The expression of matrix metalloproteinases and inhibitors in acute rupture of the anterior cruciate ligament

Rapid degeneration of the anterior cruciate ligament (ACL) may occur after ligament rupture, making primary repair of the anterior cruciate ligament difficult. Nine completely ruptured anterior cruciate ligaments were collected by arthroscopic surgery performed within 6 months of injury. The authors studied the localization of matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases in ruptured anterior cruciate ligament using immunohistochemistry, and measured messenger ribonucleic acid expression using the reverse transcriptase polymerase chain reaction. Cells in residual ligament tissue seemed to contain matrix metalloproteinases 1 and 3 and tissue inhibitors of matrix metalloproteinases 1 and 2. Promatrix metalloproteinase-9 positive cells were observed in the perivascular area. Promatrix metalloproteinase-2 positive cells frequently were seen between irregular collagen bundles in stumps of ruptured ligaments. Tissue inhibitors of matrix metalloproteinase-2 positive cells commonly were observed in ruptured ligaments. Matrix metalloproteinase-1 and matrix metalloproteinase-3 messenger ribonucleic acid were highly expressed compared with matrix metalloproteinase-2 messenger ribonucleic acid. Tissue inhibitor of matrix metalloproteinase-2 messenger ribonucleic acid was highly expressed compared with tissue inhibitor of matrix metalloproteinase 1. The authors could not identify whether these intrinsic reactions mediated by anterior cruciate ligament cells were the causes of rapid degradation or the results of the degradation process. Various amounts of matrix metalloproteinase and inhibitor production of intrinsic ligament cells were observed in the ruptured anterior cruciate ligament. The biological reaction reported in this study may suggest that pronounced metabolism is undertaken in ruptured ACL cells, and provide useful insight concerning the possiblitiy of achieving the primary repair of ruptured ACL.