Which muscle groups act on the first carpometacarpal joint to allow thumb function, including flexion and opposition?

Which muscle groups act on the first carpometacarpal joint to allow thumb function, including flexion and opposition?

• A. Abductor pollicis longus and extensor pollicis brevis
• B. Flexor pollicis longus and extensor pollicis longus
• C. Flexor and opponens
• D. Adductor pollicis and abductor pollicis brevis

Answer: (C)

At the first carpometacarpal joint, thumb function that matters for grip and precision relies on two key actions: flexion and opposition. Flexion at this joint is produced by the flexor pollicis longus crossing the joint and pulling the metacarpal toward the palm. Opposition is achieved mainly by the opponens pollicis, a muscle of the thenar group that wraps around the first metacarpal to rotate it medially, bringing the thumb pad into contact with the other fingers. When these two muscles work together, the thumb can be flexed and positioned to oppose the fingers, enabling pinching and fine manipulation. Other muscles crossing this joint primarily move the thumb in other directions (such as abduction or extension) and don’t combine the necessary flexion with the rotational positioning required for opposition, which is why the combination of a flexor and an opposer best explains thumb function at the CMC joint.

At the first carpometacarpal joint, thumb function that matters for grip and precision relies on two key actions: flexion and opposition. Flexion at this joint is produced by the flexor pollicis longus crossing the joint and pulling the metacarpal toward the palm. Opposition is achieved mainly by the opponens pollicis, a muscle of the thenar group that wraps around the first metacarpal to rotate it medially, bringing the thumb pad into contact with the other fingers. When these two muscles work together, the thumb can be flexed and positioned to oppose the fingers, enabling pinching and fine manipulation. Other muscles crossing this joint primarily move the thumb in other directions (such as abduction or extension) and don’t combine the necessary flexion with the rotational positioning required for opposition, which is why the combination of a flexor and an opposer best explains thumb function at the CMC joint.