Ossification of the posterior longitudinal ligament (OPLL) is a condition in which a flexible structure called the posterior longitudinal ligament increases in thickness and therefore becomes less flexible. This ligament assists with maintaining the integrity of the spinal column. If it calcifies it may begin to develop a bone-like quality, increasing in size and potentially causing spinal cord injury through compression. OPLL has a greater tendency of affecting men, individuals of Japanese and Korean descent, and those suffering from diabetes. Symptoms may be mild at first such as tingling, mild pain, or numbness in the hands. Most patients display no symptoms at all.