Patent Publication Number: US-11638608-B2

Title: Femoral base plate THA

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of U.S. Nonprovisional patent application Ser. No. 15/663,934, filed Jul. 31, 2017, now U.S. Pat. No. 10,441,362, which is a continuation of U.S. Nonprovisional patent application Ser. No. 15/381,031, titled “FEMORAL BASE PLATE THA,” filed Dec. 15, 2016, now abandoned, and claimed the benefit of U.S. Provisional Patent Application Ser. No. 62/267,370, titled “FEMORAL BASE PLATE THA,” filed Dec. 15, 2015, the disclosure of each of which is incorporated herein by reference. 
    
    
     INTRODUCTION TO THE INVENTION 
     The present disclosure is directed to optimization of shape, placement, and screw locations for attachment of a femoral base plate that may be used with a posterior approach for total hip arthroplasty using a surgical navigation system including inertial measurement units. As will be discussed in more detail hereafter, the shape of the femoral base plate is taken from the mean surface curvature of a statistical atlas of femoral bones at a defined base plate attachment site. This base plate attachment site may be dependent on screw length and locations, so that when placed correctly the attachment screws do not impinge on the proposed rasp and stem components. 
     It should be noted that Patent Cooperation Treaty application PCT/US14/69411, filed Dec. 9, 2014 is hereby incorporated by reference. Portions of the foregoing application are appended hereto as Appendix A. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram depicting a proximal portion of a femur that includes the femoral ball and a proposed attachment site for a bone base plate in accordance with the instant disclosure. 
         FIG.  2    is a partially resected femoral bone model showing placement of three surgical screws and the trajectory and position relative to the intramedullary canal of the femur and the boundary of the femoral stem of an orthopedic implant positioned within the intramedullary canal. 
         FIG.  3    is a partially resected femoral bone model showing an intramedullary canal of the femur and the boundary of the femoral stem of an orthopedic implant positioned within the intramedullary canal. 
         FIG.  4    is the partially resected femoral bone model of  FIG.  3    shown with the reference plane in position. 
         FIG.  5    is a table showing the mean, standard deviation, minimum, and maximum distances respective screw distal ends were with respect to the reference plane using the modeling and computations in accordance with the instant disclosure. 
         FIG.  6    is a chart depicting 13 impingement circumstances where the first screw pierced the reference plane and how far the first screws extended beyond the reference plane once pierced. 
         FIG.  7    is a chart depicting 10 impingement circumstances where the second screw pierced the reference plane and how far the second screws extended beyond the reference plane once pierced. 
         FIG.  8    is a chart depicting 2 impingement circumstances where the third screw pierced the reference plane and how far the third screws extended beyond the reference plane once pierced. 
         FIG.  9    is a diagram showing placement of the first exemplary bone reference assembly (without the IMU) on an anterior portion of a femur. 
         FIG.  10    is a diagram showing placement of the first exemplary bone reference assembly on an anterior portion of a femur. 
         FIG.  11    is a top, elevated perspective view of an exemplary femoral bone base plate in accordance with the instant disclosure. 
         FIG.  12    is a bottom, subverted perspective view of the exemplary femoral base plate of  FIG.  11   . 
         FIG.  13    is a top view of the exemplary femoral base plate of  FIG.  11   . 
         FIG.  14    is a right side view of an exemplary stem in accordance with the instant disclosure. 
         FIG.  15    is an elevated perspective view of the stem of  FIG.  14   . 
         FIG.  16    is a profile view of an alternate exemplary stem. 
         FIG.  17    is a profile view of the exemplary stem of  FIG.  14   . 
         FIG.  18    is an elevated perspective view of a fastener in accordance with the instant disclosure. 
         FIG.  19    is a bottom view of a portion of the stem of  FIG.  14   . 
         FIG.  20    is a partial exploded view showing the fastener, femoral base plate, and a portion of the stem prior to assembling them as a single element of the first exemplary bone reference assembly. 
