The 3-DEMO classification has already proven to be able to differentiate scoliosis patients from normals and to be repeatable [14, 15]. In the process of validation of a new classification, ad unavoidable step is to verify if it describes adequately the phenomenon considered (construct validity): a way to verify this issue is the comparison with already existing classifications (concurrent and criterion validity). The best correlation between 3-DEMO and one of the other clinical existing classifications of idiopathic scoliosis has been found with Ponseti-SRS one. This can be easily understood when thinking that both classifications are morphological. Interestingly, the curve that seems to drive the 3-DEMO reconstruction is the thoracic one, as can be seen from Figure 1 and 2. In particular, right thoracic curves have a prevalence of left direction that corresponds to the direction of vertebrae rotation, right shift that corresponds to curve convexity, and no sagittal shift.
Type 2 curves have been considered the most important ones in King classification , because they allow a less aggressive surgical approach [16, 6]. We found (Figure 3) that these curves behave in a very different way if compared to others, with a very high number of left directions and right shifts, and a prevalence of not sagittally shifted curves. This is true also looking at the results from the other side: almost 50% of left directions, right shift and not sagittally shifted curves are King 2. We don't know what this means, and further researches are needed to better understand the 3-DEMO classification, but this result gives a clue towards a possible clinical importance. On the contrary, we did not find any kind of correlation with Lenke classification in its single components, not even with lumbar and sagittal modifiers that in some way introduced a 3-D consideration: this should be better understood with future studies on clinical applications. Nevertheless recent papers questioned the validity of Lenke classification [17, 18], as it happened before with King classification [7, 8]: it seems that we are still searching for the best classification also in 2D, as it testifies a new proposal appeared recently while this paper was under review , even if all give some important clues to clinics.
The correlation between clinical and 3-DEMO parameters (Table 2), even if in many cases statistically significant, were very feeble (low RSquare), mainly with the exception of Cobb Index for Frontal Shift, but also Kyphosis (curiously more than Sagittal Index) for Sagittal Shift and Cobb frontal degrees for Phase.
Results about the 3-DEMO parameter Phase are peculiar, because it is not correlated with any other existing clinical classification, nor Ponseti or King or Lenke or Sagittal Configuration. This is a particularly relevant point, because in our mind the way in which frontal and sagittal curves (as we are used to see and think of in the spine) combine to cause Phase gives this parameter a real 3-D importance. The name  and the description we have just made demonstrate once again the fact that we think 2-D, but reality is 3-D: Phase is a true 3-D phenomenon, not scoliosis and kypho-lordosis as we are used to.
The modelling through a stepwise regression analysis allowed us to calculate 4 rather reliable models according to RSquare values. Interestingly, Direction and Phase have been better described using all parameters while, as awaited, Shifts required to radiographically analyze the Cobb degrees of the correspondent plane: the only exception was a light contribution of kyphosis on LL Shift. So, the "truest" 3-D parameters again appear to be Direction and Phase, confirming the already stated phenomenon that only an alteration of one of these parameters (even if both could be combined) can identify a scoliosis: we could assume that the prevalence, in one patient, of Phase or Direction can represent different types of scoliosis.