Osteonecrosis of the Knee: A narrative review

Historically, osteonecrosis of the knee was described as a progressive disease of three distinct pathologies: spontaneous, secondary, and post-arthroscopic. These were differentiated by etiology. More recently, the classical definitions have been under scrutiny due to an evolving understanding of underlying subchondral insufficiency fractures of the knee that lead to bony resorption and subchondral collapse. Research in spontaneous osteonecrosis discussing the biomechanical alterations caused by these subchondral insufficiency fractures have presented conflicting patterns. While spontaneous osteonecrosis of the knee was originally considered ischemic or traumatic, some describe the initial insult of these insufficiency fractures as the cause of bone death, subsequent loss of vascularity, and ultimately osteonecrosis, likely secondary to the underlying fracture. Others indicate these insufficiency fractures may instead represent a natural progression toward osteoarthritis. As current literature has yet to clarify whether subchondral insufficiency fracture is the root cause of spontaneous osteonecrosis of the knee, future research is still needed to determine the relationship of subchondral insufficiency fractures to spontaneous osteonecrosis or osteoarthritis. Beyond definitions, magnetic resonance imaging has improved identification of knee osteonecrosis, and novel treatment modalities have begun to describe both conservative and operative management. It is essential to delineate etiologies of osteonecrosis of the knee because of the distinct approach to their management. Thus, determining the pathogenesis of osteonecrosis is necessary to improve the understanding of avascular necrosis, which may further elucidate how osteonecrosis is considered elsewhere in the body. In this paper, we explore recent evidence that may drive better decision making and long-term outcomes for patients with osteonecrosis of the knee.