal groove  60  until the V-shaped portions  204   a ,  206   a  are positioned proximate the corresponding mating portions (not shown) formed within the groove  60 . Once the leg portions  204 ,  206  are proximate the mating portions, the leg portions  204 ,  206  rebound towards their uncompressed state and interact with their respective corresponding mating portions such that the retention mechanism  200 , and the attached probe and sensor are prevented or limited from translating or rotating relative to the implant  30 . Once targeting of one or more of the landmarks  31  is complete, the retention mechanism  200 , and the attached probe  50  and sensor, may be removed from the implant  30  by compressing the leg portions  204 ,  206  such that they no longer interact with the corresponding mating portions formed in the groove  60 , and the retention mechanism  200 , probe  50  and sensor may be removed from the implant  30  and sterilized for reuse with another implant  30 . 
       FIGS. 9-12  illustrate an alternative implementation of the orthopaedic implant assembly  28  including an orthopaedic implant  30 . As shown in  FIGS. 11 and 12 , the implant  30  includes at least one landmark in the form of a transfixion hole  31 . The implant  30  includes a longitudinal groove  60  formed in a portion of the implant  30 . The groove  60  may be formed along an outer surface of the implant  30 .  FIGS. 9 and 10  illustrate an element in the form of a bushing  70  that can be made from a biocompatible and/or biodegradable material, such as a biocompatible and biodegradable polyethylene or other suitable material. The bushing  70  includes an outwardly extending spherical nipple  72  that is received in a corresponding recess  66  defined in the groove  60  in a snap-fit arrangement. 
     The assembly  28  includes a probe  50  in the form of an elongated polymer tape or printed circuit board  52  and a first sensor  32  disposed within or on the tape or printed circuit board  52 . The tape or board  52  may also include wires (not shown) coupled to the first sensor  32  to transmit, for example, a signal from the first sensor  32  to the processor  12 . The tape or board  52  is coupled to, and in contact with, the bushing  70  via a bond  80 . Bond  80  may be formed by welding, gluing, or otherwise coupling and contacting the tape or board  52 , including the first sensor  32 , to the bushing  70 . The bushing  70  further includes a perforation  74  that permits separation of the tape or board  52  and the first sensor  32  from the bushing  70  following, for example, targeting of the landmark  31 . The perforation may be adapted to require a smaller force of breakage than that of the probe/tape. 
     In use, following calibration, and during shipping and implantation of the implant  30 , the tape or board  52  and the first sensor  32  are secured within the groove  60  via the bushing  70 . Once targeting of the one or more of the landmarks  31  is complete, the tape or board  52  and the first sensor  32  may be separated and removed from the implant  30  by separating the tape or board  52  from a portion of the bushing  70  via the perforations  74 . The tape or board  52  and the first sensor  32  may then be sterilized for reuse with another implant  30  and bushing  70 , or simply discarded. 
       FIG. 13  illustrates another implementation of the orthpaedic implant assembly  28  including the orthopaedic implant  30 . The implant  30  includes landmarks in the form of transfixion holes  31 . The implant  30  includes a longitudinal groove  60  formed on an outer surface of the implant  30 , however, the longitudinal groove is optional. The assembly  28  includes a probe  50 , which includes a tape body  51  and a first sensor  32  disposed within or on the tape body  51 . A portion of the tape body  51  and the sensor  32  may be positioned within the groove  60 . The groove  60  extends from a driving end  30   a  of the implant  30  to a non-driving end  30   b  of the implant  30  so that the first sensor  32  may be placed in a desired proximity to any of the landmarks  31  to be targeted. 
     The implant assembly  28  further includes a biodegradable and/or biocompatible polymer film  90 . The film  90  may be made from any suitable biocompatible and/or biodegradable polymer material, such as, but not limited to, polylactic acid (PLA) or polyglycolide or polyglycolic acid (PGA). Once the probe  50  (tape body  51  and the first sensor  32 ) are placed on the surface of the implant  30 , such as within the groove  60 , the implant  30  and the probe  50  are shrink-wrapped with the film  90  to limit and/or prevent movement of the probe  50  and sensor  32  relative to the implant  30 . 
     In order to remove the probe  50  from the implant  30  following, for example, targeting of the one or more landmarks  31 , the film  90  may be manufactured to include a one-way tear (not shown) or a set of perforations  92  to allow for separation of the probe  50  from the implant  30  through the shrink-wrapped film  90 . Alternatively, the probe  50  may be provided with an outwardly extending formation (not shown), such as a sharp edge or protrusion that pierces and/or cuts the shrink-wrapped film  90  as the probe  50  is pulled and separated from the implant  30 . As a further alternative, the film  90  may be made from a molecularly-oriented polymer having a minimal tear strength along one direction or axis within the film. In such an implementation, the film  90  may be oriented on the implant  30  such that when the film is wrapped around the implant  30 , the minimal tear axis is lined up with, or parallel to, the longitudinal axis of the probe  50 , such that, upon removal of the probe  50  from the implant  30 , the film  90  tears along the longitudinal axis of the probe  50  allowing for ease of removal from the implant  30 . 
     While only certain implementations have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. For example, although the portions  62  of the groove  60  have been described as having a dovetail-like cross-sectional shape, other shapes are within the scope of this disclosure. For example, alternative cross-sectional shapes include polygonal, oval, keyhole, or circular. In addition, the cross-sectional shape of portions  62  may be similar to the cross-sectional shape of portions  64  yet smaller in size such that the probe  50  is received in the portions  62  in an interference fit. In addition, the portions  62  may include protrusions added to, or formed as an integral part of the groove  60 , that provide a balanced force between rigidly and mechanically capturing the probe  50  and allowing for the release of the probe  50  upon completion of use. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.