Revisiting Rigo Concept Classification. Radiological Criteria Reliability

Revisiting Rigo Concept Classification. 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Radiological Criteria Reliability Garikoitz Aristegui, Rebecca Harding, Mina Jelacic, Amaia Molinuevo, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8378584/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract Rigo Concept classification differentiates 4 basic Clinical Types (A, B, C and E). There is a good correspondence between clinical types and radiological curve patterns. We can confirm the Clinical Types by using a very simple and objective radiological criterion, Alpha Angle, measurement of the Transitional Point and Central Sacral line Offset. Objective : Intra- and inter- observer reliability of the alpha angle in a previously non braced non operated AIS population. Methods : The Cobb angle (proximal thoracic, main thoracic, lumbar/ThL), Alpha angle, upper junction/CSL offset and T1/CSL offset, L3 tilting, L4 tilting and L4L5 counter-tilting, have been measured by 4 different observers in two different occasions (separated for a minimum of one week’s duration) in AP radiographies from 60 non-treated consecutive AIS patients. Observer 1 was the reference (manual measurements); Observers 2, 3, and 4 used digital. Intra- and Inter-observer correlation has been investigated. Results : Intra-observer correlation was excellent for all the four evaluators for the α^, with the Pearson coefficient ranging from 0.87 to 0.99, p < 0.001. The intra-observed correlation was also excellent in measuring L3 Tilting (0.91 to 0.99 p < 0.001), L4 Tilting (0.93 to 0.99 p < 0.001) and L4-L5 Counter-tilting (0.87 to 0.96 p < 0.001). Conclusion : Intra- and Inter-observer reliability of the Alpha angle, as the main radiological criterion in Rigo Concept Classification is excellent. No relevant differences between manual and digital measurements. Other radiological parameters used to confirm a good correspondence between clinical types (A, B, C and E) and radiological curve patterns showed also an excellent reliability. Idiopathic scoliosis non-operative treatment Rigo classification Radiography Reliability Figures Figure 1 Introduction Adolescent Idiopathic Scoliosis (AIS) is the most common form of structural spinal deformity affecting children. The Scoliosis Research Society (SRS) defines AIS radiologically as a lateral deviation of ≥ 10º Cobb with rotation, of unknown cause, diagnosed from 10 to 18 years of age. Despite this illusorily simple definition AIS is very complex three-dimensional deformity of the spine and the trunk. Its natural history is uncertain, with some cases reaching skeletal maturity with Cobbs under 30º, whilst others continue to progress to over 50º. Progressive AIS could be described as a ‘Growth Induced Torsion’ of the spine, with three coupled elements: lateral deviation, rotation and anterior overgrowth. Non-Operative treatment of AIS is recommended to prevent a major curvature ( ≥ 50º Cobb). Bracing combined with Physiotherapy Scoliosis Specific Exercises (PSSE) is an effective treatment (1,2,3) . Many different braces, with different mechanisms of action, have been historically developed (4) . The Rigo Concept Bracing uses a specific classification. The Rigo Concept Classification was first published in 2010 (5) . The classification presented 4 basic Clinical Types (with 9 sub-types) with a good radiological correspondence. The Rigo Classification was never considered by the author as a radiological classification. The classification aimed to pre-define some strategies for correction in bracing and PSSE under the assumption that 3D correction is so complex and individual. The Rigo Concept Classification starts with observing the patients Forward Bending Test (FBT) and Standing Global Coronal Balance (GCB) to arrive at a ‘Clinical Type’ that we then assess whether there is radiologic correspondence or not. There are 4 main Clinical Types, each with sub-types, there are Type A (subtypes A1, A2, A3), Type B (subtypes B1, B2), Type C (subtypes C1, C2) and Type E (subtypes E1, E2). The presence of a structural curvature in the proximal thoracic region is defined + D and this may occur in Clinical Types A, B and C as will be explained. The FBT is utilized to assess for the presence of a structural scoliosis in any of the three spinal region: Main/Middle Thoracic region (MTH), Lumbar or Thoracolumbar region (L/THL) and Proximal Thoracic region (PTH). When a structural scoliosis is clinically confirmed in this manner in the MTH region, then Clinical Types A, B and C are possible. Each of these may have + D if presence of a structural curve was found in the proximal region, as already described. E type is a single structural curvature in the L/THL region and thus, without a MTH structural curvature, does not present with a + D. Regarding the presence of structural curvature co-existing with Clinical Types A, B and C, Type B always has the presence of a primary structural curvature in the L/THL region as well. We assume it is a primary