Introduction: We investigated the MR signs of anterior cruciate ligament (ACL) tears and tried to assess the patterns of both the acute and the chronic phases since more MR examinations are currently performed of the knee joint in the hyper and acute post-traumatic stage.
Material and methods: December, 1994, through September, 1997, a hundred and 89 sportsmen with a history of hyper and acute knee trauma were submitted to MRI: one hundred and four of them were followed-up for 3-6 months. The MR examinations were performed with a dedicated unit (Artoscan, Esaote Biomedica, Genoa) using T1-weighted SE, T2-weighted GE and Turbo ME sequences on the sagittal, coronal and axial planes, respectively (3-5 mm slice thickness).
Results: Of 189 patients examined in the hyper and acute post-traumatic stage, 101 had a complete ACL tear, 23 had a partial tear and 65 had an enlarged and inhomogeneous ACL: Eighty-five patients underwent surgery, while the other 104 had 3-6 months' follow-up MRI. Twenty-four of the latter had a complete ACL tear, 20 had a partial tear and 60 had no MR finding of ACL interruption, with a more or less inhomogeneous ligament.
Discussion: ACL tears are difficult to demonstrate in the acute phase because of perilesional swelling, synovitis and hemorrhage; high-contrast sequences on the axial plane are therefore required. In the chronic stage, an uninterrupted ACL does not necessarily imply that function is preserved, as well as the MR finding of a deflected ligament does not necessarily imply altered biomechanics.
Conclusions: MRI of the knee joint is increasingly used to study hyper and acute ACL tears thanks to the availability of dedicated units. The MR study of ACL tears is not meant to refer the patients to surgery, which pertains to the physical examination, but it allows to assess lesion severity and to show associated injuries in other knee structures.