Patent Publication Number: US-2023157709-A1

Title: Hip Broach And Implant Designed Using Morphological Data

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of the filing date of U.S. Provisional Patent Application No. 63/282,286, filed Nov. 23, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     When a patient suffers a condition in the hip joint such as joint disease resulting from osteoarthritis, rheumatoid arthritis or post-traumatic arthritis, functional deformities, fractures in a proximal part of the femur, or a poorly performing implant from a previous procedure, such conditions may be treated through a hip joint replacement procedure. 
     During replacement surgeries, a broach is typically used to prepare a femoral canal to receive a femoral hip implant, and the hip implant is later disposed in the prepared canal. One challenge with existing broach technologies is their limited capacity to remove cortical bone in more distal regions that would receive a distal part of a hip implant. This is particularly the case when a patient is younger, as such patients may have femurs that have narrower cross-sections in the diaphysis. Under such circumstances, it may be more difficult to reach such distal regions of the femur with existing broaches and reaming tools. Insufficient broaching in the diaphysis may lead to undesirable engagement of the hip implant in that region, reducing the likelihood of a successful procedure. 
     Existing hip implant designs and methods of their implantation, particularly those intended for cementless fixation, often suffer from inefficiencies due to difficulty in obtaining a desired level of fixation between the implant and the cortical bone of the femur. For instance, existing designs exhibit limitations in controlling where fixation between the implant and the bone will occur. 
     Accordingly, there is a need for improvements in broach and femoral hip implant designs that will further enhance surgical outcomes that result from a hip joint replacement. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     The present disclosure provides improvements in hip implant procedures and hip implants themselves. A broach is contemplated that includes a proximal region and a distal region. Both regions, throughout a body of the stem, include cutting teeth. In the distal region, the teeth are more aggressive than in the proximal region. In some examples, the teeth in the distal region are diamond-shaped while the teeth in the proximal region have elongate ridges between troughs. This design minimizes excess removal of bone material in a metaphysis of a femur while promoting removal of material in a diaphysis region of the femur, where clearance between an implant surface and the cortical bone is desired. 
     The present disclosure also contemplates a hip implant in the form of a stem sized for implantation in a femur. The hip implant has a shape that optimizes engagement of medial and lateral sides of the implant with cortical bone in the metaphysis region of the femur while minimizing engagement of the implant with cortical bone in the diaphysis region. 
     In one aspect, the present disclosure relates to a broach for use in a mammalian femur. In a first example of a first embodiment of the broach, the broach includes a body with a proximal portion and a distal portion extending from the proximal portion. The proximal portion has a first surface with a plurality of first teeth and the distal portion has a second surface with a plurality of second teeth. At least one tooth of the plurality of second teeth is different from at least one tooth of the plurality of first teeth and at least one tooth of the plurality of second teeth may include a pointed protrusion that extends outward from the second surface. In some variations of the first example, at least one tooth of the plurality of second teeth is different from each of the plurality of first teeth. In other variations of the first example, each tooth of the plurality of second teeth is different from at least one tooth of the plurality of first teeth. In further variations, each tooth of the plurality of second teeth is different from each tooth of the plurality of first teeth. 
     In a second example, the first example of the first embodiment may be further defined by the pointed protrusion of the at least one tooth of the plurality of second teeth having a leading surface that is oriented at a steeper angle than a flank trailing the pointed protrusion. In a third example, the first example of the first embodiment may be further defined by the plurality of second teeth extending around an entire perimeter of the distal portion. In a fourth example, any one of the first through third examples of the first embodiment may be further defined by each of the plurality of first teeth including an elongate sharp ridge surrounded on all sides by troughs separating each elongate sharp ridge. In a fifth example, the fourth example of the first embodiment may be further defined by the proximal portion having a third surface with a plurality of third teeth different from the plurality of first teeth. In some variations, the third surface does not overlap the first surface and each of the first surface and the third surface extend along a length of the proximal portion. 
     In a sixth example, any one of the first through fifth examples of the first embodiment may be further defined by at least some of the plurality of second teeth being located less than 25% of a distance from a distal tip of the body to a proximal end of the body. In a seventh example, the sixth example of the first embodiment may be further defined by the distal portion being located entirely within 40% of a distance from the distal tip of the body to the proximal end of the body. In an eighth example, the seventh example of the first embodiment may be further defined by the plurality of second teeth extending over a majority of the second surface. Further, the second surface may be coincident with the distal portion. In a ninth example, the eighth example of the first embodiment may be defined by the plurality of second teeth being only in the distal portion. In a tenth example, any one of the first through ninth examples of the first embodiment may include a transition between the proximal portion and the distal portion that is in a range of 60 mm to 80 mm from a medial proximal end located in the proximal portion. In an eleventh example, the fourth example of the first embodiment may be further defined by the proximal portion including a third surface with a plurality of third teeth having flat protruding ridges. In a twelfth example, the eleventh example of the first embodiment may be defined by the first surface of the proximal portion including a medial surface and a lateral surface and the third surface including an anterior surface and a posterior surface. 
     The first embodiment may be varied in other ways as described through the following additional examples. In a thirteenth example, the broach of the first example may include the plurality of second teeth having pointed protrusions with leading surfaces oriented at a steeper angle than flanks trailing the pointed protrusions. In a fourteenth example, the plurality of first teeth in the broach of any one of the first and thirteenth examples may include elongate sharp ridges surrounded on all sides by troughs separating each elongate sharp ridge. In a fifteenth example, the broach of any one of the first, thirteenth and fourteenth examples may include a third surface with a plurality of third teeth different from the plurality of first teeth, the third surface not overlapping the first surface and each of the first surface and the third surface extending along a length of the proximal portion. In a sixteenth example, the proximal portion in the broach of the fifteenth example may include a third surface with a plurality of third teeth having elongate flat protruding ridges. In a seventeenth example, the body of the broach of any one of the fifteenth and sixteenth examples may include a medial surface, a lateral surface, an anterior surface and a posterior surface. The first surface may be solely on the medial and lateral surfaces in the proximal portion and the third surface may be solely on the anterior and posterior surfaces in the proximal portion such that third teeth are absent from the medial and lateral surfaces and first teeth are absent from anterior and posterior surfaces. In some examples, the first teeth may be disposed on a majority of the medial and lateral surfaces in the proximal portion. In other examples, the first teeth may be disposed on an entirety of the medial and lateral surfaces of the proximal portion. In some examples, the third teeth may be on a majority of the anterior and posterior surfaces in the proximal portion. In other examples, the third teeth may be on an entirety of the anterior and posterior surfaces in the proximal portion. In an eighteenth example, the plurality of second teeth in the broach of the seventeenth example may be disposed on the medial, lateral, anterior and posterior surfaces within the distal portion. 
     In a nineteenth example, the distal portion of the broach of any one of the first and thirteenth through eighteenth examples may be located entirely within 40% of a distance from a distal tip of the body at a distal end of the distal portion to a proximal end of the body at a proximal end of the proximal portion. In some examples, the distal portion may be located entirely within 50% of a distance from the distal tip of the body to the proximal end of the body. In some examples, the distal portion may be located entirely within 30% of the distance from the distal tip of the body to the proximal end of the body. In still further examples, the extent of the distal portion may be any value in a range from 30% to 50% of the distance from the distal tip to the proximal end. In still further examples, the extent of the distal portion may be outside of this range. Such circumstances may arise as a function of patient anatomy. 
     In a twentieth example, the broach of any one of the first and thirteenth through nineteenth examples may include at least some of the plurality of second teeth within 10% of the distance from the distal tip of the body to the proximal end of the body. In other examples, the plurality of second teeth may be disposed distally up to within 5% of the distance from the distal tip to the proximal end. In further examples, a distal extent of the second teeth of the plurality of second teeth may be even closer to the distal tip than 5% of the distance from the distal tip, or any amount from 5% to 10% of the distance. While it is possible to vary the extent of the disposal of the second teeth, many embodiments include disposal throughout a significant surface area of the distal portion to maximize cutting performance. 
