Abstract:
Femoral head modular resurfacing systems are described. The systems primarily include a head component and a stem component. The configuration of the head component and stem components allow for minimum invasiveness into the femur head region, thus conserving greater amounts of bone tissue than would be possible with conventional hip replacement systems. The systems also provide for various angles and offsets to be achieved between the systems and the femur head. The systems are useful in partial hip replacement procedures, as well as total hip replacement procedures, in which case an optional acetabular component would also be employed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation application of U.S. patent application Ser. No. 10/360,523 filed on Feb. 6, 2003, which claims the benefit of U.S. Provisional Application No. 60/355,171 filed on Feb. 6, 2002. The disclosures of the above applications are incorporated herein by reference. 
     
    
     FILED OF THE INVENTION  
       [0002]     The present invention relates generally to prosthetic components useful for hip replacement procedures, and more particularly to systems, and methods of using same, for the minimally invasive resurfacing of diseased or defective portions of the femoral head. The system primarily includes modular femoral head and stem components that permit minimal amounts of the femoral head to be resected during hip joint replacement procedures. The system also includes an optional acetabular component that properly articulates with the femoral head component.  
       BACKGROUND OF THE INVENTION  
       [0003]     A natural hip joint may undergo degenerative changes due to a variety of etiologies. When these degenerative changes become so far advanced and irreversible, it may ultimately become necessary to replace a natural hip joint with a prosthetic hip. When implantation of such a hip joint prosthesis becomes necessary, the head of the natural femur is first resected and a cavity is created (e.g., by reaming and broaching) within the intermedullary canal of the host femur for accepting the hip prosthesis, typically referred to as a femoral insert. The femoral insert may be inserted and supported within the host femur by cementing the femoral insert within the host femur. Alternatively, the femoral insert may be impacted into the host femur so that it is snugly fit and supported by the host femur.  
         [0004]     Due to any number of reasons, however, a small portion of patients that undergo such orthopedic surgical procedures may require subsequent revision surgery to replace the hip prosthesis with a new prosthetic device generally referred to as a revision prosthesis. Because conventional hip replacement procedures typically remove significant amount of bone tissue from the area surrounding the proximal intermedullary canal, there are significant problems associated with securing the revision prosthesis to the remaining femoral structure.  
         [0005]     Accordingly, there has been increasing reluctance on the part of orthopedic surgeons to remove the entire femur head as well as to remove any significant amounts of bone tissue in the proximal intramedullary canal during hip joint replacement surgery. This is especially true with respect to patients that have only slight to moderate bone tissue damage on the surface of the femur head (e.g., caused by vascular necrosis or osteonecrosis). In these cases, the limited amount of bone tissue damage on the surface of the femur head would appear to contraindicate the necessity of removing the entire femur head in order to accommodate a conventional femoral insert.  
         [0006]     This need has led to the development of femoral resurfacing components that require only that a portion of the femur head be resected, rather than the entire femur head. Presently, all currently available femoral resurfacing components are comprised of a single, unitary piece and either have a relatively short or relatively long, straight post to follow down the femoral neck. However, a major disadvantage of these components is that they significantly limit the versatility of femoral neck options and degree of offset, they are susceptible to early loosening and femoral neck fractures, and they require substantial rehabilitation periods similar to traditional total joint replacement techniques.  
         [0007]     Therefore, there exists a need for femoral resurfacing systems, and methods of using same, for minimizing the amount of bone tissue that needs to be removed from the proximal femur, such as the femur head and proximal intramedullary canal, during a hip replacement procedure and simultaneously allows a number of different configurations, angles, and offsets to be easily and inexpensively achieved.  
       SUMMARY OF THE INVENTION  
       [0008]     In accordance with the general teachings of the present invention, systems, and methods of using same, are provided for a minimally invasive partial or total hip replacement. The systems minimize the amount of bone tissue that is required to be removed from the femoral head region, thus conserving bone tissue for any future revision procedures. The system primarily includes a head component and a stem component for partial resurfacings (e.g., only the surface of the femur head is removed) and an optional acetabular component for total resurfacings (e.g., both the surface of the femur head and the surface of the acetabulum are removed). The systems may be secured in place by press fitting, cementing, or through the use of various mechanical fasteners.  
