Congenital hip dysplasia, Crown typing is more commonly used. crown typing is mainly based on the severity of dislocation, as follows: 1. type I: a kind of semi-dislocation of the femoral head with less than 50% dislocation; 2. type II: semi-dislocation of the femoral head about 50%-75%; 3. type III: semi-dislocation of the femoral head at 75%-100%; 4. type IV: complete dislocation of the femoral head. All the typing is to facilitate academic communication, guide treatment, and to determine exactly what the prognosis is. No matter what the typing is, even if it is type I, the lesion may develop gradually, and as the acetabular condition continues to develop and evolve with age, it may eventually become type IV as well, with an increasing acetabular index.