Abstract:
A kit and associated method is for implanting a prosthetic device in a resected bone such as a humerus. The kit includes a trial assembly including a trial body portion having a trial bore defined therein, and a trial head portion having (i) a trail head member which includes a trial offset indicia, and (ii) an eccentrically located trial stem extending from the trial head member, the trial head stem being configured to be received within the trial bore. The kit also includes a final prosthesis assembly including a final body portion having a final bore defined therein, and a final head portion having (i) a final head member which includes a final offset indicia, and (ii) an eccentrically located final head stem extending from the final head portion, the final head stem being configured to be received within the final bore.

Description:
This application is a continuation of application Ser. No. 09/904,752, filed on Jul. 13, 2001 now abandoned that, in turn, claims the benefit of U.S. Provisional Application Ser. No. 60/221,657 that was filed Jul. 28, 2000. 

   FIELD OF THE INVENTION 
   The present invention relates to prostheses for reconstructive surgery of a gleno-humeral joint and, more particularly, to the positioning of an eccentric head of a humerus prostheses for reconstructive surgery of a gleno-humeral joint. 
   BACKGROUND 
   In total shoulder arthroplasty, reproduction of the correct location of the humeral articular surface is critical to reestablishing joint biometrics. Translating this location to the implant is thus of critical importance. 
   Each shoulder arthroplasty needs to be adapted to the patient&#39;s unique combination of soft tissue and bone anatomy. As well, the patient typically has high expectations of the function and durability of the arthroplasty. Thus, the implant and the implant technique must be precise. 
   In view of this, there has been developed a range of prostheses designed to fit the various sizes and shapes of people&#39;s anatomy. For shoulder arthroplasty, a prosthesis with a humerus head has been developed. It has been recognized, though, that the humerus head may need to be eccentrically mounted relative to the prosthesis body in order to cover the exposed, resected humerus head. There has been a problem, however, with the ability to adequately position the eccentric head on the implant in order to meet the needs of every patient. Typically, the eccentric head is positionable in only a few select orientations relative to the eccentricity. 
   Thus, there is a need for an prosthetic implant that can utilize an eccentric head wherein the eccentric head may be positioned in any number of rotatably eccentric positions. 
   SUMMARY OF THE INVENTION 
   The present invention is a method, apparatus and corresponding implant for positioning an eccentric head on a trail implant/broach and transferring or translating the eccentric position of the head onto the actual or definitive implant. The present invention allows the eccentric head to be positioned in an infinite amount of positions or orientations to best reproduce the articular geometry of the patient. The infinite dialability is optimum for reconstruction purposes. 
   Because each shoulder arthroplasty needs to be adapted to the patient&#39;s unique combination of soft tissue and bone anatomy, the present system maximizes the surgeon&#39;s flexibility in matching a wide variety of anatomic requirements. The present invention places a premium on secure fixation, conservation of bone and optimization of mechanics. 
   During the trialing process, the humeral head trial is lockable into one of an infinite variety of rotational positions (a set orientation) that then may be transferred to the definitive humeral head of the definitive implant. A means is provided for locking the eccentric trial head to the trial/broach in a set orientation that allows for the trialing process to occur without spinning of the eccentric trial head in the broach taper. In one form, this is accomplished via a captured screw in the eccentric trial head that extends beyond the taper of a neck of the eccentric trial head. The captured screw engages threads in a bottom of a bore in a taper in the broach. 
   Once the eccentric head has been threaded onto the trial broach, it is rotated into a correct position covering the resected humeral head surface. The eccentric head may be rotated into an infinite number of positions on the trail broach without having to be locked in any particular orientation. Once the eccentric head is in position, the captured screw is tightened or locked. Trial reduction is carried out and if deemed satisfactory, the broach/eccentric head trail head assembly (or trial assembly) is removed as a one piece unit from the humerus of the patient. 
   In accordance with an aspect of the present invention, the eccentric head includes a mark or indicia showing the position of maximum offset. Once the trial assembly has been removed, from the patient&#39;s humerus, it is placed in an impaction stand or block. The impaction stand allows the measurement of the orientation of the eccentric head (by the indicia) on the trial broach, and the translation or transference of that orientation onto the definitive implant. The impaction stand has a scale or demarcations on a surface thereof. The orientation of the indicia of the eccentric head is noted relative to the scale. 
   The trial assembly is then removed from the impaction stand and the appropriate size of the definitive implant is placed in the impaction stand. An appropriate size of definitive eccentric head is placed on the definitive implant. The definitive eccentric head includes an indicia either as an etched or otherwise arrow or other marking on the nonarticulating surface (or by a removable sticker or the like on the articulating surface) showing the position of maximum offset (in like manner to the trial eccentric head). The indicia of the definitive eccentric head is orientated or aligned with the scale to the same number or marking as the trial eccentric head. 
