Comparison of push-prone and lateral-bending radiographs for predicting postoperative coronal alignment in thoracolumbar and lumbar scoliotic curves

Study Design. A comparative evaluation of supine right and left lateral- bending radiographs and push-prone radiographs in patients with thoracolumbar and lumbar scoliosis to determine postoperative correction of the curve. Objective. To determine the difference in the ability of the push-prone radiograph and the supine lateral-bending radiograph to predict postoperative coronal alignment for primary thoracolumbar and lumbar curves managed with an anterior spinal instrumentation and fusion. Summary of Background Data. Right and left supine side-bending radiographs are the standard means of evaluating curve flexibility before surgery in idiopathic scoliosis. A push-prone radiograph also has been obtained at the authors' institution as a single dynamic radiographic assessment of forced correction of the primary curve and resultant effects on compensatory curves above and below the fusion. Methods. Preoperative standing, supine right and left lateral-bending, and push-prone radiographs were performed in 40 patients who underwent anterior spinal instrumentation and fusion. Postoperative standing radiographs of the spine were obtained at 3 months after surgery. Measurements on all the radiographs included the coronal Cobb angle, the angle of the lowest instrumented vertebra to the horizontal, the rotation of the lowest instrumented vertebra, and the distance of the midpoint of the lowest instrumented vertebra from the center sacral line. Results. The lateral-bending and the push-prone radiographs predicted less correction of the Cobb angle and the angle of the lowest instrumented vertebra to the horizontal than was achieved after surgery. However, the push-prone radiograph was superior to the lateral- bending radiograph in accurately predicting the postoperative correction of the rotation of the lowest instrumented vertebra as well as the translation of the lowest instrumented vertebra from the center sacral line. Conclusions. The push-prone and lateral-bending radiographs are similar in predicting less correction of the Cobb angle after anterior spinal surgery. The push-prone radiograph helps in determining the effects that correction of the primary curve has on the curves above and below the level of fusion by better predicting the translational correction of the lowest instrumented vertebra and the rotation of the lowest instrumented vertebra.