Knee prosthesis

Abstract

A tibial insert includes a base and a post extending from the base along a longitudinal axis. The post has a medial surface, a lateral surface, and a height along the longitudinal axis. The medial surface has a medial section, and the lateral surface has a lateral section oriented substantially parallel to the medial section. The medial section and the lateral section each have a width in a substantially anterior-posterior direction that is sufficient to enable varus/valgus constraint over a flexion/extension range from extension to about 90 to 120 degrees of flexion when the tibial insert is mated with a femoral component.

1 . A single-piece tibial insert, comprising:
 an inferior surface with a planar portion;   a medial bearing surface that includes a medial concave portion; and   a lateral bearing surface that includes a lateral concave portion;   wherein the lateral bearing surface is asymmetrical with respect to the medial bearing surface; and   wherein a posterior end portion of the medial bearing surface has a slope that is steeper relative to the planar portion than a slope of the posterior end portion of the lateral bearing surface.   
     
     
         2 . The tibial insert of  claim 1 , further comprising a post between the medial bearing surface and the lateral bearing surface, wherein the post comprises a rotational offset in a superior-inferior aspect of the post. 
     
     
         3 . The tibial insert of  claim 2 , wherein the rotational offset of the post comprises a twist in the post such that a superior portion of the post is rotationally offset from an inferior portion of the post. 
     
     
         4 . A tibial inert, comprising:
 a medial bearing surface that includes a medial concave portion; and   a lateral bearing surface that includes a lateral concave portion;   wherein the lateral bearing surface is asymmetrical with respect to the medial bearing surface; and   wherein the lateral concave portion is shallower in a posterior direction than the medial concave portion.   
     
     
         5 . The tibial insert of  claim 4 , wherein a slope of the medial concave portion at a posterior end of the tibial insert is steeper than a slope of the lateral concave portion at the posterior end. 
     
     
         6 . The tibial insert of  claim 4 , further comprising a post between the medial bearing surface and the lateral bearing surface, wherein the post comprises a rotational offset in a superior-inferior aspect of the post. 
     
     
         7 . The tibial insert of  claim 6 , wherein the rotational offset comprises a twist in the post such that a superior portion of the post is rotationally offset from an inferior portion of the post. 
     
     
         8 . A method of operation of a knee prosthesis, comprising:
 permitting flexion/extension of the knee prosthesis over a flexion/extension range of approximately 0 to 150 degrees;   constraining varus/valgus alignment of the knee prosthesis over a constrained flexion/extension range from extension to about 90 to 120 degrees of flexion; and   rotating a tibial insert of a knee prosthesis relative to a femoral component of the knee prosthesis about a substantially superior-inferior axis of the tibial insert over at least a portion of the constrained flexion/extension range.   
     
     
         9 . A method of trialing a tibial insert of a knee prosthesis, comprising:
 coupling a first tibial insert to a prepared tibia or a tibial tray;   assessing the suitability of the knee prosthesis;   removing the first tibial insert from the prepared tibia or the tibial tray; and   coupling a second tibial insert to the prepared tibia or the tibial tray, the second tibial insert being configured to:
 permit flexion/extension of the knee prostheses over a flexion/extension range of approximately 0 to 150 degrees; 
 constrain varus/valgus alignment of the knee prosthesis over a constrained flexion/extension range from extension to about 90 to 120 degrees of flexion when the tibial insert mated with a femoral component; and 
 rotate the tibial insert of the knee prosthesis relative to the femoral component about a substantially superior-inferior axis of the tibial insert over at least a portion of the constrained flexion/extension range. 
   
     
     
         10 . The method of  claim 9 , wherein the first tibial insert and the second tibial insert each have a post, and the first tibial insert and the second tibial insert have differing post dimensions.