Causes of Pain in Early Stage and Advanced Stage of Non-traumatic Osteonecrosis

Non-traumatic osteonecrosis (ON) is a progressive bone disease with poorly understood natural history, pathophysiology, and pain etiology. While many cases are diagnosed incidentally in asymptomatic patients, pain typically develops as the disease advances, often correlating with specific pathological changes. Early-stage pain is frequently associated with increased intraosseous pressure, bone marrow edema, and inflammation. In later stages, pain results from subchondral fractures, joint effusion, and degenerative changes. Accurate diagnosis of pain origin is essential for targeted treatment, as timely intervention prior to subchondral collapse offers the best chance for joint preservation. This chapter explores the sources of pain in both early and advanced stages of non-traumatic ON.