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Correlation between the Measures of Impairment, According to the Modified System of the American Medical Association, and Function*

MELISSA L. MCCARTHY, M.S., BALTIMORE, MARK P. MCANDREW, M.D., NASHVILLE, ELLEN J. MACKENZIE, PH.D., BALTIMORE, ANDREW R. BURGESS, M.D., BALTIMORE, BRAD M. CUSHING, M.D.#, PORTLAND, MAINE, BARBARA J. DELATEUR, M.D.**, BALTIMORE, MARYLAND, GREGORY J. JURKOVICH, M.D., SEATTLE, WASHINGTON, JOHN A. MORRIS, M.D., NASHVILLE, TENNESSEE and MARC F. SWIONTKOWSKI, M.D., MINNEAPOLIS, MINNESOTA

Investigation performed at The R Adams Cowley Shock Trauma Center, Baltimore, Vanderbilt University Hospital, Nashville, and Harborview Medical Center, Seattle

	Abstract

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We performed a prospective study of 302 patients who had a fracture of the lower extremity. Our purpose was to determine whether there was any association between impairment ratings of the lower extremity, derived with use of the Guides to the Evaluation of Permanent Impairment by the American Medical Association, and measurements of task performance based on direct observation as well as the patient's own assessment of activity limitation and disability as recorded on the Sickness Impact Profile. The mean residual impairment of the lower extremity according to the Guides was 27 per cent one year after the injury. Only 130 subjects (43 per cent) could perform all five functional tasks without difficulty. Eighty-four subjects (28 per cent) reported functional limitations that resulted in a score on the Sickness Impact Profile that was more than one standard deviation from the preinjury norm for the sample. Impairment ratings according to a modification of the system of the American Medical Association correlated strongly with the performance of functional tasks (r = 0.57) as well as the patients' reported activity limitations as recorded on the Sickness Impact Profile (r = 0.55). Correlations were highest when measures of impairment were based on strength rather than on range of motion. The relationship between the impairment rating and function (as observed by an examiner and as reported by the patient) was not influenced by the location of the fracture or the receipt of disability compensation. Our results suggest that the American Medical Association developed a valid approach for the measurement of physical impairment after a fracture of the lower extremity. In our study, the anatomical approach of evaluation based on muscle strength that was described in the Guides to the Evaluation of Permanent Impairment was the most sensitive measure of impairment compared with the anatomical measure based on range of motion and compared with the functional and diagnostic methods for the rating of impairment. Until the diagnostic and functional approaches for the measurement of musculoskeletal impairment are refined, we recommend use of the anatomical approach when evaluating impairment after a fracture of the lower extremity.

	Introduction

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The objective rating of permanent physical impairment is an important factor used by Workers' Compensation programs, other entitlement programs, and insurers to determine an appropriate level of financial compensation^8,10. The definition of impairment in the Guides to the Evaluation of Permanent Impairment² (the Guides) closely parallels that of the World Health Organization, which defined an impairment as "any loss or abnormality of psychological, physiological, or anatomical structure or function."² Permanent impairment is defined in the Guides as a condition "that has become static or stabilized during a period of time sufficient to allow optimal tissue repair, and one that is unlikely to change in spite of further medical or surgical therapy."²

The Guides, one of the most widely used systems for rating impairment^25,27, was first published in 1971 by the American Medical Association, and the most recent edition, the fourth, was published in 1993. The Guides provide a standard framework and a method of analysis with which physicians can evaluate, report on, and communicate information about the impairment of any human organ system. As of 1991, twenty-nine of the fifty-three jurisdictions of the United States either recommended or mandated by law the use of the Guides for determining eligibility for Workers' Compensation. In twelve of the fifty-three jurisdictions, the Guides are used frequently although they are not specifically mentioned in the law². The impairment ratings of the American Medical Association are intended to represent the extent to which the capacity of an individual to perform basic functional activities of daily living is diminished. The impairment ratings are based solely on a medical evaluation of the organ system that is diseased or injured.

Disability, conversely, occurs when an individual is unable to meet the demands of his or her personal, familial, occupational, or social responsibilities because of an impairment. The Guides define disability as "the gap between what a person can do and what a person needs or wants to do." The Guides clearly state that impairment ratings should not be used to estimate disability directly. Rather, disability should be determined by combining the knowledge about the impairment with the limitations that it causes as an individual attempts to meet his or her life expectations and responsibilities.

