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Overview and Description

Physicians, particularly physiatrists, are recognized as experts for disability evaluations and for making determinations such as extent of losses, necessity of benefits and services, and appropriateness of work activities for patients.1,2

As physicians became experts for disability evaluations, a “medical model” of disease emerged as a paradigm of disablement whereby causation of disability is viewed in terms of the underlying pathology. Operationally, temporary medical disability benefits would be provided during treatment in an effort to cure or minimize the ensuing disability; once treatment was completed, long-term compensation would be provided for residual disability measured according to impairment severity and ongoing rehabilitative needs. The medical model continues to serve as a basis for the workers’ compensation and Social Security disability systems.1

In contrast, the “social model” fosters the idea that society imposes disability upon individuals with impairments through its failure to provide adequate services. Disability is everything that imposes restrictions on impaired persons, including individual prejudice, institutional discrimination, physical barriers to public access and transportation, and lack of workplace accommodation. The social model has helped to develop strategies to neutralize environmental and social barriers where possible.1

The “biopsychosocial model” is the preferred conceptual framework within which to understand human disability. It recognizes the contributions of biological/medical (physical and/or mental aspects of an individual’s health condition), psychological (personal and psychological factors creating an impact on functioning), and social (contextual and environmental factors that may detract from functioning) determinants of disability.1

As models of disease have matured, new models, terminology, and definitions have evolved applicable to U.S. disability systems. The measurement of function is becoming central to the processes of disability determination, although this often-neglected step in the physician’s disability evaluation has only recently been operationalized.1

There are two main contemporary disablement models, developed by the World Health Organization (WHO): the International Classification of Impairments, Disabilities, and Handicaps (ICIDH) and the International Classification of Functioning, Disability, and Health (ICF) [Table 1].1 The ICIDH model recognized four disablement levels: pathology, impairment, disability, and handicap. Pathology is “a disease or trauma acting at a tissue anatomical or physiological level to alter structure and/or function of an organ.” Impairment occurs at the organ level as “any loss or abnormality (resulting from pathology) of psychological, physiological, or anatomical structure or function.” Disability is “any restriction or lack (resulting from impairment) of ability to perform an activity within the range considered normal for a human being.” Finally, handicap is “a disadvantage for a given individual that limits the fulfillment of a role that is normal for that individual” acting in their societal sphere.1

The WHO then replaced the ICIDH with the ICF to be more comprehensive, recognizing three key components of disablement: body functions and body structures, activity, and participation. Body functions and body structures are “physiological functions and body parts respectively.” Activity is “the execution of a task by an individual (typically within their personal sphere).” Finally, participation is “involvement in life situation (typically within a social sphere).”1

TenetMedical model of diseaseBiopsychosocial model
Components of DisablementPathology
Body functions
Body structures
Activity participation
StrengthsRecognizes interactive role of environmental modifiers affecting handicapsImpairments, activity limitations and participation restrictions comprise a continuum of disability
Recognizes both environmental and personal nature influencing disability
Unidirectional causation
Inadequate attention to personal modifiers
Lack of explicit environmental determinants
Lacks the following components:
1. Distinction between activities and participation
2. Quality of life and satisfaction
3. Elaboration of impact of environmental factors
4. Development of personal factors
5. Validation
Table 1: Comparison of the World Health Organization’s ICDH and ICF

While the ICF model lacks elaboration on environmental factor impact, the Institute of Medicine (IOM) expanded the view of disability as a product of interactions of the individual and environment by  adding separate roles played by personal modifiers (lifestyle choices, coping strategies, belief systems) in the resulting disablement process.

The IOM model draws heavily from the Workers’ Compensation system and includes the essential features common to all disability systems designed to compensate individuals who meet criteria and for whom demonstrable losses can be measured in terms of five key domains:

  1. Medical impairment
  2. Functional limitations
  3. Work disability (earning capacity loss; actual loss of earnings)
  4. Non-work disability
  5. Quality of life

The relative weight placed upon each domain varies considerably both within and between various disability systems. Furthermore, metrics whereby these respective domains can be measured are poorly understood due to variability of disability definitions across systems and continued emphasis upon the medical construct of impairment as prime determinant of disablement.1,3

Relevance to Clinical Practice

I. Individual:

When an individual with an impairment undergoes a disability evaluation, a physician rating system is applied, but there is variation among jurisdictions, e.g., the U.S. state and federal workers’ compensation systems and domestic personal injury claims. Disability rating systems are utilized to: establish a diagnosis, ascertain the physical and functional losses at the point of Medical Maximal Improvement (MMI), enable an individual with impairment to exit a system of temporary disablement, and provide a classification of impairment severity to lead to alternative systems management of long-term disablement.1,2 One standard reference for disability evaluation is the AMA Guides to the Evaluation of Permanent Impairment, which is an objective impairment rating guide periodically revised (currently on the 6th edition), utilizing a panel of medical experts.

