Exploration of changes in spatial chondrocyte organisation in human osteoarthritic cartilage by means of 3D imaging

Using two-dimensional top-down view microscopy, researchers have recently described chondrocytes as being spatially arranged in distinct patterns such as strings, double strings, and small and large clusters. Because of the seeming association of these changes with tissue degeneration, they have been proposed as an image-based biomarker for early osteoarthritis (OA) staging. The aim of our study was to investigate the spatial arrangement of chondrocytes in human articular cartilage in a 3D fashion and to evaluate the 3D changes of these patterns in the context of local tissue destruction. Decalcified femoral condyle resections from the load-bearing area were analysed in 3D for their spatial chondrocyte organisation by means of fluorescence microscopy and synchrotron-radiation micro-computed tomography (SR-μCT). In intact cartilage chondrocyte strings can be found inthe superficial, transitional and deep zones. The proposed pattern changes accompanying tissue destruction could be located not just along the surface but also through all layers of cartilage. Each spatial pattern was characterised by a different cellular density (the only exception being between single and double strings with p = 0.062), with cellular density significantly increasing alongside the increase in local tissue degeneration as defined by the chondrocyte patterns. We can thus corroborate that the proposed cellular spatial changes are a three-dimensional function of local tissue degeneration, underlining their relevance as an image-based biomarker for the early diagnosis and description of OA