Which muscle would produce pain with radial deviation in a patient with de Quervain's tendonitis?

In the context of de Quervain's tendonitis, the muscle most associated with pain during radial deviation is the abductor pollicis longus. This condition specifically affects the tendons of the muscles that control thumb movement, particularly those involved in radial deviation and thumb abduction.

The abductor pollicis longus is responsible for moving the thumb away from the hand (abduction) and assists in radial deviation of the wrist. When a patient with de Quervain's tendonitis attempts this movement, the inflamed tendon can cause significant pain, typically felt along the radial side of the wrist and into the thumb.

Understanding the role of the abductor pollicis longus is crucial in recognizing the symptoms and the specific actions that exacerbate the pain in this condition, allowing for effective diagnosis and treatment strategies.