© 2018 Elsevier Inc. Background: Instability is a common failure mode after total knee arthroplasty. There have been only a few methods to quantify anterior translation with fixed forces applied during surgery. The purpose of the study was to measure the anterior translation with a new device and to analyze the relationships between the amount of anterior translation and the joint gaps. Methods: Fifty knees with medial osteoarthritis underwent surgery using a posterior-stabilized implant. During surgery, measurement of anterior translation was performed at 90° of knee flexion with a trial implant, applying a traction force of 70 N. The joint gap was measured using a tensor device, applying a distraction force of 178 N in flexion. The Pearson correlation coefficient was calculated between anterior translation and joint gaps and laxity. Results: On average, anterior translation during surgery was 8.5 mm (standard deviation [SD] = 3.6 mm). Medial gap (correlation coefficient [r] = 0.30), medial laxity (r = 0.33), and center laxity (r = 0.29) had a positive correlation with anterior translation, and anterior translation increased with larger joint gap or greater laxity. Conclusion: Anterior translation was measured with a new device by applying the anterior force to the tibia, and the correlations between anterior translation and joint gap and laxity were analyzed. A larger medial gap and greater medial laxity were correlated with greater anterior translation, which could cause symptomatic feelings of instability. Surgeons should pay attention to the tension of medial structures in flexion and avoid excessive medial release during surgery.