Abstract:
The femoral stem prosthesis includes a prosthesis body having a neck, stem, and porous coating receiving area. A portion of a transition between the porous coating receiving area and the stem is defined by a recess where the porous coating receiving area inwardly extends by a depth relative to the stem while the porous coating receiving area is approximately flush with the stem about a remainder of the transition between the porous coating receiving area and the stem. A porous coating overlying the porous coating receiving area has a thickness approximately equal to the depth of the recess to define a smooth transition between the porous coating and the stem along the portion of the transition by the at least one recess and a collar outwardly extending relative to the stem by approximately the thickness along the remainder of the transition between the porous coating receiving area and the stem.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to an improved femoral stem for use in hip joint arthroplasty. More specifically, the present invention relates to a femoral stem with a partially recessed porous coating that effectively forms a smooth arcuate transition at least between sections of the porous coating and the stem body to provide for smooth insertion of the femoral stem into a bone cavity during surgery, while maximizing press-fit engagement within the bone cavity. 
         [0002]    In hip arthroplasty, a broach instrument is used to cut out a cavity in the proximal femur for seated reception of a femoral stem. Preferably, this cavity provides for at least some press-fit engagement of the porous coating of the femoral stem such that the bone surrounding the cavity is encouraged to grow into the porous coating over time. As a result, the femoral stem better locks into the cavity to secure the implant to the bone. To achieve this proximal press-fit engagement, femoral stems known in the art include a proximal porous coating that protrudes beyond the distal femoral stem body. In this respect,  FIG. 1  illustrates a set of three such blade/Mueller type femoral stems  20 ,  20 ′,  20 ″ known in the prior art having an overhang or step  22 ,  22 ′,  22 ″ formed by application of a respective porous coating  24 ,  24 ′,  24 ″ to a respective portion of the stem body  26 ,  26 ′,  26 ″.  FIG. 2  is an enlarged view of the prior art femoral stem  20  of  FIG. 1 , taken about the circle  2 , and more specifically illustrates the outwardly protruding proximal porous coating  24  that creates the step  22  along the stem body  26 . This ledge or step  22  is particularly undesirable on the medial side of the femoral stem  20  as it can cause the femoral stem  20  to hang up while being seated into the femoral bone cavity during surgery. If the femoral stem  20  does hang up during surgery, it may lead to difficulties seating the femoral stem  20 , poor interdigitation of the bone with the porous coating  24 , intraoperative and/or postoperative fracture, and/or poor fixation in the femoral cavity over the long-term. 
         [0003]    Some femur stem designs known in the art attempt to rectify issues related to hang up by forming a recessed area around the entire perimeter of the femoral stem where the porous coating is applied. Example prior art devices are shown and described in U.S. Pat. Nos. 4,778,475; 5,013,324; 4,828,566; 4,608,055; 4,938,772, the contents of which are herein incorporated by reference in their entirety. The benefit of such a recessed area is that a porous coating having a certain thickness approximately equal to the depth of the recess can be applied to the stem body so the area of the porous coating is generally flush with the surrounding stem body, effectively eliminating the step. But, the drawback is that seated insertion of the femoral stem into the femoral cavity provides insufficient surface area contact of the porous coating with the bone because the porous coating is no longer outwardly extending. The Zimmer APS Natural-Hip System is another product currently available on the market that includes a recessed section on the stem body for receiving the porous coating. But, the Zimmmer APS Natural-Hip System only uses such a recessed area as a bone ingrowth surface, and not to facilitate insertion of the femur stem into the cavity of the femur. Thus, prior art devices either include the ledge or step  22 ,  22 ′,  22 ″ (thereby prone to hang up) and provide desired engagement between the porous coating and the bone, or the prior art femur stems have a recessed surface for reception of the porous coating, such as the Zimmer Natural Hip, and are undesirably incapable of press fitting the porous coating into the femur cavity to achieve desired engagement of the femur stem with the femur over the long term. Consequently, the prior art fails to disclose a recessed area or pocket along less than the entire perimeter of the femoral stem implant (e.g., only the medial side of the femoral stem implant), to eliminate the step, while maintaining substantial surface area engagement of the porous coating within the femur cavity. 
