In the hand anatomy, Structure A corresponds to the first carpometacarpal joint in the thumb. Which joint is this?

In the hand anatomy, Structure A corresponds to the first carpometacarpal joint in the thumb. Which joint is this?

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

Answer: (B)

The main idea here is identifying the joint at the base of the thumb. The first carpometacarpal joint is the articulation between the trapezium (one of the wrist bones) and the base of the first metacarpal. This joint is a saddle joint, which gives the thumb its wide range of motion and the ability to oppose the fingers. That’s what lets the thumb move in multiple directions and touch the other fingertips. The other options describe joints in the fingers rather than at the thumb’s base: a proximal interphalangeal joint and a distal interphalangeal joint are joints between phalanges of the fingers (hinge joints), and the second metacarpophalangeal joint is the MCP of the index finger (between the second metacarpal and the proximal phalanx).

The main idea here is identifying the joint at the base of the thumb. The first carpometacarpal joint is the articulation between the trapezium (one of the wrist bones) and the base of the first metacarpal. This joint is a saddle joint, which gives the thumb its wide range of motion and the ability to oppose the fingers. That’s what lets the thumb move in multiple directions and touch the other fingertips.

The other options describe joints in the fingers rather than at the thumb’s base: a proximal interphalangeal joint and a distal interphalangeal joint are joints between phalanges of the fingers (hinge joints), and the second metacarpophalangeal joint is the MCP of the index finger (between the second metacarpal and the proximal phalanx).