Which two muscles are the primary wrist extensors on the posterior forearm?

• A. Extensor carpi ulnaris and extensor digitorum
• B. Flexor carpi radialis and flexor carpi ulnaris
• C. Extensor digiti minimi and extensor pollicis longus
• D. Extensor carpi radialis longus and extensor carpi radialis brevis

Answer: (D)

Wrist extension is carried out mainly by the extensor muscles on the back (posterior) of the forearm. Among these, the two muscles that act primarily to extend the wrist are the extensor carpi radialis longus and the extensor carpi radialis brevis. They cross the wrist and attach to the bases of the second and third metacarpals, so their pull lifts the back of the hand upward at the radiocarpal joint. The longus adds some radial deviation (thumb-side movement) when the wrist is extended, while the brevis provides most of the pure wrist-extension strength.

Other choices involve muscles that either extend fingers or the thumb, or that flex the wrist from the anterior forearm, or that mainly assist with wrist movements other than pure extension. Extensor carpi ulnaris and extensor digitorum do extend the wrist to some degree, but they are not the primary wrist extensors.