Revisiting Rigo Concept Classification. Radiological Criteria Reliability

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.