While doing your rounds, you see two individuals. First is James, a 14-year-old boy who came in for chronic right knee pain, night sweats, and weight loss. He didn’t report falling or any other trauma to the region or any additional symptoms. On examination, his right knee is slightly larger than the left and, on palpation, a hard mass can be felt on the metaphysis of his right femur, close to the knee region. Then you see William, who’s 22 years old and complains of a 1-month history of bone pain along his left tibia, a problem which is worse at night. One interesting observation he made was that the pain responds well to Ibuprofen, a nonsteroidal anti-inflammatory drug. On examination, palpation reveals a bony mass on the anterior surface of the left tibial diaphysis. As expected, X-ray scans were obtained. They showed a distal sunburst appearance and Codman's triangle in James’ right femur, whereas William’s x-ray scans detected a small lesion under 2 centimeters with a radiolucent core on the anterior surface of his left tibia.
Now, both seem to have some type of bone tumor. But first, a bit of physiology. Even though the bones vary in size and shape, all bones are made of the same types of cells, and chief among them are osteoblasts which build up new bone, and osteoclasts which help with bone breakdown or resorption. Now in addition to these, there are some more primitive cells in the bone marrow called human mesenchymal stem cells and neuroectodermal cells, which can differentiate into many cell types including nerve, fat, bone, and cartilage cells. In terms of anatomy, looking at a long, bone like the femur, it has two epiphysis, which are the ends that contribute to joints with other bones. Between the two epiphyses, is the diaphysis, also called the bone shaft. In children and adolescents, there is an additional narrow portion between the epiphysis and the diaphysis called the metaphysis. The metaphysis contains the growth plate, the part of the bone that grows during childhood. In adults, the growth plate has ossified and fused with the diaphysis and the epiphysis.