An in vivo study of the rat patellar tendon healing-histological, biochemical and biomechanical aspects

Patellar tendon central one third is removed during anterior cruciate ligament reconstruction. The current study investigates an in vivo model of patellar tendon healing, histologically, biochemically and biomechanically. The histological appearance and the ultimate stress of the central one third patellar tendon were studied over time. The specimens were also analyzed for collagen and non-reducible crosslinks, as measured by hydroxyproline and pyridinoline content, respectively. Thirty days post-injury, the cellularity and the collagen matrix approached a normal tendon. The ultimate stress of the healing tendon restored to an average of 71% of the control and remained constant over time. The pyridinoline of the healing tendon was twice the values for the controls by 30 days and then reached a plateau. However, the hydroxyproline did not change significantly over time. Stepwise regression analysis demonstrated that pyridinoline was a better biochemical marker for the ultimate stress than hydroxyproline. The current study provides insights into the healing process in tendon by establishing the relationship between the biochemical parameters with the ultimate stress. This study also suggests the possibility of using pyridinoline content as an indirect marker of the ultimate stress, since in vivo clinical assessment is impossible.