         [0004]    To more specifically illustrate the abovementioned drawback,  FIGS. 3-8  illustrate insertion of the prior art femoral stem  20  into a mockup of a femoral bone cavity  28  after broaching. More specifically,  FIG. 3  illustrates initial insertion of the femoral stem  20  into the bone cavity  28 . As shown in the enlarged view of  FIG. 4 , the stem body  26  easily fits into the enlarged upper end of the bone cavity  28  for slide-in reception. The hang up is not particularly problematic at this stage given that the step  22  is still well above an upper rim  30  of the bone cavity  28  formed from broaching. But, as the femoral stem  20  is continually inserted into the bone cavity  28 , the medially outwardly projecting step  22  may have a tendency to catch on the upper rim  30 , especially if the femoral stem  20  is inserted deeper into the bone cavity along its medial edge. In this respect, the surgeon must ensure that the femoral stem  20  is positioned somewhat away from the upper rim  30  so the medially outwardly projecting step  22  does not catch or hang up on this rim  30 . If it does, the step  22  may catch, chip, fracture, or otherwise damage the bone of the upper rim  30 , which can be particularly problematic when the femoral stem  20  is hammered into place. Moreover, required offsetting to clear the step  22  from the upper rim  30  may cause the femoral stem  20  to be misaligned when hammered into place, as previously mentioned above. 
         [0005]    Even if the surgeon successfully clears the upper rim  30  without causing damage thereto, an undesirably low surface area of the porous coating  24  may abut or sit adjacent to the bone cavity  28 . In this respect,  FIG. 5  illustrates continued insertion of the femoral stem  20  into the bone cavity  28  as the stem body  28 , and particularly as a distal tip  32 , nears the bottom of the bone cavity  28 . Here, the step  22  has already bypassed the upper rim  30 , as better shown in  FIG. 6 . The femoral stem  20  is shown somewhat offset from the inner surface of the bone cavity  28 , which provides for somewhat of a gap  34 , as shown. When the femoral stem  20  is finally seated as shown in  FIG. 7  and more specifically in the enlarged view of  FIG. 8 , the step  22  has a general single point of contact with the inner wall of the bone cavity  28 , which forms the offset or gap  34  between the stem body  26  and the inner wall of the bone cavity  28 . This gap  34  is particularly undesirable as it decreases the surface area contact of the porous coating  24  with the bone cavity  28  for purposes of ingrowth engagement after the formal stem  20  is implanted. 
         [0006]    There exists, therefore, a significant need in the art for a femoral stem with a medially recessed porous coating limited only to the distal medial side of the coated area, which facilitates easier stem insertion by reducing the prior art step at the distal medial edge of the porous coating, while still allowing the femoral stem to simultaneously press-fit engage the entire porous coated surface to the femur cavity, except at the distal medial corner where there is no step. The present invention fulfills these needs and provides further related advantages. 
       SUMMARY OF THE INVENTION 
       [0007]    The femoral stem prosthesis as disclosed herein may include a prosthesis body having a neck, a stem body, and a porous coating receiving area formed from the prosthesis body. A portion of a transition between the porous coating receiving area and the stem body may define at least one recess where the porous coating receiving area inwardly extends by a depth relative to the stem body while the porous coating receiving area is approximately flush with the stem body about a remainder of the transition between the porous coating receiving area and the stem body. In this respect, applying a porous coating over the porous coating receiving area by a thickness approximately equal to the depth of the recess defines a smooth transition between the porous coating and the stem body along the portion of the transition defined by the at least one recess. That is, the porous coating effectively fills the depth of the recess so the porous coating is flush with the stem body. Furthermore, the porous coating defines a collar outwardly extending relative to the stem body by approximately the thickness along the remainder of the transition between the porous coating receiving area and the stem body. The collar forms as a result of adding a layer of the porous coating to the area of the porous coating receiving area that is otherwise flush with the stem body. 
         [0008]    In another aspect of this embodiment, the portion of the transition defined by the at least one recess may include a medial recess or a lateral recess. In this respect, there may be a smooth transitional geometry between the porous coating in the medial recess and a medially vertical section of the stem body leading toward a distal tip. The smooth transitional geometry may include a medially arcuate section that extends from the porous coating to the medially vertical section of the stem body. This facilitates implantation since the stem body can slide over an open rim of a bone cavity uninterrupted, i.e., starting at the distal tip of the stem body and over the medially vertical section of the stem body and the medially arcuate section at the transition between the stem body and porous coating. The smooth transitional geometry otherwise eliminates the lip that may catch on the open rim of the bone cavity during implantation. 
