## **Core Concept**
The question revolves around the diagnosis of hip pain and limp in an adolescent, pointing towards conditions affecting the hip joint or its surrounding structures. The differential diagnoses for hip pain in children and adolescents include transient synovitis, slipped capital femoral epiphysis (SCFE), Legg-Calvé-Perthes disease, and septic arthritis, among others.

## **Why the Correct Answer is Right**
Given the gradual development of symptoms over 3 months in a 14-year-old boy, the most likely cause of his symptoms is **Legg-Calvé-Perthes disease**. This condition is characterized by avascular necrosis of the femoral head, leading to fragmentation and potential collapse of the bone. It typically presents with hip pain and a limp, often with a gradual onset over several months. The condition is more common in children between the ages of 4 and 10 but can occur in adolescents.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Without a specific option provided, we can't directly address why it's incorrect, but conditions like septic arthritis typically present acutely with severe pain, fever, and significant limitation of movement, not gradually over months.
- **Option B:** Similarly, without specifics, conditions like transient synovitis have a more acute onset and are often associated with a recent viral illness; they usually resolve within a few weeks.
- **Option D:** Again, lacking specifics, conditions such as hip fractures or tumors could cause acute or gradual symptoms but are less common and usually have more distinctive features.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **Legg-Calvé-Perthes disease** often presents with referred pain to the knee or thigh, and patients may have limited range of motion, especially abduction and internal rotation of the hip. An important diagnostic clue is the presence of a "severe limp" and the fact that plain radiographs may show subtle changes early on, with MRI being more sensitive for early diagnosis.

## **Correct Answer: C. Legg-Calvé-Perthes disease**