Few investigators have examined the extent to which the impairment ratings derived with the system of the American Medical Association correlate with observed function and the inability to perform everyday activities¹⁵. We measured the impairment of the lower extremity, with use of the Guides, in a group of 302 individuals. These scores were then correlated with scores for function as measured through the direct observation of five tasks involving use of the lower extremities and as derived from the patients' responses on the Sickness Impact Profile^4,9.

	Materials and Methods

Top Abstract Introduction Materials and Methods Results Discussion References

 
Impairment and functional status were prospectively evaluated at six and twelve months in a group of 302 patients who had been admitted to one of three trauma centers for the treatment of a unilateral fracture of the acetabulum or lower extremity. These data were part of a larger study designed to determine the long-term physical and psychosocial consequences of a fracture of the lower extremity^23,24.

Study Population
We evaluated patients who had a unilateral fracture of the acetabulum, femur, tibia, talus, calcaneus, or forefoot and had been admitted to one of three participating level-I trauma centers. Patients were excluded if they had an isolated phalangeal or metatarsal fracture, were less than eighteen or more than sixty-four years old, did not speak English, had a major neurological injury, had a concomitant injury of the upper extremity that precluded the use of crutches at the time of discharge, had received definitive orthopaedic treatment before arrival at the trauma center, or had been previously diagnosed with a psychiatric illness.

Between May 1990 and December 1991, patients who met the eligibility criteria and who had agreed to participate in the study were asked, before they were discharged from the hospital, to describe their functional status before the injury according to the Sickness Impact Profile. Subjects were also asked to return to the trauma center at six and twelve months after the injury for an interview by the study coordinator and a clinical assessment by a registered physical therapist. The interview included questions about functional recovery and receipt of disability compensation, and the patients completed the Sickness Impact Profile questionnaire. The clinical assessment included measurement of the range of motion of the joints of the lower extremity, the strength of the muscles, and the ability of the patient to perform five different functional tasks. Physical therapists conducted the assessment of functional performance as well as impairment even though it is common for a physician to perform an evaluation of impairment. In our study, only the diagnostic part of the evaluation was carried out by an orthopaedic trauma surgeon, who measured any residual osseous displacement on radiographs. The registered physical therapists determined the anatomical and functional ratings at six and twelve months after the injury. All were trained to follow a standardized protocol, and the methods to be used were clearly described to them.

Of the 444 patients who had been initially enrolled in the study, 345 were located and interviewed one year after the injury. Despite numerous telephone calls and letters, ninety-nine patients could not be contacted. Forty-three patients completed the interview by telephone but were unable to return to the center for the clinical assessment. Because information from both the interview and the clinical assessment was considered necessary to validate the Guides, the present analysis is based on the 302 subjects for whom complete one-year data were available.

Eighty-six patients (28 per cent) had multiple fractures of the same extremity. The 302 patients sustained a total of 428 fractures (Table I); there was a wide variety of types and grades^7,29. None of the patients in the study had an isolated fracture of the pelvis or patella. Nineteen of twenty-two patients who had an isolated fracture of the foot had a fracture of the calcaneus or talus. The mean age of the 302 patients was thirty-four years (range, eighteen to sixty-three years). Before the injury, 236 patients (78 per cent) had been employed. There were 211 men (70 per cent). The fractures in 206 patients (68 per cent) were secondary to a motor-vehicle or motorcycle accident. One hundred and sixty-three patients (54 per cent) sustained injuries of the lower extremity only. The remaining 139 patients had an additional injury of the head or spine (fifty-seven patients [19 per cent]), abdomen or thorax (twenty patients [7 per cent]), upper extremity (fifteen patients [5 per cent]), or multiple body systems (forty-seven patients [16 per cent]). The mean duration of hospitalization was thirteen days (range, one to 128 days); seventy-six patients (25 per cent) were hospitalized for more than two weeks. The site of the fracture did not influence the duration of the hospitalization (p = 0.11).

