The “X-Factor” Index: a new parameter for the assessment of adolescent idiopathic scoliosis correction

Abstract

The correction rate (CR) and fulcrum bending correction index (FBCI) based on the fulcrum bending radiograph (FBR) were parameters introduced to measure the curve correcting ability; however, such parameters do not account for contributions by various, potential extraneous ''X-Factors'' (e.g. surgical technique, type and power of the instrumentation, anesthetic technique, etc.) involved in curve correction. As such, the purpose of the following study was to propose the concept of the ''X-Factor Index'' (XFI) as a new parameter for the assessment of the correcting ability of adolescent idiopathic scoliosis (AIS). A historical cohort radiographic analysis of the FBR in the setting of hook systems in AIS patients (Luk et al. in Spine 23:2303-2307, 1998) was performed to illustrate the concept of XFI. Thirty-five patients with AIS of the thoracic spine undergoing surgical correction were involved in the analysis. Plain posteroanterior (PA) plain radiographs were utilized and Cobb angles were obtained for each patient. Pre-and postoperative PA angles on standing radiograph and preoperative fulcrum bending angles were obtained for each patient.The fulcrum flexibility, curve CR, and FBCI were determined for all patients. The difference between the preoperative fulcrum bending angle and postoperative PA angle was defined as Angle XF , which accounted for the correction contributed by ''X-Factors''. The XFI, designed to measure the curve correcting ability, was calculated by dividing Angle XF by the fulcrum flexibility. The XFI was compared with the curve CR and FBCI by re-evaluating the original data in the original paper (Luk et al. in Spine 23:2303-2307, 1998. The mean standing PA and FBR alignments of the main thoracic curve were 58.3°and 24.5°, respectively. The mean fulcrum flexibility was 58.8%. The mean postoperative standing PA alignment was 24.7°. The mean curve CR was 58.0% and the mean FBCI was 101.1%. The mean XFI was noted as 1.03%. The CR was significantly positively correlated to curve flexibility (r = 0.66; p \ 0.01).The FBCI (r = -0.47; p = 0.005) and the XFI (r = -0.45; p = 0.007) were significantly negatively correlated to curve flexibility. The CR was not correlated to Angle XF (r = 0.29; p = 0.089).The FBCI (r = 0.97; p \ 0.01) and the XFI (r = 0.961; p \ 0.01) were significantly positively correlated to Angle XF . Variation in XFI was noted in some cases originally presenting with same FBCI values. The XFI attempts to quantify the curve correcting ability as contributed by ''X-Factors'' in the treatment of thoracic AIS. This index may be a valued added parameter to accompany the FBCI for comparing curve correction ability among different series of patients, instrumentation, and surgeons. It is recommended that the XFI should be used to document curve correction, compare between different techniques, and used to improve curve correction for the patient.

Predictability of Supine Radiographs for Determining In-Brace Correction for Adolescent Idiopathic Scoliosis

“…[1][2][3][4][5][6][7][8][9] Various methods for evaluating flexibility have been reported including active lateral bending radiographs in supine or standing posture, under traction or by fulcrum-bending radiographs. [1][2][3][4][5]7,[10][11][12][13][14][15][16][17][18] Spinal flexibility can also be used to predict the initial effect of orthotic treatment because more flexible spines are estimated to experience better correction by orthotic treatment. Yet, unlike the more established surgical criteria, there is no strict definition for acceptable correction in bracing.…”

Predictability of Coronal Curve Flexibility in Postoperative Curve Correction in Adolescent Idiopathic Scoliosis: The Effect of the Sagittal Profile

“…Sun et al 16 noted that "extraneous" factors (ie, X-Factor Index) exist that may describe some of the variation between the flexibility of the curve and the FBCI. The authors proposed that these "X-factors" likely involved soft tissue release, surgical technique and strategy, stronger instrumentation and improved anesthetic technique.…”

“…All patients underwent single stage posterior fusion with alternate-level pedicle screw instrumentation. 16 Assessment of curve flexibility was based on the FBR, which has been previously described. 11 In short, each patient was positioned in the lateral decubitus position.…”

Could CCI or FBCI Fully Eliminate the Impact of Curve Flexibility When Evaluating the Surgery Outcome for Thoracic Curve Idiopathic Scoliosis Patient? A Retrospective Study

“…Equations of M-CCI = (CR-0.513)/BFR and M-FBCI = (CR-0.279)/FFR were given by curve estimation to generate a best curve in eliminating the influence of flexibility on correction rate. In another study by Luk et al [ 20 ], they defined the difference between the preoperative fulcrum bending angle and postoperative PA angle as AngleXF. Proposed the notion of “XFI”, calculated by divide the AngleXF to the FFR, to measure the curve corrective ability contributed by different factors such as instrument, surgeon and so on.…”