Objective To investigate the effectiveness of Salter osteotomy combined with subtrochanteric shortening and derotational osteotomy in treating Tönnis type Ⅲ and Ⅳ developmental dysplasia of the hip (DDH) in children and explore the urgical timing. Methods A retrospective collection was performed for 74 children with Tönnis type Ⅲ and Ⅳ DDH who were admitted between January 2018 and January 2020 and met the selection criteria, all of whom were treated with Salter osteotomy combined with subtrochanteric shortening and derotational osteotomy. Among them, there were 38 cases in the toddler group (age, 18-36 months) and 36 cases in the preschool group (age, 36-72 months). There was a significant difference in age between the two groups (P<0.05), and there was no significant difference in gender, side, Tönnis typing, and preoperative acetabular index (AI) (P>0.05). During follow-up, hip function was assessed according to the Mckay grade criteria; X-ray films were taken to observe the healing of osteotomy, measure the AI, evaluate the hip imaging morphology according to Severin classification, and assess the occurrence of osteonecrosis of the femoral head (ONFH) according to Kalamchi-MacEwen (K&M) classification criteria. Results All operations of both groups were successfully completed, and the incisions healed by first intention. All children were followed up 14-53 months, with an average of 27.9 months. There was no significant difference in the follow-up time between the two groups (P>0.05). At last follow-up, the excellent and good rates according to the Mckay grading were 94.73% (36/38) in the toddler group and 83.33% (30/36) in the preschool group, and the difference between the two groups was significant (P<0.05). The imaging reexamination showed that all osteotomies healed with no significant difference in the healing time between the two groups (P>0.05). There was no significant difference in AI between the two groups at each time point after operation (P>0.05), and the AI in the two groups showed a significant decreasing trend with time extension (P<0.05). The result of Severin classification in the toddler group was better than that in the preschool group at last follow-up (P<0.05). There was no significant difference in the incidence of ONFH between the two groups (P>0.05). In the toddler group, 2 cases were K&M type Ⅰ; in the preschool group, 3 were type Ⅰ, and 1 type Ⅱ. There was no dislocation after operation.ConclusionSalter osteotomy combined with subtrochanteric shortening and derotational osteotomy is an effective way to treat Tönnis type Ⅲ and Ⅳ DDH in children, and surgical interventions for children aged 18-36 months can achieve better results.