Validation of the Hierarchical Nature of the AO Spine Sacral Classification and the Development of the Sacral AO Spine Injury Score.

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Global cross-sectional survey. The objective of this study was to validate the hierarchical nature of the AO Spine Sacral Classification System and develop an injury scoring system. Although substantial interobserver and intraobserver reliability of the AO Spine Sacral Classification System has been established, the hierarchical nature of the classification has yet to be validated. Respondents numerically graded each variable within the classification system for severity. Based on the results, a Sacral AO Spine Injury Score (AOSIS) was developed. A total of 142 responses were received. The classification exhibited a hierarchical Injury Severity Score (ISS) progression (A1: 8 to C3: 95) with few exceptions. Subtypes B1 and B2 fractures showed no significant difference in ISS (B1 43.9 vs. B2 43.4, P =0.362). In addition, the transitions A3→B1 and B3→C0 represent significant decreases in ISS (A3 66.3 vs. B1 43.9, P <0.001; B3 64.2 vs. C0 46.4, P <0.001). Accordingly, A1 injury was assigned a score of 0. A2 and A3 received scores of 1 and 3 points, respectively. Posterior pelvic injuries B1 and B2 both received a score of 2. B3 received a score of 3 points. C0, C1, C2, and C3 received scores of 2, 3, 5, and 6 points, respectively. The scores assigned to neurological modifiers N0, N1, N2, N3, and NX were 0, 1, 2, 4, and 3, respectively. Case-specific modifiers M1, M2, M3, and M4 received scores of 0, 0, 1, and 2 points, respectively. The results of this study validate the hierarchical nature of the AO Spine Sacral Classification System. The Sacral AOSIS sets the foundation for further studies to develop a universally accepted treatment algorithm for the treatment of complex sacral injuries. Level IV-Diagnostic.