Subchondral insufficiency fracture of the knee.

Subchondral insufficiency fractures of the knee (SIFK) are a relatively common cause of knee pain, particularly in middle-aged and older adults. The SIFK is a type of stress fracture that occurs when excessive and repetitive or supraphysiologic loads are applied to subchondral bone [1]. Historically, this type of fracture was termed spontaneous osteonecrosis of the knee (SONK) until advances in MRI identified underlying fractures as well as meniscal deficiency as likely attributable etiologies. Consequently, SIFK has replaced SONK as the more appropriate term to refer to this category of conditions, with SONK now viewed as an advanced SIFK lesion. With greater availability of MRI, SIFK has been more frequently recognized and not as commonly mistaken for knee osteoarthritis as it had been in the past, with important implications for treatment and management of this condition.