   Once the definitive eccentric head has been properly aligned, the definitive eccentric humeral head is impacted into place onto the definitive implant while on the impaction stand. In this manner, the appropriate position of the humeral head for the definitive implant has been successfully transferred from the trial assembly. 
   It can be appreciated from the foregoing, that the eccentric head may be rotationally positioned in an infinite number of positions, both during trialing and during the final implant. 
   In accordance with one embodiment of the present invention, there is provided a method of implanting a final prosthesis assembly in a resected bone. The method includes the step of positioning a trial assembly in the resected bone, the trial assembly including a trial body portion having a trial bore defined therein, and a trial head portion having (i) a trial head member which includes a trial offset indicia, and (ii) an eccentrically located trial head stem extending from the trial head member, the trial head stem being configured to be received within the trial bore. The method further includes the step of rotating the trial head portion relative to the trial body portion while the trial assembly is positioned in the resected bone so as to position the trial head portion relative to the trial body portion at an aligned orientation whereby the trial head portion covers a resected surface of the resected bone. In addition, the method includes the step of removing the trial assembly from the resected bone after the rotating step. The method also includes the step of positioning the trial assembly in a scale mechanism whereby the trial offset indicia of the trial head portion aligns with a value on the scale mechanism. Moreover, the method includes the step of securing a final head portion to a final body portion based on the value so as to form the final prosthesis assembly. Additionally, the method includes the step of implanting the final prosthesis assembly in the resected bone after the securing step. 
   Pursuant to another embodiment of the present invention, there is provided a method of implanting a final prosthesis assembly in a resected bone. The method includes the step of providing a trail assembly which includes a trial body portion having a trial bore defined therein, and a trial head portion having (i) a trial head member which includes a trial offset indicia, and (ii) an eccentrically located trial head stem extending from the trial head member. The method further includes the step of positioning the trial body portion in the resected bone. Also, the method includes the step of positioning the trial stem in the trial bore after the trial body positioning step. In addition, the method includes the step of moving the trial head portion in relation to the trial body portion after the trial stem positioning step so as to locate the trial head portion relative to the trial body portion at a user-selected orientation. The method also includes the step of securing the trial head portion to the trial body portion at the user-selected orientation. Additionally, the method includes the step of removing the trial assembly from the resected bone after the securing step. Furthermore, the method includes the step of positioning the trial assembly in a scale mechanism after the removing step whereby the trial offset indicia of the trial head portion aligns with a value on the scale mechanism. Moreover, the method includes the step of attaching a final head portion in fixed relation to a final body portion based on the value so as to form the final prosthesis assembly. The method also includes the step of implanting the final prosthesis assembly in the resected bone after the attaching step. 
   According to still another embodiment of the present invention, there is provided a kit used during the implantation of a prosthesis. The kit includes a trial assembly including a trial body portion having a trial bore defined therein, and a trial head portion having (i) a trail head member which includes a trial offset indicia, and (ii) an eccentrically located trial stem extending from the trial head member, the trial head stem being configured to be received within the trial bore. The kit also includes a final prosthesis assembly including a final body portion having a final bore defined therein, and a final head portion having (i) a final head member which includes a final offset indicia, and (ii) an eccentrically located final head stem extending from the final head portion, the final head stem being configured to be received within the final bore. 
   According to yet another embodiment of the present invention, there is provided a kit which includes a trial assembly including (i) a trial body portion, (ii) a trial head portion which includes a trial offset indicia, and (iii) a fastener for securing the trial head portion to the trial body portion. The kit further includes a final prosthesis assembly including a final body portion having a final bore defined therein, and a final head portion having (i) a final head member which includes a final offset indicia, and (ii) an eccentrically located final head stem extending from the final head portion, the final head stem being configured to be received within the final bore. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
       FIGS. 1A and 1B  are elevational views of exemplary humerus prostheses/trail broach bodies used in conjunction with the eccentric head of the present invention; 
       FIG. 2  is an enlarged, side sectional view of a partial humerus with a portion of the humerus head resected (removed) and a trail broach inserted into the humerus; 
       FIG. 3  is a bottom plan view of an eccentric trail humerus head; 
       FIG. 4  is a side elevational view of the eccentric trial humerus head of  FIG. 3 ; 
       FIG. 5  is a front elevational view of a partial humerus with the humerus head resected; 
       FIG. 6  is a front elevational view of the partial humerus of  FIG. 5  showing a trial standard humerus head that exposes a portion of the surface of the resected humerus head; 
       FIG. 7  is a front elevational view of the partial humerus of  FIG. 5  showing the trial eccentric humerus head covering the surface of the resected humerus head; 
       FIG. 8  is an enlarged side elevational view of the trial eccentric humerus head of  FIGS. 3 and 4  having a seating screw extending therefrom; 
       FIG. 9  is an enlarged perspective view of the seating screw of  FIG. 8 ; 
       FIG. 10  is a perspective view of a trial eccentric head being attached to the trial broach via a driver; 
       FIG. 11  is an enlarged, side sectional view of a partial humerus with the trail assembly (broach and eccentric head inserted into the humerus; 
       FIG. 12  is a top perspective view of an impaction stand; 
       FIG. 13  is a bottom perspective view of the impaction stand of  FIG. 12 ; 
       FIG. 14  is a side elevational view of the impaction stand of  FIGS. 12 and 13 ; 
       FIG. 15  is a top plan view of the impaction stand of  FIGS. 12-14 ; 
       FIG. 16  is a bottom plan view of the impaction stand of  FIGS. 12-14 ; 
       FIG. 17  is a perspective view of the impaction stand with a broach or implant seated thereon; 
       FIG. 18  is an enlarged top plan view of a trial assembly seated on the impaction stand with the indicia (notch) of the trial eccentric head positioned at “ 5 ”; and 
       FIG. 19  is a perspective view of the impaction stand with a definitive implant seated thereon with a definitive eccentric humerus head ready to be impacted onto the implant. 
