The objective of this study was to characterize the biomechanical properties of articular cartilage in the superior joint space of the porcine temporomadibular joint (TMJ). These properties and thickness of the disk and fossa cartilage were obtained from eight joints using creep indentation. Five sites per surface were tested to obtain the aggregate modulus, Poisson's ratio, permeability, creep, recovery percentage, and cartilage thickness. Histology was also performed to characterize the orientation of the collagen fibers and the proteoglycan content. It was found that the temporal fossa cartilage was 57% thinner and 50% stiffer than the disk. The aggregate modulus of the porcine TMJ disk and fossa was much smaller, but the permeability of the TMJ disk and fossa was much higher than those of articular cartilage in other joints. It was also noted that the TMJ disk did not fully recover following indentation testing unlike the articular cartilage in other joints. The biomechanical properties of the TMJ disk and temporal fossa obtained in this study are significantly different from those of cartilage present in other diarthrodial joints. This suggests that the function of the fibrocartilage in the superior TMJ space is substantially different from that of hyaline cartilage in other joints.
The in vivo assessment of the quality of cartilage is a critical tool to determine how to clinically treat damaged cartilage. Utilizing nondestructive indentation, a hand-held instrument (ACTAEON Probe) was used to rapidly measure the stiffness of articular cartilage, which can then be correlated to cartilage condition. An integrated series of tests were performed to determine whether the Probe is sensitive enough to detect early degenerative changes in articular cartilage and to examine if it is dependent on the thickness of the cartilage being tested. Results demonstrated that there is no effect of thickness on the Probe measurements for clinically relevant human cartilage samples, that the Probe is sensitive enough to detect different levels of cartilage degeneration, and that Probe data correlate well with traditional creep indentation testing. This study demonstrates the utility of the Probe for detecting degenerative changes in animal and human joints.
Previous studies have demonstrated that male Sprague Dawley (SD) rats experience age-related bone loss with the same characteristics as that in ageing men. As articular cartilage, like bone, is a critical component of the health and function of the musculoskeletal system, the authors hypothesized that articular cartilage in the untreated male SD rats could be a suitable model for studying the age-related deterioration of articular cartilage in men. To test this hypothesis, male SD rats were killed at between 6 and 27 months. The right femur of each rat was removed. The effects of ageing on the structural integrity of the distal femoral articular cartilage were studied by biomechanical testing with a creep indentation apparatus. The aggregate modulus, Poisson's ratio, permeability, thickness, and percentage recovery of articular cartilage were determined using finite element/non-linear optimization modelling. No significant differences were observed in these biomechanical properties of the distal femoral articular cartilage as a function of age. Therefore, untreated male SD rats appear to be unsuitable for studying the age-related changes of articular cartilage as they occur in men. However, and more intriguingly, it is also possible that ageing does not affect the biomechanical properties of articular cartilage in the absence of cartilage pathology.
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