Osteonecrosis of the Knee

Abstract

Spontaneous osteonecrosis of the knee (SONK) is the most common type of knee osteonecrosis. It causes subchondral bone damage and in the majority of cases leads to cartilage damage and secondary osteoarthritis. The etiology is commonly explained with two main theories, vascular and traumatic. Vascular theory is based on disrupture of bone blood supply which causes local ischaemia and subchondral bone necrosis. Traumatic theory suggests the development of subchondral insufficiency fractures due to mechanical overload, which causes local oedema, ischaemia and necrosis. SONK typically appears in middle age and older women, with acute onset of sharp pain in the medial femoral condyle without predisposing trauma. Considering that the characteristic radiological signs are not seen on conventional radiography until advanced stage, magnetic resonance imaging is the gold standard in diagnostics. Treatment depends on the size and stage of the osteonecrotic lesion. Small osteonecrotic lesions are usually successfully treated non-operatively, which is based primarily on protected weight bearing and physical therapy. Medium osteonecrotic lesions are treated either non-operatively or operatively, while large osteonecrotic lesions are almost always treated operatively. Most commonly used joint preserving procedures include arthroscopic bone marrow stimulation using microfracture technique, core decompression, osteochondral autologous or homologous transplantation, artificial graft transplantation, and medial opening-wedge high tibial osteotomy. The treatment of choice after subchondral bone collapse is knee arthroplasty.