A healthy young athlete sitting at table with knee at 90deg flexion. What will happen when he fully extends the knee?
**Core Concept**
The underlying principle being tested is the anatomy and physiology of the knee joint, specifically the movement of the patella and the quadriceps mechanism during knee extension. The **knee joint** is a complex hinge joint that allows for flexion and extension, with the **patella** embedded within the **quadriceps tendon**.
**Why the Correct Answer is Right**
When the knee is fully extended, the **patella** moves proximally into the **femoral groove**, increasing the contact area between the **patella** and the **femur**. This movement helps to increase the efficiency of the **quadriceps mechanism**, allowing for more effective knee extension.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the movement of the patella during knee extension is proximal, not distal.
**Option B:** This option is incorrect because the contact area between the patella and femur increases, rather than decreases.
**Option C:** This option is incorrect because the quadriceps mechanism becomes more efficient, rather than less efficient.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the **quadriceps mechanism** plays a crucial role in knee extension, and any disruption to this mechanism can lead to significant functional impairment.
**Correct Answer:** D. The patella moves proximally into the femoral groove.