Under normal circumstances, the human body will not cause bone marrow cavity effusion in the process of metabolism. There are several possible causes of bone marrow cavity effusion: 1. The most common is trauma, which can lead to bone marrow cavity effusion, which is a hemorrhagic fluid that may lead to exudation from the bone marrow cavity or the presence of blood, and the possibility of effusion, which can lead to local swelling, as well as pain when walking. 2. A point that causes fluid accumulation in the bone marrow cavity is the occurrence of osteomyelitis. Osteomyelitis, such as some osteomyelitis, can cause local swelling of the leg and pain after walking. And it can cause acute fever in the body, possibly high fever, such as suddenly reaching 39°C, 40°C or higher.