[Occult or unknown traumatic osteochondral lesions of the knee. Assessment of 19 cases studied with conventional radiology and magnetic resonance].

Occult fractures of the knee represent a major cause of posttraumatic knee pain in patients with negative plain films. These injuries can cause severe sequelae if they are not properly diagnosed and rapidly treated. In our series of 1330 exams of the knee we found 19 traumatic osteochondral injuries (1.5%). MR studies were performed with a dedicated permanent magnet (0.2 T) (Artoscan, Esaote Biomedica, Genoa, Italy). All the patients were submitted to conventional radiography (AP and LL projections). In 14 patients oblique plain films were also performed. The following osteochondral injuries were found: 2 purely chondral fractures, 5 occult fractures (4 tibial and 1 of the medial femoral condyle) and 12 plateau fractures of the tibial posterior margin (8 lateral and 4 medial). CT of the knee was performed in 3 patients only. In 19 patients MRI correctly showed the traumatic injury and depicted: fracture site, the morphologic characteristics of fracture line, cortical bone and articular cartilage involvement, the exact extent of marrow signal changes, the associated injury of menisci or cruciate ligaments. To conclude, MR sensitivity and diagnostic accuracy are excellent in the patients with traumatic injuries of the knee. In the patients with posttraumatic knee joint pain, MRI appears to be an extremely useful tool in the detection and assessment of bone and cartilage disorders.