Measurement of Impairment of the Lower Extremity with Use of the Guides
The systems for rating physical impairment of the lower extremity are categorized by the Guides as diagnostic, anatomical, and functional². Diagnostic measures of impairment are based on the observed abnormality or diagnosis, the presence of muscle damage or nerve injury, and the extent of residual displacement evident on follow-up radiographs when a fracture of the lower extremity is involved. Anatomical measures of impairment are based on the findings of physical examination and direct measurement of the reduced function of the body part. The Guides rely principally on the range of motion and the muscle strength as measures of anatomical impairment caused by musculoskeletal injuries. Functional measures assess impairment within controlled environments and typically consist of observed performance of specific tasks required for everyday living. According to the Guides, the score for functional impairment associated with an injury of the lower extremity is based on the severity of gait disturbance and the need for assistive devices.

The Guides recommend that the method of evaluation (diagnostic, anatomical, or functional) that demonstrates the greatest impairment be used to represent the overall impairment of the extremity and of the individual. However, anatomical measures of impairment based on the range of motion or the muscle strength are most appropriate for most patients who have impairment of a lower extremity; diagnostic and functional measures should be used only when data concerning the range of motion or the muscle strength are not available. Therefore, we chose to examine the anatomical measures of impairment in detail for all patients. The diagnostic and functional ratings were compared with the anatomical ratings of impairment for eighty-seven patients who are representative of the study population in terms of the type and severity of the fracture.

Muscle Strength
Manual muscle-testing is used to determine muscle strength in the rating of impairment according to the Guides. We measured muscle strength with use of a force-gauge that was held and stabilized by a physical therapist. The gauge (model FET5000; Force Evaluation and Testing System, Hoggan Health Industries, Draper, Utah) recorded the maximum force exerted by the patient. The decision to use a handheld force-gauge was based on recent studies^{6,7,19,21,26,30} in which these devices were shown to measure the strength of the extremities more reliably and accurately than manual muscle-testing. The measurement of the strength of the muscles of the uninjured extremity with the force-gauge was used to translate the results of the force-gauge testing on the side of the injury into a manual muscle-testing grade. The physical therapist measured the strength of the injured and the uninjured lower limb for each type of motion of the hip, knee, and ankle and calculated the ratio of the injured to the uninjured lower limb for each type of motion. This ratio represented the strength of joint motion of the injured lower limb compared with that of the uninjured lower limb, which was then translated into the equivalent grade for manual muscle-testing with use of the theoretical percentage scores of Kendall and McCreary²⁰.

According to the method of Kendall and McCreary²⁰, subjects who had a joint-motion ratio of at least 81 per cent were considered to have normal strength (zero impairment) for that joint motion and were assigned a value of impairment equivalent to grade-5 muscle strength; ratios from 51 to 80 per cent were assigned values of impairment equivalent to grade-4 muscle strength; ratios from 21 to 50 per cent, grade-3 muscle strength; and ratios of 20 per cent or less, grade-2 muscle strength. Because the Guides assign equal impairment values to muscle grades of 2 or less, we did not identify ratios that were less than 20 per cent. To calculate the score for impairment of total strength for the lower extremity, the impairment values for each motion were added within joints and combined across joints, according to the specifications in the Guides.

Range of Motion
Patients who had ankylosis of a particular joint were assigned an impairment value specified by the Guides on the basis of the degree of the fixed malposition. Impairment values for fifteen patients who had an amputated extremity were assigned a value according to a separate schedule that was based on the level of amputation. The starting and ending positions for each motion of the hip, knee, and ankle were recorded with use of positions recommended by the American Academy of Orthopaedic Surgeons¹.

The Guides recommend that the active range of motion take precedence over the passive range of motion. However, in the present study, when the active range of motion was not normal, the passive range of motion also was tested and the physical therapist recorded the better of the two measurements. The ranges of motion of each joint were assessed, and the values for impairment of each motion were added within joints and combined across joints with use of the formula specified by the Guides to estimate the score for impairment of the total range of motion of the lower extremity.

Independent Measures of Functional Limitations
Functional limitations were evaluated with use of both a task-performance measure and a patient-reported assessment of activity limitation. The performance measure was used to evaluate function in a controlled environment under a specific set of conditions, whereas the patient-reported assessment revealed the limitations that the patient had when carrying out everyday activities in his or her own environment.

