Abstract:[Objective] To compare the clinical outcomes of unicompartmental knee arthroplasty (UKA) versus high tibial osteotomy(HTO) for spontaneous osteonecrosis of the knee (SONK). [Methods] A retrospective study was conducted on 39 patients who received surgi-cal treatment for SONK treated from January 2015 to October 2021. According to preoperative doctor-patient communication, 22 patients re-ceived UKA, while the other 17 patients received HTO. The perioperative, follow-up and imaging data were compared between the twogroups. [Results] The UKA group proved significantly superior to the HTO group in terms of operating time [(53.0±6.3) min vs (60.5±8.0)min, P＜0.05] and postoperative walking time [(3.5±0.9) days vs (5.7±0.7) days, P＜0.05], despite of the fact that the former had significantlylonger total incision length than the latter [(9.2±1.1) cm vs (6.7±0.9) cm, P＜0.05]. However, there were no significant differences in intraoper-ative blood loss, incision healing grade and hospital stay between the two groups (P＞0.05). All patients in both groups were followed up for(24.7±10.0) months on an average, and the UKA group returned to full weight-bearing activity significantly earlier than HTO group [(7.1±2.0) days vs (34.5±3.6) days, P＜0.05]. The VAS, WOMAC and KSS scores were significantly improved in both groups over time (P＜0.05),whereas the knee range of motion (ROM) was not significantly changed (P＞0.05). Although there were no statistically significant differencesin the above indexes between the two groups before surgery (P＞0.05), the UKA group was significantly better than the HTO group in terms ofVAS score, WOMAC score and KSS scores at all time points postoperatively accordingly (P＜0.05), while without statistically significant dif-ferences in knee ROM between the two groups (P＞0.05). Radiographically, the UKA group had significantly better femorotibial angle (FTA)than the HTO group immediate postoperatively [(182.0±1.9)° vs (173.8±2.1)°, P＜0.05] and at the last follow-up [(182.0±1.7)° vs (173.0±2.0)°, P＜0.05]. In addition, the UKA group proved significantly superior to the HTO group at the latest follow-up in terms of the lateral com-partment Kellgren and Lawrence (K-L) classification [0/I/II/III/IV, (17/4/1/0/0) vs (6/7/4/0/0), P＜0.05] and patellofemoral K-L classification [0/I/II/III/IV, (15/5/2/0/0) vs (4/8/4/1/0), P＜0.05]. [Conclusion] Both UKA and HTO do achieve good clinical outcomes for treatment of SONK. By comparison, the UKA has considerably better early clinical consequence than the HTO.