Nagi Disablement Model

The first disablement model was introduced in 1965 by Saad Nagi,20 a sociologist, who noticed semantic and conceptual confusion in the disability literature regarding disability and its associated concepts. Nagi recognized the importance of the environment and that family, society, and community factors could all influence disability.29 Based on this assumption, the consequences of disease and injury for an individual should be described at both the level of the person and at the level of society.

Nagi created a model with 4 components (Figure 1). To illustrate the components of this model, consider a collegiate baseball pitcher with a shoulder injury that limits his ability to throw. Active injury occurs at the cellular level and is identified as a disruption or damage to the integrity of body structures. Given our patient scenario, examples may include a partial-thickness supraspinatus tendon tear or a posterior-superior labral injury. Impairments are defined as the loss or abnormality at the tissue, organ, or body system level and include clinical signs and symptoms, such as diminished internal rotation range of motion, decreased strength of the supraspinatus, and shoulder pain during throwing. Functional limitations are attributes that refer to the person, are described as restrictions in performance at the level of the whole person,19 and are particularly related to the social roles and normal daily activities of those with disabilities. Functional limitations in the baseball pitcher example may include the inability to throw at greater than 75% of maximum effort and shoulder pain that occurs while lifting a 9.07-kg (20-lb) weight to shoulder level. Functional limitations are the most direct way that disease and impairments contribute to disability because they involve tasks that are necessary for completion of important roles, both personal and social. Finally, disability is defined as the inability of a person to fulfill his or her desired or necessary social or personal roles.30 Examples of disability for a baseball pitcher with a shoulder injury would be the inability to fulfill his role as the starting pitcher or the loss of identity as a team leader and diminished self-esteem.

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The Nagi model was influential because it successfully reconfigured the perception of disability away from a focus on physical limitations by defining disability more broadly as the product of a change in the expected interaction between the individual and the environment. According to Nagi, disability is a relational concept, which indicates that it cannot be entirely accounted for by the attributes of the individual and must also consider the role expectations of the individual as well as the patient's perspective of the disability, other people's definition of the disability, and the characteristics of the environment.19,20 Therefore, to truly understand why someone becomes or does not become disabled, consideration must be given to both the capacities of the individual (a function of active disease, impairment, or functional limitations or a combination of these) and the capacities of the individual in relation to the social situations.19

Consequently, disability is the result of a change in the expected interaction between the individual and the environment, which means that impairments do not have to result in functional limitations and functional limitations do not have to result in disability.24 For example, a significant loss of glenohumeral internal rotation may not result in the inability to successfully pitch a baseball, and the inability to pitch a baseball may not mean that an athlete is unable to participate in team activities.30 Furthermore, it is possible that 2 people with the same injury (eg, a rotator cuff tear) could exhibit similar clinical signs and symptoms, including significant impairment as indicated by decreased range of motion and pain. These 2 individuals may also demonstrate similar functional limitations (eg, inability to throw a ball and difficulty with some activities of daily living, such as lifting heavy items). However, these individuals may present with 2 completely different levels of disability. One person may maintain an active social life, continue attending school classes, sustain his commitment to the baseball team, and express an overall positive attitude. In contrast, the other person may shy away from social events, stop attending school classes, remove himself from team obligations, and maintain a depressed and gloomy outlook on life. The potential for drastically different outcomes from 2 very similar injuries highlights the importance of assessing the patient from a disablement model perspective when providing patient-centered health care. The Nagi model provides a framework for understanding why 2 people with the same injury have the potential for such drastically different treatment, performance, and disability outcomes.

The Nagi model is historical and provided standardized terminology for disability. More recent models of disablement, however, have evolved from the Nagi model in an attempt to better encompass all the dimensions of disability and the external factors that influence disablement. Some adaptations have included the addition of sociocultural factors, such as the social and physical environment and personal factors (including attitudes and lifestyle behaviors), as well as an emphasis on quality of life and focus on the interaction between health conditions and contextual factors.24

Although a number of disablement models have been created, including work from the Institute of Medicine,31,32 the 2 most recent models are the disablement model of the National Center for Medical Rehabilitation Research (NCMRR)33–35 and the WHO ICF.36,37 In reviewing each model, we describe the key components, provide insight into the history and evolution, and demonstrate utility by applying it to patient encounters relevant to the athletic training profession.

