## 1 Introduction  
The first objective of this paper is to report the clinical and functional results of a cohort of patients who underwent total knee arthroplasty revision at mid-long-term follow-up. The second objective is to investigate possible differences in postoperative functional and clinical outcomes between preoperative-cause-of-revision groups. Methods: we collected data from 105 surgeries performed between January 2008 and December 2014. Eighty-five of these patients were divided into subpopulations according to the causes of revision in order to study differences regarding their outcome. All the patients underwent a standard follow-up protocol with clinical and radiological exams at 1, 3, 6, 12, 24, and 36 months and at last follow-up. During the last follow-up, patient-reported outcome measures (PROMs) were used. We implemented the functional outcomes obtained with clinical data determined by the Oxford knee score (OKS), EQ-VAS, EQ-5D-SL, Knee Society Score (KKS), and range of motion (ROM). Statistically significant differences among the medians of the groups of OKS, EQ-VAS, EQ-5D-SL, KKS, and ROM (_p_ < 0.05) were noticed. The Dunn's test was used to perform post hoc comparisons, and it determined where the differences lie. Results: the median follow-up was 99 months (interquartile range (IQR) 80-115). The median age was 71.5 (IQR 65.1-74.8) with no relevant differences between the groups. More patients presented a preoperative diagnosis of septic loosening (29%), malositioning (28%), and infection (24%), while a preoperative diagnosis of instability (11%) and periprosthetic fracture was observed in fewer cases. For OKS, the highest median value was in the periprosthetic fracture group (43.25, IQR 32.7-45.3) and the lowest median value was in the infection group (24.8, IQR 17.4-34.8). For EQ-VAS, the highest median value was in the periprosthetic fracture group (73.0, IQR 67.0-78.0) and the lowest median value was in the instability group (39.0, IQR 36.0-48.0). For EQ-5D-5L, the highest median value was in the inscription loosening group (0.81, IQR 0.74-0.85) and the lowest median value was in the infection group (0.44, IQR 0.32-0.60). For KKS, the highest median value was in the aseptic loosening group (84.0, IQR 81.0-88.0) and the lowest median value was in the malpositioning group (56.5, IQR 49.4-66.0). For ROM, the highest median value was in the periprosthetic fracture group (105.0\({}^{\circ}\), IQR 96.0-111.0\({}^{\circ}\)) and the lowest median value was in the infection group (88.5\({}^{\circ}\), IQR 77.5-98.0\({}^{\circ}\)). Conclusion: Constrained condylar knee (CCK) prostheses can also be considered a good option to manage difficult cases of total knee arthroplasty revision, with satisfactory results being maintained over time; a preoperative diagnosis of infection is associated with a worse clinical and functional outcome. LCCK; CCK; knee; TKA; revision; PROMs  
## 1 Introduction  
Since its introduction in clinical practice, total knee arthroplasty (TKA) has been considered one of the most successful procedures in orthopedic surgery, with survival rates greater than 90% for 10- and 15-year implants [1]. TKA procedures are expected to increase remarkably in future years. Forecasts estimate that the annual case number could reach from 1.3 million to nearly 3.5 million primary TKAs per year in the United States by 2030 [2]. Aging of populations, the increase in risk factors such as obesity, and the necessity of maintaining a good quality of life with an active lifestyle will continue to fuel this trend in developed countries. A parallel increase in TKA revisions is expected, with a considerable clinical burden on patients and a financial burden on healthcare organizations. The current revision rate at 10-year follow-up varies within narrow limits; the Australian register reported a rate of 5.5%, and the UK rate is slightly lower (5%) [3].