The Diagnosis-related estimate (DRE) method is the principal methodology to evaluate spinal impairment, and alteration of motion segment integrity results at least in a DRE Category IV rating, based on a single-level fusion. Multilevel fusions are rated using the range-of-motion (ROM) method. Detailed examination of the medical literature identifies definitions of loss of motion segment integrity that differ from those in the AMA Guides to the Evaluation of Permanent Impairment, (AMA Guides), Fourth and Fifth Editions. Evaluators should note that the descriptions of certain figures were revised in the Errata to the Fifth Edition of the AMA Guides. Evaluators should note three key points from the AMA Guides: permanent impairment is based on findings at maximal medical improvement (MMI); motion in the spite must be abnormal to qualify for permanent impairment; and imaging results, by themselves, cannot be used to establish a DRE impairment rating. Overall, evaluators should consider flexion/extension radiographs that are technically adequate and taken at MMI; read and understand the Errata for Figures 15-3a, 15-3b, and 15-3c; and apply only normal translation and angular motion thresholds that are consistent with the scientific literature.