The overriding concern of this manual is ease of use, but not at the expense of excluding information or cutting corners that would lead to inaccurate assessment. The number one resource by far, from which this manual draws heavily, is the American Medical Association’s Guides to the Evaluation of Permanent Impairment (1), known for short as the AMA Guides. Some aspects of that work are not readily applicable to the busy clinical practitioner, however, and therefore are not included in this manual. An example is a provision to rate arthritis based on roentgenographically determined cartilage intervals. Perhaps this would be worthwhile in an ideal situation, but patients come in many sizes, and this technique is too technologist dependent. Thus, x-ray rating of arthritis based on measuring the width of the joint space was considered too variable and is not included here. Similarly, other methods for rating are not included because they were either considered too esoteric or because the situations they were designed to exploit are encountered too infrequently.

Another step taken here to simplify the rating process is combining processes that are listed separately in the AMA Guides. For example, various tables in the AMA Guides require multiple separate calculations for loss of motion in different planes. But typically, motion is lost more or less globally in traumatic and arthritic processes. Think of ankle stiffness after a trimalleolar fracture. The AMA Guides has two main tables for the ankle; this work has one. Such complexity reaches its zenith in the hand. The AMA Guides requires that five planes of motion be measured for the thumb.