Multiscale Strain as a Predictor of Impact-Induced Fissuring in Articular Cartilage

Abstract

Mechanical damage is central to both initiation and progression of osteoarthritis (OA). However, specific causal links between mechanics and cartilage damage are incompletely understood, which results in an inability to predict failure. The lack of understanding is primarily due to the difficulty in simultaneously resolving the high rates and small length scales relevant to the problem and in correlating such measurements to the resulting fissures. This study leveraged microscopy and high-speed imaging to resolve mechanics on the previously unexamined time and length scales of interest in cartilage damage, and used those mechanics to develop predictive models. The specific objectives of this study were to: first, quantify bulk and local mechanics during impact-induced fissuring; second, develop predictive models of fissuring based on bulk mechanics and local strain; and third, evaluate the accuracy of these models in predicting fissures. To achieve these three objectives, bovine tibial cartilage was impacted using a custom spring-loaded device mounted on an inverted microscope. The occurrence of fissures was modulated by varying impact energy. For the first objective, during impact, deformation was captured at 10,000 frames per second and bulk and local mechanics were analyzed. For the second objective, data from samples impacted with a 1.2 mm diameter rod were fit to logistic regression functions, creating models of fissure probability based on bulk and local mechanics. Finally, for the third objective, data from samples impacted with a 0.8 mm diameter rod were used to test the accuracy of model predictions. This study provides a direct comparison between bulk and local mechanical thresholds for the prediction of fissures in cartilage samples, and demonstrates that local mechanics provide more accurate predictions of local failure than bulk mechanics provide. Bulk mechanics were accurate predictors of fissure for the entire sample cohort, but poor predictors of fissure for individual samples. Local strain fields were highly heterogeneous and significant differences were determined between fissured and intact samples, indicating the presence of damage thresholds. In particular, first principal strain rate and maximum shear strain were the best predictors of local failure, as determined by concordance statistics. These data provide an important step in establishing causal links between local mechanics and cartilage damage; ultimately, data such as these can be used to link macro- and micro-scale mechanics and thereby predict mechanically mediated disease on a subject-specific basis.

Low-energy impact of human cartilage: predictors for microcracking the network of collagen

“…Our procedure, based on integrating accelerating data, was sensitive to the selected integration boundaries and may be not sufficiently reliable to calculate displacements. However, given the highly heterogeneous axial strain field through the thickness of cartilage under compression, bulk strain is likely not a good predictor of local damage 46 , possibly explaining the lack of correlate that we report.…”

How Does Chondrolabral Damage and Labral Repair Influence the Mechanics of the Hip in the Setting of Cam Morphology? A Finite-Element Modeling Study

“…Failure levels for contact pressure, tensile strain, shear stress, and fluid pressure in articular cartilage and labrum vary widely based on many factors including the health, hydration, or thickness of the cartilage; the loading rate or strain rate; and the joint in question [15,18,29,48]. Thus, it is difficult to indicate the direct physical interpretation for the magnitude of the variables in this study (such as, cartilage will rupture, become damaged, or degraded, etc.).…”

Relaxation capacity of cartilage is a critical factor in rate- and integrity-dependent fracture

“…Large crack lengths and severe damage to microstructural features were induced under relatively high-frequency compressive loading 30 , 31 . Recently, the authors and others found that impact loading, simulating the onset of post-traumatic OA, caused fissures and cracks 32 – 34 and that crack nucleation in cartilage was largely rate-dependent 35 , 36 . In particular, the authors observed that the solid matrix around the crack surfaces underwent larger relaxation and rearrangement at the slow loading rate compared to the fast loading rate 36 .…”