Abstract:
A knee joint prosthesis includes a femoral component for engaging the femur having an articular surface and a recess within the articular surface, and a tibial component for engaging the tibia with a bore, and a meniscal component comprising a rotation pin configured for rotatable mounting within the bore of the tibial component. The meniscal component also includes a bearing surface for sliding contact with the articular surface of the femoral component and an elongated channel defined amid the bearing surface. A stabilizing post is provided that includes a base slidably mounted with the elongated channel and a spine post projecting from the base through the channel and into the recess when the articular surface is in contact with said bearing surface. The stabilizing post thus slides within the channel when contacted by the interior of the recess in the femoral component. In a method of the invention, a plurality of stabilizing posts can be provided for temporary mounting within the channel. A stabilizing post can be selected that provides an optimum joint movement.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to prosthetic joints, and particularly to a prosthesis for the knee joint.  
           [0002]    Implantable knee prostheses for diseased and/or damaged knees typically include three components, namely a femoral component, a tibial component and a meniscal component. The femoral component may also include a patellar element, or a separate patellar component may be provided. The prosthesis components are generally configured to restore or emulate as much of the natural motion of the knee joint as possible. The selection of the particular prosthesis components is usually dictated by the condition of the patient&#39;s knee. For instance, the condition of the distal end of the femur and proximal end of the tibia, as well as the patency of the surrounding ligaments and soft tissue can affect the form of the joint prosthesis.  
           [0003]    Generally, a total knee joint replacement includes a tibial component having a platform portion which replaces the entire superior surface of the tibial plateau and substitutes for the tibial condylar surfaces. The femoral component also includes laterally-spaced condylar portions joined by an intercondylar bridge and a patellar surface.  
           [0004]    The tibial component typically includes a tibial tray and stem for surgical attachment to the proximal end of the tibia. The component also includes an intermediate articulating surface member that is connected to the tibial tray. The intermediate member defines a bearing surface for articulation of the femoral component thereon. The mating surfaces are smoothly curved in the anterior-posterior (AP) direction to generally match the lateral profile of the natural femoral and tibial condyles, and to ultimately replicate the normal joint movement.  
           [0005]    This normal joint movement includes a translational component in the AP direction, as well as a rolling of the femoral condyles on the tibial condyles when the knee is flexed. In addition, the natural tibia is capable of rotation relative to the femur about the axis of the tibia. Thus, an ideal knee prosthesis will be able to achieve all three degrees of freedom of movement. In some cases, the patient&#39;s knee lacks adequate posterior support due to a deficient posterior cruciate ligament. In these cases, the modular knee is preferably posteriorly stabilized, meaning that posterior movement of the tibia relative to the femur is restricted. This posterior stabilization can be achieved in a typical implant by a projection or eminence on the tibial insert that engages a box-like intercondylar portion of the femoral component. Intact collateral ligaments keep the projection within the box-like portion as the knee is flexed to inhibit dislocation of the joint at hyper-extension or hyper-flexion.  
           [0006]    In order to increase the lifetime of the prosthetic knee joint, the mating bearing surfaces between the tibial and femoral components generally permit a combination of rolling and translational movement as the knee joint is flexed. These two degrees of freedom of movement change the direction of forces between the two components so the force transmitted through the joint is not focused on one location. In response to this optimum design aspect, some prosthetic knees include a translating intermediate bearing component. One problem with modular implants of this type is that the articulating and sliding components can be exposed to the soft tissue surrounding the joint.  
         SUMMARY OF THE INVENTION  
         [0007]    In one embodiment of the invention, a modular joint prosthesis comprises a first joint component having a bone engaging portion, an articular surface, and a recess defined within the articular surface. The prosthesis further includes a mating component having a bone engaging portion and defining a bearing surface for sliding contact with the articular surface of the first joint component. In one feature of the invention, a stabilizing post is slidably mounted to the mating component amid the bearing surface with the post projecting from the mating component and into the recess when the articular surface is in contact with the bearing surface.  
           [0008]    In certain embodiments, the mating component includes a second joint component including the bone engaging portion and an intermediate component connected to the second joint component, the intermediate component including the bearing surface. When the modular joint prosthesis is a total knee prosthesis, the first component is the femoral component, the second component is the tibial component and the intermediate is the meniscal component.  
           [0009]    The second joint component can define a bore, while the intermediate component can includes a pin sized to be received within the bore. The bore and pin can be configured to permit relative rotation therebetween when the pin is received within the bore to add a rotational degree of freedom between the femoral and tibial components.  