Task-Performance Measure
The ability of the subject to perform five different functional tasks was assessed by a physical therapist. The five tasks were walking 150 feet (45.7 meters) within thirty seconds, climbing a flight of stairs (twelve to fourteen steps), rising onto the toes ten times, rising from a chair five times without use of the upper limbs and within fifteen seconds, and taking eight tandem steps in a straight line without losing balance. As there is no standardized assessment of the function of the lower extremity, these five tasks were chosen because they demonstrated function along a continuum of ability and could be administered in a reliable manner. Each of these tasks was given a score of 0, 1, or 2 points. A score of 0 points was assigned if the subject had no difficulty performing the task; 1 point, if the subject could do the task but needed slight-to-moderate assistance (from either a device or a person) or needed more than the amount of time allotted to complete the task; and 2 points, if the subject could not complete the task at all or needed maximum assistance. A composite functional-performance score was calculated by adding the scores for the five tasks, so the range of possible scores was 0 to 10 points. The higher the score, the more functional limitations had been demonstrated by the subject during the physical-therapy assessment.

Patient-Reported Measure
The Sickness Impact Profile (SIP) was used to determine the patient-reported measure of function in everyday activities^4,9. The SIP has been widely used to assess the impact of different diseases and injuries on the performance of the activities of everyday life and on role function^{3,11-14,18,23,28}. This health-status measure consists of 136 items that describe psychosocial and physical health behaviors in twelve different categories of function (sleep and rest, emotional behavior, body care and movement, household management, mobility, social interaction, walking, alertness, communication, work, recreational and leisure activities, and eating). The present study focused on the physical-dimension subscore of the SIP as it deals with activity limitations that are most relevant to the function of the lower extremity (walking, mobility, and body care and movement).

The respondent was instructed to read the statements and to endorse those that described his or her health. In the present study, the five most frequently endorsed statements concerning physical limitations were (1) I walk more slowly (121 patients [40 per cent]); (2) I walk shorter distances or often stop to rest (103 patients [34 per cent]); (3) I walk by myself but with some difficulty—for example, I limp, wobble, stumble, or have a stiff leg (eighty-one patients [27 per cent]); (4) I go up and down stairs more slowly—for example, one step at a time or I stop often (eighty-one patients [27 per cent]); and (5) I change position frequently (seventy-four patients [25 per cent]). Each item had been pre-weighted according to the relative impact of the dysfunction on the activities of everyday living. The physical-limitation subscore of the SIP is calculated by combining the category scores for walking, mobility, and body care and movement. The total score for physical limitations ranges from 0 to 100 points; a higher score connotes poorer function. A score of 3 points or less is considered normal; a score between 4 and 9 points represents mild limitations; a score between 10 and 19 points, moderate limitations; and a score of 20 points or more, severe limitations⁴.

Statistical Analysis
The validity of the methodology of the Guides for measuring impairment of the lower extremity was determined by examining the relationship between the impairment and the functional status at both six months and one year after the injury. The score for impairment was correlated with both the functional-performance measure and the physical-dimension subscore of the SIP with use of Pearson product-moment correlations. As the impairment and functional scores for most subjects were distributed toward less severe outcomes, correlations were calculated with use of the natural logarithms of the observations.

The Sickness Impact Profile was administered during the initial hospitalization and at each follow-up evaluation. When the patients completed the initial evaluation, they were asked to describe their preinjury level of function. It should be noted that these baseline scores were quite similar to normative SIP scores obtained from a general population. The initial score was used to adjust for the effect of preinjury physical limitations on postinjury function by calculating a partial correlation for the SIP score. (Performance measures were not available before the injury.) The size of the correlations changed only slightly, however, because most subjects in our study were healthy and had had few functional limitations before the injury. Correlation coefficients range from -1.00 to 1.00. The closer the coefficient is to -1.00 or 1.00, the stronger the linear relationship is between the two variables. When the correlation coefficient approaches zero, it indicates little or no linear relationship between the two variables.

