Action of quadratus femoris is –
**Core Concept**
The quadratus femoris muscle is a deep muscle in the posterior thigh, which plays a crucial role in hip joint movements. It is one of the muscles that contribute to the lateral rotation of the femur (thigh bone) around the long axis of the hip joint.
**Why the Correct Answer is Right**
The quadratus femoris muscle acts to laterally rotate the femur, which is essential for movements such as walking and climbing stairs. This action is made possible by the muscle's attachment to the femur and the ischial tuberosity, allowing it to rotate the femur around the hip joint. The quadratus femoris muscle also assists in the extension and medial rotation of the hip joint.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the quadratus femoris muscle does not primarily act to flex the hip joint. While it does contribute to hip joint movements, its primary action is lateral rotation.
**Option B:** This option is incorrect as the quadratus femoris muscle does not primarily act to abduct the hip joint. Abduction of the hip joint is primarily performed by the gluteus medius and gluteus minimus muscles.
**Option C:** This option is incorrect as the quadratus femoris muscle does not primarily act to extend the hip joint. While it does contribute to hip joint extension, its primary action is lateral rotation.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the quadratus femoris muscle is a deep muscle in the posterior thigh, and its primary action is lateral rotation of the femur around the hip joint. This knowledge is crucial for understanding hip joint movements and the function of the muscles in the posterior thigh.
**Correct Answer:** C. Lateral rotation of the femur.