Which muscle medially rotates the flexed knee?

• A. Gracilis
• B. Vastus Medialis
• C. Biceps Femoris
• D. Adductor Magnus

Answer: (A)

Medial rotation of the knee when it’s flexed is produced by muscles that cross the knee on its inner (medial) side and pull the tibia inward. Gracilis is one of the muscles that inserts on the medial tibia as part of the pes anserinus, so when the knee is bent it can pull the tibia medially to rotate the leg inward. This action is supported by other medial-crossing muscles as well, but gracilis directly contributes to rotating the flexed knee inward.

The other options don’t fit as well: the vastus medialis mainly extends the knee; the biceps femoris tends to rotate the leg laterally when the knee is flexed (not medially); and the adductor magnus primarily acts on the hip as an adductor. Thus, gracilis best matches the action of medially rotating the flexed knee.