Abstract:
A kit for use in joint arthroplasty that includes a first component of a prosthesis, a second component of the prosthesis, and an assembly tool for assembling the first component to the second component. The tool includes a housing for contact with the first component and an internal component connected to the second component. The internal component includes an actuating device and an actuator rod. The actuating device has at least one scissor arm. The housing and the internal component are adapted to provide for the assembly of the first component of the prosthesis to the second component of the prosthesis. The internal component is adapted to provide relative motion of the internal component with respect to the housing when the at least one scissor arm is moved relative to the housing, the relative motion of the internal component with respect to the housing being utilized to effect the relative motion of the first component with respect to the second component to urge the second component into engagement with the first component.

Description:
[0001]    This application is a divisional application of U.S. Utility Patent application Ser. No. 11/930811 entitled “MODULAR TAPER ASSEMBLY DEVICE” which was filed on Oct. 31, 2007 by Larry G. McCleary, which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to the field of orthopaedics, and more particularly, to an implant for use in arthroplasty. 
       BACKGROUND OF THE INVENTION 
       [0003]    Patients who suffer from the pain and immobility caused by osteoarthritis and rheumatoid arthritis have an option of joint replacement surgery. Joint replacement surgery is quite common and enables many individuals to function properly when it would not be otherwise possible to do so. Artificial joints are usually comprised of metal, ceramic and/or plastic components that are fixed to existing bone. 
         [0004]    Such joint replacement surgery is otherwise known as joint arthroplasty. Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged joint is replaced with a prosthetic joint. In a typical total joint arthroplasty, the ends or distal portions of the bones adjacent to the joint are resected or a portion of the distal part of the bone is removed and the artificial joint is secured thereto. 
         [0005]    There are known to exist many designs and methods for manufacturing implantable articles, such as bone prostheses. Such bone prostheses include components of artificial joints such as elbows, hips, knees and shoulders. 
         [0006]    During performance of a joint replacement procedure, it is generally necessary to provide the surgeon with a certain degree of flexibility in the selection of a prosthesis. In particular, the anatomy of the bone into which the prosthesis is to be implanted may vary somewhat from patient to patient. Such variations may be due to, for example, the patient&#39;s age, size and gender. For example, in the case of a femoral prosthesis, the patient&#39;s femur may be relatively long or relatively short thereby requiring use of a femoral prosthesis, which includes a stem that is relatively long or short, respectively. Moreover, in certain cases, such as when use of a relatively long stem length is required, the stem must also be bowed in order to conform to the anatomy of the patient&#39;s femoral canal. 
         [0007]    Such a need for prostheses of varying shapes and sizes thus creates a number of problems in regard to the use of a one-piece prosthesis. For example, a hospital or surgery center must maintain a relatively large inventory of prostheses in order to have the requisite mix of prostheses needed for certain situations, such as trauma situations and revision surgery. Moreover, since the bow of the stem must conform to the bow of the intramedullary canal of the patient&#39;s femur, rotational positioning of the upper portion of the prosthesis is limited thereby rendering precise location of the upper portion and hence the head of the prosthesis very difficult. 
         [0008]    In addition, since corresponding bones of the left and right side of a patient&#39;s anatomy (e.g. left and right femur) may bow in opposite directions, it is necessary to provide (left) and (right) variations of the prosthesis in order to provide anteversion of the bone stem, thereby further increasing the inventory of prostheses which must be maintained. 
         [0009]    As a result of these and other drawbacks, a number of modular prostheses have been designed. As its name implies, a modular prosthesis is constructed in modular form so that the individual elements or figures of the prosthesis can be selected to fit the needs of a given patient&#39;s anatomy. For example, modular prostheses have been designed which include a proximal neck component which can be assembled to any one of numerous distal stem components in order to create an assembly which fits the needs of a given patient&#39;s anatomy. Such a design allows the distal stem component to be selected and thereafter implanted in the patient&#39;s bone in a position that conforms to the patient&#39;s anatomy while also allowing for a limited degree of independent positioning of the proximal neck component relative to the patient&#39;s pelvis. 
