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Ossification of the posterior longitudinal ligament (OPLL) is a disease, characterized by a pathological hypertrophy and prominent bony formation of the posterior longitudinal ligament. It may lead to the compression of the spinal cord and myelopathy. OPLL tends to present in the fifth and sixth decades of life. It is most frequent in the cervical region and fewer than 10% are observed in the thoracic or lumbar region. There is an association between OPLL and other diseases and pathologies such as diffuse idiopathic skeletal hyperostosis (DISH), ossification of yellow ligament (OYL) and metabolic disordres such as diabetes mellitus, hypoparathyroidism and active Vitamin D disorders. Some researchers suggest that by early detection and correction of such metabolic disorders it may be possible to eliminate the aggravation of OPLL in those cases. . The etiology of OPLL remains obscure. Laboratory examinations return normal results. However, as mentioned above there is an association with metabolic disorders.

Signs and symptoms
Symptoms caused by cervical OPLL are those of cervical myelopathy and cervical radiculopathy. At onset some report axial discomfort around the neck, and limitation of neck motion. Years later as disease progress symptoms may aggravate. Matsunaga et al. reported that about 40% of symptomatic patients presented with myelopathy. Some may be asymptomatic, however a minor trauma may reveal the disease.

About 45% of patients with OPLL have motor dysfunction of the extremities, which might impair their lifestyle. According to a nationwide survey, the symptoms are pain/numbness of the upper limb in 74%, neck/nuchal pain in 64%, changes of refl exes in the lower limbs in 58%, sensory change in the upper limbs in 55%, and changes of refl exes in the upper limbs.

The mechanism of myelopathy is far from being understood. The factors that influence the development and aggravation of myelopathy are devided to static and dynamic. The static factors that contribute to the compression of the spinal cord are consider to be the absolute residual space available for the spinal cord and relative (in %) canal occupation of the ossified mass. The dynamic factors are the Range of Motion (ROM) and cervical mobility. Mobility is associated with higher risk for the development of myelopathy. High mobility is speculated to be linked with higher ROM and hence with greater chance for myelopathy. It seems that hyper mobility especially movements that aggravate pain should be avoided. Statistically, people with continues type of OPLL suffer from decreased ROM relatively to other types of OPLL. .

History
The first report of OPLL was made in 1839. Tsukimoto presented the first Japanese autopsy case of cervical OPLL in 1960 and Terayama et al. gave the disease its name.

Diagnosis
OPLL Diagnosis is done through Imaging. MRI is the gold standard as for spinal imaging. It can show the manifestations of this disease as well.

OPLL is also well defined by CT. In addition CT myelographic images permit an analysis of the degree of encroachment on the spinal canal and compression of the cord that is superior to that obtained from conventional tomography or myelography.

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Epidemiology
There is a geographical difference in the prevalence of OPLL. In Japan, the reported incidence ranges from 1.7 to 2.4% and includes asymptomatic cases. In non-Asians, it is 0.16%. Siblings of patients with OPLL who share an increased number of human leukocyte antigen haplotypes are at increased risk for developing OPLL, suggesting a genetic factor.