     In a twenty-first example, the plurality of second teeth of the broach of any one of the first and thirteenth through twentieth examples may extend over a majority of the second surface and the second surface is coincident with an entirety of an outer surface of the distal portion. In a twenty-second example, the plurality of second teeth of the broach in any one of the first and thirteenth through twenty-first examples may be solely in the distal portion. In a twenty-third example, the proximal portion of the broach of any one of the first and thirteenth through twenty-second examples may include a medial proximal end and a transition between the proximal portion and the distal portion is in a range of 60 mm to 80 mm from the medial proximal end. In a twenty-fourth example, the broach of any one of the first and thirteenth through twenty-third examples may include teeth that define linear troughs. The plurality of first teeth may define a first plurality of linear troughs and the plurality of second teeth may define a second plurality of linear troughs. Each one of the first plurality of linear troughs may be parallel to the others and each one of the second plurality of linear troughs may be parallel to the others. The second plurality of linear troughs may be transverse to the first plurality of linear troughs. In a twenty-fifth example, the plurality of second teeth of the broach of the twenty-fourth example may define a third plurality of linear troughs, each of the third plurality of linear troughs being transverse to each of the first plurality of linear troughs and the second plurality of linear troughs. In some examples, the first plurality of linear troughs may be perpendicular to an elongate dimension of the body. In a twenty-sixth example, the body of the broach of any one of the first and thirteenth through twenty-fifth examples may include a transition region defined by a distal end region of the proximal portion and a proximal end region of the distal portion, the plurality of first teeth transitioning to the plurality of second teeth in the transition region. 
     In a first example of a second embodiment of the broach, a broach for use in a mammalian femur includes a body with a proximal portion and a distal portion separated from the proximal portion by a transition region. The proximal portion has a first toothed surface extending over a first distance along a length of the body and the distal portion has a second toothed surface extending over a second distance along the length of the body. The distances are dimensioned such that the first distance is greater than the second distance. The first toothed surface has a plurality of first cutting surfaces and the second toothed surface has a plurality of second cutting surface. A first protruding end of at least one cutting surface of the plurality of first cutting surfaces may be longer than a second protruding end of at least one cutting surface of the plurality of second cutting surfaces. In variations of the first example, at least one cutting surface of the plurality of first cutting surfaces may be longer than each cutting surface of the plurality of second cutting surfaces. In other variations of the first example, each cutting surface of the plurality of first cutting surfaces may be longer than at least one cutting surface of the plurality of second cutting surfaces. In still further variations of the first example, each cutting surface of the plurality of first cutting surfaces may be longer than each cutting surface of the plurality of second cutting surfaces. 
     In a second example of the second embodiment, the first example may be defined such that the first protruding end of the at least one cutting surface of the plurality of first cutting surfaces is an elongate ridge and the second protruding end of the at least one cutting surface of the plurality of second cutting surfaces is a sharp point. In a third example of the second embodiment, the first or second example may be defined by the first distance being in a range from 50% to 70% of a combined first and second distance. In a fourth example, any one of the first through third examples of the second embodiment may be defined such that when the broach is fully disposed in a femoral canal of the mammalian femur, the transition region is aligned with a location on the femur where a medial to lateral width of the femur changes by an amount in a range of 0.25 mm per 10 mm length to 0.35 mm per 10 mm length. In a fifth example, any one of the first through third examples of the second embodiment may be further defined such that when the broach is fully disposed in a femoral canal of the mammalian femur, the transition region is aligned with a location on the femur where a first dimension from an anterior limit of the femur to a posterior limit of the femur is between 1.0 and 1.2 times a second dimension from a medial limit of the femur to lateral limit of the femur. 
     In a third embodiment, the present disclosure relates to a broach for use in preparing a femur to receive an implant. In one example, the broach includes a proximal portion extending along a first portion of a length of the broach and a distal portion extending along a second portion of the length of the broach, the distal portion abutting the proximal portion. The broach may be configured such that when the broach is advanced into a femur, a distal tip of the distal portion is a leading end of the broach and a proximal end of the proximal portion is a trailing end of the broach. The proximal portion may include a plurality of first cutting surfaces. The plurality of first cutting surfaces may define a first plurality of linear troughs on a surface of the proximal portion, each one of the plurality of linear troughs being parallel to the others. The distal portion may include a plurality of second cutting surfaces, the plurality of second cutting surfaces defining a second plurality of linear troughs and a third plurality of linear troughs on a surface of the distal portion. The second plurality of linear troughs may be transverse to the first plurality of linear troughs. And, the troughs may be oriented such that the third plurality of linear troughs are transverse to both the first and second plurality of linear troughs. 
     In a second example of the third embodiment, the broach of the first example may have second cutting surfaces such that one or more of the second cutting surfaces of the plurality of second cutting surfaces include pointed tips. One or more of the pointed tips may be an outermost projection of a surface of the broach in the distal portion. In a third example of the third embodiment, the broach of any one of the first and second examples may have a plurality of third cutting surfaces on the proximal portion. The third cutting surfaces of the plurality of third cutting surfaces may be different from the plurality of first cutting surfaces and the plurality of second cutting surfaces. 
     In another aspect, the present disclosure relates to a femoral hip implant. In a first example of a femoral hip implant embodiment, a femoral hip implant includes a neck and a stem extending from the neck. The stem includes a proximal portion and a distal portion, the proximal portion having a proximal anterior surface, a proximal posterior surface, a proximal medial surface and a proximal lateral surface. At a proximal end of the proximal portion, a first dimension of the stem from the proximal medial surface to the proximal lateral surface is in a range from 1.8 times to 2.2 times that of a second dimension of the stem from the proximal anterior surface to the proximal posterior surface. The proximal anterior surface is oriented relative to the proximal posterior surface at a first angle of 6.5 degrees or greater. The stem also includes a distal anterior surface and a distal posterior surface in the distal portion. The distal anterior surface is oriented relative to the distal posterior surface at a second angle of 4.5 degrees or greater, the second angle being less than the first angle. 
     In a second example, the proximal portion of the stem of the first example of the femoral hip implant may extend over a first distance and the distal portion of the stem may extend over a second distance such that the first distance combined with the second distance defines a length of the stem, the first distance being in a range from 8.2% to 10.4% of the length of the stem. In a third example, the first distance of the first example of the femoral hip implant may be between 9 mm and 11 mm. In a fourth example, any one of the first through third examples of the femoral hip implant may have a difference between the first angle and the second angle that is in a range from 0.4 degrees to 2.1 degrees. In a fifth example, the first angle of any one of the first through fourth examples of the femoral hip implant may be in a range from 6.5 degrees to 7.0 degrees. In a sixth example, the second angle of any one of the first through fifth examples of the femoral hip implant may be in a range from 4.5 degrees to 6.6 degrees. 
     In a seventh example, any one of the first through third examples of the femoral hip implant may be structured such that when the stem has a length less than 100 mm, a difference between the first angle and the second angle is 2.0 degrees or more. In an eighth example, any one of the first through third examples of the femoral hip implant may be structured such that when the stem has a length less than 113 mm, a difference between the first angle and the second angle is 1.0 degrees or more. In a ninth example, any one of the first through eighth examples of the femoral hip implant may be structured such that at a location at or distal to a transition between the proximal and distal portions, a third dimension of the stem from a distal medial surface to a distal lateral surface is in a range from 1.0 times to 1.8 times that of a fourth dimension of the stem from the distal anterior surface to the distal posterior surface. In a tenth example, the stem of the ninth example of the femoral hip implant may have a length in a range from 93 mm to 109 mm and the first dimension may be in a range from 1.8 to 2.0 times that of the second dimension. Further, the third dimension may in a range from 1.0 to 1.5 times that of the fourth dimension. In an eleventh example, the stem of the ninth example of the femoral hip implant may have a length in a range from 99 mm to 113 mm. Further, the first dimension may be in a range from 1.9 to 2.1 times that of the second dimension and the third dimension may be in a range from 1.2 to 1.7 times that of the fourth dimension. In a twelfth example, the neck of any one of the first through eleventh examples of the femoral hip implant may include a collar extending medially therefrom. 
