**Core Concept**
Myositis ossificans is a condition characterized by the heterotopic ossification of soft tissue, resulting in the formation of bone within muscles. This process involves the abnormal deposition of bone tissue in areas where it is not normally present, often following trauma or injury.

**Why the Correct Answer is Right**
Myositis ossificans typically occurs in response to soft tissue injury, leading to the activation of various cell types, including osteoblasts and osteoclasts. The injury triggers an inflammatory response, which, in turn, stimulates the differentiation of mesenchymal stem cells into osteoblasts, resulting in the formation of ectopic bone. This process is often seen in areas such as the muscles of the arm, neck, and thigh.

**Why Each Wrong Option is Incorrect**
**Option A:** Myositis ossificans is not a form of osteoarthritis, which involves the degeneration of joint cartilage and underlying bone. While both conditions involve bone formation, they are distinct entities with different underlying pathologies.

**Option B:** Myositis ossificans is not a type of fibromyalgia, which is a chronic condition characterized by widespread muscle pain and tenderness. While myositis ossificans may present with muscle pain, its underlying cause is the formation of ectopic bone, not a disorder of muscle pain perception.

**Option C:** Myositis ossificans is not a form of rhabdomyolysis, which involves the breakdown of muscle tissue, often resulting in the release of muscle enzymes into the bloodstream. While both conditions involve muscle tissue, they are distinct entities with different underlying pathologies.

**Clinical Pearl / High-Yield Fact**
It's essential to note that myositis ossificans can lead to decreased mobility and function in the affected limb, making early diagnosis and treatment crucial to prevent long-term complications.

**Correct Answer:** C. Heterotopic ossification of soft tissue following trauma or injury.