Abstract:
The broach or rasp holder tool with reduced rasp moment includes an angled strike plate with an optional curved or spheroidal surface and/or an angled withdrawal plate having a contact surface for receiving a generally perpendicular strike force that generally aligns with a point along a rasp for substantially eliminating a moment applied thereto while broaching the intramedullary canal in preparation for implanting a prosthetic stem during joint replacement surgery.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to a rasp or broach holder tool with reduced rasp moment for use during joint replacement surgery. More specifically, the present invention relates to a rasp or broach holder tool having a strike plate and/or a withdrawal plate angularly aligning a rasp to reduce or eliminate the moment at the point of rasp insertion and/or removal, respectively, when broaching or rasping the intramedullary canal in preparation for implantation of a prosthetic femoral stem during total hip replacement surgery. 
         [0002]    Advancements in surgery have enhanced the feasibility of performing total joint replacement surgery, such as for the knee, hip, or shoulder, to replace natural joints that may need restoration as a result of disease or injury. For example, with respect to total hip replacement surgery, it is necessary to replace the acetabulum and femoral head with a prosthetic acetabular cup and insert, and femoral stem having an artificial femoral head sized for engagement with the acetabular cup and insert assembly. Total hip replacement surgery typically involves dislocating the femur, resecting the femoral neck, reaming the acetabulum in preparation to receive the acetabular cup, and rasping the intramedullary canal to form a shaft or channel therein suitable to receive a prosthetic femoral stem having a head thereon sized for engagement with the acetabular cup. A tool called a broach or rasp is used to contour the intramedullary canal so that the channel walls are approximately the size and shape of the overall geometry of the appropriately sized prosthetic femoral stem to ensure that the implant has a more accurate and precise fit during implantation. 
         [0003]    There are several surgical techniques known in the art for performing total hip replacement surgery. One such traditional surgical technique is a posterior approach whereby the patient is positioned on his or her side and the surgeon makes an approximately 3-6 inch incision along the rear of the body near the gluteus maximus. Here, the gluteus maximus muscle is split and requires repair during wound closure. This method provides excellent exposure to the acetabulum and femur, but has drawbacks related to dislocation and leg-length inequality. An alternative approach is an anterior approach whereby the patient lays on his or her back and the surgeon makes an approximately 3-6 inch incision along the front or side of the upper thigh. One drawback of the anterior approach is that the femur fracture rate tends to be higher when compared to the aforementioned posterior approach. 
         [0004]    As briefly mentioned above, in most cases, surgeons use a broach or rasp to open and size the intramedullary canal for preparation to receive the femoral stem implant. This may be accomplished through the use of rasps that vary in size and shape and that can be interchanged using the broach holder during surgery to attain the desired channel. In this respect, the surgeon may start with a smaller size rasp to open the channel, and then use progressively larger rasps (e.g., one or more) until the final rasp corresponds approximately to the size of the femoral prosthesis. The rasp typically includes a series of teeth to cut away the bone during insertion and removal. One of the complications that may occur during total hip replacement is an intraoperative proximal femoral fracture. The risk of these fractures has been shown to increase with the use of offset broaching tools, likely due to the non-axial forces created by the strike plate on the broach holder being offset from the central axis of the broach during impaction into the femur. Intraoperative fractures may occur during the broaching process, or during the femoral stem implantation, and postoperative fracture could occur in the weeks following hospital discharge. While the broach holder cannot directly affect forces during stem implantation, or postoperatively, the increased stresses created during broaching may weaken the bone and contribute to the increased risk of fracture even during stem implantation, or postoperatively. Intraoperative fracture increases the incidence of complication, causes additional pain, and potentially creates a significant surgical delay and/or cost to the procedure. 
         [0005]    Broach holder tools often include a curved or offset section that helps facilitate angled insertion to more accurately access the intramedullary canal, especially when performing an anterior approach. The broach holder may be straight or offset depending upon surgeon preference or approach, but the anterior approach generally prohibits such axial insertion of the broach for purposes of rasping the intramedullary canal. When using an angled broach holder tool, as opposed to a straight broach holder tool, non-axial forces are introduced to the intramedullary canal to attain adequate rasping of the canal. These non-axial forces propagate through the rasp and may create microfractures in the bone, which may lead to femur fracture. This is because the bone at the site of rasp entry into the canal may be over stressed as a result of the increased moment applied to the broach holder and rasp. Thus, a broach holder tool and rasp used for the preparation of the intramedullary canal for receiving a femoral stem implant prosthesis that includes any appreciable offset from the centerline of the rasp can greatly increase the chances of bone fracture while rasping during surgery. Microfracture may also lead to fracture postoperatively in the weeks following surgery as the patient begins to weight-bear and become more active. 