L/THL scoliosis because there is a junction in its lower limit, dissociating or uncoupling the Lumbo-Sacral-Pelvis region from it. Thus, B type presents a Lumbo-Sacral functional compensatory curvature, which produces a typical Global Coronal Balance in a way that the Middle/Upper Trunk goes imbalanced to the side of the L/THL convexity in relation to the Pelvis, which, in compensation, translates to the other side in relation to the feet position. Type E is like Type B in terms of Global Coronal Balance. The subtypes of B and E relate to the location of the apex. B1 and E1 have the apex caudal to T12 and subtypes B2 and E2 have the apex at T12. Differentiating between B1 and B2, and E1 and E2 is best achieved by looking at the radiograph. Types A and C may or may not have a secondary structural curvature in the L/THL and if present, this is subtyped A3 or C2. Differentiating between A and C is about observing the GCB. Type C presents a good GCB, with pelvis over feet and Middle/Upper Trunk over pelvis, so no relevant postural translations. Type A however has GCB in a way that the middle/upper trunk goes imbalanced to the convexity of the MTH curve in relation to the lower trunk/pelvis region, which, to compensate, translates to the contrary side in relation to the feet position. Differentiating between A1 and A2 relates to the length of the MTH where A1 is a long MTH curvature going down into the lumbar region and consequently having a lower apex, still into the TH region (T9-T11). To classify A1, it is necessary to apply a very restrictive radiological criteria: 1) L3 must be tilted to the convex TH side; 2) L2 must be rotated to the convex TH side; or, in case of not being rotated to the convex TH side, it should be the Caudal End Vertebra of the TH curvature. Any rotation at L1, L2 or L3 to the concave TH side is against classifying A1. Only when the clinical type has been already provisionally ascertained by exploring (FBT) and observing (GCB) the patient, do we then recommend looking at the radiography to see if there is curve pattern compatibility with the SRS terminology, and confirm the Clinical Type by using a very simple and objective radiological criterion. This criterion is measurement of the Transitional Point and Central Sacral Line Offset (TP/CSL offset) as measured by the Alpha angle (α^). In previous research (6) the main author of the classification (MR) did use the α^ to confirm radiologically the observed Clinical Type and discriminate between the 4 basic types. Since then, α^ is considered the Main Radiological Criterion to confirm the GCB, and together with a clinical-radiological Compatible Curve Pattern, can be used to discriminate in a simple and objective way, the four Clinical Types A, B, C and E in previously non-treated AIS. On the other hand, reliability of the α^ has not been explored yet and its capability (sensitivity and specificity) to discriminate among the clinical types has not been yet assessed in a more homogeneous population of non-treated AIS. The objective of this paper is to assess the Intra- and Inter-observer Reliability of the α^ in a previously non braced non operated AIS population, as part of a more complete investigation to know first, the sensitivity and specificity of the α^ in predicting the clinical type. Other secondary parameters potentially related to the GCB will be also explored, like the Upper Transitional Point (upper junction of the MTH curve)/CSL offset, T1 Offset, L3 Tilting, L4 Tilting and L4-L5 Counter-tilting. Material and Methods The material for this research consists in a series of 60 consecutive radiographs from non-operated, not previously braced patients with AIS, initially classified according to the clinical criteria as Type A, B, C or E, by two of the authors in their clinics, 30 cases from each one (MR and GA). The 60 collected radiographs, printed in a good quality DINA 4, were measured by these two authors and two other authors (MJ and RH). The evaluators MJ and RH made their measurements in a blind way in respect to the Clinical Type defined by MR and GA. The evaluators MR and MJ are both MD and do braces, GA is PT and Orthotist and RH is PT. The measurements of reference (EV 1) are those coming from MR, who made all the measurements manually and directly on the printed DINA 4 format using classical protractor and number 0.2 pen. The other three evaluators (EV 2, EV 3 and EV 3) took their measurements digitally (Weasis v4.0 software). All the four evaluators measured the following parameters: The Cobb angle at the Proximal Thoracic (PTH), Middle Thoracic (MTH) and Lumbar or Thoracolumbar (L/THL) curves; The Transitional Point/Central Sacral Line Offset (TP/CSL offset) or Alpha angle (α^), graphic 1; The Upper Transitional Point/Central Sacral Line Offset (UTP/CSL Offset) or Beta angle (β^); The T1/CSL Offset (T1/CSL Offset); L3 Tilting; L4 Tilting; and L4-L5 Counter-tilting. All the four evaluators did repeat the full set of measurements two times separated for a minimum of one week’s duration. In this paper, Intra-observer and Inter-observer (Pearson, Spearman and ICC) was investigated using a statistical program (R-Software) by AM. Results Intra-observer correlation was excellent for all the four evaluators for the α^, with the Pearson coefficient ranging from 0.87 to 0.99, p < 0.001. This is not relevantly different to the intra-observer correlation for the Cobb angle of the MTH (all r = 1 p < 0.001), the L/THL (ranging 0.95 to 0.99 p < 0.001) and the Proximal Thoracic (0.80 to 0.98 p < 0.001) regions. Beta angle (raging 0.86 to 0.99 p < 0.001) also showed an excellent intra-observer correlation. T1/CSL offset showed also a good correlation, but not so high (raging 0.68 to 0.98 p < 0.001). The intra-observed correlation was also excellent in measuring L3 Tilting (raging 0.91 to 0.99 p < 0.001), L4 Tilting (ranging 0.93 to 0.99 p < 0.001) and L4-L5 Counter-tilting (ranging 0.87 to 0.96 p < 0.001). Intra-observer Pearson, Spearman and ICC for all the parameters is shown in Table 1 . Inter-observer correlations were excellent too. We used the mean value of the two measurements of every parameter from each evaluator to make these correlations. Pearson coefficient for the α^ was 0.91 (EV 2 vs EV 1); 0.96 (EV 3 vs EV 1) and 0.95 (EV 4 vs EV 1), all p < 0.001. Again, not relevantly different than measuring the Cobb angle for the MTH and L/THL curvatures: 0.96 and 0.95 respectively (EV 2 vs EV 1); 0.98 and 0.97 (EV 3 vs EV 1); 0.98 and 0.97 (EV 4 vs EV 1), all p < 0.001. Beta angle also showed excellent inter-observer correlation: 0.92 (EV 2 vs EV 1); 0.97 (EV 3 vs EV 1) and 0.95 (EV 4 vs EV 1), all p < 0.001. T1/CSL showed the following Inter-observer correlations: 0.81 (EV 2 vs EV 1); 0.92 (EV 3 vs EV 1) and 0.91 (EV 4 vs EV 1), p < 0.001. The same for L3 tilting: 0.90, 0.97 and 0.96 respectively; L4 Tilting: 0.87, 0.94 and 0.94 respectively; and L4-L5 Counter-tilting: 0.77, 0.95 and 0.87 respectively, all p < 0.001. The Inter-observer correlations (Pearson, Spearman and ICC) are shown in Table 2 . Discussion The results of this first part of the whole investigation, show that Alpha angle (α^) is a highly reliable parameter when measuring X-rays, regardless of whether measurements are obtained manually or digitally, finding excellent Intra-observer and Inter-observer correlations. Its reliability was as high as that observed for the Cobb angle, when performed by experienced health professionals. In the previous research (6) , the α^ was found to be a good discriminator between the different Clinical Types in the revisited Rigo Concept Classification. With an α^> 4º to the convex thoracic side, 100% of the cases had been classified as A type. With an α^> 1º to the convex lumbar/thoracolumbar convex side, 100% had been classified clinically as B types. All the C types had an α^ between 1º to the convex L/THL side and 4º to the convex MTH side, where still some A cases were found. Thus, discriminating between A and C types, radiologically, is sometimes not possible. In any case, the principles of correction when designing braces for A and C type patients are practically the same once a Type A has been elongated and 3D aligned as a part of the defined Principles for Correction. As far as the Clinical Types A, B, C and E are related to the Global Coronal Balance, and L3 Tilting, L4 Tilting and L4-L5 Counter-tilting showed in the previous research a higher correlation with the α^ than with T1/CSL offset, we thought that the α^ is the best parameter to assess radiologically the GCB in AIS and young adults. Future research from these current obtained data will be made to stablish threshold values in the α^. We also have a plan to generate a formula, using the different studied parameters (all of them showing a high reliability according to the current results), to automatically classify and then run a different and final investigation to check how this formula predicts the real observed Clinical Type. It is important to note that the digital measurements from three different evaluators correlated well with the manual measurements performed by the author of reference (MR). One study (7) found the classification to have a moderate reliability. We note that it appears the authors of that paper were assessing photos and X-rays to calculate the ICC independently one information from the other. This is not how the classification should work. This is why the Rigo Concept Classification has been revisited, to emphasize again the recommendation to classify from exploring and observing the clinical aspects of the patient to arrive at a Clinical Type which then, using simplified and more objective radiological criteria, may be confirmed or not. Now, we are on the way to finding some reliable radiological parameters, which might allow us to classify automatically, diminishing the risk of error in classifying. It must be remembered that the most important thing is the discrimination of A and C Types from B and E Types. There is a relevant predefined way to design the lumbo-pelvic section of the Rigo-Chêneau type in accordance to these two main groups formed one by the A