Background. To prevent excessive tension on the posterior cruciate ligament (PCL) in cruciate-retaining total knee arthroplasty (CR-TKA), some knee prosthesis-systems offer the option of creating a posterior slope for the tibial polyethylene insert. Vanguard® Complete Knee System offers two different types of tibial bearing for CR. -TKA. CR Lipped Bearing (LB) has a slightly raised posterior lip, whereas CR Standard Bearing (SB) is recessed downward at the posterior margin and has 3° posterior slope. The objective of this study was to investigate the effect of the tibial bearing slope on PCL load using the original devise in vivo conditions. Material and Methods. Twenty osteoarthritic varus knees were included in this study. After implantation of the trial components, PCL stiffness was measured using the original tension analyzer intra-operatively. Elastic modulus of PCL was calculated at 90 and 120 degrees knee flexion on two types of bearing surface. Results. Elastic modulus of PCL was 7.2±0.9 N/mm (mean±SE) at 90 degrees knee flexion, and 9.5±1.1 N/mm (mean±SE) at 120 degrees knee flexion with the Lipped Bearing (no slope). With the Standard Bearing (3 degrees posterior slope), elastic modulus decreased to 6.0±0.5 N/mm (mean±SE) at 120 degrees knee flexion. Discussion and Conclusion. Higher PCL stiffness was observed at 120 degrees knee flexion than 90 degrees knee flexion with Lipped Bearing surface (no slope), but using the Standard Bearing (3 degrees posterior slope), PCL stiffness decreased significantly at 120 degrees knee flexion. Therefore a posterior tibial slope of bearing insert prevents an excessive load on PCL at high knee flexion angles

Introduction. The assumption that symmetric extension-flexion gaps improve the femoral condyle lift-off phenomenon and the patellofemoral joint congruity in total knee arthroplasty (TKA) is now widely accepted. Conventional understanding of knee kinematics suggests that the femoral component should be rotationally aligned parallel to the surgical epicondylar axis (SEA). On the other hand, the theory of the balanced gap technique suggests the knee be balanced in extension and flexion to achieve proper kinematics and stability of the knee without reference to fixed bony landmarks. The purpose of our study was to evaluate the relationship between rotation alignment of the femoral component and postoperative flexion gap balance, and the femoral rotational alignment in relation to the tibial mechanical axis in patients when implanted using a balanced gap technique. Materials and Methods. The subjects presented 53 consecutive osteoarthritic (OA) varus knees underwent primary Posterior-Stabilised (PS) -TKA (NexGen LPS-flex, Zimmer). All subjects completed written informed consent. The patient population was composed of 7 men and 35 women with a mean age of 72.5 ± 8.3 years. The average height, weight, BMI, weight-bearing FTA, and the patella height (Insall-Salvati ratio: T/P ratio) were 151.7 ± 7.7 cm, 62.6 ± 11.8 kg, 27.2 ± 4.5, 184.9 ± 5.9° and 0.93 ± 0.14 respectively. All procedures were performed through a medial parapatellar approach and a balanced gap technique used a newly developed versatile tensor device which can measure the medial and lateral gaps individually and make use of the balanced gap technique guide with patellofemoral joint reduction, which had been introduced in 56. th. ORS 2010. Pre- and post-operatively, a condylar twist angle (CTA) was evaluated using computed tomography (CT). To assess the postoperative flexion gap balance, a condylar lift-off angle (LOA) was evaluated using the epicondylar view radiographs by adding a 1.5 kg weight at the ankle. Coronal alignment of the tibial component in reference to the tibial mechanical axis (angle θ) was evaluated using plain AP radiography. Data were expressed as mean ± SD and analysed with Stat View version 5.0. Results. Extension gap was well balanced within 3 mm in all cases. The average of the preoperative CTA, the postoperative CTA, the LOA and the angle θ. were 6.0 ± 1.5°, 1.2 ± 2.4°, 0.8 ± 1.4° and 89.7 ± 1.2° respectively. No significant correlation was observed in between the postoperative CTA, the LOA and the angle θ. The degree of the clinical epicondylar axis (CEA) to the tibial machanical axis was 90.1 ± 2.9°. Only one knee needed lateral retinaculum release, because of poor patella tracking evaluated by no thumb test or one stitch method. Discussion. This study demonstrated that our balanced gap technique, using a newly developed tensor device, achieved good patellofemoral joint congruity and balanced flexion gaps postoperatively. Rotation alignment of the femoral component was slight internal rotation in reference to the CEA but not parallel to the SEA. Conclusion. The CEA was perpendicular to the tibial mechanical axis in PS-TKA with well balanced extension-flexion gap achieved by a balanced gap technique