Using a tensor for total knee arthroplasty (TKA) that is designed to facilitate soft tissue balance measurements with a reduced patello-femoral joint, we intraoperatively measured the joint gap and ligament balance of 30 osteoarthritic knees at extension and 90 degrees flexion, with the patella both everted and reduced, while performing primary posterior-stabilized TKA. At the same time, we performed the same measurements with a navigation system and identified correlations between this system and the tensor. Specifically, the R(2) values obtained with the knee in extension and 90 degrees flexion were higher with the patella reduced than with the patella everted. We thereby suggest that the navigation system we describe is reliable for obtaining accurate measurements of soft tissue balancing with the patella reduced.