QUESTION: When rating impairment after total hip replacement using the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides), Sixth Edition, I know that if using range of motion (ROM) as a stand-alone method, one would add the percentage lower extremity impairments (LEIs) for each of the six hip motions, and the total is the impairment rating. When using the diagnosis-based impairment method, I have always assumed that if all motion impairments are mild, that is a good result, and I have selected class 2 in Table 16-4, Hip Regional Grid (6th ed, 515). However, I read the report of another physician who, using the same diagnosis-based method, noted mild deficits in all six hip motions, added the percentage impairments for each, and selected class 3, a fair result with a higher rating. Whose logic is correct?ANSWER: Instructions at the top of the right column of the AMA Guides, Sixth Edition, page 543, state the following:Because total hip replacement is listed in Table 16-4, Hip Regional Grid (6th ed, 515), ROM would only rarely, if ever, be used as the rating method following this surgery.Instead, ROM is often used as one factor in physical examination adjustment for grade selection. Although not explicitly stated in the AMA Guides, less commonly, it may be one factor in class selection, eg, when the class criteria for a diagnosis or surgical procedure (such a total hip replacement) reference a good, fair, or poor result.Instructions for how to use ROM to select a class appear in the sixth edition on page 548 in step 4. After determining the total impairment of a joint due to motion loss(es), go to Table 16-25, (6th ed, 550)” … to classify the severity of the lower extremity motion measurements in the ICF [International Classification of Functioning, Disability, and Health] format.” For example, 20% LEI due to motion loss(es) of a joint is classified as moderate severity and class 2, whereas 30% LEI would be classified as severe and class 3. The classification from Table 16-25, combined with other outcome data from a total hip replacement, would be used to determine whether there was a good, fair, or poor result, corresponding to class 2, 3, and 4, respectively. Grade modification would be done following class selection. Table 16-25 shows how one determines whether joint motion loss is mild, moderate, severe, or very severe in Table 16-7, Physical Examination Adjustment (6th ed, page 517). However, to avoid “double-dipping” data, if ROM was used to select the class, it would not be used again in physical examination adjustment.Returning to the question posed, if there were mild impairment for each of the six hip motions per Table 16-24, the total would be 5% × 6 = 30% LEI. Per Table 16-25, this is severe (class 3) impairment. However, ROM is only one factor in determining the outcome of a total hip replacement, and the final class could be 2, 3, or 4, depending on whether there was a good, fair, or poor result, respectively.