Ex vivo infiltration of fibroblasts into the tendon deteriorates the mechanical properties of tendon fascicles but not those of tendon bundles.

Background: After ligament reconstruction, mechanical deterioration of the grafted tendon is observed with revascularization and cellular infiltration. However, the effect of cellular infiltration on the mechanical properties of the tendon matrix has not been fully understood.

Methods: Cultured fibroblasts derived from the rabbit patellar tendon were seeded around an acellular rabbit patellar tendon that had undergone freeze-thaw treatment. At time-0, 3, and 6 weeks after seeding the cells, we evaluated cellular distribution in the tendon using a confocal laser microscope and the mechanical evaluations of the tendon fascicles and the tendon bundles.

Findings: The confocal laser microscopic analysis showed fibroblast infiltration ex vivo into the acellular tendon matrix. We could not find significant effects of the cellular infiltration on the tangent modulus of the tendon bundle, although the ex vivo cellular infiltration significantly reduced the modulus of the tendon fascicle. In addition, the tangent modulus of the incubated tendon without fibroblasts significantly decreased with time, particularly in the tendon bundle levels.

Interpretation: The findings of this study suggested that the effects of ex vivo cellular infiltration on the mechanical properties of the tendon bundles are relatively small, compared with its striking effect on the tendon fascicles.