Ossification of posterior longitudinal ligament (OPLL) is a hyperostotic disease of the spine associated with myelopathy which is occurred by an anterior compression to the spinal cord. OPLL was first reported by Key GA in 1838, and was previously considered specific to east Asian people, especially Japanese. However, now OPLL is recognized as a subtype of diffuse idiopathic skeletal hyperosteosis, which is detected in Europe and the United States. We discuss the etiology and natural history of OPLL in this review.

Ossification of the longitudinal ligament in the spine is a disorder of unknown cause characterized by ectopic ossification. In the animal models of spinal hyperostosis, the vertebral ligament is gradually replaced by bony tissue forming an osseous bridge around enthesis, and a high turnover osteopenia occurs after the maturation in the trabecular bone of vertebrae. It has been suggested that the recruited vasculature facilitated the filling of the niche with host-derived haematopoietic cells during the ectopic ossification process. Recent data suggest that regulation of hematopoietic and osteogenic stem/progenitor cell populations may contribute to the formation of an ectopic spinal hyperostosis.

Symptom prevalence of OPLL is estimated between 20% and 50%. Patients with OPLL have neurological disorders, pain/numbness, and trunk stiffness. These symptoms of stenotic myelopathy and of ossification. spondylosis deteriorate patients'quality of life. The ossification extends and elongates very gradually and tiny ossification at first visit hardly grows up to enough to cause myelopathy. A majority of patients experience a chronic course, but some suffer spinal cord injury. Preemptive surgery should be carefully contemplated because definite criteria have not been established yet.