[Gravity sag view of lateral radiography of the knee].

The gravity sag view(GSV)is a lateral radiograph taken in the same position when the posterior sag sign is observed. The purpose of this study was to standardize the radiography technique for GSV by adjusting lateral rotation. To confirm the benchmark and correction angle(CA)for the GSV position, we assessed three-dimensional(3D)CT of the GSV position of the knee using normal volunteers. The benchmark is established at the 3-point of the leg and adjusting the CA of the knee is established by estimating from Rosenberg technique radiography. This helped not only to correct external rotation in the initial radiography but also to correct rotation for repeat radiography. Our method is quantitative and highly reproducible, and it increases the success rate in adjusting lateral radiography of the knee.