title: Depth-dependent strain of patellofemoral articular cartilage in unconfined compression.
abstract: This biomechanical study reports strain gradients in patellofemoral joint cross-sections of seven porcine specimens in response to 1% unconfined axial compression subsequent to specific amounts of off-set strain. Strain distributions were quantified with a customized laser-based electronic speckle pattern interferometry (ESPI) system in a non-contact manner, delivering high-resolution, high-sensitivity strain maps over entire patellofemoral cartilage cross-sections. Strain reports were evaluated to determine differences in strain magnitudes between the superficial, middle, and deep cartilage layers in femoral and patellar cartilage. In addition, the effect of 5%, 10%, 15%, and 20% off-set strain on depth-dependent strain gradients was quantified. Regardless of the amount of off-set strain, the superficial layer of femoral cartilage absorbed the most strain, and the deep layer absorbed the least strain. These depth-dependent strain gradients were most pronounced for 5% off-set strain, at which the superficial layer absorbed on average 5.7 and 23.7 times more strain as compared to the middle and deep layers, respectively. For increased off-set strain levels, strain gradients became less pronounced. At 20% off-set strain, differences in layer-specific strain were not statistically significant, with the superficial layer showing a 1.4 fold higher strain as the deep layer. Patellar cartilage exhibited similar strain gradients and effects of off-set strain, although the patellar strain was on average 19% larger as compared to corresponding femoral strain reports. This study quantified for the first time continuous strain gradients over patellofemoral cartilage cross-sections. Next to provision of a detailed functional characterization of normal diarthrodial joints, this novel experimental approach holds considerable attraction to investigate joint degenerative processes.
authors.affiliation: Biomechanics Laboratory, Legacy Clinical Research & Technology Center, 1225 NE 2nd Avenue, Portland, OR 97232, USA.
authors.forename: Oliver K
authors.initials: OK
authors.lastname: Erne
authors.forename: John B
authors.initials: JB
authors.lastname: Reid
authors.forename: Larry W
authors.initials: LW
authors.lastname: Ehmke
authors.forename: Mark B
authors.initials: MB
authors.lastname: Sommers
authors.forename: Steven M
authors.initials: SM
authors.lastname: Madey
authors.forename: Michael
authors.initials: M
authors.lastname: Bottlang
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000293:injuries* / Q000502:physiology; D019245:Compressive Strength; D004867:Equipment Design; D066298:In Vitro Techniques; D007719:Knee Joint / Q000473:pathology / Q000502:physiology; D007834:Lasers; D013180:Sprains and Strains / Q000209:etiology*; D013552:Swine