         [0009]    In another embodiment, the at least one recess may include a pair of recesses that include a medial pocket formed in the porous coating and a lateral pocket formed in the porous coating opposite the medial pocket. Here, the femoral stem prosthesis may include a smooth medial transition along a medial arcuate section between the porous coating over the medial pocket and a medially vertical section of the stem body. The femoral stem prosthesis may further include a smooth lateral transition along a lateral arcuate section between the porous coating over the lateral pocket and a laterally vertical section of the stem body. As such, the femoral stem prosthesis may be of a size and shape for proximal press-fit engagement with the bone cavity substantially along the remainder of the transition, but not along the portion of the transition defined by the recesses/pockets. 
         [0010]    Other features of the femoral stem prosthesis as disclosed herein may include a step between the porous coating and the neck along a medial arc. In this respect, the porous coating may extend outwardly a distance approximately the thickness of the porous coating and about the femoral stem prosthesis adjacent the neck. Also, the remainder of the transition between the porous coating and the stem body may include a collar that has a U-shape and generally encompasses an anterior, a posterior, and a lateral side of the femoral stem prosthesis. Alternatively, the at least one recess may include a recess that wraps around at least a portion of the medial, the anterior, the posterior, and/or the lateral sides of the femoral stem prosthesis. 
         [0011]    In another embodiment as disclosed herein, the femoral stem prosthesis may include a prosthesis body having a neck and a stem body generally opposite the neck. A porous coating receiving area formed from the prosthesis body may be configured to at least partially selectively receive and retain a porous coating thereon. Furthermore, the femoral stem prosthesis may include a medially arcuate section of the porous coating adjacent a medially vertical section of the stem body. A smooth medial transition between the medially arcuate section of the porous coating and the medially vertical section of the stem body may include at least one recess formed in the porous coating receiving area that extends inwardly by a depth relative to the stem body such that applying the porous coating over the porous coating receiving area by a thickness approximately equal to the depth of the recess results in the porous coating along the medially arcuate section being substantially flush with the medially vertical section of the stem body. 
         [0012]    Additionally, a collar of the porous coating may extend outwardly relative to the stem body by approximately the thickness along a portion of the porous coating receiving area adjacent to and approximately flush with the stem body. The collar may be formed substantially along an anterior, a posterior, and a lateral side of the femoral stem and include a U-shape. As such, the femoral prosthesis may have a size and shape for proximal press-fit engagement with a bone cavity substantially along the collar, but not along the smooth medial transition between the medially arcuate section of the porous coating and the medially vertical section of the stem body. Accordingly, the smooth medial transition of the femoral stem prosthesis permits continuous and uninterrupted sliding along the medially arcuate section of the porous coating and the medially vertical section of the stem body over an open rim of the bone cavity during implantation. 
         [0013]    Other features of this embodiment may include a lateral pocket formed in the porous coating receiving area opposite the at least one recess, a smooth lateral transition along a lateral arcuate section between the porous coating over the lateral pocket and a laterally vertical section of the femoral stem, and a medial step between the porous coating and the neck. Moreover, the porous coating may extend outwardly by the thickness of the porous coating about an anterior, a posterior, a lateral, and a medial sides of the prosthesis body adjacent the neck. 
         [0014]    In another aspect of the embodiments disclosed herein, an alternative femoral stem prosthesis may include a prosthesis body having a neck extending from one side thereof and a stem extending from another side thereof generally opposite the neck and terminating at a distal tip. Moreover, the prosthesis body may include a porous coating receiving area formed therein. Additionally, a medial step along a medial arc of the prosthesis body may define a medial transition wherein the stem projects out and away from the porous coating receiving area. Similarly, a lateral step along a lateral arc of the prosthesis body opposite the medial arc may define a lateral transition wherein the stem projects out and away from the porous coating receiving area. As such, a porous coating may be selectively applied to the porous coating receiving area in an amount so the porous coating is flush with the stem along the medial arc and the lateral arc and extends outwardly along the anterior and posterior sides of the femoral stem prosthesis. Accordingly, the medial arc and the lateral arc of the femoral stem prosthesis may slide in uninterrupted relation over an open rim of a bone cavity during implantation while the femoral stem prosthesis is of a size and shape for proximal press-fit engagement within the bone cavity along the anterior and the posterior sides by way of engagement with the porous coating. The femoral stem prosthesis may also include an upper step between the porous coating and the neck along the medial arc, wherein the porous coating extends outwardly about the anterior, the posterior, a lateral, and a medial sides of the prosthesis body adjacent the neck. 
