Small, shortened forearms with a tilt to the ulnar side, dislocation of the radial head, and limited forearm rotation are among the clinical symptoms of congenital ulnar agenesis. It is often caused by autosomal dominant and recessive inheritance. The disease is mostly unilateral, with a predominance on the right side, and there are more male than female patients. The child’s thumb and forefinger are present with good motor function, but the ulnar lateral column is absent. The affected side of the forearm is thin, shortened and tilted to the ulnar side, the radial head is dislocated, and the forearm rotational function is limited, but the wrist and elbow joint functions are still good. Commonly, the pea bone, hook bone, most of the coracoid and capitate bones, and sometimes the 4th and 5th metacarpal bones are also absent. The radius is bowed outward and protrudes, which is more pronounced with childhood growth. How is the disease detected clinically? Bone imaging Bone imaging can diagnose bone tumor and bone metastatic tumor 3-6 months earlier than X-ray examination, but it should be noted that this method is high sensitivity and low specificity. X-ray examination On X-ray, the ulna is only a thin cartilaginous fibrous band of parenchyma, which is shortened compared with the radius, the radial head is dislocated, the normal curvature of the radius is enlarged, and the radius protrudes to the lateral side, and the ulnar row of bones of the carpal metacarpal can disappear or merge into one piece.