The Role of Mechanobiology in the Attachment of Tendon to Bone - Structural Interfaces and Attachments in Biology - page 237

Fig. 11.9 The functionally graded transition between tendon and bone is not regenerated (hema-
toxylin and eosin-stained images are shown under bright-field on the top row and under polarized
light on the bottom row ) (reproduced, with permission, from ref. [ 129 ])

11.5.1 Injury and Repair Result in a Loss of the Functionally

Graded Tendon-to-Bone Interface

Tendon-to-bone injuries are generally characterized by rupture of the tendon,
requiring repair of the tissue to its original bony footprint. Tendon-to-bone
healing can be roughly divided into three stages: inflammation, repair, and
remodeling. The inflammation stage involves recruitmentofvascularcells,such
as erythrocytes and platelets, and immune cells, such as macrophages to the injury
site to resorb necrotic tissues via phagocytosis. The inflammatory cells also
recruit tendon fibroblasts for the repair phase, in which ECM (primarily collagen)
is synthesized and deposited at the injury site. The remodeling phase begins
approximately 2 months post-injury and is characterized by reduced cellularity
and matrix synthesis, as the tissue becomes more fibrous and is then remodeled
into scar-like tendon tissue [ 80 ].
Studies in rabbits, goats, and rats have verified that repaired interfaces have
inferior mechanical behavior, presumably because the functionally graded transition
between tendon and bone is not regenerated (Fig. 11.9 )[ 5 , 7 , 123 , 124 ]. The scar