Analysis of impairment

Impairment (of structure or function) is a crucial concept within the holistic biopsychosocial model of illness because it links disease to a disability and vice versa. In addition, it is a vital part of the biomedical model of illness because the analytic logic works from symptoms and signs back to pathology. The rehabilitation clinician needs to appreciate the nature of impairments and what she can deduce from them. I start with a general discussion about the concept, emphasising that they are, by definition, subjective reports or subjective interpretations by the clinician of observed behaviour. I then develop an analytic approach for understanding and interpreting them in a rehabilitation context. The arguments will also apply to the biomedical model.

Table of Contents


An impairment is “the state or fact of being impaired, especially in a specified faculty”, and to be impaired is to be “weakened or damaged”. [Oxford English Dictionary] It is, therefore, a relative term comparing the quality or quantity of some phenomenon against normal. The difficulty is apparent – what is normal? This is not a trivial question, and Georges Canguilhem published, in 1942, a book still relevant today, The Normal and the Pathological.  He shows that normal carries several meanings: statistical normality, normal as the ideal, normal as the expected etc. The conclusion is that we cannot easily define normal.

Some readers will be aware of but probably will not be users of the World Health Organisation’s International Classification of Functioning, Disability, and Health (WHO ICF). The classification sets out a detailed system for classifying altered anatomy and physiology. It is difficult to believe it is a feasible classification in routine clinical practice. It is impossible to be convinced that it is practically helpful, and it adds to some people’s difficulties when considering impairment.

Fortunately, it is not necessary to define normal when considering symptoms and signs in analysing a patient’s rehabilitation needs, nor is it essential to use a complicated classification system. It is the concepts that are important, not a definition of normal.

Before discussing the analysis of symptoms and signs, and the resultant formulation of a patient’s situation, one needs to understand what they are and their significance. The content of the first half of this page is summarised in a MindMap graphic.

Impairment has three meanings

The term impairment encompasses three quite different constructs. [A construct is “an idea or theory containing various conceptual elements, typically one considered to be subjective and not based on empirical evidence.” (OED)]

The first is the patient’s experiences, as reported by the patient. The person will tell you about experiences that they perceive as abnormal. A person will say that they suffer shortness of breath if, in their judgement, they cannot attribute it to the exercise they are undertaking. The patient’s report is accurate; if someone says they have severe pain, no one can gainsay them. You and the patient may have different explanations for the experience or rate their significance differently, but no other person can or should doubt the experience.

The second is entirely different because the clinician applies a label to something he cannot see or experience; it is the name of a construct. If I see someone who misuses words, cannot read, miswrites words, and misunderstands my instructions, I might say that the person has aphasia. Similarly, I can label someone with slow, stiff movements, resistance to passive motion, and brisk reflexes as having spasticity. Both would be considered impairments, but they name constructs that I deduce from behaviour observations and use to summarise a complex set of observations. Weakness is a word used to describe reduced voluntary muscle contraction. I may assume it is due to muscle atrophy, but the patient may not be making a total effort.

The third type of impairment is a visible abnormality, such as an absent limb, a scar, or a craniectomy deficit in the skull.

Thus, it is essential to be clear about the type of impairment you are considering when using the term. All are valid, but your use and interpretation may vary.

Limitations of function can be termed ‘functional impairments’. Some people might interpret this to imply that there was no pathology and that the person had a ‘functional illness”. Be careful with your words!

Origin of an impairment

Many people consider impairment as the link between pathology and disability: a disease causes symptoms and/or signs that, logically, help identify the underlying condition (the disease) and also drive and explain the disability. Unfortunately, this mechanistic link only covers a relatively small proportion of the causes of patient experience, the constructs hypothesised by clinicians, and the factors causing disability.

Many experienced and some clinician-constructed impairments arise from patients’ expectations, which arise from beliefs. For example, about one-third of people receiving the placebo COVID-19 vaccine suffer non-local adverse events. (here) They are ‘real’, not imagined. The vaccination, not the vaccine, causes them. People need to be warned and told it is not the vaccine. Some patients with clinician-diagnosed impairments have no pathological basis for the observations underlying the label; the patient reported here is a straightforward but unusual example.

