Background:In a small proportion of cases, spontaneous osteonecrosis of the knee (SONK) involves the medial tibial plateau (MT). Here, we introduced the clinical characteristics of spontaneous osteonecrosis of the MT and unicompartmental knee arthroplasty (UKA) as the favorable treatment for this situation based on a retrospective case study.Methods:Patients with spontaneous osteonecrosis of the MT, confirmed by magnetic resonance imaging (MRI) at Guangdong Provincial Hospital of Chinese Medicine (China) from March 2015 to June 2016, were included as a case serial and analyzed retrospectively. All patients underwent Oxford Medial UKA. The characteristics of their lesions, corresponding treatment, and results of follow-up were presented. The lesion scores and grade were determined according to the criteria of Ficat and Arlet.Results:In total, 22 patients (5 men, 17 women; mean age, 64.1 years) with spontaneous osteonecrosis of the MT were analyzed. The lesion stages assessment showed that 3 (14%) were Stage II, 10 (45%) were Stage III, 7 (32%) were Stage IV, and 2 (9%) were Stage V. In the sagittal plane, 7 (32%) were in the anterior region (MTa) and 15 (68%) were central (MTc). The lesion volume averaged 2.24 ± 0.79 cm3 (range: 1.57–3.08 cm3). Seventeen patients (77%) had Level III posterior medial meniscus root tears (MMRTs). All the patients underwent UKA. Average follow-up was 30.0 ± 6.4 months with a range of 23.0–38.0 months. The visual analog scale score was 7.78 ± 0.67 before surgery while decreased to 2.22 ± 1.09 at the final follow-up (P < 0.001). The Hospital for Special Surgery scores of pre-/post-surgery were 65.67 ± 5.45 and 84.10 ± 4.20, respectively (P < 0.001).Conclusions:SONK often occurs in the anterior and central tibial plateau due to abnormal stresses. Most of the patients had Level III posterior medial meniscus root tears. MRI is recommended for suspected cases to identify SONK at an early stage. The use of the Oxford Medial UKA for SONK of the MT is reliable both immediately and at follow-up.

Background: Spontaneous osteonecrosis of the knee (SONK) was defined as a distinct clinical entity with characteristical findings that subchondral lesions in the weight-bearing region of a single condyle. In the early stage of SONK, we usually think that injury of meniscus was to blame for the knee pain. Elderly patients with medial meniscus tear should be aware of the occurrence of osteonecrosis. Case presentation：A 67-year-old male complained of pain in the left knee for 3 months in 2013. Magnetic resonance imaging (MRI) revealed a medial meniscal root tear (level III), so that he patient underwent arthroscopic meniscectomy. However, no obvious pain relief achieved at the follow-up. The pain was associated with weight bearing, of which was initially intermittent, gradually progressed in intensity and became frequent even at rest. At 18 months after the first visit, we re-examined the knee MRI and results clearly revealed subchondral bone osteonecrosis of the condyle. Finally, we performed unicompartmental arthroplasty which significantly relieved the pain and restored the walking ability of the patient. Conclusions: Meniscus injury often coexist with SONK. In the early stages of SONK, the area of necrosis is small which is very easy to be ignored causing a misdiagnosis. The case reminds us should pay much attention to the possibility of subchondral bone necrosis in patients with knee pain and meniscal injury.