**Core Concept**
The popliteus muscle is a deep muscle of the posterior compartment of the leg that plays a crucial role in knee movement. It is involved in the unlocking mechanism of the knee joint, allowing for flexion and extension of the knee.

**Why the Correct Answer is Right**
The popliteus muscle is actually inserted on the lateral surface of the lateral femoral condyle and the posterior aspect of the tibia, not the medial meniscus. This insertion allows the popliteus to rotate the femur on the tibia, unlocking the knee joint and enabling flexion and extension movements. The correct function and insertion of the popliteus muscle are essential for understanding knee joint mechanics.

**Why Each Wrong Option is Incorrect**
**Option A:** Flexes the knee - While the popliteus muscle does contribute to knee flexion, its primary function is to unlock the knee joint, allowing for flexion and extension movements.
**Option B:** Unlocks the knee - This statement is true, as the popliteus muscle is responsible for rotating the femur on the tibia, unlocking the knee joint.
**Option D:** Intracapsular - The popliteus muscle is actually an extracapsular muscle, meaning it lies outside the joint capsule of the knee.

**Clinical Pearl / High-Yield Fact**
The popliteus muscle is often injured in sports that involve sudden changes of direction, such as football or soccer, due to its role in knee joint mechanics. Understanding the anatomy and function of the popliteus muscle is essential for diagnosing and managing knee injuries.

**✓ Correct Answer: C. Inserted on medial meniscus**