Morphological alterations and increased gelatinase activity in the superficial digital flexor tendon of chickens during growth and maturation.

The superficial digital flexor tendon (SDFT) connects the superficial digital flexor muscle to the digits and its main function is to participate in digit flexion. The SDFT presents different regions along its length, which adapt to different biomechanical forces. During growth and maturation, the tendon may present changes in the regions subjected to compression and tension, with variations in the composition of the extracellular matrix (ECM), in the arrangement of collagen fibers and cellularity. With the purpose of analyzing the morphological and biochemical alterations of ECM of tendons during the growth and maturation, Gallus domesticus were euthanized at 1, 5, and 8 months of age and their SDFT were divided into regions of tension/compression (Sp) and tension (Sd). From 1 month of age, the Sp region already presented fibrocartilage characteristics with cells similar to chondrocytes. At 5 and 8 months, the Sd region displayed formation of a new structure similar to bone matrix, and intense metachromasia. The animals of 5 and 8 months presented an increase in MMP-2 and -9 activities and a lower number of cells when compared with the animals of 1 month, in both regions. In conclusion, structural and biochemical alterations occur during the maturation process of the SDFT, involving a decrease in the number of cells and changes in the degradation and composition of the ECM. Anat Rec, 302:964-972, 2019. (c) 2018 Wiley Periodicals, Inc.