Objective:To investigate the clinical curative effect of closed reduction and internal fixation of Jakob type II lateral humeral condyle fractures in children under ultrasound guidance.Methods:A retrospective case series analysis was made on clinical data of 59 patients with Jakob type II lateral humeral condyle fractures treated at Children's Hospital of Chongqing Medical University from August 2016 to August 2017. There were 30 males and 29 females, with the age of 1.5-8.1 years [(4.0±1.8)years]. There were 34 patients treated by open reduction and internal fixation and monitored by the X-ray (control group), and 25 patients treated by closed reduction and internal fixation and monitored by ultrasound (study group). The operation time, bleeding volume, fracture healing time, and incidence of complications were compared between the two groups. The elbow joint function was evaluated by Broberg and Morrey standard at the latest follow-up.Results:All patients were followed up for 17-31 months[(23.2±4.2)months]. The operation time and bleeding volume in control group were (50.7±22.2)minutes and (6.1±3.8)ml, obviously higher than those in study group [(21.4±3.3)minutes, (1.1±0.3)ml] ( P<0.05). The fracture healing time was (8.0±0.8)weeks in control group and (7.8±0.7)weeks in study group ( P>0.05). According to the Broberg and Morrey standard, the good and excellent rate of elbow joint function in control group was 97%, with excellent results in 31 patients, good in 2, fair in 1, and poor in 0; the good and excellent rate of elbow joint function in study group was 100%, with excellent results in 22 patients, good in 3, fair in 0 and poor in 0 ( P>0.05). In study group, wound infection or malunion was not seen, and only two patients showed postoperative wire tail irritability and recovered after the removal of wires. While in control group, wound infection was seen in 3 patients and malunion was observed in 2 patients, but all patients were with distal humerus lateral bone formations. The incidence of complications was 15% in control group, higher than 0% in study group ( P<0.05). Conclusion:Compared to open reduction internal fixation, ultrasound-guided closed reduction and internal fixation of Jakob type Ⅱ lateral humeral condyle fractures in children has similar therapeutic effect, but it can shorten operation time and reduce bleeding and complications.