Abstract:
Disclosed is an acetabular cup implant for an artificial hip joint suitable for being fitted to a bone using a shape memory alloy. The acetabular cup implant for an artificial hip joint comprises an acetabular cup formed of a shape memory alloy having a semi-spherical shape with a hollow section, and is capable of expanding upon exposure to a body temperature. A bearing installed in the hollow section of the acetabular cup is suitable for receiving a femoral head to facilitate rotation of a femur.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to Korean Patent Application No. 10-2009-20877, filed on Mar. 11, 2009, in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field Of The Invention 
         [0003]    The present invention relates to an acetabular cup implant for an artificial hip joint fitted to a bone using a shape memory alloy, and more particularly, to an acetabular cup implant for an artificial hip joint which includes an acetabular cup for an artificial hip joint formed of a shape memory alloy having a semi-spherical shape with a hollow section and expanded upon the body temperature to be fitted to a bone, and a bearing installed in the hollow section of the acetabular cup to receive a femoral head to rotate a femur. 
         [0004]    2. Background 
         [0005]    An acetabular cup for an artificial hip joint is the most important element in hip arthroplasty, and plays an important role to determine the lifespan of an artificial hip joint. If there is a gap or relative movement between the acetabular cup and the bone, then wear particles can intrude to cause osteolysis or create soft tissues, generating larger movement. In this case, these circumstances are expansively reproduced to rapidly deteriorate the artificial hip joint, thereby separating the implant from the bone. 
         [0006]    In order to solve these problems, U.S. Pat. No. 6,626,947 discloses an acetabular cup press-fitted to a bone with a gap of about 2 mm. That is, the semi-spherical acetabular cup having a radius about 2 mm larger than that of a semi-spherical space of the bone is press-fitted into the semi-spherical space. However, such press-fitting larger than about 2 mm can injure fine tissues of the bone. For this reason, in many cases, separate screws are used to more securely fix the acetabular cup to the bone. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    Accordingly, it is an object of the present invention to provide an acetabular cup implant for an artificial hip joint capable of maximizing fitting effect of an acetabular cup to a bone by means of expansion of a shape memory alloy constituting the acetabular cup for an artificial hip joint, and maximally preventing osteolysis due to intrusion of wear particles through a gap, or relative movement between the acetabular cup and the bone, and separation of the implant from the bone caused by expansive reproduction thereof, without addition fixation using screws. 
         [0008]    In order to accomplish the above object, the present invention provides an acetabular cup implant for an artificial hip joint fitted to a bone using a shape memory alloy comprising: an acetabular cup having a hollow section, a generally semi-spherical shape, and formed of a shape memory alloy configured to expand upon exposure to a body temperature; and a bearing fitted to an inner surface of the hollow section of the semi-spherical acetabular cup and configured to receive a femoral head of a femur to rotate the femur. 
         [0009]    In some embodiments, the bearing can be inserted into the acetabular cup in a tapered fitting manner. 
         [0010]    In some embodiments, the bearing is formed of a polymer, a metal, or a ceramic. 
         [0011]    When the bearing is formed of a polymer, the exterior of the polymer can be supplemented with a metal band to obtain a friction force of the taper insertion. 
         [0012]    In another example embodiment, an acetabular cup of an acetabular cup implant for an artificial hip joint using a shape memory alloy is characterized in that the acetabular cup has a hollow section, a generally semi-spherical shape, and is formed of a shape memory alloy configured to expand upon exposure to a body temperature. 
         [0013]    The acetabular cup of an acetabular cup implant for an artificial hip joint using a shape memory alloy can include a ring-shaped member formed of a shape memory alloy that can be varied in shape by expansion due to heat supply or heat absorption from the exterior, and a body formed of a titanium alloy having no variation in shape. 
         [0014]    In some embodiments, the shape memory alloy is nitinol. 
         [0015]    The outer surface of the shape memory alloy in contact with the bone can comprise a bone compatible material. 
         [0016]    The outer surface of the ring-shaped memory alloy in contact with the bone can comprise a bone compatible material. 
         [0017]    The bone compatible material can include a titanium bead, a titanium wire, a plasma coating or oxidation. 
         [0018]    The acetabular cup can further comprise calcium phosphate, hydroxyapatite, or a bio-ceramic coating applied on the bone compatible material. 