         FIG.  21    is a left and right elevated perspective view of the components of  FIG.  20    post assembly. 
         FIG.  22    is a diagram showing placement of the second exemplary bone reference assembly (without the IMU) on a posterior portion of a femur. 
         FIG.  23    is a diagram showing placement of the second exemplary bone reference assembly on a posterior portion of a femur. 
         FIG.  24    is a top, elevated perspective view of a second exemplary femoral bone base plate in accordance with the instant disclosure. 
         FIG.  25    is a bottom, subverted perspective view of the exemplary femoral base plate of  FIG.  24   . 
         FIG.  26    is a top view of the exemplary femoral base plate of  FIG.  24   . 
         FIG.  27    is a right side view of a second exemplary stem in accordance with the instant disclosure. 
         FIG.  28    is an elevated perspective view of the stem of  FIG.  27   . 
         FIG.  29    is an elevated perspective view of a fastener in accordance with the instant disclosure. 
         FIG.  30    is a left elevated perspective view of the components of the second exemplary bone reference assembly. 
         FIG.  31    is a right elevated perspective view of the components of the second exemplary bone reference assembly. 
         FIG.  32    is a bottom view of a portion of the second exemplary stem of  FIG.  27   . 
         FIG.  33    is a partial exploded view showing the fastener, femoral base plate, and a portion of the stem prior to assembling them as a single element of the second exemplary bone reference assembly. 
     
    
    
     DETAILED DESCRIPTION 
     The exemplary embodiments of the present disclosure are described and illustrated below to encompass various aspects of orthopedics including surgical navigation aids, surgical navigation, and mass customized instruments to use with surgical navigation. Of course, it will be apparent to those of ordinary skill in the art that the embodiments discussed below are exemplary in nature and may be reconfigured without departing from the scope and spirit of the present invention. However, for clarity and precision, the exemplary embodiments as discussed below may include optional steps, methods, and features that one of ordinary skill should recognize as not being a requisite to fall within the scope of the present invention. 
     As depicted in  FIG.  1   , a plurality of femoral bone models  100  (that may be in excess of 150 models, though could certainly be less) as part of a statistical atlas (where the bone models include intramedullary canal  110  models) is utilized to identify a general attachment site  102  (i.e., landmarking) for a femoral bone base plate using bone model geometry. In other words, this attachment site  102  for the femoral bone base plate is delineated on each femoral bone model  100  of the atlas in generally the same bone model area across two or more of the bone models of the atlas. Based upon this location propagation, the atlas includes local geometry data as to the dimensions (including surface profile) of the surface of each bone model where the femoral bone base plate attachment site  102  overlaps or is otherwise bounded by. In this fashion, the bone contacting surface of the femoral bone base plate may be established by averaging or otherwise using the dimensions of the bone model at the attachment site  102  locations post propagating the attachment site across the statistical atlas. 
     The following series of steps are exemplary in nature and elaborate on an exemplary femoral bone base plate attachment site  102  (landmarking) methodology in the context of establishing anatomical landmarks and references across the bone models  100  of the statistical atlas utilized. Though not required, the following steps may be performed on each of the bone models  100  utilized as part of the statistical atlas. In exemplary fashion, each bone model  100  utilized as part of the statistical atlas is evaluated to: (1) compute the tip of the femoral lesser trochanter point (LT); (2) compute the plane marking the edge of the lesser trochanter, tangent to the femoral shaft (LTEP); (3) compute the femoral overall anatomical axis (AA); (4) compute projection of the lesser trochanter point on the femoral overall anatomical axis (PLTPAA); (5) compute projection of the lesser trochanter point on the plane marking the edge of the lesser trochanter (PLTPLTEP); (6) compute medial-lateral direction as a vector between PLTPAA and LT; (7) compute anterior-posterior direction as a cross product of the femoral overall anatomical axis and medial-lateral direction; and, (8) compute superior inferior direction as the femoral overall anatomical axis direction. 
