Radiological and Surface Topography Criteria: A Comparative Study Within the Rigo Classification

Background/Objectives: No descriptive data have been reported for the radiological criteria used in the Rigo classification system (RCS) beyond the curve pattern. This study aims to quantify, compare, and correlate the criteria using X-ray and surface topography (ST). Methods: Three observers classified ST and X-ray AIS images according to the RCS. One observer then measured the following RCS criteria on both ST and X-ray, twice for each image, and averaged the measurements: Cobb angle, T1 offset, T1 tilt, transition point (TP) offset, L3 tilt, L4 tilt, L5 tilt, and pelvic shift. Results: Between ST and X-ray, the TP offset showed no significant differences (p > 0.05) and very strong correlation (r = 0.90, p < 0.0001). T1 offset and pelvic shift had no significant differences between ST and X-ray (p > 0.05) and had moderate to strong correlation (r = 0.59 to 0.73, p < 0.001). The Cobb angle showed moderate correlation for all types (r = 0.67, p < 0.0001), but showed significant difference for the B and E types. All other criteria demonstrated strong to very strong correlation between ST and X-ray (r = 0.76 to 0.90, p < 0.05), except for T1 tilt. Significant differences existed between ST and X-ray for the following criteria and types: T1 tilt (B, C); L3 tilt (B, E); L4 tilt (A, B); and L5 tilt (A). All ST criteria demonstrated moderate to good agreement (ICC = 0.57 to 0.88, p < 0.001), except T1 tilt (ICC = 0.14). Conclusions: Both ST and X-ray provide several valuable RCS criteria, with TP offset, T1 offset, and pelvic shift showing no significant differences between imaging systems. These ST-based parameters may provide complementary value to traditional radiological criteria within the RCS framework.