Transient spontaneous osteonecrosis of the knee (SONK) shortly after SARS-CoV-2 infection: A report of 2 cases

Background. This article describes 2 cases of post-coronavirus disease 2019 (COVID-19) transient spontaneous osteonecrosis of the knee (PCT-SONK) observed in patients who had previously recovered from COVID-19 without corticosteroid administration. Objectives. The possible pathomechanisms by which a recent SARS-CoV-2 infection may contribute as a causative factor for osteonecrosis are reviewed, and the differential diagnosis and treatment are discussed. Materials and methods. Two patients (males, 45- and 47-year-old) presented with sudden onset knee pain with no trauma history. The pain persisted during rest and at night. On magnetic resonance imaging (MRI), no subchondral bone thickening was observed; bone edema was diffusely distributed in the whole femoral condyle, in contrast to the more focal edema that is typically concentrated mainly around the subchondral region in classic SONK. Both patients were treated nonoperatively with no weight bearing and pharmacological agents, and complete resolution of symptoms was achieved. Results. A follow-up MRI 10 weeks after presentation revealed a near-complete loss of signal in the medial femoral condyle in both patients. Conclusions. Orthopedic surgeons should be cautious when sudden knee pain without concurrent trauma or a history of injury occurs shortly after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, even with mild COVID-19 illness. While some studies report the development of post-COVID-19 osteonecrosis after lower doses of corticosteroids and sooner after their administration than in comparable non- COVID-19 cases, our study is the first to report 2 cases with no corticosteroid administration at all. There-fore, the authors believe it adds to the body of knowledge on the potential connections between COVID-19 and PCT-SONK. The transient nature of symptoms and radiological findings suggest that aggressive surgical treatment of non-injury local bone edema occurring shortly after SARS-CoV-2 infection should be avoided.