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Ossification of the Posterior Longitudinal Ligament – OPLL

In elderly oriental peoples; neck pain with weakness and paresthesias in upper limbs as well as spastic quadriparesis are common symptoms of ossification of posterior longitudinal ligament. There is markedly thickened and ossified posterior longitudinal ligament over the C3 to the C7 vertebral levels with resultant canal stenosis and cord compression. The cord is also decreased in caliber due to edema, ischemia and gliosis.

OPLL is commonly seen in the oriental peoples, especially the Japanese. It appears to have a strong genetic predisposition and may be associated with diabetes mellitus, abnormal calcium metabolism, ankylosing spondylitis, degenerative disc disease, diffuse idiopathic skeletal hyperostosis (DISH) or fluoride overdose.

Lesions of the PLL may include hypertrophy, calcification and ossification. Hypertrophy may occur as a primary entity or secondary to disc protrusions. OPLL usually involves the cervical spine. Occasionally it may be seen in the lumbar region, usually at the disc level. Men are more frequently involved than women, usually in the fifth to seventh decades.

PLL consists of two layers, superficial and deep. They are attached to the vertebral bodies and discs by fibrous tissue. In some, the herniated disc material may deform the deep layer of the PLL leading to reactive fibrous proliferation and inflammatory cellular changes. Proliferating small vessels may be seen in the ligament. Chondrocytes forming extracellular matrix create a mineralization or ossification front around the hyperplastic PLL. Four zones may be seen between the hyperplastic and ossified ligament – ligament, noncalcified cartilage, calcified cartilage and bone.

Clinically patients may present with neck pain, hand numbness, radicular pain, spastic quadriparesis, bladder and or bowel dysfunction.

OPLL may be overlooked on plain radiographs, whereas CT is markedly sensitive. OPLL may be classified into four types on the sagittal MR images. Continuous: extending over several vertebral bodies. Segmental: multiple separate retrovertebral lesions. Mixed : a combination of continuous and segmental and Circumscribed – confined to the retrodiscal space.

OPLL may be classified into different morphological types on the axial CT or MR images: Square; Mushroom; Hill.

Continuous type is usually thicker, may contain bone marrow and is most frequently associated with severe cord compression. Detection is dependent upon the morphology of the process, presence or absence of bone marrow or calcium in the ligament or by the effect upon the ventral subarachnoid space, dura and spinal cord. Myelopathy may develop due to direct compression on the spinal cord and anterior spinal artery.

Treatment of symptomatic OPLL is surgical and the compressing tissues are removed to decompress the spinal cord and nerves. The surgical procedures include laminectomy; expansive laminoplasty, anterior spinal fusion, anterior cervical decompression consisting of discectomy, corpectomy and resection of the OPLL mass followed by anterior interbody fusion.

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