     In one aspect, the present disclosure relates to a kit. In one embodiment, a kit includes a broach and a femoral hip implant. The broach may have a proximal portion including flat edged cutting teeth and a distal portion including pointed cutting teeth circumferentially disposed thereon. The femoral hip implant may have a stem with a medial surface, a lateral surface, an anterior surface and a posterior surface. A maximum dimension between the medial and lateral surfaces at a proximal end of the stem may be in a range from 1.8 times to 2.2 times a maximum dimension between the anterior and posterior surfaces at the proximal end. 
     In one aspect, the present disclosure relates to a method of designing a broach. In a first example of an embodiment of such a method of designing a broach, the method involves the following steps: determining a size of a femur to receive the broach; retrieving a plurality of medial-lateral dimensions of the femur, each of the plurality of medial-lateral dimensions being measured transverse to a length of the femur and being located at different locations along a length of the femur; identifying an anatomical transition region along the length of the femur based on at least a comparison of each of the plurality of medial-lateral dimensions; comparing the broach with the femur by viewing the broach in an implanted position in the femur and identifying a transition region on the broach that is coincident with the anatomical transition region; including a first plurality of teeth on a distal surface of the broach distal to the transition region, the first teeth having pointed protrusions; and including a second plurality of teeth on a proximal surface of the broach proximal to the transition region, the second plurality of teeth being different from the first plurality of teeth. 
     In a second example, the comparison step of the first example of the method of designing the broach may include the comparison of each of the plurality of medial-lateral dimensions and involve identifying a rate of change in the medial-lateral dimension of the femur along its length. The anatomical transition region may be identified as being located where the range of change of the medial-lateral dimension is between 0.2 mm per 10 mm length of the femur and 0.4 mm per 10 mm length of the femur. In a third example, the first example of the method of designing the broach may include retrieving a plurality of anterior-posterior dimensions of the femur, each of the plurality of anterior-posterior dimensions being measured transverse to a length of the femur and at the same locations as the plurality of medial-lateral dimensions. The method then proceeds with identifying an anatomical transition region along the length of the femur based on a comparison of each of the plurality of medial-lateral dimensions with the plurality of anterior-posterior dimensions, the anatomical transition region being located where the anterior-posterior dimension decreases to below 1.2 times the medial-lateral dimension in a proximal to distal direction. 
     In a fourth example, the determining step of any one of the first through third examples of the method of designing the broach may include aggregating a plurality of femur geometries into a representative femur to determine the size of the femur to receive the broach. In a fifth example, the fourth example of the method of designing the broach may involve a predetermined range of femur lengths to define the plurality of femur geometries. In a sixth example, the fourth example of the method may be performed such that the plurality of femur geometries are all dimensioned to receive a single broach size. 
     In one aspect, the present disclosure relates to a method of determining a geometry of a femoral hip implant. In a first example of one embodiment of such method, the method steps are as follows: receiving a geometry of a bone receiving the hip implant; at a first location between a neck of the bone and a lesser trochanter of the bone, taking a first planar section of the bone and determining a first medial extremity, a first lateral extremity, a first anterior extremity and a first posterior extremity, at a second location distal to the first location, taking a second planar section of the bone and determining a second medial extremity, a second lateral extremity, a second anterior extremity and a second posterior extremity, determining a first medial-lateral dimension of a stem of the hip implant at a medial proximal end of the stem as approximating a measurement from the first medial extremity to the first lateral extremity; determining a first anterior-posterior dimension of the stem of the hip implant at the medial proximal end of the stem as being between 40% and 60% of the first medial-lateral dimension; and determining a second medial-lateral dimension of the stem at a distal location on the stem closer to a distal end of the stem than the proximal end as being less than a measurement from the second medial extremity to the second lateral extremity such that the femoral hip implant in an implanted condition does not contact cortical bone of the bone at the distal location. 
     In a second example, the first example of the method of determining the geometry of the hip implant may include determining a second anterior-posterior dimension of the stem at the distal location on the stem, the second anterior-posterior dimension being between 50% and 100% of the second medial-lateral dimension. In a third example, the first or second example of the method of determining the geometry of the hip implant may include determining a first angle between anterior and posterior surfaces of the implant at the proximal end of the stem and determinizing a second angle between anterior and posterior surfaces of the implant at the distal location, the first angle being greater than the second angle. In a fourth example, the third example of the method of determining the geometry of the hip implant may be performed such that the anterior and posterior surfaces at the first angle extend to a transition depth approximately 9-10% of a distance from the proximal end of the stem to the distal end of the stem such that anterior and posterior surfaces distal to the transition depth are at the second angle. In a fifth example, any one of the first through fourth examples of the method of determining the geometry of the hip implant may be performed such that prior to receiving the geometry of the bone, a determination of a representative bone is made based on a plurality of bones grouped together based on a shared characteristic, the determined representative bone being used as the geometry of the bone. In a sixth example, the fifth example of the method of determining the geometry of the hip implant is performed such that the shared characteristic is a physical size range. 
     In one aspect, the present disclosure relates to a method of preparing a femur to receive a hip implant. In a first example of one embodiment of the method of preparing the femur, the following steps are performed: retrieving a broach with a proximal portion and a distal portion, the distal portion having a plurality of pointed teeth; driving the broach into a femoral canal accessible through a resected end of the femur creating an open volume to receive the hip implant; and inserting the hip implant into the open volume such that a proximal-medial surface and a proximal-lateral surface of the hip implant engages cortical bone of the femur while a distal most region of the hip implant is spaced apart from cortical bone of the femur. 
     In a second example, the first example of the method of preparing the femur may involve inserting the hip implant into the open volume to leave a proximal anterior surface and a proximal-posterior surface spaced apart from cortical bone of the femur such that no anterior or posterior surfaces of the hip implant engage cortical bone. In a third example, the first or second example of the method of preparing the femur may include: clearing bone material from a diaphyseal portion of the femur with the plurality of pointed teeth on the broach; clearing cortical bone material from medial and lateral sides of the femur in a metaphyseal portion of the femur; and compacting bone material from anterior and posterior sides of the femur in the metaphyseal portion of the femur. 
     In one aspect, the present disclosure relates to a method of designing a collar for a femoral hip step. In one embodiment, the method involves: determining a size of a femur to receive the femoral hip implant; selecting a femoral hip implant size based on the determined size of the femur; visualizing the femoral implant implanted in the femur and determining a first distance from a central axis of the femur to a medial-most point on a stem of the femoral implant. And, while continuing to visualize the femoral implant implanted in the femur, determining a second distance from the medial-most point on the stem to a medial cortical bone surface of the femur, the second distance being a dimension of the collar as extending from the stem. 
     In some examples of the method of designing the collar, the medial cortical bone surface may be an outer cortical bone surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will be better understood on reading the following detailed description of non-limiting embodiments thereof, and on examining the accompanying drawings, in which: 
         FIG.  1    is a front view of a broach according to one embodiment of the present disclosure. 
         FIGS.  2  and  3    are side views of the broach of  FIG.  1   . 
         FIGS.  4 A- 4 B  are detailed views of compaction teeth of the broach of  FIG.  1   . 
         FIGS.  5 A- 5 B  are detailed views of extraction teeth of the broach of  FIG.  1   . 
         FIGS.  6 A- 6 B  are detailed views of diamond teeth of the broach of  FIG.  1   . 
         FIG.  7 A  is a front view of a hip implant according to one embodiment of the present disclosure. 
         FIGS.  7 B- 7 C  are sectional views of the hip implant of  FIG.  7 A . 
         FIGS.  8 - 9    are side views of the hip implant of  FIG.  7 A . 
         FIGS.  10 - 11    illustrate a step in a method of designing a broach or hip implant according to some embodiments of the present disclosure. 
         FIGS.  12 - 13    illustrate a step in a method of designing a broach according to some embodiments of the present disclosure. 
         FIGS.  14 - 16    are side and sectional views of a hip implant in a step of a method of designing the hip implant according to some embodiments of the disclosure. 
         FIGS.  17  and  18    are front and side views of a hip implant in a step of the method of designing the hip implant according to the embodiment of  FIGS.  14 - 16   . 
         FIGS.  19 - 20    illustrate a step in a method of designing a hip implant according to some embodiments of the present disclosure. 
         FIGS.  21 - 22    are front and side views of a hip implant according to an embodiment of the present disclosure. 