   

   Corresponding reference characters indicate corresponding parts throughout the several views. 
   DETAILED DESCRIPTION 
   With reference to  FIG. 1A , there is shown an exemplary, 210 mm humerus prosthesis or trial broach generally designated  20 . The humerus prostheses/trial broach  20  includes a stem  22  extending from a neck  24 . The neck  24  terminates in a generally flat surface  26  that is adapted to be seated on a surface of a resected humerus head of a patient&#39;s humerus. In  FIG. 1B , there is shown an exemplary, 138 mm humerus prosthesis or trial broach generally designated  28 . The humerus prostheses/trial broach  28  includes a stem  30  extending from a neck  32 . The neck  32  terminates in a generally flat surface  34  that is adapted to be seated on a surface of a resected humerus head of a patient&#39;s humerus. 
   In  FIG. 2 , there is shown a patient&#39;s humerus  36  wherein the humerus head  38  has been resected in accordance with standard shoulder arthroplasty surgery. It is beyond the scope of the present invention to discuss humerus head resection. Various texts and papers may be consulted for this procedure. After the humerus head  38  has been resected, the humerus head must be sized for a prosthetic head of the implant. Various sizes are available such as 44, 48 and 52 mm. It will be assumed that an eccentric head will be chosen. In  FIG. 2 , the medullary canal of the humerus  36  has been reamed and the trial broach  20  has been placed thereon. The flat  26  is in contact with a surface  40  of the resected humerus head  38 . The trial broach  20  is ready to be fitted with a trial eccentric head. 
   Preoperative evaluation of the Humerus  36  with templates (not shown) helps determine the size of the prostheses and level of humerus head resection. Humeral head resection is accomplished as is known in the art or with other methods the detail of which is beyond the scope of the present invention and this disclosure. 
   Briefly, in  FIGS. 5-7  there is shown a reason for selecting an eccentric head.  FIG. 5  shows the humerus  36  whose humerus head  38  has been resected. It is now necessary to find a trial head that will cover the humerus surface  40  formed by the resection. In  FIG. 6  a trail standard head  60  having a tapered stem  62  is shown in position over the surface  40 . It can be seen that the surface  40  is visible around the periphery of the trial standard head  60 . A centerline shows how the trial standard head  60  fits over the surface  40 . Even with rotation of the trial standard head  60 , the surface  40  is exposed. Thus, the trial standard head  60  is not appropriate. In  FIG. 7 , a trial eccentric head  42  having a tapered stem  46  is shown in position over the surface  40 . It can be seen that with the correct rotation/orientation/placement of the trial eccentric head  42 , the entire surface  40  is covered. With an infinite number of rotational positions, an eccentric head is thus appropriate. 
   Referring to  FIGS. 3 , and  4 , a trial eccentric head  42  in accordance with the principles of the present invention is shown. Four eccentric head  42  sizes may be provided, 44 mm, 48 mm, 52 mm, and 56 mm. The trial eccentric head  42  includes a tapered stem  46  that is positioned off center (approximately a 4 mm offset) such that an eccentricity during rotation thereabout is defined or formed. The stem  46  extends essentially perpendicularly from a bottom surface  43  of the trial eccentric head  42  and includes a bore  48  that extends through the stem  46  and the head  42 . The trial eccentric head  42  includes an indicia (here a notch)  44  that indicates a maximum offset position for the eccentric head  42 . It should be appreciated that other types of indicia may be used. Here the notch  44  is located on the edge of the articular surface of the eccentric head  42 . 
