Can surface topography reliably determine the Rigo classification system?

Purpose: No studies have explored the reliability of the Rigo classification system using surface topography (ST), which would allow optimization without radiation exposure. This study aims to measure and compare the intra- and inter-observer reliability (Kappa values) and accuracy of the Rigo system between ST and X-ray for overall types and subtypes.

Methods: X-ray and ST images of 31 adolescent idiopathic scoliosis patients were selected. Three investigators were blinded to assess images using the Rigo system, twice for each patient on different weeks, with 372 overall image readings. Afterwards, all investigators agreed upon the correct Rigo scores for finalized classifications.

Results: For Rigo types, the average intra-observer Kappa value was slightly better for ST (0.77, p<0.001) than X-ray (0.75, p<0.001). For Rigo subtypes, the average intra-observer Kappa value was again slightly better for ST (0.74, p<0.001) than X-ray (0.65, p<0.001). The inter-observer reliability was expectedly lower than intra-observer, with ST (0.53, p<0.001) comparable to X-ray (0.54, p<0.001) for the type. For subtype inter-observer reliability, ST (0.43, p<0.001) was slightly better than X-ray (0.36, p<0.001). For the type, the overall accuracy of the observers was slightly lower for ST (77.96%) than X-ray (79.57%). For the subtype, the accuracy of observers was slightly higher for ST (70.97%) than X-ray (65.05%).

Conclusion: ST-based Rigo system demonstrates very good intra-rater reproducibility and moderately good inter-rater reproducibility. Surface topography is comparable to X-ray for the Rigo system, and therefore can be considered a reliable alternative in clinical application.