We further characterized the extent and nature of the relationship between impairment and functional outcome by reporting the per cent distributions of functional performance and patient-reported activity limitations within each of four levels of per cent impairment (0 to 9, 10 to 24, 25 to 49, and 50 per cent or more). For the purpose of this analysis, functional-performance and physical-dimension SIP scores were classified according to four levels of limitation (none, mild, moderate, and severe). More specifically, functional-performance scores were categorized as 0, 1 or 2, 3 or 4, or 5 to 10 points, whereas the SIP scores were categorized as 0 to 3, 4 to 9, 10 to 19, or 20 points or more.

	Results

Top Abstract Introduction Materials and Methods Results Discussion References

 
The relationships between impairment and function at six months and one year were similar; therefore, we report only the one-year results in the present study. (We previously reported the findings in this group of patients at the six-month follow-up evaluation^23,24.) One year after the injury, 282 patients (93 per cent) were able to bear weight on the limb and 269 patients (89 per cent) were able to walk without an assistive device. There was variation in terms of the levels of residual impairment, the ability to perform specific tasks, and the perceptions of activity limitations as measured with the SIP.

Impairment of the Lower Extremity at One Year
The distribution of the scores for impairment of the lower extremity was quite different when the range of motion rather than the muscle strength was used as the criterion (Table II). For 199 patients (66 per cent), measurement of the strength yielded a higher score for impairment than measurement of the range of motion. When impairment of the lower extremity was determined on the basis of the higher score, regardless of whether it was for the range of motion or for the strength, sixty-nine patients (23 per cent) were found to have 0 to 9 per cent impairment of the lower limb; ninety-seven patients (32 per cent), between 10 and 24 per cent impairment; eighty-six patients (28 per cent), between 25 and 49 per cent impairment; and fifty patients (17 per cent), at least 50 per cent impairment. The mean residual impairment of the lower extremity was 27 per cent at one year after the injury.

Functional Status at One Year
One hundred and thirty patients (43 per cent) were able to perform all five functional tasks without difficulty. Forty-five subjects (15 per cent) had difficulty rising from a chair five times within fifteen seconds, seventy-nine subjects (26 per cent) had difficulty rising onto the toes ten times, ninety-one subjects (30 per cent) had difficulty climbing a flight of stairs, ninety-one subjects had difficulty performing a tandem walk, and 101 subjects (33 per cent) had difficulty walking 150 feet (45.7 meters) within thirty seconds (Table III). One hundred and eleven subjects (37 per cent) reported no limitations of physical activity at one year after the injury. The mean SIP score for the physical dimension was 5.4 points (range, 0 to 47 points). Eighty-four patients (28 per cent) had a SIP score that was more than one standard deviation (±4.5 points) from the preinjury norm for the sample (mean, 1.1 points).

Correlation of Impairment with Functional Status
The correlation between the impairment of the lower limb and the functional status was moderately strong (Table IV). The strongest correlation was found between impairment and the performance of functional tasks (r = 0.57). In general, as the level of impairment increased, a higher percentage of subjects demonstrated moderate-to-severe difficulty in performing the physical tasks. Of the sixty-nine subjects who were characterized as having little or no impairment (0 to 9 per cent), only one had severe difficulty performing the tasks. Similarly, only one of the fifty subjects who were characterized as having severe impairment (50 per cent or more) was able to perform all five functional tasks with no difficulty.

The correlations between impairment and function (as observed by an examiner and as reported by the patient) were examined with respect to the site of the fracture and the receipt of disability compensation, but no significant differences were detected with the numbers available (p > 0.05). Thirty-two patients (11 per cent) received income from Workers' Compensation programs, and seventy-seven patients (25 per cent) received disability income from other sources, such as company or union disability plans, accident or disability insurance policies, or Federal Civil Service disability benefits. No difference was found with respect to impairment and function between the 109 patients who received some type of disability compensation and the 193 patients who did not.

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
The objective rating of impairment is essential to the process of disability evaluation used by Workers' Compensation and other entitlement programs to determine appropriate levels of financial compensation. As it is usually a physician who evaluates the extent of impairment, the American Medical Association has made a concerted effort to provide physicians with a standard framework and method of analysis with which to rate the physical impairment of any human organ system accurately and objectively. With the Guides, the physician uses accepted medical standards and expert clinical judgment to characterize impairment.

