Functioning at the Core

Functioning is a central dimension in persons experiencing or likely to experience disability. Accordingly, concepts, classifications and measurements of functioning and health are key to clinical practice, research and teaching. Within this context, the approval of the International Classification of Functioning, Disability and Health (ICF) by the World Health Assembly in May 2001 is considered a landmark event. The ICF establishes a new era of patient-oriented clinical practice, research, and teaching.

The ICF is a classification of the World Health Organization (WHO) based on the integrative bio-psycho-social model of functioning, disability and health. Functioning is the human experience related to body functions, body structures, and activities and participation. It is viewed in terms of its dynamic interaction with a health condition, personal and environmental factors. Disability, on the other hand, is the human experience of impaired body functions and structures, activity limitations and participation restrictions in interaction with a health condition, personal and environmental factors. Although distinguishing between functioning and disability is often helpful when reading medical literature, in the bio-psycho-social perspective of the ICF, functioning is implicitly addressed when disability is mentioned and vice versa.

Functioning and disability according to the integrative bio-psycho-social model of the ICF corresponds to the perspective of rehabilitation medicine i.e. functioning is seen as closely interacting with the environment and the person’s characteristics. Moreover, functioning represents not only an outcome, but also the starting point of the clinical assessment, intervention management, the post-intervention evaluation and quality management.

Literature

  • Bickenbach J. What is functioning and why is it important. In: ICF Core Sets: Manual for Clinical Practice. Bickenbach J, Cieza A, Rauch A, Stucki G. ed. Göttingen: Hogrefe; 2012.
  • Gutenbrunner C, Meyer T, Melvin J, Stucki G.  Towards a conceptual description of Physical and Rehabilitation Medicine. J Rehabil Med 2011;43(9):760-764.
  • Steiner WA, Ryser L, Huber E, Uebelhart D, Aeschlimann, A, Stucki G. Use of the ICF model as a clinical problem-solving tool in physical therapy and rehabilitation medicine. Phys Ther. 2002; 82(11): 1098-1107.
  • Stucki G. International Classification of Functioning, Disability, and Health (ICF): a promising framework and classification for rehabilitation medicine Am J Phys Med Rehabil. 2005; 84(10): 733-740.
  • Stucki G, Ewert T, Cieza A. Value and application of the ICF in rehabilitation medicine. Disabil Rehabil. 2002; 24(17): 932-938.
  • Stucki G, Cieza A Melvin J. The International Classification of Functioning, Disability and Health (ICF): a unifying model for the conceptual description of the rehabilitation strategy J Rehabil Med. 2007; 39(4): 279-285.
  • Stucki G Melvin J. The International Classification of Functioning, Disability and Health: a unifying model for the conceptual description of physical and rehabilitation medicine J Rehabil Med. 2007; 39(4): 286-292.
  • World Health Organization. International Classification of Functioning, Disability and Health, Geneva, World Health Organization; 2001.

The Integrative Bio-psycho-social Model of Functioning, Disability and Health

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A health condition is an umbrella term for disease, disorder, injury or trauma and may also include other circumstances, such as aging, stress, congenital anomaly, or genetic predisposition. It may also include information about pathogeneses and/or etiology.

Body functions are defined as the physiological functions of body systems, including psychological functions. Body structures are the anatomical parts of the body, such as organs, limbs and their components. Problems in body functions (e.g. reduced range of motion, muscle weakness, pain and fatigue) or significant deviation or loss of body structures (e.g. deformity of joints) are referred to as impairments of a body function and structure respectively.

Activity is the execution of a task or action by a person. Participation refers to the involvement of a person in everyday situations and in society. Difficulties at the activity level are referred to as activity limitations (e.g. limitations in dressing) and problems a person may experience in being or getting involved in everyday situations and in society are denoted as participation restrictions (e.g. restrictions in recreation and leisure).

Contextual factors represent the entire background of a person's life and living situation. Among the contextual factors, the environmental factors make up the physical, social and attitudinal environment in which people live. These factors are external to the person and can have a positive or negative influence, i.e., they can serve as a facilitator or a barrier for a person's functioning. Personal factors are the particular background of a person's life and living situation, and comprise features that are not part of the primary health condition. These may include but not limited to gender, age, race, fitness, lifestyle, habits, and social background. They can be considered factors which define the person as a unique individual. Like environmental factors, personal factors can have a positive or negative impact on a person's body functions and structures, and activities and participation.

Literature

  • World Health Organization. International Classification of Functioning, Disability and Health, Geneva, World Health Organization; 2001.

