Before the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides), Fourth Edition, spine impairment was based on range of motion (ROM) testing combined with ratings for specific spine disorders and neurologic impairment. The AMA Guides, Fourth Edition, uses the Injury or Diagnosis-related Estimates (DRE) Model to rate spinal impairment. This model is based on history, physical examination (but not ROM unless ROM is used as a differentiator), and other test data. Table 71, DRE Impairment Category Differentiators, lists DRE impairment category differentiators and discusses the differences between ratings, choosing between differentiators, and their reliability and validity. Guarding is “a spasm of muscles to minimize motion or agitation of sites affected by injury or disease,” and spasm often is overreported by physicians who are unaware of its definition. Loss of reflexes, presenting as diminished or absent deep tendon reflexes, remains the hallmark of objective physical evidence. Decreased circumference is associated with atrophy. Loss of motion segment integrity is measured on lateral flexion and extension x-rays. Loss of bowel or bladder control suggests significant spinal cord injury. The final differentiator is bladder studies, measured using a cystometrogram and showing unequivocal neurologic compromise of the bladder with resulting incontinence.