and C types, and the other by the B and E types. The strength of this study is that all the included patients were AIS not previously treated. Any classification has limitations, and this classification has its main limitation in the fact that a previous treatment with a brace, and possibly also with PSSE, can change the good correspondence between the clinical picture and the radiological information classically observed in non-treated AIS, producing some atypical and border cases. The incidence of atypical and border cases might be significantly higher in previously treated patients, from iatrogenesis. The weakest point of the study is that we were not able to make a design to assess the reliability of the first step to classify, the one based on clinical exploration and observation. Nevertheless, we expect we will be able to provide a useful formula to classify automatically from reliable radiological criteria, at least to make a basic differentiation between two main groups – A and C Types in one group, and B and E Types in another group. The brace design is relevantly different in these two main groups. In our experience, making a mistake in classifying between B1 and C2 is one of the main sources or error in the design of the brace associated with iatrogenesis. We hope this work contributes to diminishing this risk. Conclusions This current study shows that reliability of the alpha angle, the most commonly used radiological criterion in the Rigo Concept Classification, is excellent. We expect to confirm, with a further analysis of the current collected data, that Alpha angle is the main radiological criterion together with a curve pattern compatibility, able to discriminate between the two main groups (A and C Types Vs B and E Types) in the Rigo Concept Classification. Declarations The authors did not receive support from any organization for the submitter work and declare no competing interests. The authors declare that this research has not been previously published. References Weinstein SL, Dolan LA, Wright JG, Dobbs MB (2013) Effect of Bracing in Adolescent Idiopathic Scoliosis. N Engl J Med 369(16):1512–1521 Weinstein SL, Dobbs MB, Flynn JMJ et al (2024) BrAIST-Calc: Prediction of Individualized Benefit from Bracing for Adolescent Idiopathic Scoliosis. Spine (Phila Pa 1976) 49(3):147–156 Kwan KYH, Aldous CS, Cheng HY, Koh et al (2017) Effectiveness of Schroth exercises during bracing in adolescent idiopathic scoliosis: results from a preliminary study – SOSORT Award 2017 Winner Scoliosis and Spinal Disorders. 12:32 Negrini S, Aulisa AG, Cerny P et al (2022) The classification of scoliosis braces developed by SOSORT with SRS, ISPO and POSNA and approved by ESPRM. Eur Spine J 31:980–989 Rigo M, Villagrasa M, Gallo D A specific Scoliosis Classification correlating with brace treatment: description and reliability. Scoliosis 2010 Jan 27:5(1):1 Rigo M, Jelacic M Brace technology thematic series: the 3D Rigo-Chêneau -type brace. Scoliosis Spinal Disord 2017 Mar 16:12:10 Akçay B, Çolak TK, Apti I et al The reliability of the augmented Lehnert-Schroth and Rigo classification in Scoliosis Management Tables Tables are available in the Supplementary Files section. Additional Declarations No competing interests reported. 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1","display":"","copyAsset":false,"role":"figure","size":374910,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGraphic 1.\u003c/strong\u003e Alpha angle (a^) (TP/CSL offset)\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8378584/v1/68a7d232b675c530104ad9d2.png"},{"id":99324143,"identity":"0fa98ad4-573b-4017-8de3-d0a163eb85dd","added_by":"auto","created_at":"2025-12-31 16:47:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":670722,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8378584/v1/fa76f78c-9c5f-40a8-8576-e82b000a2e15.pdf"},{"id":99317815,"identity":"265a544b-1dc3-474a-a1e7-63bfd09bbff3","added_by":"auto","created_at":"2025-12-31 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Radiological Criteria Reliability","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAdolescent Idiopathic Scoliosis (AIS) is the most common form of structural spinal deformity affecting children. The Scoliosis Research Society (SRS) defines AIS radiologically as a lateral deviation of \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e\u0026ge;\u003c/span\u003e\u0026thinsp;10\u0026ordm; Cobb with rotation, of unknown cause, diagnosed from 10 to 18 years of age. Despite this illusorily simple definition AIS is very complex three-dimensional deformity of the spine and the trunk. Its natural history is uncertain, with some cases reaching skeletal maturity with Cobbs under 30\u0026ordm;, whilst others continue to progress to over 50\u0026ordm;. Progressive AIS could be described as a \u0026lsquo;Growth Induced Torsion\u0026rsquo; of the spine, with three coupled elements: lateral deviation, rotation and anterior overgrowth. Non-Operative treatment of AIS is recommended to prevent a major curvature (\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e\u0026ge;\u003c/span\u003e\u0026thinsp;50\u0026ordm; Cobb). Bracing combined with Physiotherapy Scoliosis Specific Exercises (PSSE) is an effective treatment \u003csub\u003e(1,2,3)\u003c/sub\u003e. Many different braces, with different mechanisms of action, have been historically developed \u003csub\u003e(4)\u003c/sub\u003e. The Rigo Concept Bracing uses a specific classification.