         FIG.  23    is a chart including performance data of embodiments of the hip implant described in the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will now be described in detail with reference to the drawings. In the drawings and in the description that follows, the term “proximal” refers to the portion of the instrument, implant or other device that is closest to the operator, while the term “distal” refers to the portion of the device that is furthest from the operator. Additionally, in the drawings and in the description that follows, terms such as front, rear, upper, lower, top, bottom, and the similar directional terms are used simply for convenience of description and are not intended to limit the disclosure attached hereto. In addition, the term “medial” indicates a direction toward the middle of the body of the patient, whilst the term “lateral” indicates a direction toward a side of the body of the patient (i.e., away from the middle of the body of the patient). The term “posterior” indicates a direction toward the patient&#39;s back, and the term “anterior” indicates a direction toward the patient&#39;s front. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. 
     The present disclosure describes instruments, implants, kits, methods of designing instruments and implants, and methods of using instruments and implants in hip surgery. 
     In one aspect, the present disclosure relates to a broach for use in creating an open volume to receive a femoral hip implant as part of a hip replacement procedure. One embodiment of such broach is broach  100  shown in  FIGS.  1 - 3   . In a proximal region of broach is a proximal end  102 . Extending proximally from a proximal end  102  of broach  100  is an optional trunnion  140  with a recess  142  therein, the trunnion adapted to engagement with a tool for insertion of broach  100  into a femur. In some examples, the trunnion may have a different shape from that shown. In still further examples, other engagement features for engagement with an insertion instrument may be included at the proximal end of the broach. 
     A body of broach  100  extends between proximal end  102  and a distal tip  104  and includes a proximal region  162  and a distal region  166  separated by a transition region  164 , shown in  FIG.  1   . In proximal region  162  anterior and posterior surfaces of the broach include compaction teeth  110 A,  110 B, where teeth indicated by reference numeral  110 A are on the anterior facing surface and those indicated by reference numeral  110 B are on the posterior facing surface in the example shown. With continued reference to proximal region  162 , medial and lateral surfaces of the broach include extraction teeth  120 A,  120 B, where teeth indicated by  120 A are on the medial facing surface and teeth indicated by  120 B are on the lateral facing surface. In the illustrated example, these teeth cover an entirety of the respective surfaces in the proximal region. It should be appreciated that such comprehensive coverage is optional and that in other examples, only subportions of one or more of the respective surfaces may include the teeth as described. 
     Turning to distal region  166 , separated from proximal region  162  by transition region  164 , a surface around a full perimeter of the body includes a single aggressive cutting surface. As described above for the proximal region, the aggressive cutting surface may cover less than an entirety of the distal region. In the embodiment shown in  FIGS.  1 - 3   , the teeth in distal region  166  are diamond teeth  130 . In other examples, other types of aggressive teeth may be included in the distal region. For example, the teeth may be spiked, pointed or acuminate with shapes other than that provided by the diamond teeth of the illustrated embodiment, shown in detail in  FIGS.  6 A and  6 B . One reason the broach is designed this way is to avoid having excessively aggressive teeth in the proximal region of the broach. In this manner, a femoral canal surface left by the extraction and compaction teeth will mimic a surface of a femoral hip implant, while the aggressive teeth active in the distal region will not, where such correspondence between bone and implant surfaces is not as significant. These purposes are described in greater detail elsewhere in the present disclosure. 
     As already noted, transition region  164  separates the proximal and distal regions. A location of transition region  164  is determined using techniques as described elsewhere in the disclosure but is ultimately identified based on particular changes in characteristics of the bone receiving a hip implant over a length of the bone. The anatomical feature that characterizes this change is the transition between the metaphyseal region of the femur and the diaphyseal region of the femur, where the bone becomes more cylindrical. Femur measurements, for instance, those analyzed through data stored in the Stryker Orthopaedic Modeling and Analytics (SOMA) database described in greater detail below, are used to determine where on the femur the rate of change in a medial-lateral width of the femur is approximately 0.3 mm per 10 mm. This location is then identified as transition region  164 , and a distal region of the broach distal to the transition region will have diamond teeth. The distal region of the broach will penetrate a part of the femur with a relatively uniform lengthwise shape where a rate of change in the medial-lateral width is less than 0.3 mm per 10 mm and likely has a cylindrical shape. Transition region  164  may also be determined based on where a ratio of an anterior-posterior dimension of bone relative to the medial-lateral dimension reaches 1.0. In some examples, transition region  164  is located 60-80 mm below a proximal medial edge  103  of broach  100 . In some examples, transition region  164  is located 50% to 70% of a distance from proximal medial edge  103  to distal tip  104 . In further examples, transition region  164  is located 64% to 69% of a distance from proximal medial edge  103  to distal tip  104 . In other examples, other distances may apply and may be guided by the anatomy of the femur under consideration. 
     Details of the various teeth on broach  100  are shown in  FIGS.  4 A- 6 B . In particular, compaction teeth  110 A are shown in  FIGS.  4 A-B , extraction teeth  120 A are shown in  FIGS.  5 A-B  and diamond teeth  130  are shown in  FIGS.  6 A-B . 
     Compaction teeth  110 A include a pattern of repeating troughs  112  and protrusions with ends in the form of flat ridges  114 . Troughs have rounded low points with a shallower angle on surface flank  115  approaching flat ridge  114  than on a leading surface  113  in front of a preceding flat ridge, as shown in  FIG.  4 B , though leading surface  113  is shallower than 90 degrees relative to an overall surface of the broach. As shown in  FIG.  4 A , flat ridges  114  have a length that extends in an unbroken fashion across a width of a surface region that includes the compaction teeth. The shape of the compaction teeth is such that they do not include a chip breaking function. In terms of performance, in use, compaction teeth  110 A reduce the tendency to extract bone and improve bone compaction for greater stability. 
     Extraction teeth  120 A have repeating troughs  122  and protrusions with ends in the form of ridges  124 , where the ridges  124  have a sharp edge with a length, shown in  FIG.  5 A , that is shorter than a distance across trailing flank  125  from trough  122  to ridge  124 , unlike the ridges of the compaction teeth. Rearward from trough  122  to a preceding ridge is a leading surface  123  of a preceding tooth. Each ridge  124  is abutted by four surfaces that protrude from troughs of the teeth. These include trailing flank  125 , side surfaces  126 A-B, and leading surface  123 . An uppermost region of leading surface  123  approaching ridge  124  is oriented approximately 90 degrees relative to a surface of the broach, unlike leading edge  113  on compaction teeth  110 A. The shape of the extraction teeth provides a chip breaking function that improves bone removal to create a surface in the bone that mimics the shape of the hip implant to be placed after use of the broach. 
     For diamond teeth  130 , a surface progresses repeatedly from a trough  132  to a protrusion with an end in the form of protrusion tip  134 , as shown in  FIG.  6 B . In a manner similar to extraction teeth, each protrusion tip  134  is abutted by four surfaces that protrude from surrounding troughs, such as trough  132 . However, for diamond teeth  130 , each of these surfaces converges at a point in the form of protrusion tip  134 . The four surfaces include flank  135 , side surfaces  136 A,  136 B and leading surface  133 . These surfaces, shown in  FIG.  6 A , may also be understood as two flanks  135 ,  136 A rising from the trough of the broach surface toward the protrusion tip, with two leading surfaces  133 ,  136 B in front of the flanks. As with the extraction teeth, the diamond teeth promote cutting of bone, although diamond teeth  130  are distinguishable in their aggressiveness and are particularly well suited for bone removal in a diaphyseal region of a femur where a purpose of the teeth is not explicitly directed to aligning an implant surface with a remaining bone surface, since clearance is desired in this region. The uniquely shaped cutting surfaces of the diamond teeth are particularly well suited to remove bone at greater distances from an entry location into a bone. 
     The broach may be made of a metal material. For example, the broach may be titanium, a titanium alloy, stainless steel, a stainless steel alloy, or a cobalt chrome alloy (CoCr). 
     The broach is advantageous in that it provides bone preparation directed to specific locations in a femur, whether anterior-posterior sides of a proximal region, medial-lateral sides of the proximal region, or in the distal region. The extraction teeth on the medial-lateral sides of the broach improve bone removal, while the compaction teeth prepare cancellous bone for receipt of anterior-posterior sides of an implant. The diamond teeth at the distal end of the broach promote more aggressive bone removal and are adapted to enhance removal of bone, including cortical bone, in a diaphyseal section of the femur, where the bone profile is much narrower than in more proximal regions of the femur. With such removal, an entire length of an inner region of the femur expected to receive a hip implant is better prepared for a secure and stable fit in a planned position. 
     The broach may be varied in many ways. In some examples, a broach may include a single type of tooth on the proximal region along with diamond teeth on the distal portion. In some of these examples, the proximal region only includes compaction teeth. In others, the proximal region only includes extraction teeth. In still further examples, the broach only includes teeth in the distal region and those teeth are diamond teeth. Such a variation may be of use when the broach is being used specifically to target the diaphyseal region of the femur. 
