Patent Publication Number: US-2013253658-A1

Title: Modular femoral stem component for a hip joint prosthesis

Description:
REFERENCE TO PENDING PRIOR APPLICATIONS 
     This application claims benefit of: 
     (1) pending prior U.S. Provisional Patent Application Ser. No. 60/219,955, filed Jul. 20, 2000 by Alfred S. Despres III et al. for MODULAR ORTHOPEDIC CONNECTION (Attorney&#39;s Docket No. HAYES-1 PROV); and 
     (2) pending prior U.S. Provisional Patent Application Ser. No. 60/219,963, filed Jul. 20, 2000 by Alfred S. Despres III et al. for FORCE COUPLE CONNECTION (Attorney&#39;s Docket No. HAYES-2 PROV). 
     The two above-identified patent applications are hereby incorporated herein for reference. 
    
    
     FIELD OF THE INVENTION  
     This invention relates to surgical apparatus and procedures in general, and more particularly to orthopedic prostheses for restoring the hip joint. 
     BACKGROUND OF THE INVENTION  
     Joint replacement surgery seeks to replace portions of a joint with prosthetic components so as to provide long-lasting function and pain-free mobility. 
     For example, in the case of a prosthetic total hip joint, the head of the femur is replaced with a prosthetic femoral stem component, and the socket of the acetabulum is replaced by a prosthetic acetabular cup component, whereby to provide a prosthetic total hip joint. 
     In the case of a prosthetic total knee joint, the top of the tibia is replaced by a prosthetic tibial component, and the bottom of the femur is replaced by a prosthetic femoral component, whereby to provide a prosthetic total knee joint. 
     The present invention is directed to orthopedic prostheses for restoring the hip joint and, more particularly, to improved prosthetic femoral stem components. 
     Prosthetic femoral stem components typically comprise a proximal section for seating in the proximal section of the resected femur and presenting a ball for seating in the acetabular socket, and a distal section for seating in the femur&#39;s medullary canal so as to extend along the shaft of the femur. 
     It is, of course, important that the prosthetic femoral stem component make a proper fit with the surrounding bone. To this end, prosthetic femoral stem components are typically offered in range of different sizes in an effort to accommodate variations in patient anatomy. However, despite this, it has been found that it can be difficult to provide the correct prosthetic femoral stem component for patients. This is due to the wide variation in patient anatomies and to the practical limitations of hospital inventory. By way of example, where a femoral component is selected having a proximal section appropriately sized for the proximal section of the resected femur, the distal section of the prosthesis may not be appropriately sized for proper seating in the distal section of the femur. This can present serious problems for the patient, including problems relating to joint stability and pain. 
     On account of the foregoing, there has been substantial interest in forming prosthetic femoral stem components out of a plurality of separate elements, wherein each of the elements may be independently selected so as to most closely approximate patient anatomy, and wherein the separate elements may be assembled to one another in situ, using modular connections, so as to provide the best possible prosthetic femoral stem component for the patient. 
     Once deployed in the patient&#39;s body, the prosthetic femoral stem component, and hence the modular connections securing the separate elements to one another, are subjected to axial, bending and torsional loads. While different types of modular connections are known in the art, no one modular connection is ideal for dealing with ail three types of loads, i.e., axial, bending and torsional loads. By way of example, taper connections generally accommodate axial (i.e., compressive; loads well, but they generally do not accommodate bending and torsional loads particularly well. By way of further example, concentric cylinder connections generally accommodate bending loads well, but they generally do not accomodate axial and torsional loads particularly well. 
     SUMMARY OF THE INVENTION  
     As a result, one object of the present invention is to provide an improved modular connection for connecting together a plurality of separate elements so as to form a prosthetic femoral stem component, 
     Another object of the present invention is to provide an improved prosthetic femoral stem component. 
     And another object of the present invention is to provide an improved prosthetic total hip joint. 
     Still another object of the present invention is to provide an improved method for restoring a hip joint. 
     These and other objects are addressed by the provision and use of the present invention. 
     In one form of the invention, there is provided an improved modular connection for connecting together a plurality of separate elements so as to form a prosthetic femoral stem, component, the improved modular connection comprising, in combination, a taper junction and an engaged-fit junction. 
     In another form of the invention, there is provided an improved prosthetic femoral stem component comprising a body element, a neck element and a stem element, with the body element, neck element and stem element being secured to one another with a modular connection, wherein the modular connection comprises, in combination, a taper junction and an engaged-fit junction. 