After a thorough physical examination and review of medical records and relevant tests, the disability examiner addresses the following in the evaluation and report4:

  1. Diagnoses and Severity
  2. Causality
  3. Necessity of diagnostic testing and treatments rendered
  4. Additional diagnostic testing and treatments needed
  5. MMI
  6. Impairment rating (permanent total or partial) and apportionment
  7. Return-to-work restrictions.

The physician report should include return-to-work restrictions, as many studies have demonstrated the advantages of early return to work after an illness or injury. Conversely, prolonged time away from work makes recovery and return to work less likely. As the insurer, employer, and society suffer the economic losses while the employee suffers the personal losses, prompt treatment and early return to work are emphasized.5

Basic requirements for reasonable workplace guidelines include an understanding of the following criteria5:

  1. Signs/symptoms
  2. Job description
  3. Essential job functions
  4. Accommodation options
  5. Employer/employee willingness
  6. Previous workplace guidelines
  7. Response to previous modifications
  8. Current work status

Return-to-work reports should be understandable in lay terms, with restrictions expressed in terms of functional impairment (e.g., lifting and motion limits) rather than job category (e.g., carpenter). Additionally, the physician can request a job description that includes a list of the essential tasks that the employee must perform as part of the job under consideration.5

II. Society:

Societal expectations demand that individuals who experience disablement as a result of illness or injury are entitled to compensation for their losses. Severity of physical and psychological loss is conventionally measured according to the construct of a medical impairment rating, a quantitative assessment of anatomical and functional loss at an organ-system level expressed in regional terms for body parts and further extrapolated to the body as a whole. Severity of functional and, hence, economic loss is generally expressed according to the construct of a disability rating, a monetary sum derived to reflect direct economic and noneconomic losses and impact upon quality of life as the result of a medical impairment. This rating often is operationally expressed as a percentage of the monetary worth of the “whole person,” with the whole person value independently set for each different disability system.1

Little research has been done to address the question of who pays for disability. Workers’ Compensation and Social Security Disability Insurance are economic mainstays of disabled workers and their families and were designed to help replace the lost earnings of covered workers who meet certain eligibility criteria. Yet neither program seeks to replace the full earnings lost as a result of disability. Consequently, the disabled individual inevitably shoulders some of the financial burden of the disability. Most Workers’ Compensation programs aim to replace two-thirds of lost gross earnings.5

III. Social Policy/Legislation:

The Americans with Disabilities Act (ADA) was a landmark civil rights law, enabling individuals with disabilities to access employment and health care for a society in which health insurance is primarily employment-based. ADA aims to protect persons with disabilities from invidious discrimination and, when needed, offer reasonable accommodations and modifications to enable full participation in society.6

The interface between physicians and the law is not always easy. The key for the physician is to understand the legal issues while focusing on the medical questions.5 Physicians working with disability must become acquainted with5:

  1. Specific provisions of Workers’ Compensations laws
  2. State regulations where they practice
  3. Social Security Act
  4. ADA
  5. Family and Medical Leave Act
  6. Regulations by federal agencies administering these statutes

Selected legal terms physicians should know5:

  1. Aggravation – a physical, chemical, or biologic factor, which may or may not be work-related, that contributed to worsening of a preexisting medical condition
  2. Possibility and probability – likelihood that an injury or illness was caused by or aggravated by a particular factor (possibility – likelihood of <50%; probability – likelihood of >50%)
  3. Medical Maximum Improvement (MMI) – when condition has stabilized and is unlikely to change substantially in next year, with or without treatment; impairment rated only on or after the MMI date
  4. Independent Medical Evaluation (IME) – a process whereby disability and impairment evaluations are often completed by a physician not involved in the patient’s care

Cutting Edge/ Unique Concepts/ Emerging Issues

  1. The ICF model continues to gain acceptance as the operational benchmark for measuring and monitoring disability of populations.1 One way to increase the conceptual understanding of rating scales, such as those for rating pain-related impairment, is by linking them to the ICF. Linking is a way of mapping the content covered by a scale, resulting in a structured description of the scale. For example, World Health Organization (WHO) developed a generic instrument for assessing health status and disability across different cultures and settings10. The tool, called World Health Organization’s Disability Assessment Schedule (WHODAS) is applicable in all adult populations and covers 6 domains of functioning10:
    1. Cognition – understanding & communicating
    2. Mobility– moving & getting around
    3. Self-care– hygiene, dressing, eating & staying alone
    4. Getting along– interacting with other people
    5. Life activities– domestic responsibilities, leisure, work & school
    6. Participation– joining in community activities
  1. The AMA Guides have adopted a more diagnosis-based (hence evidence-based) approach to impairment rating criteria to increase inter-rater reliability.1,2
  1. The term “patient-reported outcomes” (PROs) is a relative new term and expands the concept of patient-centered care. A PRO is a report on the health status or symptom, health behavior, or a health-related quality of life. The Pain Disability Questionnaire (PDQ) serves as a prime example.1,2
  1. The Patient-Reported Outcomes Measurement Information Systems (PROMIS) program developed by the National Institute of Health (NIH) is a publicly available system of highly reliable, precise measures of patient reported health status for physical, mental, and social well-being.11 This web-based resource can be used to measure symptoms and health related quality of life in children and adults, with domains such as pain, fatigue, depression, anxiety, sleep disturbance, physical function, social function, and sexual function, among other areas.11
  1. Using the IOM and the ICF models of disability, the US Department of Health and Human Services (HHS), through the National Center for Health Statistics (NCHS) and the Census Bureau’s American Community Survey (ACS), classifies adults with disabilities under six functional disability types9:
    1. Cognitive
    2. Hearing
    3. Mobility
    4. Vision
    5. Self-care
    6. Independent living

