Which finding is most characteristic of radial dysplasia?

• A. Normal thumb
• B. Absent or hypoplastic thumb
• C. Hyperextension of wrist
• D. Shortened forearm

Answer: (B)

Radial dysplasia is a radial ray deficiency where the radius is underdeveloped or absent. Because the thumb develops in close association with the radial axis, when the radius is hypoplastic or missing, the thumb is almost always affected. An absent or hypoplastic thumb is the most characteristic and reliable finding, reflecting the disruption of development on the radial side. The wrist and forearm may show other changes, such as ulnar deviation or forearm shortening, but these are less specific. So, the presence of an absent or underdeveloped thumb best identifies radial dysplasia.