Which of the following is a hallmark finding in radial dysplasia?

• A. Shortened radius
• B. Hyperextension of elbow
• C. Clubfoot
• D. Absent or hypoplastic thumb

Answer: (D)

Radial dysplasia is a congenital deficiency of the radial side of the forearm, often with the thumb being underdeveloped. The most distinctive and defining feature is an absent or severely underdeveloped (hypoplastic) thumb. This reflects radial ray deficiency and has a major impact on thumb opposition and grasp, making it the key clue for this condition. While the radius may be shortened or even absent and the wrist may deviate toward the ulna, these findings are less specific than thumb hypoplasia. Hyperextension of the elbow or clubfoot aren’t typical hallmarks of radial dysplasia.