Introduction

The use of a surgical navigation system has been demonstrated to allow to intraoperatively analyze knee kinematics during total knee arthroplasty (TKA), thus providing the surgeon with a quantitative and reproducible estimation of the knee functional behaviour. Recently severak authors used the computer assisted surgery (CAS) for kinematic evaluations during TKA, in particular to evaluate the achievement of a correct joint biomechanics after the prosthesis implantation. The major concern related to CAS is that the movements are usually passively performed, thence without a real active task performed by the subject. Starting from the hypothesis that the passive kinematics may properly describe the biomechanic behaviour of the knee, the main goal of this work was to intra-operatively compare the active kinematics of the limb, analysing a flexion movement actively performed by the patient, and the passive kinematics, manually performed by the surgeon.