With subaxial cervical spine fractures, it has not been established which injuries can be adequately stabilized by external orthoses and which will require surgical stabilization. After review of 64 consecutive patients with C3-C7 spinal injuries, fracture characteristics on admission roentgenograms were identified that accurately predict the success or failure of nonoperative management. These include evidence of severe ligamentous injury (SLI) and severe vertebral body injury (SVBI). The presence of SLI, SVBI, or both SLI and SVBI correlated strongly with nonoperative stabilization failure (p < 0.001, p = 0.002, and p = 0.004, respectively). Injuries without SLI or SVBI were all successfully stabilized by cervical orthoses. Additionally, characterizing injuries by evidence of SLI and SVBI directs the approach for surgical stabilization.