Monteggia fracture is commonly treated with open anatomical reduction and fixation of the ulna fracture. The radial head will be automatically reduced once anatomical fixation of the ulna is achieved. However, it is occasionally associated with an irreducible radial head dislocation requiring an open reduction and reconstruction of the torn annular ligament. We describe a case of traumatic Monteggia fracture which underwent initial plating, however post-operative radiograph denoted an irreducible radial head secondary to a ruptured annular ligament. We reconstructed the annular ligament with a synthetic graft sling around the radial neck with an anchor suture. The radial head was stable in all directions after annular ligament reconstruction. A two-year follow-up shows full range of motion of the elbow joint with osteolysis of the radial head, no other operative morbidity was observed.