Effect of limb rotation on radiographic alignment measurement in mal-aligned knees.

Flexion and severe coronal deformity have a significant influence on the measurement error of lower limb alignment. Errors can be amplified in the weight-bearing condition compared with the non-weight-bearing condition. When using HKA and FTA to represent the mechanical axis and the anatomical axis on LLR, limb rotation impacts the anatomic axis more than the mechanical axis in patients with severe deformities. Considering LLR as the gold standard image modality, attention should be paid to the measurement of knee alignment. Especially for the possible errors derived from weight-bearing long-leg radiographs of patients with severe knee deformities.