Comparison of Whole Spine Sagittal Alignment in Patients with Spinal Disease between EOS Imaging System versus Conventional Whole Spine X-ray

Abstract

Purpose: The biplanar whole body imaging system (EOS) is a new tool for measuring the whole body sagittal alignment in a limited space. This tool may affect the sagittal balance of patients compared to conventional whole spine X-ray (WSX). This study aimed to investigate the difference in sagittal alignment between WSX and EOS.

Materials and methods: We compared the spinal and pelvic sagittal parameters in 80 patients who underwent EOS and WSX within one month between July 2018 and September 2019. The patients were divided based on sagittally balanced and imbalanced groups according to pelvic tilt (PT) >20°, pelvic incidence-lumbar lordosis >10°, C7-sagittal vertical axis (SVA) >50 mm in WSX.

Results: In the sagittally imbalanced group, compared to WSX, the pelvic parameters demonstrated compensation in EOS with smaller PT (27.4±11.6° vs. 24.9±10.9°, p=0.003) and greater sacral slope (SS), and the patients tended to stand more upright with smaller C7-SVA (58.4±17.0 mm vs. 48.9±57.3 mm, p=0.018), T1-pelvic angle (TPA), T5-T12, and T2-T12. However, in the sagittally balanced group, these differences were less pronounced only with smaller PT (10.8±6.9° vs. 9.4±4.7°, p=0.040), TPA and T2-T12 angle, but with similar SS and C7-SVA (p>0.05).

Conclusion: EOS showed a negative SVA shift and lesser PT compared to WSX, especially in patients with sagittal imbalance. When preparing a surgical plan, surgeons should consider these differences between EOS and WSX.

Keywords: EOS; compensatory mechanism; sagittal parameters; whole spine x-ray.

Fig. 1. (A) EOS imaging system (https://www.eos-imaging.com/professionals/materials). Perpendicularly placed, vertically moving, co-linked units of X-ray tubes producing very thin collimated X-ray beams collected by unique line detectors with Nobel Prize-winning technology resulted in simultaneously captured biplanar digital images of a patient in a standing, weight-bearing position. (B) A space on which the patient stands. The width and length were about 76.5 cm each. (C) A patient with severe sagittal deformity whose entire body could not be examined with an EOS system.

Fig. 2. Comparisons of sagittal parameters between WSX and EOS in patients with sagittal imbalance. ^*Indicates significant differences in angles between WSX and EOS (p<0.05). For LL and C2-C7 Cobbs, positive values indicate lordosis and negative values indicate kyphosis. WSX, conventional whole spine X-ray; PT, pelvic tilt; SS, sacral slope; LL, lumbar lordosis (L1-S1 Cobbs angle); TPA, T1-pelvic angle; SVA, sagittal vertical axis.

Fig. 3. Typical case of the sagittally imbalanced group. Compared to WSX (A), EOS (B) showed smaller PT (60.7° to 54.0°), C7-SVA (174 to 121 mm), T2-T12 (9.7° to 0.2°), and larger SS (7.6° to 15.3°), indicating a compensation. WSX, conventional whole spine X-ray; PT, pelvic tilt; SS, sacral slope; SVA, sagittal vertical axis.

Fig. 4. Comparisons of sagittal parameters between WSX and EOS in patients without sagittal imbalance. ^*Indicates significant differences in angle between WSX and EOS (p<0.05). For LL and C2-C7 Cobbs, positive values indicate lordosis and negative values indicate kyphosis. WSX, conventional whole spine X-ray; PT, pelvic tilt; SS, sacral slope; LL, lumbar lordosis (L1-S1 Cobbs angle); TPA, T1-pelvic angle; SVA, sagittal vertical axis.

Fig. 5. A figure showing the change of the entire spinal balance in EOS. (A) Directed standing in open space (conventional whole spine X-ray, gray line) vs. (B) Directed standing within limited space (EOS, black line). WSX, conventional whole spine X-ray.