\u003c/p\u003e \u003cp\u003eThe Rigo Concept Classification was first published in 2010 \u003csub\u003e(5)\u003c/sub\u003e. The classification presented 4 basic Clinical Types (with 9 sub-types) with a good radiological correspondence. The Rigo Classification was never considered by the author as a radiological classification. The classification aimed to pre-define some strategies for correction in bracing and PSSE under the assumption that 3D correction is so complex and individual.\u003c/p\u003e \u003cp\u003eThe Rigo Concept Classification starts with observing the patients Forward Bending Test (FBT) and Standing Global Coronal Balance (GCB) to arrive at a \u0026lsquo;Clinical Type\u0026rsquo; that we then assess whether there is radiologic correspondence or not. There are 4 main Clinical Types, each with sub-types, there are Type A (subtypes A1, A2, A3), Type B (subtypes B1, B2), Type C (subtypes C1, C2) and Type E (subtypes E1, E2). The presence of a structural curvature in the proximal thoracic region is defined\u0026thinsp;+\u0026thinsp;D and this may occur in Clinical Types A, B and C as will be explained.\u003c/p\u003e \u003cp\u003eThe FBT is utilized to assess for the presence of a structural scoliosis in any of the three spinal region: Main/Middle Thoracic region (MTH), Lumbar or Thoracolumbar region (L/THL) and Proximal Thoracic region (PTH). When a structural scoliosis is clinically confirmed in this manner in the MTH region, then Clinical Types A, B and C are possible. Each of these may have +\u0026thinsp;D if presence of a structural curve was found in the proximal region, as already described. E type is a single structural curvature in the L/THL region and thus, without a MTH structural curvature, does not present with a\u0026thinsp;+\u0026thinsp;D. Regarding the presence of structural curvature co-existing with Clinical Types A, B and C, Type B always has the presence of a primary structural curvature in the L/THL region as well. We assume it is a primary L/THL scoliosis because there is a junction in its lower limit, dissociating or uncoupling the Lumbo-Sacral-Pelvis region from it. Thus, B type presents a Lumbo-Sacral functional compensatory curvature, which produces a typical Global Coronal Balance in a way that the Middle/Upper Trunk goes imbalanced to the side of the L/THL convexity in relation to the Pelvis, which, in compensation, translates to the other side in relation to the feet position. Type E is like Type B in terms of Global Coronal Balance. The subtypes of B and E relate to the location of the apex. B1 and E1 have the apex caudal to T12 and subtypes B2 and E2 have the apex at T12. Differentiating between B1 and B2, and E1 and E2 is best achieved by looking at the radiograph.\u003c/p\u003e \u003cp\u003eTypes A and C may or may not have a secondary structural curvature in the L/THL and if present, this is subtyped A3 or C2. Differentiating between A and C is about observing the GCB. Type C presents a good GCB, with pelvis over feet and Middle/Upper Trunk over pelvis, so no relevant postural translations. Type A however has GCB in a way that the middle/upper trunk goes imbalanced to the convexity of the MTH curve in relation to the lower trunk/pelvis region, which, to compensate, translates to the contrary side in relation to the feet position. Differentiating between A1 and A2 relates to the length of the MTH where A1 is a long MTH curvature going down into the lumbar region and consequently having a lower apex, still into the TH region (T9-T11). To classify A1, it is necessary to apply a very restrictive radiological criteria: 1) L3 must be tilted to the convex TH side; 2) L2 must be rotated to the convex TH side; or, in case of not being rotated to the convex TH side, it should be the Caudal End Vertebra of the TH curvature. Any rotation at L1, L2 or L3 to the concave TH side is against classifying A1.\u003c/p\u003e \u003cp\u003eOnly when the clinical type has been already provisionally ascertained by exploring (FBT) and observing (GCB) the patient, do we then recommend looking at the radiography to see if there is curve pattern compatibility with the SRS terminology, and confirm the Clinical Type by using a very simple and objective radiological criterion. This criterion is measurement of the Transitional Point and Central Sacral Line Offset (TP/CSL offset) as measured by the Alpha angle (α^).