A-12-year-old boy presents with chronic knee pain for 2 years. Knee X-ray is shown. Probable diagnosis:
**Core Concept**
The question tests the ability to identify a common cause of chronic knee pain in children and adolescents, which is often related to growth plate abnormalities. The underlying principle involves the understanding of growth plates, their development, and potential disorders.
**Why the Correct Answer is Right**
The X-ray likely shows a characteristic "corner" sign, indicating a diagnosis of Osgood-Schlatter disease (OSD). OSD is a common overuse injury in adolescents, typically affecting the tibial tuberosity, where the patellar tendon inserts. This condition is caused by repetitive tension on the patellar tendon, leading to inflammation and irritation of the growth plate at the tibial tuberosity. The growth plate is the weak link in this area, making it susceptible to injury.
**Why Each Wrong Option is Incorrect**
**Option A:** Osteochondritis dissecans is a condition where a piece of cartilage and bone becomes detached from the surrounding bone, often due to a traumatic injury. This does not match the chronic presentation and location described in the question.
**Option B:** Sinding-Larsen-Johansson syndrome is another overuse injury affecting the knee, but it involves the inferior pole of the patella. The X-ray findings and clinical presentation would differ from OSD.
**Option C:** Patellar tendinosis is a condition affecting the patellar tendon, but it is more common in adults and does not typically present with a growth plate abnormality.
**Clinical Pearl / High-Yield Fact**
Remember the "corner" sign on X-ray, which is characteristic of Osgood-Schlatter disease. This condition often affects adolescents and is caused by repetitive tension on the patellar tendon, leading to inflammation and irritation of the growth plate.
**Correct Answer: C. Patellar tendinosis**