         [0009]     A more complete appreciation of the present invention and its scope can be obtained from the following detailed description of the invention and the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0011]      FIG. 1  illustrates an exploded view of a femoral head modular resurfacing system, in accordance with one embodiment of the present invention;  
         [0012]      FIG. 2  illustrates a perspective view of a stem component, in accordance with one embodiment of the present invention;  
         [0013]      FIG. 3  illustrates a perspective view of another stem component, in accordance with one embodiment of the present invention;  
         [0014]      FIG. 4  illustrates an elevational view of an alternative head component, in accordance with an alternative embodiment of the present invention;  
         [0015]      FIG. 5  illustrates an exploded elevational view of an alternative femoral head modular resurfacing system, in accordance with an alternative embodiment of the present invention;  
         [0016]      FIG. 6  illustrates an elevational view of another alternative femoral head modular resurfacing system, in accordance with an alternative embodiment of the present invention;  
         [0017]      FIG. 7  illustrates a partial sectional view of an offset femoral head modular resurfacing system implanted into the femur head region of a patient, in accordance with one embodiment of the present invention;  
         [0018]      FIG. 8  illustrates a partial sectional view of an alternative offset femoral head modular resurfacing system implanted into the femur head region of a patient, in accordance with an alternative embodiment of the present invention;  
         [0019]      FIG. 9  illustrates a partial sectional view of a fastening member for use with an alternative offset femoral head modular resurfacing system implanted into the femur head region of a patient, in accordance with an alternative embodiment of the present invention;  
         [0020]      FIG. 10  illustrates an elevational view of a minimally invasive total hip replacement system, in accordance with an alternative embodiment of the present invention;  
         [0021]      FIGS. 11   a - 11   c  depict various views of examples of resections according to the teachings of the present invention;  
         [0022]      FIGS. 12   a - 12   c  depict modular components corresponding to the resections shown in  FIGS. 11   a - 11   c;    
         [0023]      FIGS. 13   a - 13   c  illustrate cross sectional views of the minimally invasive, compliant fixation, total hip replacement system, in accordance with the embodiments depicted in  FIGS. 12   a - 12   c;    
         [0024]      FIG. 14  illustrates a side view of an alternative embodiment of the present invention;  
         [0025]      FIG. 15  depicts the resection of the humeral components necessary to insert the embodiment shown in  FIG. 14 ;  
         [0026]      FIG. 16  illustrates a cross sectional view of the minimally invasive, compliant fixation, total hip replacement system, in accordance with the embodiments depicted in  FIG. 14 ;  
         [0027]      FIGS. 17 and 18  illustrate a partial elevational view of the system in accordance with an alternative embodiment of the present invention; and  
         [0028]      FIGS. 19 and 20  depict the method of implanting the embodiments of the present invention.  
         [0029]     The same reference numerals refer to the same parts throughout the various Figures. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]     In accordance with a first embodiment of the present invention, a femoral head modular resurfacing system generally denoted as  10  is shown in  FIG. 1 . The system  10  primarily includes a head component  12  and a stem component  14 . The intended objective of the system  10  is to provide for a head resurfacing (either partial or full) component that will allow for a variety of femoral neck segments to either act as a hemi-arthroplasty (removal of the surface of the femur head) or a total resurfacing component (removal of both the surface of femur head as well as the surface of the acetabulum).  
         [0031]     The head component  12  can be comprised of any number of biocompatible materials, such as but not limited to titanium, cobalt chrome, stainless steel, ceramics or any other material that can serve as a bearing surface. The head component  12  can articulate either on the natural acetabulum or on an acetabular component (not shown) such as one made of cobalt chrome or any other suitable biocompatible material in order to provide for a metal-metal articulation.  
         [0032]     The head component  12  is shown as being substantially hemispherical in shape, although the present invention envisions modifications to the shape shown. For example, the head component  12  can be either a full, greater than full, or partial hemisphere. The head component  12  preferably includes a substantially hemispherical outer articulating surface  16  and a substantially hemispherical inner bearing surface  18  which is intended to bear or abut against the resected surface of the femur head.  
