The method for diagnosing scoliosis based on ATR uses the phenomenon that vertebral rotation occurs in scoliosis, that is, spatial deformation of the spine in the transverse plane [3, 7]. The method based on the Cobb angle, on the other hand, uses the phenomenon that scoliosis is accompanied by the spine lateral bending, and so it measures changes in the position of individual vertebrae in relation to each other in the frontal plane . To detect interference in the presence of curvature, the ATR method estimates correlation between the co-occurrences of spinal deformities in the two planes [1, 3, 4, 7, 8]. Proper interpretation of ATR is possible when the lateral bending in the frontal plane corresponds to a linear increase in the rotation of the vertebrae. In clinical practice, however, these parameters often poorly correlate, especially in young children (6–9 years) with scoliosis in the lumbar region [1, 10, 13-14].
Scoliosis will unlikely be diagnosed in its early stadium in young children whose Cobb angle is 15° or greater (representing quite an advanced stadium of scoliosis) but ATR below 7°. Many studies have indicated the need for putting such children under active surveillance for scoliosis development as well as introducing active prophylaxis as early as at ATR of 5° . The best treatment results so far are obtained thanks to the early detection of scoliosis, followed by introducing exercises devoted to scoliosis (Physiotherapeutic Scoliosis Specific Exercises, PSEE) and – if necessary – bracing [16-22].
Some children with scoliosis have so-called side shifting, which is a lateral trunk shift at the L2–L4 level, clinically reflected in high asymmetries of the waist angles  and scoliosis of about 10°–15° in an X-ray (the Cobb angle)—but a trunk rotation of 3–5° (ATR). Figure 1 presents the hypo-rotationality of such scoliosis. The torso rotation angle would be in this situation smaller than it appears from the lateral bending value, represented by the Cobb angle in the X-ray picture.
In such situations, ATR and the Cobb angle are not correlated, with a serious consequence: while the former suggests a patient does not suffer from scoliosis, the latter indicates it has reached an advanced stadium. Failing to include such a child in active prevention may result in the development of double-arch scoliosis in the following years. Sometimes this phenomenon is accompanied by a functional inequality of lower limbs and oblique alignment of spina iliaca posterior superior (SIPS) . This situation is more common in younger children, aged 6–9 years. The development of idiopathic scoliosis in an early stadium is reflected in low-degree scoliosis of ATR below 7°.
A lack of correlation between the lateral bending of the spine and vertebral rotation may be responsible for an imprecise diagnosis of scoliosis in children based on the 7° ATR threshold, especially when a child has joint laxity or pelvis asymmetry [13, 14, 24-26]. Based on the results presented in this paper, we can hypothesise that correlation between ATR and the Cobb angle can help diagnose hypo-rotational, normo-rotational, and hyper-rotational scoliotic spinal deformation (Fig. 2).
In hypo-rotational scoliosis (Fig. 3 shows an example), ATR is smaller than the Cobb angle, and so their correlation is small, with small rotations of the vertebrae accompanied by a high lateral curvature of the spine. This is particularly common in younger children.
In normo-rotational scoliosis (Fig. 4), ATR and the Cobb angle are about the same (so their correlation is high), and so the degree of lateral bending of the spine corresponds to the degree of vertebral rotation .
In hyper-rotational scoliosis, ATR is higher than the Cobb angle (so their correlation is low), and high rotations of the vertebrae are accompanied by the slight lateral bending of the spine (Fig. 5). Hyper-rotational scoliosis is rare.
An issue arises as to whether the three types of correlation between ATR and the Cobb angle need to be distinguished. For a person diagnosing scoliosis and qualifying children for treatment, but also for those very children, the ability to distinguish them can be crucial. In the light of the results presented here, merely using one of the two criteria to diagnose scoliosis can be insufficient to diagnose the three scoliosis types discussed above. Combining the two criteria the way we propose reduces the risk that a child whose ATR is well below the threshold of 7° – and so suffers from hypo-rotational scoliosis – is not qualified for treatment.
A related issue is whether the threshold should be decreased to 5°, especially for children aged 6–10 years. In Samuelsson’s reports investigating relations between ATR and the Cobb angle in X-ray images, the correlation coefficient was low (0.57–0.65). In an extreme example, the Cobb angle of 25° corresponded to ATR of 7° in the thoracic segment and of 6° in the lumbar section . Carlson et al. pointed out that between-patient variation in ATR-Cobb correlation might be due to between-patient variation in spinal elasticity .