Reciprocal Changes in Sagittal Alignment in Adolescent Idiopathic Scoliosis Patients Following Strategic Pedicle Screw Fixation

Abstract

Study design: Retrospective observational study.

Purpose: To analyze the effect of low-density (LD) strategic pedicle screw fixation on the correction of coronal and sagittal parameters in adolescent idiopathic scoliosis (AIS) patients.

Overview of literature: LD screw fixation achieves favorable coronal correction, but its effect on sagittal parameters is not well established. AIS is often associated with decreased thoracic kyphosis (TK), and the use of multi-level pedicle screws may result in further flattening of the sagittal profile.

Methods: A retrospective analysis was performed on 92 patients with AIS to compare coronal and sagittal parameters preoperatively and at 2-year follow-up. All patients underwent posterior correction via LD strategic pedicle screw fixation. Radiographs were analyzed for primary Cobb angle (PCA), coronal imbalance, cervical sagittal angle (CSA), TK, lumbar lordosis (LL), pelvic incidence, pelvic tilt (PT), sacral slope (SS), C7 plumb line, spino-sacral angle, curve flexibility, and screw density.

Results: PCA changed significantly from 57.6°±13.9° to 19°±8.4° (p <0.0001) with 67% correction, where the mean curve flexibility was 41% and screw density was 68%. Regional sagittal parameters did not change significantly, including CSA (from 10.76° to 10.56°, p =0.893), TK (from 24.4° to 22.8°, p =0.145), and LL (from 50.3° to 51.1°, p =0.415). However, subgroup analysis of the hypokyphosis group (<10°) and the hyperkyphosis group (>40°) showed significant correction of TK (p <0.0001 in both). Sacro-pelvic parameters showed a significant decrease of PT and increase of SS, suggesting a reduction in pelvic retroversion SS (from 37° to 40°, p =0.0001) and PT (from 15° to 14°, p =0.025).

Conclusions: LD strategic pedicle screw fixation provides favorable coronal correction and improves overall sagittal sacro-pelvic parameters. This technique does not cause significant flattening of TK and results in a favorable restoration of TK in patients with hypokyphosis or hyperkyphosis.

Keywords: Low density; Pedicle screws; Radiological outcome; Scoliosis; Spinal fusion.

Fig. 1. Measurement of various radiographic parameters including both coronal (A) and sagittal parameters (B, C). Postoperative radiograph showing strategic pedicle screw fixation for the cranial and caudal foundation along with intermittent strategic placement of screws (D). PCA, primary Cobb angle; CI, coronal imbalance; CSA, cervical sagittal angle; TK, thoracic kyphosis; LL, lumbar lordosis; SS, sacral slope; PI, pelvic incidence; PT, pelvic tilt; SSA, spino-sacral angle; C7PL, C7 plumb line.

Fig. 2. Preoperative anteroposterior (A) and lateral (B) radiographs showing initial deformation in coronal and sagittal planes. Final follow-up anteroposterior (C) and lateral (D) radiographs showing final correction achieved in coronal and sagittal planes.