Joints of lower limb: practice question

A Anatomy question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anatomy · Joints of lower limb

Sample item

In the knee, 'unlocking' at the start of flexion from full extension is brought about by which muscle?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Popliteus

In the last degrees of extension the femur rotates medially on the tibia, tightening ligaments and locking the knee. Popliteus laterally rotates the femur on the fixed tibia, which slackens the ligaments and unlocks the joint.

Option by option

  • A. Sartorius

    Sartorius is a weak flexor of the hip and knee and is not the unlocking muscle.

  • B. Gastrocnemius

    Gastrocnemius flexes the knee and plantar-flexes the ankle but does not rotate the femur to unlock.

  • C. Biceps femoris

    Biceps femoris flexes the knee and rotates the leg laterally but does not unlock the extended joint.

  • D. Popliteus (correct)

    Correct. Popliteus laterally rotates the femur on the tibia, releasing the locked position.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

More Anatomy questions

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is D, Popliteus. In the last degrees of extension the femur rotates medially on the tibia, tightening ligaments and locking the knee.

Why is "Sartorius" not the answer?

Sartorius is a weak flexor of the hip and knee and is not the unlocking muscle.

Why is "Gastrocnemius" not the answer?

Gastrocnemius flexes the knee and plantar-flexes the ankle but does not rotate the femur to unlock.

Why is "Biceps femoris" not the answer?

Biceps femoris flexes the knee and rotates the leg laterally but does not unlock the extended joint.

What concept does this question test?

It tests Joints of lower limb in Anatomy. Popliteus laterally rotates the femur on the fixed tibia, which slackens the ligaments and unlocks the joint.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Joints of lower limb?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.