ABSTRACT
Background: In the present study, we conduct an immunohistochemical analysis to evaluate the expression of matrix metalloproteinase-9 (MMP-9) in the epiligament (EL) after grade III injury of the medial collateral ligament (MCL) in an experimental model of a rat knee. Methods: Twelve 8-month old male Wistar rats were used in this study. Three animals were used as controls, while the remaining nine underwent grade III injury of the MCL. The MMP-9 immunoreactivity was evaluated on the 8th, 16th and 30th day after injury. Results: We observed an intensive expression of the enzyme in all periods after injury in contrast with the control group. We also discovered that the main source of matrix metalloproteinase-9 was localized in the epiligament tissue. Immunoreactivity was highest and homogeneously distributed on the 8th day and gradually diminished, concentrating on the EL-ligament border and the perivascular zones on the 30th day. Conclusion: We present the first immunohistochemical study of the expression and distribution of the enzyme MMP-9 in the EL of the MCL and track the changes in enzyme activity on the 8th, 16th and 30th day after damage.