Rupture of the Achilles tendon is one of the most frequent tendon injuries in humans. However, there is no standard surgical technique thus far to reproduce complete rupture of this tendon in rats. Surgical procedures were performed in Wistar rats under light microscopy, with posterior longitudinal incision and preservation of the plantaris tendon. The animals were sacrificed on 2 nd and 8 th postoperative week and we used hematoxilin and eosin, picrosirius-red and Weigert's resorcin-fuchsin to observe general tendon healing. The mean operative time was one minute and 24 seconds. Histological studies showed cellular proliferation and fibrillogenesis at two weeks, with decreased amounts of cellularity and elastic fibers at the 8 th week, besides changes in structural organization of collagen fibers. The complete Achilles tenotomy in rats, was improved under light microscopy and sparing the plantaris tendon. This surgical technique was simple and quick, showed signs of normal healing process, could be easily reproducible, and triggered translational researches in this area.

Achilles tendon rupture is one of the most frequent tendon injuries. The aim of this experimental study was to evaluate the effect of a non-steroidal anti-inflammatory drug (NSAID) and of aerobic exercise, in an isolated fashion and combined, on cell proliferation and on the biomechanical aspects of the Achilles tendon during healing process after a complete tenotomy in 156 male Wistar rats. Half of the animals received an intra-muscular injection of tenoxicam for 7 days and exercise was initiated on the 8th day for half the animals of each group. Animals were sacrificed at 1, 2, 4 and 8 weeks after the tenotomy and cell proliferation was evaluated by immunohistochemistry for PCNA, biomechanical evaluation was performed with ultimate load and gait cycle analysis was also carried out. Animals were divided into four treatment groups: A) no NSAID and no exercise (control group); B) NSAID plus exercise; C) no NSAID, with exercise; D) NSAID and no exercise. We used the test of two-way analysis of variance with equal cells number, Kruskal-Wallis test and also, Bonferroni method, in the R Project program 3.5.0. The highest intensity of PCNA immunostaining was found at 2 weeks in all groups except for group A (control) that had the highest intensity at 1 week. Animals submitted to exercise had significantly higher (P = 0.02) ultimate loads when compared to animals that were not submitted to exercise at 8 weeks after injury. The animals that received NSAID presented with a more stable gait cycle than the animals that did not receive NSAID.