An in vivo model for load-modulated remodeling in the rabbit flexor tendon

This study tested the hypothesis that eliminating ill vivo compression to t he wrap-around, fibrocartilage-rich zone of the flexor digitorum profundus tendon results in rapid depletion of fibrocartilage and changes in its mech anical properties. microstructure, extracellular matrix composition. and ce llularity. The right flexor digitorum profundus tendons of 2.5-3-year-old r abbits were translocated anteriorly to eliminate in vivo compression and sh ear to the fibrocartilage zone and, at 4 weeks after surgery, were compared with tendons that had sham surgery and with untreated tendons. The translo cated tissue showed a significant increase in equilibrium strain under a co mpressive creep load (p < 0.05). The thickness and area of the fibrocartila ge zone also decreased significantly (p < 0.05). The nuclear density decrea sed by 40% in the fibrocartilage zone (p < 0.005); however, nuclear shape a nd orientation were not significantly altered. Glycosaminoglycan content in the fibrocartilage zone was also depleted by 40% (p < 0.02). The tightly w oven basket weave-like mesh of collagen fibers in the zone appeared more lo osely organized, suggesting matrix reorganization due to translocation. Mor eover. immunoreactive type-II collagen and link protein in the fibrocartila ge zone also decreased. With use of this unique in vivo model, this researc h clearly elucidates how changing tissue function (by removing compressive forces) rapidly alters tissue form.