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

This study tested the hypothesis that eliminating in vivo compression to the wrap-around, fibrocartilage-rich zone of the flexor digitorum profundus tendon results in rapid depletion of fibrocartilagc and changes in its mechanical properties. microstructure, extracellular matrix composition, and cellularity. The right flexor digitorum profundus tendons of 2.5-3-year-old rabbits were translocated anteriorly to eliminate in vivo compression and shear to the fibrocartilage zone and, at 4 weeks after surgery. were compared with tendons that had sham surgery and with untreated tendons. The translocated tissue showed a significant increase in cyuilibrium strain under a compressive creep load (p < 0.05). Thc thickness and area of the fibrvcartilagc zone also dccrcascd significantly (p < 0.05). The nuclear density decreased by 4O0% in the fibrocartilage zone (p < 0.005); however, nuclear shape and orientation were not significantly altered. Glycosaminoglycan content in the librocartilagc zone was also dcplctcd by 40% (p < 0.02). The tightly woven basket weave-like mesh of collagen fibers in thc zone appeared morc looscly organized. suggesting matrix reorganization due tv translocation, Moreover. iminunoreactivc type-I1 collagen and link protein in the fibrocartilage zone also decreased. With use ol this unique in vivo model, this research clearly cluciciatcs how changing tissue function (by removing compressive l'orces) rapidly alters tissue lorm.