AVN / SONK / Stress fracture of the knee

An uncommon cause of knee pain is AVN of the knee. This condition is poorly understood. Initially, it was thought that the blood supply to a portion of the bone in the knee was interrupted and this caused pain. This was called AVN (avascular necrosis) or SONK (spontaneous osteonecrosis knee).

More recently it has been thought that the actual precipitating event is a stress fracture.

All of these terminologies are still used to varying degrees especially by radiologists reporting MRI scans of the knee.

My view is that this condition is often a stress fracture.

Symptoms and Treatment

This condition normally occurs in people over the age of 40. Often it occurs soon after a tear of a meniscal cartilage or even after knee arthroscopy.

It is associated with the rapid onset of intense pain in the knee. Often it is not possible to take weight on the affected leg.

The treatment of this condition is difficult. If the pain occurs in association with a newly torn meniscal cartilage then resection of the cartilage via arthroscopy can be performed.

A period of non weight bearing will usually be required, this is often difficult for more elderly patients.

With non weight bearing for a period of time the symptoms can settle and the stress fracture heal. Sometimes however, particularly if weight is taken through the limb, the affected bone can collapse and knee replacement is required.