Integration of Swin UNETR and statistical shape modeling for a semi-automated segmentation of the knee and biomechanical modeling of articular cartilage.

Simulation studies, such as finite element (FE) modeling, provide insight into knee joint mechanics without patient involvement. Generic FE models mimic the biomechanical behavior of the tissue, but overlook variations in geometry, loading, and material properties of a population. Conversely, subject-specific models include these factors, resulting in enhanced predictive precision, but are laborious and time intensive. The present study aimed to enhance subject-specific knee joint FE modeling by incorporating a semi-automated segmentation algorithm using a 3D Swin UNETR for an initial segmentation of the femur and tibia, followed by a statistical shape model (SSM) adjustment to improve surface roughness and continuity. For comparison, a manual FE model was developed through manual segmentation (i.e., the de-facto standard approach). Both FE models were subjected to gait loading and the predicted mechanical response was compared. The semi-automated segmentation achieved a Dice similarity coefficient (DSC) of over 98% for both the femur and tibia. Hausdorff distance (mm) between the semi-automated and manual segmentation was 1.4 mm. The mechanical results (max principal stress and strain, fluid pressure, fibril strain, and contact area) showed no significant differences between the manual and semi-automated FE models, indicating the effectiveness of the proposed semi-automated segmentation in creating accurate knee joint FE models. We have made our semi-automated models publicly accessible to support and facilitate biomechanical modeling and medical image segmentation efforts ( https://data.mendeley.com/datasets/k5hdc9cz7w/1 ).

A numerical model for fibril remodeling in articular cartilage.

BACKGROUND: Collagen fibrils of articular cartilage have a distinct organization in mature human knee joints. It seems that a mechanobiological process drives the remodeling of newborn collagen fibrils with maturation. Therefore, the goal of the present study was to develop a collagen fibril remodeling algorithm that describes the unique collagen fibril organization in a 3D knee model. METHOD: A fibril-reinforced, biphasic cartilage model was used with a cuboid and a 3D human knee joint geometries. An isotropic collagen fibril distribution was assigned to the cartilage at the start of the analysis. Each fibril was rotated towards the direction that resulted in a maximum stretch at each time increment of the loading cycle. RESULTS: The resulting pattern for the collagen fibrils was compared with split line patterns of porcine knee joint cartilage and also data published in the literature. Fibrils on the articular surface had a radial pattern towards the geometrical centroid of the tibial and femoral cartilage. In the tibiofemoral contact regions of superficial zone, fibrils were oriented circumferentially and randomly. In the porcine samples, the split-line patterns were similar to those obtained theoretically. Depth-wise organization of fibril network was characterized by fibrils perpendicular to the subchondral bone in the deeper layers, and fibrils parallel to the surface of cartilage in the superficial zone. CONCLUSIONS: The maximum stretch criterion, coupled with a biphasic constitutive model, successfully predicted the collagen fibril organization observed in the articular cartilage throughout the depth and on the articular surface.

The influence of equine hoof conformation on the initiation and progression of laminitis.

BACKGROUND: The health and performance of horses are significantly affected by diseases associated with the hoof. Laminitis is a critical hoof disease that causes pain and, potentially, severe hoof and bone pathology. OBJECTIVE: To generate an equine hoof finite element (FE) model to investigate the impact of normal and toe-in hoof conformations on the degeneration (decrease in elastic modulus) of the laminar junction (LJ), as occurs in chronic laminitis. STUDY DESIGN: Computer software modelling. METHODS: A hoof FE model was generated to investigate the biomechanics of hoof laminitis. A 3D model, consisting of nine components, was constructed from computed tomography scans of an equine left forelimb hoof. The model was loaded with 100 cycles of trotting. Two different centres of pressure (COP) paths representing normal and toe-in conformations were assigned to the model. LJ injury was modelled by degenerating the tissue's elastic modulus in the presence of excessive maximum principal stresses. RESULTS: FE models successfully showed findings similar to clinical observations, confirming third phalanx (P3) dorsal rotation, a symmetric distal displacement of the P3 (2 mm at the lateral and medial sides) in the normal model, and an asymmetric distal displacement of the P3 (4 mm at the lateral and 1.5 mm at the medial side) in the toe-in model. The proximal distance between P3 and the ground after LJ degeneration in the current model was significantly different from experimental measurements from healthy hooves (P < 0.01). MAIN LIMITATIONS: The inability to account for variations in population geometry and approximation of boundary conditions and system relations were the limitations of the current study. CONCLUSIONS: The distribution of LJ tissue degeneration was symmetric at the quarters in the normal hoof and in comparison, there was a lateral concentration of degeneration in the toe-in model.

