J Orthopaed Traumatol (2011) 12:131–136 135 Fig. 4 Comparison between resurfaced patella (group 1, continuous line) and unresurfaced patella (group 2, dotted line) total knee arthroplasties. Kaplan–Meier curve of survival rate with Hospital for Special Surgery (HSS) total knee score of 60 points as the endpoint. Time reported in months analysed in both groups. No revision surgery was per- formed for patellar reasons in the resurfaced patella group. Conversely, in the group with unresurfaced patella, revi- sion surgery for patellar causes was performed in four cases: one lateral release, one patellar replacement for persistent pain and two of extensor apparatus realignment. Discussion This study represents a nonselected sample of PFC TKA with a ﬁxed bearing and is based on a clinical and radio- graphic evaluation. Its strength is the large number of patients, the long follow-up and the independency of the study. Clinical results were good, with a signiﬁcant increase in HSS total and partial scores. Also, patients’ range of motion and ability improved signiﬁcantly, thus conﬁrming the validity of the technique and the PFC implant. Cumulative average implant survival rate at 15 years, taking TKA revision for any cause as the end- point, was approximately 90%, as reported in the literature [13–16]. Cumulative average survival rate at 15 years was calculated using HSS score of B60 points or less as the endpoint, which can be considered as the division between satisﬁed and dissatisﬁed patients. Such an analysis has rarely been reported in the literature but is meaningful because it provides the real degree of patient satisfaction [10]. In this case, the cumulative percentage of patients satisﬁed with the implant at 15 years was approximately 95%. The two values are different because some patients with radiographic signs of osteolysis and mobilisation have no pain. In these cases, revision surgery was performed before a dramatic failure in order to conserve bone stock and ligamentous stability. Several aspects were studied to identify variability of practical value for predicting the durability of TKA implants. First, the early postoperative complications were evaluated, as the total knee replacement is a major surgery in which complications can occur: the incidence of such adverse events in this series is similar to that reported in literature [8, 9]. Moreover, the results suggest that when an accident (thrombosis, superﬁcial early phlogosis and other minor complications) is treated immediately, there is no signiﬁcant impact on implant survival. Similarly, implant alignment was considered. We obtained a correct physiologic alignment along the frontal mechanical axis plus/minus approximately 3 , whereas in the lateral view, the femoral component had a ﬂexion of approximately 3 to avoid femoral notching (potential cause of fractures). Angle values were similar to those reported in the literature [7, 17]. Then, comparison between alignment angles in the TKA group that underwent revision and those in the unrevised implant group showed no sta- tistically signiﬁcant differences, thus conﬁrming, as recently reported in the literature, that, within a physiologic range, the postoperative mechanical axis does not affect implant survival rate [18]. In this study, the selective patellar replacement was adopted with good results. There were no statistically meaningful differences in terms of implant failure and clinical results between patients with a replaced patella and those without. Nevertheless, a secondary surgery on the patella was performed in the unresurfaced group. This, plus the fact that the patella was usually replaced in knees with the worse anatomic condition would suggest that patella replacement is preferable [7, 19]. No progressive radiolu- cent lines were found in approximately half of the patients but they are not signs of early loosening. In particular, there is evidence for a predominance of radiolucent lines in the vicinity of the femoral-stem apex (zone 1 femoral) and the medial tibial plateau (zone 1 tibial). Similar data were described by Rodricks et al. [13]. Conversely, results show that progressive radiolucent lines (14.3% in this study) correlate with implant failure in 100% of cases [14, 15]. In conclusion, this study shows that the PFC prosthesis with ﬁxed bearing, cruciate sacriﬁce and cemented ﬁxation is a good prosthetic solution. Early complications, mechanical axis in the physiologic range and patellar treatment do not correlate with implant failure. Progressive radiolucent lines, conversely, are predictive of a negative result independent of when they appear. Conﬂict of interest The authors received no ﬁnancial support and have no conﬂict of interest. 123