How do joint injuries result in OA?

Chondrocytes are cells in the joint that produce cartilage. They normally die off (apoptosis) at a rate of less than 1 percent. But within 48 hours of trauma to a joint, the cell death rate shoots up dramatically—sometimes as high as 37 percent. The dying cells stimulate the release of enzymes that destroy cartilage, which in turn can lead to arthritis.