Tendons transmit loads from muscle to bone. Tendon injuries result in degenerative changes, including increased inflammatory response and poor healing. Tendon mechanical function is dictated by the composition and organization of the underlying extracellular matrix. Damage to the tendon extracellular matrix results in permanent functional decline. Provisional matrix deposition, which occurs during early tendon healing, may be influenced by sex and age. The effects of sex and age in patellar tendon injuries as well as the mechanisms that impede total restoration and therefore tendon mechanics following injury are unknown. Therefore, there is need to determine the role of age and sex on early tendon matrix deposition. Thus, the objective of this study was to examine age- and sex-dependent early tendon healing. An established patellar tendon biopsy procedure was used to evaluate changes in mechanical properties at 3-, 7-, and 14-days post injury in male and female mice. Significant differences with respect to sex and injury were found in tendon linear region elastic modulus and percent relaxation for 120-day mature mice. Mechanical properties appeared to decrease with increasing age; however, statistics could not evaluate this decrease due to low sample sizes for the 270- and 540-day mice. Sex differences in mechanical properties may be due to prolonged inflammatory response in injured female mice. Such prolonged exposure may result in increased deposition of type III collagen and thus exhibit altered mechanical function. These results provide valuable information to improve tendinopathy treatment options and to develop finite element models of tendon healing to inform surgical outcomes.
