title: Finite element modeling of soft tissues: material models, tissue interaction and challenges.
abstract: BACKGROUND
  Musculoskeletal soft tissues, such as articular cartilage, ligaments, knee meniscus and intervertebral disk, have a complex structure, which provides elasticity and capability to support and distribute the body loads. Soft tissues describe an inhomogeneous and multiphasic structure, and exhibit a nonlinear, time-dependent behavior. Their mechanical response is governed by a substance composed of protein fiber-rich and proteoglycan-rich extracellular matrix and interstitial fluid. Protein fibers (e.g. collagen) give the tissue direction dependent stiffness and strength. To investigate these complex biological systems, the use of mathematical tools is well established, alone or in combination with experimental in vitro and in vivo tests. However, the development of these models poses many challenges due to the complex structure and mechanical response of soft tissues.
  
  
  METHODS
  Non-systematic literature review.
  
  
  RESULTS
  This paper provides a summary of different modeling strategies with associated material properties, contact interactions between articulating tissues, validation and sensitivity of soft tissues with special focus on knee joint soft tissues and intervertebral disk. Furthermore, it reviews and discusses some salient clinical findings of reported finite element simulations.
  
  
  CONCLUSIONS
  Model studies extensively contributed to the understanding of functional biomechanics of soft tissues. Models can be effectively used to elucidate clinically relevant questions. However, users should be aware of the complexity of such tissues and of the capabilities and limitations of these approaches to adequately simulate a specific in vivo or in vitro phenomenon.
authors: Institute of Orthopaedic Research and Biomechanics, Center of Musculoskeletal Research Ulm, University of Ulm, Ulm, Germany. Electronic address: maren.freutel@uni-ulm.de.
authors: Maren
authors: M
authors: Freutel
authors: Julius Wolff Institut, Charité - Universitätsmedizin Berlin, Berlin, Germany.
authors: Hendrik
authors: H
authors: Schmidt
authors: Institute of Orthopaedic Research and Biomechanics, Center of Musculoskeletal Research Ulm, University of Ulm, Ulm, Germany.
authors: Lutz
authors: L
authors: Dürselen
authors: Institute of Orthopaedic Research and Biomechanics, Center of Musculoskeletal Research Ulm, University of Ulm, Ulm, Germany.
authors: Anita
authors: A
authors: Ignatius
authors: IRCCS Istituto Ortopedico Galeazzi, Milan, Italy.
authors: Fabio
authors: F
authors: Galbusera
mesh_terms: D016880:Anisotropy; D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000502:physiology*; D003094:Collagen / Q000502:physiology; D004548:Elasticity; D020342:Finite Element Analysis; D006801:Humans; D007403:Intervertebral Disc / Q000502:physiology*; D007592:Joint Diseases / Q000503:physiopathology; D007719:Knee Joint / Q000502:physiology*; D008023:Ligaments, Articular / Q000502:physiology*; D008592:Menisci, Tibial / Q000502:physiology*; D008954:Models, Biological; D017711:Nonlinear Dynamics; D011509:Proteoglycans / Q000378:metabolism; D013314:Stress, Mechanical
chemical_list: D011509:Proteoglycans; D003094:Collagen
keywords: Anisotropy; Biomechanics; Cartilage; Finite element; Intervertebral disk; Material formulations; Meniscus; Soft tissue