Which muscle does not assist with opposition of the thumb?

Which muscle does not assist with opposition of the thumb?

• A. Flexor Pollicis Longus
• B. Opponens Pollicis
• C. Abductor Pollicis Brevis
• D. Adductor Pollicis

Answer: (A)

Opposition of the thumb is the movement that brings the thumb across the palm to touch the other fingers, especially the little finger. This relies on the thenar muscles working together to position and bring the thumb across the palm: Opponens pollicis rotates the thumb so it can cross over, Abductor pollicis brevis helps position and stabilize the thumb, and Flexor pollicis brevis flexes the MCP joint to pull the thumb toward the palm. Adductor pollicis helps with pinching by bringing the thumb toward the hand’s midline, supporting grip rather than the crossing motion itself. Flexor pollicis longus, however, is a forearm muscle that flexes the distal phalanx of the thumb at the IP joint (and assists flexion at the MCP), but it does not contribute to moving the thumb across the palm. Since it doesn’t participate in the opposition movement, it is the best choice.

Opposition of the thumb is the movement that brings the thumb across the palm to touch the other fingers, especially the little finger. This relies on the thenar muscles working together to position and bring the thumb across the palm: Opponens pollicis rotates the thumb so it can cross over, Abductor pollicis brevis helps position and stabilize the thumb, and Flexor pollicis brevis flexes the MCP joint to pull the thumb toward the palm. Adductor pollicis helps with pinching by bringing the thumb toward the hand’s midline, supporting grip rather than the crossing motion itself.

Flexor pollicis longus, however, is a forearm muscle that flexes the distal phalanx of the thumb at the IP joint (and assists flexion at the MCP), but it does not contribute to moving the thumb across the palm. Since it doesn’t participate in the opposition movement, it is the best choice.