Morphometric Determinants of the Sagittal Dimensions of the Cervical Spinal Canal in Achondroplasia

Abstract

This study was undertaken to evaluate the accuracy of the Torg ratio for predicting the spinal canal stenosis in achondroplasia, by trying to establish its correlation with the corresponding effective sagittal canal diameter (ESCD) and dural sac ratio (DSR) on the MRI of the cervical spine. Lateral radiographs and the sagittal and axial MRI study of the cervical spine from C3 to C7 level were carried out in 18 asymptomatic achondroplasia subjects. A total of 90 levels were evaluated on the lateral radiographs and on the mid sagittal T2 MR images. On statistic analysis, the highest correlation coefficient for the Torg ratio compared with the ESCD was 0.74 at C6 level and the least was 0.45 at the C5 level. The highest correlation coefficient between the Torg ratio and the DSR was 0.79 at C3 level and the least was 0.42 at the C5 level. The highest coefficient of determination for the ESCD was 54% at C6 which translates into a poor correlation. The highest coefficient of determination for the DSR was 62 at C3 level, indicating a variable correlation. These results clearly show that the Torg ratio is of limited value in the assessment of the true sagittal spinal canal diameter in achondroplasia and its reliability as an indicator of severe cervical canal stenosis is questionable.

Measurement of volume-occupying rate of cervical spinal canal and its role in cervical spondylotic myelopathy

“…Measurement of cervical spinal canal using sagittal diameter of spinal canal, cervical spinal canal ratio (i.e., Torg ratio or Pavlov ratio) [3,4], ratio of effective cervical spinal canal, the sagittal diameter of secondary spinal canal, the ratio of effective cervical spinal canal (calculated using sagittal diameter of secondary spinal canal), and axial cross-sectional area of cervical spinal cord [11] have been proposed; however, various ratio methods could not reflect the size of cervical spinal canal and could not comprehensively reflect the spinal canal stenosis and compression on cervical spinal cord, thus are limited for clinical use [5][6][7]. The most ideal assessment was to measure spinal canal volume directly.…”

“…Cervical canal stenosis is an anatomic cause and a risk factor for cervical spondylotic myelopathy (CSM) [1,2]. Currently, most morphological measurements of cervical canal stenosis focused on radial line length of cervical spinal canal and cervical spinal body [3][4][5][6][7][8] or cross-sectional area of cervical spinal canal [9][10][11][12][13][14], and thus compression on the cervical spinal cord cannot be objectively and accurately examined. Some data regarding the measurement of spinal canal volume originated from cadaver specimens [15], which had reference value but could not be applied in clinical practices.…”

Comparação do Índice de Torg obtido por meio de radiografia e ressonância magnética nos pacientes com mielopatia cervical espondilótica

“…Esse dado foi semelhante ao encontrado na literatura mundial que considera o Índice de Torg um método diagnóstico de estenose do canal cervical 3,8,11,[13][14][15][16][17][18][19][20] . O índice de Torg eliminou o viés da magnificação radiológica da medida direta do canal vertebral, o qual era causado por diferenças da distância entre o paciente, o filme e o tubo de raio-X.…”