         [0006]    In this respect,  FIGS. 1 and 2  illustrate a prior art broach holder tool  20  that includes a strike plate  22  at one end of a section  24  having a rasp  26  attached thereto at an opposite end thereof. The section  24  is shown having a general “S”-shape such that the strike plate  22  resides at a point above the location where the rasp  26  attaches to the section  24 . Application of a strike force  28  on the strike plate  22 , e.g., by way of a hammer or other tool that may be used during surgery to further depress the rasp  26  into the intramedullary canal, generates a general forward force along the direction indicated by a dotted force line  30 . This force line  30  is offset from a point  32  where the rasp  26  attaches to the section  24 . As a result, application of the force  28  acts as both an axial force  33  and a moment  34  about the point  32 , or a commensurate point along the length of the rasp  26  where the rasp  26  may engage or encounter resistance within the intramedullary canal during rasping. The axial force  33  is approximately equal to the strike force  28  and is the desired force for broaching the femur. The moment can be calculated as M=(F)(D), where M is equal to the moment  34 , F is equal to the strike force  28  and D is equal to a distance  36  generally defined as between the horizontal force line  30  and point  32  (i.e., the moment arm). During broaching, this moment  34  must be resisted by reaction forces within the femur. Those forces reduce the effectiveness of the axial force  33  to move the broach more deeply within the femur in an axial path, and also create internal hoop stresses within the proximal femur. Bone has good natural compressive strength, but poor strength in tension. Accordingly, bone is relatively strong at absorbing stresses along its length, but not perpendicular thereto. Therefore, hoop stresses should be avoided. This situation also forces the surgeon to push the broach holder down to maintain proper alignment of the broach and to use higher strike forces to overcome the extra resistance. Therefore, it is unsurprising that there is an increased occurrence of proximal fractures when using the prior art broach holder tool using the anterior approach, as described above. 
         [0007]    The same issue applies when attempting to remove the prior art broach holder tool  20  by way of striking a withdrawal plate  38  or a back side  39  of the main strike plate  22 , as shown in  FIG. 2 . Here, the withdrawal plate  38  is similarly parallel to the strike plate  22 , generally perpendicular to the section  24 , and offset from the rasp  26 . Application of a withdrawal force  40  on the withdrawal plate  38  creates both an axial force  41 , and a withdrawal moment  42  that attempts to rotate or pivot the rasp  26  in the clockwise direction as indicated by the moment  42 . The moment  42  applied to the rasp  26  increases the resistance during extraction of the rasp  26  due to the reaction forces within the femur. This requires the surgeon to use an increased withdrawal force  40  to remove the rasp  26 . 
         [0008]    In another example,  FIGS. 3A and 3B  illustrate an alternative prior art broach holder tool  20 ′ that includes a section  24 ′ that positions the strike plate  22 ′ at a vertical distance above the rasp  26 ′ (e.g., as described above with respect to  FIGS. 1 and 2 ), as shown in  FIG. 3A , and a horizontal distance to the side of the rasp  26 ′, as shown in  FIG. 3B . When the strike plate  22 ′ is impacted with a strike force  28 ′, the strike force  28 ′ is offset from the point  32 ′ by a vertical distance  36 ′ and a horizontal distance  37 ′. This respectively creates two moments, a first moment  34 ′ ( FIG. 3A ) and a second moment  45 ′ ( FIG. 3B ), as a result of the “S” curved section  24 ′. During broaching, the above-identified problem is only exacerbated by the two moments  34 ′,  45 ′ that must be resisted by even more reaction forces within the femur. Those resistive forces reduce the effectiveness of the strike force  28 ′ to move the broach more deeply within the femur in an axial path (e.g., along an axial force  33 ′) and also create internal hoop stresses within the proximal femur. This only increases the risk of proximal femur fractures during broaching and makes it more difficult to control alignment of the broaching tool. 
         [0009]    There exists, therefore, a significant need in the art for a broach holder that reduces or eliminates the applied moments through the rasp which may cause unintended internal stresses within the intramedullary canal during surgery. The effect of this reduction in applied moments will substantially reduce or limit the internal hoop stresses in the proximal femur. The present invention fulfills these needs and provides further related advantages. 
