ObjectiveTo analyze the possible injury mechanisms in patients with dorsal avulsion fracture of the capitellum combined with medial or posterior medial dislocation of the elbow joint, and to discuss their treatment and prognosis. Methods Retrospective analysis was made on the clinical data of 4 patients with dorsal avulsion fracture of the capitellum combined with medial or posterior medial dislocation of the elbow joint admitted between September 2014 and September 2020, including 3 males and 1 female with an average age of 20.7 years (range, 13-32 years). There were 2 cases of dorsal avulsion fracture of the capitellum combined with medial dislocation of the elbow joint and 2 cases of dorsal avulsion fracture of the capitellum and anterior medial fracture of the coronoid process combined with posterior medial subluxation of the elbow joint. Closed reduction was performed in 3 patients with fresh fracture combined with dislocation, then 2 cases were fixed with tension band and 1 case was fixed with tension band combined with Acumed coronoid anatomic plate. And in patient with old fracture nonunion, the coronoid process was fixed with 1 screw, then the humeral sclerotic bone mass was removed, and finally the lateral collateral ligament was repaired and a hinged external fixator was added. Results All the incisions healed by first intention without early complications such as infection or peripheral nerve injury. The 4 patients were followed up 13-30 months (mean, 20.8 months). The fractures all healed with a healing time of 70-90 days (mean, 79.5 days). At 6 months after operation, heterotopic ossification was seen in the posterior aspect of the right elbow joint in 1 case, and the alkaline phosphatase level was normal (67 U/L); the tension band was removed to clear the heterotopic ossification and the elbow joint was released. The rest of the patients had no heterotopic ossification. At last follow-up, all patients had good functional recovery of the elbow joint, with a Mayo score of 85-100 (mean, 92.5), and the excellent and good rate was 100%. The elbow flexion range of motion was 120°-135°, the extension range of motion was 10°-20°, and the pronation and supination range of motion were all 75°-85°. Conclusion Dorsal avulsion fractures of the capitellum combined with medial or posterior medial dislocation of the elbow may be due to simple varus stress. If an anteromedial coronoid facet fracture also occurs, it may be for the varus posteromedial rotatory instability, which is the opposite mechanism to that of an Osborne-Cotterill lesion. For fresh dorsal avulsion fractures of the capitellum, tension band fixation can be used with good results.