To explore the application value of movable Oxford unicondylar knee replacement in the treatment of spontaneous osteonecrosis of the knee (SONK).

Retrospective analysis was conducted on 32 patients (32 knees) with SONK admitted to the Department of Orthopedics, Songjiang Hospital Affiliated to Shanghai Jiaotong University School of Medicinel from January 2015 to August 2022, including 14 patients with single-column movable Oxford knee unicondyle, 18 cases of double-column movable Oxford knee unicondyle. During the operation, after successful anesthesia, the patient was placed in the supine position, bent the knee 90° to take the approach from the medial side of the patella to the medial side of the tibial tubercle, thoroughly removed the necrotic tissue of the medial femoral condyle, and selected the osteotomy depth according to the integrity and strength of the sclerotic bone around the lesion. Small defects should be filled with bone cement, and large defects should be filled with small bone fragments made from cleared osteophytes. The Oxford knee prosthesis with single/double column and double column movement was installed. The range of motion and stability of the knee joint were re-checked, hemostasis was thoroughly stopped, the incision was fully rinsed, the cocktail analgesic mixture was inject around the joint, the drainage tube was routinely placed, layer by layer suture, and elastic bandage was used for fixation. Antibiotics were used prophylactically within 24 h after surgery, drainage tube was removed 1-2 d after surgery, and symptomatic treatment such as anticoagulation and analgesia were routinely given after surgery. After anesthesia, quadriceps muscle training and ankle pump exercises were actively performed. The operation time and postoperative hospitalization time of patients were record; the incidence of knee complications was recorded 1, 3, 6, 12, 24 and 36 months after operation; the knee function [hospital for special surgery (HSS) score, knee society score (KSS) , knee range of motion] were collected and compared before surgery and at the last follow-up; the alignment of lower limbs [the femorotibial angle of knee joint, posterior tibial slope and tibial plateau angle] were measured and compared before surgery and at the last follow-up; the knee function and the alignment of lower limbs of patients with two prostheses were compared at the last follow-up. Data were compared by t test.

All the patients successfully completed the operation, and all the surgical incisions healed in stage Ⅰ. The operation time of 32 patients was 35.0-70.0 min, and the average operation time was (45.5 ± 6.9) min; the hospital stay ranged of patients was 5.0 -8.0 days, with an average of 6.5 days. Among the 32 patients, 1 patient with double-column movable oxford knee unicondylar replacement had a dislocation of meniscus pad one month after the operation, which was improved after revision; 1 patient underwent single-column movable oxford knee single condyle replacement, and the lower limb force line changes and prosthesis loosening occurred 24 months after the operation, the revision was improved after total knee replacement. Other patients had no serious complications such as vascular and nerve injury, perioperative infection, prosthesis loosening, meniscus pad dislocation, lower extremity deep vein thrombosis. At the last follow-up, HSS score, KSS and knee range of motion were (85.6±4.4) points, (88.4±5.2) points and (108.8±8.2)°, respectively, which were significantly higher than those before surgery [(66.8±5.2) points, (61.3±9.8) points, (97.5±7.6)°], the differences were statistically significant (t=15.61, 13.81, 5.71; P<0.05). At the last follow-up, the knee femorotibial angle and tibial plateau angle were (174.4±5.6)° and (84.6±3.6)°, respectively, which were significantly lower than those before surgery [(179.5±3.8)°, (88.1±2.0)°], the differences were statistically significant (t=4.26, 4.80; P<0.05); the posterior tibial slope of tibial medial condyle of knee was (82.8±3.4)° at the last follow-up, which showed no statistically significant difference compared with that before surgery [(84.2±3.9)°](t=1.53, P=0.131). At the last follow-up, the HSS score, KSS, knee range of motion, femorotibial angle, posterior tibial slope, and tibial plateau angle of single column movable Oxford knee unicondylar replacement patients were (84.8±4.2) points, (89.2±6.0) points, (107.6±9.0)°, (175.8±6.0)°, (82.0±4.1)°, (83.8±3.2)°, respectively, compared with thedouble column movable Oxford knee unicondylar replacement patients [(86.3±4.6) points, (87.8±4.5) points, (109.8±7.9)°, (173.4±5.4)°, (83.5±3.6)°, (85.3±4.0)°], there were no statistically significant differences (P>0.05).

The movable Oxford unicondylar replacement of knee has achieved satisfactory results in the treatment of patients with SONK, with fewer complications and can significantly improve the function of the affected knee and partially correct the alignment of lower limbs, which is worthy of clinical promotion and application.