ObjectiveTo compare the effectiveness of unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) in the treatment of severe medial compartment osteoarthritis (OA).MethodsA clinical data of 69 patients (69 knees), who underwent joint replacement due to severe medial compartment OA between February 2015 and September 2018 and met the selection criteria, was retrospectively analyzed. Among them, 38 cases were treated with UKA (UKA group) and 31 cases with TKA (TKA group). There was no significant difference in gender, age, body mass index, course of disease, lesion side, and preoperative visual analogue scale (VAS) score, Hospital for Special Surgery (HSS) score, Western Ontario and McMaster University Osteoarthritis Index (WOMAC) score, Feller score, range of motion of knee, physiological and psychological scores of short-form 12 health survey scale (SF-12) between the two groups (P>0.05). The femorotibial angle (FTA) of TKA group was bigger than that of UKA group, and hip-knee-ankle angle (HKA) was smaller, showing significant differences (P<0.05). The operative time, incision length, blood loss, time for flexion 90°, ambulation time, hospital stay, and incidence of deep venous thrombosis of lower extremity were recorded and compared between the two groups. The VAS score, HSS score, WOMAC score, Feller score, range of motion, and physiological and psychological scores of SF-12 were used to evaluate patients’ quality of life. FTA, HKA, and prosthesis looseness were observed by X-ray films. Kaplan-Merier survival analysis was used to evaluate the survival rate of prosthesis.ResultsAll operations were successfully completed in both groups. Compared with TKA group, UKA group had shorter incision length, longer operative time, and less blood loss (P<0.05). There was no significant difference in time for flexion 90°, ambulation time, hospital stay, and the incidence of deep venous thrombosis of lower extremity between the two groups (P>0.05). The incisions in both groups healed by first intention. During follow-up, 3 patients in the UKA group and 1 patient in the TKA group developed mild anterior knee pain. Patients were followed up (30.7±9.6) months in the UKA group and (34.9±8.7) months in the TKA group, and the difference was not significant (t=–1.832, P=0.071). At last follow-up, there were significant differences in the HSS score, Feller score, WOMAC score, range of motion, VAS score, and physiological and psychological scores of SF-12 between pre- and post-operation (P<0.05). The range of motion in the UKA group was bigger than that in the TKA group (Z=–2.666, P=0.008), and there was no significant difference in the other indexes between the two groups (P>0.05). X-ray films showed that the alignment of the two groups recovered well, and the FTA and HKA of the two groups were improved at 1 week after operation (P<0.05). No radiolucency was found around the prosthesis during follow-up, no prosthesis loosening and meniscal bearing dislocation occurred. The survival rates of the prostheses in the two groups were 100%.ConclusionFor severe medial compartment OA, the early survival rates of the two prostheses are similar, but UKA has less traumatic, can preserve the normal structure of the knee, and the range of motion of the knee after operation is significantly better than TKA.