Southwick angle measurements and SCFE slip severity classifications are affected by frog-lateral positioning

Objective Slipped capital femoral epiphysis (SCFE) is a hip disorder where the femoral head slips relative to the neck at the physis. Appropriate treatment of SCFE depends on the severity of the slip, commonly categorised using the Southwick (SW) angle. The SW angle is measured in the frog-lateral leg position, which can be painful and potentially unattainable for patients. The purpose of this study is to determine how errors in frog-lateral radiograph positioning affect measured SW angles and slip classifications.