\u003c/p\u003e \u003cp\u003eIn previous research \u003csub\u003e(6)\u003c/sub\u003e the main author of the classification (MR) did use the α^ to confirm radiologically the observed Clinical Type and discriminate between the 4 basic types. Since then, α^ is considered the Main Radiological Criterion to confirm the GCB, and together with a clinical-radiological Compatible Curve Pattern, can be used to discriminate in a simple and objective way, the four Clinical Types A, B, C and E in previously non-treated AIS. On the other hand, reliability of the α^ has not been explored yet and its capability (sensitivity and specificity) to discriminate among the clinical types has not been yet assessed in a more homogeneous population of non-treated AIS.\u003c/p\u003e \u003cp\u003eThe objective of this paper is to assess the Intra- and Inter-observer Reliability of the α^ in a previously non braced non operated AIS population, as part of a more complete investigation to know first, the sensitivity and specificity of the α^ in predicting the clinical type. Other secondary parameters potentially related to the GCB will be also explored, like the Upper Transitional Point (upper junction of the MTH curve)/CSL offset, T1 Offset, L3 Tilting, L4 Tilting and L4-L5 Counter-tilting.\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cp\u003eThe material for this research consists in a series of 60 consecutive radiographs from non-operated, not previously braced patients with AIS, initially classified according to the clinical criteria as Type A, B, C or E, by two of the authors in their clinics, 30 cases from each one (MR and GA). The 60 collected radiographs, printed in a good quality DINA 4, were measured by these two authors and two other authors (MJ and RH). The evaluators MJ and RH made their measurements in a blind way in respect to the Clinical Type defined by MR and GA. The evaluators MR and MJ are both MD and do braces, GA is PT and Orthotist and RH is PT. The measurements of reference (EV 1) are those coming from MR, who made all the measurements manually and directly on the printed DINA 4 format using classical protractor and number 0.2 pen. The other three evaluators (EV 2, EV 3 and EV 3) took their measurements digitally (Weasis v4.0 software). All the four evaluators measured the following parameters: The Cobb angle at the Proximal Thoracic (PTH), Middle Thoracic (MTH) and Lumbar or Thoracolumbar (L/THL) curves; The Transitional Point/Central Sacral Line Offset (TP/CSL offset) or Alpha angle (α^), graphic 1; The Upper Transitional Point/Central Sacral Line Offset (UTP/CSL Offset) or Beta angle (β^); The T1/CSL Offset (T1/CSL Offset); L3 Tilting; L4 Tilting; and L4-L5 Counter-tilting. All the four evaluators did repeat the full set of measurements two times separated for a minimum of one week\u0026rsquo;s duration. In this paper, Intra-observer and Inter-observer (Pearson, Spearman and ICC) was investigated using a statistical program (R-Software) by AM.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eIntra-observer correlation was excellent for all the four evaluators for the \u0026alpha;^, with the Pearson coefficient ranging from 0.87 to 0.99, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001. This is not relevantly different to the intra-observer correlation for the Cobb angle of the MTH (all r\u0026thinsp;=\u0026thinsp;1 p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), the L/THL (ranging 0.95 to 0.99 p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and the Proximal Thoracic (0.80 to 0.98 p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) regions. Beta angle (raging 0.86 to 0.99 p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) also showed an excellent intra-observer correlation. T1/CSL offset showed also a good correlation, but not so high (raging 0.68 to 0.98 p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). The intra-observed correlation was also excellent in measuring L3 Tilting (raging 0.91 to 0.99 p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), L4 Tilting (ranging 0.93 to 0.99 p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and L4-L5 Counter-tilting (ranging 0.87 to 0.96 p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Intra-observer Pearson, Spearman and ICC for all the parameters is shown in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eInter-observer correlations were excellent too. We used the mean value of the two measurements of every parameter from each evaluator to make these correlations. Pearson coefficient for the \u0026alpha;^ was 0.91 (EV 2 vs EV 1); 0.96 (EV 3 vs EV 1) and 0.95 (EV 4 vs EV 1), all p\u0026thinsp;\u0026lt;\u0026thinsp;0.001. Again, not relevantly different than measuring the Cobb angle for the MTH and L/THL curvatures: 0.96 and 0.95 respectively (EV 2 vs EV 1); 0.98 and 0.97 (EV 3 vs EV 1); 0.98 and 0.97 (EV 4 vs EV 1), all p\u0026thinsp;\u0026lt;\u0026thinsp;0.001. Beta angle also showed excellent inter-observer correlation: 0.92 (EV 2 vs EV 1); 0.97 (EV 3 vs EV 1) and 0.95 (EV 4 vs EV 1), all p\u0026thinsp;\u0026lt;\u0026thinsp;0.001. T1/CSL showed the following Inter-observer correlations: 0.81 (EV 2 vs EV 1); 0.92 (EV 3 vs EV 1) and 0.91 (EV 4 vs EV 1), p\u0026thinsp;\u0026lt;\u0026thinsp;0.001. The same for L3 tilting: 0.90, 0.97 and 0.96 respectively; L4 Tilting: 0.87, 0.94 and 0.94 respectively; and L4-L5 Counter-tilting: 