National Center for Medical Rehabilitation Research Disablement Model

The stated mission of the NCMRR, a center within the National Institutes of Health, is to enhance the quality of life of people with disabilities through the development of scientific knowledge.33 As a result, in 1993, the NCMRR created a model that encompassed the dimensions of disablement and adapted the Nagi model by including a specific component related to societal influences as contributors to disability. Figure 2 illustrates the original NCMRR disablement model. The NCMRR model defined disability as limitations in performing tasks, activities, and roles to levels expected in personal and social contexts.33 Focus was placed on how a person with a disability adapts to functional limitations in the family, work, and local community. The major difference between the Nagi and NCMRR disablement models is that the latter includes the concept of societal limitations as a distinct dimension of the disablement process.33 Societal limitations refer to the restrictions resulting from social policy or barriers, which limit fulfillment of roles or deny access to services and opportunities associated with full participation in society.

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Recently, the NCMRR has started work on a new version of its disablement model that shifts the focus of disablement toward emphasizing the possible health care interventions in the disablement process.34,35 The key dimensions (ie, components) in this new model and measurable influences are provided in Table 1. In the evolving NCMRR model, rehabilitation interventions are considered influences and have the potential to affect the degree of organ dysfunction resulting from tissue damage, as well as the quality of task performance.34,35 Because influences act in parallel, the eventual effects of deficits in task performance on a person's roles in society can be the result of the attitudes and laws at the individual and societal levels, respectively.34,35

Table 1 National Center for Medical Rehabilitation Research Disablement Model, 2006

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For an injured collegiate baseball pitcher, influences concerning the transition from pathophysiology to organ dysfunction might include the anatomy of the injury (supraspinatus tendon tear or posterior-superior labral injury), pharmaceuticals that the athlete may be taking (anti-inflammatory medications), and acute care or treatment provided to the athlete (therapy or surgery). Influences affecting the transition from organ dysfunction to task performance might include the experience level of the athlete (high school, college, professional, recreational), the components of rehabilitation (aggressive early postoperative mobilization versus prolonged immobilization), and the preferences and values of the athlete (desire to return to full competition versus the decision to end the competitive baseball career). The transition from task performance to roles may be influenced by the environment in which the athlete lives and competes (low-profile small private school versus high-profile Division I university), the socioeconomic status of the athlete (low, middle, or upper class), the attitudes of the athlete (positive versus negative outlook on future career as a competitive baseball athlete or self-perception after injury), and attitudes of the coach (negative versus supportive).

The emphasis of the most recent NCMRR model is on understanding and changing the influences that mediate the progression of disability as opposed to characterizing impairments, functional limitations, and disabilities.34,35 In this new model, rehabilitation is seen as an active process, requiring the active participation of the patient, with the ultimate goal of improving the patient's quality of life. Through the evaluation of influences, a person's preferences and values in achieving task and role performance are highlighted.34,35 How a particular patient will participate in rehabilitation activities and overcome the challenges associated with performing tasks and roles and the eventual outcome are central to personal preferences and values.34,35 The athletic training community should keep abreast of developments regarding the new NCMRR model, as it is still under development and has not been formally adopted (http://www.nichd.nih.gov/about/org/ncmrr/).

World Health Organization International Classification of Functioning Model

The disablement model created by the WHO in 1980 has been revised several times during the last 2 decades and has been more widely used in European countries than in the United States.36,37 The most recent model is the ICF, which was introduced in 2001 with the goal of creating a common international language for disability.36,37 One major emphasis in the latest ICF revision was to remove the negative connotations associated with disability by using more positive terms to describe its characteristics, although it can be argued that all modern disablement models make this claim. For instance, reference is made to a patient's “functional abilities” as opposed to “handicaps.”29 Like its diagnostic counterpart, the International Classification of Diseases and Related Health Problems, 10th revision (ICD-10),38 the ICF provides clinicians with a detailed numerical schema that allows for specific coding of disabilities. The ICF codes, while similar to those in the ICD-10, are different in that the ICF classification scheme classifies functioning and disability, whereas the ICD-10 is an etiologic framework that classifies diseases, disorders, and injuries.36,37 Through the use of the ICF, the WHO hopes to provide both a scientific basis and a quantifiable system for identifying and studying health, health-related states, and health care outcomes. It also creates a mechanism for comparing data across countries and across health care disciplines and formulating health and disability policies.36,37

The ICF model is quite different from the Nagi and NCMRR disablement models, both conceptually and in structure. Instead of explicit dimensions and the subsequent relationships among those dimensions, the ICF is a 2-part model organized through a more complex classification of health and health-related domains (Figure 3).36,37

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In part 1 of the ICF model, the domains body functions and structures and activity and participation attempt to account for function at the levels of the body, individual, and society.36,37 Body functions and structures includes both mental and physical aspects of health, where functions are the physiologic functions of the body and structures are the anatomical parts (ie, sensory organs, limbs). Within these domains, changes or deviations from normal are referred to as impairments. Furthermore, the ICF allows the clinician to numerically code for both functions and structures and to qualify both the extent of the impairment (for both function and structure) and the nature of the change (structure only). Body function codes begin with the letter b, whereas structure codes begin with the letter s. Codes for body function require 1 qualifier, which is identified numerically on a scale of 0 to 4, with 0 indicating no impairment and 4 indicating complete impairment. Body structure codes require a first and second qualifier. The first qualifier captures the extent of the impairment in the same way the function qualifier does, and the second captures the nature of the structural change, using a slightly more expansive scale than the impairment (body function) scale.

