An infant presenting with a 90-degree deviation of the hand and wrist, shortened forearm, bowing ulna, absent or hypoplastic thumb, and limited movement of the hand, wrist, and forearm should be evaluated for which condition?

• A. Brachial plexus palsy
• B. Fractured clavicle
• C. Radial dysplasia
• D. Wrist dislocation

Answer: (C)

The key idea is radial ray deficiency presenting as radial club hand. The combination of a 90-degree hand and wrist deviation, a shortened forearm with bowing of the ulna, and an absent or hypoplastic thumb is classic for radial dysplasia (radial club hand). In this condition, the radius is underdeveloped or absent, which pulls the hand toward the ulna and limits wrist and forearm motion because the normal bony framework and tendon attachments are disrupted. The thumb, being a radial-side structure, is often missing or underdeveloped, underscoring the radial deficiency.

This pattern helps distinguish it from brachial plexus palsy, which centers on nerve weakness rather than a fixed skeletal deformity; from a fractured clavicle, which is an acute injury with localized tenderness and no congenital forearm shortening; and from a wrist dislocation, which involves joint misalignment but not the fixed forearm shortening and absent thumb typical of radial dysplasia.