A 24 year old previously healthy left handed male professional baseball pitcher was warming up on the mound before a game when he suddenly felt a vague pain in his lower left anterior-lateral rib cage region but denied hearing a pop. Pain was a localized deep ache on the lower anterior rib cage. Although he felt discomfort the player was able to complete his warm up regimen and start the game. During the game he was only able to throw four pitches prior to unbearable pain during the acceleration phase of pitching causing him to be pulled from the game and seek medical attention. PHYSICAL EXAM: Normal appearance of the chest wall. Point tenderness to palpation and a 1x1cm soft tissue mass on the lower left anterior chest wall on palpation. Any active and passive motion of the torso exacerbated the pain and the mass was exquisitely tender to palpation. Bilateral shoulder exams were within normal limits and pain was not affected by inhalation or exhalation. On exam, he was neurologically and vascularly intact. There was no winging of the scapula or crepitus along the rib cage. DIFFERENTIAL DIAGNOSIS: 1. Oblique muscle strain 2. Rib stress fracture 3. Costochondral junction avulsion fracture 4. Serratus anterior avulsion fracture 5. Intercostal muscle strain TEST AND RESULTS: Thoracic MRI findings suggested either a fracture or stress injury of the costochondral cartilage along the left anterior-inferior aspect of the ribcage. There was extensive edema present along the region that measured 8x10 cm but there was no evidence of rib fractures. Chest CT without contrast revealed edema around the costochondral junction of ribs 7 and 8 on the left with anterior prominence of the cartilage but no focal displacement or rib fractures. FINAL WORKING DIAGNOSIS: Based on Imaging, injury most likely to be costochondral junction avulsion fracture of ribs 7 and 8. TREATMENT AND OUTCOMES: The player was initially treated with 6 weeks of activity restriction and rest. Surgery was not warranted due to lack of significant separation of the fragment. Repeat radiographs were obtained at 6 weeks which revealed proper healing. After 6 weeks he began a graduated pitching regimen. Pain improved throughout his rehabilitation with rest and NSAIDS once he began physical activity. He returned to full activity at 8 weeks.