Impaired biomechanical properties correlate with neoangiogenesis as well as VEGF and MMP‐3 expression during rat patellar tendon healing

Recent studies reveal an important role of vascular endothelial growth factor (VEGF)‐induced angiogenesis in degenerative tendon diseases. The way how VEGF influences mechanical properties of the tendons is not well understood yet. We here hypothesized that tendinopathy results in a hypoxia‐mediated stimulation of VEGF and that the mechanical stability of the tendon is impaired in an angiogenic process by VEGF‐induced matrix metalloproteinases (MMPs). A modified in situ freezing model of patellar tendon was used to create a tendinopathy. 0, 7, 14, and 28 days post‐surgical animals were sacrificed and patellar tendons were dissected for biomechanical and immunohistochemical analysis. Native tendons were used as controls. Immunohistochemical staining revealed a peak in HIF‐1α stabilization immediately after surgery. Both VEGF and MMP‐3 were increased 7 days after surgery. Angiogenesis was also abundant 7 days after surgery. In contrast, biomechanical stability of the tendon was decreased 7 days after surgery. The current results reveal a time‐dependent correlation of HIF‐1/VEGF‐induced and MMP‐3‐supported angiogenesis with decreased biomechanical properties during tendon healing. The therapeutical modulation of neoangiogenesis by influencing the level of VEGF and MMP‐3 might be a promising target for new approaches in degenerative tendon diseases. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1952–1957, 2012