Congenital radial-ulnar junction is a congenital proximal radial-ulnar junction with varying degrees of anterior rotation fixation of the forearm. Approximately 60% are affected in both forearms. The incidence is 0.02%. The incidence is approximately equal in both sexes. This malformation is the result of arrested development of the longitudinal segmentation of the limb buds during embryonic life. Diagnosis 1. Clinical manifestations The radial and ulnar interosseous junctions have no rotational function of the forearm, and the forearm is fixed in a moderately or excessively anteriorly rotated position, unable to rotate posteriorly, unable to rotate the palm upward, and rotational activity is often compensated for by the glenohumeral joint when the elbow is extended. The fixed position of the forearm produces varying degrees of dysfunction, such as the inability to turn door handles, fasten buttons, and use cutlery. In children with over-rotation, the dysfunction is more significant, the palm of the hand is backward, and only the back of the hand is close to the mouth. Generally, the proximal end of the radius and ulna can be seen as a bony connection without joint formation. Sometimes the joint of radius and ulna is cartilage and fibrous tissue, which does not show up on X-ray film and is easy to misdiagnose, but the affected limb has the characteristics of radial and ulnar shape change and disproportionate spacing of the two bones, which is still easy to diagnose. Treatment This deformity is not purely a skeletal deformity, but there are extensive soft tissue deformities and contractures in the forearm. Attempts to restore the rotational function by simple osteotomies are often unsuccessful. Therefore, the indications and surgical methods should be strictly controlled according to the function of the forearm. Surgical treatment is preferred at preschool age, which is conducive to the training of children’s motor skills. Surgical methods include chiseling of the radial-ulnar junction; radial or ulnar osteotomy; and rotational osteotomy of the radial-ulnar junction.