       SUMMARY OF THE INVENTION 
       [0010]    One embodiment of the broach holder tool with reduced rasp moment as disclosed herein includes a generally elongated and rigid S-shaped broach holder body having a size and shape for broaching a bone. A selectively interchangeable rasp for broaching the bone may be selectively coupled to one end of the broach holder body. Furthermore, an angled strike plate may be coupled to another portion of the broach holder body and have a strike surface for selectively receiving a strike force perpendicular thereto that translates along an angled directional strike line extending through the rasp substantially near a drive point where the rasp enters the bone. This substantially reduces the rasp moment at the point where the rasp enters the intramedullary canal, while simultaneously permitting sufficient translation of a substantially horizontal or insertion force that permits broaching the intramedullary canal. 
         [0011]    In one aspect of this embodiment, the angled directional strike line may extend through the rasp at a maximum offset of 10 degrees from the drive point. This permits continued substantial alignment of the angled directional strike line with the drive point, as the drive point may change during the rasping or broaching process in view that the rasp moves into and out from the intramedullary canal. Additionally, the angled strike plate may include a vertical offset angle α between 10-30 degrees, which is defined by the formula: α=90−arctan (X/Y), where X is the horizontal distance between the drive point and where the strike force contacts the strike surface of the angled strike plate and Y is the vertical gain between the drive point and where the strike force contacts the strike surface of the angled strike plate. Decreasing the vertical gain may decrease the vertical offset angle α and increasing the vertical gain may increase the vertical offset angle α. Changing the gain may affect a substantially horizontal insertion force applied at the rasp, i.e., the substantially horizontal insertion force at the rasp may increase by decreasing the vertical gain and the substantially horizontal insertion force at the rasp may decrease by increasing the vertical gain, all while substantially maintaining the reduced rasp moment. 
         [0012]    In another aspect of this embodiment, the broach holder tool with a reduced rasp moment may include an angled withdrawal plate coupled to the broach holder body between the rasp and the angled strike plate. The angled withdrawal plate may include a withdrawal surface for selectively receiving a withdrawal force perpendicular thereto that translates substantially along an angled directional withdrawal line extending through a withdrawal point where the rasp is removed from the bone after broaching. Here, the angled withdrawal plate may include a vertical offset angle β defined by the formula: β=90−arctan (A/B), where A is the horizontal distance between the withdrawal point and where the withdrawal force contacts the withdrawal surface of the angled withdrawal plate and B is the vertical distance between the withdrawal point and where the withdrawal force contacts the withdrawal surface of the angled withdrawal plate. 
         [0013]    In another aspect of this embodiment, the strike surface of the strike plate may include a non-planar strike surface selected from the group consisting of a curved strike surface, a spherical strike surface, or a spheroidal strike surface. Here, the angled directional strike line may vary across the non-planar strike surface, depending where along the non-planar strike surface the strike force is applied. This allows for varying the location of the angled directional strike line relative to the drive point to help ensure that the angled directional strike line extends through the rasp at a maximum offset of 10 degrees from the drive point. To this end, striking the non-planar strike surface to vary the angled directional strike line may also correspond with a different drive point location along the length of the rasp. Alternatively, the angled strike plate may include an adjustable angled strike plate selectively positionable relative to the drive point. Here, the angled strike plate may pivot relative to the broach holder body by a lock-step engagement. 
         [0014]    Another embodiment of the broach holder tool with reduced rasp moment as disclosed herein may include a generally elongated and rigid broach holder body that has a size and shape to facilitate broaching of an intramedullary canal in a bone in preparation for implantation of a prosthetic femoral stem. In this embodiment, the broach holder body may include a selectively interchangeable rasp coupled to one end and an angled strike plate coupled to another end, opposite the rasp. The angled strike plate may include a strike surface positioned relative to a drive point near where the rasp enters the bone to translate a strike force applied perpendicular to the strike surface through the drive point. This may produce an axial insertion force into the intramedullary canal while substantially reducing or eliminating the rasp moment. In one embodiment, the angled strike plate may include a vertical offset angle α defined by the formula: α=90−arctan (X/Y), where X is the horizontal distance between the drive point and where the strike force contacts the strike surface of the angled strike plate and Y is the vertical gain between the drive point and where the strike force contacts the strike surface of the angled strike plate. 
