A clinical study of the differences between the scoliotic angles measured on posteroanterior and anteroposterior radiographs.

The scoliotic angles of 128 curves in seventy-eight patients were measured on paired anteroposterior and posteroanterior upright radiographs that had been made on the same day. The association between the difference in the measured angles and the various clinical and curve parameters was examined. The angles on the anteroposterior and posteroanterior radiographs were highly correlated (r = 0.96). The angles on the posteroanterior radiographs were larger than those on the anteroposterior radiographs by a mean of 2.4 degrees for the thoracic curves and 1.7 degrees for the lumbar curves. Only the thoracolumbar scoliotic angles measured essentially the same on the two radiographic projections. The magnitude of the difference between the two measured angles was not correlated with the age of the patient, the direction of the curve, the magnitude of the curve, or the degree of deformity in the sagittal plane.