0.77, 0.95 and 0.87 respectively, all p\u0026thinsp;\u0026lt;\u0026thinsp;0.001. The Inter-observer correlations (Pearson, Spearman and ICC) are shown in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\n"},{"header":"Discussion","content":"\u003cp\u003eThe results of this first part of the whole investigation, show that Alpha angle (α^) is a highly reliable parameter when measuring X-rays, regardless of whether measurements are obtained manually or digitally, finding excellent Intra-observer and Inter-observer correlations. Its reliability was as high as that observed for the Cobb angle, when performed by experienced health professionals. In the previous research \u003csub\u003e(6)\u003c/sub\u003e, the α^ was found to be a good discriminator between the different Clinical Types in the revisited Rigo Concept Classification. With an α^\u0026gt; 4\u0026ordm; to the convex thoracic side, 100% of the cases had been classified as A type. With an α^\u0026gt; 1\u0026ordm; to the convex lumbar/thoracolumbar convex side, 100% had been classified clinically as B types. All the C types had an α^ between 1\u0026ordm; to the convex L/THL side and 4\u0026ordm; to the convex MTH side, where still some A cases were found. Thus, discriminating between A and C types, radiologically, is sometimes not possible. In any case, the principles of correction when designing braces for A and C type patients are practically the same once a Type A has been elongated and 3D aligned as a part of the defined Principles for Correction. As far as the Clinical Types A, B, C and E are related to the Global Coronal Balance, and L3 Tilting, L4 Tilting and L4-L5 Counter-tilting showed in the previous research a higher correlation with the α^ than with T1/CSL offset, we thought that the α^ is the best parameter to assess radiologically the GCB in AIS and young adults. Future research from these current obtained data will be made to stablish threshold values in the α^. We also have a plan to generate a formula, using the different studied parameters (all of them showing a high reliability according to the current results), to automatically classify and then run a different and final investigation to check how this formula predicts the real observed Clinical Type.\u003c/p\u003e \u003cp\u003eIt is important to note that the digital measurements from three different evaluators correlated well with the manual measurements performed by the author of reference (MR).\u003c/p\u003e \u003cp\u003eOne study \u003csub\u003e(7)\u003c/sub\u003e found the classification to have a moderate reliability. We note that it appears the authors of that paper were assessing photos and X-rays to calculate the ICC independently one information from the other. This is not how the classification should work.\u003c/p\u003e \u003cp\u003eThis is why the Rigo Concept Classification has been revisited, to emphasize again the recommendation to classify from exploring and observing the clinical aspects of the patient to arrive at a Clinical Type which then, using simplified and more objective radiological criteria, may be confirmed or not. Now, we are on the way to finding some reliable radiological parameters, which might allow us to classify automatically, diminishing the risk of error in classifying. It must be remembered that the most important thing is the discrimination of A and C Types from B and E Types. There is a relevant predefined way to design the lumbo-pelvic section of the Rigo-Ch\u0026ecirc;neau type in accordance to these two main groups formed one by the A and C types, and the other by the B and E types.\u003c/p\u003e \u003cp\u003eThe strength of this study is that all the included patients were AIS not previously treated. Any classification has limitations, and this classification has its main limitation in the fact that a previous treatment with a brace, and possibly also with PSSE, can change the good correspondence between the clinical picture and the radiological information classically observed in non-treated AIS, producing some atypical and border cases. The incidence of atypical and border cases might be significantly higher in previously treated patients, from iatrogenesis. The weakest point of the study is that we were not able to make a design to assess the reliability of the first step to classify, the one based on clinical exploration and observation. Nevertheless, we expect we will be able to provide a useful formula to classify automatically from reliable radiological criteria, at least to make a basic differentiation between two main groups \u0026ndash; A and C Types in one group, and B and E Types in another group. The brace design is relevantly different in these two main groups. In our experience, making a mistake in classifying between B1 and C2 is one of the main sources or error in the design of the brace associated with iatrogenesis. We hope this work contributes to diminishing this risk.