The Content of the Classification

Structure of the ICF

This bio-psycho-social perspective guided the development of the International Classification of Functioning Disability and Health (ICF). As such, the components of the classification correspond to the components of the model. Within each component, there is an exhaustive list of ICF categories that serve as the units of the classification. ICF categories are denoted by unique alphanumeric codes and are hierarchically organized in chapter, second, third and fourth levels. When going from the chapter level to the fourth level, the category's definition becomes more detailed.

ICF categories are arranged in a stem-branch-leaf structure within each component, in which the more detailed level categories share the same attributes as the more broader level categories. Every component consists of chapters, with chapters representing the broadest level. Each chapter then consists of second-level categories, which in turn, are composed of categories at the third level. Some third level categories also include fourth-level categories. This structure can be compared to that of school books, in which the information is usually organized in chapters and subheadings to help locate the information sought.

An example from the component body functions is presented below:

CodeLevel
b2 Sensory functions and pain (chapter level)
b280 Sensation of pain (second level)
b2801 Pain in body part (third level)
b28013 Pain in back (fourth level)

Although the ICF reflects the bio-psycho-social model, there are some differences between the model and the classification. For example, the bio-psycho-social model depicts activities and participation as distinct entities. However, clearly distinguishing between them based on ICF categories is not yet possible given international variation, differing approaches of professionals and theoretical frameworks. For this reason, the ICF keeps activities and participation as one component of functioning. Moreover, although personal factors are included as a component of the bio-psycho-social model, they are not yet classified in the ICF.

ICF Qualifiers

The classification also comprises so-called ICF qualifiers, which quantify the extent of a problem experienced by a person in a specific ICF category. The World Health Organization proposes that the categories in the components of body functions and structures, and activities and participation be quantified using the same generic scale:

ValueDescription
0 NO problem (none, absent, negligible,...) 0-4%
1 MILD problem (slight, low,...) 5-24%
2 MODERATE problem (medium, fair,...) 25-49%
3 SEVERE problem (high, extreme,...) 50-95%
4 COMPLETE problem (total,...) 96-100%
8 not specified (used when there is insufficient information to quantify the extent of the problem)
9 not applicable (used to indicate when a category does not apply to a particular person)

The ICF qualifier is added to the category following a 'dot' e.g. b280.1 (mild sensation of pain) or b28013.3 (severe pain in the back).

Environmental factors are quantified with a negative and positive scale that denotes the extent to which an environmental factor acts as a barrier or a facilitator:

Qualifier - BarrierQualifer - Facilitator
0 - NO barrier +0 - NO facilitator
1 - MILD barrier +1 - MILD facilitator
2 - MODERATE barrier +2 - MODERATE facilitator
3 - SEVERE barrier +3 - SUBSTANTIAL facilitator
4 - COMPLETE barrier +4 - COMPLETE facilitator
8 - barrier, not specified (the environmental factor is a barrier; however there is insufficient information to quantify the extent of the problem) +8 - facilitator, not specified (the environmental factor is a facilitator; however there is insufficient information to quantify the extent of the facilitative inpact)
9 - not applicable (used to indicate when a category does not apply to a particular person)  

To indicate that an environmental factor serves as a barrier, the ICF qualifier is added to the category following a 'dot' e.g. e150.2 (moderate barrier posed by the design, construction, products and technology of buildings for public use). To indicate that an environmental factor serves as a facilitator, the ICF qualifier is added to the category following a plus sign e.g. e1151+4 (Assistive products and technology for personal use in daily living serves as a complete facilitator).

An ICF qualifier of '8', not specified, is used when it is known that the environmental factor is a barrier, however there is insufficient information to quantify the extent of the problem. Likewise an ICF qualifier of '+8', also not specified, is used when it is known that the environmental factor is a facilitator, however there is insufficient information to quantify the extent of the problem. The ICF qualifier of '9', not applicable, is used in the same way as with the generic scale.

It is important to note that in addition to this generic scale, the ICF contains additional qualifiers specific to the different components. For example, the second and third qualifiers of the component body structures are used to indicate the nature of a body structure change and its location respectively.

The ICF contains more than 1400 categories, making it a highly comprehensive classification. This comprehensiveness is a major advantage and strength of the ICF. It is, however, also the biggest challenge to its practicability. To enhance the applicability of the classification, ICF-based tools must to be tailored to the needs of the users - without weakening the strengths of the ICF. One approach is the development of ICF Core Sets.

Literature

  • World Health Organization. International Classification of Functioning, Disability and Health, Geneva, World Health Organization; 2001.