## **Core Concept**
The question tests knowledge of radiological findings in osteomyelitis, specifically the timeline for appearance of changes on X-ray. Osteomyelitis is an infection of bone, usually caused by bacteria. Early detection is crucial for effective management.

## **Why the Correct Answer is Right**
The correct answer, **periosteal reaction**, may not be visible until about 10-14 days after the onset of infection. However, subtle changes such as soft tissue swelling can be seen earlier. Within the first 8 days, the most reliable X-ray finding of osteomyelitis is often **soft tissue swelling** around the affected bone. This is because bone changes like lucency or sclerosis may not appear until later.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although periosteal reaction can be a sign of osteomyelitis, it typically appears later than 8 days.
- **Option B:** This is incorrect because, while bone destruction can occur in osteomyelitis, it usually takes longer than 8 days to become apparent on X-ray.
- **Option D:** This option is incorrect as there's no commonly recognized early X-ray sign of osteomyelitis by this description within the first 8 days.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that early osteomyelitis might not show significant changes on plain X-rays. **Soft tissue swelling** is often the earliest sign, and MRI is more sensitive for early detection of osteomyelitis.

## **Correct Answer:** . Soft tissue swelling.