         [0015]    Moreover, the broach holder tool with reduced rasp moment of this embodiment may also include an angled withdrawal plate coupled to the broach holder body between the rasp and the angled strike plate. The angled withdrawal plate may include a withdrawal surface for selectively receiving a withdrawal force generally perpendicular thereto that translates substantially along an angled directional withdrawal line generally aligned with a withdrawal point along the rasp. This substantially reduces the rasp moment at the withdrawal point when removing the broach holder tool from the intramedullary canal in the bone. Since the point of contact between the rasp and the bone may vary during withdrawal, the angled directional withdrawal line may extend through the rasp at a maximum offset of 10 degrees from the withdrawal point. Although, alternatively, the angled withdrawal plate may include an adjustable angled withdrawal plate selectively positionable relative to the withdrawal point to track the varying location of the withdrawal point along the rasp during removal. Here, the angled withdrawal plate may pivot relative to the broach holder body by a lock-step engagement. 
         [0016]    In another aspect of this embodiment, the angled withdrawal plate may include a vertical offset angle β that is between 10 and 30 degrees, and is defined by the formula: β=90−arctan (A/B), where A is the horizontal distance between the withdrawal point and where the withdrawal force contacts the withdrawal surface and B is the vertical distance between the withdrawal point and where the withdrawal force contacts the withdrawal surface. Another feature of this embodiment includes wherein the withdrawal surface of the angled withdrawal plate includes a non-planar withdrawal surface selected from the group consisting of a curved withdrawal surface, a spherical withdrawal surface, or a spheroidal withdrawal surface. Here, the angled directional withdrawal line varies across the non-planar withdrawal surface, depending where the withdrawal force strikes the non-planar withdrawal surface. This allows for changing the positioning of the angled withdrawal line relative to the rasp to track a varying withdrawal point along the length of the rasp as the rasp is removed from the intramedullary canal. 
         [0017]    In another embodiment, the broach holder tool with a reduced rasp moment as disclosed herein includes a generally elongated and rigid broach holder body having a size and shape for broaching a bone, a rasp selectively coupled to one end of the broach holder body, an angled strike plate coupled to another portion of the broach holder body opposite the rasp and having a strike surface positioned at a vertical offset angle α of 10-30 degrees for selectively receiving a strike force perpendicular thereto that drives through the rasp at a maximum offset of 10 degrees from a drive point where the rasp enters the bone, and an angled withdrawal plate extending out from the broach holder body between the rasp and the angled strike plate and including a withdrawal surface for selectively receiving a withdrawal force generally perpendicular thereto that translates substantially along an angled directional withdrawal line generally aligned with a withdrawal point along the rasp. 
         [0018]    Here, the vertical offset angle α may be defined by the formula: α=90−arctan (X/Y), where X is the horizontal distance between the drive point and where the strike force contacts the strike surface and Y is the vertical gain between the drive point and where the strike force contacts the strike surface. Moreover, the angled withdrawal plate may include a vertical offset angle β defined by the formula: β=90−arctan (A/B), where A is the horizontal distance between the withdrawal point and where the withdrawal force contacts the withdrawal surface and B is the vertical distance between the withdrawal point and where the withdrawal force contacts the withdrawal surface. 
         [0019]    The broach holder body may be an S-shape and a decrease in the vertical gain may decrease the vertical offset angle α and increase a substantially horizontal insertion force at the rasp. Alternatively, increasing the vertical gain of the S-shaped broach holder body may increase the vertical offset angle α and decrease the substantially horizontal insertion force at the rasp. Alternatively, the strike surface of the strike plate and the withdrawal surface of the withdrawal plate may each include a non-planar surface selected from the group consisting of a curved surface, a spherical surface, or a spheroidal surface. Additionally, the angled strike plate may be an adjustable angled strike plate that pivots relative to the broach holder body by a lock-step engagement and may be selectively positionable relative to the drive point along a selectively interchangeable rasp. 
         [0020]    In another embodiment, the broach holder tool with a reduced rasp moment may include a generally elongated and rigid broach holder body having a size and shape for broaching a bone, a rasp selectively coupled to one end of the broach holder body, an angled strike plate coupled to another portion of the broach holder body opposite the rasp and having a non-planar strike surface positioned at a vertical offset angle α of 10-30 degrees for selectively receiving a strike force perpendicular thereto that translates along an angled directional strike line extending through the rasp at a maximum offset of 10 degrees from a drive point where the rasp enters the bone, and an angled withdrawal plate extending out from the broach holder body between the rasp and the angled strike plate and including a non-planar withdrawal surface for selectively receiving a withdrawal force generally perpendicular thereto that translates substantially along an angled directional withdrawal line generally aligned with a withdrawal point along the rasp. 
