Background: Total knee arthroplasty is one of the most common orthopedic procedures. The coronal alignment of the lower limb is important for planning and assessing outcomes and should be restored. The aim of this study was to determine whether standard anteroposterior knee radiographs adequately assess lower limb alignment respect to full limb radiograph. Methods: There were obtained pre-operative and postoperative knee radiograph and weight-bearing hip-to-ankle radiograph of one hundred thirty-two knees. We analyzed the measurements on coronal plane to determinate diagnostic performance in terms of sensitivity, specificity, predictive values and likelihood ratios of these in the standard x-ray. Results: Tibiofemoral angle of preoperative and postoperative radiographs shows best performance respect the other measurements in mechanical axis assessment with sensitivity of 51.81% to 86.96% and specificity of 33.33% to 50% which increase when another abnormal or positive angle is added. Full limb radiograph analysis shows that standard knee radiograph tibiofemoral angle also has the higher sensitivity and specificity of 36.84% to 88% and of 63.64 to 100% respectively in comparison with anatomic tibiofemoral angle. Conclusions: Global trend respect to anteroposterior knee radiograph performance shows higher sensitivity in preoperative measurements but higher specificity in postoperative measurements, therefore proving that standard knee radiograph is useful for inferior limb axis assessment mainly when are considered as a positive or negative test combination of two abnormal vs normal angles (α angle plus tibiofemoral angle) or three altered vs normal angles respectively.