     In another aspect, the present disclosure relates to a hip implant. One embodiment of such hip implant is implant  200  shown in  FIGS.  7 A,  8  and  9   . It should be appreciated that references to implant are used interchangeably with stem or implant body throughout the disclosure. Implant  200  includes a neck  205  with a receiving portion  206  at a free end and a collar  207  on a medial side near an interface  202  with a stem of the implant. 
     The collar  207  extends from neck  205  such that it has a tapering shape towards a narrow lip  208  at its free end. The closest part of the body to collar  207  is at medial resection point  219 , best shown in  FIG.  7 A . A distance between medial resection point  219  and lip  208  of collar  207  represents a length of collar  207 . A distal face of collar  207  may optionally be planar between medial resection point  219  and lip  208 . On a side of collar  207  extending into neck  205 , collar has a concave surface toward receiving portion  206 . 
     The body of implant  200  includes anterior, posterior, medial and lateral surfaces that extend from interface  202  to distal tip  204 . The body is separated at a transition depth  230  into a proximal region and a distal region. The proximal region has an anterior surface  212 A, a posterior surface  212 B, a medial surface  214 A and a lateral surface  214 B. The distal region has an anterior surface  222 A, a posterior surface  222 B, a medial surface  224 A and a lateral surface  224 B. In some examples, transition depth  230  corresponds to an elbow of the implant on the lateral side, as shown in  FIG.  7 A , and may be in a range from 7 to 11% of a distance from medial resection point  219  to distal tip  204 . In other examples, transition depth may be in a range from 8 to 10% of the distance. In still further examples, it may fall within an overlapping or even non-overlapping range from the aforementioned ranges as a function of the patient bone anatomy, whether considered individually or as bone anatomy that is representative of the patient, such as may be retrieved from the SOMA database. 
     A profile of the body, or stem, viewed in a plane perpendicular to a length of the stem at one location in the proximal region is as shown in  FIG.  7 B  while a profile of the body at one location in the distal region is as shown in  FIG.  7 C . It should be appreciated that the profile of implant  200  shown in  FIGS.  7 B and  7 C  is optional and in other examples may vary from the illustrated shape. With continued reference to the illustrated embodiment, in the proximal region, medial surface  214 A is curved, anterior and posterior surfaces  212 A,  212 B each have two planar subparts that converge at an apex, and lateral surface  214 B is planar. In the distal region, the medial surface  224 A is curved with a radius larger than that present in the proximal region, anterior and poster surfaces  222 A,  222 B each have two planar subparts that converge at an apex, and lateral surface  224 B is planar. 
     When viewed from the anterior side such that the length of the body is visible, as shown in  FIG.  7 A , medial surfaces  214 A,  224 A are curved in a concave manner and lateral surfaces  214 B,  224 B are planar with lateral surface  214 B having a steeper angle than lateral surface  224 B. Lateral surfaces  214 B,  224 B converge at an apex, or elbow, located at a transition depth  230  of implant  200  that separates the proximal and distal regions. When viewed from the medial or lateral side such that the length of the body is visible, as shown in  FIGS.  8  and  9   , anterior surfaces  212 A,  222 A and posterior surfaces  212 B,  222 B are planar in respective proximal and distal regions, though a slope of each surface changes at transition depth  230 . In particular, when viewed from either a medial or lateral side of implant  200 , surfaces  212 A,  212 B in the proximal region are angled relative to one another at proximal angle θ 1  and surfaces  222 A,  222 B in the distal region are angled relative to one another at distal angle θ 2 . Proximal angle θ 1  is greater than distal angle θ 2 . In some examples, proximal angle θ 1  is in a range from 6.6 degrees to 7.0 degrees and is greater when a length of the body is longer. In some examples, distal angle θ 2  is in a range from 4.5 degrees and 6.6 degrees and is greater when a length of the body is longer. As already stated, the proximal angle is greater than the distal angle, though this difference is less with longer implants. In some examples, the difference may be approximately 2.0 degrees, while in other examples, it may be closer to 1.0 degree. 
     Implant  200  may be made of a metal material. For example, the implant may be made of titanium, a titanium alloy, stainless steel, a stainless steel alloy, or a CoCr alloy. It should also be appreciated that implant  200  may optionally include a bone ingrowth coating. Such coating may be distributed on a surface of the body of implant  200  between the neck-body interface  202  and an ingrowth coating limit  232 , shown in  FIG.  7 A . The bone ingrowth coating may be porous relative to a surface distal to ingrowth coating limit  232 . In some examples, the bone ingrowth coating may be commercially pure titanium with a hydroxyapatite spray finish, which may be a 50-micron plasma spray. In other examples, the bone ingrowth coating may be Ti-6A1-4V. In further examples, instead of bone ingrowth coating, the surface in the bone ingrowth region may be hydroxyapatite roughed through grit blasting. In still further examples, the surface may be prepared through loose metal sintering, formed through sequential impregnation/dissolution of dissolved salts to create a foam structure, or additively manufactured to create a three-dimensional porous surface. For the region below the ingrowth coating limit  232 , the surface may be coated with hydroxyapatite. The hydroxyapatite coating may be grit-blasted. In further examples, the implant may have no hydroxyapatite coating, may have a satin finish that is smooth, or may be formed through grit blasting. Any of the above examples may be varied such that regions on either side or both sides of the ingrowth coating limit may have no hydroxyapatite coating. 
     With continued reference to the body of implant  200 , we turn to relative dimensions, specifically, a ratio between a medial-lateral dimension and an anterior-posterior dimension, hereinafter referred to as an ML:AP ratio. At the medial resection point, the ML:AP ratio may be in a range from 1.8 to 2.2. The ML:AP ratio may be larger for larger implants. Thus, for example, an implant of a smaller size having a length of approximately 90 mm may have an ML:AP ratio in a range from 1.75 to 1.85. For an implant with a length of approximately 120 mm, an ML:AP ratio may be in a range from 2.15 to 2.25. Closer to distal tip  204  of implant  200 , the ML:AP ratio is smaller. At an ingrowth coating limit  232 , shown in  FIG.  7 A , the ML:AP ratio may be in a range from 1.0 to 1.8, where larger implants have larger ML:AP ratios at this level of the implant. 
     Implant  200  has a body shape such that engagement to bone in the proximal region is optimized. In particular, the ML:AP ratio in the proximal region provides an implant with enhanced medial-lateral engagement with cortical bone, while leaving space in an anterior-posterior direction for compaction with cancellous bone. Additionally, the ratio of the stem dimensions itself optimizes performance and stability. The anterior-posterior dimension is designed to fill a significant amount of space in that direction, while at the same time not superseding the desired medial-lateral engagement. This preserves the stability of the implant when subject to expected forces after surgery. And, the degree to which the femoral canal is filled in the AP direction improves stability. Further, the changing ML:AP ratio toward distal tip  204  of the implant allows for disposal of the implant in a femur with clearance from cortical bone, or put another way, with minimal engagement with cortical bone, in the distal region. The varying slope between the proximal angle of the proximal anterior and posterior surfaces and the distal angle of the distal anterior and posterior surfaces further enhance the above-described advantages. An additional advantage that should be appreciated is that the combination of fixation at proximal medial and proximal lateral sides, in combination with clearance in the distal region, improves performance of the implant relative to having only one of the design features. Further advantages include that the collar is sized to fit over the bone with minimal overhang. This is described in greater detail elsewhere in the disclosure. 
     Implant  200  may be varied in many ways. One alternative embodiment is implant  200 ′ shown in  FIGS.  21 - 22   , where the  200 ′ series of reference numerals refer to like elements in the  200  series of reference numerals unless otherwise noted. For implant  200 ′, transition depth  230 ′ is located further from the neck of the implant than the arrangement illustrated in  FIG.  7 A . In the illustrated example of such embodiment, the transition depth  230 ′ corresponds to the ingrowth coating limit  232 ′. In this manner, the proximal anterior and posterior surfaces  212 A′,  212 B′ have proximal angles, measured based on an angle between the surface and a central longitudinal axis of the implant, that extend from the neck-body interface  202 ′ to the ingrowth coating limit  232 ′ while the distal anterior and posterior surfaces  222 A′,  222 B′ have distal angles that extend from the ingrowth coating limit  232 ′ to the distal tip  204 ′ of the implant. As with other embodiments, the proximal angle is greater than the distal angle. 
     In other embodiments, a transition depth of a hip implant may be located at other locations along a length of the implant body. In some examples, this may be at a location in between that of the embodiment shown in  FIG.  7 A  and the embodiment shown in  FIG.  21   . In other embodiments, a hip implant may have an offset that is increased or decreased relative to an offset of implant  200  to accommodate the needs of certain patients. Here, offset means a distance between a femoral head center and a central femoral axis. 