HISTORIAL: La salud y el desempeño atlético de los caballos son afectados por patologías asociadas al casco. La laminitis es una enfermedad critica del casco que causa dolor y, potencialmente, patología severa del casco y ósea. OBJETIVO: Generar un modelo finito del casco equino para investigar el impacto de la conformación normal y del dedo-hacia-adentro sobre la degeneración (reducción del módulo elástico) de la unión laminar (UL), como ocurre en la laminitis crónica. DISEÑO DEL ESTUDIO: Modelado por computadora. MÉTODOS: Un modelo de elemento finito (EF) de casco fue generado para investigar la biomecánica de la laminitis en el casco. Un modelo 3D, que consistía de nueve componentes, fue construido a partir de imágenes de tomografía computarizada de un casco equino izquierdo. El modelo fue cargado con 100 ciclos de trote. Dos vías con centros de presión (VCP) distintos representando la conformación normal y dedo-hacia-adentro fueron asignadas al modelo. La lesión de la UL fue modelada degenerando el modelo elástico del tejido en la presencia de estrés principales excesivos máximos. RESULTADOS: Los modelos EF mostraron exitosamente hallazgos similares a las observaciones clínicas, confirmando que la rotación dorsal de la tercera falange (F3), con un desplazamiento distal simétrico de F3 (2 mm por medial y lateral) en el modelo normal, y un desplazamiento distal asimétrico de F3 (4 mm por lateral y 1.5 mm por medial) en el modelo dedo-hacia-adentro. La distancia proximal entre F3 y el suelo después de la degeneración de la UL en el modelo actual fue significativamente diferente de las mediciones experimentales de casco saludables (P < 0.01). LIMITACIONES DEL ESTUDIO: La inhabilidad de tomar en cuenta las variaciones en la geometría de la población y la aproximación de condiciones marginales, y relaciones de sistemas fueron las limitantes de este estudio. CONCLUSIONES: La distribución de la degeneración del tejido de la UL fue simétrico en los cuartos en el casco normal, hubo una concentración lateral de la degeneración en el modelo dedo-hacia-adentro. PALABRAS CLAVE: laminitis, conformación del casco del caballo, centro de presión, método de elemento finito, modelo hiperelástico.

Effect of collagen fibril distributions on the crack profile in articular cartilage.

BACKGROUND AND OBJECTIVE: Cartilage cracks and fissures may occur due to certain daily life activities such as sports practice, blunt trauma, and matrix fibrillation during early osteoarthritis. These cracks could further grow at the macroscopic level, alter the load distribution pattern in the matrix, limit the joint range of motion, and disturb chondrocytes synthesis. Cracks' shape and deformations in the loaded cartilage may affect the subsequent mechanobiological processes in the long term, likely because of the altered fluid exchange and excessive local deformations in the vicinity of the damage site. The fibrillar structure of the cartilage matrix appeared to have a protective effect against excessive deformations and tissue failure. Hence, in the present study, a fibril reinforced biphasic cartilage model was used to assess the potential role of different fibril orientations on the profile of a vertical crack in cartilage after applying a compressive load. METHODS: A 20 × 20 × 1.5 mm3 cartilage model was developed with a 0.7 mm length V-shape cut at the center. Using an impermeable indenter, a 27% compression was applied to immature, mature, and isotropic cartilage models. Each of immature and mature groups had 4 different split line directions with respect to the cut edges, including 90°, 45°, 0°, and random orientation. The latter represented the disrupted collagen fibril orientations in early osteoarthritis. The model was verified with the experimental results in the literature. RESULTS: In the superficial zones, the larger angle between the split lines and cut edges resulted in a wider cut opening. In the absence of collagen fibrils, the isotropic model resulted in a closed edge profile. Also, under a consistently applied compression, the OA model, with random collagen fibril distribution on its surface, had the smallest load-bearing capacity compared to the other models. CONCLUSIONS: Findings highlighted a primary role of collagen fibrils on the cut profile, which was more pronounced at dynamic rather than static conditions. Split lines perpendicular to the cut edges had some protective effects against the large dislocation of cut edges. These findings could be utilized to develop engineered tissues less susceptible to rupture. Moreover, the outcome of the present study can explain the potential causes of the crack propagation path reported in the literature.