The present study was undertaken to determine the efficacy of Lyon bracing in a case series of adolescent females with idiopathic thoracic scoliosis. The study was conducted according to the SRS Committee criteria and followed the guidelines on standard of management of idiopathic scoliosis with corrective braces in everyday clinics and in clinical research proposed by the SOSORT [5, 6]. The SRS criteria have been developed to provide uniform criteria for the inclusion of participants in brace studies and the evaluation of results . The SOSORT guidelines provide recommendations concerning the standards of brace management of idiopathic scoliosis, with the aim of ensuring a minimum quality of care, increasing the efficacy of treatment and maximizing the compliance to bracing prescription .
Analyses of our case series revealed that the large majority of patients (~85 %) obtained a curve correction after Lyon bracing, whereas a curve stabilization was achieved in ~13 % of cases. Only in one case a curve progression was observed. The greatest correction occurred early during treatment. This may be due to the fact that in the initial phase, bracing acts mostly on the elastic component of the curve, leading to an early, substantial correction. These results can be explained by the capacity of visco-elastic structures to respond promptly to the brace action, with vertebral remodeling occurring later during the course of treatment (in accordance with the law of Hüter-Volkman). As illustrated in Fig. 2, derotation and vertebral remodeling proceed over the entire duration of treatment, assuring further curve correction and its maintenance over time. Results from the present study are consistent with previous reports in JIS and AIS patients treated with Lyon brace, therefore confirming the effectiveness of this bracing device [10–15]. Furthermore, findings from the present study are in agreement with the results of recent studies performed in patients with idiopathic lumbar and thoraco-lumbar curves treated with PASB [16, 17], and indicate that an appropriate conservative approach is successful in most scoliotic curves. In a recent study, Weinstein et al.  confirmed that bracing significantly decreased the progression of high-risk curves to the threshold for surgery and that the success rate was higher in patients that had worn the brace for more hours. However, controversies still exist as to whether bracing is truly effective in the management of AIS [19, 20], highlighting the need for high-quality, large-scale clinical trials.
In another recent study conducted following the SRS and SOSORT criteria, Negrini et al.  found, in 44 cases, that treatment with several type of braces allowed a curve correction in 86 % of patients with idiopathic thoracic scoliosis and only in the most important cases the Lyon brace was used. A progression was observed in 14 % of cases. These results together with those reported here demonstrate that the adoption of conservative approaches based on the SOSORT and SRS guidelines produce better results than those that followed the SRS criteria only.
A retrospective study conducted in 1,338 AIS patients treated with Lyon brace demonstrated that only the 5 % of curves progressed more than 5° Cobb from the initial magnitude during follow-up .
A subgroup analysis in 285 patients with single thoracic curves showed that correction was obtained in 54.26 % cases, stabilization was achieved in 32.25 % of patients, while progression occurred in 12.79 %.
These findings are comparable with previous results from our group, though in our study the success rate was higher with one case of progression (1.5 %) compared to 14 and 12 percent of progression [3, 21].
The same study also reported that, when treatment is started with a Cobb value < 40°, only 2 % of patients eventually require surgery. For Cobb values > 40° at the beginning of treatment, the percentage of patients progressing to surgery is 20 %. These findings indicate that Lyon bracing represents a highly effective conservative approach to AIS, by substantially reducing the need of surgery . Other orthoses are available for the management of idiopathic thoracic curves (e.g., SpineCor, Providence, Milwaukee, etc.) [22–26]. The rate of success of these devices appears to be lower (range 15–60 %) than that achieved by the Lyon brace. It should however be considered that no studies have yet been performed to specifically compare the outcome of treatment with different orthoses in thoracic scoliotic curves, according to the SRS and SOSORT criteria. Furthermore, all the patients included in the study have worn the brace as prescribed. In a previous study in which the results were assessed according to compliance it was determined that curve progression and referral to surgery are lower in patients with high brace compliance. In particular, bracing discontinuation up to 1 month does not impact on the treatment outcome. Conversely, wearing the brace only overnight is associated with a high rate of curve progression .
This issue needs to be addressed by future investigations in order to determine the most effective bracing strategy in patients with idiopathic thoracic scoliosis.
About the patients who abandoned the treatment the results showed a progression of curve, at the time of discontinuation, only in the 5 % of cases. Therefore, were not the results to send away the patient but, probably, the trouble of a long term treatment, in particular the failure rate of treatment including the dropouts is 22 % but the surgical rate is lower.
Limitations of the study
The relatively small sample size of the present work is the main limitation. This is due to SRS criteria that limit the cases but allows comparisons with other studies adopting the same recruitment and evaluation approach. Another limitation of the study is the lack of a control group (i.e., untreated patients), but no ethics committee would allow not to treat structured and progressive scoliosis ranging from 25 to 40° Cobb at 10–12 years of age. Nevertheless, in another our study, it was demonstrated that in all our cases in which the brace is not worn correctly the evolutionary process of scoliosis, confirming its evolutivity, is resumed  and recently the efficacy of the brace against the control group was confirmed also in other paper .