686 A Figure 1. A. Sagittal view of the PFC design (left) and the CKS design (right). B. Anterior view of a computer model of the femoral compo- nents. Notice the lateral orientation of the trochlea in PFC (left) and neutral orientation in the CKS component (right). C. Posterior view of the tibial and PE insert components. The central posterior edge of the CKS insert (right) is relatively sharp compared to the PFC insert (left). Helsinki Declaration. The study was registered in the Clini- calTrials.gov Protocol Registration System (Identifier: NCT 00228137). All patients who were scheduled to undergo pri- mary total knee arthroplasty because of osteoarthritis or rheu- matoid arthritis at the Radboud University Nijmegen Medi- cal Centre were considered for inclusion and were enrolled prospectively. Exclusion criteria were dementia, hemophilia, juvenile rheumatoid arthritis, and ligament insufficiency that needed a posterior-stabilized or otherwise more constrained type of design. Between November 2002 and December 2004, 87 consecutive patients (95 knees) were assessed for eligibil- ity. 5 patients (5 knees) were excluded before randomization: 2 patients refused to participate, 2 patients had hemophilia, and 1 patient had dementia. After written informed consent had been obtained, the knees were randomly allocated to 2 groups. 45 knees received a press-fit condylar prosthesis (PFC; DePuy/Johnson and John- son, Warsaw, IN) and 45 knees received a continuum knee system prosthesis (CKS; Stratec Medical, Oberdorf, Switzer- land). Computer-generated randomization with stratification for age, co-morbidity, and flexion contracture was performed by an independent observer to allocate the patients in equal numbers to the 2 groups. Both cemented designs are PCL-retaining and have a fixed polyethelene (PE) insert on a tibial tray with central keel. The femoral and tibial components are made of the same mate- rial (cobalt-chromium-molybdenum and titanium-aluminium- vanadium alloy, respectively). In contrast to the lateral orien- tation of the patellar groove in the PFC prosthesis, the trochlea Acta Orthopaedica 2011; 82 (6): 685–691 B C of the CKS prosthesis is deeper and has a neutral direction. The femoral component of the PFC has a fixation peg in both condyles, whereas the CKS design uses one central peg. Fur- thermore, the CKS prosthesis has a different surface texture of the femoral component. Additionally, the PE insert of the CKS design has a more prominent and sharp posterior edge compared to the PFC design (Figure 1). Identical surgical techniques were used in the groups accord- ing to the manuals of the designers. 6 surgeons were involved in the study. All procedures were performed by an experienced knee surgeon or under the direct supervision of one. A pneu- matic tourniquet was used for all patients. A medial parapatel- lar capsular incision was used. No patellas were resurfaced. All implants were cemented after pulsed lavage, drying, and pressurization of the cement (Surgical Simplex, Stryker Howmedica). Continuous passive motion was started on the second postoperative day. Thereafter, active range-of-motion exercises and walking were started under the supervision of a physiotherapist. Routine follow-up evaluation was scheduled at postopera- tive intervals of 3 months, 6 months, 1 year, and annually thereafter. Preoperative and postoperative review data were recorded by a physician assistant who was blinded regarding patient allocation. At each follow-up visit, we took anteropos- terior, lateral, and skyline patellar radiographs, which were evaluated according to the guidelines of the Knee Society (Ewald 1989). The primary endpoint of the study was the between-group difference in total KSS (Insall et al. 1989). Pre-specified secondary endpoints to provide supportive evi-