**Core Concept**
The popliteal artery is a vital blood vessel that runs through the popliteal fossa, the back of the knee. It is susceptible to injury in the presence of a fracture of the lower end of the femur due to its anatomical location and proximity to the fracture site.

**Why the Correct Answer is Right**
The popliteal artery is at risk of injury during a fracture of the lower end of the femur because of its close proximity to the fracture site. When the femur is fractured, the surrounding soft tissues, including the popliteal artery, are subjected to mechanical stress and potential trauma. This can cause damage to the arterial wall, leading to a popliteal artery injury. The popliteal artery is a superficial structure and is relatively unprotected by surrounding muscles or bones, making it more susceptible to injury.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the scenario of a fracture of the lower end of the femur.
**Option B:** This option is not directly related to the anatomy of the knee or the popliteal artery.
**Option C:** This option is not a known cause of popliteal artery injury in the context of a femoral fracture.

**Clinical Pearl / High-Yield Fact**
In the setting of a femoral fracture, it is essential to assess the popliteal artery for potential injury, as this can lead to significant morbidity if left untreated. A thorough physical examination and imaging studies, such as angiography, may be necessary to diagnose and manage popliteal artery injuries.

**Correct Answer:** C.