     With respect to  FIG.  2   , the following series of steps are exemplary in nature and elaborate on an exemplary femoral bone base plate attachment site  102  (landmarking) methodology in the context of establishing instrument landmarks and directions across the bone models  100  of the statistical atlas utilized. By way of example, screw locations for securing the femoral bone base plate to the femur and directions the screws  104 - 108  will take relative to the bone are derived from a series of placement steps relative to appropriate anatomical landmarks. In this fashion, the screw locations and directions are repeatable per bone model  100  of the statistical atlas and, accordingly, allows for common analysis across the statistical atlas population utilized. Though not required, the following steps may be performed on each of the bone models utilized as part of the statistical atlas. In exemplary fashion, each bone model  100  utilized as part of the statistical atlas is evaluated to: (1) compute the shifted lesser trochanter point as PLTPLTEP is shifted 1 millimeter in the medial-lateral direction (Shifted_PLTPLTEP); (2) compute the location Screw # 1  (S 1 )  106  as the intersection of the line pointing along the anterior-posterior direction and passing through Shifted_PLTPLTEP and the femoral bone model; (3) compute the midpoint between Screw # 2   104  and Screw # 3   108  as the location of Screw # 1  (S 1 )  106  is shifted 5 millimeters in the medial-lateral direction (MP_S 2 _S 3 ); (4) compute the location of Screw # 2  (S 2 )  108  as the closest point on the femoral bone model to the MP_S 2 _S 3  point shifted 1 millimeter proximally in the direction of the anatomical axis; (5) compute the point of Screw # 3  (S 3 )  104  as the closest point on the femoral bone model to the MP_S 2 _S 3  point shifted 1 millimeter distally in the direction of the anatomical axis; (6) compute the femoral plate plane as the plane containing the screw locations for all three Screws (Screw # 1  (S 1 )  106 , Screw # 2  (S 2 )  108 , Screw # 3  (S 3 )  104 ); (7) compute the direction of Screw # 1  (S 1 )  106  as the direction normal to the femoral plate plane; and, (8) compute the direction of Screw # 2  (S 2 )  108  and Screw # 3  (S 3 )  104  to be normal to the femoral plate plane plate plane after rotating the femoral plate plane 20 degrees medially around the axis connecting the location of Screw # 2  (S 2 )  108  and the location of Screw # 3  (S 3 )  104 . 
     With respect to  FIGS.  3  and  4   , the following series of steps are exemplary in nature and elaborate on an exemplary femoral bone base plate attachment site (landmarking) methodology in the context of establishing definitions for reference plane  112  calculations across the bone models of the statistical atlas utilized. The reference plane  112  is a plane that represents the significant boundary of the implanted component with respect to the bone in question, such as a femur. In exemplary form, the reference plane  112  is defined so that it represents the expected component placement (femoral implant stem) plus a significant margin of placement error to provide a conservative estimate of the outer volume boundary of the orthopedic implant component with respect to the bone. For purposes of explanation and assessment, any fixation screw  104 - 108  is identified as having a potential impingement if its placement would result in any portion of the screw passing through the boundary delineated by the reference plane  112 . Though not required, the following steps may be performed on each of the bone models  100  utilized as part of the statistical atlas. In exemplary fashion, each bone model  100  utilized as part of the statistical atlas is evaluated to: (1) define a reference plane  112  normal to the proximal anatomical axis and the neck axis and passing through the anatomical axis point (ref_temp_plane); (2) compute the reference plane  112  as a plane rotated 5 degrees (error boundary of the system) and translated 7 millimeters (determined by using a 5 millimeter measurement of an average rasp width and 2 millimeter buffer or safe zone built in); (3) compute the distance between the terminal end of each of the three screws (S 1 , S 2 , S 3 )  104 - 108  and the reference plane  112 , as well as noting that any screw passing through the reference plane is identified as having impingement. For purposes of the foregoing, the screw length was set at 13 millimeters and presumed to be flush with the outer surface of the bone model post installation/fixation. And  FIGS.  3  and  4    depict a femoral stem prosthetic  116  being positioned partially within the intramedullary canal  110 . 
