Validation of the AO Spine Sacral Classification System: Reliability Among Surgeons Worldwide

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To (1) demonstrate that the AO Spine Sacral Classification System can be reliably applied by general orthopaedic surgeons and subspecialists universally around the world and (2) delineate those injury subtypes that are most difficult to classify reliably to refine the classification before evaluating clinical outcomes.


Agreement study.


All-level trauma centers, worldwide.


One hundred seventy-two members of the AO Trauma and AO Spine community.


The AO Sacral Classification System was applied by each surgeon to 26 cases in 2 independent assessments performed 3 weeks apart.

Main Outcome Measurements:

Interobserver reliability and intraobserver reproducibility.


A total of 8097 case assessments were performed. The kappa coefficient for interobserver agreement for all cases was 0.72/0.75 (assessment 1/assessment 2), representing substantial reliability. When comparing classification grading (A/B/C) regardless of subtype, the kappa coefficient was 0.84/0.85, corresponding to excellent reliability. The kappa coefficients for interobserver reliability were 0.95/0.93 for type A fractures, 0.78/0.79 for type B fractures, and 0.80/0.83 for type C fractures. The overall kappa statistic for intraobserver reliability was 0.82 (range 0.18–1.00), representing excellent reproducibility. When only evaluating morphology type (A/B/C), the average kappa value was 0.87 (range 0.18–1.00), representing excellent reproducibility.


The AO Spine Sacral Classification System is universally reliable among general orthopaedic surgeons and subspecialists worldwide, with substantial interobserver and excellent intraobserver reliability.