         [0010]    One issue that arises as a result of the use of a modular prosthesis is the locking of the components relative to one another. In particular, firm reproducible locking of the proximal neck component to the distal stem component is critical to prevent separation of the two components subsequent to implantation thereof into the patient. The need for the firm locking is particularly necessary if the design does not provide for positive locking with weight bearing. As such, a number of locking mechanisms have heretofore been designed to lock the components of a modular prosthesis to one another. For example, a number of modular prostheses have heretofore been designed to include a distal stem component, which has an upwardly extending post, which is received into a bore defined distal neck component. A relatively long fastener such as a screw or bolt is utilized to secure the post with the bore. Other methods of securing modular components include the impacting of one component onto the other. This method has highly variable results 
         [0011]    Current designs of modular stems include designs in which the modular connection utilizes a tapered fit between the two components. For example, the proximal body may include an internal taper, which mates with an external taper on the distal stem. Such a taper connection may be used in conjunction with additional securing means, for example, a threaded connection or may be used alone. It is important that the tapered connection be secure. For example, the proper amount of force must be applied to the tapered connection to properly secure the tapered connection so that the connection can withstand the forces associated with the operation of the stem. 
         [0012]    Current attempts to provide a device to adjoin components of a modular joint prosthesis are fraught with several problems. For example, the device may not provide sufficient mechanical advantage to securely lock the components. Further, the ergonomics available to lock the components may not be optimal. Additionally, a device relying solely on the displacement for a taper connection may not provide sufficient force as there may not be an accurate correspondence of displacement to the clamping force. Also, utilizing a displacement method may make it possible to overtighten and damage the components. Further, prior art solutions may be difficult to manufacture or expensive to make. 
         [0013]    Once a modular prosthesis, for example, a modular hip stem prosthesis, has its relative components positioned properly, the components must be firmly secured to each other. It is possible when the components are secured together that relative motion between the components may occur causing their relative position in particular their angular orientation to be disturbed. In other words, when the first and second components of the modular hip stem are drawn together, one component may rotate about the other one causing their version or orientation to be compromised. Further, whatever device is used to angularly position the components of the modular prosthesis into the proper orientation may need to be removed and an assembly device positioned on the prosthesis to secure the components to each other. Such removal of the alignment device and installation of the assembly device adds cost and complexity to the procedure, as well as, increasing the operating room time. 
         [0014]    There is thus a need to provide for an assembly and disassembly tool capable of alleviating at least some of the aforementioned problems. 
         [0015]    US Patent Application Publication No. 20040122439 entitled “ADJUSTABLE BIOMECHANICAL TEMPLATING &amp; RESECTION INSTRUMENT AND ASSOCIATED METHOD”, US Patent Application Publication No. 20040122437 entitled “ALIGNMENT DEVICE FOR MODULAR IMPLANTS AND METHOD”, US Patent Application Publication No. 20040122440 entitled “INSTRUMENT AND ASSOCIATED METHOD OF TRIALING FOR MODULAR HIP STEMS”, US Patent Application Publication No. 20040267266 published Jun. 25, 2003 entitled “MODULAR TAPERED REAMER FOR BONE PREPARATION AND ASSOCIATED METHOD”, and US Patent Application Publication No. 20040267267 published Dec. 30, 2004 entitled “NON-LINEAR REAMER FOR BONE PREPARATION AND ASSOCIATED METHOD” are hereby incorporated in their entireties by reference. 
         [0016]    Prior attempts to provide instruments to assemble modular prostheses have had problems due to the large and bulky nature of such instruments. These large and bulky instruments are difficult for the surgeon to use and provide problems in performing minimally invasive orthopedic implant surgery. Furthermore, prior art tools provide a tool designed for only one modular prosthesis. The tool may not be suitable for prostheses with other sizes and shapes. The present invention is directed to alleviate at least some of the problems with the prior art. 