     Referring to  FIGS.  5 - 8   , evaluation of the computations and determinations across all of the bone models  100  utilized as part of the statistical atlas was carried out. As depicted in  FIG.  5   , a chart provides the mean, standard deviation, minimum, and maximum dimensions in millimeters for the distance from the terminal end of a respective screw  104 - 108  to the reference plane. The foregoing analysis was performed for 150 atlas bone models. As part of the computations and determinations, 116 of 150 bone models had no instances of impingement between any of the three screws and the reference plane. In the remaining 34 cases, 15 cases had impingement of the screws  104 - 108  with respect to the reference plane  112 . It is worth noting that the reference plane  112  is defined based on femoral geometry landmarks, which in some cases might not correlate to the boundaries of the segmented intramedullary canal model. 
     The results of the computations and determinations across all of the bone models  100  utilized as part of the statistical atlas resulted in an attachment site  102  and shape of a femoral bone base plate surface configured to be adjacent the bone surface that is mass customized to fit across a range of patient femur sizes for implant sizes that vary. 
     With the shape of the exemplary femoral bone base plate surface and attachment site established, one may fabricate the femoral bone base plate  200  and use the same as part of a total hip arthroplasty procedure in order to register one or more inertial measurement units  202  with respect to a patient&#39;s femur  204  as part of a surgical navigation endeavor. As will be discussed in greater detail hereafter, the exemplary femoral bone base plate  200  works with one or more inertial measurement units  202  and a stem  206  to comprise a bone reference assembly  210 . In this fashion, the inertial measurement unit (IMU)  202  is fastened to a bone  204  (in exemplary form, a femur) in a fixed position and acts as a reference IMU, where this fixed position is retained throughout the surgical procedure (which may include final implant placement within the intramedullary canal of the femur). Reference is had to Appendix A, included herewith, that describes in more detail the interaction between reference IMU and a second IMU mounted to a surgical tool or surgical implant as part of surgical navigation in order to provide information regarding the relative positions of bone, implant, and surgical tools when direct line of sight to one or more of these objects may be absent. 
     As depicted in  FIG.  10   , an exemplary bone reference assembly  210  for a femur  204  comprises an inertial measurement unit  202 , a stem  206 , and a bone base plate  200  (in exemplary form, a femoral bone base plate). Though not necessarily limited to applications on an attachment site on the anterior region of the femur, the foregoing exemplary embodiment may be referred to as an exemplary anterior bone reference assembly  210 . 
     As depicted in more detail in  FIGS.  11 - 13   , the shape of the exemplary femoral bone base plate  200  and fixation locations are established mathematically and confirmed using bone models  100  from a statistical atlas. The exemplary femoral bone base plate  200  includes a distal, bone contacting surface  214  having a topography that generally matches and mates with the topography of an anterior portion of a femur that is exposed as part of a total hip arthroplasty procedure. Opposite the bone contacting surface  214  is a stem interfacing surface  216  that, in exemplary form, is planar. A series of holes  220 - 224  extend through the femoral bone base plate  200  from the bone contacting surface  214  to the stem interfacing surface  216 . In this exemplary embodiment, the femoral bone base plate  200  includes three holes  220  configured to receive screw fasteners (not shown) to mount the base plate  200  to the femur  204 . In exemplary fashion, each hole  220  includes a recessed collar  226  that is operative to change the cylindrical diameter of each hole so that the hole at the stem interfacing surface  216  has a larger diameter than the hole at the bone contacting surface  214 . Two additional holes  222  are provided that receive alignment studs associated with the stem  206 . A fastener hole  224  is also provided, which may include helical threads, that is configured to receive a fastener in order to retain the femoral bone base plate into engagement with the stem  206 . 
