Q. Why does arthritis tend to develop in joints that have experienced trauma earlier in life?

A. The condition known as post-traumatic arthritis develops after about half the cases of traumatic joint injury. These cases make up about 12 percent of all osteoarthritis cases, according to the National Institutes of Health, making post-traumatic arthritis a leading cause of disability, especially in wounded soldiers.

The pathway that leads from joint injury and misalignment to arthritis in the whole joint later in life has not been conclusively studied, government experts say.

Some steps that are suspected to be part of this pathway are the self-destruction of cartilage cells after the trauma, so that there are not enough of them to support the cartilage matrix that holds the joint, and a cascade of inflammatory responses within the joint, leading to degeneration of the cartilage.

Treatment of traumatic joint injury is usually limited to restoration of the surface where the bones meet, and realignment of the joint. A way to prevent subsequent arthritis has not been proven.