Abstract:
The present invention relates to an implant playing a role as a joint in coupling a revision implant in revision total knee arthroplasty and, more specifically, to an offset adapter unit comprising an adapter which couples a femoral member or a tibial member to a stem member in revision total knee arthroplasty; and a nut coupled to the adapter, thereby improving the strength by considering fracture occurring in the narrowest area.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an implant playing a role as a joint in coupling a revision implant in revision total knee arthroplasty and, more specifically, to an offset adapter unit comprising an adapter which couples a femoral member or a tibial member to a stem member in revision total knee arthroplasty; and a nut coupled to the adapter, thereby improving the strength by taking into consideration fracture occurring in the narrowest area. 
       BACKGROUND 
       [0002]    There are joints, being parts connecting bones and capable of freely moving, in a human body. Of the joints, the largest joint is the knee joint. The knee joint is disposed in a middle part of a leg and consists of a tibiofemoral joint and a patellofemoral joint. 
         [0003]    The knee joint replacement surgery is performed when there is trouble walking or discomfort in daily activities due to severe pain in the knee joint and degenerative arthritis. However, even after surgery there can be a case where pain occurs again and walking becomes problematic as time passes. Then reoperation may be done after diagnosis, which is called revision total knee arthroplasty. 
         [0004]    However, it is difficult to firmly fix an artificial joint in the revision total knee arthroplasty, unlike in the knee joint replacement surgery, because of lack of strong bones as bones around the artificial joint had already been melted at the time of the revision total knee arthroplasty. Thus, fixing force of a replacement should be reinforced by attaching an extension stem to the artificial joint. The diameter and the length can be adjusted based on size and length of the tibia and the femur. The extension stem is configured to be detachable from a main body and is fixed by twisting and tightening. Often, the extension stem is not formed straightly or the extension stem is attached to a location off-center of the replacement in preparation for a case where bone defects are irregular or bone deformities are severe. This is called off-center or offset. 
         [0005]    Referring to  FIGS. 1 and 2 , an offset adapter unit according to prior art is described. The prior adapter unit comprises an adapter  100  and a nut  200 , and the prior adapter  100  includes a head portion  110  being an upper feature and a body portion  120  being a lower feature. The head portion  110  includes a screw groove  111   a  having a center axis A 1 . Also, the body portion  120  is eccentric to the head portion  110  and includes a screw portion  122   a  having a diameter D and a center axis A 2 . However, there is a problem of increasing pain in patients and risk of reoperation due to a fractured neck  150  caused by repetitive bending moments which occur due to axial loads applied vertically when a common offset is connected and fixed to the femur or tibia. 
         [0006]    (Prior Art) Korean Patent Application Publication No. 10-1989-0019611 Modular Knee Prosthesis System 
       DETAILED DESCRIPTION 
     Technical Problem 
       [0007]    The present invention has been made in an effort to solve the problems. 
         [0008]    An object of the present invention is to provide an offset adapter unit which prevents fracture in the narrowest part (neck) by generating an expanded step in a screw connecting region of an adapter for resolving the most vulnerable part to continuously occurring bending moments. 
         [0009]    Another object of the present invention is to provide an offset adapter unit which prevents fracture in the narrowest part (neck) by covering the adapter with a nut having a step. 
       Technical Solutions 
       [0010]    In order to achieve the above object, the present invention is realized by embodiments having the following features. 
         [0011]    According to one embodiment of the present invention, an offset adapter unit comprises: an adapter which couples a femoral member or a tibial member to a stem member in revision total knee anthroplasty. 
         [0012]    According to another embodiment of the present invention, in the offset adapter unit, the adapter comprises: a head portion; and a body portion. 
         [0013]    According to still another embodiment of the present invention, in the offset adapter unit, the head portion includes a screw groove capable of coupling to the stem member. 
         [0014]    According to still another embodiment of the present invention, in the offset adapter unit, the body portion comprises: an expanded portion and a screw portion. 
         [0015]    According to still another embodiment of the present invention, in the offset adapter unit, the expanded portion forms a step in a direction of the body portion from the head portion. 
         [0016]    According to still another embodiment of the present invention, in the offset adapter unit, the screw portion is formed as a male screw to be coupled to the femoral member or the tibial member. 
         [0017]    According to still another embodiment of the present invention, the offset adapter unit further comprises a nut coupled to the adapter. 
