690 our knowledge this has not been described in the literature. We also analyzed the surface roughness of the femoral com- ponents and found that the CKS components had a lower sur- face roughness value than the PFC design (Ra = 1.3 ± 0.1 µm vs. 1.9 ± 0.3µm; p = 0.01). As shown by Walsch et al. (2004) and Manley et al. (1985), a lower surface roughness reduces fixation strength of the implant-cement interface and may explain why the revised CKS components could be removed so easily. Another difference between the designs concerns the PE insert. The CKS design uses a tibial insert with a more promi- nent and sharp posterior edge compared to the PFC design. This sharp edge may come in contact with the PCL, leading to damage and subsequent PCL laxity. In a previous study com- paring the CKS and the PFC prostheses, kinematic analysis supported the suspicion that the CKS design has larger AP translations than the PFC design (Ploegmakers et al. 2010). Although clinical ratings such as the KSS, total WOMAC, and VAS did not show any statistically significant difference in that study, subscores regarding higher flexion and higher- demanding activities showed greater limitations in knees with a CKS design. Moreover, it has been described that in addi- tion to AP instability, PCL insufficiency may cause (anterior knee) pain and result in malfunction (Waslewski et al. 1998, Pagnano et al. 1998). Thus, the worse functional outcome for the CKS system that we found may also be explained by PCL insufficiency due to in vivo damage of the PCL at the sharp posterior edge of the tibial insert. Our study had some limitations. First, a relatively high number of patients (12) died before final follow-up. Even so, all the patients were analyzed with the latest available (and minimal 1-year) follow-up. Including these patients, the mean follow-up was 5.6 years. Furthermore, no patients were lost to follow-up. Another possible limitation is the potential bias from there being 6 different surgeons involved in this study. However, since we are a teaching hospital all procedures were performed by—or under direct supervision of—an expe- rienced knee surgeon and none of the reoperated cases had originally been operated by a surgeon with low volume. One strength of our study was the randomization process with stratification for age, flexion contracture, and co-mor- bidity. Consequently, patient demographics and the baseline clinical status of both groups were similar. Thus, we are con- vinced that the differences in clinical function and survival between the groups were caused by the differences in design between the CKS and the PFC prostheses. Our study was not designed to determine the reason for the worse results of the CKS design. We believe that the reason may have been multi- factorial, and a combination of low fixation strength and pos- sible PCL insufficiency. Initially, we thought that the CKS system was very similar to the PFC system, but the large dif- ferences in clinical outcome were evident and discouraged us from further use of the CKS system. Acta Orthopaedica 2011; 82 (6): 685–691 HJM: study design, data collection, manuscript preparation. NV, CJL and MWM: study design. GH: data analysis. All authors: data evaluation, review- ing the manuscript No competing interests declared. Barink M, Van de Groes S, Verdonschot N, De Waal Malefijt M. The differ- ence in trochlear orientation between the natural knee and current pros- thetic knee designs; towards a truly physiological prosthetic groove orien- tation. J Biomech 2006; 39: 1708-15. Bellamy N, Buchanan W W, Goldsmith C H, Campbell J, Stitt L W. Vali- dation study of WOMAC: a health status instrument for measuring clini- cally important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J Rheumatol 1988; 15: 1833-40. Boonstra M C, de Waal Malefijt M C, Verdonschot N. How to quantify knee function after total knee arthroplasty? Knee 2008; 15: 390-5. Boyd A D, Ewald F C, Thomas W H, Poss R, Sledge C B. Long-term com- plications after total knee arthroplasty with or without resurfacing of the patella. J Bone Joint Surg (Am) 1993; 75: 674-81. Bozic K J, Kinder J, Meneghini R M, Zurakowski D, Rosenberg A G, Galante J O. Implant survivorship and complication rates after total knee arthroplasty with a third-generation cemented system: 5 to 8 years fol- lowup. Clin Orthop 2005; [430]:117-24. Brokelman R B, Meijerink H J, de Boer C L, van Loon C J, de Waal Male- fijt M C, van Kamapen A. Are surgeons equally satisfied after total knee arthroplasty? Arch Orthop Trauma Surg 2004; 124: 331-3. Choi W C, Lee S, Seong S C, Jung J H, Lee M C. Comparison between stan- dard and high-flexion posterior-stabilized rotating-platform mobile-bear- ing total knee arthroplasties: a randomized controlled study. J Bone Joint Surg (Am) 2010; 92: 2634-42. Clarke H D, Hentz J G. Restoration of femoral anatomy in TKA with unisex and gender-specific components. Clin Orthop 2008; (466): 2711-6. Dalury D F, Barrett W P, Mason J B, Goldstein W M, Murphy J A, Roche M W. Midterm survival of a contemporary modular total knee replacement: a multicentre study of 1970 knees. J Bone Joint Surg (Br) 2008; 90: 1594-6. Ewald F C. The Knee Society total knee arthroplasty roentgenographic evalu- ation and scoring system. Clin Orthop 1989; [248]: 9-12. Fortin P R, Clarke A E, Joseph L, Liang M H, Tanzer M, Ferland D, Phillips C, Partridge A J, Belisle P, Fossel A H, Mahomed N, Sledge C B, Katz J N. Outcomes of total hip and knee replacement: preoperative functional status predicts outcomes at six months after surgery. Arthritis Rheum 1999; 42: 1722-8. Fortin P R, Penrod J R, Clarke A E, St-Pierre Y, Joseph L, Belisle P, Liang M H, Ferland D, Phillips C B, Mahomed N, Tanzer M, Sledge C, Fossel A H, Katz J N. Timing of total joint replacement affects clinical outcomes among patients with osteoarthritis of the hip or knee. Arthritis Rheum 2002; 46: 3327-30. Gobel D, Schultz W. Clinical results and economics of two primary total knee replacement systems implanted in standardised surgical technique. Z Orthop Unfall 2008; 146: 602-8. Hanusch B, Lou T N, Warriner G, Hui A, Gregg P. Functional outcome of PFC Sigma fixed and rotating-platform total knee arthroplasty. A prospective randomised controlled trial. Int Orthop 2010; 34: 349-54. Harrington M A, Hopkinson W J, Hsu P, Manion L. Fixed- vs mobile-bearing total knee arthroplasty: does it make a difference?--a prospective random- ized study. J Arthroplasty 2009; 24: 24-7. Harwin S F. Patellofemoral complications in symmetrical total knee arthroplasty. J Arthroplasty 1998; 13: 753-62. Healy W L, Wasilewski S A, Takei R, Oberlander M. Patellofemoral compli- cations following total knee arthroplasty. Correlation with implant design and patient risk factors. J Arthroplasty 1995; 10: 197-201.