Study DesignSystematic Review.ObjectivesTo detail every historical classification system of the sacrum and pelvis and their resultant integration into the encompassing AO Spine Sacral Injury Classification System.MethodsA systematic review of MEDLINE, EMBASE and Cochrane Databases was performed in keeping with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines.Results49 studies were included in the systematic review. Historical systems fail to provide clinicians with a rational method of determining whether operative or non-operative management is appropriate. Fracture morphologies are presented in a non-hierarchical manner without considering crucial treatment changing factors such as degree of neurological injury or associated anterior pelvic injury. The AO Spine Sacral Injury Classification System introduces sacrum and pelvic fractures in a clinically meaningful manner ranging from the usually stable type A bony injures of the lower sacrococcygeal region, to the type B posterior pelvic injuries potentially involving the sacral foramina, and finally the type C unstable spino-pelvic injuries.ConclusionsThe sacrum and pelvis are biomechanically related structures and should be evaluated as a unified entity rather than separately as has been historically suggested. The AO Spine Sacral Injury Classification System achieves this by considering the integrity of the spino-pelvic bony as well as supporting ligamentous structures, whilst simultaneously providing a graded framework to guide whether surgical or non-surgical management is most appropriate.