The spinal canal in cervical spondylosis.

Cervical spondylosis was defined by Brain (1948), by Brain, Northfield, and Wilkinson (1952), and by Frykholm (1951). Its essential features are protrusion of the annulus fibrosus and changes in the adjacent vertebral margins. The size of the cervical spinal canal may play a major part in the neurological manifestations of cervical spondylosis. The antero-posterior diameters of the cervical canal in 200 normal adults were measured by Boijsen (1954). Wolf, Khilnani, and Malis (1956) in a similar study found that the antero-posterior diameter at the first cervical vertebra varied from 16 mm. to more than 30 mm. and from C.4 to C.7 varied from 12 mm. to 22 mm. The average antero-posterior diameter from C.4 downwards was 17 mm. Payne and Spillane (1957) recorded the anteroposterior diameters of the spinal canal in routine lateral radiographs in 90 adults. Measurements were from the posterior border of each vertebral body to the anterior border of the junction of the corresponding lamina. At C. 1 the measurement was taken from the posterior border of the odontoid to the anterior edge of the posterior arch of the atlas. They used standard lateral radiographs at a tube distance of 6 ft. with the patient against the film. The patients fell into three groups: 1 Normal, 2 cervical spondylosis without paraplegia, and 3 cervical spondylosis with paraplegia (myelopathy). In spondylotic spines the antero-posterior diameter tended to be less than the normal range. In those with myelopathy the reduced diameters were found throughout the cervical spine. There are possible disadvantages in assessing the significance of the size of the cervical canal in this way. Only the antero-posterior measurements are obtained, thus neglecting possible changes in the length of the canal. Precise points must be used for each measurement. For clinical purposes these measurements must be compared with a 'normal' group. The ranges of normal and the overlap of abnormal and normal are considerable. We have attempted to measure the cervical spine in such a way as to take into account both the length and all the antero-posterior diameters of the canal. In order to avoid having to make comparisons with normal ranges of measurement we have compared the canal size with one of the patient's own parameters in the region, namely, the size of the bodies of the cervical vertebrae. This method eliminates geometrical errors of radiographic projection and avoids the difficulties in measuring the varying anteroposterior diameters of the irregular canal.