Survival and patient-reported outcomes of robotic arm-assisted patellofemoral arthroplasty and patient-acceptable symptom state thresholds

Aims: The aim of this study was to assess the implant survival and patient-reported outcome measures of robotic arm-assisted patellofemoral arthroplasty (raPFA) and to define patient-acceptable symptom state (PASS) thresholds. Methods: A multicentre retrospective cohort study of 112 raPFA was undertaken. The mean age of the patients was 63.3 years (21 to 89), and 88 (78.6%) were female. Oxford Knee Score (OKS), Kujala score, EuroQol five-dimension questionnaire (EQ-5D), EuroQol-visual analogue scale (EQ-VAS), Net Promoter Score (NPS), and patient satisfaction were assessed. Mean follow-up was 3.3 years (1.0 to 7.7). Results: There were four reoperations (three revisions) during the follow-up period. The four-year survival was 94.4% (95% CI 89.9 to 98.9) for all-cause reoperation, 96.7% (95% CI 94.5 to 100) for all-cause revision, and 97.7% (95% CI 93.8 to 100) for aseptic revision. A total of 79 (76.0%), 62 (59.6%), 67 (64.4%), and 49 (54.4%) knees achieved the PASS thresholds in the OKS, Kujala, EQ-5D, and EQ-VAS scores, respectively. The satisfaction rate was 77.9% (n = 81) and the NPS was 59.7. Increasing American Society of Anesthesiologists (ASA) grade (odds ratio 0.02, 95% CI 0.00 to 0.22, p = 0.001) was independently associated with dissatisfaction. The OKS (area under the curve (AUC) 89.1, 95% CI 82.5 to 95.8) and Kujala score (AUC 86.1, 95% CI 77.7 to 94.5) were excellent, and the EQ-5D (AUC 75.4, 95% CI 61.7 to 89.1) and EQ-VAS (AUC 76.7, 95% CI 64.0 to 89.5) were acceptable discriminators of satisfaction, with PASS thresholds of 36, 72, 0.710, and 74, respectively. Using these new thresholds, the number achieving a PASS decreased in the OKS (n = 75; 72.1%), increased in the Kujala score (n = 73; 70.2%) and EQ-VAS (n = 58; 64.4%), and remained identical for the EQ-5D. Conclusion: raPFA was associated with clinically meaningful postoperative outcome measures and a high NPS. However, approximately one in five were not satisfied, which was independently associated with increasing comorbidity, and approximately one in 20 underwent reoperation in the first four years postoperatively. The defined PASS thresholds specifically for PFA could be used to help interpret outcomes in future studies.