Onlay bone graft behaviour after marrow exposure of the recipient rat skull bone

This study aimed to evaluate the effects on incorporation of onlay grafts after exposure of the marrow of the skull recipient bed. Tibial or femoral uni- and bicortical bone grafts were positioned subperiosteally or submuscularly in the parietal and temporal region, respectively, of 28 adult rats. The recipient bed was ground to remove the external cortical layer and expose the underlying marrow. The outcome was assessed after four, 12, and 20 weeks by routine histology and immunohistochemical labelling for various bone and cartilage proteins. Marrow exposure resulted in an explosive bone formation, prompt graft incorporation, earlier onset of bone remodelling, but also localized resorption at the host bed due to increased vulnerability to pressure. Graft height loss was similar relative to previous observations by us using the same experimental model but without exposure of the marrow. The investigated proteins were identified at various locations and with different temporal sequences; the technique contributed to a diversified appreciation of graft behaviour. The findings emphasize the essential role of the bone marrow constituents to bone graft-incorporation.