Low-dose stereo-radiography can provide reliable global 3D quantitative analysis

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By Brice Ilharreborde, Hôpital Robert Debré, Paris, France.

 

The clinical relevance and impact of 3D analysis in paediatric spinal disorders, and more specifically in adolescent idiopathic scoliosis, has recently been pointed out by the Scoliosis Research Society.1–3 Computer tomography (CT scan) can be used, but at the expense of high radiation exposure and with the limitation of being performed in the supine position.

Conventional plain radiographs with ionising radiation remain the gold standard in the orthopaedic community, but they have been associated with 1% to 2% increased lifetime risk of developing breast and thyroid cancer in patients with adolescent idiopathic scoliosis.4 In addition, the static global balance of a patient cannot be evaluated properly on a conventional radiograph in which all the elements of the chain of balance (lower limbs, cervical spine and head) are not taken into account. However, the EOS system (EOS imaging) may be able to avoid these drawbacks—its validity in routine preoperative and postoperative use has recently been reported.5

Accessible to clinicians since 2007, the device uses the detector of x-rays designed by Charpak (Nobel Prize of Physics in 1992), transforming the original photons in electrons, and thus significantly reducing the radiation dose received by the patient (six to 10 times).2,6,7

It is a slot-scanning radiologic device consisting of two orthogonal x-ray sources, allowing simultaneous acquisition of posteroanterior and lateral images in standing position. The source is always perpendicular to the target, avoiding any image distortion. Total body scan time in a standing position ranges from 10 to 15 seconds for a 1.7m patient. From this entire body image, one can optimise luminosity and contrast, and zoom as desired on a specific area of interest with a comparable visualisation as a focused conventional x-ray. Patient’s specific 3D spinal reconstructions can also be obtained in a functional standing position in less than 15 minutes using the dedicated validated software (SterEOS, EOS imaging).5

EOS is currently the optimal device to measure and study the static balance of the entire body, since all 3D angles are automatically calculated based on the patient’s reference defined by the centres of the hips (central hip vertical axis); therefore, reducing the measurement bias due to the patient position in the cabin. Each vertebra is localised precisely in 3D, but also globally thanks to the “top view” 3D reconstruction of the spine. These views “from the top” or “from the bottom” are explicit for comparison with normal spines, and the information given regarding 3D displacements, surfaces and volumes, junctions, and balance, is certain to progressively change the habits of the spinal community currently relying on the overly simple 2D Cobb angle, which only reflects the collapse of the spine. 

In conclusion, low-dose stereoradiography now reliably provides a global 3D quantitative analysis of scoliotic deformities (spine and trunk) in a context of routine clinical use. This innovative tool will help in the future to better understand scoliosis physiopathology, assess brace efficiency, compare different surgical techniques, and finally define appropriate course of treatment.


References

  1. Labelle H. J Pediatr Orthop 2013; 31:S37-45
  2. Ilharreborde. Eur Spine J 2013: 22: 2382–91
  3. Hong JY et al. Spine 2011; 36: E1259–65
  4. Presciutti et al. Spine J 2013: Epub
  5. Ilharreborde et al. Spine (Phila Pa 1976) 2011; 36: E1306–13
  6. Dubousset et al. Bull Acad Natl Med 2005; 189: 287–97
  7. Deschenes et al. Spine (Phila Pa 1976) 2010; 35: 989–94

Brice Ilharreborde is at Hôpital Robert Debré, Paris, France. He is a consultant for clinical research for EOS.

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