title: All-polyethylene tibial components generate higher stress and micromotions than metal-backed tibial components in total knee arthroplasty.
abstract: OBJECTIVE
  Most total knee arthroplasty tibial components are metal-backed, but an alternative tibial component made entirely of polyethylene (all-polyethylene design) exists. While several clinical studies have shown that all-poly design performs similarly to the metal-backed, the objective of this study is to perform a biomechanical comparison.
  
  
  METHODS
  Loads, constraints and geometries during a squat activity at 120° of flexion were obtained from a validated musculoskeletal model and applied to a finite element model. Stresses in the tibia and micromotions at the bone-implant interface were evaluated for several implant configurations: (1) three different thicknesses of the cement penetration under the baseplate (2, 3 and 4 mm), (2) the presence or absence of a cement layer around the stem of the tibial tray and (3) three different bone conditions (physiological, osteopenic and osteoporotic bone).
  
  
  RESULTS
  All-polyethylene tibial components resulted in significantly higher (p < 0.001) and more uneven stress distributions in the cancellous bone under the baseplate (peak difference: +128.4 %) and fivefold increased micromotions (p < 0.001). Performance of both implant designs worsened with poorer bone quality with peaks in stress and micromotion variations of +40.8 and +54.0 %, respectively (p < 0.001). Performance improvements when the stem was cemented were not statistically significant (n.s.).
  
  
  CONCLUSIONS
  The metal-backed design showed better biomechanical performance during a squat activity at 120° of flexion compared to the all-polyethylene design. These results should be considered when selecting the appropriate tibial component for a patient, especially in the presence of osteoporotic bone or if intense physical activity is foreseen.
authors.affiliation: Faculté de Médicine, Université F. Rabelais, Tours, France.
authors.forename: Jean
authors.initials: J
authors.lastname: Brihault
authors.affiliation: Department of Industrial Engineering, University of Bologna, Bologna, Italy. alessandro.navacchia@du.edu.|Computational Biomechanics Lab, University of Denver, 2390 S. York Street, Denver, CO, 80208, USA. alessandro.navacchia@du.edu.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Navacchia
authors.affiliation: IRCCS, Istituto Ortopedico Galeazzi, Milan, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Pianigiani
authors.affiliation: European Centre for Knee Research, Smith&Nephew, Louvain, Belgium.|Mechanical Engineering Technology TC, Campus Geel, KU Leuven, Louvain, Belgium.
authors.forename: Luc
authors.initials: L
authors.lastname: Labey
authors.affiliation: European Centre for Knee Research, Smith&Nephew, Louvain, Belgium.
authors.forename: Ronny
authors.initials: R
authors.lastname: De Corte
authors.affiliation: IRCCS, Istituto Ortopedico Galeazzi, Milan, Italy.
authors.forename: Valerio
authors.initials: V
authors.lastname: Pascale
authors.affiliation: European Centre for Knee Research, Smith&Nephew, Louvain, Belgium.|BEAMS Department, Université Libre de Bruxelles, Avenue Franklin Roosevelt, 50, Bruxelles, 1050, Belgium.
authors.forename: Bernardo
authors.initials: B
authors.lastname: Innocenti
mesh_terms: D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D001843:Bone Cements; D001851:Bone Diseases, Metabolic; D020342:Finite Element Analysis; D006801:Humans; D007720:Knee Prosthesis; D008670:Metals; D008953:Models, Anatomic; D010024:Osteoporosis; D020959:Polyethylene; D011474:Prosthesis Design; D016059:Range of Motion, Articular; D013977:Tibia
chemical_list: D001843:Bone Cements; D008670:Metals; D020959:Polyethylene
keywords: All-polyethylene; Implant micromotions; Metal-backed; TKA; Tibial stresses