By creating uniform data collection requirements, proportions of adults with disabilities, disability types and health related expenditures associated with disability can be estimated.9

  1. The Centers for Disease Control and Prevention (CDC) created the Behavioral Risk Factor Surveillance System (BRFSS) to collect state data about U.S. residents regarding their health-related risk behaviors, chronic health conditions, and use of preventive services12. Data collected can be used to monitor disability at a state level, examine measures of disability, and evaluate disparities in health-related quality of life, healthcare access and use of clinical preventive services.12

Gaps in Knowledge/ Evidence Base

  1. Validate Activities of Daily Living (ADL)-based functional assessment tools applicable to medical impairment rating1
  2. Demonstrate consistency and reliability of the AMA Guides’ new rating method1
  3. Refine criteria and metrics for non-medical aspects of disability (vocational, non-vocational pursuits, quality-of-life) and acquire normative data7,8
  4. Describe optimal mean to determine monetary sum for losses as result of medical impairment8
  5. Research to determine the contributors to the “medicalization” of disability and reinforcers of disability that reduce treatment compliance8


  1. Rondinelli RD. Changes for the new AMA Guides to impairment ratings, 6th ed: implications and applications for physician disability evaluations. PM&R. 2009;1(7):643-656.
  2. Rondinelli RD, Genovese E, Katz R, et al. American Medical Association Guides to the Evaluation of Permanent Impairment, 6th ed. Chicago, IL: American Medical Association; 2008.
  3. Field MJ, Jetter AM, eds. Institute of Medicine (U.S.) Committee on Disability in America. The Future of Disability in America. Washington, DC: National Academies Press; 2007.
  4. Rondinelli RD. Disability determination. In: DeLisa J, et al, eds. Physical Medicine & Rehabilitation Principles and Practice, 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005:169-178.
  5. Melhorn JM. Impairment and disability evaluations: understanding the process. J Bone Joint Surg Am. 2001;83-A(12):1905-1911.
  6. Thomas VL, Gostin LO. The Americans with Disabilities Act: shattered aspirations and new hope. JAMA. 2009;301(1):95-97.
  7. Iezzoni LI, Freedman VA. Turning the disability tide. the importance of definitions. JAMA. 2008; 299(3):332-334.
  8. Mayer T, et al. Spine rehabilitation: secondary and tertiary nonoperative care. Spine J. 2003;3(3 Suppl):28S-36S.
  9. Okoro CA, Hollis ND, Cyrus AC, Griffin-Blake S.  Prevalence of Disabilities and Health Care Access by Disability Status and Type Among Adults — United States, 2016.  MMWR Morb Mortal Wkly Rep 2018;67:882–887. DOI: http://dx.doi.org/10.15585/mmwr.mm6732a3external icon.
  10. WHO, WHO Disability Assessment Schedule 2.0 (WHODAS 2.0), 2017, http://www.who.int/classifications/icf/whodasii/en/
  11. Cella D, et al. The Patient-Reported Outcomes Measurement Information System (PROMIS) developed and tested its first wave of adult self-reported health outcome item banks: 2005-2008. J Clin Epidemiol 2010 Nov;63(11):1179-94.
  12. Centers for Disease Control and Prevention. Disability and Health Data System (DHDS) [Internet]. [updated 2018 May 24; cited 2018 August 27]. Available from: http://dhds.cdc.gov


Altman B, Bernstein A. Disability and Health in the United States, 2001–2005. Hyattsville, MD: National Center for Health Statistics; 2008.

Demeter SL, Andersson GBJ, eds. Disability Evaluation, 2nd ed. Chicago, IL: American Medical Association; 2003.

Fairbairn K, et al. Mapping Patient-Specific Functional Scale (PSFS) items to the International Classification of Functioning, Disability and Health (ICF). Phys Ther. 2012 Feb; 92(2): 310-7.

Rondinelli RD, Katz RT. Impairment Rating and Disability Evaluation. Philadelphia, PA: WB Saunders Company; 2000.

Seabury SA, et al. American Medical Association impairment ratings and earnings losses due to disability. J Occup Environ Med. 2013 Mar; 55(3): 286-91.

Talmage JB, et al. Reliability of the AMA guides to the evaluation of permanent impairment and commentary. J Occup Environ Med. 2011 apr; 53(4): 345.

Original Version of the Topic

Armando S. Miciano, MD. Disability evaluation. 10/22/2013

Author Disclosure

Kareen A. Velez, MD
Nothing to Disclose