Why is a 3D image of the whole skeleton useful in treating spinal deformities?

Abstract

The lecture discusses in detail the issues related to the EOS system, which allows scanning a patient’s skeleton from head to feet in two standard projections with x-rays perpendicular to the surface they reach. At the same time, the radiation load is reduced by a factor of 10 compared with routine spinal radiography. The EOS system is unique: simultaneous 3D study with image acquisition in any plane, including a top view, gives a real three-dimensional assessment of the spine or its deformity. Further, it is possible to carry out measurements in all planes and in all directions. To quantify spinal deformity in three planes using EOS, the Vertebral Vector Projection program has been developed. The principle is the replacement of each vertebra with an anteroposterior vector starting dorsally at the midpoint between pedicles, reaching the midpoint of the ventral surface of the vertebral body and running parallel to its cranial end plate. Thanks to the capabilities of EOS, the severity index was developed – a formula based on x-ray data. For small deformities (less than 15°), the Cobb angle, the torsion index of the curve, axial rotation of the apical vertebra, intervertebral rotation at the upper and lower ends of the curve, and apical lordosis are taken into account. The value of the index varies from 0 to 1. If it does not exceed 0.4, the deformity will not  progress, and if it exceeds 0.6, the deformity will increase in 100 % of cases. The geometric and mechanical personified 3D model allows preoperative planning for severe deformities: it helps in choosing the level and direction of the section, the magnitude of the resected angle, and in computer modeling of the closure of bone surfaces to obtain a new type of spinal alignment. The EOS imaging system helps to understand the need to distinguish between alignment (statics) and balance (dynamics) of the spinal column.