Depth-dependent strain of patellofemoral articular cartilage in unconfined compression

• Published in: Journal of biomechanics 2005-04, Vol.38 (4), p.667-672
• Main Authors: Erne, Oliver K., Reid, John B., Ehmke, Larry W., Sommers, Mark B., Madey, Steven M., Bottlang, Michael
• Format: Article
• Language: English
• Subjects: Algorithms; Animals; Articular cartilage; Biomechanical Phenomena; Cartilage; Cartilage, Articular - injuries; Cartilage, Articular - physiology; Compression; Compressive Strength; Equipment Design; In Vitro Techniques; Knee; Knee Joint - pathology; Knee Joint - physiology; Lasers; Measurement techniques; Mechanical properties; Patellofemoral joint; Sprains and Strains - etiology; Strain measurement; Swine
• ISSN: 0021-9290; 1873-2380
• DOI: 10.1016/j.jbiomech.2004.04.005

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.