         [0015]    Additionally, in other embodiments, the femoral stem prosthesis may include a medially recessed porous coating generally including a femur body including a taper, neck, porous coating receiving region, and stem body having a distal tip opposite the taper. The porous coating receiving region may include a medial recess or pocket that forms a ledge or shoulder between the receiving region and the lower stem body prior to coating the receiving region with the porous coating. The anterior, posterior, and lateral sides of the receiving region may be flush with the lower stem body. Thereafter, a porous coating having a predetermined thickness that may be approximately equal to the depth of the ledge or shoulder formed by the recess or pocket between the receiving region and the lower stem body may be applied to the receiving region. The resulting structure of the femoral stem provides for a smooth, flush, or otherwise co-planar arced medial transition between the receiving region with the porous coating thereon and the lower stem body. The anterior, posterior, and lateral sides of the receiving region with the porous coating thereon generally extend or protrude outwardly, thereby forming a U-shaped shoulder relative to the lower stem body. As a result, the femoral stem with a medially recessed porous coating effectively forms a smooth arcuate transition at least between medial sections of the porous coating and the stem body to provide for smooth insertion of the femoral stem into a bone cavity during surgery. 
         [0016]    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 
         [0017]    The accompanying drawings illustrate the invention. In such drawings: 
           [0018]      FIG. 1  is a general perspective view of three prior art femur stems including a porous coating with a medial step; 
           [0019]      FIG. 2  is an enlarged view taken generally about the circle  2  of  FIG. 1 , further illustrating the medial step of one of the prior art femur stems; 
           [0020]      FIG. 3  is a perspective view of the prior art femur stem of  FIG. 1 , illustrating initial insertion into a bone cavity; 
           [0021]      FIG. 4  is an enlarged perspective view taken about the circle  4  in  FIG. 3 , more specifically illustrating orientation of the step relative to an upper rim of the bone cavity; 
           [0022]      FIG. 5  is a perspective view similar to  FIG. 3 , illustrating further insertion of the prior art femur stem into the bone cavity; 
           [0023]      FIG. 6  is an enlarged perspective view taken about the circle  6  in  FIG. 5 , more specifically illustrating orientation of the step relative to the bone cavity during further insertion of the prior art femoral stem into the bone cavity; 
           [0024]      FIG. 7  is a perspective view similar to  FIG. 3 , illustrating final insertion of the prior art femur stem into the bone cavity; 
           [0025]      FIG. 8  is an enlarged perspective view taken about the circle  8  in  FIG. 7 , more specifically illustrating final insertion of the prior art femoral stem into the bone cavity and the gap therebetween; 
           [0026]      FIG. 9  is a perspective view of one embodiment of a femoral stem with medially recessed porous coating as disclosed herein, illustrating a medial recess before application of the porous coating; 
           [0027]      FIG. 10  is a perspective view of the femoral stem of  FIG. 9 , further illustrating the femoral stem having the medially recessed porous coating applied; 
           [0028]      FIG. 11  is a left side elevation view further illustrating the femoral stem of  FIG. 10  with the medially recessed porous coating; 
           [0029]      FIG. 12  is an enlarged left side elevation view taken about the circle  12  in  FIG. 11 , further illustrating flush medial alignment of the porous coating with the stem body, and the porous coating in stepped anterior relation; 
           [0030]      FIG. 13  is a perspective view of the femoral stem of  FIGS. 10-12 , illustrating initial insertion into a bone cavity; 
           [0031]      FIG. 14  is an enlarged perspective view taken about the circle  14  in  FIG. 13 , further illustrating initial insertion of the femoral stem of  FIGS. 10-12  into the bone cavity; 