     Referring to  FIGS.  14 - 19   , the exemplary stem  206  includes a distal adapter  230  having a pair of alignment studs  232  extending therefrom that are configured to be received within respective holes  222  of the femoral bone base plate  200 . In exemplary form, each alignment stud  232  comprises a linear, cylindrical shape that is received within a cylindrical bore of the respective holes  222 . At the same time, the distal adapter  230  includes a through hole  234  of its own that is configured to receive a fastener  250  (such as the locking screw of  FIG.  18   , which may be threaded  252 ) to mount the distal adapter to the femoral bone base plate  200 . In this exemplary embodiment, the distal adapter  230  includes a series of interconnected arcuate cut-outs  236  that unobstruct the holes  220  of the femoral bone base plate  200 . Extending proximally from the distal adapter  230  is an elongated neck  240  terminating at a proximal coupling  242  configured to engage the IMU  202 . The stem  206  is angled in three dimensions so that it can extend through a typical anterior THA incision before and after external rotation of the femur. The stem  206  has two configurations to accept the IMU  202 . The first configuration of the stem  206  features a coupling  242  to accept the locking feature of the IMU  202 . The second configuration of the stem  206  features a slide on which an IMU  202  is mounted. 
     Referring to  FIGS.  20  and  21   , attachment of the stem  206  to the femoral bone base plate  200  includes aligning the studs  232  of the stem with the respective holes  222  of the base plate. By way of example, the studs  232  are designed to fit snugly with respect to the hole  222  boundaries to avoid significant play between the stem  206  and base plate  200 . After the studs  232  are received within the holes  222 , the through hole  234  of the adapter  230  should be aligned with the hole  224  of the base plate  200  so that the fastener  250  can extend through the smooth bore hole  234  and its threads  252  can engage the protruding threads of the hole  224 . In this fashion, as the fastener  250  is rotated clockwise, the head of the fastener is operative to sandwich the adapter  230  in between the base plate  200 . Upon proper torquing of the fastener  250 , the stem  206  and the base plate  200  are fixedly mounted to one another. After being mounted to one another, the holes  222  of the base plate are available to be accessed by a drill and thereafter by a screw to mount the assembly  210  to the femur  204 , presuming the IMU  202  is mounted to the stem  206 . 
     When mounting the assembly  210  to a femur, the assembly is placed on the anterior of the proximal femur along the intertrochanteric line and perpendicular to the femoral neck axis during anterior total hip arthroplasty. It may be secured to the anterior femur with three 3.5 millimeter×20 millimeter cancellous screws (not shown). In this fashion, the reference IMU  202  is securely fixed to the patient femur. 
     Referring to  FIGS.  22  and  23   , an alternate exemplary embodiment of a bone reference assembly  310  for a femur  304  comprises an inertial measurement unit  302 , a stem  306 , and a bone base plate  300  (in exemplary form, a femoral bone base plate). Though not necessarily limited to applications on an attachment site on the posterior region of the femur, the foregoing exemplary embodiment may be referred to as an exemplary posterior bone reference assembly  310 . 
     As depicted in more detail in  FIGS.  24 - 26   , the shape of the exemplary femoral bone base plate  300  and fixation locations are established mathematically and confirmed using bone models  100  from a statistical atlas. The exemplary femoral bone base plate  300  includes a distal, bone contacting surface  314  having a topography that generally matches and mates with the topography of a posterior portion of a femur that is exposed as part of a total hip arthroplasty procedure. Opposite the bone contacting surface  314  is a stem interfacing surface  316  that, in exemplary form, is planar. A series of holes  320 - 324  extend through the femoral bone base plate  300  from the bone contacting surface  314  to the stem interfacing surface  316 . In this exemplary embodiment, the femoral bone base plate  300  includes three holes  320  configured to receive screw fasteners (not shown) to mount the base plate  300  to the femur  304 . In exemplary fashion, each hole  320  includes a recessed collar  326  that is operative to change the cylindrical diameter of each hole so that the hole at the stem interfacing surface  316  has a larger diameter than the hole at the bone contacting surface  314 . Two additional holes  322  are provided that receive alignment studs associated with the stem  306 . A fastener hole  324  is also provided, which may include helical threads, that is configured to receive a fastener in order to retain the femoral bone base plate into engagement with the stem  306 . 