Given the previous college baseball pitcher example, consider that the health condition has been established as a supraspinatus tendon tear. To the extent that the athlete was experiencing diminished strength, he would be given a function code of b730, as indicated in the ICF manual for disruptions of muscle power functions.39 If the problem affected his function only occasionally, say less than 50% of the time, we could assign a qualifier of moderate impairment (2), and the function code would become b730.2. The corresponding structures code for our example might be s7202.24.39 The structures code for muscles of the shoulder region is s7202, and the 2 indicates a moderate level of impairment. The 4 serves as a second qualifier identifying the nature of the structural change, which is an “aberrant dimension” to the structure (ie, a tear).36

Activities and participation are domains that are essentially responsible for capturing the effect of structural and functional impairment on what a person with a health condition can do in his or her environment. Admittedly, overlap between the domains makes them difficult to distinguish sometimes36 and correcting this problem is an identified goal of the Institute of Medicine going forward.27 However, Jette24 reported success in differentiating one concept from another. In general, activity is best described as a simple task or activity that has a context or meaning, whereas participation is best described as involvement in life situations.29 Activities include walking, eating, jumping, and throwing. In contrast, participation includes walking in social groups, eating out with friends, and pitching on a baseball team and represents the application of an activity to a life situation. Participation has a performance component; activity does not.24 As in the previous domains, the assigned codes for both activity and participation can be qualified. The first qualifier of an activity and participation code is a performance qualifier and speaks to the amount of participation restriction. The second qualifier is a capacity qualifier and speaks to the extent of the activity limitation, without assistance.

Activities and participation codes begin with the letter d. For the injured pitcher, the activities and participation restriction can be identified as an impairment of hand and arm use (d445), although it can then be further specified as throwing, which receives a code of d4454.39 The activities and participation code also requires performance and capacity qualifiers. Recall that the capacity qualifier accounts for the limitation in executing a task without assistance. The performance qualifier accounts for the extent of the participation restriction as the task is “performed” in a social setting. In this case, the capacity qualifier speaks to the patient's ability to throw, whereas the performance qualifier speaks to his actual ability to pitch in a game. We might assume that although the patient's capacity to throw is only mildly limited, his performance is severely restricted because he cannot pitch at 100% effort. Taking the performance qualifier first, the activities and participation code is adjusted to reflect both qualifiers and expressed as d4454.31, meaning that the patient is experiencing a throwing limitation resulting in severe performance difficulty and mild capacity difficulty.

Part 2 of the ICF model includes contextual factors, which are particularly important because they address the significant effect of environment and personal factors on overall level of functioning and disability.36 Environmental factors refer to the physical, social, and attitudinal environments in which people live and include support and relationships, attitudes, and services and policies; these can be considered at the level of the individual or society.29,36 Environment can be delineated further to include both a standard environment (in the domain of activities) and a usual environment (in the domain of participation).36,37 A collegiate baseball pitcher may identify the athletic trainer responsible for his treatment as an environmental factor. Consequently, the code e355 would be assigned, which is the environmental code for a health professional.39 The qualifier for environmental codes identifies the factor as either a barrier or a facilitator and suggests a degree of influence for that factor. In this case, we might find that the athlete believes the athletic trainer is a moderate facilitator of his ability to continue to play baseball, so the code would be adjusted to e355+2.

The final component of the ICF is personal factors, which relate to the age, coping habits, social background, education, and past and current experiences of the patient.29,36,37 Although important, personal factors are rarely coded because of the myriad of factors that have the potential to influence the situation.

To summarize the ICF disablement model, disability occurs when a health condition leads to dysfunction at the domain levels (body functions and structures and activities and participation) indicating impairment (body functions and structures), activity limitations (activities), or participation restrictions (participation), as mediated by both environmental and personal contextual factors.36 The coding mechanism associated with the ICF provides a standardized method for a clinician to classify and monitor patient functioning and disability in a systematic and consistent way. Although the WHO hopes to attain worldwide acceptance and use of its model, the feasibility of this goal remains unknown.