It is estimated that more than 600,000 individuals are hospitalized annually because of a principal diagnosis of an injury of the lower extremity¹⁶. Moreover, injuries of the lower extremity represent the second most important source of disability among individuals who survive traumatic injury²². We evaluated the extent to which the measures of impairment described by the American Medical Association correlate with individual function for one circumscribed group of individuals—namely, those who have a fracture of the lower extremity.

Our primary focus was evaluation of the validity of impairment ratings of the lower extremity with use of an anatomical approach. However, we also used the diagnostic and functional approaches, which were recommended in the Guides as well, to examine the relationship between impairment and function in eighty-seven patients. The diagnostic approach yielded higher impairment ratings than the anatomical approach for only twelve of the eighty-seven patients. Moreover, the correlations between diagnostic measures of impairment and function were substantially lower than the correlations between strength and function. The functional approach yielded higher scores for impairment (two of eighty-seven patients) even more rarely than did the anatomical approach. This finding suggests that the anatomical approach is the most appropriate method for measuring impairment after a fracture of the lower extremity.

The measures that we used to evaluate the function of the lower extremity did not characterize the complete range of function. With both the functional-performance measures and the SIP, the ability of the patient to perform normal everyday activities is evaluated; the ability to perform tasks requiring a higher level of function, such as running, jumping, or squatting, is not assessed. Consequently, the subjects in our study may have had functional limitations that were not represented by the functional measures that we used. Thus, the correlation between impairment and function may have been attenuated. Additional attenuation of the relationship may have resulted from the fact that, although an isolated muscle group may be impaired, the effect of the impairment may be compensated for by uninvolved muscle groups. Thus, an individual may exhibit normal or nearly normal function even in the presence of a measurable impairment. Furthermore, it is difficult to measure impairment or function independent of motivation because inconsistent effort during testing weakens the association between impairment and function. This difficulty is of particular concern when there is a potential for secondary gain because an individual may exaggerate impairment or functional limitations in the hope of attaining a higher disability settlement.

Assessments of impairment based on range of motion would probably yield the same results as those based on strength for patients who are severely impaired. However, strength may be a more discriminating measure for patients who are mildly impaired. The threshold amount of strength that is needed to perform a number of functional activities is higher than that needed to move a limb actively through its arc of motion. Thus, for this study population, strength seemed to be a more sensitive measure of the underlying physical impairment.

The correlations between strength and function were consistently 0.10 to 0.15 point higher than the correlations between range of motion and function. This result should be interpreted with some caution, however, because we recorded the better of the two ranges of motion (active and passive). As function depends on the ability of the individual to move the extremity actively, this practice could have weakened the association that was observed between range-of-motion impairment and functional status. Even if we had been able to calculate values for impairment of active motion only, strength would probably have remained the most important determinant of physical function for this study population.

The results of the present study must be interpreted with some caution because of certain limitations with regard to its design. First, the methods that we used to measure range of motion and strength deviated from those recommended in the Guides. As mentioned, we recorded the best range of motion, regardless of whether it was active or passive. In addition, strength was assessed with use of a handheld force-gauge instead of with manual muscle-testing. A number of studies have shown that manual muscle-testing is a less sensitive measure for subjects who have fair-to-good strength^5,21,26. Because most of our subjects were able to complete strength-testing by providing resistance in antigravity positions, manual muscle-testing would have characterized these patients as having relatively good strength (grade 4 of 5); use of the force-gauge allowed greater differentiation.

Second, our data represented the impairment and functional status of individuals at one year after the injury. These data probably characterize the permanent impairment and functional status of most of our participants. However, for some subjects, the impairment and functional outcome at one year may not have been the final values.

Third, although physicians usually assess impairment for disability evaluations, the clinical assessments in this study were performed by registered physical therapists. The physical therapists carried out the anatomical and functional approaches outlined in the Guides; only the diagnostic approach was performed by a physician (an orthopaedist). Subjects may have performed differently if they had been evaluated by a physician rather than a physical therapist.

Fourth, we evaluated the methodology described in the Guides for the rating of the impairment associated with one condition, a fracture of the lower extremity. Obviously, this does not represent a complete validation of the Guides. Additional empirical research is needed to examine the validity of the Guides methodology for other organ systems and diseases.

