You're not alone in your questions. We know that osteonecrosis is the death of bone tissue. But spontaneous osteonecrosis (SON) is sudden, unexpected, and without known cause.
Some recent reports point to a possible increase in this condition in adults over age 60. At first doctors thought it was linked with arthroscopic surgery to remove a torn meniscus. But then five new cases were reported in patients who had meniscus degeneration but no surgery.
It appears that age-related wear and tear on the meniscus may be the start of the problem. But there are still many questions about what's going on. For example, in one study of five patients, symptoms of knee pain were identified as medial meniscal degeneration.
At the time of the diagnosis, there were no changes in the bone seen on an MRI. The patients were all treated with physical therapy, exercise, and noninflammatory drugs. Two months later the symptoms increased. A second MRI showed osteonecrosis of the knee.
What happened in those two months between MRIs? Doctors just aren't sure yet but further studies may offer some insight into SON.