Abstract:
An improved one piece tibial tray uniquely characterized by its construction including an asymmetric keel extending from the bottom of the tibial tray base plate, whereby insertion of the tray during arthroplasty may be accomplished with a smaller than normal incision, enhancing the efficacy and safety of the surgical procedure. A fin on either or both sides of the asymmetric fin may be provided for enhanced stability of the tray.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an improved tibial tray that is positioned on the patient&#39;s tibia for joint replacement in a total knee arthroplasty. The improved tibial tray of this invention is of a unitary construction and comprises a unique, asymmetric keel that permits insertion through a relatively smaller incision. 
   2. Description of the Prior Art 
   Total knee arthroplasty is a common procedure performed worldwide. This procedure traditionally requires wide exposure of the distal femur and proximal tibia in order to permit appropriate preparation of the bone surfaces for implanting the components. Most implants performed today in the United States are cemented in place with polymethylmethacrylate cement. Extraneous cement is traditionally cleaned, requiring additional exposure of the femur and tibia to ensure sufficient removal and to prevent potential third body debris. 
   Over the past several years there has been a movement toward less invasive techniques for total knee arthroplasty. These less invasive techniques typically involve smaller incisions, less disruption of the musculature of the knee, and decreased visualization when compared to that of “traditional” total knee arthroplasty. One of the major technical hurdles in performing an accurate, minimally invasive total knee arthroplasty is obtaining adequate exposure in order to seat the currently available components, particularly the state-of-the-art tibial trays. 
   Traditionally, the tibial tray is cemented in place and has a relatively large keel, or a depending stem, used to control angular and rotational forces that are imparted to the tibial tray by the knee joint. Because of the size of such keels or stems today, the proximal tibia must be circumferentially exposed in order to allow appropriate preparation of the bone and seating of the implant. This requires subluxation of the tibia anteriorly and clearance of the posterior lateral femoral condyle to prevent iatrogenic fracture or improper seating of the components. 
   Furthermore, as the tibial tray is cemented in place, the most common method of prosthetic fixation, additional exposure is also necessary to debride cement as it extrudes from under the tray as the tray is forced into position. Even when traditional large incisions are used, the procedure is challenging. With the advent of minimally invasive techniques, another level of difficulty is added because the components must be placed through smaller incisions in the patient&#39;s skin. 
   One means for solving the problem is shown in prior patented devices as modular tibial trays. By use of the term “modular” it is meant that the trays include a keel or stem that is separate from the tibial base plate. In order to facilitate minimally invasive insertion, the keel or stem is inserted into the tibia, and the base plate is attached thereto. However, a relatively larger incision is still necessary for insertion of the keel or stem, and modular devices are frequently more expensive than unitary devices, and the parts may not mate properly. Furthermore, intraoperative assembly is necessary, and this may prove to be more difficult when working through small incisions. Finally, modularity can result in modular interface fatigue fracture, fretting, and/or debris generation that can compromise the effective life of the arthroplasty. 
   SUMMARY OF THE INVENTION 
   The present invention relates to an improved tibial tray used for total knee arthroplasty wherein the improved tray comprises a base plate having a top surface and a bottom surface, and an asymmetric keel depending from the bottom surface and, in a preferred construction, a pair of opposed fins depending from the bottom surface and integral with opposed sides of the keel. The asymmetric configuration of the keel not only permits insertion through a smaller incision, but also tends to expel cement toward the surgeon as the tray is inserted in place, enhancing the ease with which excess cement may be removed. The fins provide strength and rotational stability to the tray once it has been placed. 
   The invention accordingly comprises an article of manufacture possessing the features, properties, and the relation of elements which will be exemplified in the article hereinafter described, and the scope of the invention will be indicated in the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which: 
       FIG. 1  is an illustration of state-of-the-art total knee arthroplasty. 
       FIG. 2  depicts a first embodiment of the improved tibial tray of this invention with portions of the patient&#39;s tibia and fibula shown in phantom. 
       FIG. 3  is a superior plan view of the embodiment of  FIG. 2  (patient&#39;s right leg). 
       FIG. 4  is a superior plan view similar to that of  FIG. 3  (patient&#39;s left leg). 
       FIG. 5  is a side elevation of a second embodiment for the improved tibial tray of this invention. 
       FIG. 6  is an oblique elevation similar to that of  FIG. 5  showing curved fins. 
       FIG. 7  illustrates preparation of the patient&#39;s tibia for insertion of the improved tibial tray of this invention. 
       FIG. 8  depicts a third embodiment for the tibial tray of this invention in a view similar to that of  FIG. 3 . 
       FIG. 9  illustrates the beginning of insertion of the embodiment of  FIG. 8 . 
       FIG. 10  illustrates final placement of the embodiment of  FIG. 8 . 
       FIG. 11  is a view similar to that of  FIG. 1  illustrating total knee arthroplasty using the improved tibial tray of this invention 
   

   Similar reference characters refer to similar parts throughout the several views of the drawings. 
   DETAILED DESCRIPTION 
   Before providing a detailed description of the preferred embodiments of the present invention, attention is invited to the view of  FIG. 1  wherein a prior art total knee arthroplasty is indicated. As shown in the view of  FIG. 1 , a prior art tibial tray is shown at  20  and includes a prior art stem  22  which has been operatively placed within the prepared tibia  24 . A prior art condylar bearing surface  26  is provided above prior art tibial tray  20 , and a prior art femoral component  28  is shown in operative attachment to femur  30 . 
