A Monteggia fracture is a combined forearm injury that involves a fracture of the proximal part of the ulna (ulna) along with a dislocation of the head of the spindle (radius). This type of fracture accounts for approximately 1% of all forearm fractures. If a fracture is overlooked or untreated for more than 4 weeks, it is referred to as a "missed Monteggia fracture" and can lead to permanent problems such as pain, deformity, dysfunction and elbow arthritis. Treatment of a missed Monteggia fracture involves open reduction of the spindle head and corrective osteotomy of the ulna, which is successful in most cases. Preoperative MRI examination is important for evaluating the condition of the head of the spindle bone and the ulna, which is related to the outcome of the treatment. The risk of abnormalities and re-dislocation of the spindle head increases significantly if the operation is performed more than 6 months after the injury. Early diagnosis and treatment are therefore crucial for a good clinical outcome[1].