A 6-year-old boy presents to the emergency department after a fall on his outstretched hand with elbow hyperextension. On AP radiograph, you identify the normal CRITOL ossification centers. The structure marked **C** (internal/medial epicondyle) is clearly visible as a separate ossification center. However, on the lateral view, you notice an additional ossification center at the joint line that appears to be displaced medially and is NOT in its expected anatomical position relative to the trochlea. The medial epicondyle ossification center is NOT visible in its normal location on the lateral view. What is the most likely diagnosis?