Table 1.

Tonnis classification of hip dysplasia

Grade	Criteria
1	Capital femoral epiphysis medial to Perkin’s line
2	Capital femoral epiphysis lateral to Perkin’s line but below the level of the superior acetabular rim
3	Capital femoral epiphysis at the level of the superior acetabular rim
4	Capital femoral epiphysis above the level of the superior acetabular rim