Relationship Between Sagittal Bearing Movement And Posterior Tibial Slope After Oxford Mobile-bearing Unicompartmental Knee Arthroplasty

Objective:To observe the in vivo sagittal bearing movement distance and the degree of bearing overhang after Oxford unicompartmental knee arthroplasty and to study their relationship with the posterior tibial slope.Methods:Retrospective analysis of 29 patients(30 knees)with anterior medial osteoarthritis who received OUKA treatment in our department from January 2022 to March 2022,including 7 males(8 knees)and 22 females(22 knees),aged 63.3 ± 7.9 years(47-84years).Record the OKS score and knee joint ROM of patients before and 6 months after surgery,measure preoperative and postoperative PTS on lateral X-ray films,and record knee flexion 0 ° and 135 ° lateral X-ray films during surgery for measuring the bearing position.According to whether the bearing on the lateral X-ray films of 135° knee flexion is overhang or not,the patients were divided into the bearing overhang group(n=9)and the non-bearing overhang group(n=21).Compare bearing movement distance and postoperative PTS between two groups.Analyze the relationship between bearing overhang distance 、bearing movement distance 、the BP when the knee flexion was 0°、the BP when the knee flexion was 135°、postoperative PTS,and changes in PTS.Results:The mean follow-up period was 7 months(range,6-9 months).The postoperative OKS score was significantly improved compared with that before operation(19.10±6.35 VS 34.87±8.06,P =0.000).The PTS decreased significantly after surgery(4.30±2.79 VS9.43±3.72,P =0.000).A total of 9 cases of bearing overhang(30%)were observed,and the postoperative PTS of the bearing overhang group was smaller than that of the non bearing overhang group(2.78 ° ± 2.54 ° VS 4.59 ° ± 2.69 ° P=0.049),and the bearing movement distance was larger(35.32% ± 10.12% VS 23.38% ± 7.75% P=0.001).The bearing overhang was positively correlated with the bearing position when the knee flexion was 135°(r =0.913,P =0.000),negatively correlated with the change of PTS(r =-0.386,P = 0.035),and positively correlated with the bearing movement distance(r =0.673,P =0.000).The bearing movement distance was negatively correlated with the bearing position during knee extension(r =-0.815,P =0.000),positively correlated with the bearing position when knee flexion was 135°(r = 0.714,P =0.000),negatively correlated with postoperative PTS(r =-0.422,P =0.02),and negatively correlated with the change of PTS(r =-0.427,P =0.019).The influencing factors of postoperative OKS score were not found.Conclusion:Knee joint function improved after OUKA surgery.The occurrence rate of bearing overhang is about 30%,and The bearing movement distance was larger when the bearing overhung happened.The large bearing overhang distance and bearing movement distance are related to the smaller postoperative PTS.It is recommended that the surgeon should not set the PTS too small during OUKA.