Which statement correctly describes the muscles acting on the thumb's first carpometacarpal joint?

Which statement correctly describes the muscles acting on the thumb's first carpometacarpal joint?

• A. The joint is moved primarily by abductors.
• B. The joint relies on the extensor muscles for opposition.
• C. The joint is stabilized by ligaments only with no muscular action.
• D. The joint is acted upon by flexor and opponens muscles.

Answer: (D)

Opposition at the thumb’s first carpometacarpal joint comes from a coordinated action of muscles that both flex and rotate the first metacarpal. The flexor pollicis longus (and flexor pollicis brevis) helps bend the thumb at the CMC joint, bringing the pad toward the palm, while the opponens pollicis rotates and brings the metacarpal across the palm to meet the other fingers. This combination enables touching the thumb pad to the fingertips, which is the essence of opposition. Abductors primarily move the thumb away from the hand and are not the main drivers of opposition. Extensor muscles are not the primary players in opposing the thumb; they extend or reposition rather than create the opposing pinch. Ligaments provide passive stabilization, but muscular action is what actually moves the joint. So the statement that the thumb’s first carpometacarpal joint is acted upon by flexor and opponens muscles captures the key movements needed for opposition.

Opposition at the thumb’s first carpometacarpal joint comes from a coordinated action of muscles that both flex and rotate the first metacarpal. The flexor pollicis longus (and flexor pollicis brevis) helps bend the thumb at the CMC joint, bringing the pad toward the palm, while the opponens pollicis rotates and brings the metacarpal across the palm to meet the other fingers. This combination enables touching the thumb pad to the fingertips, which is the essence of opposition.

Abductors primarily move the thumb away from the hand and are not the main drivers of opposition. Extensor muscles are not the primary players in opposing the thumb; they extend or reposition rather than create the opposing pinch. Ligaments provide passive stabilization, but muscular action is what actually moves the joint.

So the statement that the thumb’s first carpometacarpal joint is acted upon by flexor and opponens muscles captures the key movements needed for opposition.