Spinal impairment evaluation includes determining the presence or absence of loss of motion segment (structural) integrity (LOMSI). The AMA Guides to the Evaluation of Permanent Impairment, Fourth Edition, defines two ways of detecting LOMSI: anterior-posterior translation of one vertebra on another (more than 3.5 millimeters in the cervical spine or 5 millimeters in the thoracic or lumbar spine); or angular motion of one vertebra on another greater than 11 millimeters (15 millimeters at L5-S1). A finding of LOMSI results in at least a diagnosis-related estimate Category IV impairment rating in any of the three spinal regions. Measurements of vertebral translation and angular motion are made using standing lateral x-rays in maximal flexion and extension. The second method of detecting LOMSI is measurement of the angular motion between three adjacent vertebrae. Flexion and extension x-rays may not be necessary in every patient undergoing spinal impairment evaluation, particularly because patients rarely have LOMSI with normal supine spinal x-rays in the absence of translational or angular abnormality on routine films. Loss of structural integrity is rare in the workers’ compensation area and is seen most commonly in middle-aged women at L4-5 or following aggressive laminectomy. Attempted but unsuccessful fusion of a motion segment does not qualify as LOMSI.