title: Subject-specific evaluation of patellofemoral joint biomechanics during functional activity.
abstract: Patellofemoral joint pain is a common problem experienced by active adults. However, relatively little is known about patellofemoral joint load and its distribution across the medial and lateral facets of the patella. In this study, biomechanical experiments and computational modeling were used to study patellofemoral contact mechanics in four healthy adults during stair ambulation. Subject-specific anatomical and gait data were recorded using magnetic resonance imaging, dynamic X-ray fluoroscopy, video motion capture, and multiple force platforms. From these data, in vivo tibiofemoral joint kinematics and knee muscle forces were computed and then applied to a deformable finite-element model of the patellofemoral joint. The contact force acting on the lateral facet of the patella was 4-6 times higher than that acting on the medial facet. The peak average patellofemoral contact stresses were 8.2±1.0 MPa and 5.9±1.3 MPa for the lateral and medial patellar facets, respectively. Peak normal compressive stress and peak octahedral shear stress occurred near toe-off of the contralateral leg and were higher on the lateral facet than the medial facet; furthermore, the peak compressive stress (11.5±3.0 MPa) was higher than the peak octahedral shear stress (5.2±0.9 MPa). The dominant stress pattern on the lateral patellar facet corresponded well to the location of maximum cartilage thickness. Higher loading of the lateral facet is also consistent with the clinical observation that the lateral compartment of the patellofemoral joint is more prone to osteoarthritis than the medial compartment. Predicted cartilage contact stress maps near contralateral toe-off showed three distinctly different patterns: peak stresses located on the lateral patellar facet; peak stresses located centrally between the medial and lateral patellar facets; and peak stresses located superiorly on both the medial and lateral patellar facets.
authors.affiliation: Department of Mechanical Engineering, University of Melbourne, Victoria 3010, Australia.
authors.forename: Massoud
authors.initials: M
authors.lastname: Akbarshahi
authors.affiliation: Auckland Bioengineering Institute, University of Auckland, Auckland 1010, New Zealand; Department of Engineering Science, University of Auckland, Auckland 1010, New Zealand. Electronic address: j.fernandez@auckland.ac.nz.
authors.forename: Justin W
authors.initials: JW
authors.lastname: Fernandez
authors.affiliation: Department of Mechanical Engineering, University of Melbourne, Victoria 3010, Australia.
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Schache
authors.affiliation: Department of Mechanical Engineering, University of Melbourne, Victoria 3010, Australia.
authors.forename: Marcus G
authors.initials: MG
authors.lastname: Pandy
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000502:physiology; D004576:Electromyography; D020342:Finite Element Analysis; D005471:Fluoroscopy; D005684:Gait / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000502:physiology; D010329:Patella / Q000502:physiology; D057071:Patellofemoral Joint / Q000502:physiology*; D013314:Stress, Mechanical; D014741:Video Recording
keywords: Cartilage stress; Contact pressure; Knee-joint loading; Osteoarthritis; X-ray fluoroscopy