         [0018]    According to still another embodiment of the present invention, in the offset adapter unit, the nut comprises: a step portion and a female screw portion. 
         [0019]    According to still another embodiment of the present invention, in the offset adapter unit, the step portion is coupled to the expanded portion by contact. 
         [0020]    According to still another embodiment of the present invention, in the offset adapter unit, the female screw portion is coupled to a part of the screw portion of the adapter. 
       Advantageous Effects 
       [0021]    According to the above-described embodiments and the following features, combinations, and relations of use that will be described later, the present invention can obtain the following effects. 
         [0022]    The present invention provides an offset adapter unit which prevents fracture in the narrowest part (neck) by generating an expanded step in a screw connecting region of an adapter for resolving the most vulnerable part to continuously occurring bending moments. 
         [0023]    The present invention provides an offset adapter unit which prevents fracture in the narrowest part (neck) by covering the adapter with a nut having a step. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is an engaged perspective view of an offset adapter unit according to prior art; 
           [0025]      FIG. 2  is an engaged section view of the offset adapter unit according to prior art; 
           [0026]      FIG. 3  is an engaged perspective view of an offset adapter unit according to the present invention; 
           [0027]      FIG. 4  is an exploded perspective view of the offset adapter unit according to the present invention; 
           [0028]      FIG. 5  is an engaged sectional view of the offset adapter unit according to the present invention; 
           [0029]      FIG. 6  is a sectional view of the offset adapter unit according to the present invention; 
           [0030]      FIG. 7  is a sectional view of the nut of the offset adapter unit according to the present invention; 
           [0031]      FIG. 8  is an engaged perspective view of a stem member, a femoral member of and the offset adapter unit according to the present invention; and 
           [0032]      FIG. 9  is an engaged perspective view of a stem member, a tibial member and the offset adapter unit according to the present invention. 
       
    
    
     BEST MODE 
       [0033]    Hereinafter, exemplary embodiments of an offset adapter unit according to the present invention will be described with reference to the accompanying drawings. In describing the present invention, unless not specifically defined, all terminologies in the specification should be interpreted based on the general meanings thereof that a person skilled in the art understands. When the general meanings of the terminologies are incompliant with those used in the specification, the terminologies should be interpreted as being defined herein. Also, well-known functions or constructions will not be described in detail in case they may unnecessarily obscure the understanding of the present invention. 
         [0034]      FIG. 3  is an engaged perspective view of an offset adapter unit according to the present invention;  FIG. 4  is an exploded perspective view of an adapter and a nut of the offset adapter unit according to the present invention;  FIG. 5  is an engaged sectional view of the offset adapter unit according to the present invention;  FIG. 6  is a sectional view of the offset adapter unit according to the present invention;  FIG. 7  is a sectional view of the nut of the offset adapter unit according to the present invention;  FIG. 8  is an engaged perspective view of a stem member, a femoral member, and the offset adapter unit according to the present invention; and  FIG. 9  is an engaged perspective view of a stem member, a tibial member and the offset adapter unit according to the present invention. 
         [0035]    With reference to  FIGS. 3 to 9 , the offset adapter unit according to one embodiment of the present invention is described. For resolving a portion which is the most vulnerable to bending moments which continuously occur, the offset adapter unit produces an expanded portion  121  in a screw connecting region of an adapter  1  and a nut  2  having a step portion  21  covers the adapter  1  to prevent fracture of a neck  15  being the narrowest portion. 
         [0036]    Referring to  FIGS. 8 to 9 , the offset adapter unit couples a stem member  3  to a femoral member  4  or a tibial member  5  in revision knee arthroplasty and comprises the adapter  1  and the nut  2 . 
         [0037]    Referring to  FIG. 4 , the adapter  1  comprises a head portion  11  being an upper structure and a body portion  12  being a lower structure. 
         [0038]    Referring to  FIG. 5 , the head portion  11  comprises a screw thread  111  having a center axis A 1 . The screw groove  111  has a female screw thread along an inner circumferential face and the pitch, angle, diameter, number and the like of the thread are formed dependent on a male screw of the stem member  3 . 
         [0039]    Referring to  FIGS. 5 and 6 , the body portion  12  is eccentric to the head portion  11  and formed around A 2  as a center axis. The body portion  12  comprises the expanded portion  121  formed by decreasing the diameter of a lower face  112  of the head portion  11  and extending downward; and the screw portion  122  formed by decreasing the diameter of a lower face  121   a  of the expanded portion  121 . 
