Traction versus side-bending radiographs: is the proximal thoracic curve the stiffer curve in double thoracic curves?

This is a consecutive study of patients with adolescent idiopathic scoliosis requiring surgical intervention. The purpose was to determine the best radiographic method of evaluating the flexibility of the proximal thoracic (PT) curve in patients with a double thoracic curve pattern. The PT curve averaged 40 degrees (range, 27 degrees-67 degrees) on posteroanterior (PA) radiographs, 30 degrees (range, 12 degrees60 degrees) on supine side-bending radiographs, and 24 degrees (range, 8 degrees -55 degrees) on traction radiographs. The flexibility index (FI) for the PT curve was 0.72 (range, 0.40-0.96) on side-bending and 0.58 (range, 0.29-0.82) on traction. The main thoracic (MT) curve averaged 62 degrees (range, 45 degrees-102 degrees) on PA, 40 degrees (range, 19 degrees-88 degrees) on supine side-bending, and 35 degrees (range, 17 degrees-76 degrees) on traction radiographs. The FI for the MT curve was 0.62 (range, 0.30-0.89) on side bending and 0.56 (range, 0.32-0.81) on traction. There was a statistically significant difference between the flexibility of the PT curve on supine traction as compared with the side-bending films (P<0.0005). Comparison of the MT curve flexibility with the PT curve demonstrated the PT curve to be less flexible in 11 of 15 cases (P = 0.16). The authors conclude that for double thoracic curve patterns, the PT curve is usually the smaller, yet often the stiffer curve. Furthermore, the supine traction radiograph demonstrates greater flexibility of the PT curve than does the supine side-bending radiograph. Clinically, this may assist scoliosis surgeons in assessing the PT curve and achieving a stable, balanced spine.