Impairment ratings should be based on demonstrable anatomical loss of function. (See the exception for pain accompanied by objective findings of pain in the section “Pain” later in this chapter.)

The accepted anatomical sites for assigning impairment ratings are as follows: whole person, upper extremity, hand, digit, lower extremity, and foot. These are often referred to as scheduled items because workers’ compensation schedules exist outlining how much is paid for injuries to each of those areas. Impairments to anatomical areas other than those listed, such as the knee or wrist, should not be cited.

Also note that the current edition of the AMA Guides does not provide for referencing impairments to the loss of a toe, although some parties may request you to do so. Toe impairments are referenced as a percentage of the foot, just as knee impairments are referenced to the lower extremity.

Unless otherwise requested, the impairment should be referenced to the smallest anatomical site that is appropriate. For example, for an injured finger, one would report the impairment as 75% permanent partial impairment (ppi) of the index finger, not as 15% hand.

Impairments should be expressed in whole digits, if necessary rounding off to the next highest number.

Conversion tables are available (Appendix A). They convert all recognized anatomical sites within an extremity to one another and to the whole person. For example, 75% ppi finger equals 15% hand, which equals 14% upper extremity, which equals 8% whole person. This approach allows different areas of impairment to be combined (Chapter 4 and Appendix B).

Take, for example, the common situation of an individual with bilateral carpal tunnel syndrome and bilateral ulnar neuropathy at the elbow. A reasonable upper extremity rating would be 5% ppi for the median nerve and 7% ppi for the ulnar nerve. Using the author’s recommended 10% rule (i.e., values under 10% can be added, bypassing the Combined Values Chart), this would total 12% ppi for each side. Using the conversion table in Appendix A, 12% upper extremity is equivalent to 7% whole person—for each side. Adding the two sides (again, using the 10% rule) results in a total impairment rating of 14% ppi whole person. At the risk of belaboring a point, following the author’s recommendation of simply adding impairments of 10% or less results in math that can be done in the head and requires the use of only one table. However, following the AMA Guides and employing the Combined Values Chart results in the use of two charts and requires four separate steps to arrive at a value of 13% for this example. The difference between the two methods is 1% ppi, well within the variability of the system.