       SUMMARY OF THE INVENTION 
       [0017]    According to one embodiment of the present invention, an assembly tool for assembly of a first component of a prosthesis to a second component of the prosthesis for use in joint arthroplasty is provided. The tool includes a housing for contact with the first component. The housing defines a housing longitudinal axis thereof. An internal component is also provided and is connected to the second component. The internal component includes an actuating device and an actuator rod. The actuator rod defines an internal component longitudinal axis that is coexistent with the housing longitudinal axis. The housing and the internal component are adapted to provide for the assembly of the first component of the prosthesis to the second component of the prosthesis. The internal component is adapted to provide relative motion of the internal component with respect to the housing when the actuating device of the internal component is moved relative to the housing in at least a direction transverse to the internal component longitudinal axis and the actuator rod of the internal component is moved relative to the housing in a direction parallel to the internal component longitudinal axis for assembly of the first component of the prosthesis to the second component. The relative motion of the internal component with respect to the housing is utilized to effect the relative motion of the first component with respect to the second component to urge the second component into engagement with the first component. 
         [0018]    According to another embodiment of the present invention, a kit for use in joint arthroplasty is provided. The kit includes a first component of a prosthesis, a second component of the prosthesis, and an assembly tool for assembling the first component to the second component. The tool includes a housing for contact with the first component and an internal component connected to the second component. The internal component includes an actuating device and an actuator rod. The actuating device having at least one scissor arm. The housing and the internal component are adapted to provide for the assembly of the first component of the prosthesis to the second component of the prosthesis. The internal component is adapted to provide relative motion of the internal component with respect to the housing when the at least one scissor arm is moved relative to the housing, the relative motion of the internal component with respect to the housing being utilized to effect the relative motion of the first component with respect to the second component to urge the second component into engagement with the first component. 
         [0019]    According to yet another embodiment of the present invention, a method for providing joint arthroplasty is provided. The method includes providing a first component and a second component removably attachable to the first component. An instrument having a housing operably associated with the first component is provided. The housing defines a longitudinal axis. The housing also includes an internal component operably associated with the second component. The internal component includes the actuating device and an actuator rod. The internal component is operably associated with the housing for relative motion there between for assembly of the first component of the prosthesis to the second component. The first component is assembled to the second component and the internal component of the tool is connected to the second component. The actuating device of the internal component is moved relative to the housing, such that the movement is at least in a direction transverse to the longitudinal axis. The actuator rod of the internal component is moved relative to the housing, the movement being along the longitudinal axis, the movement securing the first component to the second component. 
         [0020]    Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, descriptions and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in connection with the accompanying drawings, in which: 
           [0022]      FIG. 1  is a plan view partially in cross-section of an embodiment of the present invention in the form of an assembly tool including a threaded connection in operation with a prosthesis; 
           [0023]      FIG. 2  is a perspective view of another embodiment of the present invention in the form of an assembly tool with a spiral cam and follower mechanism shown in engagement with a prosthesis; 
           [0024]      FIG. 3  is a cross section view of  FIG. 2  along the line  3 - 3  in the direction of the arrows; 
           [0025]      FIG. 4  is a plan view of a two pieced modular hip stem than may be assembled with the assembly tool of  FIG. 2 ; 
           [0026]      FIG. 5  is an exploded plan view of the modular hip stem of  FIG. 4 ; 
           [0027]      FIG. 6  is a flow chart of a method of using the assembly tool of the present invention according to another embodiment of the present invention; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    Embodiments of the present invention and the advantages thereof are best understood by referring to the following descriptions and drawings, wherein like numerals are used for like and corresponding parts of the drawings. 
         [0029]    According to the present invention and referring now to  FIG. 1 , assembly tool  10  according to the present invention is shown. The assembly tool  10  is used for assembly of a first component  12  of a prosthesis  14  to a second component  16  of the prosthesis  14  for use in joint arthroplasty. The tool  10  includes a housing  18  operably associated with the second component  16 . The housing  18  defines a housing longitudinal axis  20  of the housing  18 . The tool  10  also includes an internal component  22  operably associated with the second component  16 . The internal component  22  defines an internal component longitudinal axis  24  of the internal component  22 . The internal component  22  includes an actuating device  26  and an actuator rod  28  connected to the actuating device. The actuator rod defines a transverse axis  30  that is perpendicular to the internal component longitudinal axis  24 . The internal component  22  is adapted to provide relative motion of the internal component  22  with respect to the housing  18  when the actuator rod  28  is rotated relative to the housing  18  about the transverse axis  30 . 
