During full extension of the knee, the joint is 'locked' so that standing requires minimal muscular effort. Which muscle initiates unlocking of the knee at the start of flexion from the fully extended position?
- A Popliteus ✓
- B Gastrocnemius
- C Plantaris
- D Biceps femoris
Correct answer: A. Popliteus
Explanation
In terminal rotation the femur rotates medially on the fixed tibia to lock the extended knee. The popliteus, acting on its tibial attachment, laterally rotates the femur relative to the tibia to unlock the joint before flexion begins. Biceps femoris flexes and laterally rotates the knee but does not perform this specific unlocking action, which is the classic function tested here.
Reference: Gray's Anatomy for Students, 4th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.