         [0021]    Here, the angled directional strike line may vary across the non-planar strike surface and the angled directional withdrawal line may vary across the non-planar withdrawal surface, depending where the respective strike force or withdrawal force is applied to the non-planar strike surface or the non-planar withdrawal surface. To this end, the non-planar strike surface may be selected from the group consisting of a curved strike surface, a spherical strike surface, or a spheroidal strike surface and the non-planar withdrawal surface may be selected from the group consisting of a curved withdrawal surface, a spherical withdrawal surface, or a spheroidal withdrawal surface. The angled strike plate and/or the angled withdrawal plate may pivot relative to the broach holder body by a lock-step engagement. 
         [0022]    Other features and advantages of the present invention will become apparent from the following more detailed description, when taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The accompanying drawings illustrate the invention. In such drawings: 
           [0024]      FIG. 1  is a side perspective view of a prior art broach holder tool including a strike plate perpendicular to a rasp, and illustrating creation of a moment at the rasp when applying a force at the strike plate; 
           [0025]      FIG. 2  is a side perspective view of the prior art broach holder tool of  FIG. 1 , illustrating creation of a moment at the rasp when applying a force at a withdrawal plate or a back side of the strike plate; 
           [0026]      FIG. 3A  is a side perspective view of an alternative prior art broach holder tool incorporating a vertically and horizontally offset strike plate; 
           [0027]      FIG. 3B  is a top perspective view of the alternative prior art broach holder tool of  FIG. 3A ; 
           [0028]      FIG. 4  is a side perspective view illustrating one embodiment of a broach holder tool with reduced rasp moment as disclosed herein; 
           [0029]      FIG. 5  is a side perspective view of the broach holder tool with reduced rasp moment similar to  FIG. 4 , further illustrating applying a force to the strike plate without substantial creation of a moment at the rasp; 
           [0030]      FIG. 6  is a side perspective view of the broach holder tool with reduced rasp moment similar to  FIGS. 4 and 5 , further illustrating applying a force to the withdrawal plate without substantial creation of a moment at the rasp; 
           [0031]      FIG. 7  is a side perspective view of an alternative broach holder tool with reduced rasp moment having a gain relatively larger than the gain shown with respect to the broach holder tool with reduced rasp moment in  FIGS. 4-6 ; 
           [0032]      FIG. 8  is a side perspective view of the relatively larger gain broach holder tool with reduced rasp moment similar to  FIG. 7 , further illustrating applying a force to the strike plate without substantial creation of a moment at the rasp; and 
           [0033]      FIG. 9  is a side perspective view of the relatively larger gain broach holder tool with reduced rasp moment similar to  FIGS. 7 and 8 , further illustrating applying a force to the withdrawal plate without substantial creation of a moment at the rasp. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    As shown in the exemplary drawings for purposes of illustration, a broach holder tool with reduced rasp moment is shown generally in  FIGS. 4-6  by reference numeral  46  and an alternative broach holder tool with reduced rasp moment incorporating a relatively larger gain is shown in  FIGS. 7-9  with respect to reference numeral  46 ′. First, with respect to  FIGS. 4-6 , the broach holder tool with reduced rasp moment  46  includes an angled strike plate  48 , a generally S-shaped body or section  50  having an angled withdrawal plate  52  extending out therefrom, as shown, and an attachment mechanism (not shown) configured to selectively receive and retain a rasp  54 . The attachment mechanism is preferably configured to selectively couple to multiple rasps that vary in size, shape, and/or configuration, depending on the needs during surgery (e.g., larger rasps may be needed as the intramedullary canal is sized for insertion of the prosthetic stem). In the embodiment shown in  FIG. 4 , the broach holder tool with reduced rasp moment  46  may include a gain or vertical  56  of about 3.5″ relative to a horizontal  58 . That is, the body of the section  50  carrying the angled strike plate  48  and/or the angled withdrawal plate  52  may be generally vertically offset relative to the position of the rasp  54  by the gain  56 , which may provide enhanced angular orientation and insertion of the broach holder tool with reduced rasp moment  46  during anterior total hip replacement. In this respect, the broach holder tool  46  allows the surgeon to place the rasp  54  at the point of the intramedullary canal while positioning the angled strike plate  48  and/or the angled withdrawal plate  52  away from the body of the patient. This advantageously allows the surgeon to more easily access the angled strike plate  48  and/or the angled withdrawal plate  52  during surgery. But, as mentioned above, such offset positioning generates a moment along the rasp in prior art devices and typically near the point of entry, as shown in  FIG. 1  (counterclockwise moment) with respect to applying the strike force  28  to the strike plate  22  and in  FIG. 2  (clockwise moment) with respect to applying the withdrawal force  40  to the withdrawal plate  38 . The withdrawal force  40  can alternatively be applied to the backside of the strike plate, as mentioned above with respect to  FIG. 2 , depending on surgeon preference. 
