[Concomitant occult osseous injuries in knee joint injuries]

In 28 patients with different knee injuries, we documented intraosseous lesions by MRI, although on plain X-rays no abnormality had been discovered. The intraosseous abnormalities seen by MRI were classified into four categories. 1. Cancellous bone oedema: this type of lesion showed a decrease of signal on T1 weighted images with irregular borders. These irregular areas were located in the epiphysis and sometimes even in the metaphysis. On T2 weighted images these areas showed an increased signal, which was even better visualised on short time recovery sequences. 2. Subchondral fracture with involvement of cortical bone: In these cases the involved area even reached the subchondral cortex. The fracture line could be visualised on T1- and T2-weighted images. 3. Osteochondral fractures: In two patients we found typical osteochondral fractures with a minimal displaced small fragment. 4. Subchondral sclerosis: In these cases there was a decrease of the signal on T1-weighted images, located directly adjacent to the subchondral cortical bone, without a fracture within the cortical bone and without any increase of signal on T2-weighted or STIR-images. According to our experience, isolated decrease in the signal within the subchondral cancellous bone adjacent to the knee joint, with an increased signal in STIR sequences can be taken as indirect signs for a traumatic lesion. These intraosseous lesions have a high coincidence with ligament injuries of the knee joint.