Fractures of the medial epicondyle of the humerus in children after preschool are rare, and because of the local anatomical characteristics of this period, even if a fracture occurs, it is difficult to diagnose and is often easily missed or misdiagnosed. The epiphysis of the medial humeral epicondyle is the attachment point of the flexor muscle group of the forearm, which begins to ossify at the age of 7-9 years due to the involvement of the epiphysis and heals with the backbone at the age of 16-18 years. The fracture of the medial epicondyle of the humerus in school-age children is mostly caused by indirect violence, i.e., a fall with the elbow turned out and the palm of the hand on the ground, which leads to the rupture of the medial capsule ligament of the elbow joint and the sudden tension of the flexor muscle group, resulting in the epiphysis of the medial humeral epicondyle The epiphysis of the medial humeral epicondyle may suffer from avulsion fractures of varying degrees. Diagnosis: The clinical manifestations and signs, as well as the pattern of epiphyseal fracture displacement are identical to those of adolescents; however, the only difference is that the medial epicondyle of the humerus is in the cartilaginous stage after preschool age, and therefore not easily visible on the imaging. Therefore, all cases of soft tissue contusions of the medial elbow in school-aged children should be alerted to the possibility of this disease. In children of preschool age (before 7 years of age), clinical examination should be the main focus. If a mobile bone mass can be palpated under the skin of the medial elbow, a fracture of the medial epicondyle of degree I or II should be considered; if there is a sensation of jamming or friction in the mobile elbow joint and a dislocation of the elbow joint, a fracture of the medial epicondyle of degree II or III is more likely. In addition to the clinical examination of school-age children, the nucleus of the epicondyle that is not shown or unclear in the medial elbow joint and elbow joint space should be carefully looked for in the imaging, and if necessary, compared with the built-up side, to facilitate a clear diagnosis, so as not to misdiagnose and not to miss the diagnosis. III. Treatment: The Ⅰ or Ⅱ degree fracture of this disease should be closed and reset in time, and the affected elbow should be fixed at 90 degrees of flexion for 3-4 weeks after surgery. For those who fail to achieve anatomical reduction and fibrous healing, the impact on the future function of the elbow joint is not significant. Otherwise, surgical repositioning is performed to release the epiphysis from the joint and restore the normal anatomy of the elbow joint to facilitate the functional recovery of the affected elbow.