Alterations in structure and properties of collagen network of osteoarthritic and repaired cartilage modify knee joint stresses.

Organization of the collagen network is known to be different in healthy, osteoarthritic and repaired cartilage. The aim of the study was to investigate how the structure and properties of collagen network of cartilage modulate stresses in a knee joint with osteoarthritis or cartilage repair. Magnetic resonance imaging (MRI) at 1.5 T was conducted for a knee joint of a male subject. Articular cartilage and menisci in the knee joint were segmented, and a finite element mesh was constructed based on the two-dimensional section in sagittal projection. Then, the knee joint stresses were simulated under impact loads by implementing the structure and properties of healthy, osteoarthritic and repaired cartilage in the models. During the progression of osteoarthritis, characterized especially by the progressive increase in the collagen fibrillation from the superficial to the deeper layers, the stresses were reduced in the superficial zone of cartilage, while they were increased in and under menisci. Increased fibril network stiffness of repair tissue with randomly organized collagen fibril network reduced the peak stresses in the adjacent tissue and strains at the repair-adjacent cartilage interface. High collagen fibril strains were indicative of stress concentration areas in osteoarthritic and repaired cartilage. The collagen network orientation and stiffness controlled the stress distributions in healthy, osteoarthritic and repaired cartilage. The evaluation of articular cartilage function using clinical MRI and biomechanical modeling could enable noninvasive estimation of osteoarthritis progression and monitoring of cartilage repair. This study presents a step toward those goals.