Okay, let's tackle this question. The patient had a dissecting aneurysm of the thoracic aorta that ruptured and required emergency surgery. Post-op, he develops paraplegia. The question is asking which artery was injured during the operation leading to paralysis.

First, I need to recall the anatomical relationships of the thoracic aorta. The aorta runs through the thorax and abdomen, giving off various branches. The spinal cord is supplied by arteries like the anterior spinal artery and posterior spinal arteries, but the main one at risk here is the artery of Adamkiewicz, which is a major anterior radiculomedullary artery. This artery is crucial for the blood supply to the lower thoracic and lumbar regions of the spinal cord.

During surgery for a thoracic aortic aneurysm, especially if it's near the T6-T8 level where the artery of Adamkiewicz is commonly located, there's a risk of injury. If this artery is compromised, it can lead to ischemia of the spinal cord, resulting in paraplegia. The posterior intercostal arteries and other branches might be involved, but the artery of Adamkiewicz is the key one here.

Looking at the options, the correct answer would be the artery of Adamkiewicz. The other options might be other branches of the aorta, but they don't supply the spinal cord in the same way. The anterior spinal artery is a terminal artery, but the artery of Adamkiewicz is its main contributor. So if the artery of Adamkiewicz is injured, the anterior spinal artery can't compensate, leading to infarction of the spinal cord.

**Core Concept**
This question tests anatomical knowledge of spinal cord blood supply and surgical complications of thoracic aortic aneurysm repair. The **artery of Adamkiewicz**, a major anterior radiculomedullary artery, is the primary supplier of blood to the **T6-L1 segments** of the spinal cord. Injury to this vessel during aortic surgery is a classic cause of **paraplegia**.

**Why the Correct Answer is Right**
The **artery of Adamkiewicz** arises from the thoracic aorta (typically at T8-T12) and supplies the **anterior two-thirds of the spinal cord** below T6. During thoracic aortic surgery, clamping or direct injury to this vessel can cause **ischemic necrosis** of the spinal cord, leading to **flaccid paraplegia**. The high dependency of the lower spinal cord on this single artery makes it a critical surgical risk point.

**Why Each Wrong Option is Incorrect**
**Option A:** *Posterior intercostal arteries* supply the thoracic wall, not the spinal cord.
**Option B:** *Lumbar arteries* are terminal branches of the aorta and supply pelvic organs, not the spinal cord.
**Option C:** *Phrenic artery* is a branch of the internal thoracic artery and supplies the diaphragm.

**Clinical Pearl / High-Yield Fact**
The **artery of Adamkiewicz** is the most common cause of iatrogenic paraplegia after aortic surgery. It is usually the **only major blood supply** to the thoracolumbar spinal cord

✓ Correct Answer: D. Great radicular (of Adamkiewicz)