Correlation of the Quantec Scanner Measurements with X-Ray Measurements in Scoliosis

Computerised Surface Topography is relatively a new non invasive method of assessing spinal deformities. Our experience has been with the Quantec system. The angles measured by the Quantec scanner are not the same as the Cobb angles measured from X-rays. They are topographical measurements of the spinal deformity. To evaluate the accuracy of the Quantec scanner in predicting the degree of spinal deformity a comparative correlation study was carried out. The X- rays and Quantec scans of 128 patients aged between 2 and 60 yr. (27 males, 101 females) were studied. All patients had their X-rays and scans in the same week. There were 202 curves measured. 32 were classified as single, 82 double curves and two with triple curves. 101 curves were right sided and 101 left sided. The size of the curves on X -ray ranged from 0- 96° with a mean of 27.5° and 95% confidence level of 2.5°. With the Quantec scanner the size of the curves ranged between 0-88° with a mean of 24.4° and 95% confidence level of 2.1°. The difference between the Cobb angles and the Q angles ranged from 0 -24° with a mean of -2° and 95% confidence level of 1.1°. The Quantec scanner overestimated the size of the curve by 0 - 22° with a mean of 3.94° in 119 curves and underestimated the deformity by 0- 24° with a mean of 7.4° in 83 curves relative to the Cobb angle measurement. The Correlation Coefficient for all curves was 0.90. This varied as expected at different levels being 0.91 for thoracic curves, 0.92 for thoraco-lumbar and least, 0.85 for the lumbar curves. The mathmatical equation relating the two angles is Q angle = 3.84 + 0.753x Cobb angle ( with an r2= 0.801). This shows high correlation between the two methods of assessing the severity of the spinal deformity.