The AMA Guides to the Evaluation of Permanent Impairment (AMA Guides), Fifth Edition, defines a motion segment as “two adjacent vertebrae, the intervertebral disk, the apophyseal or facet joints, and ligamentous structures between the vertebrae.” The range of motion from segment to segment varies, and loss of motion segment integrity is defined as “an anteroposterior motion of one vertebra over another that is greater than 3.5 mm in the cervical spine, greater than 2.5 mm in the thoracic spine, and greater than 4.5 mm in the lumbar spine.” Multiple etiologies are associated with increased motion in the cervical spine; some are physiologic or compensatory and others are pathologic. The standard radiographic evaluation of instability and ligamentous injury in the cervical spine consists of lateral flexion and extension x-ray views, but no single pattern of injury is identified in whiplash injuries. Fluoroscopy or cineradiographic techniques may be more sensitive than other methods for evaluating subtle abnormal motion in the cervical spine. The increased motion thus detected then must be evaluated to determine whether it represents normal physiologic motion, normal compensatory motion, motion related to underlying degenerative disk and/or facet disease, or increased motion related to ligamentous injury. Imaging studies should be performed and interpreted as instructed in the AMA Guides.

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