Which muscle is a synergist to pronator teres?

• A. Pronator quadratus
• B. Pronator teres
• C. Flexor carpi radialis
• D. Flexor digitorum superficialis

Answer: (A)

Pronation of the forearm relies on muscles that rotate the radius around the ulna, with pronator teres acting as a primary mover and pronator quadratus serving as a key synergist that assists that rotation and helps stabilize the distal radioulnar joint. The pronator quadratus sits deep in the forearm and pulls the distal ends of the radius and ulna together, directly supporting the teres’ pronation action. The other muscles here don’t primarily contribute to forearm rotation: flexor carpi radialis flexes and abducts the wrist, while flexor digitorum superficialis flexes the fingers (and some wrist flexion), so they aren’t involved as pronation synergists.