Similarly, a patient’s mood and mental state may produce both reported experiences and clinician-constructed impairments. Most psychiatric diagnoses are based on reported symptoms such as helplessness, apathy, slow movement, and anxiety or panic. Diagnoses such as functional neurological disorders and chronic fatigue syndrome are based entirely on reported experiences and observed behaviours.

Third, drugs taken are a potent cause of physiological symptoms, most arising directly from the drug but with a significant proportion originating through expectation – the nocebo effect.

Impairments may arise in many other ways, and the graphic does not show them all! For example, suppose the movement of a joint such as a shoulder is reduced, perhaps from wearing a sling to support a fractured arm or secondary to a stroke. In that case, the joint becomes stiff and painful because of immobility, not pathology. Or as another example, hyperventilation can lead to sensory changes. In both cases, the link returns to symptoms and signs from the altered activity.

A second example is the person’s environment. When studying neurology and attending neurology clinics, most medical students pass through a phase of noticing and reporting fasciculations in their muscles. Some will self-diagnose motor neurone disease—the specific environment, exposure to people, and talking about the condition that causes this. When studying in other specialities, medical students notice other ‘symptoms’ and self-diagnose other diseases.

Implications and interpretations

An impairment carries many implications, usually different for different people, and each person will interpret the significance and meaning of a symptom or sign differently. Further, the type of impairment – patient-reported or clinician-constructed – will significantly impact interpretation.

The most familiar interpretation is that the impairment is symptomatic of something else – a disease, a state of mind, taking a drug etc. This interpretation draws attention to a crucial characteristic of patient-reported impairments – the patient judges their experience as abnormal for them, thus indicating that something is wrong with their body. The challenge arises because most people have similar experiences several or many times daily, but they do not interpret them as indicating something wrong. The word symptom automatically implies something is wrong because a symptom is symptomatic of something.

Both patients and professionals may consider impairments symptomatic, but only professionals will interpret and use them as links between pathology and activities. A professional will consider, for example, whether the disease is likely to cause the observed and reported signs and symptoms and, if so, whether they think the impairment causes the limitation on activities seen. An expert professional may also consider whether it helps give a prognosis.

Some impairments are themselves painful or distressing. Sometimes, specific treatments exist to alleviate the pain of distress or some other aspect of the impairment, such as urinary incontinence or urgency.

A complete formulation of any rehabilitation problem depends on a thorough analysis of the patient’s reported experiences and assumed physiological abnormalities.

Uses and harms

The MindMap graphic above shows how knowledge of impairments can be positively helpful and how misinterpretation or misuse can be harmful in rehabilitation. Identifying limitations on bodily structure and function may help in many other ways, but if misinterpreted or misused, they may cause harm.

Failure to acknowledge or identify an impairment may also lead to harm.

Analysis of impairment

The second MindMap graphic shows similar questions used in all domains as applied to impairments. The general idea is to consider the inter-relationship between any given limitation and other physiological or reported limitations at the bodily level and changes or problems in all other domains. For each relationship, one is asking:

  • is the relationship as I would expect? If not, what is the reason?
  • does this relationship suggest that any specific intervention might help? If so, try it.
  • is there any intervention available for the limited function or structure itself? If so, consider it.

When considering and interpreting any findings, the main points to note, which also arise in most other domains, are:

  • there are inter-relationships in both directions
  • there are relationships between impairment and every domain
  • treatments, interventions to reduce the problem or to alleviate its effects, might be identified in most fields.



A good understanding of impairments will, with a systematic consideration of how they influence and influence other domains, often lead to a much better understanding of a person’s situation. This page highlighted the three classes: patient-reported experience, clinician-constructed concepts derived from observed behaviours, and visible body abnormalities. It has stressed that relationships between impairments and other components of the biopsychosocial model of illness can occur in both directions, being the cause of or caused by changes in another domain.

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