Measurement of cervical canal sagittal diameter in Chinese males with cervical spondylotic myelopathy.

BACKGROUND

Cervical canal encroachment can be properly assessed from lateral cervical radiographs either by defining its magnification rate or by a ratio-method. Data of the latter obtained from Chinese males with cervical myelopathy were compared with the data of general population in different age groups.

METHODS

A total of 200 Chinese males were included in this study. Half of them had undergone decompressive procedures for cervical myelopathy, while the remaining 100 cases were volunteers. Sagittal diameters of cervical canal and vertebra were measured from C3 to C6 on lateral cervical radiographs, while ratios (Torg-Pavlov's ratios) of the two reflected the extent of sagittal canal encroachment. Cut-off values and discriminant rates of these parameters in different age groups were obtained by discriminant analysis. The tube-to-film distance was set as 40 inches.

RESULTS

In myelopathic group (age < 55 y/o), Torg-Pavlov's ratios, as expressed by mean +/- standard deviation, were 0.77 +/- 0.12 for C3, 0.75 +/- 0.14 for C4, 0.80 +/- 0.14 for C5, and 0.81 +/- 0.15 for C6. In control group (age < 55 y/o) the ratios were 0.94 +/- 0.12, 0.95 +/- 0.13, 0.97 +/- 0.13, and 0.97 +/- 0.13 respectively. In myelopathic group (age > or = 55 y/o), the ratios were 0.76 +/- 0.09, 0.71 +/- 0.10, 0.73 +/- 0.11, and 0.76 +/- 0.11; while in control group (age > or = 55 y/o), the ratios were 0.93 +/- 0.10, 0.89 +/- 0.09, 0.88 +/- 0.11, and 0.91 +/- 0.12 respectively. The cutoff values and their discriminant rates are also presented.

CONCLUSIONS

The differences of canal sagittal diameter as well as Torg-Pavlov ratio between myelopathic and control group of Chinese males in individual age group were statistically significant. It is concluded that congenitally narrow cervical canal is a major predisposing factor to cervical spondylotic myelopathy.