Anatomic-like polyethylene insert could improve knee kinematics after total knee arthroplasty — A computational assessment Yu-Liang Liu a , Kun-Jhih Lin a,b , Chang-Hung Huang c , Wen-Chuan Chen a,b , Chih-Hui Chen a,d , Tsung-Wei Chang a , Yu-Shu Lai a,b , Cheng-Kung Cheng a,b, ⁎ a Orthopaedic Biomechanics Laboratory, Institute of Biomedical Engineering, National Yang-Ming University, Taipei, Taiwan b Orthopaedic Device Research Center, National Yang-Ming University, Taipei, Taiwan c Biomechanics Research Laboratory, Department of Biomedical Research, Mackay Memorial Hospital, Tamshui, Taiwan d Department of Orthopedics, Taichung Veterans General Hospital, Taichung, Taiwan abstract article info Article history: Received 11 January 2011 Accepted 31 January 2011 Keywords: Knee kinematics Anatomical shape Tibial insert TKA Computer simulation Backgrounds: Deficiencies in contemporary posterior crucitate retaining knee included inadequate femoral rollback and insufficient tibial rotation. Current study attempted to restore normal femoral rollback and tibial rotation to facilitate in knee flexion/extension and to achieve appropriate posture at deep knee bending after total knee arthroplasy by mimicking the morphology of convexly lateral tibial plateau of intact knee. Methods: Computational simulation was utilized to analyze motion of three-dimensional knee models, including intact, traditionally symmetrical posterior crucitate retaining and newly anatomic-like posterior crucitate retaining knees. Solid bones, attachments of ligaments and tendons of simulation models were reconstructed by magnetic resonance images of the subject. According to the representative literature, the distal femur was modeled to rotate about the specific axes and the motion of the proximal tibial was unconstrained except for the flexion/extension. Movements of the medial/lateral condyles and tibial rotation were recorded and analyzed. Findings: The newly anatomic-like posterior crucitate retaining knee improved the posterior movement of lateral condyle and tibial internal rotation significantly during full range of flexion. Compared with traditionally symmetrical posterior crucitate retaining knee, the improvements displayed by newly developed posterior crucitate retaining knee in posterior movement of lateral condyle and tibial internal rotation were 11.2 mm and 9.3° at full flexion, respectively. Interpretation: The newly anatomic-like posterior crucitate retaining knee demonstrated that mimicking the morphology of convexly lateral tibial plateau can be expected to restore normal knee kinematics. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction The long-term survival rate of commercial posterior cruciate retaining (PCR) knee had been reported at 93.7% over a 15-year lifespan (Vessely et al., 2002). However, excellent survivorship of total knee arthroplasty (TKA) does not always correlate with patient's satisfaction (Beverland, 2010). This could be due to abnormal motion, such as inadequate femoral rollback and insufficient tibial internal rotation (Most et al., 2003; Dennis et al., 2004; Casino et al., 2009; Li et al., 2009). Greater femoral rollback would improve the efficiency of quadriceps muscle (Andriacchi and Mikosz, 1991) and facilitate the achievement of higher knee flexion (Mikashima et al., 2010). Tibial rotation is associated with deep-flexion knee posture, such as squatting, kneeling or lunging (Banks et al., 2003). Modified prosthetic geometry is commonly used to restore natural knee kinematics such as motion guiding implant (Walker et al., 2009), medial pivot knee (Moonot et al., 2009) and fully flat insert designs (Gomaa and Williams, 2009). Although the abovementioned modifications offer improvements in specific motions, they still could not properly recover normal knee kinematics. A possible cause is that the prosthetic geometry of total knee system is inconsistent with the morphology of intact knee. The lateral tibial plateau of intact knee is convex, but most contemporary tibial inserts are symmetrically concave in design that could result in abnormal knee motion after TKA (Bare´ et al., 2006). To our knowledge, anatomic-like (convex) shape has never been applied to commercial PCR knee. Therefore, the purpose of the current study was to restore normal knee femoral rollback and tibial internal rotation to facilitate knee flexion/extension and to achieve appropriate knee posture at deep knee bending after total knee arthroplasy by mimicking the morphology of convexly lateral tibial plateau of intact knee. We believe that mimicking the morphology of intact knee could be expected to reproduce natural knee kinematics. Clinical Biomechanics 26 (2011) 612–619 ⁎ Corresponding author at: Orthopeadic Biomechanics Laboratory, Institute of Biomedical Engineering, National Yang-Ming University, Address: No.155, Sec.2, Linong St., Shih-Pai, Taipei, 11221 Taiwan. E-mail address: ckcheng@ym.edu.tw (C.-K. Cheng). 0268-0033/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.clinbiomech.2011.01.013 Contents lists available at ScienceDirect Clinical Biomechanics journal homepage: www.elsevier.com/locate/clinbiomech