Reviewer's comment on 'The 'X-Factor' Index: a new parameter for the assessment of the adolescent idiopathic scoliosis correction' by Yuqing Sun et al. (ESJO-D-09-00493 R1).

摘要

According to Luk et al. [1] the fulcrum bending radiograph can predict the magnitude of correction of idiopathic scoliosis. The fulcrum bending is a measure of the intrinsic properties of the scoliotic spine like fixed bony deformity of vertebrae, as well as flexibility of discs, thoracic cage, muscles, and ligaments. Correction depends on extrinsic factors: on instrumentation pattern, mobilisation technique, magnitude and sequence of applied forces and moments, as well as on positioning of the patient. Furthermore, we can expect some random variation between fulcrum bending Cobb angles and postoperative Cobb angles. According to equation 7 the authors have defined the X-Factor Index as the difference between the fulcrum bending angle and the postoperative Cobb angle, divided by a factor indicating flexibility of the curve. The dividend (fulcrum bending angle minus the postoperative Cobb angle) depends on the extrinsic factors as well as on random variation, the divisor (equation 4) is an expression of the intrinsic factors (and of the performance of the fulcrum bending radiograph).