         [0033]     A connection member  20  extends outwardly from the inner surface  18  and is intended to cooperate with a complementary connection member  22  on the stem component  14 . Although the connection member  20  is shown as comprising a female Morse taper  24 , it is also envisioned that other types of connection configurations may be employed. For example, a male Morse taper may be used as well. Furthermore, threaded configurations may also be used. Additionally, although the connection member  22  is shown as comprising a male Morse taper  26 , it is also envisioned that other types of connection configurations may be employed. For example, a female Morse taper may be used as well. Furthermore, threaded configurations may also be used.  
         [0034]     Accordingly, the locking mechanism between the two components can be a taper (either self-locking or non-self-locking) as previously described, a screw mechanism, or any other locking mechanism sound enough to hold the two components together without any appreciable movement.  
         [0035]     The stem component  14  can be configured in any number of shapes (e.g., curved (see  FIG. 2 ), tapered, conical (see  FIG. 3 ), cylindrical, radial, fluted, and so forth). The surface finish of the stem component  14  can be smooth, plasma spray  28 , porous coating  30  (see  FIG. 2 ), threaded  32  (see  FIG. 3 ), polished, grit blasted, and so forth). The material comprising the stem component  14  can be any biocompatible material such as but not limited to titanium, cobalt chrome, stainless steel, ceramics, and so forth.  
         [0036]     The cross-sectional profile of the stem component  14  may comprise many different shapes, and can either be used in a press-fit or cemented application for implantation. The stem component  14  would typically be placed into the femoral neck either with or without entering into the diaphyseal femoral canal.  
         [0037]     Referring to  FIGS. 4-6 , the head component  112  could be offset either by placing the connection member  120  (e.g., taper or whatever locking mechanism is employed) offset to the pole or by using an offset stem component  114 . In  FIG. 4 , the distance “a” from one edge of the head component  112  to the center axis X of the connection member  120  is less than the distance “b” from the other edge of the head component  112  to the center axis X of the connection member  120 . The total distance between the outer edges of the head component  112  is denoted as “c”. Accordingly, the offset feature requires that length “a” does not equal length “b”. The precise nature by which the two components are connected in the offset mode is not thought to be critical. Thus, in  FIG. 5 , the system  100  includes a head component  112  that is provided with a tapered male member  122  which is intended to mate with a tapered female member  124  on the stem component  114 . Conversely, in  FIG. 6 , the system  100  includes a head component  112  that is provided with a tapered female member  126  which is intended to mate with a tapered male member  128  on the stem component  114 .  
         [0038]     This alternative embodiment of the present invention will allow a surgeon to pick a variety of stem components to match the femoral canal and indications of the particular component. The stem component can be matched with a full or partial head component and provide for full or partial coverage in particular areas of the femoral head by utilizing the offset feature.  
         [0039]     Referring to  FIG. 7 , there is shown the offset system  100  implanted into the femur head region FH of a patient. The surface of the femur head is first resected only to the degree necessary to permit the implantation of the respective components. A bore is then provided from the resected surface of the femur head downwardly through the remaining portion of the femur head. The stem component  114  is then implanted into the bore provided in the proximal portion of the femur and can be held in place by bone cement or any other suitable means. The head component  112  bears against the resected surface of the femur head and is then fastened to the stem component  114 .  
         [0040]     Referring to  FIG. 8 , there is shown an offset system  200  implanted into the femur head region FH of a patient, in the same manner as described above. However, in this view, the head component  112  and the stem component  114  consist of a single, unitary system  200 , as opposed to individual discrete components.  
         [0041]     If a non-cemented option is desired, a fastening member  300  can be provided on the lateral side L of the femur in order to secure the stem component  114  in place, as shown in  FIG. 9 . Of course, a bore B will have to be provided on the lateral side L of the femur so that the fastening member  300  can access the stem component  114 . Additionally, a cooperating fastening member  302  must also be provided on the distal surface of the stem component  114  so as to be able to engage the fastening surface  304  of the fastening member  300 .  
         [0042]     In accordance with a second embodiment of the present invention, a minimally invasive total hip replacement system generally denoted as  500  is shown in  FIG. 10 . The system  500  primarily includes a head component  502 , a stem component  504 , and an acetabular component  506  that is intended to properly articulate with the head component  502 .  
