Association between medial meniscus extrusion and spontaneous osteonecrosis of the knee.

There was high association of medial meniscus extrusion and FTA with the radiological stage and volume of the SONK lesion. Increased loading in the medial femoral condyle with greater extrusion of medial meniscus and varus alignment may contribute to expansion and secondary osteoarthritic changes of a SONK lesion.