     Referring to  FIGS.  27  and  28   , the exemplary stem  306  includes a distal adapter  330  having a pair of alignment studs  332  extending therefrom that are configured to be received within respective holes  322  of the femoral bone base plate  300 . In exemplary form, each alignment stud  332  comprises a linear, cylindrical shape that is received within a cylindrical bore of the respective holes  322 . At the same time, the distal adapter  330  includes a through hole  334  of its own that is configured to receive a fastener  350  (such as the locking screw of  FIG.  29   , which may be threaded  352 ) to mount the distal adapter to the femoral bone base plate  300 . In this exemplary embodiment, the distal adapter  330  includes a pair of arcuate cut-outs  336  that unobstruct the holes  320  of the femoral bone base plate  300 . Extending proximally from the distal adapter  330  is an elongated neck  340  terminating at a proximal coupling  342  configured to engage the IMU  302 . The stem  306  is angled in three dimensions so that it can extend through a typical posterior THA incision before and after external rotation of the femur. The stem  306  has two configurations to accept the IMU  302 . The first configuration of the stem  306  features a coupling  342  to accept the locking feature of the IMU  302 . The second configuration of the stem  306  features a slide on which an IMU  302  is mounted. 
     Referring to  FIGS.  30 - 33   , attachment of the stem  306  to the femoral bone base plate  300  includes aligning the studs  332  of the stem with the respective holes  322  of the base plate. By way of example, the studs  332  are designed to fit snugly with respect to the hole  322  boundaries to avoid significant play between the stem  306  and base plate  300 . After the studs  332  are received within the holes  322 , the through hole  334  of the adapter  330  should be aligned with the hole  324  of the base plate  300  so that the fastener  350  can extend through the smooth bore hole  334  and its threads  352  can engage the protruding threads of the hole  324 . In this fashion, as the fastener  350  is rotated clockwise, the head of the fastener is operative to sandwich the adapter  330  in between the base plate  300 . Upon proper torquing of the fastener  350 , the stem  306  and the base plate  300  are fixedly mounted to one another. After being mounted to one another, the holes  322  of the base plate are available to be accessed by a drill and thereafter by a screw to mount the assembly  310  to the femur  304 , presuming the IMU  302  is mounted to the stem  306 . 
     When mounting the assembly  310  to a femur, the assembly is placed on the posterior of the proximal femur along the intertrochanteric line and perpendicular to the femoral neck axis during posterior total hip arthroplasty. It may be secured to the posterior femur with three 3.5 millimeter×20 millimeter cancellous screws (not shown). In this fashion, the reference IMU  302  is securely fixed to the patient femur. 
     Following from the above description, it should be apparent to those of ordinary skill in the art that, while the methods and apparatuses herein described constitute exemplary embodiments of the present disclosure, the invention is not limited to these precise embodiments and that changes may be made to such embodiments without departing from the scope of the invention as defined by the claims. Additionally, it is to be understood that the invention is defined by the claims and it is not intended that any limitations or elements describing the exemplary embodiments set forth herein are to be incorporated into the interpretation of any claim element unless such limitation or element is explicitly stated. Likewise, it is to be understood that it is not necessary to meet any or all of the identified advantages or objects of the invention disclosed herein in order to fall within the scope of any claims, since the invention is defined by the claims and since inherent and/or unforeseen advantages of the present invention may exist even though they may not have been explicitly discussed herein.