         [0040]    Referring to  FIG. 6 , the expanded portion  121  of the diameter D 2  formed by decreasing the diameter of and extending downward from the lower face  112  of the head portion  11  is formed to prevent fracture of the neck  15  vulnerable to the continuously occurring bending moments. 
         [0041]    The screw portion  122  forms a diameter D 1  by decreasing the diameter of the lower face  121   a  of the expanded portion  121  and includes a male screw thread in an outer surface of the screw portion  122 . 
         [0042]    Referring to  FIGS. 6, 8 and 9 , the screw portion  122  of the adapter  1  is formed as a male screw thread to couple to the femoral member  4  or the tibial member  5  for coupling with the femoral member  4  or the tibial member  5  including a female screw thread. The pitch, angle, diameter, number and the like of the thread of the screw portion  122  are formed dependent on the female screw of the femoral member  4  or the tibial member  5 . 
         [0043]    Referring to  FIG. 7 , the outer diameter of the nut  2  is formed by D 4  and the nut  2  includes a penetration hole  20  which penetrates therethrough. In addition, the penetration hole  20  is formed by being surrounded by the step portion  21  which makes contact with the expanded portion  121  of the adapter  1  and the female screw portion  22  coupled to the body portion  12  of the adapter  1  when the nut  2  is fastened to the adapter  1 . 
         [0044]    Referring to  FIG. 7 , the step portion  21  is a part which contacts with the expanded portion  121  when the nut  2  is fastened to the adapter  1 . The step portion  21  is formed with an inner diameter of D 3  in an upper portion of the nut  2 . Also, the step portion  21  is configured to prevent fracture of the neck  15  which is the narrowest part by covering the expanded portion  121  of the adapter  1  when the adapter  1  is fastened to the nut  2 . 
         [0045]    Referring to  FIG. 7 , the female screw portion  22  is a part which contacts with the screw portion  122  when the adapter  1  is fastened to the nut  2 . The female screw portion  22  is formed in a lower end of the step portion  21  with an inner diameter of D 1  decreased from the step portion  21 . Also, the female screw portion  22  is configured to unite the adapter  1  and the nut  2  when the adapter  1  is fastened to the nut  2  and includes screw threads in an inner circumferential face. 
         [0046]    Referring to  FIGS. 6 and 7 , the diameter D 2  of the expanded portion  121  is greater than the diameter D 1  of the screw portion  122 , and the diameter D 1  of the screw portion  122  is approximately the same with the diameter D 2  of the female screw portion. Also, the diameter D 3  of the step portion  21  is greater than or equal to the diameter D 2  of the expanded portion  12 . The outer diameter D 4  of the nut  2  is greater than the diameter D 3  of the step portion  21 . Hence, the diameters are formed to have a relationship of D 4 ≧D 3 ≧D 2 ≧D 1 . 
         [0047]    Referring to  FIG. 8 , the femoral member  4  is coupled to the body portion  12  of the adapter  1  and the stem member  3  is coupled to the head portion  11  of the adapter  1 . The femoral member  4  is configured to be fixed by the nut  2  after an axis of the femoral member  4  is adjusted when being fastened to the nut  2  in order to adjust an offset to the femur of a patient. 
         [0048]    Referring to  FIG. 9 , the tibial member  5  is coupled to the body portion  12  of the adapter  1  and the stem member  3  is coupled to the head portion  11  of the adapter  1 . The tibial member  5  is configured to be fixed by the nut  2  after an axis of the tibial member  5  is adjusted when being fastened to the nut  2  in order to adjust an offset to the tibial of the patient. 
         [0049]    Referring to  FIGS. 2 and 5 , the body portion  120  of the prior adapter  100  extends from the upper portion to the lower portion with a constant diameter D, which causes fracture in the neck  150  subjected to repetitive bending moment due to eccentricity of the axis when being fastened to the nut  200 . On the other hand, according to the present invention, the expanded portion  121  is formed in the adapter  1 , and the overall diameter of the neck  15  being the weak part is made larger by enabling the step portion  21  of the nut  2  to cover the expanded portion  121 . Accordingly, the strength of the adapter unit according to the present invention is greatly improved compared to the prior art. 
         [0050]    In the above, the applicant described preferred embodiments of the present invention. It should be interpreted that such embodiments are merely examples which implement the technical idea and any modification or revision falls within the scope of the prevent invention if it implements the technical idea of the present invention, however.