Permanent partial impairment or "PPI" refers to the extent of loss, or loss of use, of any body part-in our practice, the knee. This differs from disability, which is loss of functional ability or the alteration of an individual's capacity to meet personal, social, or occupational demands because of an impairment (AMA 5th Ed). Thus, the same impairment in two people may result in differing disability. . For example, loss of full knee flexion in a computer programmer would not prevent full duty, while the same loss of knee flexion would seriously hamper a professional catcher. Our reports will thus describe impairment. For cases in which the impairment may interfere with work duties, it may be advantageous for us to obtain a functional capacity evaluation (FCE), which is usually performed by a physical therapist or an occupational therapist.

Indiana State law permits the physician to use sound medical judgement to arrive at a PPI. Nevertheless, to aid in consistency, we utilize the AMA "Guides to the Evaluation of Permanent Impairment" (5th Edition, 2000).

In evaluating impairment, the 5th Edition Guides, considers anatomically based, diagnostically based and functionally based losses. Anatomic loss refers to specific structural damage or loss to the knee such as muscular atrophy, ankylosis, amputation, CRPS (sympathetic pain) or arthritis. Those may be combined with certain diagnoses, which also may be used independently. Examples of diagnostic loss include fractures, ligament injury, meniscal tears and joint replacement. When it is difficult to arrive at an impairment with anatomic or diagnostic descriptions the functional loss is and option. Knee function and lower extremity function are intimately intertwined. This functional loss may be on the basis range of motion, gait derangement or muscle strength. Anatomic and diagnostic descriptions receive greater emphasis for most ratings of the knee, as gait and strength, for example, are less objective than a ligament tear or meniscal tear.

Impairment of the knee and lower extremity are listed together in the Guides table of the knee and may be converted to the whole body by multiplying by 0.4. Special tables are used for combining impairments, as they are not arithmetic. Certain impairments cannot be added an these rules are outlined in a cross-usage chart for appropriate combination of evaluation methods. For example, arthritis ratings are not used with gait or range of motion methods of determining loss as per 5th Guides.