Acta Orthopaedica 2011; 82 (6): 685–691 685 Similar TKA designs with differences in clinical outcome A randomized, controlled trial of 77 knees with a mean follow-up of 6 years Huub J Meijerink1, Nico Verdonschot2,3, Corné J M van Loon4, Gerjon Hannink2, and Maarten C de Waal Malefijt1 1Department of Orthopaedics and 2Orthopaedic Research Laboratory, Radboud University, Nijmegen Medical Centre, Nijmegen; 3Laboratory for Biomechanical Engineering, University of Twente, Enschede; 4Department of Orthopaedics, Rijnstate Hospital, Arnhem, the Netherlands Correspondence HJM: hjmeijerink@hotmail.com Submitted 11-03-22. Accepted 11-07-11 Background and purpose To try to improve the outcome of our TKAs, we started to use the CKS prosthesis. However, in a ret- rospective analysis this design tended to give worse results. We therefore conducted a randomized, controlled trial comparing this CKS prosthesis and our standard PFC prosthesis. Because many randomized studies between different TKA concepts gen- erally fail to show superiority of a particular design, we hypoth- esized that these seemingly similar designs would not lead to any difference in clinical outcome. Patients and methods 82 patients (90 knees) were randomly allocated to one or other prosthesis, and 39 CKS prostheses and 38 PFC prostheses could be followed for mean 5.6 years. No patients were lost to follow-up. At each follow-up, patients were evaluated clinically and radiographically, and the KSS, WOMAC, VAS patient satisfaction scores and VAS for pain were recorded. Results With total Knee Society score (KSS) as primary end- point, there was a difference in favor of the PFC group at final follow-up (p = 0.04). Whereas there was one revision in the PFC group, there were 6 revisions in the CKS group (p = 0.1). The survival analysis with any reoperation as endpoint showed better survival in the PFC group (97% (95% CI: 92–100) for the PFC group vs. 79% (95% CI: 66–92) for the CKS group) (p = 0.02). Interpretation Our hypothesis that there would be no dif- ference in clinical outcome was rejected in this study. The PFC system showed excellent results that were comparable to those in previous reports. The CKS design had differences that had con- siderable negative consequences clinically. The relatively poor results have discouraged us from using this design. a better range of motion (high-flex TKA) (McCalden et al. 2009, Choi et al. 2010, Mehin et al. 2010), or a more anatomi- cal reconstruction of the joint—such as posterior and ante- rior cruciate ligament retaining designs (Ries 2007, Pritchett 2011) and gender-specific TKA (Clarke and Hentz 2008, Kim et al. 2010). We started to use the CKS prosthesis (Stratec Medical, Ober- dorf, Switzerland), based on previous research at our institu- tion showing that the natural patella groove does not have an isolated lateral orientation (Barink et al. 2006). In contrast to our standard prosthesis (PFC; DePuy/Johnson and Johnson, Warsaw, IN) with a lateral orientation of the patellar groove, the trochlea of the CKS prosthesis is deeper and has a neutral direction. However, in a retrospective analysis, after 1 year the CKS prosthesis tended to have worse Knee Society scores (KSSs) (Brokelman et al. 2004). We decided to compare the outcome thoroughly and started a randomized, controlled trial between the CKS and the PFC prostheses. Many randomized studies of TKAs with different bearings (Harrington et al. 2009, Rahman et al. 2010), cruciate-retain- ing or -substituting devices (Kim et al. 2009), gender-specific designs (Kim et al. 2010), and high-flex designs (McCalden et al. 2009, Choi et al. 2010, Mehin et al. 2010) generally fail to show superiority of one of the devices over the other. We therefore hypothesized that the seemingly small differences in design between the CKS and PFC system would not lead to differences in clinical outcome in our study.  Patients and methods Although current results of total knee arthroplasty (TKA) are relatively good, there is still room for improvement. There is constant research and development, with a view to obtain- ing longer survival rates (Rand et al. 2003, Julin et al. 2010), We designed a randomized, controlled trial with 2 poste- rior cruciate ligament (PCL) retaining total knee designs. The study protocol was approved by the institutional review board at our hospital and it was carried out in line with the Open Access - This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the source is credited. DOI 10.3109/17453674.2011.636677