Ganglion cysts involving the cruciate ligaments of the knee are fairly common ranging in prevalence from 0.2 per cent up to 1.9 per cent. Men are more likely to develop this type of cyst than women but the etiology (cause) is really unknown.
There are several theories. One being that the sac holding the synovial (lubricating) fluid in the knee herniates allowing the fluid to surround the cruciate ligaments that criss-cross inside the joint. Some experts have suggested that this is a congenital problem (present at birth). The synovial cells form inside the cruciate ligaments instead of inside the synovial lining.
The most widely accepted theory is that constant stress on the cruciate ligaments causing degeneration of the mucous fluid around the ligaments results in cyst formation. Sometimes there is a previous knee injury linked with cruciate ligament ganglion cysts but not always. Whether or not injuries of the joint cartilage (meniscus or articular) have a role in cyst formation remains unknown.