Patellar tendon healing after removal of its central third - A morphologicevaluation in rabbits

The central third of the patellar tendon of the right knee was removed in 4 0 adult New Zealand White (NZW) rabbits. The animals were divided into two groups of 20 animals each. In group 1 the ten don defect was left open and in group 2 the tendon defect was closed. The peritenon was closed in all ca ses. The animals were killed after 2 weeks, 1, 3, 6 and 9 months. Operated and contralateral normal tendons of each knee underwent a gross, histologic , immunohistochemical and morphometric analysis. Gross examination revealed that in the closed group there was a greater shortening of the patellar te ndon but the difference between the two groups was not statistically signif icant. The width, thickness and cross-sectional area increased progressivel y in both groups and were greater in the closed group. Histological examina tion showed that at 1 month in both groups the harvest site was filled with a loose unoriented fibrovascular tissue. In group 1, large fatty inclusion s could be seen in the deep layer, that were still present in the 3-, 6- an d 9-month samples. At 3 months in group 1 the newly formed tissue was immat ure and rich in elastic fibres, as confirmed by immunohistochemical analysi s, whereas in group 2 it was more compact and oriented. In group 1 there wa s in many cases an ossification on the lower pole of the patella, which was not seen in group 2. At 9 months a well-organized fibrous tissue could be seen in both groups at the harvest site. Histomorphometric analysis confirm ed the better orientation and the greater density of the newly formed tissu e in the closed group as compared to the open group, and the greater number of elastic fibres in the open group, even after 9 months.