         [0030]    The assembly tool  10  is suited for use with the prosthesis  14  when, for example, the prosthesis  14  includes the first component  12  and the second component  16  which are engaged and disengaged by relative motions along an axis. For example, the assembly tool  10  is suitable when the prosthesis  14  includes components, which are connected by a tapered connection. For example, as shown in  FIG. 1 , the first component  12  includes an internal taper  32  that mates with an external taper  34  located on the second component  16 . 
         [0031]    As shown in  FIG. 1 , the first component  12  is engaged with the second component  16  when the first component  12  moves in the direction of arrow  36  and/or when the second component  16  moves in the direction of arrow  38 . As shown in  FIG. 1 , the housing  18  is operably associated with the first component  12  while the internal component  22  is operably associated with the second component  16 . To provide for the operable association of the components, it should be appreciated that the housing  18  includes a housing operating feature  40 , which is operably associated with a first component operating feature  42  of the first component  12 . Similarly, the internal component  22  includes an internal component operating feature  44 , which cooperates with a second component operating feature  46  of the second component  16 . 
         [0032]    For simplicity, since the housing  18  and the first component  12  are merely required to prevent motion of the two components toward each other, the housing  18  and the first component  12  may be designed such that the housing operating feature  40  may be in the form of a bottom and/or surface  41  ( FIG. 3 ). Similarly, the first component operating feature  42  may be in the form of a top surface  43  ( FIG. 3 ) of the first component  12 . 
         [0033]    The internal component operating feature  44  and the second component operating feature  46  may be any features capable of urging the second component  16  upwardly in the direction of arrow  38 . For example, for simplicity, the internal component operating feature  44  may be in the form of internal threads  47  ( FIG. 3 ) formed on the second component operating feature  46 , which may mate with external threads  45  ( FIG. 3 ) formed on the second component  16 . 
         [0034]    The housing  18  and the internal component  22  may have any shape or configuration capable of providing relative motion along housing longitudinal axis  20  and internal component longitudinal axis  24 . For example, and as shown in  FIG. 1 , the housing  18  may be in the form of a hollow component or tube. Similarly, the internal component  22  may be in the form of a rod or cylinder, which may slideably fit within the housing  18 . 
         [0035]    Turning now to  FIG. 2 , in which a plan view of the instrument  10  is shown, the parts of the instrument  10  and their operation will be described in more detail. As shown, the housing  18  includes an outer housing  48  and the housing operating feature  40 . The outer housing  48  also includes apertures  49  for coupling the outer housing  48  to the internal component  22 . 
         [0036]    The internal component  22  includes an actuating device  50  and an actuator rod  52 . The actuating device  50  includes a screw  53  and four scissor members  54   a,    54   b,    54   c,    54   d.  The scissor members  54   a,    54   b,    54   c,    54   d  each include two legs  56   a,    56   b.  The legs  56   a,    56   b  are connected via a pin  58 . One pair of scissor members  54   a,    54   b  are also connected via the pin  58 . The other pair of scissor members  54   c,    54   d  are connected via the corresponding pin  58 . The two pins  58  also connect the screw  53  to the scissor members  54   a,    54   b,    54   c,    54   d.  Thus, when the screw  53  is rotated about the transverse axis  30 , the four scissor members  54   a,    54   b,    54   c,    54   d  expand and contract (like a car jack). The scissor members  54   a,    54   b,    54   c,    54   d  are connected to the outer housing  48  via pins  59 . The pins  59  extend through the apertures  49  in the outer housing  48 . 
         [0037]    The bottom portion of all four legs  56   b  are connected with a connecting member  62  that includes an aperture  64  for receiving a rod  66  that is a part of the actuator rod  52 . The rod  66  extends longitudinally through the outer housing  48  of the housing  18 . The bottom of the rod  66  includes the internal component operating feature  44 , which in the illustrated embodiment is a threaded aperture  68 . Surrounding and connected to the rod  68  is a cylinder  70 . When a user turns the cylinder  70 , the rod  66  also rotates. This can be used to connect the internal component operating feature  44  to the second component operating feature  46  (as shown in  FIG. 1 ). The use of the scissor members  54   a,    54   b,    54   c,    54   d  provide a greater mechanical advantage to the tool. By increasing the mechanical advantage through the use of the screw  53  and the scissor arms  54   a,    54   b,    54   c,    54   d,  the amount of force that the user has to apply to the screw is greatly decreased from prior art designs. 