           [0032]      FIG. 15  is a perspective view similar to  FIG. 13 , illustrating further insertion of the femoral stem of  FIGS. 10-12  into the bone cavity; 
           [0033]      FIG. 16  is an enlarged perspective view taken about the circle  16  in  FIG. 15 , further illustrating flush slide-in insertion of the femoral stem of  FIGS. 10-12  relative to the upper rim of the bone cavity; 
           [0034]      FIG. 17  is a perspective view similar to  FIG. 13 , illustrating final insertion of the femoral stem into the bone cavity; 
           [0035]      FIG. 18  is an enlarged perspective view taken generally about the circle  18  in  FIG. 17 , further illustrating flush medial mounting of the femoral stem of  FIGS. 10-12  within the bone cavity; 
           [0036]      FIG. 19  is a perspective view of an alternative embodiment of a femoral stem including a laterally recessed porous coating; and 
           [0037]      FIG. 20  is a perspective view of another embodiment of a femoral stem as disclosed herein, including a medially and laterally recessed porous coating. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0038]    As shown in the exemplary drawings, a femoral stem with medially recessed porous coating is referred to generally in  FIGS. 9-18  by reference numeral  36 . As discussed in detail below, in one embodiment, the femoral stem  36  creates a smooth transition between the distal stem body and the proximal porous coated area to allow the femoral stem  36  to more easily and fully seat into the femur bone cavity during hip arthroplasty procedures. Additionally, because the porous coating is left extended on all surfaces but the medial curve, the femur stem  36  still achieves proximal press-fit engagement with the bone cavity when implanted. In other words, the femoral stem  36  may seat fully within the bone cavity  28  without hanging on the upper rim  30  of the bone cavity  28  during insertion, while maintaining sufficient press-fit engagement between the bone of the cavity  28  and the porous coating. 
         [0039]    More specifically,  FIG. 9  illustrates the femoral stem  36  in an uncoated state. In general, the femoral stem  36  is shown in  FIG. 9  including a neck  38  having a head connector  40  at one end, and a porous coating receiving region  42  formed between the neck  38  and a stem body  44  terminating at a distal tip  46  at an opposite end. The medial curvature of the femoral stem  36  generally indicated by the arrow  48  in  FIG. 9  transitioning between the neck  38  and the receiving region  42  is preferably smooth or flush along the arc, as shown. But, the transition between the receiving region  42  and the stem body  44  is different. In this respect, the receiving region  42  includes a medially arcuate section  50  terminating in a medially recessed position or pocket relative to a generally medially vertical section  52  of the stem body  44 , thereby forming a ledge or shoulder  54  therebetween. During manufacture of the femoral stem  36 , and before adding a porous coating  56 , this medially recessed position or pocket of the medially arcuate section  50  may be formed by machining, forging, additive manufacturing or casting. The depth of this recess or pocket is designed to match the thickness of the porous coating  56  such that the transition between the proximal porous coating  56  and the distal stem body  44  is smooth on the medial side, as shown best in  FIGS. 10, 12, 14, 16 and 18 . 
         [0040]    Before coating, the recess or pocket generally forms the ledge or shoulder  54  between the transition of the medially arcuate section  50  of the receiving region  42  and the medially vertical section  52  of the stem body  44 , but only along the medial part of the femur stem  36 . The depth of the ledge or shoulder  54  may vary as needed and/or desired, depending on the application. The anterior, posterior and lateral surfaces of the receiving region  42  and the stem body  44  are flush or smooth in the configuration shown in  FIG. 9 . Of course, such a recess or pocket could wrap around a portion or the entire anterior, posterior, and/or lateral sides of the femoral stem  36  such that the ledge or shoulder  54  extends partially or all away around each of anterior, posterior, and/or lateral sides of the femoral stem  36 . 
