ObjectiveTo investigate the effect of body mass index (BMI) on the short- and medium-term effectiveness of unicompartmental knee arthroplasty (UKA) in the treatment of anterior medial compartmental osteoarthritis of knee joint.MethodsThe clinical data of 55 patients (61 knees) with anterior medial compartmental osteoarthritis of knee joint treated with minimally invasive UKA between May 2014 and May 2019 were retrospectively analyzed. According to BMI, the patients were divided into 3 groups: normal body mass group [group A, BMI 18.50-24.99 kg/m2, 23 cases (25 knees)], overweight group [group B, BMI 25.00-29.99 kg/m2, 23 cases (25 knees)], obesity group [group C, BMI 30.00-39.99 kg/m2, 9 cases (11 knees)]. There was no significant difference in gender, age, sides, disease duration, and preoperative American Special Surgery Hospital (HSS) score, pain visual analogue scale (VAS) score, and knee range of motion (ROM) among 3 groups (P>0.05). The operation time, intraoperative dominant blood loss, and the postoperative decreased amount of hemoglobin at 1 week were recorded and compared among 3 groups. The HSS score, VAS score, and ROM were used to evaluate the knee function and pain improvement.ResultsThere was no significant difference in the operation time, the intraoperative dominant blood loss, and the postoperative decreased amount of hemoglobin at 1 week among 3 groups (P>0.05). All the 55 patients were followed up 5-60 months, with an average of 24 months. No complication such as infection, fat embolism, or deep venous thrombosis of lower extremity occurred after operation. The anteroposterior and lateral X-ray films of the knee joint showed that no dislocation or loosening of the prosthesis occurred and the position of the prosthesis was good. At last follow-up, the HSS score, VAS score, and ROM of the 3 groups were significantly improved when compared with preoperative ones (P<0.05); but there was no significant difference among 3 groups (P>0.05).ConclusionFor obese and overweight patients with anterior medial compartmental osteoarthritis of the knee joint, the use of minimally invasive UKA can achieve satisfactory short- and medium-term effectiveness, and the long-term effectiveness needs further follow-up.