Costochondritis

Costochondritis is inflammation of the costochondral junctions — where the ribs meet their cartilage near the sternum. It's a benign musculoskeletal condition, but its clinical importance on USMLE Step 1 comes entirely from one thing: it's the answer when you need to distinguish MSK chest pain from cardiac or pulmonary causes. The exam loves to give you a young patient with sharp, reproducible chest pain and test whether you recognize that palpation-reproducible tenderness over the costochondral junctions points away from the heart, not toward it.

The way Step 1 tests this is usually through a short clinical vignette where the key discriminating detail is that pressing on the chest wall reproduces the pain. Students who don't have this concept locked in will read 'chest pain' and start chasing ACS or PE. The exam wants you to pivot on that one finding — reproducible tenderness on palpation — and confidently call it MSK. The differential angle (cardiac vs pulmonary vs MSK) is the main vehicle for this, and costochondritis is the prototypical MSK diagnosis in that list.

The trickiest part isn't the diagnosis itself — it's the Tietze syndrome distinction, which catches students off guard. Most students either don't know Tietze exists or lump it together with costochondritis. They're related but distinct: Tietze syndrome involves visible or palpable swelling at the junction (usually ribs 2–3), while costochondritis does not. That swelling detail is a classic low-yield fact that occasionally shows up as a one-liner differentiator, so it's worth having in your back pocket for USMLE Step 1.