There is only one report of ossification of the posterior longitudinal ligament (OPLL) in patients suffering from fluorosis. Deshpande, Dinakarand Reddy (1976) mention an association with fluorosis in 14 of 26 cases. OPLL is not mentioned in two reviews of fluorosis (Jolly 1981;
Reddy and Reddy 1987).

Patients. In our neurological service, we saw 15 cases of OPLL in one year, allpresenting with spinal compression. They accounted for about 1 .5% of all spinal cases. Ten of them had associated fluorosis. During the same period 17 cases of fluorosis with spinal compression were seen. The OPLL was confined to the cervical region in the five non-fluorotic cases, but in six of the ten fluorotic cases it also involved the dorsal and lumbar regions (Fig. 1). All the cases of OPLL presented with spinal compression, and with loss of about 50% of the sagittal canal width. The spinal stenosis was considerable, the OPLL further diminishing the canal already narrowed by fluorosis. Figure 2 shows a lateral view of the cervical spine in a patient with OPLL and fluorosis. The appearance of the ossified ligament was similar in fluorotic and nonfluorotic cases.

Treatment. Decompressive laminectomy in three patients produced further deterioration while expansive laminoplasty in three gave some relief of spasticity in only one.

Discussion. OPLL in its classical form is confined to the cervical spine and is not associated with any other osseous anomaly. Once thought to occur mainly in Japanese patients it is now being seen frequently in India (Deshpande et al 1976; Jayakumar et al 1987). An association with other diseases causing skeletal hyperostosis is now recognised, including diffuse idiopathic skeletal hyperostosis (DISH). Resnick et al (1978) observed OPLL in 50% of cases of DISH, and Tsuyama (1984) in 24%. Fluorosis causes extensive narrowing of the spinal canal and the root exit foramina; OPLL may cause further spinal stenosis. Probably because fluorosis produces more diffuse changes, our results of surgery in patients with fluorosis have been disappointing.

REFERENCES

Deshpande RP, Dinakar I, Reddy MS. Calcified posterior longitudinal ligament and myelopathy. Indian J of Orthopaedics 1976; 10:78-82.

Jayakumar PN, Sastry Kolluri VR, Jam VK, Chandramouli SA, Dan BS. Ossified posterior longitudinal ligament. Neurology India 1987; 35:55.

Jolly SS. Endemic fluorosis. In : Ahuja MMS, ed. Progress in clinical medicine in India. Second edition. India, etc : Arnold-Heinemann, 1981:106-25.

Reddy DR, Reddy DS. Management of fluorotic spinal compression. Neurology lndia 1987; 35:369-74.

Resnick D, Guerra J, Robinson CA, VEnt VC. Association of diffuse idiopathic skeletal hyperostosis (DISH) and calcification and ossification of the posterior longitudinal ligament. AJR 1978; 131:1049-53.

Tsuyama N. Ossification of the posterior longitudinal ligament of the spine. Clin Orthop 1984; 184:71-84.