EOS suspension test for the assessment of spinal flexibility in adolescent idiopathic scoliosis

The assessment of spinal flexibility is essential for the planning of adolescent idiopathic scoliosis (AIS) surgery. Various radiographic methods have been used but none of them has shown any superiority. The new low-dose stereography system EOS (EOS imaging, Paris, France) captures whole body images in a single scan without vertical distortion. EOS is now used in routine clinical use for AIS follow-up. The aim of this study was to prospectively evaluate the feasibility and the reproducibility of a new suspension test during the EOS imaging for the assessment of spinal flexibility in AIS.

Fifty AIS patients scheduled for surgery were prospectively included. For each patient, a standard EOS radiograph was obtained, then a suspension test in the EOS and a classic traction test on the cotrel frame were performed. The examinations were compared in terms of radiation exposure, tolerance, mean traction force, and Cobb angle reduction for each curve. Axial and sagittal reductions during suspension were analyzed on three-dimensional EOS reconstructions.

The tolerance of the suspension test was lower than the traction test but it was less operator dependent. Radiation exposure was 7 times lower during the suspension test. Cobb angle reductions achieved in the proximal and main curves by the two tests were similar. The traction test achieved greater reduction of the distal curve. Flexibility in the axial plane and in the sagittal plane was analyzed with the suspension test. The reduction in apical rotation was not correlated with the reduction in Cobb angle.

The EOS suspension test can be used for the assessment of spinal flexibility in AIS. It gives a global vision of the deformity with new flexibility indices in the axial and sagittal planes.