     In another aspect, the present disclosure relates to a hip surgery kit including one or more items such as a broach and a femoral hip implant. In one embodiment, a kit may include two or more femoral hip implants. In some examples, the two or more hip implants include two or more hip implants that are the same size. In other examples, the two or more hip implants include two or more hip implants that are different sizes. In one embodiment, a kit may include two or more broaches. In some examples, the two or more broaches include two or more broaches that are the same size. In other examples, the two or more broaches include two or more broaches that are different sizes. In one embodiment, a kit may include one or more broaches and one or more femoral hip implants. In some examples, at least one of the broaches and at least one of the femoral hip implants are the same size. In other examples, at least one of the broaches and at least one of the femoral hip implants are different sizes. In some embodiments, the two or more hip implants may include two hip implants of the same size but different medial offsets. In any one of the above embodiments, the kit or individual items and combinations thereof may be disposed within a package or a plurality of packages. For example, all of the items of the kit may be disposed within a single package. In another example, all of the broaches may be in one package and all of the hip implants in another. The items included in the kit may also be individually packaged. For example, each broach may be in its own package. Packaging each item in the kit separately or in different combinations may improve the sterility of the items in preparation for and during surgery. One reason for this is that some items may be required prior to others when implanting the hip implant. For example, the hip implant could remain in its own package while the broach is used. In any of the above embodiments, a kit may further include an instruction manual with an explanation of details relating to the contents of the kit including instructions for use of the contents. 
     In other aspects, the present disclosure relates to methods of designing a broach or a femoral hip implant. We begin with an initial step in the process that applies for both broach and implant design and involves establishing a reference geometry of a bone to receive a respective broach or an implant. In some embodiments, morphological bone data, also referred to as bone data, such as bone data for the femur, is collected from across an assortment of demographic profiles, which are first sorted into groups and then analyzed for each group to design a broach or implant. One vehicle to realize this collection and analysis is optionally through use of the SOMA database. In one example, SOMA collects and stores femur dimensions of a large number of individuals, where the information may be sourced from CT scans of such individuals. References to SOMA data of the SOMA database are made throughout the disclosure for ease of explanation though it should be appreciated that data aggregation techniques other than SOMA may also be used for the designs described in the various embodiments of the present disclosure. Additionally, it should also be appreciated that the methods described in this disclosure are not limited to reliance on aggregated data for a reference bone geometry. However, if a design is made for a specific individual, it would of course have limited, if any, use for a wider group of individuals. 
     The large volume of patient data available through SOMA may be retrieved and analyzed to provide an output that may be used to guide designs. For the broach and hip implant in particular, femur images and other source data are collected for a large number of individuals of varying demographic profiles. Such information may be analyzed using statistical modeling and, based on the determined characteristics of the femur of each individual in the data set, may be placed into groups based on shared characteristics. One way the groups may be established is by including all femurs for which a particular estimated implant size fits into a single group and doing the same for other estimated implant sizes. In one variant, the data for each femur may be evaluated to determine what size stem would fit in the medial-lateral aspect. Another way the groups may be defined is by size of the femur. As one very simple example, all data for femurs between 400 mm and 450 mm in length may be assigned to a first group, all data for femurs between 450 mm and 500 mm in length may be assigned to a second group, and all data for femurs between 500 mm and 550 mm in length may be assigned to a third group, and so on. Of course, other length ranges may be used to group the source data as desired. 
     Once the source data is assigned to an applicable group, each femur within the group is analyzed in detail to identify and store certain dimensions of the femur for use in the design process. In some embodiments, a central longitudinal axis  70  and medial, lateral, anterior and posterior extremes in each of a plurality of transverse planes  80 A- 80 N are identified, as shown in  FIGS.  10 - 11    for femur  10 , where each transverse plane is perpendicular to central longitudinal axis  70 . Identification of coordinates for each of the aforementioned extremities is performed at regular intervals along a length of the femur through the diaphysis and through at least part of the metaphysis, as shown in  FIG.  10   .  FIG.  11    illustrates representative anatomical information identified and stored at each transverse plane via the information retrieved from transverse plane  80 A. At plane  80 A, coordinates of a location of the central longitudinal axis  70  are identified and stored, along with coordinates of a medial-most point  83 A on the bone, a lateral-most point  84 A, a posterior-most point  81 A and an anterior-most point  82 A. The identified coordinates may be three-dimensional cartesian coordinates. In some examples, the transverse planes may be located at 10 mm intervals along a portion of the femur. In those and other examples, the transverse planes may be located at intervals relative to an anatomic feature, such as the lesser trochanter. In such cases, the transverse planes may be located at 10 mm multiples from the lesser trochanter, and one of the transverse planes may pass through the lesser trochanter itself. Once all data points are identified and stored for the femur, the process is repeated for each of the other femurs assigned to the group under consideration. 
     With SOMA-derived data points stored for each femur in an assigned group, the data points are analyzed determine femur dimensions and landmarks that are representative of all of the femurs in the group. Thus, a representative femoral axis is based on combining data for the femoral central axis of each femur in the group. In one example, the representative femoral central axis is based on an average of the femoral central axis for each femur. Similarly, representative medial-most, lateral-most, posterior-most and anterior-most points, for example, points  83 A,  84 A,  81 A,  82 A, at each transverse plane  80 A- 80 N, are based on combining data for such points on each femur in the group. As above, the representative points at each transverse plane may be based on an average of the points identified for each femur. Upon completion of this processing step, each group has a set of data points that are representative of the femurs in that group. 
     In some embodiments, a method of design relates to a method of designing a broach. In one embodiment of the method, design of a broach begins with a design of a femoral implant, as described below for the implant shown in  FIGS.  14 - 20   . The geometry of the femoral implant design is then used to establish the geometry of the broach. Optionally, specific surfaces on the broach may be adjusted relative to the hip implant design to achieve particular press-fit performance and clearance with the broach disposed in a femur. In another embodiment of the method, design of the broach involves collection of bone data from a collection of individuals, sorting of the data into groups, and then analysis of the data for each group to generate a data set that is representative of the data derived from all individuals assigned to the respective groups. One exemplary way this is accomplished is through the use of SOMA data, as described in detail above. It should be appreciated that the groupings for any particular design process may encompass only a single group or may include multiple groups. Each group is based on a range of femur lengths, but it is contemplated that other considerations may be used to determine an assigned group for the source data. 
     Whether the broach geometry is established by the femoral implant design or based on SOMA data, the SOMA data may be used to determine transition region  164  that separates different types of cutting surfaces. To design cutting surface regions of a broach for each group of femurs (e.g., a group representative of a size range), a medial-lateral dimension is obtained from the medial-most and lateral-most points at each transverse plane from among multiple transverse planes along a length of a representative bone geometry. These measurements are compared with the others by moving along a length of the representative bone from one end to the other. The purpose of this comparison is to capture a change in the characteristics of the femur along its length. A typical femur has a medial flare  18  in a metaphyseal region that tapers and becomes flatter and closer to collinear with central longitudinal axis  70  in a diaphyseal region, as shown in  FIG.  12   , for example. This characteristic is used in conjunction with the SOMA derived data points to determine when a rate of change in a width of the bone approaches 0.3 mm per 10 mm length moving either proximally or distally. The exact rate of change of width per unit length may vary to make a final design consistent with designs for other broach sizes or for other circumstances that may apply. For instance, a target rate of change may be modified to 0.25 mm per 10 mm length or 0.35 mm per 10 mm length. One example of the rate of change in a medial-lateral dimension of a femur along its length is shown by the extrapolation of a collection of data from the SOMA database in the chart of  FIG.  13   . 
     When the transition between metaphyseal and diaphyseal regions is determined by analysis of the data, the location is identified as a transition region such as transition region  164  in  FIG.  1    and represents where the cutting teeth on the broach change between compaction/extraction teeth and diamond teeth. Because this analysis is performed for data on a group-by-group basis, a location of such transition region on a broach may differ, and very likely differs, between groups of data points that are distinguished by femur size or other characteristics. In a study, data representative of a group of individuals retrieved from the SOMA database was used to implement the described approach to determine a transition region on the broach. In the study, the SOMA database included CT scans of femurs of over 1300 individuals. Through analysis of the data, a transition region was estimated for each of eleven different femur size ranges. The results of that analysis are summarized in Table 1 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Distance to estimated 
                 Percentage of broach 
               
