Objective To analyze the correlation between sagittal bearing movement and posterior tibial slope after Ox-ford unicompartmental knee arthroplasty(UKA)and its effect on clinical results.Methods A total of 29 patients(30 knees)with anterior medial knee osteoarthritis who underwent Oxford third-generation UKA in the Department of Joint and Sports Medicine of the Second Hospital of Shanxi Medical University from January 2022 to March 2022 were retrospectively analyzed,including 7 males(8 knees)and 22 females(22 knees),aged 63.3±7.9 years(range,47-84 years).The patients were divided into overhang group(9 knees)and non-overhang group(21 knees)according to whether there was overhang of the bearing in the sagittal X-ray film at 135° flexion after operation.The preoperative and postoperative Oxford Knee Score(OKS),tibial posterior slope angle and radiographic results of the bearing were compared between the two groups.Pearson correlation analysis was used to measure the re-lationship between postoperative sagittal bearing movement and OKS and tibial posterior slope.Results All patients successfully completed the operation and were followed up for 7.2±1.1 months(range,6-9 months).30％(9/30)of the bearing were overhung.When the knee flexion was 135°,the position of the bearing in the overhang group was 83.33％±3.46％,and the posterior suspen-sion distance was 1.12±1.80 mm,which was significantly higher than those in the non-overhang group(73.24％±3.40％and-4.45± 2.37 mm,P＜0.05).The bearing movement distance in the overhang group was 33.22％±8.51％,which was larger than that in the non-overhang group(23.36％±9.32％),and the difference was statistically significant(P＜0.05).The posterior tibial slope of the overhang group was 2.68°±2.20° at 6 months after operation,which was smaller than that of the non-overhang group(4.59°±2.69°),and the difference was statistically significant(P＜0.05).The OKS score was 19.00±8.84 in the overhang group and 19.14±7.00 in the non-overhang group at 6 months after operation,and the difference was not statistically significant(P＞0.05).Pearson correla-tion analysis showed that the overhang distance of the bearing was positively correlated with the bearing position at 135° knee flex-ion(r=0.97,P＜0.001),and negatively correlated with the posterior tibial slope(r=-0.38,P=0.041).It was negatively correlated with the change of posterior tibial slope(r=-0.37,P=0.045),positively correlated with the bearing movement distance(r=0.68,P＜0.001),and had no correlation with the position of the bearing at 0° knee flexion(r=-0.15,P=0.423).The bearing movement dis-tance was negatively correlated with the position of the bearing at 0° of knee flexion(r=-0.82,P＜0.001),positively correlated with the position of the bearing at 135° of knee flexion(r=0.70,P＜0.001),and negatively correlated with the posterior tibial slope(r=-0.48,P=0.007).It was negatively correlated with the change of posterior tibial slope(r=-0.39,P＜0.001),and positively correlated with the overhang distance of bearing at 135° knee flexion(r=0.68,P=0.033).Conclusion The incidence of bearing overhang at Oxford UKA is 30％.The bearing overhang and the increase of the bearing movement distance are related to the de-crease of the posterior tibial slope after the operation.Although no effect of bearing overhang on knee joint function was found,the posterior tibial slope should be adjusted during the operation to reduce the incidence of bearing overhang.
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