         [0035]    As more specifically shown in  FIG. 5 , the angular strike plate  48  is offset from a normal perpendicular plane (see e.g.,  FIGS. 1 and 2 ) by an offset angle α. In this respect, the offset angle α corresponds to directionally positioning the strike force  28  so that it follows an angled directional strike line  60  extending through a drive point  62  along the length of the rasp  54 . The strike line  60  extends generally perpendicular to the strike plate  48  and forward from the strike force  28  as illustrated best in  FIG. 5 . Also, in the embodiment shown in  FIG. 5 , the drive point  62  is approximately where the rasp  54  couples to the section  50 . Although, preferably, the drive point  62  is at a point along the length of the rasp  54  where the rasp  54  has a tendency to experience the greatest resistance while rasping the intramedullary canal. In an ideal condition, the broach holder tool  46  generates no moment at the drive point  62  because the strike force  28  translates through the drive point  62 , as opposed to being applied to a moment arm extending from the drive point  62 , as mentioned above. The location of the drive point  62  may change as the rasp  54  penetrates deeper into the canal or during removal, as described below, but for purposes of the present disclosure, the primary point of force translation will be described with respect to the approximate location of the drive point  62 . To this end, there may be a number of factors that determine the location and size of a moment at or near the rasp  54 . A person of ordinary skill in the art will recognize that the embodiments disclosed herein are advantageous over the prior art, such as the prior art broach holder tools  20 ,  20 ′ discussed above, by way of substantially reducing (and possibly eliminating) the aforementioned moment because the strike line  60  extending from the strike plate  48  extends through the drive point  62  (or the point where the rasp  54  connects to the section  50 ), or within 5-10 degrees thereof, to minimize any moment within the rasp  54 . 
         [0036]    Translating the strike force  28  along the angled directional strike line  60  into the drive point  62  generates two vector forces thereon, a horizontal vector  64  and a vertical vector  66 . In the embodiment disclosed in  FIGS. 4-6 , the horizontal vector  64  is of a greater magnitude than the vertical vector  66 . Although, the size of each vector  64 ,  66  may change by differing the relative positioning of the strike plate  48  relative to the drive point  62 . For example, decreasing an angular offset θ changes the magnitude of the force translated through the line  60  to the drive point  62  to be more horizontal in nature than vertical. As a result, this increases the amount of force translated into the horizontal vector  64  and decreases the amount of force translated into the vertical vector  66 . In an ideal situation, as briefly mentioned above, the strike plate  28  is located along the horizontal  58  and perpendicular thereto so the strike force  28  translates only into the horizontal vector  64  for driving the rasp  54  straight down the intramedullary canal. In this example, the entire strike force  28  translates into energy driving the rasp  54  forward. But, due to the intricacies of total hip replacement surgery, for example, and especially so with respect to the anterior approach, this is not as feasible, especially when attempting to follow minimally invasive procedures. Thus, the broach holder tool  46  preferably includes some offset angle θ between the rasp  54  and the strike plate  48 . Changing the offset angle θ changes each of the vectors  64 , 66  as described herein. 
         [0037]    Additionally, the offset angle α may vary as a function of the height and length of the section  50 . For example, in the embodiment illustrated in  FIG. 5 , decreasing the gain  56  results in the angled strike plate  48  being positioned at a lower height relative to the drive point  62 . If the strike plate  48  remains oriented at the same angle α, then the strike line  60  perpendicular thereto would move upwardly and away from the drive point  62 , thereby creating an unwanted moment, as described above with respect to  FIGS. 1-3 . Accordingly, the angular orientation of the strike plate  48  preferably changes so the strike force  28  applied perpendicular thereto drives through the strike line  60  directed into the drive point  62 . Thus, decreasing the gain  56  requires decreasing the angle α and increasing the gain  56  requires increasing the angle α to maintain this relative relationship. In this respect, the desired angular offset of the strike plate  48  can be determined as a function of a horizontal distance  68  and the gain  56 , and specifically by the formula: α=90−arctan (X/Y), where X is the horizontal distance  68  and Y is the vertical distance denoted by the gain  56 . In the example shown in  FIG. 5 , assuming the horizontal distance  68  is approximately twice the distance of the gain  56  (i.e., X=2Y), the formula changes to α=90−arctan (2Y/Y), wherein α=˜26.57°. Accordingly, in this embodiment, it is preferred that the angled strike plate  48  be offset from the vertical by approximately 26.57° to maintain the strike line  60  in line with the drive point  62 . 
