A force-sensing device to intraoperatively measure knee joint forces and moments to improve the ligament balancing procedure during total knee arthroplasty has been developed. It consists of two sensitive plates, one for each condyle, a tibial base plate and a set of wedges to vary the tibio-femoral gap. Each sensitive plate contains three deformable bridges instrumented with thick-film piezoresistive sensors, which allow the measurement of the amplitude and location of the tibio-femoral contact forces. Their net varus-valgus moment is then computed and regarded as the parameter characterizing the ligamentous balance. An accuracy study demonstrated that the maximum force amplitude and location error are 1.4 N and 0.6 mm respectively, whereas the mean absolute errors are 0.5 N and 0.2 mm. A control experiment with a plastic knee joint model equipped with spring-ligaments attested the device’s suitability for the purpose of ligament balancing. Furthermore, an in-situ trial on a cadaver demonstrated the appropriateness of the measurement scale as well as the consistency between the acquired data and the surgeon’s perception. The obtained results indicate thereby that the developed force-sensing device has a strong potential to offer useful quantitative information and effective assistance during the ligament balancing procedure in total knee arthroplasty.