[Classification, significance and sequelae of posttraumatic "occult" bone and cartilage fractures of the knee. The role of magnetic resonance].

Magnetic Resonance Imaging (MRI) shows, in the post-traumatic knee, a fairly high number of bone and cartilage injuries missed by conventional radiography and therefore called occult. Our aim is to classify these injuries, to correlate their site and distribution with associated menisco-ligamentous injuries and with trauma mechanisms. Thirty-eight patients with a history of acute knee trauma and negative X-ray findings were examined with MRI within 15 days of trauma. 1.5- and 0.5-T units and SE T1-weighted GE T2*-weighted and SE T2-weighted sequences were used. The injuries were classified as intraosseous and osteochondral bruises or fractures. Twenty-three patients with menisco-ligamentous injuries were submitted to therapeutic arthroscopy; the sites of bone and cartilage injuries depicted with MRI were studied with arthroscopy. Seven patients were followed-up with MRI at 6-12 months to investigate subchondral injury evolution: 5 of 7 patients were also submitted to arthroscopy. MRI showed a statistically significant correlation between site and distribution of bone and cartilage injuries and between internal derangement and trauma mechanisms, i.e., contusion, distortion, stress. In our experience, MRI could identify and characterize occult subchondral injuries, thus allowing appropriate treatment.