           [0010]    In one aspect of the invention, the mating component or the intermediate component defines an elongated channel. The stabilizing post includes a base configured for sliding engagement within the channel and a spine projecting from the base through the channel and into the recess when the articular surface is in contact with the bearing surface. In certain embodiments, the channel is open at one end. In these embodiments, a locking member can be provided that is configured to close the one end with the base of the stabilizing post disposed within the channel. The locking member can be configured for a press-fit within the channel.  
           [0011]    In some embodiments, the channel includes an enlarged groove at opposite sides of the channel. The base of the stabilizing post can then be configured for sliding engagement within the grooves, while the locking component can be configured for locking engagement within the grooves. Preferably, the channel has a length greater than the length of the base so that the base can translate within the channel.  
           [0012]    The recess of the first joint component can define surfaces at its opposite ends. The stabilizing post preferably includes a face opposing each of the opposite end surfaces. The recess surfaces and a corresponding opposing face of the stabilizing post are configured to provide a camming movement of the stabilizing post as the recess end surface moves in contact with the opposing face. Thus, as the first joint component rolls and translates relative to the mating component, the camming movement causes the stabilizing post to slide between the ends of the channel.  
           [0013]    In some embodiments, two faces of the stabilizing post are differently curved to provide different camming effects at opposite ends of the channel. In one feature of these embodiments, a plurality of stabilizing posts can be provided having different profiles. An appropriate stabilizing post can be selected during a total knee procedure to optimize the movement of the resulting prosthetic joint.  
           [0014]    It is one object of the present invention to provide a prosthetic joint that permits relative rolling and translation between two bone engaging components. A further object is achieved by features of the invention that reduce the exposure of articulating surfaces and components of the prosthetic joint to soft tissue surrounding the joint.  
           [0015]    These objects and certain benefits of the invention can be ascertained from the following written description taken together with the accompanying figures.  
       
    
    
     DESCRIPTION OF THE FIGURES  
       [0016]    [0016]FIG. 1 is an exploded perspective view of the components of a joint prosthesis in accordance with one embodiment of the invention.  
         [0017]    [0017]FIG. 2 is a side exploded view of the intermediate component of the joint prosthesis shown in FIG. 1.  
         [0018]    [0018]FIG. 3 is a top elevational view of the intermediate component shown in FIG. 2.  
         [0019]    [0019]FIG. 4 is an end elevational view of the intermediate component shown in FIG. 2.  
         [0020]    [0020]FIG. 5 is a side elevational view of the intermediate component shown in FIG. 2, with the stabilizing post shown in different positions.  
         [0021]    [0021]FIG. 6 is a side elevational view of the femoral component of the prosthetic joint shown in FIG. 1.  
         [0022]    [0022]FIG. 7 is a side elevational view showing one position of the femoral component relative to the intermediate component of the prosthetic joint shown in FIG. 1.  
         [0023]    [0023]FIG. 8 is a side elevational view showing another position of the femoral component relative to the intermediate component of the prosthetic joint shown in FIG. 1.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains.  
         [0025]    Referring first to FIG. 1, a modular joint prosthesis  10  is depicted that comprises a first joint component  12 , a second joint component  14  and an intermediate joint component  16 . From the perspective of a knee prosthesis, the first joint component  12  can be referred to as the femoral component, the second joint component  14  as the tibial component, and the intermediate joint component  16  as the meniscal component.  
         [0026]    The femoral and tibial components can be configured according to known designs for these elements. For the purposes of the present disclosure, certain details of these components will be described. The femoral component  12  can include an articular surface, or more particularly a pair of condylar articular surfaces  25 . These surfaces are smoothly curved and configured to emulate the shape of the natural femoral condyles. The component  12  also includes a bone engaging portion  27  which can include fixation posts  28 . The bone engaging portion  27  can be configured in a known manner for attachment to the distal femur. The femur can be prepared in a conventional manner to accept the femoral component  12 .  
         [0027]    The femoral component  12  can further include a patellar element  30  that is integral with the articular surfaces  25 . A separate patellar element can also be provided for connection to the femoral component. The component  12  also includes an intercondylar recess  32  which is preferably a box-like structure spanning the AP dimension of the component. A slot  33  can be included in the proximal face of the recess  32 . In one feature of the femoral component  12  of the present embodiment, a tab  34  can be provided at the posterior end of the recess  32 . The tab  34  can operate as a control for roll-back of the tibia relative to the femur as the joint is articulated.  
         [0028]    The tibial component  14  can be in the form of a conventional tibial tray. The component includes a proximal surface  35  that parallels the tibial plateau cut into the proximal end of the tibia to receive the component. A fixation stem  37  projects downwardly from the tibial tray and is configured for solid, permanent fixation within the prepared end of the tibia. A connection bore  39  extends from the proximal surface  35  into the fixation stem  37 . The bore is configured to receive a mating stem  45  of the intermediate joint component  16  in a known fashion. To approximate the shape of the prepared end of the tibia, the tibial component  14  can define a posterior recess  41 .  
