Joint Awareness after Unicompartmental Knee Arthroplasty Evaluated with the Forgotten Joint Score

To investigate the temporal relationship of medial unicompartmental knee arthroplasty (UKA) and forgotten joint score (FJS), and to analysis the predictive factors associated with FJS after medial UKA.

This is a cross-sectional observational study. A total of 188 cases of medial UKA were included in this study, and all the prostheses used were Oxford mobile-bearing UKA from January 2016 to January 2019. All patients have completed the questionnaire of FJS, and the relevant data were obtained for 1 month (n = 38), 6 month (n = 40), 12 month (n = 42), 24 month (n = 34), and 36 month (n = 34) patient subgroups. The score ranged from 0-100, with a higher score indicating a more natural knee joint. In addition, the associations between the potential influencing factors (body mass index [BMI], age, gender, duration of onset before surgery, Kellgren-Lawrence grade of the medial compartment before surgery) with FJS were analyzed using Pearson correlation and multiple linear regression.

Postoperative FJSs were 44.5 ± 13.5 at 1 month，63.8 ± 10.1 at 6 months, 77.1 ± 12.2 at 12 months, 78.4 ± 12.2 at 24 months, 78.9 ± 12.5 at 36 months. The postoperative FJSs were lowest at 1 month and highest at 36 month (P < 0.01). The mean value of FJS kept improving until 12 months post-operation, which was slightly lower than that of 24 months and 36 months, but there was no statistical difference between them. Pearson correlation and multiple linear regression analysis showed that gender and Kellgren-Lawrence grade of the medial compartment before surgery had no significant influence on FJS, while age, BMI, and duration of onset before surgery had significant associations with FJS after UKA. BMI was negatively correlated with FJS, while older patients (>60) and with longer duration of onset before surgery (>3 years) were a positive predictor of good outcome for the FJS.

Patients can expect marked improvement in the natural feel of the prosthesis during the first year after UKA, slight continued improvement at 2 and 3 years. Furthermore, we identified three preoperative patient-related factors (age, BMI, and duration of onset before surgery) that may predict the FJS after medial UKA, which can be used to guide surgical decision making.