Component loosening and instability are common causes of dysfunction after Total Knee Arthroplasty (TKA) and it is generally assumed that such complications are due to tibio-femoral misalignment or ligamentous imbalance. During the surgery, the ligamentous force balance is currently qualitatively assessed by the surgeon through manual trial movements of the limb. In order to improve this procedure, we developed a force-sensing device to intraoperatively measure knee joint forces and moments. The aim of this device is twofold: a) using tibio-femoral forces and moments make quantifiable measurements of what surgeons describe as a balanced knee joint b) help surgeons during TKA to reach this balance state.