Systems and methods for mobile bearing prosthetic knee

Abstract

A trial system for an implantable joint replacement includes a guide assembly having a baseplate and a guide plate, the guide plate rotatable relative to the base plate about a rotation axis extending through the guide plate and the baseplate while directly connected to the baseplate. An adjustment mechanism is actuable to selectively control the rotational juxtaposition of the guide plate relative to the baseplate. The rotation axis may be medially offset from the center of the guide assembly. A single instrument may be used to rotate the guide plate relative to the base plate and lock the plates in the selected juxtaposition. The guide plate provides in situ positionable cutting guidance for implantation of prosthetic joint components. The system may further include an articulating insert trial mounted on the guide assembly to determine preferred joint alignment and/or optimal positioning of the guide plate.

We claim: 
     
         1 . (canceled) 
     
     
         2 . A knee replacement system comprising:
 a tibial baseplate comprising a superior surface;   a femoral knee implant comprising a pair of condyles, and a cam feature;   a tibial insert comprising a baseplate facing side, a lateral articulating surface, and a medial articulating surface, wherein the baseplate facing side pivotally articulates with the superior surface, wherein the baseplate facing side defines a boss toward a medial side to provide a medially-displaced axis of rotation upon insertion of said boss into a cavity positioned medially on the superior surface, wherein the articulating surfaces articulate with the condyles, and a channel passes through the tibial insert along a direction generally perpendicular to the baseplate facing side, wherein the channel is arc shaped to guide a rotation of the tibial insert relative to the tibial baseplate about the medially-displaced axis of rotation; and   a cam post passing through the channel, wherein contact of an anterior side of the cam feature with a posterior side of the cam post provides the rotation.   
     
     
         3 . The knee replacement system of  claim 2 , wherein the superior surface further defines a hole, wherein the cam post comprises an inferior end shaped to be inserted into the hole during implantation of the knee replacement system. 
     
     
         4 . The knee replacement system of  claim 3 , wherein the cam post comprises a cam post core comprising the inferior end, and an outer sleeve that receives a superior end of the cam post core such that the outer sleeve is fixedly attached to the cam post core, wherein the outer sleeve articulates with the cam feature. 
     
     
         5 . The knee replacement system of  claim 4 , wherein the outer sleeve includes a snap fit feature, wherein the outer sleeve is snapped into engagement with the cam post core. 
     
     
         6 . The knee replacement system of  claim 4 , wherein the outer sleeve has an inferior end, wherein the outer sleeve inferior end has a sleeve notch which receives a portion of the cam post core and stops rotation of the outer sleeve when the outer sleeve is snapped into engagement with the cam post core. 
     
     
         7 . The knee replacement system of  claim 3 , wherein the cam post comprises a cam post core having a superior portion, an inferior portion and an intermediate portion between the superior and inferior portions, wherein the intermediate portion is enlarged relative to the inferior and superior portions. 
     
     
         8 . The knee replacement system of  claim 7 , wherein the intermediate portion has a bottom surface which rests upon the superior surface. 
     
     
         9 . The knee replacement system of  claim 7 , wherein the intermediate portion comprises a first wing extending medially from the intermediate portion and a second wing extending laterally from the intermediate portion. 
     
     
         10 . The knee replacement system of  claim 9 , wherein the first and second wings are positioned as a stop to engage the outer sleeve. 
     
     
         11 . The knee replacement system of  claim 2 , wherein each of the condyles comprises a radius of curvature defining flexion and extension of the knee joint, wherein each of the medial and lateral articulating surfaces comprises a radius of curvature closely matched to that of the corresponding condyle such that a center of rotation of each condyle remains substantially stationary relative to the corresponding articulating surface during flexion and extension of the knee joint. 
     
     
         12 . The knee replacement system of  claim 2 , wherein the boss is insertable into the cavity along the same direction as the cam post through the channel. 
     
     
         13 . The knee replacement system of  claim 12 , wherein the boss is substantially circular in shape. 
     
     
         14 . A knee replacement system comprising:
 a tibial baseplate comprising a superior surface, wherein the superior surface defines a cavity positioned medially on the superior surface;   a femoral implant comprising a cam feature and a pair of condyles;   a tibial insert comprising a tibial baseplate facing side, a lateral articulating surface, and a medial articulating surface, and wherein the tibial baseplate facing side defines a boss that is rotatable within the cavity to enable a pivotal articulation of the tibial baseplate facing side with the superior surface about a medially-displaced axis, wherein each of the medial and lateral articulating surfaces articulate with the pair of condyles;   the tibial insert further comprising an arc-shaped channel passing through the tibial baseplate facing side of the tibial insert, the arc-shaped channel tibial being concave toward the medial articulating surface; and   a post passing through the arc-shaped channel, wherein the pivotal articulation is provided at least partially by contact of an anterior side of the cam feature with a posterior side of the post during articulation of the pair of condyles with the medial and lateral articulating surfaces.