## 4 Discussion  
Several studies in the literature have reported good results after revision total knee arthroplasty at short and medium follow-up as long as there was a clear diagnosis [21; 22; 23; 24]. The use of metaphyseal devices to increase the fixation and stability of the implant is well accepted nowadays [18; 25]; advantages may include an easier and more predictable surgical technique, versatility of the system, and early mechanical support without the risk of late resorption and collapse. [PERSON] et al. [26] in 2015 concluded that despite the high complication rate in their series of patients, TM cones represent an attractive option for managing bone loss in complex primary and revision TKA with a high rate of ooseointegration, stating that the majority of complications were not related to the implants used. The ideal fixation is still debated, and there is no agreement in the literature on whether hybrid fixation or full cementation is the better method [27]; we adopted hybrid fixation with cementation of femur and tibia, including zone 2 [18] and patella, with smooth or splined press-fit modular stems, reserving full cementation only in case of short stubby stems. [PERSON] et al. [24] in 2015 performed a review of the studies on modes of failure in primary and revision knee arthroplasty; they found that the literature on varus valgus constrained implants was insufficient and that many outcome studies were limited by a small number of cases and short follow-ups. The authors considered ten studies, which included 294 patients overall, and found that the main causes of revision were infection (42%), aseptic loosening (34%), patellar complication (7%), and extensor mechanism complication (7%), but they concluded that a more reliable analysis of the outcomes would require larger cohorts with a longer follow-up. Based on our data, we were not able to fully demonstrate a clear correlation between preoperative diagnosis and postoperative outcomes in knee arthroplasty revision surgery. However, we found better outcomes with preoperative diagnosis of malpositioning and aseptic loosening and worse outcomes with infection diagnosis, with statistically significant differences in the clinical and functional outcomes. Despite the small sample, good results were obtained in the case of revision for periprosthetic fractures, but worse scores were observed in the instability group. Our findings are in line with those of [PERSON] et al. [21], who found better outcomes in the aseptic loosening group and moderate results in the malpositioning, instability, and infection groups at a mean follow-up of 24 months. Analyzing the outcomes of each group, we found that our results were worse for all the evaluated scores; however, it is important to underline that our cohort of patients was observed at mid- to long-term follow-up. Indeed, other studies involving series with longer follow-ups [23] obtained worse clinical and functional results than those obtained for our series. Our data are in line with those published by [PERSON] et al. [28], who performed a retrospective review of 206 cases of revision TKA performed in ten years in a single institution (2003-2012). They subdivided patients into a septic (120 cases) and an aseptic group (86 cases, with periprosthetic fracture and loosening being the main causes of the revision surgery) and evaluated the causes and outcome of the second surgery at a minimum follow-up of 2 years. In the septic group, the HSS score and KSS score were, respectively, 79.2 and 75.5 at follow-up, while in the aseptic group, the scores were, respectively, 85.5 and 86.6, showing a statistically significant difference between the two groups (\(p<0.05\)). The mean range of motion was 101\({}^{\circ}\) in the septic group and 117\({}^{\circ}\) in the aseptic group (\(p<0.05\)). The authors stated that mechanical complications that require revision (aseptic loosening and instability) decreased in relation to the development of surgical techniques and design.