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThis current study shows that reliability of the alpha angle, the most commonly used radiological criterion in the Rigo Concept Classification, is excellent. We expect to confirm, with a further analysis of the current collected data, that Alpha angle is the main radiological criterion together with a curve pattern compatibility, able to discriminate between the two main groups (A and C Types Vs B and E Types) in the Rigo Concept Classification.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eThe authors did not receive support from any organization for the submitter work and declare no competing interests.\u0026nbsp;\u003c/p\u003e\u003cp\u003eThe authors declare that this research has not been previously published.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWeinstein SL, Dolan LA, Wright JG, Dobbs MB (2013) Effect of Bracing in Adolescent Idiopathic Scoliosis. N Engl J Med 369(16):1512\u0026ndash;1521\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWeinstein SL, Dobbs MB, Flynn JMJ et al (2024) BrAIST-Calc: Prediction of Individualized Benefit from Bracing for Adolescent Idiopathic Scoliosis. Spine (Phila Pa 1976) 49(3):147\u0026ndash;156\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKwan KYH, Aldous CS, Cheng HY, Koh et al (2017) Effectiveness of Schroth exercises during bracing in adolescent idiopathic scoliosis: results from a preliminary study \u0026ndash; SOSORT Award 2017 Winner Scoliosis and Spinal Disorders. 12:32\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNegrini S, Aulisa AG, Cerny P et al (2022) The classification of scoliosis braces developed by SOSORT with SRS, ISPO and POSNA and approved by ESPRM. Eur Spine J 31:980\u0026ndash;989\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRigo M, Villagrasa M, Gallo D A specific Scoliosis Classification correlating with brace treatment: description and reliability. Scoliosis 2010 Jan 27:5(1):1\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRigo M, Jelacic M Brace technology thematic series: the 3D Rigo-Ch\u0026ecirc;neau -type brace. Scoliosis Spinal Disord 2017 Mar 16:12:10\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAk\u0026ccedil;ay B, \u0026Ccedil;olak TK, Apti I et al The reliability of the augmented Lehnert-Schroth and Rigo classification in Scoliosis Management\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"european-spine-journal","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"esjo","sideBox":"Learn more about [European Spine Journal](http://link.springer.com/journal/586)","snPcode":"586","submissionUrl":"https://submission.springernature.com/new-submission/586/3","title":"European Spine Journal","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Idiopathic scoliosis, non-operative treatment, Rigo classification, Radiography, Reliability","lastPublishedDoi":"10.21203/rs.3.rs-8378584/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8378584/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRigo Concept classification differentiates 4 basic Clinical Types (A, B, C and E). There is a good correspondence between clinical types and radiological curve patterns. We can confirm the Clinical Types by using a very simple and objective radiological criterion, Alpha Angle, measurement of the Transitional Point and Central Sacral line Offset.\u003c/p\u003e \u003cp\u003e \u003cb\u003eObjective\u003c/b\u003e: Intra- and inter- observer reliability of the alpha angle in a previously non braced non operated AIS population.\u003c/p\u003e \u003cp\u003e \u003cb\u003eMethods\u003c/b\u003e: The Cobb angle (proximal thoracic, main thoracic, lumbar/ThL), Alpha angle, upper junction/CSL offset and T1/CSL offset, L3 tilting, L4 tilting and L4L5 counter-tilting, have been measured by 4 different observers in two different occasions (separated for a minimum of one week\u0026rsquo;s duration) in AP radiographies from 60 non-treated consecutive AIS patients. Observer 1 was the reference (manual measurements); Observers 2, 3, and 4 used digital. Intra- and Inter-observer correlation has been investigated.\u003c/p\u003e \u003cp\u003e \u003cb\u003eResults\u003c/b\u003e: Intra-observer correlation was excellent for all the four evaluators for the α^, with the Pearson coefficient ranging from 0.87 to 0.99, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001. The intra-observed correlation was also excellent in measuring L3 Tilting (0.91 to 0.99 p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), L4 Tilting (0.93 to 0.99 p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and L4-L5 Counter-tilting (0.87 to 0.96 p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003e \u003cb\u003eConclusion\u003c/b\u003e: Intra- and Inter-observer reliability of the Alpha angle, as the main radiological criterion in Rigo Concept Classification is excellent. No relevant differences between manual and digital measurements. Other radiological parameters used to confirm a good correspondence between clinical types (A, B, C and E) and radiological curve patterns showed also an excellent reliability.\u003c/p\u003e","manuscriptTitle":"Revisiting Rigo Concept Classification. 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