When a 65-year-old woman in South Korea went to the doctor because of worsening knee pain, no one expected the scans to reveal anything unusual. The visit was supposed to be routine — another step in managing the osteoarthritis that had slowly been reshaping her daily life.

Instead, doctors found something that stopped them cold.

For years, she had lived with osteoarthritis, a condition that quietly erodes the cartilage meant to cushion the joints. At first, it was stiffness in the morning. Then swelling. Then pain that lingered long after she sat down to rest. Simple things — climbing stairs, standing up from a chair, walking more than a few minutes — became exhausting calculations of how much discomfort she could tolerate.