ObjectiveTo compare the effectiveness of ultrasound-guided closed reduction and Kirschner wire fixation for different unstable humeral lateralcondylar fractures of children. Methods The clinical data of 94 children with unstable humeral lateralcondylar fractures admitted to three medical centers between January 2021 and October 2022 were retrospectively analyzed. The children were divided into three groups according to the Song classification and whether the elbow joint was dislocated or not, including 42 cases of Song 4 type (group A), 38 cases of Song 5 type (group B), and 14 cases of elbow joint dislocation (group C). There was no significant difference in gender, age, side, cause of injury, and time from injury to operation among the three groups (P>0.05). All children were treated with ultrasound-guided closed reduction and Kirschner wire fixation. The operation time and complications of the three groups were recorded and compared, and the failure of closed reduction was evaluated by ultrasound. X-ray examination was performed at last follow-up to measure the Baumann angle, condylar angle, carrying angle, and lateral osteophyte of the affected side; the extension, flexion, pronation, and supination range of motion of the affected elbow joint were measured; the function of the elbow joint was evaluated by Mayo score. ResultsThe operation time in group A was significantly longer than that in groups B and C (P<0.05). There were 7, 2, and 5 cases of closed reduction failure in groups A, B, and C, respectively, and there was no significant difference in the incidence of the closed reduction failure (P>0.05). All patients were followed up 6-28 months, with an average of 15.7 months. There was no significant difference in the follow-up time among the three groups (P>0.05). Complications: in group A, there were 2 cases of delayed union, 4 cases of needle tract infection, 1 case of trochlear necrosis, and 39 cases of lateral osteophyte; in group B, there was 1 case of malunion, 5 cases of needle tract infection, 1 case of redisplacement, and 26 cases of lateral osteophyte; in group C, there were 2 cases of needle tract infection and 10 cases of lateral osteophyte. There was no significant difference in the incidence of complications among the three groups (P>0.05). No cubitus varus or cubitus valgus deformity was found in all patients. At last follow-up, except that the condylar angle in group A was significantly greater than that in groups B and C (P<0.05), there was no significant difference in other imaging indicators, elbow range of motion, or Mayo score between groups (P>0.05). ConclusionThe Song type 4 of humeral lateralcondylar fracture treated with ultrasound-guided closed reduction and Kirschner wire fixation has a longer operation time, more postoperative complications, and is more prone to lateral osteophyte.