Concise Guide to Orthopaedic & Musculoskeletal Impairment Ratings, A
1st Edition

Chapter 5
General Guidelines for Impairment Ratings
Objective Findings
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.)
Anatomical Site and Terminology
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
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).
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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.
Unlisted Ratings
It is not an uncommon occurrence for a patient’s condition to either not be listed in any rating scheme or to be inappropriate for using the loss of motion or loss of sensation tables (i.e., using them would give an erroneous picture of the situation). Three strategies are helpful: interpolation, extrapolation, and the equivalent operation concept.
Interpolation means finding an appropriate intermediate value between known values. It is a basic skill of any physician. Extrapolation involves advancing a value beyond a known range based on facts, observation, or experience. However, in the context of this manual, both interpolation and extrapolation are intended to be applied not only to integers but also to the severity or complexity of procedures and disease processes.
The equivalent operation concept can be used when other measures do not give an accurate reflection of the individual’s degree of impairment. If a surgical procedure exists that is appropriate for the individual’s condition and carries a rating, then the individual’s impairment can be referenced to that even if the procedure is not done. Consider the following examples.
  • Example 1: An individual suffered knee trauma and you performed an arthroscopic procedure and are doing the impairment rating. Findings demonstrate posttraumatic arthritis and patellar subluxation. Treatment included an arthroscopic lateral retinacular release and patellar chondroplasty. At maximal medical improvement, this individual actually demonstrates fairly good motion and strength, but pain on kneeling. However, you know he has gone through a significant surgical procedure and will have problems in the not-too-distant future.
    If this individual were rated based solely on motion and strength criteria, he would not be getting a fair deal, in your opinion. So you mentally apply the equivalent operation concept and extrapolate to what you think is an appropriate value. Based on your experience, his surgical procedure and knee problem are three times as severe as those of an individual with a standard arthroscopic meniscectomy, which typically carries a 5% ppi lower extremity rating. Therefore, you assign this patient a 15% ppi lower extremity rating.
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  • Example 2: A middle-aged woman fell at her office, sustaining a distal radius fracture that resulted in significant wrist arthritis. She has fairly good motion, diminished strength, and moderate pain. She chose not to have a surgical procedure for her arthritis. Although she could be rated on motion and strength, and perhaps pain, you feel this approach does not take into account all factors. You choose the equivalent operation concept. If she were to have an operation, the procedure would be a total wrist arthroplasty (admittedly, there are other options, but for the sake of the example we will use this), which carries a 16% ppi upper extremity rating. That value is assigned, but you point out to her, and write in your report, that you have assigned her the maximum impairment rating and that if she chooses to undergo surgery at a later date the impairment rating would not be increased.
Pain
The usual medically accepted range of pain for a medical condition is included in the value assigned in the rating table. For example, an individual who has had a lumbar discectomy and is assigned the usual 10% ppi whole-person rating should not receive any additional rating because of the complaint of back pain with heavy lifting or occasional transient radicular symptoms. That degree of pain goes with the condition. Likewise, consider an individual who has sustained a metacarpal fracture and is assigned an impairment rating based on the loss of motion table, yet who also complains of pain on usage. The pain component is built into the rating for loss of motion.
However, there are occasional circumstances in which the pain is significantly outside the customary range for a given medical condition, and the physician may want to take that into consideration. The physician should be very cautious in doing so. The propensity for exaggeration by claimants can know no bounds, and there has yet to be devised a foolproof or even completely reliable method for measuring pain.
In undertaking a consideration of pain, the physician should first ask himself or herself these questions:
  • Is the pain significantly outside the customary range for the medical condition?
  • Is the condition one in which increased pain is known to occur (e.g., complex regional pain syndrome [CRPS] or postlaminectomy radiculopathy)?
  • Is the patient credible?
  • Are there reliable, observable factors associated with the pain (e.g., tight skin in CRPS, facial grimacing associated with the straight leg raising test)?
  • Does the pain in and of itself, separate from any underlying and ratable medical condition, interfere with the claimant’s activities of daily living?
If the answer to all these questions is yes, then it may be appropriate to increase a rating based solely on pain.
The AMA Guides specifies that pain-related impairment that has increased the “burden of the condition slightly” may increase the impairment rating by 3% (1). For greater degrees of pain, categorized as mild, moderate, and severe, the AMA Guides deviates from its standard rating scheme and introduces a complexly calculated pain-related score, which is then followed with a statement as to the degree of the pain’s impact on the patient. From a practical standpoint, this method is too complex. However, much
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is to be said for including a commentary as to the degree of the individual’s pain-related impairment. Beyond that, let the judicial authorities make their own decision.
Consider this worthwhile example, found in the final paragraph of a report:
Mr. Jones, as a consequence of his multiple failed lumbar laminectomies and persistent lumbar radiculopathy, has been assigned a 35% whole-person impairment based on the impairment rating guidelines. Comment: Due to frequent flare-ups of pain and inability to function, as documented above, he is more severely impaired than the anatomical impairment rating would suggest.
If a detailed pain-related assessment is required for moderate or greater levels of pain, the examiner has the options of following the steps outlined in the “Pain” section of the AMA Guides or referring the claimant to an examiner skilled in this complex impairment rating. In the latter circumstance, members of the American Academy of Disability Evaluating Physicians, or AADEP (www.aadep.org), are a worthwhile resource.
Reference
1. Cocchiarella L, Anderson GBJ, eds. Guides to the Evaluation of Permanent Impairment. 5th ed. Chicago: American Medical Association; 2001.