               
                 Femur Size Grouping 
                 transition region 
                 length above 
               
               
                 (estimated broach 
                 (mm below medial 
                 transition region 
               
               
                 length) 
                 resection point) 
                 (%) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 0 
                 (93 mm) 
                 60 
                 65 
               
               
                 1 
                 (96 mm) 
                 60 
                 63 
               
               
                 2 
                 (99 mm) 
                 60 
                 62 
               
               
                 3 
                 (101 mm) 
                 60 
                 60 
               
               
                 4 
                 (103 mm) 
                 60 
                 59 
               
               
                 5 
                 (105 mm) 
                 60 
                 57 
               
               
                 6 
                 (107 mm) 
                 70 
                 65 
               
               
                 7 
                 (109 mm) 
                 70 
                 64 
               
               
                 8 
                 (111 mm) 
                 70 
                 63 
               
               
                 9 
                 (113 mm) 
                 80 
                 70 
               
               
                 10 
                 (115 mm) 
                 80 
                 68 
               
               
                 11 
                 (117 mm) 
                 80 
                 67 
               
               
                   
               
            
           
         
       
     
     As an additional optional step in the design method, the distance to the transition region may be modified to accommodate any need for consistency among broaches of varying sizes. Thus, for example, the above described dimensions may be modified so that a transition region is located at incrementally greater distances from the medial resection point for progressively larger implant sizes. In one illustrative example that utilizes the estimated transition regions in Table 1, a distance to the transition region for size 0 may be 65 mm and increase in 1 mm increments up to size 11, which would have a distance of 76 mm. 
     In a variation of the method of designing a broach, the SOMA data is analyzed to determine where a ratio between an anterior-posterior dimension of the femur to a medial-lateral dimension of the femur approaches 1.0 when moving in a distal direction. Ratios based on representative data at each transverse plane, e.g., medial-most, lateral-most, anterior-most and posterior most points, may be used in the analysis, where the AP:ML ratio is expected to be higher than 1 in the metaphysis while decreasing toward the diaphysis. When a location along a length of the femur having an AP:ML ratio approaching or near 1.0 is determined, such location is set as the transition region between the compaction/extraction teeth and the diamond teeth based on the broach being fully inserted into the femur as would occur during use of the broach. 
     In one embodiment, a method of design relates to a method of designing a femoral hip implant, as shown, for example, in  FIGS.  14 - 20   . In the method, femur bone data is collected from a collection of individuals, sorted into groups, and then the data is analyzed for each group to generate a data set that is representative of all individuals assigned to the respective groups. One exemplary way this is accomplished is through the use of SOMA data, as described in detail above. As with the broach design, representative data points for each group are used to design a hip implant for such groups. Specifically, this may involve the determination of representative data points for each group where each group represents a range of femur sizes or another shared characteristic. 
     The representative data for each group may include a femoral central axis and anatomical points on a series of transverse planes through the femur, as described above and shown in  FIGS.  10  and  11   . The following description is for the design of one hip implant for a femur that falls within a single group that represents a range of femur sizes, but it should be appreciated that the design for other groups may be performed in the same way, albeit with different data analysis in view of the different femur size information. Additionally, as already noted, a characteristic other than size may also be used. 
     Initially, a dimension from a medial-most point to a lateral-most point is determined at each transverse plane. For the femur group under consideration in the present embodiment, that is transverse planes  280 A- 280 K shown in  FIGS.  17  and  18   . The medial-most and lateral-most points are locations on the anatomy, here, on the femur bone, as described in the description accompanying  FIGS.  10  and  11   . One part of the implant design process involves determining a ratio between a medial-lateral dimension and an anterior-posterior dimension at different locations along a length of the implant. Because the design advantageously provides cortical bone engagement in a more proximal part of the implant and provides clearance from cortical bone in a non-overlapping distal part of the implant, this part of the design process can be broken up into two substeps: A first step to design for an engagement region  252  and a second step to design for a clearance region  254 . These regions are shown in  FIGS.  14  and  17   . During the implant design process, the SOMA data may be analyzed to estimate an optimal position of the implant via SOMA-based femoral hip centers, femoral medial resection points and femoral central axes. In this manner, the sizing of the implant may be determined in a manner that is best aligned with an expected implanted position of the implant. 
     The engagement region  252  approximately coincides with a portion of the implant that includes ingrowth coating or another engagement surface as contemplated in the present disclosure. In one embodiment, a proximal-distal extent of the engagement region  252  is based on surface engagement regions included in previously developed hip implant designs, such as that included in the hip implant of the Stryker® Accolade® II system. The distal extent of the engagement region  252  ultimately approaches the juncture between metaphyseal and diaphyseal regions but remains within the metaphyseal region. In another embodiment, determination of the engagement region  252  may be based on data from the SOMA database that is analyzed and then used to identify a physical extent of the metaphyseal part of the femur. By identifying a physical extent of the metaphysis, a determination can be made as to the portion of the implant that will be located in the engagement region within the metaphyseal part when the implant is disposed in the femur. To convert information about the femur to information about the hip implant, the hip implant may be overlaid on the femur. Methods of identifying the metaphysis may be those methods described for the design of the broach above. In one example, a limit of the metaphyseal part of the femur, at a transition to the diaphyseal part, is established as a location where the rate of change of a width of the medial-lateral dimension reaches 0.3 mm per 10 mm of length. For the purposes of this explanation, such location in  FIG.  17    is found at transverse plane  280 H, slightly distal to ingrowth coating limit  232  of implant  200  determined to approximately correspond to transverse plane  280 G. Thus, above transverse plane  280 G the implant is expected to engage with the cortical bone of the femur on the medial and lateral sides that are shown in  FIG.  17   . 
     The dimensions of the implant for engagement region  252  are established by first identifying the medial-lateral dimension of the femur at each transverse plane  280 A- 280 G in engagement region  252 . Because hip implant  200  is intended to engage cortical bone on the medial and lateral sides in this engagement region, the medial-lateral dimension of the implant is sized to measure close to or slightly greater than a distance between cortical bone surfaces in the medial-lateral direction along a length of engagement region  252 . One exemplary section cut in this region is shown in  FIG.  15   . In many examples, the medial side of the stem will more closely match the SOMA data along a length of the implant compared to the lateral side. In some examples, a portion of the lateral side inclusive of a proximal lateral relief is shaped such that when the implant is positioned in the femur, there is minimal engagement between the proximal lateral relief and cortical bone on the lateral side. This aspect of the design improves ease of implantation by providing additional clearance while also not being relied upon to obtain stability which is achieved through engagement by other areas of the implant surface. 
     When medial-lateral dimensions in the engagement region  252  are calculated and otherwise established, an anterior-posterior dimension in engagement region  252  is determined. For this part of the design, the medial-lateral dimension is used as a guide in that a ratio of the medial-lateral dimension to the anterior-posterior dimension will be approximately 2.0, though an exact ratio depends on the location on the implant stem and the overall size of the implant. Additionally, the ratio may also become smaller in more distal locations in the engagement region. This ratio represents a general shape of the hip implant profile where the implant engages cortical bone on medial and lateral sides, but has minimal or no cortical bone engagement on the anterior and posterior sides. In this manner, anterior and posterior surfaces of the implant are expected to have limited cortical bone engagement or engage with cancellous bone only. SOMA data is once again analyzed to identify anterior-most and posterior-most bone locations at each transverse plane  280 A- 280 G in engagement region  252 , and an anterior-posterior dimension of implant  200  is sized to minimize cortical bone engagement in the anterior-posterior direction. The clearance between the cortical bone and anterior/posterior implant surfaces is shown in the view of implant  200  disposed in femur  310  in  FIGS.  15  and  18   . 
     In some examples, a size in the anterior-posterior direction may be further guided by characteristics of the SOMA data such as data that show that a dimension of the femur in the anterior direction is larger than a dimension in the posterior direction, these dimensions being orthogonal to the medial-lateral direction. This difference on the anterior and posterior sides may be used to adjust the anterior-posterior dimension to ensure that an expected fit in the anterior-posterior direction does not result in engagement with cortical bone, thereby avoiding a diminished effectiveness of the engagement on the medial and lateral sides. Controlling for this desired engagement in consideration of the medial-lateral and anterior-posterior directions results in an ML:AP ratio close to 2.0 in the engagement region. In some examples, there may be some cortical bone contact on either the anterior or posterior surface, but ultimately, such contact is minimized such that medial-lateral cortical fixation is established and preserved in any implantation scenario. 
     For the smallest implants used for the smallest group of femurs, an ML:AP ratio (medial-lateral dimension to anterior-posterior dimension) at medial resection point  219  may be in a range from 1.7 and 1.9. For the largest implants used for the largest group of femurs, the ML:AP ratio at medial resection point  219  may be in a range from 2.1 to 2.3. 
     Turning to the design of clearance region  254 , data points on the series of transverse planes, here planes  280 H- 280 K, are retrieved based on the analysis of SOMA data. These are used to compare inner cortical surfaces of the bone between the medial and lateral sides. Here, clearance from the cortical bone is desired, so the medial-lateral dimension of the implant is sized to be clear of the cortical bone in its planned position disposed in the femur. As shown in  FIGS.  16 ,  17  and  18   , this means that implant  200  is clear of cortical bone in all directions in areas below ingrowth coating limit  232 , and thus below transverse plane  280 G. Similarly, clearance from the cortical bone is also desired in the anterior-posterior dimension. Advantageously, the present design approach produces a hip implant that provides ample clearance around a perimeter of the implant in clearance region  254 , and in this way prevents any difficulties obtaining engagement in the engagement region due to circumstances such as a distal hang-up due to unintended engagement with cortical bone toward the distal tip. 
     Due to the difference in shape between larger femurs and smaller femurs, the ML:AP ratio in clearance region  254  is larger for larger hip implants. For the smallest implants used for the smallest group of femurs, the ML:AP ratio at the transition between regions, e.g., ingrowth coating limit  232 , may be in a range from 0.9 to 1.1. For the largest implants used for the largest group of femurs, the ML:AP ratio at the transition between regions may be in a range from 1.7 to 1.9. ML:AP ratios have also been established based on an analysis of collected anatomical data. Using the previously mentioned SOMA data based on the CT scans of femurs of over 1300 individuals, the ML:AP ratios for twelve different size ranges, or groups, were calculated. These are outlined in Table 2 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Implant 
                 ML:AP Ratio at 
                 ML:AP Ratio at 
               
               
                 Size 
                 Medial Resection Point 
                 Ingrowth Coating Limit 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 0 
                 (93 mm) 
                 1.8 
                 1.0 
               
               
                 1 
                 (96 mm) 
                 1.8 
                 1.1 
               
               
                 2 
                 (99 mm) 
                 1.9 
                 1.2 
               
               
                 3 
                 (101 mm) 
                 1.9 
                 1.2 
               
               
                 4 
                 (103 mm) 
                 1.9 
                 1.3 
               
               
                 5 
                 (105 mm) 
                 1.9 
                 1.4 
               
               
                 6 
                 (107 mm) 
                 2.0 
                 1.5 
               
               
                 7 
                 (109 mm) 
                 2.0 
                 1.5 
               
               
                 8 
                 (111 mm) 
                 2.1 
                 1.6 
               
               
                 9 
                 (113 mm) 
                 2.1 
                 1.7 
               
               
                 10 
                 (115 mm) 
                 2.1 
                 1.8 
               
               
                 11 
                 (117 mm) 
                 2.2 
                 1.8 
               
               
                   
               
            
           
         
       
     
     In conjunction with the above design process that establishes a profile of the hip implant along its length, angulation of anterior surfaces  212 A,  222 A and posterior surfaces  212 B,  222 B is determined. Proximal anterior and posterior surfaces  212 A,  212 B are angulated at proximal angle θ 1  relative to one another while distal anterior and posterior surfaces  222 A,  222 B are angled at distal angle θ 2  relative to one another. These surfaces and angles are shown in  FIGS.  8  and  9   , for example. In embodiments that employ the implant design method, the proximal angle θ 1  of the implant is greater than distal angle θ 2 . The proximal and distal surfaces are separated at a transition depth  230 , which corresponds to the apex where lateral surfaces  214 B,  224 B meet and lies entirely within engagement region  252  as shown in  FIGS.  7 A,  8  and  9   , though may be close to or on ingrowth coating limit  232  in other embodiments. Angulations for these surfaces are established by analysis of data in the SOMA database to produce implants with ML:AP ratios that provide targeted engagement to either cortical or cancellous bone in engagement region  252  and clearance from cortical bone in clearance region  254  when hip implant is in an implanted position in a patient femur. Some exemplary locations of the transition depth on a length of the implant and specific anterior and posterior surface angles are summarized elsewhere in the disclosure and for the sake of brevity are not repeated here. 
     The transition depth  230 , i.e., the transition location between proximal AP surfaces and distal AP surfaces, relative to medial resection point  219 , was determined for twelve implant sizes based on data inclusive of elbow locations on lateral surfaces of hip implants in previously developed designs, such as Stryker® Accolade® II. Additionally, the previously referenced study of certain SOMA data was further processed to calculate proximal angle θ 1  and distal angle θ 2  for the same twelve implant sizes. These values are shown in Tables 3 and 4 below. It should be appreciated that in an alternative approach, the transition depth may also be determined using SOMA data aggregated and optionally sorted based on planned implant sizes. 
     