         [0043]     The intended objective of the second embodiment of the present invention is to provide a minimally invasive total hip replacement system (i.e., both femur head and acetabulum resurfacing) with either metal-metal or ceramic-ceramic articulation that would allow for implantation with minimal bone tissue removal.  
         [0044]     The head component  502  and the stem component  504  are similarly to the previously described components in terms of shape, configuration, materials, and so forth. The acetabular component  506  would preferably utilize optimal material and precision manufacturing tolerances for use as a metal-metal bearing. The acetabular component  506  would preferably be a press-fit component with some type of texturing on the backside to promote bone in-growth/on-growth and may or may not have a means for supplemental fixation. The typical material would be cobalt chrome, although other biocompatible materials may be used as well.  
         [0045]     The design of the acetabular component  506  is such that it requires removing a section of the acetabulum as compared to taking a spherical reamer to remove the diseased or defective area. Referring to  FIG. 11 , the sections are removed from the typical wear region WRA of the acetabulum where there is easy access to the pelvis. The cuts are made to match the implant that would have a spherical region for the bearing surface and the backside geometry would be the same as the cuts made in the pelvis. The resection would most likely occur in the superior-posterior region of the pelvis. The backside geometry of the acetabular component  506  could comprise both spherical and flat portions.  
         [0046]     The preparation of the femoral head FH is through flat cuts or via a spherical type of reamer to remove the diseased or defective portion WRF of the femur head FH. Only a minimal amount of bone tissue is removed with the systems of the present invention, as shown in  FIGS. 11   a - 11   c.    
         [0047]      FIGS. 11   a - 11   c  represent views of example resections of hips according to the teaching of the present invention. In each of the figures, the hip is distracted the minimal amount necessary to position the cutting tools so as to remove the minimal amount of tissue needed. As can be seen, generally straight cuts can be used to resect both the acetabulum and the humeral component.  
         [0048]     The implantation of this system is accomplished without dislocating the hip joint. Space is created within the joint by making both the acetabular and femoral head resection cuts. Final preparation is then completed utilizing a combination of reamers and cutting blades. The reamers are then activated by using a power handle introduced through the same incision.  
         [0049]      FIGS. 12   a - 12   c  represent portions of the implant according to the resection&#39;s shown in  FIGS. 11   a - 11   c.  In each figure, a partial humeral head components  502   a - c  is shown. As is shown in  FIGS. 1-10 , these humeral components can be coupled to with the humerus utilizing various fixation techniques, for example stems, screws, and bone cement.  
         [0050]     Further shown the acetabular components  506   a - c  which replace all or a portion of the acetabular cup. It is envisioned that each of the acetabular component will be fixed to the resected acetabulum by way of bone screws, pegs and or bone cement.  
         [0051]     The system components are then inserted together utilizing instrumentation to orient and impact the respective components. The instrument is mechanically separated through a screw (or similar) mechanism thus applying loads to both the femoral and acetabular component. The implanted system  500  is shown in  FIGS. 19-20 .  
         [0052]     This second embodiment of the present invention allows a total joint prosthesis that is completed without dislocating the hip joint and has the benefits of a metal-metal articulation. The hip joint does not need to be distracted because of the bone cuts creating the space for preparation. The implants can be implanted through one incision. This will allow a surgeon to pick from a variety of head components and acetabular components to suit the specific needs of the patient.  
         [0053]      FIGS. 13   a - 13   c  represent another embodiment of the present invention. A minimally invasive, compliant fixation, modular metal/metal total hip replacement system generally denoted as  500   a - c  are shown in  FIGS. 12   a - 12   c.  The system  500   a - c  primarily include a head component  502   a - c,  a stem component  504   a - c,  an acetabular component  506   a - c  that are intended to properly articulate with the head component  502   a - c,  and a fastening member  608   a - c  which fastens the head component  502  to the stem component  504 .  
         [0054]     The objective of this embodiment of the present invention is to provide the ability to perform a hemi-resurfacing (femoral head only) or total resurfacing (femoral head and acetabulum to provide metal-metal articulation) that would allow for a variety of head options and allow a minimally invasive preparation and implantation with minimal bone tissue removal.  