         [0038]    Additionally, the surface of the strike plate may be further optimized to maintain the angle α. In one example, the strike plate surface may include a curved or spherical surface helps align the strike force  28  through the drive point  62 . In this respect, the entire strike plate surface may have the curved or spheroidal surface or a portion of the strike plate surface may have the curved or spheroidal surface that has a radius centered, e.g., at the drive point  62 . 
         [0039]    As briefly mentioned above, the drive point  62  may vary along the length of the rasp  54 . In some embodiments, the drive point  62  may be preferred to be in the position shown in  FIG. 5 , i.e., at the point where the rasp  54  attaches to the section  50 . In other embodiments, the drive point  62  may be at a different point along the length of the rasp  54 , along the S-shaped section  50  or at another point as needed and/or desired to reduce the moment forces applied to the intramedullary canal during rasping. For example, moving the drive point  62  to the end of the rasp  54 , such as at point  70 , may lengthen the horizontal to a distance  72  that is relatively three times longer than the gain  56 . As such, the formula changes to α=90−arctan (3Y/Y), wherein α=˜18.43°. 
         [0040]    The same principles apply with respect to the withdrawal plate  52 , as more specifically shown in  FIG. 6 . Here, the withdrawal force  40  is applied generally perpendicular to the angled withdrawal plate  52  so that a withdrawal line  74  extends through the drive point  62 . Similar to the above, a withdrawal plate offset angle β is calculated by the formula β=90−arctan (A/B), where A is a horizontal distance  76  between the drive point  62  and the point of impact on the angled withdrawal plate  52 , and B is a vertical distance  78  between the horizontal  58  and the point of impact on the angled withdrawal plate  52 . In this case, while not necessarily drawn to scale, assuming the vertical distance  78  is approximately relatively 1.5 times the length of the horizontal distance  76  (i.e., wherein B=1.5 A), the formula changes to: β=90−arctan (A/1.5 A), wherein β=˜56.31°. Again, for illustrative purposes, moving the drive point  62  to the point  70  increases the horizontal distance to a distance  80 . If the horizontal distance  80  (i.e., “A”) is equal to the vertical distance  76  (i.e., “B”), then the formula changes to β=90−arctan (1), wherein β=45.00°. Accordingly, the withdrawal plate  52  should be oriented at a general 45° angle relative to the vertical to ensure that the withdrawal force  40  is aligned along the withdrawal line  74  extending through the point  70 . Aligning the withdrawal force to the desired drive point can also be accomplished with the design on the back side of the strike plate  48 , as mentioned above with respect to  FIG. 2 , to allow for surgeon accessibility. 
         [0041]    In one embodiment, the angular orientation of the angled strike plate  48  (i.e., angle α) and/or the angled withdrawal plate  52  (i.e., the withdrawal plate offset angle β) may be adjustable. For example, at the beginning of rasping the intramedullary canal, it may be that the desired drive point is closer to point  70  as opposed to point  62 . As such, the surgeon may have the option of selectively positioning the angle α at a first angular offset that is relatively smaller than a second angular offset later on in the procedure as the drive point moves closer to point  62 , and vice versa with respect to the withdrawal plate offset angle β, as the broach holder tool  46  is withdrawn from the intramedullary canal. Here, the angled strike plate  48  may pivot or rotate relative to the section  50 , such as by lock-step engagement. 
         [0042]    An alternative embodiment of the broach holder tool with reduced rasp moment  46 ′ is illustrated with respect to  FIGS. 7-9 . Here, the broach holder tool  46 ′ includes an alternative section  50 ′ having a more linear construction when compared to the more S-shaped section  50  described above. Moreover, the broach holder tool  46 ′ is shown including a gain  56 ′ relatively longer than the gain  56  described above with respect to the broach holder tool  46 , and may be as much as 8″. Despite these above differences, the principles of angularly positioning an angled strike plate  48 ′ and/or an angled withdrawal plate  52 ′ are generally the same. 
