**Core Concept**
The dial test is a clinical examination used to assess posterolateral corner (PLC) instability of the knee. It involves the patient's ability to rotate the knee while the foot is fixed on the ground, and it is considered positive if there is a significant external rotation.

**Why the Correct Answer is Right**
A positive dial test in the context of a left knee injury suggests PLC instability. This is because the PLC plays a crucial role in preventing excessive external rotation of the tibia relative to the femur. When the PLC is injured, the tibia may rotate excessively outward, leading to a positive dial test. The PLC includes structures such as the lateral collateral ligament, popliteus tendon, and biceps femoris tendon, which work together to stabilize the knee.

**Why Each Wrong Option is Incorrect**
**Option A:** Medial Collateral Ligament (MCL) Injury would typically result in a positive valgus stress test, not a positive dial test. MCL injuries are more likely to cause knee instability in the medial (inner) aspect of the knee.
**Option B:** Medial Meniscal Injury would not directly affect the dial test result, as the menisci are more involved in shock absorption and joint stability rather than rotational stability.
**Option C:** Lateral Meniscus Tear might cause some rotational instability, but it is less likely to result in a positive dial test compared to a PLC injury. The lateral meniscus is not as directly involved in the PLC as the structures mentioned above.

**Clinical Pearl / High-Yield Fact**
A positive dial test in a patient with knee trauma should raise suspicion for a PLC injury, which may require surgical evaluation and treatment to prevent further instability and potential complications.

**✓ Correct Answer: D. Posterolateral Corner Injury**