Wrist extension is primarily due to which nerve and muscles?

• A. C6, C7, C8, radial nerve - extensor carpi radialis longus and brevis, extensor carpi ulnaris
• B. C5, C6 - deltoid
• C. C7, C8 - flexor carpi radialis
• D. C8, T1 - first dorsal interosseous

Answer: (A)

Wrist extension is produced by muscles in the posterior forearm that are innervated by the radial nerve. The primary movers are the extensor carpi radialis longus, extensor carpi radialis brevis, and extensor carpi ulnaris. These muscles extend the wrist (and the ECRL/ECRB also help with some radial deviation), and their nerve supply comes from the radial nerve with root contributions around C6 to C8. This combination best fits the description of wrist extension.

Deltoid would not be involved in wrist extension; it’s a shoulder abductor innervated by the axillary nerve (C5-C6). Flexor carpi radialis is a wrist flexor in the anterior forearm, innervated by the median nerve (C6-C7). The first dorsal interosseous is an intrinsic hand muscle for finger abduction, innervated by the deep branch of the ulnar nerve (C8-T1).