Chondrocyte death during articular cartilage drying: an investigation of its effect, mechanism, and prevention
Paterson, Scott Ian
MetadataShow full item record
During open orthopaedic surgical procedures, the articular cartilage covering the exposed joint surfaces can be exposed to air for prolonged periods. This exposure facilitates cartilage drying, characterised by changes to the extracellular matrix and chondrocyte death. Due to cartilage’s limited capacity for regeneration, it has been proposed that this may lead to post-operative joint degeneration. It has been proposed that chondrocyte death occurs as a result of both drying and nutritional deficiency. It is known that death during drying correlates with the drying interval and is initiated in the superficial chondrocytes, progressing to deeper layers at higher intervals. Additionally, it is well established that periodic rewetting (e.g. using 0.9% saline solution) can reduce chondrocyte death. The work presented in this thesis aimed to characterise chondrocyte death during drying, with particular reference to the chondrotoxic/protective effect of environmental variables (airflow) and surgical interventions (irrigation solutions), mechanism of injury and cell death, and the effect of in vivo drying on joint health. An ex vivo model of cartilage drying was developed and carried out on bovine and human intact cartilage and osteochondral explants, while varying environmental factors (drying interval, airflow velocity, oxygen concentration) and interventions (irrigation solutions and protective coverings. Throughout the study, cartilage drying was assessed in terms of 1) cartilage macroscopic appearance, 2) percent chondrocyte death (PCD), 3) cartilage water content, and 4) chondrocyte morphology. Histologically and fluorescently labelled samples were imaged using light and confocal laser scanning microscopy respectively, which formed the basis of the qualitative and quantitative assessments. Experimental drying at high airflow velocities had a more severe effect on cartilage appearance, PCD, and water content than in static air. This relationship was apparent in dried intact joints and osteochondral explants and in bovine and human samples. This suggests that the effects of surgical drying (where ventilation systems and airflow are routine) may be more pronounced than previously suggested and demonstrates a correlation between PCD and water-loss. Irrigation solutions supplemented with glucose (25 -100 mM) had no significant effect on the PCD or water content in dried samples. Additionally, PCD was minimal in osteochondral explants cultured in the absence of glucose, even after 24 hr. This suggests that nutritional deficiency is unlikely to contribute to PCD during drying. However, chondrocyte death (in intact bovine cartilage) was reduced when drying was carried out at an oxygen concentration more reflective of the in vivo environment (5 %), which suggests that cell death during drying may be facilitated by a hyperoxic shock. Finally, in vivo cartilage drying was carried out on murine cartilage. Compared to sham operated controls, dried cartilage demonstrated a loss of surface integrity (4 weeks post-surgery) and fibrillations (8 weeks) and an increased modified Mankin score (at 4 and 8 weeks). Microscopically, an altered cartilage thickness, and chondrocyte density and arrangement were visible. These changes are comparable with changes in osteoarthritis. The results of this study demonstrate the importance of maintained cartilage hydration in order to avoid unnecessary chondrocyte death articular cartilage degeneration.