         [0019]    The acetabular cup can further include a film configured to minimize contact of the shape memory alloy with body fluids, connect an end of the ring-shaped member to an end of the body to smoothly expand the ring-shaped member, formed of the shape memory alloy or the titanium alloy, and having circumferential wrinkles. 
         [0020]    Specific descriptions of other example embodiments will be apparent from the detailed description and the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
         [0021]    The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail example embodiments thereof with reference to the attached drawings, in which: 
           [0022]      FIG. 1  is a schematic view showing an acetabular cup implant for an artificial hip joint fitted into a bone; 
           [0023]      FIG. 2  is an exploded perspective view of the artificial hip joint; 
           [0024]      FIG. 3  is a cross-sectional view of an acetabular cup implant for an artificial hip joint in accordance with an exemplary embodiment of the present invention fitted into a bone; and 
           [0025]      FIG. 4  is a cross-sectional view of an acetabular cup implant for an artificial hip joint in accordance with another exemplary embodiment of the present invention fitted into a bone. 
       
    
    
       [0026]    One or more embodiments of the present invention will now be described with reference to the accompanying drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    Hereinafter, example embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms. The following embodiments are described in order to enable those of ordinary skill in the art to embody and practice the present invention. 
         [0028]      FIG. 1  is a schematic view showing an acetabular cup implant for an artificial hip joint fitted into a left hip joint. In a human body, a femoral head  21  of a femur  20  is inserted into an acetabulum  11  of the pubis  10  to enable free rotation of the femur  20  with regard to the acetabulum  11 . 
         [0029]    However, bone replacement surgeries are widely operated for patients whose joints are seriously injured to an unrecoverable degree. Reviewing the structure of the artificial hip joint, a ball  31  is inserted into the acetabulum  11  of the pubis  10  so that an acetabular cup  100  can be inserted to be freely rotated. A stem  32  having the ball  31  is inserted into an upper part of the femur  20  and then fixed thereto by bone cement or directly fitted to the stem surface by bone cells themselves. 
         [0030]      FIG. 2  is an exploded perspective view of the artificial hip joint. The artificial hip joint in accordance with an exemplary embodiment of the present invention includes a stem  32  fixed to the femur at its one end and having a head formed at the other end, a ball  31  coupled to the head, a bearing  130  having a semi-spherical ball receptacle  140  in which the ball  31  is rotatably inserted, and an acetabular cup  110  coupled to the pubis  10 , wherein the bearing  130  is inserted into the acetabular cup  110  in a tapered fitting manner. As afore mentioned, the acetabular cup  110  includes a space  120  configured to receive the bearing  130 , and is formed of a only shape memory alloy more securely fitted to the pubis  10 , or a shape memory alloy and a titanium alloy. The acetabular cup using the shape memory alloy as features of the present invention will be described with reference to  FIGS. 3 and 4 . The bearing  130  can comprise various materials such as a polymer, a metal, a ceramic, etc., and fixed to the acetabular cup  110  in the tapered fitting manner as described above. 
         [0031]      FIG. 3  is a cross-sectional view of an acetabular cup implant for an artificial hip joint in accordance with an exemplary embodiment of the present invention fitted into a bone (the pubis  10 ).  FIG. 3  shows an embodiment in which the acetabular cup  110  is formed of a shape memory alloy only. When the acetabular cup  110  shown in  FIG. 2  is coupled to the bone  10 , in the conventional art, the acetabular cup  110  having a radius about 2 mm larger than that of the acetabulum  11  of the bone  10  is press-fitted into the acetabulum  11  of the bone  10 . Such press-fitting larger than about 2 mm can injure fine tissues of the bone  10 . For this reason, in many cases, separate screws are used to more securely fix the acetabular cup  110  to the bone  10 . 