         [0029]    Turning now to the intermediate component  16 , details of its design can be gleaned from FIGS.  1 - 4 . In general, the intermediate component can be configured like similar components from known modular knee prostheses. Thus, the intermediate component  16  can include opposite spaced-apart bearing surfaces  43  that are configured for articulating contact with the articular surfaces  25  of the femoral component  12 . The component  16  can also include a rotation pin  45  that is rotatably mounted within the connection bore  39  of the tibial component  14 . The interface between the rotation pin and the tibial component bore can be of conventional design that permits relative rotation between the intermediate component  16  and the patient&#39;s tibia. In the illustrated embodiment, the axis of rotation of the intermediate component  16  is at the center of the component and of the tibial component  14 ; however, other axes of rotation are contemplated as required for the particular joint anatomy and the desired movement of the joint prosthesis.  
         [0030]    In a modification from prior intermediate components, the component  16  of the present invention includes a channel  47  defined between the spaced-apart bearing surfaces  43 . In general, the position of the channel  47  corresponds to the position of the recess  32  of the femoral component  12  when the two components  12  and  16  are in articulating contact. The channel  47  can include a posterior opening  49  at the posterior side of the intermediate component  16 . A stop surface  51  is provided at the closed anterior end of the channel  47 . Opposite grooves  53  can be formed at the base of the channel  47  for reasons set forth below. As shown in the figures, the channel  47  extends substantially along the entire AP length of the intermediate joint component  16 .  
         [0031]    The channel  47  is configured to receive a further novel component of the prosthesis  10 , namely the stabilizing post  18 . The stabilizing post  18  projects upward from the intermediate component  16  to engage the intercondylar recess  32  in the femoral component  12 . As best illustrated in FIGS. 1 and 2, the stabilizing post  18  includes a base  55  that is sized for sliding engagement within the grooves  53  of the channel  47 . The base  55  and grooves  53  preferably form a close running fit so that the stabilizing post  18  can slide freely within the channel  47  without binding.  
         [0032]    The stabilizing post  18  includes a spine  57  that projects from the base  55 . The spine  57  is sized for sliding movement along the exposed length of the channel  47  facing the femoral component recess  32 . The spine  57  has a height from the base  55  that is sufficient to span the height of the recess  32  and extend at least partially into the slot  33  when the femoral component and intermediate component are in articulating contact. The spine  57  serves to limit the AP movement of the femoral component  12 . In addition, a close running fit between the spine  57  and the recess  32  helps ensure that the femoral component  12  does not rotate relative to the intermediate component  16 , even when the tibial component rotates relative to the intermediate component.  
         [0033]    As shown in FIGS.  1 - 3  and  5 , the joint prosthesis also includes a locking member  20  that closes the posterior opening  49  of the channel  47 . Thus, the locking member  20  retains the stabilizing post  18  within the channel  47 . The locking member includes locking edges  69  on opposite sides of the member that are configured for locking engagement within the grooves  53  at the posterior end of the channel  47 . The locking edges  69  and grooves  53  can be configured to achieve a variety of locking engagements therebetween to essentially permanently connect the two parts together and close the posterior opening of the channel. Thus, in one embodiment, the locking edges and grooves can form a press-fit engagement. In a specific embodiment, the press-fit engagement can be accomplished by complementary Morse taper angles. In another embodiment, the locking edges and grooves can be configured for a snap-fit engagement, sock as a locking tab and notch configuration. In yet another alternative, an independent fixation, such as a screw of even epoxy, can be used to lock the locking member  20  within the end of the channel.  
         [0034]    The locking member  20  operates to trap the stabilizing post  18  within the channel. Thus, the member includes a stop surface  71  facing the posterior end  65  of the post  18 . The stabilizing post also includes an opposite anterior end  63  that contacts the closed end  51  of the channel  47 . The stabilizing post can thus move along the length of the channel from an anterior position  18 ′ to a posterior position  18 ″, as depicted in FIG. 5.  
         [0035]    The spine  57  of the stabilizing post  18  includes an anterior face  59  and an opposite posterior face  61 . Each face exhibits a pre-defined curvature for cammed movement of the stabilizing post during articulation of the femoral component  12  on the intermediate component  16 . In order to achieve this cammed movement, the femoral component, and more particularly the intercondylar recess  32 , defines a posterior-facing cam surface  77  at one end of the recess and an anterior-facing cam surface  79  at the opposite end of the recess, as shown best in FIG. 6. In essence, the two cam surfaces  77 ,  79  extend from the posterior and anterior ends of the slot  33  (FIG. 1). These cam surfaces bear against a corresponding face  59 ,  61  of the spine  57  to urge the stabilizing post  18  along the channel in the AP direction. This feature allows the femoral component  12  to both roll and slide relative to the tibial component without exposing the articulating components and surfaces to the soft tissue surrounding the joint.  
