Permanent Impairment is defined a measurable loss of a body part or organ system when a medical condition has reached “Maximal Medical Improvement” (MMI), or become stable. The AMA Guides 5th Edition define impairment in Chapter 1 (Philosophy, purpose, and Appropriate Use of the Guides), section 1.2a, page 2, and page 601, as, “a loss, loss of use, or derangement of any body part, organ system, or organ function.” See our glossary listing for additional terms used in the California Workers’ Compensation system.