**Core Concept**
The question tests the understanding of spinal cord anatomy and its blood supply, particularly in the context of thoraco-abdominal aortic aneurysm repair. The **spinal cord** relies on a network of arteries, including the **anterior spinal artery** and **posterior spinal arteries**, for its blood supply.

**Why the Correct Answer is Right**
The most probable cause of paralysis of both lower limbs after thoraco-abdominal aneurysm repair is **ischemia of the spinal cord** due to disruption of its blood supply, particularly the **artery of Adamkiewicz**, which is a critical branch supplying the lower two-thirds of the spinal cord. This artery often originates from the lower thoracic or upper lumbar aorta, areas commonly involved in thoraco-abdominal aneurysm repairs.

**Why Each Wrong Option is Incorrect**
**Option A:** Not provided, assuming it's not related to spinal cord ischemia.
**Option B:** Not provided, assuming it doesn't involve disruption of spinal cord blood supply.
**Option C:** Not provided, assuming it's unrelated to the critical arteries supplying the spinal cord.
**Option D:** Not provided, but typically, options like these might involve other complications not directly related to spinal cord ischemia.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the **artery of Adamkiewicz** is crucial for the blood supply to the lower spinal cord, and its disruption can lead to **paraplegia**. Monitoring for spinal cord ischemia and strategies to preserve its blood supply are critical during thoraco-abdominal aneurysm repairs.

**Correct Answer:** D. Ischemia of the spinal cord.