Any loss or abnormality of a physiological, psychological, or anatomical structure or function, whether permanent or temporary. Identifying impairments that contribute to disability, a functional problem for a patient is a key factor for a health professional to determine the appropriate treatment.
See:
Functional impairment refers to limitations due to the illness, as people with a disease may not carry out certain functions in their daily lives. We operationally equate the “functional impairment” concept with “disability” in the WHO's International Classification of Functioning, Disability and Health (ICF) 6.
Yamaguchi S. Does the Rise of Objective Measure of Functional Impairment Mean the Fall of PROMs? Neurospine. 2020 Mar;17(1):283-284. doi: 10.14245/ns.2040112.056. Epub 2020 Mar 31. PubMed PMID: 32252177.
see Functional outcome.