       
         
           
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Implant 
                 Transition Distance from 
                 % Length of Stem from 
               
               
                 Size 
                 Medial Resection Point (mm) 
                 Medial Resection Point 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 0 
                 (93 mm) 
                 9.3 
                 10.0 
               
               
                 1 
                 (96 mm) 
                 9.7 
                 10.1 
               
               
                 2 
                 (99 mm) 
                 10.0 
                 10.1 
               
               
                 3 
                 (101 mm) 
                 10.4 
                 10.3 
               
               
                 4 
                 (103 mm) 
                 10.7 
                 10.4 
               
               
                 5 
                 (105 mm) 
                 10.5 
                 10.0 
               
               
                 6 
                 (107 mm) 
                 10.4 
                 9.7 
               
               
                 7 
                 (109 mm) 
                 10.2 
                 9.4 
               
               
                 8 
                 (111 mm) 
                 10.0 
                 9.0 
               
               
                 9 
                 (113 mm) 
                 9.9 
                 8.8 
               
               
                 10 
                 (115 mm) 
                 9.7 
                 8.4 
               
               
                 11 
                 (117 mm) 
                 9.6 
                 8.2 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 Implant 
                 Proximal Angle, θ 1   
                 Distal Angle, θ 2   
                 Difference 
               
               
                 Size 
                 (°) 
                 (°) 
                 (°) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 0 
                 (93 mm) 
                 6.6 
                 4.5 
                 2.1 
               
               
                 1 
                 (96 mm) 
                 6.6 
                 4.6 
                 2.0 
               
               
                 2 
                 (99 mm) 
                 6.6 
                 4.5 
                 2.1 
               
               
                 3 
                 (101 mm) 
                 6.5 
                 4.8 
                 1.7 
               
               
                 4 
                 (103 mm) 
                 6.5 
                 4.9 
                 1.6 
               
               
                 5 
                 (105 mm) 
                 6.5 
                 5.1 
                 1.4 
               
               
                 6 
                 (107 mm) 
                 6.6 
                 5.3 
                 1.3 
               
               
                 7 
                 (109 mm) 
                 6.7 
                 5.5 
                 1.2 
               
               
                 8 
                 (111 mm) 
                 6.8 
                 5.7 
                 1.1 
               
               
                 9 
                 (113 mm) 
                 6.8 
                 6.0 
                 0.8 
               
               
                 10 
                 (115 mm) 
                 6.9 
                 6.3 
                 0.6 
               
               
                 11 
                 (117 mm) 
                 7.0 
                 6.6 
                 0.4 
               
               
                   
               
            
           
         
       
     
     With continued reference to the described embodiment of the method of designing a hip implant, the completion of the design of the body, or stem, allows for the optional design of the collar. To design the collar, first, the implant body is overlaid on the representative femur  310  for the size range or other group of data points that the implant is designed for. As described elsewhere in the disclosure, such femur representation, and a position of the implant in the femur based on femoral head center and offset, may be established based on an analysis of SOMA data. This is shown, for example, in  FIG.  20   . To position the hip implant, a neck resection may be simulated for use in aligning the resection with interface  202 . The neck resection may be represented by a neck resection plane  336  that extends across the femur from a periosteal resection point  332  on a medial side of the representative femur  310 , as shown in  FIG.  19   . With implant  200  in an expected final implanted position within femur  310  as shown in  FIG.  20   , a distance  372  between femoral central axis  370 , previously established through analysis of SOMA data, and medial resection point  219  of the implant stem, is determined. Then, a remaining distance between the medial resection point  219  and a periosteal boundary outside of an outer cortical bone surface may be used to define a medial-lateral collar dimension  373 . In some specific examples, the medial-lateral collar dimension may be in a range from 5 mm to 7 mm. In other examples, the dimension  373  may be shorter or longer relative to the outer cortical bone surface, but in all cases, may be controlled and customized through the described method in a manner improved over previous approaches. In one exemplary variation, medial-lateral collar dimension  373  is sized so that in the implanted position, the collar does not overhang an outer surface of the cortical bone. In other embodiments, the collar design method may be performed as a standalone method. 
     In another embodiment, the method of designing a hip implant is employed to design implant  200 ′ shown in  FIGS.  21 - 22   . Here, the steps of determining dimensions in the medial-lateral direction and the anterior-posterior direction, and the ratio of same, are determined in the same manner as that described for implant  200  and shown in  FIGS.  14 - 18   . As to a slope of the anterior and posterior surfaces of the implant, here, a transition depth  230 ′ that is aligned with the ingrowth coating limit  232 ′ is used to determine a proximal angle θ 1 ′ and a distal angle θ 2 ′, but the implant is otherwise designed in the same manner as described for implant  200 . 
     Design of a hip implant in the manner described in the present disclosure yields improved post-surgical performance relative to existing technologies. For instance, hip implants manufactured according to the designs of the present disclosure exhibited significantly lower micromotion in both the proximal and distal regions of the implant during stair-climb loading tests, as summarized in  FIG.  23   . The micromotion analysis involved an evaluation of micromotion in the stem of the implant relative to the femur at proximal and distal points on the stem. 
     In another aspect, the present disclosure relates to methods of manufacturing a hip broach or a hip implant. In some embodiments, at least one of a broach and an implant may be additively manufactured via a layer-by-layer 3D printing process. Examples of additive manufacturing methods that may be used include Shape Deposition Manufacturing (“SDM”), Selective Laser Power Processing (“SLPP”), Direct Metal Laser Sintering (“DMLS”), Selective Laser Sintering (“SLS”), Selective Laser Melting (“SLM”), Selective Heat Sintering (“SHS”), Electron Beam Melting (“EBM”), material jetting, binder jetting, or the like. Some of these techniques are disclosed in U.S. Pat. Nos. 7,537,664; 8,728,387; 9,180,010; and 9,456,901, the disclosures of which are hereby incorporated by reference herein in their entireties. In other embodiments, at least one of a broach and implant is injection molded. For example, material for the broach or implant may be melted under high heat and disposed in a mold to form the structure. One example of an injection molding process that may be utilized is disclosed in U.S. Pat. App. Pub. No. 2021/0237149, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     In another aspect, the present disclosure relates to one or more steps in a method of placing a hip implant in a femur. In one embodiment, the method commences with pre-operative planning, neck resection, and preparation of the femoral canal already complete. Optionally, the aforementioned steps may be included as part of the method. In a first step, broaching is performed. When multiple broach sizes are available for performance of the broaching, the smallest one is inserted into the femoral canal first. This may be done by positioning the broach laterally and posteriorly relative to the femur bone. During the broaching action, and for illustration, with reference to broach  100  of  FIG.  1   , extraction teeth  120 A,  120 B remove cortical bone, compaction teeth  110 A,  110 B prepare and compact cancellous bone to receive the hip implant, and the distal diamond teeth  130  remove cortical and cancellous bone more aggressively than the extraction teeth. When broaching with the smallest size broach is complete, another broach of an incrementally larger size is retrieved and used to perform further broaching. This process of using broaches of incrementally larger sizes is repeated until a proper fit within the canal is achieved. Indications of proper fit during the broaching process include increased resistance to forward advancement, changing pitch of sound that results from mallet impacts to a broach handle, and/or lack of further motion or advancement of broach and rotational stability, which may be ascertained using the broach handle when secured to the broach. 
     Upon completion of broaching, trial reduction may optionally be performed by assembling an appropriate neck trial onto the broach and a head trial onto the neck trial and verifying the broach size. Whether or not trial reduction is performed, the final confirmed broach size is noted for hip implant selection as the broach size is expected to correspond to the correct implant size. The method continues with a step of ensuring that a bone surface surrounding the broach and the open end of the femoral canal is planar. In one example, this can be accomplished with a calcar planer that engages to a trunnion or other feature on the broach. In other examples, other tools may be used. When the surface is prepared, the broach may then be removed in preparation for placement of the hip implant. 
     A femoral hip implant with a size matching the final broach is retrieved for placement in the femur of the patient. As an optional step, the implant may be initially inserted into the femoral canal by hand until it meets resistance to position and orient the implant prior to using tools for implant securement. An implant inserter is then selected and attached to the implant for impaction of the implant into a secure position in the femoral canal. Firm seating of the implant is typically obtained either when the collar of the implant is just above or rests on the calcar bone or when resistance upon impaction suggests it is firmly seated. When implanted, and as discussed elsewhere in the disclosure, medial and lateral sides of the implant provide the primary engagement to cortical bone of the femur, with anterior and posterior surfaces being at least partially free from such engagement. Further, a distalmost part of the hip implant will be clear of cortical bone when the implant is firmly seated in its final position. The hip implant is implanted in the femoral canal in a cementless fashion. 
     Optional to this embodiment, a femoral head size may be chosen for the implant and verified. The head may then be secured to the implant and any desired verification of alignment and kinematics of the joint may be checked prior to finalization of the procedure. 
     In some embodiments, the method may be limited to steps involving the use of a broach alone, as described above. In other embodiments, the method may commence with a femoral canal ready to receive a hip implant and involve placement of the hip implant alone, as described above. In some embodiments, the broaching step of the method may involve the selection of an expected final broach size for a first broaching action, without the use of incrementally larger broaches to complete the broaching. In still further embodiments, the method of hip implant placement may be performed with the aid of robotics for one or more of the method steps. For instance, broach selection and broach use may be performed with a robotic arm controlled by software that includes all relevant surgical planning information. Similarly, hip implant placement may also be performed using robotics. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present disclosure as defined by the appended claims.