For MCP Flexion of the Thumb, which structure serves as the proximal landmark during measurement?

• A. Dorsal midline metacarpal
• B. Lateral metacarpal
• C. Proximal ulna border
• D. Volar midline metacarpal

Answer: (A)

In measuring MCP flexion of the thumb, you anchor the stationary arm of the goniometer to a reliable reference on the proximal segment—the first metacarpal. Using the dorsal midline of that metacarpal as the proximal landmark provides a stable, consistent path that follows the bone’s long axis and is less affected by soft tissue or tendon movement on the palm side. This orientation lets the moving arm track along the proximal phalanx as the thumb flexes toward the palm, giving an accurate and repeatable measure of MCP flexion. The other options either do not reflect the standard proximal reference for this joint or are unsuitable because they can introduce variability or are unrelated to the thumb’s MCP joint.