         [0055]      FIGS. 14-16  represent an alternative embodiment of the present invention. The system  550  couples to a spherically resected acetabulum. Also shown is the resected head portion. As can be seen, an initial flat resection  552  is made to humeral head  554 . Additionally, a conical surface  556  is formed using a rotating conical reamer. These resected surfaces  553  and  556  mate to a coupling surface  558  of the humeral member  560 .o  
         [0056]     As depicted in  FIGS. 17 and 18 , the components of the system  600  are similar to those depicted in connection with system  500  of the second embodiment, in terms of general shape, configuration, and materials. However, it should be noted that the stem component  604  and the fastening member  608  of the system  600  have been substantially modified, as will be described herein.  
         [0057]     The fastening member  608  is intended to fasten the head component  602  to the stem component  604 . For example, the fastening member  608  can be provided with a threaded distal portion  610  that cooperates with a threaded female surface  612  located on the undersurface of the head component  602 . Of course, a throughbore TB must be provided in the stem component  604  to receive the fastening member  608 . By rotating the fastening member  608  in the appropriate direction, the threaded distal portion  610  will eventually engage the threaded female surface  612  so as to firmly hold the respective components tightly together.  
         [0058]     Alternatively, instead of using a simple screw assembly, a compression assembly may be used, as shown in  FIG. 18 . The view shown in  FIG. 17  is the fully tightened and secured positioned. The throughbore TB of the stem component  604  contains a stack of washer elements  614 , retaining ring  616  and compression bolt  618  are contained. The set screw  620  is tightened into the fastening member  622  of the head component  602  utilizing the compression bolt  618  that has the opposite mechanism as the set screw  620 . The washer stack  614  is kept in place by the use of retaining ring  616 . The threaded portion  618 A of the compression bolt  618  extends outside of the stem component  604  with its head  618 B contained in the stem component  604  above the washer stack  614 . The anchor plug  624  is preferably made of a biocompatable material and contains a throughbore through the center which is threaded to connect to the threaded portion  618 A of the compression bolt  618 . The anchor plug  624  preferably contains holes  624 A to which one or more cross pins (not shown) are placed to secure the anchor plug  624  in place.  
         [0059]     The system  600  is loaded when the compression bolt  618  is threaded into the anchor plug  624 . As a result, the washer stack  614  is compressed, thus creating a load that tries to pull the anchor plug  624  and the stem component  604  together, thus placing load onto the femoral head and cross pins (not shown). This load creates stimulation to the femoral head, thus promoting bone in-growth.  
         [0060]     Referring to  FIG. 18 , there is shown the system  600  implanted into the femur head region FH of a patient. The system  600  is shown in its relaxed or loose state, in that the compression bolt  618  has not engaged the set screw  620 .  
         [0061]     The implantation of the system  600  is accomplished in substantially the same manner as previously described for system  500 .  
         [0062]      FIGS. 19-20  represent implantation of the system according to one embodiment of the present invention. While  FIGS. 19-20  depict the implant of the prosthetic according to  FIG. 14 , it should be understood that the same method can be used to implant any of the implants shown herein.  
         [0063]     As previously described, the joint being resurfaced, is a distracted an amount necessary for the proper resection of the articulating surfaces. Once the resected, the humeral and acetabular components are inserted between the resected surfaces. Furthermore, should bone cement be necessary, it should be inserted between the components and the resected surface prior to the coupling of the component members to the resected surface.  
         [0064]     After the humeral and femoral component has been inserted into the joint, and insertion tool  650  is inserted between the acetabular and humeral components. The components are then set onto the resected surface  651  by applying a pressure and/or forces from the insertion tool  650 .  
         [0065]     As best can be seen in  FIG. 18 , rotational forces can be applied to the handle  652  which are translated into separation all forces between top and bottom members  654  and  656 . It is envisioned that a mechanism, which can apply the necessary loading onto the humeral or acetabular components can be used.  
         [0066]     The foregoing description is considered illustrative only of the principles of the invention. Furthermore, because numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and process shown as described above. Accordingly, all suitable modifications and equivalents that may be resorted to that fall within the scope of the invention.