         [0038]    Referring now to  FIG. 3 , the engagement of the assembly tool  10  with the prosthesis  14  is shown in greater detail. As shown in  FIG. 3 , the second component  16  includes a second component operating feature in the form of external threads  45 . The external threads  45  are matingly fitted to, for example, internal threads  47  formed on internal component  22 . The first component  12  includes an operating feature in the form of, for example, a top surface  43  which mates with bottom surface  41  of the housing  18  of the tool  10 . In some embodiments, the threads may be Acme threads. 
         [0039]    Since the housing  18  is in contact with the first component  12 , when the first component is moved in the direction of arrow  80  relative to the first component  12 , the internal component  22  is moved in the direction of arrow  82  relative to the housing  18 . Thus, the relative motion of the internal component  22  with respect to the housing  18  in the direction of arrow  82  corresponds to the relative motion of the second component  16  with respect to the first component  12  in the direction of arrow  80 . 
         [0040]    Referring now to  FIG. 4 , the prosthesis  14  is shown in greater detail. The prosthesis  14  as shown in  FIG. 4  includes a taper connection  31 . As shown in  FIG. 4 , the taper connection consists of the external taper  34  formed on the distal stem  16  that engages with internal taper  32  formed on the first component in the form of the proximal body  12 . 
         [0041]    It should be appreciated that the prosthesis for use with the assembly tool  10  of  FIGS. 1 and 2 , respectively, may include the first component  12  (in this case a proximal body) and the second component  16  (here a distal stem) which have an interference connection that is, for example, an interference connection of a cylindrical bore to a cylindrical stem, as well as, a splined non-uniform cross-section stem to a splined or non-uniform cross-section opening. It should further be appreciated that proximal body and distal stem of the prosthesis  14  for use with the assembly tool of the present invention may include a taper connection in which the distal stem has an internal taper and the proximal body has an external taper. 
         [0042]    Again referring to  FIG. 4 , the prosthesis  14  as shown may include external threads  45  formed on the distal stem  16 . The proximal body  12  may include a neck  84  to which a head  86  may matingly be fitted. As an additional precaution in assuring that the proximal body  12  remains secured to the distal stem  16 , the prosthesis  14  may further include a nut  88  that threadably engages the external threads  45  of the distal stem  16 . 
         [0043]    Referring now to  FIG. 5 , the prosthesis  14  is shown with the proximal body  12  disassembled from the distal stem  16 . The external taper  34  of the distal stem  16  is defined by an included angle β 1 . In order that the proximal body  12  fits securely to the distal stem  16 , the proximal body  12  includes the internal taper  32  defined by included angle β 2 . The angles β 1  and β 2  may be generally the same. Alternatively the taper angle may be divergent. The angles β 1  and β 2  should be chosen, such that the fit of the proximal body  12  to the distal stem  16  is secure. 
         [0044]    In one embodiment, the instrument is made of stainless steel, however it is contemplated that other sterilizable metals may also be used. 
         [0045]    Turning now to  FIG. 6 , a flow chart describing the operation of the assembly tool  10  according to one embodiment will be described. At step s 100 , a first component and a second component are provided. The second component is removably attachable to the first component. An assembly tool or instrument is also provided, the assembly tool including a housing and an internal component. The internal component includes an actuating device and an actuator rod (step s 101 ). The first component is assembled to the second component at step s 102 . At step s 104 , the user connects the housing of the tool to the first component. The user also connects the internal component of the tool to the second component (step s 106 ). At step s 108 , the user moves the actuating device of the internal component in a direction transverse to a longitudinal axis relative to the housing. The actuator rod of the internal component is then moved along the longitudinal axis relative to the housing to secure the first component to the second component (step  110 ). 
         [0046]    Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.