TO THE EDITOR:
I was quite concerned with the conclusions posited by McCarthy et al. in "Correlation between the Measures of Impairment, According to the Modified System of the American Medical Association, and Function" (80-A: 1034—1042, July 1998). They stated that the correlations were highest when measures of impairment were based on muscle strength rather than on range of motion. Muscle strength was measured by a physical therapist with use of a force-gauge. Approximately one-third of the study group did not show this positive correlation, and yet recommendations were made that undoubtedly will be cited as being authoritative.
My objections are twofold. A physical therapist often cannot distinguish between true muscle weakness and feigned or nonorganic muscular dysfunction. The sensation of giving-way or cogwheel resistance that an experienced orthopaedist evaluates as psychological dysfunction is not properly evaluated by lesser-trained personnel or a machine. Strength-testing evokes a subjective response by the patient and is not an objective manifestation as proposed in this article. If secondary gains are manifest, strength-testing is an inappropriate criterion for the evaluation of impairment.
Secondly, the public looks to the Guides to the Evaluation of Permanent Impairment1 (the Guides) as an authoritative source. Insurance companies, courts, industrial compensation boards, and other entitlement providers base many of their decisions on the material in the Guides as well as on articles such as those published in The Journal. Although, as McCarthy et al. stated, the World Health Organization defines impairment as "any loss or abnormality of psychological, physiological, or anatomical structure," entitlement providers are interested in distinguishing organic impairment from nonorganic impairment. This distinction results in different levels of compensation. I do not believe that the results of strength-testing were adequately evaluated to distinguish between these two types of impairment; this may lead to confusion by interested persons when impairment is discussed.
McCarthy et al. did not mention if astasia-abasia gait patterns were tested or excluded. In fact, I am not sure if any attempt was made to distinguish organic from psychological dysfunction or if instead the authors accepted the World Health Organization's definition of impairment and combined these two types of impairment. The latter would be a great disservice to lay researchers. Muscle strength can be considered an appropriate criterion for the evaluation of impairment only if one is sure that there is no overlying psychological component. Even if one accepts the World Health Organization's definition, weakness will not correlate well with the amount of psychological impairment. This is better evaluated by an appropriate psychiatric specialist.
Samuel S. Kaplan, M.D.: Scottsdale Medical Center, 3501 North Scottsdale Road, Suite 120, Scottsdale, Arizona 85251-5625
Dr. McCarthy, Dr. McAndrew, Dr. MacKenzie, Dr. Burgess, Dr. Cushing, Dr. de Lateur, Dr. Jurkovich, Dr. Morris, and Dr. Swiontkowski reply:
Dr. Kaplan's major concern is that the findings of our study suggest that strength-testing may be the most valid measure of physical impairment after a fracture of the lower extremity. Dr. Kaplan notes that strength-testing may not be a valid measure when an individual is motivated by secondary gains. He has a valid point. The subjects in our study may have had less (if any) incentive to feign muscle weakness because we did not provide the results of the assessments to lawyers or clinicians who were conducting disability evaluations. In this context, we found that the strength of the lower extremity was more highly correlated with function than the range of motion and diagnostic findings were. We believe that these results suggest that, when an individual is well motivated to recover as fully as possible from a fracture of the lower extremity, strength-testing may be a more sensitive measure of underlying physical impairment. However, we agree that if secondary gains are an issue, then strength-testing may not be a valid way to measure physical impairment. In such cases, it is extremely important for the physician who is conducting the disability evaluation to use alternative methods to measure impairment and to try to determine the extent to which the individual's subjective complaints are supported by evidence of underlying physical impairment.
Melissa L. McCarthy, Sc.D.; Ellen J. MacKenzie, Ph.D.: Center for Injury Research and Policy, Johns Hopkins University School of Hygiene and Public Health, 624 North Broadway, Baltimore, Maryland 21205
Mark P. McAndrew, M.D.: Department of Orthopedics and Rehabilitation, Vanderbilt University School of Medicine, 1161 21st Avenue South, Medical Center North, T-4311, Nashville, Tennessee 37232
Andrew R. Burgess, M.D.: The R Adams Cowley Shock Trauma Center, University of Maryland at Baltimore, 22 South Greene Street, T3R59, Baltimore, Maryland 21201
Brad M. Cushing, M.D.: MMC Surgical Associates, 190 Park Avenue, Portland, Maine 04102
Barbara J. de Lateur, M.D.: Department of Physical Medicine and Rehabilitation, Johns Hopkins University School of Medicine, 5601 Loch Raven Boulevard, Suite 406, Baltimore, Maryland 21239
Gregory J. Jurkovich, M.D.: Department of Surgery, University of Washington School of Medicine, Harborview Medical Center, 325 Ninth Avenue, ZA-16, Seattle, Washington 98104
John A. Morris, M.D.: Division of Trauma, Vanderbilt University School of Medicine, 243 Medical Center South, 2100 Pierce Avenue, Nashville, Tennessee 37212-3755
Marc F. Swiontkowski, M.D.: Department of Orthopedic Surgery, University of Minnesota, Box 492, 420 Delaware Street S.E., Minneapolis, Minnesota 55455