Background Unicompartmental knee arthroplasty (UKA) is an established treatment option for patients with unicompartmental osteoarthritis (OA). However, strict patient selection is crucial for its success. The proposed advantages include nearly natural knee kinematics, faster rehabilitation and better functional outcomes. Despite the aforementioned facts and it’s proven cost-effectiveness, there are still hesitations for the use of UKA as an alternative to total knee arthroplasty (TKA). Key objectives of this study were therefore to assess clinical and patient-reported outcome (PRO) as well as patient’s satisfaction after medial UKA in comparison to TKA. Methods To assess the outcome after UKA we conducted a prospective multi-center study. 116 patients with unicompartmental OA and indication for UKA were included. Overall 54 females and 62 males with an average age of 62.7 years (±9.8) and an average body mass index (BMI) of 29.2 (± 3.7) were recruited. Clinical results and PRO were assessed using the Knee Society Score (KSS). Follow-ups took place 3 months, 1 and 2 years after surgery including clinical examination, radiographs, assessment of PRO and adverse events. Pain and satisfaction was evaluated using a visual analog scale (VAS, 0 (worst) to 10 (best)). For comparison with TKA a propensity score matched-pair analysis was performed to eliminate confounders. Matching criteria were gender, patient’s age, BMI and comorbidities. A total of 116 matched-pairs were analysed. Results There was no revision in the UKA group until 2 years after surgery. Revision rates were higher in the TKA group (0.6%). Preoperative KSS-Scores were higher within the UKA cohort (p <  0.001). After surgical treatment, PROMs displayed a significant improvement (p <  0,001) in both cohorts. Regarding the Knee-Score (Pain, Alignment, ROM) we observed no differences between cohorts after 12 months. The Function-Score demonstrated significantly better results in the UKA cohort (UKA vs. TKA 95 vs 80, p <  0.001). Patient satisfaction was also higher in UKA patients (UKA vs TKA 9.0 vs 8.8, p = 0.019). Conclusion Patients of both cohorts showed high satisfaction after knee arthroplasty. UKA resulted in higher function scores compared to TKA without increased revision rate during short-term follow-up. Therefore, UKA is a good treatment option for unicompartmental OA. Trial registration Clinicaltrials.gov, NCT04598568. Registered 22 October 2020 - Retrospectively registered.

BackgroundUnicompartmental knee arthroplasty (UKA) is an established treatment option for patients with unicompartmental osteoarthritis (OA). However, strict patient selection is crucial for its success. The proposed advantages include nearly natural knee kinematics, faster rehabilitation and better functional outcomes. Despite these facts and it’s proven cost-effectiveness, there are hesitations for the use of UKA as an alternative to total knee arthroplasty (TKA). Key objectives of this study were therefore to assess clinical and patient-reported-outcome (PRO) as well as patient’s satisfaction after medial UKA in comparison to TKA. MethodsTo assess the outcome after UKA we conducted a prospective multi-center study. 116 patients with unicompartmental OA and indication for UKA were included. Overall 54 females and 62 males with an average age of 62.7 years (±9.8) and an average body mass index (BMI) of 29.2 (± 3.7) were recruited. Clinical results and PRO were assessed using the Knee Society Score (KSS). Follow-ups took place 3 months, 1 and 2 years after surgery including clinical examination, radiographs, assessment of PRO and adverse events. Pain and satisfaction were evaluated using a visual analog scale (VAS, 0 (worst) to 10 (best)).For comparison with TKA a propensity score matched-pair analysis was performed to eliminate confounders. Matching criteria were gender, patient´s age, BMI and comorbidities. A total of 116 matched-pairs were analysed. ResultsThere was no revision in the UKA group until 2 years after surgery. Revision rates were higher in the TKA group (0.6%).Preoperative KSS-Scores were higher within the UKA cohort (p < 0.001). After surgical treatment, PROMs displayed a significant improvement (p < 0,001) in both cohorts. Regarding the Knee-Score (Pain, Alignment, ROM) we observed no differences between cohorts after 12 months. The Function-Score demonstrated significantly better results in the UKA cohort (UKA vs. TKA 95 vs 80, p < 0.001). Patient satisfaction was higher in UKA patients (UKA vs TKA 9.0 vs 8.8, p = 0.019).ConclusionPatients of both cohorts showed high satisfaction after knee arthroplasty. UKA resulted in higher function scores compared to TKA without increased revision rate during short-term follow-up. Therefore, UKA is a good treatment option for unicompartmental OA. Trial registrationClinicaltrials.gov, NCT04598568. Registered 22 October 2020 - Retrospectively registered, https://www.clinicaltrials.gov/ct2/show/record/NCT04598568?cond=balanSys+Uni&draw=2&rank=1