Ligament balancing during total knee arthroplasty (TKA) is a controllable and critical procedure necessary for the longevity of the prosthesis. Intraoperative knowledge of the magnitude and location of tibiofemoral forces, can guide the surgeon to an accurate balancing throughout the operation. We developed a novel sensor device in order to monitor tibiofemoral forces during TKA ligament balancing procedure. The device predicts loads with an error of ± 1.5%, following a linear trend of slope = 0.9933 and R(2) = 0.9987; while the location of load is predicted with a practically acceptable error of ± 0.5 mm. The device was subjected to a surgical validation with in situ application during simulated TKAs on composite and cadaveric knees, with a very satisfactory outcome and no operative time elongation. The device can be a useful intraoperative instrument for accurate TKA ligament balancing procedures based on objective and graphically demonstrated and recorded evidence.