     In another form of the invention, there is provided, an improved prosthetic total hip joint comprising a prosthetic femoral stem component and a prosthetic acetabular cup component, wherein the femoral stem component comprises a body element, a neck element and a stem element, with the body element, neck element and stem element being secured to one another with a modular connection, wherein the modular connection comprises, in combination, a taper junction and an engaged-fit junction. 
     In another form of the invention, there is provided an improved method for restoring a hip joint, wherein the method, comprises the steps of.: resecting the head of the femur and preparing the interior of the femur to receive a prosthetic femoral stem component; assembling a prosthetic femoral stem component comprising a body element, a neck element and a stem element by selecting appropriately sized elements and securing them together with a modular connection, wherein the modular connection comprises, in combination, a taper junction and an engaged-fit junction; and seating the prosthetic femoral stem component in the femur. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       These and other objects and features of the present invention will foe more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which are to be considered together with the accompanying drawings wherein like numbers refer to like parts and further wherein: 
         FIG. 1  is a schematic, exploded side view of a prosthetic femoral stem component formed in accordance with the present invention; 
         FIG. 2  is an enlarged, schematic, exploded side view of the modular connection used to form the prosthetic femoral stem component shown in  FIG. 1 ; 
         FIG. 3  is a schematic side view of a prosthetic total hip joint formed in accordance with the present invention; 
         FIG. 4  is a schematic side view of another form of prosthetic femoral stem component formed in accordance with the present invention; and 
         FIG. 5  is a schematic side view of a prosthetic total hip joint using the prosthetic femoral stem component shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Looking first at  FIG. 1 , there is shown a prosthetic femoral stem component  5  formed in accordance with the present invention. Prosthetic femoral stem component  5  generally comprises a body element  10 , a neck element  15  and a stem element  20 . Body element  10  includes a central aperture  22  into which portions of neck element  15  and stem element  20  extend. Body element  10  is selected so that its outer surface  25  is properly sized to foe seated in the proximal section of a resected femur. Neck element  15  is selected so that when, it is mounted to the remainder of prosthetic femoral stem component  5  deployed within, the femur, the neck element&#39;s ball  30  will foe properly seated in the hip joint&#39;s corresponding acetabular cup. Stem  20  is selected so that its outer surface  35  is properly sized to be seated within the medullary canal of the femur. 
     In accordance with the present, invention, body element  10 , neck element  15  and stem element  20  are adapted to be secured to one another using an improved modular connection  40  so as to form the complete prosthetic femoral stem component  5 . 
     More particularly, modular connection  40  comprises, in combination, two load-bearing junctions: a taper junction  45  and an engaged-fit junction  50 . 
     Looking now at  FIGS. 1 and 2 , taper junction  45  is formed by the interaction of a first taper  55  with a corresponding second taper  60 . More particulary, first taper  55  is formed on the shaft  65  of neck element  15 . Second taper  60  is formed along a portion of the sidewall defining the body element&#39;s central aperture  22 . First taper  55  and second taper  60  seat securely against one another so as to together form the load-bearing taper junction  45 . 
     Still looking now at  FIGS. 1 and 2 , engaged-fit junction  50  is formed by the interaction of a first concentric wall  70  with a second concentric wall  75 . More particularly, first concentric wall  70  is formed on shaft  65  of neck element  15 . Preferably first concentric wall  70  is disposed on shaft  65  coaxial with, and distal to, first taper  55 . Second concentric wall  75  is formed along a portion of the sidewall defining the body element&#39;s central aperture  22 . Preferably second concentric wall  75  is disposed on body element  10  coaxial with, and distal to, second taper  60 . First concentric wall  70  and second concentric wall  75  seat securely against one another so as to form the load-bearing engaged-fit junction  50 . 
     In general, the engaged-fit junction  50  is a mechanical connection that achieves stability by the deformation of one member so that it is pressure locked against a constraining second member. This deformation can be expansion (e.g., as in a taper expanded collet) or contraction (e.g., as in a force fit). The deformation can also be effected by thermal expansion or thermal contraction (e.g., as with a shape memory alloy such as Nitinol or the like). Regardless of how the deformation is achieved, the resulting mechanical connection has surfaces which are forcefully engaged against one another as a result of the deformation, whereby to establish the engaged-fit junction. 
     As noted above, there are a number of ways in which first concentric wall  70  and second concentric wall  75  can foe made to seat securely against one another so as to form the load-bearing engaged-fit junction  50 . 
