title: A patient-specific model of total knee arthroplasty to estimate patellar strain: A case study.
abstract: BACKGROUND
  Inappropriate patellar cut during total knee arthroplasty can lead to patellar complications due to increased bone strain. In this study, we evaluated patellar bone strain of a patient who had a deeper patellar cut than the recommended.
  
  
  METHODS
  A patient-specific model based on patient preoperative data was created. The model was decoupled into two levels: knee and patella. The knee model predicted kinematics and forces on the patella during squat movement. The patella model used these values to predict bone strain after total knee arthroplasty. Mechanical properties of the patellar bone were identified with micro-finite element modeling testing of cadaveric samples. The model was validated with a robotic knee simulator and postoperative X-rays. For this patient, we compared the deeper patellar cut depth to the recommended one, and evaluated patellar bone volume with octahedral shear strain above 1%.
  
  
  RESULTS
  Model predictions were consistent with experimental measurements of the robotic knee simulator and postoperative X-rays. Compared to the recommended cut, the deeper cut increased the critical strain bone volume, but by less than 3% of total patellar volume.
  
  
  CONCLUSIONS
  We thus conclude that the predicted increase in patellar strain should be within an acceptable range, since this patient had no complaints 8 months after surgery. This validated patient-specific model will later be used to address other questions on groups of patients, to eventually improve surgical planning and outcome of total knee arthroplasty.
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Biomechanical Orthopedics, Lausanne, Switzerland.
authors.forename: Adeliya
authors.initials: A
authors.lastname: Latypova
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Movement Analysis and Measurement, Lausanne, Switzerland.
authors.forename: Arash
authors.initials: A
authors.lastname: Arami
authors.affiliation: Lausanne University Hospital (CHUV), Department of Diagnostic and Interventional Radiology, Lausanne, Switzerland.
authors.forename: Fabio
authors.initials: F
authors.lastname: Becce
authors.affiliation: Vaudois Lausanne University Hospital (CHUV) and University of Lausanne, Lausanne, Switzerland.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Jolles-Haeberli
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Movement Analysis and Measurement, Lausanne, Switzerland.
authors.forename: Kamiar
authors.initials: K
authors.lastname: Aminian
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Biomechanical Orthopedics, Lausanne, Switzerland.
authors.forename: Dominique P
authors.initials: DP
authors.lastname: Pioletti
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Biomechanical Orthopedics, Lausanne, Switzerland. Electronic address: alexandre.terrier@epfl.ch.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Terrier
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery; D008954:Models, Biological; D008962:Models, Theoretical; D010329:Patella / Q000503:physiopathology* / Q000601:surgery*; D013312:Stress, Physiological / Q000502:physiology*
keywords: Arthroplasty; Finite elements; Kinematics; Knee; Patella; Strain