         [0041]      FIG. 10  illustrates the femoral stem  36  in a coated state wherein a layer of the porous coating  56  (similar to porous coating  24  described above) is applied to the receiving region  42 . The thickness of the porous coating  56  may vary depending on the femoral stem  36 , but it is preferably approximately equal to the depth of the ledge or shoulder  54  so that final finishing results in a smooth transitional geometry between the medially vertical section  52  of the stem body  44  and the porous coating  56  applied along the medially arcuate section  50  ( FIG. 9 ). As such, in the configuration shown in  FIG. 10 , the medially arcuate section  50  of the femoral stem  36  is now generally smooth or flush with the medially vertical section  52  of the stem body  44 , thereby effectively eliminating the ledge or shoulder  54  therebetween. Although, the addition of the porous coating  36  of predetermined thickness effectively increases the thickness such that the anterior, posterior, and/or lateral sides of the porous coating  56  extend outwardly relative to the anterior, posterior and/or lateral sides of the stem body  44 , thereby creating a three-sided or U-shaped outwardly protruding shoulder  58  that better maximizes surface area contact of the porous coating  56  with the bone when the femoral stem  36  is implanted. The addition of the porous coating  56  of predetermined thickness also increases the thickness thereof such that the anterior, posterior, lateral, and/or medial sides of the porous coating  56  extend outwardly relative to the anterior, posterior, lateral, and/or medial sides of the neck  38 , thereby creating a four-sided or ring-shaped outwardly protruding shoulder  60 . Of course, the porous coating  56  could vary in thickness and extent depending on the desired roughness. 
         [0042]      FIGS. 11 and 12  more specifically illustrate the femoral stem  36  having a smooth or flush transition between the medially vertical section  52  of the stem body  44  and the medially arcuate section  50  of the porous coating  56 . Note that there is a protruding or outwardly extending edge (i.e., the U-shaped shoulder  58 ) of the porous coating  56  on all faces (i.e., anterior, posterior and lateral sides). This configuration, as shown in more detail below with respect to  FIGS. 13-18 , provides for enhanced slide-in engagement into the corresponding bone cavity without any issues related to hang-up, as described above, while simultaneously providing enhanced initial press-fit engagement and fixation with increased interdigitation of bone with the porous coating  56  over time. That is, the geometry of the femur stem  36  allows it to more consistently seat along the entire medial curvature (e.g., as denoted by the arrow  48 , the medially arcuate section  50 , and, at least initially, along the medially vertical section  52 ), without digging in or catching on the upper rim  30  of the bone cavity  28  because the arcuate surfaces provide for a continuous and smooth arcuate transition between the porous coating  56  and the stem body  44  along the generally curved medial edge. Because the porous coating  56  still extends outwardly beyond the respective anterior, posterior, and/or lateral surfaces of the stem body  44 , thereby forming the U-shaped shoulder  58 , the femoral stem still attains sufficient press-fit engagement with the bone cavity  28 . 
         [0043]    To illustrate the advantages of the femoral stem  36  disclosed herein, and compared to the prior art femoral stem  20  discussed above with respect to  FIGS. 1-8 ,  FIGS. 13-18  more specifically illustrate insertion of the femoral stem  36  into a mockup of the femoral bone cavity  28  after broaching. In this respect,  FIG. 13  illustrates initial insertion of the femoral stem  36  into the bone cavity  28 . As shown in the enlarged view of  FIG. 14 , the stem body  44  similarly easily fits into the enlarged upper end of the bone cavity  28  for slide-in reception. As the femoral stem  36  is continually inserted into the bone cavity  28 , the medial side of the femoral stem  36  may have a tendency to slide near or relative to (e.g., along) the upper rim  30 . As discussed above, this was problematic for the prior art femoral stem  20  because the outwardly projecting step  22  may have a tendency to catch on the upper rim  30  as the femoral stem  20  is inserted deeper into the bone cavity  28 . But, in the case of the femoral stem  36  disclosed herein, the step  22  is largely eliminated by including a recessed receiving region  42  along the medial side of the femoral stem  36 . In turn, the medially arcuate section  50  and the medially vertical section  52  include a smooth transition between the two, thereby effectively eliminating the step  22 . The surgeon no longer needs to ensure that the femoral stem  36  clears the upper rim  30 . Rather, the surgeon can simply slide the femoral stem  36  medially and along the upper rim  30  without worrying that the femoral stem  36  will catch or hang up on the rim  30 . This provides for enhanced alignment of the femoral stem  36  within the bone cavity  28  during surgery. 
