The ulnar-radial fusion is a congenital fusion of the proximal radius and ulna, with the affected forearm fixed at a certain angle of rotation, which is a rare deformity. Bilateral disease is more, accounting for 60%. There is no difference in the incidence between men and women. An accurate diagnosis can be made on the basis of clinical manifestations and radiographs. The malformation is dominantly inherited in some patients, due to the fusion of the ulnar radius without separation between the cartilage rods of the ulnar radius during the fifth week of embryonic development or when the mesodermal tissue is filled between the ulnar radius. This deformity is generally divided into three types: Type I is a true congenital ulnar-radial fusion, in which the upper ends of the ulnar and radial bones are fused together, with no cortical bone in between, and the radial tuberosity is fused with the ulna or the radial tuberosity is completely absent, the latter often involving both sides, and the radial stem is curved and thicker and longer than the ulna. The fusion between the distal ends of the ulnar and radial bones generally does not occur. Type II is a posterior dislocation of the radial tuberosity and fusion of the proximal end with the upper part of the ulnar stem. Type III is a fusion between the ulnar and radial bones connected by a layer of interosseous ligament, which hinders the rotation function of the forearm. Clinical manifestations: there is no mobility between the ulnar and radial bones, the forearm is fixed in the anterior rotational position, the posterior rotational function is lost, the elbow joint extension is partially obstructed, and the wrist joint can move freely. The degree of impact on daily life is related to the position of the fixed deformity of the forearm; if unilateral involvement is present, the functional impact is small. The forearm of the affected limb is thin and curved in shape. A local depression of the radial tuberosity is visible in the normal part due to the underdevelopment or anterior or posterior dislocation of the radial tuberosity. Treatment: The degree of deformity of each patient should be carefully evaluated so as to decide whether surgical treatment is needed. Separation of the ulnar radius fusion site is generally not advocated because the outcome is often poor. If the deformity of forearm rotation is serious and exceeds 60°, rotational osteotomy at the proximal 1/3 of the ulnar radius can be performed to put the forearm in a functional position. Most children can compensate well for the rotational function of the forearm through shoulder activities, especially the flexion and extension of the elbow.