Regional differences in the cellularity and vascularity of the patellar tendon

The patellar tendon (PT) attaches to the apex of the patella and tibial tuberosity. Its response to tensile forces is influenced by the distribution of fibroblasts and its vascularity. The vascularity and distribution of fibroblasts influence the tendons ability to repair microtears. Microtears of the PT result in patellar tendinopathy. There is however, paucity of data on the regional distribution of vascular and cellular elements in the PT which might explain why microtears occur in the posterior-proximal third. One hundred and two pairs of patellar tendons were obtained from postmortem specimens. Sections from the proximal, middle and distal third from the anterior and posterior lamina of 20 pairs of the patellar tendon (10 male, 10 female) were processed for microscopy to demonstrate the cellularity and vascularity of the tendon. The vascularity was highest in the middle third of the anterior lamina. The posterior lamina of the tendon was less vascular than the anterior lamina. The posterior lamina was more cellular than the anterior with the proximal third showing the highest number of nuclei. These findings indicate that the pre-patellar genicular anastomosis contributes significantly to the vascularity of the anterior lamina while the anastomosis located in Hoffa’s fat pad may be less rich and thus resulting in lower vascularity for the posterior lamina. Lower vascularity implies less healing ability after microtears. Therefore, orthopedic surgeons should be aware of this precarious pattern of vascularity to the posterior lamina. The posterior lamina’s high cellularity especially in the proximal third indicates that it may experience greater stress and via durotaxis more fibroblasts migrate to that region to produce more collagen fibers for resilience. The greater tensile stress experienced by the posterior-proximal third and its lower vascularity may explain why it is most susceptible to microtears.Key words: Patella tendon, regional differences, cellularity, vascularity, patella tendinopathy