Adult Degenerative Scoliosis: Can Cobb Angle on a Supine Posteroanterior Radiograph Be Used to Predict the Cobb Angle in a Standing Position?

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It is necessary to assess coronal Cobb angle in the diagnosis and treatment of patients with adult degenerative scoliosis (ADS). But as most ADS patients are elderly patients who are difficult or unable to stand upright without assistance, it is difficult to obtain standing posteroanterior X-ray radiographs. Whether it is possible to use Cobb angle obtained on a supine posteroanterior X-ray radiograph to predict Cobb angle in a standing position remains unanswered.

To study the correlation between X-ray plain radiographic parameters obtained from the supine position and those obtained from the standing position in ADS patients.

Medical records and radiological information were obtained from ADS patients prospectively. Posteroanterior X-ray views of the spine were taken in both standing and supine positions simultaneously in the same ADS patients to record information about the position of the apical and end vertebrae in the coronal position and measure Cobb angle and rotation degree of the apical vertebra. Correlation and linear regression were used to analyze the correlation between the Cobb angle and the rotation degree of the apical vertebra on the X-ray plain radiographs obtained from the standing and supine positions.

Of 94 ADS patients who met the inclusion criteria, 14 (15%) patients were male and 80 (85%) patients were female who ranged in age from 41 to 92 years with a mean of 67 years. The mean Cobb angle on the supine X-ray radiographs was 21 ± 10° versus 26 ± 12° on the standing X-ray radiographs, the difference being statistically significant (P < 0.01). The rotation angle of the apical vertebra in the supine and standing positions was 1.8 ± 0.7 and 1.9 ± 0.7, respectively, the difference being statistically significant (P < 0.05). Correlation analysis showed a strong correlation in Cobb angle between the supine and standing X-ray plain radiographs (r = 0.92, P < 0.01). The correlation coefficient of the rotation of the apical vertebra was rho = 0.81 (P < 0.01). The equation of predicting the standing Cobb angle from the supine position as shown by the linear regression analysis is as follows: standing Cobb angle = 1.15 × supine Cobb angle + 1.53 (R2 = 0.838). There was no significant difference between supine Cobb angle +5° and standing Cobb angle (P = 0.413).

The posteroanterior X-ray plain radiograph of the spine can provide information similar to that obtained from the standing coronary position in ADS patients, including the position of the apical and end vertebrae. There was a strong correlation between the Cobb angle and the degree of rotation of the apical vertebra on the X-ray radiographs obtained from the supine and standing positions, indicating that the supine Cobb angle can be used to predict the Cobb angle on the standing X-ray radiograph. The supine X-ray radiograph can replace the standing posteroanterior radiograph in terms of the coronal parameters.

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