Reliability and reproducibility analysis of the AOSpine Sacral Fractures Classification System by spinal and pelvic surgeons

•150 patients with sacral fractures were independently classified according to the AOSpine sacral fractures classification.•The intraobserver reproducibility for the whole group was substantial (κ=0.72). The interobserver reliability was moderate, with a κ=0.57.•No significant differences in agreement were found comparing surgeon expertise (Pelvic vs spine Surgeons) or experience.•Our findings confirmed the reliability and reproducibility of the AOSpine sacral fractures classification in clinical practice. Retrospective Cohort Study The AOSpine Sacral Classification System was proposed as a comprehensive and universally accepted new classification for Sacral Fractures, and was recently internally validated. However, an external, independent and multidisciplinary reports on validation of this classification is lacking. Aim of the present study is to analyze the interobserver reliability and intraobserver reproducibility of the AOSpine Sacral Classification System for Sacral Fractures between orthopedic spinal and pelvic surgeons with different levels of experience. Our institutional database was searched to retrieve patients with acute, traumatic sacral injury admitted from June 2017 to June 2020. For each patients, X-Rays and CT scans were collected. Three Orthopedic Pelvic Surgeons (Group A) and three Spine Surgeons (Group B), with different level of experience (Junior, 〈 5 years; Middle, 5–10 years; Expert 〉 10 years) independently classified all the sacral fractures included in the dataset, with two separate evaluation three weeks apart. Both intra and interobserver reliability were calculated with k-coefficient. Overall, 150 patients were included in the final dataset, for a total of 1800 different assessments, with all the subtypes reported. The intraobserver reproducibility for the whole group was substantial (κ=0.72). Overall, the interobserver reliability was moderate, with a κ=0.57. When only fracture type was taken in account, the κ value became substantial (κ=0.62). No significant differences were found comparing group A and group B (0.55 vs κ 0.55, p>0.05). No significant differences according to surgeon's experience were found; however, the κ value was slightly lower among the junior surgeons. Our findings confirmed the reliability and reproducibility of this classification in clinical practice. In the current study the surgeon's expertise (pelvic and spinal trauma) and the level of experience does not influence the reliability of the classifi