A knee prosthesis including a femoral implant, a tibial implant, a tibial insert and a cam post. The femoral implant is secured to a femur and has a cam feature and condyles. The tibial implant is secured to a tibia. The tibial insert comprises a medial cavity with a rotational axis. The tibial insert has articulating surfaces that match the contours of the condyles of the femoral implant. The tibial insert has a medial boss that aligns with the medial cavity allowing it to rotate about the rotational axis. A cam post is secured to the tibial implant and passes through a channel of the tibial insert providing anterior and posterior stops for the rotation of the tibial insert about the rotational axis. The cam post interacts with the femoral implant cam feature and, with the tibial insert, allows more anatomically correct rollback and femoral external rotation during knee flexion.