         [0044]      FIG. 5  further illustrates continued insertion of the femoral stem  36  into the bone cavity  28  as the stem body  44 , and particularly the distal tip  46  nears the bottom of the bone cavity  28 . Here, as shown in the enlarged view of  FIG. 16 , the benefit of the smooth transition between the medially arcuate section  50  and the medially vertical section  52  can be shown moving past the upper rim  30  without interference. The femoral stem  36  is shown still being somewhat offset from the inner surface of the bone cavity  28 , before the femoral stem  36  is completely (snugly) inserted into the bone cavity  28 . When the femoral stem  36  is finally seated as shown in  FIG. 17 , and more specifically in the enlarged view of  FIG. 18 , the smooth transition between the medially arcuate section  50  and the medially vertical section  52  provides for adjacent seated reception of the medial side of the femoral stem  36  against the bone cavity  28 . This may increase the surface area contact between the medial side of the femoral stem  36  with the bone cavity  28 , as opposed to the general single point of contact (and the gap  34 ) with the inner wall of the bone cavity  28 , as described above with respect to the prior art femoral stem  20 . Accordingly, the femoral stem  36  as disclosed herein is able to effectively eliminate the undesirable gap  34  ( FIG. 8 ). Moreover, the U-shaped shoulder  58  still permits substantial engagement of the porous coating  56  with the surrounding bone cavity  28 . Depending on the geometry of this recess or pocket forming the ledge/shoulder  54 , the amount of press-fit engagement may be changed by increasing or decreasing the transition between the medially arcuate section  50  and the medially vertical section  52 , prior to addition of the porous coating  56 . Such modifications may respectively create snugger or looser feeling stems, based on surgeon preference and implant geometry. Alternatively, the femoral stem  36  may include comparable geometry with an oversized distal end, which steps down to the proximal porous coating  56 . Such a femur stem  36  could have essentially the same geometry without the pocket, per se. 
         [0045]      FIGS. 19 and 20  illustrate alternatives to the femoral stem with medially recessed porous coating  36 . In this respect,  FIG. 19  discloses a femoral stem with laterally recessed porous coating  62 . In this embodiment, the femoral stem  62  creates a smooth transition laterally between the distal stem body and the proximal porous coated area to allow the femoral stem  62  to more easily and fully seat into the femur bone cavity during hip arthroplasty procedures. Additionally, because the porous coating is left extended on all surfaces but the lateral curve, the femur stem  62  may still achieve proximal press-fit engagement with the bone cavity when implanted. In other words, the femoral stem  62  may seat fully within the bone cavity  28  without laterally hanging on the upper rim  30  of the bone cavity  28  during insertion, while maintaining sufficient press-fit engagement between the bone of the cavity  28  and the porous coating. 
         [0046]    In general, the femoral stem  62  is shown in  FIG. 19  including the neck  38  having the head connector  40  at one end, and the porous coating  56  between the neck  38  and the stem body  44 . Similar to the above, the femoral stem  62  may include a recess or pocket near arrow  64  so that, when the porous coating  56  is applied to the above-mentioned receiving region  42 , the layer of the porous coating  56  preferably approximately equals the depth of the ledge or shoulder so the final finishing results in a smooth (or smoother) transitional geometry between a laterally vertical section  66  of the stem body  44  and the porous coating  56  applied along a lateral section  68 . As such, in the configuration shown in  FIG. 19 , the lateral section  68  of the femoral stem  62  is now generally smooth or flush with the laterally vertical section  66  of the stem body  44 , thereby effectively eliminating any ledge or shoulder therebetween, as described herein. 
         [0047]      FIG. 20  illustrates another alternative embodiment of a femoral stem with medially and laterally recessed porous coating  70 . Here, the femoral stem  70  illustrated in  FIG. 20  is basically a combination of the femoral stems  36  and  62 , namely before application of the porous coating  56 , the receiving region  42  includes a medial and lateral recess or pocket, thereby forming both a medial and lateral ledge. When the porous coating  56  having a predetermined thickness preferably approximately the thickness of the depth of the ledges, this creates a smooth transition between the medially arcuate section  50  and the medially vertical section  52 , on the medial side of the femoral stem  70 , while also creating a smooth transition between the laterally vertical section  66  and the lateral section  68  on the lateral side of the femoral stem  70 . 
         [0048]    Of course, the principles of  FIGS. 19 and 20  could be extended to other surfaces. That is, the smooth transition between the porous coating  56  and the stem body  44  could be on one or more sides of the femoral stem (e.g., the medial, lateral, anterior, and/or posterior sides). Of course, in other embodiments, the smooth transition may be between just one side, two sides, three sides, or all four sides, as discussed herein. 
         [0049]    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.