Orthopaedic surgeons and their patients continue to seek better functional outcomes after total knee replacement, but TKA designs claim characteristic kinematic performance that is rarely assessed in patients. The objectives of this investigation is to determine the in vivo kinematics in knees with Cruciate Retaining TKA using Patient Specific Technology during activities of daily living and to compare the findings with previous studies of kinematics of other CR TKA designs. Four knees were operated by Triathlon CR TKA using Patient Specific Technology and a fluoroscopic measurement technique has been used to provide detailed three-dimensional kinematic assessment of knee arthroplasty function during three motor tasks. 3D fluoroscopic analysis was performed at 4-month follow-up. The range of flexion was 90°(range 5°–95°) during chair-rising, 80°(range 0°–80°) during step up and 100° (range 0°–100°) during leg extension. The corresponding average external rotation of the femur on the tibial base-plate was 7.6° (range +4.3°; +11.9°), 9.5° (+4.0°; 13.5°) and 11.6° (+4.5°; +16.1°). The mean antero-posterior translations between femoral and tibial components during the three motor tasks were +4.7 (−3.7; +1.0), +6.4 (−3.8; +2.6) and +8,4 (−4.9; +3.5) mm on the medial compartment, and −2.5 (−7.1; −9.6), −3.6 (−6.1; −9.7), −2.6 (−7.7; −10.3) mm on the lateral compartment, respectively, with the medial condyle moving progressively anterior with flexion, and the medial condyle moving progressively posterior with flexion. We compared Triathlon CR PSI TKA results from this study with Genesis II CR TKA, with Duracon CR TKA, with Triathlon CR TKA and with the healthy knee kinematics. The results of this study showed no screw home mechanism. The internal rotation of the tibia with knee flexion is close to normal, better than Genesis II, Duracon and Triathlon CR TKA operated with standard surgery. The medial condyle is characterized by the same pattern of the other implants, with a paradoxical anterior translation of 5 mm. The lateral condyle shows a posterior rollback better than Triathlon CR operated with standard surgery. For the first time is demonstrated that the surgical technique can modify the tibio-femoral kinematics.
