Healing canine flexor tendons were treated with either total
immobilization and were studied by light, scanning, and transmission
electron microscopy at ten, twenty-one , and forty-two days. The
immobilized tendons healed by ingrowth of connective tissue from the
digital sheath and cellular proliferation of the endotenon. The ingrowth of
reparative tissue from the digital sheath overwhelmed the epitenon
response. At the ultrastructural level, collagen resorption was prominent
whereas protein synthesis was limited. This was observed at all
study-intervals. In contrast, the mobilized tendons healed by proliferation
and migration of cells from the epitenon. Ingrowth of reparative tissue
from the tendon sheath was notably lacking in this group. The epitenon
cells exhibited greater cellular activity and collagen production at each
interval compared with cells of the immobilized repairs.