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

Document Type


Publication Date


Publication Title

Journal of orthopaedic trauma


washington; seattle; swedish


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

DESIGN: Agreement Study.

SETTING: All level trauma centers, worldwide.

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

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

MAIN OUTCOME MEASUREMENTS: Inter-observer reliability and intra-observer reproducibility.

RESULTS: A total of 8,097 case assessments were performed. The Kappa coefficient for inter-observer 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 inter-observer 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 intra-observer 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.

CONCLUSION: The AO Spine Sacral Classification System is universally reliable among general orthopaedic surgeons and subspecialists worldwide, with substantial inter-observer and excellent intra-observer reliability.

LEVEL OF EVIDENCE: Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Clinical Institute

Orthopedics & Sports Medicine