Vascular-mineral spatial correlation in the calcifying turkey leg tendon

Certain avian tendons are known to mineralize normally in a gender-related manner. These tendons have unique properties, as well as several features common to calcifying cartilage and bone in other vertebrate species. In cartilage and bone, mineralization has been associated with a vascular and microvascular origin, but such a relationship has not been established in the avian tendon. Here the vasculature and mineral deposition in the calcifying leg tendon of the turkey have been documented for the first time utilizing a combination of histology, immunochemistry, radiology, and novel three-dimensional image reconstruction methods based on computed tomography. The data describe the blood supply to turkey leg tendon and show that the vascularity of this tissue is correlated with the onset of mineralization: At local levels of structural hierarchy, a vascular bed precedes mineral formation and the sites of vascular invasion correspond spatially with those of mineral deposition. Relatively unvascularized tendon regions remain uncalcified. These results support the concept that vascularization and mineralization are functionally related in the tendon, and they suggest that vascular invasion provides a mechanism underlying subsequent mineral deposition in this tissue.