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.