Tibial bearing having increased axial-rotation
An orthopaedic prosthesis includes a tibial bearing and a femoral component configured to articulate with the tibial bearing. The tibial bearing and the femoral component are configured to promote outward axial rotation of the femoral component on the tibial component during knee flexion.
1. A tibial bearing comprising:
a platform having a medial bearing surface, a lateral bearing surface, and an anterior rim; and
a spine extending upwardly from the platform between the medial bearing surface and the lateral bearing surface, the spine including a posterior cam surface, a medial sidewall, and a lateral sidewall,
wherein the spine has a length when viewed in the transverse plane that is defined by a first line segment extending from a medial-lateral center point of the posterior cam surface of the spine to a medial-lateral center point of the anterior rim of the platform,
wherein the spine has (i) a first width when the tibial bearing is viewed in the transverse plane that is defined by a second line segment orthogonal to and bisecting the first line segment, the second line segment extending from the medial sidewall to the lateral sidewall of the spine and (ii) a second width when the tibial bearing is viewed in the transverse plane that is defined by a third line segment orthogonal to the first line segment and crossing the first line segment at a point on the first line segment posterior to the second line segment, the third line segment extending from the medial sidewall to the lateral sidewall of the spine,
wherein the first width is greater than the second width, and the posterior cam surface of the spine is convex such that when the tibial bearing is viewed in the transverse plane the posterior cam surface bows outwardly posteriorly to define a convex superior edge and a convex inferior edge, and
wherein the platform has a centerline axis defined in the anterior-posterior direction when viewed in the transverse plane, and the spine has a longitudinal axis defined along its length, wherein an angle is defined between the longitudinal axis of the spine and the centerline axis of the platform, when viewed in the transverse plane, and said angle is greater than about five degrees.
2. The tibial bearing of claim 1 , wherein the first width is greater than the second width by at least 0.1 millimeters.
3. The tibial bearing of claim 1 , wherein the medial sidewall and the lateral sidewall of the spine taper toward each other in the anterior-posterior direction.
4. The tibial bearing of claim 1 , wherein:
(i) the posterior half of the medial condylar bearing surface when the tibial bearing is viewed in the sagittal plane has a first radius of curvature, and
(ii) the posterior half of the lateral bearing surface when the tibial bearing is viewed in the sagittal plane has a second radius of curvature greater than the first radius of curvature.
5. The tibial bearing of claim 1 , wherein the posterior cam surface of the spine is concave in the sagittal plane.