     For example, first concentric wall  70  can be made slightly oversized relative to second concentric wall  75 , such that force fitting first concentric wall  70  internal to second concentric wail  75  will create the engaged-fit junction  50 . 
     Alternatively, and in accordance with a preferred form of the present invention, the distal end of the neck element&#39;s shaft  65  may be formed with a recess  80 , and the proximal end of stem element  20  may include a projection  85  for insertion into recess  80 . More particularly, projection  85  is diametrically oversized relative to recess  80 , such that insertion of projection  85  into recess  80  will cause a radial expansion of first concentric wall  70  into engagement with second concentric wall  75 , whereby to create the engaged-fit junction  50 . In one preferred form, of the invention, recess  50  and projection  85  are both tapered, and the distal end of neck  15  is a split collet. Alternatively, the distal end of neck  15  may be formed out of a material sufficiently resilient to engage second concentric wall  75  without being split. If desired, a threaded bolt can thereafter lock stem element  20  to neck element  15 . By way of example, neck element  15  can include a bore  87  and a counterbore  88 , and stem element  20  can include a threaded bore  89 . Then a bolt  90 , having a head  91  and a distal thread  92 , may be driven, via a recessed hex drive  93 , so that its distal thread  92  seats in stem threaded bore  89  and its head  91  seats in neck counterbore  88 , whereby to lock stem element  20  to neck element  15 . 
     Due to the unique construction of modular connection  40 , the prosthetic femoral stem component  5  is able to accommodate axial, bending and torsional loads better than prior art devices. More particularly, modular connection  40  simultaneously provides two load-bearing junctions: the taper junction  45  and the engaged-fit junction  50 . The taper junction  45  accommodates axial (i.e., compressive) loads extremely well. At the same time, the engaged-fit junction  50  accommodates bending and torsional loads extremely well. Additionally, the engaged-fit junction  50  stabilizes the taper junction  45  against bending and torsional loads. Together, the two load-bearing junctions collectively handle axial, bending and torsional loads significantly better than prior art devices. 
     Looking next at  FIG. 3 , prosthetic femoral stem component  5  is preferably used, as follows. 
     First, the patient&#39;s femur  100  is prepared, e.g., by resecting the head of the femur, and clearing the interior of the femur to receive the prosthetic femoral stem component. 
     Next., a body element  10  is selected so that its outer surface  25  is properly sized to be seated in the proximal section of the resected femur. Then a neck element  15  is selected so that when it is mounted to the remainder of the prosthetic femoral stem component deployed within the femur, the neck element&#39;s ball  30  will be properly seated in the hip joint&#39;s corresponding acetabular cup  105 . Then a stem  20  is selected so that its outer surface is properly sized to be seated within the medullary canal  110  of the femur. 
     Next, body element  10 , neck element  15  and stem element  20  are assembled into the prosthetic femoral stem component  5 . This is preferably done by passing the distal end of the neck element&#39;s shaft  65  down the body element&#39;s central aperture  22  until first taper  55  engages second taper  60 , whereby to create the tapered junction  45  ( FIGS. 1 and 2 ), and then passing the proximal end of stem element  20  up into central aperture  22  until the stem element&#39;s oversized projection  85  is inserted into recess  80 , whereupon first concentric wall  70  will expand into engagement with second concentric wall  75 , whereby to create the engaged-fit junction  50  ( FIGS. 1 and 2 ). If desired, threaded bolt  90  can be used to lock system element  20  to neck element  15 . 
     Next, prosthetic femoral stem component  5  is deployed in the resected femur, the acetabular side of the joint is prepared (i.e., prosthetic acetabular cup component  105  is deployed in the patient&#39;s acetabulum  115 ), ball  30  is set on neck element  15 , and the hip is reduced. 
     As noted above, a bolt  90  can be passed down a bore  87  in neck element  15  and secured to stem element  20  as as to secure stem element  20  to neck element  15 . Alternatively, other arrangements can also be used. Thus, for example, and looking now at  FIGS. 4 and 5 , stem element  20  can include a shaft  85 A proximal to its projection  85 , with the proximal end of shaft  85 A including screw threads  85 B, and with this shaft  85 A. being passed up through bore  87  in neck element  15 . A nut  99 A engages threads  85 B and seats in the neck element&#39;s counterbore  88  to lock stem element  20  to neck element  15 . 
     It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled the art without departing from the principles and scope of the present invention.