First described in 1968, spontaneous osteonecrosis of the knee (SONK) is a distinct clinical entity that is a common cause of acute, unilateral knee pain and swelling. Unlike secondary osteonecrosis or post-arthroscopic osteonecrosis, there is no consensus with regards to the etiology of the condition. The disease is found in the medial femoral condyle most frequently (94%); however, it can also affect the lateral femoral condyle, patella, and proximal tibia. Given the nonspecific and insidious onset of spontaneous osteonecrosis of the knee, diagnosis and treatment can be challenging. Ultimately, it can lead to subchondral collapse, secondary osteoarthritis, and the need for surgical management.