   Referring to  FIG. 9 , a retaining screw or the like  50  for the trial assembly (trial eccentric head and trial broach) is shown. The retaining screw  50  includes a head  52  having an opening  54  for receiving a screw driver or the like. The opening may be hex shape or otherwise. Extending from the head  52  is a shank  56  terminating in threads  58 . The retaining screw  50  is designed to fit into the bore  48  of the trial eccentric head  42  with its threads  58  extending therefrom (see  FIG. 8 ). 
   Referring to  FIG. 10 , the trial broach  20  is shown wherein the trial eccentric head  42  is ready to be attached thereto. Using an appropriate screw driver  66 , the eccentric trial head  42  is attached to the trial broach by threading the screw  50  into a complementary threaded bore  64  in the flat  26 . Once the eccentric head  42  is attached to the trial broach  20  it is inserted into the humerus  36  (see  FIG. 11 ). Once the trial prosthesis is in place as depicted in  FIG. 11 , the screw  50  may be loosened to rotate the eccentric head  42  to a proper orientation. Once a proper rotational orientation has been achieved, the screw  50  is tightened. The trial prosthesis may now be removed from the humerus  36 . Once the trial prosthesis has been removed from the humerus  36  it is ready to be place in an impaction stand or block in accordance with the principles of the present invention. The position of the eccentric head  42  is now ready to be transferred or reproduced in the final or definitive prosthetic implant that will remain in the patient. 
   Referring to  FIGS. 12-16 , there is shown an impaction stand or block generally designated  70  in accordance with the principles of the present invention. The impaction stand  70  may be made of a suitable plastic or the like and is essentially a hexagonal cylinder. The impaction stand  70  is designed to accommodate various sizes of trail broaches/final prostheses. To this end, the impaction stand  70  has two faces or surfaces  76  and  78  on opposite sides thereof. Extending diagonally from the surface  76  to an outside surface of the cylinder is a first channel  72 . Extending diagonally from the surface  78 , opposite in orientation to the first channel  72 , is a second channel  74 . The second channel  74  extends to an outside surface of the cylinder. The first and second channels  72  and  74  and their respective surfaces  76  and  78 , are designed to accommodate various sizes of trial broaches/final prostheses. In the figures, surface  76 /channel  72  is designed to hold trial broaches/final prostheses of sizes 6 mm, 8, and 10 mm, while the surface  78 /channel  74  is designed to hold trial broaches/final prostheses of sizes 12 mm, 14 mm, and 16 mm. Of course, it should be appreciated that the impaction block  70  may be designed for other sizes, or several blocks for the various sizes. 
   Each surface  76  and  78  includes an indicia or scale in the manner of a clock or the like that divides the periphery thereof into sections. The scale is used to reference the position of the notch  44  of the trial eccentric head  42  when the trial assembly is place in the impaction stand (as well as the final assembly as indicated below). 
   Referring to  FIGS. 17 and 18  the trial assembly is placed into the impaction stand  70  (in  FIG. 17 , the eccentric head is not present to illustrate how the stem  22  fits in the impaction stand  70 /channel  74 ). As seen in  FIG. 18  the position of the notch  44  in the trial eccentric head  42  is noted (here at position  5 ) for transference or reproduction onto the final prosthesis. 
   The final step is to fit the final eccentric head onto the final humeral stem (of the same size as the trial broach). The trial assembly is removed from the impaction stand  70  and the final humeral stem/body is placed therein (see  FIG. 17 ). In  FIG. 19 , a final eccentric head  80  is chosen of the same size as the trial eccentric head  42 . The final eccentric head  80  is held by an impactor  86  such as a Delrin-tipped impactor. The final eccentric head includes an indicia, either as a permanent mark or the like on the nonarticulating surface thereof or as a removable sticker or the like on the articulating surface thereof, that indicates the maximum offset in like manner to the trial eccentric head  42 . The indicia of the final eccentric head  80  is aligned with the marking or indicia on the scale of the surface  78  that is the same as that noted above (here “ 5 ”). The taper  82  of the eccentric head  80  is inserted into a complementary tapered bore  84 . Keeping the indicia of the eccentric head  80  as noted, the final eccentric head  80  is impacted onto the final humeral stem with a mallet (not shown) onto the impactor  86 . The final assembly is now ready to be inserted back into the patient&#39;s humerus. 
   While this invention has been described as having a preferred design and/or configuration, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains. For example, while the invention is discussed in the context of implanting a prosthesis in the humerus, the present is application to implantation of a prosthesis into any bone which forms a joint such as the shoulder, hip, etc. For instance, the present in invention is application to the implantation of a prosthesis into a femur.