Propagation of microcracks in collagen networks of cartilage under mechanical loads

Abstract

Objective: We recently demonstrated that low-energy mechanical impact to articular cartilage, usually considered non-injurious, can in fact cause microscale cracks (widths < 30 mm) in the collagen network of visually pristine human cartilage. While research on macro-scale cracks in cartilage and microcracks in bone abounds, how microcracks within cartilage initiate and propagate remains unknown. We quantified the extent to which microcracks initiate and propagate in the collagen network during mechanical loading representative of normal activities. Design: We tested 76 full-thickness, cylindrical osteochondral plugs. We imaged untreated specimens (pristine phase) via second harmonic generation and assigned specimens to three low-energy impact groups (none, low, high), and thereafter to three cyclic compression groups (none, low, high) which simulate walking. We re-imaged specimens in the post-impact and post-cyclic compression phases to identify and track microcracks. Results: Microcracks in the network of collagen did not present in untreated controls but did initiate and propagate under mechanical treatments. We found that the length and width of microcracks increased from post-impact to post-cyclic compression in tracked microcracks, but neither depth nor angle presented statistically significant differences. Conclusions: The microcracks we initiated under low-energy impact loading increased in length and width during subsequent cyclic compression that simulated walking. The extent of this propagation depended on the combination of impact and cyclic compression. More broadly, the initiation and propagation of microcracks may characterize pathogenesis of osteoarthritis, and may suggest therapeutic targets for future studies.

Pathogenesis and clinical management of obesity-related knee osteoarthritis: Impact of mechanical loading

“…[ 38 ] Cyclic loading In vivo 0.2–2.0 MPa in compression for 10,000 cycles at 2 Hz for 2 weeks By MR, loaded limbs displayed BMLs, increased tissue microdamage and bone resorption as compared to controls Santos et al. [ 53 ] Impact & cyclic compression Ex vivo 76 full-thickness, cylindrical osteochondral plugs were assigned to low-energy impact groups (none, low, high), and thereafter three cyclic compression groups (none, low, high) Microcracks in cartilage collagen network initiate and propagate under mechanical treatments. The length and width of microcracks increased by impact and cyclic compression.…”

Full-Field Strain Uncertainties and Residuals at the Cartilage-Bone Interface in Unstained Tissues Using Propagation-Based Phase-Contrast XCT and Digital Volume Correlation

“…Unconfined compression was then performed on the plug (Bose Electroforce, New Castle, DE, USA) with load applied on the free articular cartilage surface. The specimen was immersed in PBS throughout the duration of the test and pre-loaded with 0.2 N for 3000 s. Compression was then applied as a displacement of 0.2 mm (equal to~10% of the articular cartilage thickness) at a speed of 0.2 mm/s and held for 120 s to allow stress relaxation [39].…”

Sex, but not age and bone mass index positively impact on the development of osteochondral micro‐defects and the accompanying cellular alterations during osteoarthritis progression

“…A possible explanation could be that repetitive complex mechanical loading, such as the combination of impact energy and cyclic compression, has been reported to be necessary to promote microtraumas in the collagen network, to initiate the degradation of calcified tissues and affect the propagation of microcracks. 32 Contrariwise, female sex was positively associated with crack development. The combination of different hormonal factors and low bone density in female participants may be responsible for the accumulation of microdefects.…”