Changing threshold for AIS scores of thoracolumbar compression fractures

The Abbreviated Injury Scale (AIS) is an anatomical-based coding system created by the Association for the Advancement of Automotive Medicine, utilized to classify and code injuries resulting from trauma, in order of severity. According to the latest version, all Thoraco-Lumbar Compression Fractures (TLCF), even without injury to other spine components and with >20% loss of height, were branded AIS 3 injuries, reflecting a serious threat to life or permanent disability. Advances in spine imaging, recent biomechanical studies, and long-term outcomes research offer the opportunity to consider these injuries differently.

To re-evaluate the percent compression threshold of TLCF of the spine from motor vehicle crashes (MVC) for serious risk to life identified as surgical treatment, delineating a reliable cut-off for fracture severity and morbidity. Little national data considers degree of compression and provides adequate followup imaging to determine degree of compression, justifying this effort.

Charts and radiographs of patients admitted to our institution due to vehicle crashes with isolated (vertebral body only) TLCF between 2008 and 2015 were reviewed. Data were collected on degree of compression, treatment, and long-term outcomes to determine the threshold of permanent injury. Vertebral bodies at the level of fracture were measured both anteriorly and posteriorly, and compared to adjacent segments; percentage compression was calculated.

1470 patient records with diagnoses of spine trauma were reviewed; 695 isolated compression fractures were identified, of which 194 were in vehicle crashes and had adequate imaging and follow-up. Ages ranged from 19 to 82, with a male: female ratio of 60:40. No patient with vertebral body compression of less than 30% underwent surgery unless presenting with a neurological deficit. All 22 surgical patients demonstrated significant retropulsion of bone into the spinal canal. Five surgical patients suffered eight complications; there were no adverse outcomes in the nonsurgical group.

These results are consistent with evolving clinical thinking, resulting in decreasing surgical incidence and orthosis use. Our data strongly suggests that isolated compression fractures in the absence of neurologic deficit or severe cord compression due to retropulsed bone are self-limiting. Therefore, the AIS scores for these common injuries could be reconsidered and reflect their relatively benign outlook.