**Core Concept**
Myositis ossificans is a type of soft tissue ossification that occurs in response to trauma, characterized by the formation of bone tissue within muscles, tendons, or ligaments. This condition is distinct from other reactive fibroblastic proliferations due to its unique histological features.

**Why the Correct Answer is Right**
The presence of bone trabeculae and osteocytes within the proliferating fibroblastic tissue is a hallmark of myositis ossificans. This process is mediated by the differentiation of mesenchymal stem cells into osteoblasts, which then form bone matrix and calcify. The formation of bone tissue is a result of the body's attempt to repair the injured area, but it can lead to heterotopic ossification.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the presence of atypical cells or malignant features is not a characteristic of myositis ossificans. Myositis ossificans is a benign condition that is typically responsive to conservative management.

**Option B:** This option is incorrect because the presence of inflammation or infection is not a defining feature of myositis ossificans. While inflammation may be present in the surrounding tissue, the characteristic bone formation within the muscle or tendon is what distinguishes myositis ossificans from other conditions.

**Option C:** This option is incorrect because the presence of cartilage or chondroid matrix is not typical of myositis ossificans. While cartilaginous metaplasia can occur in response to injury, the formation of bone tissue is a more characteristic feature of myositis ossificans.

**Clinical Pearl / High-Yield Fact**
Myositis ossificans is often seen in young adults, particularly those involved in high-impact sports or activities. It can be challenging to diagnose, especially in its early stages, as the clinical presentation may be nonspecific. A high index of suspicion and imaging studies are often necessary to confirm the diagnosis.

**Correct Answer:** C. Heterotopic bone formation