Background. The distal radioulnar joint (DRUJ) is unique as it is not a joint but a continuation of the forearm joint. The incidence of DRUJ instability after a distal radius fracture is reported to be between 10%–40%. The triangular fibrocartilage complex (TFCC) presents a 49% prevalence in patients age 70 or older and a prevalence of 27% in patients age 30 or younger(by Casadei, Kyle, and John Kiel. 2020). DRUJ instability is an increasingly recognized clinical problem. Case report. A 38-year-old woman, fall down on the hand 6 weeks ago. First medical aid was given at the traumatological point in the locality by clinical exam and x-ray investigation. Was determine a contusion of radiocarpal joint with applying a cast for 3 weeks. After past the period of recommendation, the patient has started rehabilitation of hand function. After 10 days of kinetic therapy, the patient accuses pain in the hand, on the dorsal side. On examination, the area of maximal tenderness was in the fovea. She had pain during the distal radioulnar joint (DRUJ) shuck test, piano key test, with evidence of painful DRUJ laxity. She had pain in pronation and supination. There was no specific pain on extension and supination. Radiographs at the time showed displacement of the ulnar head form radial fovea posteriorly. On sonography, examination were visualized partial injury of fibrocartilaginous disc and totally lesion of anterior radioulnar ligaments of DRUJ. Surgical repair of distal radial instability was proposed for the patient. The patient was informed about the risks and benefits of the surgery explicitly, she accepted the surgical treatment tactic by signing the informed agreement. Surgery was made with locoregional anesthesia, by marked zone in the projection ulnar flexor of the carpus and pisiform bone, was made an incision of 4 cm up to the distal flexor plica of the wrist on anatomical layers, delimited square pronator muscle with capsule-tomia of the distal radius ulnar joint in "L", was observed a damaged triangular fibrocartilaginous complex with irreparable degenerative appearance (Palmer 2C), the superficial flexor tendon graft of 4th finger was collected, and the distal radioulnar ligaments were grafted with the anteroposterior passage of the tendon graft through the tunnel at the distal metaphysis of the radial bone, after was crossed by ulnar bone neck and suture with the forearm in the supination, the stabilization of the DRUJ was determined, then the distal radioulnar joint was fixed with 2 pins. The postoperative period has a simple evolution. The patient had a forearm-hand immobilization for 5 weeks. Conclusions. Diagnostics of the DRUJ Instability is problematic early. In this case, was determined TFCC injury type 2C by Palmer on sonographic examination was confirmed in surgery time, so it is necessary to make a study to improve the imaging quality diagnosis of TFCC injury for establishing the correct diagnostics and establishing the surgical tactic as early as possible.