To evaluate patients diagnosed with subchondral insufficiency fractures of knee (SONK) and undergo treatment, and describe the surgical conversion rate and prognosis of patients with different imaging manifestations.

Patients who were diagnosed as SONK in the First Affiliated Hospital of Fujian Medical University from January 2013 to February 2022 were retrospectively analyzed. The sex, age, (body mass index, BMI), X-ray Koshino grade, Sayyid grade of MRI and meniscus condition (whether protruding or torn) were recorded and analyzed. The treatment and outcome were recorded, and describe factors that may affect their surgical conversion rate.

A total of 61 patients were included, including eight males and 53 females, with an average age of (67±9) years. The average of BMI was (25±4)kg/m². The site of the disease: 86.9% involved the medial femoral condyle, 1.6% involved the medial tibial plateau, and 1.5% involved the medial femoral condyle and the medial tibial plateau. 62.3% of the patients had tears at the root of the posterior horn of the medial meniscus. The protruding degree of medial meniscus was measured as follows: mild was 26.2%, moderate was 54.1%, severe was 19.7%. In 20 cases of X-ray Koshino grade one and two, after conservative treatment, 13 cases were treated by operation, six cases were cured, one case improved. Forty-one cases of grade three to four were converted to operation. Of the 12 cases with MRI Sayyid grade one and two, five cases were treated by operation, six cases were cured, one case was improved, and 49 cases with MRI grade three to four were treated by operation.

Some patients of SONK may combine subchondral insufficiency fractures of knee (SIFK), so identifying SIFK by MRI and limiting weight bearing in time may prevent patients from surgical intervention.