**Core Concept**
In posterior dislocation of the hip joint, the femoral head is displaced posteriorly due to trauma, resulting in a characteristic positioning of the limb that reflects the biomechanics of joint stability and ligamentous constraints.

**Why the Correct Answer is Right**
Posterior dislocation of the hip occurs when the femoral head is displaced behind the acetabulum, typically due to high-energy trauma. The limb is positioned in **flexion, adduction, and internal rotation** because the soft tissues and ligaments pull the femur into these positions during dislocation. This alignment is due to the natural tension of the hip ligaments and the pelvic anatomy, which constrain the femoral head posteriorly. The internal rotation is particularly notable as it results from the femoral neck being pulled posteriorly and medially.

**Why Each Wrong Option is Incorrect**
Option A: Flexion, abduction, and external rotation is characteristic of **anterior dislocation**, not posterior. Abduction and external rotation are seen when the femur is displaced anteriorly, not posteriorly.
Option C: Flexion, adduction, and external rotation is not a standard finding; external rotation is inconsistent with posterior dislocation. This combination is more associated with other injuries or imaging artifacts.
Option D: Flexion, abduction, and internal rotation is not anatomically plausible—abduction contradicts the posterior displacement mechanism.

**Clinical Pearl / High-Yield Fact**
Remember the mnemonic: **"Posterior = Flexion, Adduction, Internal Rotation"** — this is a classic exam trap. Confusing it with anterior dislocation (flexion, abduction, external rotation) is a common mistake. Always associate posterior dislocation with **internal rotation** and **adduction**, not abduction.

✓ Correct Answer: B. Flexion, adduction & internal rotation