Rotational stress: role in development of ossification of posterior longitudinal ligament and ligamentum flavum.

Ossification of the posterior longitudinal ligament (OPLL) and ossification of ligamentum flavum (OLF) are characterized by progressive ectopic bone formation in the spinal ligaments. OPLL and OLF involved multiple etiological factors, and mechanical stress plays an important role. However, the details that what kind of mechanical stress promotes ligament ossification are still unknown. In this paper, we try to make a hypothesis that rotational mechanical stress might play a key role in OPLL and OLF development. It was supported by the conclusions that drawn from literature review: (1) Lumbar spine had the lowest prevalence of OPLL and OLF. (2) Lumbar spine was most rigid in axial rotation. (3) Atlanto-axial fusion might cause the development of sub-axial cervical OPLL. (4) Incidence of OLF was related to the range of rotation of the vertebrae.