         [0043]    More specifically in this respect,  FIG. 8  illustrates application of the strike force  28  generally perpendicular to the angled strike plate  48 ′ and along a strike line  60 ′, which happens to generally follow the length of the structure of the section  50 ′ in this embodiment. As such, for translating the strike force  28  through a drive point  62 ′ along a rasp  54 ′, as indicated in  FIG. 8 , the strike plate  48 ′ must be offset from the vertical by an offset angle α′. The offset angle α′ is calculated by α′=90−arctan (X′/Y′), where X′ is the horizontal distance  68 ′ and the Y′ is the vertical distance or gain  56 ′. In this embodiment, the vertical distance or gain  56 ′ is approximately 1.25 times longer than the horizontal distance  68 ′. As such, Y′=1.25X′. Accordingly, this changes the formula to α′=90−arctan (X′/1.25X′), or ˜51.34°. When comparing the two embodiments disclosed herein,  FIG. 5  illustrates α=˜26.57° and  FIG. 8  illustrates α′=˜51.34°. The difference in the offset angle α, α′ is then represented by the difference in the magnitude of the force vectors applied at the drive point  62 , namely the horizontal vector  64  of  FIG. 5  is relatively larger than the horizontal vector  64 ′ of  FIG. 8 , and the vertical vector  66  of  FIG. 5  is relatively smaller than the vertical vector  66 ′ of  FIG. 8 . This is because of the increased offset angle, which drives more of the force downwardly in  FIG. 8  so the strike line  60  extends through the drive point  62 , as opposed to some point offset therefrom, which may create an undesired moment. Of course, as described above, the drive point  62  could be moved along the length of the rasp  54 , depending on the desired drive point characteristics. So, in another aspect of  FIG. 8 , moving the drive point to point  70  increases the horizontal distance  68 ′ to a distance  72 ′, which generally increases the ratio of the distance along the horizontal  58  relative to the vertical distance or gain  56 ′. A larger ratio results in a smaller offset angle α′, and vice versa. Moreover, a smaller offset angle α′ is associated with an increased ratio of the horizontal vector  64 ′ relative to the vertical vector  66 ′, and vice versa. 
         [0044]      FIG. 9  illustrates application of the angled withdrawal plate  52 ′ in association with the broach holder tool with reduced rasp moment  46 ′ as disclosed herein. More specifically, as described above, the angled withdrawal plate  52 ′ is preferably formed perpendicular to the withdrawal force  40  applied thereto when removing the broach holder tool  46 ′ from the intramedullary canal during rasping. The withdrawal force  40  is preferably aligned along a withdrawal line  74 ′ that intersects the drive point  62 ′ as shown in  FIG. 9 . Thus, as described above with respect to the withdrawal plate  52  of  FIG. 6 , the withdrawal offset angle β′ is calculated by the formula β′=arctan (A′/B′), where A′ is the horizontal distance  76 ′ and B′ is the vertical distance  78 ′. In this embodiment, while again not necessarily being drawn to scale, the vertical distance  78 ′ (i.e., “B”) may be 1.75 times longer than the horizontal distance  76 ′ (i.e., “A”). As such, B=1.75 A, and the formula changes to β′=arctan (A′/1.75 A′), wherein β′=˜60.26°. 
         [0045]    Additionally, the magnitude of each of a horizontal vector  82 ′ and a vertical vector  84 ′ changes, depending on the offset angle β′. For example, if the offset angle β′=45.00°, then the horizontal vector  82 ′ would be equal to the vertical vector  84 ′. Increasing the offset angle β′ to a larger angle, such as to 60.26° as mentioned above, results in an increase in the vertical vector  84 ′ relative to the magnitude of the horizontal vector  82 ′, and vice versa. Accordingly, the positioning of the angled strike plate  48 ,  48 ′ and/or the angled withdrawal plate  52 ,  52 ′ can be used to reduce the stress on the proximal femur during surgery. 
         [0046]    There may be a need for some broach holder tools to have an offset in another plane, other than what is shown in  FIGS. 4-9 , such as in the horizontal plate as shown and described above with respect to  FIGS. 3A and 3B . Such a broach holder tool may be needed to facilitate increased access due to surgical approach or obstructions due to patient anatomy. Similar principles as described above with respect to  FIGS. 4-9  could be followed in all planes to ensure alignment of the strike force with some drive point along the length of the rasp. 
         [0047]    Although several embodiments have been described in detail for purposes of illustration, various modifications may be made without departing from the scope and spirit of the invention. Accordingly, the invention is not to be limited, except as by the appended claims.