**Core Concept**
Tuberculosis of the spine, also known as Pott's disease, is a form of osteoarticular tuberculosis that primarily affects the vertebral bodies, intervertebral discs, and adjacent structures. The infection is caused by Mycobacterium tuberculosis and is characterized by caseous necrosis, inflammation, and destruction of the affected vertebrae.

**Why the Correct Answer is Right**
The disease typically involves the anterior (front) part of the vertebra, including the vertebral body, the intervertebral disc, and the adjacent anterior longitudinal ligament. This is because the anterior aspect of the vertebra receives a rich blood supply, which facilitates the spread of the infection. The involvement of the anterior part of the vertebra leads to the characteristic collapse of the vertebral body and the formation of a gibbus deformity.

**Why Each Wrong Option is Incorrect**
**Option A:** The posterior (back) part of the vertebra is less commonly affected, but it can be involved in more advanced cases or as a result of secondary changes. However, the posterior elements are not the primary site of infection.
**Option B:** Although the intervertebral disc can be involved, the disc space is typically narrowed and destroyed, rather than being a separate entity.
**Option C:** The facet joints can be affected, but this is not as common as the involvement of the anterior part of the vertebra.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that Pott's disease often presents with non-specific symptoms, such as back pain, fever, and weight loss, and a delayed diagnosis can lead to significant morbidity and mortality. A high index of suspicion and early diagnosis are crucial in managing this condition effectively.

**Correct Answer:** A.