   In order to position prior art tibial tray  20  and its stem  22  within tibia  24 , rather large exposure of the proximal tibia and in-line axial impaction of the prior art tibial tray  20  is required. Because cement is typically used to fix tibial tray  20  and stem  22  to the tibia  24 , excess cement will tend to be expelled circumferentially as tray  20  is positioned. 
   Embodiments of the improved tibial tray of this invention are shown in the remaining figures, and attention is first invited to the view of  FIG. 2  wherein a first embodiment of the improved tibial tray is generally indicated as  32 . Tibial tray  32  includes a top surface  34  and a bottom surface  36 . Integrally formed on bottom surface  36  and extending downwardly therefrom is asymmetric keel  38 . Shown in phantom in the view of  FIG. 2  is an anterior view of the patient&#39;s tibia  40  and fibula  42 . Also shown in the view of  FIG. 2  are a pair of opposed fins  44 . Fins  44  are integrally formed on bottom surface  36  and extend downwardly, each including a keel edge  46  that is integral with a corresponding first side  48  and second side  50  of asymmetric keel  38 . The view of  FIG. 3  is a superior plan illustration of placement of tibial tray  32 , as shown in the view of  FIG. 2 . The view of  FIG. 4  illustrates placement of the improved tibial tray on the patient&#39;s other leg. 
   As can be seen in the views of  FIGS. 2-4 , proper placement of the improved tibial tray  32  of this invention calls for positioning the tray  32  such that the major depth of asymmetric keel  38 , indicated by edge  52 , is anchored into tibia  40  where the bone is more dense. 
   Not only is asymmetric keel  38  “deeper” at edge  52 , tapering to its opposed end, but also asymmetric keel  38  may be curved as clearly seen in the views of  FIGS. 3 and 4  in order to provide even greater stability for the final total knee arthroplasty. Dotted line A-A depicts the curvature of asymmetric keel  38 , and dotted line B-B illustrates the medial placement of improved tibial tray  32  on the patient&#39;s tibia  40 . 
   Referring once again to the view of  FIGS. 2 and 6 , one can see that in this embodiment for improved tibial tray  32  each of the fins  44  may curve away from edge  52 , and each of the fins  44  are tapered to ease insertion. 
   The view of  FIG. 5  depicts a second embodiment for the improved tibial tray of this invention, generally indicated as  32   a . In this embodiment for tibial tray  32   a , fins  44   a  are not curved, and asymmetric keel  38   a  is not curved. Furthermore, the embodiment for tibial tray  32   a  may include a single fin  44   a , and the use of a single fin may be employed in all embodiments of this invention. 
   Turning to the view of  FIG. 8 , a third embodiment for the improved tibial tray is generally indicated as  32   b . As can be clearly seen in the view of  FIG. 8 , asymmetric keel  38   b  is of a curved configuration, rather than angular. Of course, asymmetric keel  38   b  still includes an edge  52   b  that extends downwardly from bottom surface  36  to a maximum depth within tibia  40 . In this embodiment of improved tibial tray  32   b , asymmetric keel  38   b  is preferably curved as is keel  38 , but may be straight as described with regard to keel  38   a.    
   The view of  FIG. 7  is provided to illustrate preparation of tibia  40  for insertion and attachment of the improved tibial tray of this invention. A trial tray  54  is attached to tibia  40  as by pins  56 , then a chisel  58  is repeatedly struck by mallet  60  to form a void  62  for receiving the asymmetric keel of the improved tibial tray. It is, of course, to be understood that chisel  58  would be dimensioned and configured to provide a void  62  corresponding to the configuration of the chosen asymmetric keel. 
   The views of  FIGS. 9 and 10  depict insertion of improved tibial tray  32   b  after preparation of the patient&#39;s tibia  40 , as represented in the view of  FIG. 7 . The phantom oval shown in each of  FIGS. 9 and 10  schematically represents a minimal incision  64  for placement of tray  32   b.    
   As indicated by directional arrows C, tray  32   b  is inserted through incision  64  and rotated downwardly for final placement. It is primarily the shape of asymmetric keel  38   b  which permits insertion through a minimal incision  64 . It can also be appreciated that as tray  32   b  is inserted into the prepared tibia  40 , cement (not shown) will extravasate toward the surgeon, rather than away from the surgeon. This necessarily enhances the ease with which excess cement may be removed.  FIG. 11  schematically depicts the completed total knee arthroplasty using the improved tibial tray  32  of this invention. 
   Thus, the unitary improved tibial tray of this invention, including embodiments  32 ,  32   a , and  32   b , is not only more easily inserted by the surgeon with minimally invasive incisions, but also simplifies manufacturing costs. The slope of the asymmetric keel allows the surgeon to insert the posterolateral portion of the tray first, with the advantageous result that the cement mantle is then compressed from posterolateral to anteromedial as the tray is tipped and rotated into correct position and impacted for final placement. As indicated above, this allows the cement to extravasate toward the surgeon, facilitating intraoperative cleaning. By virtue of the larger medial portion of the asymmetric keel, appropriate rotational and angular stability of the tray is maintained. Of course, this is also enhanced by the presence of at least one fin. 
   It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently obtained and, since certain changes may be made in the above article without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
   It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween. 
   Now that the invention has been described,