         [0036]    This rolling and sliding movement can be appreciated from a comparison of FIGS. 7 and 8. In FIG. 7, the stabilizing post  18  is in its anterior position  18 ′ and the femur and femoral component  12  is essential at its zero degree angle relative to the tibia and tibial component  14 . The posterior-facing cam surface  77  bears against the anterior face  59  of the spine  57 . As the femoral component  12  begins to roll in the direction of the arrow R (FIG. 7), the cam surface  77  bears against the anterior face  59  of the spine  57  to push the stabilizing post  18  posteriorly. Eventually, the post is pushed to its posterior position  18 ″, as shown in FIG. 8. The slope and curvature of the anterior face  59  dictates the degree and speed of travel of the post along the channel  47 .  
         [0037]    Once the stabilizing post is in its posterior position  18 ″, the camming surface  77  no longer contacts the spine  57  as the femoral component continues to roll and translation anteriorly relative to the tibial component. Eventually, the femoral component is in the relative position shown in FIG. 8 in which the femur is at an angle of about 120° relative to the tibia. The tab  34  engages the posterior indentation  73  in the locking member  20  to prevent further relative rolling and translation (in conjunction with tension in the collateral ligaments). In this position, the anterior-facing cam surface  79  contacts the posterior face  61  of the spine  57 .  
         [0038]    As the femoral component undergoes relative rolling in the opposite direction, as designated by the arrow R′ in FIG. 8, the cam surface  79  bears against the posterior face  61  to push the spine  57  anteriorly along the channel. When the cam surface  79  breaks contact with the spine, the stabilizing post is in its relative anterior position  18 ′ (FIG. 7). The spine thus prevents further anterior relative translation of the femoral component  12 . Again, it can be seen that none of the articulating surfaces or components impinge or are exposed to the surround soft tissue, even where the femoral component moves between the extreme relative positions shown in FIGS. 7 and 8.  
         [0039]    The sliding stabilizing post  18  of the present invention provides a significant advantage during the total knee replacement procedure. In specifically, the specific post can be selected during the procedure and tested to verify optimum knee movement for the particular patient. In other words, while the post  18  shown in the present figures exhibits a certain configuration, an array of posts can be available, all with different profiles. For instance, the posts can be configured to permit greater or lesser movement within the channel  47 . In addition, one or both of the faces  59 ,  61  can be modified to achieve a specific camming action when contacted by the femoral component cam surfaces  77 ,  79 .  
         [0040]    Thus, in accordance with one feature of the present invention, the femoral and tibial components  12 ,  14  can be prepared bone surfaces. The intermediate or meniscal component  16  can be mounted to the tibial component  14  with the knee in flexion. A pre-selected stabilizing post  18  can be slid into the channel  47  and a temporary locking member can close the post within the channel. The knee can then be moved with the prosthesis in situ through certain degrees of motion to determine whether the selected post is optimum for the particular patient&#39;s anatomy. If not, the post can be removed and replaced with a different post having a different profile. Once an optimum stabilizing post has been found, the locking member  20  can be connected to the intermediate component  16  to lock the finally selected post  18  within the channel  47 .  
         [0041]    The same process can be followed with respect to the locking member  20 . Locking members having different lengths along the channel can be provided to allow more or less sliding movement of the stabilizing post  18  within the channel  47 . In some cases, a locking member can be selected that does not permit any sliding of the post  18 .  
         [0042]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected. For instance, the intermediate component  16  may be made integral with the tibial component  14 . In this case, the rotational degree of freedom would be eliminated.  
         [0043]    In addition, the engagement of the stabilizing post  18  to the channel  47  can be modified so that the both ends of the channel are closed. For example, the channel can be provided with an enlarged top opening and the base  55  of the post  18  can be configured to fit through the enlarged opening and then pivot to engage the grooves  53  at the base of the channel. Engagement of the spine  57  within the intercondylar recess  32  will prevent pivoting of the post once it is disposed within the channel.  
         [0044]    In the illustrated embodiment, the channel  47  is described as including one closed end  51  and an opposite open end  49 . Alternatively, both ends of the channel can be open with a corresponding locking member, such as the locking member  20 , closing each end to trap the stabilizing post  18  within the. channel. The two locking members can be selected intra-operatively to optimize and orient the translation of the stabilizing post within the channel.