Which Beighton criterion tests the thumb's ability to touch the forearm?

• A. Forward trunk flexion with palms on floor
• B. Hyperextension of the knee beyond 10 degrees
• C. Passive apposition of the thumb to the flexor aspect of the forearm
• D. Hyperextension of the elbow beyond 10 degrees

Answer: (C)

Beighton scoring includes a set of maneuvers to gauge overall joint mobility, and one of them specifically checks how far the thumb can move. The test involves passively bringing the thumb across to touch the flexor surface of the forearm. If the thumb can reach and contact the forearm, it indicates greater thumb mobility, which contributes to a higher Beighton score and suggests generalized joint hypermobility.

This criterion is distinct from the others: the trunk flexion test looks at how far you can bend forward with palms on the floor, while elbow and knee hyperextensions measure how far those joints can extend beyond a straight line. Neither of these directly assesses the thumb’s contact with the forearm, which is unique to the thumb apposition test.