**Core Concept**
Costochondral junction swelling is a clinical manifestation associated with inflammation, trauma, or systemic diseases affecting the costochondral joints. The costochondral joints are cartilaginous connections between the costal cartilages and the ribs, which allow for flexibility and movement of the thoracic cage.

**Why the Correct Answer is Right**
The correct answer is related to Tietze's syndrome, a condition characterized by inflammation of the costochondral joints, leading to pain, swelling, and tenderness. This condition is often caused by viral infections, such as herpes simplex or Epstein-Barr virus, but can also be associated with other systemic diseases like rheumatoid arthritis or systemic lupus erythematosus. The inflammation in Tietze's syndrome is thought to be mediated by the release of pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1β), which stimulate the production of prostaglandins and other mediators of inflammation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specifically relate to costochondral junction swelling. While conditions like costochondritis can cause pain and tenderness in the chest wall, they do not specifically involve swelling of the costochondral joints.
**Option B:** This option is incorrect because it refers to a condition that affects the intercostal muscles, not the costochondral joints. Intercostal muscle strain can cause pain and tenderness in the chest wall, but it does not typically involve swelling of the costochondral joints.

**Clinical Pearl / High-Yield Fact**
Remember that Tietze's syndrome is a clinical diagnosis that requires a combination of symptoms, including pain, swelling, and tenderness at the costochondral joints, as well as evidence of inflammation on imaging studies, such as ultrasound or MRI.

**Correct Answer: C. Tietze's syndrome**