Concomitant occurrence of subchondral cyst and ruptured anterior crucial ligament at knee joint: new findings by MRI.

The magnetic resonance imaging (MRI) in 4 cases of subchondral cyst at the knee joint region, were acquired from a 1.5 Tesla imager. We found a high incidence of concomitant occurrence of subchondral cysts with a ruptured anterior cruciate ligament (ACL) in all of these cases. The 2 men and 2 women, had an average age of 35. Clinically, they complained of dull knee pain and mild instability. Conventional radiography detected subchondral cysts in 3 of them, while MRI disclosed that all of the subchondral cysts were at the tibial plateau, close to the intercondyloid eminence. To date, MRI is the only imaging modality which can depict the concomitant occurrence of a subchondral cyst and a ruptured anterior cruciate ligament at the knee joint. Whether these subchondral cysts were the consequences of the ruptured anterior cruciate ligaments as one of the causes in addition to synovial fluid intrusion and bony contusion, need further clinical observation and investigation.