The results of this analysis suggest that the Guides offer a valid approach for the measurement of impairment after a fracture of the lower extremity. In general, the American Medical Association designed a sound and logical framework for measuring impairment of the lower extremity. This framework yields impairment ratings that demonstrate moderately strong correlations with function as observed by an examiner and as reported by the patient. At the same time, however, we support the efforts of the American Medical Association to update the Guides periodically. These updates are needed to reflect the improved understanding of disease and its manifestations, diagnosis, and treatment. It is also important for the American Medical Association to develop abbreviated procedures to simplify the rating process and to improve its reliability. The recommendation by the Guides that multiple approaches be used to measure impairment increases the chances that an underlying physical impairment will be detected. However, this multifaceted approach is time-consuming and may reduce the interrater reliability of the scale. In the same way that the Guides acknowledge the limited usefulness of the measurement of range of motion and recommend radiographic techniques for the evaluation of impairment in patients who have arthritis, the American Medical Association should develop recommendations for the most suitable techniques for the evaluation of other medical conditions and injuries. In our study, the assessment of strength yielded the highest score for impairment for 199 (66 per cent) of the 302 subjects. If these results are corroborated in future studies, a recommendation to measure strength alone to evaluate residual impairment after a fracture of the lower extremity may be useful.

In general, the impairment ratings of the lower extremity that were derived with use of the Guides correlated well with function in our study. Moderately high correlations were found between impairment and functional limitations, as determined by both performance (r = 0.57) and patient-reported measures (r = 0.55). The question arises as to whether the correlations that we found are strong enough to conclude that impairment of the lower extremity as it relates to important dimensions of function can be adequately characterized with use of the Guides methodology. We believe that the correlations are quite strong considering the methodological difficulties that are encountered when the relationship between impairment and functional status is examined.

We recommend that the Guides be used as only one part of the process for the determination of disability. The preface to the Guides clearly states that impairment ratings are intended to measure the capacity of the individual to function without reference to non-medical factors such as age; occupation; or physical, social, or economic environment. In this context, impairment ratings must be used together with other information about the individual and his or her environment to make the appropriate monetary award. To ensure the effectiveness of existing compensation programs, it is important to develop a better understanding of the factors that influence impairment, functional limitations, and disability.

NOTE: The authors thank the physical therapists at the three trauma centers included in our study: Nancy Ciesla and Karen Murdock at The R Adams Cowley Shock Trauma Center; Tracy Varga at Harborview Medical Center; and Susan Rush, Don Bursch, and Dolly Swisher at Vanderbilt University Medical Center. We also thank Arlene Greenspan, P.T., Dr.PH., for her invaluable input during the development of the physical-therapy assessments.

	Footnotes

 
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Funds were received in total or partial support of the research or clinical study presented in this article. The funding source was the Centers for Disease Control Grant CCR303568.

Center for Injury Research and Policy, Johns Hopkins University School of Hygiene and Public Health, 624 North Broadway, Baltimore, Maryland 21205. The e-mail address for Ms. McCarthy is mmccarth@hsr.jhsph.edu, and the e-mail address for Dr. MacKenzie is emackenz@jhsph.edu.

Department of Orthopedics and Rehabilitation, Vanderbilt University School of Medicine, 1161 21st Avenue South, Medical Center North, T-4311, Nashville, Tennessee 37232. The e-mail address for Dr. McAndrew is mark.p.mcandrew@mcmail.vanderbilt.edu.

The R Adams Cowley Shock Trauma Center, University of Maryland at Baltimore, 22 South Greene Street, T3R59, Baltimore, Maryland 21201.

#MMC Surgical Associates, 190 Park Avenue, Portland, Maine 04102.

**Department of Physical Medicine and Rehabilitation, Johns Hopkins University School of Medicine, 5601 Loch Raven Boulevard, Suite 406, Baltimore, Maryland 21239.

Department of Surgery, University of Washington School of Medicine, Harborview Medical Center, 325 Ninth Avenue, ZA-16, Seattle, Washington 98104. The e-mail address for Dr. Jurkovich is jerryj@u.washington.edu.

Division of Trauma, Vanderbilt University School of Medicine, 243 Medical Center South, 2100 Pierce Avenue, Nashville, Tennessee 37212-3755.

Department of Orthopedic Surgery, University of Minnesota, Box 492, 420 Delaware Street S.E., Minneapolis, Minnesota 55455.

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