In the hand anatomy, Structure A corresponds to which joint?

In the hand anatomy, Structure A corresponds to which joint?

• A. First proximal interphalangeal joint
• B. First carpometacarpal joint
• C. Second distal interphalangeal joint
• D. Second metacarpophalangeal joint

Answer: (B)

This item tests identifying the carpometacarpal joint of the thumb—the articulation between the trapezium and the first metacarpal at the base of the thumb. This joint is a saddle type, giving the thumb its wide range of motion including opposition. The other options refer to joints located elsewhere or have naming that doesn’t apply to the thumb: the thumb does not have a proximal interphalangeal joint like the other fingers (it has an interphalangeal joint between the proximal and distal phalanges), the distal interphalangeal joint listed is in a different finger, and the metacarpophalangeal joint mentioned is in the index finger.

This item tests identifying the carpometacarpal joint of the thumb—the articulation between the trapezium and the first metacarpal at the base of the thumb. This joint is a saddle type, giving the thumb its wide range of motion including opposition. The other options refer to joints located elsewhere or have naming that doesn’t apply to the thumb: the thumb does not have a proximal interphalangeal joint like the other fingers (it has an interphalangeal joint between the proximal and distal phalanges), the distal interphalangeal joint listed is in a different finger, and the metacarpophalangeal joint mentioned is in the index finger.