Prediction of local fixed charge density loss in cartilage following ACL injury and reconstruction: A computational proof‐of‐concept study with MRI follow‐up

Abstract

The purpose of this proof-of-concept study was to develop three-dimensional patient-specific mechanobiological knee joint models to simulate alterations in the fixed charged density (FCD) around cartilage lesions during the stance phase of the walking gait. Two patients with anterior cruciate ligament (ACL) reconstructed knees were imaged at 1 and 3 years after surgery. The magnetic resonance imaging (MRI) data were used for segmenting the knee geometries, including the cartilage lesions. Based on these geometries, finite element (FE) models were developed. The gait of the patients was obtained using a motion capture system. Musculoskeletal modeling was utilized to calculate knee joint contact and lower extremity muscle forces for the FE models. Finally, a cartilage adaptation algorithm was implemented in both FE models. In the algorithm, it was assumed that excessive maximum shear and deviatoric strains (calculated as the combination of principal strains), and fluid velocity, are responsible for the FCD loss. Changes in the longitudinal T 1ρ and T 2 relaxation times were postulated to be related to changes in the cartilage composition and were compared with the numerical predictions. In patient 1 model, both the excessive fluid velocity and strain caused the FCD loss primarily near the cartilage lesion. T 1ρ and T 2 relaxation times increased during the follow-up in the same location. In contrast, in patient 2 model, only the excessive fluid velocity led to a slight FCD loss near the lesion, where MRI parameters did not show evidence of alterations. Significance: This novel proof-of-concept study suggests mechanisms through which a local FCD loss might occur near cartilage lesions. In order to obtain statistical evidence for these findings, the method should be investigated with a larger cohort of subjects.

An EMG-assisted Muscle-Force Driven Finite Element Analysis Pipeline to Investigate Joint- and Tissue-Level Mechanical Responses in Functional Activities: Towards a Rapid Assessment Toolbox

“…For instance, collagen fibril strain (related to, e.g., collagen damage) and fluid flow or maximum shear strain (related to, e.g., cell death and fixed charged density loss of the proteoglycans within the cartilage) are reported as measures for the prediction of cartilage adaptation and degradation response, consistent with experiments [6,9,46,47,91]. Nonetheless, none of these studies [6,9,46,47,91] have been incorporated into a multiscale MS-FE model considering subject-specific joint loading. Integrating the EMG-assisted MS-FE pipeline of our study with cartilage remodeling algorithms [6,9,46,47,91], as a part of our further research, may bring more accuracy when subject-specific mechanically-induced soft tissue adaptation and degeneration is of interest.…”

“…The EMG-assisted MS model enables the inclusion of subject-specific muscle activation patterns that may alter in subjects with MS disorders [24–27, 76, 77]. In addition, the FE model utilized a highly-detailed FRPVE soft tissue material model that has shown potentials if tissue-level mechanical responses, such as collagen fibril and nonfibrillar matrix strain, related to mechanically-induced cartilage adaptation and regeneration, are of interest [6, 37–41, 43, 46–48]. To assess and validate the developed pipeline, we investigated the knee joint loading and tissue mechanical responses during different daily activities of the individuals with KOA.…”

“…The stress and strain within the fibrillar (collagen) and nonfibrillar (proteoglycans) matrices of the cartilage and menisci are reported as indicators governing the cartilage adaptation and degradation response [43, 46, 47]. Hence, our workflow employing the FRPVE material model may promisingly be used in the subject-specific modification of different activities and the design of rehabilitation protocols, to slow the onset or progression of the KOA according to the estimated subject-specific joint mechanics.…”

“…Summarizing, FE models utilizing subjectspecific joint geometries and complex FRPVE material models have shown great potential for estimating highly-detailed tissue mechanics and predicting cartilage damage and degeneration [6,39,43,[46][47][48]. However, creating the above-mentioned FRPVE FE models is a cumbersome manual task requiring several weeks of high-level expertise [48].…”

“…Moreover, poroviscoelasticity is needed to replicate fluid-flow-dependent and -independent mechanisms of biphasic tissues [44], with within-tissue fluid pressurization carrying up to 90% of a dynamic load [40, 45]. These characteristics of the knee soft tissue emphasize the use of a fibrilreinforced poroviscoelastic (FRPVE) material model, which can potentially provide the FE analysis with a more detailed estimation of tissue-level mechanical responses, especially if adaptation and degradation of cartilage and its fibrillar and nonfibrillar matrices are of interest [6, 43, 46, 47].…”