Deepening the subchondral insufficiency fracture and osteonecrosis of the knee dilemma: time for a new classification? – current concepts

Knee osteonecrosis (ON), often subclassified as spontaneous ON of the knee (SONK), secondary ON, and post-arthroscopic ON of the knee (PONK), is a common disorder often associated with suboptimal outcomes. Magnetic resonance imaging is the current gold standard for diagnosis, revealing bone marrow edema and subchondral fracture lines. Therapeutic methods range from conservative treatments, such as partial weight bearing, pharmaceutical interventions, and physical therapy, to surgical procedures in cases of advanced joint collapse. Available evidence from histological studies consistently shows the absence of bone necrosis, highlighting microfractures and bone remodeling as central features of these lesions. Therefore, the appropriateness of this terminology has recently been questioned, with knee ON being more accurately reinterpreted as subchondral insufficiency fractures of the knee (SIFK). This clinical problem stems from longstanding misclassification that has led to diagnostic confusion and inconsistent treatment approaches. Despite this progress, several unresolved issues persist. The precise biomechanical and biological factors that initiate SIFK remain unclear, and the optimal timing for intervention is still debated. In addition, long term outcomes of both nonoperative and operative treatments have yet to be definitively established. Addressing these gaps requires comprehensive clinical trials and advanced imaging studies that correlate histological findings with patient outcomes. This evolving understanding calls for a reclassification of knee ON lesions, aiming to enhance diagnostic accuracy and inform more effective, targeted treatment strategies.