[Biomechanics and semeiotics of traumatic lesions of the posterior cruciate ligament using magnetic resonance].

The authors reviewed 458 MR examinations of the knee to assess the potentials of this technique in the study of traumatic injuries of the posterior cruciate ligament (PCL) and to investigate the frequency of their association with injuries of other knee joints. MR images were acquired with an 0.5-T super-conductive unit with an extremity coil. T1-weighted spin-echo (SE) and T2*-weighted gradient-echo (GE) sequences were used on sagittal, coronal and, in some cases, axial planes, with 3-mm slice thickness and 0-1 mm slice gap. The following parameters were studied to diagnose partial or complete PCL tears: PCL thickness and outline, disruption of ligamentous fasci and signal intensity features. The injuries were classified as proximal, intermediate and distal according to their site. Thirteen PCL tears were detected, 5 of them complete and 8 partial. Complete tears were found in 4/5 patients in the middle third and one patient had a distal intersection tear with tibial bone avulsion. Partial tears were found in the distal tract in 5/8 patients, in the proximal tract in one patient and in the middle third in 2 patients. In 12/13 patients capsuloligamentous knee tears were associated. Overall MR rate of PCL tears was 2.8%; of them, 92.3% were associated with other capsuloligamentous injuries. MR diagnosis was confirmed at arthroscopy in 12/13 patients. The sagittal plane was best in optimally demonstrating the whole PCL and its injuries. GE T2* sagittal sequences demonstrated the site of PCL tears better than SE sagittal ones. Relative to other authors, we found MRI an extremely reliable method to distinguish partial from complete PCL tears. This was probably due to the thinner slices (3 mm) we used. MRI can accurately assess the extent of traumatic injuries of the PCL and of other capsuloligamentous parts of the knee, which is relevant from the clinical point of view. Indeed, MRI allows useless diagnostic arthroscopy to be avoided and yields major indications to choose the correct treatment.