         [0032]    The acetabular cup  110  of the present invention can be formed of a shape memory alloy, for example, nitinol. A primary pressure is generated through slight press-fitting upon an operation, and then, a secondary pressure is generated through expansion of the shape memory alloy due to variation in shape caused by a body heat. The shape memory alloy (e.g., nitinol) is shrunk at a temperature lower than the body temperature to be easily inserted into the bone, and then, expanded by variation in shape due to heat supply or heat absorption from the body heat or the exterior, thereby accomplishing the press-fitting pressure. Since the shape memory alloy of the acetabular cup  110  is varied due to the body heat to be expanded and directly fitted to the bone  10 , readily accomplishing the press-fitting of 2 mm or more, there is no need of additional use of screws in the conventional art. However, since the shape memory alloy (e.g., nitinol) is not compatible with the bone  10 , the shape memory alloy in contact with the bone  10  can be coated with pure titanium beads, titanium wire meshes, plasma coating, or micro-arc oxidation. In addition, calcium phosphate hydroxyapatite or a bio-ceramic coating can be added thereon. 
         [0033]    The bearing  130  can be formed of various materials such as a polymer, a metal, a ceramic, etc., to be fixed to the acetabular cup  110 . In the case of the polymer bearing, the tapered surface can be supplemented with a metal band to obtain a friction force of the tapered fitting. 
         [0034]    The acetabular cup implant of the present invention can maximize the fit of the acetabular cup to a bone due to expansion of the shape memory alloy, and prevent osteolysis due to intrusion of wear particles through a gap or relative movement between the acetabular cup and the bone. Furthermore, separation of the implant from the bone is minimized without the use of screws for fixing the implant to a bone. 
         [0035]      FIG. 4  is a cross-sectional view of an acetabular cup implant for an artificial hip joint in accordance with another exemplary embodiment of the present invention fitted into a bone. As shown in  FIG. 4 , the acetabular cup  110  according to this embodiment includes a ring-shaped member  111  formed of a shape memory alloy that can be varied in shape by expansion due to heat supply or heat absorption from the exterior, and a body  112  formed of a titanium alloy having no capability of variation in shape. A primary pressure is generated through slight press-fitting upon operation, and then, a second pressure is generated through expansion of the shape memory alloy due to variation in shape caused by the body heat. 
         [0036]    As described above with reference to  FIG. 3 , the shape memory alloy, for example, nitinol, is shrunk at a temperature lower than the body temperature to be easily inserted into the bone, and then, expanded by variation in shape caused by heat supply or heat absorption from the exterior, thereby accomplishing the press-fitting. 
         [0037]    However, since the shape memory alloy of the ring-shaped member  111  is not biologically compatible with the bone  10 , in order to minimize a contact with body fluids and the bone  10  and use thereof, a portion requiring no expansion can be replaced with the body  112  formed of a titanium alloy as shown in the drawing. In addition, since the shape memory alloy, e.g., the nitinol is not compatible with the bone  10 , the surface of the ring-shaped member  111  in contact with the bone  10  can be coated with pure titanium beads, titanium wire meshes, plasma coating or micro arc oxidation. Further, calcium phosphate hydroxyapatite or a bio-ceramic coating can be added thereon. 
         [0038]    Meanwhile, in order to smoothly expand the ring-shaped body  111  formed of the shape memory alloy, an end of the ring-shaped body  111  and an end of the body  112  formed of a titanium alloy can be connected to a thin film  150  formed of a shape memory alloy or a titanium alloy and having circumferential wrinkles. 
         [0039]    In addition, the bearing  130  can comprise a polymer, a metal, a ceramic, etc., to be taper-inserted into the acetabular cup  110 . In the case of the polymer bearing, the tapered surface can be supplemented with a metal band  131  to obtain a friction force of the tapered fitting. 
         [0040]    As can be seen from the foregoing, an acetabular cup implant for an artificial hip joint in accordance with the present invention can maximize fitting effect of an acetabular cup to a bone using expansion of a shape memory alloy constituting the acetabular cup for an artificial hip joint, and maximally prevent osteolysis due to intrusion of wear particles through a gap or relative movement between the acetabular cup and the bone and separation of the implant from the bone caused by expansive reproduction thereof, without addition fixation using screws. 
         [0041]    It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections can set forth one or more, but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way. Thus, while the invention has been shown and described with reference to certain example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 
         [0042]    All documents cited herein, including journal articles or abstracts, published or corresponding U.S. or foreign patent applications, issued or foreign patents, or any other documents, are each entirely incorporated by reference herein, including all data, tables, figures, and text presented in the cited documents.