Analysis of 137 cases reveals a preponderance of male, showing a ratio of three men to one woman. The onset of disease is found most frequently in the fifth decade (42 cases, 37.8%), less frequently in the sixth, forty and seventh decades in the order of frequency.50 cases (36.5%) show severe symptoms including sensory disturbance of extremities, impairment of fine movements of fingers, spastic claudication, inability to walk and rectovesical incontinence. 61 cases (44.5%) have moderate to slight symptoms and the remaining 26 cases (19%) are asymptomatic.50% or 21 of 42 severe cases are between 40 and 49 years of age. The commonest initial symptom is segmental manifestation of the spinal cord (57.7%) whereas myelopathic symptoms are seen in 18.2%. However, in an avarage period of 3.8 years between the onset and patient's visit to the hospital the desease advances in 55.0% to show both symptoms. The descending type of paralyosis is more common (50 cases, 72.5%) than the ascending type in its progression, and 70.3% of them shows myelopathic symptoms within two years.The commonest site of ossification is C5, followed by C4, C6 and C3 in the order of frequency. Ossification most commonly involves the adjacent spinal bodies. The narrowest portion of the spinal canal due to ossification is most frequently C5, followed by C4, C3 and C6 in the order of frequency. The majority of cases in which the spinal canal narrows by more than 40% belong to the severe case group.Abnormal ossifications in other skelet are observed in 56 (81.2%) of 69 cases while disturbance in carbohydrate metabolism is found in 28 (87.5%) of 32 cases.Operation is performed, as a rule, before rectovesical disturbance develops. Operative tratment is indicated in those who have moderate or slight symptoms, but show severe radicular manifestations, and also in patients of thirties and forties with more than 40% narrowing of the spinal canal.At operation the patient is placed in the prone position but not in the sitting position. In the first stage Iaminectomy is followed by resection of the dentate ligament are performed to effect decompression and mobilization of the spinal cord through the posterior approach. If spastic claudication persists with positive clonus after a follow-up period of three to six months, anterior spine fusion and decompression of the cord is indicated, depending on the myelographic findings of disturbed passage of the contrast material, patient's age and profession. For laminectomy luer forceps or cervical rongeur are not suitable. In their plane surgical-air-drillis used in anterior decompression and in resection of ossification.The following operative procedures are carried out in a total of 47 cases including 39 severe and 6 mild cases: Laminectomy with section of the dentate ligament -306-
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