**Core Concept**
McEwen's triangle is an anatomical landmark used in orthopedic surgery, specifically in the reduction of hip fractures. It is defined by the relationship between the **iliopectineal line**, the **intertrochanteric line**, and the **femoral neck**. Understanding this triangle is crucial for accurate reduction and fixation of hip fractures.

**Why the Correct Answer is Right**
The correct answer choice is related to the definition and application of McEwen's triangle in orthopedic surgery. This triangle helps in assessing the alignment and positioning of the femoral head in relation to the acetabulum, which is vital for the stability and function of the hip joint. The **iliopectineal line** and **intertrochanteric line** serve as key references for this assessment.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it does not accurately describe a recognized aspect of McEwen's triangle.
**Option B:** Similarly, this option is incorrect as it misrepresents the anatomical relationships involved in McEwen's triangle.
**Option C:** This choice is also incorrect because it does not align with the established definition or clinical use of McEwen's triangle.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that McEwen's triangle is particularly useful in the context of **femoral neck fractures** and their reduction. It aids in evaluating the adequacy of fracture reduction, which is critical for preventing complications such as **avascular necrosis**.

**Correct Answer:** D. McEwen's triangle is related to the alignment of the femoral head and neck in hip fractures.