summary Spontaneous osteonecrosis of the knee (SONK) is an idiopathic condition that leads to the development of a crescent shaped osteonecrosis lesion, mostly commonly in the epiphysis of the medial femoral condyle. Diagnosis can be radiographic for advanced disease but may require MRI in determining the extent of disease. Treatment is generally nonoperative as most cases are self-limiting. Surgical management is indicated for progressive cases that fail conservative management. Epidemiology Demographics most common in middle age and elderly affects females (>55yo) more frequently than males Anatomic location 99% of patients have only one joint involved usually epiphysis of medial femoral condyle Etiology Pathophysiology may represent a subchondral insufficiency fracture also believed to be caused by a meniscal root tear Presentation Symptoms sudden onset of severe knee pain effusion limited range of motion secondary to pain tenderness over medial femoral condyle Imaging Radiographs recommended views standing AP and lateral of hip, knee and ankle MRI most useful study is helpful to confirm the diagnosis and assist in determining the extent of disease helping guide treatment considerations lesion is crescent shaped Differential Must differentiate from osteochondritis dissecans more common on lateral aspect of medial femoral condyle in adolescent males transient osteoporosis more common in young to middle age men bone bruises and occult fractures associated trauma, bone fragility or overuse Treatment Nonoperative NSAIDs, narcotics, protected weight bearing indications mainstay of treatment as most cases resolve technique physical therapy directed at quadriceps strengthening outcomes initial conservative measure and has shown good results Operative arthroplasty indications when symptoms fail to respond to conservative treatment outcomes successful results reported with TKA (larger lesions or bone collapse) and UKA (smaller lesions) when properly indicated high tibial osteotomy indications when angular malalignment present