Influence of preoperative weight on the early and middle outcome of fixed platform medial unicompartmental knee arthroplasty

INTRODUCTION: Obesity is an important independent risk factor for the development of knee osteoarthritis .According to the data of the world Health Organization, there were more than 1.9 billion overweight adults in the world in 2014, among which at least 600 million were clinically obese .Therefore, among the patients undergoing knee replacement, the number of obese patients is increasing .The use of single condyle replacement for medial compartment arthritis of the knee began in the 1970s.With the continuous development of new implants, the continuous improvement of surgical techniques and the strict control of indications by surgeons, the 15-year survival rate of single condyle replacement is over 90%, and the 20-year survival rate is 84%, achieving good results.In the indications of knee monocepicondylar replacement, the maximum weight standard has been increased from 82kg in 1989 [8] to 90kg in 2002 [9].However, there is still controversy over the body weight cut-off point in the indications, especially the observation on the postoperative effect of single condyle replacement in obese patients, which has been rarely reported in China. HYPOTHESES: To evaluate the near and middle term efficacy of unicompartmental knee arthroplasty(UKA) in patients with medial knee osteoarthritis with different body mass index, and to determine the effect of body weight on the efficacy and complications of UKA. METHODS: A total of 128 patients who underwent UKA in department I of arthropathy, zhengzhou orthopaedic hospital from December 2016 to December 2018 due to medial knee osteoarthritis were included as study subjects, and the clinical data of the study subjects were retrospectively analyzed. There were 29 males and 99 females, with an average age of 65.13± 7.37 years (range: 51˜87 years).According to the preoperative body mass index (BMI), the subjects were divided into three groups, namely the underweight or normal weight group (BMI < 24kg /㎡), the overweight group (24kg /㎡≤BMI < 28kg /㎡) and the obese group (BMI≥ 28kg /㎡).Visual analogue scale (VAS), knee range of motion(ROM), American hospital for special surgery (HSS) score of knee joint, complications and other relevant indicators were recorded before and at the last follow-up for each group. According to the data types of preoperative and postoperative efficacy evaluation indexes of the same group, paired sample T test, c² test or Wilcoxon sign rank sum test were used for difference analysis. One-way anova, c² test or K-W rank sum test were used to evaluate the difference between groups. RESULTS: All subjects were followed up for 13-37 months (22.34± 7.22).Compared with before surgery, VAS scores of patients in the last follow-up were significantly lower in the underweight or normal weight group, the overweight group and the obese group (6.91±6.34 vs. 0.44±0.67, 6.90 ±0.77 vs. 0.63±0.68, 6.78±0.71 vs. 0.59±0.61) (t= 46.488-42.654,P values <0.01), knee ROM significantly increased (97.67±10.87 vs. 114.77±8.01, 98.96±10.67 vs. 116.03±6.96, 95.31±11.50 vs. 110.93±11.46) (t= -20.83 - -11.039,All P values were <0.01), and knee HSS score was significantly improved (51.63±0.61 vs 88.00±4.06, 50.68±6.46 vs 87.87±5.73, 48.25±6.70 vs 87.03±5.17) (t= -48.920- -34.010, all P values <0.01).There were no statistically significant differences in VAS score, knee ROM and knee HSS score between the overweight group and the obese group compared with the underweight or normal group. None of the patients had serious complications such as periprosthesis infection, simple prosthesis loosening and periprosthesis fracture. The incidence of venous thrombosis in lower extremities was 14.06% (18/128), with no significant difference between groups. There were 7 cases of poor incision healing (overweight group is 3 and obese group is 4), and the risk of poor incision healing was higher in the obese group than in the underweight or normal weight group, with statistical significance (P=0.03). CONCLUSION: UKA can achieve satisfactory clinical effect in patients with different body mass index, but patients in obesity group are prone to complications such as poor incision healing.