Radiographic methods to estimate surgical outcomes based on spinal flexibility assessment in patients who have adolescent idiopathic scoliosis: A systematic review

Background context: Adolescent idiopathic scoliosis (AIS) is a three-dimensional deformity recognized with lateral curvature of the spine as well as axial vertebral rotation. Surgical interventions are recommended when patients with AIS have severe curvature (Cobb angle >45^o). Spinal flexibility is one of important parameters for surgeons to plan surgical treatment. Few radiographic methods have been developed to assess spinal flexibility.

Purpose: A systematic review was performed to evaluate which preoperative radiographic methods should be used to estimate spinal flexibility based on the postoperative outcomes.

Study design: Studies which included any of the five radiographic methods: (1) supine side-bending (SBR), (2) fulcrum-bending (FBR), (3) traction, (4) push-prone, and (5) suspension were reviewed and compared to determine which method provided the most accurate estimation of the postoperative outcomes.

Patient sample: Seven case series, one case control, and multiple cohort studies reported the flexibility assessment methods with the estimations of postoperative outcomes on patients with AIS.

Outcome measures: The flexibility index defined as a correction rate relative to flexibility rate was used to estimate the immediate and final follow-up postoperative outcomes.

Methods: Seven databases searched included MEDLINE, CENTRAL, EMBASE, CINAHL, Web of Science, LILACS, and Google Scholar. Three independent reviewers were involved for abstracts and full-texts screening as well as data extraction. The Quality in Prognostic Studies quality appraisal tool was used to assess the risk of bias within the studies. Also, the GRADE system rate was used to assess the evidence level across the studies.

Results: Forty-six articles were included. The distribution of the five flexibility methods in these 46 studies were SBR 38/46 (83%), fulcrum bending radiograph (FBR) 16/46 (35%), traction radiograph 5/46 (11%), push-prone 1/46 (2%), and suspension 1/46 (2%). Based on the overall assessment of flexibility indices, FBR had the best estimation of postoperative correction among the five methods. FBR method provided the best estimations of immediate and final follow-up postoperative outcomes for moderate (25°-45°) and severe (>45°) curves, respectively. For main thoracic and thoracolumbar/lumbar curves, the best estimations were traction, and FBR. However, in the reviewed articles, the risk of bias was rated moderate and the quality of evidence was rated very low to low so that a strong conclusive statement cannot be made.

Conclusions: SBR method was the most commonly used method to assess the spinal flexibility. The FBR method was the most accurate method to estimate the postoperative outcomes based on the limited evidence of the 46 articles.