Grading of SUFE (slipped upper femoral epiphysis) can be made on both AP and true lateral projections.
On an AP radiograph a line along the superior margin of the femoral neck (line of Klein) should intersect the lateral corner of the epiphysis.
Slip is graded based on the displacement of the epiphysis in relation to the metaphysis 3:
mild: lateral edge of the epiphysis is within the lateral third of the metaphysis
moderate: lateral edge between the lateral 1/3 and halfway point of the metaphysis
severe: medial third (over the halfway point of the metaphysis)
On a true lateral radiograph, the angle (slip angle) which the epiphysis makes with the metaphysis may also be employed (sometimes known as the Southwick head shaft angle) 2.
normal: ~0 degrees
mild: 0-30 degrees
moderate: 30-50 degrees
severe: >50 degrees