Cervical spine stenosis measures in normal subjects

Objective: To compare 2 methods of determining cervical spinal stenosis (Torg ratio, space available for the cord [SAC]); determine which of the components of the Torg ratio and the SAC account for more of the variability in the measures; and present standardized SAC values for normal subjects using magnetic resonance imaging (MRI). Design and Setting: The research design consisted of a posttest-only, comparison-group design. The independent variable was method of measurement (Torg ratio and SAC). The dependent variables were Torg ratio and SAC scores. Subjects: Fourteen men (age = 24.4 +/- 2.5 years, height = 181.0 +/- 5.8 cm, weight = 90 +/- 13.5 kg) participated in this study. The C3 to C7 vertebrae were examined in each subject (n = 70). Measurements: The Torg ratio was determined by dividing the sagittal spinal-canal diameter by the corresponding sagittal vertebral-body diameter. The SAC was determined by subtracting the sagittal spinal-cord diameter from the corresponding sagittal spinal-canal diameter. The Torg ratio and SAC were measured in millimeters. Results: The SAC ranged from 2.5 to 10.4 mm and was greatest at C7 in 71% (10 of 14) of the subjects. The SAC was least at C3 or C5 in 71% (10 of 14) of the subjects. A Pearson product moment correlation revealed a significant relationship between the Torg ratio and SAC (r = .53, P < .01). Regression analyses revealed the vertebral body (r(2) = .58) accounted for more variability in the Torg ratio than the spinal canal (r(2) = .48). Also, the spinal canal (r(2) = .66) accounted for more variability in the SAC than the spinal cord (r(2) = .23). Conclusions: The SAC measure relies more on the spinal canal compared with the Torg ratio and, therefore, may be a more effective indicator of spinal stenosis. This is relevant clinically because neurologic injury related to stenosis is a function of the spinal canal and the spinal cord (not the vertebral body). Further research must be done, however, to validate the SAC measure.