Transarticular invasion of joints by bone tumors: hypothesis.

Eight bone tumors with associated transarticular invasion of the sacroiliac joints are described. All invaded the true synovial joint and spread to the opposing bone. One tumor was benign, and the other seven were malignant. Five of the seven were primary and two were metastatic cancer. One, a myeloma, invaded the disc spaces between the fourth and fifth lumbar vertebrae and the fifth lumbar vertebra and sacrum as well as the sacroiliac joint. The right facet joints of the two vertebrae were also invaded. After a thorough search of the literature, we find that the sacroiliac joint is the most common joint to be invaded by tumors. This is followed by the vertebral disc spaces and, last, the facet joints. Apart from these joints, we were unable to find any radiographic documentation of other joints being transarticularly invaded by tumors. We noted that there is a direct relation between transarticular tumor spread and joints that lack mobility and that certain tumors, benign and malignant, tend to invade these joints.