**Core Concept**
Pott's spine, also known as tuberculous spondylitis, is a form of spinal tuberculosis that can lead to significant morbidity if not managed properly. Identifying indicators of poor prognosis is crucial for guiding treatment decisions.

**Why the Correct Answer is Right**
A poor prognosis in Pott's spine is often associated with specific radiological and clinical features. A healed vertebral lesion suggests that the infection has been contained and may indicate a better prognosis. In contrast, a Grade 4 Pott's spine, characterized by severe vertebral body destruction and kyphotic deformity, is a marker of advanced disease and poor prognosis. A kyphotic angle greater than 60 degrees is also a sign of significant spinal deformity and instability, which can lead to further complications. Short duration of symptoms may not necessarily indicate a poor prognosis, as prompt treatment can lead to better outcomes. Acute onset of symptoms, however, may suggest a more aggressive form of the disease, which can be challenging to manage.

**Why Each Wrong Option is Incorrect**
**Option A:** Healed vertebral lesion is not a clear indicator of poor prognosis, as it suggests that the infection has been contained.
**Option B:** Grade 4 Pott's spine is a marker of advanced disease and poor prognosis, making this option correct but not the only correct answer.
**Option C:** Kyphotic angle greater than 60 degrees is a sign of significant spinal deformity and instability, which can lead to further complications, making this option correct.
**Option D:** Short duration of symptoms may not necessarily indicate a poor prognosis, as prompt treatment can lead to better outcomes.
**Option E:** Acute onset of symptoms may suggest a more aggressive form of the disease, which can be challenging to manage, making this option correct.

**Clinical Pearl / High-Yield Fact**
In Pott's spine, a kyphotic angle greater than 60 degrees is a critical threshold for determining the need for surgical intervention to prevent further spinal deformity and instability.

**Correct Answer:** C.