A knee prosthesis having a femoral component with two condyles and an opening disposed between the two condyles. The prosthesis includes a cam extending between the condyles forming a posterior boundary to the opening. Also included is a tibial component having bearing surfaces to support each of the femoral component condyles, and a post disposed between the bearing surfaces and extending superior from the tibial component. The femoral component and tibial component are engageable by contact between the femoral condyles and tibial bearing surfaces, and by contact between the cam and post during at least a portion of flexion between the femoral and tibial components. Moving the femoral and tibial components in flexion from about 45° to about 145° causes a contact region between the cam and post to move inferiorly from a first contact region to a second contact region while also causing rotation between the tibial and femoral components.
